- Email: [email protected]
Additive Influence of Hip Offset and Leg Length Reconstruction on Postoperative Improvement in Clinical Outcome After Total Hip Arthroplasty
Accepted Manuscript Additive influence of hip offset and leg length reconstruction on postoperative improvement in clinical outcome after total hip arthroplasty Moritz M. Innmann, MD, Michael W. Maier, MD, PhD, Marcus R. Streit, MD, MSc, PhD, George Grammatopoulos, MD, DPhil, Thomas Bruckner, PhD, Tobias Gotterbarm, MD, PhD, Christian Merle, MD, MSc, PhD PII:
S0883-5403(17)30696-4
DOI:
10.1016/j.arth.2017.08.007
Reference:
YARTH 56037
To appear in:
The Journal of Arthroplasty
Received Date: 3 June 2017 Revised Date:
17 July 2017
Accepted Date: 4 August 2017
Please cite this article as: Innmann MM, Maier MW, Streit MR, Grammatopoulos G, Bruckner T, Gotterbarm T, Merle C, Additive influence of hip offset and leg length reconstruction on postoperative improvement in clinical outcome after total hip arthroplasty, The Journal of Arthroplasty (2017), doi: 10.1016/j.arth.2017.08.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Additive influence of hip offset and leg length reconstruction on postoperative
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improvement in clinical outcome after total hip arthroplasty
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Moritz M. Innmann1,MD; Michael W. Maier1, MD, PhD; Marcus R. Streit1, MD, MSc, PhD;
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George Grammatopoulos2, MD, DPhil; Thomas Bruckner3, PhD; Tobias Gotterbarm1, MD,
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PhD; Christian Merle1, MD, MSc, PhD
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Landstrasse 200a, 69118 Heidelberg, Germany
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Department of Orthopaedics and Trauma Surgery, University of Heidelberg, Schlierbacher
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Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences,
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University of Oxford, Nuffield Orthopaedic Centre, Oxford, United Kingdom
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Feld 130.3, 69120 Heidelberg, Germany
Institute of Medical Biometry and Informatics, University of Heidelberg, Im Neuenheimer
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[email protected]
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Michael W. Maier, MD, PhD:
[email protected]
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Marcus R. Streit, MD, MSc, PhD:
[email protected]
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George Grammatopoulos, MD, DPhil:
[email protected]
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Thomas Bruckner, PhD:
[email protected]
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Tobias Gotterbarm, MD, PhD:
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Correspondence:
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Christian Merle, MD, MSc, PhD
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Department of Orthopaedic and Trauma Surgery, University of Heidelberg
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Schlierbacher Landstraße 200a, 69118 Heidelberg, Germany
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Telephone number: 0049 6221 56 25 000
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Facsimile: 0049 6221 56 26347
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[email protected]
[email protected]
ACCEPTED MANUSCRIPT 1
Additive influence of hip offset and leg length reconstruction on postoperative
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improvement in clinical outcome after total hip arthroplasty
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Conflict of interests: The authors declare that they have no financial or other interest in the
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products or distributor of the products related to this study. The authors do not have other
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kinds of associations, such as consultancies, stock ownership, or other equity interests or
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patent-licensing arrangements
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Ethical review committee statement: IRB approved study.
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ACCEPTED MANUSCRIPT Abstract
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Background: There is a lack of prospective studies investigating the additive effect of both
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acetabular and femoral reconstruction parameters on the functional outcome following total
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hip arthroplasty (THA).
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Methods: The aim of this prospective cohort study was to determine the combined influence
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of hip geometry reconstruction and component positioning on the clinical outcome following
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primary THA for unilateral osteoarthritis. We prospectively assessed the clinical outcome and
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radiographic parameters for hip geometry reconstruction, component position and orientation
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using validated measurements for the operated hip compared to the contralateral native hip in
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a consecutive series of 113 patients with primary unilateral cementless THA. The correlation
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of reconstruction parameters was investigated using a multivariate polynomial regression
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model for the dependent variable ∆HHS (difference between the Harris Hip Scores pre-
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operatively and 2.0-4.8 years post-operatively). Target zones for hip reconstruction and
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component positioning were investigated for an association with superior clinical outcome.
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Results: The regression model demonstrated a correlation for the ∆HHS and both hip offset
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reconstruction and leg length difference (coefficient −0.062, p=0.007; coefficient −0.085,
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p=0.031; r²=0.116). Patients with accurate to slightly increased hip offset reconstruction
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combined with balanced leg length demonstrated a significantly higher ∆HHS than patients
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outside this zone (HO: 5±5 and LLD: 0±5 mm, p=0.029). This finding could be confirmed for
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two enlarged zones (zone 1: HO: 7.5±7.5 and LLD 2.5±7.5 mm, p=0.028; zone 2: HO 7.5±7.5
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and LLD 7.5±7.5 mm, p=0.007).
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ACCEPTED MANUSCRIPT Conclusion: Hip offset and leg length reconstruction demonstrated an additive effect on
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clinical outcome and surgeons should aim for high accuracy in the reconstruction of both
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factors.
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Level of evidence: Diagnostic Level III
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Keywords: total hip arthroplasty, reconstruction, offset, geometry, anatomy, limb length
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ACCEPTED MANUSCRIPT Introduction
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Cemented and cementless hip arthroplasty have demonstrated very good survival rates into
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the third decade of 93% to 95% after 22 and 26 years[1, 2]. Besides long-term durability, an
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optimal postoperative functional outcome is essential for patient satisfaction, which has been
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reported to be associated component positioning and reconstruction of hip geometry[3].
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Reconstruction of the femoral offset (FO) accounts for joint stability reducing the risk of
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dislocation, allowing for a good range of motion with a low risk of bony or soft-tissue
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impingement, sufficient abductor muscle strength without alteration of gait and minimized
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polyethylene wear[4-8]. Leg length difference (LLD) should be kept to a minimum, while
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studies on the influence on clinical outcome are inconsistent[9-12]. The optimal target zone
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for cup positioning is still in the focus of research. Recently, a zone of 40°/15° (±15°) for
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inclination/anteversion was identified in a series of 1070 THAs, to be associated with a four
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times lower dislocation rate, while the best clinical outcome was achieved with a 45°/25°
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(±5°) zone[13]. The concept of an individual zone of optimal cup positioning is equally
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accepted, accounting for the combined anteversion of the cup and femoral stem, the intended
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range of movement after THA, implant design and lumbosacral spinal flexibility and
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balance[14-16]. It remains unclear, to what extent offset can be increased to gain a maximum
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of joint stability while avoiding leg lengthening, without compromising the functional
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outcome. Most studies focus on a limited number of parameters and have retrospective
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designs, while there is a lack of prospective studies investigating the interactive effect of
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multiple acetabular and femoral reconstruction parameters on functional outcome.
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Therefore the present prospective cohort study investigated the effect of hip geometry
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reconstruction and component positioning on improvement in clinical outcome at a minimum
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of two years after THA, specifically asking:
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1) Does the postoperative change in radiographic reconstruction parameters and
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postoperative cup positioning correlate with the pre-/postoperative difference in the
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Harris hip score (∆HHS)?
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2) Which potential target zones for combined hip offset and leg length reconstruction are associated with a better ∆HHS?
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3) Which potential target zones for combined cup inclination/anteversion are associated with a better ∆HHS?
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Patients and Methods
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Study Cohort
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This prospective cohort study investigated a consecutive case series of 113 patients with
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unilateral THA from a single academic institution. Informed consent was obtained by all
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patients. The study was approved by the institutional review board (S-464/2012) and
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conducted according to the Helsinki Declaration of 2008.
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Between December 2007 and 2009 a total of 836 primary THAs were performed at our
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institution. Inclusion criteria for patients were diagnosis of advanced unilateral primary
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osteoarthritis of the hip, mild developmental dysplasia of the hip (DDH) Crowe grade I
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(lateral center-edge angle 20-25°), avascular necrosis of the femoral head and rheumatoid
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arthritis, receiving a cementless THA with a bone preserving curved stem between December
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2007 and 2009. The contralateral hip was defined as native without deformity when the
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patient was asymptomatic without any previous surgery and without any radiographic signs of
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end-stage degenerative disease or deformity related to secondary hip OA (i.e. posttraumatic
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hip disease, slipped epiphysis of the femoral head, Perthes disease, end stage aseptic
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osteonecrosis of the femoral head, DDH with lateral center-edge angle < 20°). Indications for
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ACCEPTED MANUSCRIPT the stem were absence of severe proximal femoral deformity and adequate bone stock for
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uncemented fixation[17]. All patients were prospectively followed with our institutional
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database and at minimum follow-up of two years 113 patients (113 hips) were left for
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evaluation (Figure 1). Demographic data is given in table 1.
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Surgery was performed by five consultant surgeons in a university hospital setting using a
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modified lateral transgluteal Bauer approach in all cases[18]. Intraoperative x-ray imaging
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was used in all cases with the final cup implant and the templated femoral broach in situ. A
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curved, uncemented, bone sparing stem available in four different neck angle options (140°,
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137°, 129° and 127°) and an uncemented press-fit acetabular component was used (Fitmore®
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stem; Allofit® cup; Zimmer, Warsaw, IN, USA). A 28 mm or 32 mm diameter ceramic head
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with three neck length options (-4, 0, 4 mm) (Biolox forte®, CeramTec, Plochingen,
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Germany) and a 32 mm CoCr Femoral Head with one neck length option (8 mm) articulated
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with a highly cross-linked polyethylene liner (Durasul®; Zimmer, Warsaw, IN, USA).
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Surgeons aimed for secure press-fit fixation, neutral stem alignment for varus/valgus position,
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anteversion of the stem of 15° ±10°, and combined cup inclination/anteversion between
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40±10°/20±10°. In addition they aimed for leg length restoration and a reconstruction of hip
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offset to match the contra-lateral native hip. Standardized preoperative planning of the
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prosthesis size and position was performed in all patients.
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Radiographic Assessment
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Measurements were performed bilaterally on postoperative, calibrated, digital low-centered
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AP radiographs of the pelvis. All patients had a contralateral native hip without relevant
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deformity. Radiographs were taken with the patient in the supine position, legs in 15° internal
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rotation and centered x-ray beam on the symphysis pubis. Roman software V1.70 (Institute of
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Orthopedics, Oswestry, UK) and ImageJ software V1.44 (National Institute of Health, USA)
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ACCEPTED MANUSCRIPT were used for radiographic analysis. Measurements were performed by one reviewer (MMI),
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who was not involved in index surgery and blinded to the clinical results. A second analysis
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was performed by two reviewers (MMI, CM) two and six weeks after initial radiographic
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analysis for eleven randomly selected data sets in a blinded fashion. Intra- and inter-observer
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reliabilities were calculated, using average-measure correlation coefficients with a two-way
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random effects model for absolute agreement[19].
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The methods for radiographic measurements have been described previously in detail[20]. In
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brief, the FO was measured as the distance between the center of rotation of the femoral head
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(COR) and the proximal femoral shaft axis (FSA)[21, 22]. The acetabular offset (AO) was
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measured as the distance between the COR and a vertical line through the ipsilateral teardrop
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figure[21]. Hip offset was calculated as the sum of FO and AO[21]. The COR height (CORH)
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was measured as the distance of the COR to the trans-teardrop line (TTL). Radiographic leg
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length difference (LLD) was measured as the difference between both hips for the distance
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between the TTL and the most prominent aspect of the lesser trochanter[21, 23, 24]. Cup
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inclination was defined as the angle between the TTL and the line connecting the most
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superior and inferior aspect of the cup. Cup anteversion was measured and calculated
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according to the formula by Lewinnek et al.[25], as validated by computer tomography based
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data[26].
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Outcome measures
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The primary outcome parameter was improvement in functional outcome, defined as the
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difference between post- and preoperative assessed Harris Hip Score (∆HHS=HHSpostop –
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HHSpreop)[27, 28]. A 15.9 to 18-point difference in ∆HHS has been reported as a clinically
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important change from the patient’s perspective[29]. The power of the study was sufficient
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(80%) with the available sample size to detect a difference of 9 points for the ∆HHS (mean
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ACCEPTED MANUSCRIPT 37.2; SD 16.6) at the p<0.05 level. The HHS was assessed one to five days preoperatively and
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postoperatively at a minimum of 2.0 years of follow-up (range, 2.0 to 4.9). Secondary
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outcome measures included the registration of complications such as revision surgery,
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dislocation, nerve palsy and periprosthetic fracture.
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Statistical Analysis
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Non-parametric tests were used after testing for normal distribution. P-values of less than 0.05
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were considered statistically significant.
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A regression analysis was conducted with the ∆HHS as the dependent variable, adjusted for
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BMI, age at surgery, HO, CORH, LLD, cup inclination and anteversion. The results of the
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exploratory data analysis did not suggest a linear, but a quadratic correlation for HO and LLD
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with ∆HHS. Therefore a polynomial regression analysis was conducted.
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In order to answer question two, zones with ±5 mm intervals for combined HO difference and
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LLD were constructed. This interval has been reported to be used as a cut off value for a
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clinically relevant under- or oversized restored hip offset and leg length difference[4, 9]. The
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process was repeated for zones of ±7.5 mm for HO and LLD.
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Regarding cup positioning, only a small zone size (±5°) has been reported to be associated
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with statistically significant and clinically important improvement in ∆ Oxford Hip Score[28].
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Therefore, a ±5° zone was constructed for every possible combination of inclination (range,
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30° to 60°) and anteversion (range, 0° to 30°)[28]. The process was repeated for zones of
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±10° and ±15°. The mean ∆HHS within each zone was compared to the corresponding ∆HHS
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outside each zone, using a Mann-Whitney-U test. Statistical analysis was conducted using
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SPSS for Windows version 23.0.
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ACCEPTED MANUSCRIPT Results
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The inter- and intra-observer correlation coefficients were excellent for radiographic
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measurements (range, 0.961 (95 % CI; 0.853 – 0.989) to 0.998 (95 % CI; 0.986 – 0.999).
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Overall, patients improved significantly after surgery with a mean ∆HHS of 37.2 points (SD
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16.6). In six patients (5.3%) clinical outcome did not improve (∆HHS<18 pts). Three of these
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patients had a postoperative HO reconstruction compared to the contralateral native hip, of
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more than 10 mm difference and three patients had a LLD of 9 mm or more. Postoperatively,
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mean HO was decreased by 3.5 mm (SD 5.7) compared to the native hip and mean leg length
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difference was 2.8 mm (SD 5.2). There was no postoperative dislocation, revision surgery,
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nerve palsy or periprosthetic fracture in the study cohort.
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Answering question one, the regression analysis showed a statistically significant correlation
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for the ∆HHS and HO and LLD (coefficient −0.062, p=0.007; coefficient −0.085, p=0.031;
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r²=0.116) (table 2). The influence of HO and LLD reconstruction can be interpreted from the
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polynomial regression analysis with the following formula: ∆HHS=(-0.062*HO2)-
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(0.085*LLD2)+x points. Due to the similar correlation coefficients, the squared differences
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for HO and LLD almost equally contribute to the improvement in clinical outcome after THA.
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Regarding question two, patients with complete to slightly increased HO reconstruction
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combined with balanced leg length demonstrated a significantly higher ∆HHS than patients
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outside this zone (HO: 5±5 and LLD: 0±5 mm, 45.3 vs. 35.9 points, p=0.029). This finding
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could be confirmed for two enlarged zones (zone 1: HO: 7.5±7.5 and LLD 2.5±7.5 mm, 39.9
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vs. 33.8 points, p=0.028; zone 2: HO 7.5±7.5 and LLD 7.5±7.5 mm, 41.5 vs. 33.4 points,
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p=0.007). Patients with an under-reconstructed HO combined with leg lengthening
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demonstrated a significantly lower ∆HHS than patients outside this zone (HO: -15±5 and
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ACCEPTED MANUSCRIPT LLD: 10±5 mm, p=0.004) (table 3 & 4). The distribution of hips for HO reconstruction and
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LLD with respect to ∆HHS is illustrated in Figure 2.
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Concerning question three, no zone for combined inclination/anteversion could be identified,
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being associated with a significantly higher ∆HHS.
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Discussion
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Accurate hip geometry reconstruction has an important influence on clinical outcome,
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dislocation risk, range of motion, impingement, abductor muscle strength and polyethylene
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wear[4-8]. To our knowledge, no study has addressed yet the interaction of multiple hip
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reconstruction parameters on clinical outcome.
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The most relevant finding of our study was, that clinical outcome correlated with accurate HO
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reconstruction and minimized LLD in the polynomial regression analysis. A positive linear
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correlation has been reported for FO reconstruction and hip abductor strength, with and
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without adjustment for confounding factors [7, 30-32]. However, a recent study by
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Whitehouse et al. reported no linear correlation of LLD and Oxford Hip Score in a
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multivariate model[11]. In contrast, our polynomial regression model suggests that an
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excessive positive or negative difference in hip offset and / or leg length, is associated with a
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worse HHS and that the effects of both factors ad up.
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The results on our first and second question appear consistent. Patients demonstrated best
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improvement in clinical outcome with a combination of complete to slightly increased HO
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reconstruction and a marginal leg length difference. Significance could be demonstrated for
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both, smaller and larger zones of reconstruction (HO and LLD ±5 mm and ±7.5 mm). For the
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smaller zones, a significantly better ∆HHS could be detected only for one zone with complete
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to slightly increased HO reconstruction and minimized LLD (HO 5±5 and LLD 0±5 mm).
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ACCEPTED MANUSCRIPT Our findings are in line with a study by Mahmood et al. reporting weaker hip abductor muscle
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strength in patients with a decrease in HO by more than 5 mm, compared to the HO
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reconstructed group. Similar results have been reported for a decrease in femoral offset.
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Sariali et al. reported an altered gait with asymmetry between sides, reduced range of motion
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and a lower maximal swing speed on the operated side for patients with a minimum decrease
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in FO of 15%[5]. Cassidy et al. reported that patients with a decrease in FO of more than 5
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mm had worse WOMAC scores than patients with reconstructed or increased FO[33].
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However, both latter studies evaluated only the influence of FO without regard to the change
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in AO and HO. The change in hip offset reflects the tension of the hip abductor muscles and
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reconstruction of the lever arm, accounting for an increase in FO compensating for cup
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medialization due to a sufficient press-fit fixation. Our results for HO change are consistent
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with a recent study by Renkawitz et al., reporting a higher Froude number, normalized
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walking speed and hip range-of-motion in gait analysis for patients with HO and LLD
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reconstruction within 0±5 mm[9]. The literature on the influence of LLD is inconsistent,
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though the consensus agreement recommends that LLD should be kept to a minimum[10-12,
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34]. Interpreting our findings in context of the literature, we hypothesize that our significantly
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better improvement in clinical outcome for adequately restored HO and LLD is mainly
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attributable to better hip range of motion, abductor function and soft tissue tension, due to
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better lever arm reconstruction and minimized patient awareness of the LLD.
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We could not identify a zone for cup positioning being associated with superior outcome or
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lower risk of dislocation. A recent study on 1070 hips identified a four times lower dislocation
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rate for cups with an inclination/anteversion zone of 40°/15° (±15°) and best clinical outcome
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within a zone of 45°/25° (±5°). In contrast, Timperley et al. could not identify a zone for cup
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inclination/anteversion in a study on 1578 patients, being associated with a higher dislocation
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rate[35]. Our findings have to be interpreted with respect to the size of the study cohort, being
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ACCEPTED MANUSCRIPT too small to identify risk factors for dislocations of the hip and potentially underpowered to
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identify zones for cup orientations being associated with superior outcome. As two studies
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suggest similar zones of optimal cup positioning of 45°/25° (±5°) for combined
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inclination/anteversion, we recommend further studies on this topic[15, 28].
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Several limitations of the study have to be addressed. First and most important, we tried to
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minimize a potential selection bias by applying strict inclusion criteria, identifying a
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consecutive cohort and including only patients with a single implant design to minimize its
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effect on the potential of hip geometry reconstruction. Several patients with contralateral hip
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disease or secondary OA forms could not to be included to match the homogeneous study
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cohort with unilateral hip OA. The excluded patients were of younger age at surgery and had
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a significantly lower preoperative HHS. Both findings are attributable to the exclusion criteria
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of DDH Crowe grade II to IV, hip surgery prior to THA and bilateral THA. Since there were
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no further differences between included and excluded patients, we assume a low chance of a
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selection bias (Table 1). Moreover, the definition of primary OA in the present study cohort
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did not exclude the presence of mild hip dysplasia (lateral center-edge angle 20-25°), coxa
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profunda and morphologic alterations related to cam- or pincer-type impingement. Both bony
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over- and under-coverage (i.e. mild dysplasia) of the head as well as morphological alterations
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of the head–neck junction as potential risk factors for OA were not assessed in detail as these
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changes might be subtle and cannot be reliably identified in the present cohort with end-stage
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disease. Care must therefore be taken when applying the presented findings to patients with
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secondary forms of OA or higher grades of deformity. For patients with primary OA, the
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present cohort can be considered as representative with regard to patient demographics. This
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should be put into perspective as the leading diagnosis for THA is primary OA [36]. Second,
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measurements were performed on plain radiographs, underestimating FO by approximately
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13% and therefore influence HO calculations [22]. As the study aimed to express the
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ACCEPTED MANUSCRIPT reconstruction of hip geometry after THA compared to the contralateral native hip, the
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objective was not to provide absolute measurement values but the difference in millimeters.
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Thus, we reduced the risk of measurement bias of the femoral offset due to projection errors.
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Third, we are aware that radiographic LLD measurements do not necessarily reflect the
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clinical leg length difference[23, 37]. Therefore we aimed to determine the radiographic
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change in leg length after THA and not to give functional clinical values being a result of a
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complex interaction of the bones, implants and soft tissue contractures[21, 24]. Fourth, we
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could not measure stem anteversion and could not evaluate the influence of combined
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anteversion on clinical outcome. Fifth, the polynomial regression model detected significant
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correlations, but the r² value indicated a limited explanation of variance in the model. Lastly,
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we only evaluated the postoperative improvement in clinical outcome with the ∆HHS. With
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respect to a detailed evaluation of patient satisfaction, additional scores for health related
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quality of life might be valuable.
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Conclusions
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This study adds the new information for patients being treated with unilateral cementless
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THA due to primary osteoarthritis or mild DDH, that both hip offset and leg length should be
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reconstructed, since both factors demonstrated a comparable additive effect on clinical
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outcome.
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Level of evidence: Level III, diagnostic study
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1. Streit MR, Innmann MM, Merle C, Bruckner T, Aldinger PR, Gotterbarm T. Long-term (20- to 25year) results of an uncemented tapered titanium femoral component and factors affecting survivorship. Clinical orthopaedics and related research 471(10): 3262, 2013 2. Kim YH, Park JW, Kim JS, Kim IW. Twenty-Five- to Twenty-Seven-Year Results of a Cemented vs a Cementless Stem in the Same Patients Younger Than 50 Years of Age. The Journal of arthroplasty, 2015 3. Naal FD, Impellizzeri FM, Lenze U, Wellauer V, von Eisenhart-Rothe R, Leunig M. Clinical improvement and satisfaction after total joint replacement: a prospective 12-month evaluation on the patients' perspective. Quality of life research : an international journal of quality of life aspects of treatment, care and rehabilitation, 2015 4. Mahmood SS, Mukka SS, Crnalic S, Wretenberg P, Sayed-Noor AS. Association between changes in global femoral offset after total hip arthroplasty and function, quality of life, and abductor muscle strength. Acta orthopaedica 87(1): 36, 2016 5. Sariali E, Klouche S, Mouttet A, Pascal-Moussellard H. The effect of femoral offset modification on gait after total hip arthroplasty. Acta orthopaedica, 2014 6. Little NJ, Busch CA, Gallagher JA, Rorabeck CH, Bourne RB. Acetabular polyethylene wear and acetabular inclination and femoral offset. Clinical orthopaedics and related research 467(11): 2895, 2009 7. McGrory BJ, Morrey BF, Cahalan TD, An KN, Cabanela ME. Effect of femoral offset on range of motion and abductor muscle strength after total hip arthroplasty. The Journal of bone and joint surgery British volume 77(6): 865, 1995 8. Matsushita A, Nakashima Y, Jingushi S, Yamamoto T, Kuraoka A, Iwamoto Y. Effects of the femoral offset and the head size on the safe range of motion in total hip arthroplasty. The Journal of arthroplasty 24(4): 646, 2009 9. Renkawitz T, Weber T, Dullien S, Woerner M, Dendorfer S, Grifka J, Weber M. Leg length and offset differences above 5mm after total hip arthroplasty are associated with altered gait kinematics. Gait & posture 49: 196, 2016 10. Mahmood SS, Mukka SS, Crnalic S, Sayed-Noor AS. The Influence of Leg Length Discrepancy after Total Hip Arthroplasty on Function and Quality of Life: A Prospective Cohort Study. The Journal of arthroplasty, 2015 11. Whitehouse MR, Stefanovich-Lawbuary NS, Brunton LR, Blom AW. The Impact of Leg Length Discrepancy on Patient Satisfaction and Functional Outcome Following Total Hip Arthroplasty. The Journal of arthroplasty, 2013 12. Konyves A, Bannister GC. The importance of leg length discrepancy after total hip arthroplasty. The Journal of bone and joint surgery British volume 87(2): 155, 2005 13. Grammatopoulos G, Thomas GE, Pandit H, Beard DJ, Gill HS, Murray DW. The effect of orientation of the acetabular component on outcome following total hip arthroplasty with small diameter hard-on-soft bearings. The bone & joint journal 97-B(2): 164, 2015 14. Phan D, Bederman SS, Schwarzkopf R. The influence of sagittal spinal deformity on anteversion of the acetabular component in total hip arthroplasty. The bone & joint journal 97-B(8): 1017, 2015 15. Widmer KH. [Impingement Free Motion in Total Hip Arthroplasty - How Can We Implement It?]. Zeitschrift fur Orthopadie und Unfallchirurgie, 2016 16. Amuwa C, Dorr LD. The combined anteversion technique for acetabular component anteversion. The Journal of arthroplasty 23(7): 1068, 2008 17. Dorr LD, Faugere MC, Mackel AM, Gruen TA, Bognar B, Malluche HH. Structural and Cellular Assessment of Bone Quality of Proximal Femur. Bone 14(3): 231, 1993 18. Bauer R, Kerschbaumer F, Poisel S, Oberthaler W. The transgluteal approach to the hip joint. Archives of orthopaedic and trauma surgery 95(1-2): 47, 1979 19. Hallgren KA. Computing Inter-Rater Reliability for Observational Data: An Overview and Tutorial. Tutor Quant Methods Psychol 8(1): 23, 2012 20. Innmann MM, Streit MR, Kolb J, Heiland J, Parsch D, Aldinger PR, Konigshausen M, Gotterbarm T, Merle C. Influence of surgical approach on component positioning in primary total hip arthroplasty. BMC musculoskeletal disorders 16: 180, 2015 21. Dastane M, Dorr LD, Tarwala R, Wan Z. Hip offset in total hip arthroplasty: quantitative measurement with navigation. Clinical orthopaedics and related research 469(2): 429, 2011
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22. Merle C, Waldstein W, Pegg E, Streit MR, Gotterbarm T, Aldinger PR, Murray DW, Gill HS. Femoral offset is underestimated on anteroposterior radiographs of the pelvis but accurately assessed on anteroposterior radiographs of the hip. The Journal of bone and joint surgery British volume 94(4): 477, 2012 23. Kjellberg M, Al-Amiry B, Englund E, Sjoden GO, Sayed-Noor AS. Measurement of leg length discrepancy after total hip arthroplasty. The reliability of a plain radiographic method compared to CTscanogram. Skeletal radiology 41(2): 187, 2012 24. Meermans G, Malik A, Witt J, Haddad F. Preoperative radiographic assessment of limb-length discrepancy in total hip arthroplasty. Clinical orthopaedics and related research 469(6): 1677, 2011 25. Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hipreplacement arthroplasties. The Journal of bone and joint surgery American volume 60(2): 217, 1978 26. Lu M, Zhou YX, Du H, Zhang J, Liu J. Reliability and Validity of Measuring Acetabular Component Orientation by Plain Anteroposterior Radiographs. Clinical orthopaedics and related research, 2013 27. Harris WH. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. The Journal of bone and joint surgery American volume 51(4): 737, 1969 28. Grammatopoulos G, Pandit HG, da Assuncao R, McLardy-Smith P, De Smet KA, Gill HS, Murray DW. The relationship between operative and radiographic acetabular component orientation: which factors influence resultant cup orientation? The bone & joint journal 96-B(10): 1290, 2014 29. Singh JA, Schleck C, Harmsen S, Lewallen D. Clinically important improvement thresholds for Harris Hip Score and its ability to predict revision risk after primary total hip arthroplasty. BMC musculoskeletal disorders 17(1): 256, 2016 30. Kiyama T, Naito M, Shinoda T, Maeyama A. Hip abductor strengths after total hip arthroplasty via the lateral and posterolateral approaches. The Journal of arthroplasty 25(1): 76, 2010 31. Yamaguchi T, Naito M, Asayama I, Ishiko T. Total hip arthroplasty: the relationship between posterolateral reconstruction, abductor muscle strength, and femoral offset. Journal of orthopaedic surgery 12(2): 164, 2004 32. Asayama I, Chamnongkich S, Simpson KJ, Kinsey TL, Mahoney OM. Reconstructed hip joint position and abductor muscle strength after total hip arthroplasty. The Journal of arthroplasty 20(4): 414, 2005 33. Cassidy KA, Noticewala MS, Macaulay W, Lee JH, Geller JA. Effect of femoral offset on pain and function after total hip arthroplasty. The Journal of arthroplasty 27(10): 1863, 2012 34. Roder C, Vogel R, Burri L, Dietrich D, Staub LP. Total hip arthroplasty: leg length inequality impairs functional outcomes and patient satisfaction. BMC musculoskeletal disorders 13: 95, 2012 35. Timperley AJ, Biau D, Chew D, Whitehouse SL. Dislocation after total hip replacement - there is no such thing as a safe zone for socket placement with the posterior approach. Hip international : the journal of clinical and experimental research on hip pathology and therapy: 0, 2016 36. Hailer NP, Garellick G, Karrholm J. Uncemented and cemented primary total hip arthroplasty in the Swedish Hip Arthroplasty Register. Acta orthopaedica 81(1): 34, 2010 37. Tipton SC, Sutherland JK, Schwarzkopf R. The Assessment of Limb Length Discrepancy Before Total Hip Arthroplasty. The Journal of arthroplasty, 2015
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ACCEPTED MANUSCRIPT Acknowledgments: We want to thank Ms Marlies Krueger for data acquisition from the institutional database. Furthermore, we thank the non-commercial research fund Deutsche
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ACCEPTED MANUSCRIPT Table 1: Patient demographics and distribution of analysed and excluded cases; mean (SD) Hips analysed
Hips excluded
P Value
Number of hips
113
133
-
Gender (F:M)
53 : 60
74 : 59
0.201
Age at surgery (yrs.)
62.9 (9.5)
57.5 (15)
0.011
Body mass index (kg/m²)
26.3 (5.0)
26.2 (4.3)
0.571
Harris Hip Score preoperatively
58.1 (16.1)
51.6 (17.2)
0.001
Primary Osteoarthritis
85
57
DDH
17
44
Inflammatory
3
Osteonecrosis
8
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ACCEPTED MANUSCRIPT Table 2: Polynomial regression analysis of the effects on the dependent variable ∆HHS; (r² = 0.116) Unstandardized
Model
Standardized β
Standard error
β coefficients
P - value
coefficients
27.137
16,954
BMI
0.119
0.324
0.036
0.714
Age at surgery in y
0.201
0.167
0.115
0.231
HO difference in mm squared
-0.062
0.022
CORH difference in mm squared
0.017
0.040
Leg length difference in mm squared
-0.085
0.039
Cup inclination squared
0.000
0.003
Cup anteversion squared
-0.003
0.006
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-0.264
0.007*
0.042
0.666
-0.207
0.031*
0.004
0.964
-0.045
0.660
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0.113
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ACCEPTED MANUSCRIPT Table 3: Clinical outcome (∆HHS) for small zones of reconstruction compared to the contralateral native hip (HO ± 5 and LLD ± 5 mm) Combination of radiographic features
Hip Offset difference in mm inside : outside zone - 15 to - 5
- 10 to 0
- 5 to 5
0 to 10
n hips
19 : 94
32 : 81
21 : 92
8 : 105
mean ∆HHS (p - value)
28.0 : 39.0 (0.004*)
35.3 : 37.9 (0.331)
39.9 : 36.6 (0.383)
36.8 : 37.2 (0.755)
SD
15.1 : 16.3
17.6 : 16.2
17.1 : 16.5
17.3 : 16.6
n hips
26 : 87
54 : 59
47 : 66
17 : 96
mean ∆HHS (p - value)
33.7 : 38.2 (0.077)
36.9 : 37.5 (0.609)
40.3 : 35.0 (0.113)
42.2 : 36.3 (0.099)
SD
14.4 : 17.1
14.4 : 18.5
16.2 : 16.6
16.9 : 16.5
n hips
18 : 95
39 : 74
mean ∆HHS (p - value)
39.1 : 36.8 (0.745)
SD
17.2 : 16.6
- 5 to 5
- 10 to 0
SC
0 to 10
39 : 74
15 : 98
37.2 : 37.2 (0.923)
40.8 : 35.3 (0.071)
45.3 : 35.9 (0.029*)
15.2 : 17.5
16.0 : 16.7
15.8 : 16.4
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Leg length difference in mm
n hips
9 : 104
13 : 100
14 : 99
8 : 105
mean ∆HHS (p - value)
42.1 : 36.8 (0.414)
37.9 : 37.2 (0.964)
36.6 : 37.3 (0.886)
40.1 : 36.9 (0.509)
SD
16.4 : 16.6
16.8 : 16.7
15.1 : 16.9
15.1 : 16.8
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Mann-Whitney-U test; * indicating significance (p < 0.05)
ACCEPTED MANUSCRIPT Table 4: Clinical outcome (∆HHS) for large zones of reconstruction compared to the contralateral native hip (HO ± 7.5 and LLD ± 7.5 mm) Combination of radiographic features
Hip Offset difference in mm inside : outside zone - 15 to 0
- 10 to 5
- 5 to 10
n hips
66 : 47
75 : 38
53 : 60
mean ∆HHS (p - value)
36.6 : 38.0 (0.384)
37.1 : 37.4 (0.879)
41.5 : 33.4 (0.007*)
SD
16.7 : 16.6
16.4 : 17.1
17.3 : 16.6
n hips
72 : 41
82 : 31
- 10 to 5
62 : 51
mean ∆HHS (p - value)
37.3 : 37.0 (0.628)
38.1 : 34.9 (0.541)
39.9 : 33.8 (0.028*)
SD
15.3 : 18.8
15.6 : 19.1
15.9 : 16.9
n hips
49 : 64
56 : 57
46 : 67
SC
- 5 to 10
mean ∆HHS (p - value)
38.2 : 36.4 (0.628)
39.5 : 34.9 (0.153)
39.9 : 35.3 (0.094)
SD
15.6 : 17.4
15.6 : 17.4
15.2 : 17.3
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Mann-Whitney-U test; * indicating significance (p < 0.05)
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Leg length difference in mm
ACCEPTED MANUSCRIPT Figure legends
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Figure 1: Flow chart illustrating the identification of the study cohort
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Figure 2: Scatter plot illustrating the improvement in clinical outcome dependent on hip offset
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and leg length reconstruction compared to the contralateral hip (bubble diameter expresses
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∆HHS)
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S0883-5403(17)30696-4
DOI:
10.1016/j.arth.2017.08.007
Reference:
YARTH 56037
To appear in:
The Journal of Arthroplasty
Received Date: 3 June 2017 Revised Date:
17 July 2017
Accepted Date: 4 August 2017
Please cite this article as: Innmann MM, Maier MW, Streit MR, Grammatopoulos G, Bruckner T, Gotterbarm T, Merle C, Additive influence of hip offset and leg length reconstruction on postoperative improvement in clinical outcome after total hip arthroplasty, The Journal of Arthroplasty (2017), doi: 10.1016/j.arth.2017.08.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Additive influence of hip offset and leg length reconstruction on postoperative
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improvement in clinical outcome after total hip arthroplasty
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Moritz M. Innmann1,MD; Michael W. Maier1, MD, PhD; Marcus R. Streit1, MD, MSc, PhD;
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George Grammatopoulos2, MD, DPhil; Thomas Bruckner3, PhD; Tobias Gotterbarm1, MD,
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PhD; Christian Merle1, MD, MSc, PhD
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Landstrasse 200a, 69118 Heidelberg, Germany
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SC
Department of Orthopaedics and Trauma Surgery, University of Heidelberg, Schlierbacher
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Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences,
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University of Oxford, Nuffield Orthopaedic Centre, Oxford, United Kingdom
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Feld 130.3, 69120 Heidelberg, Germany
Institute of Medical Biometry and Informatics, University of Heidelberg, Im Neuenheimer
13 Moritz M. Innmann, MD:
[email protected]
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Michael W. Maier, MD, PhD:
[email protected]
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Marcus R. Streit, MD, MSc, PhD:
[email protected]
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George Grammatopoulos, MD, DPhil:
[email protected]
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Thomas Bruckner, PhD:
[email protected]
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Tobias Gotterbarm, MD, PhD:
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Correspondence:
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Christian Merle, MD, MSc, PhD
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Department of Orthopaedic and Trauma Surgery, University of Heidelberg
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Schlierbacher Landstraße 200a, 69118 Heidelberg, Germany
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Telephone number: 0049 6221 56 25 000
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Facsimile: 0049 6221 56 26347
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[email protected]
[email protected]
ACCEPTED MANUSCRIPT 1
Additive influence of hip offset and leg length reconstruction on postoperative
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improvement in clinical outcome after total hip arthroplasty
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Conflict of interests: The authors declare that they have no financial or other interest in the
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products or distributor of the products related to this study. The authors do not have other
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kinds of associations, such as consultancies, stock ownership, or other equity interests or
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patent-licensing arrangements
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Ethical review committee statement: IRB approved study.
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ACCEPTED MANUSCRIPT Abstract
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Background: There is a lack of prospective studies investigating the additive effect of both
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acetabular and femoral reconstruction parameters on the functional outcome following total
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hip arthroplasty (THA).
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Methods: The aim of this prospective cohort study was to determine the combined influence
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of hip geometry reconstruction and component positioning on the clinical outcome following
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primary THA for unilateral osteoarthritis. We prospectively assessed the clinical outcome and
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radiographic parameters for hip geometry reconstruction, component position and orientation
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using validated measurements for the operated hip compared to the contralateral native hip in
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a consecutive series of 113 patients with primary unilateral cementless THA. The correlation
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of reconstruction parameters was investigated using a multivariate polynomial regression
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model for the dependent variable ∆HHS (difference between the Harris Hip Scores pre-
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operatively and 2.0-4.8 years post-operatively). Target zones for hip reconstruction and
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component positioning were investigated for an association with superior clinical outcome.
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Results: The regression model demonstrated a correlation for the ∆HHS and both hip offset
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reconstruction and leg length difference (coefficient −0.062, p=0.007; coefficient −0.085,
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p=0.031; r²=0.116). Patients with accurate to slightly increased hip offset reconstruction
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combined with balanced leg length demonstrated a significantly higher ∆HHS than patients
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outside this zone (HO: 5±5 and LLD: 0±5 mm, p=0.029). This finding could be confirmed for
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two enlarged zones (zone 1: HO: 7.5±7.5 and LLD 2.5±7.5 mm, p=0.028; zone 2: HO 7.5±7.5
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and LLD 7.5±7.5 mm, p=0.007).
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ACCEPTED MANUSCRIPT Conclusion: Hip offset and leg length reconstruction demonstrated an additive effect on
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clinical outcome and surgeons should aim for high accuracy in the reconstruction of both
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factors.
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Level of evidence: Diagnostic Level III
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Keywords: total hip arthroplasty, reconstruction, offset, geometry, anatomy, limb length
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ACCEPTED MANUSCRIPT Introduction
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Cemented and cementless hip arthroplasty have demonstrated very good survival rates into
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the third decade of 93% to 95% after 22 and 26 years[1, 2]. Besides long-term durability, an
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optimal postoperative functional outcome is essential for patient satisfaction, which has been
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reported to be associated component positioning and reconstruction of hip geometry[3].
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Reconstruction of the femoral offset (FO) accounts for joint stability reducing the risk of
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dislocation, allowing for a good range of motion with a low risk of bony or soft-tissue
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impingement, sufficient abductor muscle strength without alteration of gait and minimized
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polyethylene wear[4-8]. Leg length difference (LLD) should be kept to a minimum, while
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studies on the influence on clinical outcome are inconsistent[9-12]. The optimal target zone
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for cup positioning is still in the focus of research. Recently, a zone of 40°/15° (±15°) for
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inclination/anteversion was identified in a series of 1070 THAs, to be associated with a four
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times lower dislocation rate, while the best clinical outcome was achieved with a 45°/25°
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(±5°) zone[13]. The concept of an individual zone of optimal cup positioning is equally
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accepted, accounting for the combined anteversion of the cup and femoral stem, the intended
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range of movement after THA, implant design and lumbosacral spinal flexibility and
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balance[14-16]. It remains unclear, to what extent offset can be increased to gain a maximum
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of joint stability while avoiding leg lengthening, without compromising the functional
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outcome. Most studies focus on a limited number of parameters and have retrospective
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designs, while there is a lack of prospective studies investigating the interactive effect of
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multiple acetabular and femoral reconstruction parameters on functional outcome.
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Therefore the present prospective cohort study investigated the effect of hip geometry
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reconstruction and component positioning on improvement in clinical outcome at a minimum
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of two years after THA, specifically asking:
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1) Does the postoperative change in radiographic reconstruction parameters and
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postoperative cup positioning correlate with the pre-/postoperative difference in the
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Harris hip score (∆HHS)?
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2) Which potential target zones for combined hip offset and leg length reconstruction are associated with a better ∆HHS?
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3) Which potential target zones for combined cup inclination/anteversion are associated with a better ∆HHS?
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Patients and Methods
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Study Cohort
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This prospective cohort study investigated a consecutive case series of 113 patients with
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unilateral THA from a single academic institution. Informed consent was obtained by all
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patients. The study was approved by the institutional review board (S-464/2012) and
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conducted according to the Helsinki Declaration of 2008.
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Between December 2007 and 2009 a total of 836 primary THAs were performed at our
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institution. Inclusion criteria for patients were diagnosis of advanced unilateral primary
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osteoarthritis of the hip, mild developmental dysplasia of the hip (DDH) Crowe grade I
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(lateral center-edge angle 20-25°), avascular necrosis of the femoral head and rheumatoid
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arthritis, receiving a cementless THA with a bone preserving curved stem between December
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2007 and 2009. The contralateral hip was defined as native without deformity when the
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patient was asymptomatic without any previous surgery and without any radiographic signs of
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end-stage degenerative disease or deformity related to secondary hip OA (i.e. posttraumatic
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hip disease, slipped epiphysis of the femoral head, Perthes disease, end stage aseptic
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osteonecrosis of the femoral head, DDH with lateral center-edge angle < 20°). Indications for
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ACCEPTED MANUSCRIPT the stem were absence of severe proximal femoral deformity and adequate bone stock for
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uncemented fixation[17]. All patients were prospectively followed with our institutional
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database and at minimum follow-up of two years 113 patients (113 hips) were left for
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evaluation (Figure 1). Demographic data is given in table 1.
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Surgery was performed by five consultant surgeons in a university hospital setting using a
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modified lateral transgluteal Bauer approach in all cases[18]. Intraoperative x-ray imaging
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was used in all cases with the final cup implant and the templated femoral broach in situ. A
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curved, uncemented, bone sparing stem available in four different neck angle options (140°,
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137°, 129° and 127°) and an uncemented press-fit acetabular component was used (Fitmore®
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stem; Allofit® cup; Zimmer, Warsaw, IN, USA). A 28 mm or 32 mm diameter ceramic head
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with three neck length options (-4, 0, 4 mm) (Biolox forte®, CeramTec, Plochingen,
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Germany) and a 32 mm CoCr Femoral Head with one neck length option (8 mm) articulated
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with a highly cross-linked polyethylene liner (Durasul®; Zimmer, Warsaw, IN, USA).
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Surgeons aimed for secure press-fit fixation, neutral stem alignment for varus/valgus position,
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anteversion of the stem of 15° ±10°, and combined cup inclination/anteversion between
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40±10°/20±10°. In addition they aimed for leg length restoration and a reconstruction of hip
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offset to match the contra-lateral native hip. Standardized preoperative planning of the
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prosthesis size and position was performed in all patients.
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Radiographic Assessment
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Measurements were performed bilaterally on postoperative, calibrated, digital low-centered
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AP radiographs of the pelvis. All patients had a contralateral native hip without relevant
108
deformity. Radiographs were taken with the patient in the supine position, legs in 15° internal
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rotation and centered x-ray beam on the symphysis pubis. Roman software V1.70 (Institute of
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Orthopedics, Oswestry, UK) and ImageJ software V1.44 (National Institute of Health, USA)
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ACCEPTED MANUSCRIPT were used for radiographic analysis. Measurements were performed by one reviewer (MMI),
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who was not involved in index surgery and blinded to the clinical results. A second analysis
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was performed by two reviewers (MMI, CM) two and six weeks after initial radiographic
114
analysis for eleven randomly selected data sets in a blinded fashion. Intra- and inter-observer
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reliabilities were calculated, using average-measure correlation coefficients with a two-way
116
random effects model for absolute agreement[19].
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The methods for radiographic measurements have been described previously in detail[20]. In
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brief, the FO was measured as the distance between the center of rotation of the femoral head
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(COR) and the proximal femoral shaft axis (FSA)[21, 22]. The acetabular offset (AO) was
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measured as the distance between the COR and a vertical line through the ipsilateral teardrop
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figure[21]. Hip offset was calculated as the sum of FO and AO[21]. The COR height (CORH)
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was measured as the distance of the COR to the trans-teardrop line (TTL). Radiographic leg
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length difference (LLD) was measured as the difference between both hips for the distance
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between the TTL and the most prominent aspect of the lesser trochanter[21, 23, 24]. Cup
125
inclination was defined as the angle between the TTL and the line connecting the most
126
superior and inferior aspect of the cup. Cup anteversion was measured and calculated
127
according to the formula by Lewinnek et al.[25], as validated by computer tomography based
128
data[26].
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Outcome measures
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The primary outcome parameter was improvement in functional outcome, defined as the
131
difference between post- and preoperative assessed Harris Hip Score (∆HHS=HHSpostop –
132
HHSpreop)[27, 28]. A 15.9 to 18-point difference in ∆HHS has been reported as a clinically
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important change from the patient’s perspective[29]. The power of the study was sufficient
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(80%) with the available sample size to detect a difference of 9 points for the ∆HHS (mean
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ACCEPTED MANUSCRIPT 37.2; SD 16.6) at the p<0.05 level. The HHS was assessed one to five days preoperatively and
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postoperatively at a minimum of 2.0 years of follow-up (range, 2.0 to 4.9). Secondary
137
outcome measures included the registration of complications such as revision surgery,
138
dislocation, nerve palsy and periprosthetic fracture.
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Statistical Analysis
140
Non-parametric tests were used after testing for normal distribution. P-values of less than 0.05
141
were considered statistically significant.
142
A regression analysis was conducted with the ∆HHS as the dependent variable, adjusted for
143
BMI, age at surgery, HO, CORH, LLD, cup inclination and anteversion. The results of the
144
exploratory data analysis did not suggest a linear, but a quadratic correlation for HO and LLD
145
with ∆HHS. Therefore a polynomial regression analysis was conducted.
146
In order to answer question two, zones with ±5 mm intervals for combined HO difference and
147
LLD were constructed. This interval has been reported to be used as a cut off value for a
148
clinically relevant under- or oversized restored hip offset and leg length difference[4, 9]. The
149
process was repeated for zones of ±7.5 mm for HO and LLD.
150
Regarding cup positioning, only a small zone size (±5°) has been reported to be associated
151
with statistically significant and clinically important improvement in ∆ Oxford Hip Score[28].
152
Therefore, a ±5° zone was constructed for every possible combination of inclination (range,
153
30° to 60°) and anteversion (range, 0° to 30°)[28]. The process was repeated for zones of
154
±10° and ±15°. The mean ∆HHS within each zone was compared to the corresponding ∆HHS
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outside each zone, using a Mann-Whitney-U test. Statistical analysis was conducted using
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SPSS for Windows version 23.0.
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The inter- and intra-observer correlation coefficients were excellent for radiographic
160
measurements (range, 0.961 (95 % CI; 0.853 – 0.989) to 0.998 (95 % CI; 0.986 – 0.999).
161
Overall, patients improved significantly after surgery with a mean ∆HHS of 37.2 points (SD
162
16.6). In six patients (5.3%) clinical outcome did not improve (∆HHS<18 pts). Three of these
163
patients had a postoperative HO reconstruction compared to the contralateral native hip, of
164
more than 10 mm difference and three patients had a LLD of 9 mm or more. Postoperatively,
165
mean HO was decreased by 3.5 mm (SD 5.7) compared to the native hip and mean leg length
166
difference was 2.8 mm (SD 5.2). There was no postoperative dislocation, revision surgery,
167
nerve palsy or periprosthetic fracture in the study cohort.
168
Answering question one, the regression analysis showed a statistically significant correlation
169
for the ∆HHS and HO and LLD (coefficient −0.062, p=0.007; coefficient −0.085, p=0.031;
170
r²=0.116) (table 2). The influence of HO and LLD reconstruction can be interpreted from the
171
polynomial regression analysis with the following formula: ∆HHS=(-0.062*HO2)-
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(0.085*LLD2)+x points. Due to the similar correlation coefficients, the squared differences
173
for HO and LLD almost equally contribute to the improvement in clinical outcome after THA.
174
Regarding question two, patients with complete to slightly increased HO reconstruction
175
combined with balanced leg length demonstrated a significantly higher ∆HHS than patients
176
outside this zone (HO: 5±5 and LLD: 0±5 mm, 45.3 vs. 35.9 points, p=0.029). This finding
177
could be confirmed for two enlarged zones (zone 1: HO: 7.5±7.5 and LLD 2.5±7.5 mm, 39.9
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vs. 33.8 points, p=0.028; zone 2: HO 7.5±7.5 and LLD 7.5±7.5 mm, 41.5 vs. 33.4 points,
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p=0.007). Patients with an under-reconstructed HO combined with leg lengthening
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demonstrated a significantly lower ∆HHS than patients outside this zone (HO: -15±5 and
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ACCEPTED MANUSCRIPT LLD: 10±5 mm, p=0.004) (table 3 & 4). The distribution of hips for HO reconstruction and
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LLD with respect to ∆HHS is illustrated in Figure 2.
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Concerning question three, no zone for combined inclination/anteversion could be identified,
184
being associated with a significantly higher ∆HHS.
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Discussion
186
Accurate hip geometry reconstruction has an important influence on clinical outcome,
187
dislocation risk, range of motion, impingement, abductor muscle strength and polyethylene
188
wear[4-8]. To our knowledge, no study has addressed yet the interaction of multiple hip
189
reconstruction parameters on clinical outcome.
190
The most relevant finding of our study was, that clinical outcome correlated with accurate HO
191
reconstruction and minimized LLD in the polynomial regression analysis. A positive linear
192
correlation has been reported for FO reconstruction and hip abductor strength, with and
193
without adjustment for confounding factors [7, 30-32]. However, a recent study by
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Whitehouse et al. reported no linear correlation of LLD and Oxford Hip Score in a
195
multivariate model[11]. In contrast, our polynomial regression model suggests that an
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excessive positive or negative difference in hip offset and / or leg length, is associated with a
197
worse HHS and that the effects of both factors ad up.
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The results on our first and second question appear consistent. Patients demonstrated best
199
improvement in clinical outcome with a combination of complete to slightly increased HO
200
reconstruction and a marginal leg length difference. Significance could be demonstrated for
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both, smaller and larger zones of reconstruction (HO and LLD ±5 mm and ±7.5 mm). For the
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smaller zones, a significantly better ∆HHS could be detected only for one zone with complete
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to slightly increased HO reconstruction and minimized LLD (HO 5±5 and LLD 0±5 mm).
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ACCEPTED MANUSCRIPT Our findings are in line with a study by Mahmood et al. reporting weaker hip abductor muscle
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strength in patients with a decrease in HO by more than 5 mm, compared to the HO
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reconstructed group. Similar results have been reported for a decrease in femoral offset.
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Sariali et al. reported an altered gait with asymmetry between sides, reduced range of motion
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and a lower maximal swing speed on the operated side for patients with a minimum decrease
209
in FO of 15%[5]. Cassidy et al. reported that patients with a decrease in FO of more than 5
210
mm had worse WOMAC scores than patients with reconstructed or increased FO[33].
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However, both latter studies evaluated only the influence of FO without regard to the change
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in AO and HO. The change in hip offset reflects the tension of the hip abductor muscles and
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reconstruction of the lever arm, accounting for an increase in FO compensating for cup
214
medialization due to a sufficient press-fit fixation. Our results for HO change are consistent
215
with a recent study by Renkawitz et al., reporting a higher Froude number, normalized
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walking speed and hip range-of-motion in gait analysis for patients with HO and LLD
217
reconstruction within 0±5 mm[9]. The literature on the influence of LLD is inconsistent,
218
though the consensus agreement recommends that LLD should be kept to a minimum[10-12,
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34]. Interpreting our findings in context of the literature, we hypothesize that our significantly
220
better improvement in clinical outcome for adequately restored HO and LLD is mainly
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attributable to better hip range of motion, abductor function and soft tissue tension, due to
222
better lever arm reconstruction and minimized patient awareness of the LLD.
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We could not identify a zone for cup positioning being associated with superior outcome or
224
lower risk of dislocation. A recent study on 1070 hips identified a four times lower dislocation
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rate for cups with an inclination/anteversion zone of 40°/15° (±15°) and best clinical outcome
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within a zone of 45°/25° (±5°). In contrast, Timperley et al. could not identify a zone for cup
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inclination/anteversion in a study on 1578 patients, being associated with a higher dislocation
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rate[35]. Our findings have to be interpreted with respect to the size of the study cohort, being
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identify zones for cup orientations being associated with superior outcome. As two studies
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suggest similar zones of optimal cup positioning of 45°/25° (±5°) for combined
232
inclination/anteversion, we recommend further studies on this topic[15, 28].
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Several limitations of the study have to be addressed. First and most important, we tried to
234
minimize a potential selection bias by applying strict inclusion criteria, identifying a
235
consecutive cohort and including only patients with a single implant design to minimize its
236
effect on the potential of hip geometry reconstruction. Several patients with contralateral hip
237
disease or secondary OA forms could not to be included to match the homogeneous study
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cohort with unilateral hip OA. The excluded patients were of younger age at surgery and had
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a significantly lower preoperative HHS. Both findings are attributable to the exclusion criteria
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of DDH Crowe grade II to IV, hip surgery prior to THA and bilateral THA. Since there were
241
no further differences between included and excluded patients, we assume a low chance of a
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selection bias (Table 1). Moreover, the definition of primary OA in the present study cohort
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did not exclude the presence of mild hip dysplasia (lateral center-edge angle 20-25°), coxa
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profunda and morphologic alterations related to cam- or pincer-type impingement. Both bony
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over- and under-coverage (i.e. mild dysplasia) of the head as well as morphological alterations
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of the head–neck junction as potential risk factors for OA were not assessed in detail as these
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changes might be subtle and cannot be reliably identified in the present cohort with end-stage
248
disease. Care must therefore be taken when applying the presented findings to patients with
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secondary forms of OA or higher grades of deformity. For patients with primary OA, the
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present cohort can be considered as representative with regard to patient demographics. This
251
should be put into perspective as the leading diagnosis for THA is primary OA [36]. Second,
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measurements were performed on plain radiographs, underestimating FO by approximately
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13% and therefore influence HO calculations [22]. As the study aimed to express the
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objective was not to provide absolute measurement values but the difference in millimeters.
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Thus, we reduced the risk of measurement bias of the femoral offset due to projection errors.
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Third, we are aware that radiographic LLD measurements do not necessarily reflect the
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clinical leg length difference[23, 37]. Therefore we aimed to determine the radiographic
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change in leg length after THA and not to give functional clinical values being a result of a
260
complex interaction of the bones, implants and soft tissue contractures[21, 24]. Fourth, we
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could not measure stem anteversion and could not evaluate the influence of combined
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anteversion on clinical outcome. Fifth, the polynomial regression model detected significant
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correlations, but the r² value indicated a limited explanation of variance in the model. Lastly,
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we only evaluated the postoperative improvement in clinical outcome with the ∆HHS. With
265
respect to a detailed evaluation of patient satisfaction, additional scores for health related
266
quality of life might be valuable.
267
Conclusions
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This study adds the new information for patients being treated with unilateral cementless
269
THA due to primary osteoarthritis or mild DDH, that both hip offset and leg length should be
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reconstructed, since both factors demonstrated a comparable additive effect on clinical
271
outcome.
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Level of evidence: Level III, diagnostic study
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ACCEPTED MANUSCRIPT References
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ACCEPTED MANUSCRIPT Acknowledgments: We want to thank Ms Marlies Krueger for data acquisition from the institutional database. Furthermore, we thank the non-commercial research fund Deutsche
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ACCEPTED MANUSCRIPT Table 1: Patient demographics and distribution of analysed and excluded cases; mean (SD) Hips analysed
Hips excluded
P Value
Number of hips
113
133
-
Gender (F:M)
53 : 60
74 : 59
0.201
Age at surgery (yrs.)
62.9 (9.5)
57.5 (15)
0.011
Body mass index (kg/m²)
26.3 (5.0)
26.2 (4.3)
0.571
Harris Hip Score preoperatively
58.1 (16.1)
51.6 (17.2)
0.001
Primary Osteoarthritis
85
57
DDH
17
44
Inflammatory
3
Osteonecrosis
8
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0
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ACCEPTED MANUSCRIPT Table 2: Polynomial regression analysis of the effects on the dependent variable ∆HHS; (r² = 0.116) Unstandardized
Model
Standardized β
Standard error
β coefficients
P - value
coefficients
27.137
16,954
BMI
0.119
0.324
0.036
0.714
Age at surgery in y
0.201
0.167
0.115
0.231
HO difference in mm squared
-0.062
0.022
CORH difference in mm squared
0.017
0.040
Leg length difference in mm squared
-0.085
0.039
Cup inclination squared
0.000
0.003
Cup anteversion squared
-0.003
0.006
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0.007*
0.042
0.666
-0.207
0.031*
0.004
0.964
-0.045
0.660
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0.113
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ACCEPTED MANUSCRIPT Table 3: Clinical outcome (∆HHS) for small zones of reconstruction compared to the contralateral native hip (HO ± 5 and LLD ± 5 mm) Combination of radiographic features
Hip Offset difference in mm inside : outside zone - 15 to - 5
- 10 to 0
- 5 to 5
0 to 10
n hips
19 : 94
32 : 81
21 : 92
8 : 105
mean ∆HHS (p - value)
28.0 : 39.0 (0.004*)
35.3 : 37.9 (0.331)
39.9 : 36.6 (0.383)
36.8 : 37.2 (0.755)
SD
15.1 : 16.3
17.6 : 16.2
17.1 : 16.5
17.3 : 16.6
n hips
26 : 87
54 : 59
47 : 66
17 : 96
mean ∆HHS (p - value)
33.7 : 38.2 (0.077)
36.9 : 37.5 (0.609)
40.3 : 35.0 (0.113)
42.2 : 36.3 (0.099)
SD
14.4 : 17.1
14.4 : 18.5
16.2 : 16.6
16.9 : 16.5
n hips
18 : 95
39 : 74
mean ∆HHS (p - value)
39.1 : 36.8 (0.745)
SD
17.2 : 16.6
- 5 to 5
- 10 to 0
SC
0 to 10
39 : 74
15 : 98
37.2 : 37.2 (0.923)
40.8 : 35.3 (0.071)
45.3 : 35.9 (0.029*)
15.2 : 17.5
16.0 : 16.7
15.8 : 16.4
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Leg length difference in mm
n hips
9 : 104
13 : 100
14 : 99
8 : 105
mean ∆HHS (p - value)
42.1 : 36.8 (0.414)
37.9 : 37.2 (0.964)
36.6 : 37.3 (0.886)
40.1 : 36.9 (0.509)
SD
16.4 : 16.6
16.8 : 16.7
15.1 : 16.9
15.1 : 16.8
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Mann-Whitney-U test; * indicating significance (p < 0.05)
ACCEPTED MANUSCRIPT Table 4: Clinical outcome (∆HHS) for large zones of reconstruction compared to the contralateral native hip (HO ± 7.5 and LLD ± 7.5 mm) Combination of radiographic features
Hip Offset difference in mm inside : outside zone - 15 to 0
- 10 to 5
- 5 to 10
n hips
66 : 47
75 : 38
53 : 60
mean ∆HHS (p - value)
36.6 : 38.0 (0.384)
37.1 : 37.4 (0.879)
41.5 : 33.4 (0.007*)
SD
16.7 : 16.6
16.4 : 17.1
17.3 : 16.6
n hips
72 : 41
82 : 31
- 10 to 5
62 : 51
mean ∆HHS (p - value)
37.3 : 37.0 (0.628)
38.1 : 34.9 (0.541)
39.9 : 33.8 (0.028*)
SD
15.3 : 18.8
15.6 : 19.1
15.9 : 16.9
n hips
49 : 64
56 : 57
46 : 67
SC
- 5 to 10
mean ∆HHS (p - value)
38.2 : 36.4 (0.628)
39.5 : 34.9 (0.153)
39.9 : 35.3 (0.094)
SD
15.6 : 17.4
15.6 : 17.4
15.2 : 17.3
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Mann-Whitney-U test; * indicating significance (p < 0.05)
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Leg length difference in mm
ACCEPTED MANUSCRIPT Figure legends
2
Figure 1: Flow chart illustrating the identification of the study cohort
3
Figure 2: Scatter plot illustrating the improvement in clinical outcome dependent on hip offset
4
and leg length reconstruction compared to the contralateral hip (bubble diameter expresses
5
∆HHS)
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