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Total Hip Arthroplasty With a Fully Hydroxyapatite-Coated Stem: A Cohort Study During 23-28 Years
Accepted Manuscript Total Hip Arthroplasty with a Fully Hydroxyapatite Coated Stem: a Cohort Study during Twenty Three to Twenty Eight Years Olav Reikerås, MD, PhD PII:
S0883-5403(16)30893-2
DOI:
10.1016/j.arth.2016.12.008
Reference:
YARTH 55539
To appear in:
The Journal of Arthroplasty
Received Date: 1 August 2016 Revised Date:
1 December 2016
Accepted Date: 8 December 2016
Please cite this article as: Reikerås O, Total Hip Arthroplasty with a Fully Hydroxyapatite Coated Stem: a Cohort Study during Twenty Three to Twenty Eight Years, The Journal of Arthroplasty (2017), doi: 10.1016/j.arth.2016.12.008. 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.
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Total Hip Arthroplasty with a Fully Hydroxyapatite Coated Stem: a Cohort Study during Twenty Three to Twenty Eight Years
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Olav Reikerås, MD, PhD
Orthopedic Department, Oslo University Hospital, Rikshospitalet,
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0027, Oslo, Norway
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[email protected]
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Abstract Background Long term results of a hydroxyapatite (HA) coated stem are sparse. We have
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followed a cohort of patients operated with a grit-blasted titanium stem designed for press-fit insertion and entirely plasma sprayed with hydroxyapatite (HA) up to 28 years.
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Methods
In the years 1988 to1993 we performed 323 primary total hip replacements in
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276 patients (189 women). Their mean age was 48 (15-79) years. During the following years, 83 patients with 88 hips have died, and 18 patients did not attend the follow-up examination, but had no major symptoms according to telephone interviews and control examination. Thus, 212 patients (255 hips)
Results
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were followed for more than 20 years.
Three patients were revised because of late periprosthetic infection, one because
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of a fall with periprosthetic fracture, and 2 stems were revised due to mechanical
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failure. Osteolysis was significantly associated with wear, and wear was significantly associated with the size of the femoral head. We found a small amount of proximal bone loss and a low incidence of distal hypertrophy of the bone. The bone changes confirmed a well-fixed femoral component in asymptomatic patients.
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Conclusion Our findings indicate an essentially physiological weight distribution from the stem to the femoral bone with no significant thigh pain. The changes in the bone confirmed that the femoral component was well fixed, and we conclude that a
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fully HA-coated titanium stem designed for press-fit insertion lasts for 23 to 28
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years.
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Total Hip Arthroplasty with a Fully Hydroxyapatite Coated Stem:
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Abstract
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Background
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Long term results of a hydroxyapatite (HA) coated stem are sparse. We have
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followed a cohort of patients operated with a grit-blasted titanium stem designed
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for press-fit insertion and entirely plasma sprayed with hydroxyapatite (HA) up
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to 28 years.
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Methods
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In the years 1988 to1993 we performed 323 primary total hip replacements in
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276 patients (189 women). Their mean age was 48 (15-79) years. During the
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following years, 83 patients with 88 hips have died, and 18 patients did not
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attend the follow-up examination, but had no major symptoms according to
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telephone interviews and control examination. Thus, 212 patients (255 hips)
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were followed for more than 20 years.
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Results
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Three patients were revised because of late periprosthetic infection, one because
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of a fall with periprosthetic fracture, and 2 stems were revised due to mechanical
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failure. Osteolysis was significantly associated with wear, and wear was
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significantly associated with the size of the femoral head. We found a small
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amount of proximal bone loss and a low incidence of distal hypertrophy of the
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bone. The bone changes confirmed a well-fixed femoral component in
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asymptomatic patients.
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Conclusion
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Our findings indicate an essentially physiological weight distribution from the
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stem to the femoral bone with no significant thigh pain. The changes in the bone
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confirmed that the femoral component was well fixed, and we conclude that a
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fully HA-coated titanium stem designed for press-fit insertion lasts for 23 to 28
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years.
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Key words
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arthroplasty; hip; hydroxyapatite; revision; stem
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Long term loosening of a femoral stem is a known problem, especially in
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younger men, and stem fixation in total hip arthroplasty (THA) is still a question
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of debate [1]. Uncemented components are widely used and have performed
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well, but there are concerns over stress shielding and loss of bone in the long-
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term [2].
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Bone integration of an uncemented stem is dependent on the surface structure
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and characteristics of the implant. Hydroxyapatite (HA) is often selected as
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coating material because it can enhance endosteal bone ingrowth into the
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prosthesis, and thus improve the stability with better outcomes [3, 4]. But even if
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there are good experimental results with HA coated implants, there have been
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concerns about the porosity, low fatigue strength, degradation and delamination
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during long-term implantation, and loose HA particles can induce foreign body
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reaction and subsequent osteolysis and loosening of the prosthesis [5].
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We have used a grit blasted and extensively HA coated titanium press fit stem
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since 1988, and we now present our institutional results with follow up to 28
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years.
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Materials and Methods
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We performed 323 primary total hip replacements in 276 patients with a HA
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coated prosthesis during the years 1988 to1993. There were 189 women and 87
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men aged 15 to 79 (mean 48) years. The diagnoses were primary (idiopathic)
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osteoarthritis (57 cases) and secondary osteoarthritis due to developmental
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dysplasia of the hip (189), failed femoral neck fracture (12), Calve-Legg-Perthes
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disease or epiphysiolysis (23) and various (42).
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In all cases we used a tapered straight stem designed for press fit insertion. In
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195 cases we used a hemispherical cup inserted with press fit and in 128 cases a
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hemispherical screw cup (Figure 1). Both the acetabular and femoral
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components were made of grit blasted TiAl6V4 (Landos Corail, Landanger,
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Chaumont, France), and the outer surfaces were entirely plasma-sprayed with a
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155 + 35 um layer of HA. The purity of the HA was reported to be greater than
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97%, the density between 1.2 and 1.6 g/mL, the crystallinity greater than 50%
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and the porosity less than 10%. The surface roughness of the coating was
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characterized by Ra (arithmetical mean roughness value) between 7,5 and 9,5
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um and Rt (maximum profile height) between 50 and 65. The surface roughness
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of the grit blasted metal was characterized by Ra between 4 and 6 um and Rt
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between 25 and 40. The bonding strength of the coating to the metal was
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reported to be more than 10MPa. The technical data were reported by the
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manufacturer.
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We used stems of sizes 6 in 2 cases, 8 in 3, 9 in 27, 10 in 44, 11 in 42, 12 in 65,
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13 in 46, 14 in 59 and 15 in 19 and 16 in 16 cases. The head was made of
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stainless steel (Inox) with a diameter of 28 mm in 206 cases and 32 mm in 94
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cases. In 23 cases the head was made of Al2O3 (Biolox) with a diameter of 28
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mm. The polyethylene liners were reported to fulfil the ISO standards F648.
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Sterilisation had been carried out by gamma irradiation in a dose of 25 to 35
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kGy in air.
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Surgery was standardised, using the direct lateral approach, without trochanteric
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osteotomy. We used traditional cancellous bone removal broaches to obtain
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press fit of the stem. Postoperatively, we recommended no weight bearing for 3
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months.
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During follow up, 83 patients with 88 hips have died. Furthermore 18 patients
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(20 hips) would not come for the follow up examination due to high age or as
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they were doing quite well with their prostheses. This was confirmed by
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telephone and controlled by The Norwegian Hip Arthroplasty Register. These
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patients were censored at their last control examination, and 40 of these hips had
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a follow up of more than 20 years. Then we could follow 255 hips in 212
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patients for 20 to 28 years.
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Clinical rating was according to Harris hip score [6]. In addition, each patient
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was asked specifically about thigh pain and was instructed to grade such on a
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scale from 1 to 6 with 1 as the worst and 6 as no pain at all [7].
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Radiographic evaluation included assessment of polyethylene wear, bone
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remodelling, osteolysis and fixation of the stem. Linear measurements were
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digitally made on the anteroposterior radiographs and corrected by reference to
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the diameter of the femoral head. Polyethylene wear was measured according to
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Livermore et al. [8]. Subsidence of the femoral component was referenced by
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the vertical distance from the tip of the trochanter to the lateral shoulder of the
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prosthesis, using a variation greater than 5 mm. This limit of migration was set
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arbitrarily but was based on analysis of manual measurements of migration of
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hip prostheses [9]. Alignment of the femoral component was classified as valgus
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(the tip of the stem engaged the medial cortex), neutral or varus (the tip of the
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stem engaged the lateral cortex). Femoral region analysis was performed as
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described by Gruen et al. [10]. The status of the biological fixation of the stem
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was assessed by a modification of the criteria described by Engh et al. [11].
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Radiographic bony incorporation was defined as extensive intimate bone-
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implant contact, periprosthetic bone formation and remodelling, and the
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abscence of migration. Femoral remodelling was assessed as a change in bone
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density, either as cortical or endosteal bone formation. A decrease in bone
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density was recorded as atrophy and an increase as hypertrophy. Radio dense
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lines that roughly paralleled the surface contour of the implant, but were
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separated from it by a total radiolucent zone (line) of varying thickness was
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classified as fibrous ingrowths. Focal area of cortical or trabecular bone loss was
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considered evident of osteolysis and assessed allowing approximation of the
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area using the formula for an ellipse [12].
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Kaplan-Meier survival analysis was used with removal of a component as the
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endpoint. Logistic regression analysis was employed to relate independent and
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dependent data. P<0,05 was considered significant.
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Results
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In the follow up period 58 press fit cups and 31 screw cups have been revised
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because of mechanical failure. One patient had a fall after 16 years with
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periprosthetic fracture that was revised with a longer stem. Three patients had
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periprosthetic infection after 12, 20 and 22 years that were treated with two
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stage revisions.
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Two stems have been revised due to mechanical failure. The first was a woman
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with arthrogryposis who was operated upon when she was 32 year old. After 8
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years she had a fall on her operated hip, and afterwards she experienced constant
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pain. At revision the stem was loose, and all HA coating had disappeared. The
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second was a male patient who was operated in 1991 at the age of 24 years after
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being treated for acute leukaemia. The cup was revised for mechanical loosening
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after 20 years. At the operation we found the stem to be firmly attached to bone,
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and this was controlled at follow up. However, from 2012 to 2015 the stem
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changes position and subsided (Figure 2), and at operation it was totally loose
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and all the HA coating had disappeared (Figure 3). Then, survival of the stem at
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28 years with reference to mechanical loosening was 0.997 with a standard error
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of 0.003.
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Except for these 2 cases, stem subsidence exceeding 5 mm was not recorded in
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any case. Fibrous ingrowth with radiolucency adjacent to the stem with a
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thickness from 1-3 mm was found in 17 cases (Table 1). This was located to
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zone 1 only in 11 cases, to zone 7 only in 2 cases, to both zone 1 and 7 in 2
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cases and to zone 3 only in 2 cases. Bone atrophy was found in 41 cases. It was
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located to zone 1 only in 7 cases, to zone 7 only in 22 cases and to both zone 1
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and 7 in 10 cases. Bone hypertrophy, generally in the form of endosteal
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condensation around the tip of the stem in zone 4, was found in 21 cases. In
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another 2 of these cases with a valgus position of the stem, cortical hypertrophy
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was also found in zone 5 where the tip of the stem engaged the cortex. Bone
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hypertrophy was significantly associated with a bigger stem (p<0, 0002). Focal
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osteolysis ranging from 26 to 1755 mm2 was found in 34 cases. It was located to
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zone 1 only in 14 cases, to zone 7 only in 12 cases and to both zone 1 and 7 in 8
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cases. Osteolysis was significantly associated with wear (p<0, 0001). In only 12
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patients there was a progression of bone remodelling after an observation time
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of 10 years. One of these had a spontaneous fracture of the major trochanter that
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was treated conservatively.
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Hips with mechanical loosening were excluded from the clinical evaluation of
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hip function according to Harris hip score. In the other patients Harris hip score
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ranged from 50 to 100 with a mean of 89. No patients suffered from thigh pain.
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The rating varied from 5 to 6 (mean 6) in all cases.
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Discussion
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In this study we followed a cohort of patients operated with a fully HA coated
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stem up to 28 years. Our patients tended to be younger and active. There were
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only two cases with mechanical loosening. Otherwise, one patient had a
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periprosthetic fracture and three patients had late deep infection.
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There are limitations of our study. First, we had no control group. Second, the
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high rate of cup revisions may have turned high activity patients to low activity
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patients with less demand on the stem. Third, during follow-up several patients
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have died.
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On the other hand, the age of patients undergoing total hip replacement is on
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average around 68 years. Remaining life expectancy for persons aged 68 years is
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about 18 years. Thereby, it is difficult to follow patients operated with THA for
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more than 20 years. Our patients were younger because many of them had
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osteoarthritis secondary to disease or injury. Then, we could follow a patient
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cohort with a femoral stem of the same design for more than 20 years.
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There are only a few reports on the survival of uncemented stems with a follow
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up of 20 years or more [13, 14, 15, 16]. Low rates of aseptic loosening were
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reported in the late second and early third decades. We also had a low rate of
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aseptic stem loosening, so the principle of biological fixation using a tapered
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femoral component with a grit-blasted surface allowing osseous integration
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seems to work into the third decade.
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As many of our patients were revised due to mechanical failure of the acetabular
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component, we found it difficult to evaluate the overall clinical outcome. Harris
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hip score were evaluated in the patients that had not been revised, and our
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results are in agreement with other long term results of total hip arthroplasty
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[16]. We also focused on thigh pain related to the femoral component. Thigh
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pain has been reported by the use of uncemented stems. This has been thought to
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be caused by stress shielding [2]. A striking result in our series is the absence of
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thigh pain. The absence of radiolucent lines in the diaphysis suggests a
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comprehensive diaphyseal bonding. Furthermore, new bone formation adjacent
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to the prosthesis was associated with a very moderate degree of bone
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remodelling. The low degree of proximal bone loss in our study and a low
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incidence of distal cortical hypertrophy indicate no significant net transfer of
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stress from proximally to distally and a rather physiological weight distribution
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from the stem to the femoral bone. The bone changes, then, confirmed a well
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fixed asymptomatic femoral component. We also observed a moderate incidence
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of he adaptive remodelling in the proximal femoral cortex, and after the first
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years follow-up, further radiological changes around the stem in only 12 cases.
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This observation is in agreement with Karachalios et al. who reported that the
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higher degree of bone changes was observed at the second postoperative year
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[17].
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Extensive hydroxyapatite coating for fixation of a total hip prosthesis was
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introduced more than 25 years ago to achieve durable biological fixation and
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preserve normal periprosthetic bone activity [18]. But high rates of failures of
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HA coated press fit and screw cups have been reported [19]. The survival rate of
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the smooth HA-coated press-fit cup decreased dramatically from 97% at 5 years
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to 46% at 15 years [20]. It was shown that loosening could abruptly occur by
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mechanical force on weak bone-implant integration. In addition, abrasion by HA
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particles separated from the surface of cup could lead to increased wear of the
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PE liner, periprosthetic osteolysis and early loosening [21, 22]
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The acetabular shape is hemispherical with little resistance to mechanical loads
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and shear force [23]. A femoral component with a tapered geometry is supposed
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to encourage osteointegration. In a meta-analysis it was found that in the long-
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term HA-coated stems did better than porous coated stems for hip scores and
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survivorship for aseptic loosening [24]. However, other findings do not support
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the use of HA coating to enhance implant survival of a femoral stem [25].
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Therefore, it has been an open question what will happen with a HA coated stem
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in the long run. Is the coating resorbed, but the implant stabilized in the bony
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bed with a certain risk for loosening, or is the coating in a stable position in
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relation to metal on one side and bone on the other side? If the HA coating
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bonds to bone in a stable situation, stresses on the coating could induce
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underlying failure by delamination between the coating and implant surface. On
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the other hand, if the coating is resorbed, implant fixation has to rely on
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incorporation between metal and bone. In our cohort, we had two cases with HA
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coating detached from the metal, and we ask whether the use of stems with a
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macrostructure that provides physical interlocking between the implant and
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surrounding bone is the rationale if the HA coating detaches or disintegrates in
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the long run. Our study suggests that a fully HA coated stem in total hip surgery
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can provide reliable results up to 28 years. There was a low degree of proximal
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bone loss and preservation of the diaphyseal bone. These observations indicate a
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low and rather physiologically transfer of stress from proximal to distal regions
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with no significant thigh pain.
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Compliance with ethical standards
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Funding source
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No financing has been received for this study.
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Conflicts of interest
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The author declares that there are no conflicts of interest concerning this article.
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20 C.D. Han, K.Y. Shin, H.H. Lee et al.
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23 M. Røkkum, A. Reigstad, C.B. Johansson HA particles can be released from well-fixed HA-coated stems:
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histopathology of biopsies from 20 hips 2-8 years after
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24. Y. L. Chen, T. Lin, M.M. Shi MM et al.
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25. S. Lazarinis, J. Karrholm, N.P. Hailer Effects of hydroxyapatite coating on survival of an uncemented
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hips
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Acknowledgements Dr. Bjorg Bryne and The Norwegian Hip Arthroplasty Register are
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ACCEPTED MANUSCRIPT Table 1. Distribution of femoral bone radiolucency, atrophy, hypertrophy and osteolysis around the stem in relation to Gruen zones.
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Figure legends Figure 1. X ray of HA coated total hip arthroplasty at 16 years after implantation. Press fit cup on the right side and screw cup on the left side.
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Polyethylene wear on both sides, and the left side was revised one year afterwards.
Figure 2A. An integrated HA coated stem after 21 years.
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Figure 3. At revision all HA coating had gone.
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Figure 2B. The stem has subsided and changed position after 24 years
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Figure 2 A
Figure 2 B
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Figure 3
S0883-5403(16)30893-2
DOI:
10.1016/j.arth.2016.12.008
Reference:
YARTH 55539
To appear in:
The Journal of Arthroplasty
Received Date: 1 August 2016 Revised Date:
1 December 2016
Accepted Date: 8 December 2016
Please cite this article as: Reikerås O, Total Hip Arthroplasty with a Fully Hydroxyapatite Coated Stem: a Cohort Study during Twenty Three to Twenty Eight Years, The Journal of Arthroplasty (2017), doi: 10.1016/j.arth.2016.12.008. 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.
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Total Hip Arthroplasty with a Fully Hydroxyapatite Coated Stem: a Cohort Study during Twenty Three to Twenty Eight Years
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Olav Reikerås, MD, PhD
Orthopedic Department, Oslo University Hospital, Rikshospitalet,
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0027, Oslo, Norway
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[email protected]
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Abstract Background Long term results of a hydroxyapatite (HA) coated stem are sparse. We have
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followed a cohort of patients operated with a grit-blasted titanium stem designed for press-fit insertion and entirely plasma sprayed with hydroxyapatite (HA) up to 28 years.
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Methods
In the years 1988 to1993 we performed 323 primary total hip replacements in
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276 patients (189 women). Their mean age was 48 (15-79) years. During the following years, 83 patients with 88 hips have died, and 18 patients did not attend the follow-up examination, but had no major symptoms according to telephone interviews and control examination. Thus, 212 patients (255 hips)
Results
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were followed for more than 20 years.
Three patients were revised because of late periprosthetic infection, one because
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of a fall with periprosthetic fracture, and 2 stems were revised due to mechanical
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failure. Osteolysis was significantly associated with wear, and wear was significantly associated with the size of the femoral head. We found a small amount of proximal bone loss and a low incidence of distal hypertrophy of the bone. The bone changes confirmed a well-fixed femoral component in asymptomatic patients.
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Conclusion Our findings indicate an essentially physiological weight distribution from the stem to the femoral bone with no significant thigh pain. The changes in the bone confirmed that the femoral component was well fixed, and we conclude that a
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fully HA-coated titanium stem designed for press-fit insertion lasts for 23 to 28
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years.
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Total Hip Arthroplasty with a Fully Hydroxyapatite Coated Stem:
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a Cohort Study during Twenty Three to Twenty Eight Years
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Abstract
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Background
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Long term results of a hydroxyapatite (HA) coated stem are sparse. We have
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followed a cohort of patients operated with a grit-blasted titanium stem designed
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for press-fit insertion and entirely plasma sprayed with hydroxyapatite (HA) up
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to 28 years.
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Methods
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In the years 1988 to1993 we performed 323 primary total hip replacements in
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276 patients (189 women). Their mean age was 48 (15-79) years. During the
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following years, 83 patients with 88 hips have died, and 18 patients did not
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attend the follow-up examination, but had no major symptoms according to
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telephone interviews and control examination. Thus, 212 patients (255 hips)
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were followed for more than 20 years.
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Results
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Three patients were revised because of late periprosthetic infection, one because
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of a fall with periprosthetic fracture, and 2 stems were revised due to mechanical
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failure. Osteolysis was significantly associated with wear, and wear was
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significantly associated with the size of the femoral head. We found a small
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amount of proximal bone loss and a low incidence of distal hypertrophy of the
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bone. The bone changes confirmed a well-fixed femoral component in
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asymptomatic patients.
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Conclusion
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Our findings indicate an essentially physiological weight distribution from the
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stem to the femoral bone with no significant thigh pain. The changes in the bone
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confirmed that the femoral component was well fixed, and we conclude that a
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fully HA-coated titanium stem designed for press-fit insertion lasts for 23 to 28
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years.
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Key words
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arthroplasty; hip; hydroxyapatite; revision; stem
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Long term loosening of a femoral stem is a known problem, especially in
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younger men, and stem fixation in total hip arthroplasty (THA) is still a question
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of debate [1]. Uncemented components are widely used and have performed
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well, but there are concerns over stress shielding and loss of bone in the long-
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term [2].
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Bone integration of an uncemented stem is dependent on the surface structure
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and characteristics of the implant. Hydroxyapatite (HA) is often selected as
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coating material because it can enhance endosteal bone ingrowth into the
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prosthesis, and thus improve the stability with better outcomes [3, 4]. But even if
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there are good experimental results with HA coated implants, there have been
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concerns about the porosity, low fatigue strength, degradation and delamination
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during long-term implantation, and loose HA particles can induce foreign body
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reaction and subsequent osteolysis and loosening of the prosthesis [5].
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We have used a grit blasted and extensively HA coated titanium press fit stem
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since 1988, and we now present our institutional results with follow up to 28
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years.
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Materials and Methods
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We performed 323 primary total hip replacements in 276 patients with a HA
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coated prosthesis during the years 1988 to1993. There were 189 women and 87
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men aged 15 to 79 (mean 48) years. The diagnoses were primary (idiopathic)
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osteoarthritis (57 cases) and secondary osteoarthritis due to developmental
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dysplasia of the hip (189), failed femoral neck fracture (12), Calve-Legg-Perthes
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disease or epiphysiolysis (23) and various (42).
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In all cases we used a tapered straight stem designed for press fit insertion. In
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195 cases we used a hemispherical cup inserted with press fit and in 128 cases a
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hemispherical screw cup (Figure 1). Both the acetabular and femoral
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components were made of grit blasted TiAl6V4 (Landos Corail, Landanger,
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Chaumont, France), and the outer surfaces were entirely plasma-sprayed with a
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155 + 35 um layer of HA. The purity of the HA was reported to be greater than
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97%, the density between 1.2 and 1.6 g/mL, the crystallinity greater than 50%
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and the porosity less than 10%. The surface roughness of the coating was
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characterized by Ra (arithmetical mean roughness value) between 7,5 and 9,5
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um and Rt (maximum profile height) between 50 and 65. The surface roughness
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of the grit blasted metal was characterized by Ra between 4 and 6 um and Rt
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between 25 and 40. The bonding strength of the coating to the metal was
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reported to be more than 10MPa. The technical data were reported by the
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manufacturer.
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We used stems of sizes 6 in 2 cases, 8 in 3, 9 in 27, 10 in 44, 11 in 42, 12 in 65,
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13 in 46, 14 in 59 and 15 in 19 and 16 in 16 cases. The head was made of
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stainless steel (Inox) with a diameter of 28 mm in 206 cases and 32 mm in 94
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cases. In 23 cases the head was made of Al2O3 (Biolox) with a diameter of 28
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mm. The polyethylene liners were reported to fulfil the ISO standards F648.
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Sterilisation had been carried out by gamma irradiation in a dose of 25 to 35
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kGy in air.
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Surgery was standardised, using the direct lateral approach, without trochanteric
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osteotomy. We used traditional cancellous bone removal broaches to obtain
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press fit of the stem. Postoperatively, we recommended no weight bearing for 3
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months.
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During follow up, 83 patients with 88 hips have died. Furthermore 18 patients
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(20 hips) would not come for the follow up examination due to high age or as
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they were doing quite well with their prostheses. This was confirmed by
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telephone and controlled by The Norwegian Hip Arthroplasty Register. These
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patients were censored at their last control examination, and 40 of these hips had
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a follow up of more than 20 years. Then we could follow 255 hips in 212
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patients for 20 to 28 years.
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Clinical rating was according to Harris hip score [6]. In addition, each patient
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was asked specifically about thigh pain and was instructed to grade such on a
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scale from 1 to 6 with 1 as the worst and 6 as no pain at all [7].
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Radiographic evaluation included assessment of polyethylene wear, bone
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remodelling, osteolysis and fixation of the stem. Linear measurements were
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digitally made on the anteroposterior radiographs and corrected by reference to
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the diameter of the femoral head. Polyethylene wear was measured according to
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Livermore et al. [8]. Subsidence of the femoral component was referenced by
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the vertical distance from the tip of the trochanter to the lateral shoulder of the
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prosthesis, using a variation greater than 5 mm. This limit of migration was set
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arbitrarily but was based on analysis of manual measurements of migration of
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hip prostheses [9]. Alignment of the femoral component was classified as valgus
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(the tip of the stem engaged the medial cortex), neutral or varus (the tip of the
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stem engaged the lateral cortex). Femoral region analysis was performed as
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described by Gruen et al. [10]. The status of the biological fixation of the stem
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was assessed by a modification of the criteria described by Engh et al. [11].
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Radiographic bony incorporation was defined as extensive intimate bone-
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implant contact, periprosthetic bone formation and remodelling, and the
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abscence of migration. Femoral remodelling was assessed as a change in bone
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density, either as cortical or endosteal bone formation. A decrease in bone
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density was recorded as atrophy and an increase as hypertrophy. Radio dense
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lines that roughly paralleled the surface contour of the implant, but were
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separated from it by a total radiolucent zone (line) of varying thickness was
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classified as fibrous ingrowths. Focal area of cortical or trabecular bone loss was
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considered evident of osteolysis and assessed allowing approximation of the
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area using the formula for an ellipse [12].
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Kaplan-Meier survival analysis was used with removal of a component as the
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endpoint. Logistic regression analysis was employed to relate independent and
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dependent data. P<0,05 was considered significant.
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Results
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In the follow up period 58 press fit cups and 31 screw cups have been revised
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because of mechanical failure. One patient had a fall after 16 years with
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periprosthetic fracture that was revised with a longer stem. Three patients had
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periprosthetic infection after 12, 20 and 22 years that were treated with two
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stage revisions.
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Two stems have been revised due to mechanical failure. The first was a woman
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with arthrogryposis who was operated upon when she was 32 year old. After 8
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years she had a fall on her operated hip, and afterwards she experienced constant
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pain. At revision the stem was loose, and all HA coating had disappeared. The
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second was a male patient who was operated in 1991 at the age of 24 years after
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being treated for acute leukaemia. The cup was revised for mechanical loosening
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after 20 years. At the operation we found the stem to be firmly attached to bone,
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and this was controlled at follow up. However, from 2012 to 2015 the stem
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changes position and subsided (Figure 2), and at operation it was totally loose
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and all the HA coating had disappeared (Figure 3). Then, survival of the stem at
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28 years with reference to mechanical loosening was 0.997 with a standard error
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of 0.003.
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Except for these 2 cases, stem subsidence exceeding 5 mm was not recorded in
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any case. Fibrous ingrowth with radiolucency adjacent to the stem with a
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thickness from 1-3 mm was found in 17 cases (Table 1). This was located to
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zone 1 only in 11 cases, to zone 7 only in 2 cases, to both zone 1 and 7 in 2
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cases and to zone 3 only in 2 cases. Bone atrophy was found in 41 cases. It was
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located to zone 1 only in 7 cases, to zone 7 only in 22 cases and to both zone 1
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and 7 in 10 cases. Bone hypertrophy, generally in the form of endosteal
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condensation around the tip of the stem in zone 4, was found in 21 cases. In
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another 2 of these cases with a valgus position of the stem, cortical hypertrophy
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was also found in zone 5 where the tip of the stem engaged the cortex. Bone
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hypertrophy was significantly associated with a bigger stem (p<0, 0002). Focal
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osteolysis ranging from 26 to 1755 mm2 was found in 34 cases. It was located to
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zone 1 only in 14 cases, to zone 7 only in 12 cases and to both zone 1 and 7 in 8
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cases. Osteolysis was significantly associated with wear (p<0, 0001). In only 12
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patients there was a progression of bone remodelling after an observation time
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of 10 years. One of these had a spontaneous fracture of the major trochanter that
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was treated conservatively.
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Hips with mechanical loosening were excluded from the clinical evaluation of
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hip function according to Harris hip score. In the other patients Harris hip score
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ranged from 50 to 100 with a mean of 89. No patients suffered from thigh pain.
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The rating varied from 5 to 6 (mean 6) in all cases.
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Discussion
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In this study we followed a cohort of patients operated with a fully HA coated
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stem up to 28 years. Our patients tended to be younger and active. There were
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only two cases with mechanical loosening. Otherwise, one patient had a
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periprosthetic fracture and three patients had late deep infection.
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There are limitations of our study. First, we had no control group. Second, the
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high rate of cup revisions may have turned high activity patients to low activity
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patients with less demand on the stem. Third, during follow-up several patients
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have died.
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On the other hand, the age of patients undergoing total hip replacement is on
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average around 68 years. Remaining life expectancy for persons aged 68 years is
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about 18 years. Thereby, it is difficult to follow patients operated with THA for
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more than 20 years. Our patients were younger because many of them had
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osteoarthritis secondary to disease or injury. Then, we could follow a patient
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cohort with a femoral stem of the same design for more than 20 years.
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There are only a few reports on the survival of uncemented stems with a follow
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up of 20 years or more [13, 14, 15, 16]. Low rates of aseptic loosening were
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reported in the late second and early third decades. We also had a low rate of
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aseptic stem loosening, so the principle of biological fixation using a tapered
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femoral component with a grit-blasted surface allowing osseous integration
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seems to work into the third decade.
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As many of our patients were revised due to mechanical failure of the acetabular
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component, we found it difficult to evaluate the overall clinical outcome. Harris
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hip score were evaluated in the patients that had not been revised, and our
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results are in agreement with other long term results of total hip arthroplasty
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[16]. We also focused on thigh pain related to the femoral component. Thigh
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pain has been reported by the use of uncemented stems. This has been thought to
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be caused by stress shielding [2]. A striking result in our series is the absence of
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thigh pain. The absence of radiolucent lines in the diaphysis suggests a
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comprehensive diaphyseal bonding. Furthermore, new bone formation adjacent
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to the prosthesis was associated with a very moderate degree of bone
209
remodelling. The low degree of proximal bone loss in our study and a low
210
incidence of distal cortical hypertrophy indicate no significant net transfer of
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stress from proximally to distally and a rather physiological weight distribution
212
from the stem to the femoral bone. The bone changes, then, confirmed a well
213
fixed asymptomatic femoral component. We also observed a moderate incidence
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of he adaptive remodelling in the proximal femoral cortex, and after the first
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years follow-up, further radiological changes around the stem in only 12 cases.
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This observation is in agreement with Karachalios et al. who reported that the
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higher degree of bone changes was observed at the second postoperative year
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[17].
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Extensive hydroxyapatite coating for fixation of a total hip prosthesis was
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introduced more than 25 years ago to achieve durable biological fixation and
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preserve normal periprosthetic bone activity [18]. But high rates of failures of
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HA coated press fit and screw cups have been reported [19]. The survival rate of
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the smooth HA-coated press-fit cup decreased dramatically from 97% at 5 years
224
to 46% at 15 years [20]. It was shown that loosening could abruptly occur by
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mechanical force on weak bone-implant integration. In addition, abrasion by HA
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particles separated from the surface of cup could lead to increased wear of the
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PE liner, periprosthetic osteolysis and early loosening [21, 22]
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The acetabular shape is hemispherical with little resistance to mechanical loads
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and shear force [23]. A femoral component with a tapered geometry is supposed
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to encourage osteointegration. In a meta-analysis it was found that in the long-
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term HA-coated stems did better than porous coated stems for hip scores and
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survivorship for aseptic loosening [24]. However, other findings do not support
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the use of HA coating to enhance implant survival of a femoral stem [25].
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Therefore, it has been an open question what will happen with a HA coated stem
235
in the long run. Is the coating resorbed, but the implant stabilized in the bony
236
bed with a certain risk for loosening, or is the coating in a stable position in
237
relation to metal on one side and bone on the other side? If the HA coating
238
bonds to bone in a stable situation, stresses on the coating could induce
239
underlying failure by delamination between the coating and implant surface. On
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the other hand, if the coating is resorbed, implant fixation has to rely on
241
incorporation between metal and bone. In our cohort, we had two cases with HA
242
coating detached from the metal, and we ask whether the use of stems with a
243
macrostructure that provides physical interlocking between the implant and
244
surrounding bone is the rationale if the HA coating detaches or disintegrates in
245
the long run. Our study suggests that a fully HA coated stem in total hip surgery
246
can provide reliable results up to 28 years. There was a low degree of proximal
247
bone loss and preservation of the diaphyseal bone. These observations indicate a
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low and rather physiologically transfer of stress from proximal to distal regions
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with no significant thigh pain.
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Compliance with ethical standards
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Funding source
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No financing has been received for this study.
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Conflicts of interest
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The author declares that there are no conflicts of interest concerning this article.
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20 C.D. Han, K.Y. Shin, H.H. Lee et al.
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22 K.S. Delank, P. Drees, N. Menzel et al.
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23 M. Røkkum, A. Reigstad, C.B. Johansson HA particles can be released from well-fixed HA-coated stems:
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histopathology of biopsies from 20 hips 2-8 years after
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24. Y. L. Chen, T. Lin, M.M. Shi MM et al.
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25. S. Lazarinis, J. Karrholm, N.P. Hailer Effects of hydroxyapatite coating on survival of an uncemented
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hips
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Acknowledgements Dr. Bjorg Bryne and The Norwegian Hip Arthroplasty Register are
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Osteolysis 22 20 _______________________________________________________________________
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Figure legends Figure 1. X ray of HA coated total hip arthroplasty at 16 years after implantation. Press fit cup on the right side and screw cup on the left side.
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Polyethylene wear on both sides, and the left side was revised one year afterwards.
Figure 2A. An integrated HA coated stem after 21 years.
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Figure 3. At revision all HA coating had gone.
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Figure 2B. The stem has subsided and changed position after 24 years
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Figure 1
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Figure 2 A
Figure 2 B
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Figure 3