- Email: [email protected]
The Thrust Plate Hip Prosthesis: A Follow-Up of 15-20 Years With 102 Implants
Accepted Manuscript The Thrust Plate Hip Prosthesis A Follow-up of 15 to 20 years with 102 Implants Maja Kaegi, MD, Martin L. Buergi, MD, Hilaire A.C. Jacob, PhD, Heinz H. Bereiter, MD PII:
S0883-5403(15)01030-X
DOI:
10.1016/j.arth.2015.11.020
Reference:
YARTH 54816
To appear in:
The Journal of Arthroplasty
Received Date: 15 May 2015 Revised Date:
28 October 2015
Accepted Date: 16 November 2015
Please cite this article as: Kaegi M, Buergi ML, Jacob HAC, Bereiter HH, The Thrust Plate Hip Prosthesis A Follow-up of 15 to 20 years with 102 Implants, The Journal of Arthroplasty (2015), doi: 10.1016/j.arth.2015.11.020. 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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Departement of Orthopaedic Surgery Canton’s Hospital Graubünden Loëstrasse 99 7000 Chur Switzerland
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Hirslanden Klinik Birshof Reinacherstrasse 28 4142 Münchenstein Switzerland
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Consultant in Orthopaedic Biomechanics Gernstrasse 128 8409 Winterthur Switzerland
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Maja Kaegi, MD1 Martin L. Buergi, MD2 Hilaire A.C. Jacob, PhD3 Heinz H. Bereiter, MD1
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THE THRUST PLATE HIP PROSTHESIS A Follow-up of 15 to 20 years with 102 Implants
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Please address all correspondence to: Dr. med. Heinz Bereiter Kantonsspital Graubünden Klinik für Orthopädie und Traumatologie des Bewegungsapparates Standort Kreuzspital Loëstrasse 99 7000 Chur Switzerland Phone: Fax: Email:
+41 81 256 62 25 +41 81 256 66 62 [email protected]
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Abstract
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Background: Between November 1992 and January 1999 a cohort of 102 Thrust Plate Hip
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Prostheses (TPP) was implanted. Methods: We now clinically and radiologically evaluate
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the remaining 73 prostheses with a mean follow-up of 17.2 years. Results: The Harris hip
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score increased from 51.4 points preoperatively to 94.3 points at the time of this follow-up.
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No further changes in the radiological findings occurred since the first follow-up, published
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in 2005, conducted 2 to 8 years after implantation. Within 15 to 20 years after primary
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implantation of the 102 prostheses, 6 aseptic loosenings occurred, which corresponds to a
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cumulated survival rate of 94.7% at 17 and 91.8% at 18 years. Conclusion: Even though the
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TPP is no longer marketed, the biomechanical behaviour of this unique, clinically successful
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prosthesis deserves attention.
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Key words: Hip prosthesis for younger patients, long-term follow-up, Harris hip score,
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survival rate, Thrust Plate Prosthesis
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Introduction
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Following the initial success of cemented stem prostheses in the 70-ies, the high demand for
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implants was met by the rapid increase of manufacturers with products of varying design.
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Clinical results, however, showed a high revision rate of up to 25% aseptic loosening within
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5 years [1, 2, 3]. This led, on one hand to improvement of cementing techniques, and on the
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other hand to further development of cementless implants. Biomechanical considerations
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now began to influence the design of new prostheses [4, 5]. The unphysiological loading of
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the proximal femur due to a stem prosthesis was also made responsible for the high rate of
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aseptical loosenings that were occurring. As a consequence of this, the idea of transferring
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the hip joint load directly to the strong cortex of the resected femoral neck by means of a
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thrust plate, while completely omitting an intramedullary stem, evolved. Fig.1 shows the
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implant in its final design. The aim was to optimise force transfer to the bone, making this as
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physiological as possible [6, 7, 8, 9, 10].
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In this context, and with reference to possible relative motion at the implant-bone- interface,
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a very special feature of the TPP must be mentioned: A conventional stem prosthesis with
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its intramedullar fixation is subjected to twist because of its crank-like configuration (Fig.2),
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especially when hip loads act in flexion, as when climbing stairs or rising from a seat. This
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cannot occur with the TPP due to anchorage only within the femoral neck.
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Materials and Methods
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The final design (Fig.1) was launched in 1992 [11, 12]. It is characterized by an oval thrust
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plate, now united with the mandrel which is tapered at the proximal end to fit the ball head.
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Heads of various sizes, either of metal (Metasul®) or aluminium oxide ceramic (Biolox®)
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could be fitted. While the mandrel-thrust-plate unit and the lateral plate are made of titanium
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wrought alloy (Protasul-100®), the central bolt is of high-strength, forged cobalt- chromium-
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molybdenum alloy (Protasul-21-WF®). All titanium alloy surfaces in contact with bone are
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textured and sandblasted (Fig. 1). The lateral plate is attached to the femur by means of 2
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cortical bone screws. The number of components to be assembled during surgery has been
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minimised. Between November 1992 and January 1999, 102 primary hip arthroplasties were
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carried out on 84 patients (63 men and 21 women). Fourteen men and 4 women received the
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TPP bilaterally. The mean age at operation was 54 (range 26-76) years for the men and 47
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(27-64) years for the women. The indications for surgery were primary osteoarthritis, 72%;
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idiopathic femoral head necrosis, 11%; hip dysplasia, 3%; Legg-Calve-Perthes disease, 2%;
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Epiphysiolysis, 3%; rheumatoid arthritis, 4% and posttraumatic osteoarthritis 5%. Every TPP
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that was implanted during the period between November 1992 and January 1999 was
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prospectively followed up. During the implantation period from 1992 to 1999 a bipolar
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acetabular component was used in 9 hips. 93 artificial sockets were of the press-fit
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Sulmesh® type [13]. In 54 cases, a metal-on-metal bearing was chosen (Metasul®). The
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ACCEPTED MANUSCRIPT remaining 39 TPP had alumina ceramic heads (Biolox®) paired with high-density
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polyethylene (RCH-1000) acetabular sockets.
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Surgical Technique
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The transgluteal or lateral approach according to Bauer et al. [14] was chosen in all cases.
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Particular attention was paid in planning a neck-shaft angle of between 125° and 130°.
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After high resection of the head and neck, the latter was milled with a special face-milling
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cutter down to the desired level [15]. The mandrel–thrust-plate unit was then gently
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hammered into the pre-reamed femur so that a light press-fit between mandrel and
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cancellous bone resulted. The lateral plate automatically moved into a suitable position,
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adjusting itself while the central bolt was tightened to its full extent, forcing the flat surface
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of the thrust plate to seat firmly on the resected femoral neck; after which, introduction of
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the 2 cortical screws was accomplished.
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Follow-up Analysis: Long term follow-up 15 – 20 years
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For this follow-up we review the remaining 73 (62 patients) of the initial 102 prostheses
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during a mean follow-up period of 17.2 years (15 – 20.5 yrs.) after implantation. Of the 84
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patients listed, 20 had died and only 1 patient was lost to follow-up.
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Radiological Investigations
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After the initial postoperative x-ray, radiological checks were carried out 6 and 12 weeks,
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6 months, and 1, 2, 5, 7, 10, 13, 15 and 20 years after implantation. On these occasions,
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standard pelvis overviews and axial and anteroposterior radiographs were taken. As
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pointed out by Huggler [11] and Gruber et al. [16], the anteroposterior radiographs were
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made in 20° internal rotation of the femur so that the x-ray beam runs parallel to the
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undersurface of the thrust plate to check the contact between the medial cortex and the
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thrust plate. The bone remodelling patterns as observed in the radiographs were classified
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into 3 phenotypes (Fig. 3), as published in 2005 [15].
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Type 1: When 50% or more of initial cortical bone contact in the mediocaudad zone
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from the flat surface of the thrust plate to the medial cortex.
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Type 2: When retraction of the cortical bone in contact with the thrust plate amounts to
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between 51% and 99% of initial contact. Cortical bone contact with the thrust plate still
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persists and load transmission from thrust plate to cortex continues to be effected as
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proximal as possible.
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Type 3: When bone contact with the thrust plate has been completely lost. Load transmission
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in these cases is effected only through the new bone formed between the ribs of the
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prosthesis and the medial cortex.
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Clinical Assessment
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The patients were clinically examined at the time they were radiographically reviewed. At
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each review, the range of movement and joint function was noted [15]. The clinical
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outcome was evaluated according to the Harris hip score [17]. Survival rates were
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calculated using life tables and the Kaplan-Meier method [18, 19]. The criterion defining
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the end point or failure was always aseptic loosening with explantation of the mandrel–
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thrust-plate unit.
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Results
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Of the 102 primary total hip arthroplasties carried out between November 1992 and
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January 1999, 20 patients had died. On questioning family members and family doctors
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of the 20 deceased patients, no problems were known to have occurred with the TPP and the
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hips were performing well up to the time the patients died. Only one patient was lost to
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follow-up. The remaining 73 prostheses of the initial 102 were evaluated for this review with
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a mean follow-up of 17.2 years (15.0 – 20.5 yrs.). Considering the earlier revisions because
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of aseptic loosening, as already reported in 2005 [15], a total of 6 aseptic loosenings within
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15 to 20 years after primary surgery have resulted. 2 revisions were performed during the
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ACCEPTED MANUSCRIPT first follow-up observation period, 5 and 13 months after implantation [15]. One aseptic
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loosening had occurred 13 years after implantation due to polyethylene debris. 3 aseptic
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loosenings were revised between 15 and 20 years after implantation elsewhere. All of these 6
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prostheses were revised successfully, replacing them by ones of the stem type. This
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corresponds to a cumulated survival rate of 94.7% at 17 and 91.8% at 18 years after
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implantation of the TPP, the endpoint being defined as revision of the whole femoral
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component only with regards to aseptic loosening (Fig. 4a).
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Taking into account 2 loosenings due to infection (one high-grade early infection and one
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low-grade infection one year postoperatively [15]) and one periprosthetic fracture 14 years
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after implantation, which was treated by replacement of the TPP with a long-stem prosthesis,
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we have a total of 9 prostheses that were revised. This now corresponds to a cumulative
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survival rate of 91.8% at 17 and 88.9% at 18 years after implantation, the endpoint being
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revision of the whole femoral component for whatever reason (Fig. 4b). In addition to these
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9 prostheses that were completely replaced, we carried out 3 partial revisions in connection
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with the lateral plate because of trochanter discomfort. In all 3 patients the lateral plate was
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removed after the thrust-plate had become fully osseointegrated. In one case removal was
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performed 3 years after implantation and in another, after 5 years. In the third case removal
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of the lateral plate was effected 13 years after implantation. In all 3 cases the TPP remained
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stable. Taking into account all 12 partial and full revisions, a cumulative survival rate of
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88.8% at 17 and 86.2% at 18 years after implantation is obtained, with the endpoint defined
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as partial or total revision for any cause.
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Radiological
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With reference to the classification of radiological findings, as defined in Section Material
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and Methods, no changes could be detected when compared with the radiographs analysed 2
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to 8 years after implantation of the same cohort (98 cases examined) [15]. The situation
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reported was: 86.7% of Type 1, 10.2% of Type 2, and 3.1% of Type 3. However, two
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although the patients are completely asymptomatic. With the hemi-bipolar heads increasing
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cartilage wear appeared in two cases without being clinically manifest.
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Clinical
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Preoperatively, the Harris hip score (HHS) was 51.4 +/- 11.4 (mean +/- SD) points. At the
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time of this follow-up the Harris hip score was still 94.3 (minimum 53, maximum 100)
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points (p< 0.0001).
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Discussion
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The present cohort of 102 TPP has been subjected to intermediate clinical and
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radiological evaluation during the past years, and the results reported accordingly [15,
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20]. In relation to the various bone remodelling patterns observed, as classified by 3
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radiological phenotypes (Fig. 3), an extensive discussion on this matter has been
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presented previously [15]. Nevertheless, we still have no satisfactory explanation as to
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why, occasionally, preferential load transfer through the cancellous material takes place,
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causing the cortical bone under the thrust plate to retract. The only tentative hypothesis is
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that perhaps in such cases the cancellous material was compacted to such an extent during
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the implantation that the hip force preferably passed through the compacted cancellous
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bone rather than along the medial cortex. However, the new situation, effected by
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remodelling of the bone in this area within 2 years after implantation, proves stable [15].
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This is again reflected by the fact that no changes in the radiographs of the investigated
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patients could be detected since the previous follow-up reported 10 years ago [15].
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Of the 6 aseptic loosenings which occurred, one was caused by excessive resection of the
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femoral neck that, in spite of choosing the shortest available central bolt, led to insufficient
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pre-tension between bone and prosthesis. Signs of loosening became clinically and
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radiologically manifest 3 months later, and 13 months after implantation this TPP was
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ACCEPTED MANUSCRIPT replaced by a conventional, cementless, titanium stem prosthesis. Another TPP had to be
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replaced because a longitudinal fissure along the medial cortex remained undetected during
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surgery. Radiological and clinical evidence of the disorder made revision of the TPP, 5
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months after implantation, necessary. The third case of aseptic loosening occurred 13 years
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after implantation. During revision surgery it became obvious that polyethylene wear debris
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was responsible for the osteolysis under the thrust plate. Again, as in the above mentioned
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cases, a conventional, cementless, titanium stem prosthesis was used as replacement. The 3
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remaining cases of aseptic loosening (15 to 20 years postoperative) were treated elsewhere
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and the authors are therefore only aware that in one case a conventional stem prosthesis was
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implanted with cement while the other 2 were replaced by conventional, cementless
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titanium stem prostheses. The x-rays of these 3 loosened TPP indicated bone resorption
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typically due to polyethylene wear particles.
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Even the periprosthetic fracture, 14 years after implantation of the TPP, was readily treated
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by use of a long-stem cementless titanium prosthesis, without the necessity to employ a
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claw-plate or similar device. Again, even in this case, removal of the TPP and insertion of
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the long stem was accomplished without a problem.
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In the 3 cases where, because of ‘lateral pain’, the lateral plate was removed after the
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thrust plate had become well osseointegrated, the thrust plate continued to remain stable.
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Only in one of these 3 cases removal of the lateral plate, 13 years after implantation, did
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not alleviate the disorder. In our cohort of patients, about 2 to 5 % reported discomfort in
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the trochanter region which usually subsided [15]. This has been termed „lateral-plate
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pain“, because in radiographs attention is immediately drawn to the very obvious lateral
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plate in the region of complaint. Although soft tissue irritation may cause the symptom,
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especially in slim patients where in some cases the plate is even palpable, it must be
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emphasised that literature has reported 8 – 17% of cases with trochanter pain after surgery
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with the transgluteal approach and implantation of conventional prostheses [29].
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ACCEPTED MANUSCRIPT Indications and contraindications involving diagnosis, selection of patients for implantation
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of the TPP, surgical procedure, and the revision scenario, based on previous experience
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with preliminary series of implantations, are addressed at length elsewhere [11].
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Nevertheless, we wish to give a brief account of such particulars as follows:
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Indications and contraindications for the TTP
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The indications for a TPP are basically the same as for conventional total hip prostheses;
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however, the femoral neck must exhibit strong, medial cortical bone. Particularly in
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younger patients, the TPP is a valuable alternative to other surgical procedures.
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In cases of femoral head necrosis where the neck region is also affected, the TPP might not
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be adequate. Implantation of a TPP is contraindicated in patients with pronounced coxa
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vara, coxa valga and perhaps in those with a short, narrow femoral neck. Generally, the
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TPP should be so implanted that a neck-shaft angle between 125° and 130° results.
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Considering deviations from this standard position, a valgus femoral neck angle greater
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than 140°, or a varus angle of less than 120° cannot be accepted. Also, since the TPP
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mainly follows the given femoral neck axis, correction of anteversion of the femoral neck
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is limited.
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If the above mentioned selection criteria are strictly observed, no complications should be
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expected during surgery. Explantation of a loosened TPP for the purpose of revision
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should present no problems. Because of preservation of bone stock, the femur commonly
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presents in a state as encountered during primary implantation of a conventional stem
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prosthesis.
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Specific comments with regard to components of the TPP
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Although the TPP has been taken off the market by the former manufacturer for commercial
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reasons, published reports by other users [21, 22, 23, 24, 25, 26, 27, 28] confirm the long-term
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results herewith presented. Since it is conceivable that the basic design of this prosthesis
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might find continuation in one way or another, it could be of value to communicate
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Head /cup articulation
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The head of the prosthesis was seen to have adopted an eccentric position after 15 years in a
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few cases with polyethylene cups, as a result of polyethylene wear. In the case of metal-on-
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metal combinations, all with 28 mm heads, metal wear problems were encountered. Correct
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positioning of the acetabular cup is important. With excessive anteversion there would be risk
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of dorsolateral impingement with the thrust plate.
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Thrust plate
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A greater variety of sizes, more adapted to the form of the femoral neck, especially caudal,
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would perhaps lessen the danger of impingement. The massive box-like shape of the
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intermediate part between thrust plate and mandrel could be improved. The interface exposed
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to bone must remain structured and roughened to optimise osseointegration. It might also be
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of advantage to shorten the mandrel somewhat, and to perhaps polish its lateral extension so
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as to discourage bone taking grip on this part of the prosthesis while encouraging bone
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ongrowth in the region of the thrust plate.
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Central bolt and lateral plate
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A primary, mechanically stable fixation of the thrust plate is mandatory until osseointegration
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is completed. For this reason, the central bolt and lateral plate are of necessity. With present
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high-strength materials a bolt of smaller diameter will probably suffice, especially in view of
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reducing the diameter of the bolt head which would be of immense value in minimising the
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size of the lateral plate.
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The lateral plate of titanium could almost surely be secured to the femoral shaft with only
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one cortical screw. The screw must be located in an area of substantial cortical bone.
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Together with a smaller bolt head, the size of the lateral plate could be appreciably reduced.
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Surgery
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Because of prosthesis design with multiple components and the need to operate meticulously, 9
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ACCEPTED MANUSCRIPT the implantation of a TPP puts a high demand on the surgeon.
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Bias
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Some measure of cognitive or confirmation bias might be present in this report, being from
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the author’s clinic.
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In the 90-ies there was a high demand for the TPP worldwide [28, 30, 31, 32, 33], then the
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demand dropped. This might be partially attributed to the come-back of resurfacing
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arthroplasty through McMinn. However, the thrust plate prosthesis in its final design has
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continued to be used [21, 22, 23, 24, 25, 26, 27, 28], as marketed until 2007.
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Conclusion
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In summary we may state that the TPP is a very good concept from a biomechanical
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point of view. It has proved to be clinically and radiologically successful. However,
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because of its complexity with several components that have to be assembled during
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implantation, and the need to be meticulous during surgery, the prosthesis is perhaps less
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attractive for general use than conventional ones. In our opinion, because of this, the TPP
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might be at greater risk for complications than other types of prostheses, especially for
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surgeons with less experience. The TPP has finally fallen victim to commercial and
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marketing considerations about 7 years ago and is therefore no longer available from the
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former manufacturer. Based on our long-term results, we are still confident that this
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implant shows remarkable biomechanical aspects, even taking into consideration the bias
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that might be present from the author’s clinic (inventor) point-of-view.
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The present follow-up confronted us with several unexpected problems, mainly with data
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retrieval and with locating patients. Patient’s records (clinical and radiological) must be
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protected from wilful destruction by hospital authorities, and data retrieval ensured at all
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times, especially in view of fast-changing storage technologies.
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[27] Sharma S, Verma G, Draviraj KP, Bhamra M. Early results with the thrust plate prosthesis in young patients with osteoarthritis of the hip. Acta Orthop Belg. 2005 Apr; 71(2):182-8. [28] Karatosun V, Ünver B, Gunal I. Hip arthroplasty with the Thrust Plate Prosthesis in patients of 65 years of age or older: 67 patients followed 2–7 years. Arch Orthop Trauma Surg (2008) 128:377–381. [29] Sayed-Noor AS, Sjödén GO. Greater trochanter pain after total hip arthroplasty: the incidence, clinical outcome and associated factors. Hip international. 2006; Vol 16 no 3: 202 – 206 12
ACCEPTED MANUSCRIPT [30] Yasunaga Y, Goto T, Hisatome T, Tanaka R, Yamasaki T, Ochi M. Bone-preserving prosthesis with a single axis for treating osteonecrosis of the femoral head: midterm results for the thrust plate hip prosthesis. J Orthop Sci 2003; 8: 818-822 [31] Sharma S, Verma G, Draviraj KP, Bhamra M. Early results with the thrust plate prosthesis in young patients with osteoarthritis of the hip. Acta Orthop. Belg., 2005, 71, 182188
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[32] Menge M. Acht Jahre Druckscheibenprothese – eine mittelfristige Bewertung. Orthop Praxis 2000; 36: 143 - 151
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[33] Ishaque BA, Wienbeck S, Stürz H. Mittelfristige Ergebnisse und Wechseloperationen nach Druckscheibenprothesen (DSP). Z Orthop Ihre Grenzgeb. 2004 Jan-Feb;142(1): 25-32
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ACCEPTED MANUSCRIPT LEGEND TO FIGURES On the left: The TPP in its details of components. From left to right: The central bolt, made of Protasul-21-WF® and available in 3 dimensions; the lateral plate, made of Protasul-100®; the mandrel-thrust-plate unit, also made of Protasul-100® and heads of various sizes, either of metal (Metasul®) or aluminium oxide ceramic (Biolox®). On the right: The TTP in its final design, third generation.
Fig. 2.
Crank mechanism with conventional stem prostheses.
Fig. 3.
The three radiological phenotypes in relation to the various bone remodelling patterns
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Fig. 1.
a: Revision for aseptic loosening: Kaplan-Meier survival rate: 94.7% at 17 yrs (95% Confidence Interval (CI), 90.2-99.2), 91.8% at 18 yrs (95% CI, 84.6-99.0) b: Revision for all reasons: Kaplan-Meier survival rate: 88.8% at 17 yrs (95% Confidence Interval (CI), 82.5- 95.1), 86.2% at 18 yrs (95% CI, 77.9-94.1): Revisions: N=6 asept. loosening, N=3 other reasons, N=3 partial revisions (lateral plate / bolt) after 2.7, 2.8 and 4.5 years
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a: Type 1: 0 - 50% retraction of the cortical bone in the mediocaudad zone immediately under the thrust plate b: Type 2: 51% - 99% retraction of the cortical bone in contact with the thrust plate c: Type 3: completely loss of bone contact with the thrust plate in the mediocaudad zone
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S0883-5403(15)01030-X
DOI:
10.1016/j.arth.2015.11.020
Reference:
YARTH 54816
To appear in:
The Journal of Arthroplasty
Received Date: 15 May 2015 Revised Date:
28 October 2015
Accepted Date: 16 November 2015
Please cite this article as: Kaegi M, Buergi ML, Jacob HAC, Bereiter HH, The Thrust Plate Hip Prosthesis A Follow-up of 15 to 20 years with 102 Implants, The Journal of Arthroplasty (2015), doi: 10.1016/j.arth.2015.11.020. 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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Departement of Orthopaedic Surgery Canton’s Hospital Graubünden Loëstrasse 99 7000 Chur Switzerland
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Hirslanden Klinik Birshof Reinacherstrasse 28 4142 Münchenstein Switzerland
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Consultant in Orthopaedic Biomechanics Gernstrasse 128 8409 Winterthur Switzerland
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Maja Kaegi, MD1 Martin L. Buergi, MD2 Hilaire A.C. Jacob, PhD3 Heinz H. Bereiter, MD1
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THE THRUST PLATE HIP PROSTHESIS A Follow-up of 15 to 20 years with 102 Implants
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Please address all correspondence to: Dr. med. Heinz Bereiter Kantonsspital Graubünden Klinik für Orthopädie und Traumatologie des Bewegungsapparates Standort Kreuzspital Loëstrasse 99 7000 Chur Switzerland Phone: Fax: Email:
+41 81 256 62 25 +41 81 256 66 62 [email protected]
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Abstract
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Background: Between November 1992 and January 1999 a cohort of 102 Thrust Plate Hip
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Prostheses (TPP) was implanted. Methods: We now clinically and radiologically evaluate
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the remaining 73 prostheses with a mean follow-up of 17.2 years. Results: The Harris hip
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score increased from 51.4 points preoperatively to 94.3 points at the time of this follow-up.
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No further changes in the radiological findings occurred since the first follow-up, published
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in 2005, conducted 2 to 8 years after implantation. Within 15 to 20 years after primary
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implantation of the 102 prostheses, 6 aseptic loosenings occurred, which corresponds to a
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cumulated survival rate of 94.7% at 17 and 91.8% at 18 years. Conclusion: Even though the
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TPP is no longer marketed, the biomechanical behaviour of this unique, clinically successful
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prosthesis deserves attention.
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Key words: Hip prosthesis for younger patients, long-term follow-up, Harris hip score,
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survival rate, Thrust Plate Prosthesis
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Introduction
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Following the initial success of cemented stem prostheses in the 70-ies, the high demand for
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implants was met by the rapid increase of manufacturers with products of varying design.
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Clinical results, however, showed a high revision rate of up to 25% aseptic loosening within
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5 years [1, 2, 3]. This led, on one hand to improvement of cementing techniques, and on the
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other hand to further development of cementless implants. Biomechanical considerations
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now began to influence the design of new prostheses [4, 5]. The unphysiological loading of
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the proximal femur due to a stem prosthesis was also made responsible for the high rate of
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aseptical loosenings that were occurring. As a consequence of this, the idea of transferring
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the hip joint load directly to the strong cortex of the resected femoral neck by means of a
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thrust plate, while completely omitting an intramedullary stem, evolved. Fig.1 shows the
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implant in its final design. The aim was to optimise force transfer to the bone, making this as
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physiological as possible [6, 7, 8, 9, 10].
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In this context, and with reference to possible relative motion at the implant-bone- interface,
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a very special feature of the TPP must be mentioned: A conventional stem prosthesis with
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its intramedullar fixation is subjected to twist because of its crank-like configuration (Fig.2),
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especially when hip loads act in flexion, as when climbing stairs or rising from a seat. This
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cannot occur with the TPP due to anchorage only within the femoral neck.
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Materials and Methods
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The final design (Fig.1) was launched in 1992 [11, 12]. It is characterized by an oval thrust
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plate, now united with the mandrel which is tapered at the proximal end to fit the ball head.
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Heads of various sizes, either of metal (Metasul®) or aluminium oxide ceramic (Biolox®)
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could be fitted. While the mandrel-thrust-plate unit and the lateral plate are made of titanium
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wrought alloy (Protasul-100®), the central bolt is of high-strength, forged cobalt- chromium-
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molybdenum alloy (Protasul-21-WF®). All titanium alloy surfaces in contact with bone are
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textured and sandblasted (Fig. 1). The lateral plate is attached to the femur by means of 2
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cortical bone screws. The number of components to be assembled during surgery has been
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minimised. Between November 1992 and January 1999, 102 primary hip arthroplasties were
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carried out on 84 patients (63 men and 21 women). Fourteen men and 4 women received the
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TPP bilaterally. The mean age at operation was 54 (range 26-76) years for the men and 47
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(27-64) years for the women. The indications for surgery were primary osteoarthritis, 72%;
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idiopathic femoral head necrosis, 11%; hip dysplasia, 3%; Legg-Calve-Perthes disease, 2%;
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Epiphysiolysis, 3%; rheumatoid arthritis, 4% and posttraumatic osteoarthritis 5%. Every TPP
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that was implanted during the period between November 1992 and January 1999 was
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prospectively followed up. During the implantation period from 1992 to 1999 a bipolar
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acetabular component was used in 9 hips. 93 artificial sockets were of the press-fit
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Sulmesh® type [13]. In 54 cases, a metal-on-metal bearing was chosen (Metasul®). The
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polyethylene (RCH-1000) acetabular sockets.
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Surgical Technique
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The transgluteal or lateral approach according to Bauer et al. [14] was chosen in all cases.
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Particular attention was paid in planning a neck-shaft angle of between 125° and 130°.
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After high resection of the head and neck, the latter was milled with a special face-milling
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cutter down to the desired level [15]. The mandrel–thrust-plate unit was then gently
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hammered into the pre-reamed femur so that a light press-fit between mandrel and
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cancellous bone resulted. The lateral plate automatically moved into a suitable position,
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adjusting itself while the central bolt was tightened to its full extent, forcing the flat surface
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of the thrust plate to seat firmly on the resected femoral neck; after which, introduction of
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the 2 cortical screws was accomplished.
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Follow-up Analysis: Long term follow-up 15 – 20 years
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For this follow-up we review the remaining 73 (62 patients) of the initial 102 prostheses
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during a mean follow-up period of 17.2 years (15 – 20.5 yrs.) after implantation. Of the 84
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patients listed, 20 had died and only 1 patient was lost to follow-up.
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Radiological Investigations
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After the initial postoperative x-ray, radiological checks were carried out 6 and 12 weeks,
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6 months, and 1, 2, 5, 7, 10, 13, 15 and 20 years after implantation. On these occasions,
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standard pelvis overviews and axial and anteroposterior radiographs were taken. As
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pointed out by Huggler [11] and Gruber et al. [16], the anteroposterior radiographs were
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made in 20° internal rotation of the femur so that the x-ray beam runs parallel to the
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undersurface of the thrust plate to check the contact between the medial cortex and the
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thrust plate. The bone remodelling patterns as observed in the radiographs were classified
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into 3 phenotypes (Fig. 3), as published in 2005 [15].
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Type 1: When 50% or more of initial cortical bone contact in the mediocaudad zone
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from the flat surface of the thrust plate to the medial cortex.
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Type 2: When retraction of the cortical bone in contact with the thrust plate amounts to
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between 51% and 99% of initial contact. Cortical bone contact with the thrust plate still
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persists and load transmission from thrust plate to cortex continues to be effected as
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proximal as possible.
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Type 3: When bone contact with the thrust plate has been completely lost. Load transmission
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in these cases is effected only through the new bone formed between the ribs of the
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prosthesis and the medial cortex.
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Clinical Assessment
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The patients were clinically examined at the time they were radiographically reviewed. At
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each review, the range of movement and joint function was noted [15]. The clinical
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outcome was evaluated according to the Harris hip score [17]. Survival rates were
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calculated using life tables and the Kaplan-Meier method [18, 19]. The criterion defining
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the end point or failure was always aseptic loosening with explantation of the mandrel–
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thrust-plate unit.
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Results
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Of the 102 primary total hip arthroplasties carried out between November 1992 and
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January 1999, 20 patients had died. On questioning family members and family doctors
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of the 20 deceased patients, no problems were known to have occurred with the TPP and the
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hips were performing well up to the time the patients died. Only one patient was lost to
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follow-up. The remaining 73 prostheses of the initial 102 were evaluated for this review with
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a mean follow-up of 17.2 years (15.0 – 20.5 yrs.). Considering the earlier revisions because
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of aseptic loosening, as already reported in 2005 [15], a total of 6 aseptic loosenings within
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15 to 20 years after primary surgery have resulted. 2 revisions were performed during the
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loosening had occurred 13 years after implantation due to polyethylene debris. 3 aseptic
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loosenings were revised between 15 and 20 years after implantation elsewhere. All of these 6
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prostheses were revised successfully, replacing them by ones of the stem type. This
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corresponds to a cumulated survival rate of 94.7% at 17 and 91.8% at 18 years after
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implantation of the TPP, the endpoint being defined as revision of the whole femoral
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component only with regards to aseptic loosening (Fig. 4a).
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Taking into account 2 loosenings due to infection (one high-grade early infection and one
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low-grade infection one year postoperatively [15]) and one periprosthetic fracture 14 years
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after implantation, which was treated by replacement of the TPP with a long-stem prosthesis,
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we have a total of 9 prostheses that were revised. This now corresponds to a cumulative
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survival rate of 91.8% at 17 and 88.9% at 18 years after implantation, the endpoint being
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revision of the whole femoral component for whatever reason (Fig. 4b). In addition to these
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9 prostheses that were completely replaced, we carried out 3 partial revisions in connection
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with the lateral plate because of trochanter discomfort. In all 3 patients the lateral plate was
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removed after the thrust-plate had become fully osseointegrated. In one case removal was
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performed 3 years after implantation and in another, after 5 years. In the third case removal
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of the lateral plate was effected 13 years after implantation. In all 3 cases the TPP remained
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stable. Taking into account all 12 partial and full revisions, a cumulative survival rate of
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88.8% at 17 and 86.2% at 18 years after implantation is obtained, with the endpoint defined
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as partial or total revision for any cause.
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Radiological
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With reference to the classification of radiological findings, as defined in Section Material
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and Methods, no changes could be detected when compared with the radiographs analysed 2
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to 8 years after implantation of the same cohort (98 cases examined) [15]. The situation
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reported was: 86.7% of Type 1, 10.2% of Type 2, and 3.1% of Type 3. However, two
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although the patients are completely asymptomatic. With the hemi-bipolar heads increasing
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cartilage wear appeared in two cases without being clinically manifest.
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Clinical
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Preoperatively, the Harris hip score (HHS) was 51.4 +/- 11.4 (mean +/- SD) points. At the
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time of this follow-up the Harris hip score was still 94.3 (minimum 53, maximum 100)
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points (p< 0.0001).
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Discussion
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The present cohort of 102 TPP has been subjected to intermediate clinical and
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radiological evaluation during the past years, and the results reported accordingly [15,
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20]. In relation to the various bone remodelling patterns observed, as classified by 3
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radiological phenotypes (Fig. 3), an extensive discussion on this matter has been
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presented previously [15]. Nevertheless, we still have no satisfactory explanation as to
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why, occasionally, preferential load transfer through the cancellous material takes place,
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causing the cortical bone under the thrust plate to retract. The only tentative hypothesis is
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that perhaps in such cases the cancellous material was compacted to such an extent during
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the implantation that the hip force preferably passed through the compacted cancellous
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bone rather than along the medial cortex. However, the new situation, effected by
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remodelling of the bone in this area within 2 years after implantation, proves stable [15].
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This is again reflected by the fact that no changes in the radiographs of the investigated
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patients could be detected since the previous follow-up reported 10 years ago [15].
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Of the 6 aseptic loosenings which occurred, one was caused by excessive resection of the
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femoral neck that, in spite of choosing the shortest available central bolt, led to insufficient
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pre-tension between bone and prosthesis. Signs of loosening became clinically and
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radiologically manifest 3 months later, and 13 months after implantation this TPP was
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replaced because a longitudinal fissure along the medial cortex remained undetected during
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surgery. Radiological and clinical evidence of the disorder made revision of the TPP, 5
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months after implantation, necessary. The third case of aseptic loosening occurred 13 years
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after implantation. During revision surgery it became obvious that polyethylene wear debris
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was responsible for the osteolysis under the thrust plate. Again, as in the above mentioned
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cases, a conventional, cementless, titanium stem prosthesis was used as replacement. The 3
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remaining cases of aseptic loosening (15 to 20 years postoperative) were treated elsewhere
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and the authors are therefore only aware that in one case a conventional stem prosthesis was
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implanted with cement while the other 2 were replaced by conventional, cementless
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titanium stem prostheses. The x-rays of these 3 loosened TPP indicated bone resorption
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typically due to polyethylene wear particles.
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Even the periprosthetic fracture, 14 years after implantation of the TPP, was readily treated
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by use of a long-stem cementless titanium prosthesis, without the necessity to employ a
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claw-plate or similar device. Again, even in this case, removal of the TPP and insertion of
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the long stem was accomplished without a problem.
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In the 3 cases where, because of ‘lateral pain’, the lateral plate was removed after the
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thrust plate had become well osseointegrated, the thrust plate continued to remain stable.
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Only in one of these 3 cases removal of the lateral plate, 13 years after implantation, did
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not alleviate the disorder. In our cohort of patients, about 2 to 5 % reported discomfort in
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the trochanter region which usually subsided [15]. This has been termed „lateral-plate
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pain“, because in radiographs attention is immediately drawn to the very obvious lateral
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plate in the region of complaint. Although soft tissue irritation may cause the symptom,
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especially in slim patients where in some cases the plate is even palpable, it must be
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emphasised that literature has reported 8 – 17% of cases with trochanter pain after surgery
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with the transgluteal approach and implantation of conventional prostheses [29].
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of the TPP, surgical procedure, and the revision scenario, based on previous experience
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with preliminary series of implantations, are addressed at length elsewhere [11].
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Nevertheless, we wish to give a brief account of such particulars as follows:
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Indications and contraindications for the TTP
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The indications for a TPP are basically the same as for conventional total hip prostheses;
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however, the femoral neck must exhibit strong, medial cortical bone. Particularly in
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younger patients, the TPP is a valuable alternative to other surgical procedures.
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In cases of femoral head necrosis where the neck region is also affected, the TPP might not
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be adequate. Implantation of a TPP is contraindicated in patients with pronounced coxa
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vara, coxa valga and perhaps in those with a short, narrow femoral neck. Generally, the
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TPP should be so implanted that a neck-shaft angle between 125° and 130° results.
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Considering deviations from this standard position, a valgus femoral neck angle greater
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than 140°, or a varus angle of less than 120° cannot be accepted. Also, since the TPP
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mainly follows the given femoral neck axis, correction of anteversion of the femoral neck
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is limited.
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If the above mentioned selection criteria are strictly observed, no complications should be
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expected during surgery. Explantation of a loosened TPP for the purpose of revision
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should present no problems. Because of preservation of bone stock, the femur commonly
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presents in a state as encountered during primary implantation of a conventional stem
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prosthesis.
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Specific comments with regard to components of the TPP
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Although the TPP has been taken off the market by the former manufacturer for commercial
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reasons, published reports by other users [21, 22, 23, 24, 25, 26, 27, 28] confirm the long-term
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results herewith presented. Since it is conceivable that the basic design of this prosthesis
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might find continuation in one way or another, it could be of value to communicate
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Head /cup articulation
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The head of the prosthesis was seen to have adopted an eccentric position after 15 years in a
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few cases with polyethylene cups, as a result of polyethylene wear. In the case of metal-on-
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metal combinations, all with 28 mm heads, metal wear problems were encountered. Correct
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positioning of the acetabular cup is important. With excessive anteversion there would be risk
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of dorsolateral impingement with the thrust plate.
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Thrust plate
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A greater variety of sizes, more adapted to the form of the femoral neck, especially caudal,
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would perhaps lessen the danger of impingement. The massive box-like shape of the
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intermediate part between thrust plate and mandrel could be improved. The interface exposed
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to bone must remain structured and roughened to optimise osseointegration. It might also be
217
of advantage to shorten the mandrel somewhat, and to perhaps polish its lateral extension so
218
as to discourage bone taking grip on this part of the prosthesis while encouraging bone
219
ongrowth in the region of the thrust plate.
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Central bolt and lateral plate
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A primary, mechanically stable fixation of the thrust plate is mandatory until osseointegration
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is completed. For this reason, the central bolt and lateral plate are of necessity. With present
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high-strength materials a bolt of smaller diameter will probably suffice, especially in view of
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reducing the diameter of the bolt head which would be of immense value in minimising the
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size of the lateral plate.
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The lateral plate of titanium could almost surely be secured to the femoral shaft with only
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one cortical screw. The screw must be located in an area of substantial cortical bone.
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Together with a smaller bolt head, the size of the lateral plate could be appreciably reduced.
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Surgery
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Because of prosthesis design with multiple components and the need to operate meticulously, 9
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Bias
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Some measure of cognitive or confirmation bias might be present in this report, being from
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the author’s clinic.
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In the 90-ies there was a high demand for the TPP worldwide [28, 30, 31, 32, 33], then the
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demand dropped. This might be partially attributed to the come-back of resurfacing
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arthroplasty through McMinn. However, the thrust plate prosthesis in its final design has
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continued to be used [21, 22, 23, 24, 25, 26, 27, 28], as marketed until 2007.
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Conclusion
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In summary we may state that the TPP is a very good concept from a biomechanical
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point of view. It has proved to be clinically and radiologically successful. However,
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because of its complexity with several components that have to be assembled during
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implantation, and the need to be meticulous during surgery, the prosthesis is perhaps less
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attractive for general use than conventional ones. In our opinion, because of this, the TPP
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might be at greater risk for complications than other types of prostheses, especially for
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surgeons with less experience. The TPP has finally fallen victim to commercial and
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marketing considerations about 7 years ago and is therefore no longer available from the
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former manufacturer. Based on our long-term results, we are still confident that this
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implant shows remarkable biomechanical aspects, even taking into consideration the bias
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that might be present from the author’s clinic (inventor) point-of-view.
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The present follow-up confronted us with several unexpected problems, mainly with data
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retrieval and with locating patients. Patient’s records (clinical and radiological) must be
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protected from wilful destruction by hospital authorities, and data retrieval ensured at all
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times, especially in view of fast-changing storage technologies.
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[3] Mittelmeier, H. Anchoring hip prostheses without bone cement. In: Advances in Hip and Knee Joint Technology, M Schaldach and D Hohmann Eds. Springer-Verlag 1976. [4] Jacob HAC, Huggler AH, Dietschi C, Schreiber A. Mechanical function of subchondral bone as experimentally determined on the acetabulum of the human pelvis. J Biomech. 1976; 9: 625 – 627.
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[5] Jacob HAC, Huggler AH. An Investigation into biomechanical causes of prosthesis stem loosening within the proximal end of the human femur. J Biomech.1980; 13: 159 – 173.
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[6] Huggler AH, Jacob HAC. A new approach towards hip prosthesis design. Arch Orthop Trauma Surg. 1980; 97:141. [7] Bereiter H, Jacob HAC, Huggler AH. Clinical experiences with the thrustplate hip prosthesis. Med Orthop Tech. 1986; 1:21.
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[8] Schenk RK, Hauser R, Huggler AH, Jacob HAC. Histology of the thrust-plate-bone interface. In: The thrust plate hip prosthesis, Huggler AH, Jacob HAC Eds. Springer Verlag Heidelberg 1997. [9] Bereiter H, Bürgi M, Rahn BA. Das zeitliche Verhalten der Verankerung einer zementfrei implantierten Hüftpfanne im Tierversuch. Orthopäde. 1992; 21: 63 – 70.
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[10] Bereiter H. Biomechanics of osseointegration of a cementless hip joint cup in animal experiment. In: Endoprosthetics, Morscher EW Eds. Springer Verlag 1995. [11] Huggler AH. The thrust plate prosthesis: A new experience in hip surgery. In: The thrust plate hip prosthesis, Huggler AH, Jacob HAC Eds. Springer Verlag Heidelberg 1997.
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[21] Ishaque BA, Gils J, Wienbeck S, Donle E, Basad E, Stürz H. Results after replacement of femoral neck prostheses - Thrust plate prosthesis (TPP) versus ESKA Cut prosthesis. Z Orthop Unfall 2009 Jan-Feb; 147(1):79-88. Epub 2009 Mar 4. [22] Karatosun V, Ünver B, Gültekin A, Günal I. Thrust plate prosthesis for proximal femoral deformity: a series of 15 patients. Acta Orthop Traumatol Turc 2010; 44(6):437-442.
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[23] Diederix LW, Van Winterswijk PJ, Schouten SB, Bakx PA, Huij J. The Thrust Plate Prosthesis: long-term clinical and radiological results. Acta Orthop Belg. 2013 Jun; 79(3):293-300. [24] Corner JA, Rawoot A, Parmar HV. The thrust plate prosthesis in the treatment of osteoarthritis of the hip. Clinical and radiological outcome with minimum 5-year follow-up. Hip Int. 2008 Apr-Jun; 18(2):88-94.
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[25] Bakirhan S, Ünver B, Karatosun V. The Effect of Femoral Stem Length on Inpatient Rehabilitation Outcomes. American Journal of Clinical Medicine Research 1.1 (2013): 9-14. [26] Yasunaga Y, Goto T, Hisatome T, Tanaka R, Yamasaki T, Ochi M. Bone-preserving prosthesis with a single axis for treating osteonecrosis of the femoral head: Midterm results for the thrust plate hip prosthesis. J Orthop Sci (2003) 8:818–822.
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[27] Sharma S, Verma G, Draviraj KP, Bhamra M. Early results with the thrust plate prosthesis in young patients with osteoarthritis of the hip. Acta Orthop Belg. 2005 Apr; 71(2):182-8. [28] Karatosun V, Ünver B, Gunal I. Hip arthroplasty with the Thrust Plate Prosthesis in patients of 65 years of age or older: 67 patients followed 2–7 years. Arch Orthop Trauma Surg (2008) 128:377–381. [29] Sayed-Noor AS, Sjödén GO. Greater trochanter pain after total hip arthroplasty: the incidence, clinical outcome and associated factors. Hip international. 2006; Vol 16 no 3: 202 – 206 12
ACCEPTED MANUSCRIPT [30] Yasunaga Y, Goto T, Hisatome T, Tanaka R, Yamasaki T, Ochi M. Bone-preserving prosthesis with a single axis for treating osteonecrosis of the femoral head: midterm results for the thrust plate hip prosthesis. J Orthop Sci 2003; 8: 818-822 [31] Sharma S, Verma G, Draviraj KP, Bhamra M. Early results with the thrust plate prosthesis in young patients with osteoarthritis of the hip. Acta Orthop. Belg., 2005, 71, 182188
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[32] Menge M. Acht Jahre Druckscheibenprothese – eine mittelfristige Bewertung. Orthop Praxis 2000; 36: 143 - 151
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[33] Ishaque BA, Wienbeck S, Stürz H. Mittelfristige Ergebnisse und Wechseloperationen nach Druckscheibenprothesen (DSP). Z Orthop Ihre Grenzgeb. 2004 Jan-Feb;142(1): 25-32
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ACCEPTED MANUSCRIPT LEGEND TO FIGURES On the left: The TPP in its details of components. From left to right: The central bolt, made of Protasul-21-WF® and available in 3 dimensions; the lateral plate, made of Protasul-100®; the mandrel-thrust-plate unit, also made of Protasul-100® and heads of various sizes, either of metal (Metasul®) or aluminium oxide ceramic (Biolox®). On the right: The TTP in its final design, third generation.
Fig. 2.
Crank mechanism with conventional stem prostheses.
Fig. 3.
The three radiological phenotypes in relation to the various bone remodelling patterns
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Fig. 1.
a: Revision for aseptic loosening: Kaplan-Meier survival rate: 94.7% at 17 yrs (95% Confidence Interval (CI), 90.2-99.2), 91.8% at 18 yrs (95% CI, 84.6-99.0) b: Revision for all reasons: Kaplan-Meier survival rate: 88.8% at 17 yrs (95% Confidence Interval (CI), 82.5- 95.1), 86.2% at 18 yrs (95% CI, 77.9-94.1): Revisions: N=6 asept. loosening, N=3 other reasons, N=3 partial revisions (lateral plate / bolt) after 2.7, 2.8 and 4.5 years
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Fig. 4.
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a: Type 1: 0 - 50% retraction of the cortical bone in the mediocaudad zone immediately under the thrust plate b: Type 2: 51% - 99% retraction of the cortical bone in contact with the thrust plate c: Type 3: completely loss of bone contact with the thrust plate in the mediocaudad zone
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