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Medium Term Clinical Results of Hydroxyapatite-Coated Total Knee Replacements

A prospective study of the clinical outcome in patients with a hydroxyapatite coated, uncemented total knee replacement was performed. 1000 primary total knee replacements were implanted in 692 patients for, in the vast majority, osteoarthrosis. Mean follow-up was 75 (range 40-115) months. Knee scores were significantly (p<0.001) improved postoperatively and range of movement maintained. Radiologically there were no cases of loosening. This hydroxyapatite coated total knee replacement has a good clinical outcome at medium term follow-up, comparable with prostheses using other fixation techniques. Introduction Total knee replacement (TKR) has become a routine operation with a predictable good outcome. To date, cemented fixation has represented the gold standard for TKR. Cementless prostheses have been designed for a number of reasons, primarily to try and achieve improved long-term survival of the implant. So far mediumand long-term results from cementless TKR have been satisfactory and comparable with cemented TKR [1-3]. Hydroxyapatite (HA) coating has been shown to promote osseointegration therefore potentially augmenting TKR fixation [4,5]. We conducted this prospective clinical study to assess the medium term results of a hydroxyapatite coated, cementless TKR. Materials & Methods Between August 1992 and November 1998, patients requiring a primary TKR were treated with a prosthesis implanted by the senior author using a standard technique. A combined Knee Society and Hospital for Special Surgery score [6] was recorded preoperatively and at 3,6,12,24 and 60 months post-operatively producing a maximum score out of 200. Initially specialized interface radiographs were performed routinely at 2 years post-operatively. This practice was later modified to only performing X-rays on symptomatic individuals to avoid unnecessary radiation exposure. The prosthesis is designed as a low profile resurfacing prosthesis. It is posterior cruciate retaining and stemless. The cobalt chrome femoral component is anatomically shaped and sized to produce natural condylar dimensions and minimal bone resection. The titanium alloy (Ti6Al4V) tibial component is designed to provide maximum cortical coverage. The cementless fixation of the femoral and tibial components is enhanced by sintered beads on their surfaces with a pore size between 250-400 microns to promote bony ingrowth. The prosthesis is coated with hydroxyapatite (crystallinity 75%, Porosity 20%, thickness 70 microns) using a sputter coating technique. Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 857-858 doi:10.4028/www.scientific.net/KEM.240-242.857 © 2003 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,21:21:01) Results 692 patients (Male:Female 335:357) with a mean age 68 yrs (31-88) underwent TKR mainly for osteoarthrosis(93%) and inflammatory arthropathies (rheumatoid arthritis 3%, psoriasis 1%). Mean follow up was 75 months (40-115). There were 461 unilateral (Right:Left 256:205) and 539 bilateral replacements (462 simultaneous and 77 staged). Mean preoperative score was 95/200, improving to 182/200 at most recent review. 44 patients have died (mean age 73 yrs, range 54-88). There have been 14 deep infections (1.4%), 22 proven pulmonary emboli (2.2%) and 5 periprosthetic fractures (0.5%). 5(%) revisions have been performed (Infection 4, supracondylar fracture 1). Specialised interface views performed routinely at the 2-year follow-up on the first 161 knees confirmed intimate bone growth up to the prosthesis. Radiological review has revealed no tibial or femoral osteolysis and no evidence of any subsidence of the tibial tray. There have been no cases of clinical loosening. Discussion The results of primary cementless total knee replacements are comparable with cemented total knee replacements [7,8]. However cementless TKR does offer potential advantages in terms of bone preservation, treatment of infection and ease of revision. HA coating has been shown to promote osseointegration of prostheses and therefore give good early fixation and stability. This work has been mainly done on fixation of total hip replacements but it appears to be equally applicable to knees [9,10]. Concerns have been raised regarding the fixation of uncoated cementless prostheses [7,8]. It has been reported that intrinsic stability of the prostheses and bony ingrowth may be inconsistent possibly due to inexact bone cuts. We believe that the HA coating negates this potential problem by promoting osseointegration through osteoconduction. Improved instrumentation and prosthetic design will also contribute to improved fixation. The results of this study indicate that this early stability appears to be maintained in the medium term without any increase in complication rates as compared to other studies. In particular the HA coating does not appear to give rise to any complications in its own right. Obviously this group of patients needs to be followed up beyond 10 years so that any long-term failures are recorded and investigated. References 1. A.A. Hoffman, J.D. Evanich, R.P. Ferguson, et al. Clin Orthop. 388: 85-94, 2001 2. D.A. Parker, C.H. Rorabeck, R.B. Bourne. Clin Orthop. 388: 68-76, 2001 3. A.W. McCaskie, D.J. Deehan, T.P. Green, et al. J Bone Joint Surg Br. 80(6): 971-5, 1998 4. R.W. Bassett. J Arthroplasty. 13(4): 409-13, 1998 5. M.J. Cross, G.J. Roger, R. Dimmick, et al. J Bone Joint Surg Br. 80-B (2S). 140, 1998 6. J.N. Insall, M.D. Door, R.D. Scott, et al. Clin Orthop 248: 13-14, 1989 7. L. Regner, L. Carlsson, J. Karrholm, et al. J Arthroplasty. (15)6: 681-689, 2000 8. R.G. Nelissen, E.R. Valstar, P.M. Rozing. J Bone Joint Surg. 80-A (11). 1665-1672, 1998 9. L. Palm, S.A. Jacobsson, I.J. Ivarsson. Arthroplasty. 17(2):172-5, 2002 10. C.J. Oosterbos, A.I. Rahmy, A.J. Tonino. Int. Orthop. 25(1):17-21, 2001 858 Bioceramics 15