We reviewed the outcome of 422 primary

The Kinemax total knee arthroplasty NINE YEARS EXPERIENCE D. L. Back, S. R. Cannon, A. Hilton, M. J. K. Bankes, T. W. R. Briggs From the Royal National Orthopaedic Hospital Trust, Stanmore, England We reviewed the outcome of 422 primary cemented Kinemax total knee arthroplasties implanted into 369 patients over a period of five years, from January 1989. The operations were carried out at two NHS district general hospitals and one teaching hospital by 31 surgeons. During the period of review, 49 patients died and ten knees were lost to follow-up (68 knees). The mean Knee Society score improved from 28 before to 89 after surgery, and the mean function score increased from 23 to 79. The range of flexion improved from 92 to 105. These improvements were maintained throughout the period of study. At the latest review radiolucent lines of 1 mm were seen around 15% of tibial components, 1.4% of patellar components and 9.5% of femoral components. In no case were these changes progressive. Using revision as the endpoint, cumulative survival was 99% after five years and 96.95% after nine years. All revisions were undertaken for deep infection or secondary trauma. Our study has shown that the Kinemax total knee replacement, when carried out with retention of the posterior cruciate ligament by surgeons of varying experience, produces very satisfactory results in the medium term. J Bone Joint Surg [Br] 2001;83-B:359-63. Received 3 February 2000; Accepted after revision 15 September 2000 The Kinemax Knee System (Howmedica, Rutherford, New Jersey) was introduced into the UK in 1988 after 15 years of research and design development, 1,2 much of which was undertaken at the Brigham and Women s Hospital, Boston, USA. The precursor to the Kinemax knee was the Kinematic, first implanted in 1978, 3 and long-term results for aseptic loosening of the tibial and femoral components were excellent. 4-6 There was, however, a rate of revision of 3% for the patellar component and an incidence of fracture of the tibial tray of 1.3%. These results, repeated in two separate institutions, 7-9 were disappointing because of the lower rate of loosening of the patellar component (1.2%) of the Duo-Patella system, the precursor to the Kinematic. 10 Walker 11 designed an improved tibial component with better load-bearing properties using computer software based on measurements from human knees, and reverted to the symmetrical femoral component of the Duo-Patella system. 12,13 The Kinemax system evolved further with development of a lo-stress insert, which increased the femorotibial contact area and reduced the contact stress by 25% in full extension. 14 It now consists of a standard condylar design, offering options to retain or sacrifice the posterior cruciate ligament and an anatomically symmetrical patellofemoral articulation. 15 Previous reports of the long-term outcome of this prosthesis came from the clinical units responsible for its design. These reported few problems with aseptic loosening, wear of polyethylene or patellar subluxation. We now report the results from general hospitals which represent the work of many surgeons in various stages of training. 16 D. L. Back, FRCS Ed, Specialist Registrar 108 Severalls Avenue, Chesham, Buckinghamshire HP5 3EL, UK. A. Hilton, FRCS, Specialist Registrar South-East Thames Rotation, St Thomas s Hospital, Lambeth Palace Road, London SE1 7EM, UK. M. J. K. Bankes, FRCS Orth, Specialist Registrar North-East Thames Rotation, Royal Free Hospital, Pond Street, London NW3 2QG, UK. T. W. R. Briggs, MCh (Orth), FRCS, Consultant Orthopaedic Surgeon S. R. Cannon, FRCS, Consultant Orthopaedic Surgeon Royal National Orthopaedic Hospital Trust, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK. Correspondence should be sent to Miss D. L. Back. 2001 British Editorial Society of Bone and Joint Surgery 0301-620X/01/311006 $2.00 Patients and Methods Between January 1989 and April 1994, 422 Kinemax total knee arthroplasties (right 220, left 202) were inserted for severe pain on exercise, night pain and progressive loss of independence, in the presence of radiological changes of arthritis, under the care of the senior authors (SRC and TWRB) in three NHS hospitals. The operations were undertaken by 31 different surgeons of varying experience using a standard technique. There were 369 patients (220 women and 149 men) with a mean age at operation of 69 years (46 to 89) for the whole cohort. Their mean height was 1.62 m (1.45 to 2.0) and mean weight 72 kg (45 to VOL. 83-B, NO. 3, APRIL 2001 359

360 D. L. BACK, S. R. CANNON, A. HILTON, M. J. K. BANKES, T. W. R. BRIGGS Table I. Preoperative diagnoses and types of previous knee surgery in 422 knees Number Percentage Diagnosis Osteoarthritis 354 83.9 Rheumatoid arthritis 59 14.0 Juvenile arthritis 3 0.7 Other 6 1.6 Prevalence and type of previous knee surgery Arthroscopy 36 85.0 Tibial osteotomy 34 8.1 Femoral osteotomy 21 5.0 Open meniscectomy 6 1.4 Patellectomy 5 1.2 Table II. Ethnic origins of the 369 patients Ethnic origin Number Percentage Caucasian 339 91.9 Indian subcontinent 23 6.2 West Indian 6 1.6 Chinese 1 0.3 124). Men had a lower body mass index than women, of whom 64% with a body mass index greater than 27 were classified as overweight. The mean waiting time between consultation and surgery was 18 months (6 to 36) and this did not vary during the time of the study. A valgus deformity of 10 or greater was present in 43 knees. Staged bilateral surgery was carried out in 53 patients. The preoperative diagnoses are shown in Table I and the patients ethnic origin in Table II. Previous knee surgery had been undertaken at least once in 99 patients (Table I). The incidence of prior arthroscopy increased and that of tibial osteotomy decreased during the study period. One-third of patients had received at least one other joint replacement, most commonly the hip. Patellar resurfacing was carried out primarily in 61.8% of cases for gross loss of articular cartilage. Resurfacing was more likely to be done by junior surgeons. After trial reduction, a lateral release was carried out only in the presence of lateral retinacular contracture or patellar subluxation. Release was necessary in 59 knees. Components were inserted using a single mix of cement with the knee held in full extension until the cement hardened. Prophylactic antibiotics were given in all cases consisting of 1.5 g of cefuroxime at induction and two doses of 750 mg after operation at intervals of eight hours. There was no formal anticoagulation policy, but 262 (71%) patients received 5000 IU of heparin injected subcutaneously twice a day while in hospital. Anti-embolism stockings were applied below the knee in all patients. Every patient had one vacuum drain which was removed at 48 hours. Patients were rested in bed, in either a Robert Jones bandage or a plaster backslab for 24 hours and then actively mobilised. Active assisted and continuous passive movement exercises commenced at 24 hours under the supervision of a physiotherapist. The patients were allowed home when the wounds were dry and they had achieved 90 of flexion. If this was not achieved by the tenth postoperative day, the knee was manipulated under anaesthesia. For this study, the patients were contacted by mail or telephone and invited to attend for clinical and radiological review. Those who had moved home were examined locally. The Knee Society clinical rating system gave a preoperative and most recent postoperative knee (KSS) and function score (FS) 17 and the Knee Society radiological score was recorded for each component on the most recent radiograph. For those who had died or were lost to followup, the last radiograph taken was reviewed. 18 If radiolucent lines were present all previous radiographs were compared for evidence of progression. For survivorship analysis we used the life-table method with revision of any component as the endpoint. Confidence intervals were calculated using the Rothman equation. 19 Results Of the original 369 patients (422 implants), 310 (364 implants) were reviewed after a mean follow-up period of 5 years 8 months (4 years to 9 years 3 months). A total of 49 patients (58 knees) had died from unrelated causes and ten patients with unilateral implants were untraceable. All patients replied to either the questionnaire or a telephone call, but complete radiological and clinical data were unavailable for 70. The mean KSS improved from 28 to 89 after operation, and the FS increased from 23 to 79 (Table III). Low function scores were related to coexisting cardiovascular or respiratory disease. Patients with rheumatoid arthritis had the poorest functional outcome, but were the most satisfied. Compared with the Caucasian and West Indian groups, patients from the Indian subcontinent presented at a younger age (mean 61 years), were more likely to require bilateral surgery and obtained lower mean postoperative scores (KSS and FS). The mean range of flexion, excluding Table III. Mean (range) preoperative and postoperative KSS and FS KSS FS Preop Postop Preop Postop Osteoarthritis 28 (10 to 69) 89 (28 to 98) 23 (0 to 55) 79 (25 to 100) Rheumatoid arthritis 26 (10 to 48) 56 (34 to 72) 20 (0 to 40) 45 (25 to 60) Indian subcontinent 26 (10 to 52) 52 (28 to 95) 20 (10 to 45) 60 (25 to 100) THE JOURNAL OF BONE AND JOINT SURGERY

THE KINEMAX TOTAL KNEE ARTHROPLASTY 361 patients with rheumatoid arthritis, improved from 10 to 92 to 5 to 105 at the latest review. Anterior knee pain was experienced by 24 patients with unresurfaced patellae, although these patients did not request further surgery. Complete radiolucent lines of 1 mm were found around 15% of tibial components, 1.4% of patellar components and 9.5% of femoral components. 18 In no case were these changes progressive. Incomplete radiolucent lines were found adjacent to 5.2% of tibial components; all were found medially in zone 1 and were not progressive. 18 Radiolucent lines on the postoperative radiograph were found more commonly after surgery undertaken by junior surgeons. The overall complication rate was 12.7% (Table IV) with postoperative haematoma and manipulation occurring more often in operations performed by junior surgeons. The mean length of hospital stay was nine days (5 to 29), being longest for the teaching hospital at 11 days. Secondary patellar resurfacing was necessary in four knees, three for anterior knee pain and one for maltracking. Components were revised in 12 knees (2.85%). Deep infection was the most common reason for revision, occurring in seven knees (1.7%). Staphylococcus aureus and Staph. epidermidis were each responsible in two cases and Pseudomonas in one. No organism was isolated from two patients. Haematogenous infection was thought to be probable in two previously asymptomatic knees since both Table IV. Details of complications Complication Number Percentage Medical Urinary-tract infection 18 4.2 Urinary retention 10 2.3 Deep-vein thrombosis 14 3.3 Pulmonary embolus 2 0.47 Decubitus ulcer 2 0.47 Guillain-Barré syndrome 1 0.24 (Miller-Fisher variant) Intestinal obstruction 1 0.24 Surgical Manipulation under anaesthesia 23 5.4 Haematoma 9 2.1 Infections Superficial 9 2.1 Deep 7 1.7 Secondary patellar resurfacing 4 0.95 Intraoperative fracture 4 0.95 Cement reaction 1 0.24 Common peroneal nerve palsy 1 0.24 patients had undergone surgery, prostatic resection or total hip replacement, within six months of presentation. Posttraumatic periprosthetic fractures, occurring at five and six years, accounted for two revisions. A further two were carried out at other institutions for reasons that could not be determined. A single patellar component was revised after three years for maltracking. The life-table is shown in Table V and the survivorship curve in Figure 1. Using any Table V. Life-table for 422 Kinemax total knee replacements Years since Number Number Annual failure Cumulative 95% confidence operation at start Failure Withdrawn Lost (%) Dead at risk rate (%) survival (%) limits 0 to 1 422 0 0 0 0 422 0.00 100.00 99.1 to 100 1 to 2 422 2 0 0 0 422 0.47 99.53 98.3 to 99.9 2 to 3 420 2 2 0 2 419 0.48 99.05 97.6 to 99.6 3 to 4 416 0 7 2 5 412.5 0.00 99.05 97.6 to 99.6 4 to 5 409 0 8 0 8 405 0.00 99.05 97.6 to 99.6 5 to 6 401 0 10 4 6 396 0.00 99.05 97.6 to 99.6 6 to 7 391 3 9 2 7 386.5 0.78 98.28 96.5 to 99.2 7 to 8 379 3 12 4 8 373 0.80 97.49 95.5 to 98.6 8 to 9 364 2 18 8 10 355 0.55 96.96 94.8 to 98.2 Fig. 1 Graph showing the survivorship analysis for the 422 primary cemented Kinemax total knee arthroplasties implanted in 369 patients. VOL. 83-B, NO. 3, APRIL 2001

362 D. L. BACK, S. R. CANNON, A. HILTON, M. J. K. BANKES, T. W. R. BRIGGS revision as the endpoint, the cumulative survival after nine years was 96.95%. Discussion This medium-term review of the Kinemax total knee replacement shows a low revision rate and low complication rate at five years. We present data from a specialist orthopaedic teaching hospital and two general hospitals using the same prosthesis. The operations were undertaken by 31 different surgeons, which is the largest number in any reported knee series, although many of the junior surgeons were operating under the supervision of a consultant. 20,21 Only the specialist hospital had dedicated theatres used solely for orthopaedic surgery. Despite this, there was no discernible difference in the outcome between any of the hospitals. These data suggest that the Kinemax is a userfriendly implant. Ewald 22 reported an evaluation for five to eight years of 521 consecutive Kinemax total knee replacements carried out over a similar period of time. Compared with our series, their patients were younger, less severely affected and the patella was resurfaced more frequently. The KSS improved from 38 to 85 and the FS from 49 to 76. This implies that this design of knee is capable of producing a similar outcome regardless of the severity of the preoperative disease. Preoperative knee function scores are based on the initial presentation. In the UK there can be considerable delay before surgery is carried out; therefore, the KSS and FS may be somewhat lower at the time of surgery. It is emphasised that the versatility of this knee system can produce excellent initial results and maintain them in the medium term. All knees in this series were inserted utilising the Gobot system. This requires adjustment to produce a balance of the soft tissues before dividing the femur. The lack of the cement wedge sign implies that soft-tissue balance was achieved and supports the use of the Gobot system. 23 The postoperative alignment appeared to be satisfactory, although a minor fixed flexion deformity was common. Only seven knees required revision for infection (1.7%), in two of which it was a late sequela secondary to other surgery. To our knowledge, no knee has been revised for aseptic loosening. One of the satisfactory features of this series is the low incidence of patellar problems and anterior knee pain. The Kinematic replacement had a patellar complication rate of 3.9%, in most cases a loose patellar prosthesis. 24 Previous reports on the Kinemax have shown a low incidence of patellar problems. 25 It is thought that the symmetrical femoral component is more anatomical compared with other right and left prosthetic femoral components. 24,26 This low incidence of patellofemoral complications supports the hypothesis that a symmetrical femoral component (as in the Kinemax) is preferable to the non-anatomical asymmetrical knee arthroplasties. Even when the patella is not resurfaced, there appears to be an absence of anterior knee pain with this prosthesis. The incidence of the need for lateral release is low when compared with other series. 20 During the course of the study, the age of patients undergoing total knee replacement has decreased markedly, reflecting growing confidence in the surgical technique and the implant. Review of the 1995 to 1996 cohort shows even more patients presenting at less than 60 years of age. These patients have a higher KSS and FS than older patients, but are more demanding. As confidence with implants grows and surgery is undertaken on younger patients, it will be interesting to see if revision problems increase in the future. Coupled with this decreasing age at the time of arthroplasty is the decreasing incidence of tibial osteotomy; no patient who underwent surgery in the final year of this study had had a previous tibial osteotomy. We have also observed that patients from the Indian subcontinent present at a younger age with a lower KS and FS. This medium-term review of the Kinemax knee arthroplasty has shown that it is possible to obtain equally good results in general hospitals as in specialist centres in the UK 25-27 and for the surgery to have a good outcome when undertaken by relatively inexperienced surgeons. With a cumulative survival of 99% at five years, the Kinemax represents a safe system for total knee arthroplasty. Although none of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article, benefits have been or will be received but are directed solely to a research fund, foundation, educational institution, or other non-profit institution with which one or more of the authors is associated. References 1. Rothman KJ. Estimation of confidence limits for the cumulative probability of survival in life table analysis. J Chronic Dis 1978;31:557-60. 2. Murray DW, Carr AJ, Bulstrode C. Survival analysis of joint replacements. J Bone Joint Surg [Br] 1993;75-B:697-704. 3. Thomas WH, Ewald FC, Poss R, Sledge CB. Duopatella total knee arthroplasty. Orthop Trans 1980;4:329-30. 4. Cobb AC, Ewald FC, Wright J, Sledge CB. The kinematic knee survivorship analysis of 1934 knees. 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