Purpose of the study: The aim of this study was to report outcome after more than six years follow-up of a series of 122 unicompartmental prostheses.

Material and methods: Cemented HLS® unicompart-mental surface-coated prostheses were implanted in 111 patients (122 knees, 88% medial and 12% lateral) between January 1995 and November 1997 by the same surgeon. These knees presented unicompartmen-tal osteoarthritis (91%) or unicondylar necrosis (9%). An independent senior surgeon reviewed 94 prostheses. Seventeen patients died and ten institutionalized patients free of complaints about their knee could not be fully assessed. Only three patients (2.7%) were lost to follow-up). Clinical data were assessed with the IKS criteria. A complete radiological work-up was available to compare preoperative images with the last follow-up results. Mean follow-up was 88 months (range 72–108 months).

Results: After the implantation, 96% of patients were satisfied or very satisfied; 84% had no or little pain. Mean flexion was 133° (range 90–150°). The mean knee score at follow-up was 86/100 (40/100 preoperatively), mean function score 77/100 (61/100 preoperatively). Mean residual misalignment was 6° (7° varus for medial prostheses and 4° valgus for lateral prostheses). Tibial or femoral lucent lines were observed for 22% of the prostheses but with no change and no clinical expression. There was one case of tibial polyethylene wear (1mm). There were eight failures (all before 24 months) with revision with a total knee arthroplasty (two infections, one overlarge component, two tibial loosenings, 3 unexplained pain). The Kaplan-Meier survival at maximum follow-up of 108 months was 93.67%.

Discussion: The prostheses implanted in this series were correct indications according to the preceding symposiums. We analyzed the clinical and radiological outcome (overall axial correction, tibial and femoral correction), failures, and reasons for incomplete results.

Conclusion: Outcome at more than six years in this series of resurfaced knee prostheses with a polyethylene plateau was good, supporting the correct choice of implant and technique. These results also enabled validation of the principle that unicompartmental arthroplasty is a valid alternative for the treatment of unicompartmental osteoarthritis of the knee joint. Analysis of the failures and the incomplete results discloses interesting avenues for optimizing the surgical technique and improving future clinical and radiological results.

Purpose: Postoperative undercorrection is recommended for unicompartmental prostheses. The long-term effects of this undercorrection on polyethylene wear and recurrent deformation have not been evaluated to date. We studied the influence of undercorrection on polyethyl-ene wear and the risk of recurrent deformation in uni-compartmental prostheses reviewed at more than 14 years (14–22 years).

Material and methods: Forty unicompartmental prostheses with a polyethylene plateau without a metal back were evaluated at last follow-up. We assessed radiographs performed under fluoroscopic control to obtain a ray tangential to the polyethylene plateau. This film was used to assess penetration of the femoral component into the polyethylene. Goniometry, performed at last follow-up was compared with the postoperative goniometry to measure recurrent deformation. We retained only unicompartmental prostheses with preservation of the anterior cruciate at implantation in order to rule out possible influence of the absence of this ligament.

Results: There was a significant relationship (p< 0.05) between residual postoperative varus and rate of femoral component penetration into the polyethylene. Mean polyethylene wear was 0.15 mm per year for unicompartmental prosthesis with postoperative varus greater than 10°. There was also a correlation (p< 0.01) between recurrent deformation (difference between the last follow-up and postoperative goniometry) and postoperative varus. Schematically, deformation was correlated with penetration of the femoral component into the polyethylene. Finally, recurrent deformation and rate of penetration of the femoral component into the polyethylene was greater with thinner polyethylene inserts (p< 0.05).

Discussion: While undercorrection appears to be desirable for unicompartmental prostheses, it should be moderate. Excessive postoperative varus raises the risk of more rapid polyethylene wear and recurrent deformation. Furthermore, even for minimal undercorrection, the correction achieved postoperatively does not remain constant and varus defomation tends to recur. This phenomenon probably has a protective effect on the contra-lateral femorotibial compartment but in the long-term exposes to the risk of wear and recurrent deformation.

Purpose: The purpose of this work was to analyse results of revision procedures for unicompartmental prostheses (UNI) replaced by total knee arthroplasty (TKA) and to detail technical difficulties.

Material and methods: This series included 54 UNI revised with TKA. There were 45 medial and nine lateral UNI. The cause of failure was determined from the clinical history, the postoperative x-rays following UNI implantation and the preoperative x-rays before TKA as well as the operation report. Mean time from failure of UNI to TKA was four years. Clinical results were assessed with IKS criteria. The radiological work-up included an AP and lateral view in single leg stance and goniometry in 44.5% of the cases. Twenty-seven patients were reviewed with standard x-rays, eight patients were lost to follow-up, and 19 were studied from the medical files. One patient died.

Results: Mean follow-up was four years (range 2–12 years). There were seven failures (13%). We noted six cases of phlebitis, two plumonary emoblisms, one secondary infection, and three mobilisations under general anaesthesia. 55.5% of the patients were very satisfied, 36% were satisfied and 8.5% were disappointed. Revision was considered easy or moderately difficult in 82% of the cases. A standard gliding TKA was implanted in 39 cases (72%). Mean knee score was 85 points. Mean flexion was 113°. The mean function score was 62 points. For 91% of the cases, there was no laxity. The femorotibial angle was 90° in 54% of the cases and the mechanical tibial angle was 90° in 46%.

Discussion: Our results are similar to those reported in the literature. They were better than reports of TKA revision TKA. Results of TKA revision of UNI have been good. There is no technical problem related to bone loss, generally at the tibial level (45%). Preoperative planning allows defining the revision modalities (long pivot, metal backing, revision prosthesis). We recommend a long tibial pivot in the event of important tibial bone loss.

Purpose of the study: We reviewed 69 consecutive cases of total knee arthroplasty revisions to analyze the causes of failure.

Material and methods: Sixty-nine total knee arthroplasty revisions were required between 1990 and 1997 for non-septic failure. Five categories of failures were identified: 30 loosenings including 11 with an initial malposition (varus position of the tibial component in 8 cases), 14 laxities (medial in 5, lateral in 5 and anteroposterior in 4), 11 stiff knees with no other clinical or radiological anomaly, 6 patellar failures (2 dislocations, 2 cases of excessive wear, 2 painful knees with a Freeman prosthesis), and 8 cases of painful knees with no other detectable anomaly.

Results: A three-phase reconstruction procedure was used after removing the failing TKA:1) reconstruction of the tibia with replacement of lost bone, 2) reconstruction of the femur with balanced flexion determining the size of the implant, 3) balanced extension determining the distal/proximal position of the femoral component. A “simple” sliding prosthesis was used in 16 cases, a modular reconstruction prosthesis in 40 cases and a hinge prosthesis in 13 cases. Mean follow-up for functional and radiographic assessment after revision surgery was 37 months (59 cases) with a minimum follow-up of 1 year. The best outcome was observed in the “loosening”, “laxity”, and “stiffness” patients. Outcome was less favorable for the group “isolated pain” with IKS functional scores of 35.5 ± 16 and 52.5 ± 21.

Discussion: In 36 p. 100 of cases, TKA failure was related to a technical mistake (component malposition, poor ligament alignment). In 33 p. 100, failure was patient related (multiple procedures, congenital hip dysplasia, rheumatoid arthritis...). Outcome after revision TKA was less favorable than after primary TKA, particularly in case of painful knees with no other detectable anomaly.

Conclusion: Surgical revision of TKA must follow a rigorous procedure with a detailed preoperative work-up. The decision for revision must not be made unless a precise anomaly has been identified.