ALPINA UNICOMPARTMENTAL KNEE PROSTHESES: PROSPECTIVE EVALUATION AT FIVE YEARS

Abstract

Purpose: The reputation of unicompartmental knee prostheses (UKP) has suffered from “errors of youth” but within the limits of the indication and with precise implantation, they have provided excellent results with miminal morbidity. We evaluated the five-year clinical and radiological outcomes with the Alpina-UNI prosthesis.

Material and methods: Fifty-eight Alpina-UNI prostheses (88% medial) were implanted in 1995 by two operators. Radiographic analysis was performed by an independent observer. The mean patient age at implantation was 72 years. Patients were evaluated at three months and one and five years. The Knee Society knee score as well as radiographic findings were noted. Indications were essential, traumatic, and necrotic non-displaced lateralised degeneration. Cemented implants were used for 92% of the knees. Results were analysed with SPSS software.

Results: At five years, 51 patients were reviewed, there were four deaths, one patient lost to follow-up and two early failures (secondary ACL tear, anterior descent of the tibial baseplate). Follow-up at 70 months was 95%. The KSS was significantly improved (+61%, p< 0.001) and remained stable during follow-up. Mean flexion at five years was 131°. Radiographic findings were satisfactory: no degradation of the contralateral compartment or the patellofemoral joint, no implant loosening or migration, no abnormal polyethylene wear. Stable lucent lines were observed for 17% of the implants, all measuring less than 1 mm. The mean tibial slope was 5°. There was no significant difference between the pre- and postoperative femoroatibial epiphyseal inclinations. The mechanical axis (HKA) was significantly improved (p< 0.001) and remained unchanged throughout follow-up, maintaining a 1°–5° undercorrection.

Discussion: The conclusions of the 1995 SOFCOT symposium emphasised the importance of indications and precise implant position for the prevention of early failure. The Alpina-UNI system has enabled reproducible accuracy for the femoral and tibial epiphyseal inclinations in the cuts allowing restoration of the initial anatomy, the correction of the HKA being explained solely by wear correction. This can explain the low rate of loosening and wear in this series. Unicompartmental replacement remains an excellent solution in the older patient due to the lesser morbidity. Mid-term results are encouraging. Further ten-year evaluation will provide information on implant longevity.