Patient-specific implants for lateral unicompartmental knee arthroplasty.

PURPOSE: The lateral compartment of the knee is biomechanically and anatomically different from the medial compartment. Most commercially available unicompartmental implants are not designed specifically for the lateral compartment. Patient-specific custom-made unicompartmental knee arthroplasty (UKA) are designed to provide optimal fit on both femoral and tibial surfaces. This study aimed to determine if the use of patient-specific lateral unicompartmental implants provide better bone coverage than standard, off-the-shelf commercially available unicompartmental implants in lateral unicompartmental knee arthroplasties. As a secondary question, we wished to determine if patient-specific unicompartmental implants provide good clinical outcomes in surgical treatment of lateral unicompartmental osteoarthritis.

METHODS: We prospectively evaluated 33 patients who underwent lateral unicompartmental arthroplasty using patient-specific implants and instrumentation with a minimum of 24 months of follow-up. We analysed bone coverage observed in plain radiographs in 33 patient-specific lateral unicompartmental arthroplasties and compared to 20 lateral unicompartmental arthroplasties performed with commercially-available, standard off-the-shelf unicondylar implants.

RESULTS: The mean tibial implant lateral coverage mismatch in the patient-specific implant group was 1.0 mm (S.D. 1.2, range 0-5.7 mm ) versus 3.3 mm (S.D. 2.43, range 0.4-7.8 mm) in the conventional implant group (p < 0.01). In the patient specific cohort, pre-operative limb alignment was 3.3 (valgus) and post-operative limb alignment was -0.9 (varus). The Knee Society score improved from 48 (S.D. 16.2) to 95 (S.D. 7.6). Survivorship in the patient-specific implant group was 97% at an average follow up of 37 months, versus 85% at a follow-up period of 32 months for the standard implant group.

CONCLUSIONS: Patient-specific lateral unicompartmental knee replacements demonstrated better tibial coverage and provide excellent short-term clinical and radiological results as compared to a standard lateral UKA.