Poor results of the Optetrak™ cemented posterior stabilized knee prosthesis after a mean 25-month follow-up: analysis of 110 prostheses

Introduction: The introduction of a new knee arthroplasty model, even if it differs from a validated implant by only a few details, should be followed by rigorous assessment. The Optetrak™ cemented posterior stabilized knee prosthesis evolved from the Insall prosthesis with a smaller tibial keel associated with a higher tibial cam and increased femorotibial congruency as well as a more posterior-stabilized trochlea.

Hypothesis: We hypothesized that this implant with only minor modifications to the Insall prosthesis would provide as favorable results as the Insall prosthesis.

Materials and methods: A continuous series of 110 prostheses (106 patients) implanted between 2005 and 2007 was retrospectively analyzed with a mean follow-up of 25 months (range, 12-42 months) by an independent observer. The follow-up was based on the IKS score and the radiological assessment was conducted by three senior surgeons.

Results: The mean IKS score was 83.7 (range, 13-100) points at the last follow-up, the mean function score was 82.6 (range, 30-100 points), and mean flexion was 120° (range, 80-140°). Seventeen patients (15%) were disappointed or dissatisfied, 25 knees (22%) were painful, requiring regular painkillers. The prostheses had a satisfactory mechanical axis, with a mean HKA angle of 177.4 ± 4°, but 25 prostheses (22%) presented rims evolving toward tibial implant loosening, and 24 (21%) developed signs of patellofemoral conflict. With follow-up less than 5 years, nine cases were revised for tibial loosening, three for patellofemoral instability, and one for patellofemoral pain. The cases of tibial loosening were particular because they occurred at the cement-tibial-implant interface. The cumulated survival rate at 36 months was 80.97 ± 9.1% and 76.74 ± 12% at 45 months.

Discussion: This tibial implant with a small keel does not resist the stresses applied by posterior stabilization, with notably a higher level of stress than the Insall prosthesis from which it was derived. In cases of centering defect, the design of the trochlea can lead to impingement between the edges of the patella and the prominent edges of the prosthetic trochlea. We have suspended implantation of this prosthesis and continue to monitor the progression of patients having received these implants.

Level of evidence: Level IV, retrospective study.