[The 2-year follow-up results of a patient-specific interpositional knee implant]

Besides the primary goal of functional improvement and pain reduction, the operative treatment of unicompartmental arthritis in younger patients is focused on preservation of intact bone and joint structures. The question arises whether an interpositional knee implant based on magnetic resonance imaging (MRI) data can be an alternative treatment option to the established procedures of high tibial osteotomy and unicompartmental knee arthroplasty.

From June 2004 to May 2008 a total of 33 patients suffering from unicompartmental knee arthritis received a patient-specific interpositional implant (31 medial and 2 lateral) within a single arm trial. The mean follow-up time was 26.6 months (range 1-48 months) and the mean age of the patients was 54.5 years (range 39-65 years). In addition to the clinical results the Western Ontario and McMaster Universities Osteoarthritis index (WOMAC) function scale and the Knee Society scores were measured. A descriptive data analysis, a variance analysis for repeated measurements and a determination of significance level were carried out.

The 2-4 year results showed a significant improvement in the WOMAC function scale as well as the Knee Society scores. The knee function after 2 years was comparable to the preoperative situation with an extension to flexion of 0/2/130°. The dislocation rate was 6% and the overall revision rate 21%.

Despite acceptable functional results a significant pain relief, a complete preservation of bone and a lower rate of dislocations compared to the off-the-shelf Unispacer implant there were only limited indications for the customized interpositional knee implant with respect to the given contraindications due to the high 2 year revision rate.