The Unispacer™ unicompartmental knee implant: its outcomes in medial compartment knee osteoarthritis.

Introduction: A new concept has been recently developed for use in the treatment of isolated medial tibiofemoral osteoarthritis: the Unispacer™ implant. This mobile interpositional, self-centering implant replicates the meniscal shape. This mini-invasive device does not require bone cuts or component fixation. The implant trajectory is guided by the medial condyle.

Hypothesis: The Unispacer™ knee implant enhances knee function in the treatment of isolated tibiofemoral osteoarthritis graded 2 and 3 according to Ahlbäck radiographic evaluation scale.

Material And Methods: This prospective study involved 17 Unispacer™ knee systems implanted in 16 patients between April 2003 and March 2009 within the frame of a clinical research project (CRP). Patients were clinically (IKS score) and radiographically evaluated during a mean follow-up period of 40 months.

Results: Nine patients (10 implants) had a IKS score>160. The mean overall knee score at reassessment, including failures, increased from 51 points preoperatively to 78 points postoperatively. The mean overall Knee Society Function score increased from 55 preoperatively to 75/100 postoperatively. The reported complication rate was 35% (pain or implant instability). One-third of the failures were not technique- or implant-related but rather induced by the use of an inappropriate width in the frontal plane.

Discussion: Good results regarding pain relief and function are reported when using a mobile implant with no peripheral overhang which could be responsible for medial capsuloligamentous impingement. The Unispacer™ has three theoretical advantages: no bone resection, no implant fixation, no polyethylene wear debris. On the basis of its uncertain clinical results and high revision rate (six cases out of 17), we do not recommend this system despite the expected improvements on this range of implants.

Level Of Evidence: Level III, prospective study.