Five year survivorship of primary non-modular stemless constrained knee arthroplasty

Recent development of stemless non-modular constrained (NMC) condylar components has offered solutions to end of stem pain, canal invasion, and complicated revision. However, supposed improvement in fixation associated with stems has led to some fears about non-modular (NM) devices and aseptic loosening. The purpose of this study was to evaluate the average five-years survivorship and clinical results of this newer primary NM constrained condylar arthroplasty.

We retrospectively reviewed 184 primary (TKAs) (140 patients) utilizing a newer NMC condylar implant from 1999 to 2008. Pre-operative range of motion and Knee Society function scores were obtained and compared to that of the patients' most recent follow-up. Statistical analysis included Kaplan-Meier survivorship analysis of all knees, with failure defined as the removal of the implant for any reason.

Follow-up averaged 5years (range: 2-9). Of the entire cohort, 42 patients are deceased and 14 knees have been revised. Of the 7 patients revised for loosening, 6 were isolated for femoral component loosening (3.3%). There was a significant improvement in both postoperative knee score and function score (p<0.05). The 5-year survival was 97.3%.

The use of constraint should be judicious and ligament balancing, but we recommend using the least amount of constraint necessary to achieve stability. In addition, because of a significant number of isolated femoral loosenings observed in our cohort of stemless NMC knee prostheses, we recommend the use of a femoral stem with constrained condylar knee prosthesis in patients that have osteopenia and require a constrained knee.