Purpose

The purpose of this study is to identify patient factors and surgical characteristics predictive of unicompartmental failure to determine perioperative and operative factors associated with poor outcomes following partial knee replacement. We compared medial versus lateral, onlay versus inlay and bicompartmental versus unicompartmental prosthesis.

Methods

A prospectively maintained institutional data base was retrospectively queried between January 2010 to December 2016 for all patients that received unicompartmental or bicompartmental robotically assisted arthroplasty. Survivorship analysis was performed to determine factors associated with conversion to total knee arthroplasty and functional results were measured by Oxford Scores.

Results

A total of 1,867 knees in 1,567 patients underwent arthroplasty. There were 1,445 medial only, 188 lateral only, 131 bicompartmental, and 101 patella femoral only. There were 1,743 knees with 2 years follow up and 1,273 knees with 4 years follow up. At four years there were 67 deaths.

Conclusions

On lay prosthesis outperformed inlay prosthesis in all groups medial, lateral and bicompartmental. Preoperative joint space of more than 2 mm on the operative side increased the odds of conversion to total knee arthroplasty by 5 times. BMI showed no statistical difference. Oxford Scores showed a minimally clinically important difference (MCID) (which is 5 for the Oxford Score) in 86 percent of patients. The mean change of the Oxford Score was 15 points. At four years, 92 percent of patients had their original prosthesis.