The Valgus Stress Radiograph Does Not Determine the Full Extent of Correction of Deformity Prior to Medial Unicompartmental Knee Arthroplasty.

Routine preoperative stress radiographs have been advocated, in part, to determine "full correctability" of deformities before proceeding with unicompartmental knee arthroplasty (UKA) despite limited data supporting their utility. Fifty consecutive patients undergoing medial UKA with robotic navigation were studied. In 20° of flexion, significantly greater correctability was achieved after removal of osteophytes by an additional 1.8°, with a mean corrected alignment of 2.5° varus. Seventy-four percent of knees were not correctable to neutral alignment or more. In conclusion, preoperative stress radiographs have overstated value in patients undergoing medial UKA since the full extent of correctability of varus deformity cannot be determined until after removal of osteophytes and since most deformities are not fully correctable to neutral in UKA.