How accurate are arthroplasty surgeons in visually estimating extension and flexion gaps in total knee arthroplasty?

The ability of a surgeon to provide accurate visual estimates of intraoperative gaps during total knee arthroplasty (TKA) is not well understood. This study evaluated: 1) the accuracy of gap estimation in extension and in flexion; 2) the accuracy of gap estimation in the medial and lateral compartments, also in extension and flexion; 3) the differences in accuracy among surgeons; and 4) the frequency of clinically significant errors in gap estimation, defined as greater than 1 mm.

A posterior stabilized TKA was performed on seven cadaveric knees. Five fellowship-trained arthroplasty surgeons and one orthopaedic resident manually stressed each knee, and visually assessed the medial and lateral gaps in full extension and 90° of flexion. Gaps were objectively measured via a motion capture system. Gap estimation error was calculated as the difference between the surgeons' visual assessment and the measured gaps.

Across all surgeons and knees, the mean gap estimation error was -0.4 mm (SD 0.7), with the majority (72%) of gaps being underestimated. Errors were greater in extension (-0.7 mm (SD 0.8)) than in flexion (-0.2 mm (SD 1.0)) (p < 0.001). Lateral gap error was less in flexion (-0.1 mm (SD 1.0)) than extension (-0.7 mm (SD 0.8)). Gap estimation error pooled for all assessments differed between surgeons, ranging from a mean error of -0.8 mm (SD 0.8) to 0.2 mm (SD 1.2) (p < 0.001). Clinically significant gap estimation errors (> 1 mm) occurred in 33% of assessments in extension and 26% in flexion (p = 0.315, not statistically different). The frequency of such errors varied by surgeon ranging from 18% to 42% (p = 0.370).

Surgeons tend to underestimate intraoperative gaps during TKA, particularly in extension. Clinically meaningful gap estimation errors (> 1 mm) occurred in up to 33% (26/78) of exams, supporting the need to enhance gap assessment accuracy.