The objective measurement of hypoaesthesia after Total Knee Arthroplasty and its correlation with skin incision length: a prospective study.

Purpose: This study aims to measure the peri-incisional numbness developing after Total Knee Arthroplasty (TKA) performed using the midline skin incision. It studies the natural course of the numbness and determines its correlation with the skin incision length (SIL).

Materials & methods: 66 knees undergoing primary TKA with a standard midline incision were evaluated. The SIL and the area of numbness (AON) were measured in complete knee extension and 90° of flexion. The area was marked by the patient using a sketch pen and then determined by an independent observer using monofilament testing. The "ImageJ" software was used to calculate the area.

Results: All patients developed numbness around the knee after TKA. There was a statistically significant correlation between the SIL and AON in both flexion and extension at two weeks (p < 0.001) and three months (p < 0.001). However, there was a weak and insignificant correlation at six months (p = 0.217).

Conclusion: When TKA is performed using the midline skin incision, the SIL positively correlates with the AON postoperatively during the initial short-term follow-up. At six monthly follow-ups, there is no significant correlation between the two.