Numbness after medial unicompartmental knee arthroplasty: Prevalence and effect on functional outcome.

Background: The prevalence of skin sensation alteration after total knee arthroplasty is well established but less so in medial unicompartmental knee arthroplasty (MUKA). The aim of this study was to determine the prevalence, extent of numbness and its effect on mid-term functional outcomes after MUKA.

Methods: A level 2 prospective cohort study was conducted. Twenty patients (21 knees) were recruited. Demographics, length of surgical incision and the thigh-to-calf ratio was recorded. At the 1-year postoperative period, the extent of numbness was measured using a quantifiable grid-based system for both pinprick and fine touch. Preoperative, 3 months and 1 year postoperative Knee Society Scores (KSS) and 36-Item Short Form Health Survey (SF-36) scores were recorded.

Results: At the 1-year postoperative period, the prevalence of numbness to both fine touch and pin prick was 58% and 66%, respectively. The mean area of numbness to fine touch and pin prick was 336 mm and 521 mm respectively. The prevalence and extent of numbness was not significantly associated with surgical factors such as incision length and thigh-to-calf ratio. Prevalence and extent of numbness was not significantly associated with SF-36 scores and KSS at the 1-year postoperative period.

Conclusions: There is a high prevalence of numbness around the knee 1 year after MUKA. Surgical incision length and thigh-to-calf ratio was not associated with the extent of numbness. The presence and extent of numbness did not affect functional outcomes scores at the 1-year postoperative period. This study finding allows for accurate preoperative counselling with regards to numbness and its effects for patients undergoing MUKA.