The Journal of Arthroplasty Vol. 10 No. 1 1995 Lateral Skin Flap Numbness After Total Knee Arthroplasty N. R. Borley, MB, BS, D. Edwards, FRCS, and R. N. Villar, MS, FRCS Abstract: The authors report the results of a study of lateral skin flap numbness in 25 consecutive primary total knee arthroplasties following the use of a midline, parapatellar incision. All 25 scars were found to have some degree of skin flap numb- ness, with 24 having an affected skin area of greater than 40 cm 2. In two patients (7%), this was considered a significant problem and there appeared to be little improve- ment with time. The authors therefore feel that lateral skin flap numbness is a signifi- cant complication of total knee arthroplasty when a midline, parapatellar incision is used, and patients should be made aware of this complication before surgery. Key words." knee arthroplasty, numbness. Primary total knee arthroplasty (TKA) is a wide- spread orthopedic procedure in the United Kingdom and abroad with evidence that it will become more popular in the future. 1,2 Complications such as infec- tion, loosening, prosthesis failure, and fracture are among those that are clearly recognized and quanti- fied 3-~ and patients are advised accordingly prior to surgery. Although many surgical aspects of the var- ious approaches to the knee have been well docu- mented, 6 lateral skin flap numbness has not, to our knowledge, been similarly assessed. In this age of increasingly informed consent and need for accurate awareness of operative complications, we felt that the complication of lateral skin flap numbness should be investigated and quantified to enable better pa- tient information and preparation for surgery. Materials and Methods Twenty-three consecutive patients who had undergone primary TKA for osteoarthritis (27 TKAs) under the care of one surgeon (R. N. V.) were invited for assessment. Twenty-five scars on the 21 patients assessed were examined by a single observer. All scars were midline incisions using a median, subcu- taneous parapatellar approach. Patients were asked if they had noticed any prob- lems with their scar or the skin around it. If they denied any problems, they were specifically asked about areas of numbness. The extent of any numb- ness was then measured using cotton wool for light touch and a blunt pin for pin-prick sensation. The results were marked on a standard diagram of the knee with the incision included. The results were then correlated to the degree of numbness recorded at the postoperative assessments. The following in- formation was also recorded: sex distribution (48% male, 52% female), length of time since operation (median, 11 months; range, 4-48 months), and age distribution (median, 79 years; range, 41-88 years). Any history of diabetes mellitus, peripheral neuropa- thy, previous knee surgery, or preoperative anesthe- sia of the knee skin was noted. Each patient was then asked if they felt the area of numbness (if present) to be shrinking or the degree of numbness to be im- proving. Results From the Department of Orthopaedic and Trauma Surgery, Adden- brooke's Hospital, Hills Road, Cambridge, United Kingdom. Reprint requests: Dr. N. R. Borley, 12 The Close, Montreal Park, Sevenoaks, Kent, TI'¢13 2HE U.K. The median length of the scar was 15.4 cm (range, 13. l- 17.0 cm). All 25 scars were found to have some degree of lateral skin flap numbness. Ten patients 13