Application of saphenous nerve infrapatellar branch protection technique in total knee arthroplasty

Objective Compared with the traditional surgical method, this study aims to explore a saphenous nerve infrapatellar branch protection technique to address the issue of numbness and pain in the anterolateral skin of the knee joint after total knee arthroplasty, thereby improving patient satisfaction. In this study, we compared the effects of the modified TKA surgical incision and the traditional median surgical incision on anterolateral skin numbness and pain, as well as the protective techniques targeting the infrapatellar branch of the saphenous nerve. The goal was to reduce sensory disorders in the anterolateral skin of the knee, alleviate pain in the operative area, and ultimately improve patient satisfaction after surgery. Methods In this study, 60 patients who underwent TKA for the first time at Zhejiang Provincial Hospital of Traditional Chinese Medicine between January 2022 and June 2023 were selected and randomly divided into two groups: Modified group (M group n = 31) and Traditional group (T group n = 29). In M group, a modified approach was used to incise and visualize the articular cavity. The skin incision was the same length as that in the classic median knee surgery, and the visualization of the articular cavity was performed in two steps. First, an incision was made above the knee joint line, similar to the classic medial parapatellar approach, but the proximal end was extended proximally along the medial femoral tendon to relax the knee-extension device. In the second step, the proximal incision was retracted to both sides, and the skin below the joint line was incised longitudinally to protect all subcutaneous soft tissues in the superficial layer of the patellar tendon, which contained branches of the infrapatellar branch of the saphenous nerve, while maintaining skin tension. In T group, the articular cavity was exposed through the traditional medial parapatellar approach. All 60 patients underwent TKA performed by the same attending surgeon, and the same brand of knee prosthesis was uesd for all patients (no patellar surface replacement, only patellofemoral plasty). The skin sensation around the incision was statistically observed preoperatively, and at 2 weeks, 1 month, 3 months, 6 months, and 1 year postoperatively. This included the size of the distribution area of skin numbness and changes in numbness. The two groups were compared and analyzed to determine differences in anterior-lateral knee skin numbness and pain between the two surgical techniques. Data were collated through statistical analysis to compare the differences in numbness and pain between the two groups. This study aimed to explore whether the improved surgical technique was more effective in reducing the occurrence of numbness and pain in the postoperative period and to draw a conclusion. Results There was no statistically significant difference in the baseline characteristics between the two groups (P > 0.05). The P-value of the HSS scores of the two groups was greater than 0.05 in the preoperative, at 7 days postoperatively, at 2 weeks postoperatively, and at 1 month postoperatively, indicating no statistically significant difference. The P-value of the VAS scores of the two groups were greater than 0.05 preoperatively and at 1 day postoperatively, indicating no statistically significant difference. However, the P-value of the VAS scores were less than 0.001 at 3 days postoperatively, 7 days postoperatively, and 2 weeks postoperatively, indicating a statistically significant difference. The P-values for the numbness area of the two groups were less than 0.001 at 2 weeks postoperatively, 1 month postoperatively, 3 months postoperatively, 6 months postoperatively, and 1 year postoperatively, indicating a statistically significant difference. The area of numbness was smaller in the group with the modified surgical technique compared to the traditional surgery at the same time points. Additionally, numbness on the outer side of the incision in some of the patients treated with the modified technique was completely recovered. Conclusion The modified incision-exposure technique used in this study effectively protects the infrapatellar branch of the saphenous nerve without causing operational difficulties in osteotomy, ligament balancing, gap balancing, or prosthesis implantation during total knee replacements. This technique results in a smaller area of postoperative skin numbness compared to the traditional surgical method, with less postoperative pain and faster recovery.