Anatomy of the infrapatellar branch in relation to skin incisions and as the basis to treat neuropathic pain by cryodenervation.

BACKGROUND: Neuropathic knee pain, particularly of the infrapatellar branch, is an important complication of knee replacement surgery, with an incidence as high as 70%. The increasing number of elderly patients requiring knee surgery, including total knee arthroplasty (TKA), has contributed to an increase in the number of patients with this pathology. Treatment includes neurectomy, infiltration therapy, and cryodenervation. Percutaneous cryodenervation of the infrapatellar branch is a promising option.
OBJECTIVE: To provide the necessary anatomical analysis to optimize percutaneous cryodenervation of the infrapatellar branch by defining sections of the unbranched ramus infrapatellaris to demonstrate the risk of nerve injury through 3 different skin incisions typically used during TKA. STUDY
DESIGN: Anatomical study.
METHODS: Cadavers were used for assessment. Exclusion criteria were scars from knee surgery, deep wounds, and a flexion angle of no more than 90°. We compared 3 frequently used skin incisions with the course of the infrapatellar branch and identified sections of the unbranched nerves that were suitable for percutaneous cryodenervation.
RESULTS: In total, 18 formalin-fixed cadavers (mean age, 78.9 years) contributed 30 knees (15 pairs) for dissection. We identified the following 4 anatomical variations of the ramus infrapatellaris in relation to the sartorius muscle: anterior, posterior, penetrating, and pes anserinus types. Sections were then found to treat the nerve branch types. The nerve sections were localized using the medial pole of the patella as a palpable landmark and varied in length between 15 mm and 40 mm. The medial parapatellar skin incision showed the highest risk of lesions to the infrapatellar branch (53.3%) followed by the midline skin incision (46.7%) and the lateral parapatellar skin incision (30.0%). LIMITATIONS: This was an observational study, performed using a limited number of cadavers. This therefore precluded generalization and statistical analysis. Significantly more female (13) cadavers were examined compared to male (5). Further studies in human populations, and with larger samples, are necessary to confirm these results.
CONCLUSION: Based on our findings, the surgeon can localize the unbranched main nerve. Compared with the current practice, our approach should allow for a lower impact on tissues and should facilitate complete pain relief through a single cryodenervation. Furthermore, we propose that the lateral parapatellar skin incision is an acceptable alternative surgical approach in knee replacement surgery because it is associated with the lowest risk of damage to the infrapatellar branch.