Minimally Invasive Dorsal Cheilectomy of the first metatarsal

Abstract

Category: Other Introduction/Purpose: Traditionally, a dorsal cheilectomy of the first metatarsophalangeal (MTP) joint is performed with an open approach through a dorsomedial or midmedial incision. It is now possible to perform minimally invasive dorsal cheilectomy (MIDC) of the first metatarsal with a wedge burr. The stab incision for MIDC needs to be dorsomedial to allow an ergonomic sweeping movement of the burr. This potentially puts the dorsomedial cutaneous nerve (DMCN) to the hallux at risk. There have been no clinical or cadaveric studies to date quantifying the risk to the DMCN and the surrounding structures when a Wedge burr was used for MIDC. We aim to determine this by using fresh-frozen cadaveric specimens in a “high-risk” situation in which most of the surgeons were novices to the technique. Methods: A total of 13 fresh-frozen cadaveric specimens (7 right, 6 left) amputated below the knee were obtained for this study. 13 foot and ankle surgeons (2 left handed, 11 right handed) who had no or minimal experience in MI surgery participated in this study. After a demonstration by an experienced MI surgeon and a practice on sawbones by participants, each surgeon performed a MIDC over the first metatarsal. Fluoroscopic guidance was available throughout the procedure. After the procedure, the specimens were dissected and the DMCN and the extensor hallucis longus (EHL) were inspected for damage. The same dissection steps were used for each specimen. The relationship of the DMCN to landmarks were measured. All measurements were made to the nearest millimetre. Results: Dissection of the specimens revealed that the DMCN to the hallux was cut completely in two specimens (15%). All the EHL tendon were intact, although in one specimen, the tendon showed some fraying on the underside of the tendon, estimated to be 15%. The average distance of the stab incision from the first MTP joint was 17.7 (range: 10 – 23) mm. In terms of the relationship of the DMCN to the stab incision in specimens where the DMCN was not cut, the DMCN was superior in five specimens and inferior in six specimens. The distance of the DMCN to the incision was 3.8 (range: 0 -7) mm. Conclusion: The DMCN to the hallux has been well studied by several authors and has a variable course. This nerve is at high risk of being damaged with open surgery and is a commonly reported complication of surgery to the hallux with rates reportedly as high as 45%. This nerve was damaged in 15% of our specimens following MIDC in a “high-risk” situation. Patients need to be specifically made aware of this risk when being consented for surgery. A carefully made working capsular pocket for the burr and marking this nerve before placing the incision if palpable could mitigate this risk.