The safety of forefoot metatarsal pins in external fixation of the lower extremity.

Background: External fixation is widely used for trauma and reconstruction of the lower extremity. External fixator devices spanning the ankle or portions of the foot often utilize pins placed across the metatarsal bases. While this forefoot fixation is occasionally necessary to achieve reduction and alignment, it is also useful to prevent an equinus contracture. We undertook an anatomical study to evaluate the safety of pins placed across the bases of the first and second metatarsals, spanning the first intermetarsal space.

Methods: Under fluoroscopy, a single 4.0-mm Schanz pin was advanced percutaneously from medial to lateral across the bases of the first and second metatarsals in ten cadaver feet. This was accomplished in a fashion identical to the application of typical forefoot external fixation as described in the literature. Specimens were then dissected. Injury to the deep plantar branch of the dorsalis pedis artery, when present, was recorded. When injury was not present, the distance from the pin to the deep plantar branch was recorded.

Results: In five of the ten feet, the deep plantar branch of the dorsalis pedis artery was lacerated by the transmetatarsal pin. In four feet, the pin contacted the artery but did not visibly damage it. In the remaining foot, the pin was noted to be only 4 mm from the artery. Any pin with a starting point within 18 mm of the first metatarsocuneiform joint placed the artery at risk.

Conclusions: Placement of external fixation pins through the proximal bases of the first and second metatarsals, within 2 cm of the first tarsometatarsal joint, consistently places the deep plantar branch of the dorsalis pedis artery at risk. Given the clinical importance of this artery, transmetatarsal pinning in this fashion is not advised. Other methods of obtaining forefoot or midfoot external fixation are recommended in order to avoid vascular injury.