Flexor Tendon Injury Risk With Percutaneous Intramedullary Screw Fixation for Lesser Metatarsal Fractures: A Cadaveric Study.

Background: Percutaneous intramedullary screws have recently become a fixation option for the surgical management of lesser metatarsal fractures. Their advantages over Kirschner (K)-wire fixation include avoidance of pin site complications, fixation stability, and need for removal. To date, there has been limited literature published on their use and safety profile. The purpose of this study is to determine the frequency and extent of flexor tendon disruption associated with percutaneous intramedullary screw fixation for lesser metatarsal fractures.

Methods: Seven left and right lower extremity cadaver specimens were procured. A cannulated 3.6-mm screw was placed percutaneously in the second through fifth metatarsals (MTs) in a retrograde fashion. The plantar surface of each specimen was then exposed to visualize the flexor tendons. The tendon location relative to the drill hole, incidence of tendon disruption, percentage of tendon disruption, and the distance between the tendon and the drill hole were measured.

Results: Overall, 21 of 56 (37.5%) flexor tendons were damaged, 5 (35.7%) in the second MT, 7 (50%) in the third MT, 9 (64.3%) in the fourth MT, and 0 (0%) in the fifth MT. The percentage of tendon disruption for each metatarsal was 15%, 11%, 11%, and 0%, respectively. The mean distance from uninjured tendons to the drill hole was 1.07 mm, 0.94 mm, 0.9 mm, and 2.03 mm, respectively. Across all metatarsals, the majority of flexor tendons were located medial to the drill hole, with the greatest clearance seen in the fifth metatarsal.

Conclusion: Percutaneous insertion of intramedullary screws for lesser metatarsal fixation resulted in a 37.5% rate of flexor tendon injury, primarily affecting the fourth metatarsal. Although these disruptions involved 10% to 20% of tendon width, their clinical impact remains uncertain. Adjusting the starting point to a slightly more lateral position, if possible, may minimize the risk of flexor tendon injury. Future studies should assess functional outcomes, plantar plate involvement, and biomechanical consequences of partial tendon injury.