The Effect of Percutaneous Retrograde Metacarpal Intramedullary Screw Insertion on the Extensor Tendon.

Abstract

Purpose: Both limited-open and percutaneous techniques have been described for retrograde insertion of intramedullary metacarpal screws. The percutaneous approach does not allow direct visualization of the starting point at the metacarpal head. However, it limits soft tissue dissection and expedites the procedure. The purpose of our study was to determine whether percutaneous, retrograde intramedullary screw fixation causes substantial iatrogenic damage to the extensor tendon. We also investigated whether larger sized screws would cause greater tendon injury compared to smaller screws.

Methods: Eight fresh frozen cadaver hands were used for percutaneous, retrograde intramedullary screw insertion of the index, long, ring, and small finger metacarpals of each specimen. Three different types of headless compression screws were used: a small fully threaded screw, a large fully threaded screw, and a Herbert-style partially threaded screw. After insertion, dissection was carried down to the screw entry site. Extensor tendon damage was evaluated, including tendon defect size and any irregularities noted in the tendon.

Results: There was no statistical difference with respect to how frequently a screw perforated the extensor tendons between all four finger metacarpals. Overall, the defect width caused by the screw was minimal, ranging from 0.66 mm to 1.89 mm for all finger and screw types. The large style screw did cause the greatest mean defect width, however, this was not statistically significant. When normalized to total tendon width, the defect was less than 28% of the total tendon width, with an average of 20% for all finger and screw types. Upon gross inspection, there was no fraying or irregularity noted at the screw-tendon insertion site, and it was often difficult to identify the screw entry site through the tendon by direct visualization alone. No tendon ruptures were noted.

Conclusions: This study found that percutaneous insertion of a retrograde, intramedullary metacarpal screw causes minimal extensor tendon injury. In contrast to the limited-open approach, the percutaneous technique requires less soft tissue dissection and the possibility of reduced swelling, scarring, and risk of adhesions. Moreover, it has the potential to allow for early functional rehabilitation and reduced operative time. Interestingly, none of the tendons demonstrated fraying or rupture, as one might expect to occur with blind passage of a drill and screw through a tendon. Overall, the percutaneous, retrograde intramedullary screw technique appears to cause minimal iatrogenic injury to the extensor tendon.