Soft Tissue Violation Following Intramedullary Screw Fixation of Fractures in the Thumb: A Cadaveric Study.

PURPOSE Thumb phalangeal and metacarpal fractures are undergoing surgical intervention more frequently and can be stabilized using a range of modalities. Intramedullary screw (IMS) fixation has become more common in the management of these fractures. Violation of the articular cartilage and the extensor tendon is a concern when IMS fixation is used. The aim of this study was to assess the cartilaginous and soft tissue footprint resulting from retrograde IMS insertion in the proximal phalanx and metacarpal of the thumb.

METHODS Ten cadaveric thumbs underwent radiographic guided insertion of 2.8, 3.6, and 4.1 mm diameter headless compression screws. The width of the extensor tendon lesion was measured using a ruler, and the surface area of the defect within the articular cartilage using digital processing software.

RESULTS The mean footprint in the proximal phalanx following insertion of a 2.8 mm screw involved 15.58% of the extensor tendon width and 2.45% of the articular surface, increasing to 16.19% and 3.73%, respectively, when a 3.6 mm screw was inserted. The mean lesion in the metacarpal when a 3.6 mm screw was used was 14.79% of the extensor tendon width and 2.35% of the articular surface, with 9.29% tendon width and 4.10% articular surface disruption observed with the insertion of a 4.1 mm screw.

CONCLUSIONS The use of retrograde intramedullary screw fixation in the proximal phalanx and metacarpal of the thumb results in violation of the articular cartilage and terminal extensor tendon that is comparable to prior reports assessing the lesser digits.

CLINICAL RELEVANCE This study quantifies the disruption of the articular cartilage and terminal extensor tendon when intramedullary screws are inserted into thumb proximal phalanges and metacarpals in a retrograde fashion and finds comparable results to prior reports assessing the lesser digits. Quantification of articular and extensor tendon defects can be used with clinical outcomes to examine the benefits and detriments of intramedullary fixation of the thumb metacarpal and proximal phalanx.