Extensor tendon attachment to the dorsum of the proximal phalanx may fully extend the finger metacarpal phalangeal joint (MPJ). 15 fresh-frozen cadaveric hands were axially loaded in the line of pull to the extensor digitorum comunis of the index, middle, ring and small finger at the level just proximal to the MPJ. We measured force of extension at the MP joint in 3 groups: 1) native specimen, 2) extensor tendon release at the proximal interphalangeal (PIP) joint with release of lumbricals/lateral bands, 3) extensor tendon release at the PIP joint and dorsal proximal phalanx and lumbrical/lateral band release. Degree change of extension was calculated using arctan function with height change of the distal aspect of the proximal phalanx, and the length of the proximal phalanx. We used Student T-test to determine significant decrease in the extension of the phalanges. Extension of all fingers decreased slightly when the extensor tendon were severed at the PIP joint with release of the lateral bands/lumbricals (8deg+/−2deg). After this release, the finger no longer extended. Slight loss of extension was not statistically significant (p >.05) between group 1 and group 2. Groups 1 and 2 were significantly different compared to group 3. In summary, distal extensor tendon transection and release of lateral bands/lumbricals resulted in little change in force and degree of finger extension. The distal insertion of the extensor, released when exposing the PIP joint dorsally, may not need to be repaired to the base of the middle phalanx.

We hypothesized that the finger extensor mechanism has attachments along the dorsal surface of the entire length of the proximal phalanx and that this anatomy has not been clearly defined. The attachment along the dorsal aspect of the proximal phalanx of the index, middle, index and small fingers was dissected in 20 fresh-frozen cadavers. The lateral bands and attachments along the lateral and medial surface were released to appreciate the attachments along the dorsal aspect. We characterized the ligament attachments as very robust, moderately robust, and minimally robust at the distal, middle, and proximal portions. Three orthopaedic surgeons quantified the attachment, finding that 93% of specimens had tendinous attachments and the most robust attachment found at the most proximal and distal aspects adjacent to the articular cartilage. 87% of the specimens had very robust attachments at the proximal portion of the proximal phalanx. The middle portion of the proximal phalanx had moderate to minimally robust attachments. Greatest variability in attachment was found along the most distal portion of proximal phalanx adjacent to the proximal interphalangeal joint (26% of specimens had moderate to minimal robust attachment; 74% had robust attachments). The attachments along the proximal phalanx were attached on the dorsal half of the proximal phalanx, with no fibrous attachments extending past the lateral bands. In summary, we found tendinous attachment along the proximal phalanx that may assist in finger extension and may extend the digit at the metacarpal phalangeal joint without central band contribution.