Articular Surface Involvement With Retrograde Headless Screw Fixation of the Proximal Phalanx.

PURPOSE: Intramedullary (IM) screw fixation of proximal phalanx (P1) fractures is a treatment option increasing in popularity. This study aimed to quantify the articular surface loss after retrograde screw insertion and to determine the range of motion (ROM) of the proximal interphalangeal (PIP) joint while the defect in the P1 head is engaged with the base of the middle phalanx (P2).

METHODS: Twelve fresh frozen cadaver hand specimens were analyzed for prefixation ROM of the PIP joint. A retrograde screw was placed using a percutaneous technique under fluoroscopic guidance. Following screw insertion, specimens were dissected to determine size of the extensor mechanism defect, evaluate the lateral bands with passive ROM of the PIP joint, and determine the angle at which the dorsal aspect of P2 ceases to engage with the defect and the amount of articular surface loss. The percentage of articular surface loss was calculated using a digital image software program.

RESULTS: The angle at which P2 ceased to engage with the articular surface defect was an average of 36.8° of PIP joint flexion. In full PIP joint flexion, the average extensor mechanism defect was 8.8%. The average total articular surface loss was 4.4% across all digits.

CONCLUSION: Percutaneous retrograde P1 intramedullary screw fixation results in minimal damage to the extensor mechanism and articular surface. The arc during which the defect in the head of P1 engages the base of the P2 is almost entirely outside the functional ROM of the PIP joint.

CLINICAL RELEVANCE: Quantifying the amount of articular surface loss through the P1 head and extensor apparatus damage in IM screw fixation can inform surgeons of the consequences of this technique. This study supports the use of a retrograde intramedullary screw as a safe option for fixation of P1 fractures.