Relative Metacarpal Shortening as a Radiographic Measure of Fourth and Fifth Carpometacarpal Fracture Dislocation

Area of Science:

• Orthopedic surgery
• Radiology
• Hand surgery

Background:

• Carpometacarpal (CMC) fracture dislocations, particularly of the fourth and fifth digits, are often not apparent on standard X-rays.
• Early and accurate diagnosis is crucial for appropriate management and preventing long-term complications.

Purpose of the Study:

• To introduce and evaluate a novel radiographic measurement, the relative metacarpal shortening (RMS), for diagnosing fourth and fifth CMC fracture dislocations.
• To test the hypothesis that RMS values are significantly higher in patients with these injuries compared to controls.

Main Methods:

• A retrospective analysis of posteroanterior hand radiographs was conducted.
• Radiographs from patients with confirmed fourth/fifth CMC fracture dislocations were compared to those from a control group.
• The fourth and fifth RMS were calculated by comparing specific metacarpal lengths on posteroanterior radiographs.

Main Results:

• The study included 42 controls and 41 patients with CMC fracture dislocations.
• The RMS values for both the fourth (0.16 vs. 0.12) and fifth (0.31 vs. 0.26) metacarpals were significantly higher in the fracture group compared to controls.
• Inter-reviewer agreement for RMS measurements was found to be almost perfect (intraclass correlation coefficient range: 0.82-0.94).

Conclusions:

• The relative metacarpal shortening (RMS) is a reliable radiographic measurement for identifying fourth and fifth CMC fracture dislocations.
• Elevated RMS values (fourth RMS >0.13, fifth RMS >0.28) should raise suspicion for CMC fracture dislocation in patients presenting with ulnar-sided hand pain.