AAHS - Evaluating the Efficacy of Intramedullary Screw Fixation for Very Proximal Metacarpal Base Fractures

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Evaluating the Efficacy of Intramedullary Screw Fixation for Very Proximal Metacarpal Base Fractures
Majd Mzeihem, MD^¹, Dmitriy Peresada, MD^¹, Yeseop Park, PhD^¹, Jiries Fakhouri, BS^¹, Danil Rybalko, MD^¹; Farid Amirouche, PhD^{^1,2}
(¹)University of Illinois at Chicago, Chicago, IL, (²)Northshore University Health System, Evanston, IL

Introduction
Intramedullary screw fixation has shown promising results in metacarpal shaft and neck fractures; however, metacarpal base fractures remain understudied biomechanically. Limited clinical data suggest that intramedullary screws may outperform plates; however, these studies are small and lack biomechanical support. No biomechanical research has assessed how proximally intramedullary nails can stabilize these fractures.

Methods

This biomechanical study utilized 36 cadaveric metacarpals (index, middle, and ring fingers) from 12 upper limbs to identify the most proximal site where intramedullary (IM) screws can stabilize extraarticular base fractures. Bones were skeletonized, measured, and marked at 10%, 20%, and 30% from the proximal end, then potted distally. Transverse fractures were made at each mark with an oscillating saw. Specimens were fixed using antegrade IM headless screws, which were buried beneath the articular surface (Figure 1). Cantilever bending tests were performed using an MTS machine at a rate of 0.3 mm/s. The primary and secondary outcomes were the ultimate failure load and stiffness.

Results

A total of 36 cadaveric metacarpals (12 each of index, middle, and ring fingers) were randomized to undergo simulated transverse fractures at 10%, 20%, or 30% of total metacarpal length from the distal aspect (n = 12 per location). Biomechanical testing revealed that intramedullary (IM) screw fixation provided the highest ultimate failure load at the 10% fracture location (mean 190.45 N), followed by 30% (166.77 N) and 20% (142.16 N). For the middle finger, this trend was consistent; however, in the index finger, the 30% fracture had the highest load to failure, followed by the 10% and 20% fractures. For the ring finger, the 10% location demonstrated the most significant strength (135.82 N), with decreasing values at 20% (116.16 N) and 30% (96.75 N) (Table 1). Statistically significant differences in failure load were observed at the 10% fracture location when comparing the index and middle fingers to the ring finger (213.81 N and 221.42 N vs. 135.82 N, p < 0.05).

Conclusion

Intramedullary screw fixation can effectively stabilize extraarticular metacarpal base fractures as proximal as 10% of total metacarpal length, with biomechanical strength sufficient to support early mobilization protocols. The highest failure loads were observed at the 10% fracture location, particularly in the index and middle metacarpals, suggesting reliable fixation even in very proximal shaft fractures.

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