The Swiss Cheese Effect: A Biomechanical Study of Fifth Metacarpal Structural Integrity After Multiple Kirschner Wire...

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Hand Surgery

Background:

• Percutaneous pinning with Kirschner wires (K-wires) is a common technique in hand surgery for fracture fixation.
• A clear threshold for the number of K-wire passes that compromise bone integrity is not established.
• Understanding the biomechanical implications of multiple K-wire passes is crucial for preventing iatrogenic fractures.

Purpose of the Study:

• To investigate whether an increased number of K-wire passes in the fifth metacarpal weakens the bone to a clinically significant degree.
• To determine if multiple K-wire insertions increase the risk of bone fracture during simulated functional loading.

Main Methods:

• A biomechanical study using paired cadaveric hands with simulated fifth carpometacarpal dislocations.
• Specimens underwent either one (control), three parallel, or eight crossing K-wire passes.
• Cyclic grip simulation and load-to-failure testing were performed to assess bone integrity and construct strength.

Main Results:

• All specimens, regardless of the number of K-wire passes, survived simulated grip cycles without fracture.
• Load-to-failure testing revealed no statistically significant differences between control (one pass) and experimental groups (three or eight passes).
• The mean load-to-failure values for one versus three passes were 97 N vs. 105 N, and for one versus eight passes were 212 N vs. 196 N (P > .05).

Conclusions:

• The number of extra K-wire passes (up to eight) did not meaningfully weaken the fifth metacarpal in this cadaveric model.
• These findings suggest that constructs with multiple K-wire passes are biomechanically stable.
• The results support the safety of early motion and light gripping following procedures involving multiple K-wire passes for carpometacarpal joint dislocations.