Off-axis loading associated with a fall onto the outstretched hand is hypothesized to induce distal radius failure at lower magnitudes than the axially directed loading—commonly used in biomechanical models for estimating fracture risk.

The goal of a new study published in the Journal of Orthopaedic Research was to compare distal radius failure loads between forearm pairs experimentally tested in an axial or off-axis loading configuration.

The present study entailed collection of 18 pairs of cadaveric forearms from 18 female donors. Each forearm pair was tested to failure using either an axial compression test—vertical orientation with 0° dorsal inclination, 3°-6° radial inclination, or an off-axis test corresponding to the hand position during a fall—15° dorsal inclination, 3°-6° radial inclination. Failure testing was performed at 3 mm/s onto the palm of the hand until fracture occurred.

The findings revealed that of the 18 pairs, 11 sustained a distal radius fracture. Failure loads were compared between the two groups – using a paired t test. The failure load under off-axis loading was 29% lower than failure load under axial compressive loading.

From the results, it was inferred that off-axis loading associated with a fall onto the outstretched hand resulted in a 29% lower failure load. It was stated that integrating an off-axis loading configuration into current biomechanical models of distal radius bone strength may prevent overestimating of failure load and may offer a clinically relevant option to estimate distal radius fracture risk and monitor therapy efficacy.

Source: Journal of Orthopaedic Research. 2020 Jan 28. doi: 10.1002/jor.24601.