The effect of radial head implant length on radiocapitellar articular properties and load transfer within the forearm.

BACKGROUND

The effect of radial head implant length on forearm biomechanics is not well understood. This study examined the influence of an increase or a decrease in radial head implant length on forearm load transfer as measured by interosseous membrane (IOM) tension and changes in radiocapitellar joint contact properties.

METHODS

An upper extremity simulator was used to examine 6 cadaveric specimens with 5 different radial head implant lengths (-4 mm, -2 mm, anatomically correct, +2 mm, and +4 mm). A load-sensing device was woven into the fibers of IOM to quantify its tension. An interpositional pressure measurement sensor was used to determine radiocapitellar joint contact area and pressure. Axial loads of 160 N were applied to the forearm through active pronation and supination with the elbow fixed at 90 degrees of flexion.

RESULTS

Increasing radial head implant length by 4 mm unloaded the IOM in all cases. Decreasing implant length by 4 mm significantly increased the IOM tension (P = 0.005). No significant differences were found in IOM tension between the correct head implant length and the -2 mm implant (P = 0.29). Contact pressure significantly increased with increasing radial head implant length (P = 0.021) and contact area diminished with both an increase and a decrease in radial head implant length, but this was not statistically significant (P = 0.051).

CONCLUSIONS

Increasing radial head implant length decreased IOM tension and increased radiocapitellar joint contact pressure.

CLINICAL RELEVANCE

These findings illustrate the importance of precise restoration of radial length when performing a radial head replacement. If the native radial head length is difficult to accurately assess, avoid increasing the length of the radial head to prevent detrimental changes in the biomechanics of the forearm and the potential for clinically important radiocapitellar joint pathology.