Effect of Radiocapitellar Joint Over/Under Stuffing on Elbow Joint Contact Pressure

Abstract

Comminuted radial head fractures are commonly treated by surgical resection or replacement with a prosthesis. A potential problem with radial head replacement is overlengthening of the radial neck ("overstuffing" of the radial head), which has been shown to affect both ulnohumeral kinematics and radiocapitellar pressures. We hypothesized that an overstuffed radial head prosthesis increases capitellar pressure and reduces coronoid pressure. Seven human cadaveric elbows were prepared on a custom-designed apparatus simulating stabilizing muscle loads, and passively flexed from 0° to 90° under gravity valgus torque while joint contact pressures were measured. Each elbow was tested sequentially with different neck lengths, starting with the intact specimen followed by insertion of understuffed (-2 mm), standard-height (0 mm), and overstuffed (+2 mm) radial head prostheses in neutral forearm rotation, 40° pronation, and 40° supination positions, respectively. Capitellar mean contact pressures significantly increased after insertion of an overstuffed radial head prosthesis. In valgus position with neutral forearm rotation, capitellar mean contact pressure on the joint with an intact radial head averaged 227 ± 70 kPa. Insertion of understuffed, standard-height, and overstuffed radial head prostheses changed the mean contact pressures to 152 ± 76 kPa, 212 ± 68 kPa, and 491 ± 168 kPa, respectively. The overstuffed radial head group had significantly lower whole coronoid mean contact pressures (153 ± 56 kPa) compared with the intact (390 ± 138 kPa) and standard-height (376 ± 191 kPa) radial head groups. An increase in radial prosthesis height significantly increases capitellar contact pressures and reduces coronoid contact pressures. Restoration of the anatomic radial head height is critical when performing radial head arthroplasty to maintain normal joint biomechanics. Elevated capitellar contact pressures can potentially lead to pain and early degenerative changes.