Purpose: Unrepairable fractures of the radial head are often treated with radial head arthroplasty. Insertion of a radial head prosthesis that is too thick, or overstuffed, is believed to be a common complication that may result in pain, arthrosis, capitellar wear and decreased elbow range of motion. The purpose of this study was to develop guidelines for determining the appropriate thickness of radial head implants. We hypothesized that

radiographic incongruity of the medial facet of the ulnohumeral joint and that

Method: Six human cadaveric upper extremities were used to evaluate the clinical and radiographic effects of overstuffing of a radial head arthroplasty. Each specimen received an anatomic radial head replacement and then underwent overstuffing with +2 mm, +4 mm, +6 mm and +8 mm lengths. Gross lateral ulnohumeral joint spaces were measured, and anteroposterior radiographs were taken of the elbow from which radiographic medial and lateral ulnohumeral joint spaces were measured.

Results: Intraoperative gapping of the lateral ulnohumeral facet was shown to be highly reliable for detecting radial head overstuffing, increasing from a mean of 0.0 mm at standard length to 1.0 mm with 2 mm overstuffing (p < 0.05). Radiographically, the congruity of the lateral ulnohumeral facet was significantly different with 2 mm of overstuffing as compared to the anatomic length (p < 0.05). The congruity of the medial ulnohumeral facet only became significantly different with +6 mm of overstuffing as compared to the anatomic length (p < 0.05).

Conclusion: Radiographic incongruity of the medial facet of the ulnohumeral joint was an unreliable indicator of radial head overstuffing. Radiographic gapping of the lateral ulnohumeral facet demonstrated sufficient sensitivity to diagnose radial head overstuffing when compare to the standard length implant radiographs. Visual gapping of the lateral ulnohumeral facet on the cadaver specimens reliably indicated radial head overstuffing and should be a useful anatomic feature to assess intraoperatively.