Landmarks for rotational alignment of the humeral component during elbow arthroplasty

The reference points for rotational orientation of the humeral component during elbow arthroplasty typically are on the articular surface or the humeral epicondyles. With bone loss, these landmarks may be compromised. Our purpose was to assess whether the flat posterior humeral cortex proximal to the olecranon fossa is a reliable landmark with which to orient the humeral component during elbow arthroplasty.

Fifty cadaveric elbows (mean age [and standard deviation] at the time of death, 73 ± 12 years) underwent computed tomography (CT) scans. The flexion-extension axis (FEA) was determined by sphere-fitting the capitellar surface and circle-fitting the narrowest portion of the trochlea. The posterior humeral cortical line (PCL) was drawn on the flat posterior humeral cortex proximal to the olecranon fossa. The transepicondylar axis (TEA) was determined by a line between the most prominent points on the epicondyles. The angles between the PCL and FEA and the TEA and FEA were calculated and were compared by using two-tailed t tests.

The PCL was externally rotated by a mean (and standard deviation) of 14.0° ± 4.2° (p < 0.001) relative to the FEA (males: 12.6° ± 3.6°, females: 16.4° ± 5.2°; p = 0.002). The TEA was externally rotated by a mean of 2.8° ± 3.5° (p < 0.001) relative to the FEA (males: 2.7° ± 3.4°, females: 2.6° ± 3.7°; p = 0.96). The intraobserver and interobserver reliability was >0.98 for the capitellar and trochlear centers, while the cumulative intraobserver and interobserver reliability was 0.8 and 0.5 for the FEA-PCL angle and 0.4 and 0.3 for the FEA-TEA angle.

The posterior humeral cortex is a reproducible landmark that is externally rotated with respect to the flexion-extension axis of the distal part of the humerus. The surgeon must be aware of the need for an internal rotation correction factor and consider the influence of the patient's sex on this correction when using the posterior humeral cortex as a landmark to avoid humeral component malrotation.

While the PCL is better than the TEA as a reference point, neither is able to accurately identify the FEA because of considerable normal variation. Future studies are needed to evaluate the effectiveness of computer-assisted techniques or a preoperative CT scan of the contralateral, unaffected elbow in identifying rotational landmarks for the elbow undergoing arthroplasty.