Excessive lengthening of the radius with use of a radial head implant, a common cause of capitellar wear and clinical failure, is difficult to identify on radiographs of the injured elbow. The purpose of this study was to determine if a novel measurement technique based on radiographs of the contralateral elbow could be used to accurately estimate the magnitude of overlengthening due to the radial head implant. In part I of this study, we examined the side-to-side consistency of radiographic landmarks used in the measurement technique. In part II, the technique was validated in a cadaveric model with simulated radial head implant overlengthening.Methods:
In part I of the study, a side-to-side comparison of elbow joint dimensions was performed with use of 100 radiographs from fifty patients. In part II, radial head prostheses of varying lengths (leading to 0, 2, 4, 6, and 8 mm of overlengthening) were implanted in four pairs of cadaveric specimens (eight elbows). Radiographic measurements were performed by two examiners blinded to the implant size to determine if radiographs of the contralateral elbow could be used to diagnose, and provide a valid estimate of the magnitude of, implant overlengthening. Intrarater and interrater reliability ratios, absolute measurement errors, and diagnostic accuracy were determined.Results:
No significant side-to-side differences (p > 0.2) in radiographic measurements were identified between paired elbows. In the cadaveric model, the measurement technique involving use of radiographs of the contralateral elbow was successful in predicting the implant size (± 1 mm) in 104 (87%) of the 120 scenarios tested. The sensitivity of the technique—i.e., the ability of the test to correctly identify overlengthening (within ± 1 mm) when it was present—was 98%, with a positive likelihood ratio of 49 and a negative likelihood ratio of 0.02. The reliability of the radiographic measurements, based on repeated measurements performed by a single blinded orthopaedic surgeon on two separate occasions or based on separate measurements performed by two different orthopaedic surgeons, was excellent (intraclass correlation coefficient > 0.95).Conclusions:
A measurement technique based on radiographs of the contralateral elbow can be used to diagnose and calculate the magnitude of radial overlengthening due to the use of an incorrectly sized radial head implant.Clinical Relevance:
Implantation of a radial head prosthesis of incorrect size is not uncommon. The described technique can be used to diagnose and determine the magnitude of overlengthening of the radius.