Abstract
Purpose
Radial head implant over-lengthening, a common cause of capitellar wear and clinical failure, is difficult to diagnose using radiographs of the injured elbow. The purpose of this study was to determine if a novel measurement technique based on contralateral elbow radiographs, termed the RACER method, could be used to accurately estimate the magnitude of radial head implant over-lengthening. Part I of this study examined the side-to-side consistency of radiographic landmarks used in the measurement technique. Part II of this study validated the technique using simulated radial head implant over-lengthening in a cadaveric model.
Method
Part I: A side-to-side comparison of elbow joint dimensions was performed in 50 patients (100 radiographs). Part II: Radial head prostheses of varying lengths (0,+2mm,+4mm,+6mm,+8mm) were implanted in 4 paired cadaveric specimens (8 elbows). Radiographs were obtained and measurements were performed by 2 examiners blinded to implant size to determine if contralateral radiographs could diagnose and provide a valid estimate of the magnitude of implant over-lengthening. Intra and inter-rater reliability was determined.
Results
No significant side-to-side differences (p>0.2) in radiographic measurements were identified between paired elbows. The RACER measurement technique using contralateral radiographs was successful in predicting the implant size (1mm) in 104 of 120 (87%) of scenarios tested. The sensitivity of the technique, the ability of the test to correctly identify over-lengthening when it was present within 1mm, was 98%. The intra-rater agreement for a single orthopaedic surgeon measuring on 2 separate occasions was excellent (ICC>0.90). The inter-rater agreement between two separate surgeons was also excellent, with the 95% lower confidence interval exceeding 0.90 in all cases.
Conclusion
A novel measurement technique based on contralateral elbow radiographs can be used to diagnose and calculate the magnitude of radial head implant over-lengthening. Clinical Significance: Implantation of an incorrectly sized radial head prosthesis is not uncommon. The described technique can be used to effectively diagnose and determine the magnitude of over-lengthening.
