Selecting the diameter of a radial head implant: an assessment of local landmarks

INTRODUCTION: Little information exists on radial head implant diameter sizing methods. When the native head is absent due to extensive comminution or previous excision, the lesser sigmoid notch may be a useful landmark for sizing. We evaluated the reliability of native radial head measurements, and the lesser sigmoid notch, as landmarks for radial head implant diameter sizing. METHODS: We examined 27 fresh frozen ulnae and their corresponding radial heads. The maximum, minimum, and dish diameters of the radial heads were measured. A radial head implant diameter was selected based on the congruency of the trial implants with the radius of curvature of the lesser sigmoid notch. Intraobserver and interobserver reliability for all measurements and implant selection were assessed using intraclass correlation coefficients (ICC). Correlations between the native radial head measurements and the selected radial head implant diameter or the lesser sigmoid notch radius of curvature were assessed using the Pearson correlation coefficient (PCC). RESULTS: Radial head diameter measurements demonstrated strong to excellent intraobserver (ICC ≥ 0.75) and interobserver reliability (ICC ≥ 0.82). The lesser sigmoid notch sizing method showed poor interobserver reliability (ICC = 0.34). Only a moderate correlation was found between the native radial head and the lesser sigmoid notch (PCC ≤ 0.80) or the selected radial head implant size (PCC ≤ 0.59). CONCLUSION: Radial head diameter measurements showed excellent reliability, suggesting that the excised radial head, when available, should be used to select the implant diameter. The reliability of using the lesser sigmoid notch for sizing the diameter of radial head implants was only moderate, suggesting this is an unreliable landmark for implant diameter sizing.