The radial head size in relation to osseous landmarks of the forearm.

Radial head fractures are regularly treated with radial head arthroplasty. To prevent limited motion or pain, the implant's size should match its normal anatomy. Preoperative estimation of the radial head size helps in finding the correct head component. The aim of this study was to measure bony landmarks in proximity to the radial head to estimate the required size of a prosthesis preoperatively. Anatomical landmarks on 82 elbows from 41 embalmed specimens (19 male, 22 female) were measured using a digital caliper after removal of the specimens' tissue: the largest and smallest radial head diameter, length of the radius (styloid tip to radial head articular surface), and the length of the ulna (styloid tip to coronoid base). Additionally, cranio-caudal and antero-posterior diameters of the capitulum on scaled lateral elbow X-ray images were measured. The mean largest and smallest radial head diameters were 24.2 mm (± 2.2, range 19.9-30.3; ICC = 0.992) and 22.5 mm (± 2.0, range 18.9-27.5; ICC = 0.985). The mean radius length was 23.8 cm (± 1.6, range 20.1-27.1; ICC = 0.986), and the mean ulna length was 23.1 cm (± 1.6, range 19.3-26.3; ICC = 0.969). The mean antero-posterior capitulum diameter was 16.2 mm (± 2.4, range 10.4-21.0; ICC = 0.506), and the mean cranio-caudal diameter was 17.0 mm (± 3.3, range 10.0-23.9; ICC = 0.529). The highest correlation to radial head diameters could be shown for diameters of the contralateral radial head and the radius length. For preoperative estimation of the radial head, the diameters of the contralateral radial head or the radius length are the most accurate.