Anatomical variations of the trochlear notch angle: MRI analysis of 78 elbows

BACKGROUND: Little is known about the anatomical variations of the trochlear notch angle, nor do we know whether the cartilaginous layer modifies the trochlear bony contour. Our aim was to assess the variability of the bony and cartilaginous trochlear notch angles. MATERIALS AND METHODS: We assessed 78 healthy elbows (39 patients, 19 females and 20 males) with a mean age of 28 years (range 21-32). High-definition MRI coronal scans at the level of the flexion-extension axis were performed. The cartilage thickness, the notch angle, and trochlear width were calculated at the level of the deepest point of the trochlear sulcus, the edge of the lateral and medial ridge. Patient height was used as indirect measurement of humerus length. Pearson correlation and Student's t tests were performed. RESULTS: Mean cartilage thickness was 1.00 mm (range 0.62-1.83), with significant differences between the medial trochlear ridge and the other landmarks. The notch angle ranged from 124° to 156° (mean 142°) with no differences between the bony and cartilage layers. Trochlear width ranged from 1.57 to 2.75 cm (mean 2.24) and correlated with humerus length. No correlation emerged between the trochlear notch angle, trochlear width, or humerus length. The only significant difference between sexes was the width value, with a wider trochlea in males. CONCLUSIONS: The trochlear notch angle varies considerably, determining anatomical variations in trochlear shape which ranges from less concave to more concave types. Moreover, the cartilaginous layer does not modify this angle at the level examined. These findings may be relevant to anatomical implant design for distal humerus hemiarthroplasty.