Accuracy of the Lesser Trochanter Profile as a Marker of Femoral Rotation: Computed Tomography-Based Study of 1,722 Femora.

BACKGROUND: The lesser trochanter (LT) profile is an often-used marker for proximal femoral rotation, particularly during the operative fixation of femoral fractures. Previous studies have come to conflicting conclusions about its reliability for this purpose.

METHODS: The SOMA (Stryker Orthopaedic Modeling and Analytics) database (Stryker) was used to identify 1,722 computed tomographic (CT) scans of whole femora. Each femur was taken through an 80° rotational arc in 2.5° increments, and the LT profile was constructed for each position. These 56,826 LT profile measurements were then correlated with the femoral rotation.

RESULTS: Across the arc of motion studied, the LT correlated weakly with proximal femoral rotation (R2 = 0.32). There was a 35° arc, between 10° and 45° relative external rotation of the proximal femur, within which the LT profile only changed by 1 mm. The mean overall femoral anteversion was 21.2°, and women tended to have more femoral anteversion (23.9°) than men (19.2°). On average, men had a 1.6-mm more prominent LT than women. Side-to-side differences in femoral anteversion as well as LT position and size were not significant or were clinically unimportant.

CONCLUSIONS: A large-scale, CT-based study shows that the LT profile is a less reliable marker of proximal femoral rotation than previously thought. This is true particularly if there is relative external rotation of the proximal femur, where the proximal femur can undergo up to 35° of rotation before 1 mm of change in the LT profile occurs. Care must be taken to check other markers of rotation such as by clinical examination during fixation of femoral fractures and not rely solely on the LT profile.

CLINICAL RELEVANCE: In the largest study of its kind, this CT-based study of 56,826 LT profile measurements found that when the proximal femur is externally rotated, the LT profile becomes an unreliable marker of rotation, which can lead to excessive internal rotation of the distal fracture fragment. The LT profile should be used with caution, and confirmation of rotation by other means is recommended.