A new classification system of superior and inferior gemelli muscles: a cadaveric study

The superior and inferior gemellus muscles are small components of the deep gluteal region that contribute to lateral rotation and stabilization of the hip joint. Despite their functional importance, these muscles display notable morphological variability with potential clinical relevance. The aim of this study was to classify the morphological variations of the superior and inferior gemellus muscles observed during anatomical dissection.

A total of 60 lower limbs (28 male lower limbs and 32 female lower limbs; 30 right and 30 left) from 30 cadavers of a Central European population, fixed in a 10% formalin solution, were examined.

Upon dissection, the morphology of the superior and inferior gemellus muscles was assessed. Based on their course and the number of muscle bellies, four types of the superior gemellus muscle and three types of the inferior gemellus muscle were identified. The superior gemellus muscle was present in 86.7% of cases and the following types were distinguished: Type 1 (65%) was characterized by a single belly proximally attached to the external surface of the ischial spine and distally attached to the trochanteric fossa. Type 2 (10%) consisted of a double belly arising as a common muscular mass from the external surface of the ischial spine; the upper belly was distally fused with the piriformis tendon and attached to the tip of the greater trochanter, whereas the lower belly was distally attached to the trochanteric fossa of the femur. Type 3 (11.7%) presented as a single belly proximally attached to the external surface of the ischial spine and fusing with the piriformis muscle tendon. Their common tendon was distally attached to the tip of the greater trochanter. Type 4 (13.3%) was characterized by the absence of the superior gemellus muscle. The inferior gemellus muscle was present in 80% of cases and following types were identified: Type I (75%) consisted of a single belly proximally attached to the upper part of the ischial tuberosity and distally attached to the trochanteric fossa. Type II (5%) showed a double belly proximally attached to the upper part of the ischial tuberosity, fusing into a common muscular mass and distally attached to the trochanteric fossa. Type III (20%) - characterized by the absence of the inferior gemellus muscle.

The superior and inferior gemellus muscles demonstrate considerable morphological variability. Knowledge of these variations is essential for clinicians involved in diagnostic imaging, surgical procedures, and the management of neurovascular compression syndromes.