The lesser trochanter is a feature of the femur, the large long bone of the upper leg that spans from the hip to the knee. Found at the top of the bone near the hip joint, the lesser trochanter is a small, rounded bump that emanates from the posterior side of the bone on the femoral neck. This feature is significant as the insertion point for two muscles of the hip flexor group: the psoas major and the iliacus.
As a long bone, the femur consists of a narrow shaft that is capped at either end by multiple rounded projections. These eminences form the hip and knee joints as well as serve as sites where the muscles that move the joints can attach to the bone. At the top end of the bone are several such bony projections. The head of the femur anglesinward, as well as upward, from the neck of the bone. This inserts into the hip to form the “ball” component of the ball-and-socket joint found here.
Just below and lateral to the head and neck of the femur is a curved, upward-pointing projection known as the greater trochanter. Though the greater trochanter is not a part of the hip joint, several ligaments surrounding and encapsulating the joint attach here, as do multiple muscles that move the hip, including the gluteus maximus and the piriformis. Below the greater trochanter on the front side of the bone is where the shaft of the femur begins.
On the back side of the femur, however, is where the lesser trochanter is found. Upon viewing the upper femur from behind, it can be seen at the base of the curved greater trochanter right where the shaft begins. Located on the back of the bone toward the medial side, the side on which the head and neck of the femur are found, the lesser trochanter resembles a convex and slightly cone-shaped knob or bump that is perhaps one-tenth of the size of the head of the femur.
Since it is so small, it does not provide a great surface area for muscle attachment. Therefore, only one shared tendon belonging to two muscles affixes to the lesser trochanter. One muscle is the psoas major, the larger of the iliopsoas or hip flexor complex. This muscle originates on the lowest thoracic as well as the lumbar vertebrae in the spine, crosses the pelvis to the front of the hip joint, and inserts via the iliopsoas tendon on the groin side of the hip joint to the lesser trochanter.
The other iliopsoas muscle, the iliacus, originates several inches below the psoas major at the top of the pelvis on the ilium bone. It then crosses the front of the pelvis alongside the psoas and merges its fibers with those of that muscle to form the iliopsoas tendon. This tendon attaches to the lesser trochanter and produces the motion of hip flexion, meaning that when the two muscles contract, they pull upward on the femur and lift the leg forward relative to the hip joint.