Trochanter

The trochanter is a bony protrusion of the femur.

The two trochanters of the femur. The lesser trochanter, circled in red, is located in the inner region; the greater trochanter, circled in orange, is located in the external region of the femur.

The femur is the longest and most voluminous bone in the human body, which forms the skeleton of the thigh.

Specifically, for each femur, two trochanters are recognized: a large (more voluminous) trochanter located externally and a smaller (smaller) trochanter located internally.

The trochanters serve as the point of insertion for several muscles involved in the movement of the hip and thigh.

The femur and trochanters

The femur is the longest, most voluminous and resistant bone in the human body. It belongs to the category of the so-called long bones and as such, from the anatomical point of view, it presents:

• an elongated central part, called the body or diaphysis:
• two extremities, called epiphyses:
  • the upper extremity (proximal epiphysis) presents:
    • a head: it has the shape of a hemisphere (2/3 of a sphere), whose rounded part (covered with cartilage) articulates with the acetabulum of the iliac bone to form the hip joint (or coxofermoral joint) ; the cartilaginous lining is missing in a dimple (fovea capitis) where the round ligament of the femur is inserted, which serves to keep the coxofemoral joint in position
    • a neck: it is the portion of connection between the head and the proximal shaft; cylindrical in shape, it is about 5 centimeters long and forms an angle with the diaphysis that varies from 120 ° to 145 ° (it is generally lower in the female than in the male, having a wider pelvis). The neck has a large number of channels for the passage of blood vessels.
  • the lower extremity (distal epiphysis) has two large condyles and articulates with the tibia to form the femoro-tibial joint and with the patella to form the patellofemoral joint; both are part of the knee joint.

    

In the upper part of the diaphysis, at the base of the neck, two rather pronounced bony ridges can be recognized, called trochanters.

• The greater trochanter is located lateral to the neck
• The lesser trochanter is located internally behind and below the neck.

Some sources consider the trochanters to be regions of the proximal epiphysis.

Greater trochanter

The greater trochanter is a large bony prominence, quadrangular in shape, palpable on the lateral surface of the hip.

It is located above the body of the femur and marks its upper limit. It develops in the area where the body joins the neck of the femur, in a lateral position.

Posteriorly, the greater trochanter is rounded and delimits a deep depression on the inner surface, called the trochanteric fossa. On the lateral wall of this fossa there is an evident oval dimple for the insertion of the external obturator muscle.

On the anterolateral surface, the greater trochanter has an elongated crest for insertion of the gluteus maximus. Another similar crest is found on the lateral surface, but in a more posterior position; it acts as an insertion of the gluteus medius. Between these two points the greater trochanter is palpable.

On the inner-superior part of the greater trochanter, just above the trochanteric fossa, there is a small area for the insertion of the internal obturator and the twin muscles; immediately above and behind it the margin of the trochanter inserts the piriformis muscle.

Figure: posterior view of the upper extremity of the femur.

Lesser trochanter

The lesser trochanter is smaller in size than the greater trochanter. Its shape is conical and squat, blunt. It protrudes opposite the greater trochanter, therefore in the internal region of the femur, just below the junction with the neck.

Under the lesser trochanter is the surgical neck of the femur which - according to some sources - marks the end between epiphysis and diaphysis.

The lesser trochanter is the site of insertion for the combined tendons of the greater psoas and iliac muscles (called ileo-psoas).

Between the two trochanters extend:

• anteriorly the intertrochanteric line
• posteriorly the intertrochanteric crest

These bony ridges separate the body from the femoral neck and represent connecting lines between the two trochanters.

Intertrochanteric line

This bony crest is located on the anterior surface of the upper body margin. It originates from a tubercle located on the anterior surface of the base of the greater trochanter and descends to a position just anterior to the base of the lesser trochanter. Below it is continued with the pectin line (or spinal line) which curves medially under the lesser trochanter and around the body of the femur until it joins the medial lip of the linea aspera at the back of the femur.

The intertrochanteric line provides insertion to the joint capsule on the anterior aspect of the bone.

Intertrochanteric crest

This bony crest is located on the posterior surface of the femur and descends from the posterior margin of the greater trochanter to the base of the lesser trochanter. It looks like a bony, smooth crest with a prominent tubercle (called the square tubercle) located in the upper half, which provides the insertion for the square muscle of the femur.

Fractures of the trochanters

Fractures of the femur involve - in most cases and especially in the elderly - the neck of the femur. Indeed, after the age of 70, fractures of the femoral neck are the most frequent fractures, both in men and especially in women (for whom the risk is greater).

This is because on the one hand the proximal end of the femur is often undermined by osteoporosis and on the other because in the elderly the way of falling tends to expose this area to trauma.

The most serious consequence of such femoral neck fractures is the possible blood disruption of the femoral head. In fact, the blood supply of the head and neck depends mainly on a ring of arteries located at the base of the neck.

In the absence of blood supply, the head of the femur undergoes necrosis, that is, it "crumbles" little by little. In the elderly, a fracture of the femoral neck almost always leads to the implantation of a total hip prosthesis, while in younger patients an attempt is made to preserve the joint by healing the fracture by means of osteosynthesis.

Fractures of the proximal femur have been divided into various categories based on the area where they occur. In detail, the following are presented:

• intertrochanteric fractures;
• fractures of the femoral neck;
• subtrochanteric fractures;
• fractures of the greater trochanter.

Quite common are the so-called intertrochanteric (or pertrochanteric) fractures. In this type of injury, the fracture line usually runs from the greater to the lesser trochanter without involving the colus of the femur. In these cases, the blood supply to the neck is preserved and there is no ischemia and consequent necrosis of the head.

Fractures of the greater trochanter are quite rare and, in addition to traumatic causes, can result from excessive muscular effort.