The hip is a relatively stable ball-and-socket joint that allows a considerable range of multi-directional movement. The ‘ball’ is formed by the head of the femur and the ‘socket’ is formed by the acetabulum of the pelvis. The acetabular socket is strong and deepened even further by the presence of a cartilaginous disc that rims the circumference of the acetabulum. This disc, the acetabular labrum, is responsible for improving the congruence of the joint, as well as distributing forces through the joint.
The head of the femur which is connected to shaft of the bone by the femoral neck covers 60-70 % of a sphere within the acetabulum. The neck-shaft angle (see below) ranges between 120-130 degrees. In addition to this, the femoral head is rotated anteriorly (forward) between 15 and 20 degrees. This is known as the angle of anteversion. A decreased angle of rotation is known as retroversion. The individual variations in these angles affect the way the shaft of the bone lies as well as the forces that the surrounding muscles generate. An increased angle of anterversion for instance, can cause in-toeing.
The main ligaments of the hip are the ischifemoral, iliofemoral and pubofemoral ligaments. These ligaments form the capsule of the hip joint, offering it stability and resisting various planes of movement. Two other ligaments, the angular ligament and the Ligamentum Teres, also form part of the hip complex. Whilst these smaller ligaments are less involved in providing stability to the joint, the Ligamentum Teres contains a branch of a blood vessel so plays an important part in providing joint nutrition.
The 22 muscles about the hip can be grouped anatomically or functionally.
The muscles that adduct (bring the leg towards the body), are known as the adductor group of muscles and consist of the following : anteriorly; the adductor magnus, longus and brevis, gracilis and pectineus; posteriorly; the obturator internus and externus.
The iliopsoas (made up of the iliacus and psoas major and minor muscles) is the major flexor of the hip joint. Along with the Sartorius, rectus femoris and tensor fascia latae (TFL) muscles, the iliopsoas allows bending at the hip. The Sartorius muscle is also responsible for moving the limb up and outwards (abduction and external rotation).
The muscles at the back of the hip function to extend, externally rotate (rotate outwards) and adduct (bring towards the body) the hip. The muscle action varies based on the attachments and fibre directions, and several muscles have dual functions. For example, the Gluteus maximus, which is the largest muscle of the group, serves to extend and externally rotate the hip. The piriformis muscle is a much smaller muscle with similar functions. Other muscles at the back of the hip include the gemelli superior and inferior, the obturator internus and externus, and quadratus femoris.
The two muscles that serve to abduct or move the lower limb away from the body are the gluteus medius and minimus. These muscles are located on the outside of the hip and are essential for maintaining pelvic stability. This is by the presence of a ‘Trendelenburg’ gait. This occurs when the gluteus medius muscle is weak on the weight bearing side and hence causes the pelvis to sag on the opposite side.
How do the muscles of the hip provide protection?
While the muscles of the hip primarily function to allow movement of the lower limb, they also protect the femur from excess loads by providing counteracting compressive forces to the shaft of the femur. This protective mechanism is especially important in those who are diagnosed with osteoporosis.
How can a Physiotherapist help you?
While this article covers the very basic contents of hip musculoskeletal anatomy, there are several neural and vascular structures that can also influence pain patterns in the patient. As a clinician, the first step to forming a diagnosis is the patient history.
The mechanism of injury, areas affected and behaviour of the symptoms are the most useful pieces of information one can gather. Following this, an objective assessment including an assessment of gait, range of movement and special tests of musculoskeletal structures will usually allow for a hypothesis to be made. In some instances, an assessment of the pelvis or lower back may be necessary. Finally, to obtain a finalised, accurate diagnosis, radiological imaging may be advised. In less severe cases, such as a minor sprain or muscular tightness, expensive imaging is unnecessary and symptoms will often resolve with gentle therapy and exercise.
As daunting as the task may appear, an experienced and knowledgeable physiotherapist is well-equipped to provide the inquisitive patient with an answer or in very tricky cases, a few possible hypotheses and a referral to the radiologist. From then on, you’re on the road to recovery!
Are you experiencing pain around the hip? Our experienced team at Pivotal Motion can help you. Book an appointment online or call us today on 07 3352 5116.