The Hip – Part Two

Small movements which allow a glide and a slide inside a joint are essential for the normal use of the joint but cannot be done in isolation, occurring with other movements. These are called accessory movements and their presence is vital to joint function, a reduction in available range or a pain problem resulting if they are lost or reduced. The hip is a deep joint with significant stability so the accessory movements are rather subtle, with the main one being compression and distraction, the pushing in to and pulling out of the ball from the socket.

Walking and bearing weight involve reciprocal cycles of relaxation and compression, which promotes the nutrition and health of the articular cartilage. On compression the cartilage will be indented to a degree and once the force is released it will move back towards its normal shape. In this way fluid is forced out of the tissue under compression and sucked back in again on relaxation of the pressure. This pumps fluid from inside the articular cartilage and from the bone under it, setting up a system of fluid replacement.

The typical mechanical stresses through the joints stimulate the production of new cartilage cells, with the on-off stresses being important to counter the high forces involved when we put our heels down in gait. Bigger movements in larger amplitudes may encourage cartilage growth whilst absence of stresses or sustained loads may impede synthesis of cartilage. Cartilage breakdown may be encouraged by high bodyweight, static loading for long periods or by reducing loads such as by use of a stick.

While resting a joint may reduce the pain at first it may not be the most successful treatment for a painful joint. The normal processes of cartilage regeneration do not occur when insufficient force is applied to the joint and the joint capsule may shrink to some degree, tightening the joint. This tightness may increase the typical joint compression and so the pain. It is important to take into account any pain in a joint but on average it is better to keep arthritic joints mobile rather than still. A good blood circulation to the areas around the hip is kept up by the rhythms of cyclical gait.

The ligamentum teres, a band like structure running from the head of the femur to the socket, has blood vessels which may be affected by the cycle of gait which produces a effect of pumping fluid through. This may allow better blood supply to the head of the femur and keep the bone healthy. To maintain the density and normal composition of the bone in the upper femur it is important for this area to be subject to normal forces such as walking. Use of a walking aid or resting in bed can cause loss of bone density and mineralisation, with the bone becoming less flexible and less resistant to jars and strains.

In western societies we typically use little of the relatively large available ranges of movement of the hip joint. We walk in a limited, repetitive range and when we sit we typically do so at a mostly high level so our hips don’t go beyond 90 degrees flexion. We seldom push our hips to the extremes of movement of which they are capable and this tendency increases greatly with age. Overall the hip will benefit from maintaining a variety of its movements and from placing it at the ends of its ranges at times. Eastern peoples typically squat or sit cross legged, even to iron, and seem to have lower levels of hip arthritis.

An increased tightness in the joint capsule can result from a person not taking advantage of their full joint ranges over a time period, elevating the tendency for the head to be compressed into the socket. If there is a discrepancy in leg length this can primarily affect hip extension as the hip and knee are maintained in slight flexion to keep the eyes and head level. This fixed flexion deformity of the hip limits extension excursion of the joint in walking and changes the pattern of gait.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapist in hartlepool. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.