The Hip – Part Two
Accessory movements are the small gliding and sliding movements which occur inside a joint during normal movement but which cannot be performed in isolation by a person. They are essential to the function of a joint and if lost can interfere with the ability to perform movements or can contribute to painful conditions. In the hip the accessory movements are not obvious with few gliding and sliding movements due to its deep and stable nature. One accessory movement which does occur is upwards and downwards, i.e. compression into the socket and distraction of the femoral head out of the socket.
The health and well-being of the articular cartilage are related to the repeated cycles of compression and relaxation applied to the joint such as with weight bearing and walking. The cartilage is pressed downwards to a degree when pressure is applied and this indentation returns to normal once the pressure is relieved. This engages a fluid pumping system where it is squashed out of the cartilage under compression and pulled back in on relief of the pressure. This pumping of fluid from the deeper cartilage and underlying bone keeps the surface healthy.
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.
When a joint is painful it may not always be the best idea to rest it although pain will be reduced at least initially. Without normal forces the cartilage regrowth stimulation does not occur and there may be a tightening of the joint capsule and a loss of the full movement of the joint. The joint may then become more painful as the tightness increases compressive forces. Respecting a painful joint is important but overall it is better to keep an arthritic joint moving than to keep it static. The normal cyclical rhythm of gait is very important in maintaining movement and good blood supply to the upper hip area.
In the inside of the hip, leading from the acetabulum to the femoral head, is the band like ligamentum teres which carries blood vessels that can be stimulated by the typical cycle of gait and allow a fluid pump. The may give an improved blood supply to the femoral head and maintain bone health. The normal forces which walking places on the upper femoral region are vital to keeping the bone composition and density within normal ranges. Resting in bed or using a walking aid can both contribute to a reduction in mineralisation and density in bone, making it less flexible and so less able to counter strains and jars.
Typically in western countries people utilise only a small part of the rather large range of movements available to the hip. Walking is a repetitive movement in only a small range and on sitting we don’t often go over ninety degrees flexion. As we get older we are less and less inclined to make our hips go to the ends of the ranges they are capable of. Hips seem to benefit particularly from keeping a variety in their movement available and stressing them to their extremes now and again. In eastern societies squatting, even to iron, is common, and our levels of hip arthritis
A lack of use in the end ranges of a joint can mean the joint capsule will exhibit some tightening and in this way increase the compressive forces suffered by the head. Extension of the hip can be particularly affected by a difference in leg length. The longer leg in standing will tend to bend slightly at the hip and knee to keep the head level for the eyes to function best. This compensation can lead to stiffness developing with some loss of hip and knee extension as the hip develops a fixed flexion deformity.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain
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