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.The cycles of compression and relaxation which occur with weight bearing and gait are essential to the health and nutrition of cartilage. As the cartilage is compressed it gives to some extent even though it is quite dense and once this is released it reverts to normal shape, squeezing the fluid out of it under pressure and then sucking it back in as force is removed. This sets up a pumping action of fluid up from within the cartilage and underlying bone, providing an essential fluid replacement mechanism to keep cartilage healthy.When the joints experience normal mechanical stresses they respond with the synthesis of new cartilage, with the cyclical stresses with rest periods important to cope with the levels of force involved just in heel strike in gait. Encouraging growth of cartilage may be possible by using the joints in big movements through their ranges but it may reduce cartilage growth if stresses are removed or it is subjected to static loads over time. These static loads when kept up, using a stick to reduce hip forces and having high bodyweight may all contribute.Resting a joint when it is painful is not a clearly positive strategy. Pain may be reduced when resting but the mechanisms which encourage regrowth of cartilage are not stimulated and the joint capsule may stiffen and reduce the available range of movement at the joint. This may increase the compressive forces in the joint and produce more pain. Whilst painful joints do need respect, in general arthritic joints are worse being still and better being kept moving about. The ability to achieve a rhythmical cycle of gait is very beneficial for the movements and the blood supply of the upper femoral structures.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.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
Physiotherapists, physiotherapy,
Physiotherapists in Windsor, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
