Workings Of The Hip Joint-Part 2

                                                                                         

A normal joint exhibits accessory movements which are small sliding and gliding motions inside the joint, occurring during movement but a person is incapable of performing them in isolation. They are very important in joint function and should they be reduced or lost this will impact on the ability to use the joint and could cause pain. Because the hip joint is stable and very deep it is not obvious there is much in the way of accessory movement. The main one is a downwards and upward movement of the head in and out of 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.

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.

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.

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.

Western individuals normally take advantage of only a small proportion of the large ranges of movement which the hip possesses. The repeated nature of walking only occurs in small ranges and we rarely go over 90 degrees flexion when we are sitting. As time goes on we push our hips less and less towards the ends of their movement, allowing loss of motion. Keeping the full ranges of movement available is beneficial to hips as is pushing them as far as they will go from time to time. In the east many people squat, even for ironing, and may have lower incidence of hip arthritis than western populations.

If the ranges of movement are not routinely used the capsule of the joint will tend to tighten to a degree, increasing the forces which compress the head into the socket. A discrepancy in the length of leg can have a subtle effect on the hip range of movement, particularly of extension. When standing the longer leg will tend to shorten itself slightly to compensate for its length and keep the head and eyes at a normal angle. This means it is held forward by a slight flexion of the hip and knee and so some of the range of hip extension is lost as a hip flexion contracture develops.

About the author:
Jonathan Blood Smyth is the Superintendent of Physiotherapists at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for physiotherapist in Blackpool visit his website.

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