The Hip Joint - Part Two
November 10th, 2009 Posted by: Robert Bonello
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.
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.
The production of new cartilage is in response to the daily expected mechanical stresses put on a joint, and with the high forces involved in heel strike the cycle of stresses and relaxation are important to counter this. Encouraging larger movements in greater ranges may be useful to encourage growth of cartilage, however if loads are static or significantly reduced the opposite may occur. Loss of cartilage may occur with continued static loading, high bodyweight and allowing the joint forces to reduce by using a walking aid.
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 cyclical nature of gait may have other effects such as creating a pumping effect in the blood vessels of the ligamentum teres, a cord like structure which runs from the inside of the socket to the femoral head. This may increase the blood throughput to the head and so provide better nutrition. Continuing to walk places stresses on the hip which the upper femur needs, to keep the bones dense and healthy, with reduction of this from bed rest or using a stick potentially causing loss of bone minerals and overall density. This can also make the bone less flexible and increase the effects of jarring or other stresses on the area.
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.
