The trunk and the legs are connected mechanically at the large ball and socket joints of the hips. The acetabulum, the large rounded and deep hip socket with a cartilage rim, neatly covers the similarly shaped femoral head, the ball at the top of the thigh bone. This is a stable joint with deep structure and strong stabilisers. The surfaces of the hip joint are covered by an almost friction-free material called articular cartilage which allows movement to occur easily under stress, a vital ability in this joint. The greatest weight is taken in the roof of the socket and the uppermost part of the femoral head and this is where cartilage is thickest.
The socket, head and neck of the hip joint are completely enveloped by the hip capsule, a ligamentous bag which is well strengthened by the large and powerful ligaments of the hip. Lined by the synovial membrane which secretes nutritional and lubricating synovial fluid, the capsule runs from the margins of the socket, down over the head and neck to its base. The thigh bone travels upwards towards the body but the hip socket is at the side of pelvis and faces outwards and down, requiring the femur to make a 125 degree turn inwards at the top to allow the hip joint to form. This facilitates the appropriate mechanical structure.
Inside the hip the bony anatomy of the supporting struts or trabeculae are also mechanically aligned along the lines of most force, responding to the requirements of bodily motion and bearing weight. The densest areas reinforce the parts suffering the highest stresses. If the hip copes with these stresses by developing strengthened areas it also has areas of less strength which can become relevant in older people as they fall and suffer fractured necks of femur across these areas. As the number of older people dying after this fracture is relatively high, this matter is of concern.
Standing, the control of locomotion and coping with moving the body are the main functions of the hip joints. The muscles of the hip area are the strongest in the body and are capable of keeping the body stable or of moving it with speed and power. The main muscle groups are the gluteal muscles, the abductors and the adductors. The side to side stability of the pelvis is performed mostly by the hip abductor muscles and the most powerful muscle, the gluteus maximus, functions to move the body weight.
When performing activities such as climbing stairs, jumping or running, the joint surfaces of the hip are exposed to much higher mechanical stresses than just the body weight. To allow for this the most exposed areas to the weight are covered by the thickest cartilage. The underlying bone and the synovial membrane fluid are responsible for nutrition to the cartilage but this is not a very strong process. Cartilage turnover is slow with some forming at the base as the upper layers get damaged and are lost.
The synovial membrane lines the capsule of the hip and performs the secretion of small amounts of synovial fluid. This fluid is not present in large amounts but is thought to lubricate the movements of the joint, help particles of wear be absorbed to prevent a grinding paste being developed and spread mechanical loads throughout the joint. If the joint is under great load, the synovial membrane can respond to the cyclical stresses by increasing its secretion rate to protect the joint and lubricate it during periods of high activity.
If the hip movements are compromised in some way this is likely to have knock on effects on its primary function which is walking. Normal daily locomotion is allowed by having a gait pattern which is balanced and an even length of stride. The stride pattern of any individual is fairly stereotypical and limited and the earliest movement limitation noticed is usually hip extension. The hip has about twenty degrees of extension, which is the movement of taking the leg behind the body, particularly when the other leg is moving forward. Flexion of the hip is typically 130 degrees and any loss much less noticeable. - 14130
The socket, head and neck of the hip joint are completely enveloped by the hip capsule, a ligamentous bag which is well strengthened by the large and powerful ligaments of the hip. Lined by the synovial membrane which secretes nutritional and lubricating synovial fluid, the capsule runs from the margins of the socket, down over the head and neck to its base. The thigh bone travels upwards towards the body but the hip socket is at the side of pelvis and faces outwards and down, requiring the femur to make a 125 degree turn inwards at the top to allow the hip joint to form. This facilitates the appropriate mechanical structure.
Inside the hip the bony anatomy of the supporting struts or trabeculae are also mechanically aligned along the lines of most force, responding to the requirements of bodily motion and bearing weight. The densest areas reinforce the parts suffering the highest stresses. If the hip copes with these stresses by developing strengthened areas it also has areas of less strength which can become relevant in older people as they fall and suffer fractured necks of femur across these areas. As the number of older people dying after this fracture is relatively high, this matter is of concern.
Standing, the control of locomotion and coping with moving the body are the main functions of the hip joints. The muscles of the hip area are the strongest in the body and are capable of keeping the body stable or of moving it with speed and power. The main muscle groups are the gluteal muscles, the abductors and the adductors. The side to side stability of the pelvis is performed mostly by the hip abductor muscles and the most powerful muscle, the gluteus maximus, functions to move the body weight.
When performing activities such as climbing stairs, jumping or running, the joint surfaces of the hip are exposed to much higher mechanical stresses than just the body weight. To allow for this the most exposed areas to the weight are covered by the thickest cartilage. The underlying bone and the synovial membrane fluid are responsible for nutrition to the cartilage but this is not a very strong process. Cartilage turnover is slow with some forming at the base as the upper layers get damaged and are lost.
The synovial membrane lines the capsule of the hip and performs the secretion of small amounts of synovial fluid. This fluid is not present in large amounts but is thought to lubricate the movements of the joint, help particles of wear be absorbed to prevent a grinding paste being developed and spread mechanical loads throughout the joint. If the joint is under great load, the synovial membrane can respond to the cyclical stresses by increasing its secretion rate to protect the joint and lubricate it during periods of high activity.
If the hip movements are compromised in some way this is likely to have knock on effects on its primary function which is walking. Normal daily locomotion is allowed by having a gait pattern which is balanced and an even length of stride. The stride pattern of any individual is fairly stereotypical and limited and the earliest movement limitation noticed is usually hip extension. The hip has about twenty degrees of extension, which is the movement of taking the leg behind the body, particularly when the other leg is moving forward. Flexion of the hip is typically 130 degrees and any loss much less noticeable. - 14130
About the Author:
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Manchester. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
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