Hip joint is a type of synovial joint – ball and socket type of joint. When two or more bones meet it forms a joint. In this type of joint the fit is similar to a ball in a socket – i.e the concave socket of one bone provides a fit to the round end of the other bone.
In the hip joint the femur which is the thigh bone meets with the pelvis bones. Three bones make up the pelvis structure, the ilium (rear), ischium (lower front) & pubis. In this joint all three meet with the thigh bone. The hip bone has a concave socket, the hipbone fits into this socket. This pelvis socket is called acetabulum which makes half of the joint sphere. The thigh bone head called the femoral head makes two – third of the sphere. A shiny white cartilage covering the femoral head is ¼ inch thick is slippery and smooth and is kept more so by a fluid made in the joint lining which is called the synovial membrane. Because of this the bones making up the joint move easily against each other without friction and pain. The hip joint is also called the joint capsule which apart from this has large ligaments, muscles and tendons. They keep the bones in place and prevent dislocation.
The articular cartilage in the joint provides protection to this weight bearing structure. The synovial fluid lubricates this cartilage which is slippery, flexible, toughest structure next to bones in the body. This smooth and greasy combination of the cartilage and the synovial fluid which is sticky and viscous lubricant gives the body the flexibility to flex joints under great weight bearing conditions and pressure comfortably preventing wearing and tearing of the joint.
This hip joint a major pressure and weight bearing joint and it is also one of the most complex joints in the body. It bears the weight of the entire body while walking which can be 5 times of the body weight of the person. Any injury/disease which may lead to change in the hip joint structure has significant impact on the gait of the person and abnormal stress is placed on the bones and the hip joint.
A major impact during an injury/accident would cause any damage to the hip joint as it is supported by strong thigh muscles. Disease like osteoarthiritis can adversely affect the joint as the bones become brittle in this disease. Due to this the weight bearing capacity gets affected and may result in fractures.