INTRODUCTION
Hip joint is a major joint of the human body which acts as the bearer of weight. Due to certain abnormalities, such as wear and tear, or some accidents there may occur a failure of this joint. Then arises a need for replacement of this joint, which is called as hip prosthesis.
Common Causes of Hip Joint Pain leading to Hip Replacement
The most common cause of chronic hip pain and disability is arthritis. Osteoarthritis, rheumatoid arthritis, and traumatic arthritis are the most common forms of this disease.
- Osteoarthritis. This is an age-related ”wear and tear” type of arthritis. It usually occurs in people 50 years of age and older and often in individuals with a family history of arthritis. The cartilage cushioning the bones of the hip wears away. The bones then rub against each other, causing hip pain and stiffness. Osteoarthritis may also be caused or accelerated by subtle irregularities in how the hip developed in childhood.
- Rheumatoid arthritis. This is an autoimmune disease in which the synovial membrane becomes inflamed and thickened. This chronic inflammation can damage the cartilage, leading to pain and stiffness. Rheumatoid arthritis is the most common type of a group of disorders termed ”inflammatory arthritis.”
- Post-traumatic arthritis. This can follow a serious hip injury or fracture. The cartilage may become damaged and lead to hip pain and stiffness over time.
- Avascular necrosis. An injury to the hip, such as a dislocation or fracture, may limit the blood supply to the femoral head. This is called avascular necrosis (also commonly referred to as ”osteonecrosis”). The lack of blood may cause the surface of the bone to collapse, and arthritis will result. Some diseases can also cause avascular necrosis.
- Childhood hip disease. Some infants and children have hip problems. Even though the problems are successfully treated during childhood, they may still cause arthritis
later on in life. This happens because the hip may not grow normally, and the joint surfaces are affected.
HIP JOINT
Hip joint is a joint in the human body designed naturally for weight bearing of the body and also provides stability. The hip joint is by default a ball and socket synovial joint formation between the pelvic acetabulum and the head of the femur. It is mainly formed by the articulation of these bones. The main focus of this joint is stability and weight bearing, as mentioned earlier, rather than allowing a large range of movements. This joint acts as a connection between the lower limb and the pelvic girdle.
STRUCTURES OF THE HIP JOINT
Articulating Surfaces
The hip joint consists of an articulation between the head of femur and acetabulum of the pelvis.
The acetabulum is a cup-like depression located on the inferolateral aspect of the pelvis. Its cavity is deepened by the presence of a fibrocartilaginous collar – the acetabular labrum. The head of femur is hemispherical, and fits completely into the concavity of the acetabulum.
Both the acetabulum and head of femur are covered in articular cartilage, which is thicker at the places of weight bearing.
The capsule of the hip joint attaches to the edge of the acetabulum proximally. Distally, it attaches to the intertrochanteric line anteriorly and the femoral neck posteriorly.
Fig : The articulating surfaces of the hip joint: the pelvic acetabulum and head of the femur.
Movement and Muscles
The movements that can be carried out at the hip joint are listed below, along with the principle muscles responsible for each action:
- Flexion – iliopsoas, rectus femoris, sartorius, pectineus
- Extension – gluteus maximus; semimembranosus, semitendinosus and biceps femoris (the hamstrings)
- Abduction – gluteus medius, gluteus minimus, piriformis and tensor fascia latae
- Adduction – adductors longus, brevis and magnus, pectineus and gracilis
- Lateral rotation – biceps femoris, gluteus maximus, piriformis, assisted by the obturators, gemilli and quadratus femoris.
- Medial rotation – anterior fibres of gluteus medius and minimus, tensor fascia latae
The degree to which flexion at the hip can occur depends on whether the knee is flexed – this relaxes the hamstring muscles, and increases the range of flexion.
Extension at the hip joint is limited by the joint capsule and the iliofemoral ligament. These structures become taut during extension to limit further movement.
Stabilising Factors
The primary function of the hip joint is to weight-bear. There are a number of factors that act to increase stability of the joint.
The first structure is the acetabulum. It is deep, and encompasses nearly all of the head of the femur. This decreases the probability of the head slipping out of the acetabulum (dislocation).
There is a horseshoe shaped fibrocartilaginous ring around the acetabulum which increases its depth, known as the acetabular labrum. The increase in depth provides a larger articular surface, further improving the stability of the joint.
The iliofemoral, pubofemoral and ischiofemoral ligaments are very strong, and along with the thickened joint capsule, provide a large degree of stability. These ligaments have a unique spiral orientation; this causes them to become tighter when the joint is extended.
In addition, the muscles and ligaments work in a reciprocal fashion at the hip joint:
- Anteriorly, where the ligaments are strongest, the medial flexors (located anteriorly) are fewer and weaker.
- Posteriorly, where the ligaments are weakest, the medial rotators are greater in number and stronger – they effectively ‘pull’ the head of the femur into the acetabulum.
Fig : The extra capsular ligaments of the hip joint .
HIP PROSTHESIS
Hip joint failure is a commonly discussed issue. Hip joint prosthesis is basically a surgical procedure where the degenerated hip joint is replaced by prosthetic hip implants as total hip arthroplasty or hemi replacement. The purpose of this replacement is to develop an environment
to restore the properties of motion of the locomotory, thereby allowing it to withstand the physiological conditions.
Fig : TOTAL HIP PROSTHESIS
HISTORY
To start from the very beginning of the first applications of artificial hip joint, the progress in developing the design and selecting materials meeting the specific requirements is commendable. First performed in 1960, hip replacement surgery is one of the most successful operations in all of medicine. Since 1960, improvements in joint replacement surgical techniques and technology have greatly increased the effectiveness of total hip replacement. As implant technology is evolving, development of hip prosthesis in this field falls in as this century’s most challenging issues among others. In an attempt to heal arthritis cases, the first attempts of hip surgery can be traced back to 1750, in England. To heal the hip the first proposal came to design a prosthesis in 1840, where the procedure was limited to alterations in the femoral head with the use of a wooden block in the hip articulation in places where the terminal parts were damaged. But this procedure proved devastating due to the release of wear particles in the body. To resolve the devastating effects biological elements such as skin, pig bladder, gold foil, etc. were used for compatibility purposes. In 1880, the first ever ivory ball and socket prosthesis was implant by Prof. Themistocles Gluck, where screws were used to fix it to the bones. San Baw an orthopedic surgeon began performing hip replacements, with in and around 300 ivory hip replacements, over a period of twenty years, and with a commendable success rate of 88%.
However, Sir John Charley is recognized as the pioneer of THA. He carried out the earliest replacement in Germany in early 1960. During 60’s the concept of Low Fiction Arthoplastry (LFA)was defined by Sir Charnley. Made of stainless steel stem his first prosthesis was fixed with acrylic cement, the cup made of polytetrafluoroethylene (PTFE) which was coupled with a 22.2 diameter head. Finding various wear and tear problems in PTFE, Sir Charnley started experimenting
with polymers like high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE) and also the acetabular cup was experimented with cement fixation. These experimentations were a success and Sir Charnley thereafter has various modified design of his original design leading to many successful operations.
COMPONENTS OF TOTAL HIP ARTHOPLASTRY
In a total hip replacement (also called total hip arthroplasty), the damaged bone and cartilage is removed and replaced with prosthetic components.
- The damaged femoral head is removed and replaced with a metal stem that is placed into the hollow centre of the femur. The femoral stem may be either cemented or ”press fit” into the bone.
- A metal or ceramic ball is placed on the upper part of the stem. This ball replaces the damaged femoral head that was removed.
- The damaged cartilage surface of the socket (acetabulum) is removed and replaced with a metal socket. Screws or cement are sometimes used to hold the socket in place.
- A plastic, ceramic, or metal spacer is inserted between the new ball and the socket to allow for a smooth gliding surface.
Fig: Typical form and position of hip joint prosthesis