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Hip Arthroplasty
Replacement of the hip with a prosthesis

Over 160,000 hip replacements are carried out every year in the United Stated. The most common reason is degenerative arthritis, the gradual deterioration or wearing out of the hip joint. In this procedure the two parts of the hip joint are removed and replaced with a metallic prosthesis. The surgery is better than 90% successful allowing a person to return to normal function.

Anatomy and Function of the Hip

  • The hip is a 'ball and socket' joint formed between two bones, the hipbone and the femur (Figure 1)
  • The hipbone on each side is attached to the sacrum, the lowest bone in the spine and the three form the bones of the pelvis
  • The hipbone forms the bony connection between the spine and leg and is formed by the fusion of three bones, the ilium, ischium and pubis.
  • The ilium is the bone found on each side just below the belt line, the most prominent part being the crest
  • The ischium protrudes backwards and is the bone that is sat upon
  • The pubis is the bone found just above the genital organs
  • The acetabulum is a half sphere shaped depression in the hipbone and formed by contributions from all of the three component bones. It is lined with smooth cartilage
  • The femur is the long bone that extends from the hip to the knee
    1. The upper end consists of the head, neck, greater trochanter and lesser trochanter
    2. The head and neck come off the shaft of the femur at approximately 125 degrees
    3. The two-thirds spherical shaped head is covered with smooth cartilage. The head fits into the acetabulum to form the hip joint
    4. The greater trochanter is a rounded protrusion of the femur that can be felt at the upper end of the thigh about 4 inches (10 centimeters) below the crest of the ilium
  • A fibrous joint capsule is lined with synovium, a special tissue that lines all motion joints and produces a lubricating fluid
  • The joint capsule, muscles and ligaments hold the two bones of the joint together
Figure 1 - Anatomy of the hip joint. Note the parts of the femur (left). The hipbone is made up of three bones, the ilium, ischium and pubis (middle). The head of the femur fits into the acetabulum of the hipbone to form the hip joint covered by a capsule.

Pathology

  • Osteoarthritis is the most common form of arthritis that leads to hip replacement surgery
    1. In this form or arthritis, the cartilage and synovium gradually wear down to expose the underlying bone so that the femoral head and acetabulum grind directly on each other (bone-on-bone) (Figure 2)
    2. Osteoarthritis is usually seen over the age of 60 years
    3. Occasionally abnormalities of the hip that occur in childhood cause irregularities of the surface of the joint that cause degeneration later in life
  • Traumatic arthritis occurs following injury to the hip causing damage to the joint particularly the joint cartilage
    1. If the neck of the femur is fractured or the hip dislocated, the blood supply to the head may be lost giving rise to death and collapse of the head (avascular necrosis) and degeneration of the joint
    2. Avascular necrosis have also been linked to alcoholism and extended use of cortisone
  • Occasionally hip deterioration due to rheumatoid arthritis may require hip replacement
    1. Rheumatoid arthritis may attack any joint in the body
    2. The body's immune system attacks the synovium and cartilage of the joints causing damage to the joints
    3. This results in painful swelling and deformity with loss of joint motion
    4. Women are more often affected than men

History and Examination

  • Osteoarthritis
    1. Pain in the joint develops slowly over time
    2. Older population, usually greater than 60
    3. Obese patients
    4. Individuals that have repeated minor injuries (e.g. football player)
    5. Familial history of osteoarthritis
    6. Major joint inflammation is usually not seen
  • Traumatic arthritis
    1. History of significant or repeated injury to the hip
    2. Usually only one joint involved
  • Rheumatoid arthritis
    1. Usually progressive joint involvement
    2. Many joints involved at the same time
    3. Marked stiffness of the joints after resting
    4. Marked tenderness in all the inflamed joints
    5. Women predominate
    6. Major joint inflammation commonly seen
    7. Associated joint deformity
    8. Nodules beneath the skin at sites of chronic irritation
  • Examination
    1. Pain on walking or on rotating the hip
    2. Limping to protect the painful hip
    3. The normal range of motion of the hip is lost
    4. There may be weakness in the muscles about the hip
Tests
  • Plain X-rays of the hip in both the anterior-posterior (front to back) and lateral (side to side) views are taken to determine the degree of degenerative changes in the joint, such as a loss of joint space or irregularity of the joint surface (Figure 2)
  • CT (computerized tomography) may be helpful in showing fracture or changes in the bony surface
  • MRI (magnetic resonance imaging) is now the method of choice for evaluating the non-bony (soft) tissues of the hip. It is helpful in determining if avascular necrosis is present.
Figure 2 - X-ray of the right hip demonstrating loss of the joint space so that bone rubs on bone. Also note the spur at the edge of the acetabulum. Courtesy S. Kassab, M.D.

Non-operative therapy

  • Hip surgery should not be considered unless medical and physical therapy have been exhausted.
  • Nonsteroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofin), aspirin and COX-2 inhibitors (e.g. celecoxib, rofecoxib) may give symptomatic relief of pain
  • Drugs used specially for rheumatoid arthritis (e.g. gold compounds, methotrexate)
  • Use of a cane to decrease weight bearing and help reduce pain
  • Local heat or cold for temporary pain relief
  • Weight reduction program to reduce stress on the hip
  • Exercise program to improve hip motion and muscle tone and strength
  • Injection of steroids into the hip joint

Indications and Contraindications

  • Indications for surgery
    1. Hip pain severe enough not only to prevent work but also activities of everyday living
    2. Limitation and stiffness of the hip
    3. Failure of conservative measures to relieve the pain
    4. Advanced degenerative changes in the hip by X-ray
  • Contraindications to surgery
    1. Inadequate bony support for the prosthesis in the femur hipbone
    2. Previous joint infection
    3. Degeneration of the nerves to the joint
    4. Conditions that increase the load on the implanted prosthesis and reduces the chance of a satisfactory long term result (e.g. marked obesity)
    5. Skeletally immature bone structure

Surgical Procedure

  • Surgery is resorted to only if conservative measures fail. The object is to remove the painful hip and replace it with metal prostheses covering both the femoral and acetabular ends
    1. A strong, smooth, low-wearing plastic insert anchored to the hipbone is placed between the two metal prostheses and creates a smooth surface for the moving metal parts
    2. The prosthesis may be cemented or uncemented
    3. The cemented prosthesis is secured to the bone with cement
    4. The uncemented prosthesis has a mesh of holes on its surface. The prosthesis is secured as the surrounding bone grows into the mesh
  • An incision about eight inches long is made over the hip (Figure 3A)
  • The ligaments and muscles are separated to expose the bones of the hip joint
  • The femoral head is dislocated from the acetabulum (Figure 3B)
  • The femoral head is removed by cutting through the neck of the femur (Figure 3B)
  • The cartilage is then removed from the acetabulum with a special reamer that reforms the acetabular cup into a hemisphere (Figure 3C)
  • The acetabular prosthesis is inserted into the reamed bone. In the uncemented type the prosthesis is press fit or secured with screws. With the cemented type, the prosthesis is secured with special cement (Figure 3D)
  • A hard smooth plastic cup is then inserted into the metal acetabular prosthesis
  • The femur is then prepared with special instruments to shape and hollow out the center of the femur to the shape of the stem of the femoral prosthesis (Figure 3E)
  • The stem of the femoral prosthesis is then inserted into the center of the femur. If an uncemented type prosthesis is used it is press fit, otherwise the prosthesis is cemented in place (Figure 3F)
  • A metallic ball that replaces the femoral head is attached to the stem (Figure 3G)
  • The ball is inserted into the acetabular prosthesis following which the wound is sutured closed (Figures 3H and 4)
Figure 3aFigure 3b
Figure 3cFigure 3d
Figure 3eFigure 3f
Figure 3gFigure 3h
Figure 4 - Postoperative X-ray of right hip of patient shown in figure 2 showing the acetabular prosthesis into which is fit the ball of the femoral prosthesis. Courtesy S. Kassab, M.D.

Complications

  • Difference in leg length
  • Stiffness of the hip
  • The femoral ball dislocates from the acetabular cup
  • Hemorrhage
  • Infection
  • Fracture of the femur or acetabulum
  • Blood clots in the legs
  • Blood clots to the lung
  • Urinary tract infection
  • Increased wear of the plastic surfaces of the prosthesis
  • Loosening of the prosthesis due to resorption (softening) of the bone
  • Dislocation, excessive rotation or loss of motion of the prosthesis
  • Foreign body reaction to the prosthesis or cement
  • Delayed skin healing or sloughing of skin
  • Sensitivity reaction to the metal
  • Loosening or migration of the prosthesis due to injury or loss of fixation
  • Damage to adjacent blood vessels
  • Damage to surrounding nerves causing pain, numbness, or weakness
  • Calcification about the joint with loss of motion

Postoperative Care

  • There may be a drain in the wound attached to a suction device which is usually removed a day or two after surgery
  • Intravenous fluids may be given as well as antibiotics
  • Pain medication is given as necessary
  • Elastic stockings, air compression stockings and blood thinners are usually used after surgery to decrease the chance of blood clots
  • Physical therapy aimed at getting the patient in and out of bed, standing and walking is started the following day
  • Standing and walking is aided with crutches or a walker
  • Discharge from hospital occurs usually in three to five days with a program of continued physical therapy

After Care

  • Contact the surgeon if
    1. There is an elevated temperature
    2. Drainage from the wound
    3. Increased swelling, redness or pain
  • Antibiotics should be ordered for future surgery or dental work
  • For the first 6-8 weeks, sitting may cause dislocation of the ball from the prosthetic acetabulum