Revision Hip Replacement

Revision hip replacement is a surgery to replace the components of a Total Hip replacement. Hip is a large ball and socket joint which may be damaged due to arthritis or other cause.  The surgery involves replacing the parts forming the Hip joint with prosthetic/man made parts.

Total hip replacement is one of the most successful surgeries in modern medicine. On an average, hip replacement surgery may last for 15-20 years or more. Due to various biological and mechanical reasons the parts may fail, requiring a surgery involving removal of implant and replacing them.

Revision hip replacements are usually more complex surgeries than primary total Hip replacements requiring extensive planning and use of special implants. The ultimate goal however remains the same as of primary replacement.  The aim of providing pain free mobility so that the patients can return to activities they enjoy. 

Components of Total Hip Replacement

• Acetabulum cup made of metal alloy or ceramic. It is is fixed with screws or press-fitted in the socket forming the Hip joint after removing damaged 
• A special form of highly durable plastic called polyethylene is placed in the socket to allow smooth gliding
• A stem made of metallic alloy is inserted in the upper part of the thigh bone (femur). The stem may be press-fit or fixed using a special form of bone cement.
• A prosthetic head made of metal alloy or ceramic is placed on the stem replacing the natural head of the femur.

The acetabular shell is usually press fitted in the acetabular cavity. The acetabular cavity is prepared by reaming the cavity that allows new bone to grow into the outer porous coating of the acetabular shell. The multiple screw options are advantageous in revision surgery.

The acetabular liner made of highly cross linked polyethylene fits in the acetabular shell and provides a smooth surface for the prosthetic head to rotate in the cavity. The prosthetic head may be made of ceramic or cobalt chromium alloy.

During revision surgery, a fully porous coated femoral stem is usually used for a better stability of the component. The stem is also longer than the primary prosthesis to provide more stability. Other types of stems may be used that may have detachable upper and lower parts (modular stems).

Causes of Component Failure

Like any mechanical device, the components of hip replacement surgery can fail over time. Number of factors can contribute to their failure and need for revision surgery. 

Wear and Tear : The implant (femoral stem and acetabulum cup) must be firmly fixed to the underlying bone. This is achieved either by the use of bone cement or the implant is press fit. Press fitting allows bone to grow onto the implant. 

The failure of bone to grow on the implant or loosening of bone cement weakens the fixation. This may lead to chronic pain with decrease in mobility.

Younger patients with a total Hip replacement outlive the lifespan of the implant requiring revision. Additionally, individuals who are overweight and engaging in high impact activities require a revision surgery sooner. This is due to excessive forces acting about the joint loosening the fixation. 

The plastic liner which is made of high quality polyethylene wears out over time giving out tiny particles. These are attacked by the body’s immune system recognizing them as foreign bodies causing inflammation. The immune cells fighting the plastic breaks also attack the healthy bone which leads to loosening of implant known as osteolysis. 

Infection : Every surgery carries a risk of infection which may occur immediately or occur in several months or even years. Infectious organisms accumulating in and around the prosthesis cause the implant to become loose same fail. 

Obese patients with diseases such as diabetes are at an added risk of infection. Infectious bacteria can enter into blood from distant sites such as teeth and accumulate forming an abscess around the prosthetic joint. Symptoms usually are pain or even a draining abscess from the joint. 

Trauma : Injuries sustained to the hip during a trauma caused by fall or accident can cause loosening of prosthesis. There may be a fracture of the bone around the implant (periprosthetic fracture) or rarely breakage of the metal implant itself. The revision usually requires use of special implants depending upon the amount of remaining bone. 

Dislocation : For the joint to function the ball must remain in the socket at all times. Dislocation occurs when the ball pops out of the socket due to trauma or certain positions of the artificial joint. Proper alignment of the components and balancing of forces by muscles and tendons is important. 

Once dislocated the joint becomes more prone to recurrent dislocations as muscles and tendons around the joint get damaged. This may warrant a revision surgery to properly align the prosthetic components preventing dislocation. 

Management

Revision hip replacement is a complex Surgery requiring special implants work increased surgery and recovery time. Usually more number of investigations are needed. The patient may be subjected to blood tests and imaging studies (X-ray, CT scan, MRI, Bone scan). In case the surgeon suspects an infection, a joint aspiration may be done to rule out or confirm the infection. 

The surgical procedure on the day of surgery after anesthesia is more complex than primary replacement. The surgeon gets an access to the joint through the same incision or a different one. Careful examination of the soft tissues is done to look for infection and examine the components which are loose. 

Only the plastic liner and head of stem is replaced in some cases. This is done in case of the firm contact of acetabulum cup and femoral stem. In case of loose implant, they are extracted carefully trying to preserve the bone. Sometimes a controlled fracture may be done to gain access to the implant for removal. 

Specialized implants are used to recreate the Hip joint. It may sometimes require bone graft (from deceased compatible ) and metals to augment/compensate for the lost/damaged bone. 

A modular prosthetic stem allows the surgeon to compensate for excessive bone loss during extraction of the primary component. The modular stem may consist of holes for screw fixation and fully porous coating for bone ingrowth. The upper part of the prosthesis is designed to transfer load to the stronger inner of the bone.

In case of infected prosthesis, the revision surgery becomes more complicated. Decision regarding the surgery is made after assessing the duration and severity of the infection. Usually a two stage surgery is performed where in the first stage the infected implant is removed. 

The Hip joint is thoroughly washed and a cement spacer is introduced which is impregnated with antibiotics. After clearance from infection in a few weeks a second surgery is performed removing the spacer and introduction of new implants. 

In a selected few cases a single stage surgery may be performed depending upon the severity of infection. Infected protestors requiring revision usually remain a long time on iv antibiotics with a very prolonged recovery period. 

Recovery

Revision hip replacements usually have a prolonged recovery period depending upon the cause of revision. Daily activities such as cooking, shopping, bathing, laundry, driving are limited for several weeks. Patients usually walks work an aid of crutches/walker with precautions restricting certain activities. 

Full recovery and return to activities the enjoys takes about 6 months.  Regardless most patients enjoy pain free mobility offered by the surgery allowing them to carry on their daily activities. 

Complication

The risk of complications are more in revision hip replacement owing to prolonged surgery time and prolonged recovery period. There are risks of infection, blood clots, pulmonary embolism (blood clots in lung). Additionally there may be damage to nerve/blood vessel or leg lengthening/shortening. There is also a risk of failure of bone to attach to the prosthetic implant and implant loosening. 

All the potential complications are discussed by the surgeon with the patient. Certain measures like compression stockings, blood thinners, physical therapy, antibiotics and precautions are undertaken to prevent complications. 

Outcome

A greater number of revisions are being performed today successfully. This has lead to pain free hip joint, promising return to activities the patients enjoy. Although the revision surgeries are complex with a prolonged recovery time, long term outcomes are excellent.