When the ball of the femoral component is dislocated from the acetabular cup.
This occurs when the ball of the femoral component is dislocated from the acetabular cup, when the hip is put into an extreme or unusual position. This usually occurs when the hip is flexed and the operated leg is rotated. In this situation the muscles around the hip joint are relaxed and dislocation can occur if leverage is applied to the joint. This occurs in approximately 0 – 5% of primary hip replacements but is more common in revision hip surgery.
It is more likely to occur in the early post operative period but late dislocations may occur due to stretching of the capsule and weakening of the muscles surrounding the hip joint. This complication is more often than not multifactorial.
Dislocation is also more common following radiation therapy and avascular necrosis. It can also occur after a sudden injudicious movement.
When dislocation occurs the patient is aware of sudden pain within the hip joint and an inability to put weight on the affected lower limb.
The hip needs to be relocated with full muscle relaxation and more often than not requires a general anaesthetic. A further operation is rarely required to open the joint and reduce the hip back into position.
The hip joint that dislocates repeatedly may require revision of one or more of the components. Often a ‘capture’ liner (a constrained liner) is used to stabilise the hip joint following recurrent dislocation.
Surgeons who perform a large number of hip replacements, complex surgery and regular revision surgery, have fewer dislocations than surgeons who perform a small number of operations.
The dislocation rate in the Medicare Study (USA) showed that the dislocation rate for orthopaedic surgeons who perform a high number of operations was 1.5% compared with a dislocation rate of 4.2% for surgeons who perform fewer operations.
Dislocation may often be preventable by post-operative care, physiotherapy and patient education.
A bacterial invasion of the hip joint.
This is the most devastating complication but it is very uncommon (1–2% of patients). If infection cannot be eradicated by antibiotics, removal of the components may be required. Infection can occur at any time but often appears some time after the hip surgery. The incidence of infection is increased in patients with rheumatoid arthritis, an existing infection, obesity, diabetes, alcoholism and those who are taking immunosuppressive drugs and steroids.
Infection presents with pain and discomfort localized to the affected hip. The most common organisms include Staphylococcus aureus, Staphylococcus epidermidis (a common skin commensal), Streptococcus, Escherichia coli and Pseudomonas aeruginosa.
Infection of the hip prosthesis may require removal of the prosthesis and antibiotic treatment.
The recurrence of infection following revision hip surgery is common and still occurs in 5-10% of cases. The treatment of the infected hip joint may be done in one operation (primary exchange) or it may be done in two stages.
Thromboembolism: Deep Vein Thrombosis - DVT
Blood clots and migration of the clot to the lungs.
As with any major surgery, a blood clot can form in the veins of the legs. Deep vein thrombosis (DVT), or blood clots are usually harmless but in approximately 3% of patients they can cause problems. They can occur any time in the first weeks after operation.
Patients experience problems such as pain and swelling in the affected leg. This does not affect the hip replacement and does not lead to revision surgery, but they may involve a prolonged hospital stay and prolonged post operative care until the condition is adequately controlled.
Pulmonary Embolism - PE
Pulmonary Embolism (PE) occurs when the blood clot(s) in the leg veins break apart and travel to the lung. Usually the clot is dissolved and dissipated in the lung but sometimes they get lodged in the capillaries of the lung.
The latter can cause shortness of breath or chest pain (about 2%) and very rarely, if the clot is very large, death. When a pulmonary embolism is suspected, a lung scan is performed. If an embolism is confirmed, treatment is similar for a major DVT.
The surgeon will take into account the known risk factors of individual patients and provide prophylactic treatment as necessary.
Attempts are made to reduce the chances of thrombosis or embolism. Broadly speaking there are two forms of prophylaxis.
Prevention of blood clots and their sequelae:
1. Improving blood flow in the legs - this reduces the stagnation of blood, which is what allows clots to form.
- Spinal or epidural anaesthetic - This is left to the discretion of the anaesthetist.
- Compression stockings - These are worn for up to six weeks after the operation.
- Early mobilisation - Physiotherapists, nurses and doctors will insist that the legs are used as soon as possible after the operation.
- Foot pumps - A slipper on the foot squeezes every twenty seconds, thus flushing the blood out of the feet and up the leg.
- Calf compression - A cup around the calf intermittently squeezes the calf, thus emptying the calf of blood and forcing it further up the leg into the general circulation.
2. Anti–coagulant medication - this reduces the clotting ability of the blood. Although anti–coagulant drugs reduce the chance of clot formation they carry a slight increased risk of causing bleeding from the wound.
- Aspirin - Aspirin only has a weak effect in reducing blood clots following a THR.
- Low molecular weight Heparin - An injection is given once a day under the skin until discharge from hospital. No blood tests are required.
- Warfarin - Tablets which are given to thin the blood and may be required for three months or more. Regular blood tests are necessary to ensure that the dose is correct.
- Fondaparinux - A synthetic inhibitor of Factor Xa. This drug is highly selective for its target and is efficacious in reducing blood clots.
There are advantages and disadvantages for each of these methods. The surgeon will consider these when advising which combination should be used for any particular/individual patient.
It should be noted that the National Institute of Clinical Excellence' view on thromboprophlaxis is that patients undergoing orthopaedic surgery should be offered low molecular weight heparin (LMWH).
Leg length discrepancy
The goals of total hip replacement (THR) are to relieve pain and correct the functional deficit. In doing so, the surgeon sometimes needs to correct leg length discrepancies which may be present prior to the surgery. However, the surgeon also needs to avoid creating a leg length discrepancy as a result of the surgery.
Limb length discrepancies of up to 2cms are relatively common in the general population and the majority are asymptomatic.
At consultation the importance of placing the hip in the correct anatomical position and then adjusting for leg length discrepancy is emphasised to the patient. However the patient should be aware that there is a risk of the operated leg either being shortened or lengthened.
It is necessary to template the hip prosthesis with the aid of the pelvic radiographs before proceeding to operation.
Heinz Wagner stated that 'the operating theatre is for doing what you have planned, not for planning what you must do'. At the operation the leg lengths are assessed on the operating table and intra-operatively and may be checked by referencing from a fixed point from the patient’s pelvis.
It is always difficult for the surgeon to accurately equalise leg lengths. Within the limits of surgical tolerance, more experienced and specialist hip surgeons, have less leg length discrepancies compared to trainee surgeons performing THR.
If leg lengthening occurs following the THR the patient may require a heel raise for the opposite leg.
If a significant leg length discrepancy of greater than 2cms occurs this may be a reason for continued and unexplained pain following a THR. If there is a significant marked increase in leg length discrepancy then the patient may require revision of the THR. Significant leg length discrepancy may be associated with nerve palsies.
It should be noted that despite pre–operative templating of radiographs and intra-operative planning, leg length discrepancy can often not be avoided without putting the hip replacement at further risk of dislocation.
The surgeon will always endeavour to keep leg length discrepancy to a minimum.
Fracture of the femur
A crack or split/break of the thigh bone.
Fracture of the femur including the greater trochanter can occur during insertion of the prosthesis. This problem is usually treated with fixation, cables and/or wires. Intra operative fractures range between 0.1-1.0% in cemented THR and is increased when using a cementless prosthesis between 3-29%.
Penetration or incision of an artery or vein.
These can occur from screws which are inserted to hold the acetabular cup in place. Penetration of the femoral bone by the prosthesis can occur with difficult revision hip surgery, particularly in patients with bone stock loss and osteoporosis.
Injury of a nerve can be caused by stretching, cautery or by an incision.
The sciatic, femoral and obturator nerves may be injured during hip replacement surgery. Although every effort is made to avoid these problems, the nerves may be cut, cauterized or stretched. The nerve may be stretched as it crosses the knee during the operation. When the nerves have been stretched, weakness of the foot may be noticed post operatively. Usually a spontaneous recovery occurs, but this can take several months. A foot support or splint may be utilised during the period of weakness. Sciatic nerve injuries tend to be more common than femoral or obturator nerve injuries.
Numbness (sometimes permanent or temporary) may occur due to damage to superficial nerves when incising the skin and subcutaneous tissue.
Non union of the greater trochanter
The greater trochanter (upper end of the thigh bone) fails to unite following an osteomy.
Sometimes during the surgery the greater trochanter is removed to improve surgical exposure or it may be removed when using the direct lateral approach to the hip. This may lead to an increased incidence of non union of the greater trochanter, which occurs when the greater trochanter does not reunite with the remainder of the femur (up to 17%).
New bone formation where bone is not normally present.
New bone formation occurs in tissues where bone is not normally present, such as in the muscles adjacent to the surgical site. There is an increased incidence in males and those who have secondary osteoarthritis following a traumatic event. Treatment includes low dose radiotherapy or use of non steroidal anti-inflammatory tablets. Occasionally, the new bone that has formed needs to be excised. If he new bone formation is extensive, this may cause problems for the patient.
A crack or fracture of the femoral stem.
Breakage of the stem is rare, but when it does occur it is usually in the region of the highest tensile stress. A small crack occurs within the metal stem which may propagate, ultimately causing the stem to break (a fatigue fracture). This problem was more common in older implants with fractures occurring in the neck region of the metal stem.
Loosening of the hip joint prostheses.
The most common long term complication is loosening of the components. This may in part be caused by a biological reaction to microscopic particulate debris released from bone cement, polyethylene (plastic) and metal. The particles stimulate cellular activity by activating macrophage cells.
A membrane develops, interposed between the bone and cement layers, which may initiate resorption of bone (osteolysis), which in turn may result in loosening of the components. In most patients there is an inert response to the components. The loosening can also result from mechanical factors, such as implant design or an inadequate cement mantle.
Loosening tends to be more frequent in younger and more active patients and in those who have undergone previous hip surgery. A diagnosis of loosening is based on the patient's symptoms, radiographic changes and other tests, such as bone scans or an arthrogram.
There have been great advances in extending the life of artificial joints. However most joints eventually loosen and will require replacement, but in many cases a primary hip replacement can last in the region of 15 years. In some cases the hip may loosen earlier. Younger patients must be aware that the primary hip replacement will fail within their life-time and that they will require revision hip surgery at some point in time.
The erosion of the surface of two materials in contact with one another.
Wear and debris formation is a continuous and relentless process that occurs with all hip replacements. Wear of the bearing surfaces is accelerated in people with a high activity profile and with inferior materials or designs. If the implant bearing surface, such as the inner plastic liner in the cup wears out, this may require exchange of the specific part or a total revision of the implant.
A bowel problem related to antibiotic treatment.
Following the prophylactic use of Cephalosporin antibiotics, a standard practice for total hip replacements, Clostridium difficile bacteria may overgrow in the bowel. They produce a toxin which damages the bowel lining, resulting in diarrhoea. Onset of symptoms usually occurs after the pre-operative and post-operative dose of antibiotic treatment. Most patient’s symptoms resolve due to the fact that drug treatment has been discontinued, but others may require specific antibiotic therapy to treat the bacteria causing the colitis. Only rarely is the colitis severe and protracted and bowel perforation may occur. Patients with metabolic imbalance and bowel problems can become severely ill and die.
Rarely, complications may result from a general and/or spinal or epidural anaesthetic.
A rare complication following hip surgery. This may occur in more elderly patients with co-morbid medical problems. The literature shows the overall incidence of death to be around 0.3%.