Medical condition Hip prosthesis – the artificial hip joint
It is only when a joint no longer works properly that we realise just how important it is for our day-to-day mobility. Climbing stairs, kneeling down, playing sport and even just normal walking without limitations is only possible with a healthy joint.
The hip joint is made up of the hip socket (acetabulum) and the femoral head (caput femoris). These are covered by a protective layer of cartilage which absorbs the friction between these two surfaces and lubricates the joint at the same time. The rim of the hip socket is surrounded by the labrum, a ring of fibrous cartilage which seals the joint. Finally, the entire hip joint is surrounded by a tight capsule and a powerful layer of muscle. As a ball-and-socket joint, the hip joint enables movement in different directions. It also has to distribute the weight of the body to the legs and ensure the stability of the upper body. The hip joint can be affected by a variety of problems and limitations.
The most common condition affecting the hip joint is osteoarthritis, when the layer of cartilage protecting the femoral head and the hip socket is gradually worn away as a result of constant friction during movement. The joint loses its fit, the bone forms deposits (osteophytes) around the edges and wear particles develop which cause inflammation and pain. The onset of hip osteoarthritis can be as early as between the ages of 30 and 40, but is usually seen between the ages of 50 and 60.
Initially, osteoarthritis can be treated conservatively, but use of an artificial hip joint must be considered, depending on the patient’s suffering (level of pain) and limitation of mobility. There have been major advances in artificial joints in recent years. Today, the operation is considered a routine procedure.
The symptoms of hip osteoarthritis vary according to the extent of wear involved. At first, the hip may only hurt a little, but in the advanced stages, every movement can be agony. Walking downhill and stop and go movements put particular strain on the worn joint and result in instant pain. Pain after waking up in the morning is also common. Later on, osteoarthritis can also cause pain when sitting and lying down (pain at rest) and, in the worst case, can lead to the collapse of the femoral head and the inability to move.
While it was previously believed that osteoarthritis was wear of the joint cartilage purely as a function of age, it is now known that an awkward shape of the femoral head and hip socket can be an important contributing factor in osteoarthritis. Significant strain caused by certain types of sports can also increase the risk of developing osteoarthritis. A hereditary predisposition is also no longer ruled out.
If the osteoarthritis isn’t yet severe or if it causes few limitations, it is treated conservatively. Painkillers and anti-inflammatory drugs are often used. In the early to medium stages, hyaluronic acid injections or PRP therapy are also used. Cortisone injections into the affected joint are also possible for activated osteoarthritis. Physiotherapy is mainly helpful when muscles have tensed up due to pain or when there are muscular deficiencies. Alongside this, the application of heat or cold, possible adjustments to footwear (insoles) and walking sticks also provide relief.
Depending on the severity of the condition, shoes with well-sprung soles can help, as can regular exercise which is gentle on the joint and lubricates it, such as cycling, aquafit or walking, preferably on soft terrain.
Surgical treatment/hip joint replacement
When suffering is severe and quality of life badly impaired, use of an artificial hip joint (prosthesis) must be considered. It is always the patient who decides what constitutes suffering and the severity of this. Total hip replacement with a prosthesis is one of the most successful operations and is considered a routine procedure nowadays. The unhealthy femoral head and part of the femoral neck are surgically removed and the hip socket is smoothed. The stem of the prosthesis is then inserted into the femur and an artificial socket is fixed into the pelvis. The prosthetic components can be fixed with a special cement or inserted without cement. Hip operations are either carried out under general anaesthetic or with a spinal anaesthetic. The operation takes around 1.5 hours and full loading of the operated hip is possible again immediately after the operation.
Hip prosthesis materials
Classic prostheses (known as stem prostheses) are made from various metal alloys (titanium, cobalt-chromium). The head (the ball) of the prosthesis itself is made from ceramic or metal and is placed onto the cone of the stem. Different stem lengths enable an exact reconstruction of the leg length and the rest of the anatomy. The socket is also made from a metal alloy (in most cases titanium) and is fitted with a ceramic or plastic insert (polyethylene). These materials are perfectly compatible with the body – allergies to titanium, ceramic or polyethylene are largely unknown.
Nowadays, cement-free implants made from titanium alloys are used when the bone quality is good. These fix securely into the bone (primary stability). In addition, the bone grows onto the porous titanium surface within a short period of time, helping to fix the implant in place (secondary stability). When the bone is weaker (e.g. osteoporosis), a cemented prosthesis is used instead.
Follow-up treatment and rehabilitation
The first steps are taken on the day of the operation itself, using two walking sticks and under the guidance of a physiotherapist. After four to five days, the patient can leave the clinic. Due to the minimally invasive (gentle) surgical techniques which are now increasingly being used, walking sticks are only needed for security and to relieve pain. Depending on the surgical technique used, however, certain precautions and lifestyle rules should be followed in the first few weeks. 14 days after the operation, the skin sutures are removed by the GP. Absorbable skin sutures are also sometimes used, however, and these do not need to be removed. After the inpatient stay, one or two courses of physiotherapy are recommended. When the first check-up has been carried out by the surgeon (usually after six weeks), joint mobility and loading can be progressively increased. The period of inability to work ranges between three and twelve weeks depending on the physical demands of the patient’s work. The greatest progress is made in the first three months. The end result is usually achieved after a year.
Dental work after a hip operation
In the first year after the hip operation, we recommend that you don’t have any dental work done to avoid any risk of infection. Good and regular dental hygiene is fundamentally important and antibiotic prophylaxis before visiting the dentist is only necessary in rare cases.
Life span of a hip prosthesis
With the materials currently used, a hip prosthesis will last for around 15 to 25 years. With advancing technology and new materials, we can expect an even longer lifespan in the future. Lifespan also depends heavily, however, on the amount of strain and on other factors such as bone quality etc. Stop and go sports can have a negative impact on the prosthesis and should be avoided.
Reasons for changing the prosthesis
Even an artificial joint produces friction and will wear over time, potentially causing inflammation. The bone then recedes from the prosthesis and the prosthesis becomes loose, affecting either the socket, the stem or both. The most common reasons for changing a hip prosthesis (revision) are wear and loosening, osteoporosis, repeated dislocation (luxation), bone fractures and infections.
Complications and risks
As with any operation, hip operations also entail risks. These are rare overall, however, and can be kept to a minimum thanks to constantly improving techniques, advanced materials and specialised doctors. As well as the general risks of surgery, there are also specific risks associated with hip joint replacement. One possible complication of an artificial joint is dislocation (luxation), where the femoral head springs out of the hip socket. Dislocation is painful and an anaesthetic is often required to put the joint back into place. Another complication is possible infection. If an infection cannot be controlled, the joint has to be removed and a new one inserted once the infection has cleared up (two-stage revision process).