- How is the hip joint structured?
- What are the reasons for hip replacement surgery?
- What happens in cases of hip osteoarthritis?
- What conservative treatment options are available for hip osteoarthritis?
- What is avascular necrosis of the femoral head?
What is the structure of the hip joint?
The hip joint connects the pelvis to the thigh. Due to its anatomical structure, it allows for extensive mobility in the lower extremity and is therefore also referred to as a ball-and-socket joint (a special type of spherical joint). The joint consists of the joint socket (= acetabulum) and the head of the thigh bone (= femoral head) (Fig. 1).
All three bones of the pelvis, the ilium, pubic bone and ischium, are involved in the structure of the hip socket. The socket itself corresponds to a hollow hemisphere. An arched fibrocartilage lip (=labrum) surrounds almost the entire acetabulum beyond the equatorial plane and encloses the adjacent femoral head. This is why it is also called a ball-and-socket joint, which allows for flexion, extension, abduction, adduction and rotation. Strong ligaments surrounding the hip joint and the muscles near the hip joint prevent the joint from dislocating despite the large range of motion. The head and socket are almost completely covered with hyaline cartilage. A strong joint capsule surrounds the entire hip joint.
What are the reasons for hip replacement surgery?
The need for an artificial hip joint can be caused by malformations in childhood, but also by later diseases in adulthood. In terms of the age of onset, hip dysplasia, a form of anatomical malformation of the hip joint, is particularly noteworthy. Flattened hip sockets lead to selective misalignment and thus to premature wear. Spontaneous detachment of the femoral head (= epiphysiolysis capitis) is less common in young people, but can also lead to endoprosthetic treatment later on. In adulthood, degenerative changes in the joint (= osteoarthritis) are the main reason for needing an endoprosthesis and are described in more detail in the next section.
Inflammatory (e.g. rheumatological) or infectious diseases (bacterial infection) as well as accidents (e.g. fractures) can lead to significant destruction of the joint over time. A particular condition worth mentioning is avascular necrosis of the hip, in which the bony parts of the femoral head do not receive sufficient blood supply and die off (= necrosis). The exact causes are not known in detail, but diabetes mellitus (diabetes), alcoholism or systematic cortisone therapy seem to contribute to the occurrence of this disease. A special form of hip necrosis is Perthes disease in childhood, which can also cause destruction of the hip joint.
What happens in hip joint osteoarthritis?
Accident-related injuries to the joint and long-term excessive or incorrect strain can lead to damage to the cartilage surface with progressive joint wear (= osteoarthritis). Doctors refer to osteoarthritis of the hip joint as ‘coxarthrosis’. The human body cannot replace lost cartilage. Misalignments of the axis lead to rapid progression of the disease. This causes inflammation of the synovial membrane, which then produces more joint fluid, resulting in hip joint effusion. Tension in the joint capsule causes increased discomfort and pain, referred to as ‘activated osteoarthritis’. In the final stage of osteoarthritis, complete loss of cartilage can occur, leading to restricted movement and ultimately stiffening of the hip joint. In addition to initial pain during activity, pain at rest also occurs increasingly. Typical for osteoarthritis is the so-called ‘start-up pain’. In the morning after getting up or after sitting for a long time, the first steps are difficult because the joint is ‘rusty’.
What conservative treatment options are available for hip joint osteoarthritis?
Treatment is tailored to the cause and extent of osteoarthritis (stage). In the early stages, physiotherapy, pain medication, shock-absorbing insoles and reduced everyday and occupational stress can help. The cause of the wear process should be clarified at an early stage in order to also consider corrective surgery on the femoral head or hip socket (= femoroacetabular impingement). As osteoarthritis progresses, the only remaining treatment option is medication for pain relief. Physiotherapy can counteract joint stiffness and its effects on the spine or knee joint. If pain increases, prosthesis implantation is indicated.
What is aseptic necrosis of the femoral head?
A local circulatory disorder of the femoral head leads to tissue death (necrosis). Cartilage and bone tissue lose their mechanical function in this area. Movement in the affected hip becomes painful. Treatment is tailored to the stage of the disease and initially consists of intravenous medication or drilling. If the deformity worsens, the only option left is a prosthesis.
With the kind support of Dr Kathi Thiele (Charité Berlin)
The artificial hip joint consists of a socket component that is anchored in the pelvis and a stem that transfers movements to the thigh bone. The artificial femoral head (e.g. metal, ceramic) is attached to the thigh stem and moves in the socket insert (= inlay) of the new socket component (=metal). The inlays are usually made of UHMWPE (ultra-high molecular weight polyethylene) or, increasingly, of highly cross-linked polyethylene (HXLPE) and ceramic. The polyethylene (PE) used in prosthetics is a specially hardened plastic that exhibits low friction and therefore low wear or deformation in interaction with other joint partners.
In cases of large bone defects, either primary or following multiple interventions, both the cup and stem components must be custom-made. Other cup designs, such as rings or cups with screw systems, are available for prosthesis replacement (revision). The stem lengths and anchoring may also vary (Fig. 2).
How long does an artificial hip joint last today?
The lifespan of a hip prosthesis depends, among other things, on the following factors:
- Age at the time of the first operation
- Duration and intensity of strain
- Anatomy of the joint (malalignment)
- Cause of joint wear / metabolic bone diseases
- Quality of the implantation
- Abrasion due to the release of particles from the prosthesis
For this reason, the lifespan of hip prostheses cannot be specified precisely. Data from international patient registries demonstrate the very good long-term performance of hip prostheses. Around three-quarters of hip prostheses today have a lifespan of 15–20 years, and at least half have a lifespan of 25 years (1,2,3).
What do ‘cemented’ and ‘cementless’ mean in hip prosthetics?
In cemented hip replacement, a load-bearing bond between the implant and the bone is created using a biocompatible synthetic resin cement. This allows the hip to bear weight at an early stage following the operation. In a cemented hip, the contact between the bone and the implant is established solely by the shape of the implant (design, surface). By preparing the bone, the surgeon optimises the fit with the prosthesis to ensure its long-term durability. However, the bone still needs to grow into or onto the surface of the prosthesis after the operation, which is why the treating doctor often recommends partial weight-bearing on the leg for several weeks. The decision as to which type is best suited to you as a patient depends on many factors (age, fitness, bone quality, anatomy, etc.) and is decided on an individual basis by the treating doctor in consultation with you.
How is hip replacement surgery performed?
The native hip joint is usually accessed via an anterior, lateral or posterior skin incision. The aim here is to minimise soft tissue trauma as much as possible. Once the joint has been opened, the worn femoral head and part of the femoral neck are removed. Subsequently, both the acetabulum and the femur are shaped using special instruments to achieve the required form, ensuring a precise fit with the implants. Depending on the implant used, the prosthesis may be cemented or cementless. After implantation of the metal components (stem, cup), including the so-called inlay, the inserted joint is reduced and checked for dislocation resistance (= the joint must not dislocate when moved). Finally, the wound is closed in layers whilst visualising the extensor mechanism. Once the operation is complete, an X-ray is taken to confirm the precise positioning of the prosthesis.
Text: With the kind support of Dr Kathi Thiele (Charité Berlin)
The decision for an artificial joint is not easy to make and, despite all the developments in this field, it does lead to some changes in your life. The following questions and answers may help to make the decision-making process easier.
- Am I ready for a hip replacement?
- I am overweight. Should I lose weight before a hip replacement?
- Does smoking affect the outcome of the hip replacement operation?
- I have a metal allergy. What should I bear in mind regarding the hip replacement?
- Which type of anaesthesia is suitable for me?
- When is a blood transfusion necessary?
- How high is the risk of contracting hepatitis or even HIV from a hip replacement?
- What should a diabetic bear in mind regarding hip surgery?
- How does osteoporosis affect the lifespan of the artificial hip joint?
Am I ready for a hip replacement?
Please answer the following questions for yourself. If you answer ‘yes’ to most of them, you would benefit from having an artificial hip joint fitted.
- Does your hip pain significantly limit your daily activities?
- Does your hip pain not improve significantly even after taking painkillers?
- Do you experience hip pain not only during the day but also at night?
- Do you suffer from the side effects of taking painkillers regularly, such as nausea, stomach ache or loss of appetite?
- Are alternative conservative treatment methods no longer yielding any significant results at this stage?
If you answer ‘yes’ to any of the following questions or if you have any of the following conditions, you should consider having surgery:
- Osteoarthritis of the hip
- Rheumatic inflammation of the hip joint
- Avascular necrosis of the femoral head
The decision as to whether surgery is necessary and which type of prosthesis is best suited to you as a patient depends on many factors and will be decided on an individual basis by your treating doctor in consultation with you.
I am overweight. Should I lose weight before having a hip replacement?
Weight loss is not strictly necessary, but it is highly beneficial for your general physical condition and the longevity of the prosthesis. Being extremely overweight increases the risk of poor wound healing or thrombosis. Furthermore, high body weight places increased mechanical stress on the prosthesis. This can have a negative impact on the implant’s lifespan.
The extent of your personal excess weight can be calculated, for example, using the Body Mass Index (BMI) according to the following formula: body weight (kg) divided by height (in metres) squared. Values of approximately 18.5–25 kg/m² correspond to a normal weight. Values between approx. 25 and 30 kg/m² are classified as overweight. Values above this range are classified as obesity (severe overweight). In such cases, dietary advice and weight loss are recommended.
BMI = Body weight (kg) : Height x Height (m)
Does smoking affect the outcome of prosthetic surgery?
Smoking has a negative effect on blood circulation and significantly impairs wound healing. This can lead to dangerous wound infections. To achieve the best possible surgical outcome, it would be beneficial to stop smoking.
I have a metal allergy. What should I bear in mind regarding implant placement?
During the preliminary consultation, you should list any allergies you are aware of. Metal allergies to chromium or nickel, for example, can cause redness or itching on contact with the skin. This can be caused by items such as costume jewellery or metal buttons. The surgeon has access to special prostheses to minimise the risk of metal intolerance. Accordingly, a suitable type of prosthesis can be selected for you; however, knowledge of the specific metal intolerance and allergic predisposition is a prerequisite for this. It must be noted, however, that the significance of metal allergies in the implantation of artificial joints has not yet been conclusively clarified.
Which type of anaesthesia is suitable for me?
Generally, the operation is performed under general anaesthesia (anaesthetic injection and anaesthetic gas via a breathing tube) or under regional anaesthesia (anaesthetic injection into the spinal cord; the patient remains awake). The most suitable form of anaesthesia for you will be determined in a consultation with the anaesthetist. Both types of anaesthesia have proven effective in prosthetic surgery.
When is a blood transfusion necessary?
A blood transfusion is administered in cases of a shortage of red blood cells (erythrocytes). These cells transport oxygen (O₂), which is vital for the cells. If the number of red blood cells drops (anaemia), the cells are at risk of dying due to a lack of oxygen. This can lead to impaired organ function. The heart, brain, kidneys and liver are particularly affected. The body’s tolerance in a deficiency situation depends, among other things, on pre-existing underlying conditions and age. Overall, the need for a blood transfusion is significantly reduced during the initial implantation of an artificial joint. In exceptional cases, however, a blood transfusion may be necessary.
How high is the risk of contracting hepatitis or even HIV through a prosthetic implant?
The prosthetic implant itself cannot cause hepatitis (liver inflammation caused by hepatitis viruses) or HIV infection. A possible route of transmission is contact with donor blood, such as during a blood transfusion or the injection of clotting factors. The processing of blood products is subject to a very strict procedure, whereby donors and blood products are carefully screened for viruses. Nevertheless, a minimal residual risk remains.
What should a diabetic bear in mind when undergoing hip surgery?
Surgery disrupts your daily routine and puts stress on the body, which is accompanied by changes in your metabolism. Both of these factors usually lead to a slight, temporary fluctuation in blood sugar levels. You should therefore adjust your insulin dose in consultation with your doctor to suit your changed circumstances. If you are taking blood sugar-lowering tablets, discuss with your doctor before the operation whether and to what extent a temporary rise in blood sugar levels will be tolerated by your body. You may also need to temporarily stop taking some diabetes medication before the operation.
Before making any changes to your medication, discuss this with your doctor!
How does osteoporosis affect the lifespan of an artificial hip joint?
Osteoporosis involves a reduction in calcium salts in the bone tissue, which leads to reduced stability. This increases the risk of fracture regardless of whether surgery has taken place. Using the appropriate surgical technique, the prosthesis can be firmly anchored even in osteoporotic bone. There is currently no evidence to suggest that the prosthesis loosens more quickly. Nevertheless, you should avoid falls or sports that put strain on the joints, as these can lead to fractures of the surrounding bone.
Text: With the kind support of Dr Kathi Thiele (Charité Berlin)
- What is a hip prosthesis infection?
- What is ‘aseptic’ hip prosthesis loosening?
- Is there a risk of a leg length discrepancy following the implantation of an artificial hip joint?
- What does the term ‘heterotopic ossification’ mean?
- When does a hip prosthesis need to be replaced?
- What is bursitis in the area of the operated hip prosthesis?
- What does the term ‘Girdlestone hip’ mean?
What is a hip prosthesis infection?
A hip prosthesis infection is a bacterial infection. A distinction is made between an early infection (within three weeks of the operation) and what is known as a late infection. The latter can occur years later and often develops gradually. An infection is suspected if there is pain, swelling, redness of the skin, or prolonged discharge from fresh wounds. Treatment may involve flushing the surgical wound, administering antibiotics, or, in persistent cases, removing or replacing the hip prosthesis.
You should therefore inform your doctor, both before the operation and whilst the prosthesis is in place, of any inflammation in the dental or ear, nose and throat areas, or of infections of the gastrointestinal tract. Similarly, injuries to fingernails and toenails can act as small entry points for germs and must therefore be treated appropriately before the procedure and whilst the prosthesis is in place. Any loosening of hip implants within the first three years is always indicative of a possible infection.
What is ‘aseptic hip prosthesis loosening’?
Despite correct surgery, prostheses may become loose in individual cases. The term ‘aseptic’ means that no bacteria are involved in the loosening process of the implanted prosthesis. In the case of a cemented prosthesis, the cement mantle around the prosthesis is usually broken, so that the metal no longer has a firm hold on the bone. In cementless prostheses, there is no longer sufficient contact between the bone trabeculae and the metal. The prosthesis vibrates with every movement instead of lying firmly on the bone tissue. A common reason for aseptic prosthesis loosening is increased abrasion, which can occur under increased stress. The abrasion particles trigger an inflammatory cascade, which in turn causes the prosthesis to loosen.
Is there a risk of a leg length discrepancy following the implantation of an artificial hip joint?
Modern, improved planning methods, in conjunction with pre-operative X-rays, allow for precise planning of the implant to be used. However, the previously determined leg length may need to be adjusted to ensure optimal muscle tension or a precise fit between the patient’s individual anatomy and the prefabricated implants. Differences of more than 1 cm are generally only to be expected if there is also a pathology on the opposite side of the hip and the correction is not carried out immediately.
What does the term ‘heterotopic ossification’ mean?
Heterotopic ossification describes the formation of bone tissue in areas where muscles and tendons normally run. In extreme cases, once bone formation is complete, these should be surgically removed as they can cause severe restriction of movement. As a preventive measure against ossification, short-term use of medication or a single course of radiation therapy prior to any necessary surgery has proven effective.
When does a hip prosthesis need to be replaced?
Painful, loose prostheses infected with bacteria should generally be replaced. Another reason may be persistent thigh pain following the insertion of a cementless hip prosthesis.
What is bursitis in the area of the operated hip prosthesis?
At hip level, there is a bursa between the thigh bone and the thigh tendons. Irritation (=inflammation) can cause pain. Discuss possible treatment options with your treating doctor.
What does the term “Girdlestone hip” mean?
The term “Girdlestone hip” describes the condition following the removal of a hip prosthesis. Nowadays, it is generally regarded as a temporary solution as part of a two-stage treatment for infection. However, in patients with very poor general health or a severe bone defect, the Girdlestone arrangement may also be considered a permanent solution. Thigh muscle strength is reduced in the operated leg with a “Girdlestone hip”. Walking sticks compensate for this.
Text: With the kind support of Dr Kathi Thiele (Charité Berlin)
- How will I manage getting about in my local area after hip replacement surgery?
- How can I protect myself from deep vein thrombosis after hip replacement surgery?
- How can I protect myself from implant dislocation shortly after hip replacement surgery?
- What does thigh pain mean after hip replacement surgery?
- How long will I be in hospital?
What is an implant passport?
How do I get back to normal in my daily life after hip replacement surgery?
Following hip replacement surgery, physiotherapy will help you get out of bed unaided, walk with crutches and climb stairs. The physiotherapist will also show you which movements you must avoid at all costs to prevent dislocation.
A special hospital bed is rarely necessary. It is helpful if, during the first few weeks, you can place a chair in the shower or a seat board over the edge of the bath.
How can I protect myself from deep vein thrombosis after hip replacement surgery?
Thrombosis is a vascular condition in which a blood clot forms in a blood vessel. Firstly, it is advisable to discuss your personal risk of developing thrombosis with your GP or surgeon before hip replacement surgery: Have you ever been diagnosed with thrombosis before? Do you have any risk factors that increase the likelihood of thrombosis? Are you taking any medication that affects blood clotting? After the operation, compression stockings, leg muscle exercises and special vein cuffs, amongst other things, help to keep the risk as low as possible. If you are unable to bear full weight, blood-thinning (anticoagulant) therapy must be continued after the operation (postoperatively) in the form of injections or tablets, in accordance with the instructions of the treating doctor.
Make sure you drink enough fluids, unless your doctor advises otherwise due to a heart or kidney condition. Some hospitals have a specialist outpatient clinic to advise on how to manage conditions affecting the coagulation system.
How can I protect myself from implant dislocation shortly after hip replacement surgery?
Sitting down low (on a chair or toilet), putting on shoes whilst squatting, turning over in bed onto the side that hasn’t been operated on, and crossing your legs are risky for the position of the newly fitted hip prosthesis. You should avoid these actions at all costs during the first 6 weeks after the operation. There are aids, such as shoe horns, seat cushions and toilet seat raisers, which can help protect you from this problem. In the first few days after the operation, physiotherapy will teach you the correct way to get out of bed, as well as the precautions to take when sitting down.
What does thigh pain mean following hip replacement surgery?
With cementless femoral stems, load-dependent pain may occur, which does not necessarily indicate a problem or complication with the prosthesis. Other conditions, such as knee osteoarthritis, back problems, a fracture or even a vascular disorder, can also cause discomfort in the thigh. However, if the prosthesis has not caused any symptoms to date and the thigh pain is a new symptom, it is essential to investigate whether the prosthesis has become loose.
How long is the hospital stay?
The length of your hospital stay depends on the type of operation, any underlying medical conditions and how you recover. It currently averages between seven and ten days, but may well be shorter or longer. A longer stay is to be expected, particularly in the case of replacement surgery.
What is an implant identification card?
An identification card is issued for every operation in which a patient receives an artificial implant. The so-called implant passport (Fig. 3) contains personal details as well as information on the date of the operation, the affected limb and the implant used. You can use this to identify yourself, for example, when passing through metal detectors at the airport. You must bring this card with you to every medical appointment, as it provides the doctor with important information.
Text: With the kind support of Dr Kathi Thiele (Charité Berlin)
- Will I be able to return to work after hip replacement surgery?
- Will I still be able to play sport with a hip replacement?
- Will my sex life be affected after a hip replacement?
- Will I be completely pain-free after a hip replacement?
- Can I help to extend the lifespan of my artificial hip?
Will I be able to return to work after hip replacement surgery?
Generally speaking, the aim of hip replacement surgery is to improve your quality of life and thus enable you to resume your daily activities after the operation.
In the first twelve weeks following the operation, you should avoid impact loads, squatting or kneeling, compressive loads, lifting and carrying heavy loads, strenuous exertion and heavy physical work. Instead, continue with the physiotherapy exercise programme you learnt after being discharged from hospital. After this, you should be able to return to work for sedentary and light physical activities. An assessment of the level of activity permitted following implantation cannot usually be made until at least 6 weeks post-operatively.
You should no longer carry out work on uneven ground, physically demanding activities (e.g. road construction), or regular standing and walking on ladders, scaffolding or roofs. You should also avoid regular work involving bending, kneeling or working in low-ceilinged rooms. Driving cars and lorries is generally possible, but whether the joints and muscles can cope with a full working day of eight hours or more without pain must be decided on a case-by-case basis.
Can I still take part in sport with a hip replacement?
The scientific evidence regarding the ability to participate in sport following hip replacement surgery is not yet fully established. The key factors are your fitness level and experience in your chosen sport prior to the operation. Sports themselves are categorised as either ‘low-impact’ or ‘high-impact’.
The greater the impact on the artificial joint, the higher the risk of loosening or fracture. Moderate sports involving low impact are particularly beneficial. These include, for example, walking, cycling and swimming. So-called explosive and contact sports (squash, tennis, ball sports) can lead to significantly higher mechanical stress on the artificial joint due to sudden acceleration and braking manoeuvres. This can result in a faster wear-and-tear process, which is why they are generally not recommended. Jogging, skiing, combat sports and most competitive sports can also shorten the lifespan of the implant if practised beyond the level of amateur sport.
These sports are therefore also viewed very critically. However, your treating doctors will advise you individually on the specific options available. Please generally avoid sports that carry an increased risk of falling. Overall, with the development of new prosthesis designs and bearing surfaces, it has become more feasible to participate in sports involving higher peak loads.
Is sexual activity restricted after a hip replacement?
Once the wound has healed, intimate contact is possible. Avoid hip movements that could cause dislocation or pain, such as severe bending or twisting.
Will I be completely pain-free after a hip replacement?
Areas of the hip joint worn down by osteoarthritis are replaced with an artificial implant, leading to a significant reduction in symptoms. The extent of the areas to be replaced depends on the degree of damage present. However, the implants alter the natural anatomy and mechanics of the joint. For this reason, a complete reduction in symptoms cannot be guaranteed in every case.
Can I help extend the lifespan of my artificial hip?
The prosthesis is subject to natural wear and tear, which may lead to the implant needing to be replaced over the years. Your personal lifestyle can have a significant impact on the implant’s lifespan. Avoid falls! Lifestyle and dietary habits influence bone metabolism and the mechanical stress on the prosthesis. Avoid sports with an increased risk of falling and excessive strain on the joints. Discuss your personal risk with your doctor.
Texts: With the kind support of Dr Kathi Thiele (Charité Berlin)
If conservative treatment approaches fail, surgical intervention should be considered. Here are a few comments on this.