What is Hip Pain
Hip pain affects millions of people worldwide. Pain can be experienced while walking. It also occurs during normal movements of the legs or pelvis, and can be so severe that normal activity becomes nearly impossible. Hip pain can be associated with bone, muscle, tendon, ligament, or cartilage damage.
Hip pain is particularly associated with age-related joint damage. It is estimated that one in four people will suffer from hip injuries, or degeneration, by the age of 85. This is due to a number of factors, such as bone abnormalities and loss, deteriorations in joint movement, and weakness of the muscles and other tissues around the joint that increase with age. These factors result in chronic pain, often accompanied by a decrease in the ability to move and function normally. The damaged or failing joint must often be operated on to remove it and replace it with a synthetic prosthesis. Alternatively, the joint can be repaired by augmenting the bone with synthetic material until it conforms to a normal shape and function again. Post-operative hip pain is also a component of noxious stimuli in these patients.
Hip pain is not exclusively reserved for the elderly, however. A range of structural abnormalities, disorders, disease states, and occupational injuries can cause pain in the hip region to younger adults and children. Some conditions in childhood or infancy can cause both chronic (i.e. constant and long-lasting) or acute (sudden and often temporary) hip pain. A large proportion of complaints of hip pain in adolescents and young adults come from athletes. Though healthy and active, athletic individuals, particularly competitive sports players and runners, incur a high risk of hip damage through overuse of the joint, tears and strains in the muscles, ligaments, and tendons surrounding it, and accidents. In the worst cases, fractures and dislocations of the joint can occur. The sufferers may have to undergo intensive rehabilitation or surgery to repair the damage.
Accidents resulting in more minor hip fractures are also relatively common in children, in the course of normal play and activity. They must also undergo surgery to repair this, which may be particularly traumatic to a young child. Hip pain in children can also be the result of transient, chronic, or genetic diseases. For example, Down’s syndrome and cerebral palsy are associated with weakness in the hip joint and with chronic hip pain. Hip abnormalities can often occur in infants. In these cases, pain is not usually experienced further on in life, if they are adequately addressed with corrective procedures as soon as possible. Another common source of hip pain in children and younger adults is a tear in the labrum, a structure surrounding and supporting the hip joint. This can lead to a medium- to long-term source of pain, as labral tears are often misdiagnosed as other conditions such as groin strain or bone damage.
Causes of Hip Pain
The hip joint is a critically important structure of the human anatomy. Without it, it would be impossible to walk, stand upright, sit, bear the load of the spine or trunk, or perform complex maneuvers such as jumps, twists, or bends. The hip is a type of joint known as a ball-and-socket, a term based on its appearance. In the case of the hip joint, the “ball” is the top of the femur (thigh bone), commonly known as the femoral head. The “socket” is the acetabulum of the pelvis, which forms a shallow bowl in which the femoral head fits. Both the femoral head and acetabulum are covered with a protective layer of cartilage, called the hyaline or articular cartilage. A viscous material called synovial fluid is located between the surfaces of the joint, to form a buffer and to further facilitate movement. Without these, the two bony components of the hip joint would wear each other away, resulting in chronic pain and a loss of normal motion.
Ligaments attach the femur to the pelvis, both above and below the joint. The hip joint, in normal ideal circumstances, has an impressively wide range of motion and resilience. Motion is mainly limited by the pelvic angles, which are defined by the structure of the pelvis, and by the labrum, which encases and protects the joint. Pain occurs when the bones, cartilage, labrum, or other tissues making up the hip region are damaged.
Hip Pain in the Elderly
The femoral head is connected to the main shaft of the femur by a relatively (especially to the head and shaft) thin piece of bone called the femoral neck. This is vulnerable to damage, and is often the part of the bone that fractures in old age. Fractures are mainly the result of osteoporosis (brittle bones caused by a progressive lack of density), commonly associated with old age. A factor that interacts with osteoporosis to worsen the risk of hip fractures is the increased probability of falls in the elderly. This is naturally a source of chronic pain and functional deterioration in this population. Another main source of bone-related damage is the wearing away of the femoral head where it meets the acetabulum. This is caused by osteoporosis in that part of the bone. It can cause loss of motion and pain in the joint.
Another common age-related disease that is responsible for hip pain is osteoarthhritis. This autoimmune disease attacks the joint, particularly the synovial fluid between the bones, and causes the release of inflammatory molecules into the joint and surrounding tissues. Inflammation is widely acknowledged as a source of pain. Though osteoarthritis may not cause bone damage, it is a leading basis for hip replacement, in order to prevent or reduce the chronic pain associated with this condition.
Hip Pain in Children
In children, breaks and other damage in the hip joint can occur through accidental injury or disease. Slipped capital femoral epiphysis (SCFE), in which the femoral head cracks along its growth plate (the part of the bone from which new material is released to facilitate elongation) is a common problem in children and adolescents. This can cause chronic hip pain. It can also lead to other, more serious conditions, such as early-onset arthritis and avascular necrosis. This condition is the gradual necrosis (death) of the femoral head due to lack of blood supply. Therefore, total hip replacement is often indicated in cases of SCFE. SCFE is associated with accidental injuries, a very high degree of activity, and with increased body mass.
Obesity is also more generally associated with hip pain in childhood. Genetic diseases, such as Down’s syndrome and cerebral palsy, are also associated with hip pain and abnormalities. Down’s syndrome is capable of causing total femoral head collapse, which is referred to as Legg-Calvé-Perthes syndrome. Transient synovitis is a condition that can cause acute hip pain in children, and possibly also thigh and lower leg pain, but is often temporary and does not affect movement or function later on in life.
Hip Pain in Adolescents and Young Adults
SCFE can also cause femoroacetabular impingement (FAI). This is an abnormal increase in the friction between the ball and socket of the joint, causing pain and functional decreases. FAI is also commonly associated with adolescents and young adults involved in heavy athletic activity, due to the simple over-use of the joint in training. It is common in runners, and in people involved in high-speed and impact sports such as soccer and ice hockey. FAI is often misdiagnosed as other common, sports-related sources of hip pain, such as labral tears and strain to the adductor muscles of the groin. FAI and labral tears can be treated with reconstructive surgeries, sometimes involving a graft from the patient’s own ligaments or other tissues.
There are two main types of FAI. Cam-type impingements occur when the femoral head is forced closer against the acetabulum. This is due to abnormal growth of the femoral neck, or of the junction between the head and the neck of the bone. Pincer-type impingements occur due to abnormalities or abnormal growth of the acetabulum. This results in increased contact of it, or of the acetabular labrum, with the femoral head.
Another factor that can contribute to musculoskeletal problems of the hip, lower back, and pelvis is wearing shoes that affect spinal load and gait in abnormally stressful ways. The leading example of this is high-heeled shoes, worn mostly by women and teenage girls.
Other Conditions Related to Hip Pain
There are several other possible causes for hip pain. For instance, if the sacroiliac joint is damaged, the resulting pain can be perceived in the hip and/or pelvic region. Another source of hip pain can be spinal surgery. Operations on the lower back (carried out, ironically, to relieve pain) can result in inadvertent nerve damage, and thus cause pain in the hip region.
An unusual source of hip pain is damage to the central nervous system. This can cause heterotopic ossification, or abnormal bone growth in the femoral head, thus causing abnormalities in the joint and increasing the risk of hip pain. Heterotropic ossification can also cause inflammation in the joints affected, which leads to more pain.
Pain arising from other sources, such as cancer, is rare. Cancer patients at risk of hip pain are those with tumors in the pelvic region or the structures within. These are mainly endometrial cancers. In these cases tumors of the uterus may metastasize and press on nerves or other tissues to cause pain. In some cases, the cancer may invade the bones of the hip or upper thigh. Tumors located in or near the major spinal nerves that serve the hip and surrounding tissues can also cause damage, and as a result, hip pain. Cancer treatments, such as chemotherapy or radiotherapy, can also cause pain as a side effect, as they can destroy healthy tissue, such as nerves, and even the bones of the joint itself. If they press on the nerve, this can be a source of chronic pain.
Post-operative pain, after hip replacements or other corrective surgeries, is also a source of hip pain. Replacement, or hip arthroplasty, is a very common procedure in which the femoral head and/or acetabulum are removed and a prosthetic is implanted in their place. The most modern of these are acrylic and titanium-based with acetabular and femoral head acrylic analogs. Certain types of implants have been more associated with post-operative and implant pain. Another major component of post-operative hip pain is implant failure. This is mostly due to slippage or loosening of the prosthetic hip, a situation in which the implant migrates away from its desired location or orientation in the joint. This can be due to simple mechanical failure, i.e. the implant slips out of the normal position in relation to the acetabulum during movement of the patient. It can also be a result of infection of the prosthesis, by bacteria or fungi. This is known as septic loosening or slippage.
Slips or failures can happen for other reasons, such as when the replacement femoral head does not fuse to the rest of the bone. Prosthetics can be attached to the shaft of the femur by screws or acrylic cement, which have an approximately equal chance of detachment. Some failures that occur for no apparent reason at all (i.e. idiopathic loosening) are also possible. Infection of the implant without loosening is also a source of chronic post-operative pain.
Pain from these sources is transmitted to the brain by important nerves in and along the spine. These nerves, which control sensation in the hips, are located in the lumbar (lower back) or sacral (tailbone) region. If these nerves are injured or inflamed, the result is pain in the hips or lower extremities.
Diagnosis of Hip Pain
Analysis of hip pain can be a complex process, since there are many possible causes. The risk factors mentioned above are taken into account in diagnosing hip pain. A patient will be asked about the nature of the pain. This will include describing the location of the pain, how long the patient has experienced the pain, whether it is chronic or a sudden attack, and if it is in one hip or both. A family history of osteoporosis or osteoarthritis can also contribute to a diagnosis. Imaging techniques such as magnetic resonance imaging (MRI) and ultrasound are of increasing use and efficacy in determining the cause of hip pain. These techniques can visualize bone or other tissues, and locate damage such as fractures accurately. Computerized tomography is also used in hip pain analysis, but is reported to be less effective than MRI in diagnostic ability.
Physical examination by a medical professional also has a valid role in hip pain diagnosis, especially in cases of athletic injury. An experienced doctor can often spot conditions, such as labral tears, if missed by imaging. Radiography, such as X-ray imaging, is also still used in hip pain analysis, but is often discouraged for use on children due to safety concerns. Radiography is also used in cases where MRI would be inappropriate or dangerous, such as in patients with metal hip implants.
Scoring of patient self-reports of pain is also useful in both diagnosis and assaying the effect of subsequent treatment. Outcome scores used in hip pain are the Harris Hip Score and the International Hip Outcome Tool (iHOT12). More specific measures are those related to separate conditions, such as the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Nerve or joint blocks, which are described in more detail below, are also used in diagnosing hip pain, in order to determine if the pain is specifically coming from nerves associated with the hip, or directly from the joint itself.
Treatment for Hip Pain
A first line of treatment for hip pain is conventional painkillers, administered orally or intravenously. An example of these is opiods, such as morphine and codeine. These are a type of drug that blocks pain receptors in the spinal cord. Opioids are often prescribed to cancer patients to manage pain resulting from tumors or their treatments. Another opioid, fentanyl, is often prescribed to post-operative arthroplasty patients. Fentanyl is delivered through intrathecal pumps in these cases. Opioids have drawbacks as a treatment option due to their highly addictive nature and potential for tolerance. These drugs carry a risk of liver failure and respiratory depression, especially with chronic intake.
There are various alternatives to opioids that work to stop pain signaling in the nerves associated with hip and back pain. Non-steroid anti-inflammatory drugs (NSAID, e.g. naproxen or aspirin) are often prescribed for hip pain. These reduce inflammation in the joint and surrounding tissues. They are most effective in treating hip pain associated with athletic injury. NSAID intake carries the risk of organ failure if they are taken constantly over a prolonged period. Newer anti-inflammatories, known as COX-2 inhibitors, are also effective in treating athletic or accidental hip pain.
Other Treatment and Management Strategies for Hip Pain
Alternatives to opioids include spinal nerve blocks. Blocks are injections of pain-relieving medications (e.g lidocaine or mepivacaine) into the space near the affected nerves. These injections can also contain steroids to treat the inflammation that is often a source of pain. This procedure begins with the application of a local anesthetic to the skin in the area where the injection is to be given. Nerve blocks are administered with the aid of imaging techniques, such as MRI or ultrasound. This ensures accuracy in locating the target for the injection, and of delivery of the medication to the appropriate location. The formulation is injected into the immediate vicinity of the nerve, called the epidural space. Here, the anesthetics and/or steroids take effect and block the pain signals of the nerve. A similar procedure is a hip joint injection, in which either anesthetics or steroids are injected directly into the joint to relieve pain.
The benefits of blocking injections are that they are relatively non-invasive, and an alternative to surgery for patients who cannot or wish not to undergo operations.
The risks associated with these procedures include nerve damage or loss of sensation. Inadvertent injection into a blood vessel or into the wrong area of the spine can occur, most often in the absence of adequate visualization. This can result in discomfort, loss of sensation, and paralysis in severe cases. Temporary neurological complications such as headache can also occur. If steroids are included in the formulation, they may cause immune system depression, weight gain, and mood changes as side effects. Steroids are also associated with an increased risk of arthritis and osteoporosis development. In the case of hip joint injections, skin discoloration, swelling, and (in very rare cases) rupture of tendons can also occur.
Another nerve-blocking technique is radiofrequency ablation. In this procedure, the skin and tissue over the nerve is numbed with a local anesthetic, and a probe is inserted until it comes into close proximity with the affected nerves. The probe will then apply radiofrequency energy (in the form of heat) to the nerve, creating a lesion on it. This will reduce its ability to send pain signals to the brain, but is not severe enough to prevent its normal functions. Imaging equipment and pharmacological nerve challenges can accurately locate specific parts of the nerve that transmit noxious information (“pain fibers”) and thus target the probe to selectively create lesions on these. Risks of ablation are infections at the probe insertion site, along with bleeding and discomfort. If the imaging or physician is inaccurate, this can cause serious nerve damage, as with nerve blocks. The procedure can result in several months of pain relief if successful, however.
Another option to relieve chronic pain may be the implantation in the lumbar regionof a spinal stimulators(SCS) that causes interference in pain signaling. Stimulators are specially designed devices for safe and effective implantation into the back. They are thin wires in a soft, flexible material, so that damage from their placement is minimal. Test devices are initially implanted in a medical facility to assess the response of a patient’s pain levels to the treatment. This device may remain implanted for several days as the individual tries it out. If this trial produces a positive response, a permanent device may be implanted. The stimulator is usually connected to a hand-held controller via leads. This can activate the pain-blocking stimulus as needed. SCS carries risks of scarring and inadvertent nerve damage. Other risks include bleeding and infection of the insertion site, and inadvertent worsening of the pain response. However, these side effects are rare. Spinal cord stimulation is effective in many cases, and is becoming increasingly popular in pain management.
Another method of stimulating analgesic responses in spinal nerves is through the use of transcutaneous electrical nerve stimulation (TENS). In this procedure, pads or a cap that deliver pain-blocking electrical impulses are applied to the affected area, and the impulses or waves used travel through the skin to the nerve(s) targeted. TENS is often recommended for use by elderly patients to control pain related to osteoporosis or osteoarthritis. TENS in the treatment of post-operative hip pain significantly reduced fentanyl reliance compared to a sham treatment in a small-scale trial of 68 patients, indicating that this technique also has potential in treating arthroplasty-related pain. TENS has relatively few risks and adverse effects. The most common of these is a stinging or mildly burning sensation in the skin where pads are applied, transient muscle pain, and skin redness.
Alternative or Complementary Treatments
Movement and function tend to decrease after hip replacement. This can set off a vicious cycle of pain and further functional decline, as the patient may find it more painful to move, due to the lack of rehabilitation in the muscles and ligaments. Physical therapy is associated with a return of function and the reduction of pain after time. Therapy can take the form of low-impact exercise, resistance training, stretching, and joint movement. Newer forms of physical rehabilitation are kinesitherapy and constrained movement therapy that are based on central nervous system responses to movement. Physical therapy is also indicated for athletes recovering from corrective surgeries who wish to return to their pre-operative form.
Acupuncture has been reported as effective in controlling hip pain, particularly after arthroplasty procedures. This traditional Chinese method of pain relief has been practiced and improved on over time up to the present day. Modern acupuncture should be administered by a doctor or certified practitioner. Sterilized, fine stainless steel needles are used. The insertion of acupuncture needles is not usually painful, as they are fine enough not to elicit a pricking sensation. Several needles are placed in appropriate locations to stimulate spinal nerves to produce an analgesic, or pain-blocking response. The needles are sometimes carefully moved, or deliver electrical stimulation, to enhance this effect. Numbness or tingling after the needles have been inserted may be experienced. The needles stay in place for 15 to 30 minutes over a typical session. Most practitioners will recommend several treatments to assess the effects of acupuncture on pain.
The main benefits of acupuncture are that it is a drug-free option of pain management and that the procedure is relatively quick and convenient. Normal activity can be resumed immediately after treatment. Risks and complications associated with the procedure are rare and few in number. The main risks may include an increased risk of superficial bleeding or bruising at the needle sites. Acupuncture may be unsuitable for people with disorders such as hemophilia, or those in need of blood-thinning medication (e.g. regular aspirin). Finding a reputable, professional practitioner or doctor is important, as a serious but very rare risk is the transmission of infectious disease due to a lack of needle sterilization, or needle re-use.
Prevention of Hip Pain
The most effective way to reduce the risk of hip pain is to avoid conditions and occupational hazards that are associated with it. This is particularly relevant to athletes who may incur hip damage through over-training or inappropriate running or movement styles. Running and/or gait analyses are very useful in these cases. Data from these evaluations can assess the cause of hip wear and tear through methods of running or walking that result in extra load or stress on the joints and muscles. Another method of prevention is adequate warming-up, cooling down, and stretching. This reduces the chances of muscle strains and tears, and of labral tears. If pain occurs, or if a running analysis indicates there is a strong risk of developing a painful condition, re-thinking or reduction of a training program may be necessary to avoid either. Certain activities, such as running downhill, are associated with a greater risk of hip damage. The design of fitness regimens that avoid these activities may be vital in preventing hip pain.
Moderate resistance and flexibility training with increased age is currently promoted as a preventative measure against hip pain and damage in the senior population. This is due to observations that regular movement is associated with bone maintenance and a reduction in sarcopenia. This is age-related deterioration in muscle mass, associated with an increased risk of osteoporosis-induced fractures, and with osteoarthritic pain. As hip integrity is associated with the support of the muscles, ligaments, and tendons that surround it, this seems a positive strategy to limit hip pain in old age. This is due to the increased tendency of bone tissue to grow and regenerate in response to the stimulus of tendons and muscles exerting pressure on it.
Other Methods of Hip Pain Management
There are some applications and treatments designed to treat hip pain that are currently under scientific or clinical evaluation. Foremost among these are alternatives to and developments in total hip arthroplasty directed at reducing post-operative pain. Minimal-incision (MI) arthroplasty differs from standard procedures (SI) in the number and orientation of open surgical wounds used in the course of the hip implantation. However, while MI has achieved significant reductions in blood loss and hospital recovery times, the procedure appears not to differ from SI in terms of reducing pain intensity or duration. An alternative to arthroplasty is femoral head reconstruction, in which damage to the bone’s surface is repaired using surgical cement. This procedure, however, also appears not to be significantly superior to total arthroplasty when it comes to pain reduction.
A main concern with hip pain management is the loss of the synovial fluid normally present between the acetabulum and femoral head. Reductions in the volume of this material, seen in arthritis and FAI, increases friction in the joint, and results in pain. A method of replacing this, with sterile bio-medical products such as hyaluronate, has shown promise in alleviating pain, and is currently applied to the treatment of osteoarthritis. This technique is known as viscosupplementation. However, despite its positive impact on knee-joint arthritis, large-scale trials of viscosupplementation in hip joints are yet to be conducted.
Arthroscopy of the hip joint has undergone a significant amount of advancement in the last few years. This is a type of surgery done through an endoscope, with minimal incisions and post-operative injury. Hip arthroscopy is conducted with the patient lying on the side opposite to the joint to be operated on, or on their back. (This is the preferred position for many hip surgeons, and may be associated with better outcomes due to its familiarity.) It may be carried out under general anesthesia, spinal nerve block, or femoral nerve block. The surgical team will have to apply traction to the hip, in order to get access to the joint. This means the ball of the joint must dissociate from the socket a little. Imaging such as x-ray fluoroscopy will be used to further enhance the visibility of the hip. Sterile fluid may also be injected into the joint to improve accessibility and visualization. Arthroscopy is used to treat FAI and labral tears. In the case of FAI, the abnormal bone growth on either joint surface can be removed, using surgical micro-burr tools not unlike a dentist’s drill. Labral tears can be sealed, cut away, or repaired using autografts. The procedure is also successful in correcting infantile hip abnormalities such as dysplasia, thus preventing pain later in life.
Arthroscopy is increasingly associated with positive outcomes and recovery in the treatment of these conditions. Arthroscopy is also linked to significant reductions in pain severity and duration after surgery. Athletic patients treated with arthroscopy have shown a significantly faster return of normal function and competitive ability after arthroscopic intervention, compared to traditional surgery. The procedure does have risks, as do all operations. The main risks are associated with general anesthesia, which include chest numbness and discomfort, urinary retention, and nausea. If nerve blocks are used, the adverse effects as described earlier can occur. Infection of the joint or incisions is relatively rare, reported in about 1% of cases. Mechanical damage to the surrounding nerves, caused by surgical implements or traction, is possible. This may cause intense or chronic pain. This is more often felt in the legs or pelvic region rather than the hip, however. The success of arthroscopy indicates that it may be positively applied to hip replacement failures or treatment of painful prosthesis.
Nerve growth factor (NGF), which controls the elongation of nerve cells in order to meet their targets (muscles or other nerves), is a current source of interest in pain research. This molecule has a central role in controlling pain signal transmission at a cellular level. Some trials of NGF-blocking regimens have shown positive results in hip pain control. In these trials, anti-NGF drugs with or without the addition of NSAIDs were more effective than NSAIDs alone. However, this combination is associated with an exacerbation of osteoarthritis, sometimes resulting in the need for arthroplasty. Therefore, anti-NGF drugs may be a viable option as a stand-alone drug, but require more clinical evidence of their efficacy. More information on the severity of their adverse effects, which include parasthesia, is also needed before they can be developed as therapeutics.
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Hip pain can be debilitating, as it can adversely affect normal movement, function, and autonomy. This type of pain can have many sources, including injury, joint damage, and inflammation of the nerves involved in sending pain signals to the brain. Hip pain is most commonly seen in the elderly; however, it is also observed in children and young adults.
Treatment for hip pain can come in the form of conventional drugs such as morphine, which are associated with risks of addiction and tolerance. Other treatments are anesthetic injections directly into the spinal nerves controlling the hip joint. Radiofrequency ablation, or partial lesioning of the nerve, is also a long-term and effective treatment. Spinal cord stimulators may also be an option for chronic pain in the legs or hips. Acupuncture, if administered by a competent and reputable professional, is also a viable option of pain relief. Another increasingly popular method of pain management is transcutaneous electrical stimulation (TENS).
Rehabilitation and physical therapy also play important roles in restoring function in both athletes and those recovering from hip replacement surgery. Some encouraging developments in hip pain management include anti-NGF compounds, and modern-day arthroscopy. The latter has increased drastically in popularity, due to an increase in development as a surgical procedure. Avoiding hip pain through regular movement and appropriate exercise is also important in preventing disability resulting from conditions such as osteoporosis and arthritis in old age.