‘Hip’ pain

Article Outline

• Abstract
• 1. Epidemiology
• 2. Hip pain in children
  • 2.1. Acute transient synovitis
  • 2.2. Perthes' disease
  • 2.3. Slipped capital femoral epiphysis (SCFE)
  • 2.4. Congenital dysplasia of the hip joint (CDH)
  • 2.5. Tumours
• 3. Hip pain in adolescents
• 4. Hip pain in adults
  • 4.1. Fracture/stress fracture
  • 4.2. Avascular necrosis (AVN) of the femoral head
  • 4.3. Strains/tendinitis
  • 4.4. Piriformis syndrome
  • 4.5. Bursitis
  • 4.6. Labral tears
  • 4.7. Osteoarthritis
  • 4.8. Rheumatoid arthritis
  • 4.9. Neurological disorders
  • 4.10. Tumours and metastatic lesions
  • 4.11. Septic arthritis
• 5. Differential diagnosis of diseases not related to the hip joint
• 6. Diagnostic algorithm
• 7. Summary
• References
• Copyright

Abstract 

‘Hip’ pain is usually located in the groin, upper thigh or buttock and is a common complaint. Slipped capital femoral epiphysis, avascular femoral head necrosis and apophyseal avulsion are the most common diagnoses in childhood and adolescents. Strains and fractures are common in sport-active adults. Osteoarthritis occurs in middle-aged and older adults. Trauma may result in femoral head fracture or typical muscle and tendon sprains and bursitis. Septic or inflammatory arthritis can occur at every age. Septic arthritis, fractures and acute epiphyseal slipping are real emergency cases. Congenital dysplasia of the hip joint may lead to labral tears and early osteoarthritis.

The most important hip problems in children, adolescents, adult and older people are discussed; these problems originate from intra-articular disorders and the surrounding extra-articular soft tissues. Medical history, clinical examination and additional tests, including imaging, will be demonstrated. Principles of treatment are given for specific disorders.

Keywords:  hip joint, septic arthritis, tumour, osteoarthritis, rheumatoid arthritis, avascular necrosis of the femoral head

‘Hip’ pain is a common complaint with many possible causes. If talking about ‘hip’ pain, patients usually think of a pain located in the groin, the proximal thigh or the buttock. The anatomical region of the hip and pelvis is complicated. Big joints (hip and ilio-sacral joint) and different groups of muscles, tendons and bursae are located in the region. Major vessels and nerves cross the hip joint on their way from the intra-abdominal region to the periphery of the legs. Referred pain may arise from lesions of the iliopsoas region, lumbar spine or the retroperitoneal space. So, urogical, gynaecological and gastrointestinal problems may also cause ‘hip’ pain and have to be evaluated.

Due to the principle of referred pain we also have to examine the adjacent joint regions: lumbar spine and the knees. This chapter deals with the most common orthopaedic disorders originating in or around the hip joint. Conditions of the lumbar spine referring to the dorsal region of the hip and thigh are not included.

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1. Epidemiology 

From the standpoint of a clinician, hip pain in childhood and in adults should be looked at separately because of the very specific differences and causes of hip pain in these different age groups.

Acute hip pain in children is a very common finding, and the highly concerned parents will look for immediate help in emergency rooms. Most often the cause of hip pain is acute transient synovitis of the hip. Septic arthritis has to be excluded. The incidence of slipped capital femoral epiphysis is about 6.1 (per 10 000) in boys and 3.0 in girls.¹ The incidence of Legg–Calvé–Perthes' disease² is about the same range of 1.5–5 (per 10 000).

Hip pain is also very common in people older than 60. In the NHANES III Study³, 14.3% of the representative sample of older adults in the United States reported hip pain during the previous 6 weeks. Self-reported knee pain in the same population⁴ is more common (18.1% of men and 23.5% of women). People whose leisure-time activities involve physical exercise have less frequent hip pain.

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2. Hip pain in children 

In childhood there are three very common disorders of the hip joint which lead to acute pain: acute transient synovitis or coxitis fugax, Perthes' disease and slipped capital femoral epiphysis. The typical sign and hint of a hip disorder in childhood is a referred pain to the anterior thigh and knee joint resulting in limping and refusing to walk.

2.1. Acute transient synovitis 

Acute transient synovitis (ATS) is a self-limited inflammatory condition with effusion of the hip joint. In most cases a clear cause cannot be found, although in more than half of the patients, there is a history of infection of the upper respiratory tract or mild trauma in the near past. In ATS the children have a limited motion and present the hip in flexion, abduction and external rotation. Mostly there are no other signs of an inflammatory disease. Laboratory tests are normal or give only hints of a non-specific mildly inflammatory process (mildly elevated ESR, WBC and CRP). Ultrasound shows signs of joint effusion. X-rays [anterior–posterior (a.p.) and lateral view of both hips] have to exclude the other typical hip disorders of childhood. Further imaging techniques, such as MRI and bone scintigraphy, usually are not necessary for this diagnosis. Aspiration of the effusion is indicated if the child has an elevated temperature or other signs of septic arthritis.⁵ Treatment consists primarily in bed rest, followed by a period of no weight-bearing until the hip is pain-free and fully movable and the application of anti-inflammatory drugs. The condition is usually gone within 2 weeks; very seldom does the condition last longer.

2.2. Perthes' disease 

Perthes' disease is a self-repairing ischaemic necrosis of the femoral head leading to the collapse of the epiphysis followed by a remodelling process. Onset of Perthes' disease occurs in the age range 2–13 years, mostly between 4 and 9 years; boys are more often affected than girls. About 50% of untreated patients develop early-onset osteoarthritis.

Clinical examination shows a limitation in the range of motion. Abduction and internal rotation are particularly limited. Laboratory tests are normal. Ultrasound shows effusion of the joint and irregular formation of the epiphysis. Standard X-rays of the pelvis in a.p. and frog-leg lateral view confirm the diagnosis. Initially, joint space widening may be the first sign, followed by a crescent-shaped radiolucent line. In the next stage the epiphysis shows a fragmentation. End stage is the complete reossification—very often resulting in a residual deformity with the femoral head bigger than the acetabular cup.

The disease, which is self-repairing, lasts for up to 2–4 years. Treatment consists of reducing pain and inflammation by non-steroidal anti-inflammatory drugs (NSAIDs) and physical exercises to prevent the development of flexion and adduction contracture of the involved hip joint. To prevent deformity of the femoral head the so-called containment is important. This means optimal positioning of the femoral head in the cup by bracing or operatively by proximal femoral osteotomy.

2.3. Slipped capital femoral epiphysis (SCFE) 

Slipped capital femoral epiphysis (SCFE) is a disease with ‘softening’ of the epiphyseal cartilage during adolescence. The peak incidence age for girls is 11.5 and that for boys is 13.0 years; it is twice as common in boys and even more common in summer than in winter. Children with certain endocrinopathies, such as hypogonadism, hypopituitarism and hypothyroidism, demonstrate a typical habitus. Pain and altered gait (external rotation of the leg) are the most common clinical signs. At clinical examination the fixed external rotation in flexing the hip is the most important sign. Shortening of the affected leg or atrophy of the thigh are symptoms of a long-standing disease. Ultrasound shows effusion and also the slipping of the epiphysis. X-rays of both hips in a.p. and lateral frog-leg view show the amount of displacement of the epiphysis, increased physeal thickness and bony irregularity of the physis. Duration of disease classifies an acute form from a chronic SCFE. Treatment has to stop further slipping and to correct severe deformities. Usually surgical treatment is the first choice. Usually both epiphyses are fixed, because more than 50% of the primarily unaffected sides are at risk of slip in the near future. Only acute slipped epiphysis can be reduced—this should never be done in chronic forms. Severe grades of slipping have the risk of avascular necrosis or chondrolysis. The residual deformity of the femoral head is a risk factor for early osteoarthritis of the hip joint.

2.4. Congenital dysplasia of the hip joint (CDH) 

CDH is a common developmental disease of the hip joint. Clinical screening of the newborn may lead to early diagnosis of a pathological hip situation. Especially painful abduction of a hip joint or reduced range of abduction is a strong clinical hint for a pathological condition in a newborn child. Due to improved preventive diagnostic tools (ultrasound examination) early diagnosis and treatment (starting with an abduction pillow) it is possible to prevent later osteoarthritis. If early diagnosis and treatment is missed, some pathology of the hip joint may be the cause of pain in childhood. Especially limping and weakness of the surrounding muscles are the typical clinical signs. X-rays of the pelvis make the underlying dysplasia obvious. Treatment is age dependent according to the self healing forces of the growing organism. Very often it is necessary to correct the pelvic deformity with osteotomies in order to restore the physiological alignment of the actabulum.

2.5. Tumours 

It is very important not to miss the diagnosis of a malignant tumour. Malignant tumours are very rare diseases in childhood. The symptoms of benign or malignant tumours are not very specific. Symptoms arise if bone stability is compromised. Hence, ultrasound and X-rays are the most important diagnostic tools for detecting changes in bone and the surrounding soft tissues, leading to uniform diagnostic algorithm for diagnosis of bone and soft-tissue tumours.

Osteosarcoma and the malignant tumours of the Ewing type group are the most common. The incidence is about five per million per year for osteosarcoma and 0.6 for Ewing sarcoma. About 10% of these tumours are located in the region of hip and pelvis.^6., ^7.

More common are the benign tumours originating from cartilage: enchondroma and cartilagineous exostoses. Solitary bone cysts and fibrous dysplasia of bone can be easily diagnosed. Most of these tumours can be diagnosed by their typical appearance in X-rays and MRI. Osteoid osteoma is a benign bone tumour, which typically leads to exacerbation of pain during the night; pain is relieved by aspirin. Clinical and radiological signs of this small (usually 0.5cm in diameter) benign tumour may mimic many other diseases. Pain relief can be obtained immediately after surgical removal.

Repeated clinical and X-ray or MRI examination in defined time intervals is the treatment of choice for benign bone tumours. Operative treatment is necessary only if the affected bones are at risk for fracture.

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3. Hip pain in adolescents 

There is a special problem in adolescents who are very active in sports.⁸ Owing to the special situation in the region of epi- and apophyses, it is possible that so-called avulsion fractures occur after a direct injury to the insertion of muscles (Table 1). This is a fracture through the cartilagineous site of the bony insertion of a tendon (especially M. rectus femoris, M. iliopsoas, M. adductor magnus, M. sartorius). Clinically, motion against resistance of the affected muscle is painful. First X-rays may show no displacement of the fracture apophysis. Further controls make the increasing gap and bony reactions obvious. Treatment usually consists primarily of rest and non-steroidal drugs. It is a self-healing process.

Table 1. Apophyseal attachment of muscles around the hip/pelvis

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4. Hip pain in adults 

Most common hip pain located in the groin in adults is due to a fracture of the femoral head or acetabulum resulting from acute trauma, stress fractures of the femoral neck or pelvis, avascular necrosis of the femoral head, strains of the adductor or iliopsoas muscles and tendons, iliopectineal bursitis, first signs of residual developmental disorders of the hip joint, labral tears, osteoarthritis or other inflammatory joint diseases.⁹

4.1. Fracture/stress fracture 

Acute or chronic pain with weight bearing, external rotation and shortening of the leg, and being unable to put full weight on the foot after acute trauma with impact to the hip joint or pelvic region, are the common clinical signs of a hip fracture. After clinical examination, X-rays in a.p. and lateral view are the diagnostic tools of choice to secure a diagnosis. Bone scintigraphy, MRI or CT scans are further diagnostic tools in unclear cases, especially in stress fractures. Treatment can be non-operative only in special ‘stable’ fracture situations (bed rest followed by a longer period of non-weight bearing). Displaced fractures are treated by osteosynthesis or—if there is a high risk of femoral head necrosis or underlying osteoarthritis—by a femoral head or total hip arthroplasty. Stress fractures result from chronic repetitive overloading. Causes are increased mechanical loads in athletes or reduced mechanical properties of bone in special situations (e.g. osteoporosis, athletic amenorrhoea, glucocorticoid treatment).

4.2. Avascular necrosis (AVN) of the femoral head 

Each year 15 000 people in the United States are diagnosed with AVN of the hip joint. This diagnosis has great impact because it strikes young adults and is in a high amount of patients progressing despite of different kinds of treatment. Most of the patients are under the age of 50 years. Young men are more commonly affected than women (8:1–4:1). About 10% of the total hip replacements in the United States are due to AVN.¹⁰ AVN is caused by ischaemic death of the bony and marrow tissues as a sequel to different conditions and underlying systemic diseases:

In about 25–40% of the patients no underlying cause could be found (idiopathic form). Ischaemia of the femoral head leads in the course of the disease to microfractures within the subchondral bone plate causing a rapidly progressing arthropathy after the collapse of the articular surface. Transient self-healing osteoporosis could be distinguished from AVN¹¹ with typical MRI findings.

Clinical signs are untypical. Most of the patients have slowly progressing hip pain, increasing under load and walking, for weeks and months without any radiological signs. Pain is usually located in the groin, radiating down to the medial thigh. Pain at rest is a sign of advanced-stage AVN and is attributed to the elevated intraosseous pressure. In the early stages the range of motion is normal. Joint destruction in advanced stages leads to limitation of extension, internal rotation and abduction. Limping and atrophia of rectus and gluteus muscles are non-sensitive signs of pain-related disuse of the joint.

Regarding the natural course and indication for treatment of AVN staging is very important. ARCO (International Association Research on Circulation Osseous) has proposed a staging of AVN (Table 2) which is very similar to that of Steinberg et al.^12., ^13. Steinberg et al gave an additional quantification of the extent of involvement (Table 3) based on the outcome of more than 1000 treated cases.¹³ Stage 0 means no clinical or radiological signs in cases where AVN can only be found in histological specimens. In stage 1 only bone scans or MRI show abnormal signs while X-rays are still normal. Clinical signs may be absent or mild. In stage 2 X-rays show pathological signs such as cystic or sclerotic changes within the femoral head, located mostly in the ventral region. Stage 3 seems to be the stage where the disease changes for the worse. Subchondral collapse of cancellous trabeculae is evident, producing the crescent sign. This means bony destruction without flattening of the femoral head. In stage 4 the femoral head loses its round shape and becomes flattened. This is the stage of irreversible damage of the femoral head. Stage 5 shows flattening of the femoral head and narrowing of the joint space as signs of the beginning of osteoarthritis. Stage 6 is the end stage, with changes resulting from advanced osteoarthritis or complete loosening of the femoral head and also acetabular changes.

Table 2. Staging of avascular necrosis of the femoral head.^12., ^13.

Table 3. Quantification of the extent of involvement by avascular necrosis of the hip joint

Stage	Grade	Extent of involvement
1 and 2	A mild	<15% of femoral head involvement
	B moderate	15–30% of femoral head involvement
	C severe	>30% of femoral head involvement
3	A mild	Subchondral collapse beneath <15% of articular surface
	B moderate	Subchondral collapse beneath 15–30%
	C severe	Subchondral collapse beneath >30%
4	A mild	<15% of surface collapse, depression <2mm
	B moderate	15–30% of surface collapse, depression 2–4mm
	C severe	>30% of surface collapse, depression >4mm
5	A mild	<15% of head involvement and acetabular involvement
	B moderate	15–30% of head involvement and acetabular involvement
	C severe	>30% of head involvement and acetabular involvement

Non-operative therapy consists of administration of NSAIDs, reducing weight-bearing and eliminating risk factors. It is well known that non-operative treatment in AVN of the hip in adults leads to poor results. About 80% of all stages progress to full collapse of the femoral head with consequent development of severe degenerative changes of the affected hip joint—ending up in total hip replacement. Core decompression is the method of choice and is widely used in the early stages (stages 0–2).³ Steinberg et al¹⁴ presented results of 406 treated hips in 285 patients with AVN. Some 36% of the patients required total hip replacement in the course of the study, with a mean 48 months' follow-up; more patients in the steroid and alcohol-risk groups required total hip replacement. Survival of femoral heads was three times greater in the surgical group than in a non-operative group. The effect of lesion size at the time of surgery was evaluated and it seemed to be even more important than the stage (0–3). Best results are obtained if the lesion size is under 15% of the femoral head.¹⁰

Another form of treatment is flexion osteotomy of the proximal femur; the underlying idea is to rotate the intact portion of the femoral head under the acetabulum. This form of treatment is indicated in the early stages before flattening of the femoral head occurs. Recent results again demonstrated a high percentage of patients (37.5%) converting to a total hip joint.¹⁵ With a mean follow-up of 5 years, vascularized transplants show better results in the early stages^1., ^2., ^3., with a lower conversion rate to total hip replacement in about 20%. Some 50% of the treated hips have no further increase in stage and remain under stage 3.¹⁶ All hips in stages 4–6 are subjects for total hip replacement. Results are comparable to standard procedures, with 93.4% survival after 10–15 years despite the increased risk factors.¹⁷

4.3. Strains/tendinitis 

Strain is an acute damage to muscle or tendon. Tendinitis is the result of chronic overuse. The muscles most likely to be involved are adductor longus, rectus femoris and the iliopsoas. Adductor strains (rider's strain) arise in people who ride horses and also in those who ski or skate—or step inadvertently in a hole. Pain is located in the medial thigh or anterior groin. Squeezing something between the knees is painful.^8., ^9.

Clinically there is a pain that increases with continued activity or in resistance testing. Local tenderness or crepitus may be present in superficial regions. Iliopsoas tendonitis may produce a snap or clunk, especially when an inflamed iliopsoas bursa is present. Strains can be diagnosed clinically by locating the pain in the anatomically defined muscle or tendon and the weakness on manual muscle testing. X-rays are indicated only if a bony avulsion fracture is suspected. Ultrasound can demonstrate the site and amount of tissue disruption. Acute treatment consists in rest, application of ice, compression and avoidance of painful activity. A rehabilitation programme follows with mild exercises, pain-free stretching grading up to sport-specific activity. Surgical treatment is indicated only in full-thickness tears of tendons. Muscle tissue usually cannot be repaired by surgery. Treatment in chronic tendonitis is similar. Correction of poor technique or biomechanical dysfunction is essential to prevent further damage.

4.4. Piriformis syndrome 

A special entity results from irritation of the sciatic nerve by the M. piriformis.¹⁸ The clinical sign is a dull posterior hip pain radiating down the leg, mimicking radicular symptoms. The cause may be a direct trauma to the buttock or a history of prolonged sitting. Clinical examination shows limping, moderate weakness of gluteal muscles, and pain exacerbation on active external rotation or passive internal rotation on palpation of the sciatic notch. Sometimes a sausage-shaped mass can be palpated painfully over the piriformis muscle. Traction of the affected leg may give mild pain relief.

Treatment consists of stretching exercises, NSAIDs, relative rest and correction of offending activity. Seldom is surgical exploration and decompression of the sciatic nerve necessary to improve symptoms.¹⁹

4.5. Bursitis 

Around the hip joint there are some bursae which may lead to hip pain: iliopectineal bursitis and bursitis trochanterica. Pain arising from iliopectineal bursitis is located in the groin region. The groin region is tender on palpation. Clinical examination may—as in iliopsoas tendonitis—show a certain weakness in hip flexion in the sitting patient. Bursitis trochanterica is very common. Clinically there is a local tenderness over the greater trochanter. Even crepitus may be present. Abduction against resistance and passive internal rotation are common clinical signs. Ultrasound can visualize the bursitis in the typical location. Treatment options are NSAIDs or local injections with crystalline steroids.

4.6. Labral tears 

The acetabulum is surrounded by a cartilaginous ring—labrum acetabulare. In residual dysplasia of the hip joint lesions of this labrum are common findings²⁰ and often represent the first painful clinical sign of residual hip dysplasia (acetabular rim syndrome). Labral tears and concomitant pathological findings, such as intra- and extra-articular ganglia or oedema of the subchondral bone, are well known conditions leading to early osteoarthritis. This finding may be the first step and an indicator for the beginning of biomechanical decompensation of the dysplastic hip joint. Clinical signs are a ‘knife sharp’ groin pain, a painful giving-way syndrome of the hip, a painful clunk in the hip joint, a snapping hip, painful apprehension test (forced hyperextension-external rotation in slight abduction leads to painful anterior hip pain often combined with a snapping phenomenon) and a painful impingement test (forced flexion adduction). The intra-articular injection of a local anaesthetic may give an immediate relief from pain and is a sign of intra-articular pathology. Normal MRI is not able to detect labral tears. Only MRI arthrography—a highly standardized tool—can diagnose this special entity with a high degree of accuracy—over 90%.²¹ Treatment consists of diagnostic arthroscopy with labral resection, a very demanding operation to be performed only by very experienced surgeons. It is still controversial whether an open operation with labral repair or resection should be combined with the biomechanical correction of the dysplastic acetabulum. But this seems to become the treatment of choice for the future thus having a joint preserving treatment option for remaining dysplastic conditions.

4.7. Osteoarthritis 

Osteoarthritis is the most common cause of hip pain in people over 50 years of age. Pain starts slowly, worsening with activity. A limping gait develops, and pain increases with internal rotation and hyperextension of the hip. The range of motion decreases—especially in abduction and hyperextension. X-rays show the loss of cartilage height and the formation of subchondral sclerosis, osteophytes and bone cysts. Treatment^22., ^23. consists primarily in modification of life style and sports activity, exercises and the use of canes. The use of paracetamol in mild pain or nonsteroidal antiinflammatory drugs in moderate and severe pain are the next steps in treatment. Opioids may be useful for the short-term treatment of severe pain. Total hip replacement is the end-stage procedure with good and long-lasting results.

4.8. Rheumatoid arthritis 

Rheumatoid arthritis or other inflammatory joint diseases may affect the hip joint in the course of the disease. Pain and morning stiffness, improving with activity, are more typical of inflammatory conditions. Especially internal rotation and hyperextension are painful. Flexion and adduction contracture are common signs of longer lasting arthritis of the hip joint. In these situations clinical examination shows the signs of a systemic rheumatoid disease on many other joints. Laboratory tests give elevated inflammatory parameters. Ultrasound shows effusion and there may also be signs of bony erosions. X-rays demonstrate effusion, joint space narrowing, absence of osteophytes, osteoporosis, erosions and bone cysts. Aspiration of joint fluid gives a white cell count of more than 2500 per mm³ up to more than 50 000 cells. In patients receiving higher doses and/or long-lasting treatment with corticosteroids the risk of avascular necrosis (AVN) of the femoral head increases.

Systemic treatment consists of non-steroidal, steroidal and disease-modifying drugs. A local treatment option is the instillation of crystalline steroids to reduce synovitis and intra-articular pressure.

4.9. Neurological disorders 

Meralgia paraesthetica²⁴ is caused by the irritation of the lateral femoral cutaneous nerve (LFCN). The irritation may be spontaneous or iatrogenic, mechanical local pressure by belts or iatrogenic in spinal surgery. The LFCN has an intrapelvic course, and exiting the pelvis it turns down to the thigh. In all parts of its course there can be local damage. Mostly these injuries occur as the nerve exits the pelvis. Clinical signs are thigh pain, numbness, paraesthesia in the anterolateral thigh. Hyperextension of the affected hip joint is a provocation test. Relief of pain and paraesthesia after injection of a local anaesthetic is a diagnostic sign. Conservative treatment consists in removal of compression forces, repeated injections with local anaesthetics, systemic NSAIDs and local corticosteroid injection. Usually meralgia improves with these forms of treatment. Surgery can be useful in cases where conservative treatment gives no benefit. Neurolysis of the nerve and widening of the canal may be useful.

4.10. Tumours and metastatic lesions 

In the older population primary malignant bone tumours (chondrosarcoma) and tumorous conditions (multiple myeloma) or metastatic lesions of the pelvis or femur are common problems associated with hip pain.⁶ Often a spontaneous fracture through the affected bone is the first sign from a metastasis from a tumour which tends to send malignant cells to the bone (such as breast and lung cancer, prostate cancer). Clinical signs are not specific for these tumours. X-rays, bone scan, CT and MRI lead to diagnosis. Treatment consists of resection of tumours, autografts and osteosynthesis of lesions and fractures. Joint replacement with special devices may be necessary in extensive lesions. Radiation therapy or multidrug chemotherapy is indicated in relation to the underlying tumour.

4.11. Septic arthritis 

Septic arthritis of the hip joint is one of the real emergency cases in childhood and also in later ages. Because of the strong and narrow joint capsule, every infection leads to an increase in intra-articular pressure, causing disturbances in the critical blood supply to the femoral head. Hence, early diagnosis and immediate release of intra-articular pressure by repeated aspiration or open surgery is required.

Clinical signs of a septic hip joint are serious pain on movement, impossibility of weight-bearing, feeling severely ill, and fever. These signs indicate the use of ultrasound for evaluation of synovitis and effusion, X-rays for demonstrating the osseous changes, and laboratory tests for inflammatory reactions such as elevated sedimentation rate, C-reactive protein, white and red blood cell counts. Aspiration and analysis of the fluid is mandatory. More than 2000 cells/ml of synovial fluid strongly suggest an inflammatory effusion, more than 20 000 reactive arthritis, and more than 50 000 septic arthritis. Microbiological examination with gram stains (which are available immediately) and an antibiogram, will give further hints.

If clinical examination, laboratory tests and ultrasound or X-ray provoke suspicion of an infection, immediate aspiration and the removal of effusion are the initial treatments of choice. In our practice we would then do an arthroscopic joint lavage in the early stages (duration of infection less than 5 days, no synovitis, no osteoarticular damage). If there is a significant involvement of the synovial tissue (after more than 5 days) arthroscopic or even open synovectomy is the next invasive stage of treatment. In further advanced stages (after weeks of infection), with destruction of cartilage or deep involvement of bone (osteoarticular panarthritis), resection of the femoral head and removal of the cartilage of the acetabulum offers the chance of curing this osteoarticular septic process. In a second-stage procedure total hip replacement can be done.

Antibiotic treatment should be started immediately after the first aspiration of joint fluid or material, with two broad-spectrum compounds working against commonly found bacteria (Staphylococcus epidermidis, Staph aureus). Antibiotic treatment lasts for up to 12 weeks—at least 2 weeks longer than complete clinical and laboratory recovery.

Septic arthritis is still a life-threatening disease with a mortality of 2–5% and high morbidity. Early and aggressive treatment gives the chance of full recovery of joint function. In worse cases the two-stage treatment gives satisfactory results after total hip replacement.

A special form of infectious arthritis is osteoarticular tuberculosis of the hip joint. Among the 30 million people worldwide suffering from tuberculosis, about 1–3% have an osteoarticular involvement. Of these, 15% have an affected hip joint. In particular, the HIV-positive tuberculosis patients have a 60% rate of osteoarticular infection.²⁵ Diagnosis is made from joint material obtained by aspiration or open surgical treatment.²⁶ PCR is a fast and reliable diagnostic tool. Treatment consists of multidrug chemotherapy for 18 months, traction, synovectomy, joint debridement, excision arthroplasty, joint replacement and even arthrodesis. Reactivation of tuberculosis can occur after years or decades in up to 30%. In children the outcome is relatively good (90% in normal type). Initial joint space narrowing of less than 3mm hints at a poor outcome.²⁷

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5. Differential diagnosis of diseases not related to the hip joint 

Many disorders originating from the intra-abdominal region, the lumbar spine or even the knee may produce a ‘hip’ pain. If the above mentioned hip-related diseases are excluded in the differential diagnosis, diseases originating from the intra-abdominal region have to be considered. Intra-obdominal disorders causing ‘hip’ pain are listed below:

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6. Diagnostic algorithm 

Each age has its specific and typical hip problems and diseases (Figure 1), so that the first step in the diagnostic algorithm is dividing patients according to age. The next step is to exclude emergency cases—fracture and septic arthritis and severe diseases such as malignant tumours.

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• Figure 1. 

  Age related distribution of common causes of hip pain.

Medical history and the type of pain are the most important features to direct future diagnostic tools. Clinical examination has primarily to discriminate between articular involvement and referred pain, especially pain originating from sciatica. In our hands, ultrasound is an easy and fast non-invasive tool for detecting effusion in the joint, bursitis or tendon lesions. Standard X-rays are important for detecting changes in bone and hip joint. Laboratory tests are necessary for excluding septic or rheumatoid inflammatory joint disease. MRI seems to be the most important tool for diagnosing the remaining diseases, which are not apparently obvious up to this point in the diagnostic process.

If a child has pain in the groin region, thigh or knee region, with limping or refusing to walk, the typical diseases for this age have to be checked. The medical history of an infection of the respiratory tract may be the cause of ATS. Clinical examination has to exclude neurological signs of peripheral nerves or lumbar nerve roots and to detect joint-related pathology such as a limited range of motion, fixed external rotation contracture (slipped epiphysis) or very painful internal rotation (fracture, septic arthritis). Ultrasound gives information about the amount of effusion in the affected joint. Experienced examiners can also find hints for Perthes' disease (femoral head necrosis or slipped epiphysis). X-rays in a.p. and frog-leg lateral view of both hips exclude fractures, bone tumours, osteomyelitis or other severe developmental deformities. Laboratory tests are essential for excluding inflammatory systemic diseases. Fever is a sign of septic arthritis leading to aspiration of joint fluid in joints with effusion. If all other possible diseases are excluded the diagnosis of ATS can be made by exclusion.

If an adolescent has pain in the groin region, thigh or knee region, first of all clinical examination has to make sure that the pathology really originates from the hip joint and is not a referred pain from the lumbar spine (dorsal hip pain, lateral hip pain going down to the dorsal lateral thigh, knee or toes) or from knee-joint pathology. Signs of hip-joint pathology are groin pain and pain at passive movement of the hip, especially in flexion and internal rotation. Fever and severe pain at passive motion is a warning sign for infectious disease or septic arthritis. Ultrasound is an easy diagnostic tool, which gives information about the pathology of the surrounding soft tissues (bursitis, tendonitis) and is the tool of choice for diagnosing effusion in the joint. X-rays are important for further diagnosis to exclude fractures and developmental disorders of the joint. In sport-active adolescents avulsion fractures (insertion of rectus, gracilis and adductor muscles) around the hip joint have to be excluded by X-rays. Laboratory tests are performed only if these diagnostic tools have not led to a certain diagnosis; they have to exclude acute or chronic inflammatory diseases.

In adults and elderly people, acute pain after trauma usually reflects fracture of the femur or parts of the pelvis; chronic hip pain is very often caused by osteoarthritis or rheumatoid arthritis. Primary bone tumours (especially chondrosarcoma), metastatic bone disease or bone involvement in systemic diseases such as multiple myeloma have to be excluded.

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7. Summary 

Hip pain is a common disorder in all ages. First of all, in looking for the underlying cause of the pain it is important to find out whether there is a real emergency problem—such as fracture, avulsion fracture, acute slipping of the femoral epiphysis or septic arthritis. In the next step, severe and significant diseases—such as malignant tumours—have to be considered and excluded.

One can now look for the typical non-emergency problems. There are typical age-related disorders of the hip joint. In children ATS is most often the cause of pain. Avascular necrosis (Perthes' disease) of the femoral head and slipping of the epiphysis of the femoral head are the next typical and common problems. In adolescents avulsion fractures of the major muscle group, originating in the pelvis, are common. Sport-active patients frequently suffer from sprains of the major tendons or from bursitis at typical locations. In the young adult avascular necrosis of the femoral head is commonly due to a range of different diseases. Labral tears are now more often diagnosed as early signs of detoriation of developmental hip dysplasia. Osteoarthritis and rheumatoid arthritis are common in later ages. Diseases of the lumbar spine and lower abdomen may also cause referred pain in the hip region. Clinical examination, standard laboratory tests, ultrasound examination and standard X-rays are easy and inexpensive tools for finding out the majority of hip-related problems. MRI has become the important ‘golden tool’ for detecting intraosseous vascular disorders and soft-tissue lesions.Box 1Box 2

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