The patient who complains of joint pain is a common presentation, with a very broad differential diagnosis. A structured approach is essential to narrow down the list of possibilities.
The first step in the evaluation is to determine the exact joints involved. This shows that the pain is localized to the large joints of the right lower limb.
However, examination of the right knee shows no evidence of inflammation or swelling, and all active and passive movements are unrestricted – findings that make knee joint pathology highly unlikely. This is not necessarily a surprise: pain in the hip is often referred to the knee – and at times even be perceived as only involving the knee.
Examination of the right hip joint confirms the presence of restriction of movements, indicating that this is indeed where the pathology lies. This is further supported by the coxalgic gait, which shifts the patient's center of gravity in such a manner that the forces acting upon the hip joint are reduce
Following identification of the joints involved, the next step should be close assessment of the specific characteristics of the pain, including the location, onset, and duration.
The pain is localized to the anterior hip. This is classically associated with intraarticular pathology. Key etiologies to consider include fractures of the proximal femur, iliopsoas bursitis, tendinitis of the hip flexors, acetabular labral tears, osteoarthritis, osteonecrosis (avascular necrosis), inflammatory arthritis, septic arthritis, and tuberculous arthritis.
The pain was insidious in onset and has persisted for an extended period of time. This argues against septic arthritis, where symptoms are typically florid and rapid in onset. The lack of recent trauma argues against a fracture, although stress fractures cannot be ruled out. Iliopsoas bursitis, hip flexor tendinitis, and hip labral tears are mainly encountered in athletes, as a consequence of overuse or sports injury. Inflammatory arthritis is clinically less likely, as there is no pain at rest or relief or reduction of pain with activity. Neither is tuberculous arthritis likely, as there is no history of immunocompromise, or a contact history with tuberculosis.
Osteoarthritis is a possibility, although it is somewhat less common in patients <40 years of age. This could either be primary or secondary to another disease process. In particular, when considering secondary osteoarthritis in a patient of this age, the possibility of old Legg-Calve-Perthes' disease should be kept in mind. This often causes transient symptoms during childhood, which the patient may not recall unless explicitly prompted.
Osteonecrosis is an even stronger possibility. In particular, alcoholism is a major risk factor for the condition.
The next step in his workup should be targeted investigations, starting with plain radiographs showing an anteroposterior view of the pelvis and a frog-leg lateral view of the symptomatic hip. It is probably also prudent to obtain x-rays of the right knee as well. These reveal sclerotic and lytic lesions of the right femoral head, along with partial subchondral collapse and narrowing of the joint space – imaging findings highly suggestive of osteonecrosis of the femoral head.
Follow up magnetic resonance imaging (MRI) confirms these findings. Note also that this indicates stage V osteonecrosis, as per the Steinberg classification (i.e., early collapse of the femoral head).
Once femoral head collapse has taken place, total hip arthroplasty (THA) is the preferred management technique. Core decompression is mainly useful in early disease (i.e., before collapse has occurred). Glucocorticoid therapy is a risk factor for osteonecrosis and is contraindicated here. Neither is there any indication for antibiotic therapy.
Osteonecrosis (also known as avascular necrosis) is defined as the death of bone cells and bone marrow secondary to the loss of blood supply. It is most common between the 3rd of 5th decades of life, with a male preponderance. In the United States, 10,000-20,000 cases are reported annually. Overall, osteonecrosis accounts for 5-12% of all total hip replacements performed each year.
Osteonecrosis can be associated with traumatic or non-traumatic insults to the femoral head blood supply. Traumatic insults include displaced fractures and dislocations of the hip. The two most common atraumatic insults are corticosteroid therapy and heavy alcohol consumption.
The pathophysiology of alcohol-induced osteonecrosis is not fully understood. Potential mechanisms include increased accumulation of lipids inside the osteocytes of the femoral head resulting in compression of their nuclei; and/or a direct toxic effect of alcohol on osteocytes causing chronic cellular lesions that are unable to heal. The ultimate outcomes are cell death and eventual collapse of the femoral head. The mechanism of steroid induced osteonecrosis is also believed to be due to changes in lipid metabolism within the femoral head.
Note also that connective tissue disorders, vascular disorders, vasculitis, and orthopedic conditions such as developmental dysplasia of the hip, congenital hip dislocation, hereditary dysostosis, Legg-Calve-Perthes' disease, and slipped capital femoral epiphysis may also cause osteonecrosis. Up to 10-20% of cases have no identifiable cause and are classified as idiopathic.
Osteonecrosis can present with many different clinical manifestations; and in some cases, may be clinically silent. The chief presenting complaint is pain, often localized to the anterior hip or groin, and occasionally to the ipsilateral buttock or knee.
Physical examination typically reveals pain with both active and passive motion of the affected hip, and a coxalgic gait. Pain with internal rotation, clicking of the hip, and a reduced range of motion are signs that the femoral head has collapsed. A complete evaluation of the contralateral hip should always be undertaken, as 40-80% of cases are bilateral.
Anteroposterior and lateral ("frog-view") hip x-rays are important first-line investigations. However, as bone remodeling is relatively slow, there may be no x-ray changes in early disease. Magnetic resonance imaging (MRI) is the current gold standard, with a sensitivity and specificity of 99%; it can detect changes as early as 5 days after the initial insult. Bone scans may also detect early remodeling, but can be misleading, with a 25% to 45% false negative rate.
Over 16 major classification systems are used to stage osteonecrosis. These include the Ficat classification, which uses x-ray appearances; and the Steinberg system that additionally uses information from MRIs and bone scans.
Treatment options for osteonecrosis include medical and physical measures and operative techniques. In general, in early disease, prophylactic measures are instituted to prevent further progression, while in the latter stages, a reconstructive procedure is the treatment of choice.
Physical treatment options include the use of raised shoes, walking aids, the avoidance of squatting positions and preferable adoption of a sitting position. Medical options include bisphosphonates to reduce osteoclast activity, lipid-lowering drugs to correct altered lipid metabolism, and vasodilators to reduce intraosseous pressure. Novel techniques that are being evaluated include extracorporeal shock wave therapy, pulsed electromagnetic therapy, and administration of hyperbaric oxygen.
The surgical management of osteonecrosis can be divided into head-preserving procedures and arthroplasty.
Patients who are pre-collapse are generally treated with head-preserving procedures; these include core decompression and limited femoral resurfacing. Core decompression involves drilling a single large hole in the femoral head. This reduces the intraosseous pressure in the femoral head and promotes new bone formation and angiogenesis. Limited femoral resurfacing can be used in late to mid collapse to salvage the femoral head provided there is no acetabular involvement. In younger patients, the above techniques have several potential advantages, including preservation of femoral bone stock, low dislocation rates, simplicity of revision, and deferral of total hip arthroplasty.
In patients who have experienced collapse of the femoral head or osteoarthritis, arthroplasty is preferred. Total hip arthroplasty (THA) is the single treatment with the highest likelihood of providing excellent early pain relief and good functional outcome. However, it sacrifices more host bone and narrows future operative options. Relative contraindications to the procedure include the younger patient in whom head preserving options may be more appropriate, and individuals who may be at risk of recurrent dislocation, such as alcoholics.
Note also that in all patients, modifiable risk factors such as alcohol abuse should be assessed and treated as appropriate.