A 54-year-old male farmer presented with a 4-week history of left hip pain. He described spontaneous onset of pain involving his left hip and groin. The pain was aggravated by ambulation and had worsened progressively over several weeks. The patient noted particular discomfort with hip flexion when getting on and off his tractor. The pain occasionally radiated anteriorly to the top of his knee. He denied worsening of pain with Valsalva maneuver, radiation of pain distal to the knee, and low back pain. Rest and avoidance of hip flexion briefly reduced the pain. The patient denied preceding trauma and any associated hypesthesia or paresthesia. He was a previous smoker, consumed alcohol occasionally, and had never used corticosteroids. The patient denied systemic signs of illness, weight loss, and nocturnal symptoms. Over-the-counter medications and complete avoidance of activity provided little relief.

1. Which one of the following is the most likely diagnosis based on our patient's history?

a. Malignancy

b. Meralgia paresthetica

c. Avascular necrosis of the hip (AVN)

d. Polymyalgia rheumatica

e. L4-5 radiculopathy

Malignancy is unlikely without associated systemic signs and symptoms, weight loss, or night pain. Meralgia paresthetica, a localized area of pain described as a burning or an uncomfortable heightened sensation, is not influenced by direct pressure, hip movement, or lower back movement, which differs from the presentation in our patient. Avascular necrosis of the hip has been known by many terms including aseptic necrosis and osteonecrosis. Various factors leading to AVN have been identified, including corticosteroids and alcohol. Of the choices provided, AVN is the most likely diagnosis. Polymyalgia rheumatica is a common disorder that occurs often in persons older than 50 years. Classically, it presents with subacute onset of symmetrical aching and morning stiffness involving the shoulders, hip girdles, neck, and torso, symptoms inconsistent with those of our patient. Lumbar radiculopathy most commonly involves the L4-5 nerve roots and causes lateral hip pain that radiates down the leg and into the foot, with or without associated foot numbness. Our patient denies worsening of pain with Valsalva maneuver, paresthesias, or radiation of pain distal to the knee; thus, lumbar radiculopathy is an unlikely cause of his symptoms.

Physical examination revealed normal vital signs. The patient had an antalgic gait without focal tenderness over the lateral hip or groin. There was no discrepancy in leg length. The patient had full range of motion of his hips and knees, although abduction and adduction of the left hip reproduced the pain. The pain was most marked with flexing, abducting, and externally rotating the patient's leg such that the ankle of that leg was on top of the opposite knee (fabere or Patrick test). Straight leg raise did not reproduce his pain or cause radicular symptoms. The patient had no spinal tenderness or scoliosis. Neurologic evaluation revealed only give-way weakness of the left hip secondary to pain. Findings on the rest of the examination were unremarkable.

2. Which one of the following is the next best step in the treatment of our patient?

a. Local injection for presumed trochanteric bursitis

b. Plain radiography of the lumbar spine, hip, and pelvis

c. Reassurance with no further testing

d. Bed rest for 1 week followed by physical therapy and strength training

e. Testing to determine serum protein electrophoresis, erythrocyte sedimentation rate, prostate-specific antigen level, and complete blood cell count

Inflammation of the trochanteric bursa, one of the most common causes of hip pain, results from exaggerated movements of the gluteus médius tendon and the tensor fascia over the femur. Patients typically experience lateral hip and thigh pain that worsens with ambulation or direct pressure over the area. Our patient's symptoms do not correlate with trochanteric bursitis. Plain radiography, the correct choice, should be considered for all patients with both acute and chronic hip pain to exclude fracture and to provide information regarding arthritis or lytic lesions of the femur. Reassurance, bed rest, physical therapy, and further laboratory testing may be appropriate, but only after obtaining radiographs.

Plain radiographs of the lumbar spine, hips, and pelvis revealed mild osteopenia of the femoral neck and head. Results of laboratory studies including serum protein electrophoresis were normal. Initially, our patient was treated conservatively, with limited weight bearing and nonsteroidal anti-inflammatory drugs (NSAIDs). Despite these measures, 3 weeks later he continued to have pain that limited his ability to complete his harvest.

3. Which one of the following is the most appropriate step at this time in our patient's evaluation?

a. Continued conservative treatment and initiation of physical therapy

b. Radionuclide bone scanning

c. Magnetic resonance imaging (MRI) of the hip

d. Ultrasonography of the hip with needle aspiration if effusion is present

e. Referral to an orthopedic surgeon for hip replacement

Our patient's pain has not responded to conservative measures for more than 8 weeks. The persistence of symptoms warrants further evaluation. Therefore, continued conservative treatment alone is incorrect. Radionuclide bone scanning usually is reserved for suspected pathology not revealed by plain radiography when MRI is not available.

Magnetic resonance imaging is the radiographie study of choice for evaluation of hip joint pathology.' Besides allowing early diagnosis and staging of osteonecrosis,MRI enables the clinician to evaluate for potential infection, tumor, and pathology within the surrounding tissue. Immediate arthrocentesis is reserved usually for acute and severe hip pain in patients with findings suggestive of infection. An imaging technique such as ultrasonography for assistance with aspiration is advised. However, our patient's case does not warrant aspiration, and given the available information, there is no indication for surgical intervention.

Magnetic resonance imaging of our patient's hip with and without gadolinium revealed diffusely increased T2 signal with partial loss of T1 signal involving the femoral neck and head. There was moderate soft tissue edema in the adjacent fat, vastus intermedius muscle, and adductor muscle, with little effusion. Our patient returned to see his physician the following day.

4. Based on MRI findings, which one of the following is the most likely diagnosis?

a. AVN

b. Bone marrow edema syndrome (BMES)'/'transient osteoporosis of the hip

c. Ewing sarcoma

d. Osteoid osteoma

e. Adductor tendinitis

Findings that suggest AVN/osteonecrosis include the pathognomonic double line or crescent sign (subchondral radiolucency), which represents evidence of subchondral collapse.2 Such findings may be seen on plain radiographs or T2-weighted coronal MRI and represent a high-intensity rim within a low-intensity margin surrounding necrotic tissue.3 In our patient, these findings were not seen on MRI. Our patient's findings of increased T2-weighted signal with corresponding decreased signal intensity on Tlweighted images are characteristic of BMES and are present early in the disease course.4 6 Therefore, BMES is the most likely diagnosis. Ewing sarcoma affects the long bones of the extremities, usually the femur and the pelvis. Patients typically experience localized pain or swelling for a few weeks or months and worsening nocturnal pain. Radiographically, the tumor is described as having a "moth-eaten" appearance. The classic finding of Codman triangle (expansion of the cortex with a displaced periosteum from the underlying tumor) was absent in our patient. Osteoid osteomas are benign bone-forming tumors that characteristically produce nocturnal bone pain relieved by aspirin. This is unique among bone tumors and absent in our patient. Tenderness over the involved tendon and pain with resisted adduction of the lower extremity are characteristic of adductor tendinitis and may reproduce the medial thigh and groin pain of hip disease. However, this disease does not explain the changes of the femoral head seen in our patient on MRI.

Our patient's hip pain decreased with continued conservative treatment with NSAIDs and limited weight bearing, and repeated MRI 10 weeks later revealed improvement of the edema. The patient returned to his physician 5 months later with similar pain in his left knee. Because of his history, MRI of the knee was performed, which revealed patchy edema in the distal femur, in the lateral and medial femoral condyle, and in the proximal tibia on T2-weighted imaging with fat saturation.

5. Based on these new findings, which one of the following is the most likely diagnosis?

a. Osteoarthritis

b. Regional migratory osteoporosis

c. Osteosarcoma

d. Occult knee fracture

e. Pseudogout

Our patient's MRI findings are not consistent with osteoarthritis and suggest this process is similar to the one identified in his hip. When bone marrow edema involves more than one joint or moves from one joint to another, it is referred to as regional migratory osteoporosis, which is a migrating arthralgia of the weight-bearing joints of the lower limbs. This is the most likely diagnosis, based on the new findings. Osteosarcomas are uncommon primary malignant tumors of bone and occur primarily in children and adolescents. In our patient, there was no radiographic evidence of osteosarcoma.

Although MRI is the study of choice for occult knee fracture not identified on plain radiography, in our patient MRI indicated no discrete area of fracture. Furthermore, he had no findings consistent with pseudogout.

After 4 additional months of taking NSAIDs, our patient's limited weight-bearing activity slowly advanced through physical therapy, and he had complete resolution of all symptoms. Our patient is now pain free and has no residual sequelae.

DISCUSSION

Hip pain is extremely common in adults. Of those older than 60 years, 14% have reported substantial hip pain on most days.7 There are numerous etiologies for hip pain, and we describe a potential diagnosis that may be overlooked.

Curtiss and Kincaid8 first described transient osteoporosis in 1959 after finding an association between hip pain in the third trimester of pregnancy and radiographic bone demineralization. Since this original description, the syndrome has been referred to by several different terms. Transient osteoporosis of the hip is the term credited to Lequesne from his 1968 report.9 Although this condition is seen classically in the third trimester of pregnancy, men in their fourth through seventh decades of life account for more than 60% of reported cases.9-12 The term bone marrow edema syndrome was introduced to replace transient osteoporosis of the hip and is based on characteristic MRI findings.4,5,13,14 The joints of the lower extremities are affected much more frequently than the upper extremities, and symptoms occur most often in the hip followed by the knee, the foot, and the ankle.10 Bone marrow edema syndrome may affect the hip or knee as the single joint involved.4,5,11,13,16 Regional migratory osteoporosis (or migratory BMES17) was described first in 1967 as a migratory osteolysis, and its etiology remains unknown.18 It is characterized as a migrating arthralgia of the weight-bearing joints of the lower extremities associated with a focal osteoporosis. The migration occurs from one articulation to another and is the feature that separates regional migratory osteoporosis from BMES involving the hip or knee alone.10,19-21

In BMES, patients present with progressive, ill-defined unilateral hip pain, usually described as a deep ache localizing to the medial or anterior thigh without radiation below the knee. Symptoms present acutely without inciting trauma and often render patients unable to ambulate without assistance. Pain worsens primarily with activity, whereas pain on resting, back pain, and neurologic dysfunction are not characteristic of BMES and suggest an alternative diagnosis.

Physical examination findings of hip involvement most commonly include guarding during hip range of motion, especially with abduction or rotation of the hip, and an antalgic gait. Tenderness over the greater trochanter and adjacent adductor and hip flexor muscle groups may be present. Provocative tests with a fabere/Patrick test, resisted straight-leg raise, or hip joint compression or rotation loads may reproduce the pain. Results of spine and knee examinations and neurologic examination will be normal.6

Laboratory tests generally do not help with the diagnosis. Plain radiographic findings obtained during the first 2 to 4 weeks of symptoms are usually normal. After 4 to 8 weeks of pain, osteopenia may be evident with a preserved joint space and no osseous erosion or subchondral collapse.5 After this point, various degrees of cortical thinning and osteopenia around the intertrochanteric region and femoral head and neck have been described. This is in contrast to AVN, in which sclerosis progresses to articular surface flattening and eventual subchondral collapse.22

Computed tomograms of BMES provide findings similar to those on plain radiographs.11 Radionuclide bone scans are often positive within the first week of symptoms, revealing homogenously increased uptake of the area involved.11,12 Magnetic resonance imaging is the modality of choice to exclude alternative diagnoses while revealing characteristic findings of bone marrow edema as early as 48 hours after onset of pain.13,23,24 Bone marrow edema identified with use of MRI is 100% sensitive but not specific for BMES,13,25 which is identified best by a coronal plane section with increased T2-weighted signal with a corresponding low signal or decreased signal intensity on T1-weighted images.4,5 Use of gadolinium will result in marked enhancement without focal changes.26 Also, edema seen with BMES usually is more extensive than that seen with AVN.5 The bone cortex may appear thinned but intact. Unlike in AVN, there should be no evidence of subchondral defects.

Avascular necrosis of the hip is a progressive condition resulting from an interruption of the vascular supply to the femoral head. The early features of transient osteoporosis/ BMES may be confused with AVN,3 which has fueled debate about whether BMES and AVN of the femoral head represent the same disease at different ends of a spectrum13 or separate diseases.10,12 Clinically, this distinction is critical because each diagnosis has substantially different prognostic features, and incorrect diagnosis may lead to unnecessary surgical referral and potential intervention.

Most reports suggest that BMES is a self-limited disease. The natural history of this entity is that of a symptom plateau followed by a gradual resolution of symptoms over 3 to 9 months. Migratory recurrence of symptoms occurs usually within the first 2 years after pain relief.10 Treatment includes supportive care, with initiation of pain management and physical therapy with use of protected weight bearing. Usually, NSAIDs ameliorate the symptoms sufficiently; however, opioids may be necessary during the acute setting. Physical therapy to provide gait retraining and protected weight-bearing techniques allow for easier pain control and increased function. As symptoms allow, a low-impact strengthening routine should be used, aimed at flexibility and increased range of motion to prevent deconditioning. The most feared complications are insufficiency and subcapital fractures of the femoral neck, which require orthopedic evaluation. For this reason, protected weight bearing is essential.

One case report suggested that alendronate may provide significant pain relief and improve ambulatory function in patients with BMES.27 Much like with the etiology of BMES, cautious observation vs intervention as treatment of BMES is controversial. Authors have suggested that surgical core decompression may be used in BMES, especially in patients with refractory pain despite use of conservative measures."

Bone marrow edema syndrome is an often-overlooked etiology for acute hip pain both in pregnant women and in middle-aged men. Conservative treatment is usually sufficient, but patients may require surgical intervention or alendronate for symptomatic relief. Correct identification of features consistent with BMES rather than AVN is critical to avoid unnecessary interventions or delays in therapy in patients with AVN. Bone marrow edema syndrome should be considered in the differential diagnosis of middle-aged men and young women with hip pain.

Correct answers: 1. c, 2. b, 3. c, 4. b, 5.b