Femoral Head Osteonecrosis in Military Training Recruits: A Report of Two Cases

Transcription

1 MILITARY MEDICINE, 174, 11:1231, 2009 Femoral Head Osteonecrosis in Military Training Recruits: A Report of Two Cases Capt Susan M. Eckert, USAF MC * ; Maj Meredith Warner, USAF MC ; Lt Col James A. Keeney, USAF MC INTRODUCTION Osteonecrosis of the femoral head has been well described as a source of hip pain among young and middle-aged adults. While the most common etiologies include medical corticosteroid use, alcohol consumption, and major hip trauma, a variety of factors may contribute to a transient or extended period of decreased blood flow into the femoral head and the resulting clinical and radiographic findings. 1,2 (Table I ) When endurance athletes and military training recruits present for the evaluation of groin pain, common diagnostic considerations include stress reaction, stress fracture, labral pathology, and extra-articular tendonopathies. While osteonecrosis is a potential etiology, it is encountered with significant infrequency in this patient population. Existing literature has not reported a significant association of femoral head osteonecrosis among either endurance training athletes or military recruits.3 6 A recent report classified these injuries as subchondral fatigue fractures. 7 In this report, we present two female patients presenting with a bone marrow edema syndrome and a variable clinical course, with one patient progressing rapidly to femoral head collapse. CASE REPORT Case 1 A 20-year-old female with no prior medical illnesses, family history of sickle cell disease or thalassemia, or prior injury entered basic military training (BMT) in April She had participated in limited high-impact activity and physical conditioning before her entry to BMT. Four weeks into training, she developed right foot and groin pain after a long march. She was seen in the emergency room where plain radiographs ( Fig. 1 ) demonstrated no appreciable abnormality of either the hip or foot. A technecium bone scan was performed and demonstrated diffuse radiopharmaceutical uptake in the right femoral head. ( Fig. 2 ) She was placed on weight-bearing restriction, but allowed to bear weight to pain tolerance using crutches. The patient presented 2 weeks later to her primary care physician with persistent right groin and bilateral foot pain. *Office of Medical Education, School of Medicine, SUNY at Buffalo, 3435 Main Street, Rm 40 BEB, Buffalo, NY Department of Orthopedic Surgery, Wilford Hall Medical Center, 2200 Bergquist Drive, Lackland AFB, TX This manuscript was received for review in February The revised manuscript was accepted for publication in July Physical examination demonstrated a full range of motion without pain, normal hip strength, and a normal neurologic and vascular examinations. She remained on weight bearing to tolerance with crutch support, was referred to physical therapy, and was started on a rehabilitation protocol for a femoral neck stress reaction. Two months after the onset of symptoms, the patient noted resolution of her groin pain, but retained a sensation of stiffness in her anterior thigh. Physical examination demonstrated a full range of motion, no pain with axial loading of the hip, and no pain with hip range of motion or provocative testing for hip impingement. Gait, motor strength, and neurologic and vascular examinations were normal. A radiograph taken during this visit suggested the presence of early osteonecrosis ( Fig. 3 ). A magnetic resonance imaging (MRI) study performed 3 weeks later was interpreted to be consistent with a diagnosis of osteonecrosis ( Fig. 4 ). The patient remained on weight-bearing precautions and an orthopedic consultation was requested. Three months after initial symptoms, physical examination during her orthopedic clinic visit was notable for decreased hip flexion (0 100 ) compared with her contralateral hip (0 120 ), pain with hip rotation in both flexion and extension, and an antalgic gait. Hip radiographs demonstrated significant involvement of the femoral head with advanced collapse. ( Fig. 5 ). Case 2 A 19-year-old female without prior medical illnesses, family history of sickle cell disease or thalassemia, or prior injury entered basic military training (BMT) in August She had participated in cross country during high school, but had taken several months off before entering her BMT program. She noted right groin pain approximately 2 weeks into training while performing in a group physical fitness training program. Initial examination demonstrated pain with hip flexion and internal rotation. Sensory and motor examinations of her lower extremities were normal. Initial radiographs of her hips demonstrated no abnormality ( Fig. 6 ). She was placed on restricted activity with crutch support and physical therapy. After 3 weeks, she had persistent hip pain, was referred for orthopedic evaluation, and underwent evaluations with both a bone scan, which demonstrated diffusely increased activity in the femoral head ( Fig. 7 ) and an MRI which demonstrated increased marrow edema signal ( Fig. 8 ). The MRI scan also demonstrated a small focal abnormality attributed to MILITARY MEDICINE, Vol. 174, November

2 TABLE I. Risk Factors for Osteonecrosis Medical Corticosteroid Use Trauma Alcohol Abuse Sickle Cell Anemia Systemic Lupus Erythematosus Coagulopathy Glycogen Storage Diseases Hypercholesterolemia Hyperlipidemia Chronic Pancreatitis Tobacco Use Radiation Treatment Arterial Disorders Idiopathic FIGURE 1. Initial radiograph demonstrating normal right hip appearance. FIGURE 2. Tc-99 radionuclide study demonstrating increased uptake in right femoral head. FIGURE 3. Two months after initial symptoms. Early femoral head changes and mild loss of femoral head sphericity. FIGURE 4. MRI demonstrating femoral head lesion and bone marrow edema (precollapse). either a subchondral stress fracture or early osteonecrosis. She was placed on strict nonweight-bearing activity status with crutches. Her pain level improved but had not fully resolved over the next 3 months and she was unable to complete training. Repeat radiographs ( Fig. 9 ) and MRI ( Figs. 10, 11 ) demonstrated significant resolution of the marrow edema, but a residual area of bone infarction in the anterior femoral head without femoral head collapse. She was seen again 8 months after onset of symptoms with stable conventional radiographs, but with persistent hip pain MILITARY MEDICINE, Vol. 174, November 2009

3 FIGURE 5. FIGURE 6. Osteonecrosis right femoral head with collapse. Initial radiograph demonstrating normal right hip appearance. FIGURE 7. Tc-99 radionuclide study demonstrating increased uptake in right femoral head. FIGURE 8. MRI demonstrating bone marrow edema and small subchondral infarct versus stress fracture. DISCUSSION Groin pain is uncommonly experienced among young adults participating in intense physical or endurance training. When it occurs, it is most frequently attributed to a femoral neck stress fracture or stress reaction. 3 6 In the absence of abnormal findings on conventional radiographs, some military recruits may be allowed to return to activity rather than be placed on an extended period of weight-bearing restriction. In our institution, approximately 600 active duty military servicemen and servicewomen between the age of 17 and 30 are evaluated annually for hip pain. The majority of them are treated by either primary care physicians or physical therapists. Approximately 15% of them (80 patients per year) have refractory hip pain and have been referred for orthopedic surgery consultation. Of the patients referred for orthopedic consultation, only these two patients were identified with radiographic findings, including femoral head sclerosis that would be consistent with osteonecrosis. Song et al. reported a group of five male recruits (seven hips) that were released from military service after being diagnosed with osteonecrosis. The authors subsequently reclassi- MILITARY MEDICINE, Vol. 174, November

4 FIGURE 9. AP radiograph (4 months) demonstrating central sclerosis without collapse. FIGURE 10. MRI (4 months) demonstrating bone marrow edema resolution and small anterosuperior infarct. fied all five patients with a femoral head subchondral fatigue fracture.7 These five patients were placed on weight-bearing restric tion and, although five hips in three patients resolved with restricted activity over a period of 6 months, two hips in the two other patients had presented with early femoral head collapse and required reconstructive surgical procedures that are commonly performed for patients with osteonecrosis. In spite of the early collapse noted in these two patients (40% of patients in their study), Song et al. did not consider these cases FIGURE 11. MRI demonstrating involvement in anterior femoral head. to be consistent with osteonecrosis because the MRI findings did not support a gradual process of creeping substitution into an area of necrotic bone before the development of femoral head collapse or subchondral fracture. 7 The radiographic findings on bone scan and MRI for the two female patients presented in this case report are similar to those observed by Song et al. in their male patients, with early diffuse bone scan activity in the femoral head and diffuse marrow edema in the femoral head and neck on MRI. The plain films for both of these patients, however, suggest the development of bone infarction within the femoral head. Similar to the seven male patients in the report by Song et al., these two female patients demonstrate the potential for a variable clinical course, without a clear distinction for the cause of progression to radiographic collapse or clinical resolution. The patient who remained on partial weight bearing for an extended period of time rapidly developed subchondral collapse. The patient who was placed on early, complete, weightbearing restriction has not had full symptom resolution within 6 months, but also has not demonstrated radiographic progression. While the small number of patients presented does not allow prediction of factors associated with either progression or resolution, early protected weight bearing is strongly advocated in management of these patients. The common finding in each of the cases in this report is the development of a bone marrow edema syndrome in the proximal femur that precedes the development of either femoral head collapse or the development of a subchondral fatigue fracture. Other authors have reported an association of bone marrow edema syndromes with femoral head subchondral insufficiency fractures, osteonecrosis, and transient osteoporosis of the hip. 8 Because patients may present when they have 1234 MILITARY MEDICINE, Vol. 174, November 2009

5 been symptomatic for a significant period of time, distinctions between these three conditions may not be conclusively made on individual radiographic studies at a specific point in time. The clinical resolution of both transient osteoporosis of the hip and subchondral femoral head fatigue fractures may suggest that these are a variant of bone marrow edema syndromes that are reversible, although a small minority of patients may develop an irreversible bone marrow edema syndrome that progresses to femoral head collapse, with a clinical outcome that resembles that of advanced stages of osteonecrosis. While femoral head osteonecrosis typically develops over an extended period as bone necrosis and remodeling precede femoral head collapse, our first case example highlights that rapid clinical progression to collapse can occur in some patients after exposure to high-intensity physical conditioning. Reduction of blood flow into the femoral head has been associated with both external and internal sources. During traumatic hip dislocation, extraosseous interruption of blood flow to the femoral head has been associated with the development of osteonecrosis. 9 High-dose, long-term corticosteroid therapy, associated with oral prednisone doses exceeding 30 mg/day and alcohol consumption greater than 400 ml per week have been associated with an increased risk for osteonecrosis.2,10 Sickle cell disease can also be associated with cases among individuals of African heritage. 11 Recent reports in radiology and orthopedic literature have proposed an association between bone marrow edema syndromes, transient osteoporosis of the hip, and osteonecrosis. 8,12 14 The MRI obtained on both patients, within two months after the start of symptoms, demonstrated significant bone marrow edema in the femoral neck and appears to be consistent with this reported relationship. Presumably, the magnitude and duration of edema within the femoral neck for the first patient contributed to impaired blood flow into the femoral head and contributed to the development of radiographic collapse. A radiographic staging system originally proposed by Ficat15 has been most widely used in guiding surgical intervention for patients with osteonecrosis ( Table II ). The presence of a subchondral fracture, represented by a crescent sign on radiographs, typically precedes radiographic collapse and has been associated with a less predictable response to core decompression.10,16 More substantial involvement of the femoral head has also been associated with an increased risk of collapse and clinical failure. 17,18 Vascularized fibular autograft reconstruction can be effective in slowing progression of the condition for symptomatic patients, but may not be universally durable. 19 Arthroplasty can provide significant early pain relief, but significant concerns persist with respect to longterm outcomes for young active patients. Although alternative bearing surfaces have provided many patients and surgeons with optimism, no long-term studies are available to substantiate arthroplasty as an acceptable approach to management. Because osteonecrosis may become a bilateral process, arthrodesis may be contraindicated for a patient in the absence of a specific traumatic event before the onset of the condition. TABLE II. Modified Ficat Classification for Osteonecrosis of the Femoral Head Modified Ficat Stage Clinical Findings Radiographic Findings Stage 0 Asymptomatic hip X-ray negative, MRI positive Stage I Symptomatic hip X-ray negative, MRI positive Stage IIA Symptomatic hip Negative crescent, no collapse Stage IIB Symptomatic hip Positive crescent, collapse Stage III Symptomatic hip Collapse, no degenerative changes to hip joint Stage IV Symptomatic hip Collapse, degenerative changes to hip joint The time course from an identifiable inciting condition to advanced radiographic femoral head collapse in the first patient highlights the importance of early advanced radiographic assessment for patients involved with either endurance or basic military training who present for the evaluation of groin pain. Evaluation with magnetic resonance imaging may be useful in delineating a variety of conditions that may affect the proximal femur and should be considered early in the assessment of endurance athletes and military recruits with groin pain. 20 A bone scan can also be utilized to evaluate these patients. Isolated involvement in the femoral neck is consistent with a diagnosis of a stress reaction or stress fracture whereas diffuse involvement of the entire femoral head involvement should caution toward the development of a subchondral fatigue fracture or femoral head collapse, whether this is the result of an insufficiency fracture or an osteonecrosis variant. Limitations in surgical options for treatment of the postcollapse hip in young, active patients underscores the importance of identifying the condition early while other treatment options may be entertained with an increased potential for success. REFERENCES 1. 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