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[Case Report]

Progressive Knee Pain in a Young Football Player

Scott A. Paluska, MD; Douglas B. McKeag, MD, MS

American Medical Society for Sports Medicine Case Report Series

THE PHYSICIAN AND SPORTSMEDICINE - VOL 28 - NO. 2 - FEBRUARY 2021


In Brief: An 11-year-old male football player had a 3-month history of persistent right thigh pain. He had continued to play regularly despite intermittent pain and cramping, but symptoms had worsened significantly and he had lately had occasional flulike symptoms and mild fever. X-rays and an ultrasound vascular study were normal, but an MRI revealed a possible femoral sarcoma. A biopsy demonstrated osteomyelitis of the right femur with an adjacent abscess. After a course of parenteral antibiotics, he recovered fully and returned to competitive football. Osteomyelitis in adolescents can lead to a variety of nonspecific symptoms, and heightened awareness is important for accurate diagnosis and treatment.

Osteomyelitis is a relatively rare but significant disorder in children and adolescents. Before antibiotics became widely available, osteomyelitis had a high mortality rate (1). Unrecognized osteomyelitis may produce extensive morbidity, bone destruction, and growth disturbances (2). Clinical recognition can be challenging in younger patients, because the classic symptoms of chills, fever, pain, and swelling may be absent (3).

Several tests and studies are currently available to help guide diagnosis and treatment of osteomyelitis (4). Significant delays or errors in diagnosis may occur because osteomyelitis may mimic malignant bone tumors or soft-tissue infections (5). As demonstrated in the following case report, a thorough diagnostic work-up is essential to identify osteomyelitis correctly and treat it before physeal damage or limb deformity occurs.

Case Report

An 11-year-old boy presented with persistent right distal thigh pain. He remembered having felt a "pull" in the back of his right thigh 3 months earlier while practicing football. He denied trauma or swelling and had treated his discomfort conservatively without seeking medical care. He had played football regularly for 2 months but experienced intermittent pain and cramping. He also had several brief, low-grade fevers that resolved spontaneously.

Five days before evaluation, he felt a "pop" followed by immediate pain, warmth, and swelling in the back (posteromedial) of his thigh while running. Pain caused him to discontinue football and see his regular physician. Despite the rest and analgesia that his physician had prescribed for a presumed distal hamstring strain, the boy had rapidly intensifying discomfort, increased swelling, night pain, and an inability to ambulate. In addition, he began to have persistent fevers of 102° to 104°F (38.8° to 40° C).

His medical history was significant only for uncomplicated Kawasaki syndrome at age 5; he was otherwise healthy, and immunizations were current.

Physical examination. On initial examination, oral temperature was 101° F (38.3° C) and pulse was 95 per minute. He had regional warmth and substantial tenderness overlying the distal medial right hamstring that was associated with soft-tissue swelling. No knee effusion was present, and the anterior aspect of the knee was normal. Active and passive knee ranges of motion (ROM) were limited by pain to 20° to 90° of flexion. Strength testing was not done because of patient discomfort. Lachman's and anterior and posterior drawer tests were normal, and no varus or valgus laxity was observed.

The right thigh circumference was 1 cm larger than the left. Hip ROM was normal and pain free bilaterally, but tender inguinal lymphadenopathy was present on the affected side. Femoral and popliteal pulses were normal. A new grade 2/6 systolic ejection murmur was noted over the left upper sternal border. His physical development was Tanner stage 2, and the remainder of the examination was normal.

Tests. The patient was admitted to the hospital, and plain radiographs of his right knee (figures 1a, 1b) were interpreted as normal. Radiographs of the right femur were not obtained at that time. Ultrasound examination of his lower extremities (figure 1c: not shown) revealed normal venous and arterial flow patterns with no evidence of abnormal fluid collections or cysts. Initial blood tests demonstrated a white cell count of 13,700/mm3 with a left shift, an erythrocyte sedimentation rate (ESR) of 1 mm/hr, and a hematocrit of 37.5%. Urinalysis and antinuclear antibody titer were normal. Blood cultures were negative for any bacterial growth.

[Figure 1]

A two-dimensional echocardiogram, ordered to evaluate the new cardiac murmur, revealed normal chambers, valves, and function. A whole-body technetium Tc 99m bone scan demonstrated increased uptake in the right femur on perfusion and blood pool images but minimally increased uptake on the delayed image.

Repeat blood tests revealed an increased white cell count of 16,000/mm3 with a left shift, an ESR of 95 mm/hr, and a C-reactive protein (CRP) of 39.6 mg/L. The patient's temperature remained elevated, and empiric antibiotics were begun.

A magnetic resonance imaging (MRI) scan with contrast of the right lower extremity was performed and showed an abnormal marrow pattern that extended from the mid-to-distal diaphysis to the epiphyseal plate (figure 2). Associated inflammatory changes in the adjacent muscles and femoral cortical thickening were also noted.

[Figure 2]

After pediatric orthopedic and oncology consultations, surgical exploration of the distal right thigh with possible above-the-knee amputation was scheduled. The patient and his family were informed that osteogenic sarcoma remained part of the differetial diagnosis based on the combined interpretations and clinical symptoms.

Treatment. Intraoperative biopsy revealed femoral osteomyelitis with an adjacent abscess. Staphylococcal species were cultured from the abscess, but no source was identified. The patient received 6 weeks of parenteral antibiotics and had no complications. Pain and fevers resolved within 1 week, and physical therapy was begun. He regained full strength and ROM of the affected extremity within 4 months. Follow-up femoral radiographs demonstrated open growth plates and healing of the affected femur. Leg lengths remained equal, but the right thigh had a circumference that was persistently 3 cm greater than the left. He successfully returned to athletics 5 months post-operatively and resumed full football participation 8 months following surgery. Examination 1 year after initial presentation revealed full recovery of function with no new findings; the difference in thigh circumference remained 3 cm.

Discussion

Osteomyelitis in children and adolescents most commonly occurs in the distal metaphysis of long bones such as the femur or tibia (2). It is usually caused by hematogenous seeding of bacteria that localize in the slow, turbulent blood flow present in the developing metaphysis (5). In most cases, a single bacterial organism (usually Staphylococcus aureus) is implicated (6). Other, less common causative organisms include group A beta-hemolytic streptococci and Haemophilus influenzae (7).

Laboratory tests. Diagnosis of suspected osteomyelitis often begins with laboratory tests; common findings may include elevated white blood cell counts and increased ESRs (8). Some physicians suggest measuring CRP levels in addition to an ESR and white blood cell counts to aid early diagnosis (1). However, laboratory studies in children who have bone or joint infections may be misleading because the tests may be normal with the disease present (high false-negative rate). Laboratory results should be considered in light of the clinical picture and additional tests (7).

Radiography. Several radiographic modalities have been recommended for diagnosing suspected osteomyelitis. In almost all instances, plain radiographs should be the initial imaging study of choice (4). X-rays have the advantage of being convenient, inexpensive, and reproducible. Early findings may be subtle, and noticeable bony changes may not be evident before 7 to 10 days after acute infection (3). In addition, 30% to 50% of bone mineral must be lost before plain x-rays reveal osteomyelitic changes (5).

Scintigraphy with triple-phase Tc 99m methylene diphosphonate (MDP) is a useful adjunct for early identification of osteomyelitis. The advantages of the technique include allowing visualization of the entire skeleton and having a high sensitivity (84% to 100%) and specificity (70% to 96%) (4). The bone scan is typically positive for all three phases in acute osteomyelitis, while septic arthritis or cellulitis usually has a normal third (delayed) phase uptake (3). Ultrasound may also help identify soft-tissue abnormalities, periosteal elevation, or an abscess, but the technique's utility depends on the operator's experience. Ultrasonography is not useful for evaluation of intraosseous abnormalities, however (5).

MRI is commonly used in cases of suspected osteomyelitis because the technique has excellent sensitivity (88% to 100%) and specificity (75% to 100%) (9). MRI allows one to establish clearly the extent and location of the infection with good visualization of bone structures and delineation of soft tissues (3). Typically, osteomyelitis produces low signal intensity on T1-weighted images and increased signal intensity with T2-weighting (6). Some physicians state that contrast enhancement with gadolinium may improve detection of early osteomyelitis, but the utility of the technique is debatable (9).

Computed axial tomography (CT) is occasionally used to diagnose osteomyelitis, especially when assessing the integrity of bone (6). CT is useful for preoperative planning because it can detect osseous abnormalities, foreign bodies, or necrotic debris; the technique has excellent spatial resolution (5).

Treatment. Prompt recognition and aggressive treatment of osteomyelitis is essential to improve long-term prognosis (8). Cultures of blood and infected tissue should be obtained, and antibiotic therapy should be started immediately (7). Most cases of acute osteomyelitis respond well to antibiotic treatment and do not require surgery (1). After several days of treatment with parenteral antibiotics, most patients who have childhood hematogenous osteomyelitis can be treated with oral antibiotics for the duration of the 4- to 6-week course (2).

Patients who do not respond within 36 to 48 hours of appropriate parenteral antibiotics merit additional investigation (1). These patients may have isolated necrotic bone surrounded by granulation tissue (bony sequestrum) or a central, subcortical, or cortical bone abscess (Brodie's abscess) that necessitates surgical exploration and debridement (9). Inadequate or delayed therapy may also result in a generally poor outcome (1). Potential complications include prolonged fever, persistent pain, limited ROM, chronic osteomyelitis, pathologic fractures, extremity-length discrepancy, and need for amputation (2,5,8).

With appropriate recognition and treatment, however, most individuals have excellent prognoses and outcomes (6). After recovery, most children and adolescents can return to competitive activities without significant disability.

References

  1. Wall EJ: Childhood osteomyelitis and septic arthritis. Curr Opin Pediatr 192021;10(1):73-76
  2. Lew DP, Waldvogel FA: Osteomyelitis. N Engl J Med 1997;336(14):999-1007
  3. Abernethy LJ, Carty H: Modern approach to the diagnosis of osteomyelitis in children. Br J Hosp Med 1997;58(9):464-468
  4. Jaramillo D, Treves ST, Kasser JR, et al: Osteomyelitis and septic arthritis in children: appropriate use of imaging to guide treatment. Am J Roentgenol 1995;165(2):399-403
  5. Boutin RD, Brossmann J, Sartoris DJ, et al: Update on imaging of orthopedic infections. Orthop Clin North Am 192021;29(1):41-66
  6. Mader JT, Ortiz M, Calhoun JH: Update on the diagnosis and management of osteomyelitis. Clin Podiatr Med Surg 1996;13(4):701-724
  7. Matan AJ, Smith JT: Pediatric septic arthritis. Orthopedics 1997;20(7):630-635
  8. Longjohn DB, Zionts LE, Stott NS: Acute hematogenous osteomyelitis of the epiphysis. Clin Orthop 1995;316:227-234
  9. Gylys-Morin VM: MR imaging of pediatric musculoskeletal inflammatory and infectious disorders. Magn Reson Imaging Clin North Am 192021;6(3):537-559

Dr Paluska is a member of the Rex Sports Medicine Institute in Raleigh, North Carolina. Dr McKeag is professor and chair of the department of family medicine at Indiana University School of Medicine in Indianapolis. This series of case reports from the American Medical Society for Sports Medicine is edited by Kimberly G. Harmon, MD, Seattle. Address correspondence to Dr Scott A. Paluska, MD, Rex Family Practice of Cary, 1515 Southwest Cary Parkway, Suite 200, Cary, NC 27511; e-mail to [email protected].


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