SUBACUTE EPIPHYSEAL OSTEOMYELITIS

TIMOTHY P. DOMER, D.O., Orthopaedic Surgery Resident

KIRK DABNEY M.D., Attending Pediatric Orthopaedic Surgeon

January, 29, 1996

CLINICAL CASE PRESENTATION

ORTHOPAEDIC DEPARTMENT

THE ALFRED I. DUPONT INSTITUTE

WILMINGTON, DELAWARE

CASE HISTORY:

PATIENT 1.

• HISTORY: This 9-year-old female who presented to the emergency room with a four day history of mild right knee pain. She limps on the affected extremity when ambulating but has minimal to no pain at rest. No history of trauma was reported. She has had mildly elevated temperatures over the past several days according to the mother. There is no history of joint stiffness or chronic fatigue. No other joints are involved. There is no history of tic exposure. She has been otherwise healthy in the past.
• PHYSICAL EXAM: On physical examination of the right knee there is no limitation in flexion or extension. There is mild diffuse tenderness that is poorly localized over the medial femoral condyle. There is no soft tissue swelling or joint effusion noted. No pain is elicited with ROM of the knee. The remaining extremities are without tenderness or swelling. Temperature is 38.8* C
• LABS: WBC 13,400 Differential-- 73% polys, 8% lymphs, 1% bands, Sed rate 41mm/hr
• XRAYS: No bony abnormalities noted on plain x-ray of the knee
• TREATMENT: The patient was discharged home and re-checked the following day. Because of persistent tenderness over the knee and new physical findings of swelling and pain with ROM of the knee, the following diagnostic studies were obtained:

1. Bone scan: Revealed increased uptake in the region of the distal femur with a predominant epiphyseal location and slight uptake in the metaphysis on the flow and pool images. Delayed images showed focally increased uptake in the epiphysis of the distal right femur.
2. CT scan: No subperiosteal fluid collections were noted. There was an area in the region of the distal femoral epiphysis that contained a difference in density from the surrounding bone.
3. Ultrasound: Soft tissue swelling in the region of the distal femur

The patient was taken to the operating room for fluoroscopic guided needle aspiration of the distal femoral metaphysis and epiphysis and the proximal tibial metaphysis. Aspiration of the knee joint was also performed.

Final cultures: Blood cultures obtained at initial presentation were positive for Staphylococcus aureus. Aspirates of the distal femoral epiphysis were positive for Staphylococcus aureus

• FOLLOW-UP: The patient remained in the hospital for a total of 14 days. She was discharged on IV cefuroxime to complete a six week course of antibiotic therapy. At seventeen months follow-up she had painless full ROM of her knee and no radiographic evidence of bony abnormality.

SUBACUTE EPIPHYSEAL OSTEOMYELITIS

Pathogenesis:

Predisposing factors that may influence the septic process in bone:

1. Host resistance
2. Virulence of infecting organism
3. Adequacy of antibiotic therapy
4. Trauma resulting in vascular injury and hypoxemia in bone

Staphylococcus aureus is the most common bacterial isolate, and it has been found that S. aureus has a certain affinity for epiphyseal cartilage.

Pathoanatomy:

• Main blood supply to the epiphyseal end of long bones is through the Hunter circle -- a large encircling artery that gives off branches to both the metaphysis and epiphysis.
• Arcades are formed from epiphyseal branches which eventually end in venous sinusoids in the form of loops, which may be analogous to the sluggish blood flow that occurs in the metaphysis.
• The blood supply in the venous loops may be analogous to the sluggish flow in the metaphyseal sinusoids, which is often the site of acute hematogenous osteomyelitis.
• Physeal blood supply peripherally is via epiphyseal and periosteal circulation, whereas central circulation is solely provided by epiphyseal circulation.

Radiographic features:

• Benign appearing-- lesion is lytic, circular, and well circumscribed with a sclerotic margin
• Malignant appearing-- bony cortex is eroded

Radiographic differential diagnosis (of all locations of subacute osteomyelitis)

• chondroblastoma
• osteoid osteoma
• Ewing's sarcoma
• eosinophilic granuloma
• unicameral bone cyst
• Brodies abscess
• osteogenic sarcoma

Radiographic classification:

Ia-- metaphyseal; punched out lucency suggestive of eosinophilic granuloma

IIb-- metaphyseal ; sclerotic margin with classic appearance for Brodies abscess

III-- diaphyseal ; localized cortical and periosteal reaction simulating osteoid osteoma

IV-- diaphyseal ; onion-skin periosteal reaction simulating Ewing's sarcoma

V-- epiphyseal ; concentric radiolucency

VI-- vertebral body ; erosive or destructive process

Treatment:

Ross and Cole used the radiographic appearance of lesions associated with subacute osteomyelitis to classify their patients into two groups as follows:

• Group 1 -- Aggressive lesions- the initial presentation of these children was that of primary malignant bone tumors based on clinical, radiographic and hematologic studies.
• Group 2 -- Cavities in the region of the metaphysis and epiphysis- these children presented with a more typical picture of subacute osteomyelitis having cavities involving either the metaphysis or the epiphysis or both.

All patients were initially treated with two days of intravenous antibiotics and then were switched to oral antibiotics to complete a six week course.

Results:

Treatment of group 1 lesions

• Consisted of curettage followed by six weeks of antibiotics and immobilization -- 25/26 healed.

Treatment of group 2 lesions

• Those not operated on at the time of presentation -- 32/37 healed without operation, including all 5 epiphyseal lesions. Of those not healing initially without operation, three were confined to the metaphysis and two were combined metaphyseal and epiphyseal lesions. All of these went on to heal after curettage and an additional six week course of antibiotics.
• Those operated on at the time of presentation -- 7/11 patients underwent drainage and eventually healed after antibiotics; 4/11 patients had biopsies to establish the diagnosis of subacute osteomyelitis- there is no mention of formal drainage or whether there was complete healing.

References:

1. Green,N.E., Beauchamp,R.D., Griffin, P.P. Primary subacute epiphyseal osteomyelitis. J Bone Joint Surg 63-A:107, 1981.
2. Green, N.E. Osteomyelitis of the epiphysis. In Behavior of the growth plate. Raven press, 1988.
3. Letts, R.M. Subacute osteomyelitis of the growth plate. In Behavior of the growth plate. Raven press, 1988.
4. Lindenbaum,S. Alexander, H. Infections stimulating bone tumors: a review of subacute osteomyelitis. Clin. Orthop. 184:193, 1984.
5. Roberts, J.M., Drummond, D.S., Breed, A.L., Chesney, J. Subacute hematogenous osteomyelitis in children: a retrospective study. J Pediatr Orthop 2:249, 1982.
6. Ross, E.R.S., Cole, W.G. Treatment of subacute osteomyelitis in childhood. J Bone Joint Surg 67-B:443, 1985.