A 29-year-old man sustained injuries to his left lef in a motorcycle accident seven months ago. He had been treated for three months with external fixation, followed by long leg casting. Several months later, the man was treated for oral keflex for a positive wound culture for pseudomonas. He now presents to the emergency room complaining of continued pain and deformity of his left leg one day after cast removal.
A 29-year-old man sustained injuries to his left leg in a
motorcycle accident seven months ago. He had been treated for three
months with external fixation, followed by long leg casting.
Several months later, the man was treated with oral keflex for a
positive wound culture for pseudomonas. He now presents to the
emergency room complaining of continued pain and deformity of his
left leg one day after cast removal. Radiography studies of the
left tibia and fibula were obtained.
Infected nonunion of the tibial shaft fracture with pintract
AP and lateral views of the left tibia and fibula reveal
ununited fractures, medial-posterior angulation of the distal
fragments, sclerosis at the fracture margins, and a multilaminar
periosteal response (figure 1). In addition to generalized
osteopenia, there are multiple focal lucencies within the tibia
surrounding the sclerotic "rings" of prior pin tracts (figure 2).
These findings are consistent with infected nonunion and pin-tract
osteomyelitis, signified by ring sequestra.1 Note the proximity of
the inferior tibial pin-tract relative to the fracture site.
Physical examination in the emergency room revealed a cutaneous
fistula at the anterior lower leg, with extrusion of bony
fragments. The differential diagnosis is limited. Other, less
likely diagnostic considerations include myeloma, lymphoma,
adamantioma, or pathologic fracture associated with metastatic
disease. The "end on" appearance of these lesions simulates the
nidus of osteoid osteoma, although the broad surrounding lucency
and clinical features exclude this lesion.
Percutaneous external pin fixation is a commonly used method for
fracture reduction and stabilization because it allows transmission
of forces across the fracture without violating the fracture site.2
Minor pin-tract infections with purulent drainage that respond to
antibiotic therapy and local wound care are seen in 5% to 10% of
patients. A major complication of pin fixation is pin-tract
osteomyelitis, which may be encountered in up to 4% of patients.3
Factors predisposing to pin-tract osteomyelitis include poor
hygiene, taut skin surrounding the pin penetration site,
intracortical placement, pin motion, pins-in-plaster, and immune
compromise.3,4 Flat bones (e.g. pelvis) are affected less commonly
than long, tubular bones.5
Thermally-induced osteocytic death with subsequent medullary
bone repair is a normal osseous response to pin placement. It is
seen radiographically as a zone of sclerosis surrounding the pin
tract. Cell death increases with high speed drills and blunt pin
tips, which cause higher heat production compared to hand drilling
with sharper drill bits.3 In supervening pin-tract infections, the
zone immediately surrounding the pin tract becomes necrotic and is
separated from viable bone by inflammatory tissue. This phenomenon
is seen on the radiograph as a ring sequestrum. Additional
radiographic findings suggesting infection include periosteal
reaction and soft tissue swelling.1
Detection of ring sequestra requires a radiographic projection
with the pin tract approximately parallel to the central ray.
Fluoroscopically-guided positioning may be helpful. Thermal
osteonecrosis is seen as a broad zone of pin-tract sclerosis, with
an occasional subtle radiolucent halo. Normal pin tracts may show a
focal, central radiodensity after pin removal. Pin loosening
appears as a lucency between the metallic pin and the sclerotic pin
Common infecting organisms are Staphylococcus aureus,
Pseudomonas aeruginosa, Proteus mirabilis and Streptococcus
marcescens. Staphylococcal osteomyelitis is more common in
short-term fixator use (less than four months), while gram-negative
rod infections are more often associated with long-term use.5
Therapy includes removal of pins, appropriate antibiotic therapy,
and overdrilling of the infected tract with or without delayed
autologous bone grafting.3,5
1. Nguyen VD, London J, Cone RO: Ring sequestrum: Radiographic
characteristics of skeletal fixation pin-tract osteomyelitis.
Radiology 158:129-131, 1986.
2. Sisk TD: General principles and techniques of external
skeletal fixation. Clinical Orthop Rel Res 180:96-100, 1983.
3. Green SA: Complications of external
skeletal fixation. Clin Orthop Rel Res 180:109-116, 1983.
4. Selegson D, Harman K: Negative experiences with
pins-in-plaster for femoral fractures. Clin Orthop Rel Res
5. Green SA, Ripley MJ: Chronic osteomyelitis in pin-tracts. J
Bone Joint Surg 66:1092-1098, 1984.