Image Quiz

Swelling and Pain in the Knee of a Thirty-Month-Old Child (continued)

Answer: Tuberculosis of the proximal part of the tibia involving the growth plate.

Chemotherapy with isoniazid, 200 mg/day, and rifampicin, 140 mg/day, was begun. However, despite this treatment the surgical wound remained open, and a radiograph showed that the radiolucent lesion in the proximal part of the tibia had increased in size (Figs. 2-A and 2-B).


Fig. 2-A
Fig. 2-B		 Figs. 2-A and 2-B Radiographs of the right knee, made before the second operation, showing radiolucent zones in both the epiphysis and the metaphysis of the proximal part of the tibia and disruption of the growth plate.

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A second surgical procedure, performed through a posterior approach, demonstrated an osteolytic lesion of the tibial metaphysis and epiphysis extending through the growth plate. This lesion was curetted aggressively. As a result of the curettage, the center of the growth plate contained a defect that measured 1.5 × 2.0 cm (Figs. 3-A and 3-B). Chemotherapy was switched to 200 mg/day of isoniazid, 140 mg/day of rifampicin, and 28 mg/72 hr of streptomycin for one month and then to 200 mg/day of isoniazid and 140 mg/day of rifampicin for nine more months.


Fig. 3-A
Fig. 3-B		 Figs. 3-A and 3-B T2-weighted magnetic resonance images of the right knee made after curettage of the proximal part of the tibia.
Fig. 3-A On the coronal view, the high signal intensity involves both the metaphysis and the epiphysis. The image shows a growth plate defect 1.5 cm wide and 2 cm deep.
Fig. 3-B On the sagittal view, a large defect in the posterior cortex can be seen as well.

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After the second surgical procedure, the tibia was immobilized in a long leg cast and no weight-bearing was permitted for three months. Range-of-motion knee exercises and walking with an ischial weight-bearing brace were then begun. Postoperative radiographs showed reduction of the area of the bone defect in the proximal tibial epiphysis, and weight-bearing was permitted (Figs. 4-A and 4-B).


Fig. 4-A
Fig. 4-B		 Figs. 4-A and 4-B Postoperative changes in the bone defect seen on the radiographs. The central growth plate gradually remodeled and maintained its growth function.
Fig. 4-A At four months postoperatively.
Fig. 4-B At eleven months postoperatively.

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Discussion

The incidence of bone tuberculosis in children is low. Pulmonary lesions are rarely associated with tuberculous osteomyelitis, and the BCG vaccination itself may cause osteomyelitis, although the origin of the infection is sometimes unclear. The route of infection in our patient was also unclear. Bacteriological and histological examination suggested the tuberculosis after surgical débridement and curettage. However, polymerase chain reaction tests did not reveal the DNA of Mycobacterium tuberculosis in the material draining from the infected area of the tibia. It took eighty days after the patient's first visit to the hospital to establish the correct diagnosis. Chen et al. reported an average 6.6-month delay in the diagnosis of tuberculous osteomyelitis, indicating the difficulty in making the diagnosis quickly.

There are few reported cases in which the origin of osteomyelitis was in the epiphysis of the proximal part of the tibia. Radiographs of our patient showed an osteolytic lesion in both the metaphysis and the epiphysis, although the main osteomyelitic lesion was thought to be in the metaphysis. During the first surgical débridement, an abscess with posterior cortical disruption was found in the metaphysis. The growth plate did not appear to be damaged even though the initial magnetic resonance image had shown a change in signal intensity in the proximal tibial epiphysis alone.

It is well known that growth disturbances occur after trauma to growth plates. Shear stress, extreme compression force, and traction on the physis can injure the physeal cartilage. Drill holes through the physis as well as curettage of the growth plate are also thought to cause growth disturbances in some instances. However, the extent of curettage of the growth plate that would cause its early closure is unknown. Makela et al. reported that injury to 7% of the cross-sectional area of a rabbit femoral growth plate caused growth disturbance. Osterman reported, in an experimental study, that resection of 65% of the physis caused early closure but the closure could be prevented by inserting an interpositional fat graft. One possible mechanism of early closure of the growth plate was described by Barash and Siffert, who suggested that progression of ossification of the epiphysis facilitated the formation of bridging callus through the growth plate but not the metaphysis. Kameyama reported that the low growth-plate activity due to aging would be expected to retard the regeneration of the growth plate.

In our patient, a large area of the metaphysis and epiphysis was curetted through the growth plate. The growth plate was damaged in an area 1.5 cm wide and 2 cm deep, which was half of the whole diameter in the sagittal plane and one-third of the whole diameter in the coronal plane, or one-sixth of the total cross-sectional area of the physis.

This case should remind orthopaedic surgeons to consider tuberculous osteomyelitis in the differential diagnosis of bone infection in a child. Thorough surgical débridement is needed to eradicate the infection even if the physis is involved, since there may be full recovery following substantial physeal damage, as there was in our patient, despite the extensive curettage.

Reference

1. Ohtera K, Kura H, Yamashita T, and Ohyama N. Long-term follow-up of tuberculosis of the proximal part of the tibia involving the growth plate. A case report. J Bone Joint Surg Am. 2007;89:399-403.