Osteopetrosis is a hereditary bone disorder caused by a failure of osteoclasts to resorb bone. Failure of resorption leads to decreased or absent bone marrow cavity formation and increased radiodensity.9,21,22 Although the bones show increased density on radiographs, they are weak and subject to fracture if exposed to the same mechanical stresses that normal bone can withstand. There are three types of osteopetrosis based on severity and pattern of inheritance.4 The most severe is the malignant infantile form inherited in an autosomal recessive manner.20 Patients may worsen rapidly and have a high death rate.8,15,21 The second type is autosomal recessive, which is diagnosed in the first decade of life.14 Clinical manifestations include repeated fractures after minimal trauma, osteomyelitis, and long bone deformity such as coxa vara and genu valgum.14 The third form is autosomal dominant, diagnosed in adulthood.5 This form does not shorten life expectancy, but causes an increased fracture rate and bony deformity.5
We report a 14-year-old girl diagnosed with intermediate-type osteopetrosis who presented with a 4.8-cm leg- length discrepancy secondary to premature distal femoral growth plate closure. She had a projected leg-length discrepancy of 7 cm at maturity. One of our primary concerns was whether osteopetrosis would affect the reliability of the growth chart in predicting leg lengths.20
We evaluated a 14-year-5-month-old girl referred for a leg-length discrepancy. She was diagnosed with intermediate-type osteopetrosis when she was 7 months old. When she was 5 years old, she was hospitalized with septic arthritis of the left knee, which was treated with antibiotics and surgical drainage. The infection resolved but her left distal femoral growth plate prematurely closed. She also had a history of multiple fractures: the forearm (2 years old), right humerus (5 years old), right ankle (7 years old), and left tibia (7 years old).
On clinical evaluation, she had a disproportionate short stature at 146 cm, which was below the third percentile for height. Her leg-length discrepancy was 4.5 cm as measured by blocks. She also had genu valgum and clinically evident pelvic obliquity secondary to the leg-length discrepancy. There was no evidence of cranial nerve palsies, hepatosplenomegaly, or visual and hearing disturbances. Additional laboratory tests revealed normal hematologic parameters, thyroid, adrenal function, and L-dopa growth hormone stimulation studies.
Radiographs showed increased radiodensity of the entire skeleton, absence of the medullary canal, bilateral coxa vara with congruent mushrooming of the femoral heads, and bilateral valgus deformity of 20° in the proximal tibia (Fig 1). A 4.8-cm leg-length discrepancy was measured by orthoroentgenogram (right longer than left). Bone age was determined using the method developed by Greulich and Pyle.11 The patient's bone age was 12 years (chronologic age, 14 years) using this method. The projected 7-cm leg-length discrepancy at maturity was calculated using the Moseley chart.17 This discrepancy was projected to be reduced to 3 cm with an epiphysiodesis on the contralateral femur and tibia.
Percutaneous epiphysiodesis was performed using the technique described by Bowen and Johnson.6 The technique consisted of identifying the growth plate medially and laterally. Small incisions were placed over the identified sites. Curettage of the peripheral 1⅓ of the growth plate was done medially and laterally to ensure growth arrest. Intraoperatively, the bone was found to be harder than normal; however, the procedure was completed without problems (Fig 2). The total operative time was 1 hour, and there were no intraoperative complications.
The patient was discharged on crutches, and weight-bearing was not allowed for 3 weeks. Active knee motion was started 1 day postoperatively, and 115° active knee flexion was obtained 3 weeks postoperatively. The patient was followed up periodically, and the leg-length discrepancy decreased to 3 cm at maturity (Fig 3).
Treatment of leg-length discrepancy in this patient presented a dilemma. There are no clear standards for treating leg-length discrepancies in patients with osteopetrosis. A predicted 7-cm shortening at maturity can cause serious disability and may require treatment. Standard treatment options for addressing leg-length discrepancies include limb lengthening and the various techniques of epiphysiodesis.
One might anticipate problems performing lengthening in patients with osteopetrosis. Lengthening procedures have high complication rates, and additional problems treating patients with osteopetrosis might include difficulty applying pins, wires, or screws in the osteopetrotic bone,7,10,20 delayed or prolonged bone healing,16 and recurrent fractures.7,10,12,13 A higher incidence of bone infections, presumably because of poor blood supply to sclerotic bone coupled with impaired leukocyte function, also has been reported in patients with osteopetrosis.18,20 Epiphysiodesis using staples or transphyseal screws is another option to be considered, although we were also concerned about using staples or transphyseal screws in osteopetrotic bone.7,10,20 The difficulty in placing any implant in osteopetrotic bone cannot be overemphasized. Another concern with epiphysiodesis is the short stature and delayed growth in children with osteopetrosis,20 which may affect the reliability of the growth chart in predicting leg lengths.
We performed a percutaneous epiphysodesis6 for minimal surgical exposure and because hardware was not required. The extreme hardness of the bone did not cause any intraoperative complications. A bone bridge was generated by the epiphysiodesis, and the leg-length discrepancy was reduced to the goal of 3 cm at maturity.
We found the straight-line graph method reliably predicted leg-length discrepancy at maturity and calculated the proper skeletal age for epiphysiodesis. Some authors have reported short stature in patients with osteopetrosis because of a delay in growth or multiple fractures.1-3,14,23
This affects the reliability of the Moseley chart if children with this condition do not follow a predictable growth pattern. Our patient had a delayed skeletal age and was consistently below the third percentile for height; however, a predictable growth pattern was observed that gradually increased (Shapiro Type I).19 We think that the information presented in this case report should be considered when treating leg-length discrepancies in patients with osteopetrosis. A limitation of this report is that it involves just one case. It may be that the predictability of growth seen in this case cannot be extrapolated to all children with osteopetrosis. Operative planning must be considered on a case by case basis.
Our patient presented with osteopetrosis and a severe leg-length discrepancy. We found that her remaining growth was predicted by the Moseley chart, and that a percutaneous epiphysiodesis treated the leg-length discrepancy.
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