Bilateral angular deformity of the lower extremity in children is common, and it is often due to benign physiological conditions in which the deformity corrects with growth1,2. However, unilateral angular deformity is rare and usually involves an abnormal condition such as Blount disease, fibrous dysplasia, Ollier disease, dyschondrosteosis, neurofibromatosis, a growth disturbance resulting from a physeal injury or infection, or even a rare condition described as tibia vara caused by focal fibrocartilaginous dysplasia2. To our knowledge, only five children with unilateral angular deformity of the distal end of the femur secondary to a focal fibrous tether have been described in the literature, and only two of them had a valgus deformity1,3.
We describe a boy who had a progressive genu valgum secondary to a tether of fibrous tissue, confirmed by histological examination, at the distal end of the femur.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
†Department of Orthopaedic Surgery and Traumatology, University Clinic of Navarra, Avenue Pio XII 36, 31008 Pamplona, Spain. E-mail address for Dr. Mora: gmorag@cun.unav.es.
A twenty-seven-month-old boy was referred to us for evaluation of a valgus deformity of the distal aspect of the right femur. The mother had first noted the deformity when the child was twelve months old. At that time, the tibiofemoral angle measured 18 degrees radiographically.
When the boy was eighteen months old, the tibiofemoral angle was 24 degrees (Fig. 1) and a varus osteotomy and a tenotomy of the iliotibial tract was performed by another surgeon. A biopsy of the bone revealed normal findings. The deformity recurred nine months later, with a resultant tibiofemoral angle measuring 40 degrees of valgus radiographically (Fig. 2).
When we first saw the patient, physical examination revealed a limp and 40 degrees of genu valgum in the right lower limb. Radiographs showed sclerosis at the lateral aspect of the distal metaphysis of the right femur, secondary to the previous biopsy and osteotomy, and the valgus deformity. At that time, a lateral percutaneous varus osteotomy of the distal end of the femur was performed and a Wagner external fixator was applied. After the osteotomy, the extremity was well aligned with 5 degrees of physiological valgus angulation. The fixator was removed two months postoperatively (Fig. 3).
Fifteen months later, the deformity recurred and the tibiofemoral angle measured 26 degrees of valgus (Fig. 4). At that time, magnetic resonance imaging showed a mass of high signal intensity consistent with soft tissue on the lateral aspect of the distal end of the femur (Figs. 5-A and 5-B). The tissue was difficult to evaluate because of the two previous operations in that area. Another operation was performed because of progression of the deformity, and a fibrous band (1.2 by ten centimeters) was found at the lateral aspect of the femur, from the diaphysis to the distal femoral epiphysis. The band was removed completely. An opening-wedge osteotomy of the distal end of the femur was performed, and the site of the osteotomy was fixed with Blount staples. A cylinder cast that extended from the groin to the foot was worn for forty days. Histological examination of the excised band showed well organized dense fibrous tissue. Five years after the operation, the alignment of the extremity was normal (Fig. 6).
Beaty and Barrett, in 1989, were apparently the first to describe a lesion similar to the one in our patient. They reported on four children who had an angular deformity of the distal part of the femur secondary to an unusual fibrous tether. According to its medial or lateral location, this tether produced a varus or valgus deformity of the distal end of the femur; two children had a varus deformity and two, a valgus deformity (Table I). The deformity was painless, and none of the patients had a history of injury, infection, or any other abnormal condition.
More recently, in 1994, Vallcanera et al. described a similar lesion that caused a varus deformity at the distal end of the femur (Table I). As in our patient, the deformity in the five children described by Beaty and Barrett and Vallcanera et al. was located at the distal end of the femur and did not improve spontaneously. Because the deformity progressed, all six patients needed a corrective osteotomy and an excision of the fibrous band. Excision of the band is necessary because, without it, the deformity returns. It is interesting to speculate whether a deformity that is not severe could be corrected with excision of the fibrous band alone (that is, without an osteotomy).
The origin of the fibrous tether is unknown. Beaty and Barrett stated that they could "only speculate as to the etiology of this lesion, but possible explanations include occult trauma near the metaphysis or physis, an extensive subperiosteal fibroma with intraosseous extension (although the lesion we are reporting has a different pathology), and a remnant of accessory muscle." We believe, as did those authors, that although this lesion is rare it should be recognized as a possible cause of unilateral angular deformity, especially when radiographs reveal cortical irregularities or a tunnel-like lesion in association with the angular deformity.
Operative correction should be considered when progression of the deformity has been confirmed, as is recommended for the treatment of infantile Blount disease. Lesions in the region of the distal end of the femur should be investigated for the possibility of a fibrous tether, and we believe that magnetic resonance imaging may help in the identification of such a tether. In our patient, an operation to remove the fibrous band was necessary because it was the basic cause of the deformity.