INTRODUCTION

The focal fibrocartilaginous dysplasia (FFD) is a rare anomaly affecting the proximal metaphysis of the tibia, but may also compromise other bones such as the femur, humerus and ulna(1,2,3). It represents one of the causes of early appearance unilateral varus knee of the childhood.

It was first described by Bell et al, in 1985, as a fibrocartilaginous defect at the medial region of the proximal tibial metaphysis at the pes anserinus insertion and, ever since, new cases and new topographies have been reported(1).

It is radiographically characterized by a radiolucent defect at the medial face of the tibial metaphysis, partially delimited by distal sclerosis, without apparent compromising of growth plate. Histology studies previously performed are compatible with fibrocartilaginous tissue involved by a dense fibrous tissue, similar to a tendon(4).

Despite unknown etiology, serial radiographic control suggests a self-limited disease. The defect initially found at the tibial metaphysis ossifies, and the sclerotic lesion gradually migrates to the diaphysis, and disappears with growth. The angular deformity is clinically corrected at the cost of asymmetric growth of the proximal tibial physis, thus indicating the large correction potential of the growth plate(4).

The purpose of this study is to report the evolution of six children with FFD, involving four tibiae and two femora.

MATERIAL AND METHODS
In the period between May 1993 and October 2002, at "Pavilhão Fernandinho Simonsen", Departamento de Ortopedia e Traumatologia da Santa Casa de São Paulo, Brazil, eight children with lower limb deformities had a diagnosis compatible to FFD. The retrospective analysis of the medical records was performed, and the patients were called for a new evaluation. Six patients were followed in an outpatient basis.

All patients were girls, with ages ranging from 14 to 22 months, mean of 18 months at the time of diagnosis. In four children the tibia was involved, and in two, the femur.

In all cases, diagnosis and follow-up were made upon orthopedic physical examination and X-rays in serial anteroposterior, lateral, and panoramic views of the lower limbs. Clinically, the main and sole fact was the deformity. Radiographically, the bone defect at the medial cortical of the proximal metaphyseal region of the tibia or distal metaphysis of the femur, partially surrounded by adjacent bone sclerosis, was considered typical. The tibiofemoral angle, the distal metaphyseal-diaphyseal angle of the femur, and the Levine and Drennan angle were measured(5).

The mean period between the initial and final evaluation was 16.5 months, ranging from three to 47 months. The mean period of patient follow-up was 40 months, ranging from 14 to 83 months (figures 1, 2, 3 and 4).

RESULTS
In the initial evaluation of the six patients, both the tibiofemoral and the metaphyseal-diaphyseal angles were noticed to be increased in relation to normal values, contributing to lower limbs deformity. In the presence of the maximal deformity, tibiofemoral angle ranged from 4° to 22° of varus deviation (mean, 16°). The distal femoral metaphyseal-diaphyseal angle ranged from 10° to 24° (mean, 17°). The Levine and Drennan angle ranged from 10° to 25° (mean, 19°).

In five cases, the maximal deformity occurred in ages below two years and, in another case, it was observed at the age of four years.

During outpatients' follow-up, a spontaneous resolution of the deformity was noticed, occurring in all patients until the age of six (tables 1 and 2, figures 5 and 6).

DISCUSSION
The alignment upon physiological development of the lower limbs is characterized by varus knee since the child is born. After gait initiation, varus is spontaneously corrected and, gradually, gives place to a valgus knee, between the ages of two and three years. Until the age of seven, the valgus should be corrected to normal adult values, which are 8° for men and 9° for women(6). Those six assessed children had an early diagnosis, mostly accomplished between the first and second years of life (mean, 18 months), probably due to the asymmetry and to a deformity that corresponded to an exaggerated varus (mean, 15°), except in one patient who had an affected femur, and presented a valgus knee of 12°. In this study, all children between the first and second year of life had mean age of 18 months, and presented unilateral deformity that, despite a common presentation at this age group, was exaggerated and asymmetric in relation to the expected.

No invasive or more expensive examination was necessary for the diagnosis, besides clinical and radiographic features of the FFD. Simple X-rays of the lower limbs is an easy to perform and interpret examination, yielding lesion identification and follow-up, along with the measurement of the tibiofemoral angle and of the metaphyseal-diaphyseal angle. The biopsy of the metaphyseal lesion had been performed by some authors when little was known on FFD(1,4). We consider such invasive procedure to be unnecessary for the correct diagnosis. On the other hand, the nuclear magnetic resonance may be suggested as a supplementary type of diagnosis(7). In our opinion, this examination is not necessary.

Bell et al, in 1985, when reporting the first three cases of FFD, had detailed the disease under histological viewpoint as characterized by a mass of dense, fibrous tissue, and cells with a lacunar arrangement, similar to a fibrocartilage at the central region, and to a tendon at the peripheral area(1). The finding was identical to the tissue normally found at the insertion of the tendons of pes anserinus. Although the authors had chosen a surgical approach in two cases that evolved with good results, they also noticed the spontaneous correction of the deformity in the third patient, and thus drew the attention to the possibility of conservative treatment, which would have led to the cure, avoiding surgeries.

Three years later, Bradish et al reported five more cases of the disease(8). In one of surgically treated cases, there were complications such as fibular nerve palsy, and valgus hypercorrection, whilst in other conservatively treated cases there was a spontaneous regression of the deformity around six years of age. They justified the surgery at an early age - around two years old - due to the magnitude of initial deformity. They noticed that regression of the deformity started after the age of two, and acknowledged that spontaneous correction would have occurred in all cases if they had waited for the natural evolution. We noticed this evolutionary behavior, observing deformity worsening until the age of two and, subsequently, spontaneous correction occurring until the age of six in all of our patients.

Kariya et al, in 1991, suggested that it was a self-limited disease, observing that the metaphyseal injury migrates to the diaphysis with growth. Such fact could be documented in our patients(4). They considered that the ossification of the fibrocartilaginous defect and the vicarious asymmetric growth at the contralateral half of the proximal tibial physis contributed to the deformity correction.

The literature reveals that, as the FFD became better understood, there was a trend to wait longer for the spontaneous correction of the deformity(9,10,11).

From the large review by Choi et al, until 2000, there were only 46 published cases of FFD(12). The analysis of cases revealed that the potential for spontaneous correction of the deformity seems to vary according to the affected site. The tibial correction is the most common; the femoral correction is the least frequent. They also concluded that the surgical treatment of FFD takes place only for the cases that after a long observation period would still persist with an important deformity. There was no evolutionary difference in our patients, as both cases involving tibia and femur have showed an equally favorable correction.

It is crucial to emphasize the importance of FFD differential diagnosis. The first one to be considered is the physiological varus knee. However, it shows bilateral and symmetric presentation, and can be ruled out by the absence of metaphyseal defect(6). Blount's disease, with unilateral or bilateral compromising of posteromedial proximal epiphysis, physis and tibial metaphysis, is clinically and radiographically very similar, but differs on the trend of deformity progression, requiring surgical correction. There are also post-infectious and post-traumatic varus deformities that differ from the FFD by deformity persistence or progressiveness, as determined by the normal growth of the intact portion of the physis(9).

It is important to highlight that, in face of a diagnosis of FFD, parents shall be informed that the deformity will increase during the first two years of life and the child will be periodically evaluated until - around the age of six - presenting an alignment considered as physiological.

CONCLUSION
The focal fibrocartilaginous dysplasia affects children in early ages and should be recalled in the differential diagnosis of lower limbs angular deformities.

Based on the favorable evolution observed in six evaluated patients and on what is described in the literature, we can conclude that follow-up upon serial clinical and radiographic evaluation makes the best treatment choice.

REFERÊNCIAS / REFERENCES

Bell S.N., Campbell P.E., Cole W.G., Menelaus M.B.: Tibia vara caused by focal fibrocartilagenous dysplasia. J Bone Joint Surg [Br] 67: 780-784, 1985.

Meyer J.S., Davidson R.S., Hubbard A.M., et al: MRI findings of focal fibrocartilagenous dysplasia. J Pediatr Orthop 15: 304-306, 1995.

Lincoln T.L., Birch J.G.: Focal fibrocartilagenous dysplasia in the upper extremity. J Pediatr Orthop 17: 528-532, 1997.

Bradish C.F., Stuart J.M., Malone M.: Tibia vara due to focal fibrocartilagenous dysplasia. J Bone Joint Surg [Br] 70: 106-109, 1988.

Macnicol M.F.: Focal fibrocartilaginous dysplasia of the femur. J Pediatr Orthop [Br] 8: 61-63, 1999.

Herman T.E., Siegel M.J., McAlister W.H.: Focal fibrocartilagenous dysplasia associated with tibia vara. Radiology 177: 767-768, 1990.

Kariya Y., Taniguchi K., Yagizawa H., Ooi Y.: Focal fibrocartilagenous dysplasia: consideration of healing process. J Pediatr Orthop 11: 545-547, 1991.

Zayer M.: Tibia vara in focal fibrocartilagenous dysplasia. A report of 2 cases. Acta Orthop Scand 63: 353-355, 1992.

Levine A.M., Drennan J.C.: Physiological bowing and tibia vara: the metaphyseal-diaphyseal angle in the measurement of bowleg deformities. J Bone Joint Surg [Am] 64: 1158-1163, 1982.

Husein A.M., Kale V.R.: Tibia vara caused by focal fibrocartilagenous dysplasia. Clin Radiol 40: 104-105, 1989.

Choi H.I., Kim C.J., Cho T., et al: Focal fibrocartilagenous dysplasia of long bones: report of eight additional cases and literature review. J Pediatr Orthop 20: 421-427, 2000.

Vankka E., Salenius P.: Spontaneous correction of severe tibiofemoral deformity in growing children. Acta Orthop Scand 53: 567-570, 1982.