Congenital Diastasis of the Distal Tibia and Fibula

ROBERT J. RUDERMAN, M.D. JOHN D. LUCEY, M.D.


Introduction

Only three cases of congenital diastasis of the distal tibia and fibula have been reported 1,2 ; all had limited follow-up. Tuli and Varma maintained their patients in ischial-weight-bearing calipers, and Bose utilized an ankle-foot orthosis. Because of the limited experience with this condition, the possibility of future amputation has been entertained. We recently had the opportunity to evaluate a fourth patient whose three-and-one-half-year course since initial correction sheds some light on these issues.

Case Report

T.J.W. was initially seen at Duke University Medical Center in November of 1976. She was a 3 and 1/2-year-old female who was a 4.03-kilogram (8-pound 14-ounce) product of an uncomplicated pregnancy ( Figure 1 ). Mother was a primigravida and had no unusual illness or medications. The delivery was vaginal and uncomplicated. There were no neonatal episodes of respiratory distress, jaundice, or other difficulties. The child was entirely normal with the exception of what appeared to be a severe right "clubfoot." X-rays in the perinatal period ( Figure 2-A and Figure 2-B ) defined the condition. The limb was casted prior to discharge from the hospital at

5 days of age, and the patient underwent serial casting weekly until operative correction was undertaken at the age of to weeks. The operative procedure was performed through an anterior approach, and reduction and closure of the diastasis were accomplished after resecting one centimeter of the distal tibia. Reduction of the talus within the mortise was ensured by a longitudinal smooth pin inserted through the calcaneus, talus, and into the tibia. This pin was removed six weeks postoperatively, and plaster immobilization was continued until age 7 months. No further casting or operative procedures have been carried out. The only orthotic device utilized has been a 19-millimeter (34-inch) heel lift on the right. The child walked at age 8 months and has enjoyed normal motor and mental growth and development. She runs and plays with her peers.

At the time of follow-up examination, the child was entirely normal with the exception of the right lower limb. She stood erect, and with the pelvis leveled with blocks, the spine was straight. The limb-length discrepancy was measured at 4 centimeters clinically and by tape measure from the anterior superior iliac spine to the sole of the foot. Hips had a full range of motion, and the femur was clinically slightly longer on the right. The right limb exhibited slight genu valgum which approximated that on the left: this was accentuated by the prominent fibular head, which had migrated superiorly and posteriorly. The range of motion at the knee was complete, and the knee was stable to varus, valgus, and anterior-posteriOr stress. The tibia was shortened and medially bowed, and the small medial malleolus was posterior in relation to the distal fibula. The ankle could not be brought to a neutral position with the foot inverted, but with eversion the hindfoot could he brought to 10 degrees of dorsiflexion by bypassing the ankle joint. Forty degrees of plantar flexion were possible at the ankle. There was good subtalar motion with some limitation of inversion, and the talus was stable within the

ankle mortise. The forefoot was supple, but there was a forefoot hook and a hypoplastic first ray. The neurovascular status of the limb was normal. The X-ray appearance of the foot and ankle is illustrated in Figure 3-A , Figure 3-B , Figure 3-C , and Figure 4 . Orthoroentgenograms confirmed the normal development of the pelvis and femur, and the total measurable limb-length discrepancy was 3.9 centimeters. Comparable films taken one year prior to examination also showed a 3.9-centimeter deficiency. The right femur measured 0. 1 centimeter longer than the left, and the entire deficiency was in the tibia and ankle joint.

Discussion and Conclusions

One case hardly qualifies as a broad experience, and a three-and-one-half-year follow-up is incomplete for a congenital abnormality. Nevertheless, the present case provides several points worth noting. All the cases to date have involved the right side, and three of four have presented in first-born females. Only further experience will tell whether this is anything more than an interesting coincidence.

Tuli and Varma did not comment on their patients' feet, hut the development of the first ray appears normal in the published photographs. Based on this experience, they hypothesized that the reported defect might he classed with the localized osteochondroses. The hypoplasia of the first ray noted by Bose led him to consider this a more generalized congenital hypoplasia. Our case supports this concept.

Our patient has now been over three years without orthotic support. Despite this, the foot has remained grossly aligned, plantigrade, and is certainly service able. Indeed, our patient has developed a valgus, pronated deformity, apparently secondary to chronic heel-cord contracture, and not the varus, internal-rotation deformity Bose feared. This condition will probably require heel-cord lengthening and possible subtalar stabilization, but it is questionable whether this deformity could have been prevented by an orthosis. The fate of the ankle joint is still indeterminant.

A 4-centimeter limb-length discrepancy is significant in a 3 and 1/2-year-old but is not crippling. It is interesting that this is the same shortening Bose measured in his patient at 3 years 4 months. Our patient's shortening has not progressed over the past one to two years. It appears to be limited to the tibia and should be manageable with epiphysiodesis and/or lengthening at the appropriate time. It seems clear that the remainder of the limb will develop normally and that the overall deficit will not be so great that one need consider amputation.

References:
1. Tuli, S. M., and B. P. Varma. Congenital diastasis of tibio-fibular mortise. J Bone Joint Surg, 54-B:346-350, May 1972.

2. Bose, K., Congenital diastasis of the inferior tibio-fibular joint. J Bone Joint Surg, 58-A:886-887, September 1976.