The Telescoping Bifurcation Synostosis in the Treatment of Incomplete Longitudinal Tibial Deficiency
LESLIE C. MEYER, M.D. RONI I. SEHAYIK, M.D. HOWARD DAVIS, M.D.
This article presents three cases of incomplete longitudinal deficiency of the tibia in which a synostosis was created between the proximal tibial epiphysis and the osteotomized fibula, creating a one-bone below-knee amputation. The fibular head was excised in one case and left intact in two. Retention of the fibular head provides an anchor for the periosteal new bone strut which attaches to the distal fibular fragment. This technique adds stability to the articulation as well as to the synostosis. Supplemental bone grafting may be necessary to provide union. A growth arrest of the proximal fibular epiphysis is also necessary because of increasing prominence of the fibular head and some interference with prosthetic fitting.
In cases of incomplete tibial deficiency in which there is a proximal metaphyseal or diaphyseal segment, there is no problem in creating a synostosis between this segment and the osteotomized fibula, thereby providing a stable one-bone below-knee amputation which can be satisfactorily fitted with a prosthesis. The transplanted fibula hypertrophies, and the distal end of the fibula with its epiphysis provides a good end-bearing stump.
This article deals with management of the Jones, Barnes, and Lloyd-Roberts 4 type 1-B classification of incomplete longitudinal deficiency of the tibia in which the distal femoral epiphysis is normal. There is an articulating tibial remnant which is not radiologically visible at birth. Its presence is manifested, however, by a palpable segment to which the patellar ligament is attached, thereby providing some knee extension. This attachment may be abnormal, however, and if so there will be some fixed flexion deformity of the tibial remnant. The fibular head may or may not have an anatomical relationship to the proximal tibial segment. We have found an arthrogram to be an additional aid in detecting the quality of the proximal tibial segment. It may help to outline the tibio-femoral relationship and predict a functioning knee joint. The presence of a well-formed distal femoral epiphysis is probably the best indication of a proximal tibial remnant suitable for synostosis 4 .
The extremity presents marked shortening of the leg. There is instability of the knee joint, and there is usually a small dimple just below the knee. The degree of flexion deformity of the knee varies and depends upon the adequacy of insertion of the patellar ligament and upon the presence of congenital webbing in the popliteal space. The foot may have varying degrees of equinus and varus deformity 1,2,5 (Figure 1. and Figure 2. ).
Once the status of the proximal tibial remnant is established, the decision should be made to preserve the knee and create a one-bone below-knee amputation. At the time this decision is made, however, the parents should be aware of the possible need to abandon this approach at the time of surgery and proceed with a disarticulation of the knee. It is now our opinion that the synostosis procedure should be accompanied by a Syme disarticulation of the foot, with retention of the distal fibular epiphysis. This course prevents possible emotional fixation on the foot or foot remnant.
Case No. 1--D.M., a white female born October 1959, was evaluated at the age of 3 months with a diagnosis of incomplete tibial deficiency and equinovarus deformity of the foot. The upper tibial remnant could not be definitely palpated, and there was instability of the knee and progressive deformity of the foot despite a tendo-Achilles lengthening. With bracing, the fibula ultimately subluxed above the knee joint. At 6 years of age the patient was given a telescoping synostosis of the osteotomized fibular segment into a very short tibial remnant. The subluxed fibular head was excised, along with repair of the lateral collateral ligament and suture of the biceps tendon into the deep fascia. A year later the ankle was disarticulated and the limb was fitted with a Syme-type prosthesis. The tibio-fibular telescoping synostosis did not unite, and bone grafting was carried out with subsequent union. Examination at 18 years of age demonstrated moderate laxity of the knee joint, necessitating a prosthesis with a knee joint and a thigh corset. Range of knee motion was 0 to 140 deg. with 20 deg. of valgus laxity of the knee in full extension. Some posterior displacement of the tibia on the femur was noted in flexion. Motor functions of the quadriceps and biceps were rated as good. The patient functioned well without discomfort.
Case No. 2--D.C., a white male born September 1971 was evaluated at the age of 9 months with the diagnosis of incomplete longitudinal deficiency of the right tibia and an associated equinovarus deformity of the foot (Figure 1. ), and syndactyly of the right hand. The patient had an unstable knee with antero-posterior subluxation, prominent fibular head, and good quadriceps function. The proximal end of the tibia was palpable and had an attached patellar ligament. Initially the foot was serially casted into a plantigrade position and was then progressed to an ischial-weight-bearing caliper. At the age of 2 years, a knee arthrogram demonstrated acceptable articulation of the proximal tibia with the femur (Figure 3. ). The extremity was then placed in a urethane splint, and full weight-bearing was encouraged while awaiting ossification of the proximal tibia epiphysis (Figure 4. ). At the age of 5 years the patient underwent an osteotomy of the proximal fibula and insertion of the distal segment into the ossific nucleus of the tibial remnant with K. wire fixation. The fibular head was not excised. Three months postoperatively, radiographs demonstrated subperiosteal new bone formation along the fibular periosteal tube connecting the head of the fibula to the telescoped fibular segment (Figure 5. ). The patient was then fitted with a below-knee prosthesis with a knee joint and thigh lacer. At the age of 7 he had a good gait, normal patellar tracking, range of motion 0 to 140 deg., 10 deg. of varus-valgus laxity with stress, antero-posterior instability, and a prominent fibular head. The quadriceps and hamstrings rated as good. Knee alignment was good, and the telescoping synostosis was clinically solid (Figure 6. and (Figure 7. ). An epiphysiodesis of the proximal fibula was carried out at the age of 7 because of increasing prominence of the fibular head.
Case No. 3--K.M., a white female born in February 1973, was seen at age 4 months with a diagnosis of incomplete longitudinal deficiency of the left tibia (Figure 2. ). Identical deformities had occurred in her father and in her paternal grandmother. Physical examination showed a palpable proximal tibial remnant in about 45 deg. of fixed flexion, a weakened quadriceps, proximal subluxation of the fibular head, and equinovarus deformity of the foot. X-rays showed no evidence of a tibial anlage, but the distal femoral epiphysis appeared well formed. At 4 years of age there was still no radiologically demonstrable ossific nucleus, but the distal femoral epiphyses appeared normal for the child's age. It was then decided to proceed with a knee disarticulation if the tibial remnant appeared unsuitable for a synostosis. At surgery, a cartilaginous anlage was found along with a subluxed fibular head and a poorly demonstrated patellar ligament insertion. The tibial remnant had a fixed flexion deformity of 45 deg. The osteot-omized fibular segment was placed in the cartilaginous remnant and immobilized with the segment in 45 deg. of flexion to accommodate the deformity of the tibial remnant. Subsequent wedging casts corrected the flexion deformity, and the patient was given a below-knee prosthesis with a knee joint and a thigh corset. Two years later at the age of 6, the child is ambulating satisfactorily with her prosthesis. Flexion is 90 deg., and her knee is stable in extension. She has functioning extensor mechanism and hamstrings. She lacks 5 deg. of reaching full extension. Union appears to have occurred, both clinically and by X-ray, between the tibial remnant and the fibula(Figure 8. ). The fibular head is quite prominent, and growth arrest of the proximal fibular epiphysis will be necessary.
The surgical procedure consists of an osteotomy of the fibular metaphysis after careful subperiosteal dissection (Figure 9. ). The distal fragment is then placed in a centrally placed drill hole in the ossific nucleus of the tibia and fixed with two threaded pins (Figure 10. ). Hatt 3 has demonstrated that knee fusion can be successfully accomplished by placing a graft through the center of the epiphysis without interrupting the growth of the epiphysis. In our third case, the procedure was carried out with no X-ray evidence of the ossific nucleus.
A new bone strut quickly forms in the preserved periosteal tube, adding stability to the tenuous synostosis between the fibular metaphysis and the proximal tibial segment, which is largely cartilage (Figure 11. ). Grafting was required in our first case, in which the fibular head was excised, but solid clinical and X-ray union developed in the second and third cases, which had benefit of the new bone strut. Supplemental grafting may still be necessary and should be done without hesitation.
- In cases of incomplete longitudinal tibial deficiency, a very short proximal tibial remnant consisting of the tibial epiphysis which is not radiologically visible should be preserved in preparation for a fibular synostosis. This course provides for a satisfactorily functioning knee joint.
- Patellar ligament attachment, radiologic position of the fibular head, and an arthrogram may be of value in establishing the quality of the tibial segment prior to its being visualized by X-ray. A normal distal femoral epiphysis is probably the best indicator of a cartilaginous anlage of the upper tibial fragment.
- The fibular head should not be excised at the time of the tibio-fibular synostosis. A careful subperiosteal dissection results in the development of a new bone strut along the periosteal tube, thereby adding to the stability of the synostosis and the knee joint. Bone grafting of the synostosis was not necessary in the two cases treated without fibular head excision, but it should be done without hesitation if union does not progress.
- Disarticulation of the foot, with retention of the distal fibular epiphysis, provides a satisfactory below-knee stump which can be successfully fitted with a prosthesis. This disarticulation should be done at the time of the synostosis.
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