Congenital absence of the Fibula

Randal A Williams, M.D.


Paraxial fibular hemimelia, or congenital absence of the fibula, is not an uncommon anomaly. Studies of congenital deficiencies by Coventry and Johnson1 have shown that the fibula is the most commonly absent long bone, followed by the radius, femur, tibia, ulna, and humerus, in that order. The anomaly may be terminal or intercalary, depending upon the presence or absence of the corresponding portion of the foot, and it may be complete or incomplete.

These authors advance two theories as to the origin of the condition. The first is that it results from a defect in the germ plasm of the developing limb, and occurs by the sixth or seventh week of embryonic life. The second theory postulates that the absence of the fibula results from maturational failure, and is accompanied by relative shortening of the calf and peroneal muscles. Heredity does not appear to play a significant role in congenital absence of the fibula.

The classical picture consists of a complete or almost complete absence of the fibula, shortening of the extremity, anterior bowing of the tibia (if the bowing is marked, there may be a skin "dimple" over the point of greatest angulation), marked equinovalgus of the foot, absence of one or more rays of the foot with absence of the associated tarsal bones, and fusion of two or more tarsal bones. Thompson2 demonstrated a tight fibrocartilagenous band in the posterolateral aspect of the calf. When this band was removed, the result was at least partial correction of each element of the deformity except for leg length. Many observers have noted a delay in appearance of the ossification centers for the proximal and distal tibial epiphyses. Harmon3 does not believe that lack of weight-bearing is the principal factor which causes shortening, although he advocates early ambulation. Kruger and Talbot(4) demonstrated increasing leg-length discrepancy with growth despite weight-bearing.

The classification of the deformity into three categories by Coventry and Johnson is a useful aid in determining the prognosis. Type 1 includes partial, unilateral absence of the fibula with a normal foot, little or no bowing of the tibia, moderate shortening, and no associated congenital anomalies of any other parts of the body. Type 2 includes complete or almost complete unilateral absence of the fibula, marked shortening, absence of tarsal bones or rays, and the classic equino-valgus deformity of the foot. Type 3 includes types 1 and 2 with other associated congenital deformities, as well as those with bilateral absence of the fibula. The prognosis is least promising for type 3.

It is not our intention to discuss all of the factors of treatment and the various surgical and conservative means of management, but rather to present a type 3 patient with a rather unusual recurrent deformity, together with her management.

Case Report

L.V. was first seen in the Louisiana Crippled Children's Clinic on May 10, 1956, at the age of 3 years and 7 months. She had bilateral terminal complete paraxial fibular hemimelia and a terminal transverse hemimelia of the right upper extremity (elbow disarticulation). There was no history of trauma during gestation nor any familial history of this or other congenital anomalies. The girl had received no previous treatment, and severe equinovalgus deformities were present in both feet. She had moderate anterior bowing of the tibiae with no skin dimples; but internal torsion and marked bilateral genu valgus were evident, the malleoli being approximately 7 inches apart when the knees were together. The right leg was approximately three-quarter inch shorter than the left.

Osteotomies

On November 13, 1956, a derotational osteotomy of both tibiae was done with some attempted correction of the valgus. The osteotomies healed well, but to correct the persistent valgus at the knees, an osteotomy of the left distal femur was done on January 29, 1957. At the same time an osteotomy to correct anterior bowing of the right tibia was carried out. These surgical procedures healed well.

L.V. was again operated upon on April 12, 1957, when an osteotomy on the right distal femur was done to correct valgus. The osteotomy on the right femur healed also, and overall good alignment of both lower extremities was achieved.

Ankle Disarticulations and Prostheses

Bilateral ankle disarticulations were done on June 21, 1957, and after healing the patient was fitted with patellar-tendon-bearing (PTB) prostheses with some end-bearing. She was able to ambulate very well with these prostheses. However, on March 6, 1958 (Fig. 1 and 2 ), X-rays showed some deterioration of the epiphyses on the lateral

sides of the proximal tibiae, the defect being more severe on the left side. The patient was also beginning to subluxate the left tibia on the femur. L.V. continued to wear her PTB prostheses, but by November 20, 1958, the valgus was again increasing. In February 1959 she was walking poorly because of the recurring valgus at both knees.

On March 20, 1959, the patient underwent bilateral tibial osteotomies to correct the valgus deformity. After the osteotomies healed, she was again placed in bilateral PTB prostheses. She had some mild persistent valgus and some anteroposterior laxity of both knees. She ambulated with prostheses until September 4, 1959, when a wedge osteotomy on the right tibia became necessary because of the recurrent valgus. She was refitted with a modified PTB prosthesis with knee locks and thigh lacers postoperatively.

On April 28, 1961, L.V. was referred to the Juvenile Amputee Clinic, at which time she was wearing her prostheses with the knee locks, utilizing a stiff knee gait. The left knee subluxated posteriorly and demonstrated 45 degrees of valgus. Approximately 25 degrees of valgus was present on the right. PTB prostheses were furnished, and the patient ambulated well. She continued to wear this type of prosthesis, although genu valgus persisted, being more severe on the left side, with some anteroposterior instability. Prosthetic fitting was achieved by building valgus into the socket.

Because of a persistent 40-degree valgus and instability of the left knee (Fig. 3 ), a high medial closing wedge osteotomy was done on the left tibia on June 30, 1967, in order to achieve more normal weight-bearing alignment and to correct the subluxation of the knee. After the wound healed, L.V. was placed in a walking caliper cast (Fig. 4 and 5 ). The osteotomy healed (Fig. 6 ), and she was again placed in bilateral PTB prostheses of the porous laminate type. Following this last surgery she has regained stability of the left knee and has shown no evidence of the recurrent valgus (Fig. 7 and 8 , Fig. 9 and 10 and Fig. 11 ).

Discussion

Genu valgus has not previously been a problem in our management of congenital absence of the fibula nor has it been a common finding in our experience, although Thompson listed genu valgum in eight out of 31 limbs with this anomaly. When valgus was present in our previous cases, it was not severe enough to require osteotomies. Prosthetic fitting was achieved by building valgus into the socket. The patient presented is the only one in whom valgus recurred after prosthetic fitting and ambulation.

The etiology of the recurrent genu valgus in this patient is obscure. It is conceivable that a persistent fibro-cartilagenous band could result in lateral bowing of the proximal tibia or at the knee joint. There was no description of any bands at the time of her previous osteotomies, and none was found at the time of the last operation. When the child was 5 years of age, X-rays of the lateral side of the proximal tibial epiphyses showed definite dysplasia. These changes may have been secondary to the genu valgus or they may represent a primary defect in the epiphysis itself.

This girl does not have normal knee joints. The high tibial osteotomy did improve the overall weight-bearing alignment, but her prognosis must still be uncertain. At the present time she is able to wear her porous laminate PTB prostheses all day every day. She has a full range of motion in both knees, and the muscle strength about the knees is good. She now has stable knees with no evidence of laxity. Since the last osteotomy was done after epiphyseal closure, the likelihood of recurring valgus is greatly reduced.

Randal A Williams, M.D. is associated with the Juvenile Amputee Clinic Crippled Children's Hospital of New Orleans, Louisiana

References:
1. Coventry, M.B., and Johnson, E.W., "Congenital Absence of the Fibula," JBJS, 34A:941-955, October 1952. 
2. Thompson, T.C., Straub, L.R., and Arnold, W.D., "Congenital Absence of the Fibula," JBJS, 39A:1229-1237, December 1957. 
3. Harmon, P.H., and Fahey, J.J., "The Syndrome of Congenital Absence of the Fibula. Report of Three Cases with Special Reference to Pathogenesis and Treatment," Surg. Gynec, and Obstet. 64:876-887, 1937. 
4. Kruger, L.M., and Talbot, R.D., "Amputation and Prosthesis As Definitive Treatment in Congenital Absence of the Fibula," JBJS, 43A: 625-642, July 1961.