Congenital limb deficiencies
Features
Treatment options
Femoral deficiencies
Congenital short femur (femoral length >50% of normal side)
If congenital short femur, then lengthen femur (or shorten contralateral femur)
Proximal femoral focal deficiency (PFFD)
If PFFD with stable hip, length <50%, then proximal femoral osteotomy, foot ablation, and knee fusion with fitting as a through-knee amputee
Stable hip (coxa vara, has proximal femur and acetabulum ± pseudarthrosis
Unstable hip or subtotal absence of proximal femur
If PFFD with unstable or subtotal absence, then foot ablation and knee fusion or custom prosthesis
Longitudinal deficiency of the fibula
Femoral deficiency common
If three or more rays on foot, then foot reconstruction, epiphysiodesis versus lengthening for leg length inequality
Fibula absent or hypoplastic
Knee cruciate deficiency, patellar dysplasia
If severe leg length discrepancy anticipated and/or severe foot deformity (<2 rays), then foot ablation and prosthetic fitting as a below-knee amputee
Tibia short with anteromedial bow
Equinovalgus foot with tarsal coalition, lateral deficiency
Longitudinal deficiency of the tibia
1/1 million births
If no tibia present and no knee extension, then through-knee amputation and prosthetic fitting as through-knee amputee
Most sporadic, rarely genetic (AD, AR)
Hand anomalies most common, visceral rare
If proximal tibia present, then foot ablation ± proximal tibiofibular synostosis and prosthetic fitting as a below-knee amputee
Femoral hypoplasia
Tibia can be (1) completely absent, (2) proximal tibia present with intact extensor mechanism, or (3) distal tibial deficiency with diastasis between tibia and fibula
If distal diastasis, then foot ablation and prosthetic fitting as a below-knee amputee
Knee cruciate deficiency, patellar dysplasia
Fibula angulated, dislocated proximal tibiofibular joint
Equinovarus or equinus foot
A spectrum of abnormalities occurs in patients with longitudinal deficiencies of the femur, tibia, and fibula. Variations of femoral deficiency include (a) congenital short femur and (b–d) proximal focal femoral deficiency. Tibial deficiencies include (e, f) complete absence of the tibia, (g, h) presence of an intact proximal tibia and extensor mechanism, (i) tibiofibular diastasis, (j) a fibular deficiency with a dysplastic fibula, and (k) postsurgical fibular to proximal tibial transfer with fusion of the calcaneus to the distal fibula (modified Boyd) to improve function as a below-knee amputee.
It is important to address the family’s fears of the recurrence of similar deformities or deficiencies in future offspring. However, if there is not already a family history, it is extremely unlikely future children will be affected as most cases are thought to be spontaneous mutations.
Modified Marquardt procedure. The periosteum is reflected off the distal aspect of the recipient bone, as well as off the proximal end of the “cap” (fibular head). The proximal aspect of the fibular graft is placed into the recipient bone, and the periosteal sleeve from the fibular graft is repaired. The periosteal sleeve from the recipient bone is wrapped around the graft and sutured to itself and to the periosteum over the distal aspect of the fibular graft
Patient Evaluation
What are the missing segments, and how do they affect function?
Are there any muscle, nerve, fat, or skin abnormalities or dimples to suggest additional soft tissue involvement?
What is the resting posture of the limb?
What muscle groups are used to effectively flex, extend, abduct, and adduct the limb?
Which joints are stable or unstable?
Thoroughly examine both upper and lower extremities, look at the spine, and watch the child move around and do activities of daily living. Focusing the exam on the most severely involved limb is a common pitfall. Carefully consider what tasks are functionally important for the child and how surgery may improve or worsen their function. For instance, a child with PFFD may have a very externally rotated femur with limited hip range of motion. Internally rotating the femur may improve the gait but will not easily allow for sitting cross-legged on a floor, which is important in some communities. If there is an associated scoliosis, determine how important spine flexibility is for gait and other activities.
For the lower limbs, determine the length inequality. The relative contribution of the femoral segment is determined with the hips and knees flexed while the child lies supine on a firm surface. The relative contribution from the leg and foot segments is determined with the child prone with the hips extended and the knees flexed. For children who can stand, the total discrepancy can be measured with the patient standing on calibrated wooden blocks or a measurable platform. Contractures at the hip, knee, and/or ankle may contribute to the functional discrepancy, as may shortening associated with a foot deformity, such as clubfoot.
Additional Studies
X-rays supplement clinical information regarding the location of a bone deformity and the limb length discrepancy. If there is a joint contracture or the child is very young, lateral views of both lower limbs give a good idea of any relative discrepancy. Delayed ossification of the cartilage anlage can give the appearance of a missing joint. Look for secondary signs of joint formation by examining the more normal side of the joint. For instance, a well-defined acetabulum indicates the presence of a cartilaginous femoral head. An ultrasound can help identify an unossified or partially ossified cartilaginous anlagen. If the local anatomy remains unclear, it may be wise to wait and reevaluate in 1 or 2 years.
General Treatment Considerations
Predicting future growth is essential, and the surgeon should be prepared to predict the projected discrepancy.
For an infant or small child with a congenital, (non-acquired) deficiency, the limbs will grow proportionally. An estimate of the projected discrepancy will determine if an amputation at a young age should be considered. A useful tip: when comparing limb lengths, a heel on the shorter side that rests at the level of the mid-tibia on the longer side will also rest at this level at skeletal maturity. In an average height person, the distance from the mid-tibia to the ground is about 20 cm, which is about the maximum difference one would consider lengthening a limb in a resource-rich country. This can help project length differences and guide whether an amputation or length equalizing surgery is most appropriate.
At maturity, the average length of a femur is 41 cm for girls and 44 cm for boys [1, 2]. The average length of a tibia is 34 cm for girls and 37 cm for boys [1, 2]. For example, if the affected femur measures 80% of the length of the normal, contralateral femur, a rough estimate of the discrepancy at maturity will be 20% of 44, or 8.8 cm, for a boy.
Another rough guide: girls reach half their skeletal height by age 3 and boys by age 4. The discrepancy at these ages can be doubled for an estimate of final discrepancy. At ages 6 for girls and 8 for boys, the discrepancy can be multiplied by 1.5 [3].
