Proximal Femoral Deficiencies and Congenital Anomalies of the Lower Leg

Introduction

The congenital deficiencies of the lower limb constitute one of the most complex areas of pediatric orthopedics. They range from minor isolated reductions of a single segment to extensive multisegmental absence requiring lifelong prosthetic or surgical management. The principal entities covered in this chapter are: proximal focal femoral deficiency (PFFD) / congenital femoral deficiency; fibular hemimelia (postaxial longitudinal deficiency of the fibula), which is the commonest long-bone deficiency in children; tibial hemimelia (preaxial longitudinal deficiency of the tibia); and congenital pseudarthrosis of the tibia. Each is associated with a characteristic set of foot, ankle, knee, and pelvic anomalies, and each demands an individualized management plan that integrates parental counseling, careful staging of surgery, prosthetic provision where indicated, and the management of associated upper-limb and visceral anomalies. The classifications used in this chapter follow those of Aitken (PFFD), Achterman and Kalamchi (fibular hemimelia), Jones (tibial hemimelia), and Crawford and Boyd (congenital pseudarthrosis of the tibia), as elaborated in Tachdjian’s Pediatric Orthopaedics, Apley & Solomon’s, Miller’s Review, and Netter’s Concise Orthopaedic Anatomy.

Proximal Focal Femoral Deficiency (PFFD, Congenital Femoral Deficiency)

Definition and Epidemiology Proximal focal femoral deficiency, also called congenital femoral deficiency, is a sporadic congenital disorder characterized by a spectrum of severity ranging from mild femoral shortening with a partially formed hip to complete absence of the proximal femur, the femoral head, and the acetabulum. The incidence is approximately 1 in 50,000 live births. The condition is typically unilateral (90%) but bilateral in 10% of cases. The etiology is largely unknown but maternal exposure to thalidomide in the 1960s produced a characteristic teratogenic pattern of PFFD with phocomelia, and other teratogens have been implicated; the great majority of cases, however, occur without identifiable teratogen exposure. Associated anomalies are common: fibular hemimelia coexists in 60-80% of cases, contralateral hip dysplasia or coxa vara, and absent or short cruciate ligaments; the proximal tibial and femoral epiphyses may be hypoplastic. Aitken Classification The Aitken classification, the most widely used scheme, divides PFFD into four classes (A through D) based on the presence and morphology of the femoral head and the acetabulum. Class A: The femoral head is present in a developed acetabulum. There is a varus deformity of the femoral neck or a pseudarthrosis at the subtrochanteric level. The femoral shaft is short but present.

Class B: The femoral head is present in a developed acetabulum, but there is no bony connection between the femoral head and the femoral shaft. The trochanteric region is connected to the shaft. Class C: The femoral head is absent or rudimentary and the acetabulum is severely dysplastic. The femoral shaft is severely shortened. Class D: Both the femoral head and the acetabulum are absent. The proximal end of the femur tapers to a point. The Pappas classification, developed later, extends the Aitken framework into nine classes that better describe the more subtle minor forms of femoral hypoplasia. Modern practice often uses both classifications in combination with the Paley classification, which emphasizes the functional considerations of hip stability and the potential for reconstruction. Clinical Features The presentation is at birth or in infancy with a striking limb-length discrepancy, the limb- length discrepancy often being concealed initially by the contralateral hip’s apparent prominence as the child stands. Examination reveals a short thigh, an externally rotated and flexed limb position, the apparent “knee at hip level” appearance in severe cases, and limited hip range of motion with deformity. The foot of the affected limb is often at the level of the contralateral knee. Associated fibular hemimelia produces additional shortening below the knee, foot deformity (typically equinovalgus), and the absence of foot rays. Stability of the hip joint depends on the Aitken class: Class A and B hips, with a femoral head in an adequate acetabulum, can be made stable by reconstruction, while Class C and D hips, with absent femoral head or acetabulum, cannot be made stable by reconstructive surgery alone. Investigations and Imaging Plain radiographs at birth may underestimate the severity of the deficiency because the femoral head is unossified; nonetheless they show the general extent of femoral shortening, the presence or absence of trochanteric ossification, and the morphology of the acetabulum. Ultrasound of the hip is useful in the neonate for assessing the cartilaginous femoral head and the acetabular cup. MRI in later infancy is the imaging modality of choice for definitive Aitken classification, identification of pseudarthrosis at the subtrochanteric level, and characterization of the cruciate ligaments and other associated knee anomalies. Repeat imaging through childhood is required to assess ossification of the femoral head and to identify the eventual class of deficiency. Treatment The fundamental treatment decision in PFFD rests on the predicted final limb-length discrepancy and the functional potential of the affected limb. A discrepancy of less than 20% (≤7-8 cm at maturity) is typically managed with limb-lengthening procedures combined with hip reconstruction; a discrepancy greater than 20% (sometimes quoted as

30-40% in severe Class D) typically commits the patient to amputation and prosthetic reconstruction or to one of the alternative procedures discussed below. Limb-lengthening protocols in Class A and B PFFD employ the Ilizarov method or the Taylor Spatial Frame, with serial distraction-osteogenesis lengthening procedures of the femur and sometimes the tibia, combined with hip reconstruction (Sofield-type osteotomy for sub-trochanteric pseudarthrosis, valgus-extension osteotomy of the proximal femur). Multiple lengthenings over the growing years are usually required to address the cumulative discrepancy, and the protocols are technically demanding, with significant complication rates including pin-track infection, premature consolidation, joint stiffness, and refracture. Knee fusion and Van Nes rotationplasty. For Class C and D deficiencies in which limb- lengthening is not feasible, the Van Nes rotationplasty offers a functional alternative: the limb is shortened, the knee is fused, the foot is rotated 180° on the longitudinal axis of the tibia so that the ankle joint serves as the functional knee, and the patient is fitted with a below-knee prosthesis that articulates with the rotated ankle. The procedure preserves an active joint (the ankle/now-knee) with proprioception and active control by the patient’s own muscles, and the functional outcomes are significantly better than those of an equivalent-level amputation. The cosmetic appearance — a foot pointing posteriorly at the level of the contralateral knee — is initially confronting for families, and careful preoperative counseling is essential. Knee fusion with Symes amputation and prosthetic conversion is a third option, in which the foot is removed and the ankle/leg complex is fused to the residual femur, producing a functional above-knee limb that fits an above-knee prosthesis. The outcome is good for activities of daily living but does not match the functional capability of the Van Nes procedure. Hip reconstruction in PFFD addresses the residual hip deformity: subtrochanteric osteotomy for varus correction, fusion of the pseudarthrosis when present, and pelvic osteotomy in Class A and B when the acetabulum requires improvement. In Class C and D, hip stability cannot be achieved by reconstruction and the patient depends on the prosthesis to provide hip stability. Outcomes Modern multidisciplinary management of PFFD produces good functional outcomes for most children. The Van Nes rotationplasty in particular has been the subject of long-term follow-up studies showing excellent functional outcomes, high participation in athletic and occupational activities, and reasonable cosmetic acceptance with appropriate prosthetic clothing. The lengthening protocols for Class A and B disease produce equivalent functional outcomes when successful, but at the cost of multiple operations, prolonged frame wear, and significant complication rates.

Fibular Hemimelia (Postaxial Longitudinal Deficiency of the Fibula)

Definition and Epidemiology Fibular hemimelia is the commonest long-bone deficiency in children, with an incidence of approximately 1 in 50,000 to 1 in 100,000 live births. The condition is characterized by partial or complete absence of the fibula, with associated deformities of the tibia, the foot, and the ankle. The fibular hemimelia spectrum is best understood as a whole-limb deficiency rather than an isolated fibular defect, with PFFD coexisting in many cases, anteromedial bowing of the tibia, tibial shortening, anteromedial dimple of the leg, foot deformity (typically equinovalgus), and absence of the lateral foot rays. The Achterman and Kalamchi classification divides fibular hemimelia into three types: Type IA, with a fibula present but shortened; Type IB, with a partial fibula and a fibrous tether to the talus; and Type II, with complete absence of the fibula. The Achterman-Kalamchi Type II — complete fibular absence — is the most severe and is associated with the greatest degree of tibial bowing, foot deformity, and PFFD. Clinical Features Presentation is at birth with the constellation of anteromedial bowing of the tibia, a skin dimple over the apex of the bowing, foot deformity ranging from mild valgus to severe equinovalgus, and absence of the lateral foot rays (most commonly the fifth and fourth rays, and in severe cases the third). The fibula may be palpable as a partial bone, a fibrous bandlike structure (the cartilaginous anlage), or entirely absent. The knee shows associated anomalies — cruciate ligament absence is common, particularly the anterior cruciate, with consequent knee instability that becomes clinically important as the child grows. The hip is often associated with PFFD or simple femoral shortening. Limb-length discrepancy at maturity ranges from a few centimeters in the mildest cases to 20 cm or more in the most severe. Treatment Management decisions in fibular hemimelia are based on the predicted limb-length discrepancy, the foot deformity, and the function of the foot. The classical teaching, formulated by Birch and others, emphasized the function of the foot rather than its appearance: a foot that can be made stable, plantigrade, and adequately positioned within a normal shoe is worth preserving, while a foot that cannot be made functionally useful is better amputated. The critical assessment is therefore of foot function: a foot with three or more rays is generally considered salvageable, while a foot with fewer than three rays is generally considered better amputated. Limb-lengthening with foot reconstruction is the treatment of choice for patients with adequate foot function and a discrepancy projected to be less than 20% at maturity. Serial tibial lengthenings using Ilizarov or Taylor Spatial Frame, combined with corrective osteotomies of the tibia to address the anteromedial bowing, foot reconstruction (often including a Syme-amputation-style approach but preserving foot rays where possible, or a Boyd procedure with calcaneo-tibial arthrodesis), and ligament reconstruction of the knee,

achieve excellent functional outcomes in many cases. Multiple operations over the growing years are typically required. Syme amputation (disarticulation at the ankle, preserving the heel pad), or its variant Boyd amputation (incorporation of the calcaneus), is the alternative for patients with a non-functional foot or a discrepancy too severe for lengthening. Early amputation in the first year of life is generally well-accepted; the residual limb develops with the child, the prosthesis is upgraded as the child grows, and functional outcomes are excellent in long- term studies. The decision between amputation and lengthening should be made in conjunction with the family, with attention to the practical demands of multiple lengthening operations over years and the contrast between excellent prosthetic function and the unpredictability of complex limb reconstruction.

Tibial Hemimelia (Preaxial Longitudinal Deficiency of the Tibia)

Definition and Epidemiology Tibial hemimelia, the partial or complete absence of the tibia with a preserved fibula, is substantially less common than fibular hemimelia, with an incidence of approximately 1 in 1,000,000 live births. Unlike fibular hemimelia, tibial hemimelia is frequently familial, with autosomal dominant inheritance described in many series, and is often associated with hand anomalies and other syndromic features (Werner syndrome, tibial aplasia- ectrodactyly).

Jones Classification The Jones classification, the standard scheme, divides tibial hemimelia into four types based on the radiographic appearance of the tibia. Type I, the most severe, comprises Type IA (complete absence of the tibia, hypoplastic distal femur) and Type IB (complete absence of the tibia but normal distal femur). Type II is partial absence of the distal tibia with a preserved proximal tibia and a functional knee. Type III is partial absence of the proximal tibia with a preserved distal tibia and a functional ankle. Type IV is the diastasis variant, in which both the tibia and fibula are present but the distal tibiofibular relationship is markedly abnormal with the foot displaced into varus. Clinical Features and Treatment Presentation at birth shows the characteristic short limb with the foot in varus, the absent or hypoplastic tibia palpable as a short bony stump or no tibia at all, the fibula prominent on the lateral side, and associated hand anomalies in many cases. The knee functions only when the proximal tibia is present (Jones Types II and III); in Type I disease, no functional knee exists and reconstruction must address this deficit. Treatment decisions follow the Jones type. For Type I disease, knee disarticulation and a prosthesis is the standard treatment, with reasonable functional outcomes. For Type II and Type III disease, fibular centralization (Brown procedure, where the fibula is centralized to function as a tibia) can be attempted, but the long-term functional outcomes have been disappointing because the centralized fibula often fails to support body weight; below-knee amputation with a functional ankle prosthesis is often preferred. For Type IV disease, ankle reconstruction

with re-establishment of the distal tibiofibular relationship and foot stabilization is the treatment.

Congenital Pseudarthrosis of the Tibia

Definition, Epidemiology, and Classification Congenital pseudarthrosis of the tibia (CPT) is a rare congenital condition characterized by anterolateral bowing of the tibia in infancy that progresses to spontaneous fracture, followed by failure of normal fracture healing — a true pseudarthrosis. The incidence is approximately 1 in 250,000 live births. Approximately half of cases are associated with neurofibromatosis type 1 (NF1), and CPT is one of the classical orthopedic manifestations of NF1; the remainder are sporadic or associated with fibrous dysplasia. The Crawford classification, the most widely used, divides CPT into four types based on the radiographic morphology of the affected tibia. Type I: Anterolateral bowing of the tibia with a thickened cortex and a normal or thickened medullary canal. The bowing has not yet progressed to fracture. Type II: Anterolateral bowing with a sclerotic, narrow, or absent medullary canal but no fracture. Type III: Anterolateral bowing with a cystic lesion of the tibial diaphysis. Type IV: Established pseudarthrosis with frank discontinuity of the tibia. The Boyd classification, an earlier scheme, uses descriptive categories from “constricted” (Type I) through “non-progressive” (Type V) and remains in occasional use. Clinical Features Presentation is in infancy with an anterolateral bowing of the tibia, often noted in the first 6-12 months of life as the child begins to bear weight. The bowing progresses, the affected leg shortens, and a spontaneous fracture may occur without significant trauma, typically between 12 and 24 months of age. Once fracture has occurred, the pseudarthrosis fails to heal with standard fracture management — closed reduction, casting, or even intramedullary fixation — and progressive shortening, deformity, and recurrent failed surgical attempts are the natural history. Café-au-lait spots, axillary or inguinal freckling, neurofibromas, Lisch nodules, and other features of NF1 should be sought. Treatment CPT is one of the most difficult problems in pediatric orthopedics. The natural history of untreated disease is progressive deformity, shortening, and disability; the surgical management requires balancing the goal of achieving union with the realities of multiple operations, prolonged immobilization, and the high failure rate of every available technique. The current standard of care combines several principles: protection of the bowed but unfractured tibia with bracing to prevent the index fracture; aggressive resection of the pseudarthrotic segment back to healthy bone if and when fracture has

occurred; restoration of length and alignment; reliable internal fixation, traditionally with an intramedullary rod (the Williams rod or the Fassier-Duval telescoping rod) augmented in some centers by external fixation; biological enhancement of the pseudarthrosis site with autogenous bone graft, BMP-2 (or BMP-7) infusion, and adjunct therapies; and protection of the healed segment with continued bracing until skeletal maturity. The Ilizarov method, with resection-compression of the pseudarthrosis and lengthening of the adjacent normal bone, has produced good results in experienced hands. Vascularized fibular grafting from the contralateral leg, popularized by the work of Weiland and others, is an option for refractory cases. Despite all of these techniques, refracture is common, multiple operations are usually required, and amputation remains a legitimate option for patients with extensive failure and disability.

Other Congenital Anomalies of the Lower Leg

Posteromedial Bowing of the Tibia Posteromedial bowing of the tibia is a congenital deformity of the tibial diaphysis with the apex pointing posteromedially. In contrast to anterolateral bowing (which is associated with CPT), posteromedial bowing is benign and typically resolves spontaneously over the first few years of life, although it produces a predictable limb-length discrepancy that requires later management. The condition is typically isolated and not associated with neurofibromatosis. The natural history is one of progressive resolution of the bowing with growth, but with a predictable shortening of the affected tibia that ranges from a few millimeters to several centimeters at skeletal maturity; epiphysiodesis of the contralateral distal femur or proximal tibia, planned by careful prediction of remaining growth, addresses the discrepancy.

Anterolateral Bowing of the Tibia Anterolateral bowing — the precursor of CPT and almost always associated with NF1 — is discussed in the preceding section. The critical clinical importance is the prevention of fracture by bracing during infancy and early childhood.

Congenital Pseudarthrosis of the Fibula Congenital pseudarthrosis of the fibula is much less common than the tibial form and typically requires no specific treatment, since the fibula contributes only a small fraction of lower-limb load-bearing. Symptomatic cases can be treated by partial fibulectomy or pseudarthrosis revision. Congenital Pseudarthrosis of the Clavicle Congenital pseudarthrosis of the clavicle is included here for completeness, though it is an upper-limb condition. It is almost always right-sided (the rare left-sided cases are typically associated with dextrocardia), produces a painless or mildly painful prominence at the mid-clavicle in infancy or early childhood, and is treated by resection of the pseudarthrosis with bone graft and internal fixation when symptomatic; many cases require no treatment.

General Principles of Management

The management of congenital limb deficiencies follows several unifying principles. First, the assessment must be comprehensive: the entire affected limb, the contralateral limb, the pelvic and hip joints, the spine, and the upper limbs and viscera must be examined and imaged, since associated anomalies are common. Second, the projection of final limb-length discrepancy at skeletal maturity — using the Moseley straight-line graph, the multiplier method, or the more sophisticated Paley methods — is the foundation of treatment planning, since the discrepancy guides the choice between lengthening, amputation, or compensatory shortening of the contralateral limb. Third, the treatment plan must be developed in close consultation with the family, with realistic discussion of the multiple operations and prolonged rehabilitation that limb-lengthening protocols entail versus the predictable and rapid recovery of a well-fitted prosthesis. Fourth, the function of the foot — its potential to bear weight, fit in a shoe, and contribute to gait — is often the single most important factor in deciding between salvage and amputation. Fifth, the timing of definitive procedures must be coordinated with the child’s growth and developmental milestones; early amputation in the first year of life allows prosthetic adaptation through development, while lengthening protocols are typically initiated in early childhood and continued through adolescence.

Summary and Take-Home Points

The congenital deficiencies of the lower limb form a spectrum of conditions whose management is among the most challenging and rewarding in pediatric orthopedics. Proximal focal femoral deficiency (PFFD) ranges from mild femoral hypoplasia to complete absence of the hip joint, classified by Aitken and managed by limb-lengthening, hip reconstruction, knee fusion with Symes amputation, or Van Nes rotationplasty depending on the predicted limb-length discrepancy and the morphology of the proximal femur. Fibular hemimelia, the commonest long-bone deficiency, is best understood as a whole- limb deficiency with associated tibial bowing, foot deformity, and frequent PFFD; the decision between lengthening with foot reconstruction and Syme amputation rests on foot function and the predicted limb-length discrepancy. Tibial hemimelia is rare, often familial, and classified by Jones into four types whose management ranges from knee disarticulation for complete absence to below-knee amputation or fibular centralization for partial defects. Congenital pseudarthrosis of the tibia, half of cases associated with neurofibromatosis type 1, is one of the most difficult problems in pediatric orthopedics, requiring multiple operations, biological enhancement, and lifelong protection; amputation remains a legitimate option for refractory cases. Across all of these conditions, the principles of comprehensive assessment, projection of final limb-length discrepancy, multidisciplinary discussion with the family, and integration of foot function into the treatment decision determine successful outcomes.