Congenital Foot, Ankle, and Lower Extremity Conditions

TYLER A. GONZALEZ

RAYMOND HSU

Congenital foot and ankle conditions are common problems that pediatricians and orthopedic surgeons see throughout their careers. Pediatric foot and ankle surgery is becoming its own unique field within orthopedics, and knowledge of these conditions is a key component in orthopedic education. In general, pediatric foot and ankle conditions can be seen at birth, progress over time, or develop in adolescence. Many of these resolve spontaneously, but others may require operative management in order to improve ambulation, create a plantigrade foot, or even permit shoe wear. Congenital disorders of the foot and ankle can occur in isolation; however, many occur as sequela of genetic syndromes or neuromuscular diseases. Orthopedic surgeons, podiatrists, and other musculoskeletal clinicians should be cognizant of the potential underlying systemic implications of these congenital manifestations. Just as critical is an awareness among other clinicians of what foot and ankle deformities may be attributed to congenital etiologies. This chapter discusses the most common congenital foot, ankle, and lower extremity conditions, their etiology, associated conditions, and treatment options.

Knee Dislocations

Congenital Dislocation of the Knee

Congenital anterior dislocation of the tibia relative to the femur is a rare condition, with an estimated incidence of less than 1 per 100,000.¹ Examination findings range from a hyperextension deformity of the knee or genu recurvatum to the most severe form demonstrating frank dislocation. Radiographs confirm a fixed anterior subluxation or dislocation of the tibia on the distal femur. Although it may occur in isolation, there is an association with arthrogryposis, Larsen syndrome, and myelomeningocele.²,³ There is also an increased incidence with breech delivery and other “packaging disorders” including clubfeet, congenital vertical talus (CVT), and developmental hip dysplasia.²,³,⁴,⁵

Simple hyperextension deformities and dislocations not associated with other disorders can generally be treated early with gentle stretching, serial casting, or splinting in a Pavlik harness.²,⁵,⁶ Frank dislocations or cases that fail conservative management may need surgical treatment with either (1) quadriceps lengthening and anterior capsulotomy or (2) femoral shortening and variable anterior releases.⁷ With appropriate early treatment, conservative or surgical, patients can generally expect to have functional range of motion and ambulate without a brace, but may have a stiff-knee gait pattern.²,⁷ There are only a few case reports of congenital dislocations identified and treated in adolescence.⁸,⁹,¹⁰ All required surgical treatment with some combination of quadricepsplasty, open reduction, frame distraction, and femoral shortening to reconstruct an extremity that allowed ambulation.

Congenital Dislocation of the Patella

Congenital dislocation of the patella is characterized by irreducible lateral dislocation of the patella, flexion contracture of the knee, knock-knee deformity (genu valgum), and rotation deformity of external tibial torsion. The fixed deformity is not to be confused with patellar instability or recurrent patella dislocation, more often seen later in development, which can often be treated conservatively.¹¹,¹²,¹³ The congenital disorder is almost if not always associated with systemic disorders such as arthrogryposis and chondrodysplasia punctata. In addition, at least two published series have found that all patients have associated foot deformities.¹¹,¹⁴

Although the knee deformity is not subtle and generally recognized at birth, the diagnosis may be delayed because the patella does not ossify and is not visible on radiographs until 3 to 5 years of age. Palpation, however, should identify the patella laterally and demonstrate the absence of the patella anteriorly. Ultrasound may confirm the diagnosis early. By definition, conservative measures are ineffective, and early surgical correction involves quadriceps lengthening, lateral release, and medial tightening. Without early surgical correction, significant disability results including compromised ambulation. If surgery is delayed until adolescence or early adulthood, treatment requires bony reconstruction with distal femoral and tibial tubercle osteotomies combined with soft tissue reconstruction.¹⁵ Treatment even later in life after the development of arthritis may be addressed with arthroplasty and concurrent soft tissue reconstruction.¹⁶,¹⁷

Tibial Bowing

Anterolateral Bowing

Congenital bowing at the middle and distal third junction of the tibia with the apex in the anterolateral direction and with a high risk of progressing to pathologic fracture is characteristic of neurofibromatosis type 1 (NF1). Although the bowing is often noted at birth, there may be a delay in recognition of the fracture risk and the underlying systemic syndrome. The bowing in combination with any one of the other seven diagnostic criteria for the syndrome is sufficient to make the clinical diagnosis of NF1.¹⁸ Patients with NF1 present with wide clinical variability, however, and less than 5% have tibial pathology.¹⁹ Radiographs of anterolateral bowing associated with NF1 will confirm the direction of bowing and demonstrate cortical thickening, particularly on the posteromedial aspect, and a narrower medullary canal.²⁰ Pathologic fractures, however, frequently occur at the apex, which heal abnormally leading to nonunion or pseudoarthrosis (Fig. 13-1). Although typical of anterolateral bowing, tibial pseudoarthrosis may also be seen with amniotic bands, fibrous dysplasia, intrauterine trauma, osteogenesis imperfecta, or any endocrine process that weakens the bone.¹⁸

Although the entire entity is often referred to as congenital pseudoarthrosis of the tibia, this is a misnomer as the bowing is congenital, but the fracture and subsequent pseudoarthrosis are almost always seen only later.²¹ Unlike the early stages with cortical thickening, later radiographs will demonstrate cystic changes, frank fracture, or tapered thin cortices of a pseudoarthrosis. Even when fractures heal, healing is usually abnormal, and the risk of refracture is high.

FIGURE 13-1. Anteroposterior and lateral radiograph of anterolateral tibial bowing with pseudoarthrosis.

The goal of treatment in children identified with anterolateral bowing is prevention of fracture. The conservative approach involves casting in young children and bracing in older children until skeletal maturity, with obvious compliance difficulties. Success with purely conservative measures, at least in patients with NF1, appears to be rare.²¹,²² Surgically, prophylactic bypass strut grafting has been shown to be successful in several series.²¹,²² Simple osteotomy of the bowed segment with local bone grafting and intramedullary rod fixation appears to inevitably fail and only hasten the development of a pseudoarthrosis. In patients who have already fractured and developed a pseudoarthrosis, options include intramedullary nailing with bone graft, vascularized fibular grafting, and thin-wire external framing.²,²¹,²³

Refracture even after bone grafting and fixation is relatively common, and skeletal maturity is believed but not proven to be a milestone for diminished risk.²³,²⁴ Other long-term functional issues include leg length discrepancy, ankle stiffness if intramedullary rods crossed the ankle joint, and valgus ankle deformity if there was a concurrent fibular pseudoarthrosis.²¹,²²,²³,²⁴

There also exists a separate subset of anterolateral tibial bowing associated with ipsilateral hallux duplication.²⁵,²⁶,²⁷,²⁸,²⁹,³⁰ Recognizing these patients as a different cohort from patients with NF1 is important as this “benign” form is not associated with the development of pseudoarthrosis. Although some may still benefit from operative correction, many of these resolve spontaneously, with only a subclinical leg length difference. Additionally, fractures and osteotomies tend to heal normally in these patients in contrast to NF1-associated bowing. Other than the obvious duplication of the hallux, the bowing also tends to be more proximal and mid-tibial, and there may be a duplication of the medullary canal at the apex of the tibial bow.

Anteromedial Bowing

Anterior or anteromedial tibial bowing with the apex pointed away from the fibula is associated with fibular hemimelia.³ Radiographs reveal a deficient fibula and are diagnostic. Associated conditions and prognosis are per the underlying fibular hemimelia.

Posteromedial Bowing

Posteromedial bowing of the tibia has an undetermined etiology but is associated with calcaneovalgus deformity of the foot. The deformity is obvious at birth, with the combination of tibial and foot deformity causing the foot to be in a severely dorsiflexed position.³ Although the majority of the angular deformity spontaneously resolves, residual clinically relevant shortening typically persists.³¹,³²,³³ Fracture and pseudoarthrosis do not develop as with anterolateral bowing. The posterior bowing is more likely to completely correct than the medial bowing, leading to a residual valgus deformity. Treatment ranges from conservative approach with bracing and stretching to surgical with osteotomies to correct angulation and length. The deformity is almost always unilateral, and the severity of bowing is predictive of the degree of eventual limb length discrepancy.³² With incomplete correction, limb length discrepancy, valgus deformity, and weak plantar flexion may all be symptomatic later in life.

Limb Deficiencies

Proximal Femoral Focal Deficiency

Proximal femoral focal deficiency (PFFD) is a congenital abnormality of the proximal femur that occurs in 1 in 52,000 live births.³⁴ The spectrum of disease ranges from a short femur, to an absent femur, to an absent hip or even a femoral neck pseudoarthrosis. PFFD is often sporadic, but there are rare autosomal dominant forms that frequently occur with abnormal facies.³⁵ There are several associated conditions including fibular hemimelia, anterior cruciate ligament (ACL) deficiency, knee contractures, and coxa vara.

Physical exam and observation include a short and bulky thigh that is flexed, abducted, and externally rotated. Instability of the hip and knee are common physical exam findings. The ACL is often absent, and there can be an associated flexion contracture of the knee. In up to 45% of cases, there is associated fibular hemimelia with a short tibia and equinovalgus foot deformity.³⁵ Radiographs of the femur, tibia, and foot should be obtained bilaterally.

The most common classification system used is described by Aitken. It is divided into four classes based on radiographs of the acetabulum, femoral shaft, femoral head, and attachment between the femoral head and the shaft at maturity.

Class A: Femoral head present, acetabulum normal

Class B: Femoral head present, acetabulum mildly dysplastic

Class C: Femoral head absent, acetabulum severely dysplastic

Class D: Femoral head absent, acetabulum absent

Treatment is dependent on the function of the foot, hip joint stability, and ultimate leg length deficiency. Initial decision making includes determining the final limb length discrepancy at maturity; deciding whether or not the foot should be saved, amputated, or rotated; determining if the knee should be fused; and determining if the hip stability is sufficient or if it should be stabilized by fusing the proximal femur to the pelvis.³⁵

Fibular Hemimelia

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