Congenital Longitudinal Deficiency of the Tibia

Jorge A. Fabregas MD, FAAOS

Rebecca C. Whitesell MD, MPH, FAAOS

Dr. Fabregas or an immediate family member serves as a paid consultant to or is an employee of Astura Medical. Neither Dr. Whitesell nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

ABSTRACT

Congenital deficiency of the tibia or tibial hemimelia is characterized by partial or complete absence of the tibia. Many of these patients have other associated anomalies. Although the true incidence of this condition is unknown, it has a bilateral presentation in approximately 30% of patients. Treatment varies depending on the amount of tibia that is absent and the presence or absence of the extensor mechanism.

Introduction

Congenital longitudinal deficiency of the tibia is the term used to describe a longitudinal deficiency of the tibial (medial) side of the lower limb. The tibia and the medial aspect of the foot are involved to various degrees. This condition has been known by many names in the literature, including tibial hemimelia, tibial meromelia, tibial anomaly, congenital tibial absence, congenital aplasia/dysplasia of the tibia, and congenital preaxial deficiency of the lower extremity.¹^,²^,³ The two most frequently used terms in modern literature and practice are congenital longitudinal deficiency of the tibia and tibial hemimelia.

Congenital longitudinal deficiency of the tibia is defined as partial or complete absence of the tibia, with a relatively unaffected fibula. Associated limb anomalies that occur in conjunction with the tibial deficiency include varying degrees of limb shortening, an equinovarus foot, knee joint abnormalities, and longitudinal deficiencies of the foot.⁴^,⁵^,⁶^,⁷ Frequently, there is bilateral involvement (up to 30% in some case series), and patients may have other limb anomalies such as proximal femoral focal deficiency (PFFD), a lobster claw hand deformity, or radial longitudinal deficiency of the upper limbs. The incidence of longitudinal congenital deficiency of the tibia has historically been estimated as one in one million live births in the United States,⁸ but the true current incidence of the disease has not been reported. The database of the National Center on Birth Defects and Developmental Disabilities of The Centers for Disease Control and Prevention groups all limb deficiencies into either upper or lower limb deficiencies. The annual incidence of reduction deformity in the lower limbs is approximately two in 12,000 births; however, further data identifying only tibial deficiencies are unavailable.⁹

Clinical Presentation

In some instances, congenital longitudinal deficiency of the tibia can be difficult to distinguish from the much more common fibular deficiency, especially because it is difficult to precisely palpate and differentiate the soft, cartilaginous tibia and fibula in a small infant. The best clinical clue is that patients with a fibular deficiency always have an equinovalgus foot deformity, whereas patients with tibial deficiency almost always have an equinovarus foot deformity⁶^,¹⁰ (Figure 1). If there are associated ray abnormalities in the foot, patients with fibular deficiencies will have lateral ray deformities or deficiencies, and patients with tibial deficiencies will have medial ray deformities or deficiencies. The knee should be evaluated for the presence of a palpable patella, quadriceps, and a patella tendon. It should also be determined if there is active extension of the knee (functional quadriceps) because this will guide surgical decision-making.

History

Otto is widely accepted as the first person to report on a patient with tibial hemimelia in the English literature in 1841.¹ In 1877, Albert described the transference of the fibula to the distal aspect of the femur to create a fibulofemoral arthrodesis. In the early 1900s, Myers¹ described fibular transfer to recreate a knee joint. Helferich, Patrona, Motta, Busachi, and Joachimstal all individually reported single procedures in which they made slight modifications to Albert’s described procedure to achieve a fibulofemoral arthrodesis.¹
Brown¹¹ was the first to report on a series of three patients in which he performed a fibulofemoral transfer to recreate the knee joint.

In 1961, Frantz and O’Rahilly¹² were the first to attempt to define a unified language to describe all limb deficiencies. Jones et al¹³ were the first to create a classification system designed specifically to distinguish types of tibial deficiencies (known as the Jones classification). In an effort to create a classification system that would help dictate potential surgical interventions, Kalamchi and Dawe⁷ modified the Jones classification scheme.

After Brown¹¹ first described his fibular transfer technique in 1965, a substantial number of articles regarding tibial hemimelia were published until the early 1980s. By the early 1980s, some authors estimated there were up to 300 reported cases of the deficiency.³ Since the 1980s, there have been relatively few articles published regarding this deficiency, and most of the current literature focuses on the genetic aspects of the disorder. Tibial hemimelia is unique among congenital limb deficiencies because it is genetically transmitted in a substantial number of patients.³ For example, bilateral tibial deficiency associated with central cleft defect is inherited as an autosomal dominant condition.

FIGURE 1 Clinical photograph of a 3-month-old infant with an absent tibia showing the typical equinovarus position of the foot. Note the dimpling along the medial border of the missing tibia.

Classification

The ideal classification system for congenital longitudinal deficiency of the tibia would incorporate treatment guidelines, help determine a prognosis, and aid in future research. The classification system would categorize the deficiency by the variables known to affect the patient’s outcome and help identify potential interventions.

In tibial deficiencies, quadriceps function and strength, the length of the tibial remnant, the degree of ankle joint and foot involvement, and any associated musculoskeletal anomalies help determine potential interventions and can affect the patient’s overall outcome.⁶^,¹⁴ The Jones classification system, which was published in 1978, remains the most widely used system to describe tibial deficiencies.¹³ This system, however, is based on radiographic appearance and does not incorporate any of the variables known to influence patient outcomes. The classification system developed by Kalamchi and Dawe⁷ attempts to incorporate some clinical factors in the classification scheme, but this system is less widely used by clinicians. Most recently, Weber¹⁵ developed a classification and scoring system, but it is a rather detailed system and has not achieved wide popularity among clinicians.

Jones System

In the Jones classification system, groups are separated by radiographic appearance.¹³ In type 1 deficiencies, the tibia is not visible on radiographs. In type 1a deficiencies, the proximal tibia is completely absent, and the distal femoral epiphysis is hypoplastic. In type 1b deficiencies, the proximal tibia is absent on radiographs, but unossified small tibial cartilaginous anlage can be viewed by ultrasonography, arthrogram, and MRI, or can be appreciated on surgical dissection. The most distinguishing radiographic characteristic between type 1a and type 1b deficiencies is the normal distal femoral epiphysis in a type 1b deficiency. Williams et al⁴ performed surgical dissections on several patients classified as having a type 1b deficiency and found no tibial anlage despite that finding in the patient cohort used to create the Jones classification in which all type 1b patients had a tibial anlage on surgical exploration.¹³ An additional distinguishing feature between Jones type 1a and type 1b deficiencies is a lack of quadriceps function (absent active knee extension) in the type 1a group.

In type 2 deficiencies, the proximal tibia is visible on radiographs, but the tibia is substantially shortened, with the distal part at least partially absent or substantially hypoplastic. In type 3 deficiencies, the distal tibial epiphysis is visible as either a fully ossified entity or as localized calcification with the proximal tibia poorly defined. Type 3 deficiencies are very rare. In type 4 deficiencies, the tibia is shortened, and there is tibiofibular diastasis. The Jones classification is very useful for defining various tibial deficiencies based on radiographic appearance, but outcome-based factors, such as quadriceps strength, foot anomalies, and overall limb length, are not used as a basis for classification.¹³

Kalamchi and Dawe System

The Kalamchi and Dawe⁷ classification system is based on the type and degree of deformity, which the authors proposed would lead to defined treatments. Three groups are described based on clinical and radiographic findings. Type I is characterized by total absence of the tibia, proximal fibular migration, and distal femoral epiphysis hypoplasia on radiographs. Clinically, patients with type I deficiency have knee flexion contractures greater than 45°, no quadriceps function, marked equinovarus foot deformity, and, occasionally, medial ray deficiencies. Type II deficiency is defined as distal tibial aplasia. On radiographs, the proximal fibular migration is not as severe as in type I, and the distal femoral metaphyseal width and epiphyseal ossification are normal. Clinically, patients with
type II deficiency have milder knee flexion contractures (25° to 45°), positive quadriceps function, and a relatively normal knee joint articulation. Type III deficiency is defined as dysplasia of the distal tibia, with diastasis of the tibiofibular syndesmosis. Radiographically, the distal tibia shows varying degrees of hypoplasia and shortening, the amount of syndesmotic diastasis can vary, the foot is in varus, and the talus may have a nearly vertical orientation. Clinically, patients with type III deficiency have normal knee joints and well-developed quadriceps function.

Weber System

In 2008, Weber¹⁵ proposed a new classification and scoring system for tibial deformities. The classification system was developed to create a more modern system that incorporates correct anatomic terms, all types of deficiencies, and the inclusion of a scoring system to weight various associated anomalies in accordance with their effects on clinical decisions. The classification system identifies seven types of tibial deficiencies (I through VII), and five of the types have subgroups, depending on whether a cartilaginous tibial anlage is present or absent. The higher the number assigned to the classification, the more severe the tibial deficiency.

The scoring system assigns points for the presence or absence of a patella and the state of the hip, the femur, the fibula, the foot, and associated muscle function. The scoring system has a minimum score of 0 and maximum assigned value of 39; the higher the score, the less severe the impairment.

Type I is tibial hypoplasia, and type II is tibial fibular diastasis; these types have no subgroups. Type III is distal aplasia, type IV is proximal aplasia, type V is biterminal aplasia, type VI is agenesis with double fibulae, and type VII is tibial agenesis with a single fibula. Types III through VII each include two subgroups: in subgroup a, cartilaginous anlage is present; in subgroup b, cartilaginous anlage is absent.

Paley Classification

In 2003, and later modified in 2015, Paley proposed a new classification system to ensure it as an accurate descriptor of the level of tibial deficiency. It attempts to create a direct relationship between classification type, treatment, and prognosis. There are five main types, but as many as 11 subtypes (Figure 2).

Paley type I has hypoplastic nondeficient tibia: genu valgum with relative overgrowth of proximal fibula, plafond present and normal. Paley type II has proximal and distal tibial epiphysis present, but with a dysplastic ankle. They are further subdivided into A, B, and C. Paley type III is characterized by the presence of proximal tibia and knee joint, medial malleolus present, and tibio-fibular diastasis present. Further subdivision into A and B takes place. Paley type IV, with two subtypes, describes distal tibial aplasia; and type V, which has three subtypes, has complete tibial aplasia. There are modifiers to describe the presence or absence of associated deficiencies and duplications.

Comparisons

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