Tibial Deficiency (Pediatric)

INTRODUCTION

Definition

A spectrum of deformity characterized by a longitudinal deficiency of the tibia with a shortened or absent tibia and relatively unaffected fibula.

Epidemiology

• One of the rarest congenital lower-limb deformities where the incidence is 1 in 1 million live births.
• The condition is bilateral in about 30% of patients.
• There are four syndromes that include tibial deficiency as their component:
  • Werner syndrome (polydactyly-triphalangeal thumb syndrome)
  • Tibial hemimelia diplopodia.
  • Tibial hemimelia-split hand/foot syndrome.
  • Tibial hemimelia-micromelia-trigonal brachycephaly syndrome.

Etiology

Unknown etiology. Most cases occur spontaneously although autosomal dominant or recessive transmission patterns exist.

Pathoanatomy

Tibial deficiency may be terminal or intercalary, complete or incomplete.

Classification

Jones classification: Classifies the condition into four types based on radiographic appearance. It is the most used classification for tibial deficiency.
Kalamachi and Dawe classification: Is an alternate classification system.

Jones Classification
Type	Description
1A	Tibia is completely absent (complete absence of the proximal tibial anlage).  No proximal tibia is visible on x-ray. There will be no attachment of the quadriceps mechanism to the lower leg (the extensor mechanism is absent). Hypoplastic distal femoral epiphysis.
1B	Tibia is completely absent (a proximal tibial anlage exists). Proximal tibia eventually ossifies. The extensor mechanism will function and the knee is generally functional (there is an attachment site for the quadriceps). Distal femoral epiphysis appears normal.
2	The proximal epiphysis is preserved with a short segment of tibia. The distal epiphysis is absent. The knee is functional.
3	The distal epiphysis is present with a short segment of tibia. The proximal epiphysis is absent. This is the least common type of tibial deficiency.
4	The proximal tibia is present. The fibula is relatively longer and displaced proximally at the knee. Diastasis of the ankle (distal tibio-fibular joint). The knee is functional.

CLINICAL FEATURES

Symptoms

Short leg is present at birth.

Signs

Inspection:

• Leg deformities: 
  • Shortening of the affected extremity.
  • Anterolateral bowing of the tibia.
  • The fibula is intact and may be palpable with a prominent fibular head. 
  • The knee is usually flexed and there is an associted knee flexion contracture of variable degree. 
  • Sometimes there is a skin dimple in the area of the proximal tibia.
• Foot deformities:
  • Often a supination deformity of the foot with the plantar surface pointing toward the perineum. 
  • There might be duplication of rays, shortening of the first metatarsal, and loss of medial rays with multiplication of lateral rays.
  • Duplication of the great toe may be the only clinical sign of tibial deficiency in very mild deformities. 

Motion/ROM: 

• Usually knee flexion contracture.
• The foot is often a rigid equinovarus, especially of the hindfoot.
• It is important to check stability of the knee joint in all planes and quadriceps function because treatment is primarily based on the stability of the knee joint and quadriceps function.

Associated Conditions

Tibial deficiency is associated with musculoskeletal conditions that are present in 75% of patients: 

• Preaxial polydactyly.
• Ectrodactyly.
• Ulnar aplasia.
• DDH (occurs in 20 %).
• Lobster hand (common).

DIAGNOSIS

Conventional Radiography

Projections: AP and lateral tibia/fibula
Findings: Hypoplasia or absence of tibia with an intact fibula.

• A small and minimally ossified distal femoral epiphysis may be shown on early radiographs.
• A distal femoral hypoplasia may be seen if the tibia is completely absent. 
• The proximal tibial anlage may be cartilaginous in nature and therefore will not appear on convential radiographs in young children.

Magnetic Resonance Imaging (MRI)

MRI may be helpful for evaluation of a cartilaginous anlage in a younger patient.

TREATMENT

Overview

• The aim of treatment is to achieve a functional limb equal in length to the normal limb at maturity, with a plantigrade, stable and flexible foot. The quadriceps function will determine prognosis and choice of surgical procedures. 
• Majority of patients will require surgical treatment of some form for their deformity. 

Operative Treatment

Type 1A: Knee disarticulation and prosthetic treatment because above-knee amputation may lead to a problematic stump overgrowth later on.
Type 1B and 2: 

• A tibiofibular synostosis is generally preferred.
• Syme or similar partial amputation if a functional ankle cannot be obtained.

Type 2 and 4:

• Amputation may be required distally, depending on the extent of foot and ankle deformities. 

Operation Methods

Knee disarticulation:

• Indication: 
  • Complete absence of tibia.
  • No active knee extension present (most cases).
• Method: The disarticulation is followed by prosthestic fitting.

Tibiofibular synostosis with modified Syme amputation:

• Indication: Proximal tibia present with intact extensor mechanism and minimal flexion contracture. 

Syme/Boyd amputation:

• Indication: 
  • Ankle diastasis.

Brown procedure:

• Indication: Not longer recommended due to high failure rate.
• Method: Centralization of fibula under femur.