Congenital dislocation of the knee in a three-year-old-child with Larsen syndrome: Treatment with a hexapod-type external fixator

Abstract

Congenital knee dislocation (CDK) is a rare condition, and its treatment is subject to debate. Here, we report on a new treatment for CDK (using a hexapod-type external fixator, HEF) in a three-year-old child with Larsen syndrome and grade III anterior dislocations of both knees. The left knee was treated with serial splints, whereas an HEF was used to treat an irreducible dislocation of the right knee. Two HEF aluminium rings were applied surgically. The procedure involved a distraction of the knee, then tibial posterior translation, and lastly progressive flexion. The clinical and radiological outcomes were good; after four years of follow-up, the right knee had stabilized and had a range of motion of 110°. We conclude that as an innovative, effective option for the management of CDK, the use of an HEF may constitute a relatively advantageous alternative to quadriceps tenotomy.

Introduction

Congenital knee dislocation (CDK) is a rare condition [1] that may occur alone or in association with other pathologies, such as Larsen syndrome (LS), arthrogryposis and Marfan syndrome. Larsen syndrome worsens the prognosis in CDK [2], which often requires surgery and is unlikely to resolve spontaneously [3]. The estimated incidence of this rare skeletal dysplasia is one per 250000 live births. The main clinical abnormalities include multiple dislocations of the knee, hip and elbow joints, clubfoot, relatively short stature, facial dysmorphism (hypertelorism, prominent forehead, and a depressed nasal bridge), cleft palate, and hearing loss. Reported skeletal features include joint dislocation, spinal anomalies (scoliosis and cervical kyphosis), anarchic carpal and tarsal ossification, short distal phalanges, and supranumerary carpal bones [4]. The FLN-B gene is responsible for LS, and the inheritance is dominant [5]. Larsen syndrome is classified as a filamin group and related disorder (group 7 in the international Nosology and Classification of Genetic Skeletal Disorders) [6].

Mehrafshan et al.'s new classification (based on the reductibility of the dislocation and the stability of the knee) distinguishes between three types of CDK: type I, reductible; type II, recalcitrant; and type III, irreductible [1]. Although the natural history of CDK has been described [1], [2], [3], [7], [8], [9], [10], [11], orthopaedic treatment at birth (physiotherapy, and use of a splint and cast for a few weeks to obtain and maintain the CDK reduction) is recommended for types I and II CDK [2]. For type III CDK, the methods for orthopaedic and surgical management remain subject to debate, and range from cast immobilization and axial traction [12] to surgical management with extensive quadriceps mobilization and percutaneous quadriceps tenotomy. A hexapod-type external fixator (HEF) is frequently used to correct three-dimensional deformations of the limb [13]. Here, we report on a case of CDK treated with an HEF.