RADIAL LONGITUDINAL DEFICIENCY
|Forearm Manifestations of Radial Longitudinal Defeciency|
The cause of radial longitudinal deficiency remains unknown. Several factors have been proposed as potential insults to the developing limb, including intrauterine compression, vascular insufficiency, environmental insults, maternal drug exposure, and genetic mutations. Upper limb development occurs during the first 4 to 7 weeks of embryonic life and coincides with the appearance of the cardiac, renal, and hematopoietic systems. Thus, single or multiple embryonic insults can result in malformations of several organ systems. Therefore, all children presenting with a radial-sided dysplasia, regardless of severity, mandate thorough evaluation for associated medical conditions. Of primary concern are the cardiac, renal, gastrointestinal, and hematopoietic systems. The spectrum of these malformations ranges from mild to devastating.
ANATOMIC MANIFESTATIONS AND CLASSIFICATIONS
The length of the average thumb extends to the distal half of the index finger’s proximal phalanx in adduction, reaching the palmar surface of the small finger’s proximal phalanx in opposition. Absence of thumb function, either from congenital or traumatic afflictions, has been estimated to diminish overall hand function by 40%.
Blauth classified thumb hypoplasia into five types according to thumb size, depth of the first web space, intrinsic muscle deficiency, extrinsic muscle deficiency, and bony/ligamentous joint stability. Manske and col-leagues divided type III thumb hypoplasia into subtypes IIIA and IIIB, based on the presence or absence of a stable first carpometacarpal joint. This subdivision has critical implications to surgical management and separates the reconstructible thumb (IIIA) from the largely nonreconstructible thumb (IIIB).
The forearm in radial dysplasia has a deficient skeleton, hypoplastic or absent musculature, and altered neurovascular anatomy. Forearm length and radial deviation of the hand/carpus are directly related to the severity of radial deficiency. The relative shortening of the limb remains constant throughout growth.
Bayne and Klug classified radial dysplasia into four types based on the radiographic severity of skeletal deficiency. Type IV dysplasia is the most prevalent, defined by complete absence of the radius. The ulna is bowed with marked radial and palmar displacement of the hand. The forearm in Type IV dysplasia averages 60% of the length of the contralateral normal side.
The overall health of the child and the severity of the osseous and soft tissue deformities guide long-term treatment plans. Parents and families are instructed on realistic goals for improving function and cosmesis of the upper limb.
Nonoperative management is the definitive treatment for children with minimal deformity and stable joints as well as in children with severe deformity and/ or associated anomalies precluding safe surgical intervention. Absolute contraindications to operative reconstruction include (1) adults and older children with established patterns of functional compensation, (2) mild deformities with good function and cosmesis, (3) associated medical anomalies precluding safe operative reconstruction, and/or (4) severe, bilateral elbow extension contractures that rely on wrist flexion and radial deviation for placement of the hand to the face.
The goals for operative reconstruction are to optimize upper limb length, straighten the forearm axis, and either reconstruct or ablate the thumb and pollicize the index finger. The forearm and thumb are addressed in staged procedures. The initial surgery is undertaken at 6 to 12 months of age and involves realigning and stabilizing the hand/carpus on the distal ulna. Thumb reconstruction/ablation begins 6 months after wrist realignment with the overall goal of completing all reconstructions by 18 months of age, thus allowing the child to achieve usual developmental milestones.
Current techniques attempt to achieve and maintain deformity correction and stability while optimizing growth, improving digital and wrist range of motion and enhancing function. Maintaining the bony carpus and distal ulnar physis are critical to optimizing upper limb length, wrist motion, and future growth potential, which are prerequisites for a successful surgical outcome. Recently, soft tissue distraction devices have been utilized as a staged procedure to achieve passive reduction of the hand/carpus in recalcitrant cases.
Anatomic reconstruction is appropriate in children demonstrating functional incorporation of their thumbs. The objective is to obtain a stable digit for pinch, grip, and prehension. Reconstruction has the advantages of maintaining a five-digit hand with the potential for polyaxial rotation at the thumb’s basilar joint surgical impossibilities with ablation and index finger pollicization.
Children with Blauth types IIIB, IV, and V have poor cerebrocortical representation of their thumbs. Reconstruction may improve cosmesis but will not restore functional use of an ignored digit. With time, the functionally excluded thumb will become a liability. The surgical details of ablation and index finger pollicization have been well documented. The goals of pollicization are to (1) preserve the neurovascular anatomy, (2) shorten the index metacarpal via diaphyseal deletion, (3) rotate and stabilize the index finger (in 120 degrees pronation, 40 degrees abduction, and 15 degrees extension), and (4) reattach and balance the musculotendinous units.
|Type II Hypopastic Thumb|
Management of radial longitudinal deficiency challenges even the most experienced orthopaedic surgeon. Cooperative effort between the orthopaedist, pediatrician, geneticist, and medical specialists ensures optimal medical evaluation and treatment of these children.
Surgical reconstruction aims to realign and stabilize the forearm, wrist, and hand while providing a functional thumb for strong pinch and grasp. Current and future research strives to identify the underlying developmental insults responsible for deformity and to enhance operative management to optimize forearm length, minimize recurrence, improve both wrist stability and motion, and further advance thumb reconstruction/ablation-pollicization.