Radial Dysplasia

Etiology

The genetic cause of radial dysplasia remains unknown, but suspicion has long rested on a decrease in the fibroblast growth factor function as a result of a sonic hedgehog gene mutation.[3] Several potential causes of radial club hand have been proposed, including vascular insufficiency, intrauterine compression, environmental causes, drug exposure in utero, and genetic causes.[4]

Epidemiology

Radial dysplasia is an uncommon condition, but it is still the most common type of congenital longitudinal deficiency.[5] Radial dysplasia occurs in a higher prevalence in boys, with a 3 to 2 ratio.[6] Radial club hand has been estimated to occur in an estimated 1 in 55,000 births, although a study in Finland estimated radial dysplasia to occur in close to 1 in 5,000 live births.[5][7]

History and Physical

Children with radial dysplasia will present with a wide variety of abnormal thumb and forearm manifestations, as the disease represents a spectrum ranging from mild to severe. They will often present with a radially-directed angulation deformity of the hand such that the hand is often perpendicular to the forearm. The thumb is generally hypoplastic or absent. The bony abnormalities are most apparent, but underlying muscles, tendons, nerves, and joints are affected as well. The ulna is also short and bowed radially as well, generally matching the degree of radial deficiency.[4] Radial club hand is often bilateral, and children with radial dysplasia in one extremity should undergo a thorough examination of both upper extremities.[5]

Evaluation

Radiographically, the involvement of the thumb, radius, and carpal bones increases as the severity of the disease increases. Radial club hand is classified by radiographs and was classified into four types by Bayne and Klug in 1987.[8] Type I is characterized by a short distal radius (the distal growth plate is present). Type II involves a hypoplastic radius where it is smaller and thinner than the ulna, and no growth plate is present. Type III shows a partial absence of the radius (a small proximal segment of the radius remains). Type IV involves a total absence of the radius.

The condition is also commonly associated with a number of congenital syndromes. Indeed, only one-third of patients with radial dysplasia present with an isolated upper extremity malformation, thus underscoring the need for a complete physical examination to reveal commonly associated congenital syndromes.[9] A consultation with a clinical geneticist is recommended to identify possible congenital syndrome associations. Some of the most common congenital syndromes associated with radial dysplasia are VACTERL Association, VATER syndrome, Holt-Oram syndrome, TAR syndrome, and Fanconi anemia. Spine x-rays, renal ultrasound, complete blood count, and echocardiography are needed to identify associated conditions that may be present.[9] 

VACTERL association (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal abnormalities, and limb abnormalities) is usually a sporadic event, thought to be due to an error in mesodermal development.[10] 

Holt-Oram syndrome is an association of cardiopulmonary and limb defects (also known as heart-hand syndrome).[11] The error has been identified as a mutation on chromosome 12.[12]

In individuals with TAR (thrombocytopenia-absent radius) syndrome, the radius is completely absent in addition to thrombocytopenia. The thumb is usually present but hypoplastic.

Fanconi anemia is an autosomal recessive condition characterized by severe hypoplasia or aplasia of the bone marrow with anemia, leukopenia, and thrombocytopenia. In addition to genetic counseling to discover possible associations with the previously mentioned conditions above, it is also recommended to screen for Fanconi anemia in all patients with radial dysplasia who do not have a known identifiable syndrome. It is possible to diagnose Fanconi anemia before bone marrow failure occurs, and early diagnosis would provide sufficient time to search for a bone marrow match that would prevent the child from dying from aplastic anemia. Chromosomal breakage studies are recommended for all children with deficiencies of the thumb and radial border of the forearm.[4]

Treatment / Management

Treatment of radial dysplasia should start soon after birth. Initial management consists of stretching, manipulation, and splinting. This stretches tight soft tissues and radial-sided structures to help with passive correction of the deformity and allows the hand to become aligned with the ulna. Stretching should be done until the time of surgery, as preoperative soft-tissue stretching is necessary for any successful surgical procedures. This can be done by application of various splints or with serial casting. A stretching program may be conducted at home in combination with night splinting.[4] 

Additionally, the application of an external fixation device may aid with stretching tight radial tissues. This type of distraction with external fixation prior to surgery is especially helpful for children with more severe stages of radial dysplasia.[13][14](B2)

Children with mild radial dysplasia may require only stretching and splinting. Nonsurgical treatment is also indicated for children with stable joints and minimal deformity, as well as children with abnormalities that would preclude surgery. Surgery is avoided if a child has an elbow extension contracture, as the radial deviation of the wrist is necessary for the child to bring the hand to their face.[4] 

Surgical treatment of radial dysplasia aims to straighten the forearm axis and increase upper limb length, as well as either reconstructing or ablating the thumb with pollicization of the index finger. The thumb and forearm corrections are done as staged procedures. The first procedure is to align the hand and wrist onto the distal ulna, and this is generally done before one year of age. The next stage, thumb reconstruction or ablation with index pollicization, is done approximately 6 months afterward.[4]

There are two general methods to align the wrist onto the distal ulna: wrist centralization and radialization. Bringing the wrist into alignment with the distal ulna aims to increase stability and functional use of the hand and wrist. Both centralization and radialization require soft-tissue releases to be able to translate the carpus ulnarly. This often requires shaving the distal ulna or carpal resection or may require the application of an external fixator and completion of wrist realignment at a later procedure.[4] A bilobed skin flap or dorsal rotation flap can help to transfer extra tissue from the ulnar side of the wrist to the radial side.[15]

Wrist centralization aligns the distal ulna with the third digit metacarpal with fixation of pins for stability.[5] Radialization aligns the distal ulna with the index metacarpal to correct the radial deformity.[16] Centralization and radialization have shown equivalent outcomes in long-term deformity correction.[17](B2)

In radial dysplasia, the affected forearm is significantly shorter than the unaffected forearm. This difference in length can be corrected by lengthening the ulna with distraction techniques. This correction can be done after centralization in older children. These procedures can affect ulnar growth, however, and additional lengthenings may be required to maintain the correct ulnar length.[18]

Mild thumb hypoplasia that has adequate function and stability for pinch, grip, and prehension may not need surgical correction. Worse thumb deformity and function may require various reconstructive procedures.[4] Severe thumb hypoplasia often requires ablation to remove the thumb, followed by pollicization of the index finger to construct a functional thumb.[19]

Differential Diagnosis

Differential diagnoses that must be considered include TAR (thrombocytopenia absent radius) syndrome, Fanconi anemia, aneuploidy (trisomies 13 and 18), VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal abnormalities, and limb abnormalities), diabetic embryopathy, teratogens, ectrodactyly, and amniotic band syndrome.[20]

Staging

Bayne and Klug categorized radial dysplasia into four categories as per the amount of radius present.[8] Mild radial shortening is considered type 1. Type II is characterized by radius hypoplasia, type III represents cases with partial radial absence, and complete absence of the radius constitutes type IV. Then, James et al. modified the classification scheme by adding type N and 0 to describe isolated carpal anomalies in patients with a normal length distal radius. Type III and IV are the most common categories and are associated with the greatest amount of wrist radial deviation.[1][21]

Prognosis

Patients can expect to experience some degree of recurrence of wrist radial angulation.[5][8] Long-term studies have shown that although children with radial dysplasia may have significant restrictions in strength and joint mobility, they had little or no limitations on activity. Participation in society was not affected by their physical limitations.[22]

Complications

Follow-up studies show the most common complications of wrist realignment procedures are stiffness and recurrence.[17][23] While the most common complication of reconstruction is pin tract infection, vascular complications are rare and result in long-term growth problems in the transferred bones.[24]