The term congenital clasped thumb implies a spectrum of thumb anomalies ranging from mild deficiencies of the thumb extension to severe abnormalities of the thenar muscles, web space, and soft tissues. It is also called congenital contracted or clenched thumb.
Congenital clasped thumb is rare anomaly. Involvement is almost always bilateral.
Males are more commonly affected than females and familial incidence has been observed.
Classification of Congenital Clasped Thumb
Following is an old classification and no longer used as it was clinically not relevant.
Deficient extension only. Extensor pollicis brevis is hypoplastic or absent. Sometimes the extensor pollicis longus muscle may also be involved.The tendons of these thumb extensors are not completely absent.They are attenuated into thin thread-like tendinous structures which narrow proximally and terminate into fibrofatty tissue and there is no real muscle attached to them. There is no fixed contracture and there are no other finger or hand anomalies.
Deficient extension combined with flexion contracture.There is flexion contracture of the thumb.There are significant flexion contracture of the other digits and, occasionally, mild flexion contracture of elbows and knees.
Hypoplasia of the thumb associated with deficiencies of muscles and tendons.The involvement is more severe and diffuse.
The thumb is small, the first metacarpal and its phalanges are hypoplastic, and the metacarpophalangeal joint is unstable.
There is partial or complete absence of the extensor tendons of the thumb, thenar muscles, and abductor pollicis longus.This group probably represents a mild form of longitudinal deficiency of the radial ray.
The few cases not falling in the first three groups. Cases usually represent varying degrees of polydactyly with associated musculotendinous weakness.
Therefore following classification was proposed by McCarroll and expanded by Mih. This classification is more useful than previous one.
This initial classifications attempted to subdivide the anomaly into individual types had not been useful in the clinical setting.
Type I Congenital Clasped Thumb
Type I Congenital Clasped thumb is usually supple, and the extensor mechanism is either absent or hypoplastic.
Type II Congenital Clasped Thumb
Type II congenital clasped thumb is complex with additional findings of joint contracture, abnormality of collateral ligament , contracture of first web space , and abnormality of thenar muscle .
Type III Congenital Clasped Thumb
Type III congenital clasped thumb, clasped thumb is associated with arthrogryposis or its associated syndrome, the extensor mechanism may have minimal or no abnormality.
Presentation of Congenital Clasped Thumb
It must be noted that the first three to four months of infancy, grasp reflex is normal-the thumb is flexed across the palm and the fingers are flexed over the clutched thumb. Spontaneously and upon stimulation, the infant will actively extend his fingers and thumb.This normal grasp posture should be distinguished from congenital clasped thumb.
At initial evaluation, the thumb rests in flexion with an extension lag. Hypoplasia of the extensor pollicis brevis, extensor pollicis longus and abductor pollicis longus may be present resulting in various positions of thumb.
Xrays of bilateral hands and upper limbs should be done to find any bony abnormality and associated syndromes.
Treatment of Congenital Clasped Thumb
Type I congenital clasped thumbs are treated wit splinting of the affected joints in extension so as to prevent additional further weakening of hypoplastic extensors. Surgery is required for patients in who splinting has failed or are seen when their age is more than 2 years.
The degree of problem guides for the treatment and it must be considered during formulation of a treatment plan.
An extension that interferes with grasp or associated thumb MP joint or thumb–index finger web space contracture require surgery.
In a type I clasped thumb, skin and subcutaneous tissue release is usually enough to correct the contracture. Z plasty or dorsal rotation advancement flap may be required.
Palmar skin deficiency requires a rotational flap into the palmar aspect of the thumb MP joint.