Congenital clasped thumb describes a condition present at birth (but potentially not recognized until 3-4 months of age or even later) in which the thumb is flexed into the palm. Congenital clasped thumb may affect one or both thumbs but more commonly affects both. Most newborns keep the thumb positioned in the palm for the first months of life and, therefore, the diagnosis may not be clear. With age and an interest in grasping objects in the world, the clasped thumb becomes more apparent.
The basic problem in congenital clasped thumb is that there is a muscular imbalance: the muscles/ tendons that bend (flex) the thumb are stronger than those that straighten (extend) the thumb. The flexed position of the thumb is most often related to weakness of the key muscles that extend the thumb- extensor pollicis brevis and/ or the extensor pollicis longus. Other possibilities include shortening of the flexor tendons (flexor pollicis longus) or weakness of the abductor tendons (in my mind, the least likely cause). The space between the thumb and the index finger may also be tight (first webspace contracture). It is unclear if this is a cause of the problem or a secondary effect of the muscle imbalance.
|Patient is attempting to grab pen with thumb. Note flexed thumb in congenital clasped thumb (difficult to see).|
|Another view of congenital clasped thumb– note flexed position of thumb.|
McCarroll and Manske in this article classified these congenital clasped thumbs as either supple or fixed (complex). The citation was primarily in reference to the treatment of Freeman Sheldon Syndrome (windswept hand). Tsuyuguchi in this article included 3 types, supple, fixed, and associated with arthrogryposis. Multiple other diagnoses can be considered but 2 are most common: locked trigger thumb and cerebral palsy (spasticity). Both of these diagnoses are usually clear.
Treatment for most children is passive stretching of the thumb: bringing it out of the palm and holding it in an extended position. Splinting in a position of extension can also be helpful. Hard splints are one option but can be uncomfortable and therefore a challenge in the young child. Benik splints, soft neoprene splints, are an excellent choice as they provide some stretch while being comfortable even for the young child with clasped thumb.
If the thumb is not better by age 3, surgery is considered to provide better balance to the thumb. Sometimes we widen the thumb- index web space with a skin rearrangement (z- plasty) or, in situations in which the web is very tight, a flap of skin may be moved into the web. However, the key concept is to release or lengthen the tight muscles on the palm side of the thumb and strengthening the extensor tendons, often with a tendon transfer. Rarely, the thumb is so flexed that it is fused (stiffened) in a straighter position. Clearly, the type and severity of congenital clasped thumb affects the treatment but patients do well with surgery. More importantly, most patients can avoid surgery with appropriate therapy to include stretching and splinting.