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Discussion |
An 8-year-old boy presented with inability to extend his fingers. Examination revealed congenital hypoplasia of the extensor tendons. He was treated with tendon transfers. We present a review of the literature and management of such cases.
Keywords: clasped thumb, extensor tendon deficiency, fingers, tendon transfer,
J.R.Coll.Surg.Edinb., 46, February 2001,57-58
Of the many congenital anomalies of the hand those involving the extensor mechanism are very rare. Zadek reported the first case on 20th of October 1933 at the meeting of New York Academy of Medicine.1 These were first described in relationship to a clasped thumb.1 It is extremely rare, however, to find cases of total absence of finger extensors. Review of the literature has revealed only seven cases reported, to date; five by Tsuge in 1975, one by Inokuchi in 1973 and one by Vartany et al in 1996.2,3,4 White and Jensen (1952) described eight cases of clasped thumb in which five also had finger involvement.5 Weckessere in 1955 reported five cases of which three had finger involvement as well.6 Crawford et al (1956) reviewed six further cases and noted finger involvement in four cases with no family history.7 Weckesser (1955) in an excellent review of the congenital clasped thumb, classified the condition into four groups. The first group, with isolated thumb involvement, showed a sex-linked recessive inheritance, while in the remainder there was no distinctive hereditary pattern.8
This is a heterogeneous trait. It has been reported as an autosomal dominant,5,9 autosomal recessive,10 and X-linked recessive trait.11 By contrast, Crawford et al (1966) and Tsuge (1975) did not find any obvious family history in their patients.2,7
JM, an 8-year-old boy, was first seen in 1996 with the complaint of inability to extend his fingers and thumb since birth. Born to healthy parents, he had normal intelligence. He was able to grasp small objects but was unable to grasp large objects. Examination revealed loss of extension at the metacarpophalangeal (MP) joints of the fingers and thumb. Apart from this deficit, there was no other neuromuscular deficit noted in his limbs. The wrist extensors were working normally. There was no history of any systemic illness or any family history of a similar condition.
He underwent tendon transfer for correction of this extensor deficiency. At surgery, tendons of extensor pollicis longus, extensor indicis, extensor digitorum comminus and extensor digiti quinti were present but were very hypoplastic. The brachioradialis tendon was transferred with a palmaris longus graft to extensor pollicis longus. Extensor carpi radialis longus, with a graft harvested from extensors of third and fourth toe, was then attached by a multitail graft to the extensor expansion of the four fingers. Postoperatively, the patient required active physiotherapy to regain extension of the MP joints.
The most challenging aspect of this anomaly is to account for its pathogenesis. Crawford et al (1966) proposed that the defect occurs most probably at the myoblastic stage of development, which would account for the rudimentary musculotendinous structures.7 Weckesser et al (1968) relate some of these cases to arthrogryphosis and describes a sexlinked recessive mode of inheritance.6
One hypothesis is that it is due to failure of the radial nerve to innervate the affected muscle groups during foetal development.
At 6 weeks the muscles have become distinctive and by 7 weeks tendons are seen as distinct entities. Innervation is deferred until 26-28 weeks, when motor end plates appear. Thus, innervation plays no part in morphogenisis of muscles. Though not essential for development of skeletal muscles, normal innervation is essential for maintenance of normal function.9 The postulate that congenital absence of the skeletal muscles is secondary to degenerative change of once developed muscles, due to lack of later innervation,9 is supported by the generalized electrophysiological abnormalities in motor and sensory nerve conduction velocities.10 However, Takahashi et al (1978) found that extensor digitorum comminus was replaced by fibrofatty tissue in the forearm and a branch of the radial nerve was found to enter into the fibrofatty tissue.12
When all the fingers are involved, the tendons of extensor digitorum comminus are hypoplastic. They are usually subluxed into the valleys at the MP joints and insert into a poorly developed extensor expansion. The extensor indicis proprious and extensor digiti minimi may be absent, but the wrist extensors are usually normal. The abnormal tendons end proximally in the forearm in fibrofatty tissue with no muscle fibres present.2,3
Patients with extensor hood deficiency in isolated fingers cannot extend the proximal interphalangeal joint (PIP) but can readily extend the MP joint. Those with all finger involvement have loss of active MP joint extension. Pronation and suppination are not affected. Tendons are dislocated in the ulnar valleys between the metacarpal heads.
There is an association of extensor muscle aplasia with generalized polyneuropathy.11 Generalized electro-physiological abnormalities, such as delayed motor and sensory conduction velocities, low sensory nerve action potential and neurogenic electromyographic (EMG) patterns, have been described in some cases.
Splintage is used to minimize the severity of the contractures. Almost all of these fingers develop flexion contracture that have to be released prior to definitive corrective surgery.
Surgery is also required for cases resistant to conservative treatment. The recommended age for soft tissue release is one to two years. Tendon transfer is done around 5 years of age. Loss of extensor mechanism over the proximal inter-phalangeal joints is corrected either by transferring flexor superfacialis to the extensor mechanism or adopting the lateral band and attached intrinsic muscles from an adjacent normal finger, as a motor unit in the abnormal finger.13
When all extensor tendons are absent, extensor carpi radialis longus is used with a multi-tail graft from palmaris longus to supply MP extension.
When one digit is involved most of the release procedures can be done at one sitting. All areas of secondary shortening must be corrected; this may include the palmar skin, superficial flexors, palmar plate as well as palmar half of the collateral ligament. The flexor superficialis tendon can be transferred as advocated by Crawford et al (1966). Postoperatively, both MP and PIP joints are held in full extension for 6 weeks.
Flexion contractures of the hand are complex diagnostic problems, caused by joint abnormalities, cerebral palsy, flexor and extensor anomalies. Congenital extensor hypoplasia should be considered in the differential diagnosis of flexion contractures of the thumb and fingers. The more extensive ones are difficult to differentiate from the milder form of arthrogryphosis multiplex or congenital amyoplasia. In these latter cases, treatment is usually by tendon transfer but the difficulty lies in the choice of tendons to be used for transfer. Extensor carpi radialis longus and flexor carpi radialis can be used with good results.2 However; a superficial finger flexor tendon can also be used, as described by Crawford et al (1966) Absence of finger extensors appears to be a very rare deformity, although cases have been reported.1,5,6,7,8,9,10,11 However, when carefully reviewed these are associated with other congenital abnormalities. From our review of the literature it appears that this is only the third report in the English literature of total absence of finger extensors without any other congenital deformity.14
Copyright date: 8th May 2000
Correspondence: Mr M A Wajid, Department of Orthopaedics, North Tyneside General Hospital, North Shields NE29 8NH, U.K.
E-mail: mawajid@rcsed.ac.uk
©2001 The Royal College of Surgeons of Edinburgh, J.R.Coll.Surg.Edinb.