Mirror-image trigger thumb in dichorionic identical twins

Trigger Twins: 2 Cases of Ipsilateral Twin Trigger Digit and a Review of Published Literature

Background

The aetiology of trigger digits has been debated since Notta first described them in 1850. Aetiology has been segregated for adult and paediatric presentations. While an adult trigger digit is most likely an acquired inflammatory process, the same is not true for cases in children: no inflammatory reaction is seen on microscopic evaluation. We wish to add strength to a genotypical aetiology for paediatric cases.

Methods

We present two cases of monozygotic twins with trigger digits managed in our institution. A comprehensive review of literature was conducted for cases of trigger digit in monozygotic twins to support our theory.

Results

Our two sets of twins enjoyed a full recovery from surgery at one-month follow-up. A total of seven other cases of monozygotic twins were found in literature.

Conclusion

Our cases add to the growing body of evidence supporting a genotypical aetiology for paediatric trigger digit.

The “Trigger” Thumb Locked in Extension – An Unusual Presentation of a Common Paediatric Condition

Background: We report a variant of paediatric trigger thumb which is locked in extension rather than flexion.

Methods: Eleven children with 14 trigger thumbs (three bilateral) locked in extension were reviewed retrospectively over a 12-year period. The number of flexed trigger thumbs encountered over this period was established from the operating room database.

Results: All children were treated with release of the A1 pulley. Nine children achieved a full range of motion at the interphalangeal joint. One child with bilateral extended trigger thumbs required bilateral dorsal capsulotomy and another child developed temporary mild triggering in flexion.

Conclusions: Approximately 1% of trigger thumbs treated operatively at this institution presented as the extended variant. Trigger thumb locked in extension should be considered in a child presenting with inability to flex the thumb.

A review of the mechanisms and evidence for typical and atypical twinning

The mechanisms responsible for twinning and disorders of twin gestations have been the subject of considerable interest by physicians and scientists, and cases of atypical twinning have called for a reexamination of the fundamental theories invoked to explain twin gestations. This article presents a review of the literature focusing on twinning and atypical twinning with an emphasis on the phenomena of chimeric twins, phenotypically discordant monozygotic twins, mirror-image twins, polar body twins, complete hydatidiform mole with a coexistent twin, vanishing twins, fetus papyraceus, fetus in fetu, superfetation, and superfecundation. The traditional models attributing monozygotic twinning to a fission event, and more recent models describing monozygotic twinning as a fusion event, are critically reviewed. Ethical restrictions on scientific experimentation with human embryos and the rarity of cases of atypical twinning have limited opportunities to elucidate the exact mechanisms by which these phenomena occur. Refinements in the modeling of early embryonic development in twin pregnancies may have significant clinical implications. The article includes a series of figures to illustrate the phenomena described.

Pediatric Trigger Digits

Pediatric trigger thumb presents not at birth but early in childhood. Most evidence suggests that it is caused by a developmental size mismatch between the flexor pollicis longus tendon and its sheath. Patients generally present with the thumb interphalangeal joint locked in flexion. Surgical reviews report near universally excellent outcomes after open release of the A1 pulley. However, recent reports indicate that there may be a role for nonsurgical treatment for families that are willing to wait several years for possible spontaneous resolution of the deformity. Triggering in digits other than the thumb in children is generally associated with an underlying diagnosis including anatomic abnormalities of the tendons, and metabolic, inflammatory, and infectious etiologies. Although some have advocated nonsurgical treatment, surgery is often necessary to address the underlying anatomic etiology. More extensive surgery beyond simple A1 pulley release is often required, including release of the A3 pulley and resection of a slip of the flexor digitorum superficialis tendon.