Assessment of surgery for the underdeveloped thumb

Many congenital conditions result in an underdeveloped thumb. Classical thumb hypoplasia is part of the spectrum of radial longitudinal deficiency. Thumb duplication, even when accompanied by one clearly dominant thumb, presents with some deficiencies of both when they are compared with a normal thumb. The thumb of symbrachydactyly is underdeveloped, particularly that of the more severe types. Cleft hand complex, so often accompanied by synpolydactyly, may have, in simpler cases, first web deficiency and, in more complex cases, partial or complete thumb absence. The ‘clasped thumb’ of arthrogrypotic children, thumb absence in ulnar dimelia and the abnormal development of a triphalangeal thumb or the radial digit of a five-fingered hand are other examples of conditions in which the thumb is underdeveloped. This begs the question as to what determines normal thumb function. The characteristics of a normal thumb are its size, shape, stability and mobility. After surgery external scars are present, as are other biological responses. Furthermore an, assessment of these characteristics demands consideration of the appearance of nail, pulp and shape; measurement of length and width; the presence of deformity within bone or at the joint(s); stability and movement at interphalangeal, metacarpophalangeal (MP) and carpometacarpal (CMC) joints; measurement of strength through assessments of various forms of pinch and gross grip of objects of different diameters; and testing of sensibility. Although the thumb is said to provide for 40%–50% of hand function, the status of the fingers must also be considered. To achieve dexterity of pinch to the index or middle finger, and incorporation of the thumb into power grip activities requires mobility and stability of the radial two fingers for the former and preferably four digits of mobility, stability and strength, unaffected by stiffness or absence, for the latter. How do we best assess thumb function after surgery? Six of seven articles dealing with congenital hand anomalies in this issue detail outcomes following reconstructive surgery of the thumb. Remarkably, different assessment criteria are utilized to describe thumb function in each, possibly because different parameters of measurement may be more appropriately applied to specific conditions and are less applicable for other conditions, e.g. a greater emphasis on distal joint function in type 2 or type 4 thumb duplications as against a need to better assess CMC joint function following pollicization. Al-Qattan (2016) addresses the problem of severe flexion contractures and instability of the proximal interphalangeal joint of an index finger to be pollicized. That these factors do not prevent pollicization is a point well made. His assessment of thumb function following surgery is simple and practical, but differs in turn from the assessment processes utilized by de Kraker et al. (2016) in their assessment of surgical reconstruction of grade 2 and grade 3A thumb hypoplasia, which differs from the outcome assessment for radial polydactyly used by Djikman et al. (2016) from the same department. This modifies the assessment chart of the Japanese Society for Surgery of the Hand (JSSH). It is impressive in intent and content. It increases the weight of aesthetic outcome measures and subjective patient opinion. However, whether this chart improves the ability to define a successful reconstruction is unclear. The decision to decrease the relative importance of measurement of MP joint deviation is questionable. The last article is in conflict with He and Nan (2016), who devote their article to revision surgery for post-operative failures, in which MP joint deviation reflects a failure to realign the skeleton axially or correct soft tissue deforming forces, and is one of the main indications for revision surgery. MP joint instability is an important outcome measurement in the article of de Kraker et al. (2016). Failure to correct MP joint instability will affect the quality of function at the CMC joint, particularly motion in palmar abduction and opposition, no matter which opposition transfer is used. Interestingly, their transfer of flexor digitorum superficialis failed to provide MP joint stability by their definition in 60% of grade 3A thumbs. Although some are critical of comparison with a normal opposite thumb, the worth of this is emphasized in the article of Engelhardt et al. (2016) in which the range of ulnar and radial deviation on stress testing in normal MP joints is very broad. A normal opposite thumb, when present, gives indication of the normal parameters for that particular patient. The Assessment of surgery for the underdeveloped thumb 625146 JHS0010.1177/1753193415625146Journal of Hand Surgery (European Volume)Editorial research-article2015