There is little fundamental data on paediatric metacarpophalangeal joint instability in radial polydactyly following surgical reconstruction. We evaluated 27 thumbs in a healthy paediatric population (Group A: eight girls and 19 boys with a mean age of 9.7 years (range 2.7-14.2)) and 12 thumbs following Wassel-IV reconstruction (Group B: eight girls and four boys with a mean age at follow-up of 10.6 years (range 2.7-13.2)). Metacarpophalangeal joint radial deviation, ulnar deviation on stress testing, interphalangeal joint and metacarpophalangeal joint alignment on posterior-anterior radiographs were measured and scored according to parameters defining joint instability. The aim of our study was to provide fundamental data on thumb metacarpophalangeal joint mobility patterns and alignment for further postoperative evaluations in children. The average ulnar deviation and radial deviation on stress testing of the healthy (Group A) metacarpophalangeal joints was 25° (10°-45°) and 30° (10°-55°), respectively. In the operated (Group B) thumbs, the ulnar deviation and radial deviation was greater at 35° (10°-55°) and 30° (10°-70°). Ulnar deviation (UD) of the proximal phalanx at the metacarpophalangeal joint on posterior-anterior radiographs was a mean of 10° (range -10°-30°) in Group B; this was significantly greater than in Group A at a mean of 5° (range -5-20°) (p = 0.029). The mean radial alignment of the interphalangeal joint (distal phalanx relative to the proximal phalanx) was significantly higher in Group B (15°) than Group A (0°) (p = 0.221). In the literature on radial polydactyly, cut off values defining metacarpophalangeal joint instability in children range from 5° to 20°. According to our results, high but physiological metacarpophalangeal joint mobility of the thumb needs to be taken into consideration when evaluating children following reconstruction. Ulnar or radial deviation greater than 30°, in combination with the lack of a definite end point on metacarpophalangeal joint stress testing, may be regarded as unstable. Based on our study on healthy paediatric and reconstructed thumbs, comparison of joint stability with the healthy contralateral hand is recommended in order to define pathological instability.
Level of evidence: II.
Keywords: Joint stability; Wassel classification; radial polydactyly; thumb.
© The Author(s) 2015.