gms | German Medical Science

Objectives/Interrogation: Radial or preaxial polydactyly (PPD) is a common congenital hand difference of varying severity, popularly classified as according to Wassel's classification (1969) depending on the level of skeletal duplication. Much of the focus, therefore, has been on the bony architecture in PPD, rather than the soft tissues. Embryologically, PPD is classified as a malformation in the radial-ulnar axis under the Oberg Manske Tonkin (OMT) classification, with the underlying pathology thought to be due to abnormal Sonic hedgehog (SHH) expression in the limb bud. Other than digit number and identity, the SHH-axis controls musculature, tendon and vascular patterning. The aim of this study is to investigate the relationship between the bony architecture and the associated soft tissues, including anatomical variations in musculature and innervation in an animal model of induced polydactyly.

Methods: We induced PPD in a chicken limb model using beads soaked in either SHH protein or retinoic acid (SHH agonist) implanted into the anterior early limb bud (20HH/3.5 days of development, equivalent to Carnegie stage 130). Manipulated embryos were examined at seven days of development after cartilage pattern of digits has been established. In addition to skeletal anatomy, secondary changes in limb patterning affecting the soft tissues were also studied using wholemount RNA in situ hybridisation in combination with histology. Muscle was labelled with MyoD, nerves with Schwann cells marker, tendons with Scleraxis and cartilage was stained with Alcian Green.

Results and Conclusions: Polydactyly was reliably induced both in models using retinoic acid or SHH protein beads. As predicted, soft tissue anatomy was also altered in polydactylous limbs. The changes were categorised and compared to control limbs (without manipulations). Results will be discussed.

We present an early model which can be utilised in the future to assist prediction of not just skeletal duplications, but also deviations in soft tissue anatomy in polydactylous digits.