Mechanical sensibility in free and island flaps of the foot

Mechanical sensibility in 20 free skin flaps and four dorsalis pedis island flaps, used for the reconstruction of foot defects, was analyzed with conventional clinical methods and by determining sensibility thresholds to vibration frequencies of 20, 80, and 240 Hz. To eliminate inter-individual variability, a score was calculated for each frequency by dividing the thresholds determined for each flap with values obtained from the corresponding area on the uninjured foot. The soft tissue stability of the reconstruction was assessed. Patients were divided into three groups according to the scores. In the group of flaps with the best sensibility, the threshold increases were low at all frequencies. In the group with intermediate sensibility, the relative threshold increases were greater, the higher the frequency. In the group with the poorest sensibility, no thresholds were obtained with 240 Hz frequency and the thresholds increases were very high at all frequencies. Sensibility was not related to the length of follow-up time, nor to the type or size of the flap. However, flap sensibility was closely associated with that of the recipient area, where sensibility was usually inferior to that of normal skin. The island flaps generally had better sensibility than the free flaps. There was a good correspondence between the levels of sensibility determined by clinical and quantitative methods. The quantitative data on the level of sensibility obtained with the psychophysical method were found to be reliable and free from observer bias, and are therefore recommended for future studies. The degree of sensibility may have contributed to, but was not essential for, good soft-tissue stability of the reconstruction.