Pressure neuropathy in the hind foot of the guinea-pig

Patients who regularly exert pressure with the palm of the hand may develop a lesion of the deep branch of the ulnar nerve. The hypothenar muscles are usually spared, weakness and wasting being con-fined to the interossei and adductor pollicis (Russell and Whitty, 1947). In such cases conduction velocity is markedly reduced in the terminal parts of the motor nerve fibres (Simpson, 1956; Ebeling, Gilliatt, and Thomas, 1960) but the underlying pathological changes in the nerves have not been studied in man as no material has been available. The purpose of the present paper is to report a localized peripheral nerve lesion in the guinea-pig which shows some similarities with the human condition described above. The animal lesion was discovered in the course of some experiments in which guinea-pigs were kept in small cages on wire-mesh flooring for periods of up to a year. Abnormalities of conduction were observed in nerves supplying the small muscles of the hind foot, suggesting that the wire-mesh floors of the cages might have produced local damage to the plantar nerves (Fullerton and Gilliatt, 1965). This phenomenon has now been further investigated. METHODS Healthy male and female guinea-pigs aged 3-24 months were studied. The animals may be divided into four groups: A Young guinea-pigs, aged 3-6 months, which had been reared and kept in large pens with solid floors. B Old guinea-pigs, aged 18-24 months, which had been reared and kept in similar pens. C Guinea-pigs which had been reared in large pens with solid floors and transferred, at ages varying from 2 to 16 weeks, to small cages with wire-mesh floors, in which they were kept for further periods of eight to 12 months. The cages measured 25 x 40 cm. The mesh flooring con-sisted of 1 mm. gauge wire arranged in 1 cm. squares. D Guinea-pigs which were similar to those in group C except that they were transferred from large pens to small cages (25 x 40 cm.) with solid floors covered by a deep layer of sawdust.