Risk of sural nerve injury with intramedullary screw fixation of fifth metatarsal fractures: a cadaver study.

The risk of injury to the sural nerve and its branches during operative procedures performed on the lateral foot and ankle is well recognized; however, there have been no anatomic studies demonstrating the proximity of the sural nerve branches to the head of an intramedullary screw used for fixation of fractures of the proximal fifth metatarsal. Dissection of 10 cadaver specimens, after insertion of 4.5-mm screws, demonstrated that the screw head was within 2 mm of the dorsolateral branch of the sural nerve in five specimens and within 3 mm of eight specimens. Irritation of or injury to the nerve during screw insertion may explain the persistence of pain after screw removal in some patients. Furthermore, patients could sustain injury to the sural nerve at the time of screw removal. Careful surgical technique, including the use of drill guides and tissue protectors, may help lessen the risk of sural nerve injury and subsequent neuroma formation.

Bile acid transport by the rat liver canalicular bile acid transport/ecto-ATPase protein is dependent on ATP but not on its own ecto-ATPase activity.

We have shown that bile acid efflux and ecto-ATPase activities are two distinct properties of a single rat liver hepatocyte canalicular membrane protein (Sippel, C. J., Suchy, F. J., Ananthanarayanan, M., and Perlmutter, D. H. (1993) J. Biol. Chem. 268, 2083-2091). Bile acid efflux in COS cells transfected with this rat hepatocyte canalicular bile acid transport/ectoATPase cDNA is stimulated by ATP and inhibited by nonhydrolyzable ATP analogs. In this study, we depleted transfected COS cells of ATP to examine whether bile acid efflux mediated by this transporter was dependent on ATP or just stimulated by ATP. We also used mutagenesis of an ATPase consensus sequence in the ectoplasmic domain to examine the relationship of ATPase activity to bile acid efflux mediated by the same polypeptide. The results indicate that bile acid transport is abrogated by ATP depletion and reconstituted by exogenous ATP in a concentration-dependent and saturable manner. Introduction of mutations at amino acids Gly97 and Arg98 in the ATPase consensus sequence abrogated ATPase activity but did not affect synthesis or cell surface delivery of the transporter and did not affect its bile acid transport activity. Taken together, the data indicate that bile acid efflux mediated by the rat hepatocyte canalicular bile acid transport/ecto-ATPase protein is dependent on ATP but not on its own ATPase activity. The data, therefore, imply that 1) ATP affects its bile acid transport activity through an entirely distinct mechanism; and 2) if there is any functional relationship between the ecto-ATPase and bile acid transport properties, it is mediated indirectly through regulation of net ATP concentrations in the canalicular space by the ecto-ATPase.