Age-related changes in protein phosphorylation by rat hepatocytes.

The qualitative and quantitative changes in the phosphorylation of specific proteins in hepatocyte suspension from 5-, 12- and 22-month-old male Fischer F344 rats were analyzed by two-dimensional polyacrylamide gel electrophoresis. No qualitative changes in phosphorylation of individual proteins were observed with age. In addition, very few quantitative changes (less than 2% of proteins studied) in protein phosphorylation were detected. The phosphorylation of two acidic proteins decreased (50%) with age while the phosphorylation of one basic protein increased (300%) with age. The two acidic proteins and one basic protein that showed quantitative changes with age were found predominately in the microsome and nuclear fractions of hepatocytes, respectively. The effect of dietary restriction on the phosphorylation of proteins in male Fischer F344 rats was also studied. Although, dietary restriction alters the age-related incident of disease and prolongs longevity, it did not have any significant effect on phosphorylation of individual proteins in the liver.

Internal fixation of calcaneus fractures: an anatomical study of structures at risk.

This study examines the risk of injury to medial soft-tissue structures during the fixation of calcaneal fractures performed through a lateral approach. An L-shaped lateral incision was performed on 10 fresh cadaver feet. The calcaneus was divided into three zones for study. Ten K-wires were inserted in a standard configuration from a lateral starting point extending through the medial cortex. The feet were dissected medially to measure the distance from each exiting K-wire to the medial and lateral plantar vessels, the calcaneal branch of the posterior tibial nerve, and the tendons of the flexor hallucis longus, flexor digitorum longus, and posterior tibialis. The mean risk of injury to these medial structures was calculated for each lateral insertion site. Wires placed in the subchondral bone of the posterior facet or anterior to the critical angle of Gissane were determined to be at high risk of injury to the medial soft tissues. Structures at risk included the medial and lateral plantar nerves and vessels and the flexor hallucis longus tendon. Caution should be exercised when inserting K-wires, drills, and screws into high-risk areas to avoid iatrogenic injury to the medial structures.

Intraarticular calcaneus fractures: a biomechanical comparison or two fixation methods.

OBJECTIVE: To compare the strength of fixation obtained using two unicortical 4.0 mm diameter cancellous screws versus two bicortical 3.5 mm diameter cortical screws in the fixation of intra-articular calcaneus fractures. DESIGN: In eight paired fresh frozen cadaver feet, the subtalar joint complex, consisting of the talus, interosseous ligaments, and calcaneus was removed as a unit. An oblique osteotomy of the calcaneus was then created in the sagittal plane. The two fragments were reduced and stabilized using either two unicortical 4.0 mm diameter cancellous screws or two bicortical 3.5 mm diameter cortical screws. A force was then applied to the medial calcaneal tuberosity until failure occurred. In all specimens testing was discontinued due to ligamentous failure, without causing bony disruption. RESULTS: In all specimens the forced applied to the calcaneus created a disruption of the interosseous ligaments across the subtalar joint and rotation of the calcaneus on the talus. Thus in each specimen, testing was discontinued due to interosseous ligamentous failure, without causing bony disruption. There was no statistically significant difference in force to failure between the specimens fixed with 3.5 mm diameter cortical screws as compared to those fixed with 4.0 mm diameter cancellous screws. CONCLUSIONS: The lack of a statistically significant difference in force to failure of the intra-articular calcaneus fractures fixed using 3.5 mm diameter cortical screws as compared to those fixed using 4.0 mm diameter cancellous screws and, the fact that the mode of failure was a disruption of ligaments rather than bony disruption suggest that either method of screw fixation is biomechanically adequate.