George Piotrowski

The throw: biomechanics and acute injury:

The throw and its modifications are integral components of many sports. This study correlates case histories of acute injuries in throwing with a biomechanical analysis of the throw ing mechanism. Comparisons are made with a similar analysis of the kick analyzed by the same film technique and computer program. Just prior to ball release, the pitching arm extends through an arc of about 73 degrees in 40 msec, beginning with the elbow flexed at 80 degrees. This produces an axial load on the humerus and coincides with a pulse of external torque at the shoulder. This acts as stress protection to the humerus which is developing an internal torque of 14,000 inch-Ib prior to ball release. The change in angular velocity, or the angular acceleration, during the throw is acquired in a much shorter time than in the kick. Torque is directly proportional to angular acceleration. This necessitates the development of substantially higher torques in the humerus during the throw than about the knee during a kick. The kinetic energy in the arm is 27,000 inch-Ib during the throw. This is much higher than the kinetic energy in the kicking leg because the kinetic energy varies proportionally with the square of the angular velocity of the extremity. The angular velocity of the arm is about twice that of the leg. Thus, the pitching arm contains about four times as much kinetic energy as the kicking leg. These severe overload ing conditions predispose the upper extremity to injury in the throwing mechanism.

Geometric properties of equine metacarpi

Paired equine metacarpals were harvested, cleaned and sectioned transversely every 20 mm, and the bone geometry analyzed with a computer program. The cross-sectional area is largest in the middle third of the bone, and tapers off at either end. The principal axes are typically within 15 degrees of the anatomical axis, with the distal end rotated internally relative to the proximal end. At midshafts the bending stiffness in the antero-posterior plane is about 2/3 of the stiffness in the medio-lateral plane. The torsional stiffness is highest proximally. The equine third metacarpal appears to be designed to resist axial compression and mediolateral bending very well, and exhibits uniform resistance to torsion along its length.

The STRESS program: A computer program for the analysis of stresses in long bones

Abstract A computer program was developed to compute torsional and bending stresses in long bones. The input format for the program is designed to be as convenient to the user as possible, allowing him to transmit to the program only as many points as he feels are required to describe the cross-sectional geometry. The program permits the user to specify by which method torsional stresses are to be computed, what type of stresses are to be computed, and to what accuracy the results are desired. Computation times are of the order of 5 sec or less (on an IBM 360), making use of the program more economical than manual computations.

The kick: biomechanics and collision injury.

an important element. The admixture of bony and soft tissue injuries suggests high energy mechanisms, and studies were done to explore the biomechanical factors involved. The objectives of this study were to (1) describe the motion of the lower extremity in the act of kicking a ball, (2) to define the magnitude and types of loads transmitted by the soft and hard structures about the knee, and (3) to obtain an appreciation of the potential for injury during such activity. The results of this study were correlated with the several case histories. CASE HISTORIES

BIOMECHANICAL PROPERTIES OF PAIRED CANINE FIBULAS

Abstract This paper is concerned with the determination of the side-to-side variations of the biomechanical properties of canine fibulas. It also compares the relation of the fracture lines to the microanatomical structure of bone. Twenty sets of paired canine fibulae were subjected to rapid torsional loading and the torque, deformation, and energy at fracture were recorded. Maximum stress at the fracture was then computed. Micro-radiographs were prepared from cross sections of the fractured specimens. The results show that side-to-side variations in torques show the least scatter, while the side-to-side variations in stresses, deformations, and energies fall over a much larger range. The micro-anatomy of bone failed to significantly influence the route of the fracture line. This data therefore provides a range of normal variation between paired canine fibulae which will enable the use of one of the fibulae as a valid control in experimental procedures which may alter the biomechanical properties of the other fibulae.

A brief note on the variability of the torsional strength of paired bones

Abstract The distribution of the per cent side-to-side differences of the torsional strengths of three groups of paired animal bones was compared. These distributions were centered about 0 per cent side-to-side difference, indicating no left-right bias in the torsional strengths. The scatter in the per cent side-to-side differences can be characterized by a standard deviation of about 0·093, with all three distributions showing similar standard deviations.