Double injuries of the forearm: a common occurrence.

To evaluate the frequency of different types of forearm fractures and, in particular, determine the frequency of double injury to the forearm, the authors prospectively examined 119 consecutive forearm fractures and found double injuries to the forearm in all but five cases. In 79 of the 119 patients (66%), ligamentous injury was seen in addition to the obvious fracture. Nine patients with apparent isolated fractures on initial radiographs underwent examination by means of radionuclide bone scanning, which revealed a second injury in eight of them. Four patients with apparent single fractures did not undergo bone scanning because of their critical conditions. In four patients, a single fracture was initially diagnosed, but after reduction and casting, dislocation of the radioulnar joint was seen. These findings indicate that injury to the forearm almost invariably occurs at two or more sites and involves either both bones or bone and ligament. Because the distal radioulnar joint was affected in 71 patients (60%), scrutiny of the wrist is imperative whenever injuries to the bones of the forearm are discovered.

Update on the anatomy of the pulley system in the chicken foot long digit.

The pulley system in the flexor sheath of the long toe of the white leghorn chicken foot was studied. Histologic sections of the pulleys were prepared, and the mechanics of flexion of the long toe was analyzed. An annular flexor pulley that attached to the third phalanx was identified. This pulley, which has not been described previously, was found to be essential for proper flexion of the third interphalangeal joint.

Silver-nylon: a new antimicrobial agent.

The potential effectiveness of a silver nylon (SN) fabric as an antimicrobial agent was evaluated in a series of in vitro experiments. The results indicated that silver ions from the SN fabric penetrated 2 mm of agar and killed a challenge of 6.9 X 10(7) Pseudomonas aeruginosa, 4.1 X 10(7) Staphylococcus aureus, and 1.4 X 10(7) Candida albicans organisms per cm2 of SN fabric after 24 h of incubation at 37 degrees C. To determine some of the microbicidal limits of the SN, the distance between the SN fabric and the microbial challenge was increased. Increasing the height of the agar column overlying the SN fabric diminished the inhibitory effect of SN on microbial growth. For each increase in agar height of 2 mm, up to a total height of 8 mm, the effectiveness of SN to inhibit microbial growth decreased by a factor of 10. This distance-related decrease in the microbicidal ability of SN could be overcome by placing the SN fabric in contact with the agar column for 24 to 72 h before microbial challenge. On the basis of these experiments, it appears that SN is an effective antimicrobial agent, although further work must be performed before it is applied clinically.

Biomechanical evaluation of metacarpophalangeal joint prosthesis designs.

A laboratory biomechanical analysis of metacarpophalangeal joint prosthesis designs was done with fresh cadaver finger rays. The center of rotation, range of motion, tendon excursion, and fingertip force were determined on the specimens before and after implanting Swanson, Niebauer, Steffee II, St. Georg-Buchholz, Schultz, and modified Strickland prostheses. Their biomechanical behavior varied considerably and none duplicated the normal metacarpophalangeal (MP) joint. Each has design characteristics that may be clinically advantageous as well as disadvantageous. Irrespective of the design, the studies done cannot be divorced from the following factors: (1) implant material properties--silicone rubber implants buckled with tendon loading; this deformity created a significant flexor mechanical advantage and an extensor mechanical disadvantage; (2) implant fixation--freely movable implant stems dampened part of the applied load; braided suture provided inadequate immediate fixation; (3) implantation technique--the articulated prostheses can be technically unforgiving; errors in technique resulted in alteration of their biomechanical behavior.

Kinematics of the wrist. II. Clinical applications.

A reproducible method of measuring carpal height and carpal-ulnar distance and expressing them as ratios of these distances to the length of the third metacarpal, as reported in a previous paper9, was applied to serial roentgenograms of seventeen patients with rheumatoid disease and six patients with Kienböck's disease. These ratios provide an accurate expression of the extent of carpal collapse and of ulnar translation. However, once carpal collapse has occurred, the trajectory of hand motion becomes flattened, and, as a result, the carpal height ratio will vary as the wrist moves from maximum radial to maximum ulnar deviation. These ratios may be of use in predicting a patient's clinical course, but a larger clinical study is necessary before use of the measurements for this purpose can be recommended with assurance.

Kinematics of the wrist. I. An experimental study of radial-ulnar deviation and flexion-extension.

The kinematics of the wrist during radial-ulnar deviation and flexion-extension were studied in several ways. In six fresh cadaver wrists, the forearm was fixed in full pronation, each motion was constrained to one plane, and two metal markers were placed in each of the finger metacarpals, as well as in the radius and all of the carpal bones except the pisiform and greater multangular. Radial ulnar and flexion-extension movements in these wrists were studied roentgenographically. In the wrists of six normal volunteers, a similar roentgenographic analysis was carried out and the trajectories of wrist motions also were studied using light-emitting diodes. Finally, roentgenographic measurements were made on 100 wrists of normal subjects. From these studies, it was concluded that: (1) during each of these motions, rotation occurs about a fixed axis located within the head of the capitate, and the location of each axis is not changed by the position of the hand in either plane; (2) the distance from the base of the third metacarpal to the distal articular surface of the radius (the carpal height), measured along the proximally projected axis of the third metacarpal on posteroanterior roentgenograms, is constant throughout radial-ulnar deviation of the normal wrist and can be used as a measure of carpal collapse; and (3) the perpendicular distance of the fixed axis of rotation for radial-ulnar deviation from the distally projected longitudinal axis of the ulna can be used as a quantitative measurement of the amount of translation of the carpus in pathological conditions.