PubMed Health⌕ Search

Biomedical subjects

F W Werner

Publications and source records attributed to F W Werner.

52 records · Page 3Linked to original sources
PubMed1986

Digital tourniquets: a pressure study with clinical relevance.

This study measured the pressures under the three most commonly used digital tourniquets--the Penrose drain, the rolled rubber glove, and the rubber band. A miniature pressure transducer and a digital strain indicator were used to measure pressures generated by the various tourniquets. The rolled rubber glove technique was highly consistent, irrespective of the clinical experience of the subject, and uniformly generated pressures of less than 500 mm Hg. Pressures generated by Penrose drains and rubber bands were highly variable and were significantly greater than 500 mm Hg. The so-called calibrated Penrose drain generated the highest pressures in the study. The relationship between tourniquet pressures and neurovascular injury in the human digit is not clearly defined.

Finger Injuries↗
PubMed1986

Force transmission through the distal radioulnar carpal joint: effect of ulnar lengthening and shortening.

Although numerous surgical procedures are performed on the wrist joint, little has been written regarding the effect of these procedures on the biomechanics of the wrist. This study has been undertaken to examine the in vitro consequences of ulnar lengthening and shortening. We have measured the axial forces transmitted through the distal radius and ulna and the pressure distribution on the articulating surface of the radius and triangular fibrocartilage complex for the intact wrist, with ulnar lengthening and with ulnar shortening. Lengthening of the ulna by 2.5 mm in the intact wrist increased the force borne by the ulna from 18.4% to 41.9% of the total axial load. Shortening of the ulna by 2.5 mm decreased axial load borne by the ulna to 4.3%. Removal of the articular disc portion of the triangular fibrocartilage complex decreased the load on the intact ulna from 18.4% to 6.2%. The peak pressure at the ulnolunate articulation increased from 1.4 N/mm2 for the unaltered wrist to 3.3 N/mm2 when the ulna was lengthened by 2.5 mm. These results suggest that the biomechanics of the wrist joint can be dramatically altered with relatively small (2.5 mm) changes in ulnar length and by removal of the articular disc portion of the triangular fibrocartilage complex.

Biomechanical Phenomena↗
PubMed1985

The extensor retinaculum of the wrist: an anatomical and biomechanical study.

Through an anatomical and biochemical study, utilizing sixty-five cadaver specimens, the extensor retinaculum of the wrist was examined. It is a complex variable fibrous structure, whose functions are to prevent dorsal bowstringing of the extensor tendons and to prevent radial and ulnar displacement of extensor tendons. We recommend that a portion of the extensor retinaculum be preserved or reconstructed at the time of dorsal wrist surgery.

Biomechanical Phenomena↗
PubMed1985

Functional wrist motion: a biomechanical study.

A triaxial electrogoniometer was used to measure functional wrist motion. Wrist motion was evaluated in 10 normal subjects who performed 52 standardized tasks. The wrist joint was found to have three degrees of freedom (flexion-extension, radioulnar deviation, and rotation). The normal functional range of wrist motion is 5 degrees of flexion, 30 degrees of extension, 10 degrees of radial deviation, and 15 degrees of ulnar deviation.

Activities of Daily Living↗
PubMed1985

A biomechanical analysis of spinal instrumentation systems in thoracolumbar fractures. Comparison of traditional Harrington distraction instrumentation with segmental spinal instrumentation.

A total of 61 biomechanical tests were performed on 25 cadaveric spinal segments to investigate the comparative strengths of three instrumentation systems: 1) conventional Harrington distraction instrumentation (HRI), 2) segmentally wired Harrington distraction rods, and 3) Luque segmental spinal instrumentation (SSI). In type I testing in which axial preload was applied to normal specimens, and then progressive rotation until ultimate failure followed, five of six Harrington systems failed at the bone-metal interface. In contrast, all six Luque SSI vertebral segments disrupted in a location removed from the bone-metal interface. In Type-II testing (six specimens) in which axial loading of experimentally produced unstable burst fractures was applied, the most stable fixation in resisting compressive loads was segmentally wired Harrington distraction rods (P less than 0.001). In Type-III testing (six specimens), there was axial preloading, then progressive rotation applied to translational fracture-dislocations and this showed that the ability to resist torsion was lowest with plain HRI, slightly improved by segmentally wired HRI, and the stiffest system was Luque SSI (P less than 0.05). The three methods of testing cadaveric segments provided a relevant laboratory model for investigation of spinal instrumentation systems in thoracolumbar fracture stabilization. The results compare favorably with other biomechanical studies, information derived from in vitro and ex vivo animal models and clinical experience with failures of fixation. The biomechanical advantages of segmentally wired Harrington distraction instrumentation in resisting axial loads seem to justify this method of fixation in unstable burst fractures. Similarly, the use of Luque segmental spinal instrumentation with L-rods coupled together is the best method of achieving rotational stability in translational injuries (fracture-dislocations). However, the above biomechanical considerations should be balanced against the increased operative time, more exacting technical expertise required, and possible risk of iatrogenic neurologic sequelae in implementing segmental fixation in unstable thoracolumbar fracture management.

Adolescent↗
PubMed1983

Mechanical and functional properties of implanted freeze-dried flexor tendons.

Tendons harvested from donor dogs were freeze-dried and implanted as free allografts in the paws of recipient experimental animals; the tendons were subsequently tested for mechanical properties, clinical function, and histologic appearance. Free tendon autografts, normal tendons in the operated experimental paw, and normal tendons in the unoperated paw were used as controls and compared with the allografts. Mechanically, the free tendon allografts and autografts were similar. The ultimate strength of the two grafts was statistically the same but significantly less, about one-third, than that of normal tendons. The implanted allografts appeared to be tolerated well by the host and to allow flexor tendon function similar to that allowed by autografts. The histologic appearance of the allograft and autograft tendons was similar at three and six months. Freeze-dried flexor tendon allografting is a satisfactory alternative to free tendon autografting.

Animals↗
PubMed1983

Freeze-dried flexor tendons in anterior cruciate ligament reconstruction.

Flexor tendons were harvested from donor dogs, freeze-dried, and reimplanted into six mongrel dogs that were made surgically anterior cruciate ligament (ACL) deficient. After one month of immobilization the dogs were allowed to run free for eight months. At this time all ACL substitutes were found to be intact and repopulated by host cells. Mechanical testing showed the freeze-dried allograft ACL to be significantly weaker than the normal control ligament but similar in strength to implanted tendon autograft ligament substitutes.

Animals↗
PubMed1981

The triangular fibrocartilage complex of the wrist--anatomy and function.

The anatomy and function of the triangular fibrocartilage complex (TFCC) of the wrist was studied through anatomic dissections and biomechanical testing of 61 specimens. The TFCC was found to be a homogenous structure composed of, but not dissectable into, the articular disc, the dorsal and volar radioulnar ligaments, the meniscus homologue, the ulnar collateral ligament, and the sheath of the extensor carpi ulnaris. The TFCC was found to be perforated in 53% of specimens dissected, and all of the wrists with a demonstrable perforation showed evidence of damage or erosion of the cartilage of the lunate and/or distal ulna. Biomechanical studies suggest that the TFCC functions both as a cushion for the ulnar carpus and as a major stabilizer of the distal radioulnar joint. Perforations of the TFCC can result in the ulna-lunate abutment and cartilage erosion. Since excision of the TFCC may lead to ulnolunate abutment, chronic wrist pain, and/or instability of the distal radioulnar joint, it is not recommended.

Adult↗
PubMedDate not supplied

Biomechanical comparison of seven internal fixation devices for the lumbosacral junction.

For comparison purposes, seven different internal fixation systems were applied sequentially to each of six fresh-frozen cadaver spines at the lumbosacral junction. The spines were loaded to a maximum flexion bending moment of 12 Newton meters and an extension moment of 6 Nm. Resultant angular motion was recorded with an electrogoniometer. The Synthes and Kaneda devices provided the most rigid fixation in flexion and extension testing. The Luque internal fixation system was as effective as the Kaneda and Synthes systems at limiting extension but was slightly less successful at limiting flexion. The Knodt system was effective at limiting extension but less effective in limiting flexion. The interfacet screws were effective at limiting flexion but less effective at limiting extension. Harrington rods to the sacral alae were the least effective system in both directions. Sublaminar wires did little to improve their performance.

Biomechanical Phenomena↗
PubMedDate not supplied

A biomechanical study of the static stabilizing effect of knee braces on medial stability.

The purpose of this project was to determine if commercially available braces could be shown to produce objective evidence of medial stabilization of the knee. Commercially available athletic braces were evaluated for their effect on abduction forces applied to a cadaver knee with no instability and with experimentally created medial instability. Under computer control, abduction forces were applied while simultaneous data were obtained from an electrogoniometer and transducers applied to the anterior cruciate ligament and the superficial medial collateral ligament at 0 degrees, 15 degrees, and 30 degrees of flexion. Our results showed a reduction in abduction angle using functional braces, whereas prophylactic braces demonstrated little or no protective effect.

Biomechanical Phenomena↗
PubMedDate not supplied

The effect of knee braces on lateral impact loading of the knee.

Disruption of the medial supporting structures of the knee occurs commonly in contact sports such as American football and lacrosse. A limited number of clinical and laboratory studies currently document the effectiveness of bracing. The purpose of this project was to determine if commercially available bracing could be shown to produce objective evidence of medial stabilization of the knee. Our model involves the use of a cadaver lower extremity with a fixed foot and suspended femur with a free knee and a lateral impact load applied simulating a clipping injury. Force transducers were placed on the ACL and medial collateral ligament (MCL) and an electrogoniometer was attached to the extremity. The prophylactic braces studied had a limited capacity to protect the MCL from direct lateral stress with the knee in full extension. In flexion or with a change in direction of the load, the protective effect is greatly reduced. The functional braces had a capacity to limit abduction and rotational stresses on the MCL in flexion and extension.

Braces↗
PubMedDate not supplied

Posterior stabilization of pelvic fractures by use of threaded compression rods. Case reports and mechanical testing.

Threaded compression rods were placed between the posterior-superior spines as a means of posterior stabilization of pelvic fractures. To document the increase in sacroiliac stability afforded by this technique, biomechanical testing was performed. Malgaigne-type fractures with sacroiliac disruptions were created in four cadaver pelvises. The fractures were stabilized with anterior frames of the Slatis or Pittsburgh type and subjected to longitudinal and torsional loading patterns on an Instron machine. The anterior fixation was then augmented with threaded compression rods placed between the posterior-superior spines to compress the disrupted sacroiliac joints, and repeat testing was conducted. Anterior frames alone were found to provide little stabilization of the disrupted sacroiliac joints with either longitudinal or torsional loading. Markedly improved stabilization in both loading modes was achieved with posterior augmentation. Two typical cases are presented to demonstrate that posterior stabilization is as efficacious in clinical practice as in the biomechanics laboratory.

Adult↗
PubMedDate not supplied

Biomechanics of the distal radioulnar joint.

The distal radioulnar joint is an intricate part of wrist function. The radius and hand move in relation to, and function about, the distal ulna. Significant loads are transmitted to the forearm unit through the distal ulna via the triangular fibrocartilage. The anatomic relations between the distal radius and ulna and the ulnar carpus are precise, and even minor modifications in these relations leads to significant load-pattern changes. The authors can only speculate on the clinical ramifications of such load-pattern modifications. Since M. DeSault's dissertation on dislocation of the distal radius, published in 1791, much has been written on injuries to, and afflictions of, the radiocarpal area. Although injuries and afflictions in this area undoubtedly have not changed throughout the years, an increasing variety of ulnar wrist syndromes and treatment programs are being recognized. This phenomenon attests not only to the need for continuous investigations of wrist problems but also to the great excitement that presently exists in the field. Better understanding of the anatomy and newer knowledge of the biomechanics of the distal radioulnar joint should herald an ulnar wrist renaissance.

Biomechanical Phenomena↗