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Biomedical subjects

B D Beynnon

Publications and source records attributed to B D Beynnon.

At least 55 records · Page 3Linked to original sources
PubMed1994

Posterior cruciate ligament strain biomechanics in total knee arthroplasty.

To evaluate the role of the posterior cruciate ligament in total knee arthroplasty, 8 normal whole-leg cadaveric legs were studied. Strain patterns of the posterior cruciate ligament were measured during active and passive knee flexion extension. Total knee arthroplasty was performed, and posterior cruciate ligament strain was measured again. The standard tibial insert was removed, and 3 additional tibial trays were used: flat, 10 degrees sloped, and 15 degrees sloped. The posterior cruciate ligament strain was recorded for each tibial insert. Total knee arthroplasty with a standard insert produced a large range of posterior cruciate ligament strain values (+/- 6%). Of the 8 specimens, 3 produced excessively taut posterior cruciate ligament strain, 3 were slack, and 2 returned strain to the baseline strain value. Changing the surface contour and slope of the tibial inserts did not produce any consistent change in the posterior cruciate ligament strain pattern. The ability of total knee arthroplasty to reproduce normal posterior cruciate ligament strain behavior has not been demonstrated.

Biomechanical Phenomena↗
PubMed1993

Dynamic elongation behavior in the medial collateral and anterior cruciate ligaments during lateral impact loading.

The objectives of this experimental study were to determine (a) how quickly the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) elongate when a lateral impact force is imparted to the knee and if a person can react rapidly enough to provide protective muscle forces in the case of such an impact, (b) if the MCL and the ACL elongate simultaneously during a lateral impact, and (c) if resection of the ACL affects elongation of the MCL during a lateral impact. Eight whole-leg cadaver specimens were used. Each leg was mounted vertically in a testing-frame with the knee in 0 and 30 degrees of flexion. A submaximal impact was delivered from the lateral side by a pendulum instrumented with a force transducer. Elongation of the midsubstance of the MCL and the ACL was measured with Hall-effect displacement transducers. The ACL was resected and the entire test sequence was repeated. Following a lateral impact, elongation of the MCL and ACL reached peak values by 70 ms. This study indicated that contraction of the leg musculature would not protect the MCL and ACL from injury when a lateral impact load is applied to the knee. The MCL and the ACL never elongated simultaneously during a lateral impact. After lateral impact loading, the time required to reach maximum elongation (peak delay) averaged 52 ms in the anterior MCL fibers and 61 ms in the ACL when the knee was in 0 degrees of flexion. At 30 degrees of flexion, the peak delay averaged 38 ms in the anterior MCL fibers and 22 ms in the ACL.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Morphometry of the semitendinosus and gracilis tendons with application to anterior cruciate ligament reconstruction.

The length and cross-sectional area of human semitendinosus and gracilis tendons were measured in both single- and multi-strand configurations for the purpose of anterior cruciate ligament graft preparation. The average lengths of the semitendinosus and the gracilis tendons were 235 +/- 20 mm (mean +/- SD) and 200 +/- 17 mm, respectively. The cross-sectional area of a doubled semi-tendinosus tendon (two strands) was significantly less than that of a 10-mm-wide patellar tendon graft (P < 0.001). The cross-sectional area of the tripled semitendinosus tendon (three strands) and the 10-mm-wide patellar tendon were similar. Doubling of the combined semitendinosus and gracilis tendons (four strands) and tripling of this combination (six strands) resulted in a significantly greater cross-sectional area in comparison to the 10-mm-wide patellar tendon (P < 0.05, four strands; P < 0.001 six strands). This investigation demonstrates that anterior cruciate ligament grafts fashioned using multiple-strand combinations of the semitendinosus and gracilis tendons result in a cross-sectional area that is comparable to the bone-patellar tendon-bone graft. This is an important finding since cross-sectional area reflects the intra-articular volume of collagenous tissue. This information should be helpful to surgeons considering using the hamstring tendons as an anterior cruciate ligament graft.

Aged↗
PubMed1993

An in vivo comparison of anterior tibial translation and strain in the anteromedial band of the anterior cruciate ligament.

The objective of this in vivo study was to determine if strain in the anteromedial band (AMB) of the anterior cruciate ligament (ACL) may be predicted by an external measurement of anterior tibial-femoral translation. A Hall effect strain transducer was implanted on the AMB of five human subjects with normal intact ACLs. AMB strain was then measured during anterior shear loading of the tibia relative to the femur, with the knee flexed to 30 and 90 degrees, simulating the loads applied in the Lachman and anterior drawer tests, respectively. The Knee Signature System, a commercially available arthrometer, was used to simultaneously measure anterior tibial translation relative to the femur. The resulting AMB strains and translations during anterior shear loading of the tibia with respect to the femur at 30 and 90 degrees were compared using a regression analysis to determine if AMB strain could be predicted from a measure of anterior tibiofemoral translation at either flexion angle. AMB strain at 150 N anterior shear load at 30 degrees flexion (3.0%) was significantly greater than that at 150 N anterior shear load at 90 degrees flexion (0.9%). During anterior shear loading at 30 degrees flexion, AMB strain correlated with anterior tibial translation (r2 = 0.59). However, there was no significant correlation between AMB strain and anterior tibial translation for anterior shear loading at 90 degrees flexion (r2 = 0.002). Therefore, AMB strain was not accurately predicted from an external measurement of tibial displacement at 90 degrees in this experiment.

Adult↗
PubMed1992

The effect of functional knee-braces on strain on the anterior cruciate ligament in vivo.

Functional knee-braces are widely used to protect injured or reconstructed anterior cruciate ligaments, despite the fact that few scientific data support their efficacy. We studied seven functional braces, representative of both the typical custom-fit and off-the-shelf designs. The braces were tested on subjects who had a normal anterior cruciate ligament and were scheduled for arthroscopic meniscectomy or exploration of the knee under local anesthesia. After the operative procedure, a Hall-effect strain-transducer was applied to the anterior cruciate ligament. Under low anterior shear loads, two braces provided some protective strain-shielding effect compared with no brace, but this strain-shielding effect did not occur at the higher anterior shear loads expected during the high-stress activities common to athletic events. The DonJoy, Townsend, C.Ti., and Lenox Hill braces demonstrated a strain-shielding effect on the anterior cruciate ligament with an internal torque of five newton-meters applied to the tibia. None of the braces had any effect on strain on the anterior cruciate ligament during active range of motion of the knee from 10 to 120 degrees or during isometric contraction of the quadriceps. Wearing of a brace did not produce an increase in the value for strain on the anterior cruciate ligament. For the activities that were evaluated in this study, none of the braces produced adverse effects on the anterior cruciate ligament, and there were no significant differences in the strain on the anterior cruciate ligament between the use of a custom-fit or an off-the-shelf brace design. There were no apparent advantages of the more expensive custom-made braces compared with the off-the-shelf designs.

Adult↗
PubMed1991

ACL reconstruction: in vivo measurement of patellar tendon graft elongation.

The implantation of a free autogenous patellar tendon graft is the surgical technique that currently offers the best results in anterior cruciate ligament reconstruction. However, numerous aspects regarding both technique and postoperative rehabilitation can still be improved. The aim of this study was to measure the elongation of the patellar tendon in vivo in the operating room after reconstructive surgery, subjecting the knee to normal strain such as passive mobilization or anterior displacement of the tibia. Three volunteers were studied. Our results were different from those reported in a previous study conducted in vivo on a normal anterior cruciate ligament (ACL). In spite of the isometric position of the tendon, passive mobilization provoked a progressive increase in the elongation of the graft within each cycle of flexion-extension and between one cycle and the next. This also occurred during the Lachman test. These findings suggest that the graft undergoes a process of tensile adjustment when it is first put under strain. Continued elongation once this process appears stabilized raises doubts as to the reliability of isometric measuring devices.

Adult↗
PubMed1991

The effect of bracing and taping in sports.

There has been an increase in the use of bracing, and to some extent taping during the last decade. The sports medicine community has not only developed a greater interest in the prevention of injuries, e.g. ligament injuries to the knee and ankle, there has also been an interest in an early return of the injured athlete to sports after both operative and non-operative treatment programs. This interest, coupled with the injured athlete striving to return to his/her original sport at the same intensity level, has challenged the limits of joint support provided by bracing and taping. The purpose of this paper is to review the biomechanics of bracing and taping as they apply to both the knee and ankle joints.

Ankle Injuries↗
PubMed1989

Placement of transpedicular vertebral screws close to anterior vertebral cortex. Description of methods.

Strengthening of the screw-vertebra interface has been shown to occur with implantation of longer transpedicular screws, the tips of which are placed closer to the anterior cortex of the vertebral body. Such implantation probably results in increased risk for anterior cortex penetration and associated vascular or pulmonary damage. Typically recommended lateral and posterior-anterior radiography is shown here to provide potentially misleading visualization during implantation. To reduce the risk of anterior cortical penetration, presented here are 1) a radiographic method ("near approach view") that avoids this problem and allows direct visualization of the relationship between drill bit or screw tip and anterior vertebral cortex, and 2) a surgical technique ("mallet method") that provides both an audible and a palpable change when the drill bit contacts the anterior cortex.

Bone Screws↗
PubMed1988

Depth of insertion of transpedicular vertebral screws into human vertebrae: effect upon screw-vertebra interface strength.

Improvement in the strength of the transpedicular screw-vertebra interface by increasing the depth of screw insertion may provide improved performance of spinal implants using such screws. Within human cadaveric vertebrae, we measured the failure strength of Vermont Spinal Fixator (VSF) screws under flexion or torsion loads and of Schanz screws under pull-out loads (along the screw axis). Comparisons between opposite pedicles of vertebral specimens were made at 50 vs. 80% and 80 vs. 100% of maximum available insertion depth. Mean failure strength of VSF screws at 50% depth was 75-77% (depending upon load type) of that at 80% depth; strength for screws at 100% ("to-cortex") depth was 124-154% of that at 80%. Reanalysis of the data from Lavaste shows, contrary to his conclusion, a 26% increase in strength from a 5-mm increase in screw depth of insertion. All these differences were significant (p less than 0.05) by the matched-pairs t test. Benefit from the increased strength of deeper screw placement must be balanced against possible increased operative risk. A "near-approach" x-ray view is suggested here to decrease that presumed operative risk.

Bone Screws↗
PubMed1988

Morphometry of the thoracic and lumbar spine related to transpedicular screw placement for surgical spinal fixation.

Vertebral transpedicular screws provide secure attachment for posterior spinal fixation devices. Screw design details, biomechanics, and implantation safety depend upon anatomic constraints, especially from the pedicle and body. Previous morphometric data were limited; thus, a retrospective study was undertaken using computerized axial tomograms (CT) of 91 vertebrae (T9-L5). In addition, eight cadaver vertebrae were CT scanned and then cut transversely to compare x-ray measurements with direct physical measurements. Measured parameters included pedicle width, pedicle length, angle of pedicle axis to sagittal plane, and transpedicular cortex-to-cortex chord length. Good correlation is shown to occur between CT scan and direct physical measurements of human vertebrae. Implications for spinal implant screw dimensions and safety of implantation are discussed. Comparison with previously available data is made.

Adolescent↗
PubMed1988

A new halo-vest: rationale, design and biomechanical comparison to standard halo-vest designs.

The traditional halo-vest rigidly grips the cranium, but not the torso. Unexpectedly large motion and forces in the cervical spine have been shown by others to be present during halo-vest wear. In an effort to reduce these motions and forces, an experimental vest has been designed. Motion of the vest on the thorax has been measured on four normal volunteers, for each of nine load types, for each of seven commercially available vests as well as the experimental vest. Despite its lighter weight and less cumbersome structure, the experimental vest has the lowest mobility score of all the vests tested.

Biomechanical Phenomena↗
PubMed1986

An internal fixator for posterior application to short segments of the thoracic, lumbar, or lumbosacral spine. Design and testing.

A new spinal implant has been designed and biomechanical testing completed, intended for application to "short-segment" spinal defects such as disc degeneration, fracture, spondylolisthesis, or tumor. Major improvements over currently available devices include: only 2-3 vertebrae are spanned, not 5-7 as with Harrington rods; true three-dimensional fixation is achieved, preventing such problems as hook or rod dislocation; three-dimensional adjustment is easily accomplished, allowing fracture or spondylolisthesis reduction to be readily performed; attachment to vertebrae is by means of transpedicular screws eliminating deliberate encroachment into the spinal canal, such as Luque wires or Harrington hooks; no special alignment between screws is needed (such as with holes or slots in a plate), allowing screw placement to fully conform to anatomic structures; and laminectomy sites and lumbosacral junction are readily instrumented. Background investigations presented here for design of this device include: CT-defined pedicle morphometry showing that screws may be larger than those currently used; effect of pitch, minor diameter, and tooth profile on screw pull-out strength; mechanical testing of a compact, three-dimensionally adjustable, strong, nonloosening articulating clamp; and establishing of the relationship between depth of penetration and strength of fixation of transpeduncular screws.

Adolescent↗
PubMedDate not supplied

Normal kinematics of the unconstrained glenohumeral joint under coupled moment loads.

The glenohumeral joint presents difficult experimental challenges, large ranges of motion, coupled motions, and multi-planar motions. Many biomechanical tests performed on the glenohumeral joint constrain it or provide conditions that might not be reproducible within and among specimens or treatments. The goal of this study was to determine a means to test the glenohumeral joint in vitro with coupled moments applied to the unconstrained humerus and recording its "6 degrees of freedom" motion relative to the glenoid. This procedure was achieved with the development of a new testing apparatus. Kinematics were described in abduction-adduction, flexion-extension, and abduction, extension, and external rotation, simulating the cocked phase of throwing. The advantage of the techniques was that only the glenohumeral capsule and articular surface contact control the motion of the humerus in response to the applied loading pattern. Also, the motions were unconstrained by the loading apparatus, allowing coupling of rotations and translations and multiplanar motions. Rotations were found to be coupled with translations. For adduction-abduction and flexion-extension, the humeral head was found to translate first in 1 direction, opposite the direction of increasing rotation, at low moments. Then, with increasing moment and angle of rotation, translations changed direction and moved with the primary motion. This occurrence indicates the existence of a region of joint laxity or neutral zone. Rotations were found to be coupled during motion to the cocked position of throwing, as the humerus adducted with extension from full abduction and then adducted further and extends with external rotation. Changes in these motion patterns with pathologic conditions may provide useful information about the nature of shoulder dysfunction and provide insight into appropriate means of repair.

Adult↗
PubMedDate not supplied

The benefit of a single-leg strength training program for the muscles around the untrained ankle.

Severe ankle injuries can require extended periods of immobilization that adversely affect the strength of the ankle muscles. We have investigated a single-leg strength training program of the muscles surrounding the ankle to determine if it produces a crossover benefit for the contralateral ankle muscles. Twenty subjects without any history of ankle injuries were randomly divided into a control and a training group. Both groups underwent isokinetic testing of the ankle muscles at the beginning and end of an 8-week period. The control group maintained normal activities between the tests. Half of the training group trained the dominant leg only and the other half trained the nondominant leg only for the 8-week period, three times per week. The subjects who trained the dominant leg improved peak torque values by 8.5% in the trained leg and 1.5% in the untrained leg. Similarly, the subjects who trained the nondominant leg improved peak torque values by 9.3% in the trained leg and 3.5% in the untrained leg. In contrast, the control group showed no significant change in peak torque, power, or endurance between the initial and final tests. With improvements in peak torque as high as 40% in the trained leg and a crossover benefit of 19% in the untrained leg in eccentric inversion, this strength training technique deserves further investigation in an injured population where the benefits may be more substantial.

Adolescent↗
PubMedDate not supplied

The influence of functional knee bracing on the anterior cruciate ligament strain biomechanics in weightbearing and nonweightbearing knees.

Functional knee braces are commonly prescribed after anterior cruciate ligament injury or reconstruction; however, their ability to protect the ligament, or graft, remains unclear. Our objective was to evaluate the anterior cruciate ligament strain response in braced and unbraced knees during weightbearing and nonweightbearing in combination with three externally applied loads: 1) anterior-posterior shear forces, 2) internal-external torques, and 3) varus-valgus moments. The Legend brace was tested. All external loads were applied to the tibia with the knee flexed to 20 degrees. Reproducible data were obtained from 11 subjects. For anterior shear loads up to 130 N, the brace significantly reduced strain values compared with the unbraced knee during nonweightbearing and weightbearing conditions. For internal torques of the tibia (up to 9 N x m), strain in the braced knee was significantly less than in the unbraced knee when the knee was nonweightbearing only. The brace did not reduce strain values when the knee was subjected to external torques (9 N x m) or varus-valgus moments (10 N x m) in weightbearing and nonweightbearing knees. These data indicate that a functional knee brace can protect the anterior cruciate ligament during anterior-posterior shear loading in the nonweightbearing and weightbearing knee and during internal torques in the nonweightbearing knee.

Adult↗
PubMedDate not supplied

The elongation behavior of the anterior cruciate ligament graft in vivo. A long-term follow-up study.

The relationship between the elongation values of an autogenous bone-patellar tendon-bone graft immediately after fixation and the anterior-posterior laxity of the knee 5 years later was studied in vivo. Immediately after fixation, the change in the graft midsubstance length during passive knee flexion-extension was measured using a Hall-effect transducer, and anterior-posterior knee laxity was measured with the KT-1000 arthrometer. Subjects were divided into group 1 (N = 6), with graft elongation values bounded by the 95% confidence intervals of the normal anterior cruciate ligament elongation values, and group 2 (N = 7), subjects with values outside these intervals. Immediately after reconstruction, the side-to-side difference in anterior-posterior laxity between the reconstructed and uninjured knees was not different between group 1 (-2.6 +/- 0.7 mm, mean +/- SEM) and group 2 (-1.7 +/- 1.0 mm) (P = 0.49). At 5-year follow-up, the difference was 1.2 +/- 0.7 mm for group 1, while for group 2 it was significantly greater at 4.7 +/- 0.6 mm (P = 0.004). At surgery, graft elongation values produced by flexion of the knee that are outside the limits of the anterior cruciate ligament result in significant increases in anterior knee laxity at long-term follow-up, while grafts with elongation values similar to the normal anterior cruciate ligament do not. Not only is restoration of anterior-posterior laxity values to within normal limits important, but the biomechanical behavior of the graft produced by flexion-extension of the knee should be appreciated.

Adult↗
PubMedDate not supplied

Isometric versus tension measurements. A comparison for the reconstruction of the anterior cruciate ligament.

This study was designed to compare the displacement patterns of an isometer, used to determine graft placement during reconstruction, with the actual tensions on an anterior cruciate ligament substitute. In cadaveric specimens, a Kevlar anterior cruciate ligament substitute was implanted in three separate femoral sites, each of which was subsequently fixed to two different tibial sites. The initial tension of the Kevlar substitute was set to 22 or 33 N at 20 degrees of knee flexion. The displacement patterns for each position were recorded during passive flexion-extension using the isometer. Using a custom-designed tensiometer, the tensile forces on the substitute after rigid fixation at the tibia and femur were measured. During passive flexion-extension, the maximum change in tension of the anterior cruciate ligament substitute, measured by the tensiometer, was correlated with the maximum change in displacement between attachment sites, measured by the isometer. The coefficient of determination was equal to 0.15, indicating that the isometer may not accurately predict the tensions developed in the substitute.

Anterior Cruciate Ligament↗