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B D Beynnon

Publications and source records attributed to B D Beynnon.

64 records · Page 4Linked to original sources
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The relationship between anterior-posterior knee laxity and the structural properties of the patellar tendon graft. A study in canines.

We studied the relationship between anterior-posterior knee laxity and the structural properties of autogenous patellar tendon grafts used to replace the anterior cruciate ligaments in dogs 1 year after reconstruction. At 30 degrees (full extension for the dog), 60 degrees, and 90 degrees of flexion a significant inverse correlation was found between anterior-posterior knee laxity and the ultimate failure strength of the graft. Likewise, at 60 degrees and 90 degrees of flexion a significant inverse correlation was found between knee laxity and the linear stiffness of the graft. In all cases, as knee laxity increased, the ultimate failure load and linear stiffness values of the graft were found to decrease. There was also a significant increase in anterior-posterior knee laxity of the reconstructed knees (produced by an increase in anterior translation of the tibia relative to the femur) compared with the contralateral control knee. The group of dogs that underwent a sham operation without reconstruction of the anterior cruciate ligament had no change in anterior-posterior knee laxity or the structural properties of the anterior cruciate ligament. The clinical significance of this investigation is that knee laxity measurements demonstrating an increase in anterior translation of the tibia relative to the femur during graft healing may indicate that the graft has weakened and reduced structural properties.

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Anterior cruciate ligament strain behavior during rehabilitation exercises in vivo.

Before studying the biomechanical effects of rehabilitation exercises on the reconstructed knee, it is important to understand their effects on the normal anterior cruciate ligament. The objective of this investigation was to measure the strain behavior of this ligament during rehabilitation activities in vivo. Participants were patient volunteers with normal anterior cruciate ligaments instrumented with the Hall effect transducer. At 10 degrees and 20 degrees of flexion, ligament strain values for active extension of the knee with a weight of 45 N applied to a subject's lower leg were significantly greater than active motion without the weight. Isometric quadriceps muscle contraction at 15 degrees and 30 degrees also produced a significant increase in ligament strain, while at 60 degrees and 90 degrees of knee flexion there was no change in ligament strain relative to relaxed muscle condition. Simultaneous quadriceps and hamstrings muscles contraction at 15 degrees produced a significant increase in ligament strain compared with the relaxed state but did not strain the ligament at 30 degrees, 60 degrees, and 90 degrees of flexion. Isometric contraction of hamstrings muscles did not produce change in ligament strain at any flexion angle. Exercises that produce low or unstrained ligament values, and would not endanger a properly implanted graft, are either dominated by the hamstrings muscle (isometric hamstring), involve quadriceps muscle activity with the knee flexed at 60 degrees or greater (isometric quadriceps, simultaneous quadriceps and hamstrings contraction), or involve active knee motion between 35 degrees and 90 degrees of flexion.

Adult↗
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Biomechanical assessment of the healing response of the rabbit patellar tendon after removal of its central third.

The objective of this study was to determine the biomechanical properties of the healing patellar tendon after removal of its central third. This was accomplished by removing the central third of the patellar tendon from the right limb of 30 mature New Zealand White rabbits. The tendon of the contralateral normal limb served as the unoperated control. The rabbits were separated into five test groups according to healing time: time of surgery and 1, 2, 3, and 6 months after surgery. The ultimate failure strength of the patellar tendons with the central third removed was significantly less than the failure strength of the contralateral normal patellar tendons at all time intervals after surgery. At the time of surgery, the ultimate failure strength values of the operated patellar tendons were on average 53% of the normal patellar tendons, increasing to 72% of normal at 6 months. There was a significant correlation between the ultimate failure strength of the operated tendons and healing time. The positive slope for this regression indicated that the ultimate failure strength of the operated tendons converged toward normal as healing progressed. Failure mode of the operated tendon did not depend on healing time.

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The effect of anterior cruciate ligament graft elongation at the time of implantation on the biomechanical behavior of the graft and knee.

This investigation determined the effect that anterior cruciate ligament graft elongation at the time of surgical reconstruction has on the long-term biomechanical behavior of the graft and knee joint. We chose the canine model for anterior cruciate ligament reconstruction, using the medial third of the patellar tendon with attached proximal bone block. Elongation of the graft was measured immediately after graft fixation during passive knee flexion using the Hall effect transducer. The dogs were divided into either Group 1 (graft elongation behavior within the 95% confidence limits of the normal anterior cruciate ligament) or Group 2 (graft elongation behavior more than the 95% confidence limits of the normal anterior cruciate ligament). All of the dogs were sacrificed 18 months postoperatively, and we evaluated anteroposterior load displacement (i.e., anteroposterior laxity) of the knee and the structural properties of the graft. The anteroposterior laxity behavior of the reconstructed knees in Group 2 was significantly more than that of Group 1. Group 2 had significantly less linear stiffness of the graft than Group 1. There was no difference in the ultimate failure load and absorbed energy at failure values of the grafts between Groups 1 and 2. The findings from this investigation indicate that the graft elongation behavior at the time of reconstruction is a critical factor that influences the long-term success of anterior cruciate ligament reconstruction.

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The effect of functional knee bracing on the anterior cruciate ligament in the weightbearing and nonweightbearing knee.

We investigated the effect of functional bracing on anterior cruciate ligament strain in humans by arthroscopic implantation of a differential variable reluctance transducer on the ligament and measurement of its strain behavior. Strains were measured while "injury mechanism" loads were applied to the weightbearing and nonweightbearing knees for both braced and unbraced conditions. For the unbraced knee, there was a significant increase in ligament strain values when subjects went from a seated position (minimal shear and compressive loads across the knee) to a standing posture (substantial shear and compressive loads across the knee). Similar strain values were found between these same seated and standing postures when a 140-N anterior-directed load was applied to the tibia. This indicates that the ligament is strained during weightbearing and demonstrates that the compressive load across the knee produced during weightbearing does not significantly reduce ligament strain values in comparison with the unweighted joint with relaxed muscles for the 140-N load limit of our anterior shear test. Bracing produced a protective effect on the ligament by significantly reducing the strain values for anterior-directed loading of the tibia up to 140 N with the knee in both weightbearing and nonweightbearing conditions. Likewise, bracing produced a protective effect on the ligament by significantly reducing strain values in response to internal-external torque of the tibia up to 6 N-m with the knee nonweightbearing. The brace strap that contacts the tibia just distal to the insertion of the patellar tendon was instrumented with a load sensor, allowing us to measure the posterior-directed loads applied by the brace to the tibia. Adjustment of strap tension between low and high settings did not modulate the protective effect of the brace on the ligament.

Adult↗
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The strain behavior of the anterior cruciate ligament during squatting and active flexion-extension. A comparison of an open and a closed kinetic chain exercise.

The effects of weightbearing (closed kinetic chain) and nonweightbearing (open kinetic chain) exercises on the biomechanical behavior of an injured anterior cruciate ligament or a healing anterior cruciate ligament graft are unknown. To understand the effects of these exercises on the healing graft, we measured the strain behavior of the normal anterior cruciate ligament in human subjects while they performed squatting, a closed kinetic chain exercise, and active flexion-extension of the leg, an open kinetic chain exercise. The maximum anterior cruciate ligament strain values obtained during squatting did not differ from those obtained during active flexion-extension. Also, anterior cruciate ligament strain values obtained during squatting were unaffected by the application of elastic resistance intended to increase muscle activity. These findings indicate that squatting, which produces a substantial compressive joint force, does not necessarily protect the anterior cruciate ligament more than active flexion-extension of the leg, which is characterized primarily by contraction of the dominant quadriceps muscle. These findings also demonstrate that increasing resistance during the squat exercise does not produce a significant increase in anterior cruciate ligament strain values, unlike increased resistance during active flexion-extension exercise.

Adult↗
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The strain behavior of the anterior cruciate ligament during bicycling. An in vivo study.

Stationary bicycling is commonly prescribed after anterior cruciate ligament injury or reconstruction; however, the strains on the ligament or ligament graft during stationary bicycling remain unknown. In this study we measured ligament strain on eight patients who were candidates for arthroscopic meniscectomy under local anesthesia. Six different riding conditions were evaluated: three power levels (75, 125, and 175 W), each of which was performed at two cadences (60 and 90 rpm). The peak ligament strain values ranged from 1.2% for the 175-W, 90-rpm, condition to 2.1% for the 125-W, 60-rpm, condition. No significant differences were found in peak strain values due to changes in power level or cadence. Thus, the strain values were pooled across the six riding conditions tested. The mean peak strain value was 1.7%, a value that is relatively low compared with other rehabilitation activities previously tested. These data suggest that knee rehabilitation programs can be designed to include this selection of power and cadence levels without significantly changing ligament strain values. Thus, stationary bicycling is a rehabilitation exercise that permits the patient to increase muscle activity by increasing the power level or decreasing the cadence without subjecting the ligament or ligament graft to higher strain values.

Adult↗
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The effect of screw insertion torque on tendons fixed with spiked washers.

The long-term success of a hamstring tendon graft depends not only on the type of device that is used for fixation but also on the mechanical interlocking of the soft tissue between the fixation device and bone. The purpose of this study was to evaluate the effect of screw insertion torque on the structural properties of soft tissue fixed to bone with a spiked metal washer. Two bovine tendons, one similar in size to a human semitendinosus tendon and the other similar in size to a human gracilis tendon, were secured to a bovine femur using a figure-of-8 technique with screws and metal spiked washers. A single load to failure was applied at 25 mm/sec. A significant positive linear correlation was observed between fixation screw insertion torque magnitude and the ultimate failure load value. An increase in the fixation screw insertion torque produced an increase in the ultimate failure load value. Similarly, there was a significant positive linear correlation between fixation screw insertion torque magnitude and the average maximum linear load value. No relationship was detected between screw insertion torque magnitude and the linear stiffness values of the tendon-fixation construct, indicating that a reproducible model was used. This study demonstrates that screw insertion torque is an important variable that controls the initial strength of soft tissue fixation to bone.

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The effect of anterior cruciate ligament trauma and bracing on knee proprioception.

We studied the effect that chronic anterior cruciate ligament disruption, functional bracing, and a neoprene sleeve have on knee proprioception by measuring the threshold to detection of passive knee motion in all three conditions. The threshold to detection of passive knee motion was worse in knees with chronic anterior cruciate ligament insufficiency when compared with uninjured knees. This difference was small, on average an additional 0.28 degree of flexion-extension rotation was required for the anterior cruciate ligament-deficient knee before the subject detected motion, and of questionable significance from a clinical and functional perspective. Wearing a functional brace or neoprene sleeve on the anterior cruciate ligament-deficient knee did not significantly change the threshold to detection of passive motion in comparison with the same knee without a brace, although improvements were observed. There was no relationship between the most common clinical means of characterizing altered biomechanics of the anterior cruciate ligament-deficient knee (that is, the magnitude of anterior-posterior knee laxity and the grade of pivot shift) and the threshold to detection of passive knee motion.

Adult↗