The mechanical properties of anterior cruciate bone-ligament-bone specimens from humans and rhesus monkeys were determined in tension to failure under high strain-rate conditions. The age range of the human specimens was from sixteen to eighty-six years. The values fro human specimens obtained from young adults with regard to elastic modulus, ultimate tensile stress, and strain energy to failure were approximately two to three times those for specimens from humans in the sixth decade and older. The major mode of failure was ligament disruption in the specimens from young adult humans and avulsion of bone beneath the ligament insertion site in the specimens from older humans. The difference in mode of failure correlated with histological observations of decreased bone mass at the site of ligament attachment in the specimens from older humans. Rhesus monkey specimens had higher values for elastic modulus, failure stress, and strain energy. Significant reductions in strength and stiffness properties of ligament units were shown to occur with advancing age to a greater degree than expected. All experiments in which specimens from older human cadavera are used should be interpreted with caution when the results are applied to mechanisms of ligament failure for younger or athletic individuals.

Adolescent↗

PubMed1976

Cruciate ligament prosthesis: strength, creep, and fatigue properties.

The mechanical properties of the Richards polyethylene ligament implant were studied and compared with the strength of human cruciate ligament preparations. The implant yields and plastically deforms at a force of 420 newtons (ninety-four pounds) and approximately 10 per cent elongation when tested at a strain rate of 100 per second. This is one-fourth the average tensile strength of the human anterior curciate ligament preparations. When tested at a strain rate of 1 per cent per second the implant's yield-point force was lowered by 15 per cent. The implant exhibits considerable viscoelastic behavior and will progressively elongate under repetitive loads when insufficient time is allowed for it to return to its original length. In bending, the implant did not fail after eighty million stress reversals (forty million revolutions) when tested while immersed in saline solution at body temperature. The tests indicate that the tensile strength of the implant is low in comparison with both the strength of human preparations and estimates of actual in vivo functional loads. We conclude that caution is required in the use of this implant.

Age Factors↗

PubMed1975

Influence of crossbridge compliance on the force-velocity relation of muscle.

It is shown that muscle models which describe force generation as being dependent on the extension of the individual crossbridges produce a force-velocity relation of the form: Vf= Visotonic--1/KHS dP/dt. The derivation of this equation is independent of the details of activation and the kinetics of the crossbridges. The velocity, Vf, represents the relative filament velocity, and Visontonic is the relative filament velocity which would maintain a constant muscle force. P. The quantity KHS is the net stiffness of all the force-generating crossbridges in one-half a sarcomere. Experimental methods for determining KHS are suggested . To study the force-velocity relation, computer simulations based on A. F.Huxley's 1957 kinetic model were conducted for isometric and isotonic twitch contractions. The relative filament velocity is found to depend on the contraction mode, exhibiting a sudden increase in an isometric-to-isontonic changeover and a decrease in the reverse process.

Biomechanical Phenomena↗

PubMedDate not supplied

Two-bundle posterior cruciate ligament reconstruction. An in vitro analysis of graft placement and tension.

This study had two purposes: first, to determine how femoral attachment location affects the load sharing between the two bundles of a Y-type posterior cruciate ligament reconstruction, and second, to determine how the bundles, separately and in combination, control posterior tibial translation throughout the full range of knee flexion. One and two-bundle reconstructions were performed in 12 cadaveric knees. The one-bundle reconstructions were attached within the femoral posterior cruciate ligament footprint at one of three locations, high and shallow (S1), mid and shallow (S2), or mid and deep (D). The two-bundle reconstructions comprised an S1 bundle with either an S2 or a D bundle. Posterior translation and bundle tension were measured as the knee was flexed from full extension to 1,200 of flexion while a posterior force of either 50 or 100 N was applied to the proximal tibia. The shallow one-bundle reconstruction restored posterior translation to within 2 mm of that of the intact knee over the entire range of knee flexion. The deep reconstruction did not control abnormal posterior translation above 45 degrees. The tension in the shallow bundles increased with knee flexion, and the deep bundle tension remained nearly constant throughout knee flexion. Both two-bundle reconstructions controlled posterior translation, but with different load-sharing characteristics. The S1-S2 configuration resisted posterior tibial translation as both bundles became taut in flexion. In contrast, the S1-D configuration resisted posterior translation in a reciprocal fashion with the D bundle tension being the greatest in extension and the S1 bundle tension being the greatest tension in flexion.

Aged↗

PubMedDate not supplied

Freeze dried anterior cruciate ligament allografts. Preliminary studies in a goat model.

One ACL in each of 11 mature goats was replaced with a freeze dried bone-ACL-bone allograft. One year following implantation the goats had their knees evaluated biomechanically and for microvascularity and histologic changes. The reconstructed knees had a significantly greater total AP laxity (3.8 +/- 0.6 mm) (mean and SEM) than the controls (1.0 +/- 0.1 mm). Differences in primary AP laxity were responsible for 81% of the difference in total laxity, with only a 0.4 mm difference in secondary laxity. Neutral stiffness in the reconstructive knee was 17% of control, while stiffness at 30 newtons (N) of anterior force was approximately 50% of controls. Ligament stiffness in the linear region for the ACL allograft was 35% of the control value of 686 N/mm. The maximum load of the allografts was 571 +/- 45 N, or 25% of the contralateral ACL control strength (2301 +/- 155 N). Five of the seven allografts failed at the femoral insertion. Both elongation (83%) and energy (21%) to maximum load were less for allografts than controls. Histologic evaluation of the allografts revealed the presence of a regular oriented dense connective tissue which resembled a normal ligament. Microangiography revealed a periligamentous and endoligamentous vascular pattern reminiscent of a normal ACL and complete revascularization of the bone plugs.

Animals↗

PubMedDate not supplied

Cruciate reconstruction using freeze dried anterior cruciate ligament allograft and a ligament augmentation device (LAD). An experimental study in a goat model.

One ACL in each of 11 mature goats was replaced with a freeze dried bone-ACL-bone allograft and a ligament augmentation device (LAD). The LAD was released from its tibial fixation at 3 months postoperation. Biomechanical, microvascular, and histological changes were evaluated 1 year following implantation. The reconstructed knees had a significantly greater total AP translation (3.1 +/- 0.5 mm) (mean and SEM) than the contralateral controls (1.0 +/- 0.1 mm). Differences in primary AP translation were responsible for 59% of the difference in total translation, with only a 0.6 mm difference in secondary translation. Neutral stiffness in the reconstructive knee was 22% of control, while stiffness at 30 N of anterior force was approximately 35% of controls. Ligament stiffness in the linear region for the ACL allograft/LAD was 53% of the control value of 691 N/mm. The maximum load of the allograft/LADs was 1,052 +/- 145 N, or 43% of the contralateral ACL control strength (2,448 +/- 144 N). Five of the six allografts failed at the femoral insertion. Energy (39%) to maximum load was less for allograft/LADs than controls but elongation to maximum load was the same as control. Histologic evaluation of the allograft/LADs revealed soft tissue cellular ingrowth into the LAD in the extraarticular portions. No bony growth into the LAD was observed. The collagen fibers of the graft appear to be arranged in a longitudinal orientation although some areas show chaotic collagen fibers. Microangiography revealed a periligamentous and endoligamentous vascular pattern reminiscent of a normal ACL and complete revascularization of the bone plugs.

Animals↗

PubMedDate not supplied

The effects of processing techniques on the mechanical properties of bone-anterior cruciate ligament-bone allografts. An experimental study in goats.

There has been a growing interest in the use of allografts as ACL substitutes. Allografts are often freeze dried to increase shelf storage time and sterilized with ethylene oxide. This study was conducted to determine the effect of a specific ethylene oxide sterilization procedure and freeze drying process on the initial mechanical properties of femur-ACL-tibia preparations. Twelve knees (stifle joints) from six mature goats were divided into two groups (one knee of pair to each group). Knees were cleaned of all soft tissue except for the anterior cruciate, posterior cruciate, and collateral ligaments. Group 1 was sterilized with ethylene oxide (simulating clean procurement) then freeze dried. Group 2 was freeze dried only (simulating sterile procurement). The knees were rehydrated and then tested in tension to failure to determine their structural mechanical properties. The ethylene oxide-freeze dried specimens (Group 1) had a mean maximum load before failure of 2059 +/- 273 newtons (N) (+/- SE) which was not statistically different than the maximum load of the freeze dried specimens (Group 2) of 2023 +/- 214 N. The average strength of Group 1 and 2 combined was not significantly different than a third group of 12 normal femur-ACL-tibia controls which had an average maximum force of 2403 +/- 133 N. No significant differences between the groups were observed for stiffness, energy to maximum strength, or elongation to maximum force. It appears the freeze dry processing, with or without ethylene oxide sterilization, using the procedure we used, has, at most, a small effect on the initial mechanical properties of the preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Factors affecting the region of most isometric femoral attachments. Part I: The posterior cruciate ligament.

We measured how the distance between selected tibial and femoral attachments of the PCL changes with knee flexion in six intact cadaver knee. The femoral location was the primary determinant of whether the distance increased, decreased, or remained nearly constant. The proximal-distal location of a fiber's femoral attachment had a stronger effect than had the anterior-posterior location. The tibial location had only a small statistically significant effect. These results suggest that the function of fibers within the PCL is determined primarily by their femoral attachment location. We determined all femoral attachments whose tibio-femoral distance changed 0, 2, 4, 6, 8, and 10 mm during flexion from 0 degrees to 90 degrees. No absolutely isometric point existed. Attachments whose separation distance changed less than 2 mm formed a bullet-shaped region whose base was against the roof of the intercondylar notch and whose nose pointed posteriorly and slightly distally. The axis of the "bullet" was near the proximal edge of the femoral insertion of the PCL. Along the axis, anterior attachments, located near the roof of the intercondylar notch, were more isometric than were posterior attachments, located near the cartilage. Attachments located distal to the axis moved away from the tibial insertion of the PCL when the knee was flexed. The more distal the femoral attachment, the larger the increase in tibiofemoral distance that occurred with flexion. The opposite was true of attachments proximal to the 2 mm region.

Adult↗

PubMedDate not supplied

Factors affecting the region of most isometric femoral attachments. Part II: The anterior cruciate ligament.

During flexion of the intact knee, we measured the changes in distance between possible tibial and femoral attachments of an intraarticular ACL substitute. The change in distance during motion was described by the difference between the longest and shortest distances measured. Using knees from eight cadaver donors, we studied the effects of varying tibial and femoral attachment locations, applying anterior and posterior forces, and altering the range of flexion. We found that altering the femoral attachment had a much larger effect than had altering the tibial attachment. No femoral attachments were completely isometric. Femoral attachments that produced the smallest change in tibiofemoral distance, 2 mm and less, formed a band whose greatest width ranged from 3 to 5 mm. The axis of the 2 mm region was nearly proximal-distal in orientation and located near the center of the ACL's femoral insertion. Attachments located anterior to the axis moved away from the tibial attachment with flexion, whereas attachments located posterior to the axis moved toward the tibia. The AP position of the tibial attachment affected the orientation of the 2 mm region. Moving the tibial attachment posteriorly caused the proximal part of the region to move anterior, with little change in the location of the distal part of the region. Changing the applied joint force from anterior to posterior was similar to moving the tibial attachment posteriorly, but the effect was less pronounced. Increasing the range of flexion from 90 degrees to 120 degrees caused the 2 mm region to become narrower and changed its orientation.

Adult↗

PubMedDate not supplied

Reproducibility of Genucom knee analysis system testing.

The Genucom knee analysis system was studied to determine the reproducibility of test results. In the first phase of the study we investigated the reproducibility of anterior/posterior stress tests at 30 degrees and 90 degrees of flexion and varus/valgus stress tests at 20 degrees of flexion in 10 control subjects during three seatings on 3 separate days. In the second phase we studied the effect of errors in the digitization procedure (a part of the patient installation process) on anterior/posterior translation measurements. In the third phase we studied the reproducibility of a battery of tests in patients with chronic unilateral ACL deficient knees. The test battery was repeated 8 times on each knee on 6 separate days. In Phase I, analysis of variance revealed no significant differences between tests within a single seating. The day-to-day variance of all subjects was not significant, but we found a significant interaction between day and subject which was due to significant day-to-day differences in individual subjects. We found in Phase II that changing the location of the tibial joint line digitization points in the anterior/posterior or proximal/distal direction affected anterior/posterior translation measurements. Effects were larger at 30 degrees of flexion than at 90 degrees and when both the medial and lateral points were moved. Movement of the femoral condylar points resulted in a similar pattern of effects. In Phase III, although we found significant differences between our two examiners, there were no significant intraexaminer test-to-test (within seating) effects. Additionally, while there was no significant day-to-day variance overall, we found a significant interaction between day and subject.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMedDate not supplied

Repeatability of the KT-1000 arthrometer in a normal population.

Despite its popularity, the MEDmetric KT-1000 arthrometer's reliability remains inadequately documented. We conducted this study to determine the magnitude of trial-to-trial (within installation), installation-to-installation (within day), and day-to-day (between day) variability of anterior/posterior translation measurements in normal knees. We selected six normal subjects, three males and three females, and tested each on 6 consecutive days with three separate installations per day. We recorded the total anterior/posterior translation at +/- 89 and +/- 134 N force at 25 degrees of flexion during three consecutive trials in a single installation. Analysis of variance showed that no significant difference existed between trials (within installation) or between installations (within day) for all parameters. However, we did find a significant difference between days for individual right and left knee translation measurements at 89 and 134 N force. More importantly, no significant difference existed between days for right to left differences at both force levels. The magnitude of the expected measurement variability was expressed by computing 90% confidence limits for total anterior/posterior translation at +/- 89 N force. These were +/- 1.5 mm for the right knees, +/- 1.4 mm for the left knees, and +/- 1.6 mm for the right-left differences. Fischer's protected least significant difference post hoc test revealed that for all parameters, the 1st day measurements were significantly less than those on following days, suggesting that patient and examiner adjust to the testing procedure. We conclude that the standard KT-1000 evaluation should report paired differences rather than individual knee measurements. Additionally, initial evaluation should be supplemented by follow-up examinations for verifying translation values.

Adult↗

PubMedDate not supplied

An analysis of the pivot shift phenomenon. The knee motions and subluxations induced by different examiners.

The description of the pivot shift test and its modifications is for the most part based on clinical observations. We wished to precisely determine the knee motions and medial-lateral tibiofemoral compartment subluxations that examiners induce in the knee joint to produce the pivot shift phenomenon. Eleven skilled knee surgeons performed the pivot shift test on an instrumented cadaveric lower limb. The anterior cruciate and superficial medial collateral ligaments (long fibers) of one limb were sectioned to produce an abnormal state. An instrumented spatial linkage allowed all six degrees of freedom motions to be measured. Before and after ligament sectioning we determined the limits of knee motion under defined loading conditions. The tibial and femoral bony landmarks were digitized to determine the positions of the medial and lateral tibial plateaus in reference to the femoral condyles during the pivot shift tests. Each examiner performed his pivot shift test. The analysis of the data showed that examiners typically induced a coupled anterior translation and internal tibial rotation to produce an anterior tibial subluxation, and a coupled posterior translation and external tibial rotation to induce the reduction event. The magnitude of anterior subluxation of each plateau depended upon the examiner's technique. The maximal anterior subluxation of the lateral tibial plateau varied from 14 to 19.8 mm (mean, 17.2 +/- 2.0 mm), whereas anterior subluxation of the medial tibial plateau ranged from 6 to 16.9 mm (mean, 11.2 +/- 3.3 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

Femur↗

PubMedDate not supplied

The diagnosis of knee motion limits, subluxations, and ligament injury.

The clinical diagnosis of knee ligament injuries requires the clinician to: 1) estimate the abnormal motion limits that occur in one or more of the six degrees of freedom that comprise three-dimensional motion; 2) determine the abnormal position (subluxation) of the medial and lateral tibiofemoral compartments; and 3) precisely define the anatomical structures injured and degree of that injury. To determine the clinician's ability to perform these tasks, we evaluated 11 knee surgeons' clinical examination for knee instability. The positions and motions included were measured in right-left cadaveric knees by a three-dimensional instrumented spacial linkage. We compared the clinicians' estimate of knee motion limits and subluxations with the actual measured values. Before and after the clinicians' examination, the three-dimensional limits of knee motion were measured in the knees in the laboratory under defined loading conditions. Also, in one knee, the ACL and superficial medial collateral ligament were cut and the examiners, none of whom were informed of the sectioning, were asked to arrive at a diagnosis. The results for all of the clinical instability tests were similar. There was wide variability between examiners in the starting position of knee flexion and tibial rotation and in the amount of tibial translation and rotation induced. Although some examiners displaced the knee to the maximal displacement limits obtained in the laboratory, others did not, by a substantial margin. This suggests a wide variation in the loads applied by examiners to the knee joint during the tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Anterior Cruciate Ligament↗