Empirical Relationship Between Lengthening an Anterior Cruciate Ligament Graft and Increases in Knee Anterior Laxity: A Human Cadaveric Study

2006 ◽  
Vol 128 (6) ◽  
pp. 969-972 ◽  
Author(s):  
Dustin Grover ◽  
Dustin Thompson ◽  
M. L. Hull ◽  
S. M. Howell
Keyword(s):  
Femoral Tunnel ◽  
Cruciate Ligament ◽  
Empirical Relationship ◽  
In Vitro Tests ◽  
Fixation Device ◽  
Femoral Fixation ◽  
Fixation Devices ◽  
Anterior Laxity ◽  
Anterior Cruciate

Lengthening of an anterior cruciate ligament (ACL) graft construct can occur as a result of lengthening at the sites of tibial and/or femoral fixation and manifests as an increase in anterior laxity. Although lengthening at the site of fixation has been measured for a variety of fixation devices, it is difficult to place these results in a clinical context because the mathematical relationship between lengthening of an ACL graft construct and anterior laxity is unknown. The purpose of our study was to determine empirically this relationship. Ten cadaveric knees were reconstructed with a double-looped tendon graft. With the knee in 25° of flexion, the position of the proximal end of the graft inside the femoral tunnel was adjusted by moving the femoral fixation device until the anterior laxity at an applied anterior force of 134N matched that of the intact knee. In random order, the graft construct was lengthened 1, 2, 3, 4, and 5mm by moving the femoral fixation device distally along the femoral tunnel and anterior laxity was measured. The increase in the length of the graft construct was related to the increase in anterior laxity by a simple linear regression model. Lengthening the graft construct from 1 to 5mm caused an equal increase in anterior laxity (slope=1.0mm∕mm, r2=0.800, p<0.0001). Because an anterior laxity increase of 3mm or greater in a reconstructed knee is considered unstable clinically and because many fixation devices in widespread use clinically allow 3mm or greater of lengthening in in vitro tests, our empirical relationship indicates that lengthening at the site of fixation probably is an important cause of knee instability following ACL reconstructive surgery. Our empirical relation also indicates that an important criterion in the design of future fixation devices is that lengthening at the sites of fixation in in vitro tests should be limited to less than 3mm.

An Implantable Transducer for Measuring Tension in an Anterior Cruciate Ligament Graft

1998 ◽  
Vol 120 (3) ◽  
pp. 327-333 ◽  
Author(s):  
C. P. Ventura ◽  
J. Wolchok ◽  
M. L. Hull ◽  
S. M. Howell
Keyword(s):  
Anterior Cruciate Ligament ◽  
Measurement Accuracy ◽  
Femoral Tunnel ◽  
Cruciate Ligament ◽  
Full Range ◽  
Fixation Device ◽  
Anterior Cruciate Ligament Graft ◽  
Graft Tension ◽  
Load Cells ◽  
Anterior Cruciate

The goal of this study was to develop a new implantable transducer for measuring anterior cruciate ligament (ACL) graft tension postoperatively in patients who have undergone ACL reconstructive surgery. A unique approach was taken of integrating the transducer into a femoral fixation device. To devise a practical in vivo calibration protocol for the fixation device transducer (FDT), several hypotheses were investigated: (1) The use of a cable versus the actual graft as the means for applying load to the FDT during calibration has no significant effect on the accuracy of the FDT tension measurements; (2) the number of flexion angles at which the device is calibrated has no significant effect on the accuracy of the FDT measurements; (3) the friction between the graft and femoral tunnel has no significant effect on measurement accuracy. To provide data for testing these hypotheses, the FDT was first calibrated with both a cable and a graft over the full range of flexion. Then graft tension was measured simultaneously with both the FDT on the femoral side and load cells, which were connected to the graft on the tibial side, as five cadaver knees were loaded externally. Measurements were made with both standard and overdrilled tunnels. The error in the FDT tension measurements was the difference between the graft tension measured by the FDT and the load cells. Results of the statistical analyses showed that neither the means of applying the calibration load, the number of flexion angles used for calibration, nor the tunnel size had a significant effect on the accuracy of the FDT. Thus a cable may be used instead of the graft to transmit loads to the FDT during calibration, thus simplifying the procedure. Accurate calibration requires data from just three flexion angles of 0, 45, and 90 deg and a curve fit to obtain a calibration curve over a continuous range of flexion within the limits of this angle group. Since friction did not adversely affect the measurement accuracy of the FDT, the femoral tunnel can be drilled to match the diameter of the graft and does not need to be overdrilled. Following these procedures, the error in measuring graft tension with the FDT averages less than 10 percent relative to a full-scale load of 257 N.

scholarly journals Evaluation of Adjustable Loop Suspensory Anterior Cruciate Ligament Fixation Devices

2019 ◽  
Vol 5 (1) ◽  
pp. 505-507
Author(s):  
Mira Dreier ◽  
Samuel Bachmayer ◽  
Christian Baumgartner ◽  
Jörg Schröttner
Keyword(s):  
Anterior Cruciate Ligament ◽  
Cruciate Ligament ◽  
Healing Process ◽  
Bone Tunnel ◽  
Test Series ◽  
Fixation Device ◽  
Test Protocol ◽  
Graft Tension ◽  
Fixation Devices ◽  
Anterior Cruciate

AbstractAlong with increasing enthusiasm for sports comes an increase of sport related injuries. One of the most common injuries in the human knee is the tear of the anterior cruciate ligament (ACL). The selection of a graft fixation device is an important factor that determines the outcome of an anterior cruciate ligament reconstruction. Before the healing process is completed, the graft is dependent on tibial and femoral fixation devices to maintain normal ACL graft tension. Among various devices, the use of an adjustable loop suspensory fixation device (ALD) in soft-tissue graft reconstruction attracts current interest. An advantage of the ALD is the ability to draw the graft to the depth of the bone tunnel to achieve adequate graft tension while minimizing the empty space in the tunnel. In this study a comprehensive controlled laboratory investigation is performed to examine the biomechanical properties of commonly used cortical fixation devices, with the aim of implementing a standard testing procedure for adjustable loop devices. The procedure consists of three test series, a loop shortening test and two different stability test series (singe device and tendon device test). Those test series are used to compare the performance of a new ALD from Arthrex (Naples, USA) with five competitor devices already on the market. In order to obtain representative results eight samples of each device are tested. In comparison to the previously performed studies, a complete unloading is applied in the stability tests, which allows for a detailed examination of the ALDs locking mechanisms in dynamically loaded test situations. Furthermore, the performed loop shortening tests reveal important aspects, such as the shortening accuracy and settling effects of the loops, that are not found in previous studies. Therefore, the used test protocol can be recommended for further testing.

Static and Fatigue Strength of a Fixation Device Transducer for Measuring Anterior Cruciate Ligament Graft Tension

2000 ◽  
Vol 122 (6) ◽  
pp. 600-603 ◽  
Author(s):  
Isaac Zacharias ◽  
M. L. Hull ◽  
Stephen M. Howell
Keyword(s):  
Anterior Cruciate Ligament ◽  
Fatigue Strength ◽  
Cruciate Ligament ◽  
Fixation Device ◽  
Structural Failure ◽  
Femoral Fixation ◽  
Anterior Cruciate Ligament Graft ◽  
Scale Error ◽  
Anterior Cruciate

To determine which exercises do not overload the graft-fixation complex during intensive rehabilitation from reconstructive surgery of the anterior cruciate ligament (ACL), it would be useful to measure ACL graft loads during rehabilitative activities in vivo in humans. A previous paper by Ventura et al. (1998) reported on the design of an implantable transducer integrated into a femoral fixation device and demonstrated that the transducer could be calibrated to measure graft loads to better than 10 percent full-scale error in cadaveric knees. By measuring both the static and fatigue strengths of the transducer, the purpose of the present study was to determine whether the transducer could be safely implanted in humans without risk of structural failure. Eight devices were loaded to failure statically. Additionally, seven devices were tested using the up-and-down method to estimate the median fatigue strength at a life of 225,000 cycles. The average ultimate strength was 1856±74 N and the median fatigue strength was 441 N at a life of 225,000 cycles. The maximum graft load during normal daily activities is estimated to be 500 N and the 225,000 cycle life corresponds to that of the average healthy individual during a 12-week period. Considering that patients who have had an ACL reconstruction are less ambulatory than normal immediately following surgery and that biologic incorporation of the graft should be well developed by 12 weeks thus decreasing the load transmitted to the fixation device, the FDT can be safely implanted in humans without undue risk of structural failure. [S0148-0731(00)00606-3]

How Four Weeks of Implantation Affect the Strength and Stiffness of a Tendon Graft in a Bone Tunnel

2002 ◽  
Vol 30 (4) ◽  
pp. 506-513 ◽  
Author(s):  
Wamis Singhatat ◽  
Keith W. Lawhorn ◽  
Stephen M. Howell ◽  
Maury L. Hull
Keyword(s):  
Anterior Cruciate Ligament ◽  
Cruciate Ligament ◽  
Tendon Graft ◽  
Interference Screw ◽  
Bone Tunnel ◽  
Fixation Device ◽  
Fixation Devices ◽  
Soft Tissue Graft ◽  
Anterior Cruciate ◽  
Strength And Stiffness

Background For a tendon graft to function as an anterior cruciate ligament, the tendon must heal to the bone tunnel. We studied the effect of 4 weeks of implantation on the strength and stiffness of a tendon in a bone tunnel using two different fixation devices in an ovine model. Hypothesis The type of fixation device in anterior cruciate ligament reconstruction may affect early healing, which can be measured as the strength and stiffness of a tendon in a bone tunnel. Study Design Controlled laboratory study. Methods An extraarticular tendon graft reconstruction was performed in ovine tibias. The graft was fixed with either a bioresorbable interference screw or a WasherLoc. After 4 weeks of implantation the strength and stiffness of the complex and the tendon graft-bone tunnel interface were determined by incrementally loading specimens to failure. Results For the interference screw, the strength deteriorated 63% and the stiffness deteriorated 40%. For the WasherLoc, the strength was similar and the stiffness improved 136%. Conclusions The type of fixation device determines whether the strength and stiffness of a tendon in a bone tunnel increases or decreases after implantation. Clinical Relevance The pace of rehabilitation may need to be adjusted based on the type of fixation device used to secure a soft tissue graft.

scholarly journals Biomechanical Comparison of Epiphyseal Anterior Cruciate Ligament Fixation Using a Cortical Button Construct Versus an Interference Screw and Sheath Construct in Skeletally Immature Cadaveric Specimens

2018 ◽  
Vol 6 (6) ◽  
pp. 232596711877695
Author(s):  
Alex G. Dukas ◽  
Kevin G. Shea ◽  
Carl W. Nissen ◽  
Elifho Obopilwe ◽  
Peter D. Fabricant ◽  
...  
Keyword(s):  
Cruciate Ligament ◽  
Peak Load ◽  
Biomechanical Testing ◽  
Interference Screw ◽  
Skeletally Immature ◽  
Femoral Fixation ◽  
Fixation Devices ◽  
Cortical Button ◽  
Load To Failure ◽  
Anterior Cruciate

Background: Anterior cruciate ligament (ACL) ruptures have become increasingly common in pediatric and adolescent athletes. While multiple methods exist, all-epiphyseal ACL reconstruction is a popular technique in the skeletally immature patient. Given the high rate of reruptures in this population and the increasing number of commercially available fixation devices, biomechanical testing is crucial to understand the performance of these devices in pediatric epiphyseal bone. To our knowledge, there has not been a biomechanical analysis of ACL fixation devices in skeletally immature bone. Purpose: To compare cortically based button fixation with interference screw and sheath fixation in skeletally immature femoral epiphyseal cadaveric bone. Our hypothesis was that there would be no difference in peak load to failure, stiffness, or cyclic displacement between these 2 fixation constructs. Study Design: Controlled laboratory study. Methods: Fresh-frozen matched-pair knees from 3 pediatric cadaveric specimens were obtained. A synthetic graft was fixed in an all-epiphyseal femoral tunnel. Both the lateral and medial condyles were utilized to increase the sample size. Specimens were randomized and assigned to receive either an interference screw and sheath construct designed for pediatric patients or an adjustable loop cortical button. Biomechanical testing was performed to obtain ultimate load to failure, stiffness, total displacement after 500 cycles, and the failure mode for each condyle. Results: Each medial and lateral condyle in 3 pairs of skeletally immature cadaveric knees (ages 7, 9, and 11 years) was utilized for testing. One specimen was excluded after it failed by having a transphyseal fracture. The median peak load to failure was 769.80 N (interquartile range [IQR], 628.50-930.41 N) for the screw and sheath group and 862.80 N (IQR, 692.34-872.65 N) for the button group ( P = .893). The median displacement after 500 cycles for the screw and sheath group was 0.65 mm (IQR, 0.47-1.03 mm) and 1.13 mm (IQR, 0.96-1.25 mm) for the button group ( P = .08). The median stiffness of the screw and sheath group was significantly higher than that of the button group (31.47 N/mm [IQR, 26.40-43.00 N/mm] vs 25.22 N/mm [IQR, 21.18-27.07 N/mm], respectively) ( P = .043). Conclusion: When comparing femoral fixation with a screw and sheath construct developed for pediatric patients to an adjustable loop cortical button in skeletally immature bone, our results showed that fixation did not significantly differ with respect to cyclic displacement or peak load to failure. While the screw and sheath construct was significantly stiffer, its effect on clinical outcomes is not yet known. Clinical Relevance: With regard to femoral fixation, there is no significant biomechanical difference between the use of cortically based button fixation or interference screw and sheath fixation in pediatric epiphyseal cadaveric bone.

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