Compaction of a Bone Dowel in the Tibial Tunnel Improves the Fixation Stiffness of a Soft Tissue Anterior Cruciate Ligament Graft

2005 ◽  
Vol 33 (5) ◽  
pp. 719-725 ◽  
Author(s):  
Stephen M. Howell ◽  
Phil Roos ◽  
Maury L. Hull
Keyword(s):  
Anterior Cruciate Ligament ◽  
Soft Tissue ◽  
Cruciate Ligament ◽  
Tibial Tunnel ◽  
Tendon Graft ◽  
Joint Line ◽  
Fixation Device ◽  
Yield Load ◽  
Anterior Cruciate Ligament Graft ◽  
Anterior Cruciate

Background Despite increasing attention on fixation of a soft tissue anterior cruciate ligament graft in the tibia, there have been no studies on the use of a bone dowel as a joint line fixation device for promoting fixation properties, especially stiffness at the time of implantation. Purpose To determine whether compacting a bone dowel into the tibial tunnel improves fixation stiffness, yield load, and resistance to slippage of a soft tissue anterior cruciate ligament graft. Study Design Controlled laboratory study. Methods A double-looped tendon graft was fixed at the distal end of the tibial tunnel with a WasherLoc in 24 calf tibias. The tibial tunnels were treated with or without a dowel of cancellous bone. The bone dowel was harvested from the tibial tunnel and then compacted into a tapered space anterior to the anterior cruciate ligament graft as a joint line fixation device. A cyclic load and measurement test was administered to determine fixation stiffness, yield load, slippage, and failure mode. Results The specimens with the bone dowel had 58 N/mm more stiffness (P =. 04); however, the yield load and resistance to slippage were similar in specimens with and without the bone dowel. Conclusions A bone dowel harvested from the tibial tunnel can be used as a joint line fixation device in series with a distal fixation method to improve initial fixation stiffness and increase the fit, which is known to enhance tendon graft-to-bone healing in the tibia.

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.

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.

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