Tendon Graft Fixation Research Articles

The Modified Finger-Trap Suture Technique: A Biomechanical Comparison of a Novel Suture Technique for Graft Fixation

The purpose of this study was to compare the tendon graft holding power of the newly devised modified finger-trap (MFT) suture technique with other currently used sutures. We used 40 fresh-frozen porcine flexor profundus tendons randomly divided into 4 groups of 10 specimens. The experimental procedure was designed to assess percent elongation of the suture-tendon construct across four different tendon-grasping techniques: MFT suture, Krackow stitch, locking SpeedWhip stitch (Arthrex, Naples, FL), and nonlocking SpeedWhip stitch. The suture configurations of the MFT suture and Krackow stitch were completed with a No. 2 FiberWire suture (Arthrex). The locking SpeedWhip and nonlocking SpeedWhip stitches were completed with a loop of No. 2 FiberWire suture and a FiberLoop needle (Arthrex). Each tendon was pre-tensioned to 100 N for three cycles and then cyclically loaded to 200 N for 200 cycles. Finally, each tendon was loaded to failure. Percent elongation, load to failure, and mode of failure for each suture-tendon construct were measured. During the pre-tension phase, the MFT suture had the smallest percent elongation (P = .021) of the suture-graft construct (13.5% ± 1.9%) compared with the Krackow (16.9% ± 1.2%), locking SpeedWhip (17.6% ± 0.6%), and nonlocking SpeedWhip (33.3% ± 5.6%) stitches. During cyclic loading, the MFT suture also showed a significantly smaller percent elongation (P = .037) of the suture-graft construct (27.8% ± 4.9%) than the Krackow (35.8% ± 5.4%), locking SpeedWhip (33.7% ± 5.4%), and nonlocking SpeedWhip (43.8% ± 7.8%) stitches. The load to failure and cross-sectional area were not significantly different across all the suture groups. The newly devised MFT suture provided better percent elongation and equal load to failure compared with the Krackow and SpeedWhip suture techniques tested in this in vitro biomechanical evaluation. The MFT suture is a simple method that is an attractive alternative to the Krackow and SpeedWhip suture techniques for tendon graft fixation in ligament reconstruction.

Contact pressure on ACL hamstring grafts in the bone tunnel with interference screw fixation — Dynamic adaptation under load

IntroductionInterference screws used in fixation of anterior cruciate ligament (ACL) hamstring grafts create mechanical hold by forcing the graft into frictional contact with the bone tunnel. We analyzed the resultant graft–tunnel contact pressure using an in vitro model of human cadaver 8mm hamstring grafts. MethodsContact characteristics were assessed using both pressure sensitive films and a force sensor. Two screw sizes were investigated (8 and 9mm in an 8mm Sawbone tunnel), both with and without a bone wedge between graft and screw. Separately, time dependent relaxation of contact force was recorded over a one hour epoch and associated tendon water loss was measured. Pullout testing of 8mm tendon grafts from 8mm holes in Sawbone and porcine femora were performed after 1min and 1h. ResultsDuring screw insertion, measured peak pressures (>40MPa) exceeded the compressive failure stress of metaphyseal bone by more than an order of magnitude. Using a bone wedge between tendon and screw reduced local peak pressure by 85% but produced also inferior average contact pressure. In all approaches, initially achieved graft contact pressure rapidly decreased to approximately 25% within 30min. Pullout strength was significantly reduced after 1h in comparison to 1min in porcine bone as well as Sawbone. ConclusionViscoelastic adaptation of the tendon is severe and critically reduces effective graft–bone contact pressure. Consideration of this newly recognized effect may open new and improved approaches for tendon graft fixation.

Supplemental bio-tenodesis improves tibialis anterior allograft yield load in extremely low density tibiae

Improved soft tissue tendon graft mechanical properties have led to their increased use for anterior cruciate ligament (ACL) reconstruction. Because they do not have an osseous component; however, there are greater concerns regarding tibial graft slippage during early postoperative rehabilitation and activities of daily living, particularly in patients with poor bone mineral density (BMD), such as older patients, women, smokers, and patients undergoing revision ACL reconstruction surgery. This in vitro biomechanical study attempted to determine the effectiveness of supplemental ACL graft fixation in low BMD tibiae. Eight paired knees (16 specimens) were harvested from female cadavers (mean age=76, range=60-88years). Tibiae were assigned to either a combination bioabsorbable interference screw, bio-tenodesis screw group (Group 1, n=8, apparent BMD=0.44±0.13g/cm(2)) or a bioabsorbable interference screw group (Group 2, n=8, apparent BMD=0.44±0.14g/cm(2)). Double-strand (single loop) tibialis anterior tendon allografts were fixed in matched diameter tibial tunnels. Using a custom 6° of freedom jig, potted constructs were mounted on to a servo hydraulic device with the axial loading force aligned directly with the tibial tunnel. Constructs underwent progressive cyclic tensile loading from 10 to 150N with a 25N load increase every 20 cycles. This was followed by yield load to failure testing (20mm/min). Groups did not display displacement differences during progressive cyclic loading. Group 1 (312.7±67.5N) displayed 25% greater yield load at failure than Group 2 (235.0±47.6N), P=0.045. Both groups displayed fixation levels well below the previously reported minimal safe threshold estimate for early unrestricted weight bearing, accelerated rehabilitation and activities of daily living. Supplemental bio-tenodesis fixation may improve early tibial-soft tissue tendon graft fixation in patients that have poor tibial BMD, but study results suggest that both methods may require weightbearing, rehabilitation, and activity of daily living restrictions during the early postoperative period to prevent graft slippage.

Thumb Carpometacarpal Arthroplasty Using an Absorbable Interference Screw for Flexor Carpi Radialis Ligament Reconstruction

Few surgical techniques that address advanced thumb carpometacarpal osteoarthrosis specifically allow early mobilization postoperatively. After trapeziectomy, we carry out a ligament reconstruction using an absorbable interference screw to secure a flexor carpi radialis tendon autograft within the first metacarpal base. Theoretically, superior tendon graft fixation strength allows early mobilization within 2 weeks postoperatively. We have retrospectively compared our clinical results using this technique with another group of patients who underwent traditional ligament reconstruction and tendon interposition as described by Burton and Pellegrini. There were no differences in the verbal pain score, satisfaction rating, or DASH scores between groups. There was a statistically significant decrease in trapezial space ratio both at rest and with stress for the experimental group. Although the clinical significance of this finding is largely unknown, it did not correlate with clinical outcome in our patients. Although no conclusions could be drawn regarding early mobilization after thumb carpometacarpal arthroplasty, further studies are planned to investigate this intriguing aspect of postoperative care. In this article, we present the details of the surgical technique and postoperative rehabilitation.

Hybrid hamstring graft tibial fixation in anterior cruciate ligament reconstruction

Tibial fixation of the anterior cruciate ligament hamstring tendon graft is commonly considered more problematic than femoral fixation. When interference screws are used for tibial hamstring tendon graft fixation, graft sometimes looses its tension, so a hybrid fixation (more than one method of fixation) must be applied. Biomechanical studies show that an implementation of interference screws combined with different indirect distal hamstring tendon fixation techniques can withstand much higher tearing forces when compared with one type of fixation. We made a technique of hybrid tibial fixation of the hamstring graft using round interference screws and an additional bi-cortical 4.5-mm diameter screw with a modified head that allows control over the initial tension of the graft.

Hamstring graft fixation in MPFL reconstruction at the patella using a transosseous suture technique

Controversy still exists about fixation methods of a hamstring graft to the patella in case of medial patellofemoral ligament (MPFL) reconstruction. This article presents a surgical technique of hamstring tendon graft fixation to the anatomical MPFL insertion on the patella using transosseous sutures. A superficial bony sulcus is created at the anatomical MPFL insertion site on the medial patellar rim with a bur. A looped hamstring tendon graft is fixed to this superficial sulcus by a pair of nonresorbable transosseous sutures passed across the patella. The retinaculum is sutured on top of the hamstring tendon graft at the level of the patella for additional fixation. The technique avoids bone tunnels as well as hardware at the patella. It reduces the risk of intraoperative or postoperative patella fracture or implant-related complications. The stable transosseous fixation technique allows for early rehabilitation.

Influence of the Crosshead Rate on the Mechanical Properties of Fixation Systems of ACL Tendon Grafts

Anterior cruciate ligament (ACL) reconstruction is one of the most important aspects of knee surgery. For this purpose, several fixation devices have been developed, although the interference screw is the most frequently used. The most typical biomechanical test of these devices consists of placing them in a testing machine and subjecting them to a pull-out test. However, insufficient attention has been paid to the influence of the displacement test rate on the mechanical properties of the fixation system. The aim of this study is to compare the influence of the crosshead rate in the biomechanical test of two different devices for the fixation of ACL tendon grafts. One hundred in vitro tests were performed using porcine tibiae and bovine tendons. The fixation devices used were (1) an interference screw and (2) a new expansion device. All ACL reconstructions were subjected to pull-out test to failure. Five crosshead rates were employed in a range from 30 mm/min to 4000 mm/min. Statistical analyses of the results show that, for the two devices, the rate has a significant effect on both maximum force and stiffness. Moreover, the new expansion device showed lesser dependency on the crosshead rate than the interference screw.

Comparison of Different Sizes of Bioabsorbable Interference Screws for Anterior Cruciate Ligament Reconstruction Using Bioabsorbable Bead Augmentation in a Porcine Model

The aim of this study was to compare the initial fixation strength of tendon grafts between different sizes of bioabsorbable interference screws (BioScrew; Linvatec, Largo, FL) with bioabsorbable bead (EndoPearl; Linvatec) augmentation through biomechanical analysis of a porcine femoral bone model. Forty pairs of porcine femurs and porcine flexor digitorum profundus tendons were divided into control and study groups. In the control group 8 x 30-mm BioScrews alone (n = 10) were inserted, whereas different sizes of BioScrews, measuring 7 x 30 mm (n = 10), 8 x 30 mm (n = 10), and 9 x 30 mm (n = 10), with 8-mm EndoPearl augmentation were inserted individually for fixation of tendon grafts in the study groups. All specimens were cyclically loaded with axial forces between 50 and 250 N at 1 Hz for 3,000 cycles and then incrementally loaded to failure at a rate of 150 mm/min. BioScrews with EndoPearl augmentation had a significantly higher failure load than BioScrews alone (8-mm BioScrew alone v 8-mm BioScrew and EndoPearl, P < .05). There were no significant differences in the ultimate failure load (8 mm v 7 mm and 9 mm, P = .201 and P = .871, respectively), stiffness (8 mm v 7 mm and 9 mm, P = .789 and P = .823, respectively), displacement (8 mm v 7 mm and 9 mm, P = .695 and P = .781, respectively), and bone mineral density (P = .728 for all comparisons) except insertion torque (8 mm v 7 mm and 9 mm, P = .045 and P = .518, respectively) between study groups. Less tendon laceration by the screw thread was noted in the group in which smaller-sized BioScrews were used. When EndoPearl augmentation was used, smaller-sized BioScrews (BioScrew size 1 mm smaller than bone tunnel) offered equivalent graft fixation strength to BioScrews of similar or larger sizes. Smaller-sized BioScrews can be chosen if EndoPearl augmentation has been used, and EndoPearl augmentation may reduce the risk of tendon rupture while BioScrews are inserted.

Tension Degradation of Anterior Cruciate Ligament Grafts With Dynamic Flexion-Extension Loading: A Biomechanical Model in Porcine Knees

This study investigates the influence of various femoral anterior cruciate ligament graft fixation methods on the amount of tension degradation and the initial fixation strength after cyclic flexion-extension loading in a porcine knee model. One hundred twenty porcine digital extensor tendons, used as 4-stranded free tendon grafts, were fixated within porcine femoral bone tunnels by use of extracortical button, cross-pin, or interference screw fixation. One hundred twenty porcine patellar tendon-bone grafts were fixated by use of cross-pin, interference screw, or press-fit fixation. Each femur-graft complex was submitted to cyclic flexion-extension loading for 1,000 cycles throughout different loading ranges, and the total loss of tension was determined. After cyclic testing, the grafts were loaded to failure, and the data were compared with a pullout series without cyclic loading. Tension degradation after 1,000 cycles of flexion-extension loading averaged 62.6% +/- 10.0% in free tendon grafts and 48.9% +/- 13.35% in patellar tendon-bone grafts. There was no influence of the loading range on the total amount of tension degradation. The total amount of tension degradation was the highest with interference screw fixation of free tendon and patellar tendon-bone grafts. Despite excessive loss of tension, the initial fixation strength of the femur-graft complex was not reduced. The method of femoral graft fixation significantly influenced tension degradation during dynamic flexion-extension loading. Femoral graft fixation methods that secure the graft close to the tunnel entrance and that displace the graft substance from the center of the bone tunnel show the largest amount of tension degradation during cyclic flexion-extension loading. The graft substance, not the fixation site, was the weakest link of the graft complex within this investigation. We believe that the graft fixation method should be considered when aiming to improve the precision of femoral graft placement in anterior cruciate ligament reconstruction.

Soft Tissue Tendon Graft Fixation in Serially Dilated or Extraction-Drilled Tibial Tunnels

Background Tibial tunnel preparation may contribute to improved soft tissue graft fixation. Hypothesis Step dilation produces greater tunnel wall bone volume than does extraction drilling and increases fixation strength. Bioabsorbable interference screw divergence decreases fixation strength, regardless of tunnel preparation method. Study Design Controlled laboratory study. Methods Twenty porcine tibias were divided into 2 groups of 10 with matching mean apparent bone mineral density. One group received 9-mm-diameter extraction-drilled tunnels, and the other group received 7-mm-diameter extraction-drilled tunnels followed by step dilation to 9 mm. High-resolution quantitative computerized tomography scans and voxel analysis techniques determined tunnel wall bone volume fraction. Screws secured 8.5-mm-diameter porcine grafts in the tunnels. Repeat scans were used to determine screw divergence. Cyclic loading was performed in a servohydraulic device before load to failure testing. Results The step dilation group had greater tunnel wall bone volume/total volume than did the extraction drilled group; however, a significant increase in fixation strength was not detected. Specimens with screw divergence angles less than 15° had superior fixation and insertion torques compared with specimens with angles 15° or more. Screw divergence correlated more strongly with fixation strength than did mean apparent bone mineral density or screw insertion torque. Conclusion Step dilation increased tunnel wall bone volume/total volume, but fixation strength did not improve. Screw divergence ≥15° decreases graft-bone tunnel fixation whether or not step dilation is performed. Clinical Relevance Screw alignment plays a greater role in anterior cruciate ligament graft fixation than does extraction drilling or step dilation tunnel preparation methods in healthy bone.

Revision Anterior Cruciate Ligament Reconstruction with Hamstring Tendon Autograft

Background The results of revision anterior cruciate ligament reconstruction are limited in the current literature, and no studies have previously documented the outcome of revision anterior cruciate ligament reconstruction using solely hamstring tendon grafts. Hypothesis Revision anterior cruciate ligament reconstruction with 4-strand hamstring tendon graft affords acceptable results and is comparable to reported outcomes with the bone–patellar tendon–bone graft. Study Design Case series; Level of evidence, 4. Methods Fifty-seven consecutive revision anterior cruciate ligament reconstructions with the hamstring tendon graft and interference screw fixation were assessed a mean time of 89 months (range, 60-109 months) after surgery. Assessment included the International Knee Documentation Committee knee ligament evaluation, instrumented laxity testing, and radiologic examination. Results Of the 50 knees reviewed, 5 (10%) had objective failure of the revision anterior cruciate ligament reconstruction. Of the 45 patients with functional grafts, knee function was normal or nearly normal in 33 patients (73%). An overall grade of normal or nearly normal was found in 56% of patients. The mean side-to-side difference on manual maximum testing was 2.5 mm (range,–1 to 4 mm). Degenerative changes on radiographs were identified in 23% of patients at the time of surgery, increasing to 56% of patients at review. The status of the articular cartilage at the time of revision surgery was the most significant contributor to successful outcome. Conclusion Revision anterior cruciate ligament reconstruction with hamstring tendon graft and interference screw fixation affords acceptable results at a minimum of 5 years’ follow-up. Good objective results can be obtained, but subjectively, the results appear inferior to those of primary anterior cruciate ligament reconstruction in the literature, which may be related to the high incidence of articular surface damage in this patient population. We recommend that, when available, hamstring tendon autografts should be considered for revision anterior cruciate ligament reconstruction.

Bioabsorbable screw divergence angle, not tunnel preparation method influences soft tissue tendon graft-bone tunnel fixation in healthy bone

Bone tunnel fixation of a soft tissue tendon graft is the weak link immediately following ACL reconstruction. This biomechanical study evaluated the influence of extraction drilled or step dilated bone tunnels and bioabsorbable screw divergence on soft tissue tendon graft fixation. From an initial group of 50 available specimens, similar apparent bone mineral density porcine tibiae (1.2 +/- 0.24 g/cm2) were divided into two groups of ten specimens each. Group 1 (extraction drilled) received 9 mm diameter tunnels. Group 2 (step dilated) received 7 mm diameter tunnels that were dilated to 9 mm. Grafts were secured in tunnels using 10 mm diameter, 35 mm long tapered screws. After high resolution CT scanning to evaluate screw divergence, constructs were pretensioned on a servo hydraulic device between 10 and 50 N for 10 cycles, and isometric pretensioned at 50 N for 1 min, prior to 500 sub-maximal loading cycles (50-200 N) and load to failure testing at 20 mm/min. Wilcoxon Signed Rank tests and Mann-Whitney U-tests were used to evaluate group differences. Coefficient of determination values (r2) were calculated to further delineate statistically significant relationships. Tunnel preparation method did not display statistically significant effects on insertion torque, displacement during cyclic testing, relative stiffness during cyclic testing, load at failure, stiffness during load to failure testing or displacement during load to failure testing. Screw divergence < 15 degrees produced lower displacement and greater relative stiffness during cyclic testing and greater load at failure and stiffness during load to failure testing. Screw divergence angle displayed moderate relationships with construct displacement during cyclic testing (r2 = 0.54), stiffness during load to failure testing (r2 = 0.60), and load at failure (r2 = 0.41). Tunnel dilation does not enhance soft tissue tendon graft fixation strength in healthy bone. Bioabsorbable screw divergence of > or = 15 degrees significantly reduces soft tissue tendon graft-bone tunnel fixation.

Tensile Strength of a New Suture for Fixation of Tendon Grafts When Using a Weave Technique

To evaluate a new corner stitch construct for tendon graft or tendon transfer fixation and compare the tensile strength with a conventional central cross-suture design in human cadaver tendons. Flexor digitorum profundus tendons of the index, middle, and ring fingers (48 total) were used as recipients and palmaris longus, extensor indicis proprius, and extensor digitorum communis tendons of the index finger (48 total) were used as grafts from 16 fresh-frozen human cadaver hands. We compared the cross-stitch technique with a new corner stitch technique in tendon repairs made with 1, 2, or 3 weaves (8 per group). Tendons were sutured at each weave with either 2 full-thickness cross-stitches or 4 partial-thickness corner stitches of 4-0 nylon. Mattress sutures also were placed through the free tendon end for each repair type. The tensile strength of the tendon-graft composite was measured with a materials testing machine. The tensile strength of the repairs increased significantly with the number of weaves. When 2 or 3 weaves were used with the corner stitch or when 3 weaves were used with the cross-stitch, the repairs were significantly stronger. Although no significant difference in strength to failure was noted when comparing cross and corner stitches with equivalent numbers of weaves, qualitatively there was a difference in mode of failure with the 3-weave corner stitches failing primarily by intrasubstance tendon failure and the 3-weave cross-stitch repairs failing by tendon pullout. The corner stitch is as strong as conventional cross-stitch repairs and its superficial placement may be more favorable to tendon blood supply. This repair may be advantageous for clinical applications.

Gender Differences in Outcome after Anterior Cruciate Ligament Reconstruction with Hamstring Tendon Autograft

Background It is now well documented that women are more likely to suffer anterior cruciate ligament injuries than are men. A few studies have examined gender differences in the outcome of anterior cruciate ligament reconstruction with patellar tendon graft and hamstring tendon with Endo Button fixation, but no well-controlled studies have specifically compared men and women after anterior cruciate ligament reconstruction with hamstring tendon graft and interference screw fixation. Hypothesis There is no difference in outcome between men and women after anterior cruciate ligament reconstruction with hamstring tendon autograft and interference screw fixation. Study Design Cohort study; Level of evidence, 3. Methods There were 100 men and 100 women who underwent isolated anterior cruciate ligament reconstruction by a single surgeon. Patients were assessed preoperatively and at 1, 2, and 7 years after surgery. Variables were compared between female and male patients. Results Laxity on physical evaluation was greater in women than in men on Lachman (P= .04), pivot-shift (P= .05), and mean manual maximum testing (P= .05) at 7 years. However, the magnitude of this difference was small. No patient had a greater than grade 1 Lachman or pivot-shift test result, and the mean difference between men and women was 0.6 mm on instrumented testing. Anterior cruciate ligament graft rupture occurred in 11 men and 10 women. There was no difference between male and female patients for self-reported knee function or symptoms of instability or radiologic examination. Conclusion Anterior cruciate ligament reconstruction using hamstring tendon autograft affords excellent self-reported and objective results in both men and women after 7 years. Although significantly greater laxity on physical examination was present in female patients than in male patients, the magnitude of this difference was small and had no effect on activity level, graft failure, or subjective or functional assessment.

Residual Strength of the Quadriceps Versus Patellar Tendon After Harvesting a Central Free Tendon Graft

Free tendon grafts for reconstruction of the anterior cruciate ligament have become more prevalent with the desire for reduced morbidity, earlier postoperative rehabilitation, and improved free tendon graft fixation. The central quadriceps tendon autograft is an alternative to bone-patellar tendon-bone and free hamstring autografts. The purpose of this study was to measure the postharvest reduction in quadriceps extensor mechanism strength when a central quadriceps free tendon graft is removed. The strength deficit was compared with that associated with harvesting a central free patellar tendon graft, excluding the effects of harvesting bone blocks. Experimental laboratory study. Fourteen knee extensor mechanisms were divided into quadriceps and patellar tendon constructs. Constructs were tested to failure in tension in either the intact state or after removing 10-mm wide central free tendon grafts. Failure strengths of the quadriceps and patellar tendon constructs were compared statistically using paired and unpaired t tests. The average strength (+/-SD) measured for the native quadriceps tendon was 3,660 +/- 830 N, decreasing to 2,430 +/- 680 N after removing a partial-thickness 10-mm wide central free graft. The average strength measured for the native patellar tendon was 1,920 +/- 330 N, decreasing to 1,460 +/- 740 N after removing a 10-mm wide central free graft. The tensile strength of the quadriceps tendon is reduced by approximately one third after harvesting a partial-thickness 10-mm wide central free tendon graft. This postharvest strength of the quadriceps tendon is higher than that of the intact patellar tendon. Surgeons can be assured that harvest of a central quadriceps free tendon graft leaves a stronger extensor mechanism than harvest of a patellar tendon graft.

Fixation of Tendon Grafts for Collateral Ligament Reconstructions: A Cadaveric Biomechanical Study

To compare the biomechanical properties of 4 methods of fixation of tendon grafts to bone as used for ligament reconstructions. Thirty-two metacarpals were harvested from fresh-frozen cadavers and stripped of soft tissue. Flexor tendons were harvested from the same cadavers and cut into 2-mm-wide strips. Each tendon was fixed to a metacarpal head at the site of origin of a collateral ligament. Four different methods of fixation were tested. In group 1 the tendon was fixed to the bone with a 4.0-mm Arthrex bio-tenodesis interference screw (Arthrex, Inc., Naples, FL). In group 2 the tendon was passed through a bone tunnel and fixed with a 3.2-mm mini-Acutrak screw (Acumed, LLC, Hillsboro, OR) that was inserted in interference mode. In group 3 the tendon was passed through a bone tunnel and fixed with sutures tied over a polyethylene button. In group 4 the tendon was fixed with a mini-Mitek bone suture anchor (Mitek Worldwide, Norwood, MA). All specimens were clamped into a linear loading machine and loaded until failure. Statistical analysis was performed by 1-way analysis of variance testing. The differences in maximal tensile strength and stiffness were statistically significant when comparing any 2 groups. The Arthrex biotenodesis interference screw was the strongest and stiffest fixation method, followed by the Acutrak screw inserted in interference mode. Next was the suture tied over a button method. The mini-Mitek bone suture anchor was the weakest. Interference screw fixation of tendons to bone has statistically significant higher pullout strength and stiffness than 2 other commonly used fixation methods. The use of interference screws for fixation of tendon grafts to bone for hand ligament reconstructions is a promising new surgical technique.

The biology of integration of the anterior cruciate ligament

The anterior cruciate ligament (ACL) is a short, stout, intra-articular, extrasynovial structure which acts to control rotational movements and anterior translation of the femur upon the fixed tibia.[1][1] Rupture is a traumatic event, often as a consequence of twisting upon the weight-bearing limb

Stiffness characteristics of hamstring tendon graft fixation methods at the femoral site

In ACL reconstruction, stiffness and strength of a tendon graft complex are important features for knee stability and rehabilitation. The fixation between tendon and bone is known to be one of the weakest components of the graft complex. We examined the tensile load-displacement characteristics of looped semitendinosus tendons in a porcine femoral tunnel. Two groups of six cadaveric semitendinosus tendons and porcine femurs were tested, secured with either an aperture or non-aperture fixation method. Constructs were tested at 1 mm/s until failure in a materials testing machine, which allowed force and displacement data to be recorded. The non-aperture fixation group was significantly less stiff for the first 4 mm of displacement and had significantly higher ultimate failure loads. Provided that adequate ultimate strength can be achieved, stiffness properties of a tendon graft will be improved by using aperture fixation in femoral-site ACL reconstruction.

Graft-bone motion and tensile properties of hamstring and patellar tendon anterior cruciate ligament femoral graft fixation under cyclic loading

Graft-bone motion and tensile properties of hamstring and patellar tendon anterior cruciate ligament femoral graft fixation under cyclic loading

Graft-bone motion and tensile properties of hamstring and patellar tendon anterior cruciate ligament femoral graft fixation under cyclic loading

To assess longitudinal graft-bone motion and tensile properties of the femur-anterior cruciate ligament (ACL) graft fixation-ACL graft complex based on the hypothesis that there is little difference in graft-bone motion between suspensory and aperture hamstring ACL femoral graft fixation techniques, and between hamstring and patellar tendon ACL femoral graft fixation techniques. In vitro biomechanical study using human cadavers. The distal femur-ACL graft fixation-ACL graft complex was cyclically loaded between 50 and 250 N at 1 Hz for 1,000 cycles with the direction of the load applied parallel to the axis of the femoral bone tunnel. Graft-bone motion was measured indirectly using retroreflective markers and a video motion-analysis system. Tensile testing to failure was performed at 1 mm/sec for fixation techniques completing 1,000 cycles without fixation failure. Among the hamstring fixation techniques, 4 of 13 Bio-Interference screws (Arthrex, Naples, FL), 2 of 12 LinX HT fasteners (DePuy Mitek, Norwood, MA), and 1 of 11 TransFix cross-pins (Arthrex) failed before completing 1,000 cycles. Five of 13 patellar tendon grafts fixed with metal interference screws, and 2 of 12 patellar tendon grafts fixed with a plastic button and No. 5 sutures failed before completing 1,000 cycles. Suture/button fixation of patellar tendon grafts resulted in significantly more graft-bone motion than hamstring tendon grafts fixed using the Bone Mulch Screw (Arthrotek, Warsaw, IN), or interference screw fixation of patellar tendon and hamstring grafts. Otherwise, there was no significant difference in graft-bone motion among the various hamstring fixation techniques or the various hamstring fixation techniques and interference screw fixation of patellar tendon grafts. Maximum graft-bone displacement after cyclic loading was significantly greater for hamstring grafts fixed with the EndoButton and EndoButton Tape (Smith & Nephew Endoscopy, Andover, MA) compared with the other hamstring fixation techniques and interference screw fixation of patellar tendon grafts. All fixation techniques except hamstring tendon grafts fixed with the Bio-Interference screw achieved at least 59% of maximum graft-bone displacement after 20 cycles. Hamstring tendon grafts fixed with the EndoButton CL were significantly stronger than all other hamstring and patellar tendon fixation methods. Patellar tendon grafts fixed with interference screws and hamstring tendon grafts fixed with interference screws and the Bone Mulch Screw and TransFix were significantly stiffer than hamstring tendon grafts fixed with the EndoButton CL. There is no significant difference in graft-bone motion between aperture and suspensory femoral fixation methods when the stiffness of the femur-ACL graft fixation-ACL graft complex is similar. The small differences in graft-bone motion reported in our study provide further evidence that graft-tunnel motion or the so-called bungee effect is unlikely to be the primary cause of radiographic bone tunnel enlargement following ACL reconstruction.