Biomechanical properties of interference screw implantation in replacement of the anterior cruciate ligament with patellar and hamstring transplants. An experimental study using roentgen stereometry analysis (RSA)

This experimental roentgen stereometric analysis (RSA) study was performed to measure micromotions between the graft and tunnel under submaximal load in anterior cruciate ligament (ACL) reconstruction. The aim was to evaluate the maximum load at failure, linear stiffness, and slippage of bone-patellar-tendon-bone (BPTB) grafts fixed with interference screws compared to quadrupled hamstring grafts fixed with interference screws. We used 15 porcine tibia specimens for the study. In the BPTB group, the 10 x 25-mm bone plugs were fixed in a tunnel with 10 mm in diameter using a 7 x 25-mm titanium interference screw (n = 5) or a biodegradable screw (n = 5). The five hamstring transplants were folded to a four-stranded graft and armed with a baseball stitch suture. The sutured side was fixed with a 7 x 25-mm biodegradable polylactide screw in an 8-mm tunnel. The tibial bones, tendon grafts, and interference screws were marked with tantalum beads. The grafts were mounted to a custom made load frame and loaded parallel to the axis under RSA control increasing the force in steps of 50 N. Micromotions between bone plug, screw, and tibia were measured with RSA. Accuracy of RSA for the in vitro study was evaluated as 0.05 mm. Hamstring grafts failed at significantly lower maximum loads (492 +/- 30 N) than BPTB grafts (658 +/- 98 N). Linear stiffness of the hamstring graft fixations was eight times lower compared to the BPTB grafts (403 +/- 141 N/mm vs 3500 +/- 1300 N/mm). There was no significant difference between the biodegradable and titanium screws in the BPTB group. Slippage of the graft started at 82 +/- 35 N load in the hamstring group and at 428 +/- 135 N in the BPTB group. Slippage of the graft at 75% of the maximum pull-out strength was measured as 0.36 +/- 0.25 mm in the BPTB and 2.58 +/- 1.08 mm in the hamstring group. The interference screw fixation of a quadrupled hamstring graft showed a lower linear stiffness and an earlier slippage compared to a patellar tendon bone plug. Slippage of the hamstring grafts at submaximal loads may result in fixation failure during rehabilitation.     

Evaluation of an interference screw for tendon reattachment to small bones

OBJECTIVES: To compare the strength of interference screw fixation of the tendon to suture button fixation and staple fixation methods. DESIGN: Biomechanical study. METHODS: The femurs and flexor digitorum tendon of twelve rabbits were used. The tendon was attached to the medial condyle of the femur using one of the following three surgical procedures: (a) interference screw fixation: tendon-junction screw was used as an interference screw, (b) suture button fixation: the tendon was inserted through a hole and attached with a button on the opposite side, and (c) staple fixation: the tendon was attached using two staples. Strengths of the attached tendons were then measured using a universal testing machine. RESULTS: The ultimate failure load of interference screw fixation was 62.8 +/- 9.0 N, whereas that of suture button fixation was 13.9 +/- 3.8 N and staple fixation was 23.9 +/- 2.6 N. CONCLUSION: Interference screw fixation provides significant initial fixation strength (p < 0.05).     

Axial load in case of press-fit fixation of the ACL graft--a fundamental study

AIM: The aim of this study was the determination of the axial fixation load resting on smooth press-fit dowels needed for fixation of the patellar tendon graft (BTB) in order to reach the same fixation properties compared to the interference screw on anterior cruciate ligament (ACL) plasty. METHOD: Bovine test specimens with 27 BTB grafts fixed in tibial drill holes were used and divided in 3 groups: interference screw, and press-fit cylinder (? 7 mm) with 150 N and 100 N axial loads. Prior to fixation, impactation of the transplant into bone was carried out. Failure testing was done in a tensiometer at a cross-head speed of 50 mm/min. Determinations of peak load and stiffness were also made. RESULTS: Similar peak loads and stiffness were reached on introducing a press-fit dowel (slashed circle 7 mm) with 100 N and 150 N axial load compared to interference screw fixation of the BTB graft. Peak load: 988.1 N +/- 365.1 (screw) versus 1 210.4 N +/- 292.4 (dowel 150 N) and 1 109.8 N +/- 505.4 (dowel 100 N). Stiffness: 86.4 N/mm +/- 20.5 (screw) versus 102.4 N/mm +/- 15.2 (dowel 150 N) and 77.1 N/mm +/- 11.0 (dowel 100 N). There was no significant difference. CONCLUSION: When introducing a press-fit dowel (slashed circle 7 mm) with 100 N axial load into a preformed bone bed, the same fixation properties are reached as in the case of an interference screw on BTB-ACL plasty.     

Impact of tendon suturing on the interference fixation strength of quadrupled hamstring tendon grafts

Introduction

Interference screw fixation of soft tissue grafts has been a widely used fixation technique for cruciate ligament reconstruction. Suturing of the graft construct prior to graft fixation has been proposed to increase fixation strength; however, the effect on mechanical properties has not been well characterized. The goal of this study was to determine whether uniform suturing of the tendon graft affects (1) ultimate fixation strength of the hamstring tendon graft and (2) motion of the tendon in the bone tunnel during cyclic loading when comparing sutured grafts vs. unsutured grafts.

Method

Eight pairs of matched mature porcine tibias (age <2 years) and eight paired fresh-frozen human quadrupled hamstring tendon grafts were used. One quadrupled graft from each pair was placed into one of two groups. In the group A a single cerclage suture 3 cm from the doubled end of the graft was placed to join the four tendon strands. In group B a heavy suture was used to tightly unite the four strands of tendon graft to provide a better grip for the interference screw during fixation. The grafts were placed in tibial bone tunnels that matched the graft’s diameter and fixed with an interference screw. The looped end of the graft and the attached tibia were rigidly fixed in a material testing machine. The graft constructs were subjected to 100 cycles of 20–250 N load, followed by a load-to-failure test. In addition, a motion analysis system was used during cyclic testing to better determine the amount of elongation at the graft–tunnel interface. Statistical analysis of the failure load and stiffness and the overall elongation following cyclical loading was performed using the Wilcoxon rank sum test. Level of significance was set at p < 0.05.

Results

Elongation at the tendon–bone interface during sub-maximal cyclic loading was 2.4 ± 1.4 mm (unsutured) vs. 2.0 ± 0.7 mm (sutured) (p > 0.05). Failure load of the grafts without sutures (634 ± 86 N) was significantly lower than with the sutures (837 ± 183 N). Ultimate stiffness of group A (283 ± 34 N/mm) was lower than that of group B (331 ± 51 N/mm); however, this was not statistically significant (p = 0.051).

Conclusion

This study confirms that suturing of the graft construct before interference screw fixation may increase ultimate failure load. However, an improvement of structural properties in response to cyclic loading with sub-maximal loads could not be confirmed. Clinicians using interference screw fixation may suture the graft to improve fixation strength; however, suturing does not appear to allow a more aggressive rehabilitation after surgery.     

Failure strengths of concentric and eccentric implants for hamstring graft fixation

The purpose of this study is to compare the initial failure strengths of various interference screw devices used for tibial fixation of hamstring grafts in anterior cruciate ligament reconstruction and the effect of concentric or eccentric screw position. Quadrupled tendon grafts were harvested from freshly killed sheep. The grafts were then prepared and fixed in the distal femur using various devices (Intrafix (DePuy Mitek Raynham, MA, USA), RCI screw (Smith and Nephew Acufex, Mansfield, MA, USA), Wedge screw (Stryker Endoscopy, San Jose, CA, USA) in concentric position and Wedge screw in eccentric position with an interlock pin). The load required to cause mechanical failure of each construct was measured. The Intrafix device had a significantly greater mean strength to failure than all the other implants (mean 941 +/- 280 N) (P = 0.015 to P < 0.0001). The wedge screw inserted concentrically (737 +/- 134 N) had significantly greater initial failure strength than the wedge eccentric with interlock pin (458 +/- 266 N) (P = 0.03) and the RCI screw (464 +/- 107 N) (P = 0.00036). In this sheep model the Intrafix device with sheath inserted concentrically had significantly greater initial failure strength than the other interference screws. Concentric positioning of the wedge interference screw gave significantly greater initial failure strength of a quadruple tendon graft than eccentric positioning. The use of the Intrafix device or concentric positioning of an interference screw should result in increased initial fixation strength of hamstring grafts. This may allow more vigorous early rehabilitation and may result in less late graft laxity after anterior cruciate ligament reconstruction.     

Fifth metatarsal tuberosity fracture fixation: a biomechanical study

This study tested the hypothesis that fixation of a fifth metatarsal tuberosity fracture with a lag screw that engages the intact medial cortex is biomechanically stronger than fixation with a long intramedullary screw (control). The right and left feet from 10 male cadavers were alternately assigned to the two fixation groups. After fracture reduction and fixation, each specimen was potted in acrylic cement and tested on a servohydraulic testing machine. The repairs were then distracted until failure by placing the peroneus brevis tendon under tension at a rate of 1 mm/s. The lag screw technique resulted in a significantly greater mean (+/- SD) load to failure (150 +/- 90 N) than did intramedullary screw fixation (70 +/- 60 N) (p < .05) and may offer a useful method of internal fixation of fifth metatarsal tuberosity fractures when surgical stabilization is indicated.     

Fixation of tendon grafts for collateral ligament reconstructions: a cadaveric biomechanical study

PURPOSE: To compare the biomechanical properties of 4 methods of fixation of tendon grafts to bone as used for ligament reconstructions. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

A biomechanical comparison of four reconstruction techniques for the medial collateral ligament-deficient elbow

The initial strength of the intact medial collateral ligament (MCL) of the elbow and the strength of 4 reconstruction techniques were compared. Twenty cadaveric upper extremities were mounted in a custom jig with the elbow at 90 degrees , and a pneumatic cyclic valgus loading protocol was used. The mean peak load to failure was 142.5+/-39.4 N for the intact ligaments and 53.0+/-9.5 N for the docking reconstructions, 52.5+/-10.4 N for the EndoButton reconstructions, 41.0+/-16.0 N for the interference screw reconstructions, and 33.3+/-7.1 N for the figure-eight reconstructions. The peak load to failure of the MCL reconstructions was inferior compared with the intact ligament (P<.001). No difference in strength was found between the docking and single-strand medial collateral reconstruction with the use of an EndoButton for ulnar fixation (P>.05, beta=.14). Both of these reconstruction methods were stronger than the interference screw or figure-eight technique (P<.004). The optimal fixation method for a single-strand MCL reconstruction may require improved interference screws or a modified EndoButton procedure.     

Biomechanical evaluation of patellar- and hamstring tendon graft fixation for anterior cruciat ligament reconstruction using a poly-(D, L-lactide) interference screw

Anterior cruciate ligament (ACL) reconstruction using autologous hamstring tendons are being performed more frequently and satisfactory results have been reported. Advantages such as low donor site morbidity and ease of harvest as well as disadvantages like low initial construct stiffness have been described. Recently, it has been demonstrated that graft fixation close to the original ACL insertion sites increases anterior knee stability and graft isometry. Hamstring tendon fixation techniques using interference screws offer this possibility. To reduce the risk of graft laceration, a round threaded titanium interference screw (RCI) was developed. To improve initial fixation strength, fixation techniques for hamstring tendons with separate or attached tibial bone plugs were introduced. However, data on fixation strength do not yet exist. With respect to the proposed advantages of biodegradable implants, like undistorted magnetic resonance imaging, uncompromised revision surgery and a decreased potential of graft laceration during screw insertion, we performed pullout tests of round threaded biodegradable and round threaded titanium interference screw fixation of semitendinosus (ST) grafts with and without distally attached tibial bone plugs. Data were compared with bone-tendon-bone (BTB) graft fixation using biodegradable and conventional titanium interference screws. We used 56 proximal calf tibiae to compare maximum pullout force, screw insertion torque, and stiffness of fixation for biodegradable direct ST tendon and bone plug fixation (group I: without bone plug, group II: with bone plug) versus titanium interference screw fixation (group III: without bone plug, group IV: with bone plug). A round threaded biodegradable poly-(D, L-lactide) (Sysorb) and a round threaded titanium interference screw (RCI) were used. As a control calf bone-tendon-bone (BTB) grafts fixed with either poly-(D, L-lactide) (group V) or conventional titanium (group VI) interference screws were used. ST tendons were harvested either with or without their distally attached tibial bone plugs from human cadavers and were folded to a three-stranded graft. Specimen were loaded in a material testing machine with the applied load parallel to the long axis of the bone tunnel. Maximum pullout force of ST bone plug (group III: 717 N +/- 90, group IV: 602 N +/- 117) fixation was significantly higher than that of direct tendon (group I: 507 N +/- 93, group III: 419 N +/- 77) fixation. Maximum pullout force of biodegradable screw ST fixation was higher than that of titanium screw fixation in both settings. There was no significant difference in pullout force between biodegradable (713 N +/- 210) and titanium (822 N +/- 130) BTB graft fixation or between ST fixation with bone plug and biodegradable screw with BTB fixation. Pullout force of hamstring tendon interference screw fixation can be improved by using a biodegradable implant. In addition, initial pullout force can be greatly improved by harvesting the hamstring tendon graft with its distally attached tibial bone plug. This may be important, especially in improving tibial graft fixation. This study encourages further research in tendon-bone healing with direct interference screw fixation to confirm the potential of this advanced method.     

Biomechanical comparison of different fixation techniques for reconstruction of tibial avulsion fractures of the anterior cruciate ligament

Purpose

The most common fixation techniques for tibial avulsion fractures of the anterior cruciate ligament (ACL) described in the literature are screw and suture fixation. The fixation of these fractures with the TightRope® device might be an alternative. Up to now it has been commonly used in other injuries, such as acromioclavicular joint or syndesmosis ruptures. The purpose of this study was to evaluate the biomechanical properties of different fixation techniques for the reconstruction of tibial avulsion fractures.

Methods

Type III tibial avulsion fractures were simulated in 40 porcine knees. Each specimen was randomly assigned to one of four groups: (1) anterograde screw fixation, (2) suture fixation, (3) TightRope® fixation or (4) control group. The initial displacement, strength to failure and the failure mode were documented.

Results

The maximum load to failure was 1,345?±?155.5 N for the control group, 402.5?±?117.6 N for the TightRope® group, 367?±?115.8 N for the suture group and 311.7?±?120.3 N for the screw group. The maximum load to failure of the control group was significantly larger compared to all other groups. The initial dislocation was 0.28?±?0.09 mm for the control group, 0.55?±?0.26 mm for the TightRope® group, 0.84?±?0.15 mm for the screw group and 1.14?±?0.9 mm for the suture group. The initial dislocation was significantly larger for the suture group compared to the TightRope® and control groups.

Conclusions

The TightRope® fixation shows significantly lower initial displacement compared to the suture group. The TightRope® fixation might be an alternative for the repair of ACL tibial avulsion fractures that can be used arthroscopically.     

Biomechanical evaluation of open suture anchor fixation versus interference screw for biceps tenodesis

Biceps tenodesis provides reliable pain relief for patients with biceps tendon abnormality. Previous cadaver studies have shown that, for biceps tenodesis, an interference screw provides biomechanical strength to failure superior to that of suture anchors. This finding has led some providers to conclude that screw fixation for biceps tenodesis is superior to suture anchor fixation. The purpose of the current study was to test the hypothesis that the strength of a 2-suture-anchor technique with closing of the transverse ligament is equal to that of interference screw fixation for biceps tenodesis.In 6 paired, fresh-frozen cadaveric shoulder specimens, we excised the soft tissue except for the biceps tendon and the transverse ligament. We used 2 different methods for biceps tenodesis: (1) suture anchor repair with closing of the transverse ligament over the repair, and (2) interference screw fixation of the biceps tendon in the bicipital groove. Each specimen was preloaded with 5 N and then stretched to failure at 5 mm/sec on a materials testing machine. The load-to-failure forces of each method of fixation were recorded and compared. Mean loads to failure for the suture anchor and interference screw repairs were 263.2 N (95% confidence interval [CI], 221.7-304.6) and 159.4 N (95% CI, 118.4-200.5), respectively. Biceps tenodesis using suture anchors and closure of the transverse ligament provided superior load to failure than did interference screw fixation. This study shows that mini-open techniques using 2 anchors is a biomechanically comparable method to interference fixation for biceps tendon tenodesis.     

A biomechanical comparison of repair techniques in posterior type II superior labral anterior and posterior (SLAP) lesions

The purpose of this study was to compare the 3 different fixation methods of posterior type superior labral anterior posterior (SLAP) II lesion. Fifteen cadavers were randomly divided into 3 groups to compare the initial strength of 3 different fixation methods in posterior type II SLAP lesions. Group I used 1 anchor for 1-point fixation with a conventional simple suture; group II used 1 anchor passing both limbs through the posterior-superior labrum in a mattress fashion; and group III used 2 anchors for 2-point fixation with conventional simple sutures. Repair failure (2 mm permanent displacement of repaired site) and ultimate failure were measured. The mean load to (clinical) failure was 156 +/- 22 N in group I, 117 +/- 33 N in group II, and 161 +/- 44 N in group III. The mean load to ultimate failure was 198 +/- 6 N in group I, 189 +/- 23 N in group II, and 179 +/- 22 N in group III. The specimen stiffness was equivalent among groups. In mode of failure, clinical failure (more than 2 mm separations) first occurred between the markers on the biceps tendon just above (A) and below (B) compared to other markers, and ultimate failure occurred at the labral-implant interface. A single simple suture anchor repair in posterior type II SLAP seems sufficient to withstand the initial load without clinical failure. A mattress suture, although it anchors the biceps root, seems to be inferior than simple suture technique.     

An in vitro study comparing the use of suture anchors and drill hole fixation for flexor digitorum longus transfer to the navicular

BACKGROUND: The surgical management of posterior tibial tendon dysfunction often includes transfer of the flexor digitorum longus (FDL) tendon through a tunnel in the navicular. Fixation often is obtained by sewing the tendon back onto itself. The purpose of this study was to compare this standard method of fixation with suture anchor fixation, a technique that may be associated with less surgical morbidity, because it requires the harvesting of less tendon length. METHODS: FDL tendon transfer to the navicular was done in 13 fresh-frozen cadaver specimens. In six feet comprising the standard group, the FDL tendon was transected distal to the master knot of Henry, placed through a drill hole into the navicular, and sutured back onto itself. In seven feet the FDL tendon was transected proximal to the master knot of Henry, placed into a drill hole into the navicular, and fixed with a suture anchor. Load was applied to the proximal FDL muscle and tendon using a materials testing system (MTS) machine and peak load to failure was measured. RESULTS: The mean load to failure was 142.48 N +/- 38.06 N for the standard group and 142.12 N +/- 59.26 N for the suture anchor group (p = 0.305 for the Student-t test and p = 0.945 for the Mann-Whitney test). CONCLUSION: Transfer of the FDL tendon to the navicular using suture anchor fixation requires less tendon length yet provides similar fixation strength as compared to sewing the tendon back onto itself. However, suture anchors are considerably more expensive than sutures. CLINICAL IMPLICATIONS: Suture anchors allow comparable fixation of FDL tendon transfer into a navicular without the need to disrupt the master knot of Henry. This technique may be associated with less morbidity including a shorter incision, decreased risk of medial plantar nerve injury, and decreased loss of lesser toe plantarflexion strength secondary to maintenance of the normal interconnections between the flexor hallucis longus (FHL) and FDL tendons.     

Implantatfreie tibiale Fixierung des hinteren Kreuzbandes

Background

A secure tibial press fit technique in posterior cruciate ligament reconstructions may be a relevant alternative to common techniques because no hardware is necessary. Up to the present point in time no biomechanical data exist for a tibial press fit posterior cruciate ligament (PCL) reconstruction. This study compares the biomechanical properties of hamstring and quadriceps tendon grafts using a press fit technique with those of an interference screw fixation.

Methods

Quadriceps and hamstring tendons of 20 human cadavers (age 49.2±18.5 years) were used. A press fit fixation with a knot in the semitendinosus tendon (K) and a quadriceps tendon bone block graft (Q) were compared to an interference screw fixation (I) in 27 porcine tibiae. In each group, nine constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were investigated.

Results

The maximum load to failure was 518±157 N (387–650 N) for the K group, 558±119 N (466–650 N) for the I group and 620±102 N (541–699 N) for the Q group. The stiffness was 55±27 N/mm (18–89 N/mm) for the K group, 117±62 N/mm (69–165 N/mm) for the I group and 65±21 N/mm (49–82 N/mm) for the Q group. The stiffness of the I group was significantly larger (ANOVA on ranks, P=0.01). The elongation during cyclical loading was significantly larger for all groups from the 1st to the 5th cycle compared to the elongation in between the 5th and the 20th cycle (P<0.03).

Conclusion

All techniques exhibited larger elongation during initial loading. Load to failure and stiffness were significantly different between the fixations. The Q fixation showed equal biomechanical properties compared to a pure tendon fixation (I) with an interference screw. The results of group K were inferior. All three investigated fixation techniques exhibit comparable biomechanical properties. Preconditioning of the constructs is critical. Future randomized, clinical trials have to investigate the biological effectiveness of these fixation techniques.     

Influence of the diameters of tendon graft and bone tunnel in hamstring ACL reconstruction. A bovine model

In an animal model of Anterior Cruciate Ligament reconstruction by hamstring tendons and 8mm diameter biodegradable interference screws, we aimed to investigate whether pull out forces and failure modes were influenced by changing tendon and bone tunnel diameters. Three groups of 10 calf tibiae each were prepared with 8, 9 and 10mm diameter proximal tunnels fitted respectively with 8, 9 and 10mm diameter tendon grafts. Mean +/- SD pull out force was 607.9 +/- 191.5N in the 8mm group, 494.2 +/- 206.2N in the 9mm group and 530.4 +/- 212.5N in the 10mm group. These differences were not significant at t-test. 8mm specimens failed by tendon rupture, 10mm specimens failed by screw pull out and 9mm specimens failed in both ways. In this ACL reconstruction model, safe pull out forces were achieved by fixing tendon grafts to bone by 8 mm absorbable interference screws regardless of tendon and bone tunnel diameter.     

Structural properties of sutures used in anchoring multistranded hamstrings in anterior cruciate ligament reconstruction: a biomechanical study.

Sutures are frequently used in anchoring hamstring or quadriceps tendon grafts in cruciate ligament reconstruction. Trumpet like widening of the femoral bone canal was found in patients having had anterior cruciate ligament reconstruction with hamstring autograft. We investigated 5-mm Polylene tape (Genzyme, Boston, MA) and Mersilene tape (Ethicon, Somerville, NJ) as well as No. 6 Ethibond sutures (Ethicon) for ultimate load, stiffness, and elongation under tension of 50 N, 150 N, 250 N, and ultimate load. The Mersilene and Polylene tapes were tested in single loops and Ethibond in double loops having a length of 30 mm. The length is similar to that used intraoperatively for the graft fixation. The suture materials were loaded using a material testing machine at a strain rate of 60 mm/min. The ultimate loads of the loops with knots were 474 N +/-24.7 N for Polylene, 437 N +/-38.2 N for Mersilene, and 338 N +/-16.8 N for Ethibond, and was statistically significant (analysis of variance [ANOVA], P<.05). The elongation under a tension load of 50 N was similar for Ethibond (1.2+/-0.216 mm) and Polylene (1.3+/-0.32 mm). Mersilene (1.7+/-0.34 mm) showed an increased elongation (ANOVA, P=.03). The stiffness for Ethibond was 37.1+/-2.7 N/mm, for Mersilene 38.4+/-3.8 N/mm, and for Polylene was 47+/-3.1 N/mm. The Polylene tape appears to be the most suitable material in terms of strength and stiffness. Nevertheless, the stiffness of all the tested materials is greatly inferior to the stiffness of the commonly used grafts. We believe that a stiffer graft construct might reduce motion during the early period of ingrowing.     

Cyclic loading of Achilles tendon repairs: a comparison of polyester and polyblend suture

BACKGROUND: Early functional rehabilitation is widely used after open suture repair of the Achilles tendon. To our knowledge, no previous studies have assessed gap formation from cyclic loading and subsequent failure loads of simulated Achilles tendon repairs. A synthetic (polyblend) suture has been introduced for tendon repairs with reportedly greater strength than polyester suture. This stronger, stiffer suture material may provide stronger repairs with less elongation of the tendon repair. METHODS: Simulated Achilles tendon ruptures in bovine Achilles tendon were repaired with a four-strand Krackow suture technique using No. 2 polyester suture. Specimens were loaded for 3,000 cycles at maximal loads of 50, 75, 100, or 125 N, and gap formation at the repair site was continuously measured. After cyclic loading, each specimen was loaded to failure. Identical repairs were performed with number 2 polyblend suture and cyclically loaded to 75 N for 3,000 cycles. All specimens were loaded to failure. RESULTS: Cyclically loading polyester suture repairs to 50, 75, 100, or 125 N for 3,000 cycles resulted in mean gapping at the repair site of 3.0 +/- 0.8, 4.9 +/- 1.0, 7.2 +/- 0.9, and 7.9 +/- 0.8 mm, respectively. Cyclically loading the polyblend suture repairs for 3,000 cycles at 75 N, resulted in 3.3 +/- 0.3 mm of gap formation at the repair site, significantly less than polyester suture repairs (p < 0.001). The mean load to failure for polyester suture repair was 222 +/- 19 N and for polyblend suture repair was 582 +/- 49 N, a statistically significant difference (p < 0.001). Gap formation at 100, 1,000, and 2,000 cycles, as a percentage of total gap formation at 3,000 cycles, was 64.3%, 87.5%, and 95.4% for polyester suture and 45.8%, 78.5%, and 90.1% for polyblend repairs. All specimens in all groups failed at the knots during load-to-failure testing. CONCLUSIONS: Cyclic loading of simulated Achilles tendon repairs using a Krackow, four-core polyester suture technique showed progressive gap formation with increasing load. All repairs failed at the knot, and suture pull-out from tendon was not observed. Polyblend suture repair, when compared to identical repairs with braided polyester suture, resulted in a 260% higher load to failure and 33% less gap formation at the repair site after 3,000 cycles. CLINICAL RELEVANCE: The use of polyblend suture in a four-stranded Krackow configuration provides stronger repairs with less gap formation, which may provide increased security during early functional rehabilitation.     

Tenodesis of the long head of biceps brachii: cyclic testing of five methods of fixation in a porcine model

For pathologies of the long head of the biceps brachii, various surgical treatment options have been described, ranging from tenotomy to different open and arthroscopic techniques for tenodesis. We analyzed the biomechanical properties of 5 widely used operative techniques for tenodesis of the long head of the biceps brachii: an interference screw (7 x 23-mm Arthrex BioTenodesis screw), a suture anchor (5 x 15-mm Arthrex BioCorkscrew), a ligament washer, the keyhole technique, and the bone tunnel technique. Ten porcine humeri for each technique were used to evaluate the ultimate failure load and cyclic displacement. Tenodesis with the interference screw showed a significantly greater ultimate failure load compared with every other technique (480.9 +/- 116.5 N, P < .005) and the least displacement after 200 cycles, significantly less in comparison to the keyhole and bone tunnel techniques (4.28 +/- 1.44 mm, P < .05). Interference screw fixation has superior biomechanical properties with respect to cyclic displacement and primary fixation strength.     

Methods of operative fixation of the acromio-clavicular joint: a biomechanical comparison

PURPOSE: Three different methods of fixation used in acute disruption of the acromio-clavicular (AC) joint-namely, the coraco-clavicular Bosworth screw (CC Screw), a coraco-clavicular sling of Mersilene #5 tape (CC Sling), and a Hook Plate-were compared to baseline to see which could most closely replicate the stiffness of healthy cadaveric AC specimens (Intact). HYPOTHESIS: It is hypothesized that the Hook Plate method, as compared with the other reconstructions tested, will be most similar mechanically to the intact AC joint with respect to present outcome measures. METHODS: Five matched pairs of fresh-frozen cadaveric specimens were tested. Stiffness was tested with superior cyclic loads to 70 N. The stiffness for each specimen was initially tested with all the ligaments in place (Intact). The AC and CC ligaments were then sectioned, and stiffness was tested, in varying order, with reconstructions using the CC Screw, the CC Sling, and the Hook Plate. Failure testing consisted of taking either the CC Screw or Hook Plate to failure within each matched pair. RESULTS: The CC Screw and the CC Sling, respectively, showed stiffnesses of 46 +/- 23 N/mm and 15 +/- 8 N/mm, which was significantly different from the Intact specimen (P < 0.05). The Hook Plate had a stiffness of 26 +/- 17 N/mm, most comparable to the Intact joint stiffness of 25 +/- 8 N/mm (P = 0.785). With failure testing, the CC Screw failed at a significantly higher load than the Hook Plate (744 +/- 184 N vs 459 +/- 188 N) (P = 0.034). CONCLUSION: The CC Screw demonstrated the greatest stiffness with repetitive loading to 70 N. The Hook Plate had a stiffness most similar to the normal physiologic state of the AC joint. The CC Sling was significantly less stiff than the Intact joint or the other methods of fixation. SIGNIFICANCE: Although the stiffest construct is the CC Screw, Hook Plate fixation allows physiologic motion without pathological deformation and most closely resembles the stiffness of the native AC joint for the current test procedure used.     

The effect of tubularization on the mechanical properties of patellar tendon grafts

To determine the effect of tubularization on the prefailure mechanical properties of bone-patellar tendon-bone autografts used for anterior cruciate ligament repair, 10 bovine bone-patellar tendon-bone grafts were tested in tension before and after tubularization with running suture. The testing protocol involved a 5-N preload, 10 preconditioning cycles to 200 N, and a final test cycle to 950 N at 1000 N/sec. Five of the grafts were tested first as harvested (flat) and then again following tubularization. The remaining five grafts were tubularized prior to the initial testing, and final testing was done with the suture removed. Raw testing data were reduced to determine the amount of stretching associated with preconditioning, as well as laxity and stiffness of the preconditioned grafts. Tubularized grafts stretched significantly more than flat grafts during preconditioning: 3.5 times as much after the first preconditioning cycle (3.8+/-1.9 mm versus 1.1+/-0.78 mm) and 3.1 times as much after 10 cycles (5.0+/-2.1 mm versus 1.6+/-0.9 mm). There was no statistically significant difference in the stiffnesses of the tubularized and flat grafts, nor did tubularization have an effect on graft laxity. Interestingly, there was a slight increase in laxity the second time each graft was tested, regardless of whether the graft was flat or tubularized when it was first tested. These results highlight the importance of preconditioning patellar tendon grafts before fixation, especially those that have been tubularized.