The biomechanics of interference screw fixation of patellar tendon anterior cruciate ligament grafts

Smaller diameter femoral tunnel biocomposite interference screws provide adequate fixation strength in anterior cruciate ligament reconstruction

PURPOSE

The purpose of this study was to evaluate the effect of bioabsorbable interference screw diameter on the pullout strength and failure mode for femoral tunnel fixation in primary anterior cruciate ligament reconstruction (ACLR) at time zero fixation using bone-patellar tendon-bone (BTB) autograft in a cadaveric model.

METHODS

Twenty-four fresh-frozen cadaveric knees were obtained from 17 different donors. Specimens were allocated to three different treatment groups (n = 8 per group) based on interference screw diameter: 6 mm, 7 mm, or 8 mm biocomposite interference screw. All specimens underwent dual energy X-ray absorptiometry (DEXA) scanning prior to allocation to ensure no difference in bone mineral density among groups (n.s.). All specimens underwent femoral-sided ACLR with BTB autograft. Specimens subsequently underwent mechanical testing under monotonic loading conditions to failure. The load to failure and failure mechanism were recorded.

RESULTS

The mean pullout force (N) at time zero for each group was 309 ± 213 N, 518 ± 313 N, and 541 ± 267 N for 6 mm, 7 mm, and 8 mm biocomposite interference screw diameter, respectively (n.s.). One specimen in the 6 mm group, two specimens in the 7 mm group, and one specimen in the 8 mm group failed by screw pullout. The remainder in each group failed by graft failure (n.s.).

CONCLUSION

Biocomposite interference screw diameter did not have a significant influence on fixation pullout strength or failure mode following femoral tunnel fixation using BTB autograft at time zero. A 6 mm interference screw can improve preservation of native bone stock, increase potential for biologic healing, and decrease the risk of damage to the graft during insertion without significantly compromising fixation strength. This study supports the use of smaller 6 mm interference screw diameter options for femoral tunnel fixation in ACLR.

Pediatric Revision Anterior Cruciate Ligament Reconstruction: Current Concepts Review

OBJECTIVE

We present a review of revision anterior cruciate ligament (ACL) reconstruction in pediatric patients, discussing risk factors for rerupture, physical examination and imaging, treatment principles and surgical techniques, postoperative rehabilitation, and clinical outcomes.

DATA SOURCES

PubMed, Cochrane, and Embase databases were queried for relevant articles about revision ACL topics. All types of manuscripts, including clinical studies, basic science studies, case series, current concepts reviews, and systematic reviews were analyzed for relevant information. Current concepts on risk factors for rerupture, physical examination and imaging, treatment principles and surgical techniques, postoperative rehabilitation, and clinical outcomes were synthesized.

MAIN RESULTS

Surgical treatment should be individualized, and the graft type, fixation devices, tunnel placement, and complementary procedures (eg, extra-articular tenodesis) should be tailored to the patient's needs and previous surgeries. Rehabilitation programs should also be centered around eccentric strengthening, isometric quadriceps strengthening, active flexion range of motion of the knee, and an emphasis on closed chain exercises. Despite adherence to strict surgical and postoperative rehabilitation principles, graft refailure rate is high, and return to sports rate is low.

CONCLUSION

Rerupture of the ACL in the pediatric population is a challenging complication that requires special attention. Diagnostic evaluation of repeat ACL ruptures is similar to primary injuries. Although outcomes after revision ACL reconstruction are expectedly worse than after primary reconstruction, athletes do return to sport after proper rehabilitation. Further research is needed to continue to improve outcomes in this high-risk population, aimed at continued knee stability, graft survivorship, and improved quality of life.

Significant Loss of ACL Graft Force With Tibial-Sided Soft Tissue Interference Screw Fixation Over 24 Hours: A Biomechanical Study

Background

Tibial-sided graft fixation is thought to be critical for the success of anterior cruciate ligament (ACL) reconstruction. Nevertheless, little is known about the graft force after fixation during the first 24 hours after surgery or the influence of screw diameter and length during this time.

Purpose

To investigate the force, over the course of 24 hours, in soft tissue grafts secured with a tibial interference screw and to evaluate the effect of different screw diameters (7, 8, and 9 mm) and lengths (25 and 30 mm) on the force in these grafts.

Study Design

Controlled laboratory study.

Methods

Quadruple-strand flexor tendon grafts were fixed with bioabsorbable interference screws in 60 porcine tibiae. Grafts were pretensioned at 80 N over 10 minutes, and screws were inserted outside-in while a preload force of 80 N was applied. Different screw lengths (25 and 30 mm) and diameters (7, 8, and 9 mm), resulting in 6 groups with 10 specimens each, were tested. After release of the preload, graft force was recorded over 24 hours.

Results

A significant decrease in graft force progressed in all groups over the 24-hour period. In total, a median loss of 75 N (IQR, 68-79 N) compared with the initial loading force was observed. Compared with the loading force of 80 N, this corresponded to a median loss of 91%. No significant differences in the remaining graft force could be found among the 6 different screw length and diameter groups after 10 minutes, 100 minutes, or 24 hours.

Conclusion

Graft force in soft tissue grafts secured with a tibial interference screw decreased substantially over the first 24 hours after fixation. Neither the screw diameter nor the screw length affected the decrease in graft force. This raises substantial questions regarding the remaining fixation strength in vivo.

Clinical Relevance

It should not be expected that ACL reconstruction can mechanically restabilize an injured knee as would an intact ACL. Reconstructed knees should be protected from mechanical overload in the early postoperative period.

Athletes With Bone-Patellar Tendon-Bone Autograft for Anterior Cruciate Ligament Reconstruction Were Slower to Meet Rehabilitation Milestones and Return-to-Sport Criteria Than Athletes With Hamstring Tendon Autograft or Soft Tissue Allograft : Secondary Analysis From the ACL-SPORTS Trial

OBJECTIVE

Graft choices for athletes undergoing anterior cruciate ligament reconstruction (ACLR) include bone-patellar tendon-bone (BPTB) and hamstring tendon (HT) autografts and soft tissue allografts. The objective was to assess time to meet clinical milestones by graft type in athletes who completed a return-to-sport (RTS) program after ACLR.

DESIGN

Retrospective cohort study.

METHODS

Seventy-nine athletes enrolled after ACLR (allograft, n = 18; BPTB, n = 24; HT, n = 37). Time from surgery to meet (1) enrollment criteria (12 or more weeks post surgery, 80% or greater isometric quadriceps strength index, minimal effusion, and full knee range of motion), and (2) RTS criteria (90% or greater quadriceps strength index, hop testing limb symmetry, and patient-reported outcomes) was calculated. Quadriceps strength, hop performance, and patient-reported outcomes were measured before and after training, and at 1 year post surgery. Descriptive statistics, chi-square tests, and 1-way analyses of variance (α = .05) were used to analyze differences among graft types.

RESULTS

On average, the BPTB group (28.5 ± 7.6 weeks) took longer to meet enrollment milestones than the HT (22.5 ± 7.6 weeks, P = .007) and allograft (18.9 ± 5.8 weeks, P<.001) groups. The BPTB group (44.7 ± 15.8 weeks) took longer from surgery to meet RTS criteria than the HT (32.5 ± 9.9 weeks, P = .001) and allograft (29.3 ± 9.0 weeks, P<.001) groups. After training, the quadriceps strength index was lower in the BPTB group (86.1% ± 11.4%) than it was in the HT (96.1% ± 12.9%, P = .004) and allograft (96.9% ± 5.9%, P = .009) groups.

CONCLUSION

Athletes with a BPTB autograft may take longer than athletes with an HT autograft or a soft tissue allograft to complete postoperative rehabilitation, recover quadriceps strength, and meet RTS criteria. J Orthop Sports Phys Ther 2020;50(5):259-266. Epub 27 Nov 2019. doi:10.2519/jospt.2020.9111.

Femoral Interference Screw Fixation in ACL Reconstruction Using Bone-Patellar Tendon-Bone Grafts

» Anterior cruciate ligament (ACL) reconstruction is a commonly performed orthopaedic procedure with numerous reconstructive graft and fixation options. Interference screws have become one of the most commonly utilized methods of securing ACL grafts such as bone-patellar tendon-bone (BPTB) autografts. » The composition of interference screws has undergone substantial evolution over the past several decades, and numerous advantages and disadvantages are associated with each design. » The composition, geometry, and insertional torque of interference screws have important implications for screw biomechanics and may ultimately influence the strength, stability of graft fixation, and biologic healing in ACL reconstruction. » This article reviews the development and biomechanical properties of interference screws while examining outcomes, complications, and gaps in knowledge that are associated with the use of femoral interference screws during BPTB ACL reconstruction.

Design of a new magnesium-based anterior cruciate ligament interference screw using finite element analysis

Background/objective

In anterior cruciate ligament ​reconstruction, a tendon graft, anchored by interference screws (IFSs), is frequently used as a replacement for the damaged ligament. Generally, IFSs are classified as being either metallic or polymeric. Metallic screws have sharp threads that lacerate the graft, preventing solid fixation. These constructs are difficult to image ​and can limit bone--screw integration because of the higher stiffness of the screw. Polymeric materials are often a better match to bone's material properties, but lack the strength needed to hold grafts in place. Magnesium (Mg) is a material of great promise for orthopaedic applications. Mg has mechanical properties similar to bone, ability to be seen on magnetic resonance imagings, and promotes bone healing. However, questions still remain regarding the strength of Mg-based screws. Previous ex vivo ​animal experiments found stripping of the screw drive when the full torque was applied to Mg screws during surgery, preventing full insertion and poor graft fixation. The similar design of the Mg screw led to questions regarding the relationship between material properties and design, and the ultimate impact on mechanical behaviour. Thus, the objective of this study was to analyze the stresses in the screw head, a key factor in the stripping mechanism of IFS, then use that information to improve screw design, for this material.

Methods

Using finite element analysis, a comparison study of six drive designs (hexagonal, quadrangle, torx, trigonal, trilobe, and turbine) was performed. This was followed by a parametric analysis to determine appropriate drive depth and drive width.

Results

It was observed that with a typical torque (2 ​Nm) used for screw insertion during anterior cruciate ligament reconstruction, the maximum von Mises and shear stress values were concentrated in the corners or turns of the drive, which could lead to stripping if the values were greater than the yield stress of Mg (193 ​MPa). With a four-time ​increase in drive depth to be fully driven and a 30% greater drive width, these maximum stress values were significantly decreased by more than 75%.

Conclusion

It was concluded that improving the design of a Mg-based screw may increase surgical success rates, by decreasing device failure at insertion.

The translational potential of this article

The results of this work have the potential to improve designs of degradable IFSs, allowing for greater torque to be applied and thus greater screw fixation between host bone and the graft. Such a fixation will allow greater integration, better patient healing, and ultimately improved patient outcomes.

Hyperflexion and Femoral Interference Screw Insertion in ACL Reconstruction

Background:

In anatomic anterior cruciate ligament (ACL) reconstructions produced with flexible reamers and no knee hyperflexion, it is unknown whether knee hyperflexion is necessary for femoral interference screw insertion.

Purpose:

To compare femoral screw-graft divergence in anatomic ACL reconstructions with endoscopic interference screws placed without knee hyperflexion and with the use of flexible versus rigid screwdrivers.

Study Design:

Controlled laboratory study.

Methods:

Ten matched pairs of cadaveric knees had bone-tendon-bone graft ACL reconstructions with anatomic femoral tunnels. The knees were flexed to 90°. Femoral interference screws (7 × 20 mm) were placed in pairs of knees: in 1 knee with a flexible screwdriver and in the opposite knee with a rigid screwdriver. Graft-screw divergence was imaged with computed tomography scans and tested with cyclic and static biomechanical tests.

Results:

The mean screw-graft divergence was 12.07° ± 4.04° with the rigid screwdriver and 10.68° ± 3.23° with the flexible screwdriver (P = .35). The cyclic tests with screws placed by a rigid screwdriver had a mean increase in displacement of 0.56 ± 0.20 mm. For screws placed with the flexible screwdriver, the mean increase in displacement was 0.58 ± 0.32 mm (P = .66). Yield load was 393.3 ± 95.1 N for screws placed by a rigid screwdriver and 408.2 ± 119.0 N for screws inserted with the flexible screwdriver (P = .78). Maximum load was 523.1 ± 88.7 N for screws placed by a rigid screwdriver and 467.1 ± 107.3 N for screws inserted with the flexible screwdriver (P = .09).

Conclusion:

With either a rigid or a flexible screwdriver, there were no significant effects on screw divergence or fixation strength.

Clinical Relevance:

Knees can be kept at 90° during endoscopic femoral interference screw insertion. The use of a traditional rigid or flexible screwdriver will not affect screw-graft divergence or fixation strength.

Quantitative assessment of patellar vascularity following bone-patellar tendon-bone autograft harvest for ACL reconstruction

PURPOSE

Recent anatomic studies have suggested that the dominant arterial supply of the patella enters through the inferior pole. Based upon these findings, we hypothesized that bone-patellar tendon-bone graft harvest can significantly diminish patellar vascularity.

METHODS

Nine matched pair cadaveric knee specimens (mean age 47.4 years) were dissected and cannulated. A single knee was selected to undergo routine graft harvest, and the contralateral knee was left intact to serve as a control. Gadolinium was injected, and magnetic resonance imaging (MRI) signal enhancement was quantified to determine differences in uptake. Each matched pair was subsequently injected with a urethane polymer compound and dissected to correlate vessel disruption with MRI findings.

RESULTS

We identified two predominating patterns of vessel entry. In one pattern, the vessel entered the inferomedial aspect (five o'clock/right, seven o'clock/left) of the patella and was disrupted by graft harvest in 2/9 (22.2 %) pairs. In the second pattern, the vessel entered further medial (four o'clock/right, eight o'clock/left) and was not disrupted (7/9, 78.8 %). The mean decrease in gadolinium uptake following disruption of the predominant vessel measured 56.2 % (range 42.6-69.5 %) compared to an average decrease of 18.3 % (range 7.1-29.1 %) when the dominant arterial supply to the inferior pole remained intact (p < 0.04).

CONCLUSION

Medial entry of the predominant vessel precluded vessel disruption. Disruption of the dominant arterial supply can result in a significant decrease in patellar vascularity. Modification of graft harvest techniques and areas of surgical dissection should be explored to minimize vascular insult. Further correlation with clinical studies/outcomes is necessary to determine a potential association between vascular insult and anterior knee pain.

[Ligament bracing--augmented cruciate ligament sutures: biomechanical studies of a new treatment concept]

BACKGROUND

In the context of acute knee dislocations, suture repair of ruptured cruciate ligaments leads to good clinical results in 80% of cases. Disadvantages are low primary stability and subsequently secondary elongation of the sutured ligaments. In the present study, we compared primary stability of suture repair, reinforced by different suture augments, to cruciate ligament reconstruction.

OBJECTIVE

The concept of ligament bracing with transosseous suture repair of the cruciate ligaments and additional suture augmentation is biomechanically superior to cruciate ligament reconstruction.

MATERIAL AND METHODS

A total of 42 porcine knee joints divided into seven groups were examined. The stability of four different suture/augmentation combinations were compared to cruciate ligament reconstruction with human hamstring tendons. The investigational setup consisted of testing 1000 cycles with 20 N to 154 N load in a.-p. translation and 60° flexion. Elongation and load to failure were measured.

RESULTS

Neither reconstruction (3.13 ± 1.65 mm; 362 ± 51 N) nor augmented suture repair (1.89-2.5 mm; 464-624 N) achieved the primary stability of the intact cruciate ligament (0.63 ± 0.34 mm, 1012 ± 91 N). In comparison to ligament reconstruction, all four augmented suture repairs showed minor elongation in the cyclic test and a higher load to failure. The isolated suture repair showed poor results (6.79 ± 4.86 mm, 177 ± 73 N).

CONCLUSION

Augmented suture repair provides significantly higher stability compared with isolated suture repair and reconstruction with hamstring tendons. The concept of ligament bracing could be a promising future treatment option in acute knee dislocations. Clinical results remain to be seen.

Interference screws should be shorter than the hamstring tendon graft in the bone tunnel for best fixation

PURPOSE

Interference screw fixation of hamstring tendon grafts in bone has to overcome the challenges that tendons have a slippery surface and viscoelastically adapt under pressure. As the typical failure mode of the graft is to slip past the interference screw, it was hypothesized that the position and configuration of the graft end may be of influence on the fixation strength.

METHODS

Different configurations of the graft ending and its effect to primary fixation with interference screws after viscoelastic adaptation were tested in six groups: I: graft and the screw inserted at the same depth, II/III: the graft overlaps the tip of the screw (interference screw of 28 and 19 mm in length, respectively), IV: strengthening of the graft ending with additional suture knots, V: Endopearl, respectively, and VI: effect of partial retraction of the screw after excessive insertion. In vitro tests were performed with fresh calf tendon grafts and interference screws in bone tunnels (fresh porcine distal femur) all of 8 mm in diameter.

RESULTS

The relative position of the graft ending to the tip of the interference screw thereby was recognized as a significant factor on pullout forces. Further strengthening at the graft endings with additional suture knots or an Endopearl device could improve primary hold as well.

CONCLUSIONS

Better fixation strength is achieved if the tip of interference screw does not extend past the end of a tendon graft. Enforcement of the tendon end with sutures or an implant can further improve fixation.

Biomechanical properties of porcine flexor tendon fixation with varying throws and stitch methods

BACKGROUND

The well-known suture technique configurations used for hamstring tendon autograft preparation in anterior cruciate ligament (ACL) reconstruction are the Krackow locking stitch and nonlocking stitch, such as a baseball stitch and a whipstitch. However, there are few data in the literature regarding biomechanical comparisons of suture techniques.

PURPOSE

The purpose of this study was to determine the properties of several current techniques of tendon graft suture employed in ACL reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty-two fresh-frozen porcine flexor digitorum tendons were used. Three stitch configurations (Krackow stitch [group K], baseball stitch [group B], and whipstitch [group W]) were assessed with varying suture throws (6 throws, group×6; 10 throws, group×10) using No. 5 Ethibond sutures. Each group was tested at 1500 loading cycles between 50 and 200 N. After loading cycles, the surviving tendons underwent a load-to-failure test.

RESULTS

During the loading cycles, 3 of 7 specimens in group B×6 and all specimens in group W×6 failed by suture pullout. Four of 7 specimens in group B×10 and all specimens in group W×10 showed partial tearing of the tendon. Elongation of group B×10 and group W×10 showed significantly greater elongation than other groups (P < .05). Maximum loads at failure showed significant differences between group K and the other groups (K×6, 436 ± 52 N; K×10, 419 ± 34 N; P < .05). Most specimens failed by rupture of the suture thread in group K. Pullout of the suture from the tendon was observed most in groups B and W.

CONCLUSION

The Krackow stitch was superior to other stitch methods. There was, however, no significant effect of the number of throws on the holding strength.

CLINICAL RELEVANCE

The Krackow stitch could prevent suture slippage by a locking mechanism. The whipstitch is not suitable for clinical application even with an increased number of throws.

Femoral tunnel-interference screw divergence in anterior cruciate ligament reconstruction using bone-patellar tendon-bone graft: A comparison of two techniques

BACKGROUND

Interference screw is a popular fixation device used to rigidly fix bone-patellar tendon-bone (B-PT-B) graft both in femoral and tibial tunnels in anterior cruciate ligament (ACL) reconstruction. Parallel placement of screw is difficult in transtibially drilled femoral tunnel but always desired as it affects pullout strength of the graft. Commonly, interference screw into the femoral tunnel is inserted through the anteromedial (AM) or accessory AM portal. These portals are not-in-line with the transtibially drilled femoral tunnel. Furthermore, these portals increase the divergence of the interference screw in the femoral tunnel. We hypothesized that interference screw placement through patellar tendon (PT) portal (through donor defect) in transtibially drilled femoral tunnel can be less divergent. We report the prospective randomized study to investigate the difference of divergence of interference screw placed through PT portal and AM portal and its clinical relevance.

MATERIALS AND METHODS

Forty-one patients underwent femoral tunnel B-PT-B graft fixation through AM portal (group 1) and other 41 (group 2) through PT portal. Femoral tunnel-interference screw divergence was measured on postoperative digital lateral X-rays. Ha's method was used to grade divergence. The clinical outcome was assessed by postoperative intervention knee documentation committee grading (IKDC) and Lysholm score at 2 years followup.

RESULTS

Mean tunnel-screw divergence in sagittal plane through AM portal was 13.38° (95% CI: 12.34-14.41) and through PT portal was 7.20° (95% CI: 6.25-8.16) (P<0.0001). In AM portal group, 82.9% patients had divergence in either grade 3 or 4 category, whereas in PT portal group, 82.9% patients were in grade 1 or 2 category (P<0.0001). Mean Lysholm score were 92.8 and 94.5 at two-year follow-up in both groups which were statistically not significant. The International knee documentation committee grades of patients in both groups were similar and had no statistical significance.

CONCLUSION

Femoral interference screw placement through the PT portal leads to significantly less screw divergence as compared with screw placement through the AM portal. However, this difference in divergence is not reflected in clinical outcome.

BIOMECHANICAL TESTING PROCEDURES IN TENDON GRAFT RECONSTRUCTIVE ACL SURGERY

This paper, describes the biomedical testing of an Anterior Cruciate Ligament (ACL) reconstruction using an interference screw fixation on the bovine and porcine tissues. The harvesting procedure, experimental setup, mechanical testing, and evaluation of the tendon graft interference screw fixation are all presented throughout this study. A guideline has also been introduced to evaluate the basic mechanical properties of the bone components and the tendon graft.

The effect of interference screw diameter on fixation of soft-tissue grafts in anterior cruciate ligament reconstruction

PURPOSE

The purpose of this study was to evaluate the effect that interference screw diameter has on fixation strength of a soft-tissue anterior cruciate ligament (ACL) graft.

METHODS

We prepared 32 fresh-frozen bovine tibiae with 9-mm ACL tibial tunnels. Accompanying 9-mm soft-tissue bovine Achilles grafts were also prepared. Bioabsorbable interference screws of increasing diameters were used for tibial fixation. There were 4 groups, consisting of 8-, 9-, 10-, and 11-mm screws for fixation of the 9-mm graft in the 9-mm tunnel. Tensile testing and cyclic loading from 50 to 250 N at 2 Hz for a total of 1,500 cycles were performed with a hydraulic biaxial materials testing machine. Graft slippage was measured with a video analysis technique with photo-reflective markers. At the end of cyclic testing, the grafts were loaded to failure, and the ultimate strength was recorded.

RESULTS

All grafts failed at the tendon-bone-screw interface. The ultimate strength (+/- SD) was greatest for the 11-mm screw (624 +/- 133 N), with slightly decreased strength for the 10-mm (601 +/- 54 N), 9-mm (576 +/- 85 N), and 8-mm (532 +/- 185 N) screws. Graft slippage (+/- SD) was least for the 9-mm screw (2.65 +/- 2.38 mm). There were no statistically significant differences in ultimate strength and graft slippage between screws (P = .45 and P = .34, respectively).

CONCLUSIONS

All interference screws tested provided adequate fixation strength. The results of this study show no statistical significance for ultimate strength or graft slippage with variable screw diameter.

CLINICAL RELEVANCE

Aperture fixation with the interference screw technique provides adequate stability for soft-tissue grafts in ACL reconstruction. Although no statistical significance was found, there was a trend toward less graft-site motion when we used a screw diameter equal to tunnel size.

Fixation strength of biocomposite wedge interference screw in ACL reconstruction: effect of screw length and tunnel/screw ratio. A controlled laboratory study

Background

Primary stability of the graft is essential in anterior cruciate ligament surgery. An optimal method of fixation should be easy to insert and provide great resistance against pull-out forces.

A controlled laboratory study was designed to test the primary stability of ACL tendinous grafts in the tibial tunnel. The correlation between resistance to traction forces and the cross-section and length of the screw was studied.

Methods

The tibial phase of ACL reconstruction was performed in forty porcine tibias using digital flexor tendons of the same animal. An 8 mm tunnel was drilled in each specimen and two looped tendons placed as graft. Specimens were divided in five groups according to the diameter and length of the screw used for fixation. Wedge interference screws were used. Longitudinal traction was applied to the graft with a Servohydraulic Fatigue System. Load and displacement were controlled and analyzed.

Results

The mean loads to failure for each group were 295,44 N (Group 1; 9 × 23 screw), 564,05 N (Group 2; 9 × 28), 614,95 N (Group 3; 9 × 35), 651,14 N (Group 4; 10 × 28) and 664,99 (Group 5; 10 × 35). No slippage of the graft was observed in groups 3, 4 and 5. There were significant differences in the load to failure among groups (ANOVA/P < 0.001).

Conclusions

Longer and wider interference screws provide better fixation in tibial ACL graft fixation. Short screws (23 mm) do not achieve optimal fixation and should be implanted only with special requirements.

Torsional stability of interference screws derived from bovine bone--a biomechanical study

Background

In the present biomechanical study, the torsional stability of different interference screws, made of bovine bone, was tested. Interference screws derived from bovine bone are a possible biological alternative to conventional metallic or bioabsorbable polymer interference screws.

Methods

In the first part of the study we compared the torsional stability of self-made 8 mm Interference screws (BC) and a commercial 8 mm interference screw (Tutofix^®). Furthermore, we compared the torsional strength of BC screws with different diameters. For screwing in, a hexagon head and an octagon head were tested. Maximum breaking torques in polymethyl methacrylate resin were recorded by means of an electronic torque screw driver. In the second part of the study the tibial part of a bone-patellar tendon-bone graft was fixed in porcine test specimens using an 8 mm BC screw and the maximum insertion torques were recorded. Each interference screw type was tested 5 times.

Results

There was no statistically significant difference between the different 8 mm interference screws (p = 0.121). Pairwise comparisons did not reveal statistically significant differences, either. It was demonstrated for the BC screws, that a larger screw diameter significantly leads to higher torsional stability (p = 9.779 × 10^-5). Pairwise comparisons showed a significantly lower torsional stability for the 7 mm BC screw than for the 8 mm BC screw (p = 0.0079) and the 9 mm BC screw (p = 0.0079). Statistically significant differences between the 8 mm and the 9 mm BC screw could not be found (p = 0.15). During screwing into the tibial graft channel of the porcine specimens, insertion torques between 0.5 Nm and 3.2 Nm were recorded. In one case the hexagon head of a BC screw broke off during the last turn.

Conclusions

The BC screws show comparable torsional stability to Tutofix^® interference screws. As expected the torsional strength of the screws increases significantly with the diameter. The safety and in vivo performance of products derived from xenogeneic bone should be the focus of further investigations.

ACL fixation devices

Secure graft fixation for anterior cruciate ligament reconstruction is an important goal. Optimally, graft fixation allows for an aggressive postoperative rehabilitation program with the goals of immediate full range of motion, full weight bearing, and an early return to athletic activity. Current anterior cruciate ligament reconstruction techniques advance soft tissue grafts with or without bone plugs into the joint to replace the damaged ligament. Segments of these grafts are fixed within a bone tunnel or on the periosteum at a distance from the normal ligament attachment site. The graft fixation should be secure, allow normal tendon healing, and provide the graft construct with biomechanical properties, which approach that of the native ligament. Several different fixation devices are available for anterior cruciate ligament construction.

Comparative biomechanical study of the Ligament Plate and other fixation devices in ACL reconstruction

The objective of this study was to evaluate and compare the biomechanical properties of the Ligament Plate with other femoral fixation devices. The Ligament Plate and three different femoral fixation devices were used in fixation of 60 porcine femora and harvested porcine tendons. For each fixation device, a porcine graft-tendon complex was used for the simple load-to-failure test and the load-to-failure test after a cyclic loading test, and the maximal failure load was measured. The amount of graft elongation and failure pattern after the cyclic loading test and load-to-failure test were evaluated. In the BioScrew group, the mean maximal failure load in the load-to-failure test and load-to-failure test after a cyclic loading test was significantly lower and significant graft elongation was noted. There were no significant differences between the other groups. The Ligament Plate provided adequate initial fixation power suitable for early rehabilitation.

Complications of anterior cruciate ligament reconstruction with bone-patellar tendon-bone constructs: care and prevention

Rupture of the anterior cruciate ligament is a common injury. Correct diagnosis and patient selection, along with proper surgical technique, with careful attention to anatomic graft placement, followed by attention to proper rehabilitation, leads to predictably good to excellent results. This article reviews the recognition and avoidance of complications associated with bone-patellar tendon-bone constructs of anterior cruciate ligament reconstruction.

Biomechanics of intratunnel anterior cruciate ligament graft fixation

Interference screw fixation of bone-patellar tendon-bone grafts now is considered the standard against which all ACL graft-fixation techniques are compared, but mechanical fixation of the ACL graft in the bone tunnels is the weak link in the early postoperative period. This article discusses some of the limitations of in vitro biomechanical studies and reviews variables that influence the tensile properties of intratunnel fixation methods for bone-tendon-bone and soft tissue grafts.

Comparison of femoral fixation methods for anterior cruciate ligament reconstruction with patellar tendon graft: a mechanical analysis in porcine knees

The aim of the present study was to evaluate the structural properties of femur-patellar tendon graft complex in anterior cruciate ligament (ACL) reconstruction using different femoral fixation devices. Type of study is biomechanical testing. An ACL reconstruction was performed on 40 cadaver porcine knees, using patellar tendon (PT) graft. Specimens were divided into four groups according to the femoral fixation: interference absorbable screw (Group A), metallic setscrew (Group B), absorbable pins (Group C), and a combination of metallic setscrew and pin (Group D). Other ten knees were used as controls. On each sample, a cyclic loading test, then a load-to-failure test were performed. Elongation after 1,000 loading cycles, ultimate failure load, yield load, stiffness, deformation at the yield point, and mode of failure were recorded. Kruskal-Wallis test and Tukey test were used to compare the differences between groups. The lowest mean elongation after 1,000 load cycles was observed for Group B (1.7 +/- 1.4 mm) and D (1.2 +/- 0.3 mm). Ultimate failure load of Group D (1,021.8 +/- 199.4 N) was comparable with that of normal ACL (1,091.2 +/- 193.3 N) and PT graft (1,140.6 +/- 285.7 N). All other groups were lower than the controls. For mean stiffness, all the groups, excepting for Group D (172.8 +/- 40.4 N/mm), were significantly lower than PT control group (216 +/- 78.4 N/mm). Mode of failure was graft pullout for Groups A and B, distal pin breakage for Group C, and midsubstance graft rupture in 80% of the cases for Group D. Only combined compression and suspension fixation did not show significantly different structural properties in comparison with normal ACL and PT graft. Furthermore, it showed no risk of graft pullout or hardware breakdown in comparison with other fixation devices.

Current concepts review: revision anterior cruciate ligament reconstruction

Failed anterior cruciate ligament (ACL) reconstruction presents a difficult clinical challenge. Successful revision ACL reconstruction depends on identifying the causes of failure and correcting technical or diagnostic errors. Failed ACL reconstruction may be either traumatic or atraumatic. Atraumatic failures may be attributable to technical errors, diagnostic errors, or failure of graft incorporation. Published outcomes of revision ACL reconstruction have been worse than for primary ACL reconstruction. The preoperative evaluation, surgical techniques, and clinical outcomes of revision ACL reconstruction are reviewed.

Hybrid femoral fixation of soft-tissue grafts in anterior cruciate ligament reconstruction using the EndoButton CL and bioabsorbable interference screws: a biomechanical study

PURPOSE

The purpose of this study was to evaluate the effect of hybrid femoral fixation with bioabsorbable interference screws (BioRCI; Smith & Nephew Endoscopy, Andover, MA) and EndoButton CL (Smith & Nephew Endoscopy) fixation.

METHODS

Biomechanical testing of 3 different fixation techniques was performed by use of porcine hind-limb distal femurs and mature bovine extremity common extensor tendons. Two independent testing sessions were examined. The first testing session (group A) compared femoral fixation via the EndoButton CL device (n = 6) with femoral fixation via the EndoButton CL device with the addition of a BioRCI screw (n = 6). The second testing session (group B) compared femoral fixation via BioRCI screws alone (n = 6) with femoral fixation via the EndoButton CL device with the addition of a BioRCI screw (n = 6). The femur-graft complex was cyclically loaded between 50 and 250 N at 1 Hz for 1,000 cycles. After cycling, the amount of graft slippage was determined by measuring the change in grip-to-grip distance. The complex was then loaded to failure at 1 mm/s, and the ultimate tensile strength, stiffness, and mode of failure were determined.

RESULTS

In group A the addition of an interference screw to the EndoButton CL fixation increased the ultimate tensile strength (1,364.7 +/- 102.4 N for EndoButton CL alone v 1,449.3 +/- 94.4 N for combined technique, P = .035) and stiffness (195.5 +/- 12.1 N/mm for EndoButton CL alone v 307.3 +/- 54.9 N/mm for combined technique, P = .004) and decreased the amount of graft slippage (2.6 +/- 0.5 mm for EndoButton CL alone v 2.0 +/- 0.3 mm for combined technique, P = .017). In group B the addition of the EndoButton CL device to interference screw fixation significantly increased the ultimate tensile strength (643.5 +/- 148.4 N for BioRCI screws alone v 1,290.3 +/- 254.4 N for combined technique, P = .004) but had no effect on stiffness (315.7 +/- 38.9 N/mm for BioRCI screws alone v 341.5 +/- 64.0 N/mm for combined technique, P = .267) or graft slippage (2.7 +/- 1.0 mm for BioRCI screws alone v 2.0 +/- 0.6 mm for combined technique, P = .087).

CONCLUSIONS

Our study shows that hybrid femoral fixation of double-looped gracilis-semitendinosus grafts via the EndoButton CL device and a bioabsorbable interference screw is stronger than interference or EndoButton CL fixation alone with respect to ultimate tensile strength, stiffness, and slippage. The addition of an interference screw to suspensory fixation via the EndoButton CL device increased the ultimate tensile strength from 1,360 N to 1,450 N, improved reconstruction stiffness from 200 N/mm to 300 N/mm, and decreased the amount of graft slippage resulting from cyclic loading from 2.6 mm to 2.0 mm.

CLINICAL RELEVANCE

The hybrid fixation of the EndoButton CL device and an interference screw is a stronger and stiffer construct than either device alone and allows for aperture fixation, which may translate into better clinical results.

Reconstruction of the anterior cruciate ligament using bone-patellar tendon-bone graft with double biodegradable femoral pin fixation

The purpose of this study was to evaluate the early clinical outcomes of the bone-patellar tendon-bone (BPTB) anterior cruciate ligament (ACL) reconstruction using biodegradable cross pin fixation. The nature of this study is a prospective nonrandomized clinical outcome study. Thirty-five patients who underwent BPTB ACL reconstruction with a minimum of 2 years follow-up evaluation were included in the study. Thirty BPTB autografts and five BPTB allografts were fixed with two biodegradable 2.7 mm cross pins (Rigid Fix) on the femoral side. Clinical evaluation included International Knee Documentation Committee (IKDC), Lysholm and Tegner activity score, and Telos stress device measurements. The average Lysholm knee score was 94.7 (of 100). Twenty-four patients reported an excellent result. The other eight patients were in a good group. According to the IKDC scores, 23 (66%) patients reported normal function, 12 (34%) patients reported nearly normal function, and no (0%) patient reported abnormal or severely abnormal function. Telos stress device values were less than 3 mm of sagittal displacement in 28 patients and 5 mm in 7 patients. No patients complained that their knees gave way fully, even with moderate or strenuous activities. All of the patients have returned to their preinjury level of activity and athletic participation. Clinical results support this technique as a reliable alternative for patellar tendon fixation in ACL reconstruction.

Biomechanical evaluation of a bioabsorbable expansion bolt for hamstring graft fixation in ACL reconstruction: an experimental study in calf tibial bone

INTRODUCTION

The purpose of our study was to evaluate and compare the primary fixation strength of a novel bioabsorbable two shell expansion bolt (EB) with that of a well-established interference screw-fixation technique in hamstring reconstruction of the anterior cruciate ligament.

MATERIALS AND METHODS

Thirty calf tibia plateaus (age 5-6 months) were assigned to three groups: In group I (n = 10) triple-stranded hamstring grafts were fixed with titanium interference screws (7 mm thread / 8 mm head x 25 mm). Specimens of group II (n = 10) received bioabsorbable poly-L-lactide interference screws (8 x 23 mm). In group III (n = 10), the grafts were fixed using bioabsorbable poly-D,L-lactide expansion bolts (5.8/8.5/10 mm x 35 mm). The tensile axis was placed parallel to the bone tunnel. The construction was then loaded until failure under a displacement rate of 1 mm per second.

RESULTS

There were no significant differences concerning the maximum pullout force (group I: 357 N +/- 61; group II: 326 N +/- 92; group III: 343 N +/- 55). In case of the expansion bolt, we found the stiffness to be higher (61 N/mm) when compared to group I (48 N/mm), and group II (52N/mm) (P < 0.01 I vs. III). Using interference screws, we were able to demonstrate a strong correlation between torque and pullout forces (group I: r2 = 0.7; group II: r2 = 0.92). Ruptures of the suturing material occurred only in groups I and II.

CONCLUSION

We conclude that hamstring graft fixation, using the presented expansion bolt, demonstrates fixation strength similar to the established screw fixation and can therefore be regarded as a reasonable alternative fixation method. Especially, since some specific disadvantages of screw fixation can be prevented by application of the bolt fixation.

Anterior cruciate ligament reconstruction with hamstring tendons and cross-pin femoral fixation compared with patellar tendon autografts

PURPOSE

To investigate the outcome of arthroscopic anterior cruciate ligament (ACL) reconstruction with hamstring autograft using femoral cross-pin fixation compared with patellar tendon autografts.

TYPE OF STUDY

Matched retrospective cohort.

METHODS

Twenty-one patients who underwent ACL reconstruction with hamstring autograft and femoral cross-pin fixation were evaluated at an average of 16.4 months postoperatively. Subjective data were collected using the International Knee Documentation Committee (IKDC) and the Cincinnati Knee Scale. Objective data included a comprehensive knee examination, plain radiographs, and KT-1000 measurements. The results were compared with 19 matched patients who had previously undergone ACL reconstruction using patellar tendon autograft.

RESULTS

The average KT-1000 maximal manual side-to-side difference was 1.63 +/- 0.68 mm. Eighty-six percent of IKDC scores were normal or nearly normal. The average overall Cincinnati Knee Scale subjective symptom rating was 8.7 +/- 1.2. There was no significant difference in subjective or objective data between the 2 groups.

CONCLUSIONS

ACL reconstruction using femoral cross-pin fixation is a reliable technique showing outcomes comparable to other established methods of fixation.

LEVEL OF EVIDENCE

Level IV, case series.

Expansion anchors for use in anterior cruciate ligament (ACL) reconstruction: establishing proof of concept in a benchtop analysis

The current method for graft fixation in bone tendon-bone anterior cruciate ligament (ACL) reconstruction is the interference screw. Although this method of fixation provides for adequate graft fixation with respect to strength, intraoperative placement is difficult and the failure rate is high. To address these concerns, we have designed and fabricated prototype expansion anchors that could be expanded to anchor the graft in the bone tunnel. As a first step in assessing the validity of this concept, in the current work, we demonstrate that these systems are of comparable fixation strength (biomechanical pullout testing) to the standard interference screw, are smaller at the time of insertion and thus provide for increased visibility and ease of placement. The increased visibility should result in better placement and reduced failure rates. The increased ease of placement should result in significant savings in decreased OR time.

Reverse achilles tendon allograft technique for anterior cruciate ligament reconstruction

Because of the increasing popularity of allograft anterior cruciate ligament (ACL) reconstructions, the technical difficulties with posterior bone loss in revision ACL surgery, and the limited supply of bone-patellar tendon-bone donor grafts, we have developed a technique using a reversed Achilles tendon allograft to reconstruct the ACL-deficient knee. This technique allows for bony tibial fixation with an interference screw by rotating the graft 180 degrees and optimizing soft-tissue fixation at the femur with an EndoButton CL (Smith & Nephew, Andover, MA). Short-term follow-up (average, 26.4 weeks) of 10 patients undergoing the reversed Achilles technique has shown excellent results, with Lysholm scores between 91 and 100 and 84 and 90 in 8 of 10 and 2 of 10 patients, respectively. Objective stability assessments, including the Lachman test, anterior drawer, and pivot-shift tests, were also encouraging. Reverse Achilles tendon allografts can be excellent alternatives for ACL reconstruction when bone-patellar tendon-bone grafts are not indicated.

Investigation of a hybrid method of soft tissue graft fixation for anterior cruciate ligament reconstruction

To increase knee stability following anterior cruciate ligament (ACL) reconstruction, development of increasingly stronger and stiffer fixation is required. This study assessed the initial pullout force, stiffness of fixation, and failure modes for a novel hybrid fixation method combining periosteal and direct fixation using porcine femoral bone. A soft tissue graft was secured by combining both an interference screw and an EndoButton (Smith and Nephew Endoscopy, Andover, MA). The results were compared with the traditional direct fixation method using a titanium interference screw. Twenty porcine hindlimbs were divided into two groups. Specimens were loaded in line with the bone tunnel on a materials testing machine. Maximum pullout force of the hybrid fixation (588+/-37 N) was significantly greater than with an interference screw alone (516+/-37 N). The stiffness of the hybrid fixation (52.1+/-12.8 N/mm) was similar to that of screw fixation (56.5+/-10.2 N/mm). Graft pullout was predominant for screw fixation, whereas a combination of graft pullout and graft failure was seen for hybrid fixation. These results indicate that initial pullout force of soft tissue grafts can be increased by using the suggested novel hybrid fixation method.

The load of an implanted graft during and after fixation in anterior cruciate ligament reconstruction

Although the importance of initial graft load has been discussed in the literature, it has not been confirmed whether a surgeon can provide the desired load to an implanted graft in anterior cruciate ligament reconstruction. The purpose of this study was to compare the set force (initial load given to the graft before fixation) and residual load in the implanted graft using three different fixation techniques. A total of ninety porcine knees were tested using bone-patellar tendon-bone autograft. Each bone-tendon-bone autograft was fixed to the tibia with either the interference-fit screw, fixation post, or button technique. Graft load was monitored during fixation procedures, and for 10 min after fixation. Residual graft load with each fixation technique exhibited unique features. Highest graft load was obtained by the interference-screw fixation technique; however, the graft was usually over-loaded beyond the intended set force with this technique. In the fixation-post technique, the load of the graft increased while the screw was retightened. The graft load in the button-fixation technique was low, probably due to slight slippage of the button. When the graft was fixed under maximum manual tension, the graft loads at completion of fixation for the interference fit screw, fixation post, and button techniques were 116.3, 54.2, and 25.9 N respectively.

Correlation of interference screw insertion torque with depth of placement in the tibial tunnel using a quadrupled semitendinosus-gracilis graft in anterior cruciate ligament reconstruction

PURPOSE

To evaluate the insertion torque of a soft-tissue interference screw in relation to depth of insertion into the tibial tunnel when used for fixation of a quadrupled semitendinosus-gracilis autograft in anterior cruciate ligament reconstruction.

TYPE OF STUDY

Biomechanical cadaver study.

METHODS

Ten quadrupled semitendinosus-gracilis grafts were harvested from fresh-frozen cadaver knees and fixed in donor proximal tibias using 10-mm bioabsorbable interference screws (Arthrex, Naples, FL). A cannulated torque screwdriver was used to measure screw insertion torque at 3 depths in the tibial tunnel: the outer cortex (distal third), the articular surface (proximal third), and between these 2 points (middle third).

RESULTS

The mean insertion torques for the distal third, middle third, and proximal third were 8.7, 4.7, and 4.3 in/lb, respectively. The insertion torque was significantly higher at the outer cortex (distal third) than the middle third and proximal third (joint line of the tibial tunnel) ( P < .05).

CONCLUSIONS

Our results indicate a correlation between insertion torque and depth of placement of bioabsorbable interference screws used for fixation of a semitendinosus-gracilis graft. Lower insertion torque at the articular surface, resulting in lower peak load or pullout strength, may outweigh the proposed benefits of joint-line fixation of a semitendinosus-gracilis graft used for anterior cruciate ligament reconstruction.

CLINICAL RELEVANCE

Studies have suggested that anatomic proximal fixation of ACL grafts in the tibial tunnel produces stability similar to intact knees. The results of our study indicate that lower insertion torque at the articular surface results in lower peak load and pullout strength of the graft, which may outweigh the proposed benefits of joint-line fixation.

Biomechanical evaluation of press-fit femoral fixation technique in ACL reconstruction

In this experimental study, the authors evaluated the biomechanical properties of the femoral press-fit graft fixation technique in ACL reconstruction. 20 fresh frozen distal femurs, patellae and patellar ligaments were used from 10 cadaver specimens. Three bone-patellar tendon grafts of 10 mm width were prepared from each sample; altogether 60 bone-patellar tendon grafts were prepared for the experiment. Three 9 mm wide tunnels were drilled in each distal femur at different angles (0, 15, 30, 45, and 60 degrees). This means that 60 tunnels were drilled into the 20 femurs, 12 at each angle. The trapezoid bone blocks were impacted into the holes. The primary stability and stiffness of this press-fit fixation method were measured with a Zwick 020 computer-controlled testing device using maximum-failure tensile-strength tests. The ultimate tensile strength was the greatest at 45 degrees (534+/-20 N, range 507-554), with 118+/-10 N/mm (range 99-126) stiffness, followed by 485+/-35 N (range 416-510) with 122+/-13 N/mm (range 104-136) stiffness at 30 degrees, 353+/-18 N (range 320-371) with 113+/-13 N/mm (range 83-124) stiffness at 15 degrees, and 312+/-30 N (range 261-343) with 89+/-14 N/mm (ranged:68-103) stiffness at 0 degrees. In the cases of 0, 15, 30 and 45 degrees the bone blocks were pulled out of the drilled holes, but at 60 degrees rupture of the patellar tendon or breakage of the bone block occurred more frequently. It can be seen that the ultimate tensile strength increased with the angle between the loading direction and the bone block. When compared to data in the literature, these data showed similar and satisfying biomechanical properties of femoral press-fit fixation. Because of the known advantages of an implantation-free fixation technique, the femoral press-fit fixation technique can be a good alternative in ACL surgery. These results provide the basis for future studies involving the postoperative healing process of this femoral press-fit fixation technique in porcine knees.

Fixation strength of a novel bioabsorbable expansion bolt for patellar tendon bone graft fixation: an experimental study in calf tibial bone

This biomechanical study compares the initial fixation strength of a novel bioabsorbable two-shell expansion bolt (EB) with that of a well-established interference-screw technique in bone-patellar tendon-bone (BPTB) reconstruction in a calf model. Thirty tibia plateaus (age 5-6 months) were assigned to three groups: In groups I and II, trapezoidal bone plugs of BPTB grafts were fixed with bioabsorbable poly-L-lactide interference screws (8 x 23 mm) or titanium interference screws (8 x 25 mm) respectively. In group III, semicircular grafts were fixed using bioabsorbable poly-D, L-lactide expansion bolts (5.8/8.7 x 10 x 35 mm). The tensile axis was parallel to the bone tunnel, and the construction was loaded until failure applying a displacement rate of 1 mm per second. In group II the mean ultimate loads to failure (713 N+/-218 N) were found to be significantly higher than those of groups I (487 N+/-205 N) and III (510 N+/-133 N). Measurement of stiffness showed 45 N/mm+/-13.3 in group I, 58 N/mm+/-17.4 in group II and 46 N/mm+/-6.9 in group III, and did not demonstrate significant differences. We found a correlation between insertion torque and wedge insertion force and ultimate loads to failure in all groups (r=0.53 in group I, r =0.54 in group II, and r =0.57 in group III). Cross-section planes of bone tunnel increased by 51%, 30% and 31% respectively, following insertion of screws or expansion of bolts (p<0.05). We conclude that ACL graft fixation by means of the presented expansion bolt demonstrates a fixation strength similar to the established bioabsorbable screw fixation, and is a reasonable alternative fixation method, especially since some of the specific pitfalls of screw fixation can be avoided.

A biomechanical evaluation of transcondylar femoral fixation of anterior cruciate ligament grafts

BACKGROUND

Interference screw fixation of the graft in anterior cruciate ligament reconstruction is considered the gold standard, but limited clinical experience suggests that transcondylar fixation is equally effective.

PURPOSE

To compare transcondylar and interference screw fixation.

STUDY DESIGN

Ex vivo biomechanical study.

METHODS

Twenty pairs of unembalmed knees underwent anterior cruciate ligament reconstruction with patellar tendon autografts. In 1 knee of each pair, the bone plug was stabilized in the femoral tunnel with standard interference screws; in the other knee, transcondylar screws were used. Testing to failure occurred immediately or after 1000 cycles of sinusoidal loading (30 to 150 N) (20 paired reconstructions each). Fixation stiffness, strength, graft creep, displacement amplitude, and change in amplitude were measured and compared (repeated measures anaylsis of variance with Tukey test; P <.05).

RESULTS

There was no significant difference in acute strength, maximum load within 3 mm, or stiffness between transcondylar fixation (410 +/- 164 N, 183 +/- 93 N, and 49.6 +/- 28 N/mm, respectively) and interference fixation (497 +/- 216 N, 206 +/- 115 N, and 61 +/- 37.8 N/mm, respectively). Similarly, there was no significant difference in cyclic strength, maximum load within 3 mm, or stiffness between transcondylar fixation (496 +/- 214 N, 357 +/- 82.9 N, and 110 +/- 27.4 N/mm, respectively) and interference fixation (552 +/- 233 N, 357 +/- 76.2 N, and 112 +/- 26.8 N/mm, respectively). Predominant modes of failure were bone plug pullout (transcondylar fixation) and tendon failure or bone plug fracture (interference fixation).

CONCLUSIONS

Transcondylar screw fixation of the patellar tendon autograft into the femoral tunnel performed mechanically as well as interference screw fixation.

CLINICAL RELEVANCE

The results suggest that transcondylar and interference screws provide similar fixation for anterior cruciate ligament reconstruction.

Porcine tibia is a poor substitute for human cadaver tibia for evaluating interference screw fixation

BACKGROUND

Animal tissues are commonly used in anterior cruciate ligament graft fixation studies.

HYPOTHESIS

Porcine bones and tendons provide good surrogates for human cadaver tissues in the biomechanical evaluation of anterior cruciate ligament reconstruction.

STUDY DESIGN

Randomized experimental study.

METHOD

Three different tissue models-pure porcine (porcine graft fixed in porcine tibia, group 1), combination (human hamstring graft and porcine tibia, group 2), and pure human (human graft and tibia, group 3)-were compared using both cyclic-loading and subsequent single-cycle load-to-failure tests to assess the effect of graft and bone tissue source (porcine vs human) on the fixation strength of anterior cruciate ligament reconstruction.

RESULTS

In the cyclic-loading test, the displacement (slippage) after 1500 cycles was 2.0 mm +/- 0.7 mm, 1.6 mm +/- 0.4 mm, and 4.4 mm +/- 1.9 mm for groups 1, 2, and 3, respectively (P <.001 between 1 and 2 vs 3). In the subsequent single-cycle load-to-failure test, the corresponding average yield loads were 668 N +/- 157 N, 962 N +/- 238 N, and 448 N +/- 98 N, all differences being statistically significant.

CONCLUSIONS

In comparison to young human cadaver tibia, porcine tibia underestimate graft slippage and overestimate the failure load of the soft tissue graft in anterior cruciate ligament reconstruction.

CLINICAL RELEVANCE

Porcine tibia does not provide a reasonable surrogate for human cadaver tibia for evaluating ACL reconstructions.

Allograft interference screw fixation in meniscus transplantation

Allograft meniscus transplantation is indicated to restore proper knee biomechanics and prevent subsequent articular degeneration in patients with a meniscus-deficient knee. A variety of techniques for fixation of meniscal transplants exist, with some techniques using soft-tissue fixation of the meniscal horns and others using bony fixation. The authors present a technique of meniscus transplantation using a tibial slot with allograft interference screw fixation. We have had excellent early results with this technique and believe that a cortical allograft interference screw reliably maintains the anatomic position of the meniscal attachments that are critical to the biomechanics and functional outcome of meniscus transplantation.

Interference screw fixation of soft tissue grafts in anterior cruciate ligament reconstruction: part 1: effect of tunnel compaction by serial dilators versus extraction drilling on the initial fixation strength

BACKGROUND

Compaction of the bone-tunnel walls by serial dilation is believed to enhance the interference screw fixation strength of the soft tissue grafts in anterior cruciate ligament (ACL) reconstruction.

HYPOTHESIS

Serial dilation enhances the fixation strength of soft tissue grafts in ACL reconstruction over extraction drilling.

STUDY DESIGN

Randomized experimental study.

METHODS

Initial fixation strength of the doubled anterior tibialis tendon grafts (fixed with a bioabsorbable interference screw) was assessed in 21 pairs of human cadaver tibiae with either serially dilated or extraction-drilled bone tunnels. The specimens were subjected to a cyclic-loading test, and those surviving were then tested using the single-cycle load-to-failure test.

RESULTS

During the cyclic-loading test, there were 3 fixation failures in the serially dilated and 6 failures in the extraction-drilled specimens but no significant stiffness or displacement differences between the groups. In the subsequent load-to-failure test, the average yield loads were 473 +/- 110 N and 480 +/- 115 N for the 2 groups respectively (P =.97) and no difference with regard to stiffness or mode of failure.

CONCLUSIONS

Serial dilation does not increase the strength of interference fixation of soft tissue grafts in ACL reconstruction over extraction drilling.

CLINICAL RELEVANCE

The results of this experiment do not support the use of serial dilators in ACL reconstruction.

Metal vs bioabsorbable interference screws: initial fixation

Interference screws are used for graft fixation in anterior cruciate ligament reconstruction. There is current debate as to whether metal or bioabsorbable varieties provide the optimal results. This paper provides a critique of the single load-to-failure uniaxial tensile test data available in the literature, which provide the initial postoperative characteristics. Both metal and bioabsorbable screws were found to give similar levels of pull-out force and stiffness when used on similar types of graft material. Screws with bone-patellar tendon-bone grafts provided the greatest values, exceeding the forces transmitted through the native anterior cruciate ligament during normal daily activities. Hamstring grafts provided lower values, only being comparable with the forces of daily living. Consequently, this raises the question as to whether the rehabilitation regime of the hamstring patient must not be aggressive in the early postoperative stages when using either metal or bioabsorbable screws. This would ensure that the graft will not fail in the initial postoperative period before biological fixation occurs, which will then boost the strength to an acceptable level.

Compaction drilling does not increase the initial fixation strength of the hamstring tendon graft in anterior cruciate ligament reconstruction in a cadaver model

BACKGROUND

Compaction of the bone tunnel walls has been proposed to increase the fixation strength of soft tissue grafts fixed with an interference screw in anterior cruciate ligament reconstructions.

HYPOTHESIS

Compaction drilling does not increase the initial fixation strength of the hamstring tendon graft in comparison with conventional extraction drilling.

STUDY DESIGN

Randomized experimental study.

METHODS

Initial fixation strength of quadrupled hamstring tendon grafts fixed with bioabsorbable interference screws was assessed in 22 pairs of human cadaveric tibiae. Bone tunnels were drilled with either a compaction drill or a conventional extraction drill. Specimens underwent a cyclic-loading test and the surviving specimens were then loaded to failure in a single-cycle load-to-failure test. Trabecular bone mineral density at the site corresponding to the actual site of the tibial bone tunnel was determined by using peripheral quantitative computed tomography.

RESULTS

During the cyclic-loading test, no significant stiffness or displacement differences were observed between the two drilling techniques. Three specimens failed in the compaction-drilling group, whereas there were no failures in the extraction-drilling group. In the subsequent single-cycle load-to-failure test, no significant differences between the two drilling techniques were found with regard to displacement at yield load, stiffness, or mode of failure. There was no significant difference in trabecular bone mineral density between the two groups.

CONCLUSIONS

Compaction drilling does not increase the initial fixation strength of the hamstring tendon graft compared with conventional extraction drilling.

Quadriceps tendon impingement from a femoral interference screw

Interference screws are a popular method of securing tendon grafts during anterior cruciate ligament reconstruction. This report describes the case of a patient with anterior knee pain, limited flexion, and partial-thickness tear of the quadriceps tendon caused by a protruding femoral interference screw following hamstring tendon anterior cruciate ligament reconstruction. The interference screw was radiolucent, requiring magnetic resonance imaging to visualize its location. Removal of the protruding portion of the interference screw and debridement of the partial-thickness tear of the quadriceps tendon led to rapid restoration of knee flexion and alleviation of the anterior knee pain.

Analysis of initial fixation strength of press-fit fixation technique in anterior cruciate ligament reconstruction. A comparative study with titanium and bioabsorbable interference screw using porcine lower limb

We performed a controlled laboratory study to evaluate the initial fixation strength of press-fit technique. Forty porcine lower limbs were used and divided into four groups according to the method of fixation; group 1 (press-fit+1.4 mm), in which the diameter difference between the bone plug and the femoral tunnel was 1.4 mm; group 2 (press-fit+1.4 mm, 30 degrees), in which the diameter difference was the same with group 1, but the tensile loading axis was 30 degrees away from the long axis of the femoral tunnel; group 3 (titanium), in which a titanium interference screw was used for fixation; group 4 (bioabsorbable), in which a bioabsorbable interference screw was used for fixation. The graft in the press-fit group was harvested with a hollow oscillating saw with inner diameter of 9.4 mm to obtain consistent and completely circular shape of the bone plug. The femoral tunnel with diameter of 8 mm was drilled at the original ACL insertion. Following the bone plug insertion into the femoral tunnel and applying a preload of 20 N, the specimen underwent 500 loading cycles between 0 and 2 mm of displacement. Thereafter the specimen was loaded to failure. There was no fixation site failure during the cyclic loading test. Significant differences in the stiffness, linear load, or failure mode among the groups were not found. The average ultimate failure load of group 1 and group 2 were not significantly different from those of group 3 and group 4. The press-fit groups demonstrated sufficient fixation strength for the rehabilitation and interference screw groups. The completely circular shape of the bone plug and increased diameter difference between the bone plug and the femoral tunnel seemed to contribute to the strong fixation.

The effect of screw length and position on fixation of four-stranded hamstring grafts for anterior cruciate ligament reconstruction

The aim of this study was to examine interference screw fixation of four strand hamstring grafts for anterior cruciate ligament reconstruction in vitro. Bovine tibiae and cannon tendons were used. Screws were introduced from 'outside-in'. The tendons were loaded cyclically to 150 N to simulate walking and 450 N to simulate jogging. Slippage of the tendon from the anchorage was recorded after 100, 300 and 1000 cycles. Cortico-cancellous and cancellous only fixations were compared using a 7-mm screw in an 8-mm tunnel with a 7-mm graft. The effect of screw length was studied by comparing 8 x 25 and 8 x 45 mm screws. Graft slippage with cancellous only fixation was significantly greater than with cortico-cancellous screw fixation (P<or=0.007). The grafts tended to slip more with a 25-mm screw than with a 45-mm screw but, while this difference was not significant (P>0.105), the longer screws gave more consistent behaviour. We concluded that the screw should be placed so that its head engages the cortex, while increasing screw length within cancellous bone did not significantly improve graft fixation. Cyclical load testing reflects the repetitive forces imposed in the early post-operative period following hamstring anterior cruciate ligament reconstruction and is important for the evaluation of graft fixations.

Revision anterior cruciate ligament reconstruction

Revision ACL surgery is indicated in patients who present with pathologic anterior laxity on clinical examination that reproduces their symptoms of instability during activities of daily living or athletic activities. The goals of the revision ACL surgery are to stabilize the knee, prevent further injury to the articular cartilage and menisci, and maximize the patient's function. Successful revision ACL surgery requires a thorough preoperative evaluation, including a detailed history, physical examination, and radiographic evaluation. Preoperative planning begins with a determination of the mechanisms of failure for the initial ACL reconstruction. Often a primary, as well as secondary cause, for failure can be identified. The determination of the cause of failure is the first step in a carefully-constructed treatment plan, which includes consideration of skin incisions to be used, method of graft removal, hardware removal, the need for a staged procedure or concomitant surgery, graft material selection, tunnel placement, graft fixation, and postoperative rehabilitation protocol. Despite the most meticulous planning, unanticipated findings may be encountered in the operating room, and the preoperative plan should have enough flexibility to accommodate these developments. Finally, it is crucial to counsel the patient preoperatively to limit his or her expectations regarding their surgical outcome. Given the complexity of revision ACL reconstruction, patient expectations must be adjusted to realistically match the potential for success. With proper planning, attention to detail, and appropriate patient expectations, revision ACL surgery can result in a beneficial and satisfying patient outcome.