Biomechanical comparisons of anterior cruciate ligament: reconstruction procedures with flexor tendon graft

Double-bundle anterior cruciate ligament reconstruction using autologous hamstring tendon hybrid grafts in a patient with hypermobile Ehlers-Danlos Syndrome: A case report

BACKGROUND

Ehlers-Danlos syndrome (EDS) is a connective tissue disorder characterized by skin hyperextensibility, joint hypermobility, and tissue friability. Hypermobile type Ehlers-Danlos syndrome (hEDS) is considered one of the EDS subtypes characterized by generalized joint hypermobility. Although there have been a few case reports which described surgical considerations for anterior cruciate ligament (ACL) reconstructions in patients with other types of EDS, no reports have described those in patients with hEDS.

CASE PRESENTATION

We report a case of ACL injury in an 18-year-old male patient with hEDS. The patient was successfully treated with an anatomic double-bundle ACL reconstruction using autologous hamstring tendon hybrid grafts which consist of hamstring tendons connected in a series with commercially available polyester tape. The autogenous tendon portion of the anteromedial and posterolateral bundles were composed of 4 and 2 strands of hamstring tendons, respectively. After 2 weeks of knee joint immobilization, continuous passive motion exercise of the knee joint and partial weight-bearing was allowed. A hinged knee brace was used for a period of 5 months postoperatively. Second-look arthroscopy at 30 months showed that the ACL graft had no laceration and an excellent coverage of the synovium. At 36 months after surgery, the side-to-side differences in the anterior laxity was remarkably improved. The operated knee showed negative Lachman test and had a full range of motion.

CONCLUSIONS

To the best of our knowledge, this represents the first report of anatomic double-bundle ACL reconstruction in patients with hEDS and demonstrates excellent clinical and functional outcomes.

A Higher Initial Tensioning Force of an ACL Graft Results in a Higher Graft Force After Screw Fixation Irrespective of the Screw Diameter: A Biomechanical Study

BACKGROUND

The intra-articular graft force (IAGF) in anterior cruciate ligament reconstruction decreases quickly over the first hours after surgery. Nevertheless, little is known about whether the initial extra-articular tensioning force (EATF) and screw diameter affect the graft force after fixation.

PURPOSE

To investigate the effects of different EATFs on the IAGF of a soft tissue graft fixated via a bioabsorbable interference screw over 100 minutes after fixation and to evaluate the effects of different screw diameters within 1 mm of the tunnel width during this process.

STUDY DESIGN

Controlled laboratory study.

METHODS

In this biomechanical study, a porcine quadruple-strand soft tissue graft was inserted into the tibial anterior cruciate ligament tunnel. On the extra-articular side, 3 loads were applied during retrograde insertion of the bioabsorbable interference screw (6, 7, and 8 mm): 20 N, 80 N, and maximum manual EATF (N_max). Nine study groups consisting of 10 tibiae each were created to test the effects of different EATFs and screw sizes. The IAGF was measured up to 100 minutes after the EATF was released.

RESULTS

An EATF ≥80 N resulted in a larger IAGF for all screw sizes at 100 minutes. There were no significant associations between the IAGF at 100 minutes and different screw diameters. Inserting the tibial screw significantly increased the IAGF in all groups, with the exception of N_max applied in groups with 7- or 8-mm screws. When compared with the end of screw insertion, after the release of the EATF, the IAGF dropped by 55% to 77 % at 100 minutes.

CONCLUSION

An initial EATF ≥80 N is associated with a significantly larger IAGF at 100 minutes in this cadaveric simulation. The IAGF in soft tissue grafts decreased substantially after the retrograde placement of an interference screw. A recommendation regarding screw diameter with respect to the IAGF cannot be given.

CLINICAL RELEVANCE

To obtain a higher residual graft force after bioabsorbable interference screw fixation, an initial EATF ≥80 N should be applied according to this model. The significant decrease in graft force after the release of the EATF indicates that the reconstructed knee cannot be mechanically stabilized after the surgery.

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.

Double-Bundle Anterior Cruciate Ligament Reconstruction Using Hamstring Tendon Hybrid Grafts in Patients Over 40 Years of Age: Comparisons Between Different Age Groups

Background:

Several recent studies have reported that favorable clinical results and a high level of patient satisfaction can generally be obtained with no increased risk of complications after single-bundle anterior cruciate ligament (ACL) reconstruction performed in patients >40 years of age. However, no studies have yet clarified the age-based differences in clinical outcomes after double-bundle reconstruction.

Purpose:

To compare clinical outcomes after double-bundle ACL reconstruction using hamstring tendon hybrid grafts between patients in 2 different age groups: ≥40 years and <40 years.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A retrospective study was conducted using 96 patients (48 men, 48 women ; mean age, 37 years) who underwent unilateral ACL reconstruction between 2008 and 2011. These patients were divided into 2 groups: group M included patients ≥40 years of age (n = 40 patients), and group Y included patients <40 years of age (n = 56 patients). All patients underwent the same anatomic double-bundle ACL reconstruction procedure. Clinical outcomes were evaluated at 2 years after surgery. Tunnel enlargement was also evaluated by computed digital radiography at 1 week and 2 years after surgery.

Results:

Mean postoperative side-to-side differences in anterior laxity were 0.5 ± 1.9 mm and 1.2 ± 1.5 mm in groups M and Y, respectively; there was a significant difference between the 2 groups (P = .039). There were no significant differences between the groups in Lysholm knee scores, International Knee Documentation Committee (IKDC) scores, or peak muscle torque of the hamstring. On the other hand, peak muscle torque of the quadriceps was significantly lower in group M (81%) than in group Y (89%) (P = .025). With respect to femoral tunnel enlargement, the posterolateral tunnel in group M was significantly larger than that in group Y on anteroposterior and lateral radiographs (P = .015 and P = .002, respectively).

Conclusion:

Equivalent clinical outcomes were seen between the 2 age groups after double-bundle ACL reconstruction. Postoperative anterior laxity was significantly less in older patients than in younger patients, however, older patients had significantly less quadriceps muscle strength than younger patients. Surgeons should be aware of residual muscle weakness and tunnel enlargement when performing double-bundle ACL reconstruction in older patients.

Magnetic Resonance Imaging and Clinical Results of Outside-in Anterior Cruciate Ligament Reconstruction: A Comparison of Fixed- and Adjustable-Length Loop Cortical Fixation

Background

Cortical suspensory femoral fixation is commonly performed for graft fixation to the femur in anterior cruciate ligament (ACL) reconstruction using hamstring tendons. The purpose of this study was to compare graft healing in the femoral tunnel, implant-related failure, and clinical results between fixed- and adjustable-length loop devices in outside-in ACL reconstruction.

Methods

A total of 109 patients who underwent ACL reconstruction using the outside-in technique from December 2010 to July 2014 were included. For femoral graft fixation, a fixed-length loop device was used in 48 patients (fixed-loop group) and an adjustable-length loop device was used in 61 patients (adjustable-loop group). For evaluation of graft healing in the femoral tunnel, magnetic resonance imaging was performed at postoperative 6 months and the signal-to-noise ratios (SNRs) of the tendon graft and tendon-bone interface in the femoral bone tunnel were evaluated. The presence of synovial fluid was evaluated to determine loop lengthening at the femoral tunnel exit. Clinical results assessed using International Knee Documentation Committee score, Tegner-Lysholm Knee Scoring scale, and knee instability tests were compared between groups.

Results

The SNRs of the tendon graft and tendon-bone interface were not statistically different between groups. The presence of synovial fluid at the femoral exit showed no statistical difference between groups. Clinical results were not significantly different between groups.

Conclusions

The adjustable-length loop device provided comparable graft healing, implant-related failure, and clinical results with the fixed-length loop device, allowing adaptation of the graft to the different tunnel lengths. Therefore, it could be effectively used with an adjustment according to the femoral tunnel length.

Novel technique for repairing posterior medial meniscus root tears using porcine knees and biomechanical study

Transtibial pullout suture (TPS) repair of posterior medial meniscus root (PMMR) tears was shown to achieve good clinical outcomes. The purpose of this study was to compare biomechanically, a novel technique designed to repair PMMR tears using tendon graft (TG) and conventional TPS repair. Twelve porcine tibiae (n = 6 each) TG group: flexor digitorum profundus tendon was passed through an incision in the root area, created 5 mm postero-medially along the edge of the attachment area. TPS group: a modified Mason-Allen suture was created using no. 2 FiberWire. The tendon grafts and sutures were threaded through the bone tunnel and then fixed to the anterolateral cortex of the tibia. The two groups underwent cyclic loading followed by a load-to-failure test. Displacements of the constructs after 100, 500, and 1000 loading cycles, and the maximum load, stiffness, and elongation at failure were recorded. The TG technique had significantly lower elongation and higher stiffness compared with the TPS. The maximum load of the TG group was significantly lower than that of the TPS group. Failure modes for all specimens were caused by the suture or graft cutting through the meniscus. Lesser elongation and higher stiffness of the constructs in TG technique over those in the standard TPS technique might be beneficial for postoperative biological healing between the meniscus and tibial plateau. However, a slower rehabilitation program might be necessary due to its relatively lower maximum failure load.

Evaluation of biomechanical properties: are porcine flexor tendons and bovine extensor tendons eligible surrogates for human tendons in in vitro studies?

INTRODUCTION

Porcine flexor tendons, bovine extensor tendons, and human (semitendinosus) tendons are frequently used as substitutes for human ACL grafts in biomechanical in vitro studies. This study compares the biomechanical properties and structural differences of these tendons.

MATERIALS AND METHODS

In this biomechanical study, fresh-frozen porcine flexor tendons, bovine extensor tendons, and human semitendinosus tendons were used (n = 36). The tendons were mounted in a uniaxial testing machine (Zwick/Roell) with cryo-clamps, leaving a 60 mm tendon part free between the two clamps. Specimens have been loaded to failure to evaluate the biomechanical parameters stiffness, yield load, and maximum load. A Total Collagen Assay Kit was used to detect differences in the total collagen type I concentration (n = 30). A one-way ANOVA was performed to detect differences in the means. The significance level was set at p < 0.05.

RESULTS

There were no significant differences in the stiffness between the groups (bovine 194 ± 43 N/mm, porcine 211 ± 63 N/mm, and human cadaveric 208 ± 58 N/mm). The yield and maximum loads were high (>1000 N) in all groups, but they were significantly increased in both animal specimens (means of 1681-1795 N) compared with human cadaveric specimen (means of 1289-1406 N; p < 0.01). No difference in the collagen type I concentration was detected (N.S.).

CONCLUSION

Porcine flexor and bovine extensor tendons are eligible substitutes with similar stiffness and high failure loads compared with human cadaveric semitendinosus tendons in in vitro studies.

Are porcine flexor digitorum profundus tendons suitable graft substitutes for human hamstring tendons in biomechanical in vitro-studies?

INTRODUCTION

Although a plenty of studies exist assessing the strength of ligamentous fixation techniques using porcine flexor digitorum profundus tendons as graft substitutes for human hamstring tendons, there is no biomechanical study comparing these two tendons. To interpret the results obtained with porcine flexor digitorum profundus tendons, knowledge of their biomechanical properties is essential. The purpose of this study was to compare the biomechanical properties of human hamstring tendons and porcine flexor digitorum profundus tendons.

MATERIALS AND METHODS

A total of six human hamstring tendons and six porcine flexor digitorum profundus tendons were analysed in this study. Quadruple-bundle human hamstring tendons and double-bundle porcine flexor digitorum profundus tendons with a diameter of 9 mm were used. Specimens were placed into a tensile loading fixation of a servohydraulic testing machine. Biomechanical analysis included pretensioning of the constructs at 50 N for 10 min following cyclic loading of 1500 cycles between 50 and 200 N at 0.5 Hz for measurement of elongation. Subsequently, ultimate failure load and failure mode analysis were performed with a ramp speed of 20 mm/min.

RESULTS

Human hamstring tendons showed significantly higher maximum load to failure values compared to porcine flexor digitorum profundus tendons (1597 ± 179.6 N vs. 1109 ± 101.9 N; p = 0.035). Human hamstring tendons yielded significantly lower initial elongation during preload, but not during cyclical loading.

CONCLUSIONS

When porcine flexor digitorum profundus tendons are used as graft substitutes for human hamstring tendons in biomechanical studies, maximum load to failure is underestimated while elongation is comparable to that of human hamstring tendons. Transferring results of biomechanical studies into clinical practice, the lower maximum load to failure of porcine flexor digitorum profundus tendons needs to be taken into consideration.

Cortical femoral suspensory fixation using screw post in anatomic single-bundle anterior cruciate ligament reconstruction: a prospective study and mid-term outcome results

PURPOSE

Cortical femoral suspensory fixation using screw post in ACLR has the advantage of allowing complete filling of the femoral tunnel with graft tissue. In addition, the low cost of the implants is an advantage in countries where cost is an issue of concern. The purpose of the current study was to evaluate the clinical functional outcome results of cortical femoral suspensory fixation using screw post at mid-term follow-up.

METHODS

Single surgeon single centre prospective case series study. Sixty two patients having complete ACL tears were included in the current study. Average follow-up was 52.6 months (range 38-68). Objective and subjective IKDC scores, Lysholm knee score, SF-36 score, VAS for patients' satisfaction, VAS for pain and Kellgren & Lawrence (K/L) classification of osteoarthritis were used for follow-up evaluation.

RESULTS

Objective IKDC score revealed that 59 patients had grade "A" and 3 had grade "B", while no single patient had neither grade "C" nor "D". The average Lysholm score was 90.7, average subjective IKDC was 89.5. Average SF-36 score was 94.8. The average VAS for operation satisfaction was 9.4. Average VAS for pain was 0.2. Forty six patients were classified as normal K/L classification, nine were grade "1", seven were grade "2". Comparing pre-operative and follow-up objective IKDC, subjective IKDC, Lysholm, SF-36, and VAS for pain scores revealed statistically significant differences (P-value <0.05).

CONCLUSION

Femoral suspensory fixation using screw post in ACLR showed excellent functional outcome results at mid-term follow-up.

Biomechanical analysis on transverse tibial fixation in anterior cruciate ligament reconstructions

Objective

Methods

Results

Conclusion

A biomechanical comparison of anterior cruciate ligament suspensory fixation devices in a porcine cadaver model

BACKGROUND

Suspensory fixation use during anterior cruciate ligament reconstruction has increased due to ease of use and high pullout strength. We hypothesize that there are no significant differences in biomechanical performance among four types of suspensory fixation devices: Stryker VersiTomic G-Lok, Smith & Nephew Endobutton, Biomet ToggleLoc, and Arthrex RetroButton.

METHODS

Forty fresh frozen porcine femurs and flexor digitorum profundus tendons were obtained. Each tendon graft was sized to 8.5mm or 9.0mm. Ten of each device were used to fix the grafts in the femur at the 2 o'clock (left) or 10 o'clock (right) position. The graft-femur complex was secured to a servohydraulic test machine in line with the femoral tunnel. The graft was cyclically loaded from 50 to 250 N for 1000 cycles at 1 Hz then loaded to failure at 20mm/min. Actuator load and displacement were recorded. Data were analyzed with multiple one-way ANOVA and Tukey HSD post-hoc tests. Bonferroni correction was applied resulting in P ≤ 0.005 considered statistically significant for ANOVA, P ≤ 0.05 for Tukey.

FINDINGS

There were no significant differences in cyclic displacement among any of the groups (P=0.43). The only significant difference in failure properties is the Endobutton exhibited at least 50% greater displacement at failure than the other three devices.

INTERPRETATION

Suspensory femoral soft tissue fixation devices are biomechanically similar with respect to failure load but differ in failure displacement. However, there was no significant difference in displacement after cyclic loading. All four fixation devices should withstand the forces associated with daily activities without failure.

Prospective clinical comparisons of semitendinosus versus semitendinosus and gracilis tendon autografts for anatomic double-bundle anterior cruciate ligament reconstruction

BACKGROUND

The data available from the previously reported clinical studies remains insufficient concerning the hamstring graft preparation in double-bundle anterior cruciate ligament (ACL) reconstruction.

OBJECTIVE

To test the hypothesis that there are no significant differences between the semitendinosus tendon alone and the semitendinosus and gracilis tendon graft fashioning techniques concerning knee stability and clinical outcome after anatomic double-bundle ACL reconstruction.

METHODS

A prospective study was performed on 120 patients who underwent anatomic double-bundle ACL reconstruction according to the graft fashioning technique. The authors developed the protocol to use hamstring tendon autografts. When the harvested doubled semitendinosus tendon is thicker than 6 mm, each half of the semitendinosus tendon is doubled and used for the anteromedial (AM) and posterolateral (PL) bundle grafts (Group I). On the other hand, when the harvested semitendinosus tendon is under 6 mm in thickness, the gracilis tendon is harvested additionally. The distal half of the semitendinosus and gracilis tendons are doubled and used for the AM bundle graft, and the remaining proximal half of the semitendinosus tendon is doubled and used for the PL bundle grafts (Group II). Sixty-one patients were included in Group I, and 59 patients in Group II. The two groups were compared concerning knee stability and clinical outcome 2 years after surgery.

RESULTS

The postoperative side-to-side anterior laxity averaged 1.3 mm in both groups, showing no statistical difference. There were also no significant differences between the two groups concerning the peak isokinetic torque of the quadriceps and the hamstrings, the Lysholm knee score, and the International Knee Documentation Committee evaluation.

CONCLUSION

There were no significant differences between the two graft fashioning techniques after anatomic double-bundle ACL reconstruction concerning knee stability and postoperative outcome. The present study provided orthopedic surgeons with important information on double-bundle ACL reconstruction with hamstring tendons.

LEVEL OF EVIDENCE

Level II; prospective comparative study.

A novel medial collateral ligament reconstruction procedure using semitendinosus tendon autograft in patients with multiligamentous knee injuries: clinical outcomes

BACKGROUND

Several new procedures for medial collateral ligament (MCL) reconstruction using a hamstring tendon graft have been reported in the 2000s. However, the midterm and long-term clinical outcomes of these procedures have not been reported.

HYPOTHESIS

Postoperative medial stability of the knee that underwent our MCL reconstruction may not be significantly different from that of the noninjured knee.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A total of 37 patients who sustained multiligamentous knee injuries underwent combined MCL and cruciate ligament reconstruction at our institution between 1994 and 2007. Thirty of the 37 patients were clinically evaluated at least 2 years after surgery. Sixteen had combined MCL and anterior cruciate ligament (ACL) reconstruction, 5 had combined MCL and posterior cruciate ligament (PCL) reconstruction, and 9 had combined MCL, ACL, and PCL reconstruction. The International Knee Documentation Committee (IKDC) evaluation form and Lysholm score were used to evaluate postoperative knee function. Anteroposterior knee laxity was examined with a KT-2000 arthrometer. To assess objective medial instability, we performed a stress radiograph examination under valgus stress with the knee at 20° of flexion.

RESULTS

At the final follow-up, 1 patient showed a loss of knee extension of more than 3°. Five patients revealed a loss of knee flexion of 6° to 15° and 2 patients of 16° to 25°. Lysholm scores averaged 94.8 points. In the IKDC evaluation, 9 patients were graded as A, 17 were graded as B, 3 were graded as C, and 1 was graded as D. In the stress radiograph examination, the mean medial joint opening was 8.5 ± 1.6 mm in the reconstructed knee and 8.0 ± 1.2 mm in the healthy opposite knee. There was no significant difference in the medial joint opening between reconstructed and intact knees.

CONCLUSION

Medial collateral ligament reconstruction for chronic combined knee instabilities can be safely performed using hamstring tendon autografts, and the clinical outcome with a minimum 2-year follow-up was favorable with satisfactory stability.

Close-looped graft suturing improves mechanical properties of interference screw fixation in ACL reconstruction

PURPOSE

In anterior cruciate ligament reconstruction with looped soft-tissue grafts, an interference screw is frequently used for tibial fixation. This study compared three alternatives thought to improve the initial mechanical properties of direct bioabsorbable interference screw fixation: suturing the graft to close the loop, adding a supplementary staple, or increasing the oversize of the screw diameter relative to the bone tunnel from 1 to 2 mm.

METHODS

Twenty-eight porcine tibiae and porcine flexor digitorum profundus tendons were randomized into four testing groups: a base fixation using 10-mm-diameter screw with open-looped graft, base fixation supplemented by an extracortical staple, base fixation but closing the looped graft by suturing its ends, and base fixation but using an 11-mm screw. Graft and bone tunnel diameters were 9 mm in all specimens. Constructs were subjected to cyclic tensile load and finally pulled to failure to determine their structural properties.

RESULTS

The main mode of failure in all groups was pull-out of tendon strands after slippage past the screw. The sutured graft group displayed significantly lower residual displacement (mean value reduction: 47-67 %) and higher yield load (mean value increase: 38-54 %) than any alternative tested. No other statistical differences were found.

CONCLUSIONS

Suturing a soft-tissue graft to form a closed loop enhanced the initial mechanical properties of tibial fixation with a bioabsorbable interference screw in anterior cruciate ligament reconstructions using a porcine model, and thus, this may be an efficient means to help in reducing post-operative laxity and early clinical failure. No mechanical improvement was observed for an open-looped tendon graft by adding an extracortical staple to supplement the screw fixation or by increasing the oversize of the screw to tunnel diameter from 1 to 2 mm.

Clinical comparison of two suspensory fixation devices for anatomic double-bundle anterior cruciate ligament reconstruction

PURPOSE

The aim of this study was to compare the operation time required and the clinical outcome 2 years postoperatively, after anatomic double-bundle ACL reconstructions using hamstring tendon grafts fixed with either the EndoButton-CL-BTB(®) (ECL-BTB) or the EndoButton-CL(®) (ECL).

METHODS

Forty-six patients, who underwent anatomic double-bundle ACL reconstruction, were non-randomly divided into 2 groups. Patients with a combined ligament injury or complete meniscal tear were excluded from this study. In group I, an ECL was used with 23 patients. In group II, an ECL-BTB was used with the remaining 23 patients. In groups I and II, the ECL or ECL-BTB was attached to the femoral ends of the hamstring tendon autografts. In both groups, a polyester tape was connected in series with the tibial ends of the grafts. The patients were examined with standard clinical evaluations at 2 years after surgery.

RESULTS

The operation time in group II was significantly shorter than that in group I (P = 0.0459). Concerning the intra- and postoperative complications, there were no serious complications in either group. No significant differences were found between the 2 groups in terms of knee laxity measurements, the peak muscle torque of quadriceps and hamstrings, the Lysholm score and the IKDC evaluation.

CONCLUSIONS

This study demonstrated that the usage of the ECL-BTB for graft preparation significantly shortens the total operation time in comparison with the ECL and that there were no significant differences in the 2-year clinical outcome and the intra- and postoperative complications between the 2 graft preparation procedures of the anatomic double-bundle ACL reconstruction. The ECL-BTB can be an alternative device for the hamstring tendon graft in double-bundle ACL reconstruction.

LEVEL OF EVIDENCE

Prospective comparative cohort study, Level II.

A pilot study of anatomic double-bundle anterior cruciate ligament reconstruction with ligament remnant tissue preservation

PURPOSE

The purpose of this pilot study was to evaluate the preliminary results of an anatomic double-bundle anterior cruciate ligament (ACL) reconstruction procedure with ligament remnant tissue preservation.

METHODS

By use of the transtibial technique, 2 doubled semitendinosus tendons were grafted into 4 tunnels created at the center of each bundle attachment, penetrating the ACL remnant tissue. In total, 44 patients (27 male and 17 female patients) with an isolated ACL injury underwent ACL reconstruction with this procedure. The mean age of the patients was 29 years (range, 17 to 58 years). Postoperative clinical evaluations were performed at 16.6 months on average (range, 12 to 23 months). Radiologic evaluations were also performed to evaluate the tunnel location in the femur and the tibia.

RESULTS

The mean operation time was 86 minutes (range, 72 to 96 minutes) in the cases with ACL reconstruction only. Postoperatively, the mean anterior laxity was 0.7 mm. The postoperative pivot-shift test was negative in 81.8% of the patients, whereas there were no patients evaluated as ++. No patients showed any extension or flexion deficit. There were no patients evaluated as "nearly abnormal" or "abnormal" according to the International Knee Documentation Committee evaluation. The tunnel angles of the 4 tunnels were identical to those reported in a previous study.

CONCLUSIONS

The minimal 1-year clinical results of anatomic double-bundle ACL reconstruction with ligament remnant tissue preservation were comparable to previously reported results of anatomic double-bundle reconstruction without remnant tissue preservation.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

A biomechanical comparison of tibial back side fixation between suspensory and expansion mechanisms in trans-tibial posterior cruciate ligament reconstruction

Soft tissue grafts have attracted increasing attention in anterior cruciate ligament (ACL) reconstruction and offer a number of advantages Therefore, it can also be attractive for trans-tibial PCL reconstruction, if four-strand hamstring or two-strand tibialis grafts could be converted for this use. We intended to investigate the biomechanical properties of fixation devices that are frequently used for the soft tissue graft in the trans-tibial PCL reconstruction.Thirty-six fresh adult porcine knees were used in this study. Porcine digital extensor tendons were used as two-stranded soft tissue grafts. The tibial side of the PCL was fixed using a bio-TransFix of suspensory mechanism (TransFix system®: Arthrex, Naples, FL, USA) device (group I) or a RIGIDFIX of expansion mechanism (RIGIDFIX system®: Mitek, Johnson & Johnson, USA) device (group II). We performed biomechanical testing to identify maximum failure load, stiffness, and displacement for both devices.Maximum mean failure loads in groups I and II were 907.3±142.2 and 701.9±101.5N, respectively (p=0.03). Stiffness was 65.6±16.8 and 63.1±15.1N/mm, respectively (p=0.85). Mean displacements were 23.9±6.0 and 19.8±7.9mm, respectively (p=0.37).Suspensory and expansion mechanisms used for tibial back side fixation in the trans-tibial PCL reconstruction using soft tissue grafts showed acceptable biomechanical properties and could be a good choice in case of short multi-stranded soft tissue graft.

Comparisons of femoral tunnel enlargement in 169 patients between single-bundle and anatomic double-bundle anterior cruciate ligament reconstructions with hamstring tendon grafts

PURPOSE

Authors have hypothesized that the incidence and the degree of femoral tunnel enlargement after the hamstring ACL reconstruction may be significantly less in the anatomic double-bundle procedure than in single-bundle procedure. The purpose of this study is to test this hypothesis.

METHODS

Seventy-two patients who underwent single-bundle reconstruction (Group S) and 97 patients who underwent anatomic double-bundle reconstruction (Group D) were followed up for 2 years after surgery. The hamstring tendon grafts were used in each procedure. All of the 169 patients were examined with computed radiography, and the standard clinical evaluation methods.

RESULTS

In Group S, the incidence of femoral tunnel enlargement was 48.6 and 54.2% in the anteroposterior and lateral views. In Group D, the incidence of femoral anteromedial and posterolateral tunnel enlargement was 36.1 and 23.7%, respectively, in the anteroposterior view, and that of femoral anteromedial and posterolateral tunnel enlargement was 33.0 and 21.6%, respectively, in the lateral view. The incidence of femoral tunnel enlargement was significantly less in Group D than in Group S (P < 0.0133). Concerning the degree of the tunnel enlargement, a similar tendency with statistical significance was observed (P < 0.0001). In each group, there were no significant relationships between the degree of tunnel enlargement and each clinical measure.

CONCLUSION

Both the incidence and the degree of femoral tunnel enlargement after anatomic double-bundle reconstruction with the hamstring tendon grafts are significantly less than those after single-bundle reconstruction with the same graft.

LEVEL OF EVIDENCE

Prospective comparative cohort study, Level II.

Is supplementary fixation necessary in anterior cruciate ligament reconstructions?

BACKGROUND

There has been concern regarding the fixation of anterior cruciate ligament reconstruction, with soft tissue grafts being strong and stiff enough to allow for early accelerated postoperative rehabilitation. Therefore, some have recommended supplementary fixation for soft tissue tibia interference screw fixation with a staple, to improve the strength and stiffness of the fixation. Unfortunately, with staple supplementation, there is a risk for symptomatic hardware, which may require a second surgery to remove the staple.

HYPOTHESIS

Supplementary fixation with a bioabsorbable knotless suture anchor will improve the structural properties of soft tissue tibia bioabsorbable interference screw (BIS) fixation and be comparable with supplementary fixation with a staple.

STUDY DESIGN

Controlled laboratory study.

METHOD

Fifteen porcine tibias and flexor profundus tendons were randomized into 3 fixation study groups: group 1, BIS; group 2, BIS + staple; and group 3, BIS + push-lock screw. The structural properties of the 3 fixation groups were tested under displacement-controlled cyclic loading and load to failure.

RESULTS

No significant difference in mean stiffness (N/mm ± SEM) under cyclic loading was found for BIS (335.31 ± 15.43), BIS + staple (344.81 ± 44.97), and BIS + push-lock (353.28 ± 38.93). Under load-to-failure testing, there were no differences found in stiffness, yield load, displacement at yield load, displacement at ultimate load, and energy absorbed among the 3 fixation methods. BIS + push-lock fixation had a significantly higher ultimate load than BIS alone and BIS + staple (917.85 ± 58.30 N vs 479.83 ± 66.04 N, P = .0003 vs 618.89 ± 8.94 N, P = .004).

CONCLUSION

Supplementary fixation with staple or push-lock screw did not significantly increase the structural strength and stiffness of the BIS soft tissue graft fixation under cyclic loading, but it did show improvement under load-to-failure testing for ultimate tensile load.

CLINICAL RELEVANCE

The indication for supplementary fixation for tibial BIS soft tissue graft fixation depends on the fixation that the BIS achieves at the time of the surgery because the tensile load is transferred to the secondary fixation if and only when there is slippage of graft at the primary fixation. The supplementary fixation may be of value in those cases with poor bone quality, such as revision surgery with tunnel widening and/or graft-tunnel mismatch, or possibly in cases with older patients or patients with disorders affecting bone mineral density.

Biomechanical evaluation of a novel application of a fixation device for bone-tendon-bone graft (EndoButton CL BTB) to soft-tissue grafts in anatomic double-bundle anterior cruciate ligament reconstruction

PURPOSE

The purpose of this biomechanical study was to compare the structural properties of the flexor tendon graft connected to the EndoButton CL BTB (ECL-BTB) (Smith & Nephew Endoscopy, Andover, MA), which is newly developed to fix the bone-tendon-bone graft, with those of the same graft connected to the EndoButton CL (ECL) (Smith & Nephew Endoscopy), which is commonly used as a standard fixation device.

METHODS

We randomly divided 40 porcine flexor digitorum profundus tendons into 4 groups. An ECL and an ECL-BTB were attached to the doubled tendon measuring 6 mm in diameter in groups I and II, respectively. An ECL and an ECL-BTB were attached to the doubled tendon measuring 7 mm in diameter in the same manner in groups III and IV, respectively. Tensile testing was performed with a tensile tester.

RESULTS

The linear stiffness of the tendon-device composite (mean +/- SD) was 131.8 +/- 18.3 N/mm, 109.7 +/- 14.9 N/mm, 132.4 +/- 20.5 N/mm, and 123.8 +/- 10.7 N/mm in groups I, II, III, and IV, respectively. The 2-way analysis of variance (ANOVA) showed a significant difference (P = .0058) between the ECL and the ECL-BTB. Concerning the maximum load and the elongation at failure of the tendon-device composite, the 2-way ANOVA showed no significant difference between the 2 fixation devices. Regarding the cross-sectional area, the 2-way ANOVA indicated no significant difference between the 2 fixation devices.

CONCLUSIONS

This study has shown that the maximum load of the flexor tendon graft connected to the ECL-BTB is similar to that of the ECL whereas the stiffness of the ECL-BTB is inferior to that of the ECL.

CLINICAL RELEVANCE

This study has suggested that patients should not be permitted to perform vigorous activities in the early period after anterior cruciate ligament reconstruction by use of the ECL-BTB fixation technique, because of its low stiffness compared with the ECL device.

Post-operative assessment of an implant fixation in anterior cruciate ligament reconstructive surgery

The objective of this paper is to numerically simulate the behaviour of an anterior cruciate ligament (ACL) reconstructed knee using interference screw fixation under a single cycle loading or a cyclic loading test and to compare the numerical results with experimental tests using porcine samples of knee joint. A hyper-elastic material model was used to model the tendon graft and evaluate its elongation during continuous and cyclic tensile loading. The rigidity of the interference screw fixation was also examined using the finite element based numerical model. The finite element model uses the benefit of an anatomical 3D geometry of the tibial bone and tendon graft which was created from a CT scan of a patient.

Effect of tendon tensioning: an in vitro study in porcine extensor tendons

Graft tensioning is a controversial issue in anterior cruciate ligament reconstruction (ACLR) that has not achieved consensus between peers. The purpose of this study is to determine if after tensioning tendon length and resistance to maximal load changes. We performed an in vitro study with 50 porcine extensors tendons. The first group (P=25) was tensioned with 80 N (19.97 lb) for 10 min, using an ACL graft preparation board. The second group (C=25) was used as control and was not tensioned. The average initial (groups P and C) and post tensioning tendon length (group C) were measured; the average initial and post tensioning tendon diameter were measured as well. All samples were fixated in a tube-clamp system connected to a tension sensor. The samples were stressed with continuous and progressive tension until ultimate failure at maximum load (UFML) occurs. The initial mean length was: P before tensioning=13.4 mm+/-1.4 mm (range 10.5-16.5); P after tensioning=13.8 mm+/-1.4 mm (range 11.5-16.5); C=13 mm+/-1.35 mm (p=0.005). The mean diameter was: P=5.6 mm (4.5-6); C=5.5 mm (range 4.5-6) (p>0.05). The UFML was: P=189.7 N (114-336); C=229.9 N (143-365) (p=0.029). Tendon tensioning with 80 N for 10 min produced 3% average elongation. These could be beneficial in ACLR since tendon tensioning decreases elongation of the graft after fixation. Regardless, tendon tensioning is not innocuous since it diminishes their resistance when continuously stressed until complete failure occurs.

Post-operative analysis of ACL tibial fixation

The main aims of the study were to describe the mechanical behaviour of the bone and tendon graft in ACL reconstruction. We also wanted to evaluate the stresses upon the tendon and try to relate these to modes of healing observed in animal studies. An MRI scan of a knee from a 22-year-old male patient, 3 months post ACL reconstruction, was used to generate a finite element model for assessing the stresses on the tendon and bone. A 200 N force, equivalent to the force during normal gait, was placed on the graft and the stress distribution recorded. The maximum stress was found on the tendon graft at the proximal end of the tibial tunnel. Direct tendon healing, which has been observed in animal studies, maybe as a result of the increased stress in this area.

Mechanical comparison of biodegradable femoral fixation devices for hamstring tendon graft--a biomechanical study in a porcine model

BACKGROUND

Initial fixation strength is critical for the early post-operative rehabilitation of patients with anterior cruciate ligament reconstructions. However, even the best femoral fixation devices remain controversial. We compared the biomechanical characteristics of tendon grafts fixed by different biodegradable femoral fixation devices following anterior cruciate ligament reconstruction.

METHODS

The Bio-TransFix, Rigidfix, Bioscrew with EndoPearl augmentation and Bioscrew devices were used to fix porcine flexor digitorum profundus tendon grafts in 32 porcine femora. Displacement of each tendon graft was evaluated after cyclic loading testing. Stiffness, ultimate failure load and failure mode of these fixation devices were measured with load-to-failure testing.

FINDINGS

The displacement of the femur-graft-cement complex in response to cyclic loading was lower (P<0.05) for the Bio-TransFix than the Rigidfix, Bioscrew with EndoPearl augmentation, and Bioscrew groups. The fixation stiffness values of the Rigidfix and the Bioscrew were significantly greater (P<0.05) than that of the Bio-TransFix. The ultimate failure load was significantly greater for the Bio-TransFix and the Rigidfix than the Bioscrew with EndoPearl augmentation or the Bioscrew (P<0.05).

INTERPRETATION

The Bio-TransFix provided the least graft displacement under cyclic loading. However, this device gave less stability. The Rigidfix device provided better stability and stiffness of the tendon graft among those fixation devices that showed no significant differences in graft displacement under cyclic loading. However, no single fixation device provided less displacement along with a larger failure load and stiffness in this study.

Prospective clinical comparisons of anatomic double-bundle versus single-bundle anterior cruciate ligament reconstruction procedures in 328 consecutive patients

BACKGROUND

Several trials have been conducted to compare the clinical results between anatomic double-bundle and single-bundle anterior cruciate ligament (ACL) reconstruction procedures. In these studies, however, the number of patients was insufficient to compare the clinical results of the 2 procedures.

HYPOTHESIS

The anatomic double-bundle procedure may be significantly better concerning the anterior laxity and the pivot-shift test than the single-bundle procedure, while there may be no significant differences in the other clinical evaluations and the intra-operative and postoperative complications between the 2 procedures.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Three hundred and twenty-eight patients with unilateral ACL reconstruction using hamstring autografts were divided into 2 groups. The first 157 consecutive patients underwent single-bundle reconstruction and the remaining 171 patients underwent anatomic double-bundle reconstruction. Concerning all background factors, there were no statistical differences between the 2 groups. Each patient was examined 2 years after surgery.

RESULTS

No serious complications were experienced in either group. The anterior laxity was significantly less in the double-bundle reconstruction (mean, 1.2 mm) than in the single-bundle reconstruction (mean, 2.5 mm). In the pivot-shift test, the double bundle (+ indication, 16%; ++, 3%) was significantly better than the single bundle (+ result, 37%; ++, 12%). The mean Lysholm score averaged 96.5 points and 97.3 points in single-bundle and double-bundle reconstructions, respectively, while the International Knee Documentation Committee evaluation showed that 90 and 110 patients, respectively, were evaluated as rank A (no significant difference between groups). There were no significant differences in the other clinical evaluations and the complications between the 2 procedures.

CONCLUSIONS

The postoperative anterior and rotational stability after the anatomic double-bundle ACL reconstruction was significantly better than that after the single-bundle reconstruction, although there were no significant differences between the 2 procedures concerning the complications and the clinical evaluations.

Comparison of fixation methods of double-bundle double-tibial tunnel ACL reconstruction and double-bundle single-tunnel technique

An experimental study was conducted in order to evaluate biomechanical methods of single-bundle reconstruction in ACL and compare it with a new double-bundle double-tibial tunnel technique. Twenty-four porcine cadaver knees, divided into 4 groups of 6 knees each and 48 proper extensors of the fourth toe tendons, were used for the fixation techniques. In groups A and B, a double-bundle technique with a single femoral and tibial tunnel was used, fixed to a femoral and tibial post with screws and with buttons, respectively. In groups C and D, a double-bundle technique (technique Delta) with two separate tibial tunnels was used, fixed to a femoral and tibial post with screws and with buttons, respectively. A material testing system (Instron) was used for anteriorly translating the tibia until failure. The femoral and tibial post as a fixation method is superior to the conventional buttons technique. The more anatomical double-bundle reconstruction technique provided significantly higher structural properties and smaller loss of fixation compared with the single-bundle reconstruction technique. The comparison of the two techniques gave superior results to the femoral and tibial screws over the buttons. The double-bundle technique attempts to restore the anterior stability of the knee joint.

Hybrid fixation improves structural properties of a free tendon anterior cruciate ligament reconstruction

PURPOSE

This study sought to characterize the structural properties of a combined bioabsorbable interference screw and closed loop and button fixation technique (Hybrid) for femoral fixation of a free tendon graft versus a bioabsorbable interference screw or closed loop and button suspension fixation method alone.

METHODS

Eighteen porcine femora and quadrupled cadaveric flexor tendons were treated in 3 experimental fixation study groups: (1) closed loop and button suspension (CLBS), (2) bioabsorbable interference screw (BIF), and (3) closed loop and button suspension with supplemental biodegradable interference screw (Hybrid). An Instron testing machine (Instron, Canton, MA) was used to quantify each group's structural properties with cyclic loading and tensile load-to-failure. A video digitizing system measured graft deformation during load-to-failure.

RESULTS

The Hybrid fixation group had significantly greater structural properties compared with the CLBS or BIF group. Ultimate loads (mean [SEM] in Newtons) were 1184 (88) N, 813 (83) N, and 561 (62) N for the Hybrid fixation group, CLBS group, and BIF group, respectively. Quasi-steady state cyclic stiffness (mean [SEM] in Newtons per millimeter) was also greatest for the Hybrid fixation group at 165 (11) N/mm, compared with CLBS (122 [8] N/mm), and BIF (95 [9] N/mm).

CONCLUSIONS

Femoral free tendon hybrid fixation provides superior structural properties under tensile and cyclic displacement conditions while preserving the working length of the native anterior cruciate ligament.

CLINICAL RELEVANCE

Hybrid femoral fixation may minimize postoperative laxity for free tendon anterior cruciate ligament reconstruction.

Comparison of initial mechanical properties of 4 hamstring graft femoral fixation systems using nonpermanent hardware for anterior cruciate ligament reconstruction: an in vitro animal study

PURPOSE

To compare the initial mechanical characteristics of 4 systems used to fix tendons to the femur during anterior cruciate ligament reconstruction.

METHODS

A total of 32 porcine femurs were used to study the following fixation systems: Bioabsorbable interference screw (Stryker, Kalamazoo, MI), Bio-Transfix Cross-pin (Arthrex, Naples, FL), Biosteon Cross-pin (Stryker), and a fixation technique based on wrapping the graft around the femoral condyle itself, thus allowing it to be fixed in place without the use of any hardware. The mechanical characteristics of each system were obtained by a preconditioned failure tensile test.

RESULTS

The yield load values (990.9 +/- 242.6 N for Bio-Transfix, 905.1 +/- 158.8 N for Biosteon Cross-pin, 684.4 +/- 119.7 N for the without-hardware system (WHS), and 369.4 +/- 120.1 N for the interference screw) revealed significant differences between the techniques that used cross-pins and the other 2 techniques (P < .006) on the one hand, and between the without hardware technique and the interference screw (P < .004) on the other. The stiffness of the 2 cross-pin fixation systems (117.6 +/- 22.5 N for Bio-Transfix and 112.6 +/- 22.5 N for Biosteon) was greater (P < .01) than those of the other systems (79.4 +/- 15.2 N for the WHS and 68.5 +/- 13 N for the interference screw).

CONCLUSIONS

The initial biomechanical properties of the 2 cross-pin fixation systems proved to be superior to those of the other 2 systems studied. The WHS fixation system exhibited better mechanical properties than its interference screw counterpart.

CLINICAL RELEVANCE

The better initial mechanical characteristics encountered using the Bio-Transfix and Biosteon Cross-pin systems indicate that these systems are better equipped to bear the loads generated by aggressive rehabilitation. The WHS fixation system provides an alternative to interference screw fixation.

Primary stability of three posterior cruciate ligament reconstruction procedures: a biomechanical in vitro study

PURPOSE

Posterior cruciate ligament (PCL) reconstruction procedures have not been thoroughly evaluated under cyclic loading conditions. We tested the hypothesis that PCL reconstruction with a quadrupled flexor-tendon graft and fixation using tapes and staples is biomechanically superior to that fixed with sutures, a button, and a post-screw, and is comparable to reconstruction with a bone--patellar tendon--bone (BPTB) graft.

STUDY DESIGN

In vitro biomechanical study.

METHODS

A total of 45 porcine knees were used. The quadrupled flexor-tendon graft was fixed using the suture/button/post-screw procedure in 15 knees, and with the tape/staples procedure in another 15 knees. The remaining 15 knees underwent reconstruction with a BPTB graft secured with screws as the standard control. In each group of 15 knees, 5 underwent tensile testing without cyclic loading, and 10 underwent the same tensile test after 5,000 cycles of load-controlled or displacement-controlled loading.

RESULTS

Each type of cyclic loading produced larger biomechanical changes in the knees fixed with the suture/button/post-screw procedure than in the knees secured using the other 2 procedures.

CONCLUSIONS

In PCL reconstruction, the tape/staples procedure is biomechanically superior to the suture/button/post-screw procedure, and is comparable to the BPTB/screws procedure with regard to the ultimate failure load. Neither of the procedures using the quadrupled flexor-tendon graft was comparable to the BPTB graft in linear stiffness and the initial displacement after load-controlled cyclic testing.

CLINICAL RELEVANCE

The biomechanical behaviors of PCL-reconstructed knees are significantly different, depending on surgical techniques.

The effect of cyclic loading on the biomechanical characteristics of the femur-graft-tibia complex after anterior cruciate ligament reconstruction using Bone Mulch screw/WasherLoc fixation

BACKGROUND

The Bone Mulch screw/WasherLoc fixation system has attracted notice because of its possible advantages. The purpose of the present study was to compare the biomechanical properties of this fixation system for the double-looped flexor tendon graft with those of two standard fixation techniques that had been commonly performed in anterior cruciate ligament reconstruction.

METHODS

Anterior cruciate ligament reconstruction was carried out in each group using one of three different procedures (n=14 for each procedure). For each group, seven femur-graft-tibia complexes underwent submaximal cyclic displacement of 5000 cycles after an initial tension of 20N was applied. Then, tensile testing was performed for the complex at a single position, 45 degrees of knee flexion, in which the longitudinal axis of the graft coincided with the axis of the bone tunnels. The remaining seven complexes in each group were examined in the same tensile test without applying any cyclic displacement.

FINDINGS

At the 5000th cycle of the displacement, the peak load of the complex with the Bone Mulch screw/WasherLoc system was significantly higher than that with the Endobutton technique (P<0.0001). After 5000 cycles of displacement, the initial stiffness and the linear stiffness of the complex with the Bone Mulch screw/WasherLoc system were significantly higher than those with the double-looped tendon graft and the Endobutton technique (P<0.0001 for both comparisons), while those with the Bone Mulch screw/WasherLoc system were significantly lower than those with the patellar tendon graft with interference screws (initial stiffness: P=0.0004, linear stiffness: P=0.0007).

INTERPRETATION

The present study has clarified that the Bone Mulch screw/WasherLoc system provides high stiffness to the complex for the double-looped flexor tendon graft.

Predicting in vivo clinical performance of anterior cruciate ligament fixation methods from in vitro analysis: industrial tests of fatigue life and tolerance limits are more useful than other cyclic loading parameters

BACKGROUND

Anterior cruciate ligament graft fixations experience cyclic loads in vivo. Present cyclic loading studies testing fixation use "incremental cycling," "residual strength" protocols, or a combination. Industrial standards, however, rely on fatigue life testing and use tolerance limits to determine guaranteed minimum levels of cycles to failure.

HYPOTHESIS

Industrial standards of fatigue life and lower tolerance limits provide a more conservative assessment of cycles to failure than do currently used cyclic loading models, and they facilitate interpretation of data toward clinical performance.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Fatigue life curves and lower tolerance limits were calculated for porcine patellar tendon graft fixations that were tested to failure in single pulls or cycled to failure at 2 different load levels. A log curve was constructed so that the expected values at other load levels could be calculated. Comparison of a metal and a composite resorbable interference screw design was used as an example.

RESULTS

Cycles to failure of both screw designs varied widely at each load level. The guaranteed minimum number of cycles calculated by tolerance limits was therefore much lower than the mean cycles to failure at any given load level. For example, at a load of 250 N, the predicted mean life for the composite screw and the metal screw was 2513 and 1490 cycles, respectively, whereas the 80/80 tolerance limits (the value that 80% could be expected to achieve with 80% confidence) were only 63 and 68 cycles, respectively. Small reductions in load level gave very large increases in minimally expected life.

CONCLUSIONS

Fatigue testing of anterior cruciate ligament reconstructions better shows the wide variation between specimens and the large effect of load levels on expected life. Wide scatter makes mean levels over-optimistic and difficult to interpret. Tolerance limits give estimates that are more conservative and facilitate data interpretation.

CLINICAL RELEVANCE

A method for testing and analyzing fatigue properties was presented, results of which are more readily interpreted to clinical practice.

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.

Anatomic reconstruction of the anteromedial and posterolateral bundles of the anterior cruciate ligament using hamstring tendon grafts

PURPOSE

To develop and evaluate an anatomic reconstruction procedure of the posterolateral and anteromedial bundles of the anterior cruciate ligament (ACL).

TYPE OF STUDY

Anatomic study and case series.

METHODS

The femoral attachment of the anteromedial and posterolateral bundles of the ACL was anatomically analyzed with 5 cadaveric knees. Using another 3 cadaveric knees, anatomic reconstruction of the posterolateral and anteromedial bundles was performed with the transtibial technique, and tunnel positioning and graft function in a range of knee motion was observed. Based on this anatomic study, an anatomic reconstruction procedure of the anteromedial and posterolateral bundles was developed using hamstring tendon autografts. This procedure was carried out in 57 consecutive patients with an ACL-deficient knee. The patients were followed-up for a minimum of 24 months.

RESULTS

We developed the arthroscopically assisted anatomic reconstruction procedure of the posterolateral and anteromedial bundles, involving a new method of creating the tibial and femoral tunnels for the posterolateral bundle. To visualize the femoral attachment of the posterolateral bundle, the medial infrapatellar portal was more useful than the lateral portal. In clinical results, the side-to-side difference of anterior laxity averaged 1.0 mm with a standard deviation of 0.9.

CONCLUSIONS

The anatomic reconstruction of the anteromedial and posterolateral bundles using hamstring tendon autografts is clinically practical in the treatment for the ACL-deficient knee.

LEVEL OF EVIDENCE

Level IV.

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

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

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.

Biomechanical comparisons of three posterior cruciate ligament reconstruction procedures with load-controlled and displacement-controlled cyclic tests

BACKGROUND

Biomechanical behaviors of posterior cruciate ligament reconstructions under cyclic loading have not been sufficiently clarified.

HYPOTHESIS

Biomechanical behaviors of the reconstruction that involves use of flexor tendons and an Endobutton are significantly different under cyclic loading from behaviors of the two standard reconstructions in which bone-patellar tendon-bone graft is used.

STUDY DESIGN

Controlled laboratory study.

METHODS

In a porcine model, the tendon/Endobutton reconstruction, the tendon-bone/interference screw reconstruction, and the tendon-bone/tibial-inlay reconstruction were biomechanically compared by using two cyclic tests. In each group of 15 specimens, 5 knees underwent tensile testing without cyclic loading, and the remaining 10 underwent the same tensile test after 5000 cycles of load-controlled or displacement-controlled loading.

RESULTS

At the 5000th cycle, the peak displacement or the peak load was affected by each type of cyclic loading to a significantly greater degree in the knees with the tendon/Endobutton procedure than in the knees reconstructed with the other two procedures.

CONCLUSIONS

Plastic deformation occurred more easily during cyclic loading in the knees with the tendon/Endobutton reconstruction than in the knees with the tendon-bone reconstructions.

CLINICAL RELEVANCE

When the tendon/Endobutton reconstruction is used, a longer period of postoperative immobilization is necessary.