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

Influence of tibial hybrid fixation on graft tension and stability in ACL double-bundle reconstruction

PURPOSE

Initial graft tension in anterior cruciate ligament (ACL) reconstruction affects stability and tension loss at follow-up. This study investigated the influence of hybrid tibial fixation in 3-tunnel double-bundle ACL reconstruction on initial graft tension and tension change and stability under anterior and combined rotatory loads.

METHODS

Eleven fresh-frozen cadaveric knees were reconstructed with an ACL double bundle using a 3-tunnel technique. Grafts were tightened to 80 N in 60° (AM bundle) and 15° (PL bundle) of flexion. Anterior tibial translation under 134 N of anterior shear load and translation under combined rotatory and valgus loads (10 Nm valgus stress, 4 Nm internal tibial torque) were determined at 0°, 30°, 60°, and 90° flexion. In addition, graft tension under continuous passive motion was determined. Intact, ACL-resected and ACL-reconstructed joints with either tibial extracortical graft fixation or extracortical plus supplemental aperture graft fixation (hybrid fixation) were tested.

RESULTS

Hybrid fixation did not increase graft tension in either bundle during fixation or in motion without additional load. AM-bundle tension increased (p < 0.05) at 0° under combined rotatory and valgus loads and at 30° and 60° under both loading conditions without decreasing the anterior tibial translation. PL-bundle tension increased (p < 0.05) only at 90° under combined rotatory and valgus loads.

CONCLUSIONS

Tibial hybrid fixation in 3-tunnel double-bundle ACL reconstruction increases time-zero AM- and PL-bundle tensions under loading conditions, generating greater construct stiffness. This could lead to a longer preservation of ACL-graft stability in clinical follow-up before bony incorporation.

Comparison of outside-in and inside-out technique for tibial fixation of a soft-tissue graft in ACL reconstruction using the Shim technique

INTRODUCTION

The aim of this study was to compare the biomechanical properties of tibial fixation of a free tendon graft in ACL reconstruction using the Shim, a new wedge-shaped implant, in an outside-in technique to fixation by the Shim used in an inside-out technique and fixation by interference screw in a porcine model.

MATERIALS AND METHODS

Porcine tibia and flexor tendons were used. In Group 1, the Shim was applied outside-in. In Group 2, the Shim was inserted inside-out. In the Group 3, an 8-mm interference screw was used. Ten specimens were tested in each group. Load-to-failure, elongation, stiffness and failure mode were recorded. Cyclic loading was performed between 5 and 250 N for 1,000 cycles, followed by a load to failure testing.

RESULTS

Mean maximum load-to-failure was 629.53 N in Group 1,648.54 N in Group 2 and 749.53 N in Group 3. There was no significant difference between the groups. Stiffness varied between 127.34 N/mm in Group 1, 151.27 N/mm in Group 2 and 182.25 N/mm in Group 3. No significant differences were found between outside-in Shim and interference screw fixation. No significant difference was found for elongation among the three groups. The main failure mode was a rupture of the tendon in the IFS group and a slippage of either the implant or the tendon in both groups using the Shim.

CONCLUSIONS

As no statistically significant difference could be seen concerning load to failure, stiffness and elongation between the inside-out and the outside-in techniques, the Shim can be used for tibial fixation in an outside-in or inside-out technique depending on the preference of the surgeon. To prevent slippage of the graft a hybrid fixation should be considered.

Graft failure versus graft fixation in ACL reconstruction: histological and immunohistochemical studies in rabbits

The causes of graft failure after anterior cruciate ligament (ACL) reconstruction are multifactorial including the methods of graft fixation. The purpose of this study was to examine the ACL graft failure in three different methods of graft fixations including interference screw fixation, suture-post fixation and combined interference screw and suture-post fixation. We hypothesized that the fixation method after ACL reconstruction can affect the graft healing in tibial tunnel. Eighteen New Zealand white rabbits were categorized into three groups according to the method of fixation in unilateral ACL reconstruction with long digital extensor autograft. Histological examination demonstrated that the combined fixation and suture-post fixation groups showed significantly better integration between tendon and bone (P = 0.04). In immunohistochemical analysis, the combined fixation and suture-post fixation groups showed significantly higher BMP-2 and VEGF expressions than interference screw (P < 0.01). The tendon-bone healing after ACL reconstruction was affected by the method of graft fixation. Combined fixation with interference screw and suture-post reduced graft-tunnel micromotion and improved the graft healing in tibial tunnel.

Hybrid tibial fixation for anterior cruciate ligament reconstruction with Achilles tendon allograft

PURPOSE

To compare clinical outcomes of tibial fixation between a biodegradable interference screw only and a biodegradable interference screw supplemented by a post-tie using a washer screw in single-bundle anterior cruciate ligament (ACL) reconstruction with 2-strand free tendon Achilles allograft in active young men.

METHODS

A prospective study was performed in 80 subjects who underwent single-bundle ACL reconstruction. A 2-strand free tendon Achilles allograft fixed with an EndoButton (Smith & Nephew, Andover, MA) in the femoral tunnel and with a Bio-Interference screw (Arthrex, Naples, FL) in the tibial tunnel was used in group I. Supplementary fixation was performed with a post-tie using a washer screw in group II. The Lachman test, pivot-shift test, International Knee Documentation Committee classification, Lysholm score, range of knee motion, and side-to-side difference were evaluated preoperatively and at the last follow-up. The Tegner activity scale was evaluated before injury and at the last follow-up. The 1-leg hop test was assessed at the last follow-up.

RESULTS

Of the patients, 36 in group I and 35 in group II could be followed up for at least 2 years. At the last follow-up, 7 patients in group I and 1 in group II showed a 2+ or 3+ on the Lachman test (P = .027). The mean side-to-side difference was 2.9 ± 2.3 mm in group I and 1.4 ± 1.6 mm in group II at the last follow-up (P = .002). The other clinical outcomes were not significantly different between the 2 groups.

CONCLUSIONS

Supplementary tibial fixation with a post-tie in ACL reconstruction using 2-strand free tendon Achilles allograft was more effective than a biodegradable interference screw only in restoration of the anterior stability of the tibia.

LEVEL OF EVIDENCE

Level II, randomized controlled trial.

In vitro biomechanical testing of anterior cruciate ligament reconstruction: traditional versus physiologically relevant load analysis

Various anterior cruciate ligament (ACL) graft-fixation devices exist. In this in vitro study a comparison of biomechanical characteristics of the cross-pin and button type fixation devices under practical rehabilitation loads was done. Forty bovine knees and hoof extensor tendons were harvested. After disarticulation, the femoral end of an ACL was prepared with either fixation, using the extensor tendon as graft. The mechanical test was either a single load to failure or load to failure after cycling loads. Twenty specimens were loaded to failure at a rate of 1mm/s, remaining specimens were cycled between 50 and 250 N for 1000 cycles then failure tested in a similar manner. Results show that both forms of fixation are able to withstand loads that exceed those observed in performing functional activities. Activity-specific stiffness (loads comparable to walking, jogging and stair descent) was lower than linear stiffness for both endobutton and cross-pin, without prior cycling. After cycling, activity-specific stiffness increased to linear stiffness values for the cross-pin for all activities. Thus, suggesting that the cross-pin provides a more rigid fixation after initial implantation over a wider range of activities, which would theoretically permit a more aggressive rehabilitation protocol and possibly an earlier return to regular activity. In contrast, activity-specific stiffness increased above linear stiffness values for the endobutton only under heavier loads (jogging and stair descent). Dynamic stiffness was higher and displacement lower for cross-pin throughout the cycle test. These results indicate, in ACL reconstruction, that graft complex stiffness should be considered at relevant loads only.

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.

Graft healing in anterior cruciate ligament reconstruction

Graft healing within the bone tunnel after anterior cruciate ligament (ACL) reconstruction is still a complex, poorly understood biological process that is influenced by multiple surgical and postoperative variables. However, remarkable advances in knowledge of this process have been made based primarly on animal models. According to the findings of this review, some surgical and postoperative variables are known to directly affect time-course and quality of graft-tunnel healing. The type of graft, graft motion, and fixation methods have shown to directly affect time-course and quality of graft-tunnel healing. Therefore, the application of early and aggressive rehabilitation protocols should be cautious when using soft-tissue graft, allografts, and direct or aperture type of fixation for ACL reconstruction. With regard to graft placement, several cadaveric models showed biomechanical advantages of a more anatomical graft location; however, there are no studies that explore the relationship between graft placement and healing process. The precise effect of graft tensioning, graft/tunnel diameter disparity, and graft length within the bone tunnel in the graft healing process remains unclear and requires more research. To enhance graft-tunnel healing, tissue-engineering approaches, including the use of growth factors, mesenchymal stem cells, and periosteum graft augmentation, have been tested on animal models. These have shown promising results in terms of enhancement of bone-graft healing rate.

Peripheral versus aperture fixation for anterior cruciate ligament reconstruction

Because both the young and aging population are showing increasing interest in sports participation, the number of sports related injuries and in particular anterior cruciate ligament (ACL) injuries have been increasing. Because of these injuries much time and energy has been focused on ACL reconstruction in order to return these individuals to their optimal level of participation in their sport. This article explores and reviews the concepts of ACL fixation location and how this affects the ultimate outcome of this reconstructive procedure.

Initial fixation strength of a new hybrid technique for femoral ACL graft fixation: the bone wedge technique

BACKGROUND

Aperture fixation with interference screws matching the diameter of the tunnel is associated with the risk of graft laceration and graft rotation.

HYPOTHESIS

A hybrid fixation technique (extracortical and aperture fixation) with undersized interference screw placed behind a bone wedge provides a higher fixation strength as aperture fixation with a screw alone matching the size of the tunnel.

STUDY DESIGN

Experimental laboratory study.

METHODS

We evaluated the initial fixation strength (single cycle and cyclic loading tests) of hybrid and interference screw aperture fixation using different sized interference screws in porcine knees.

RESULTS

Analysis of yield load, maximum load and stiffness in the single cycle loading test showed no statistically significant differences for hybrid fixation with a 1 mm undersized screw and aperture fixation with a screw matching the size of the tunnel. The use of an undersized screw alone resulted in low fixation strength.

CONCLUSION

The initial fixation strength of the hybrid technique with undersized screws is comparable to that of interference screw fixation matching the size.

CLINICAL RELEVANCE

The new "bone wedge fixation" is an alternative for ACL graft fixation without the risk of graft laceration and graft rotation.

Evaluation of tendon graft fixation using alpha-BSM calcium phosphate cement

PURPOSE

Many ligament reconstruction procedures require tendon healing within a surgically prepared bone tunnel. The interface between the graft and tunnel wall is the "weak link" in the initial phase of this process. By providing additional fixation and serving as a carrier for bone-derived growth factors, calcium phosphate cements may augment healing. The purpose of this study was to evaluate alpha-BSM calcium phosphate cement as the sole method of fixation for tendon and bone-tendon-bone grafts in an in vitro porcine model.

METHODS

Ten tendon grafts and ten bone-tendon-bone grafts were fixed within porcine femoral and tibial bone tunnels by use of alpha-BSM calcium phosphate cement. The grafts were then loaded to failure. The ultimate pullout strength and the site of failure were recorded for each specimen.

RESULTS

The bone-tendon-bone grafts achieved a mean pullout strength of 224.8 N (+/-79.9 N). Of the grafts, 6 failed at the cement-bone plug interface, 2 failed because of fracture of the bone plug, and 2 failed at the tendon-bone plug interface. The tendon grafts had a mean load to failure of 81.2 N (+/-23.7 N), and all 10 failed at the tendon-cement interface. The difference in fixation strength between these graft types was significant (P < .05).

CONCLUSIONS

Though inadequate as the sole means of graft fixation, alpha-BSM calcium phosphate cement can help to augment bone plug fixation during the early phase of tendon-bone healing. In addition, alpha-BSM may provide added graft fixation and increased stiffness and act as a growth factor carrier for both tendon grafts and bone-tendon-bone grafts in ligament reconstruction surgery.

CLINICAL RELEVANCE

This study evaluated the ability of alpha-BSM cement to augment tendon-bone healing because it may play a role as a growth factor carrier in future tendon healing models.

Biomechanical analysis of femoral tunnel pull-out angles for anterior cruciate ligament reconstruction with bioabsorbable and metal interference screws

BACKGROUND

Fixation strength of metal and bioabsorbable interference screws has not been evaluated while varying the anterior cruciate ligament graft tension angle.

HYPOTHESIS

There is no difference in fixation strength between 2 types of interference screws for anterior cruciate ligament graft fixation while the graft tension angle is varied relative to the femoral tunnel.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty-eight anterior cruciate ligament reconstructions were performed using immature porcine femurs stripped of soft tissue and doubled-over porcine flexor digitorum profundus tendon grafts. Specimens were randomized to bioabsorbable or titanium interference screw fixation. Specimens were randomized to one of three pull angles (0 degrees , 30 degrees , 60 degrees ) representing loading at different knee flexion angles (n = 8/group). Reconstructed ligaments were tensioned to 10 N followed by 200 loading cycles between 10 and 150 N and a final failure test. Construct elongation (mm) at 100 and 200 cycles and failure load (N) were analyzed using a 2-way analysis of variance (P < .05).

RESULTS

Screw material interacted significantly with graft tension angle, as the bioabsorbable screw specimens demonstrated significantly greater fixation strength when tensioned at greater angles. Specimens fixed with bioabsorbable screws showed significantly less elongation at both 100 and 200 cycles and significantly greater failure load compared with titanium screws.

CONCLUSION

Bioabsorbable interference screws acutely have increased fixation strength compared with titanium interference screws for anterior cruciate ligament grafts loaded at greater tension angles.

CLINICAL RELEVANCE

The strength of anterior cruciate ligament reconstruction fixation increases with increasing divergence between the tension angle and femoral tunnel, a condition seen when the knee approaches full extension.

Initial fixation strength of a hybrid technique for femoral ACL graft fixation

Aperture fixation with interference screws matching the diameter of the tunnel is associated with the risk of graft laceration and graft rotation. A hybrid fixation technique (extracortical and aperture fixation) with undersized interference screws provides a higher fixation strength when compared to an aperture fixation using only a screw matching the size of the tunnel and also reduces the risk of graft laceration. This research is an experimental laboratory study. We evaluated the initial fixation strength at time-zero of an extracortical-, a hybrid- and an aperture fixation in ACL reconstruction using extracortical buttons and different sized interference screws in porcine knees. The tests were performed using a single cycle and cyclic loading protocol. Analysis of yield load, maximum load and stiffness in the single cycle loading test showed no statistically significant differences for hybrid fixation with a 1 mm undersized screw and aperture fixation with a screw matching the size of the tunnel. Cyclic loading tests showed a statistically significant difference between hybrid and aperture fixation. The use of an undersized screw alone in aperture fixation resulted in insufficient fixation strength. The initial fixation strength of the hybrid technique with undersized screws is higher compared to an interference screw fixation alone. The hybrid fixation technique is an alternative for ACL graft fixation.

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.