Treatment of Acute Proximal Anterior Cruciate Ligament Tears—Part 1: Gap Formation and Stabilization Potential of Repair Techniques

Abstract

Background: Recently, there has been a resurgence of interest in primary repair of the anterior cruciate ligament (ACL), with fixation techniques evolving. However, to date, there have been no biomechanical studies comparing fixed to adjustable fixation repair techniques. Hypothesis: Adjustable ACL repair provides for improved stabilization compared with fixed techniques with respect to both gap formation and residual load-bearing capability. Study Design: Controlled laboratory study. Methods: A total of 4 different ACL repair techniques (n = 5 per group), including single– and double–cinch loop (CL) cortical button fixation as well as knotless single–suture anchor fixation, were tested using a porcine model. For adjustable single-CL loop fixation, additional preconditioning (10 cycles at 0.5 Hz) was performed. The force after fixation and the actuator displacement to achieve a time-zero preload of 10 N were measured for fixed techniques. Incrementally increasing cycling (1 mm/500 cycles) from 1 to 8 mm was performed for 4000 cycles at 0.75 Hz before pull to failure (50 mm/min). The final residual peak load and gap formation for each test block were analyzed as well as ultimate strength. Results: Knot tying of a single-CL over a button (mean ± SD, 0.66 ± 0.23 mm) and knotless anchor fixation (0.20 ± 0.12 mm) resulted in significant time-zero gaps ( P < .001) and significantly higher overall gap formation at reduced residual loading (analysis of covariance, P < .001) compared with both the double-CL loop and adjustable fixation techniques. The adjustable group showed the highest failure load and stiffness, at 305.7 N and 117.1 N/mm, respectively. The failure load of the knotted single-CL group was significantly reduced compared with all other groups ( P < .001). Conclusion: Adjustable single-CL cortical button fixation with intraoperative preconditioning optimized time-zero ACL tension and led to significantly improved stabilization and reduced gap formation, with the highest ultimate strength. Single-CL loop knot tying over the button and knotless anchor fixation resulted in time-zero gaps to achieve slight tension on the ACL and significantly higher gap formation at reduced load-bearing capability. Clinical Relevance: Although the clinical relevance of gap formation is uncertain, a biomechanical understanding of the stabilization potential of current ACL repair techniques is pertinent to the continued evolution of surgical approaches to enable better clinical outcomes.

Treatment of Acute Proximal Anterior Cruciate Ligament Tears—Part 2: The Role of Internal Bracing on Gap Formation and Stabilization of Repair Techniques

“…The fixed groups already experienced gap formation at the initial load level (50 N) but remained below a 3-mm gap at 350 N. The CLS-ALD technique showed no gap formation up to 150 N and revealed a mean gap of 0.85 ± 0.31 mm at 350 N. Previously shown gap formation behaviors of the same ACL repair techniques without an internal brace (see part 1 6 ) served as a reference for the test results and exhibited substantial gap formation at lower loads.…”

“…Thus, the peak elongation behavior between fixed internally braced ACL repair and isolated internal brace groups at different load levels did not significantly differ, combined functional zones were established ( Figure 3) compared with the CLS-ALD technique as well as available ACL repair data (see part 1 6 ) and the native ACL. 7 The native ACL zone was based on available literature data 4,9,24,29,40,45,47 and was established to quantify and qualify the stabilization potential of ACL reconstruction.…”

“…Loads applied longitudinally to the ACL should comply with requirements of worst-case testing for ACL repair and are in line with most commonly used in vitro loading scenarios for ACL reconstruction. 7,27 The stabilization potential of previously established non-internally braced ACL repair constructs (see part 1 6 ), isolated internal brace groups, and the native ACL functional zone 7 served as references and baseline for the obtained internally braced repair results. ACL repair with internal brace augmentation almost completely restored the native ACL function, whereas the same ACL repair techniques without an internal brace showed considerable Figure 5.…”

“…ACL repair with internal brace augmentation almost completely restored the native ACL function, whereas the same ACL repair techniques without an internal brace showed considerable Figure 5. Gap formation zones (including mean and standard deviation data) over peak loads with linear regression curves for adjustable and merged fixed anterior cruciate ligament (ACL) repair techniques in reference to ACL repair without an internal brace (see part 1 6 ). lengthening at low loads.…”

“…Ultimately, 4 different ACL repair techniques as previously reported (see part 1 6 ) were internally braced with a nonabsorbable high-strength suture tape (2-mm FiberTape; Arthrex) and tested in this study. These suture repair techniques are based on CL and multiple cross-stitch fixation and were utilized in a similar fashion to the aforementioned study to reattach the ACL to the femoral bone.…”