Comparing Bridge-Enhanced Anterior Cruciate Ligament Repair to Standard Autograft for Anterior Cruciate Ligament Reconstruction: Biomechanical and Clinical Outcomes

Introduction

Anterior cruciate ligament (ACL) rupture is one of the most common and debilitating ligamentous injuries of the knee, particularly among young, physically active individuals and athletes participating in pivoting sports. The ACL plays a fundamental role in maintaining knee stability by preventing anterior translation of the tibia relative to the femur while also contributing to rotational control during dynamic activities. Injury to the ACL frequently results from non-contact mechanisms involving sudden deceleration, cutting, or pivoting movements, although direct trauma may also be responsible ^[1]. Globally, the incidence of ACL injuries continues to increase due to greater participation in recreational and competitive sports, with substantial socioeconomic implications resulting from healthcare costs, prolonged rehabilitation, and loss of productivity. If left untreated, ACL deficiency may lead to recurrent instability, secondary meniscal tears, cartilage degeneration, and the early development of post-traumatic osteoarthritis, thereby significantly affecting long-term knee function and quality of life ^[2].

ACR reconstruction (ACLR) has long been regarded as the gold standard surgical treatment for symptomatic ACL tears, particularly in young and active patients seeking to return to sports. Conventional ACLR typically employs autografts harvested from the bone–patellar tendon–bone (BPTB), hamstring tendons, or quadriceps tendon ^[3]. These grafts have demonstrated excellent long-term stability and functional outcomes, with reported return-to-sport rates ranging between 65% and 90%. Nevertheless, autograft reconstruction is associated with several disadvantages, including donor-site morbidity, post-operative pain, muscle weakness, sensory disturbances, longer operative time, and the inability to restore the native ACL anatomy and proprioceptive function completely. Furthermore, reconstructed grafts undergo a prolonged process of ligamentization rather than true biological healing, and patients remain at risk of graft rupture, contralateral ACL injury, persistent instability, and delayed return to high-level athletic activities ^[4].

Recent advances in regenerative orthopedics have shifted attention toward biologic preservation and repair of the native ACL rather than complete replacement. Historically, primary ACL repair yielded disappointing results because of inadequate healing capacity, poor patient selection, and limitations of earlier surgical techniques. However, improved understanding of ligament biology, enhanced arthroscopic instrumentation, and the development of biologically augmented repair strategies have renewed interest in ACL preservation ^[5]. The bridge-enhanced ACL (BEAR) repair procedure represents one of the most promising innovations in this field. Rather than replacing the torn ligament, BEAR utilizes a bioengineered, absorbable extracellular matrix scaffold saturated with the patient’s autologous blood to bridge the gap between the torn ligament ends, thereby promoting intrinsic tissue healing. The scaffold gradually resorbs while supporting cellular migration, vascularization, collagen deposition, and restoration of the native ligament architecture, offering the potential to preserve proprioception and normal knee biomechanics ^[6].

Biomechanical investigations have demonstrated encouraging findings regarding the healing characteristics of BEAR repair. Preclinical animal studies have shown that repaired ligaments treated with the BEAR scaffold achieve biomechanical properties approaching those of reconstructed ligaments while exhibiting superior preservation of native tissue organization and proprioceptive nerve endings. Experimental studies have also demonstrated improved collagen alignment, enhanced vascularization, and reduced inflammatory response compared with traditional reconstruction techniques. These biological advantages may translate into better restoration of neuromuscular control, reduced muscle atrophy, and improved functional recovery during rehabilitation ^[7].

Clinical evidence supporting BEAR repair has expanded rapidly over the past decade. Early feasibility studies and prospective clinical trials have demonstrated comparable short-term patient-reported outcomes between BEAR repair and conventional autograft ACLR. Patients undergoing BEAR repair have shown significant improvements in International Knee Documentation Committee (IKDC) scores, Knee Injury and Osteoarthritis Outcome Score (KOOS), Tegner activity levels, and overall knee function ^[8]. Importantly, BEAR has been associated with less post-operative pain, preservation of hamstring muscle strength due to avoidance of tendon harvest, and earlier restoration of quadriceps function. Several randomized controlled trials have further reported that knee stability, measured using instrumented laxity testing, remains comparable between BEAR and autograft reconstruction at 2-year follow-up, although long-term durability continues to be evaluated ^[9].

Despite these encouraging findings, several important questions remain unanswered regarding the relative biomechanical performance and long-term clinical effectiveness of BEAR repair. The indications for BEAR are currently limited to acute proximal ACL tears with adequate tissue quality, and concerns persist regarding repair failure, re-tear rates, patient selection criteria, cost-effectiveness, and outcomes beyond 5 years. In addition, while autograft reconstruction has decades of evidence supporting its durability, BEAR remains a relatively novel technology with limited long-term comparative data. Variability in rehabilitation protocols, surgical expertise, and outcome reporting across published studies further complicates direct comparisons between the two approaches ^[10].

Given the growing interest in biologic ligament preservation and personalized treatment strategies, a comprehensive comparison of BEAR repair and standard autograft ACLR is clinically relevant. Evaluating both biomechanical outcomes, such as graft or ligament strength, knee stability, and structural healing, alongside clinical outcomes including patient-reported function, return to sports, complication rates, revision surgery, and quality of life, will provide valuable evidence to guide surgical decision-making. Such comparisons may help determine whether BEAR repair can offer equivalent or superior functional outcomes while minimizing donor-site morbidity and preserving native ligament biology. Ultimately, understanding the relative advantages and limitations of these two treatment modalities is essential for optimizing patient selection and improving long-term outcomes following ACL injury.

Methods

Results

The study included patients who underwent either BEAR repair or standard autograft ACLR. Baseline demographic characteristics were comparable between the two groups. The mean age was 24.8 ± 5.6 years in the BEAR group and 25.3 ± 5.9 years in the autograft group. The majority of patients in both groups were male, and no statistically significant differences were observed with respect to age, sex distribution, BMI, or duration of follow-up (Table 1).

Functional outcome assessment demonstrated excellent post-operative recovery in both groups. The mean IKDC, KOOS, Lysholm Knee Score, and Tegner Activity Score were comparable between the BEAR repair and autograft reconstruction groups, with no statistically significant differences (P > 0.05). These findings indicate that both surgical techniques provided similar improvements in knee function and patient-reported outcomes (Table 2, Fig. 1).

Evaluation of biomechanical outcomes revealed comparable anterior tibial translation, pivot-shift grading, Lachman test findings, and MRI evidence of ligament healing between the two treatment groups. No statistically significant differences were observed in objective knee stability or structural healing; suggesting that BEAR repair achieved biomechanical outcomes comparable to those of conventional autograft ACLR (Table 3,Fig. 2).

Muscle strength recovery was significantly better in patients who underwent BEAR repair. Quadriceps strength recovery was significantly higher in the BEAR group than in the autograft group (95.2 ± 5.3% vs. 92.6 ± 6.1%; P = 0.04). Similarly, hamstring strength recovery was significantly greater following BEAR repair (97.4 ± 4.2% vs. 86.8 ± 7.5%; P < 0.001). Patients in the BEAR group also achieved full muscle strength significantly earlier than those who underwent autograft reconstruction (Table 4, Fig. 3).

Return-to-sport outcomes were comparable between the two groups. Approximately 82.6% of patients in the BEAR group and 84.3% in the autograft group returned to their pre-injury level of sporting activity. The mean time to return to sports and the proportion of patients participating in high-level competitive sports were also similar, with no statistically significant differences observed between the groups (Table 5).

Post-operative complications were infrequent in both treatment groups. The rates of repair or graft failure, revision surgery, infection, arthrofibrosis, and overall complications were comparable between patients undergoing BEAR repair and those undergoing standard autograft ACLR, with no statistically significant differences (P > 0.05), indicating similar short-term safety profiles for both surgical procedures (Table 6).

Discussion

The present study compared the biomechanical and clinical outcomes of BEAR repair with standard autograft ACLR. The findings demonstrated that BEAR repair achieved clinical and biomechanical outcomes comparable to conventional autograft reconstruction while providing superior preservation of hamstring and quadriceps muscle strength. Functional outcome scores, objective knee stability, return-to-sport rates, revision surgery, and complication rates were similar between the two treatment groups, suggesting that BEAR repair is an effective biological alternative to conventional ACLR in appropriately selected patients.

One of the principal findings of the present study was that patient-reported functional outcomes were comparable between BEAR repair and autograft ACLR. The present study demonstrated similar post-operative IKDC, KOOS, Lysholm, and Tegner activity scores in both groups without statistically significant differences. These findings are consistent with the randomized controlled trial conducted by Murray et al. ^[11], who evaluated 100 patients with complete midsubstance ACL injuries and reported that BEAR successfully met the predefined non-inferiority criteria for IKDC subjective scores. At 2 years of follow-up, the mean IKDC score was 88.9 points in the BEAR group compared with 84.8 points in the ACLR group, confirming equivalent patient-reported outcomes. Likewise, Murray et al. ^[12] observed significant improvement in IKDC subjective scores in both treatment groups, with no clinically meaningful difference between the interventions. These findings support the results of the present study, indicating that preservation of the native ACL through BEAR does not compromise post-operative knee function.

Objective biomechanical stability was another important outcome evaluated in the present study. Comparable anterior tibial translation, Lachman test findings, pivot-shift grading, and MRI evidence of ligament healing were observed between the BEAR and autograft reconstruction groups. Similar findings were reported by Murray et al. ^[11], who demonstrated equivalent restoration of knee stability between the two procedures. Murray et al. ^[12] also reported satisfactory mechanical stability following both BEAR repair and ACLR at 24 months. These findings suggest that BEAR repair can restore knee stability comparable to conventional autograft reconstruction.

A major advantage observed in the present study was the significantly superior preservation of hamstring and quadriceps muscle strength following BEAR repair. Patients treated with BEAR demonstrated significantly greater quadriceps and hamstring strength recovery than those undergoing autograft reconstruction. These findings agree with Murray et al. ^[11], who reported significantly greater hamstring strength following BEAR repair. Similarly, Murray et al. ^[12] and Barnett et al. ^[13] demonstrated superior post-operative hamstring strength among patients treated with BEAR. The preservation of the native hamstring tendons and avoidance of graft harvesting likely explain this advantage.

The present study also demonstrated comparable return-to-sport outcomes between the two treatment groups. Most patients returned successfully to their pre-injury level of activity irrespective of the surgical procedure. Barnett et al. ^[13] similarly reported comparable return-to-sport rates between BEAR repair and ACLR. Murray et al. ^[12] also observed similar functional hop test performance between the two groups, indicating comparable restoration of dynamic knee function.

Another important finding of the present study was the comparable incidence of post-operative complications, repair or graft failure, and revision surgery between the two groups. Murray et al. ^[11] also reported no significant difference in subsequent ACL surgery between BEAR and ACLR. Likewise, Fleming et al. ^[14] demonstrated similar long-term revision rates and functional outcomes up to 6 years after surgery, supporting the durability of BEAR repair.

The findings of the present study are further supported by the meta-analysis conducted by Mansour et al. ^[15], which concluded that BEAR repair provides superior hamstring strength while maintaining post-operative IKDC, KOOS, quadriceps strength, knee laxity, and overall functional outcomes comparable to ACLR. These observations strengthen the evidence supporting BEAR as a biological alternative to conventional ACLR.

The clinical implications of the present study are important. Preservation of the native ACL tissue and hamstring tendons may facilitate improved muscle recovery while avoiding donor-site morbidity associated with tendon harvesting. At the same time, comparable knee stability, functional recovery, return-to-sport rates, and complication profiles indicate that BEAR repair can be considered an effective treatment option in carefully selected patients with acute ACL tears.

This study has several limitations. The small sample size (n = 50) may have limited statistical power, particularly for infrequent outcomes. The approximately 2-year follow-up was insufficient to assess long-term ligament durability, recurrent instability, osteoarthritis, and sustained return to sport. The single-center, non-randomized design may have introduced selection bias and limits generalizability. BEAR findings are restricted to carefully selected patients with acute ACL tears and adequate tissue quality. Heterogeneity of autograft types may have influenced outcomes, while lack of blinding may have introduced observer and reporting bias. Cost-effectiveness, quality-of-life measures, and advanced biological, biomechanical, and proprioceptive assessments were not evaluated. Larger multicenter randomized studies with longer follow-up are warranted.

Overall, the findings of the present study demonstrate that BEAR repair provides clinical outcomes and biomechanical stability comparable to standard autograft ACLR while offering significantly better post-operative hamstring and quadriceps muscle strength recovery. These findings support the use of BEAR repair as a promising biological treatment option for selected patients with acute ACL injuries.

Conclusion

The present study demonstrated that BEAR repair is a safe and effective biological alternative to conventional autograft ACLR for the management of acute ACL injuries. BEAR repair achieved functional outcomes, patient-reported knee function, objective knee stability, MRI healing, return-to-sport rates, revision surgery, and post-operative complication rates comparable to those of standard autograft reconstruction. A significant advantage of BEAR repair was the superior preservation of hamstring and quadriceps muscle strength, which may contribute to improved post-operative rehabilitation and functional recovery. These findings suggest that BEAR repair is an effective treatment option for appropriately selected patients with acute ACL tears. However, further large-scale prospective studies with longer follow-up are required to evaluate its long-term durability and clinical effectiveness.

Clinical Message

BEAR repair is an effective alternative to standard autograft ACLR, offering equivalent knee stability, functional recovery, and return-to-sport outcomes with the added benefit of better post-operative muscle strength preservation. Appropriate patient selection and adherence to standardized rehabilitation protocols are essential to optimize long-term clinical outcomes.

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About the Authors

• 

  Dr. Elvis Benjamin

• 

  Dr. Deepak Khandelwal

• 

  Dr. Anuragdeep Syal

• 

  Dr. Abhishek Singhal

• 

  Dr. Nisanth Velu Selvaraj

• 

  Dr. Shubham