European Journal of Cardiovascular Medicine

Anterior cruciate ligament (ACL) injuries are among the most common and debilitating musculoskeletal injuries encountered in athletes, accounting for a significant proportion of knee-related morbidity and time lost from competitive sports (1). Surgical reconstruction is widely regarded as the gold standard for managing ACL tears, especially in individuals aiming to return to high-level physical activity (2). Two primary graft options are frequently employed in ACL reconstruction: autografts, typically derived from the patient’s hamstring or patellar tendons, and allografts, sourced from cadaveric donors (3,4).

Autografts have long been considered the preferred choice due to their lower risk of immune reaction and higher graft incorporation rates. However, they are associated with donor site morbidity and prolonged postoperative pain (5). In contrast, allografts offer the advantage of reduced surgical time and the absence of donor site complications, but they may carry a higher risk of delayed incorporation, graft laxity, and potential disease transmission (6,7). These differences have prompted ongoing debate regarding their comparative efficacy in terms of functional recovery, particularly isokinetic muscle strength — a crucial parameter in determining readiness to return to sport and preventing re-injury (8).

Isokinetic dynamometry allows objective assessment of quadriceps and hamstring muscle strength during controlled angular velocities, serving as a reliable tool to monitor postoperative progress (9). Although several studies have explored the biomechanical and clinical outcomes of ACL graft types, few have focused specifically on the pattern and rate of isokinetic strength recovery among competitive athletes — a population with unique demands and higher expectations of functional performance (10).

This study aims to compare isokinetic strength recovery following ACL reconstruction using autograft versus allograft in competitive athletes, providing valuable insights into graft selection for optimal rehabilitation outcomes.

A total of 60 competitive athletes, aged between 18 and 30 years, diagnosed with isolated ACL rupture and scheduled for primary reconstruction were recruited. Inclusion criteria included: (1) active participation in competitive sports, (2) no prior knee surgeries, and (3) willingness to follow a standardized rehabilitation protocol. Exclusion criteria included: (1) multi-ligamentous injuries, (2) significant cartilage damage or meniscal root tears requiring repair, and (3) systemic illnesses affecting musculoskeletal function.

Study Groups
Participants were randomly assigned into two equal groups using a computer-generated allocation sequence:

• Group A (n=30): Underwent ACL reconstruction using autograft (semitendinosus-gracilis tendon).
• Group B (n=30): Underwent ACL reconstruction using allograft (tibialis anterior tendon).

All surgeries were performed arthroscopically by a single experienced orthopedic surgeon to minimize technique variability. Both grafts were fixed using standardized fixation methods (femoral end with an endobutton and tibial end with an interference screw).

Rehabilitation Protocol
All participants followed a uniform rehabilitation regimen designed by the same physiotherapy team. The protocol emphasized early range-of-motion exercises, progressive weight-bearing, and sport-specific training, with gradual return to activity allowed after 6 months based on functional assessments.

Isokinetic Strength Assessment
Isokinetic muscle strength testing was conducted using a computerized dynamometer (e.g., Biodex System 4 Pro). Quadriceps and hamstring strength were measured at angular velocities of 60°/sec and 180°/sec. Assessments were performed at 3, 6, and 12 months postoperatively. Key parameters recorded included:

• Peak torque (Nm) normalized to body weight (%BW)
• Limb Symmetry Index (LSI): calculated as the ratio of operated limb to non-operated limb strength, expressed as a percentage.

Statistical Analysis
Data were analyzed using SPSS version 25.0 (IBM Corp., Armonk, NY). Continuous variables were expressed as mean ± standard deviation. Between-group comparisons were made using independent t-tests, and within-group changes over time were assessed using repeated measures ANOVA. A p-value of <0.05 was considered statistically significant.

A total of 60 participants (30 in each group) completed the 12-month follow-up. The mean age was 24.3 ± 3.1 years in Group A (autograft) and 24.6 ± 3.4 years in Group B (allograft), with no significant difference in baseline demographics (p > 0.05). All subjects adhered to the standardized rehabilitation protocol and returned for isokinetic strength assessments as scheduled.

Quadriceps Strength Recovery
At 3 months post-surgery, Group A demonstrated significantly higher mean quadriceps peak torque normalized to body weight (1.37 ± 0.12 %BW) compared to Group B (1.21 ± 0.15 %BW; p = 0.018). This trend persisted at 6 months (Group A: 1.51 ± 0.14 vs. Group B: 1.33 ± 0.13; p = 0.009) and showed convergence by 12 months, with values of 1.69 ± 0.10 in Group A and 1.65 ± 0.11 in Group B (p = 0.324) (Table 1).

Hamstring Strength Recovery
Hamstring strength was also superior in the autograft group at all time points. At 3 months, peak torque was 1.15 ± 0.09 %BW in Group A vs. 1.02 ± 0.12 %BW in Group B (p = 0.027). At 6 months, Group A reached 1.32 ± 0.10 while Group B was at 1.20 ± 0.11 (p = 0.015). By 12 months, values were closely matched (Group A: 1.48 ± 0.09; Group B: 1.43 ± 0.10; p = 0.156) (Table 2).

Limb Symmetry Index (LSI)
At the 3-month mark, the mean LSI was significantly higher in Group A (78.5% ± 5.2%) compared to Group B (70.2% ± 6.1%, p = 0.001). At 6 months, LSI improved in both groups but remained superior in Group A (88.4% ± 4.3% vs. 83.1% ± 5.6%, p = 0.008). By 12 months, both groups achieved comparable symmetry (Group A: 93.6% ± 3.7%; Group B: 91.8% ± 4.1%; p = 0.287) (Table 3).

These results indicate a faster initial recovery of isokinetic strength in the autograft group, with both groups reaching similar functional outcomes by one year postoperatively (Tables 1–3).

Table 1. Quadriceps Peak Torque (% Body Weight) at Different Time Points

Table 2. Hamstring Peak Torque (% Body Weight) at Different Time Points

Table 3. Limb Symmetry Index (LSI) at Different Time Points

The present study compared the isokinetic strength recovery in competitive athletes undergoing ACL reconstruction using autografts versus allografts. Our findings demonstrated that the autograft group showed significantly faster recovery in quadriceps and hamstring strength, particularly during the early postoperative period (3–6 months). However, by 12 months, both groups exhibited comparable functional outcomes, as reflected by similar limb symmetry indices. These results contribute to the ongoing debate regarding optimal graft selection in high-demand populations.

The superior early strength recovery observed in the autograft group aligns with previous studies reporting that autografts promote faster graft integration and neuromuscular adaptation compared to allografts (1,2). Hamstring autografts, in particular, have been associated with accelerated tendon-to-bone healing due to the preservation of viable cells and growth factors (3,4). In contrast, allografts undergo a prolonged remodeling phase, which may delay revascularization and incorporation into host tissue (5,6).

Several studies support our observation that autografts are advantageous for early return to sport. For example, Shelbourne et al. noted improved early functional outcomes with hamstring autografts in athletes undergoing accelerated rehabilitation (7). Similarly, a randomized controlled trial by Webster et al. demonstrated significantly greater quadriceps torque at 6 months in the autograft group compared to the allograft group (8). These differences may be critical in populations such as competitive athletes, where the timing of return to play and performance readiness are paramount (9).

The limb symmetry index (LSI) is a valuable marker for functional recovery and risk stratification. In our study, LSI values were significantly higher in the autograft group during the initial follow-ups, suggesting superior recovery of muscle balance (Table 3). This observation is consistent with the work of Keays et al., who highlighted that achieving LSI >90% is crucial for safe return to sports and reducing the risk of secondary injury (10). Although both groups approached this benchmark by 12 months, the delayed trajectory in the allograft group reinforces the importance of tailored rehabilitation programs based on graft type (11).

Despite the favorable early outcomes, the choice of graft must also consider potential complications. While autografts are associated with donor site morbidity, including hamstring weakness or anterior knee pain (12), allografts may carry risks of graft laxity, infection, and re-rupture, especially when sterilized using high-dose irradiation (13,14). In our study, allografts were processed using low-dose gamma irradiation and had no reported graft-related complications during the follow-up period, supporting their viability with careful selection and processing (15).

The main limitation of our study is the relatively short follow-up duration of 12 months, which may not capture long-term graft durability and re-injury rates. Additionally, we did not assess subjective outcome scores such as IKDC or Tegner Activity Scale, which could offer insights into patient-reported functional outcomes. Future studies with larger sample sizes and extended follow-up periods are warranted to validate these findings and explore the role of graft choice in long-term athletic performance and knee stability.

In conclusion, autografts offer superior early isokinetic strength recovery compared to allografts in competitive athletes, making them a more suitable option for individuals requiring expedited return to sports. However, with appropriate surgical technique and rehabilitation, allografts can achieve comparable long-term outcomes.

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