ACL Reconstruction and Return to Sport
By: Ian M. Al’Khafaji, M.D., FAANA, Member, AANA Communications and Technology Committee
Anterior cruciate ligament reconstructions (ACLR) are widely recognized as the standard treatment to restore biomechanical stability – both sagittal and rotational – to an athlete's knee following an ACL injury. Preoperatively, patients often harbor high expectations for returning to their preinjury levels of activity. Despite advancements in surgical techniques and rehabilitation protocols, reinjury rates among young athletes remain troublingly high, ranging from 4% to 40% depending on the sport. Furthermore, only 65% of athletes manage to return to their previous levels of participation. This reality has spurred interest in developing return-to-sport (RTS) guidelines aimed at reducing the incidence of ACL graft injuries. However, despite extensive research, there is currently no scientific consensus on RTS criteria that can ensure athletes return to sports with a low risk of re-rupture.
RTS tests generally focus on obtaining objective data across several domains, including lower extremity strength, performance and quality of movement. Within each domain, various tests can be utilized to evaluate whether an athlete meets the necessary criteria. Additionally, the time elapsed since surgery is a well-documented factor in determining readiness for sports. Recently, the psychological readiness of athletes has also emerged as a crucial element in the RTS process.
Research indicates that delaying a return to sports for more than nine months can significantly reduce the risk of reinjury. Although this timeframe is not definitively correlated, it is believed to provide sufficient time for the graft and any concomitant injuries to heal, allowing for adequate recovery of the lower extremity. This timeline can help manage patient expectations regarding rehabilitation duration. However, a considerable number of patients still do not achieve adequate rehabilitation after nine months, and there is no consensus on the optimal timing for conducting RTS assessments.
Muscle strength evaluation is a common practice, primarily because it can be conducted manually with relative ease. For strength testing to be reliable, it is best performed using an isokinetic dynamometer, particularly for assessing the quadriceps and hamstrings. Nevertheless, the practical use of isokinetic devices in clinical settings is often limited due to space requirements, time constraints and the need for specialized training to ensure consistent and accurate data collection. Traditionally, a limb symmetry index (LSI) greater than 90% has been used as a benchmark for determining adequate strength in the affected muscle groups. However, this metric is criticized for assuming that the contralateral limb serves as a true healthy reference. Studies have shown that the contralateral limb of an ACL-injured knee may exhibit weakness compared to healthy controls. Therefore, greater emphasis should be placed on alternative references, such as strength-to-body mass ratios, agonist-to-antagonist muscle group ratios and comparisons to normative strength data. Furthermore, most evaluations focus on peak isometric strength, which does not provide a comprehensive view of an athlete’s overall strength, as it neglects factors like the rate of force development, power and reactive strength.
Performance assessments often employ single-leg hop tests (single hop, triple hop or triple crossover hop) to measure distance, typically using an LSI of greater than 90% as a threshold for readiness to return to sport. However, similar to strength assessments, these performance metrics can be problematic when comparing the injured extremity to the contralateral knee, as they may not align with normative data. Additionally, hop tests do not fully reflect the demands of actual gameplay. It is also important to recognize that a patient may excel in hop tests while displaying poor movement quality, potentially increasing the risk of reinjury.
Quality of movement can be assessed subjectively through visual observation, which is straightforward but can struggle to capture complex movement patterns. Alternatively, objective motion capture technology offers a more thorough analysis but requires specialized expertise and time for setup and interpretation. Tasks such as single and double-leg drop jumps can be used to assess compensatory strategies employed to protect the rehabilitated limb, as maladaptive movement patterns can lead to altered center of mass dynamics relative to the knee and create asymmetric forces on the graft.
Finally, psychological factors play a critical role in the return-to-sport decision. The Anterior Cruciate Ligament Return to Sport Index (ACL-RSI) score has been highlighted as a significant predictor of an athlete's readiness to return. Lower scores correlate with a decreased likelihood of returning to sport, while higher scores are associated with a successful return to preinjury levels. Despite these findings, strategies to enhance psychological readiness have not been thoroughly explored.
In summary, the lack of validated RTS criteria highlights the need for innovative approaches in this field, which may offer better insights into helping patients achieve their goals. Collecting metrics on strength, performance and movement quality can assist in creating focused rehabilitation protocols throughout the recovery journey. Lastly, while significant attention is paid to preventing reinjury in the reconstructed knee, further validation of RTS criteria for the healthy contralateral knee is essential to mitigate the risk of contralateral injury.
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