**4. Discussion**

The most important finding of the present study was that patients with higher values of ACL-RSI scores showed better functional clinical outcomes according to Lysholm and Tegner scores as well as improved performance as measured with side-hop test six months after ACL reconstruction.

According to our results, six months after surgery, subjective knee function according to point-scales significantly improved compared to pre-operatory status, thus supporting the efficacy of hamstring ACL reconstruction in athletes.

Functional tests are commonly used to assess the return-to-sport ability following ACL reconstruction. In our cohort of patients, a test battery of vertical jumps measured with an optical acquisition equipment was adopted to evaluate jump performance following ACL surgery. Assessment of vertical jump to detect function deficits of the lower limb with ACL injury or following ACL surgery has been previously reported [11,12,24]. The battery of vertical jump tests used in the present investigation involved bipodalic SJ, bipodalic and monopodalic CMJs, and 30 s side hop test. Such tests, by measuring jump height as an expression of knee explosiveness, coordination, and dynamic knee stability, are reliable predictors for the return to sport after ACL surgery. Based on the results of these test batteries, LSI was calculated to evaluate knee status and patient ability to return to cutting and pivoting sports.

Six months after surgery, the ability to perform bipodalic CMJ, monopodalic CMJ on the injured limb, and a 30 s Side Hop test on the injured limb significantly improved at follow-up compared to pre-operatory status. Similarly, an improvement in LSI recorded while performing CMJ and Side Hop test LSI was observed.

Previous studies investigated the relationship between psychological readiness and functional performance [13,25,26]. The ACL-RSI score demonstrated to be a reliable scoring scale while evaluating psychological readiness for return to sports after ACL reconstruction [17,18]. In the study by McPherson et al., patients who underwent ACL re-rupture trended toward lower ACL-RSI scores [19], while according to Sadeqi et al., ACL-RSI score ≥ 60 months after surgery is a reliable predictor of return to preinjury sport [27]. According to the study by Aizawa et al., in our case series, we considered 60 as a cut-off value to evaluate psychologic readiness to return to sport six months after surgery [13]. Webster et al. followed up with 635 athletes 12 months after ACL reconstruction, and observed that greater limb symmetry while performing a single-legged hop for distance positively correlates with the ACL-RSI score [26]. Similarly, in the study by Aizawa et al. on athletes aiming to return to sport participation six months after surgery, LSI while performing jump tests affected the ACL-RSI score [25].

According to our findings, using individual changes with respect to baseline, patients with ACL-RSI score > 60 reported higher Lysholm and Tegner score and higher performance in the side-hop test six months after ACL surgery compared to patients with ACL-RSI score < 60. Sport-related performances such as vertical jump following ACL reconstruction are affected by muscular co-ordination recovery, leg power, and symmetry in isokinetic lower limb strength. Our study demonstrated that the ability to perform a side-hop test was significantly higher in the group with better psychological readiness. Similarly, patients with higher confidence tended towards higher PROMs compared to patients not meeting the ACL-RSI threshold of 60 points. This confirms our hypothesis that psychological readiness is strictly related to jumping ability. Interestingly, no difference with respect to subjective IKDC score, SJ, and CMJs were reported between the two groups considered. Further research is needed to investigate the most reliable predictors affecting ACL-RSI score at the time of return to sport.

Return to pre-injury activity level represents one of the most important issues in patients following ACL reconstruction. According to our results, average activity level did not statistically differ from pre-operative at follow-up, thus supporting the findings that most patients return to pre-injury activity level up to 12 months after surgery [28].

Future studies should build on current preliminary findings to help to evaluate returnto-sport readiness following ACL surgery, taking into account functional ability and psychological readiness when planning sport resumption. Long-term studies are needed to investigate prognostic factors which may allow for more appropriate decision-making strategies and give a reliable prediction on return-to-sport ability [29,30].

This study possesses limitations. The relatively small sample size may not have allowed for the detection of small differences between groups regarding some parameters. A trend for increased IKDC score in patients with ACL-RSI > 60 failed to demonstrate statistical significance. A greater number of patients could have enhanced the power of the results obtained. We acknowledge that jumping ability is influenced by many variables, and correlating jump height with neuromuscular restoration following ACL surgery is a further study limitation. The OptoGait device was chosen to instrumentally assess jump performance because it is simple, relatively inexpensive, and easily reproducible in the clinical setting allowing us to perform reliable measurements of functional ability. The male/female ratio of the patients recruited was biased towards the male gender, therefore our findings may not be generalizable to female athletes. Another limitation was the lack of a control group of healthy individuals. Finally, relying on subjective questionnaires could potentially bias the results. Long-term prospective follow-up studies with larger cohorts are required to corroborate these findings.

## **5. Conclusions**

Patients with higher values of ACL-RSI scores showed better functional and clinical outcomes as well as improved performance six months after ACL reconstruction. Psychological readiness to return to sport reflects a better recovery of knee function following ACL surgery.

**Author Contributions:** Conceptualization, A.V.; methodology, C.L. and M.D.R.; software, M.V.; validation, C.L. and E.B.; formal analysis, C.L., M.V. and M.D.R.; investigation, M.D.R.; resources, A.V. and E.B.; data curation, C.L., M.V. and M.D.R.; writing—original draft preparation, C.L.; writing review and editing, A.V. and G.M.P.; visualization, C.L.; supervision, A.V. and G.M.P.; project administration, A.V.; funding acquisition, C.L. and A.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Italian Ministry of Health.

**Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki. The study received Institutional Review Board approval (IRB number: 57/INT/2020, released from IRCCS San Raffaele Hospital, Milan, Italy).

**Informed Consent Statement:** Informed consent was obtained from all participants involved in the study.

**Data Availability Statement:** Raw data will be provided on request.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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