*2.4. Statistical Analysis*

Statistical analyses were performed using Graphpad Prism v8.0 (Prism software, La Jolla, San Diego, CA, USA). Shapiro–Wilk test was used to test the distribution of each variable. In case of normal distribution, paired Student t tests were used to assess differences between pre-operative and 6-month values. Patients were dichotomized by post-operative ACL-RSI score into two groups: group A (ACL-RSI > 60), and group B (ACL-RSI < 60); unpaired t test were used to evaluate differences between the two groups. In case of non-normal distribution, the same assessments were performed by Wilcoxon signed-rank test for matched pairs and Mann–Whitney U test, respectively. Difference between proportions were assessed by Fisher's exact test. *p* values < 0.05 were considered statistically significant. Post-hoc power analysis was performed for the test evaluating the improvements in Lysholm, ACL-RSI, and IKDC after surgery. For a test with alpha = 0.05, the study sample size provided a test power > 90% for each score.

## **3. Results**

### *3.1. Demographic Data*

Six patients (16%) were lost at follow-up. Overall, there were 29 males and two females available for clinical evaluation. Mean age at surgery was 34.2 years (SD 11.3). Mean body mass index (BMI) was 25.4 (SD 3.7). Average time interval between injury to surgery was 2.7 months (SD: 1.1). Patients' demographics and anthropometric data are reported in Table 1. At the time of injury, 21 patients practiced contact sports (soccer, basketball, rugby). Noncontact sports (volleyball, skiing, cycling, running, swimming, tennis) were practiced in 28 cases. Eleven patients practiced sport at an agonistic level, 20 were amateurs.


**Table 1.** Patient demographics and anthropometric data.

ACL-RSI: Anterior Cruciate Ligament Return to Sport after Injury; SD: standard deviation; BMI: Body Mass.

#### *3.2. Subjective Knee Function*

The mean overall Lysholm score increased from a pre-operative mean of 68.4 (SD: 15.6) to 87.1 (SD: 11.2), showing a statistically significant difference (*p* < 0.001). IKDC subjective score improved from 51.9 (SD: 13.0) to 77.1 (SD: 14.6) (*p* < 0.001). Similarly, ACL-RSI changed from 46.2 (SD: 23.2) to 68.3 (SD: 16.2) (*p* < 0.001). Concerning Tegner activity level, no statistically significant differences were reported between pre- and post-operative status (mean value 4.2, SD: 2.4, and 5.1, SD: 1.8, respectively, *p* = 0.161) (Table 2, Figure 5).

**Table 2.** Overall comparison between pre-operative and follow-up status.


SD: standard deviation; IKDC: International Knee Documentation Committee; ACL-RSI: Anterior Cruciate Ligament Return to Sport after Injury.

**Figure 5.** Box-plots showing differences in outcome scores from pre-operative to 6-month follow-up after surgery. The black line inside the box represents median value. The lowest bar represents the minimum value, the bottom and top of the boxes represent the interquartile range (25th and 75th percentiles), and the top bar represents the maximum value. Points outside the limits represent outliers \*\*\* *p* < 0.001.
