## 4 Discussion
Higher values of these scores parallel the course of rehabilitation after ACL-R [35]. In the present study, the SLVHT jump height correlated with these established scores at 6 months postoperatively, demonstrating that subjective perception is well represented by the objectively measurable jump height. To objectively measure functional performance during rehabilitation after ACL-R in clinical settings, the single-leg hop for distance is an alternative test that is widely used and has also been included in the International Knee Documentation Committee (IKDC) objective form [11]. A jump distance of 90% that of the non-injured side (LSI) was used as a criterion for a return to contact sports [13; 14]. It is under debate as to whether horizontal or vertical hop tests provide better functional information on the joint status and how these tests should be combined in different settings. Interestingly, in our study, the jump height in the SLVHT with the injured leg correlated with the jump width during the distance hop at 6 months postoperatively. Conclusively, both tests tend to represent similar muscle activation patterns and neuromuscular demands and are responsive to functional improvement. However, it was shown previously that the vertical jump height is more sensitive than the horizontal jump value in detecting functional deficits [17] and that the SLVHT is more reliable in detecting functional asymmetries after ACL-R [32; 36]. Furthermore, in our experience, the SLVHT can be performed earlier after surgery than distance hops. In our study, most patients did not have sufficient confidence in their injured leg to perform a maximal single-leg distance hop after three months. In contrast, none of the patients who came for follow-up after three months refused to perform an SLVHT. In addition, the landing phase of a distance hop may produce shear forces that increase the risk of re-injury [37]. Therefore, this jump is usually performed late in rehabilitation when sufficient stability of the knee can be expected. In this study, the SLVHT could be performed after only 3 months without adverse events. Previously, we showed that 80% of the patients after ACL-R were able to perform the SLVHT as early as 8 weeks post-surgery [38]. These results are supported by the fact that the SLVHT results with the injured leg did not differ between patients with isolated ACL-R and those with ACL-R with meniscal involvement in our study. Repair of the meniscus often requires a limitation on the range of motion and/or a prolonged time to partially bear weight on the injured leg. Even though we did not differentiate between meniscal repair and resection, additional restrictions in the first 6 weeks after surgery did not seem to affect the jump height after 3 or 6 months. We explain these differences with the fact that muscular status is mostly affected by partial weight bearing. Regardless of a meniscal repair, almost all our patients were allowed to bear full weight after 3 weeks, except for those with complicated buckle handle tears, which are rare. So, we assume that both groups started training at the same point, after 6 weeks, with only minor differences in neuromuscular status. Furthermore, the SLVHT appliesmainly vertical forces to the joint, which do not stress the meniscus as torsional or shear forces, so the SLVHT seems to be a safe tool even after meniscal surgery. Functional testing, in recent years, sometimes even with on-field testing for athletes, has high technical and personnel resource requirements that have made it only available for professional athletes and specialised institutions. With further developments in recent years, alternative techniques have been introduced to determine jump heights with less technical effort [22; 23; 39] to make such testing more clinician-friendly and available for a broader audience.