**10. Anterior Cruciate Ligament (ACL)**

As a result of the growing popularity of growth factor treatment techniques, PRP treatment applications have increased for both soft and bone tissue therapies. Several studies include positive results from such treatments. Repair of ligament injuries was tested by Sánchez et al., resulted in better healing outcomes and fewer complications after applying PRP to 100 patients with ACL reconstruction [93]. Fixation of the PRPG graft was studied by Radice et al. and the results were evaluated using MRI images of the interior of the ACL graft and concluded a 48 % faster and completely homogenous repair of the PRPG graft in the experimental group [83, 94,95].

Controversial opinions are shared on the application of PRGF/PRP in the reconstruction of the ACL and posterior cruciate ligament (PCL), such as the degree of effectiveness in the integra‐ tion of the graft into the bone tunnel and rates of graft maturation [29,94,96]. A statistically significant difference (p = 0.023) was found during stimulation of both ACL graft maturation and ACL graft-bone healing with PRP application [93]. After histological assessment of the ACL grafts with and without PRP, Sanchez et al. found "a significantly better maturity index for ACL grafts (12 pts vs. 14 pts, p = 0.024), and more newly developed synovial tissue enveloping the platelet treated grafts (77% of cases) compared to the control grafts without platelets (40%)" [93].

#### **11. Muscle**

The use of PRP in muscle injury treatment still hasn't been studied thoroughly in humans [74, 97]. There are a number of studies on the effects on muscle tissue. For instance, Shen et al. stated that the inflammatory phase of skeletal muscle healing was controlled by growth factors, macrophages, and COX-2 pathway products [90]. According to Sánchez et al. "the clinical benefits of the ultrasound-guided application of growth factor in physical therapy, electro‐ therapy, and isometric exercise" for athletes include "a decrease in pain and swelling, a complete recovery of functional capacities before the expected time, and regeneration of the muscle tissue according to ultrasound". No evidence of fibrosis and no recurrence of injuries were found in any of the treated athletes [65,98].

Nevertheless, there still have to be more studies necessary to define the efficiency of PRP in acute muscle injury treatment and to create adequate protocols for administration. The main reason is the insufficient number and low methodological quality of the current studies on the use of PRP in human muscle injuries [38].
