Introduction
SIS, functional disability, SIS-pain, pain, tendinopathy, disability of the arm and, as a consequence
INFILTRATION, MUSCULOSKELETAL DISEASES, COMPLICATIONS, SHOULDER IMPINGEMENT SYNDROME
Shoulder impingement syndrome (SIS) has a prevalence of 10–16% in the general population and is one of the most common musculoskeletal diseases. If not treated, it may lead to disability of the arm and, as a consequence, to reduced quality of life [SIS therapy is a symptom-focused intervention. First of all, the non-surgical options should be addressed. There are two major complains by SIS-pain and functional disability. The first one, pain, can be treated by oral analgesics and physiotherapy. If it is not sufficient, the next step is an infiltration of the subacromial space either with local anesthesia, cortison or both. The common use of combined corticosteroid-local anesthetic (CSA) injections in SIS is controversially discussed in the current literature [The potential advantages of a combination of ACP and a plant scaffold with recombinant human collagen type I (ACP/STR) has not yet been investigated until now. One single injection of the ACP/STR is hypothesized to be less traumatizing than the standard of multiple injections of ACP or repeated CSA injections with a decreased risk for complications. Moreover, the scaffold is expected to provide longer retention and bioavailability of the GFs in subacromial space, thereby preventing an early wash-out of GFs from the injection site [Therefore, we questioned if non-operative treatment of SIS due to rotator cuff tendinopathy (RCT) or partial-thickness rotator cuff tears (PTRC) with a single subacromial ACP/STR injection, and physical therapy may be superior to CSA injection and physical therapy. Additionally, we proved the influence of potential limiting factors such as GF concentration, age and acromial morphology.