The purpose of this study is to test the hypothesis that the application of PRP leads to faster wound healing, less wound healing disorders, less pain and faster functional recovery after subacromial surgery.

Subacromial surgery of the shoulder is performed often. It concerns space creating interventions (open and arthroscopic subacromial decompression) and rotator cuff surgery (open and arthroscopic). In this kind of surgery good wound healing and tissue recovery is of great importance to achieve optimal results. Wound healing disorders, pain and the formation of adhesions may negatively influence the postoperative course and lead to extended rehabilitation. This has an unfavourable influence on the personal well being of the patient and the possibility to return to labour. Especially in cuff surgery the course is strongly influenced by the healing of the attachment of the cuff to the bone. Besides the development of minimal invasive techniques, it's necessary to look for possibilities to decrease the morbidity of these procedures. Recent studies show that growth factors play a major role in wound healing. This concerns particularly TFG-B (transforming growth factor B) and PDGF (platelet derived growth factor) present in thrombocytes. They act as chemotactic agents for polymorphonuclear leucocytes, macrophages, fibroblasts and lymphocytes. Both growth factors stimulate the wound healing and cause improved angiogenesis and fibroplasia. They also play a role in wound retraction and remodelling. In animal-experimental models it is proved that the application of TGF-B and PDGF improves woundhealing and leads to better mechanical properties of the scar tissue. Faster and better wound healing and decreased development of adhesions after subacromial surgery can possibly be influenced favourably by using thrombocyte concentrate. In the treatment with autologous thrombocyte concentrate a thrombocyte rich concentrate is obtained by a centrifuging method (Gravitational Platelet System (GPS), Biomet, Warsaw USA) (platelet rich plasma or PRP), that can be applied in the operating field. The concentrate is harvest from the patients own blood, sampled during the procedure. At random the concentrated is applicated and both groups are compared postoperatively.

Inclusion Criteria:

• Age >18 years old
• Given informed consent
• Clinical indication for Arthroscopic Sub-acromial decompression, i.e.: Painful arc, pain at abduction, positive Hawkinstest Insufficient clinical improvement after (at least) 6 months of conservative treatment or Clinical indication for a arthroscopic cuff repair of a MRI-proven treatable rotator cuff tear.

Exclusion Criteria:

• Coagulopathy
• Thrombocytopenia
• Use of corticosteroids
• Diabetics Mellitus
• Omarthritis
• AC-arthrosis
• Cuff arthropathy
• Neurological deficit at the ipsi-lateral extremity
• (Wish for) Pregnancy
• VAS <2 or VAS >9