Together osteoarthritis (OA) of the knee, epicondylitis of the elbow and tendinopathy of the shoulder rotator cuff (RC) affect 5.9% to 13.8% of the general population worldwide. These conditions cause significant disability to the general population and burden the healthcare system. Common treatments for these conditions include physical therapy (PT), pain medication, and various injection therapies. The problem with these conditions is that the damaged tissue has poor or no direct blood supply, thus, the natural healing process may become hindered and tissue becomes worn and damaged. The advancements in molecular biology have made doctors seek new methods to treat these common conditions.

Platelet-rich plasma (PRP) is a concentrate derived from whole blood and depleted of red blood cells through centrifugation. PRP is defined as a minimum of 1,000,000 platelets / microliters in a plasma solution. Platelets and this concentrate contain growth factors (GF) and other cytokines that may stimulate healing in joints and soft tissue. PRP was first utilised in veterinary medicine and dentistry, gradually finding its way to medicine. The theory is to take natural biological autologous growth factors (GF) from human blood and inject them where they would facilitate normal tissue healing. PRP’s effects are complex and somewhat unknown as not all the signal pathways and interactions are known down to the finest detail.

This doctoral thesis mainly aims to 1) determine whether PRP postpones the need for knee arthroplasty in knee osteoarthritis (KOA); 2) investigate the long-term effects of PRP on the RC tendinopathy of the shoulder; 3) determine the effectiveness of PRP treatments in chronic lateral epicondylitis of the elbow; 4) study whether any subgroups of patients concerning the degree of OA or body mass index (BMI) benefit from the treatment more than other potential subgroups. This thesis is based on five retrospective studies following the aforementioned patient groups who received PRP injection treatments or conservative treatments that are widely accepted for their musculoskeletal disorder. The patients were treated at the district hospital of Forssa, in the Welfare District of Forssa.