Treatment of chronic elbow tendinosis with buffered platelet-rich plasma.
Mishra A, Pavelko T.  Am J Sports Med. 2006 Nov;34(11):1774-8.

This is the first study supporting the use of PRP for chronic tendon problems.  93% reduction in pain at average 2 year follow up.

Treatment of tendon and muscle using platelet-rich plasma.  Mishra A, Woodall J Jr, Vieira A.Treatment of Tendon and Muscle  Clin Sports Med. 2009 Jan;28(1):113-25.

This is a review article that includes basic science, animal and human data including a reference to Dr. Gosens' work showing PRP improves patient pain and function when compared to cortisone in a 100 patient double-blind prospective randomized trial. 

Platelet-rich plasma enhances the initial mobilization of circulation-derived cells for tendon healing.
Kajikawa Y, Morihara T, Sakamoto H, Matsuda K, Oshima Y, Yoshida A, Nagae M, Arai Y, Kawata M, Kubo T.   J Cell Physiol. 2008 Jun;215(3):837-45.

This study confirms PRP can help attract cells that contribute to a healing process in a tendon.  

Comparison of surgically repaired Achilles tendon tears using platelet-rich fibrin matrices.
Sánchez M, Anitua E, Azofra J, Andía I, Padilla S, Mujika I. Am J Sports Med. 2007 Feb;35(2):245-51.

This study showed PRP may accelerate healing from Achilles Tendon repair surgery.

Can platelet-rich plasma enhance tendon repair? A cell culture study.
de Mos M, van der Windt AE, Jahr H, van Schie HT, Weinans H, Verhaar JA, van Osch GJ. Am J Sports Med. 2008 Jun;36(6):1171-8.

This study confirms PRP enhances tenocyte proliferation and collagen production.

Cellular effects of platelet rich plasma: a study on HL-60 macrophage-like cells.  Woodall J Jr, Tucci M, Mishra A, Benghuzzi H.  Biomed Sci Instrum. 2007;43:266-71

This study found PRP initially inhibits the inflammatory Macrophage cell.  This helps explain why PRP may be useful for tissue healing.