Regenerative Medicine Soft Tissue Platelet Rich Plasma PRP injection therapy David L. Harshfield, Jr. M.D. M.S. Medical Director, College of Integrative Medicine Little Rock, Arkansas Director of Interventional Radiology, Medical Center of South Arkansas Eldorado, Arkansas. Chairman- Institutional Review Board, International Cellular Medicine Society

Tendon

It was believed previously that tendons could not undergo extracellular matrix (ECM) turnover and that tenocytes were not capable of repair. However, it has been shown more recently that throughout the lifetime of a person, tenocytes in the tendon actively synthesize ECM components as well as enzymes such as matrix metalloproteinases (MMPs) that can degrade the matrix Tendons are therefore capable of healing and recovering from injuries in a process that is controlled by the tenocytes and their surrounding extracellular matrix. However, the healed tendons are thought to never regain the same mechanical properties as before the injury. Tendon

Tendon Animation

Tendon The three main stages of tendon healing are inflammation, repair or proliferation, and remodeling, which can be further divided into consolidation and maturation. These stages can overlap with each other. 1.In the first stage, inflammatory cells such as neutrophils are recruited to the injury site, along with erythrocytes. Monocytes and macrophages are recruited within the first 24 hours, and phagocytosis of necrotic materials at the injury site occurs. After the release of vasoactive and chemotactic factors, angiogenesis and the proliferation of tenocytes are initiated. Tenocytes then move into the site and start to synthesize collagen III. The inflammation stage usually lasts for a few days, and the repair or proliferation stage then begins. 2.In the second (repair or proliferation) stage, which lasts for about six weeks, the tenocytes are involved in the synthesis of large amounts of collagen and proteoglycans at the site of injury, and the levels of GAG and water are high. 3.The third (remodeling) stage begins after about six weeks. The first part of the remodeling stage is consolidation, which lasts from about six to ten weeks after the injury. During this time, the synthesis of collagen and GAG is decreased, and the cellularity is also decreased as the tissue becomes more fibrous as a result of increased production of collagen I and the fibrils become aligned in the direction of mechanical stress. The final maturation stage occurs after ten weeks, and during this time there is an increase in crosslinking of the collagen fibrils, which causes the tissue to become stiffer. Gradually, over a time period of about one year, the tissue will turn from fibrous to scar-like.

Matrix metalloproteinases MMPs have a very important role in the degradation and remodeling of the ECM during the healing process after a tendon injury. Certain MMPs including MMP-1, MMP-2, MMP-8, MMP-13, and MMP-14 have collagenase activity, meaning that unlike many other enzymes, they are capable of degrading collagen I fibrils. The degradation of the collagen fibrils by MMP-1 along with the presence of denatured collagen are factors that are believed to cause weakening of the tendon ECM and an increase in the potential for another rupture to occur. In response to repeated mechanical loading or injury, cytokines may be released by tenocytes and can induce the release of MMPs, causing degradation of the ECM and leading to recurring injury and chronic tendinopathy Tendon

While stretching can disrupt healing during the initial inflammatory phase, it has been shown that controlled movement of the tendons after about one week following an acute injury can help to promote the synthesis of collagen by the tenocytes, leading to increased tensile strength and diameter of the healed tendons and fewer adhesions than tendons that are immobilized. In chronic tendon injuries, mechanical loading has also been shown to stimulate fibroblast proliferation and collagen synthesis along with collagen realignment, all of which promote repair and remodeling. Tendon

Several mechanotransduction mechanisms have been proposed as reasons for the response of tenocytes to mechanical force that enable them to alter their gene expression, protein synthesis, and cell phenotype and eventually cause changes in tendon structure. A major factor is mechanical deformation of the extracellular matrix, which can affect the actin cytoskeleton and therefore affect cell shape, motility, and function. Mechanical forces can be transmitted by focal adhesion sites, integrins, and cell-cell junctions. Changes in the actin cytoskeleton can activate integrins, which mediate “outside-in” and “inside-out” signaling between the cell and the matrix. G-proteins, which induce intracellular signaling cascades, may also be important, and ion channels are activated by stretching to allow ions such as calcium, sodium, or potassium to enter the cell. Tendon

Elbow Distal Biceps Tendon treated with Platelet Rich Plasma

Distal Biceps Tendon 3 sets of MRI images in this caseare arranged in chronological order: 1. Immediate (1 week) post injury, 2. 2 weeks post PRP therapy (3 weeks post injury), and 3. 9 months post PRP injection therapy. All 3 of these series are T2 weighted without contrast, and are obtained transversely (short axis) thru the elbow.

Distal Biceps Tendon 1 week post injury 3 weeks post injury/ 2 weeks post PRP injection 9 months post injury/PRP therapy

The initial set of 5 images represents the earliest, immediate (1 week post injury), depicting near complete disruption of the expected “dark” smooth tubular appearance of the distal biceps tendon due to the high grade tear involving the insertion point upon the radial tuberosity (far left image). There is fluid signal in the antecubital fossa due to vascular congestion as well as the contribution of 3cc’s of ultrasound guided PRP injectate placed into and surrounding the few remaining intact fascicles. The injured but intact bicipital tendon aponeurosis is preventing complete musculotendinous retraction of the distal biceps (not demonstrated, being superficial to this field of view). Distal Biceps Tendon

The second series of 5 images represent the MRI appearance 2 weeks post PRP injection (3 weeks post injury), and are just beginning to show reorganization, but without identifiable “dark” defined tendon morphology. The fluid signal in these images is a manifestation of both the inflammatory/reparative process (extra cellular fluid) accompanied by venous vascular congestion (intravascular blood). Also note the subtle muscle volume loss (atrophy) compared to the initial series, as the patient was utilizing a sling to immobilize the elbow during much of the day. Distal Biceps Tendon

The third and most recent MRI series of 5 images obtained at 9 months post injection, reveal reconstitution of the now “dark”, tubular, functioning tendon. The “dark” hypointensity of the tendon is indicative of “new” type I collagen, and if we were to image the patient's contralateral intact biceps tendon it would appear “gray” intermediate in intensity, as most of us demonstrate type II and III collagen as a manifestation of the normal aging process. The fluid signal in these images represents slow moving venous blood within the intact, normal veins and arteries occupying the antecubital fossa. The “dark” flow void signal can be seen as a manifestation of fast moving blood within the normal arterial structures in the region, the “bright” within veins. Distal Biceps Tendon

This patient happens to be a neurologist colleague, and in spite of the early “markedly abnormal” appearing shredded tendon, the pain abated within three days post injection, and he began functioning normally at 2 to 4 weeks after the PRP injection (his interventional practice consists primarily of a pain medicine clientele). I asked him to come in for a “validating” MRI over the holidays, to which he graciously agreed, providing us with the 9 months post procedure images. Typically, tendons show this kind of regenerative growth at 2 to3 months, but once the patient is back to “normal” function; it is difficult to convince them to return for the “defining” and validating post procedure MRI (everybody is busy). The fluid signal in the third and final set of five images represents slow flowing venous blood contained within the normal veins that occupy the antecubital space (“dark”, flow void signal can be seen within the arterial structures due to normal fast moving blood). Distal Biceps Tendon

The muscle atrophy is no worse on the final images compared to the second series of images obtained two weeks post PRP, and may improve as the patient resumes normal activity and pursues specific post procedure rehabilitative exercises. We have found that it is important that we carefully and precisely inject the PRP into all abnormal and torn portions of the involved tendons and ligaments (insertional and interstitial components) and also carefully inject into the intra-articular as well as the extra- synovial spaces. This is particularly important when dealing with an abnormal ACL in the knee to obtain best results both when addressing acute ACL tears as well as patients with generalized osteoarthritis of the knee from chronic ACL insufficiency. This is in contradistinction to the high success rate obtained with a “close is good enough” approach to injecting MCL/LCL and most ligament and capsular pathology encountered in a MSK practice. Also, we inform our patients that NSAIDs, steroids, statins, ace inhibitors and many other pharmaceuticals all work against the PRP’s healing mechanism. Distal Biceps Tendon

Next Month’s Case

Shoulder Rotator Cuff Tear treated with Platelet Rich Plasma