The first article in this two-part series discussed the general principles of musculotendinous injury in dogs and the common modalities and techniques used in making a diagnosis of such injuries. This second article will discuss some of the new treatment options used in treating these conditions.
Management of both muscle and tendon injuries follow the same principle, in that the primary objective is the avoidance of scar tissue. Rehabilitation of chronic injury has now moved away from concentric training to progressive eccentric loading, a strategy that is now backed by substantial evidence in the human field. More recently, the use of laser therapy, regenerative medicine techniques and extracorporeal shockwave therapy (ECSWT) has resulted in improved outcomes for the treatment of a variety of musculotendinous injuries.
Light amplification by stimulated emission of radiation (or simply laser) light uses photons to stimulate cellular metabolism, thereby stimulating the healing process. Class IV lasers emit photons in the near infrared spectrum which penetrate deep into tissue to stimulate cells and promote healing. Eye protection must be worn when using Class IV lasers as they can cause serious harm if used inappropriately. Laser therapy is most useful in the early stages of injury to expedite healing, but it is relatively ineffective in treating chronic tendinopathies (Figure 1).
Regenerative medicine refers to methods of replacing or regenerating cells, tissues or organs to restore or establish normal function. This innovative and evolving field holds the promise of restoring damaged tissues and organs via a stimulation of the body’s own repair mechanisms.
Platelet-rich plasma (PRP) is autologous (self-derived), conditioned plasma that contains high concentrations of platelets which, in turn, contain large quantities of bioactive proteins and growth factors. One of the many growth factors is vascular endothelial growth factor (VEGF). As its name suggests, VEGF improves blood supply by angiogenesis and, subsequently, stimulates and accelerates the healing process. Anti-VEGF medications have been shown to reduce tumour growth in a variety of cancers by reducing the ability of the tumour to produce new blood vessels (antiangiogenesis). These growth factors attract other cell types to the site of injury, and initiate and accelerate the repair and regeneration of a variety of tissues. They also promote extracellular matrix formation and hyaluronic acid production and are potent inhibitors of apoptosis.
The goal of PRP production is to obtain the highest concentration of platelets and growth factors while removing the red and white blood cells, which can be deleterious. There are a number of PRP systems available in the UK; however, many are designed for human applications and have not been validated in veterinary species.
In a study that set out to compare key parameters of the PRP product from five commercial canine PRP systems, only two systems had significantly increased platelet numbers, and one of these systems failed to reduce neutrophil numbers (Carr et al., 2016). No claims were made, however, regarding the efficacy of the PRP therapy in clinical cases. Based on the findings of this study, the PRP system used at the author’s hospital yields a 550 percent mean increase of platelets while removing greater than 95 percent of the RBCs, 19 percent of the WBCs and 85 percent of neutrophils, which best fits our current thinking of an ideal PRP product (Figure 2).
PRP therapy is usually performed as a series of one to three injections, two to four weeks apart. About 50 percent of dogs require more than one injection for significant improvement. Sedation is usually required depending on the location of the injection. For soft tissue injuries, ultrasound guidance is essential to ensure accuracy of the injection and, if an intra-articular administration is required, the clinician must be proficient in performing these procedures (Figure 3).
NSAIDs are typically avoided for at least one week before and after administration as, theoretically, these drugs may negate some of the positive “proinflammatory” effects of the growth factors released by the platelets. Likewise, ice packs and cryotherapy should be avoided following the injection as this has been shown to decrease platelet activation. Mild discomfort, or “flare”, is occasionally seen for the first 24 to 72 hours following injection, but this is easily managed with paracetamol.
The combination of laser treatment with PRP has been shown to accelerate the healing of injured tendons in rabbits when compared to using either PRP or laser therapy alone (Allahverdi et al., 2016).
Stem cell therapy
Stem cell therapy is the process by which a tissue sample is obtained from the patient, processed to isolate the stem cells and then administered back into the patient at the site of injury. Stem cells may be classified as embryonic, foetal/placental or adult. Currently, only adult stem cells are commonly used in veterinary practice. Stem cells are pluripotent and have the ability to differentiate into many types of tissue. They migrate to dying cells and donate their mitochondria to improve the cell’s function. They also activate surrounding cells to aid tissue repair and reduce the development of fibrosis which is the major impediment to subsequent muscle and tendon function after musculotendinous injuries.
In-house stem cell systems that allow same-day treatment produce what is known as the stromal vascular fraction (SVF) by mincing and washing either fat or bone marrow, followed by collagenase digestion and centrifugation. The SVF pellet is then resuspended and injected back into the patient. The total cell count is low and variable, and can contain as little as 5 percent viable stem cells (Hill and Miller, 2017). On the other hand, cultures of mesenchymal stem cells may take several weeks to complete, but result in 94 percent viable stem cells with no presence of other cells, and the number of cells can be controlled (Figures 4 and 5).
Stem cells have been shown to migrate to a PRP clot (Cell Therapy Sciences, 2021) , and the use of these two modalities in combination is showing promising results in clinical cases in the author’s hospital using a concentration of 250 million culture expanded stem cells/ml (Armitage and Reid, 2019).
Extracorporeal shockwave therapy
ECSWT is a non-invasive treatment in which a device is used to pass acoustic shockwaves, at a set frequency, through the skin to the affected area. It is purely a mechanical wave, not an electrical one. ECSWT was initially developed for lithotripsy, a treatment which mechanically disintegrates urinary stones. The shockwaves can be focused to reach deeper tissues, or radial to treat wider areas. The treatment reinitiates an inflammatory response in the affected tissue that is being treated, and is most suited to chronic conditions where the inflammatory response needs to be restarted so that healing can progress. The shockwaves can break down regions of fibrosis and calcifications. As a result of cellular tissue microtrauma, ECSWT can also provide a temporary analgesic effect on afferent nerves providing immediate pain relief, known as “hyperstimulation anaesthesia”. On a very basic level, ECSWT could be considered as an intense, targeted “sports massage”.
ECSWT is delivered via a compressed air impulse through a handpiece attached to the shockwave machine. Contact gel is applied to the skin to improve the transmission of the shockwave. ECSWT is loud and acutely painful and sedation or anaesthesia is therefore required. Treatment time depends on the amount of energy delivered and the number of locations treated. A common dose of 2,500 to 3,500 pulses per area requires approximately eight minutes to deliver. For treatment of chronic musculoskeletal conditions, four to six treatments are recommended at weekly intervals or until clinical improvement or resolution has been achieved. ECSWT should be used in conjunction with an integrated physiotherapy and rehabilitation programme.
There are no major safety concerns associated with ECSWT, and it is included in the NICE guidelines for the management of refractory (chronic) tendinopathies in humans, such as plantar fasciitis, Achilles tendinopathy and tennis elbow. ECSWT is commonly used at the author’s veterinary hospital to treat cases of chronic iliopsoas and supraspinatus tendinopathy (Figure 6), but it can be used for any chronic condition where issues are related to the formation of fibrosis.
In acute injuries, the prompt instigation of the widely accepted PRICE – protect, rest, ice, compress, elevate – treatment plan should be employed to reduce the risk of further injury and reduce swelling and inflammation. Muscle has good blood supply and, with appropriate management, a return to full function is achievable. Tendons have a much-reduced blood supply and thus healing is much slower. It is vital to understand that all of these additional therapies should be seen as an adjunct to a tailored physiotherapy programme, with controlled and progressive eccentric loading the mainstay of therapy (Figure 7). Recovery can be slow and, in many cases, can take four to six months.