Tendon & Ligament Injuries
Undoubtedly, ultrasound is one of the most effective diagnostic imaging modalities available to assess tendon and ligament injuries. We primarily evaluate THREE things when interpreting tendon and/or ligament injuries ultrasonographically:
The degree of fiber compromise (mild, moderate, or severe),
The percentage of fiber compromise (0-100%), and
The location of fiber compromise.
The combination of these findings gives us insight into the type of lesion(s), prognosis for future performance, the most appropriate therapeutic strategy(ies), approximate time required for the injury to heal adequately, and amount of time required for the horse to resume a normal work routine once the lesion(s) has healed.
TENDON/ LIGAMENT HEALING
Tendon and/or ligament injuries heal via the formation of scar tissue which takes the place and function of the original fibers. Regardless of the percentage of fibers that are damaged, it takes 10-12 MONTHS for scar tissue to gain its maximum strength. As a general rule, scar tissue will never be as strong as normal tissue.
The process of replacing damaged fibers with scar tissue (i.e. "making" scar tissue) takes approximately 90 days. Once the scar tissue is present, it takes another 7-9 months for it to reach maximum strength (hence the 10-12 months total).
In cases in which a small percentage of fibers are compromised, there are still a majority of normal fibers present. These normal fibers will continue to accommodate most of the weightbearing load of the tendon/ligament structure. For example, if 5% of the fibers are compromised then 95% of the fibers are still intact. Even though the scar tissue will take 10-12 months to completely mature and strengthen, the horse will eventually be relying on 95% normal tissue and only 5% scar tissue. In this case, the horse is likely to resume work much sooner and have a better prognosis for future soundness.
On the other hand, if 95% of the fibers are compromised then only 5% of the fibers are still intact. Eventually, the horse will be relying almost completely on scar tissue to perform the function of the tendon/ligament structure. In these cases, we have to make sure that the scar tissue is as strong as possible prior to challenging it with a normal workload. Therefore, this case would warrant a year out-of-work and carry a guarded prognosis for future performance.
GOALS OF TREATMENT
It is the veterinarian's responsibility to use the information gathered during clinical and ultrasonographic examination to formulate an appropriate therapeutic regimen. The treatment plan should have the following primary goals:
Resume work/exercise as quickly as possible, and
Minimize the risk for reinjury once exercise is resumed.
Scar tissue is made up of collagen fibers which organize and mature during the initial 90-day period following the injury. Once the scar tissue has developed, then we focus our efforts on improving strength so that eventually the overall demands of the tendon/ ligament are met.
Rehabilitating horses with tendon and/or ligament injuries generally involves a period of stall rest with handwalking followed by a slow and deliberate increase in work intensity.
During the period of stall rest it is very important to regularly handwalk the horse. In order to maximize the eventual strength and function of the scar tissue, we have to make it appear and work as much like normal (original) tissue as possible. As the collagen fibers are being created, they will respond to applied stress. If we can apply a small but consistent amount of stress along the longitudinal length of the limb during the initial 90-day period, the collagen fibers will respond by "lining themselves up" in an attempt to accommodate this "tugging" on either end. In doing so, the scar tissue will mimic the appearance and function of the original tendon/ligament fibers. Remember, our goal to is end up with a structure that will adequately handle its intended workload.
We strongly DISCOURAGE turnout (i.e. pasture rest) during the initial post-injury period due to the fact that the horse will only use level of comfort to determine his/her exercise intensity and will not consider the physiology of tissue remodeling. Therefore, TURNOUT GREATLY PREDISPOSES THE HORSE TO REINJURY.
Once the period of stall rest has been completed, a second ultrasonographic evaluation is performed to confirm adequate healing of the tissue prior to resuming exercise. Interestingly, completely-healed scar tissue will never have the same echogenicity (i.e. the same degree of echo) as the original tissue when viewed with an ultrasound machine.
If the ultrasonographic appearance of the scar tissue is not acceptable, then more stall rest and/or the addition of other therapeutic strategies (see below) are implemented.
If the scar tissue appears adequately mature and organized during followup ultrasonographic evaluation, then a "Back-to-Work" Schedule is implemented for the horse.
BACK TO WORK
All tissue (bone, muscle, ligament, tendon, scar, etc.) will only strengthen as much as is absolutely necessary to accommodate applied stress. Following the initial 90-day rest period, scar tissue is present but has not yet been challenged. Therefore it is very weak. Furthermore, the primary structure (i.e. original intact tendon or ligament) has not been stressed and is therefore also weak. The idea of the Back-to-Work Schedule is to stress to the tendon or ligament in a way that improves strength but does not predispose the structure to reinjury. Increased stress is applied in small increments with graduating intensity. This way, the structure has time to remodel and adapt to the increase in workload.
In general, lesions requiring 3 months or less of stall rest will require a comparable amount of time to strengthen. For example, horses requiring 2 months off would resume exercise using the 60-day Back-to-Work schedule as a guide. Horses laid up for more than 3 months can typically return to a normal work routine using the 90-day Back-to-Work Schedule as a guide.
OTHER TREATMENT MODALITIES
In some cases, we recommend adjunctive treatment modalities designed to do one or both of the following:
I. Local injection is often performed in acute cases of tendon/ligament compromise.
At the time of injury, the damaged fibers are replaced with blood. This is sometimes referred to as a "core lesion" since the torn group of fibers frequently appears similar to a black hole residing within the main body of the structure when viewed ultrasonographically. Tears can also occur on the edge of the structure rather than as core lesions. During the initial period following the injury, the red blood cells are reabsorbed into the system leaving serum within the defect. Within several days following the injury, scar tissue begins to fill in the defect left by the damaged fibers. The more serum and blood that initially forms within the structure, the more scar tissue that will eventually develop.
In cases in which a lesion is identified soon after the injury is sustained, blood and/or serum can be drained from the defect with a needle. Less blood/ serum translates into less eventual scar tissue. Less scar tissue relative to normal tissue means better eventual function of the structure. At The Atlanta Equine Clinic, we often infuse a combination of a small amount of steroid (triamcinilone) and antibiotic (Amikacin) into the defect immediately following aspiration of the blood/serum. This dramatically reduces the amount of overall scar tissue that will persist within the structure. The end result is improved appearance and function of the tendon/ ligament.
II. Extracorporeal High-Energy Shockwave Therapy (ESWT) is a treatment methodology that is currently gaining popularity in the world of performance horse medicine. ESWT was first developed for humans as a treatment for the disintegration of kidney stones. Subsequently, it was recognized that ESWT might have applications in orthopedics as well. High-intensity waves apply mechanical pressure and tension on tissues. These forces stimulate osteogenesis (new bone formation) and removal of excessive osseous tissue (calcification). The effects of shock waves occur in regions where tissue density changes, such as bone/ tendon or bone/ ligament interfaces. Therefore, it has shown promise in treating such conditions as stress fractures, navicular disease, distal tarsitis, suspensory desmitis, ligament and tendon fibrosis and/or ossification, etc. Preliminary research studies show better quality healing and improved recovery rates.
In our hands, ESWT has shown to be the most effective way to both hasten and improve return to function in horses with chronic tendon/ ligament injuries.
III. The Atlanta Equine Clinic also has extensive experience using Infrared Laser and Therapeutic Ulrasound for these type of injuries. Although there appears to be enhanced scar tissue strength, these modalities have not been very effective at reducing healing time.
IV. Urinary Bladder Matrix (UBM) or "ACell" is a medical device derived from the lining of urinary bladders of specially bred pigs. This modality has also shown promise for healing equine tendon and ligament injuries.
Urinary bladder matrix (UBM), sold under the name ACell Vet, is a naturally occurring extracellular matrix scaffolding that promotes remodeling of injured tissue. ACell recruits cells from the circulatory system and local tissues for the purpose of tissue differentiation. The idea is to replace damaged cells with cells designed to function like normal tendon/ ligament cells. This product is typically distributed as a thin, dehydrated or hydrated membrane which can be injected directly into a tendon or ligament lesion.
V. In our experience, the most effective way to promote stem cell function within tendon or ligament tissue is through the use of platelet-rich plasma (PRP).
Numerous growth factors have been used in the horse with the intention of enhancing synthesis and reducing breakdown of tendon/ ligament tissue pursuant to injury. Historically, these growth factors have been harvested from bone marrow and/or fat aspirates, which also contain increased concentrations of stem cells.
More recently, platelet-rich plasma (PRP) has been gaining popularity as a treatment designed to augment equine tissue repair.
Platelet-rich plasma (PRP) is an autologous concentration of platelets in a small volume of plasma. Plasma is the straw-colored liquid in which blood cells are suspended. PRP is generated through relatively simple centrifugation of blood. Because it is a concentration of platelets, it is also a concentration of 7 fundamental protein growth factors known to be secreted by platelets in response to wound healing. PRP also contains proteins known to promote cell adhesion during tissue rebuilding.
Platelets perform many functions in the body, including formation of blood clots and release of growth factors into wounds. The rationale for the use of PRP as a treatment strategy for tendonitis (tendon damage) and desmitis (ligament damage) stems from the increased platelet release of multiple growth factors in response to an injury. Two additional incentives for using PRP include its relative ease of collection and the unlikelihood that it will result in immune rejection since it is autologous (produced from the patient's own blood).
At The Atlanta Equine Clinic, PRP has been used to successfully treat the following soft tissue injuries: tendon strain, muscle strain, ligament strain, and joint capsular laxity. PRP has also been used to treat intraarticular injuries. Examples include arthritis, arthrofibrosis, articular cartilage defects, meniscal injury, and chronic synovitis (joint inflammation).
VI. Finally, the exploration of interleukin-1 receptor antagonist protein (IL-1Ra or "IRAP") as a treatment for tendon/ligament injuries began shortly after its first published characterization in 1984. The ability of this molecule to act as both a symptom- and disease-modifying agent in various species (including horses and humans) has prompted its clinical application as a treatment for tendon/ligament injury.
The goal behind IRAP treatment is to use the body's own inflammation-fighting cells to reduce inflammation rather than the synthetically-produced antiinflammatory medications that we buy in a bottle. Because the antiinflammatory cells are produced by the host body itself, we can often expect an improved degree of response as well as a longer duration of response.
A TREATMENT PLAN
A typical treatment plan for most tendon and ligament injuries consists of the following:
1) Drainage of blood and serum from the injury site. This approach is only possible for core-type lesions that have recently developed and are still "fresh". Draining fluid reduces the size of the defect which in turn results in less scar tissue formation.
2) Intralesional injection of the injury site. IRAP, PRP, or steroid is infused into the tissue defect to minimize inflammation and improve healing. The product used is determined by the age, appearance and nature of the lesion.
3) Dexamethasone Sweat Spray. Topical application of this product (formulated in our pharmacy) can reduce inflammation usually accopmanying this type of injury during the acute stage. If you would like to order some spray, please click HERE.
A small amount is applied to the affected area(s) once daily until inflammation/ swelling/ heat/ pain has resolved. No bandaging of the limb is necessary.
4) Stall rest and handwalking ONLY for a period of time dictated by the severity and characteristics of the injury. There is no limit to the amount of handwalking. However, anything beyond handwalking is strongly discouraged during this period.
In some cases, horses will get "stall crazy" if couped up for a prolonged period of time. Short of recommending tranquilizers/ calming agents, etc., we might suggest altering the diet. Please click HERE for more information.
5) Extracorporeal Shock Wave Therapy (ESWT). We recommend implementing this treatment starting at approximately 30-45 days post-injury. This will help to improve both form and function of the scar tissue developing within the structure. In many cases, this modality also accelerates the horse's return to work. ESWT can be performed after the horse resumes light exercise if necessary.
6) Clinical and Ultrasonographic Reexamination. This should be performed at the conclusion of stall confinement to determine if exercise can be resumed or if further rest is required.
Ultrasonographic examination is ALWAYS required to determine if the tissue is "ready" to handle an increase in workload.
7) Resume Exercise. Once it has been determined that the scar tissue is ready, exercise must be introduced GRADUALLY. One of the three BACK-TO-WORK SCHEDULES is used as a guideline.