Equine suspensory desmitis (Proceedings)

Equine suspensory desmitis is a common cause of lameness in the athletic equine, regardless of discipline. The condition seems to be different in the forelimb and hindlimb, so these will be discussed independently.

Forelimb suspensory desmitis, including proximal, body, and branch lesions can result in a very mild or subtle lameness or performance decrease, to a more severe lameness. When a lameness is present, it is often more evident on soft ground, and often more evident when the lame leg is on the outside of the circle. The lameness is best described as an advancing leg lameness, meaning the maximal head excursion is during the swing phase of the stride. The problem can affect one or both legs. When both legs are involved, a change in gait or gait quality is seen rather than a distinct lameness.

Horses with forelimb suspensory desmitis will have a variable response to forelimb flexion tests, but most often are positive to both distal limb and carpal flexions. I have found that horses with insertional lesions (either proximal or distal insertions) usually react very strongly to both of these flexions. Digital palpation is extremely important in evaluating forelimb suspensory ligament disorders. Normal horses should not be painful to palpation of the suspensory ligament. In addition to pain on palpation, I evaluate size differences in the branches or any enlargements in the body. In some horses, particularly those with subtle problems, palpable pain and a positive response to flexion are only seen after some degree of work. Often times the reaction to flexion tests will worsen at subsequent flexions.

It is important to remember that there is rarely any external abnormality (swelling) with even the most severe form of suspensory desmitis. However, most branch lesions will have some enlargement or peri-ligamentous swelling, but this may only be able to be detected by digital palpation with the limb off of the ground. It is also important to remember that forelimb suspensory desmitis, while it can be the sole cause of the lameness, often can be present in combination with other sources of lameness, so a thorough lameness examination is always necessary.

With obvious forelimb suspensory desmitis, diagnostic anesthesia may not be necessary. However, one has to be certain that it is the sole cause of the lameness. Routine diagnostic anesthesia of the distal limb is usually employed to rule out lameness arising from below the fetlock. Low volar anesthesia will alleviate pain from the suspensory branches and body. A lateral palmar nerve block will alleviate most of the pain from the entire suspensory ligament; however, pain coming from the suspensory origin will only be variably blocked. In some horses, the palpable pain in the suspensory can be alleviated with diagnostic anesthesia, but not the clinical lameness. In these cases I will infiltrate the proximal suspensory with local anesthetic. This will usually alleviate lameness arising from the origin of the suspensory.

One must be careful with interpreting perineural nerve blocks above the palmar digital nerves. I have found that marked proximal diffusion of local anesthetics can occur from abaxial and low volar blocks, leading to false conclusions. Therefore, intra-articular blocks are generally used to help rule out fetlock and pastern problems rather than perineural nerve blocks.

Routine diagnostic imaging of the suspensory ligament includes ultrasound and radiology. When evaluating the suspensory ligament with the ultrasound, the entire ligament (origin, body, and branches) should be evaluated in both a transverse and longitudinal orientations. Thickness and cross sectional area of the structures should also be ascertained. A systematic approach should be used so that one becomes accustomed to what the normal appearance should be. Ultrasonographic abnormalities include changes in echogenicity (hypoechoic to anechoic), changes in fiber length and orientation, or enlargements of the structure. If insertional disease is suspected or visualized on the ultrasound, the insertion points (proximal metacarpus and sesamoid bones) should be radiographed to evaluate any bony abnormalities. MRI analysis of the suspensory apparatus is also sometimes utilized and may further pinpoint lesions that may not be apparent by any other diagnostic means.

When determining the most appropriate therapy for horses with forelimb suspensory desmitis, I like to place these horses into 1 of 3 categories: suspensory desmitis with no major ultrasonographic or radiographic abnormalities, suspensory desmitis with obvious ultrasonographic and/or radiographic abnormalities, and insertional suspensory desmopathy (proximal or distal). A large number of horses in my practice that I diagnose with suspensory desmitis fit into the category of having pain and lameness without any obvious diagnostic abnormalities. These horses generally respond very favorably to extracorporeal shock wave therapy. My standard treatment protocol is to shock wave these horses, apply topical diclofenac (Surpass) twice a day, place in a reduced exercise schedule (walking primarily), and to recheck in 2 weeks. Approximately 90% or more of the horses in this category will be sound at the 2 week recheck, and can be placed back into full training. A small percentage of horses may be improved but not sound. These horses will receive a second treatment of shock wave therapy and will have continued reduced exercise. If there is no difference in lameness at the 2 week re-examination, I will recheck the diagnosis or look for an additional cause of lameness. Horses with an insertional desmopathy also tend to respond favorably to extracorporeal shock wave therapy. When there is evidence of osteolysis of the proximal palmar metacarpus or proximal sesamoid bones, adjunctive therapy with systemic tiludronate is often instituted.

In those horses that fail to respond to extracorporeal shock wave therapy, and there is still no evidence of significant lesions on ultrasound or radiographs, I generally recommend a series of peri-ligamentous injections with interleukin 1 receptor antagonist protein (IRAP). The injections are repeated either weekly or biweekly, and the horses placed in the same reduced exercise program.

Horses with obvious ultrasonographic changes in the suspensory ligament or branch are commonly treated with one or more methods of regenerative therapy. This includes intra-lesional therapy in the form of autologous adipose derived stem cells, platelet rich plasma, the combination of these two, or extracellular matrix (ACell). The choice of these therapies is dictated by the severity of the lesion and budget. For mild to moderate lesions where the budget is unlimited, I prefer to inject a combination of adipose derived stem cell in combination with platelet rich plasma. Depending on the case, this therapy can be used every 30-60 days as necessary. For severe injuries to the forelimb suspensory ligament, I generally recommend intra-lesional injection with extracellular matrix followed by aggressive anti-inflammatory therapy. This therapy seems to be good at stimulating fibrosis quickly, which can help provide mechanical support. All intra-lesional injections are performed using ultrasound guidance, so that there is precise placement of the material. These horses are placed on a restricted or greatly reduced exercise program, and re-evaluated at 6-8 week intervals.

With these advanced, regenerative treatment modalities, I have seen superior healing in less time than with the traditional methods based around the concept of extended rest. Sometimes I will use extracorporeal shock wave therapy on these horses alone or in addition to other regenerative therapies, but the dose and energy levels are reduced from those used in horses without ultrasonographic lesions. I do feel that these horses do better with some sort of post-injury rehabilitation exercise depending on the severity of the injury, and this must be adjusted regularly based on healing and response to treatment. Increase in exercise should be based on decreases in lameness and palpable pain in addition to ultrasonographic findings.

The use of rest alone for the treatment of forelimb suspensory desmitis has been disappointing in my experience, as the healing and return to soundness does not appear to be predictable. Other, less expensive alternatives for treatment of forelimb suspensory desmitis include peri-ligamentous injection with anti-inflammatories. This can have a transient positive effect on lameness, but can delay healing of lesions. The use of topical diclofenac alone can be effective in mild cases of suspensory desmitis. I typically recommend using the product twice a day for 2 weeks followed by once a day for an additional 2 weeks. Cold therapy can be used to help reduce the incidence of recurrence of suspensory desmitis, and can help reduce swelling in the acute cases. I prefer to ice legs after exercise. It is also important to correct any predisposing problems, particularly foot imbalance.

Suspensory desmitis in the hind limb is also a common cause of lameness in the athletic horse. In my practice proximal suspensory and suspensory branch desmitis are the most common forms of hind limb suspensory disease. Suspensory body disease in the hind limb seems to be much less common, but when it does occur it seems to mostly be a distal extension of proximal suspensory desmitis, and tends to be severe in my experience. Hindlimb suspensory branch disease seems to be equally or more common than forelimb suspensory branch disease.

The lameness induced by rear limb proximal suspensory desmitis can be described as a shortened cranial phase of the stride, which often appears to be worse with the leg on the outside of the circle. In contrast to the front limb, it is extremely uncommon to detect palpable sensitivity in the proximal or suspensory body in the rear limb. It is also extremely uncommon to detect any external or palpable swelling in this area. The proximal splint bones on the rear limb are particularly large and therefore hide the proximal suspensory ligament. These horses are usually equally positive to all 3 flexions of the rear limb. Bilateral involvement is common, although one leg is usually worse. In horses with bilateral involvement, I have found that they may have a hard time or be reluctant to back.

A diagnosis is usually made by diagnostic anesthesia. Lameness in the distal limb is ruled out by standard perineural anesthesia. The proximal suspensory ligament is best anesthetized by local infiltration with the leg in a non-weight bearing position. If proximal suspensory desmitis is suspected, I prefer to ultrasound the area prior to blocking, as the block can create sonographic artifacts. The proximal suspensory area in the hind leg can be somewhat challenging to evaluate. The best acoustic window to image the proximal suspensory ligament is plantar medial. I also employ a small stand-off pad in this area to help with contact. Fiber pattern disruptions, enlargements in the thickness of the ligament, and insertional changes at the proximal plantar metatarsus are the most common abnormalities noted. If the suspensory origin at the bone is suspected to be involved, radiographs of this area are obtained. Many horses in my practice have abnormal appearing (by ultrasound) rear proximal suspensory ligaments that may not be lame, so clinical assessment along with diagnostic anesthesia is necessary. This also points out that proximal suspensory desmitis is more often a culmination of chronic changes than an acute event.

Suspensory branch problems are also common in the hind limbs of performance horses. These horses will have pain to palpation and thickening over the affected branch, often only detectable with the leg off of the ground. Distal limb flexion will often be positive or strong positive. If necessary, low volar diagnostic anesthesia will alleviate the lameness. Ultrasound and radiographs are crucial in determining the extent of the injury, and both should be performed in all horses that have suspected suspensory branch problems.

Proximal suspensory desmitis in the hind leg is a different entity than proximal suspensory desmitis in the forelimb. There is unique anatomy in the proximal plantar metatarsal area that complicates the treatment and prognosis. The proximal splint bones in the rear leg are quite large and completely block the ability to palpate the proximal suspensory. On the plantar aspect of the proximal suspensory, there is a thick retinaculum that creates an inelastic compartment bordered by the proximo-plantar aspect of the metatarsus, the axial aspects of the proximal splint bones, and this retinaculum. Proximal suspensory desmitis in the hind limb can be strictly a soft tissue problem or a soft tissue problem in combination with insertional disease, and is usually accompanied by some degree of enlargement and fiber disruption. A far smaller percentage of these horses will improve with extracorporeal shock wave therapy than with the similar condition in the forelimb. The most likely explanation for this is the compartment type syndrome that can occur. The most effective therapy that I have found for horses that have rear limb proximal suspensory desmitis without major fiber disruption is a course of periligamentous injections with IRAP, either at weekly or biweekly intervals. If there is a suspicion of insertional disease as well, I will combine the IRAP injections with extracorporeal shock wave therapy. Additionally, I like to concurrently treat the tarsometatarsal joint with hyaluronic acid and corticosteroids, as the anti-inflammatory effect of this intra-articular treatment can extend into the proximal suspensory region. If there is significant fiber disruption apparent on ultrasound, particularly in combination with enlargement of the structure, the prognosis for successful medical treatment is poor. Many of these horses will have extension of the fiber disruption into the body of the suspensory as well. For these horses, or those that have not responded to medical therapy, I will perform a surgical retinaculum release (also called a plantar fasciotomy) combined with ligament splitting and intra-lesional injection of adipose derived stem cells. An additional surgical procedure that can be performed is neurectomy of the lateral branch of the plantar nerve. Many of these horses will become sound in 60-120 days, but I prefer not to return them to full exercise for at least 6 months. Suspensory branch lesions in the rear limb are treated similarly to those in the forelimbs. Horses with enlargements and pain may respond to extracorporeal shock wave therapy alone. When there is significant fiber disruption on ultrasound, I prefer to inject them with adipose derived stem cells combined with platelet rich plasma. Sometimes I will combine this with suspensory ligament branch splitting, particularly in the more severe cases. More hind limb branch lesions have proximal sesamoid bone involvement, often with some degree of sesamoiditis or avulsion fractures. Horses that have radiographically detectable osteolysis are treated with systemic tiludronate. It may be necessary to surgically remove some of the larger avulsion fractures from the apex of the proximal sesamoid bones.

Suspensory desmitis of the fore and hindlimb are common causes of lameness and decreased performance in the athletic horse. An attempt should be made to determine the location of the lesion or lesions (proximal, body, or branch), so that an appropriate treatment protocol can be instituted, and so that follow-up examinations are accurate. The many different treatment modalities for suspensory desmitis alludes to the challenging nature of the disease. With confidence in diagnosis and experience, you can dictate the many treatment protocols to suit your practice.