Soft tissue injuries
Tendinitis and desmitis
Introduction
Thirteen to 18% of equine athletes sustain a soft tissue injury sufficiently severe to require a period of rest each year. Horses at greatest risk are those whose work load is increasing rapidly, for example, horses undertaking work at racing speed prior to their first race or dressage horses training to achieve the next training level.
Tendons and ligaments have a slow metabolic rate of activity and require a period of 8–14 months to return to the normal tensile strength range after damage, depending on the severity of the injury. Confinement and rehabilitative exercise needed for optimum healing are expensive and time consuming; therefore an accurate diagnosis of all injuries currently affecting the horse is very important to allow for simultaneous rather than sequential treatment. Tendons and ligaments in varying locations respond to treatment and rehabilitation in a relatively similar fashion therefore if one is confronted with a new or unusual injury, basic treatment principles apply. Although the published prognosis is fair or even poor for many soft tissue injuries, early diagnosis, good client compliance with repeated clinical and ultrasound examinations and a controlled exercise program tailored to the stage of healing of the injured tendon or ligament have improved the prognosis for most injuries. The prognosis for return to full athletic soundness is often good when using these principles, as long as adequate care and time are provided to allow for complete healing.
Superficial digital flexor tendinitis
Recognition
History and presenting complaint
Horses presented for superficial digital flexor (SDF) tendinitis are usually in full athletic use. Affected horses often have a workload that consists primarily of galloping and/or jumping (Fig. 20.1). Most tendon injuries are due to cumulative damage rather than a single event, the exception being a fall or a strike from another limb. Horses often develop clinically apparent pain, swelling and lameness 2–3 days following SDF injury.
Physical examination
Lameness ranges from grade 1 to 3 of 5 and is often transient or intermittent. Lameness often resolves rapidly with the use of ice, rest and anti-iflammatory agents. There will acutely be pain on palpation, heat and swelling at the lesion site. Pain on flexed palapetion is often the sign with longest duration as the lameness resolves. Affected horses frequently exhibit a decrease in performance ability after the initial lameness resolves.1,2
Differential diagnosis for lesions in the metacarpal/metatarsal region is limited as the SDF tendon is readily palpated and separated from deeper structures. Carpal sheath synovitis may be associated with proximal SDF tendinitis. Digital sheath synovitis may be associated with SDF tendinitis in the fetlock and pastern regions. The manica flexoria portion of the SDF tendon may be damaged deep to the deep digital flexor tendon in conjunction with digital sheath synovitis. Differential diagnosis in the pastern region includes damage to the sesamoidean ligaments or the collateral ligaments of the proximal interphalangeal or distal interphalangeal joints.
Special examination
For SDF branch lesions, a low palmar digital nerve block generally provides analgesia. For SDF lesions in the metacarpal/metatarsal region, a high palmar nerve block resolves the lameness.3
Increased size of the affected tendon region combined with loss of echogenicity and normal parallel linear fiber pattern observed with diagnostic ultrasonography provides the definitive diagnosis (Fig. 20.2, Fig. 20.3, Fig. 20.4, Fig. 20.5, Fig. 20.6).4–10
Tenoscopy of carpal and digital sheaths provides diagnostic information as well as further treatment options. For example, under arthroscopic guidance debridement of frayed tendon fibers and resection of proliferative synovium and adhesions may be performed.11,12
Treatment and prognosis
Therapeutic aims
• to control inflammation and prevent further tendon injury directly, through reducing tendon fiber swelling and influx of inflammatory mediators, or indirectly, through further exercise
• provide adequate tendon support, primarily through shoeing
• provide adequate rest followed by graduated increases in exercise to allow for optimum tendon healing.
Therapy
Initial therapy is directed at controlling excessive inflammation and should include anti-inflammatory therapy such as 1% diclofenac cream applied twice daily to the affected area.
Cold therapy, such as ice for 20 minutes 2–3 times/day for three weeks, is an effective adjunct to reduce inflammation. Treatment with intramuscular polysulfated glycosaminoglycan, 500 mg every four days for seven treatments, has been shown to improve tendon healing.13
Although stem cell and platelet rich plasma (PRP) injections are in common use, no contolled study has yet shown that they produce collagen within injured tendon or ligament. A recent paper has shown that mesenchymal stromal cells survivied for approximately 10 days when injected into damaged tendon, and that they did not migrate, indicating little viable activity.14 Embryonic stem cells were able to survive for 120 days and to migrate indicating that futher research is warranted to determine if embryonic cells might produce viable tendon collagen. Another recent paper has shown that insufficient amounts of growth factor are released from platelets using current techniques to induce collagen growth.15
Stall (12′ by 24′) confinement with hand-walking should be initiated following examination. Unless the tendon is so severely damaged that rupture appears likely (rare), hand-walking is an important part of treatment and should not be delayed. If a free or box stall type of mechanical exerciser is available, horses can exercise up through the trot phase on this equipment. Walking times can be moderately increased above hand walking times. All exercise should be under supervision. Aquatic treadmills are also useful for horses when they reach the level of healing equivalent to the trot phase; earlier use may be excessive work for healing soft tissues.16
Following an initial period of stall rest and hand-walking, the SDF tendon should be re-evaluated using physical examination and ultrasonography to assess healing.17 Increasing exercise should be based upon examination findings rather than time elapsed. The horse should be confined to a space small enough so that it can only walk when not undergoing controlled exercise until healing is sufficient to allow canter work under saddle for one week. Please refer to Tables 20.1–5 for detailed exercise protocols.
Table 20.1
Exercise protocol following the first examination (0–60 days). Horse is confined to a stall or equivalent size paddock (12′ by 24′ maximum)
INJURY | 0–30 DAYS | 30–60 DAYS |
Mild | Hand-walk 15 minutes twice daily | Increase walking time by 5 daily minutes per week |
Moderate | Hand-walk 15 minutes twice daily | Increase walking time by 5 daily minutes per 2 weeks |
Severe | Hand-walk 10 minutes twice daily | Hand walk 15 minutes twice daily |
Table 20.2
Exercise protocol following the second examination (60–120 days). Horse is confined to a stall or equivalent size paddock (12′ by 24′ maximum)
PROGRESS | 60–90 | 90–120 DAYS |
Good | Ride at walk 25 minutes dailyIncrease 5 minutes every 2 weeks | Same protocol |
Fair | Same as above | |
Poor | Hand-walk 30 minutes twice daily | Ride at a walk for 20 minutes; hand walk for 20 minutes at another time |
Table 20.3
Exercise protocol following the third examination (120–180 days). Horse is confined to a stall or equivalent size paddock (12′ by 24′)
PROGRESS | 120–150 DAYS | 150–180 DAYS |
Good | Add a 5 minute trot set every 2 weeks | Add a 5 minute trot set every 2 weeks |
Fair | Ride at a walk for 40 minutes daily and hand walk | Add a 5 minute trot set every 2 weeks |
Poor | Re-evaluate case to determine cause and discuss further treatment options |
Table 20.4
Exercise protocol following the fourth examination (180–240 days). Horse can be turned out after riding exercise when it has been cantering five minutes for one week
PROGRESS | 180–210 DAYS | 210–240 DAYS |
Good | Add canter 5 minutes every 2 weeks | Add canter 5 minutes every 2 weeks begin ground pole exercises |
Fair | Add trotting 5 minutes every 2 weeks | Add canter 5 minutes every 2 weeks |
Poor | Re-evaluate case and discuss further treatment options |
Table 20.5
Exercise protocol following the fifth examination (240–300 days)
PROGRESS | 240–270 DAYS | 270–300 DAYS |
Good | Racing speed work, jumping or other competitive training | Ready for competition |
Fair | Add canter 5 minutes every 2 weeks | Full flat work; no racing speed work or jumping |
Poor | Re-evaluate case and discuss further treatment options |
Surgical options
If an anechoic or mostly anechoic core lesion is seen on ultrasonographic examination, ultrasound-guided tendon splitting to decompress the core lesion should be performed as soon as possible, ideally 2–14 days following injury, to prevent further compression injury of the surrounding normal fibers.
If a subcutaneous hematoma is detected, injection of hyaluronic acid between the tendon and the skin should be performed as soon as possible, ideally 2–14 days following injury to attempt to prevent development of adhesions between the subcutaneous tissue and the SDF tendon.
Superior check ligament desmotomy has been shown to improve SDF appearance in the short term; long-term results have been less encouraging. Superior check desmotomy has been associated with significantly increased strains on the SDF tendon and SL.18 Horses treated surgically were 1.2 times more likely to develop recurrent or new injuries after returning to training than horses managed non-surgically. Racehorses that have undergone a superior check ligament desmotomy are 5.5 times as likely to suffer a subsequent suspensory ligament injury as are horses without desmotomy.19
Prognosis
The prognosis is excellent for life and good for return to full athletic use, if aggressive treatment followed by controlled rehabilitation is performed. If the tendon appears 95% healed based on size, echogenicity and fiber pattern on the final ultrasound exam, the horse is at no greater risk of re-injury than of any athletic use injury upon return to full work. A superficial digital flexor tendon that has luxated from its calcaneal attachment also has a good prognosis with aggressive medical treatment for inflammation and a full rehabilitation program.
Etiology and pathophysiology
The SDF tendon, in conjunction with the suspensory ligament, acts to keep the fetlock from extending to the ground when the horse is weight bearing. The SDF actively participates in limb flexion during the swing phase of locomotion through contraction of the SDF muscle.
The SDF tendon has little margin of safety as horses in full work such as galloping or jumping generate forces near to its breaking strength.20,21 The SDF tendon and the suspensory (interosseous) ligament are the primary load bearing structures in the forelimb22 and are the soft tissues at greatest risk of injury in the horse that is working at speed. Factors that place excess load on the tendon, such as muscle fatigue which places increasing load on the much smaller, tendinous portion of the muscle/ tendon unit, poor hoof conformation/shoeing or lameness in another limb, place the tendon at increased risk of failure.
Athletic performance deteriorates in horses with SDF tendinitis due to initial lameness, followed by prolonged tendon weakness during the recovery phase. If excessive exercise is attempted while the tendon is relatively weak, the risk of tendon re-injury is high, leading to a repetitive syndrome of repeated short periods of acute lameness followed by longer periods of inability to perform regular work at a previous or expected level. If the tendon is damaged repeatedly, fibroblast damage occurs (tendinosis), resulting in inability to generate normal repair collagen. At this stage the tendon’s ability to heal is compromised.
Prevention
SDF tendinitis prevention consists of:
• increasing work load gradually rather than abruptly. A 5% increase in workload per week is generally a safe guideline
• being attentive to hoof shape and shoeing to avoid a long toe, low heel configuration and to prevent a break in pastern/hoof axis
• early recognition and treatment of other lameness to prevent compensatory tendon overload
• recognition that certain conformational faults, particularly ‘back at the knee’ conformation, load the SDF additionally and place the horse at increased risk of tendon injury when in full work.
• fifteen minutes of walk warm up prior to faster work in every exercise session will preload the SDF tendon to better withstand the forces applied without injury.
Deep digital flexor tendinitis
Recognition
History and presenting complaint
Forelimb deep digital ßexor (DDF) damage occurs most frequently in the pastern region of horses used for athletic pursuits which involve twisting and turning, such as polo, endurance riding in rough terrain or roping. In the foot region of fore- and hindlimbs, DDF tendinitis often occurs in middle-aged horses. It is often concurrent with navicular disease, particularly navicular bursitis. Hindlimb metatarsal region DDF tendinitis is most frequently seen in hunters/jumpers, primarily middle-aged geldings that have had years of work and is often accompanied by tarsal sheath synovitis.
Physical examination
Grade 1–3 out of 5 lameness is observed and is often intermittent or transient. Heat, swelling and pain will be present on palpation of the DDF.
Differential diagnoses depend on location; in the metacarpal/ metatarsal region, inferior check ligament(ALDDF or accessory ligament of the deep digital flexor tendon) desmitis is the major differential. Tarsal sheath synovitis may be associated with hindlimb DDF tendinitis. In the pastern the SDF tendon and the sesamoidean ligaments must be included in the differential diagnoses. Digital sheath synovitis is often associated with pastern region DDF tendinitis. In the foot, navicular bursitis, navicular bone changes and other causes of heel pain should be considered as differential diagnoses.
Special examination
Diagnostic nerve blocks will localize the region of the DDF involved and begin the process of elucidating the source(s) of heel pain, if present. Radiographs of the foot will provide information regarding bone and joint involvement. MRI will define both hard and soft tissue injuries and their inter-relationship MRI is providing a large amount of new information that is important in a complete diagnosis but that also needs to be interpreted in light of clinical significance.
Diagnostic ultrasonography will define the presence and extent of DDF damage (Fig. 20.7).23,24 For a diagnostic examination of the DDF within the hoof, as well as the navicular bursa and the impar ligament, the shoe should be removed and the frog should be pared to provide a level surface for good transducer contact. The foot should be soaked in water overnight to further soften the tissues. The insertion of the DDF on the solar aspect of the distal phalanx, the navicular bursa and the impar ligament can then be evaluated for disease (Fig. 20.8). Ultrasonography will also allow for sequential examinations, which are critical for the accurate assessment of healing stage of injured tendon so that an appropriate treatment and rehabilitation plan can be formulated for each stage of healing.17
Treatment and prognosis
Therapy
For general tendinitis medical treatment, please refer to the section on SDF tendinitis.
DDF tendinitis in the region of the navicular bone is frequently associated with navicular bursitis. If this is the case, therapy should include injection of the navicular bursa with a symptom modulating and preferably a disease modulating agent. Steroids remain the gold standard for anti-inflammatory activity. Hyaluronic acid, IRAP, or polysulfated glycosaminoglycan are also useful. Injection of the coffin joint rarely provides sufficient clinical and ultrasonographic signs of resolution of bursitis, even if the horse responds to coffin joint anesthesia. Reasons include:
• diffusion of local anesthetic across membranes which are not sufficiently permeable to allow diffusion of larger molecules.25
• anesthesia of local nerves proximal to the bursa, causing reduction in pain that was not the result of inflammation within the bursa.
Tarsal sheath synovitis may be treated medically in a similar fashion to the digital sheath (see following section. Tenoscopy of the sheath is an effective treatment for chronic/complicated cases with extensive synovial membrane proliferation and/or adhesions.26
Etiology and pathophysiology
The DDF tendon acts to keep the third phalanx/toe of the hoof from overextending and actively participates in flexion of the limb during the swing phase of locomotion through contraction of the DDF muscle. Factors that place excess load on the tendon include the following:
• muscle fatigue, placing increasing load on the much smaller, tendinous portion of the muscle/tendon unit, poor hoof conformation/shoeing, or lameness in another limb
• once a few fibers are damaged, strength is reduced and the tendon is predisposed to further fiber rupture with continued work
• hemorrhage at the site of ruptured fibers and associated inflammatory mediator release cause further fiber damage either through compression by hematoma expansion or the detrimental effects of inflammatory products
• palmar digital neurectomy used to treat heel pain likely leads to atrophy of the deep digital flexor tendon, placing horses at increased risk of DDF injury or rupture after the procedure. Also, following neurectomy horses lose the ability to protect the DDF tendon from over strain or to show clinical signs of DDF damage until they lose control of their ability to place the toe following complete tendon rupture.
Athletic performance deteriorates in horses with DDF tendinitis due to initial lameness, followed by prolonged tendon weakness during the recovery phase. If excessive exercise is attempted while the tendon is relatively weak, the risk of tendon reinjury is high, leading to a repetitive syndrome of repeated short periods of acute lameness followed by longer periods of inability to perform regular work.
Prevention
DDF tendinitis prevention consists of:
• increasing workload gradually rather than abruptly. A 5% increase in workload per week is generally a safe guideline
• being attentive to hoof conformation and shoeing to avoid a long toe, low heel configuration and to prevent a break in pastern/hoof axis
• early recognition and treatment of other lameness to prevent compensatory tendon overload
• recognition that ‘heel pain’ may be due to excess strain on the DDF and that navicular bursitis may lead to secondary adhesions between the bursa and the DDF, leading to DDF damage.
Accessory ligament of the deep digital flexor tendon desmitis
Recognition
History and presenting complaint
Desmitis of the accessory ligamentof the deep digital flexor tendon (AL-DDFT) is usually observed in horses that are starting into regular work if the condition is developmental, or in middle-aged horses (10–14 years) which have been in regular use, particularly as jumpers.
AL-DDFT desmitis can also occur secondary to moderately severe or severe SDF tendinitis, if the SDF tendon becomes sufficiently enlarged to contact the medial and lateral borders of the AL-DDFT. Adhesions may subsequently develop which cause AL-DDFT inflammation and damage.27
Physical examination
Grade 2–3 out of 5 lameness is present and is usually persistent. Heat, swelling and pain are felt on palpation, most often at the accessory ligament-DDFT junction in the palmar/lateral midmetacarpal region. AL-DDFT desmitis occurs less frequently at the origin of the ligament.
Differential diagnoses include DDF tendinitis and suspensory ligament desmitis. The AL-DDFT is often damaged at the midmetacarpal level, where its fibers join those of the DDF tendon.
Special examination
A high two-point nerve block (lateral and medial palmar nerves) should ablate the lameness and will confirm that the lameness is localized to the metacarpal region.
Diagnostic ultrasonography will reveal AL-DDFT enlargement, loss of echogenicity and deterioration of fiber pattern (Fig. 20.10).27 AL-DDFT desmitis and associated enlargement of the ligament may cause the DDF tendon to be completely encircled and compressed by the SDF and the AL and may be an additional source of the chronic pain often associated with AL desmitis (Fig. 20.11).