History and presenting complaint

Synovitis manifests as lameness associated with significant synovial effusion. Synovial effusion alone in young racehorses that are not showing lameness or training problems is not uncommon. However, the effusion may be significant if there is a history of training-associated problems or lameness with the horse.

Physical examination

Synovial effusion in the carpal joints can occur in both the dorsal and palmar aspects. Synovial effusion can be graded as mild, moderate or severe. Mild effusion is palpable on the dorsal aspect of the carpal joints, while severe is palpable effusion that can also be detected on the palmar aspect of the joint. It is typical to see pain with static flexion in horses with synovitis and focal pain on palpation can sometimes be appreciated in those with synovitis and other associated injuries leading to synovitis. Heat on palpation is not uncommon in horses with synovitis; however, the presence of topical medications and recent bandaging may influence surface heat.

Most horses with synovitis will be lame at the trot and, in carpal lameness in particular, wide movement of the forelimbs is appreciable. This wide movement occurs because horses with synovitis, and the resulting pain in the carpal joints, do not want to flex their carpi. Consequently, they will circumduct the limb, leading to a wide moving gait. Furthermore, in cases of carpal synovitis, it is quite common to see worsening of the lameness after flexion.

Special examination

Regional anesthesia of the carpus, although often unnecessary for diagnosis of synovitis, can be accomplished by performing a median and ulnar nerve block after perineural anesthesia below the carpus has been performed. Intra-articular anesthesia is usually not necessary to diagnose synovitis of the carpal joints but occasionally may be needed to confirm carpal disease and rule out other diseases in the limb. As an example, it may be prudent to block the carpal joints and eliminate the lameness there in order to document additional lameness in another area of the limb. Although carpal joint blocks have been described elsewhere, it is important to remember that the radiocarpal and intercarpal joints should be blocked separately. Radiographs are usually negative; however, good-quality radiographs in multiple views are necessary to rule out any small or subtle injuries. In many cases of primary synovitis, it is not uncommon to see soft tissue thickening or dorsal displacement of the fat pad on the dorsum of the carpus on the radiographs.

Advances in ultrasonographic examination of joints have given clinicians a better impression of soft tissue injuries. Because soft tissue injuries can lead to synovitis, documentation of capsular and synovial lining thickening and edema can help not only to diagnose the primary problem but also to monitor therapy over time. Ultrasound also allows the clinician to rule out extracapsular thickenings such as hygromas and synovial hernias. An in-depth review of ultrasonographic examination of joints has been documented.¹

Synovial fluid can also be evaluated subjectively. It is not uncommon in cases of synovitis to see a watery, clear to light yellow fluid. In some cases, there is increased opacity and flocculants in the fluid. In cases such as this, laboratory examination of the synovial fluid may be necessary to rule out septic arthritis.

Laboratory examination

Synovial fluid analysis results can be variable in cases of synovitis although most white blood cell counts are less than 1000 cells/mm³ and total protein concentrations are generally between 2.5 and 4.0 g/dL. Biomarker analysis often shows elevated concentrations of prostaglandin E2.²

Diagnostic confirmation

The lack of radiographic findings, which rules out osteochondral fragmentation and fracture, is often enough to lead to a diagnosis of synovitis, although a negative diagnostic arthroscopy is needed to completely rule out intra-articular ligament disease. It is often difficult to justify diagnostic arthroscopy in cases that are most likely synovitis compared to intra-articular ligament injury; therefore most veterinarians will monitor response to medical therapy. Refractory cases are then easier to justify as needing surgery as synovitis usually responds well to intra-articular medications. MRI is not required to make a diagnosis of synovitis although this condition is readily detectable when performed (Fig. 17.1).

Therapeutic aims

The goal of therapy is to provide timely, effective anti-inflammatory medications either systemically, locally or topically.

Therapy

Systemic anti-inflammatory medications, such as non-steroidal anti-inflammatory medications or intravenous hyaluronic acid, are the simplest forms of therapy which are often very effective for controlling synovitis. However, intra-articular anti-inflammatory medication in the form of corticosteroids and/or hyaluronic acid may be necessary to provide effective treatment. Interleukin-1 receptor antagonist protein (IRAP) or topical diclofenac sodium can also be used for refractory cases. Physical therapy methods such as ice, hydrotherapy, daily range of motion exercises and walking are often used in addition to medications. Intra-articular morphine (20 mg) with ropivacaine (20 mg) has been used in experimental settings to provide up to 24 hours of pain relief for acute cases of synovitis.³

Prognosis

The prognosis for synovitis is often excellent for resumption of athletic training with rapid, effective therapy barring predisposing conformational abnormalities, osteochondral disease or intra-articular ligament disease.

History and presenting complaint

Capsulitis can be caused by several disease processes so the history can be quite variable. For instance, it is not uncommon to see capsulitis in horses with a history of carpal disease such as osteochondral fractures, fragmentation or ligamentous injuries. However, capsulitis can also result from non-articular diseases, such as extracapsular ligament damage or capsular injury. In some cases, capsulitis can also occur because of acute injury, which may lead to edema and possibly fibrosis of the joint capsule. In some recurrent or unresponsive idiopathic synovitis cases, capsular thickening and scarring can also result. In most of these cases in athletes, the animal will fail to train and will have chronic unresponsive joint disease.

Physical examination

Horses with capsulitis typically show soft tissue thickening over the dorsal aspect of the carpus. However, the severity of effusion can be difficult to appreciate because of this thickening. Range of motion is often restricted and maximal flexion often results in a painful response. At the trot, these horses typically move wide and are often significantly worse after carpal flexion. Occasionally, pain on palpation will be apparent on the dorsal aspect of the carpus, especially in acute cases. Although capsular swelling is difficult to appreciate on the palmar aspect of the joint, horses with palmar capsular pain are extremely sensitive to carpal flexion.

Special examination

Horses with acute capsular changes may show no radiographic changes; however, those horses with capsular tearing, especially at the insertion of the capsule into the bone, will often show enthesophyte formation several weeks after injury. Enthesophytes can vary in severity and location; however, in most equine athletes, especially racehorses, enthesophyte formation on the dorsal aspect of the carpal bones is quite common (Fig. 17.2). Ultrasound examination of the joint capsule in horses with acute capsulitis will often show edema formation within the capsular tissues, and thickening of those tissues. Nuclear scintigraphy may also be helpful in some cases, especially in the vascular and soft tissue phases. CT examination may be of little use in these cases unless a primary osteochondral disease process is leading to the capsular change. As for synovitis, MRI is rarely needed to make a diagnosis of capsulitis but is often seen with this modality (Fig. 17.1).

Laboratory examination

Synovial fluid analysis in horses with capsular damage is often quite variable.

Diagnostic confirmation

As mentioned previously, radiographs are usually only suggestive of capsular changes. In particular, enthesophyte formation certainly indicates previous capsular insertional damage and peri-articular lysis may indicate acute inflammation at the insertion. Even though capsular damage can occur by itself, other intra-articular diseases must be ruled out, either by the special examinations mentioned above or, as in most cases by diagnostic arthroscopy.

Finally, capsulitis is sometimes diagnosed based on response to therapy. For instance, some cases of acute capsular tearing may respond well to intra-articular anti-inflammatory medications. Unlike secondary capsulitis, which occurs in response to other osteochondral diseases, primary capsular damage will usually respond to medical therapy. However, this is dependent upon the severity of damage.

Therapeutic aims

The principal therapeutic aim is to remove the primary disease. In cases of secondary capsular damage, the primary objective is to remove the intra-articular damage that is leading to capsulitis. Second, inflammation must be reduced by either systemic or intra-articular methods. Finally, because capsular disease often leads to scar tissue formation, methods that help restore function and range of motion are essential to decrease scar tissue formation. Effective regimens include passive range of motion, hypothermia/hydrotherapy, massage therapy and progressive increases in exercise in an attempt to restore full function to the joint.

Therapy

Arthroscopic removal or fixation of the primary problem is essential to overcoming capsular damage. Systemic and intra-articular anti-inflammatory medications and physical therapy, including passive range of motion, are also essential in dealing with capsular damage. Topical diclofenac cream is also an effective medication.

Prognosis

The prognosis in cases with capsular damage can be quite variable. In cases of acute, mild capsulitis or capsular damage, the prognosis is usually quite good with prompt identification of the disease process and therapy. However, severe cases of capsular damage can be quite limiting to the prognosis of an athlete and often require ongoing medical management to continue competing. Decreased range of motion and pain on flexion often hinder the horse’s ability to use the limb properly. The prognosis for cases of secondary capsulitis or capsular damage is dependent on the severity and form of the primary disease process.

History and presenting complaint

Most horses with osteochondral fragmentation appear to have a history of acute lameness isolated to the carpal joints. However, in some cases, especially in racehorses, synovial effusion or synovitis often precedes diagnosis of osteochondral fragmentation. Unusual traumatic events, e.g. recovery from anesthesia, can also be rare causes of osteochondral fragmentation.

Physical examination

Clinical signs in horses with osteochondral fragmentation are very similar to those in horses with synovitis.

Special examination

Radiographs are often diagnostic in cases of osteochondral fragmentation; however, radiographs often underestimate the severity of damage. CT examination has proven beneficial in diagnosing unusual cases of osteochondral fragmentation, as has MRI.

Laboratory examination

Standard synovial fluid analysis is not beneficial for identifying cases of osteochondral fragmentation. However, synovial fluid markers (specifically type II collagen degradation products) have been shown to increase following OC injury within the carpus and have also been correlated with the severity of injury.⁴ Other biomarkers have also been shown to increase significantly above exercise related increases⁵ including prostaglandin E2 concentrations which are raised in synovial fluid following OC fragmentation². Although not commonly performed, monitoring of these may lend useful information regarding the severity of pathological changes to articular cartilage and the degree of the inflammatory response within the joint. Cartilage oligomeric matrix protein (COMP) has also been shown to be elevated in the urine of horses with osteochondral fragmentation with osteophyte production⁶ and also in synovial fluid⁷, but not in joints with osteoarthritis.⁸

Diagnostic confirmation

Diagnostic arthroscopy is by far the best means of characterizing osteochondral fragmentation, identifying any associated gross pathological changes to articular cartilage and also has the benefit of allowing for treatment of the disease. In most cases, standard radiographic projections of the carpus including flexed and skyline views, are used for confirmation of disease (Fig. 17.2). The palmar surface of the carpal bones must be closely examined on radiographs prior to surgery so that arthroscopic examination of this area is performed, if necessary (Fig. 17.3).

Therapeutic aims

Removal of the fragment is essential for restoring the joint to normal function. Accurate grading of articular cartilage lesions is also essential and, of course, much like all other cases, decreasing inflammation is also essential.

Therapy

Arthroscopic removal of the fragment and use of anti-inflammatory medications are necessary in treating these diseases. Furthermore, chondral supplementation, be it by intra-articular or systemic means, is also beneficial, especially in severe cases of osteochondral fragmentation. The authors also find physical therapy to be beneficial in these cases, to limit the amount of capsulitis that can accompany osteochondral fragmentation. Selected use of intra-articular triamcinolone acetonide with hyaluronic acid may also be of benefit in some cases.⁹ Selective use of subchondral micropicking with mesenchymal stem cell therapy as an intra-articular injection may benefit cases with more severe cartilaginous degeneration.

Prognosis

The prognosis following arthroscopic removal of the osteochondral fragment varies with articular cartilage erosion severity. In particular, return to racing at equal to or better than before surgery was 71.1% for grade 1 lesions, 75% for grade 2 lesions, 53.2% for grade 3 lesions and 54% for grade 4 lesions.¹⁰ Grade 4 lesions (which involve a significant loss of the subchondral bone) have also been repaired with 2.7 mm lag screw fixation with reported success of 68% return to racing.¹¹ In addition the presence of palmar carpal fragments with or without dorsal osteochondral fragmentation has a negative effect on prognosis. When present, these palmar fragments can be a continual source of inflammation and can themselves be associated with cartilaginous degeneration/loss¹² and removal should be attempted where possible.

History and presenting complaint

Acute, severe lameness often accompanies osteochondral fracture; however, some horses may not be lame acutely but rather may manifest severe lameness within 24 hours.

Physical examination

Horses with osteochondral fracture appear to be severely lame compared to horses with other disease processes within the carpus, and they are very responsive to carpal flexion. In some cases, the horse may actually resent even partial flexion of the carpus and the clinician must take care when performing the flexion test.

Special examination

The authors do not recommend intra-articular diagnostic analgesia in cases of severe carpal lameness with severe response to flexion. Instead, a complete series of radiographs is essential, including skyline and, in some cases, special views to highlight the fractures. CT and MRI are also valuable, especially in assessing those fractures that are not absolutely clear on radiographs. However, since both modalities require general anesthesia, it is recommended that the surgeon perform these imaging studies just prior to surgery so the fracture can be repaired to prevent further comminution that may occur during recovery.

Laboratory examination

There are no synovial fluid parameters that are specific for osteochondral fracture; however, hemorrhage into the joint is not uncommon.

Diagnostic confirmation

Radiographs and diagnostic arthroscopy are helpful to confirm the diagnosis. Visualization of the slab fracture in orthogonal planes helps to determine the treatment recommendation i.e. removal or internal fixation. Of note, sagittal slab fractures are best seen on a DL-PaMO view.

Therapeutic aims

The aim of therapy is to restore the articular surface to as normal congruence as possible and to provide axial support to the limb.

Therapy

Internal fixation or removal of the fracture fragment via arthroscopy are considered the treatments of choice. Only small fractures or fractures within the palmar aspects of the joints should be removed and usually only if they are not suited for screw placement. Since there is often significant articular cartilage loss, systemic and/or intra-articular chondro-protective agents are often used to treat associated articular cartilage damage. Mesenchymal stem cells may provide regenerative benefit to the cartilaginous surfaces as a part of the rehabilitation program.

Prognosis

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