The Carpus



The Carpus


Alexander J. Daniel and Christopher E. Kawcak



Introduction


Diseases of the carpus commonly affect racehorses, in which repeated stress from training and racing can lead to degradative changes within synovium, joint capsule, articular cartilage, subchondral bone and ligaments. These chronic changes often lead to acute problems ranging from synovitis to catastrophic injuries. Identification and prevention of the chronic processes and risk factors that lead to the development of clinical disease should be the ultimate goal. With advances in biomarkers, three dimensional imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI) our understanding of disease processes has progressed. Consequently therapeutics have advanced and become more specified towards certain conditions which has had a profound effect on our ability to effectively treat conditions. In many instances, the clinical manifestation of carpal disease results in synovial effusion, pain on flexion with or without reduction in the range of motion of the limb and therefore additional testing is required to characterize disease. This can be achieved with radiographic imaging, ultrasound, three dimensional imaging (CT and MRI), biomarker analysis and diagnostic arthroscopy.


Carpal disease in racehorses is common and the lesions occur in consistent areas. This permits in-depth clinical study of carpal diseases, allowing practitioners to give an accurate prognosis for a particular injury based on these studies. Carpal injuries can also affect other types of equine athlete; however, these disease processes are usually manifested as acute, traumatic injuries which sometimes occur in uncommon areas of the carpus. In either situation, accurate diagnosis of these conditions is essential when determining the prognosis for these types of injuries however this has historically been difficult due to lack of sufficiently sized clinical studies.



Synovitis






Recognition




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.




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).




Treatment and prognosis




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







Capsulitis






Recognition





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).





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.



Treatment and prognosis









Osteochondral fragmentation (chip fracture)






Recognition






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).




Treatment and prognosis





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.



Etiology and pathophysiology


Evaluation of post-mortem cases9 has shown that most osteochondral fragments in racehorses are acute manifestations of chronic disease processes. In particular, most fragments occur in areas of stress-induced subchondral bone sclerosis, in which micro damage exceeds healing and acute fragmentation results. Although there is a healing response, as shown by the presence of granulation tissue at these sites, continued training ultimately results in fragmentation through the granulation tissue bed.





Osteochondral fracture (slab fracture)






Recognition








Treatment and prognosis




Jun 18, 2016 | Posted by in EQUINE MEDICINE | Comments Off on The Carpus
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