Ankylosis
Ricardo Loinaz
■ Definition and Etiology Ankylosis refers to the abnormal fusion of bones in a joint, which can occur naturally or as a desired result of treatment. Facilitated ankylosis refers to a medical fusion and thus is different from arthrodesis, or surgical fusion, of two or more bones into a single structure.1 Naturally occurring ankylosis is often the result of disease or trauma to the joint and bones involved.
Septic arthritis with subsequent DJD and associated prolonged therapy, including joint immobilization, are often the inciting factors for ankylosis. Congenital ankylosis is the absence of an articulation, and it is a rare condition in horses and cattle, often associated with other congenital abnormalities.2 Congenital ankylosis of the DIJ in both hindlimbs, with concurrent dysplasia of the distal sesamoid bone in all four limbs, has been reported in a 2-year- old Arabian horse.3 In calves and foals, congenital ankylosis may occur between vertebrae or in multiple joints of the limbs, resulting in dystocia related to musculoskeletal inflexibility.2Joint fusion is initiated by biomechanical and biochemical factors, leading to instability and degeneration of cartilage and chondrocytes.2 Periarticular contracture, joint capsule fibrosis, and chronic muscle spasm all contribute to joint immobility, which leads to synovitis and cartilage destruction. Ossification of periarticular soft tissues develops, resulting in partial bone bridging across the joint. The final stage of ankylosis is complete bone bridging with trabecular bone and joint obliteration.
Common sites of ankylosis in horses include the distal hock joints (distal intertarsal [DIT] and tarsometatarsal [TMT]), the thoracolumbar intervertebral articulations, and the proximal interphalangeal (PIP) joint.
These low-motion joints are more likely to achieve complete bone bridging without surgical intervention. In high-motion joints (antebrachiocarpal, mid- carpal, metacarpophalangeal, scapulohumeral, and distal interphalangeal), naturally occurring complete bone bridging is rare, and the resulting cartilage degeneration leads to severe lameness. In these cases, surgical fusion or arthrodesis using internal fixation techniques is required if treatment is to be attempted.4 Large animals with vertebral ankylosis may show neurologic deficits caused by bony impingement on the spinal cord or by dynamic compression leading to abnormal motion or spinal ligament hypertrophy.2■ Clinical Signs and Differential Diagnosis Indications for ankylosis include stiffness of a joint and associated immobility, degenerative joint changes, decreased range of joint motion, and varying degrees of lameness. Decreased ROM is most obvious if high-motion or multiple joints are involved. Degree of lameness can range from mild to severe, particularly in the acute phase when local inflammation contributes to the degree of lameness. Enlarged and thickened periarticular structures, conformational abnormalities, disuse atrophy of muscles or disuse osteopenia of bones, and gait stiffness may also be identified. Once bone bridging is complete and no articular cartilage remains, the condition is no longer painful, and the articulation is immobile.
Differential diagnoses include soft tissue injuries or contracture, intraarticular or periarticular adhesions, joint luxation, neoplasia, arthrodesis, spondylosis, an intraarticular mass, osteomyelitis, and fracture. Diagnosis of ankylosis should be based on a complete physical and musculoskeletal examination, lameness evaluation, and radiography. Multiple radiographic views should be available for definitive diagnosis, but additional imaging techniques such as ultrasonographic evaluation of relevant soft tissues and joint spaces, CT, and MRI may be useful and provide more detailed information that may influence the treatment option chosen.
■ Treatment and Prognosis Treatment in the acute phase focuses on providing comfort to the animal, because ankylosis is a chronic and progressive disease process. A complete treatment plan should be tailored to the specific case and is often determined by the presence or absence of infection or severe joint instability. Antiinflammatory medications (phenylbutazone, firocoxib, flunixin meglumine, intraarticular corticosteroids) are necessary in most cases. Additional oral joint supplements, hyaluronic acid, or polysulfated polysaccharides may also be beneficial as chondroprotectants. Although joint immobilization and a decrease in exercise are often necessary, low-level exercise appears to be beneficial in some cases because it helps increase and stimulate development of new bone formation, promoting faster and more complete ankylosis.2 Unstable joints or actively septic joints, however, require immobilization with splints or casts to allow the fusion to progress and improve the animal's comfort level. Animals that remain lame, have end-stage joint disease, or are not completing ankylosis naturally require surgical or chemical arthrodesis to improve the comfort level and chances of returning to performance activity.
Different methods of facilitated ankylosis can be used to promote joint fusion. The speed at which complete bone bridging occurs may be enhanced through chemical chondrocyte destruction or surgical obliteration of the articular cartilage. Chemical methods of ankylosis include the use of sodium monoiodoacetate (MIA) and ethyl alcohol, but MIA has been associated with considerable morbidity and signs of severe pain.1 In addition, postinjection soft tissue swelling, progression of osteoarthritis to adjacent unaffected joints, severe soft tissue necrosis, variable length of convalescence, and inconsistent outcomes are why MIA-mediated ankylosis can no longer be recommended.5 Ethyl alcohol ankylosis works via nonselective protein denaturation and cell protoplasm precipitation and dehydration.
One of the first controlled studies investigating the use of ethyl alcohol in horses found that 70% ethyl alcohol injected in the TMT joint of healthy horses with no radiographic evidence of joint disease resulted in a pain-free fusion by 4 months in 8 of 16 horses and complete fusion by 12 months post injection in 15 of 16 horses.6 A recent study evaluated the safety and efficacy of ethyl alcohol-mediated ankylosis of the DIT and TMT joints in horses with lameness localized to those joints and found a significant reduction in posttreatment lameness in all treated horses but evidence of joint collapse and progressing ankylosis by 3 months post injection.1 Another study looked at 24 horses that received ethyl alcohol injections in the distal hock joints; 52% had improved lameness scores at 6- and 9-month follow-up, whereas 19% had deteriorated.7 A recent study looked at 70% ethyl alcohol injection alone or in combination with lag screw placement for PIP fusion, and in both instances alcohol treatment failed to produce reliable fusion of PIP joints.8 Another recent study looked at facilitated ankylosis of PIP joints using ethyl alcohol and reported that 50% of horses were sound and 34% were improved but not sound at time of follow-up.9 The median time for horses to become sound enough to return to work in this study was 8 months, suggesting that ethyl alcohol-facilitated ankylosis may be more effective and work faster in DIT and TMT joints than in PIP joints.Facilitated ankylosis via surgical debridement of articular cartilage and use of casts or transfixation casts is recommended in the initial treatment of septic PIP joints instead of surgical arthrodesis in the acute phase.5 Laser-facilitated ankylosis using a neodymium-doped yttrium aluminum garnet (Nd:YAG) or a diode laser to destroy articular cartilage by superheating and vaporizing synovial fluid, resulting in chondrocyte death, can also be used for facilitated ankylosis. Experimental studies using laser-facilitated ankylosis in DIT joints found that partial ankylosis was achieved in 5 to 12 months.5 Transarticular drilling has been used as a method for ankylosis of the DIT and TMT joints, alone or in combination with laser application, and estimates of outcomes suggest that this technique is 47% to 85% successful.5
Ankylosis may require 6 to 12 months for complete bone bridging after surgical or chemical treatment methods. This process can take several years if left to natural ankylosis. Prognosis depends on which joint is involved and the expectations for use of the animal. Low-motion joints have a good prognosis for returning the horse to soundness and athletic performance once the fusion process is completed. High-motion joints have a poor prognosis for return to use in horses.