Orthopaedic Conditions in Geriatric Cats
Philip Witte, BSc, BVSc, MRCVS
Harry Scott, BVSc, Cert SAD, CBiol, MIBiol, DSAS (Orth), FRCVS
Age is frequently a diagnostic pointer in small animal disease. Cats live longer and the disease patterns in our feline patients are changing. When presented with an older cat that shows evidence of a musculoskeletal disorder, the clinician should consider conditions that have a tendency to be specific to this age-group of patients as well as more universal problems; this article offers an overview on some of the most common problems encountered in geriatric patients.
Degenerative joint disease
Degenerative joint disease (DJD) is a general descriptive term for degenerative changes occurring in any type of articulation. Osteoarthritis (OA) is a specific type of DJD that affects diarthrodial synovial articulations. It is characterized by deterioration of articular cartilage, osteophyte formation, bone remodeling, changes in peri-articular tissues and low-grade non-purulent inflammation. Feline DJD is common. In one study 90% of a hospital’s feline population showed evidence of DJD in one or more joints (1). In the past OA has been overlooked as a cause of morbidity in cats but recent evidence suggests that the disease is more prevalent than previously presumed (2). In cats overt lameness is not the most significant clinical sign of OA and radiographic severity often correlates poorly with clinical signs. In one study only 33% of cats with OA showed obvious lameness (3). Cats are less demonstrative than dogs in indicating that they are in pain, and resentment to handling, aggression and lack of responsiveness to human attention may be the most obvious manifestations of both acute and chronic pain. Radiography should be performed in geriatric cats where these clinical signs are observed. Radiographic signs of OA include osteophytes, enthesiophytes, subchondral bone sclerosis, bone remodeling, soft tissue mineralization (intra-articular, capsular or extra-articular), joint capsule thickening and soft tissue swelling (Figures 1-4). Entheses are the osseous attachment sites of tendons and ligaments; pathology at these sites is known as enthesiopathy and generally results in the formation of enthesiophytes. In the spine enthesiophytes are termed spondylosis deformans (see below). Degenerative enthesiopathy may accompany OA and other joint disorders such as synovial osteochondromatosis (Figure 5) but its sole presence is not indicative of OA and enthesiophytes may be seen in elderly cats as an incidental finding.
Treatment options include the usual triad of conservative management (body weight restriction, exercise modulation and medical therapy), and salvage surgeries. Surgical options include femoral head and neck osteotomy or total hip replacement to address lameness associated with coxofemoral osteoarthritis, or arthrodesis for some other joints. Cats tend to limit their own activity appropriately when they have painful joints (which may contribute to the late recognition of OA in this species), but management may include techniques such as feeding from the floor and providing steps up to favorite perches to minimize the amount of jumping required.
Hyperparathyroidism is an overactivity of the parathyroid glands resulting in an excessive production of parathyroid hormone. Hyperparathyroidism leads to osteopenia and predisposes to pathological fracture (Figure 6). The condition most commonly occurs in geriatric cats secondary either to chronic kidney disease (renal secondary hyperparathyroidism) or hyperthyroidism (hyperthyroid-related hyperparathyroidism).
No discussion of the elderly cat is complete without a mention of hyperthyroidism, as it is the most common endocrine disorder in the species. Hyperthyroid cats have a significant derangement of calcium metabolism with a variable degree of secondary hyperparathyroidism. Hyperthyroidism has also been shown to cause a severe reduction in bone density (thyroid hormones favor bone resorption) in humans which has been reported to lead to pathological fractures in untreated chronic cases (4). It may be prudent to perform serum biochemical testing and urinalysis to ascertain both renal and thyroid function in any elderly cat presented with a fracture, particularly where the bones appear osteopenic radiologically, prior to consideration of repair.
Treating hyperparathyroidism which is secondary to kidney dysfunction will include standard therapies for renal disease, whilst if hyperthyroidism is present treatment options include thyroid ablation using radioactive iodine, surgical thyroidectomy and medical management with anti-thyroid drugs (5). Bone mineral density improves following treatment in humans (4), and appropriate therapy of hyperthyroidism may be expected to result in a reduction in the risk of hyperparathyroidism-related fractures in cats.
Spondylosis of the feline vertebrae is most commonly seen in the thoracolumbar and lumbosacral regions of the spine of older cats (Figure 7). The pathogenesis is related to the formation of enthesiophytes associated with degeneration of the annulus fibrosus of the intervertebral disc. Spondylosis deformans may be seen either as an incidental finding or may be associated with mild to moderate spinal pain. Spondylosis deformans on plain radiography in the presence of neurological dysfunction is an indication for more advanced imaging and should not be considered a diagnostic finding (Figure 8). Note that Hansen type I and II intervertebral disc disease has been reported in cats (6), and surgical management of these conditions has resulted in more favourable outcomes in cases in the literature (7).
Aortic thromboembolism is one of the most common causes of hindlimb paresis and paraplegia in cats. It is usually secondary to cardiomyopathy and left atrial dilatation. Thrombi form in the dilated left atrium or auricle and fragments (emboli) break off and travel through the blood vessels, occluding the distal aorta at the level of the iliac arteries by formation of a “saddle thrombus” (Figure 9). Occasionally thromboemboli may lodge at other sites. The presence of the clot then triggers local vasoconstriction which further reduces circulation to the hindlimb. Ischemia leads to myopathy and neuropathy of the affected limbs. Reperfusion injury can occur when circulation returns and potentially fatal arrhythmias can result secondary to hyperkalemia. The typical presentation is peracute paraplegia, pain and dyspnea, which can mimic the signs seen in cats following unobserved pelvic/spinal and thoracic trauma resulting from a road traffic accident. Physical examination will confirm an absence of femoral pulses, cold distal limbs and cyanosed pads, firm hindlimb muscles, absence of deep pain perception, lack of anal tone and a distended bladder in severe cases. Signs of cardiac disease such as tachypnea, tachydysrhythmia, heart murmur and gallop sounds may also be evident. Serum biochemistry abnormalities include elevated muscle enzymes and lactate and various manifestations of poor renal perfusion. Treatment options are numerous (8) and in-depth discussion is outwith the scope of this review - the clinician is directed to current literature for full details. However options include immediate analgesia, oxygen supplementation, frusemide (if pulmonary edema is present) and intravenous fluid therapy to address hyper kalemia, renal hypoperfusion and cardiovascular shock. Therapy after the initial 6-12 hours involves vigilant monitoring of ECG, acidosis and potassium levels, with appropriately targeted medical treatment. Heart therapy may be required for congestive heart failure in the medium to long term and thromboembolism prophylaxis (aspirin, clopidogrel, low molecular weight heparin), all with unproven efficacy, may be administered to prevent the risk of future episodes.
Neoplasia of the skeletal system is uncommon in cats. Most bone tumors in cats are malignant, with osteosarcoma, chondrosarcoma (most commonly arising from the mandible, proximal tibia and scapula) and fibrosarcoma being most common (9) (Figure 10). Treatment by aggressive surgery (such as amputation) can be curative in cases of primary bone neoplasia, though meticulous staging (local biopsy, thoracic radiography in three views, abdominal ultrasonography) should be performed prior to consideration of such a procedure.
When faced with possible musculoskeletal problems, lameness, stiffness and weakness are common presenting signs with older cats; a thorough clinical examination, coupled with relevant diagnostic tests, should enable the veterinarian to work towards a definitive diagnosis. Age can be a diagnostic pointer in many of these conditions.
This article was kindly provided by Royal Canin, makers of Mobility diet for dogs and cats. For the full range please visit www.RoyalCanin.co.uk or speak to your Veterinary Business Manager:
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