Feline Orthopedic Disease

By Sue Casale, DVM, DACVS
angell.org/surgery
surgery@angell.org
617-541-5048

Cats and dogs can be affected by many similar orthopedic conditions.¹ Because cats are a different species, they do have some unique conditions and anatomic differences when compared to dogs which may alter presentation, treatment and prognosis.¹ Cats also have different lifestyles than dogs. Unlike most dogs, cats are generally not known to be athletic. They are light and agile and have the ability to jump and climb which allows them to escape when threatened. They are sprinters, not long distance runners and tend to hunt for their food by stalking the prey, and pouncing. Anatomically, cats have fewer bones than dogs. They have a clavicle but it is floating which allows them to squeeze through smaller spaces. They have very large eye sockets and bigger eyes which is helpful because they are nocturnal and makes it easier for them to see at night. Cats also have fewer teeth and their jaw is short with a hinge joint so no lateral motion. They do not grind their food and instead eat it in chunks.

The cat appendicular skeleton has numerous subtle differences compared to dogs. Cats tend to have a more shallow acetabular fossa and this must be taken into account when interpreting radiographs for hip dysplasia.² Cats have a high degree of pronation and supination in their elbow joint and about 40% will have a sesamoid in the supinator muscle that can be mistaken for a chip fracture.² Their ulna distal growth plate is straight resulting in fewer angular limb deformities. Cats typically have 18 digits, 5 on each front paw and 4 on each hind paw. Polydactaly is seen in cats, most commonly on the front legs, with the highest number digits reported is 28.

Examination of the lame cat can be difficult. Owner history is often not helpful because most injuries are not witnessed. Cats can be highly anxious in a hospital setting and may be aggressive. Sedation with gabapentin and/or trazodone, prior to the appointment may be needed. Gait examination is almost impossible as cats tend to refuse to walk on command and may slink into a hiding place. A laser pointer or flashlight can be used to get a cat to move around the exam room but encouraging owners to obtain video footage of their cats limping at home can be the most useful tool to examine their gait.

Hip dysplasia is seen in 6.6% to 32% cats, depending on the breed.^3,4,5 Cats tend to show more radiographic signs of hip dysplasia with degenerative change on the craniodorsal acetabulum with minimal remodeling of the femoral head and neck^.1 Treatment is similar to dogs’ with medical management being the first recommendation. Environmental changes such as a low edge litter box and steps to the bed/window/couch to avoid jumping can be very helpful. Other recommendations include weight loss, physical therapy, diet modulation (omega-3 fatty acid rich), neutroceuticles and pain medication. Surgical management with either a femoral head and neck ostectomy (FHO) or total hip replacement can be considered in cases refractory to medical management. Coxofemoral luxations are seen in cats secondary to trauma.¹ Closed reduction can be attempted with about a 50% success rate. Cats do not tolerate any type of sling and it is not recommended as it has not been shown to prevent re-luxation. FHO, total hip replacement or toggle pin stabilization can all be used to treat hip luxations.⁶ Slipped capital femoral epiphysis or spontaneous femoral capital physeal fractures occur without trauma in young, large, neutered male cats.^7,8,9 The condition can be unilateral or bilateral. Castration at an early age delays physeal closure. Histologically, the physis appears to have irregular chondrocyte clusters in abundant extracellular matrix which differs from what is seen with a traumatic fracture.⁹ More than half of the cats seen with this condition are Maine Coon cats.⁸ Treatment is FHO or total hip replacement.

Right femoral neck fracture in a young cat

Cats can experience elbow luxations from trauma. These can be closed reduced or may require open reduction and surgical stabilization.  Osteoarthritis is common in the feline elbow (17% of cats >12 years of age) but literature is lacking on elbow dysplasia in the cat.¹⁰ Case reports of fragmented medial coronoid process exist but a majority of cases of osteoarthritis in cats are more likely due to a subtle mal-articulation or low grade trauma to the joint.¹¹ Cats tend to have little crepitus, effusion or loss of range of motion. Peri-articular thickening is the most common clinical sign.

Ectopic mineralization disorders seen in cats include osteochondromas, osteochondromatosis, synovial osteochondromatosis, Scottish Fold osteochondrodysplasia, and medial humeral epicondylitis (MHE).^12,13,14,15  Osteochondromas are benign, slow growing solitary lesions found in middle age cats. Prognosis is good with surgical excision although recurrence is common. Osteochondromatosis is an aggressive expansile lesion of young cats that is associated with the feline leukemia virus. It has characteristics of malignancy, has continuous growth and the prognosis is poor.¹² Synovial osteochondromatosis consists of multiple well circumscribed intra-articular mineral opacities. This condition is benign and is thought to be secondary to chronic inflammation. They can be excised but tend to recur if the source of the inflammation is not treated. MHE is an avulsion of the flexor tendons from the medial epicondyle with resultant calcification. This is thought to occur from repetitive trauma such as jumping from a height. MHE is often treated medically but surgery has a better prognosis.¹³ Scottish Fold osteochondrodysplasia is an inherited defect in endochondral ossification. This results in severe osteoarthritis, synovitis and periarticular bone formation in the lower limb joints. There is no treatment for this condition and long term pain control is required. Meniscal mineralization, seen on radiographs, is common in cats with 37% of stifles in one study.¹⁶ This may be a response to degenerative change within the stifle joint or it may be a normal variant. The mineralization may be small, well-circumscribed and surrounded by normal fibrocartilage or it may be large and within the joint capsule or fat pad. The larger mineralizations are more likely to be associated with a cranial cruciate ligament rupture.¹⁷

Osteochondroma associated with a metacarpal bone

Cranial cruciate ligament (CrCL) ruptures are less common in cats because their CrCL tend to be larger than the caudal cruciate ligament (CaCL) which is the opposite of what is seen in dogs. Patella luxations are also less common in cats but mild subluxation of the patella is considered normal in this species so care should be taken when diagnosing this condition in cats. Patella fractures may be traumatic although most cases are atraumatic and are believed to be stress fractures in young cats.¹⁸

Carpal injuries are rare in cats and are most commonly traumatic in origin.¹⁹ Tarsal injuries are much more common with talocrural luxations seen most frequently.²⁰ Arthrodesis of the joints can result in very good function in most cats. Metacarpal and metatarsal fractures can be treated with external coaptation or internal stabilization with external coaptation. Cats also tolerate stabilization with an external skeletal fixator very well. Fractures and luxations of the digits occur in cats but tumors and infection are also seen. Onychectomy can result in subtle behavioral changes which may indicate chronic pain, such as aggression, biting and inappropriate litter box behavior.²¹

Many orthopedic conditions in cats result in chronic pain and require some degree of management. Treatment of chronic pain is difficult in cats. Non-drug therapy such as acupuncture and laser is often the first line of treatment because of the side effects of medications in cats. One survey of veterinarians showed that gabapentin was the most commonly prescribed medication for chronic pain in cats.²² We do not have clinical data supporting its use in cats but it has a perceived high safety margin. Tramadol was shown to subjectively improve quality of life in 85% of cats being treated for osteoarthritis.²³ Palatability may limit its usefulness. Further research into a safe, effective medication for treatment of chronic pain in cats is necessary.

Meniscal mineralization with synovial osteochondromatosis

Scottish Fold osteochondrodysplasia

References

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