'For every diagnosis missed for not knowing, ten are missed for not looking.'¹

Most lameness in cats can be attributed to traumatic fractures or abscesses. Other causes can present more of a diagnostic challenge to the clinician and some of the conditions that cause lameness are unique to the cat.^2,3 A thorough examination of the cat is important to localise the problem, and distinguish neurological from non-neurological causes of lameness and identify multiple problems. Cats with obvious gait abnormalities due to an open hock luxation for example may have other more proximal injuries such as femoral head and neck fractures or a dislocated hip that may be missed if a thorough examination is not performed. A full description of orthopaedic examination of the cat is given in Chapter 1 of Feline Orthopaedic Surgery and Musculoskeletal Disease² and in an article by Kerwin 2012:¹ a summary of pertinent points is given here. It is necessary to have a calm and patient approach to examining the cat. Ideally the examination is done in a room that is kept free from dogs and in a room that has no escape routes or hiding places.

Visual Exam of Gait - Reduced Weight Bearing or Abnormal Stance

An area should be identified that is free of encumbrances where cats can hide and be difficult to extricate. It can be useful to place the cat at one side of the room and its basket at the other end as it may choose to seek refuge in the basket. Although have an assistant ready to shut the door and prevent its re-entry if the examination has not been completed. If the cat refuses to walk in the consultation room having the owner video the cat in its home environment can be useful.

Standing Exam of the Cat - Gentle Palpation for Symmetry and Comparison Between Limbs

One hand may need to be placed under the abdomen to keep the cat standing up. Cats are best examined using minimal restraint, flat hands can be used to provide gentle containment. Avoiding scruffing, if possible, as this will cause the cat to tense up and limit further examination. However there may be the occasion where it is necessary to scruff a cat to suspend it to examine a single lame limb. Careful assessment of the limbs and skin for swelling and scabs or puncture wounds that occur in the case of bite wounds is an important part of the orthopaedic examination in cats. Some fractious cats will not allow any physical examination; in this case the examination may need to be performed after anaesthesia or sedation. In animals with painful fractures in which a complete examination is not possible in the conscious animal then further assessment should be performed after anesthesia.

Examination of Joints - Swelling, Pain, Instability, Range of Motion and Manipulation

This is best done with the cat lying down. An assistant uses two flat hands to gently hold the cat on the table with one hand over the cats' pelvis and one on the shoulders and around the neck to prevent the cat turning its head and biting. If the cat will not lie on its side then it is easier if the cat is held slightly suspended under its abdomen or supported under its chest while examining each limb. All four limbs should be systematically examined starting at the toes and working proximally examining for swelling of joints, pain, particularly when taking joints through the range of motion, and whether the range of motion is normal. Cats have greater laxity in their joints than dogs so before deciding that a joint has normal or abnormal laxity it is important to compare it with the contralateral side or with normal values for cats.

Further Investigations

Following the gait evaluation and standing and lateral recumbent physical examination further investigations may be required to aid in obtaining a diagnosis. Investigations may include a more thorough examination under sedation or anaesthesia, clipping of hair to look for puncture wounds or evidence of cellulitis, aspiration of joint fluid or swellings with cytological analysis and/or culture. Diagnostic imaging modalities that are useful include radiology, ultrasound, CT and MRI. The investigation of hindlimb lameness in cats (excluding common fractures and abscesses) will be illustrated by discussing the following conditions:

Pelvic Limb Lameness

Slipped Capital Femoral Epiphysis

Affected cats are usually young male neutered cats that present with unilateral hind limb lameness often of insidious onset. Radiographs show a slipped femoral epiphysis, there may be 'apple coring' of the femoral neck. Treatment is femoral head and neck excision or total hip replacement. The other femoral head may fracture at a later date.

Cranial Cruciate Ligament Disease

Cats that suffer cruciate ligament rupture are generally heavier than the general population of cats and there is evidence reported that this injury parallels the degenerative cranial cruciate ruptures seen in overweight small breed dogs. They have similar bilateral hind limb stiffness or unilateral pelvic limb lameness, stifle swelling and instability associated with the ruptured ligament.

Patella Luxation

Patellar luxation should be considered as a cause of hind limb lameness in cats. It is generally seen in young cats and clinical signs vary from stiffness, reluctance to jump, unilateral hind limb lameness to marked reluctance to bear weight on either hind limb. Low-grade luxation can be associated with lameness of the same severity as high-grade luxation.

Patella Stress Fracture

An atraumatic transverse stress fracture of the patella has been recognised in young cats that present with marked unilateral hind limb lameness associated with quadriceps insufficiency and an inability to extend the stifle. A careful oral examination will reveal retained deciduous teeth in many affected cats. Cats will commonly fracture the contralateral patella within 2–3 months of the first and then other bones such as the tibia, pelvis and humerus as they grow older.⁴

Myositis Ossificans

Generalised and localised forms of myositis ossificans have been reported in cats. The generalised form is known as progressive ossifying fibrodysplasia. The localised form tends to occur in specific muscles such as the biceps femoris or semitendinosus bellies. Its formation may be related to local or repetitive trauma. Recurrence of the lesion in cats is likely after excision.

Lumbosacral Disease

Clinical signs in cats with lumbosacral disease include reluctance to jump, low tail carriage, elimination outside the litter box, reluctance to ambulate, pelvic-limb paresis, single limb lameness, urinary incontinence, and constipation. Cats will usually have lumbosacral hyperpathia on palpation. A normal cat will tolerate full extension of the tail and side to side movement, in a cat with lumbosacral disease movement of the tail may cause pain. A combination of radiographic, myelographic CT and magnetic resonance imaging findings have been used to confirm the suspected diagnosis of disc-associated lumbosacral disease in the various reports in the literature.

Myasthenia Gravis⁵

Cats with myasthenia gravis (MG) may present with generalised weakness or exercise intolerance, muscular weakness and apparent stiffness. The gait may be mistaken as being associated with bilateral hind limb problems such as hip dysplasia, or patella luxation. Other clinical signs indicative of neuromuscular disease include neck ventroflexion, lack of palpebral reflexes, dysphonia and less commonly regurgitation. The Abyssinian and Somali cat are predisposed breeds, and cats are usually older than 3 years. MG is a condition whereby muscles are unable to contract or maintain contraction due to a deficiency or disorder of acetylcholine receptors (congenital form) or blockage of the receptors by immune complexes (acquired form). The acquired form is more common in the cat. The disease is confirmed by testing for acetylcholine receptor (AChR) antibodies. Many cats with MG will have a cranial mediastinal mass, most commonly a thymoma.

Arterial Thromboembolism

Ischemic neuromyopathy results from embolization or long standing compression of arteries. It is usually seen in cats with cardiomyopathy. The most common site of obstruction by emboli is the aortic trifurcation. The onset of signs is acute and painful paraparesis or paralysis occurs. Limbs are cool on palpation, there is absence of a femoral pulse and the nail beds appear blue or cyanotic. Gastrocnemius muscles are firm on palpation and can be painful. Pain sensation is often absent in the distal limbs. The ability to extend and flex the hip and stifle joints is usually preserved and the patellar reflex remains intact. Initially the hind limbs may be held in extension due to ischaemic muscle contracture.

Pelvic Limb Peripheral Neuropathy

Usually due to pelvic fracture or repair, femoral fracture repair, sacroiliac fracture luxation or repair and injections into the caudal thigh muscles.⁶ The sciatic nerve and its branches the peroneal and tibial are most commonly involved. Peroneal nerve injury results in knuckling and loss of dorsal limb sensation and an inability to flex the stifle and hock. Tibial neuropathy results in a dropped hock with decreased hock extension.

The Dropped Hock

A common gait abnormality seen in the cat is that of a dropped hock. Evaluating these from a distance may suggest that the underlying cause is a tibial neuropathy but other causes exist. These include Achilles tendinopathy, calcaneal fracture, SDFT luxation and avulsion of the origin of the gastrocnemius.

Thoracic and Pelvic Limb Lameness

Plasma Cell Pododermatitis

Affected animals have enlarged food pads, usually metacarpal or metatarsal pads, and the pads have a soft spongy consistency and mauve colouration. Ulceration of the pads may occur. The condition is suspected to be an immune mediated or allergic disease.

Digital Metastases

A cause of lameness in middle to older aged cats is digital metastases usually from a primary bronchial carcinoma; squamous cell carcinoma has also been reported.⁷ Affected cats usually present with lameness. Thoracic and distal limb radiographs are indicated to check for a primary lesion. Overall the prognosis is poor for cats with metastatic digital tumors, with median survival times of 1–2 months.⁷

Diabetic Neuropathy

Peripheral neuropathy is a recognised complication of diabetes mellitus in cats. Cats usually have a symmetrical distal limb polyneuropathy and a plantigrade stance, paraparesis, distal limb muscle atrophy and pelvic limb hyporeflexia. Cats can have difficulty jumping, abduction of the pelvic limbs and weakness when standing.

Nerve Root Signature

The nerve root signature is lameness associated with nerve root pain from a physical obstruction or inflammatory condition adjacent to the nerve root, most likely a disc protrusion, osteomyelitis, neoplasia or a fracture fragment. The author has seen this condition in a cat with a sacral fracture. The diagnosis of these diseases requires careful attention to the signalment, a complete history, and a thorough physical examination focusing on the neurologic and orthopedic components. Ancillary testing should be selected based on these results. Electrodiagnostic testing, radiography, and advanced imaging may help to localize the lesion more precisely and sometimes to confirm the diagnosis. Surgical exploration and histopathology often provide the definitive diagnosis. These cases of non-weight-bearing lameness are a diagnostic challenge, but when successful resolution can be reached, it is gratifying to the clinician, client, and patient.

Diagnosing the underlying cause of lameness in a cat can be a challenge a patient, cat centred approach is needed to optimise the chances of identifying the problem(s).

References

1.  Kerwin S. Orthopaedic examination in the cat. J Feline Med Surg. 2012;14:6–12.

2.  Montavon PM, Voss K, Langley-Hobbs SJ. Patient assessment. In. Feline Orthopedic Surgery and Musculoskeletal Disease. Elsevier Saunders; 2009:3–10.

3.  Langley-Hobbs SJ. Musculoskeletal oddities in the cat: an overview of some curious causes of lameness. J Feline Med Surg. 2012;14:31–42.

4.  Langley-Hobbs SJ. Fifty two patella fractures in the cat. Vet Rec. 2009.

5.  Shelton GD, Ho M, Kass PH. Risk factors for acquired myasthenia gravis in cats: 105 cases (1986–1998) J Am Vet Med Assoc. 2000;216:55–57.

6.  Garosi L. Neurological lameness in the cat. J Feline Med Surg. 2012;14:85–93.

7.  Gottfried SD, Popovitch CA, et al. Metastatic digital carcinoma in the cat: a retrospective study of 36 cats (1992–1998). J Am Anim Hosp Assoc. 2000;36:501–509.