Degenerative Osteoarthritis

Definition

A disorder involving the progressive deterioration of the articular cartilage in the joints, outgrowth of new bone at the margins, and changes in the synovial membrane.

Clinical Signs

May observe any of the following:

A gradual stiffness in the joints, and limbs.
Gait dysfunction (i.e., a wide, flat-footed stance and gait).
Pain with certain types of movement (i.e., unable to climb or maneuver ladders like before ).
Limping, gradual hind limb weakness (i.e., may affect one side more than the other ).
Paralysis in hind limbs that progresses due to eventual compression of spinal cord and nerve roots.
Tail dragging if paresis/paralysis.

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.

Etiology

Osteoarthritis is a degenerative disorder of aging that can affect any joint, but is most noticeable in the sternum, hips, knees, toes, and especially the spine. The condition generally affects rats greater than one year old and has no apparent sex predilection, although the severity of the condition may vary among strains of rats (Smale et al., 1995).

In osteoarthritis there is increased water content and a decreased protein makeup of cartilage. The cartilage begins to degenerate by becoming soft and flaking into the joints losing its ability to cushion. This results in rubbing and friction between the joints. Osteophytes (outgrowth of new bone), commonly called “spurs”, form at the edges of the joint surfaces while joint capsules and synovial membranes thicken, and joint spaces narrow and lose their stability. All these changes lead to pain, inflammation and limited mobility.

When osteoarthritis occurs in the lumbar spine (spondylosis), degeneration of the intervertebral discs, and narrowing of the spinal canal (spinal stenosis) result. This degeneration and narrowing can cause nerve root (radiculopathy) and spinal cord compression resulting in weakness of the hind limbs progressing to hind limb paralysis. This condition is seen mainly in male rats.

A factor besides aging that may contribute to the development of osteoarthritis is obesity. Other factors are repetitive stress to the joints, infection, or injury.

As the prognosis is progressive, in rats, the focus is on treating clinical signs present, and maintaining comfort and safety.

Figure

Case History of Degenerative Osteoarthritis

Fig. 1: Case History of paralysis and X-rays of spine in 2.2-year-old male rat (Nimbus)

Diagnostics

Obtain history. If paralysis presents rule out other causes.

X-ray of spine may show narrowed joint space, and an increase in the density of subchondral bone and osteophytes (spurs) at the edges of the joints.

Lab: sed rate and erythrocyte counts may reflect normal to moderate increase.

Treatment

Early Clinical Signs

For arthritic joints, may apply topical DMSO gel (found in pet and feed stores).

Also include an oral herbal supplement, Glucosamine-Chondroitin.

If signs of limping or weakness of hind limbs present:

A suggested aid thought to help slow progression of paralysis is a B complex vitamin supplement. It can be purchased in a liquid or capsule form. The latter is the least expensive. The capsule form can be made into solution by opening up a B50 capsule and dissolving the powder in 2mL of water. According to a hospital pharmacy, the B vitamin can be suspended in water for one week by refrigerating the solution. This 2mL of solution can be drawn up in a small 3 mL needleless syringe. The syringe needs to have the tenths of a mL markings on the syringe barrel, as the dosage may only be about 0.2 mL.

If using either the liquid or capsule dissolved in water, the dose is based on the amount of B12 noted in the solution/capsule. The recommended dosage is based on 1 to 5 mcg’s (micrograms) of B12 in the B complex, and is given PO (oral) daily. ³^, ¹²

In the event of mild to moderate pain, or to reduce swelling and inflammation: treat with NSAIDs such as ibuprofen, or meloxicam, or piroxicam.

Advancing symptoms

Discuss with veterinarian changing from NSAIDsto a corticosteroid such as prednisone or prednisolone

Since at this point long term use of corticosteroids are likely, discuss introducing a prophylactic, broad-spectrum antibiotic. Also remember to include probiotics to promote gut health if choosing to include an antibiotic.

For information pertaining to medications refer to the Rat Medication Guide.

Nursing Care

Follow medication regimen as prescribed by veterinarian to reduce pain and inflammation and preserve function.
Do gentle range of motion exercises to preserve muscle tone and reduce stiffness.
Limit having to climb or stretch by providing: a one level cage or housing, or low wide ramps with covering that can be gripped when pulling up. Cover any wide or exposed wire to prevent injury from getting hind limbs caught.
Keep beds or hammocks low to cage floor to prevent falls or having to climb to get into them. Homemade nest boxes with soft padded bedding (shoeboxes are handy) are easy to get in and out of.
Body temperature control may be poor, especially if the rat is elderly. Provide additional warmth to maintain body temperature within normal limits. It is essential that the rat does not become overheated or dehydrated. The rat should also be able to move away from the heat source if it becomes uncomfortable. If the rat is unconscious or immobile extreme care must be taken to keep the heat low and stable.
- You can use an isothermic product that is heated in the microwave such as SnuggleSafe®. Make sure to follow the product directions carefully and wrap in a towel before placing in the cage. SnuggleSafe® will provide heat for 12 hours before needing to be reheated. Other similar types of products may vary in re-heat time. Check directions for individual product.
- If using a heating pad (good for long term use) use only the low heat setting, put a thick towel in between the pad and the cage bottom, and place beneath a corner of the cage.
- In the event none of these options are available you can use a plastic bottle filled with hot water, and wrapped in a towel, in the corner of the cage.
Prevent litter getting into rat’s eyes or mouth by switching to cloth bedding.
Place sipper bottles and food dishes within easy reach.
For rats having difficulty holding food or having a poor appetite, provide soft, pureed foods such as baby food, pureed vegetables and fruits, or rat blocks soaked in soy milk. Also, food supplements or high calorie foods like Nutri-Cal Paste, canned Ensure, avocado, or yogurt can be given. A vitamin and mineral supplement (found in pet stores) may also be added to the diet, if intake is poor or inadequate.
Assist with grooming by wiping down coat with damp cloth and brushing with a soft brush (an old toothbrush will work).
Due to paralysis, bladder and bowel control are often lost. Prevent urine burns and skin break down by gently washing area and belly after urination or stooling.
In male rats, paralysis and age may prevent them from being able to groom and clean the penis effectively. Hardened white secretions may form a vesical proteinaceous plug in the urethra that can block urine from flowing and set up an environment for infection. Clean this area by gently pulling down the sheath of the penis (a white plug may be visible), use a damp cloth to remove the plug, and gently replace sheath.
Keep back claws clipped since the paralyzed rat will be unable to wear them down.
Clean gently around portion of the outer ear with a Q-tip (cotton swab) to remove any buildup of wax. Refrain from inserting the Q-tip (cotton swab) into the ear canal as it may cause injury.

Outcome

Pain and inflammation is reduced.
Progression of paralysis is slowed.
Protected from injury to joints and spine.
Urinary obstruction is prevented.
Weight loss is prevented.
Skin breakdown is prevented.

Prevention

Maintaining a healthy weight for your rat and preventing obesity may help to delay onset and progression of the disease.