Definition

A dislocation is displacement of a bone from its normal anatomic position in a joint.

Clinical Signs

May observe any of the following:

• Manifestations of pain: limping, guarding of movement, squeaking when touched.
• Local swelling, skin discoloration at site.
• Nerve, soft tissue (tendons and ligaments), vein and or artery impairment if complete dislocation due to trauma.
• A loss of function, immobility of affected limb.
• A possible deformity in appearance at site (e.g., limb tucked, rotated outward, shorter limb compared to opposite limb).

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

Etiology

A dislocation occurs when a joint exceeds its range of motion thereby causing joint surfaces to no longer be in contact.

Dislocations may result from trauma, disease, congenital or genetic malformation or predisposition to joint dysplasia.

In rats, dislocations are generally the result of traumatic accident such as: being stepped on while free ranging, a fall from heights, getting limbs caught in wire exercise wheels or inappropriate cage floorings.

When congenital dislocation occurs, it may be a result of heredity or of extended extension of the limb prior to or during birthing.

In genetic malformation or predisposition to joint dysplasia, the condition may become more apparent as the rat grows. This results in the joint becoming more unstable and loose causing abnormal movement and deformity. The joint becomes lax and unstable, tendons stretch, cartilage deteriorates. Pain is present and mobility is impaired. While genetics or predisposition may be the cause obesity in the rat can play a factor in contributing to the worsening of the condition.

Types of dislocation:

• Luxation: A complete, abnormal, separation from within the joint where two or more bones meet which can result in damage to soft tissue, nerve, and blood supply to area.
• Subluxation: A partial or incomplete dislocation from joint which may not sustain damage to surrounding tissue.

  Although the joint is directly affected, the severity of the injury may cause additional trauma to surrounding tissues, muscles. Swelling may be seen if there is bleeding into the soft tissue. There may be a rupture of tendons, severed nerves, and damaged blood vessels. Prognosis will depend on type, extent, severity of dislocation and procedure required.

Complications that may be associated with dislocations:

• Avascular necrosis
• Osteoarthrtis

While rat’s small size can make it difficult to immobilize the injured area, helping to keep the rat calm and confined to a small one-level cage, reducing further trauma to area, and reducing pain (until seen by a veterinarian) will greatly help with comfort.

Figures

Case Histories and Photos

• Fig. 1: Dislocation and amputation in rat (Peaches)

Diagnostics

Assess for shock, hemorrhage, pain, respiratory compromise and treat accordingly.

When stable obtain history.

Do an orthopedic and neurovascular assessment. *Note: Ortoloni Sign (clicking sound when attempting to reduce dislocation) may or may not be audible or practical in the rat.

Perform radiography to detect type, extent and severity of dislocation.

Treatment

Warning: Pet owners should not attempt to splint or wrap a dislocation on their own without guidance by their veterinarian. Doing so could cause further damage to tissue, nerve, or blood supply to area. See veterinarian as quickly as possible.

Until an appointment is able to be made to see the veterinarian, a small cold pack may be applied to the site if the rat will tolerate. Tylenol may be given for discomfort if there is no hepatic impairment. While veterinarians may splint with wrap in simple dislocations for purpose of immobilization in larger animals, it is almost impractical in the rat. In the majority of cases the options, based on veterinary assessment, are: to leave off the splint with wrap if the rat can be kept in a smaller one level type cage where the rat doesn’t climb, do an open reduction (surgically opening joint) under anesthesia to realign joint, or in a complete dislocation/luxation where there is impaired circulation (i.e.; avascular necrosis [death of bone tissue]) of joint, persistent pain, impaired mobility and function for the rat, amputation of the limb may be required.

Caution: giving NSAIDs such as ibuprofen or meloxicam if bleeding is present, or giving before seeing veterinarian, may interfere with the treatment the veterinarian needs to perform.

In the event signs of shock or if bleeding present in traumatic injury, use a clean cloth to cover wound and control bleeding, keep rat warm and get to a veterinarian quickly as these symptoms are life threatening! The veterinarian will want to start fluid replacement of warmed SQ fluids, oxygen therapy, and possibly a glucocorticoid such as dexamethasone. Once the rat is stabilized, x-rays can be taken to determine type and severity of the dislocation. The veterinarian may then, after anesthetizing the rat, try to realign joint to a normal position if possible, or if very severe to amputate limb.

Rats do experience pain with surgical procedures. The type of pain medication used post-op should be determined based on extent of procedure and the anticipated severity of pain.

• For severe pain or first 24 hours post-op: Buprenex (buprenorphine), or Torbugesic (butorphanol).

• For mild to moderate pain : Banamine (flunixin meglumine), Metacam (meloxicam), or carprofen. Do not use if a corticosteroid has already been prescribed.
• *Note: for pain not controlled by the use of an NSAID (e.g., Banamine, meloxicam, or carprofen), alone, consider alternating or co-administering with a narcotic (e.g., buprenorphine or butorphanol) or narcotic-like (e.g., tramadol) medication.

In the event trauma and damage is too severe to permit quality of life euthanasia may have to be considered.

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

Nursing Care

The following can be applied for both non-post-op and post-op care as appropriate.

• If surgery is required, provide the following post-op care:
  • A hospital cage (small individual cage), clean non-litter bedding such as felt, soft t-shirt type material, or ink-free paper towels. Clean and change bedding daily. Avoid litter-type bedding to prevent the chance of wound contamination or infection.

• 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.
  • If 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.

• Medicate for pain as prescribed.
  • Remember not to over-medicate for pain. Allowing the rat to feel slight discomfort will help to alert the rat that the injury is not yet healed and prevent further injury or delayed healing.

• If required give antibiotics as prescribed.
• Because hypovolemia (loss of fluid volume primarily due to bleeding) may be present it is important for the rat to stay hydrated.

  *Note: juicy types of fruit provide an additional source of fluid in the diet.

• Monitor for neurovascular changes, and report to veterinarian if limb becomes cooler, pale or cyanotic, or if signs of pain or condition worsens.
• Whether surgery was required or not, proper healing may require several weeks (although rats, especially very young rats, can heal in a shorter amount of time). Be sure to provide a cage that is one level to prevent further injury from climbing or jumping during time of healing.

Outcome

• Pain controlled
• Return of mobility
• Free of deformity

Prevention

• Check the rat’s environment frequently for hazards.
• Supervise free ranging time and alert other members in home when rats are free ranging.
• Be observant and aware of rat’s proximity when opening and closing doors to rooms or cage.
• Put other pets in another room if rat is in danger of injury.
• For tall cages or cages placed on high stands: provide carpeting, rugs, or padding around the base of the cage if the rat is permitted to climb on the outside of the cage.
• Think Rat Safety!

*Note to Breeders: the continuation / direction of the lines may need to be evaluated in the event the condition presents as a genetic malformation.

Consultant

• Adele Wharton, BVSc, MRCVS, CertGP (F&L) Veterinary Surgeon

References

1. Sijbrandij, S. (1965). Dislocation of the hip in young rats produced experimentally by prolonged extension. The Journal of Bone and Joint Surgery. British Volume, 47-B(4), 792-795. doi:10.1302/0301-620x.47b4.792*Warning: pictures in this reference article are very graphic!