Skipping Dogs — Patellar Luxations

The knee joint -- the knee cap is under the ligament and rides on the upper bone (femur)

The knee joint — the knee cap is under the ligament and rides on the upper bone (femur)

I figured we would continue our discussions on the knee and give you one more article on pathology in the knee. I just happened to see a dog this week with luxating patella and I felt this article would be appropriate.

Patellar luxation is a dislocation of the knee cap and may be congenital or traumatic in origin.  The knee joint is comprised of the femur (thigh bone), tibia (shin/lower leg), knee cap (patella) which is located inside the patellar ligament and ligaments to each side (collateral).  The tibia has a V-shaped groove in it called the trochlear groove and the patella should ride in this groove.

Patellar luxation usually occurs by one of three methods:

  1. Collateral ligament is too tight and pulling the patella out of alignment.
  2. Collateral ligament is too loose and not holding the patella in alignment.
  3. The trochlear groove is not deep enough and the patella scoots where it wants to go.

Most patellar luxations occur in small dogs with a medial or inward luxation being the most common.  Large dogs tend to have a lateral or outward luxation.  Most of the small dog luxations are due to conformation issues with the legs usually being bowlegged.  You usually don’t see signs of a problem until later in life but you can see evidence of patellar luxation at early as four months on a radiograph.

 

Clinical signs are seen as:

  • Rear leg lameness

  • Skipping gait

  • Carrying a rear leg for a few steps before putting it down

  • Kicking back of a rear leg

  • “Dance” to move leg into place

  • A popping noise may also be heard or felt

There are four grades of patellar luxation:

Grade 1 is seen with intermittent luxation and lameness, full flexion and extension with no crepitus (crunchiness) and the patella can be luxated manually but returns to normal when released.

Grade 2 has frequent luxation, pet may carry the leg partly flexed, crepitus may be present, and the patella can be manually luxated or may luxate spontaneously when the leg is flexed (bent) but when extended the patella returns to normal or can be manually reduced.

Grade 3 has a patella that is luxated most of the time, the leg is almost always flexed, degenerative changes are seen, and the patella can be reduced manually with the joint extended but flexion and extension of the knee results in relaxation of the patella.

Grade 4 has a permanent luxation and it cannot be placed back into the groove, the pet usually walks in a crouched position, and the trochlear groove is not present or very shallow.

Surgery is recommended for grades 2, 3, and 4.  Grades 1 and 2 may be able to have rehabilitation for strengthening and may not need surgery.  Grades 3 and 4 are always recommended for surgery to help correct the misalignment and to decrease pain.  Surgeons do not know exactly which surgery they will be doing until they are in the joint.  They may need to release a ligament, tighten a ligament, deepen the groove or even realign the femur and/or tibia.

Rehabilitation or physical therapy is recommended for all grades of patellar luxation.  Post-surgical rehabilitation focuses on cryotherapy, short leash walks, and pain medications for the first few weeks after which strengthening exercises are then incorporated.

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