Patellar luxation is usually a congenital condition in which the kneecap, or patella, dislocates outside of its normal trochlear groove. Dislocation, clinically referred to as luxation, can occur on either the medial, or inside surface, or the lateral, or outside surface, of the knee. There are varying degrees of patellar luxation that are graded depending on whether the patella is intermittently or constantly luxated. This abnormal displacement of the kneecap results in pain, cartilage damage, and arthritis. There are varying degrees of severity of this disease, and surgery may be needed.
Lameness that is often intermittent, and may be unilateral or bilateral; thick, swollen stifles; pain on range-of-motion; crepitus; palpable luxation; inability to jump or walk normally; medial displacement of quadriceps muscle group; lateral bowing of the distal third of the femur.
Symptoms include: Intermittent or consistent lameness; bowlegged stance; reluctance to walk or jump; occasionally holding a rear leg out to the side when walking.
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Treatment involves replacing the kneecap into the groove, and preventing it from popping in and out. The following procedures can be used alone or in combination as necessary to maintain the proper function of the knee.
Imbrication
Tightening the joint capsule, known as imbrication, is done on the opposite side of the luxation to prevent the kneecap from having enough slack to pop out of the trochlear groove. Thus a medial patellar luxation is treated with a lateral imbrication, and vice-versa. Additionally, the joint capsule can be loosened on the side of the luxation; this is called a release incision. This procedure relieves the tension that the joint capsule is placing on the patella, thus allowing it to ride in the trochlea.
In severe cases a synthetic suture is sometimes necessary to keep the kneecap in place. This suture is placed on the side opposite the luxation, and goes from behind the femur to the patellar tendon. It also prevents the kneecap from popping over to the other side.
Trochleoplasty
Deepening of the trochlear groove, or trochleoplasty, can be accomplished with a variety of techniques. A chondroplasty technique involves cutting out a taco-shaped wedge of cartilage, removing a small portion of bone beneath it, and then replacing the cartilage. The result is a deeper groove. This procedure can only be performed on very young dogs, because their cartilage is thicker.
Trochlear recession involves cutting out the cartilage and bone in such a way as to create a deeper trough. This trough will then fill in with scar tissue over time. Because this scar tissue is not as good as cartilage for joint function, this technique has given way to others that attempt to preserve normal cartilage. It can, however, be useful in carefully selected cases.
Wedge recession creates a taco-shaped piece of cartilage and underlying bone. Then, the bone below the wedge is removed and the wedge is replaced, forming a deeper groove. Block recession is identical in principle to wedge recession, except that a rectangular piece of cartilage and bone, rather than a wedge, is removed.
Tibial Tuberosity Transposition
The kneecap attaches to the lower leg via its patellar tendon at a bony site called the tibial tuberosity. Many times this site forms abnormally on the inside, as with MPL, or on the outside, as with LPL. In this procedure, the surgeon moves the tibial tuberosity back into proper alignment and secures it in place with a pin or wire. Realigning the joint, kneecap, and tendon prevents dislocation from reoccurring.
Osteotomy
In severe cases, with malformation of the tibia or femur, corrective bone cuts known as osteotomies may be required.
Affenpinscher
Basset Hound
Bichon Frise
Border Terrier
Briard
Brussels Griffon
Cavalier King Charles Spaniel
Chihuahua
Chinese Crested Dog
Cocker Spaniel
Dandie Dinmont Terrier
English Springer Spaniel
Lhasa Apso
Maltese
Papillon
Pomeranian
Poodle
Pug
Shar-Pei
Silky Terrier
Toy Fox Terrier
Yorkshire Terrier
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