Luxating patella is the dislocation of the kneecap–the small bone in front of the knee joint.
Your veterinarian might recommend surgical intervention for patellar luxation grade II or higher.
Kneecap anatomy
At the top, the kneecap attaches to the quadriceps tendon and at the bottom to the patellar ligament. The kneecap not only protects the front of the knee. It also assists with the joint movement–straightening of the knee.
In a normal knee, the femoral groove constrains the kneecap movement. The groove allows the patella to slide up and down but not to the side. When the kneecap luxates–slips out from the groove–it impairs the function of the joint.
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| Patella/kneecap. Image The Code Company |
Kneecap dislocation grades
Luxating patella grading is based on whether the kneecap
- pops back into proper position on its own
- can be pushed back into the groove
- or stays dislocated, and how often this happens
| Grade I | the patella can be manipulated out of groove but returns into position on its own |
| Grade II | kneecap occasionally rides out but can be manipulated back into position |
| Grade III | kneecap frequently dislocates but can be placed back |
| Grade IV | dislocated kneecap remains dislocated |
The grade determines treatment options.
If the kneecap dislocates frequently, or cannot be pushed back into place, veterinarians recommend surgery.
A genetic predisposition is the main predictor of patellar luxation. Trauma is rarely the cause.
The problem behind patellar luxation goes beyond a shallow groove–its a result of faulty biomechanics and conformation.
The rather complex issue might involve :
- an abnormal hip joint
- abnormalities in the conformation of the thigh and shin bones
- a patellar ligament that is too long
- muscle issues
The surgical repair might involve a combination of deepening of the groove and/or realignment of other parts.
Tibial Tuberosity Transposition
This surgery realigns the pull on the kneecap. It does involve cutting the bone to which the patellar tendon attaches and securing it into a position where it better aligns with the groove. The reasoning behind this method is that bone heals better than a tendon would.
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| Tibial Tuberosity Transposition. Image North Downs Specialist Referrals |
Recession sulcoplasty/Trochleoplasty
This is the most obvious repair-deepening of the groove if it is very shallow.
Ridge Stop
This procedure involves placing an implant which increases the height of the affected ridge. Most commonly, the patella dislocates medially, toward the inside of the leg.
Medial muscle release
With a prolonged dislocation, the muscles opposite of the position of the kneecap stretch and the ones on the same side shorten. Once things are in their proper position, the surgeon will tighten the loose muscles and free up the tight ones.
Femoral osteotomy
This is a procedure to straighten the thigh bone in dogs who have a severe bow.
The surgeon removes a wedge of the thigh bone and secures it with a plate and screws to become more straight.
A potentially much more complicated fix than you’d think, isn’t it?
Fortunately, unless your dog has other issues, such as hip dysplasia, the outcome of surgical repair is quite positive. In such cases, the chances that lameness returns are low.
Related articles:
Primer on Patellar Luxation in Dogs
Juno’s Luxating Patella
Further reading:
Patellar Luxations