07/09/2024
Patella luxation
What is patella luxation?
The patella is a small bone at the front of the stifle joint (knee cap in humans).
The Patella is positioned between the quadriceps muscle and a tendon that attaches to the shin bone (tibia). Also known as the quadriceps mechanism.
The patella will glide into a groove at the end of the thigh bone (femur) as it's flexed and extended.
Occasionally the patella can slip out of the groove. This is known as Patella luxation. Generally it's the medial aspect of the knee (inside) but can happen laterally (outside).
Why does the patella luxate?
This happens because the Patella doesn't align properly with the underlying groove (trochlea). The result is abnormal tracking or movement so it slips out of the groove.
The cause of abnormal alignment is sometimes complex, involving varying degrees of deformity of the femur (thigh bone) and tibia (shin bone). If the case is very severe the femur can be bowed due to abnormal growth. They can have a bowed leg or knock kneed appearance.
This is common in poodles, Yorkshire terriers, staffs and Labradors. It's normally bi lateral and genetic.
Luxation due to trauma (injury) is uncommon.
What are the signs of Patella luxation?
A skipping action with the hind leg being carried for a few steps. This occurs when the patella slips out of the groove and back in again. If both patellas slip at the same time the dog or cat may struggle to walk and have a crouched action.
A vet will examine your dog and may find some atrophy (muscle wastage) over the quadriceps. Manipulation of the knee joint can detect the level of instability in the patella as it slips in and out of the groove.
The severity is then scored 1-4 with 4 being the most severe.
X-rays will provide more information about the presence of osteoarthritis and how severe it might be.
Treatment
Some dogs with Patella luxation can be managed without surgery. The milder the grade and smaller the dog the better chances of being successful. Hydrotherapy is often beneficial but normal exercise should be restricted. There are 3 types of surgery Quadriceps realignment surgery, trochlea deepening and femoral Ostetomy.
Quadriceps realignment surgery
This surgery involves moving a small piece of bone (tibial tuberosity) at the top of the shin that's attached to the patella and repositioning it so the patella is aligned with the groove. This procedure is called tibial tuberosity transportation. The bone that's transported is then attached with one or two small pins with it without additional support of a figure of 8 wire.
Following this surgery exercise must be restricted for the first few weeks until the bone and soft tissues heal. Keeping them on lead is best to keep them fully restricted. Confinement is recommended and no jumping or stairs. Hydrotherapy will be recommended.
Trochlea groove deepening surgery
This is a surgery that involves removing a wedge of bone or cartilage from the groove, to then deepen the groove and then replacing the block or wedge. This is a recession technique since they recess the surface of the groove and make it deeper. Whilst protecting the surface (cartilage) of the groove.
Femoral Ostetomy surgery
This surgery involves changing the shape of the deformed bone, cutting it and stabilising it in a new position with a plate and screws. This may be all that's needed to stabilise the patella but sometimes a tibial tuberosity transportation is performed.
Exercise needs to be restricted until the cut bone has healed. Lead exercise is recommended to avoid strenuous activity. Jumping and climbing should be avoided. X-rays are performed 6-8 weeks later following surgery to ensure bone is healing with no complications. Exercise can be increased in a controlled manner and hydrotherapy can begin.
Photo PDSA