Damaged Ridge.
Damaged Trochlear ridge.
This shows abnormal wear of the medial ridge of the Trochlea.
Trochlear Prosthesis
A Titanium Trochlea has been used to replace the damaged Trochlea.
This allows the patella to sit within a very smooth and deep artificial Groove. This reduces pain and resolves dislocation.
Patellar luxation means dislocation of the knee cap and is a common problem in dogs of all sizes and in cats. It is most common however in Terrier breeds, Cavalier King Charles and many of the other small breeds. Another form of patellar problems is seen most commonly in Bull type breeds (Staffordshire Bull Terriers, English and French Bulldogs and English Bull Terriers.
The method of surgery most appropriate for management depends very much on the grade of patellar luxation and the health of the cartilage on the back of the patella and the groove itself.
In patients with healthy cartilage we perform the following sequence of work. Not all procedures mentioned here is necessary in all patients.
Grades 1 to 3
Not all patients will need to have all of the components mentioned in this section. The surgeon deploys the methods in sequence until the knee cap is stable before closing the joint.
Step 1: If the groove is shallow, this is made deeper by taking a wedge or block of cartilage and bone from the groove. The “trough” that remains is then made deeper. The wedge or block is then replaced in the deepened trough. This recesses the wedge or block and makes the groove deeper.
Step 2: If the joint capsule is very tight on the side to which the patella is luxating, the capsule is incised to release the tension. Sometimes (Grade 3 and above) the quadriceps muscle attached to the patella needs to be freed up to allow the patella to be mobile enough to sit back in the groove.
Step 3: If the patella still dislocates when the shin bone is rotated inwards (in medial patellar luxation) or outwards (in lateral patellar luxation), the surgeon will separate the tip of the shin bone from the body and then move it in the direction opposite to the direction of patellar luxation. When the optimal position has bee established, it will be attached to the shin bone using two very small pins.
Step 4: The joint capsule opposite to the direction of luxation is usually very stretched and this is tightened up by overlapping it when closing the joint.
Grades 3 to 4
In patients with deformity of the knee usually associated with bending of the thigh bone we will sometimes have to straighten this bone. This is done by making a carefully planned fracture, removing a wedge of bone from the thigh bone. The fracture is then stabilised using a plate and screws. Often all of the procedures described above (for Grades 1 to 3) will then have to be applied in sequence to assure stability of the patella.
Trochlear Prosthesis (for patients with cartilage loss behind the patella)
We are one of only fifteen practices in the world that can offer this surgery. In this surgery we remove the old groove and replace it with an artificial groove made from Titanium and coated with a “diamond like coating”. The coating is incredibly smooth and results in very low friction between the patella and the artificial groove. This low friction allows the damage behind the patella to heal and reduces the pain that was associated with the rubbing between the patella and thigh bone. This new form of management has successfully allowed patients to have improved knee mechanics by allowing the patella to sit within a perfectly engineered groove that is deeper than we can provide with the surgical methods discussed in the section above.
Read more about this problem and the surgical options here