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Hospital Cases  > Surgical  > Dislocating patella
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Dislocating Patella: Block Stabilisation

Hazmat, a young male terrier cross, had a nasty limp in his right hind leg. On examination, he had a dislocating kneecap (patella) which continually locked itself in an abnormal position on the inside (medial aspect) of his knee (stifle).

Surgery was scheduled using a new technique to deepen the groove in which the patella slides up and down. In Hazmat's case, the inside (medial) ridge of this groove had flattened out due to the patella continually dislocating medially and wearing the ridge out.

The patella is attached to the big group of muscles at the top front of the leg- the quadriceps. The patella is attached by a tendon on its lower edge to the tibial crest ( a ridge of bone on the top front of the tibia).This is the same tendon the doctors tap on to test your reflexes. If you feel that tendon, you can see how it is attached to the ridge of bone below your knee- the tibial crest.

In Hazmat's case, he had been born with a tibial crest that was off centre and was positioned too far medial (inside) which gave an unnatural "pull" on the patella tendon attached to it above. This "pull" was towards the medial (inside) aspect of the leg. The constant "pulling" made the patella slide out of its groove and flatten the inside ridge. In other words, the whole patella apparatus was out of alignment with a natural tendency to pull the patella out of its groove in a medial direction.

Hazmat was placed on an IV drip and given IV Alfaxan to anaesthetise him. He was then placed o Isoflurane gas to maintain the anaesthetic.

A lateral (outside) approach was made to the stifle (knee) joint. After incising the lateral tissues (fascia lata) the joint capsule was exposed. This was also incised exposing the inside of the joint. The flattened ridge of bone in the groove below the patella could be seen.

Using a small bone saw, 2 parallel cuts were made in this groove running form top to bottom. Then using a bone chisel, 2 parallel cuts were made across the joint forming a rectangular/block cut. The chisel was then placed at the top and bottom of the block and the whole section was gently lifted ff the bone.

The underlying groove was deepened using a special bone rasp. The rectangular block was then replaced into the deepened groove giving a nice ridge to stop the patella from slipping out of the groove.

The next part of the operation was to move the tibial crest to a more outward (lateral) position in order to straighten up the pull of the quadriceps muscles on the patella. Using a bone saw, the tibial crest was cut off its attachment to the tibia. It was moved approx 3-4mm laterally before it was pinned in its new position using 2 thin orthopaedic pins (K wires).

The final part of the operation was to overlap the tissues (lateral fascia lata) on the outside of the stifle thereby pulling the patella laterally and away from its tendency to want to dislocate medially.

The stifle was irrigated with sterile saline and a soluble antibiotic was placed in the joint. Hazmat received post op pain relief and made a great recovery.

At 3 weeks, Hazmat is starting to weight on the leg and we expect a great result.

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