The patella or knee cap normally runs in a groove at the bottom of the thigh bone (femur). Luxation is the term used to describe dislocation of the patella. If the patella luxates out of the groove, the knee no longer functions normally. If the patella dislocates towards the inside of the knee, this is termed medial patella luxation. If towards the outside, this is termed lateral patella luxation. Medial patella luxation is much more common than lateral.
This condition is most frequently seen as a developmental disorder developing over time. There is often a malalignment of the muscular system. This condition is seen in many dog breeds, and cats can also be affected. Trauma is another potential cause of patella luxation.
The most common sign of patella luxation is a skipping limp on a back leg. Some patients will show other signs such as stiffness after rest, bowlegged hind limbs or an inability to jump.
Patella luxation is often predominantly diagnosed from clinical examination. Radiographic assessment under sedation or anaesthesia will be necessary to check for any other contributing factors to the lameness and give an indication of the presence of osteoarthritis in more chronic cases.
A grading system is used to describe the severity of patella luxation:
The patella sits within the groove. The patella will dislocate but immediately returns to the groove after the knee is released.
The patella sits within the groove. The patella will dislocate and stays dislocated. The patella returns to the groove with stifle manipulation.
The patella sits outside the groove. The patella will return to the groove but immediately dislocates.
The patella sits outside the groove. The patella will not return to the groove.
Dependant on the grade of patella luxation the patella moves in and out of the groove and causes abnormal wearing of the articular cartilages. Patella luxation is managed surgically and is advised from a Grade II luxation.
Surgical management usually combines several different techniques dependant on each individual case.
Groove deepening is performed if the trochlear groove is too shallow. Either a wedge or block of bone is removed from the groove, the groove is deepened and the wedge or block of cartilage is replaced. This technique preserves the articular cartilage as much as possible. If this procedure is performed alone without addressing the alignment issues, failure of the repair may occur.
If the extension mechanism of the knee (the quadriceps mechanism) is out of alignment then this needs to be addressed above all other issues. The realignment is most commonly achieved by moving the front part of the tibia, the tibial tuberosity. The bone is cut and the tuberosity is moved to improve alignment. Once in the correct position, it is stabilised with pins and wire.
If the malalignment comes from a deformity in the bones, then a corrective osteotomy or ostectomy may be required. These would be stabilised with a plate and screws.
Joint imbrication is when the additional tissue around the joint is tightened or removed. Tightening the lax tissue helps keep the patella from easily luxating.
Most patients have a good to excellent outcome following surgical management. Patients return to off-lead exercise and are free of long term medication
Potential complications following surgery include re-luxation, seroma, infection, failure of the surgical implants and fracture of the tibial tuberosity. Keeping the patients appropriately confined and rested for the appropriate post-operative time, keeps complication rates to a minimum.
A fracture is a break in a bone. Fractures can be simple (if there are only 2 pieces) or comminuted (when the bone shatters). Bones can penetrate through the skin and these are referred to as open fractures. If a fracture affects a joint it is called an articular fractures. If a fracture affects the shaft of the bone it is called a diaphyseal fracture. A Slater fracture is a type of fracture that occurs through a growth plate of your pet and can be problematic for young pets still growing. A greenstick fracture is where the bone does not completely break, so a partial incomplete break in the bone.
Fractures can happen in any number of ways from a fall, stumbling in a field, a road traffic accident, or in a more traumatic circumstance.
When a bone fractures, swelling (inflammation) can occur and your pet will become suddenly lame on the limb and unable to weight bear.
What do you do when you think your dog or cat has broken its bone:
Try to immobilise your pet so they can not move. Be careful and sensitive to the aspect that your pet could be in pain, any movement attempts might result in them biting. It's nothing personal, they're painful and don't know how to tell you. Confine your pet in a cage or small space while you transport them to the veterinary centre. Essentially you want space for them to lie and not move. Once arriving at the veterinary centre your pet will be evaluated by the surgeon on duty, who will determine if the animal is stable, needs pain management, or sedation. Sedation is usually administered to further assist Veterinary professionals in obtaining X-rays (radiographs). These are integral in creating a treatment plan for a fracture repair.
Fixing the fracture
Each Fracture is unique to each animal and are treated accordingly, the fracture repair method is chosen dependant on factors that include your pets:
Methods of fracture repair
There are a number of methods used when fixing a fracture:
Owners ability to manage the after care
After care and complications
It is essential that you follow the veterinary surgeons advice during the recovery period, even if your pet seems back to normal, to minimise complications and extended recovery time. It is normal for pets to be on cage rest for several weeks after surgery. Complications can arise during the recovery period and some fractures are prone to complications.
External fixators connecting to straight bars
Cranial Cruciate Ligament Rupture
Disease of the cranial cruciate ligament is a common cause of lameness. The cranial cruciate ligament is one of the four main ligaments in the knee joint (stifle). The ligaments attach the femur (thigh bone) to the tibia (shin bone) preventing sliding motion to the knee joint.
Rupture of the cruciate ligament is often trauma related, however in dogs it can be a degenerative condition which results in gradual weakening and ultimate rupture of the cruciate ligament.
The menisci (joint cartilages) may often be damaged secondary to cranial cruciate ligament injury due to the increased instability of the knee joint.
The most common sign of cranial cruciate disease is limping on the back leg. This can occur suddenly or may develop slowly. The lameness may vary from non-weight bearing to subtle.
Diagnosis is usually confirmed by examination and radiography (x-rays) under sedation or anaesthesia. Radiographs may show signs consistent with joint inflammation and osteoarthritis.
Non-Surgical / Conservative:
Exercise restriction, non-steroidal anti-inflammatory drugs and dietary supplements.
This offers a very unpredictable outcome and these patients usually develop severe osteoarthritis making the long-term outcome poor. Small dogs may respond better.
Many different techniques have been described for this condition. There is a growing body of recent evidence which suggests TPLO (Tibial plateau levelling osteotomy) offers the best functional outcome. TPLO is our preferred technique.
Other techniques can be performed in appropriate cases:
TPLO – Tibial Plateau Levelling Osteotomy
In recent studies, this procedure has shown to be the technique most likely to return maximal limb function. The TPLO procedure changes the forces in the joint to create a more stable knee angle when the dog is weight bearing.
The technique makes use of creating a semi-circular cut in the top of the tibial bone and the top section is rotated to a calculated angle to improve stability in the joint. The cut bone is stabilised with a plate and screws.
Most dogs are weight bearing on the leg within 48 hours of surgery. Most patients have a good to excellent outcome following TPLO surgery. Dogs should return to off -lead exercise and be free of medication. This procedure offers athletic or working dogs the best potential to achieve the same levels of ability after surgery.
Potential complications for TPLO are low. The most common complications are infection, late meniscal injury, fracture, and failure of the surgical implants. Keeping animals appropriately confined and preventing over-activity in the early postoperative period keeps the complication rate to a minimum although this does not completely eliminate all risk.
TTA – Tibial Tuberosity Advancement
This technique also uses a cut in the top of the tibia bone, and the front portion pushed forward to change the forces in the knee.
Recent literature suggests higher incidences of cartilage injury after surgery (late meniscal injury) compared to TPLO.
A prosthetic ligament (Lateral extracapsular suture or fabellotibial suture).
Nylon or Fibrewire is often used as the substitute ligament material.
Suture usually stretches or breaks over time, while fibrewire is more robust.