Patellar Ligament Disease. The patellar ligament disease is a condition of the stifle where the cartilage keeping the patella in place over knee joint is weakened or damaged. The patella is held in place by ligaments and slides in a groove in the femur called the trochlea and should be inline as shown in the picture below on the left. If the groove is too shallow, the patellar will slip out when the knee bends which is a patellar luxation (as shown in the picture above on the right). Patellar luxation is usually an inherited defect, which occurs during the developmental stages of the fetus and is rarely as a result of trauma. The patella luxates, which causes pain in the limb and the dog has difficulty in weight bearing on the affected leg. Page 1 of 9
1. Patella 2. Femur 3. Patellar ligament 4. Tibial Tuberosity 5. Medial Luxation of Patella 6. Lateral Luxation of Patella The anatomy in patellar luxations revolves around the relationships among the femur, tibia, pelvis, and hock joint. The relationships among these structures determine the position of the soft tissues and therefore whether the patella sits within the trochlear groove or beside it. The medial and lateral femoropatellar ligaments are delicate bands of loose connective tissue that connect the patella to the fabella on the lateral surface and the periosteum of the epicondyle of the femur on the medial side A medial patellar luxation is when the patella slips out going to the inside of the leg (as shown in the picture above) and is more common in the small breeds (i.e. toy and miniature dog breeds). The dog may have a gait, which is sometimes normal and sometimes abnormal, as the patella may slip in and out of place. When it is out, the affected leg is usually carried with the joint bent and the foot turned inward. A lateral patella luxation is when the patella slips out going to the outside of the leg (as shown in the picture above) and is more common in the large breeds (i.e. rottweillers, Page 2 of 9
german shepards etc) and is usually seen in dogs between 5 to 6 months old. The dog develops a knock-kneed type of stance and the foot often twists outward as weight is placed on the affected leg. The examining veterinarian will often make a diagnosis from a physical examination however, x-rays are needed to determine the degree of arthritis, and deturmine any malformation of the femur and tibia, the two major bones in the leg, which are joined together at the knee. The X-ray below shows a severer skeletal abnormality of a medial patellar luxation in a dog. There are four grades of patellar luxation based on the severity as follows: 1. Patella can be luxated but returns to normal position when released and the dog is not lame. 2. Patella luxates with the stifle flexion or on manual manipulation and remains luxated until the stifle is extended or manually moved into place. The dog will have intermittent lameness and/or will have occasional skipping gait. Page 3 of 9
3. Patella permanently is luxated which can be manually returned to normal position but spontaneously reluxates. The dog will usually be persistently lame which will worsen with time. 4. Patella permanently luxated and cannot be manually moved back into position. The dog will be lame also walks in a crouched position and cannot fully extend the joint. Surgical Techniques Trochleoplasty This procedure involves deepening the trochlear grove using a bone rasp, bone burr or rongeurs which removes the articular cartilage and subchondral bone to achieve 50% of the patella height. The healing process forms fibrous scar and fidrocartilage in the groove. Removing articular cartilage and bone with a bone rasp, power burr, or rongeurs to a depth at which the patella rides within the new sulcus. The medial and lateral trochlear ridges are made parallel to each other and the base of the groove perpendicular to each trochlear ridge. Page 4 of 9
Trochlear Wedge Recession This procedure also deepens the trochlear groove while preserving the articular cartilage. A V shaped cut is made and the wedge of bone is removed, a thin wafer of bone is removed from both sides of the wedge before it is replaced in to the groove. This results in the patella sitting deeper in the trochlear groove preventing it from slipping out. Trochlear Block Recession Trochlear block recession deepens the trochlear groove to restrain the patella and maintain the integrity the patellofemoral articulation. In larger dogs, an oscillating saw is often used, but in smaller breeds and toy breeds, a fine-toothed, hand-held saw or the cutting edge of a scalpel blade and mallet may be used to make the cuts in the trochlea as shown below. Page 5 of 9
Trochlear block recession. A, Use a thin saw blade to make two parallel cuts, axial to both trochlear ridges. B, Use an osteotome from proximal and distal to elevate an osteochondral block from the patellar groove. C, The bone from the bottom is removed from the incised block to deepen the sulcus. D, The osteochondral block is then replaced. Chondroplasty The hyaline cartilage is lifted from the subchondral bone so that the bone underneath can be deepened to increase the depth of the groove. The cartilage is then replaced. Tibial Tubersity Transposition This procedure is carried out if the tibial tuberosity is deviated medially, improving the alignment of the patella mechanism. It involves sawing through the tuberosity, leaving a small periosteal attachment distally. The tuberosity is then swiveled until the muscle and patella are in a straight line. Finally the tibial tuberosity is then pinned in its new position. Page 6 of 9
Medial Desmotomy A desmotomy is simply a release of the medial or lateral retinaculum on the side toward which the patella was luxated. When the patella luxates medially, retinacular tissues on that side contract and either prevent reduction of the luxation or provide enough tension to easily reluxate the patella. The incision is usually left open to prevent tension from redeveloping. Lateral Capsular Imbrication Tightening the joint capsule, known as imbrication, is done on the opposite side of the luxation to prevent the kneecap from having enough slack to pop out of the trochlear groove. A medial patellar luxation is treated with a lateral imbrication, and vice-versa also the joint capsule can be loosened on the side of the luxation, this is called a release incision. This procedure relieves the tension that the joint capsule is placing on the patella, allowing it to ride in the trochlea. In severe cases a synthetic suture is sometimes necessary to keep the kneecap in place. It is placed on the side opposite the luxation, and goes from behind the femur to the patellar tendon. It also prevents the kneecap from popping over to the other side. Page 7 of 9
Corrective Osteotomies A corrective osteotmies is the repositioning of the lateral patellar luxation and is accomplished by medial and lateral arthrotomy incisions on either side of the patella, beginning at the tibial tuberosity and extending proximally to above the patella. The tibial tuberosity is then osteotomized and relocated medially in a new position, which is aligned properly for the patella to ride in the trochlea. If the attachment of the patellar ligament to the tibia (this is called the tibial crest) is in the wrong position, it is repositioned. This is done by creating a cut in the tibial crest (see picture above) and reattaching the bone in a position so that the patella is realigned within the trochlear groove. Pins are used to fasten the bone in place, which will remain in place unless they migrate out of position or a bubble of fluid (seroma) develops over the end of the pin. The soft tissues along the side of the patella usually are stretched and are tightened to provide additional support to keep the patella in the trochlear groove. The femur bone may be twisted in some dogs, which worsens the condition of the luxating patella. Page 8 of 9
Aftercare After consultation with the veterinary surgeon the postoperative patient can have hydrotherapy but caution in the beginning must be taken. Swimming might be too strenuous for an unstable joint, especially early after surgery. Some vets consider the underwater treadmill is a better alternative, because there the dog is allowed to exercise under better control and quietly in a closed kinetic chain. When the dog enters the hydrotherapy centre it is important that the dog does not slip on the wet floor and should remain on a stable surface. Measurements of the limbs chest and waist before the initial hydrotherapy session, which is repeated after each fifth session to highlight muscle, gain. The hydrotherapist should also help the dog to enter and leave the pool to also prevent the dog from slipping / falling when using the ramp. Short swims are to be conducted at first to build up the muscles, which have been lost post operation. During each rest period the dogs limb is to be monitored for signs of reduced weight bearing on the affected limb as it is essential excessive stain is not put on the joint. I also highlight to the owner the importance that the dog does do any running, jumping or climbing stairs during recovery period. Page 9 of 9