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Patella Subluxation (Slipping Kneecap)

Clinical Description / Symptons
Dislocation, for that is what is meant by the term slipping, of the patella (kneecap) is a common orthopaedic problem in dogs. In the normal dog virtually no sideways movement of the patella can be produced by manual pressure on it. The problem of the slipping patella may be categorised generally as intermittent or permanent and the classical signs associated with these are substantially different.

In the case of the intermittent, the patella dislocates spontaneously during the dog's moving but will return to its normal position unaided. In the permanent type the patella will not do this and cannot even be manually manipulated back. The direction of dislocation is usually medial (middle) Lateral (sideways) dislocation is infrequent. Intermittent dislocation is characterised by sudden leg carriage during movement, sometimes accompanied by a cry of pain, and within a few strides the leg is normal again. This may occur once a day, once a week or several times a day. The variation in frequency depends upon the amount of anatomical defect present. Sometimes the dislocation does not go back of its own accord and requires manual correction. When the dislocation is medial the stifle is rotated inwards and the hock is turned out. With lateral dislocation there is a marked outward turning of the foot and inward movement of the hock - this is the more severe disability of the two.

The permanent form is more serious and usually comes after a severe form of intermittent dislocation. When this form occurs in very young puppies, say three or four months old, a very severe deformation of the stifle joint can occur which can result in crippling lameness. This means that the stifle cannot be properly extended and when the puppy stands thus putting weight on the joint, the puppy crouches rather than stands upright. If both legs are affected then this crouching is severe. Some puppies with this learn to move just on their front legs whilst others are totally immobile. There are several reasons for the patella to move from its correct position although the main reason is rotation of the tibial crest. Briefly, and firstly, if the ligaments holding the patella are, for some reason, not as taut as they should be it will slip. These ligaments run in grooves on the bones either side of the knee joint. Secondly, when the groove in the femur is too shallow, or in some cases non-existent, then the patellas will slip. Thirdly, when there is little if any angulation of the stifle the patella has a tendency to pop out. A much rarer reason is following injury in the leg. Occasionally, for instance, a dog free running slips and catches its leg in a pot hole the leg will twist and damage the ligaments and the patella will pop out.

Diagnosis
The Vet will easily recognise the problem when you visit. Your description of your observations will immediately suggest luxating patella and a simple manual examination of the leg will confirm. There is rarely a need to X-ray in this case but it may be useful to assess the degree of deviation. The Vet should check for concomitant problems.

Treatment
The most common treatment is surgical. An operation can be performed to either deepen the grooves in the bones, or shorten the ligaments supporting the patella but tibial crest transposition is the most common operation. After the operation the vet may prescribe a short course of anti-biotics and anti-inflammatories. Alternatively, depending upon the degree of luxation and the amount of pain the dog is in, the condition can be left alone. It is also worth mentioning that correct weight management could help the dog.

Management After Surgery
When the dog comes home follow the vet's instructions regarding exercise. He will probably tell you to confine your dog i.e. crate, for several days apart, of course, from the calls of nature. He may, if your dog is over weight, also give you dietary advice. When you do start walking your dog again, do not give too much exercise at once, start to build up to your normal distance gradually. It is also advisable to keep your dog grounded, no more attempted glides across the room off the back of the chair!

Breeding Advice
Slipping patella is caused by a deformity. However, as already stated there are varying degrees of severity from those that can be manipulated by hand but never slip out on their own, to those that are out permanently. As Breeder/Exhibitors our aim should be to produce the perfect animal. Slipping patella is as much a deformity as a severely roached back, but much less obvious. It is generally accepted to be a problem that passes down the generations. It is therefore recommended that severely affected dogs are not used in breeding programmes. However, in a breed like ours with a small breeding pool, we cannot afford to ignore an animal with many great virtues that may have a very slight problem. If a mate were carefully selected which did not exhibit the same problem it may achieve the right result. We therefore recommend that breeding stock be checked by a vet for slipping patellas before they are used. A slipping patella is at the very least uncomfortable, usually painful and even if treated by operation the damage left behind can lead to arthritic conditions in later life.

Further Information
If you want to find out more about luxating patella problems talk to your vet who should be able to explain things simply. For more reading on the subject 'Luxation of the Patella' by Mike Stockman (Our Dogs 26.2.88). A bit technical to start with but when he gets down to calling a spade a spade it is full of good sensible advice. 'Dislocation of the Patella in small animals' by Leslie C. Vaughan DSc., FRCVS., DVR. This is almost a D.I.Y. manual on diagnosis and treatment. If you want copies of these papers please contact any member of the committee.

The Affenpinscher Club Recommended patellae grading results - click here