Orthopaedic problems of long-bodied, short-legged dogs
Andrew Miller BVMS DSAO MRCVS
RCVS Specialist in Small Animal Surgery (orthopaedics)
Andrew Miller Orthopaedics
Broadleys Veterinary Hospital
Craig Leith Road
Stirling FK7 7LE
A number of breeds of dog are classified hypochondroplastic. This just means that they have an inborn growth abnormality that results in their developing with relatively short, relatively deformed limbs. The Dandie Dinmont is one such breed; other examples include the dachshund, Jack Russell terrier etc. Some breeds also have skull and facial abnormalities eg. pug etc. Basically think of any of the smaller breeds with “Queen Anne” style legs.
The metabolism and conformation of these breeds potentially predispose them to a number of orthopaedic abnormalities, which will be discussed briefly below.
One of the metabolic alterations seen in hypochondroplasia is premature degeneration of the intervertebral discs. The centre of the disc, instead of being a clear jelly-like material, changes to cartilage – this can affect many or potentially all the discs in the body and can happen as early as 12 months of age. The abnormal cartilage in the disc may then have calcium deposited within it, producing the so-called calcified or mineralised disc. This disc then may or may not cause problems. Mineralisation is not in itself problematic, but the abnormal disc is prone to protrusion (Type 1 protrusion / “slipped disc”) and can cause spinal pain, weakness or paralysis of the limbs, reduction or loss of bladder / bowel control or reduction or loss of sensation caudal to the lesion. The exact signs in any particular case depend upon the location and severity of the disc protrusion. Disc protrusion most commonly affects the cervical spine (neck) and thoracolumbar region (around the level of the last rib).
Diagnosis of disc disease (mineralisation) can be made by X-ray but a specialised contrast agent test (myelography) is generally required to show whether or not a mineralised disc has actually protruded and by how much. It is important to be aware that mineralised discs do not necessarily cause problems! Computed tomography (CT scan) and MRI scanning are also occasionally performed in dogs with disc problems.
Some dogs can recover spontaneously from the disc protrusion but about one in three will have a recurrence of signs at some point in the future. Further attacks may be more serious than the first. More severely affected dogs are better treated surgically, usually by removal of the offending disc +/- some of its neighbours. Overall, the results of disc surgery in dogs are very good indeed, with the majority of paralysed dogs able to walk again following surgery.
The forelimb conformation of hypochondroplastic breeds may result in a disparity in length of the two forearm bones, the radius and ulna. Usually, the ulna tends to be too short. This results in the radius pushing the end of the humerus upwards at the elbow joint, resulting in a partial dislocation of the humerus from the ulna. This causes joint pain and lameness and will predispose to osteoarthritis and separation of the anconeal process of the ulna, a protruding beak-like process of bone at the back of the joint.
The abnormality can be diagnosed easily by X-rays, where an abnormal (increased) joint space between the humerus and the ulna can be seen. Quite frequently, both elbows are affected. This can confuse the physical signs seen, as dogs with bilateral lameness may appear sound.
Treatment is easy and involves sectioning the ulna immediately below the elbow. It is important to cut the bone at an angle, to help with stability and healing. The bone ends spring apart when the cut is completed in some cases, signifying correction of the deformity and this can be seen on a post-operative X-ray. In other cases the bone slides gradually into place over 2-3 weeks. There will usually be lameness until the cut in the bone heals, which takes 6-10 weeks in small dogs. Usually an ununited anconeal process will heal spontaneously. Occasionally, the cut in the bone does not heal and further treatment may be necessary to achieve this.
The usual appearance of the forelimbs is of lateral (outwards) deviation of the carpus and foot. There is usually bowing of the radius and outwards rotation of the foot. These features lead to abnormal loading and, potentially, instability of the carpus, although actual lameness problems are rare.
The hindlimbs tend to be bow-legged and this can lead to a waddling gait. The shortness of the limbs and a tendency towards restricted stifle movement can lead to a gait that originates mainly from the hips. This gives the appearance of “goose-stepping” in many individuals, especially at faster paces. This causes no problems and is probably best regarded as a normal feature.
In some dogs, the bow-legged posture can be associated with imbalanced thigh muscling. This can in turn lead to patellar luxation. Usually the patella moves medially (towards the inside of the leg) in small breeds. Medial patellar luxation may cause problems of any severity; some dogs will have no problems, some may have mild or intermittent lameness, whereas some unfortunate individuals will be severely handicapped. The only possible treatment is surgery, if clinical signs require it. The direction of the muscle forces can be realigned by transposition of the tibial tuberosity, the point of insertion of the quadriceps (major thigh muscles) and the femoral trochlear groove, where the patella runs, can be deepened if required. The former surgery is the more useful. Deepening the trochlear groove by gouging out cartilage is very detrimental to the joint and should not be undertaken; the groove is better deepened by an operation called “wedge recession sulcoplasty”, which preserves the joint cartilage.
Varus (inwards) angulation of the tarsus and foot below the hock is common and usually causes no problems. Occasionally, lameness can be attributed to this, in which case surgical correction is possible by osteotomy of the distal tibia.
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