The Short Ulna Syndrome

The short ulna syndrome is mainly seen in dogs with short legs such as Dachshund, Basset, Welsh Corgi, etc. Although trauma is a frequent cause of premature closure of this growth plate, the heritability of premature ulnar physeal closure as related to conformational development of specific breeds has also been reported. Hence breeds such as Welsh Corgis are genetically more prone to this kind of malformation.

The following pictures show a Cardigan Welsh Corgi with a malformation that is not caused by a trauma but is due to a genetic disposition; some of his siblings are equally afflicted. However, the photos illustrate very well what a shortening of the ulna can induce.

At 9 weeks

At about 6 months

At 1 year,
a few days before the operation

About 6 months
after the operation (osteotomy)

Same dog at 8 years

In the spring of 2016, the Norwegian Kennel Club (NKK) informed the Norwegian Welsh Corgi Club that for the time being they will discontinue to read ED-X-rays of the following breeds: Dachshund, Basset, Drever (Swedish Dachsbracker), Welsh Corgi, Skye Terrier, Pekingese, Tibetan Spaniel, Shih Tzu, Lasha Apso and Swedish Vallhund.

This decision was taken on the grounds that short-legged breeds can suffer of other elbow diseases than what is termed "ED". The current reading is therefore inadequate and can give a false diagnosis for these breeds.

Small (light) and chondrodystrophic (short-legged) breeds such as the corgis have practically no ED - thus there is no need to spend time and money on ED X-rays.

Chondrodystrophic dogs can have a so-called subluxation in their elbows due to the short ulna syndrome. This type of elbow disease is not covered by the term ED. When radiologists receive pictures of dogs who do not have ED but subluxation in their elbows, they cannot classify the readings within the range of the usual ED examination. The radiologist can therefore be forced to declare the dog free of ED which again makes the owner believe that his dog has "sound" elbows.

The present examination for ED only requires one side shot of the elbows whereby the dog is photographed with his elbow at a very tight angle. Such an X-ray is not ideal for the evaluation of subluxation.

The short ulna syndrome
Premature closure of the distal ulnar physis has been reported to be the most frequent (63%) growth plate injury in dogs. It is well accepted that the geometric configuration of the distal ulnar growth plate is the primary reason why the distal ulna is affected by premature physeal closure. Most physes, such as the proximal and distal radial physes, are relatively flat and thus are predisposed to shear fractures. Longitudinal growth may continue uninterrupted from these relatively flat physes, as long as the germinal cells are uninjured and remain attached to the epiphys. However, the distal ulnar physis is conical in shape and thus is unable to shear, regardless of whether the offending force is axial or lateral in nature. Thus, excessive force applied from any direction can cause compression of one side of the conical physis, resulting in injury to the germinal cells and subsequent retardation or cessation of ulnar growth.

Because 100% of ulnar growth distal to the elbow joint arises from the distal ulnar physis, injury to this physis frequently results in greater alteration in antebrachial morphology than injury to either of the radial physes. Retardation of growth of the distal ulnar physis can result not only in a shortened ulna but, because of intimate attachments between radius and ulna, in conformational changes in the radius. Although this is not always the case, typical changes seen in the radius subsequent to premature closure of the distal ulnar physis include shortening, procurvatum, distal valgus, and torsion. These changes occur as the radius continues to grow "around" the distal ulna, which is located caudolateral to the distal radius. The severity of these changes is dependent on the degree of ulnar growth retardation and growth potential remaining at the time of the insult. In addition to its effect on the radius, shortening of the ulna can cause humeroulnar incongruity, resulting in placement of excessive biomechanical loads on both the radial head and the anconeal process). These changes may ultimately lead to elbow joint osteoarthritis.

Pure shortening of the ulna at the level of the elbow joint can occur in the absence of closure of the distal ulnar physis. Any condition that results in radioulnar synostosis before closure of the proximal radial physis may produce a shortened ulna. In the absence of antebrachial angulation the main surgical treatment for a shortened ulna is a lengthening procedure. Similar to radial lengthening, surgical options include both acute and gradual techniques.

In skeletally immature patients, dynamic ulnar ostectomy has been advocated as the treatment of choice. This procedure frees the proximal aspect of the ulna, so it is no longer constrained by retarded growth of the distal physis, thereby allowing the ulna to move proximally and optimize congruency with the humerus. The act of releasing the retarding (bowstring) effect of a slower growing ulna may also prevent the worsening of coincident radial angulation, if growth potential still resides in the radius. In the immature patient, ostectomy is preferable to an osteotomy if the degree of ulnar lengthening required is relatively small, in that the resulting bone gap will be larger. This larger gap will help prevent the ulna from completing osseous union before cessation of radial growth. If the ulna heals before completion of longitudinal growth of the radius, additional surgery may be required.

Asymmetric Physeal Disturbance and Angulation During Development
Developmental abnormality resulting in pure shortening of the radius or the ulna is rare, as asymmetric physeal damage seems to occur more frequently than symmetric closure. Developmental antebrachial angulation can arise from (1) asymmetric premature closure of the physis of the proximal or distal radius or both, (2) premature closure of the distal ulnar physis with continued radial development, or (3) a combination of the two.

When an antebrachial angular limb deformity is first detected, the surgeon is faced with a number of decisions regarding timing and the type of corrections to be completed. For a skeletally immature dog, the risk of performing any kind of correction before development ceases is that angulation can return and additional surgery will be required. The alternative is to delay surgery until the animal is mature, at which time a definitive correction can be completed with no risk of subsequent reangulation. The risk of waiting is that the angulation will negatively affect the distribution of biomechanical loads placed on the joints, thereby creating stress on the joint and resulting in uneven wear on the articular surfaces. These changes can result in early-onset osteoarthritis and potential remodeling of the subchondral bone.

Reference: Veterinary Surgery: Small Animal, 2 volume set by Karen M. Tobias, Spencer A. Johnston

Can Ulnar Shortening Be Prevented?
Here is what Julie Morris, Dorwyn Cardigans, Australia, writes:
"The "short ulna syndrome" is a problem in Australia also. Unfortunately a lot of breeders apparently didn't notice it crawling in, not so much the older ones as I guess we were taught to look for the longer ulnas many years back when we first had our conformation lessons. Also we were taught about diet and it was recommended that puppy food not be used for Cardigans. Thus, apart from the initial few weeks when the pups were weaned by 8 weeks, they were on mushy adult kibble.
"I am happy to report that no Dorwyn puppies have suffered from "puppy limp" and I presume that between the selected breeding programme and the diet we have been able to steer clear of that problem. I am very thankful to my early mentors back in the 1970's who guided me tirelessly and imparted all their knowledge to me.
"I must admit that my Skye Terrier did suffer from puppy limp for about 1 week for which I blame myself. He was 7 weeks and semi-weaned when my Roary/Loopy litter were whelped and I was so caught up in that litter of 8 that I completely forgot to change him over to raw at the correct time. The first time I saw my Skye Terrier limp I immediately realised what had happened and changed him over immediately. His movement was back to normal within the week and that is one mistake I will never allow myself to make again. It proved to me just exactly how important diet is to the dwarf breeds".

Bridget Smeeton, Rodwell Welsh Corgis, New Zealand: An Injury, Its Cause And Effect On The Cardigan Welsh Corgi.

My own experience: I have had Cardigan Corgis since 1979, all from different lines. As far as I remember four of them started to limp on one foreleg at the age between 7-9 months. Fortunately, none of them needed an operation, pain killers and restrained exercise and play was enough. None of my dogs have been allowed to leap off high places or sofas or running up and down stairs before they were about 8 months of age. However, my present two Cardigans (11 years and 9 months) have, at the recommendation of their respective breeder, been fed with adult food from the age of about 12 weeks and neither of them has ever had a limp. - ANo