Oestrus and Hips
by Fred Lanting
Reproduced with permission 2005
A reader sent a question about bitches getting looser during their heat seasons, and a report that one got permanently worse after being spayed. The idea and question has been around since most of this site's readers were toddlers. :-) There is very probably old misinformation on this topic. Can a bitch's heat cycle alter the outcome of the radiographic diagnosis? Not likely, at least not in the distraction view and probably not in the hip-extended view, either. There is not enough strong scientific evidence that estrus affects the laxity of the joints, despite what we used to think. The closest anybody has come to a cause-and-effect claim was: Keller GG, Bouchard G, et al. Influence of the estrus cycle on coxofemnoral joint subluxation. Canine Practice 1993. If estrus affects ANYthing, it would be in the OFA-type legs-extended position, but that has not been shown to have statistical significance in any really controlled study. On the other hand, since "Laxity can't hide from the P-H method", it makes one wonder if the position/technique would make a difference.
More than one breeder has tried to test this "heat theory" and report that it appears to be true in their dogs. Some correspondents told me shortly before I finished this work that they had their bitches radiographed as they were "coming in"; the evaluation by the vets was that the hips were close but probably wouldn't pass OFA. Then they were tested again 60-90 days after they were finished with the "season" (per OFA encouragement) and both were rated "good". However, knowing how males and non-estrus females can be read differently by different people or by the same evaluator just hours or days apart, we cannot ascribe different readings to actual differences in the hips. There are too many "buts" and questions about such testimonials to allow us to count them as reliable, although they may be good reason to investigate scientifically. You know how people often tend to trust in testimonials rather than controlled scientific studies. If vets would compile good records, make sure all control protocols were followed, and have the results published, it would be the start of a definitive answer to this question. So far, nobody has done this, although there has been a start. Do not rule out the possibility of the same difference being seen simply because it was a different date that the second radiographs were made. Unless everything is exactly the same, it is not a controlled experiment. The amount of sedative, level of sedation, methodology of vet and technicians, etc. must be the same, and then repeated trials with the same results should follow. Further, other researchers must get the same results in order for it to be accepted that there is any connection between estrus and laxity.
A magazine editor, among others, had recently asked me to comment on the effect of estrus (heat cycle). For many years we breeders have been assuming that there (regularly) were differences in observable hip joint laxity between films made in or near estrus and those made in complete anestrus (not close to a heat cycle). We also told each other that to get the best picture and the best chances of "passing OFA", we should take the pictures in the afternoon, after the dog had been exercised and "toned up", on a dog with good muscle development from regular exercise over a longer period of time, not within a couple weeks of estrus or several weeks of pregnancy, and without sedation. This was based on intuitive supposition, and the OFA even made statements to the effect that they were true concepts. There are two holes in this otherwise neat scenario:
One is that there has never been any scientific study (except the Keller reference above that was apparently described as lacking by the data in the Hassinger study) to prove the idea that joints are truly tighter or looser than at other times. It simply "made sense" to many of us, because conventional wisdom shows us that we are slightly longer when we wake up than after a day of gravity compressing our spinal disks, and that hormones in late pregnancy cause a woman's pelvic symphysis to relax or bend so that there is more room for the child exiting the birth canal. But does that necessarily mean that the other joints are likewise affected, and that ligaments somehow relax more than they would in other circumstances? No. It is possibly a faulty assumption, with little to support it. In fact, a definitive study in 1997 indicated that hip laxity is not changed by estrus cycle using either the OFA or the PennHIP method. (Hassinger KA, et al. Effect of the oestrus cycle on coxofemoral joint laxity. Veterinary Comparative Orthopaedics and Traumatology. (F.K.Schattauer Publ.), 1997. Also in Proceedings. An. Conf. Vet. Orth. Soc. 1997.) There is no significant change in DI attributable to a bitch being in heat, or to the other reasons, when this method is used. All of the OFA's contentions, and breeders' assumptions about the effect of estrus, are unfounded, according to this journal report. In fact, researchers at Penn also cite scientific evidence that it simply is not true in either view, that no examples show significantly increased laxity with estrus.
That was a prospective study of fluctuating hormone levels throughout the estrus cycle and the effect on hip joint laxity. The main conclusion: "Neither statistically nor clinically significant changes in hip laxity were observed." And, intra-class correlations suggested that "...any hormone-related variation in hip laxity, if present, was minimal (<7% for distraction index, 18% for Norberg angle)." Further, "Although it is statistically impossible to prove the null hypothesis [i.e., no effect], if an effect existed within this sampling of dogs, it was small and clinically insignificant."
Still, there may be that other problem with our assumptions, which is (as I said above) that we were basing them on the old and imprecise leg-extended position. As you can imagine, this natural position for humans but unnatural position for quadrupeds tends to wind up and artificially tighten the muscles, tendons, and ligaments in the area of the hip. We do not frequently get repeatable results with that position.
With the knees flexed and the distractor unit employed in the PennHIP technique, however, the same objectively measurable amount of laxity is seen (with few and minor exceptions) time after time. The dog's full laxity is seen each time the dog is radiographed in this position.
I agree that it would seem to make sense that estrogens have an effect on joints, but the only scientific study I am aware of on the subject (Kassinger's has what is accepted as statistical significance) indicates that it does not. The published reports in the 1960s and 1975 indicated "exogenously administered estrogen" caused some increase in hip joint laxity, but injection with steroids or hormones is not the same as changes resulting from the bitch's own endocrine system. That one study by Keller et al in 1993 indicated a possible connection, but the correlation was not considered "statistically significant" by colleagues.
In order to make a strong conclusion that would be accepted by scientists, two things must happen:
1. There must be statistical significance, and
2. Other researchers must get similar results.
Neither of these conditions for scientific conclusion has yet been attained. Corley in 1987 said, in a NON-peer-reviewed press release, that some "bitches demonstrate subluxation while in season, but appear normal when not in season." But this has yet to be verified or quantified in repeated or scientific studies. If there ever is sufficient evidence to come to a scientific conclusion that the two are related in a cause-and-effect way, my guess is that there would be more apparent correlation in the artificially tightened leg-extended view, and nothing statistically important in the distraction view.
So, the conclusion of the estrus-laxity question is (again) that true laxity does not hide from the distraction procedure, that it very well might be hidden in the leg-extended view, and that the role of hormones in canine hip joint laxity (whatever it might be in other species and anatomical locations) is not present, or is immeasurable. We need verification of either viewpoint, as one or two small studies on each side of the question are not enough for us to make nearly absolute statements.
As to a bitch limping AFTER having been spayed, you cannot assign cause to that effect, unless you compare a large number of "limpers" to a large number of such instances with "twins" (as identical as you can get the control group) who have NOT been spayed, to see if they ALSO developed a limp at about the same age. In other words, if you see a limp, it may as well have been brought on by something you did NOT see instead of the big spaying event. It probably would have happened at that time if you had not spayed her. Whatever feedback you get from testimonials, they would only be if use if they led to enough case histories to be entered into a controlled, retrospective statistical study.
Copyright Fred Lanting, All rights reserved, but reprinting allowed after permission. Please read his other articles on SiriusDog.com, for example, or e-mail him at Mr.GSD@netscape.com or Mr.GSD@Juno.com for specific articles.
Editors Note: A well-respected and frequent GSD specialty and all-breed judge for many clubs around the world, with KC and other-country credentials, Mr. Lanting since 1966 has lectured on Gait-and-Structure, Canine Orthopedic Disorders, and other topics, and has judged in about 30 countries. He has been described by a former OFA director as the worlds leading non-veterinarian authority on hip dysplasia. He has lectured at numerous veterinary schools in the USA and abroad, and is the author of the following must read books for the dog owner (E-mail for curriculum vitae). Canine HD and Other Orthopedics Disorders : This expanded revision is a comprehensive (nearly 600-page), amply illustrated, annotated, monumental work that is suitable as a coffee-table book, a reference work for breeders and veterinarians, and a study adjunct for veterinary students. It is equally valuable for the owner of any breed. It covers every aspect of HD and other orthopedic, bone, or spinal disorders, and includes genetics, diagnostic methods, treatment options, and the role of environment. Your autographed copy will be mailed from the USA as soon as the appropriate amount is received and is processed. Pricing: US $68 in the U.S., or ask about mail overseas. Combine orders with The Total German Shepherd Dog by the same author ($50 plus $4 postage). 17 of the 20 chapters are suitable for owners of any breed. Order both at once direct from the author, and the postage will be waived.