In this section we will present the developmental orthopedic joint disorders early spay/neuter produces and/or exacerbates, as well as its relationship to osteoarthritis. At the heart of the matter is how spay/neuter affects the dog’s hormones. When a dog’s reproductive organs are surgically removed, the “sex hormones” they produce in large part disappear, at least temporarily. The sex hormones are responsible for more than just sexual behavior, in fact they are known to affect bone and muscle, and one of their responsibilities is regulating growth.60,61,89,108
For inherited orthopedic conditions, such as hip and elbow dysplasia, or the predisposition for cranial cruciate ligament tear, removing the gonadal hormones that regulate the duration of bone elongation would be expected to alter growth patterns and subsequent joint alignment exacerbating any preexisting heritable propensity for disease.183 To the extent spay/neuter disrupts the production of sex hormones in an individual dog, it will delay the closure of growth plates on the long bones, provided the spay or neuter occurs before the growth plates have closed.61,108 The closure of bony growth plates generally occurs when the dog is between the ages of 4 and 18 months. Unfortunately, for the most part neutering (or spaying) is being performed prior to 6 months of age as advocated by many veterinarians and animal activists.
In 2014, UC Davis released research which allows us to amplify the findings of the 200783 systematic review referred to in our Research, Spay and Neuter sections of this site. The 2014 study 61 acknowledges that in the last three decades, the practice of spaying female dogs and castrating males (both referred to in this study as neutering) has greatly increased. Generally, spay/neuter is advocated prior to 6 months at UC Davis. A 2008 study 89 concludes that the prevalence of hip dysplasia and cranial cruciate ligament tear have also increased over the last four decades.
The aforementioned 2014 UC Davis study combined the incidence of all three joint disorders that have shown evidence of being increased by spay/neuter (i.e., hip dysplasia, cranial cruciate ligament tear, and elbow dysplasia) for one data-point representing the incidence of dogs diagnosed with at least one of the joint disorders. This analysis was also deemed logical for pathophysiological reasons because a disruption of the growth plate closure by gonadal hormone removal in the joint developmental stage would be expected to apply to all the joint disorders.
In fact, the 2014 UC Davis study showed that in Labrador Retrievers, about 5% of the sexually intact males and females had one or more joint disorders. Spay/neuter at less than 6 months doubled the incidence of joint disorders in both sexes.
In Golden Retrievers, the sexually intact males and females had the same 5% incidence of one or more joint disorders. However, spay/neuter at less than 6 months increased the incidence of joint disorders to 4-5 times that of intact dogs.61
In 2016, a UC Davis study of German Shepherds reveals that in males and females, neutering or spaying within the first year of life is associated with a highly significant, threefold risk of acquiring at least one joint disorder.108
In July of 2020, the research team at UC Davis followed up with studies from the same database to look at the aforementioned orthopedic joint disorders among 35 other dog breeds as well as mixed breed dogs. The breed-specific results were helpful in that they revealed a wide range of differences in disease vulnerability to spay/neuter. The variability with respect to dogs developing any one of these disorders, or all three, is dependent upon the time frame chosen for the spay/neuter and the actual genetically determined time frame for closure of growth plates in the individual dog. The researchers endeavored to evaluate the variables and provide specific advice regarding the timing of spay/neuter to minimize these orthopedic problems within specific breeds.180 Among mixed breed dogs the major differences in vulnerability seemed to be based upon size, with dogs under 43 lbs. showing less vulnerability to the orthopedic problems specific to these studies.181
The limitation we see with these studies is that the median age of the dogs’ last visit was at 4.9 to 6.0 years old. Certainly if the orthopedic malady is diagnosed when the dog is older than this age range, the study will not be able to record that diagnosis, and this makes the conclusions of this study less reliable.
Because these orthopedic disorders are so often associated with obesity rather than spay or neuter within the veterinary community, it bears mention that the interim findings in the Golden Retriever Lifetime Study (GRLS) show a strong connection between spay and neuter, obesity, and orthopedic injury. At the Aug 21, 2018 Fetch dvm360 conference in Kansas City, Missy Simpson, DVM, PhD, epidemiologist for the Morris Animal Foundation’s GRLS presented. She reported compared to intact dogs, dogs that underwent gonadectomy (spay or neuter) when they were 1 year old or younger faced a two-times higher risk for overweight or obesity. Dogs older than 1 year had a 40% increased risk for overweight or obesity. Further, Dr. Simpson shared that for every year older the dog was when gonadectomy occurred, it reduced the risk of overweight and obesity by 70%. Additionally, overweight or obese dogs that had undergone gonadectomy showed a 300% increased risk of chronic non-traumatic orthopedic injury (osteoarthritis, cranial cruciate ligament disease). Dr. Simpson says veterinarians should share with owners that if they keep their dogs lean, owners can reduce the risk of these orthopedic problems by almost half.
We see the take-home message differently: if you do not spay or neuter your dog (instead provide hormone-sparing tubal ligation or vasectomy) your dog will have a reduced risk of developing orthopedic joint disorders. Second, independent of the joint disorders, if you do not spay or neuter your dog (instead provide hormone-sparing tubal ligation or vasectomy) your dog will have a greatly reduced likelihood of becoming obese. We look to a 2019 review which summarizes the effects of neutering on cancer, orthopedic, and immune disorders in the dog and also explores the potentially exacerbating factor of body weight. Their review of relevant research confirms our conclusion; with respect to orthopedic joint disorders, weight did not exacerbate nor ameliorate the risk associated with neutering.183
In an all breed analysis, neutered males had elevated risk for intervertebral disk disease/herniation (IVDD) and (IVDH).183 Dachshunds are particularly noted for IVDD diagnosis with being neutered described as a risk factor for the condition. A recently published retrospective analyses demonstrated a correlation between early neutering (<12 months of age) and risk of intervertebral disc herniation in dachshunds of both sexes.185
Osteoarthritis is an ever-increasing medical condition within the canine community. Veterinarians generally point a finger at obesity for the prevalence of osteoarthritis, ignoring the possibility that loss of sex hormones due to spay/neuter may be largely responsible. On our “Obesity” page, we point out that in dogs that are not overweight, osteoarthritis often follows injury even if a reparative procedure is performed. Using our Billy as an example, although he was at an ideal weight, he sustained a cranial cruciate ligament tear which required TPLO surgery.
Unfortunately, his TPLO surgery did not prevent arthritis in the repaired joint. In fact, studies show arthritic changes start almost immediately after surgery.64 The American College of Veterinary Surgeons confirms rupture of the CrCL is one of the most common reasons for hind limb lameness, pain, and subsequent knee arthritis.
The salient point here is that rupture of the cranial cruciate ligament generally occurs as a result of improper bone growth due to a deficiency of sex hormones during development. Obesity is not responsible for an orthopedic deformity such as this. Further, we wonder if the ongoing deficiency of sex hormones brought about by spay/neuter has any role in the development of osteoarthritis even after reparative measures are implemented.
Utilizing the “Canine-Human Connection“, we looked to see if research on humans took into consideration sex hormone levels when evaluating the incidence of osteoarthritis. We found with respect to humans, in addition to age, obesity, genetics and other factors, Medscape specifically lists “reduced levels of sex hormones” as a primary risk factor for osteoarthritis. Interest in estrogens was stimulated by the dramatic rise in osteoarthritis prevalence among postmenopausal women. Research is ongoing to obtain a better understanding of the role that estrogen and its deficiency plays in menopause-induced osteoarthritic changes. Both experimental and observational evidence support a relevant role for estrogens in the homeostasis of joint tissues and, hence, in the health status of joints. 178
A study published in the journal Arthritis and Rheumatism 179 looked at how sex hormones (estrogen and testosterone) can affect people with osteoarthritis. In this study, researchers wanted to look at chondrogenic progenitor cells (CPCs). These cells are in tissue that’s affected by osteoarthritis, and they can help the tissue regenerate itself – if they’re activated by sex hormones.
The researchers found putting estrogen or testosterone into the tissue cell did increase the regenerative properties of the CPCs. Tissue from women was most influenced by estrogen; tissue from men was most influenced by testosterone.
Applying the results of human studies to our canine companions, it does appear that a deficiency of sex hormones in spayed/neutered dogs may enhance the development of osteoarthritis. Injured cartilage cannot regenerate or heal in the absence of adequate sex hormones. In cases of injury like CCL tear, even if reparative procedures are undertaken (e.g. TPLO surgery), the absence of adequate sex hormones precludes regeneration/healing of cartilage in the affected joint, and osteoarthritis is the unfortunate result.