The word "dysplasia" means "developmental abnormality". The elbow is a complex joint because it involves the articulation of three bones. If the three bones do not fit together quite perfectly as a result of abnormal development, the consequence is the abnormal concentration of forces on a specific region of the elbow joint.
The 2014 UC Davis 61 study confirms that early spaying (or castration) is a major risk factor for a dog developing elbow dysplasia. In short, sterilization delays the closure of growth plates on long bones, provided that sterilization occurs before the growth plates close. Closure of the bone growth plates usually occurs when the dog is between 4 and 18 months old. If the dog is spayed or neutered before the age of 8 months, the likelihood of the dog developing elbow dysplasia, hip dysplasia, and / or cranial cruciate ligament tear is significant.