Anatomy of the Hip Joint
The acetabulum (socket) is formed by the union of four bones, the ilium, ischium, pubis and acetabula. The edge of the acetabulum starts out as soft cartilage until 3-4 weeks of age, then slowly converts to bone until about 10 months of age. The femur starts out as cartilage as well, starting to calcify at 3-4 weeks of age, and is bone around one year of age, or a bit later in large dogs.
The femoral head (the ball) looks like ⅔ of a spherical ball, merging into the femoral neck. The acetabulum (socket) is like the inside of a bowl, and should approximate the round shape of the femoral head.
The ligament of the head of the femur (aka teres or round ligament) attaches from the head of the femur to a notch in the acetabulum which is not weight bearing. The joint capsule and rim or labrum also acts to significantly stabilize the hip joint.
Extensor muscles of the hip include middle gluteal, biceps femoris, semimembranosus, and semitendinosus. Flexor muscle include iliopsoas, rectus femoris, tensor fascia latae and sartorius. Adductors are pectineus, adductors and gracilis. Abductors are gluteals and tensor fascia latae. External rotators are internal and external obturator, gemelli, quadratus femoris and sometimes piriformis. Internal hip rotators are gluteals and sometimes piriformis.
Movement of the Hip Joint and Pelvic Angulations
It is very hard to quantify what is normal hip movement in a dog. This is due to breed conformation differences. What movement is there needs to be symmetrical and of an adequate range of motion to allow the dog to thrive in its activities without undue stress on the ligaments and the still forming, soft, cartilaginous joint.
Most dog breeds have well defined breed standards, including the p elvic angle of inclination. The average dog has an angle of about 30 degrees, but may approach 35 degrees in a german shepherd or be as low as 20 in a lhasa apso.
This variation may be further exaggerated by pelvic misalignment, rotating to a flatter or steeper pelvic angle of angulation. In dogs with a flatter pelvic angle, the amount the rear leg can reach forward is limited by the hip joint and by the muscles of the back of the leg. This shortened stride length in which the foot is on the ground further caudally than ideal. This causes the foot to leave the ground early causing an exaggerated hip hike.
Can Hip Dysplasia be Prevented? Any or all of these may help.
Chiropractic. Animal chiropractors treat dogs with misaligned and poorly moving (subluxated) hips, pelvis and vertabrae. This leads to altered movement patterns, joint angles, ranges of motion and muscle tone that affect the hip. It is reasonable to suggest that subluxations can lead to altered hip joint function and thus dysplasia. Therefore it is reasonable that early chiropractic intervention to attempt to prevent the laxity and subsequent dysplasia. Pelvic and spinal misalignment can often cause a functional short leg, strained, tight and weak hamstrings and gluteal, and strained hip flexor muscles. This can cause a change in the movement pattern leading to laxity in the hip joint. This poorly controlled motion putting abnormal forces on the soft cartilage is often the start of the spiral down into dysplasia.
Limit exercise especially jumping exercises like frisbee until mature. But do exercise the dog to increase rear end musculature, like moderate occasional off-leash running (nothing repetitive like fetch) and swimming. At 3 months old limit walking to two, twenty minute walks a day, preferably on slightly rolling terrain. At 4 months of age increase the pace but keep the duration to twenty minutes. At 5 months of age increase distance to about two miles. At 6 months keep the distance at about two miles but add more varied terrain, hills, trail, side slopes and a little jumping and some stairs. At eight months gradually increase the exercise to two walks of one hour per day. Always exercise to tolerance - if the puppy wants to stop, then stop.
Weight management. A slightly calorie limited diet early in life slows growth and thus delays the amount of force on the immature hip joint until after the joint is turning to bone. Puppies on a slightly calorie controlled grow more slowly but attain the same size as puppies allowed to eat freely.
Supplements that may help: Glucosamine and chondroitin, MSM, green lipped mussels, essential fatty acids from fish oils, turmeric. Cannabidiol for pain and inflammation.
Helpful tip: Buy a spring or summer puppy who has had room to romp outside on a farm or larger backyard from a breeder that will limit exercise to several short romps per day. Cold weather and puppy mill set-ups limit appropriate early exercise causing weakness in the hip musculature needed to stabilize the hip joint.
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Development of Hip Dysplasia
Environmental factors are important! Puppies are born with normal hips. Puppies that go on to develop HD fail to sustain proper alignment and stability. This leads to bone remodelling also known as dysplasia.
Forces from resisting gravity and from muscles in movement are factors. As the body grows, it weighs more adding to the force of gravity. As the puppy starts putting on muscle mass, it gets stronger and stronger. Yet the acetabulum is still weak, partially made of cartilage, a tissue which is deformable.
This process can start as early as two weeks of age as stretching of the ligament of the head of the femur and the joint capsule. By 4 weeks of age inflammation may be noted. By 12 weeks of age changes in the synovium and articular cartilage.
These changes lead to imbalanced muscle tone, ligament weakness, cartilage damage, joint inflammation all leading to the femoral head going out of alignment on weight bearing. Once the femoral head shifts, the ossification of the femoral head and dorsal labrum is delayed because of increased pressure. Decreased pressure on the lateral part of the femoral head and ventral part of the acetabulum speed ossification and limit the chance of corrective remodelling. This leads to a flatter, shallower acetabulum. More force is transmitted to the femoral head and dorsal part of the acetabulum. This leads to degenerative joint disease.
To sum up and simplify, if you have stable hip joints at six months of age, they are unlikely to degenerate.
Dr. Paul Rosenberg & Dr. Craig Landry 416.231.2487
Can hip dysplasia be prevented?
Hip dysplasia (HD) is caused by genetic and environmental factors. It is not congenital, meaning the pups are born with perfect hips. The gene or genes that cause the dysplasia are not yet fully known. However some genes associated with hip dysplasia have been found in some breeds. The bigger, stockier, wrinklier, broad headed, barrel chested dogs who are appetite indulgent, uncoordinated and reach sexual maturity early are most prone to hip dysplasia. Genetic variation only causes 15 - 40% of hip dysplasia, with the bulk of the cases being from environmental factors.
Dogs are born with normal alignment/congruence and stability between the femoral head (the ball) and the acetabulum (the socket). The malformation of the soft cartilaginous acetabulum (socket) in the juvenile dog is caused by the lack of conformity, congruence and laxity of the muscles and ligaments. Once the joint is partially deformed even resisting gravity, whether standing, walking or romping in the park with the other dogs leads to abnormal forces and motion in the joint, leading to further malformation, the stretching of ligaments eventually causing osteoarthrosis and degenerative joint disease. How do we keep the forces normal until the cartilage has become bony enough to withstand the forces being applied!? Some more details first!
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