Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry to hear about Samson's weakness and instability.
Has he ever had radiographs of his spine or hips?
If you pinch his toes on his rear feet does he feel it?
If you support him standing and flip his feet so the topside is down does he immediately right them?
It is important to find out whether he is too weak and painful to move properly, or whether he has lost the neurologic ability to do so. Some big dogs are very stoic, and because they have been uncomfortable their whole life they don't complain, they just suffer in silence and tend to become even less active, because it hurts to move.
Is he able to hold his eliminations and go consciously or has he has lost the ability to control his urine and stool (incontinence)? If he has loss of control he has likely has loss of neurologic function.
It is very possible that he is dysplastic. Sometimes it is simply too painful to get up and move and they can become quite stiff. Symptoms can worsen suddenly if a piece of the arthritic changes in his hip breaks off and is free in the joint.
But if he is dragging his toes that can signify neurologic problems, such as an intervertebral disc(s) (cushions between the bony vertebrae) that are out of place or spinal arthritis putting pressure on the spinal cord or even a mass in or around the spinal cord.
Another possibility is a condition called FCE, fibrocatilagenous emboli, where a chunk of cartilage breaks off and lodges in the blood vessels that supply the spinal nerve roots. It is very painful initially as blood supply to tissue is blocked off. The pain only lasts a short time, less than a few hours to a day, but the weakness from the nerve damage it causes it can last for weeks or in rare cases is permanent.
Rotties, Mastiffs, and German Shepherds are prone to a disease process that affects the rear legs called lumbosacral stenosis (LSS).
It can have many of the same symptoms as a FCE as it causes neurologic symptoms too. It is caused by weak spinal ligaments that allow the bones in the spinal column to move and place pressure on the spinal cord or it can be due to inflammation of the ligaments inside the spinal cord canal causing pressure on the spinal cord leading to loss of function, just like a FCE.
FCE are initially painful but after that it's just a matter of regaining function.
LSS can be painful on and off until the spinal column is stabilized and the pressure is taken off the spinal cord permanently.
Another possibility if this has been slowly progressive and he seems not painful is a condition called ascending myelopathy. This is a progressive degeneration of the spinal nerves that begins with incoordination of the rear legs then progresses to the front legs and loss of urine and stool control (continence).
He really needs a veterinary examination as soon as possible. Radiographs to look for a collapsed disc space or arthritis of the spine and hip dysplasia would be helpful. We need to know what the problem is to treat it successfully.
If those look fine then an MRI of his spinal cord in the back of the body will be helpful.
Pain and inflammation in these conditions is controlled with nonsteroidal anti-inflammatories like Metacam, Deramaxx or Rimadyl as well as Tramadol and/or Gabapentin.
You can use these with the omega 3's and glucosamines if arthritis or hip dysplasia is diagnosed. These nutraceuticals help improve cartilage and joint fluid health as well as reduce inflammation.
I recommend using a combination of a glucosamine/chondroitin product (examples are Dasuquin or Cosequin) and an omega 3 fatty acid (like 3V Caps or Derm Caps). I recommend an omega 3 fatty acid dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give him 20mg of EPA per pound of body weight per day. For example an 80 pound dog could take 1600mg of EPA per day. Omega 3's and glucosamine/chondroitins work synergistically and improve cartilage health and joint fluid quality and quantity as well as reducing inflammation. They can take several weeks to see full improvement but some dogs do very well with them alone. They are available over the counter.
Another option is a product called Duralactin. This is an anti-inflammatory product derived from milk proteins and it also has omega 3 fatty acids incorporated into it which can be very helpful. See this link for further information: http://www.duralactin.com/products_canine.html
There is no treatment for myelopathy, unfortunately. We can only truly diagnose that condition after death because it requires a biopsy of spinal cord tissue. We usually rule out everything else and with a history of little to no pain and a gradual onset then we assume it is myelopathy. There is a recently developed blood test that looks for genetic markers for myelopathy. If you want to test him for the disease this blood test is pretty accurate. Here is a link to a website which will give you information about how to get him tested:http://www.offa.org/dnatesting/dm.html
If he is not responding to cortisone or nonsteroidals then I think that more diagnostic testing should be done. An MRI of his spinal cord will help diagnose intervertebral disc disease or lumbosacral stenosis. Those conditions can be treated surgically.
In the meantime try and keep your pup quiet. With spinal instability the more they do, especially jarring activities like running and stairs, the faster the condition can progress.
Please let me know if you have any further questions.