Experienced and professional animal trainer provide their insights in answering this question :
A. You should take him to your vet for examination and maybe x-ray. He may have problem with patella, hip any other joint in hind leg

How to Identify Common Pet Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced pet care professionals :

If your dog is suddenly limping on its back leg, it is important to have them seen by your veterinarian as soon as possible. There are many possible causes of sudden limping in the back leg of dogs, including a ruptured ACL, strain and sprains, IVDD, fracture/dislocation and iliopsoas muscle injury.
The most common causes of acute or sudden lameness in dogs are soft tissue injury (strain or sprain), injury to a joint, bone fracture, or dislocation. Osteoarthritis and hip dysplasia may also cause lameness in dogs. Lameness can affect dogs of any age from growing puppies to senior dogs.
What is Hind Leg Lameness? Hind leg lameness is a painful condition similar to a broken bone, sprained ligament, or pulled muscle. Most cases require professional veterinary care. Some pups may need to undergo emergency treatment to reduce complications with their mobility and stance.
In general, gradual onset limps in dogs are caused by an underlying, chronic or degenerative condition, such as osteoarthritis or dysplasia. Sudden onset limps, on the other hand, are usually caused by an injury or trauma. Just because your dog has a gradual limp does not mean you should put off making an appointment.
Weakness in back legs of dogs can be caused by a variety of things, including myasthenia gravis, heart problems, anemia, hypothyroidism, and Addison`s disease.
If he is having a hard time walking, or he is staggering and wobbling on his feet, this back leg weakness may be a result of muscle atrophy, pain, or nerve damage. Other signs that can alert you to this condition are a reluctance or inability to stand, lameness, or paralysis in the legs.
Severe, acute onset lameness most commonly involves the foot, but may also be caused by more serious conditions such as a fracture or tendon/ligament injury. If the lame leg is obviously injured, swollen or broken, then it is vital to contact the practice as soon as possible to arrange an emergency visit.
Secondary Lameness – compensatory movement to offload a limb with pain causing overload of a second limb, ultimately leading to pain in that second limb.
Lameness or limping happens when your dog can`t use one or more of his legs properly. Pain and injury are usually linked to this condition. Limping can happen gradually or suddenly. Gradual limping affects your pup over time, while sudden limping occurs after an injury or trauma.
Treatment of lameness

For minor causes of lameness (sprain) restricting your dog`s exercise, or complete rest for a few days is usually adequate. If the exact cause is not known, a period of exercise reduction together with anti-inflammatories and pain killers may be required to see if the lameness improves.

If your pet is limping but not showing any signs of pain, it is still worth contacting your vet for advice. Because dogs can`t speak, it can sometimes be difficult to spot when they`re in pain, whether it be as a result of injury or an underlying issue.
A mild limp means your dog is still using the leg but not putting as much weight on it. If your dog has just developed a mild limp, but appears comfortable and healthy in all other ways, it`s not unreasonable to encourage them to take it easy for a few days and see what happens.
Spinal compression, herniated discs, and nerve problems can all disrupt the communication between a dog`s spine and brain. When the nerves are unable to function normally, dogs will lose the ability to walk, stand, and control their legs.
A dog limping but not crying or showing other signs of pain should still be taken seriously. Dogs are tougher than you think, and just because your dog isn`t howling in pain doesn`t mean there isn`t any pain. It would be best if you still got your dog to a vet for a check-up.
Causes of your puppy Limping

Heading the list are muscular sprains and strains, therefore there`s no need to panic if your puppy limps initially get some rest, and if the matter persists, get your puppy checked by the vet. Trauma is another biggie, and as young bones are soft, this could mean fractures.

A common explanation for frequent limping after lying down is arthritis. A dog with arthritis will limp after lying down for some time, but according to VetInfo.com, these dogs also walk more slowly than they used to, their gait may change, and there may be tenderness, warmth, and swelling around their joints.
There are still other reasons for your dog`s limping. It could be a side effect of infection such as Lyme disease or a cancer like osteosarcoma that affects bones. If you have a large breed puppy like a Great Dane, they might limp due to conditions such as hypertrophic osteodystrophy or panosteitis.
Neurological issues are conditions and diseases that block or negatively affect the ability of your pet`s central nervous system to communicate properly various parts of your pet`s body.
3: Lameness is consistently observable at a trot. 4: Lameness is obvious at a walk, and may not fully weight bear at stand. 5: Lameness produces minimal/non weight bearing in motion and/or at rest or a complete inability to move.
3: Lameness is consistently observable at a trot under all circumstances. 4: Lameness is obvious at a walk. 5: Lameness produces minimal weight-bearing in motion and/or at rest or a complete inability to move.
/ˈleɪmnəs/ [uncountable] ​the condition of being unable to walk well because of an injury to the leg or foot. The disease has left her with permanent lameness.
Non-steroidal anti-inflammatory drugs (NSAIDS), such as meloxicam (brand names: Metacam®, Rheumocam®), deracoxib (brand name: Deramaxx®), carprofen (brand names: Rimadyl®, Novox®), grapiprant (brand name: Galliprant®), firocoxib (brand name: Previcox®), robenacoxib (brand name: Onsior®), relieve pain and inflammation …
The specific causes of neurological problems vary, but can include genetic disorders, congenital abnormalities or disorders, infections, lifestyle or environmental health problems including malnutrition, and brain injury, spinal cord injury or nerve injury.
Sudden onset of collapse can be secondary to a variety of disorders including spinal cord injury, orthopedic disease, or systemic illness. This sudden hind-leg weakness may be a sign of a disease that requires prompt attention from your regular veterinarian. Or even a trip to the emergency room.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Q. 6 Mo MinPin rear leg goes lame mostly left leg. No pain no tenderness. Intermittent but occurring more frequently
ANSWER : A. You should take him to your vet for examination and maybe x-ray. He may have problem with patella, hip any other joint in hind leg

Read Full Q/A … : Vetinfo

Q. Shiba Inu. He periodically shakes and trembles, usually unrpovoked and seeming for no reason. Usually cuddling helps but not always. Becomes reclusive
ANSWER : A. I do find that Shiba Inu’s are a really sensitive breed. I think the first thing to rule out is pain. That could be pain from a muscle injury or even gastrointestinal pain. Try to pinpoint whether it occurs after a meal or not. He might be painful due to something going on in his GI tract, and the pain is at its worse after he eats.

I’ve also seen a lot of small breeds like Shibas get back pain, and shaking can definitely accompany that as well. If you haven’t see your vet who can perform a good physical exam and look for any signs of muscular pain along the spine or elsewhere. It’s not a bad idea at this point to consider doing some blood work just to screen for any problems that could be affecting organ function, for example.

If he’s healthy otherwise, I think it’s likely that there’s something that’s scaring him at home. These things can be really difficult to identify, and you have to be really aware and note exactly when the shaking occurs, how long it lasts, etc, and look for patterns. Dogs can hear things we can’t, and he may be hearing things you’re missing, and the noise is disturbing to him. Cuddling is a good idea, also working to distract him and desensitize him with toys and treats might help. But like I said above – definitely rule out pain first.

Q. Hello.. My jack russel has started to get a bowed front leg at the ankle and is causing him to limp quiet a lot.. Is there anything that can be done.?
ANSWER : A. It is possible an injury or deformity of the leg is causing the limp and physical changes you are seeing. Sprains, breaks, strains and even nutritional deficiencies may cause the leg to bow and pain/limping to occur. Having a vet take an X-ray and examine the leg is best to determine the cause of the changes and limp as well as the treatment needed. Casting, bed rest, and medications to treat pain may all be needed to help the leg heal. Until you can get to the vet, a regime of strict kennel rest with leashed walks only to go potty outside will help reduce any further injury to the leg and decrease pain.

Read Full Q/A … : Jack Russell FAQs Page!

Q. My 5 year old Dachshund has broken his rear leg. A trip to the vet is impossible for two more days (rural area), can I give him something for pain?
ANSWER : A. If your dog has a broken leg, then veterinary care is a must. If you can get into contact with your local vet before seeing him or her, they may be able to give you information on an OTC pain medication that could be safe to give dogs. Do not attempt to give any medications without first consulting your vet as many pain meds can cause kidney/liver failure or stomach ulceration if given to dogs. In the meantime, keep your dog on strict kennel or bed rest and only taking him out for short potty breaks is best to keep pain down and from letting the leg get further injured.

Q. My pomeranians back leg is bothering her I believe it is sprained she cant walk on it.she can stand on it and is not in any pain should she see vet
ANSWER : A. If you believe the leg may be sprained or you are seeing signs of injury such as pain, swelling, limp or loss of use of the leg, then scheduling a veterinary appointment is best. Your vet can examine the leg, and may also recommend an X-ray to check for breaks, sprains and dislocations that can all cause these issues. Until you can get into your vet it is best to limit all activity to strict kennel rest and leashed walks outside ONLY to go potty to help reduce the pain and decrease further injury to the limb.

Q. My 13 yr old male indoor cat displays tenderness to touch in his sides/haunches and it is increasing. Recently put him on diet for arthritis.
ANSWER : A. While tenderness in the back and hips can indicate arthritis pain, it can also sometimes indicate pain internally such as stomach or other organ issues. Cats and other pets will often stiffen their backs to protect the abdomen when in pain. If the pain continues or your cat is still in pain with arthritis treatment it is best to schedule a checkup with your vet to make sure there is not another source for the issue.

Read Full Q/A … : Vetinfo

Q. 6 lbs Chi pup, left leg sprain but she is constipated and refusing to eat. Only eats a few bits here and there
ANSWER : A. If your pup has not yet been seen by a vet, it may be a good idea due to the number of symptoms your puppy is experiencing. Leg sprains can be painful, and the pain may be causing nausea or a refusal to eat. Bloating and constipation can be due to a number of things ranging from internal illness, nausea and not feeling well, or even problems with digesting food or having internal parasites. Until you can get to the vet, enticing your pup to eat with a bland diet of plain boiled chicken and plain white rice may encourage some eating and can sometimes help settle an upset stomach.

If she is showing signs of severe distress such as extreme bloating, painful panting or whimpering, blue or pale gums and tongue, loss of consciousness or attempting to vomit or defecate without any results, it may indicate a serious condition called Bloat. This is a medical emergency and should be brought to your vet or ER clinic as soon as possible.

Q. I have two labs,one is not putting her leg down and her hip.it’s the back leg,I know she’s in pain I try to massage it what can I do for her
ANSWER : A. Labs can be prone to many issues with their hips. She also may have injured her leg through some form of trauma. Unfortunately there is no pain relief you can give her from home other than bed rest. If he pain continues it may be time to take her to the vet for an exam and pain medication.