My Dog Is Limping on Their Back Leg: Could It Be a Cruciate Ligament Tear?

If your dog has suddenly started limping on one of their back legs, the most likely orthopaedic cause is a cranial cruciate ligament (CCL) injury. The CCL is the equivalent of the anterior cruciate ligament (ACL) in humans, and rupture of this ligament is the single most common orthopaedic condition seen in dogs worldwide.

Unlike in humans, where ACL tears are almost always caused by a single traumatic event, CCL rupture in dogs is usually a degenerative process. The ligament weakens gradually over months or years before it eventually gives way, often during something as ordinary as jumping off the sofa or playing in the garden. This is why some owners are surprised when their dog starts limping with no obvious accident.

Certain breeds are significantly overrepresented: Labrador Retrievers, Rottweilers, Golden Retrievers, Staffordshire Bull Terriers, and West Highland White Terriers. Overweight dogs are also at substantially higher risk. A 2008 study published in the Journal of the American Veterinary Medical Association found that overweight body condition was one of the strongest predictors of CCL disease.

The cranial cruciate ligament sits inside the stifle joint (the dog's knee) and has two main functions: it prevents the tibia from sliding forward relative to the femur, and it stops the stifle from overextending or rotating excessively.

When it ruptures, even partially, the joint becomes unstable. The tibia shifts forward under the femur with each step, causing pain, progressive joint damage, and inflammation. Over time, this instability leads to osteoarthritis within the stifle joint. The sooner the instability is corrected, the less arthritis develops.

The following signs suggest your dog may have a CCL injury and should be examined by a vet:

• Sudden lameness in a hind leg, especially after exercise

• Toe-touching lameness that persists beyond 48 hours

• Intermittent lameness over several weeks that worsens with activity

• Reluctance to exercise, jump, or climb stairs

• Swelling on the inside of the stifle joint

• Muscle loss in the affected hind limb over time

• A clicking sound from the knee when the leg is moved

Some dogs with a partial CCL tear show mild, intermittent lameness for weeks before a full rupture occurs. If your dog is showing any of these signs, it is worth having them assessed before the situation worsens.

One useful indicator is called the sit test. Ask your dog to sit and observe the position of their legs. A healthy dog sits with both hind legs tucked symmetrically underneath their body. A dog with a CCL injury will often sit with the affected leg stuck out to the side, avoiding bending the knee fully because of pain or instability.

This is a useful observation, but it is not a definitive test. Many conditions can cause a dog to sit awkwardly, including hip problems. A proper clinical examination is always needed to confirm the cause.

At the clinic, your vet will perform a physical examination of the stifle joint. The most important diagnostic manoeuvre is the cranial drawer test and the tibial compression test, both of which detect abnormal forward movement of the tibia relative to the femur. In an awake, tense dog this can sometimes be difficult to feel, and sedation may be recommended for a more reliable assessment.

X-rays of the stifle are an important part of the workup even though the ligament itself is not visible on X-ray. Radiographs show the degree of joint effusion (fluid), any bone remodelling from chronic instability, the tibial plateau angle (relevant for surgical planning), and whether there is any concurrent bone pathology.

For dogs under 10-15 kg with a partial tear, strict rest combined with physiotherapy and anti-inflammatory medication can sometimes allow sufficient scar tissue to form for the dog to regain acceptable function. This is not a cure — the joint remains arthritic — but in small dogs the outcome can be acceptable without surgery.

For medium and large dogs, conservative management rarely provides lasting relief. The joint instability continues, arthritis progresses, and many dogs go on to rupture the ligament fully even if they initially appear to improve with rest. Surgery is strongly recommended for most dogs over 15 kg.

There is also a significant risk of injuring the other leg. Studies have found that up to 60% of dogs with a unilateral CCL rupture will rupture the contralateral ligament within two years. This makes prompt treatment of the first leg particularly important.

If your dog has been limping for more than 48 hours, or if the lameness is severe, book a veterinary assessment rather than waiting to see if it improves on its own. Giving anti-inflammatories without a diagnosis can mask the pain and lead to a dog using an unstable joint, which accelerates joint damage.

At Mike's Vet, our surgical team assesses orthopaedic cases including CCL injuries regularly. We will perform a full clinical examination, take X-rays, and give you a clear picture of what is happening and what your options are. No referral is needed.