The frog walk: femoral weakness


This post is about a dog that is very weak on the hind limbs, can’t extend the limbs and is squatting and at a glance we could be mistaken with an orthopedic problem.

The femoral nerve is a major nerve that originates from the lumbar spine and provides motor and sensory function to the muscles and skin of the hindlimbs in dogs. Specifically, the femoral nerve innervates the quadriceps femoris muscle group, which is responsible for extending the knee joint and flexing the hip joint.

In addition to its motor function, the femoral nerve also provides sensory innervation to the skin on the medial and anterior thigh, the medial llimb, and the foot.

Damage or dysfunction of the femoral nerve can lead to weakness, but what is particular about this weakness it that the limb is not able to extend. This can result in abnormal gait, difficulty standing or walking, and even a loss of muscle mass in the affected limbs. I like to call this walk the “frog walk” because the patient will literally walk like a frog with the knees flexed, squatting, very weak.

We could find these clinical presentation when both femoral nerves are not working properly, and this is much more possible when we have a lesion affecting the L4L6 spinal cord segment.

How could be sure this a problem with the femoral nerve and the spinal cord or not just a knee/orthopedic problem?

The femoral nerve is tested by doing the patellar reflex. This reflex is important in assessing the function of the lower motor neurons and spinal cord segments L4-L6. It’s a reflex arc that is initiated by tapping the patellar tendon first. When the patellar tendon is tapped, it stretches the quadriceps muscles in the thigh, which activates sensory receptors called muscle spindles. These muscle spindles detect the change in muscle length and send a signal through the sensory fibers of the femoral nerve to the L4L6 spinal cord segment. In the spinal cord, the sensory fibers synapse with motor neurons that innervate the quadriceps muscles. The motor neurons are then activated, causing the quadriceps muscles to contract and extend the leg at the knee joint: A patellar reflex will make the knee to extend, it will kick you. The patellar reflex is an example of a monosynaptic reflex, meaning that there is only one synapse between the sensory neuron and the motor neuron in the spinal cord.

When we have a lesion into the L4L6 spinal cord segment we will have reduced patellar reflex but we will also have paresis and/or ataxia and/or proprioceptive deficits. SO THAT’S an important sign. With an orthopedic disease in the knees, you will NOT observe paresis or ataxia or proprioceptive deficits! It’s true that some old dogs, also if the knees are really arthritic might revealed absent patellar reflex, so this is why it’s important that you evaluate how they walk.

IF YOUR PATIENT HAS ABSENT PATELLAR REFLEX BILATERALLY AND WALKS NORMALLY, that is probably an incidentan finding,,,,does this make sense?

What can we see on this video?

You can see a non-ambulatory paraparesis: This dog can’t support its own weight, he is weak and  only  the hind limbs are affected. When we perform the neurological exam you can see the slow proprioception on the right hind limb only (even if both hind limbs are affected when walking) and the slow withdrawal and patellar reflex.

This is a young dog that was presented for an acute presentation of progressive hind limb problems and spinal pain not responding to medical treatment which consisted on NSAIDs and pain relief. The full neurological examination revealed a dog that was bright an alert, with an ambulatory paraparesis with reduced spinal reflexes on the hind limbs but normal cranial nerves examination. The anatomical localization was L4-S1 based on the full neurological examination.

The main differential diagnosis based on the clinical history and the VITAMIN D were: T:traumatic (disc extrusion) I:inflammatory ( MUO: meningo myelitis of unknown origin) and tumor. An MRI of the spinal cord was performed and a slipped disc was diagnosed. The dog recover a completely normal walk once the disc was removed surgically.