What we previously called CPs (conscious proprioception) we now call the paw replacement test. Yes, if you haven't heard,CP is now the "old fashioned" term and has been replaced with the much less sexy term "paw replacement test". Why?? (You might ask.) The reason is simple: we were lying when we said we were evaluating just the conscious proprioception pathway! When the paw goes on the dorsum, conscious, unconscious and even a bit of motor pathways are involved in righting it to the correct position. Sometimes the truth isn't sexy, but alas, here we are.
What parts of the nervous system must work for the paw replacement test to work?
An abnormal paw replacement test almost always indicates a neurological problem however the lesion may be located anywhere along the pathway involved. The pathway is: peripheral nerve --> ipsilateral spinal cord -->ipsilateral medulla and pons --> cross in midbrain --> end in prosencephalon. Some branches also go: peripheral nerve --> ipsilateral spinal cord --> ipsilateral medulla --> ipsilateral cerebellum. You can see that a LOT is involved with this pathway so you really need to put together the remainder of the neurologic exam to appropriately utilize this test. The paw replacement test is one of several ways to test the proprioceptive pathways and they are often collectively referred to as "postural reactions".
What are postural reactions?
Paw replacement test: While providing support, and on stable footing, turn a paw upside down and place it on the dorsum. The animal should right the paw to the normal position with minimal to no delay, or scuffing. Want to brush up on your technique? See my YouTube channel with this link: https://youtu.be/vEFEVvO4TCQ
Placing (visual or tactile): A useful test for cats. The animal is blinded and advanced towards a horizontal surface such that the paw gently touches the surface. A correct response occurs when the animal places the limb on the surface. Want to see a video? Check out: https://youtu.be/VDyaL2kHNV8
Hopping: One leg is on the ground; the other 3 legs are removed from support. Gently, the animal is pushed in the lateral direction from the direction of the leg on the ground and the animal should hop.
Learning to perform postural reactions can take years...lots of practice...and seeing lots of different animals with different diseases. Paw replacement deficits are critical for localizing many parts of the CNS so, in my opinion, it is worth it to get this test right! If you want to get comfortable with these tests consider performing one or more of them on every patient you evaluate.
Thanks for reading! I hope you have a wonderful week. I will have limited service next week so please plan ahead if you have a case needing to be seen. Thanks!
