Always check the “down” leg!
Occasionally, patients have a reduced to absent patellar reflex in the non-recumbent (“up”) leg when lying in lateral recumbency, but this might not be an abnormal / pathologic finding. If the patellar reflex were truly reduced to absent, this would imply that there is disease in the L4-L6 region of the spinal cord, peripheral femoral nerve, or quadriceps muscle. As a result, gait analysis should demonstrate decreased to absent ability to extend the stifle during the midstance phase of the stride.
If the “up” leg has a reduced patellar reflex, check the patellar reflex again when it’s the recumbent (“down”) leg. If the patellar reflex can be elicited in the “down” leg, then the patellar reflex is likely normal even though it could not be elicited as the “up” leg. There is no easy explanation for this phenomenon, but it could be that one of the following is occurring:
- The patient is nervous/anxious or has increased tone in the limb that overrides the reflex in the “up” leg, but the limb is more relaxed when it’s the “down” leg.
- Some normal geriatric patients have a reduced to absent patellar reflex even in the absence of other neurologic signs. In one small study, 4 of 14 normal dogs (28%) older than 10 years of age had a decreased to absent patellar reflex in one or both legs compared to 2 of 72 dogs less than 10 years of age.
