Absent patellar reflex in the dog: femoral nerve and L4-L6
4-year-old German Shepherd hit by a car 2 days ago. It does not bear weight on the left pelvic limb: on weight-bearing, the stifle flexes and the limb collapses.
| Parameter | Result | Reference |
|---|---|---|
| Patellar reflex | Left absent; right normal | Normal (2+) |
| Left withdrawal reflex | Hock and digit flexion present | Normal |
| Sensation, medial left crus | Reduced | Present |
Where is the lesion located?
chevron_right Show answer and explanation
A. Left femoral nerve or L4-L6 spinal cord segments
Correct. The femoral nerve supplies the quadriceps (stifle extension and the patellar reflex arc) and its saphenous branch carries sensation from the medial limb. Without it, the limb cannot bear weight.
B. Left sciatic nerve
A sciatic lesion abolishes hock and digit flexion in the withdrawal reflex and causes knuckling; the patellar reflex is preserved or even appears increased.
C. T3-L3 spinal cord
A T3-L3 lesion causes upper motor neuron signs in the pelvic limbs: the patellar reflex would be normal or increased, never absent.
D. Left obturator nerve
The obturator nerve supplies the adductors; an isolated lesion makes the limb splay on slippery floors, but it does not abolish the patellar reflex or prevent weight-bearing.
lightbulb Key takeaway
Absent patellar reflex and a limb that collapses at the stifle = femoral nerve or L4-L6. The patellar is the most reliable myotatic reflex, but it may be reduced bilaterally in geriatric dogs without clinical significance. Confirm with sensation on the medial aspect (saphenous nerve).
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.