Figure 2-10. Checking the plantar reflex.
(d) Patellar reflex (knee jerk). Test the reflex in this manner:
1 Have the patient sit on a table or high bed to allow his legs to
2 Tap the patellar tendon directly with a rubber hammer.
3 Normally, the knee extends.
If muscle centers in the second, third, or fourth lumbar segments of the spinal
cord are damaged, the reflex may be blocked. People with chronic diabetes
or neurosyphilis may not have that reflex.
4 Conduct the reflex check as shown in figure 2-12 if the patient
must be lying down. Put your hand under the popliteal fossa and lift the patient's knee
from the table or bed. Tap the patellar tendon directly.