The role of exaggerated patellar tendon reflex in knee joint position sense in patients with cerebral palsy.
A big knee-jerk reflex in CP does not signal poor knee position sense.
01Research in Context
What this study did
The team tested knee position sense in kids with cerebral palsy.
They tapped the patellar tendon to check if the reflex was exaggerated.
Then each child tried to match the angle of one knee with the other while blindfolded.
What they found
Legs with big reflexes did as well as typical kids.
Legs with calm reflexes made bigger angle errors.
So an exaggerated reflex does not mean poor proprioception.
How this fits with other research
Lam et al. (2011) saw the same surprise in autism: no proprioceptive loss even though people expected one.
Gofer-Levi et al. (2013) found a different hidden problem—kids with CP could not learn a motor sequence by practice.
Sherwell et al. (2014) warn that motor tasks can make kids with CP look worse than they are; our paper adds that reflex size can make clinicians think there is a sensory deficit when there is not.
Why it matters
Do not blame clumsy movement on poor joint sense just because the knee jumps high.
Test position sense directly with a simple blindfold matching task.
If the child fails, look beyond the reflex and check other factors like attention or weakness.
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Blindfold-match knee angles before you label a child as having proprioceptive deficits.
02At a glance
03Original abstract
The aim of this pilot study was to determine if exaggerated patellar tendon jerk affects knee joint position sense (JPS) in cerebral palsy (CP) patients, by comparing JPS of the knee between participants with normal and exaggerated reflexes. The thresholds for reflex classification were based upon the data from able-bodied volunteers. JPS was measured as the ability of a subject (with eyes closed) to replicate a knee joint position demonstrated by an examiner. Tendon jerk was measured as the moment of force in response to patellar tendon taps. Data was collected from 27 limbs of CP patients (N=14) and 36 limbs of able-bodied volunteers (N=18). JPS was less accurate (p=0.014) in limbs with non-exaggerated reflexes (50.28±43.63%) than in control limbs (11.84±10.85%). There was no significant difference (p=0.08) in JPS accuracy between limbs with exaggerated reflexes (18.66±15.50%) and control limbs. Our data suggests that one component of sensorimotor impairment, JPS, is not as commonly affected in CP patients as previously reported. JPS of the knee is reduced in limbs with non-exaggerated reflexes; however in limbs with exaggerated reflexes which is seen in the majority of CP patients, JPS is not affected.
Research in developmental disabilities, 2015 · doi:10.1016/j.ridd.2015.07.021