Quadraceps lag

I want to know the definition of "Quads lag" and why is it clinically important? Is there any article that i can read about it?

A quads lad typically refers to an inability to contract the quadriceps group during terminal knee extension. This may be seen in longsitting or in supine. The different positions will to a larger or lesser extent assess rectus femoris's inolvement vs the other quads.

Quads lag can be the result of any trauma to the thigh or more importantly the knee. Effusion over 15-30ml of fluid will maintain inhibition to the quadriceps and can delay resolution of a lag. Sever fractures to the femur or tibial plateau can also prolong a quads lag, as does the usual join replacement surgery.

Importantly for the neurological patient, a quads lag at the terminal 15 degrees of knee extension can and often leads to hyperextension and damage to the joint. This results from the hamstrings pulling the knee into extension to lock the knee. In these patients bracing is useful until the quads function has been restored. I hope this gives some overview about quads lag. There are many more scenarios.. regards richard

How does one measure a quads lag? I've seen different therapists do different things, but it's really hard to find a standardised protocol.

Thanks!

Position a rolled towel under the heel/achilles so the leg falls into passive knee extension (measure this angle and record as the passive lack). Ask the patient to maintain knee extension and ankle dorsiflexion and attempt to raise (straight leg raise) the whole leg a few inches off the towel without losing knee extension - measure the angle of knee extension again. Subtract the initial angle (i.e. the passive lack) from this angle and that gives you the active lag measurement.

E.g. passive lack = 15deg (i.e. fixed flexion of 15 deg); during straight eg raise the angle increased to 30deg as the patient couldn't maintain the 15 deg of knee extension. The lag angle therefore is 30-15=15 degrees of active lag.

Hope that makes sense.

What happens with active lag in gravity eliminated positions? still lag (aka no change)? gets corrected?

added later: found an article that said that extensor lag may be caused by muscular weakness, joint distension, joint stiffnes and pain but I found a test online with multiple choice questions and this asked the cause and gave four poosible options: with TKR what could be the reason for a lag? quad inhibition? swelling and pain? prior weakness? hamstring tightness?

So a bit confused

Heaps of thanks to anybody who is willing to share their thoughts

Quadricep lag cause of VMO muscle was not active, and it call muscle imbalance. It need to re-analysis muscle tigthness n function of proximal core stability

Rasyid, from indonesia