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5 Reasons Why You Need to Restore Terminal Knee Extension

Is terminal knee extension important? Everyone works on flexion, but what about passive, end range knee extension?
Restoring full terminal knee extension (TKE) should be a top priority if your patients are lacking it.  Functioning/playing without full knee extension motion can cause problems not only at the knee joint but also up & down the kinetic chain.
Here's what one study said:
"Loss of full knee extension is a potentially debilitating problem. It is thought that a lack of symmetrical knee extension after ACL reconstruction is more debilitating than preoperative instability and that a small loss of extension is particularly detrimental for the active population." (1)
And just so we’re all clear, stopping at 0° is not restoring full TKE.  Measure the other knee (as long as that side isn’t dysfunctional/pathological) and that is what your goal should be.  Most people have about 5° of hyperextension (6° in female and 5° in male high school athletes [2]), but it may be more or less so, again, measure the uninvolved knee.
Check out this video on a quick and easy way to assess knee extension ROM – it’s how I do it unofficially and then I follow up with an actual goniometer measurement…and yes, I still actually use a goniometer.

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So why is it so important to restore terminal knee extension for your patients?

1 - Leads to worse patient outcomes

Limited terminal knee extension 
  • this study "showed that the most statistically significant factor related to lower subjective scores was lack of normal knee extension" - and they considered normal knee ROM to be within 2° of extension, including hyperextension (3)

2 - Increases the risk for developing arthritis

multiple studies have shown 
  • "less than normal knee extension ROM at discharge was a predictive factor for developing OA after ACL surgery" (4)
  • "loss of normal knee ROM at final follow-up was associated with a higher prevalence of OA" (5)

3 - Causes Abnormal Gait

  • this should be rather obvious - if you're lacking extension motion, you can't achieve TKE during terminal stance...which puts more strain/stress on other structures in the kinetic chain
  • this slightly flexed position causes abnormal joint loading too

4 - Beats up the patella tendon

  • If someone's knee never gets fully straight (and into the closed-pack position) and is always slightly flexed, then it will put more strain & constant stress on the patella tendon

5 - Limits the ability of the knee muscles to optimally function

  • a lack of full knee extension will impair the quad's ability to generate force, leading to reduced knee extension torque (3)
  • maybe this weakness isn't directly because of limited knee ext, rather it could be because of pain, irritated patella tendon, OA, etc.  But regardless, the evidence is still there that there is a correlation 

5 - Limits the ability of the quad and other muscles to optimally function

  • limited knee extension will also affect other joints, most notably the ankle and hip.  Think about the triple extension required in most athletic activities - if the knee can't fully extend, then the ankle and hip have to overcompensate and will have a hard time generating the appropriate force - leading to decreased performance and possible injury.

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original blog post with references