Threats to a Proper Knee Replacement Recovery (Lack of Full Knee Extension)

by PJ Ewing

This is Part 3 of a series of articles on threats to a proper knee surgery recovery. In this installment we discuss achieving full knee extension after knee replacement. I encourage you to explore the other articles in the series which you can find by clicking on the link below.

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Deep Vein Thrombosis and Knee Replacement

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Infection and Knee Replacement

Getting to 0º: Achieving Full Extension

Physical therapists, surgeons, exercise physiologists, personal trainers all emphasize full terminal knee extension for their knee patients after surgery. Why?

Let's start with defining our terms. Terminal Knee Extension is achieved when the angle of your leg is 0º when extending it out in front of you. 0º means it is perfectly straight. PTA Yvonne LaCrosse defines extension and flexion in this short video.

The Immediate Impact of Extension Loss

Loss of knee extension has a dramatic impact on gait, muscle activity, and normal tibiofemoral and patellofemoral arthrokinematics (the connectivity and function of your knee cap in relation to both the tibia and femur).

Imagine not being able to straighten your knee out. You can’t lock out your knee for stability. You naturally will shift your weight to the other extremity and overload your other knee, hip, and probably even your back. Your quadriceps and hamstring muscles never get to turn off and relax. Your patellar tendon will probably be on fire. And your patella (knee cap) will always be in use and engaged, taking stress. (5)

Lack of Full Knee Extension (1)

Here are five key results of the lack of proper knee straightening. Lack of a straight knee:

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Leads to worse patient outcomes and statistical success scores

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"The most statistically significant factor related to lower subjective scores was lack of normal knee extension. Normal knee straightening is considered to be within 2° of extension, including hyperextension." (3)

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Increases the risk for developing arthritis

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Multiple studies have shown that people with limited knee extension have a higher prevalence of arthritis (even in as little as a 3° loss). For example:

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"Less than normal knee extension ROM at discharge was a predictive factor for developing Osteoarthritis after ACL surgery" (3)

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"Loss of normal knee ROM at final follow-up was associated with a higher prevalence of Osteoarthritis" (4)

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Causes an abnormal walking pattern or gait

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If you're lacking knee extension motion, you can't achieve TKE during terminal stance (fully straighten your leg, stand erect). Therefore this puts more strain/stress on other structures in the kinetic chain.

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A slightly flexed position causes abnormal joint loading.

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This abnormal joint loading makes it easier for you to fall by catching your foot as opposed to walking heel to toe

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Higher demand on the patella tendon (what connects your kneecap to the tibia, the bone below your knee)

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If your knee never gets fully straight (and into the closed-pack position) and is always slightly flexed,