Normal range of motion (ROM) of the knee joint is from 0 to 135 degrees in an adult. Full knee extension should be no more than 10 degrees. In genu recurvatum (back knee), normal extension is increased. The development of genu recurvatum, may lead to knee pain and knee osteoarthritis.
You can watch full video explanation about Causes and management of hyperextension of knee in this video
Hyperextension of the knee may be mild, 
moderate, or severe.
knee hyperextension in stance
This common gait deficit occurs when the quadriceps fail to perform their customary role during loading responseand the first part of midstance.
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LOADING RESPONSEOrientation of ground reaction force vector (GRFV) in sagittal planeNormal GRF is located |
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- posterior to ankle joint
- posterior to knee joint
- anterior to hip joint
What effect will this have on joint motion and muscle activation?
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LOADING RESPONSEOrientation of ground reaction force vector (GRFV) in frontal planeNormal GRF is located |
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- lateral to subtalar axis
- medial to knee joint
- medial to hip joint
What effect will this have on joint motion and muscle activation?
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During loading response, ground reaction force produces |
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- a plantar flexion moment at the ankle joint
- a flexion moment at the knee
- a flexion moment at the hip
The body controls these moments with
- eccentric activity in the ankle dorsiflexors
- eccentric activity in the knee extensors
- isometric activity in the hip extensors
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During loading response, ground reaction forces produce: |
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- a pronation moment at the subtalar joint
- a varus moment at the knee
- an adduction moment at the hip
The body reponds to these moments with
- eccentric activity in the intrinsic foot muscles and other supinator muscles to control subtalar pronation.
- passive tension in the lateral knee structures. Active force in the tensor fascia lata could contribute to knee stability in the frontal plane
- activity in hip abductor muscles
return to using ground reaction forces…
Visualizing ground reaction force vectors (GRFV) to understand typical gait patterns
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DURING LOADING RESPONSE |  |
DURING MIDSTANCE |
|---|---|---|---|
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DURING TERMINAL STANCE |  |
DURING PRESWING |
The quadriceps may not act appropriately in the event of:
- Quadriceps weakness
- Pain with quadriceps activation
- Proprioceptive deficit
When the knee extensors fail to control the ground reaction force’s knee flexor moment, the person must compensate to preserve knee stability.
These compensations will likely hyperextend the knee during stance. The compensations might include one or more of the following:
- Substitution of another muscle in a closed chain
For example,
- Increased hip extensor force
- Increased ankle plantar flexor force
- Motions that relocate the GRF vector, changing the moment the GRF produces at a joint.
For example,
- Forward trunk lean during loading response and mid stance
- FORWARD TRUNK LEAN IN STANCE
during LOADING RESPONSE during MIDSTANCE
This common gait deficit occurs when the quadriceps fail to perform their customary role during LOADING RESPONSE and the first part of midstance. This might occur in the event of:
- QUADRICEPS WEAKNESS
- PAIN WITH QUADRICEPS ACTIVATION
- PROPRIOCEPTIVE DEFICIT
During loading response, a forward leaning of the trunk produces an anterior inclination in the ground reaction force vector. Because this relocated vector passes closer to the knee joint, it produces a smaller flexor moment at the knee. If the GRF vector passes in front of the knee joint, it can hyperextend the knee during loading response.
When the person leans forward with the trunk DURING MID STANCE, but not during loading response, quadriceps weakness or knee pain are less likely causes. Instead, it may be a compensation that helps move the body’s center of gravity forward over the stance foot. This compensation is necessary when:
- the ankle has limited range of motion in dorsiflexion
- plantar flexor strength is inadequate to control midstance dorsiflexion.
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Flat Footed Initial Contact
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Foot flat at initial contact
At initial contact, the ground reaction force vector’s point of application is ordinarily near the heel.. As loading response progresses, the ground reaction force vector moves posterior to the knee, producing a flexor moment. 
By contacting the ground initially on a flat foot, the person moves the ground reaction force vector’s point of application anteriorly…so that the more anteriorly situated force vector is closer to the knee joint throughout loading response, and so produces a smaller knee flexor moment during that period.If the ground reaction force moves anterior to the knee joint’s lateral axis, it produces a knee extensor moment. Therefore, people may compensate for knee extensor weakness by contacting the floor with a relatively flat foot.
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Motions that relocate the joint axis, changing the moment the GRF produces at a joint
For example,
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Decreased forward pelvic rotation
Hemiplegic patient have a common gait deviation during their gait training is hyper-extension of knee or genu recurvatum.
Cause of genu recurvatum are
1. Weakness of plantar flexors:
2. Flail foot i.e. polio, cerebral palsy etc
3. Tightness of plantar flexors (TA tendon)
4. Quadriceps weakness
5. Use of AFO also causes hyper extension
Because of above factors patient shows a poor loading response in gait.
In normal loading response ankle goes from 10 degree of plantar flexion to 10 degree of relative dorsiflexion and knee in 10-20 degree of flexion. There is anterior translation of tibia over the fixed foot.
This anterior translation of tibia over the fixed foot is affected due to TA tightness.
In weakness of plantar flexors & flail foot if tibia moves over the fixed foot and goes in to relative dorsi flexion then this may lead to buckling of knee and lead to poor stability during loading response to mid stance. to avoid this patient does the compensatory movement of, avoiding the anterior translation of tibia and forward lurching gait, with locking of knee. frequent use of this pattern of locking mechanism of knee during walk leads to hyper extension of knee.
Gait of RT hemiplegic Patient with genu Recurvatum
Video of hyperextension of knee in hemiplegic patient Click here
Video of the Para Knee Hyperextension Lat View click here
Para Knee Hyperextension Anterior View
1. In case of weakness of platar flexors , flail foot & weakness in whole limb use HIGH AFO. That is the posterior strap of the AFO is hiogh enough up the lower margin of popliteal fossa. This long leverage prevents it from going backward. 
https://www.youtube.com/watch?v=LPxuXqNNz_U
https://www.youtube.com/edit?video_id=LPxuXqNNz_U&video_referrer=watch
Video of correction of hyper-extension of knee with high AFO click here
https://www.youtube.com/watch?v=LPxuXqNNz_U
2.But this will not work in patients who walk with forward lurch posture or those who take bigger step length of opposite unaffected leg.the solution for this is very simple reduce the step length of opposite leg and allow him to step by the affected leg instead of going ahead. this will pull back the line of gravity which was falling forward to knee and reduce hyper extension.
3. knee Brace: Swedish knee brace and check knee brace
Swedish knee brace Swedish hinged knee brace
check knee brace video of check knee brace in walking click here
https://www.youtube.com/watch?v=BMoBAwz8l1k
4. In the patients having sever hypertension and can’t be corrected by all these measures then the last solution is use KAFO for walking.
