What is Screw home mechanism?
- Occurs in the knee joint, due to differences in size of the medial and lateral condyles and different surface areas of the medial and lateral tibial plateaus. It helps in achieving terminal extension.
- In an open chain extension, knee locking occurs with external rotation of tibia.
- In closed chain extension, locking occurs due to internal rotation of the femur.
Paradoxical Screw Home Mechanism (A surprising phenomenon)
- During loading response, at about 15° knee flexion, the tibia rotates externally (Locking mechanism). This rotation is maintained up to mid-stance.
- This locking during flexion is called “paradoxical screw home mechanism /movement” as it is well known that the tibia internally rotates in a flexed position (unlocking).
- Apparently, this is saves energy during gait, as less energy is used for knee joint locking during the double support than single support.
Screw Home movement during pre-swing and swing
- Expectedly, during rapid flexion in pre-swing, the tibia internally rotates (Unlocking mechanism) & maintains this rotation till the peak flexion of the initial swing.
- During complete extension in the late swing, the tibia rotates externally. (Locking mechanism)
This “Paradoxical Screw Home mechanism /movement” which showed
- Tibia rotating in a closed chain position
- Locking occurring in flexion
was observed in 2015 for the first time by Kim et. all 2015 after which there has been no data on this paradox.
In contrast, all studies before 2015 have not observed such a phenomenon.
What are your thoughts on this phenomenon?
ABOUT THE AUTHOR
GAYATRI SURESH (PT)
Gayatri Suresh (PT) is a Biomechanist who has completed her B.P.Th from DES College of Physiotherapy and M.P.T (Biomechanics) from SRM College of Physiotherapy, SRMIST. Her field of clinical expertise is in movement assessments through video analysis. Apart from her work at Auptimo, she works as a Clinical Specialist at Rehabilitation Research and Device Development, IIT Madras. She has won gold medals for her Research presentations and for securing First rank with distinction in her MPT degree respectively.
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