Screw home mechanism (loking and unlocking of knee)

Timesphysio Institute – The Nerve of Learning

Locking and Unlocking of Knee Joint
 Also called screw home mechanism
 Locking – when knee is in full extension that is standing
 Unlocking – Initial flexion from locked knee

 Definition – The rotations that occurs between the femoral
condyles and tibia during final degrees of extension is called
Screw home mechanism.


Anatomical basis of locking and unlocking
 Articular surface of tibia and femur are not congruent
 Medial condyles has large antero-posterior diameter than lateral
condyles


Mechanism of Locking (when femur is fixed)
(1) During last 30 – 0 degree of extension locking is evident in last
5 degree of extension


(2) The A-P diameter of lateral condyles is less than that of medial
condyle




Notes by – Dr. Mitali Yadav Page 1