Knee joint

• There are four main movements that the knee joint permits:

NORMAL KNEE – RANGE OF MOTION

Normal range of motion of knee is:

• Flexion – 120-150 degrees
• Internal rotation with knee flexed – 10 degrees
• External rotation with knee flexed – 30-40 degrees

The total range of motion is dependent on several parameters such as soft-tissue restraints, active insufficiency, and hamstring tightness.

MOVEMENTS OF KNEE JOINT:

FLEXION & EXTENSION 

• Flexion and extension are the chief movements. 
• These take place in the upper compartment of the joint, above the menisci.
• They differ from the ordinary hinge movements in two ways:
• Transverse axis around which these movements take place is not fixed.
• During extension, the axis moves forwards and upwards, and in the reverse direction during flexion.
• These movements are invariably accompanied by rotations (conjunct rotation). 
• When a person gets up from sitting position the femur internally (medially) rotates on the fixed tibia.
• Medial rotation of the femur occurs during the last 30 degrees of extension and
• In full extension collateral ligaments are taut .
• When the foot is off the ground, the tibia rotates instead of the femur, in the opposite direction.

ROTATORY MOVEMENTS:

• Rotatory Movements at the knee are of a small range.
• Rotations take place around a vertical axis, and are permitted in the lower compartment of the joint, below the menisci.
• Rotatory movements may be combined with flexion and extension (conjunct rotations), or may occur independently in a partially flexed knee (adjunct rotation).
• In the flexed position, the collateral ligaments are relaxed while the cruciate ligaments are taut.
• Rotation is controlled by the twisted cruciate ligaments.
• The conjunct rotations are of value in locking and unlocking of the knee.

PASSIVE MOVEMENTS :

• Passive movements can be performed in a partially flexed knee. 
• There is lack of conformity between bony surfaces that allows translating movements in three planes.

This movement include

• A wider range of rotation
• Anteroposterior gliding of the tibia on the femur
• Some adduction
• Some separation of the tibia from the femur.

 LOCKING AND UNLOCKING :

• Locking is a mechanism that allows the knee to remain in the position of full extension without much muscular effort. 
• Locking occurs in extension when the femur is internally (medially) rotated on a fixed tibia.
• Locking occurs as a result of medial rotation of the femur during the last stage of extension caused by Osgood shalter & Loose body in knee joint.
• Locking is a mechanism that allows the knee to remain in the position of full extension as in standing without much muscular efforts & is caused by quadriceps femoris.
• Unlocking of knee is required when flexion is initiated from fully exrended position.
• It involves External rotation/ Lateral rotation of femur on a fixed tibia.
• Unlocking is brought about by the action of popliteus muscle.
• When a person gets up from sitting position the femur internally (medially) rotates on the fixed tibia.