The screw-home mechanism of the knee joint during terminal extension involves which motion of the tibia relative to the femur?
- A 5-10° of medial rotation of the tibia locking the knee in full extension
- B Anterior translation of the tibia (drawer effect)
- C 5-10° of lateral rotation of the tibia locking the knee in full extension ✓
- D Posterior glide of the femur during active quadriceps contraction
Correct answer: C. 5-10° of lateral rotation of the tibia locking the knee in full extension
Explanation
In the final 5-10° of knee extension (open kinetic chain), the tibia externally rotates relative to the femur — the screw-home mechanism — due to the longer medial femoral condyle articular surface, tightening the cruciate and collateral ligaments to 'lock' the knee for weight-bearing. Unlocking requires initial medial rotation of the tibia by popliteus before flexion can resume. Anterior tibial translation would imply ACL laxity. The screw-home is a passive anatomical event, not an active quadriceps effect.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.