From the Research
The screw home mechanism is a crucial aspect of knee joint stability, and its disruption can lead to significant morbidity and mortality in terms of quality of life, particularly in patients with knee injuries or conditions affecting joint mechanics. The screw home mechanism is a natural rotational movement that occurs in the knee joint during the final stages of extension, as the femur internally rotates on the tibia, causing the joint to "lock" into a stable position 1. This mechanism is essential for normal knee function and stability during walking and standing.
Key Points
- The screw home mechanism begins when the knee is about 30 degrees from full extension and completes when the knee is fully extended.
- The medial femoral condyle is larger than the lateral condyle, which causes this asymmetrical rotation as the femur rolls and glides on the tibial plateau.
- This locking mechanism provides stability to the knee when standing, requiring minimal muscle activity to maintain an upright posture.
- The process reverses during knee flexion, with the femur externally rotating on the tibia to "unlock" the knee.
Clinical Implications
- Disruption of the screw home mechanism can lead to instability or difficulty with normal gait patterns, particularly in patients with knee injuries or conditions affecting joint mechanics 2.
- Evaluation and treatment of knee pain, including osteoarthritis, patellofemoral pain, and meniscal tears, should take into account the screw home mechanism and its potential disruption 2.
- Conservative management, including exercise therapy and education, should be the first line of treatment for knee injuries and conditions affecting joint mechanics, with surgical referral considered for patients with end-stage osteoarthritis or severe traumatic meniscal tears 2, 3.