Introduction The knee is comprised of 2 joints tibiofemoral joint patellofemoral joint Patellofemoral Articulation Function transmits tensile forces generated by the quadriceps to the patellar tendon increases lever arm of the extensor mechanism patellectomy decreases extension force by 30% Biomechanics patellofemoral joint reaction force up to 7x body weight with squatting 2-3x body weight when descending stairs Motion "sliding" articulation patella moves 7cm caudally during full flexion maximum contact between femur and patella is at 45 degrees of flexion Stability passive restraints to lateral subluxation medial patellofemoral ligament login to view 2 more bullets medial patellomeniscal ligament login to view 1 more bullet medial retinaculum login to view 1 more bullet dynamic restraint quadriceps muscles Q angle definition login to view 1 more bullet normal Q angle login to view 7 more bullets pathology Tibiofemoral Articulation Function transmission of body weight from femur to tibia Biomechanics tibiofemoral joint reaction force 3x body weight with walking 4x body weight with climbing Motion in sagittal plane range of motion 3 degrees of hyperextension to 155 degrees of flexion thigh-calf contact is usually the limiting factor to full flexion normal gait requires ROM from 0 to 70 degrees Rotation instant center of rotation definition login to view 1 more bullet relevance login to view 4 more bullets "screw home" mechanism definition login to view 1 more bullet cause login to view 1 more bullet relevance login to view 1 more bullet Stability varus stress lateral collateral ligament valgus stress superficial portion of medial collateral ligament anterior translation anterior cruciate ligament login to view 13 more bullets posterior translation posterior cruciate ligament login to view 12 more bullets external rotation posterolateral corner is the primary stabilizer of external tibial rotation