Athlete is sitting on the edge of table with knees flexed at 90 degree. When he extends his knee fully, what will happen to the tibial tuberosity in relation to patella
C i.e. Movement of TT towards lateral border of patella Tibial tuberosity is in line with midline of patellaQ at 90deg of knee flexion. However, when the knee is extended fully the TT moves laterally towards the lateral border of patella because of screw home mechanism (i.e. lateral rotation of tibia in non weight bearing or medial rotation of femur in weight bearing individuals). The Q. (quadriceps or patello-femoral) angle provides a concomitant lateral (valgus) force on patella which tends to make the patella track laterally. These last few degree of motion lock the knee in extension & referred to as screw home mechanism. With the knee fully extended, an individual can stand for a long time with out using muscles. The knee must be unlocked by the femur rotating laterally on tibia (by popliteus) for knee flexion to occur. Law of valgus: Because the femur normally runs slightly obliquely inwards, the Q (quadriceps) angle (i.e. angle that patellar tendon makes relative to shaft of femur) is formed, with its concomitant tendency to pull the patella laterally. This predisposition for lateral motion of patella is referred to as the law of valgus. Since the patella is relatively free to move upon the femur when the knee is extended. When the quadriceps femoris muscle contracts it will try to establish a straight line between its proximal attachment onto the femur & pelvis and its distal attachment onto the tibial tuberosity. Thus the Q angle provides an indication of the lateral force (vector) applied to the patella, which tends to make the patella track laterallyQ in order to establish a straight line relationship between the proximal & distal attachment of quadriceps femoris muscle group during extension. Q (patello-femoral or quadriceps) angle is the angle between the quadriceps muscle, primarily the rectus femoris muscle & the patellar tendon. It is determined by drawing a line from ASIS (anterior superior iliac spine) to the midpoint of patella and from tibial tuberosity to mid point of patella. Although the rectus femoris attaches to AIIS (anterior inferior iliac spine), the ASIS lies just above AIIS and is easier to palpate. Normally it is 13-18deg in knee extension.
No change
Movement of TT towards medial border of patella
Movement of TT towards lateral border of patella
Movement of TT towards centre of patella