The Femoral Groove (Trochlea)
The end of the femur is angled relative to the long axis of the leg. This angulation helps produce the different appearances of women’s and men’s legs. Most women have more angulation at the femur than men. This is called knock-knee or valgus. Men generally, have straighter legs than women. They may be straighter or bow-legged (varus). Increased angulation or valgus, most often seen in women, effects the patellofemoral mechanism by placing the tibial tubercle more lateral to the patella.
The patellar tendon attaches to the tibial tubercle and as the quadriceps muscle tightens to straighten the knee, the mechanism is pulled in line from the tibial tubercle to the quadriceps muscle origin near the hip. Lateral position of the tibial tubercle pulls the patella lateral as the quadriceps tightens. The more lateral the tubercle, the more the patellar mechanism must resist this pull.
The angle that the patellar tendon makes from the patella to the tibial tubercle is called the Q Angle. The greater the Q Angle, the greater the lateral pull on the patella. Increased valgus at the knee or outward (external) rotation of the tibia increases this angle.
The Q Angle changes from extension to flexion and is higher in flexion. The tibia usually turns outward as the knee flexes because of the shape and contour of the lateral side of the end of the femur. This moves the tibial tubercle lateral and increases the Q Angle. The result is increased pressure on the patella. This is why a common complaint with patellar problems is inability to sit for long periods with the knee bent. The increased Q Angle with knee flexion produces increased pressure on the patella.
The end of the femur where the patella slides is called the femoral trochlea. This has a groove that generally matches the shape of the patella. The groove can be normal, deeper than normal, shallow, or even absent. A shallow groove is referred to as trochlear hypoplasia. The depth of the groove varies from the top of the trochlea where the patella starts in extension to the lower part where the patella ends in flexion. Usually, the top of the trochlea is shallower and the bottom is deeper. Depth of the femoral trochlea adds to the mechanical stability of the patella. A shallow groove in combination with patella Alta is almost always associated with significant patellar instability.
The shape of the trochlea can be assessed by x-ray. X-rays to evaluate the trochlea should be taken at no more than 45 degrees of knee flexion, the Merchant view. X-rays taken at greater than 45 degrees, commonly called the sunrise view, do not provide useful information. In addition to evaluating the trochlear shape, the Merchant view also assesses patellar position and contour. CT or MRI scans are not necessary to evaluate the patellar mechanism.
The end of the femur is angled relative to the long axis of the leg. This angulation helps produce the different appearances of women’s and men’s legs. Most women have more angulation at the femur than men. This is called knock-knee or valgus. Men generally, have straighter legs than women. They may be straighter or bow-legged (varus). Increased angulation or valgus, most often seen in women, effects the patellofemoral mechanism by placing the tibial tubercle more lateral to the patella.
The patellar tendon attaches to the tibial tubercle and as the quadriceps muscle tightens to straighten the knee, the mechanism is pulled in line from the tibial tubercle to the quadriceps muscle origin near the hip. Lateral position of the tibial tubercle pulls the patella lateral as the quadriceps tightens. The more lateral the tubercle, the more the patellar mechanism must resist this pull.
The angle that the patellar tendon makes from the patella to the tibial tubercle is called the Q Angle. The greater the Q Angle, the greater the lateral pull on the patella. Increased valgus at the knee or outward (external) rotation of the tibia increases this angle.
The Q Angle changes from extension to flexion and is higher in flexion. The tibia usually turns outward as the knee flexes because of the shape and contour of the lateral side of the end of the femur. This moves the tibial tubercle lateral and increases the Q Angle. The result is increased pressure on the patella. This is why a common complaint with patellar problems is inability to sit for long periods with the knee bent. The increased Q Angle with knee flexion produces increased pressure on the patella.
The end of the femur where the patella slides is called the femoral trochlea. This has a groove that generally matches the shape of the patella. The groove can be normal, deeper than normal, shallow, or even absent. A shallow groove is referred to as trochlear hypoplasia. The depth of the groove varies from the top of the trochlea where the patella starts in extension to the lower part where the patella ends in flexion. Usually, the top of the trochlea is shallower and the bottom is deeper. Depth of the femoral trochlea adds to the mechanical stability of the patella. A shallow groove in combination with patella Alta is almost always associated with significant patellar instability.
The shape of the trochlea can be assessed by x-ray. X-rays to evaluate the trochlea should be taken at no more than 45 degrees of knee flexion, the Merchant view. X-rays taken at greater than 45 degrees, commonly called the sunrise view, do not provide useful information. In addition to evaluating the trochlear shape, the Merchant view also assesses patellar position and contour. CT or MRI scans are not necessary to evaluate the patellar mechanism.
