In 60-90 degrees of knee flexion, what percent of the patella's surface is in contact with the femur?

In 60-90 degrees of knee flexion, what percent of the patella's surface is in contact with the femur?

• A. 10%
• B. 60%
• C. 20%
• D. 30%

Answer: (D)

As the knee flexes into mid to deep flexion, the patella settles into the femoral trochlea and only a portion of its surface can articulate with the femur. The groove’s geometry and the way the patella tracks mean contact is concentrated on a limited area, not the entire patellar surface. In the 60–90 degree range, this contact is mainly on the inferior portion of the patella against the lower part of the trochlea, so roughly about one-third of the patellar surface is actually in contact with the femur. This reflects how the patellofemoral joint bears load: more flexion increases contact compared to full extension, but the area in contact remains a fraction of the patella’s total surface. Keep in mind that exact percentages can vary between individuals and with measurement methods, but around 30% is a commonly cited estimate for this range.

As the knee flexes into mid to deep flexion, the patella settles into the femoral trochlea and only a portion of its surface can articulate with the femur. The groove’s geometry and the way the patella tracks mean contact is concentrated on a limited area, not the entire patellar surface. In the 60–90 degree range, this contact is mainly on the inferior portion of the patella against the lower part of the trochlea, so roughly about one-third of the patellar surface is actually in contact with the femur. This reflects how the patellofemoral joint bears load: more flexion increases contact compared to full extension, but the area in contact remains a fraction of the patella’s total surface. Keep in mind that exact percentages can vary between individuals and with measurement methods, but around 30% is a commonly cited estimate for this range.