National Physical Therapy Examination (NPTE) Practice Exam

The choice of isometric quadriceps contraction at 15 degrees as the activity that poses the greatest strain on an ACL post-reconstruction is grounded in understanding the biomechanics of the knee joint during rehabilitation.

At 15 degrees of knee flexion, the tension on the ACL is significantly higher compared to other angles of flexion. This is largely due to the anatomy of the knee and the engagement of the quadriceps in this position. When the knee is near full extension, the ACL is naturally under its greatest tension due to the positioning of the femur and tibia. At lower degrees of flexion, especially around 15 degrees, the quadriceps are effectively able to exert force while the ACL is still engaged in stabilizing the knee.

Moreover, during quadriceps contractions, the anterior pull from the quadriceps is counteracted by the posterior stabilizers such as the ACL; thus, when the quadriceps are activated at this low degree of knee flexion, it creates a substantial load across the ACL. This heightened strain at 15 degrees can increase the risk of complications or failure of the reconstructed ACL since the graft is still healing and is at its most vulnerable during the early phases of rehabilitation.

In contrast, isometric contractions performed at higher