Figure 2.11 shows the left tibia subluxed forward with a quadriceps contraction. This is indicative of an ACL-deficient knee. When the quadriceps is contracted against resistance with the knee flexed at 30° and without weight bearing, there is an anterior displacement of the tibia (this is an open kinetic chain exercise). Figure 2.11 shows the tibia sub-luxed anteriorly. This nonweight-bearing exercise is called open kinetic chain exercise.
Open kinetic chain exercise is also seen with the patient on the quadriceps machine in a fitness room. The athlete sits on the leg extension machine and extends the knee. The quadriceps pulls the tibia forward if there is no ACL or causes significant strain on the ACL graft. In the early rehabilitation phase, this exercise must be avoided to prevent strain on the recently implanted graft.
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