Spot on Karin!!! Terminal knee extension or extended the leg with resistance, a load, ankle weights, etc from 15 degrees to neutral biomechanically creates a shearing force of the ACL on the tibia placing increased load on the graft and should be avoided. There are studies that have examined how many forces, I am not aware of that information measured in newtons(F), but it is out there.
Lunges BTW do not hurt the graft after 8 weeks of healing also! That is also a misnomer.
Answered by Robert Newman, P.T. Manager Outpatient Therapy Services, United Regional Hospital, Wichita Falls, TX
I am a practicing P.T. for 30 years and have seen a large evolution with surgeries and in the rehabilitation of ACL injuries.
Studies have shown that short arc open chain knee extension creates very high anterior excursion forces on the ACL. I have done over 200 studies with the KT1000 & KT2000 knee ligament arthrometer. One of the tests for ACL tear is the active extension test, which is a short arc knee extension. This test for ACL tear would demonstrate more anterior tibial excursion than performing a 30 Newton Lachman Test.
Fleming et al. Performed a study on Peak ACL Strain Values that you might want to look up. In his study, the highest forces on the ACL were:
Isometric quad sets at 15 degrees of flexion – 4.4%
Squatting with a sports cord – 4.0%
Active Flexion/Extension w/weight boot (45N) – 3.8%
Lachman Test at 30 degrees – 3.7%
Squatting – 3.6%
Active flex/ext 2.8%
I would suggest: mini-squats 0 – 30, Open chain weighted quad extensions from 90 – 45 degrees, and closed chain step exercises in the early rehab. If patellar tendon is used, No plyometrics for 12 weeks as some studies have shown patellar fracture with this activity due to the removal of the bone plug from the patella.
Be wise. There is no hurry.