ACL reconstruction surgery replaces the torn ligament with a new tissue graft to restore knee stability. The six-week mark signifies a progression to the intermediate recovery phase of rehabilitation. This is a significant milestone where patients typically transition from crutches and braces to focusing on more active strengthening and functional movements. While the initial surgical fixation is strong, the biological healing process is still highly active, requiring careful adherence to medical guidance. Protocols vary based on the surgeon’s preference, graft type, and whether other injuries were addressed simultaneously.
Understanding the Graft Status
The six-week phase occurs during ligamentization, where the transplanted tendon tissue begins to biologically transform into a ligament. Immediately after surgery, the graft is strong due to the hardware used for fixation within the bone tunnels.
Around six to eight weeks, the graft tissue is biologically at its weakest point, known as the necrosis and revascularization phase. During this time, the graft loses some initial strength as the body breaks down old cells and establishes a new blood supply. This vulnerability necessitates continued caution, even as the knee feels more stable and surgical pain subsides. Most patients are cleared for full weight-bearing by this time, provided they have sufficient muscle control and did not require a protected weight-bearing status due to a complex meniscal repair.
Key Rehabilitation Milestones
The physical therapy goals during this phase focus on restoring full, symmetrical range of motion and initiating low-impact strengthening. Achieving full knee extension (0 degrees) is a primary goal to normalize walking mechanics. Flexion, or bending the knee, is also progressively advanced, often aiming to reach 90 to 110 degrees of bend.
The structured exercise program introduces controlled resistance to rebuild muscle strength lost during recovery. Permitted exercises typically include static quadriceps contractions (quad sets) and straight leg raises in multiple directions. Low-resistance activities like stationary cycling are encouraged, as they promote range of motion and circulation without excessive impact or shear forces on the knee joint. Balance and proprioception work, such as single-leg stance with support, also begins to retrain the joint’s sense of position in space. Patients with a hamstring autograft are cautioned against resisted hamstring curls until the 12-week mark to allow the donor site to heal fully.
Returning to Daily Life
Increased mobility and reduced pain at six weeks allow for a return to normal daily activities. Driving is often permitted, provided the patient is no longer taking narcotic pain medication and has regained necessary reaction time and muscle control. If surgery was on the right leg, the return to driving may be delayed slightly longer than for those with a left leg surgery, especially with an automatic transmission vehicle.
Navigating stairs typically progresses from a step-by-step pattern to a more normal alternating step pattern, relying on the improving strength of the operative leg. Returning to work is usually possible for those with sedentary or light-duty occupations, but heavy manual labor requires extended modification or time off. Light household activities, such as standing at the sink or preparing simple meals, are appropriate, but heavy lifting or carrying anything over 10 to 15 pounds should be avoided to prevent undue strain.
Critical Limitations and Safety Precautions
Due to the temporary biological weakening of the graft, specific activities must be strictly avoided to protect the surgical repair from failure. Any movement that involves sudden deceleration, twisting, or cutting motions is prohibited, including running, jumping, and pivoting. Ballistic movements or exercises that load the knee with sudden impact are also restricted.
Deep squats or lunges that require a high degree of knee flexion under heavy load are not appropriate at this stage of recovery. Patients should avoid engaging in contact sports or activities that carry an inherent risk of falling or unexpected impact. Adherence to these limitations is paramount, as prematurely stressing the graft during this vulnerable phase significantly increases the risk of re-injury and may compromise the long-term success of the reconstruction.