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Rehabilitation after ACLR

Primary Purpose

Satisfactory rehabilitation is essential to a successful outcome after ACL reconstruction. The primary purposes of rehabilitation are to restore knee motion, knee strength, and knee proprioception (position sense).

Avoiding Overzealous Rehab in the Early Post-Operative Period

All ligament grafts undergo a temporary but profound weakening after reconstruction. The graft goes in a tendon but is transformed into a ligament. During this process the graft swells and animal studies have shown that it temporarily loses a majority of its strength as it remodels. This is true of both hamstring and patellar tendon grafts. It is estimated that this period lasts for 3 to 4 months after surgery. During this period the graft is subject to being stretched if it is not protected. Also, the attachments of the graft in the bony tunnels is not yet mature and the graft is also subject to being loosened from these sites. It is therefore imperative that rehabilitation during this period be done carefully so that the graft is not loosened.

Phase I: Restoration of Motion and Gait Training

On the third or fourth day after surgery, patients begin physical therapy to restore range of motion. This three-day break gives the initial post-operative soreness a chance to subside. The process of restoration of motion from fully straight (zero degrees) to nearly fully flexed (120 degrees) generally takes about three weeks to accomplish. Full flexion and hyperextension are avoided during this phase to avoid stretching the graft. Therapy is attended three times per week during this period. Specific strengthening exercises are avoided during this period to avoid traumatizing the graft although walking and swimming (when the incisions have healed) are permitted.

Phases II and III: Restoration of Strength

Normal gait and subsidence of swelling allow a gradual increase in muscle tone. At the three-month mark when the period of maximum graft weakness has passed, specific strengthening exercises are begun. These emphasize the hamstrings, abductors, and adductors initially. NordicTrack and/or elliptical trainer are also begun. The hamstrings protect the quadriceps and should be strengthened first. The quadriceps are then strengthened under controlled circumstances as follows.

The Quadriceps-ACL Interaction

Quadriceps contractions when the knee is between zero and sixty degrees of flexion cause a significant strain or stretch to be applied to the ACL graft. This is a result of the geometry of the knee and in particular the cam shape of the femoral condyles. This unopposed strain can damage the graft. Thus quadriceps exercises must be undergone with caution and with specific safeguards to protect the graft. Accelerated rehab programs that work the quadriceps aggressively in the early post-operative period are not used at ISMOC but are used by many surgeons. These have their greatest utility for patellar tendon ACL reconstructions in which permanent quadriceps weakness can be a significant problem. It is felt by many surgeons that the risks of graft trauma by aggressive early quadriceps rehab are more than counterbalanced by the importance of trying to avoid significant quadriceps weakness in patients who have had patellar tendon grafts. Hamstring grafts do not similarly predispose the quadriceps to weakness. Therefore with a hamstring ACL reconstruction there is no need to incur the risk of loosening the knee with early aggressive quadriceps strengthening. Rather the aggressive quadriceps strengthening is done a little later when the graft is not so fragile.

There are three factors which decrease the strain on the ACL graft when quadriceps exercises are being done. The first is to keep the knee axially loaded, or a “closed kinetic chain.” This simply means that there must be compression across the knee such as is seen with a leg press or squat exercises but which is not present in a seated leg extension exercises.

The second factor is to contract the hamstring simultaneously with, or before, the quadriceps contraction.

The third factor is to not let the knee straighten beyond 60 degrees while the quadriceps is being exercised. Thus the knee may have an arc of, for example, 60 to 100 degrees of flexion during this activity. It is important to have a trained physical therapist supervise these exercises.

While this rehab program is less aggressive than some, it must be remembered that maintaining knee stability is the paramount goal. At ISMOC a recent meta-analysis has shown our knee stability rate to be among the highest in the world’s literature and to be significantly higher than the average stability rates found in patellar tendon reconstructions. We believe that modulation of activities during the first few months after repair, as described above, has helped produce these superior stability results. At the same time we have had an excellent record of restoration of knee motion, strength, and return to work and sporting activities.

Return To Sports

At or before eight months post-operatively, the patient should be ready for full unrestricted athletic activities.


Credibility Logo

  • American Academy Regenerative Medicine
  • American Academy and Board of Regenerative Medicine
  • American Orthopaedic Society for Sports Medicine
  • isakos
  • Rush University Medical Center
  • American Association of Nurse Anesthetists
  • American Academy of Orthopaedic Surgeons
  • European Society of Sports Traumatology, Knee Surgery Academy
  • International Cartilage Repair Society