Written By: Joseph M. Villena, PT, MPT, OCS, CSCS, COMT

The vast majority of athletes who suffer an ACL injury will undergo surgical reconstruction. Expectations for rehab professionals are to utilize an evidence-based approach when determining appropriate exercises and progressions for treatment. What goes into developing a successful ACL rehabilitation program? Here are 5 key factors that you have to consider:


I. Understand the healing rate of the ACL graft and critical time points during rehab.

The ACL graft undergoes a process of remodeling known as “ligamentization” which can be generally defined by three phases 3.

  • Early healing: 3-6 months
  • Remodeling: 6-12 months
  • Maturation: 12 – 24 months+

The first critical time point during rehab is at 6-8 weeks when revascularization begins and the graft is at its weakest 10. Ideally, the graft should have achieved full revascularization by 6 months, but it can take up to 12 months to complete 5. The graft may also show differences in its collagen cross-link ratios at 6 months 11. Your athletes will be anxious to return to their sports or activities as quickly as possible. However, you have to educate them that there is a higher risk for reinjury if they return before the graft is ready. The re-injury rate can decrease up to 51% for every month return to sport is delayed up to 9 months 6. Therefore, return to sport is not recommended until 9 months pending passing all functional tests and criteria for discharge.

II. Know what type of graft was used.

Autografts are generally used for younger, active populations while allografts are used for less active and/or older populations.

This table breaks down some of the main pros and cons between graft types.





Bone-Patellar-Bone Autograft (BTB)

  • Decreased failure rate and rate of revision
  • Better stability 15
  • Fixation strength in 6-8 weeks4
  • Increased anterior knee and kneeling pain
  • Donor site discomfort, sensitivity
  • Chronic histological abnormalities8
Hamstring Autograft
  • Decreased anterior knee symptoms
  • Higher density of collagen fibrils and fibroblasts versus BTB
  • Higher risk of revision versus BTB9,14
  • Fixation strength up to 12 weeks4
Quadriceps Tendon Autograft
  • Decreased donor site morbidity and absence of anterior knee pain
  • 20% more collagen versus BTB16
  • Increased risk for developing a cyclops lesion17
  • No donor site problems
  • Decreased number of procedures during surgery 
  • Fixation strength may be twice as long versus autograft4
  • Decreased stability rate15
  • Higher rate of failure when return to sport <9 months19

It is important to know which graft type was used because it can guide you as to how aggressive or conservative you will need to be with progressing your patient through their rehab.

III. Train for equal weight bearing with basic and advanced squat activities

ACL post op patients are at high risk for sustaining a second ACL injury to their contralateral side within 24 months of return to sport even with excellent functional testing and isokinetic scores 13,18. Why you might ask? One research article showed that post-operative ACL subjects unloaded their affected limb with basic squatting up to 48% of their body weight between the first 1 ½ to 4 months post-operative and 28% between 6 to 7 months. The difference in loading response was worse with adding external weight or with performing a deeper squat 12.  Watch the videos below and see if you can figure out which direction these athletes are compensating (spoiler alert: both athletes compensate to the left).




This type of compensation compromises the affected limb’s abilities to develop appropriate strength and stability while increasing the work load and risk of injury to the unaffected side. To mitigate this, train squatting with equal weight bearing early in the rehab. Some easy and effective ways to know if they are weight bearing equally are to use a mirror to monitor for their position or use low cost weight scales to get more accurate measures of weight distribution.



Once your patient has mastered this, advance to squatting with weight as tolerated. Eventually you can progress to jumping and landing with equal weight in multiple planes.



IV. Don’t overemphasize training on unstable versus stable surfaces

Training on unstable surfaces is important for getting more global muscle recruitment and improving proprioception and balance. However, unstable conditions make it difficult to train muscles in isolation and decreases the amount of force an athlete can produce 1,2. This decreases the ability to use heavier loads to maximize force production during an exercise. In doing so, athletes may not get appropriate hypertrophy training to offset muscle atrophy and subsequently limit their capabilities to tolerate higher level power movements later in rehab.

V. Train the brain

 Participation in sports involves varying degrees of complex neurologic and motor planning. Think of a soccer player that must coordinate muscle and joint function to sprint, cut, and pivot up the field while simultaneously processing locations of various defenders, teammates, and where and how to kick the ball.

As task complexity increases, neuromuscular control is deteriorated in individuals with an ACL reconstruction possibly due to an overload of motor planning resources 7. In attempting to regulate neuromuscular control in the presence of decreased somatosensory input, the nervous system supplements with increased motor planning, conscious cortical involvement, and a greater reliance on visual feedback 7.

Neuroplasticity can be defined as the ability of the brain to form and reorganize synaptic connections in response to learning, experience, or following an injury. Although the development of this impairment is complex, the strategies to correct it are actually simple and easy to implement. For example, you can incorporate reaction-time components (i.e. target acquisition, ball tracking, unanticipated direction changes, etc.), dual task training (actively use the upper extremity during lower extremity exercises), or adding eyes closed or cognitive decision making.


You can start with something simple:



And eventually progress to something advanced:



Make sure your patient can perform the base movements well with good form before implementing these concepts.

You can learn more about developing a successful ACL program from my upcoming live webinar Advanced Concepts in Post-Operative ACL Rehabilitation on Sep. 01, 2020 6pm – 8pm (EST).  Click here to register!

You can also learn more about sports rehab in general by taking my 6-hour course, “A Comprehensive Approach to Sports Rehab.” My course is available via live or online video. To learn more about this course, click here! 



  1. Behm DG, Andersen K, Curnew RS. Muscle force and activation under stable and unstable conditions. J Strength Cond Res 16:416-422, 2002
  2. Chulvi-Medrano, I., García-Massó, X., Colado, J. C., Pablos, C., de Moraes, J. A., & Fuster, M. A. (2010). Deadlift muscle force and activation under stable and unstable conditions. The Journal of Strength & Conditioning Research24(10), 2723-2730.
  3. Claes, S., Verdonk, P., Forsyth, R., & Bellemans, J. (2011). The “ligamentization” process in anterior cruciate ligament reconstruction: what happens to the human graft? A systematic review of the literature. The American journal of sports medicine39(11), 2476-2483.
  4. Escamilla, R. F., Macleod, T. D., Wilk, K. E., Paulos, L., & Andrews, J. R. (2012). Anterior cruciate ligament strain and tensile forces for weight-bearing and non-weight-bearing exercises: a guide to exercise selection. The Journal of orthopaedic and sports physical therapy42(3), 208.
  5. Falconiero, R. P., DiStefano, V. J., & Cook, T. M. (1998). Revascularization and ligamentization of autogenous anterior cruciate ligament grafts in humans. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 14(2), 197-205.
  6. Grindem, H., Snyder-Mackler, L., Moksnes, H., Engebretsen, L., & Risberg, M. A. (2016). Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. Br J Sports Med, 50(13), 804-808.
  7. Grooms, D., Appelbaum, G., & Onate, J. (2015). Neuroplasticity following anterior cruciate ligament injury: a framework for visual-motor training approaches in rehabilitation. journal of orthopaedic & sports physical therapy45(5), 381-393.
  8. Kartus, J., Movin, T., & Karlsson, J. (2001). Donor-site morbidity and anterior knee problems after anterior cruciate ligament reconstruction using autografts. Arthroscopy: The Journal of Arthroscopic & Related Surgery17(9), 971-980.
  9. Maletis, G. B., Inacio, M. C. S., Desmond, J. L., & Funahashi, T. T. (2013). Reconstruction of the anterior cruciate ligament: association of graft choice with increased risk of early revision. The bone & joint journal95(5), 623-628.
  10. Manske, R. C., Prohaska, D., & Lucas, B. (2012). Recent advances following anterior cruciate ligament reconstruction: rehabilitation perspectives. Current reviews in musculoskeletal medicine5(1), 59-71.
  11. Marumo, K., Saito, M., Yamagishi, T., & Fujii, K. (2005). The “ligamentization” process in human anterior cruciate ligament reconstruction with autogenous patellar and hamstring tendons. The American journal of sports medicine, 33(8), 1166-1173.
  12. Neitzel, J. A., Kernozek, T. W., & Davies, G. J. (2002). Loading response following anterior cruciate ligament reconstruction during the parallel squat exercise. Clinical Biomechanics17(7), 551-554.
  13. Paterno, M. V., Rauh, M. J., Schmitt, L. C., Ford, K. R., & Hewett, T. E. (2014). Incidence of second ACL injuries 2 years after primary ACL reconstruction and return to sport. The American journal of sports medicine42(7), 1567-1573.
  14. Persson, A., Fjeldsgaard, K., Gjertsen, J. E., Kjellsen, A. B., Engebretsen, L., Hole, R. M., & Fevang, J. M. (2014). Increased risk of revision with hamstring tendon grafts compared with patellar tendon grafts after anterior cruciate ligament reconstruction: a study of 12,643 patients from the Norwegian Cruciate Ligament Registry, 2004-2012. The American journal of sports medicine42(2), 285-291.
  15. Prodromos, C., Joyce, B., & Shi, K. (2007). A meta-analysis of stability of autografts compared to allografts after anterior cruciate ligament reconstruction. Knee Surgery, Sports Traumatology, Arthroscopy15(7), 851-856.
  16. Slone, H. S., Romine, S. E., Premkumar, A., & Xerogeanes, J. W. (2015). Quadriceps tendon autograft for anterior cruciate ligament reconstruction: a comprehensive review of current literature and systematic review of clinical results. Arthroscopy: The Journal of Arthroscopic & Related Surgery31(3), 541-554.
  17. Sonnery-Cottet, B., Lavoie, F., Ogassawara, R., Kasmaoui, H., Scussiato, R. G., Kidder, J. F., & Chambat, P. (2010). Clinical and operative characteristics of cyclops syndrome after double-bundle anterior cruciate ligament reconstruction. Arthroscopy: The Journal of Arthroscopic & Related Surgery26(11), 1483-1488.
  18. Sousa, P. L., Krych, A. J., Cates, R. A., Levy, B. A., Stuart, M. J., & Dahm, D. L. (2017). Return to sport: Does excellent 6-month strength and function following ACL reconstruction predict midterm outcomes?. Knee surgery, sports traumatology, arthroscopy25(5), 1356-1363.
  19. Van Eck, C. F., Schkrohowsky, J. G., Working, Z. M., Irrgang, J. J., & Fu, F. H. (2012). Prospective analysis of failure rate and predictors of failure after anatomic anterior cruciate ligament reconstruction with allograft. The American journal of sports medicine40(4), 800-807.