ACL Injuries

The Anterior Cruciate Ligament (ACL) plays an important role in providing stability in the knee. In particular, it restrains the lower leg (Tibia) from translating forward in relation to the thigh (Femur). Injury to this ligament is one of the most common sports injuries with estimates between 75,000 - 250,000 new reports in the US each year 1.

The highest incidence of ACL reconstructions are found in Skiing, followed by Australian Rules Football (AFL), Rugby, Netball and Soccer 2. In soccer, ACL injuries account for 1.3% of injuries in males and 3.7% for females 3.



The reason for the increased incidence of ACL injuries in female sports people isn't clear, however studies suggest potential factors such as anatomy, hormones, strength and conditioning. The physical structure of the ligament in females has been found to be geometrically smaller than in men. Additionally it has been shown to have lower linear stiffness which is characterised by minor elongation and lower energy absorption under load when compared with males. Evidence has indicated that hormonal factors may play a role, with a significantly higher incidence of injury in the pre-ovulatory phase of the menstrual cycle 2, 18, 21 .

What Are Common Mechanisms Of ACL Injury?

Anterior cruciate injuries often occur while decelerating while landing from a jump or from running while the knee is slightly flexed. At the time of injury, a combined motion of knee valgus and knee internal-external rotation are common 7 .

Here we can see the left foot is fixed, while the knee moves in to a valgus while the leg is internally rotated.

Here we can see the left foot is fixed, while the knee moves in to a valgus while the leg is internally rotated.

Types Of ACL Repairs

Debate exists about the appropriateness of surgical repair for ACL injuries and is typically determined by the patients knee function or by their expectations to return to sport.  


The harvesting of the patients own tissue from various donor sites.  Tissue commonly harvested includes the Semitendinosis tendon, Gracillis Tendon, Patellar Tendon or Quadricep tendon.

Synthetics - LARS Graft

A synthetic ligament which may be threaded through the stumps of the injured ligament to aid with support and healing of the tissue.  Debate exists about the longevity of these artificial grafts.


Donated tissue from a cadaver.  The harvested tissue may be the Patellar tendon, hamstring tendon or even the Achilles tendon.

Typical ACL Rehab Programs


Week 1

  • Regular icing and elevation to reduce swelling
  • The goal of full extension and 700 of knee flexion by the end of the first week
  • The use of knee brace and crutchs are essential
  • Strengthening exercises fo the calf, hamstring and quadriceps (vastus medialis)

Week 3-4

  • Aim to increase the stance phase of the operated leg during gait
  • Weaning off crutches

Week 5

  • Commencement of close chain exercises for the hamstrings and quadriceps (bike, leg press, step)
  • Proprioception and coordination exercise may be started if strength is good

Week 10

  • Forward, backward and lateral dynamic movements can be included

Month 3

  • The patient can move on to functional exercises such as running and jumping
  • Exercises increase in complexity, challenging speed, performance, balance and strength

Month 4-5

  • Final goal is to maximise endurance and strength of the knee stabilisers
  • Acceleration, deceleration, and cutting manoeuvers are done to improve arthrokinetic reflexes
  • Sports specific exercise

ACL Injury Prevention Programs

As previously mentioned, altered neuromuscular control is suggested as a risk factor for non-contact ACL injuries. There have been several programs developed which aim to improve neuromuscular and proprioceptive abilities, such as the following:

  • The PEP Program
  • The Vermont ACL Program
  • The Cincinnati Sportsmetrics Training Program
  • The Henning Program
The Preventitive injury and Enhancement Program (PEP) is a specific training session that replaces a traditional warm-up. Its main forcus is to educate players on strategies to avoid injury vulnerable positions, while increasing flexibility, strength, and proprioception. In a recent study of Luke et al., young female soccer players who underwent the PEP Program had 88% less ACL injuries in the first year and 74% in the following year1.

The PEP Program

Section 1 - Warm-Up

The purpose of the warm-up is to prepare yourself for activity which inturn reduces your risk of injury. This section consits of running in a line, running from side to side, and backward running.

Section 2 - Strengthening

This section is focused on increasing leg strength and therefore creating a more stable knee. Exercises consist of walking lunges, russian hamstring, and single toe raises.

Section 3 - Plyometrics

This section helps to build power, strength, and speed. Exercises include lateral hops over a cone, forward/backward hops over a cone, single leg hops over a cone, vertical jumps with headers, and scissor jumps.

Section 4 - Agility

Working to increase dynamic stability of the hip, knee and ankle complex. Exercises include a forward run with 3 step deceleration, lateral diagonal runs, and bounding runs.

Your usual training program is done here

Section 5 - Stretching

By preforming stretches, you can maintain your range of motion, reducess post-exercise stiffness/soreness, reduce joint stiffness, and improve your overall mobility. Stretches include calf stretching, quadricep stretching, figure four hamstring stretching, inner thigh stretching, and hip flexor stretching.

An example of setting up your field for the PEP program is shown below.

If you would like to read more about the PEP program, by following this link.


1 Tandoğan, R. N., Mann, G., & Verdonk, R. (2011). Sports injuries: prevention, diagnosis, treatment and rehabilitation. M. N. Doral (Ed.). Springer Science & Business Media.

2 Janssen, K. W., Orchard, J. W., Driscoll, T. R., & Van Mechelen, W. (2012). High incidence and costs for anterior cruciate ligament reconstructions performed in Australia from 2003–2004 to 2007–2008: time for an anterior cruciate ligament register by Scandinavian model?. Scandinavian journal of medicine & science in sports, 22(4), 495-501.

3 Alentorn-Geli, E., Myer, G. D., Silvers, H. J., Samitier, G., Romero, D., Lázaro-Haro, C., & Cugat, R. (2009). Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 1: Mechanisms of injury and underlying risk factors. Knee surgery, sports traumatology, arthroscopy, 17(7), 705-729.

4 Arendt, E.A.: Musculoskeletal injuries of the knee: are females at greater risk? Minn. Med. 90, 38–40 (2007)

5 Slauterbeck, J.R., Fuzie, S.F., Smith, M.P., et al.: The menstrual cycle, sex hormones, and anterior cruciate ligament injury. J. Athl. Train. 37, 275–278 (2002)

6 Wojtys, E.M., Huston, L., Boynton, M.D., et al.: The effect of men- strual cycle on anterior cruciate ligament in women as determined by hormone levels. Am. J. Sports Med. 30, 182–188 (2002)

7 Physiopedia - ACL Rehabilitation, accessed 22/5/2015