ACL Injury

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The anterior cruciate ligament (ACL) is an important ligament for stabilisation of the knee. It is frequently injured by athletes and trauma victims


Main article: Knee Joint

The ACL arises from the posteromedial aspect of the lateral femoral condyle, runs distally in an anterior and medial direction, and inserts on the anteromedial aspect of the tibia in the intercondylar region. It has two bundles: an anteromedial bundle and posterolateral bundle. The anteromedial bundle is tight in flexion. The posterolateral bundle is tight in extension.

The ACL provides the primary resistance to anterior translation of the tibia on the femur. It also provides secondary restraint against tibial rotation, varus, and valgus forces.


Main article: Knee Biomechanics
  • The ACL is the primary restraint to anterior tibial displacement.
  • Resists 75% of anterior force at full extension and addition 10% up to 90° of knee flexion.
  • The bulk of the fibres are tight in maximal extension.
    • In extension: the posterolateral bundle is tight and the anteromedial bundle is moderately lax
    • In flexion: the femoral attachment of ACL is more horizontal, causing the anteromedial bundle to tighten and the posterolateral bundle to relax
  • The anteromedial bundle is the predominant restraint to anterior tibial displacement.
  • The posterolateral bundle stabilises the knee near full extension especially against rotatory loads.


* Type 1 - minimally/non-displaced fragment * Type 2 - anterior elevation of the fragment * Type 3 - complete seperation of the fragment. 3b - Involves the majority of the eminence. * Type 4 - comminuted avulsion or a rotation of the fragment.

The most commonly used classification is from Zarincznyj in 1997, which was modified from Meyers and McKeevers in 1959. Under this system, injuries are classified into four types.

Clinical Features

Inspect for quadriceps wasting and effusion. Assess range of motion, there may be loss of terminal extension.

Special Tests

Test Sens Spec LR + LR - Kappa
Lachman's Test[1][2] 81% 81% 4.26 0.24 0.19
Prone Lachman's Test[3] 70% 80% 3.5 0.57 0.6
Anterior Drawer[2][4] 38% 81% 2.0 0.77 0.34
Pivot Shift Test[2] 28% 81% 1.47 0.89
Loss of Extension Test 78% 95% 15.6 0.23

Associated Injuries

Due to uncontrolled rotation, injury to the lateral meniscus is very common in ACL rupture. It is more common than the well-known "unhappy triad" which refers to injury to the medial meniscus, MCL, and ACL. Test MCL stability to valgus load in extension at 20 degrees of flexion.

Kissing bone bruises are often seen on MRI imaging due to the combination of unrestrained extension and medial rotation. This allows the tibia to slide anteriorly and strike the lateral femoral condyle.


ACL Surgery

Once torn, it doesn’t heal. Reconstruction does not make it normal – posttraumatic osteoarthritis can occur regardless of management

Surgical vs non-surgical management

  • RCT of 121 “young active adults”
  • Rehab (plus delayed surgery if needed) vs rehab plus early surgery
  • 5 year follow up: no differences in ability to return to sport, knee function, or rate of meniscal injury
  • 50% crossover (50% in rehab group crossed over to surgery)
  • Take-away: 50% can be managed non-operatively[5]
  • In my opinion we don’t know if those other 50% eventually managed operatively would have better outcomes than sham surgery

Subsequent OA and Meniscal Tears

  • Metanalysis 2019, comparing surgery vs non-surgical treatment with 10 year follow up
  • Patient reported outcomes the same
  • Higher rate of radiographic knee OA
  • Lower rate of secondary meniscal injury and meniscal surgery
  • Reduced laxity
  • Significant methodological flaws in the included studies and heterogeneity[6]

Copers vs non-copers

  • Copers – use neuro-musculo-skeletal strategies to dynamically stabilise their ACL-deficient knee even with pivoting
  • Non-copers – knee instability, higher rates of surgery
  • Not possible to classify this early on
  • in one study 70% of those initially classified as non-copers, were copers after 1 year of non-operative management. And only 60% of potential copers were true copers.[7]

ACL Reconstruction

  • Indications??
    • Recurrent instability
    • Associated tear when amenable to repair
    • Associated ligament injury especially posterolateral corner
    • Professional and elite players
    • High-risk occupation (where instability could cause harm)
    • ?Adolescents, risk of instability, ?protect against future meniscal and chondral damage.
  • Delay surgery until normal range of motion, effusion largely resolved and able to walk comfortably (to reduce risk of athrofibrosis i.e. stiffness)

ACL Graft Selection

  • Bone-Patella-Bone
    • possible earlier graft fixation and stability due to included portion of bone
    • anterior knee pain up to 1 year
    • possible higher rate of OA.
  • Hamstring
    • Initial fixation may be slower and weaker (no bone), but quadruple strand is stronger than B-P-B
    • Donor site pain resolves by 3 months
    • hamstring strength normal by 12 months.
  • Other: Allografts, quadriceps graft,

ACL Postoperative

  • Graft re-rupture (from surgical failure or re-trauma)
  • Outcomes worse for revision ACL repair
  • Increased risk tear contralateral knee – 7% cumulative incidence
  • 5770 reconstructed knees – 60% returned to pre-injury level, and 44% returned to competitive sport.
  • Professional players – 90% return to play by 12 months, sensible?? Shorter careers.[8]

Unknown Unknowns

  • Cultural norms in professional sport and other areas
  • ?Uncertainty of non-operative treatment
  • Loss of option of early ACL repair
  • ACL-deficient sport ?future meniscal and cartilage injury
  • What is success, return to pivoting sport? What is in the athlete’s best interest?
  • “Doing nothing” is hard[9]

Rehabilitation for Athletes

  1. Protection and controlled mobilisation
  2. Controlled training
  3. More intensive training
  4. Return to play (many months)[10]


  1. Cooperman JM, Riddle DL, Rothstein JM. Reliability and validity of judgments of the integrity of the anterior cruciate ligament of the knee using the Lachman’s test. Phys Ther. 1990;70:225-233.
  2. 2.0 2.1 2.2 Van Eck CF, van den Bekerom MPJ, Fu FH, et al. Methods to diagnose acute anterior cruciate ligament rupture: a meta-analysis of physical examinations with and without anaesthesia. Knee Surg Sports Traumatol Arthrosc. 2013;21(8):1895-1903.
  3. Mulligan EP, Harwell JL, Robertson WJ. Reliability and diagnostic accuracy of the Lachman test performed in a prone position. J Orthop Sports Phys Ther. 2011;41(10):749-757.
  4. Wood L, Peat G, Wilkie R, et al. A study of the noninstrumented physical examination of the knee found high observer variability. J Clin Epidemiol. 2006;59:512-520.
  5. Frobel R et al, Treatment for acute anterior cruciate ligament tear: five year outcome of randomised trial BMJ 2013;346:f232
  6. Lien-Iversen, T., Morgan, D. B., Jensen, C., Risberg, M. A., Engebretsen, L., & Viberg, B. (2019). Does surgery reduce knee osteoarthritis, meniscal injury and subsequent complications compared with non-surgery after ACL rupture with at least 10 years follow-up? A systematic review and meta-analysis. British Journal of Sports Medicine, bjsports–2019–100765.
  7. Moksnes, H., Snyder-Mackler, L., & Risberg, M. A. (2008). Individuals With an Anterior Cruciate Ligament-Deficient Knee Classified as Noncopers May Be Candidates for Nonsurgical Rehabilitation. Journal of Orthopaedic & Sports Physical Therapy, 38(10), 586–595. doi:10.2519/jospt.2008.2750 
  8.  Ardern CL, Webster KE, Taylor NF, Feller JA. Return to sport following anterior cruciate ligament reconstruction surgery: a systematic review and meta-analysis of the state of play. Br J Sports Med 2011;45:596-606.
  9. Weiler, R. (2015). Unknown unknowns and lessons from non-operative rehabilitation and return to play of a complete anterior cruciate ligament injury in English Premier League football. British Journal of Sports Medicine, 50(5), 261–262. doi:10.1136/bjsports-2015-095141
  10. Bizzini, M., Hancock, D., & Impellizzeri, F. (2012). Suggestions From the Field for Return to Sports Participation Following Anterior Cruciate Ligament Reconstruction: Soccer. Journal of Orthopaedic & Sports Physical Therapy, 42(4), 304–312. doi:10.2519/jospt.2012.4005 

Literature Review