ACL Injuries

Question 1

ACL Anatomy

Answer 1

• The cruciate ligaments are the Anterior Cruciate Ligament and the Posterior Cruciate Ligament.
  
  • They cross each other in the knee joint in an X-shape, which is where the name cruciate comes from.
  • The ACL has a large blood supply from the middle genicular artery (a branch from the popliteal artery). This is a crucial consideration in ACL injuries, because it explains why patients get a significant swelling or effusion when they rupture the ACL. One of the key fundamental points of the ACL is that it has a good blood supply, so when it ruptures, blood goes everywhere and we get a big intracapsular hemarthrosis in the middle of the knee so patient presents with massive effusion.
  • The posterior and lateral side of the knee have a lot more supporting structures around them, compared to the anterior and medial side.
  • We have a group of ligaments called posterior lateral corner of the knee which is made up of the lateral collateral ligament, popliteofibular ligament, and popliteus tendon which support the posterior knee to maintain stability.
    Less support for the anterior knee, meaning the anterior-medial knee is more vulnerable to injuries.

Question 2

Anterior Cruciate Ligament

Answer 2

• Origin - Posteromedial aspect of lateral femoral condyle.
  
  • Insertion - Anterior intercondylar eminence of the tibia.
  • The ACL runs from the posterior femur to the anterior tibia, from a slightly lateral position to a slightly medial position.
    Role - The main role of the ACL is to prevent excessive anterior translation of the tibia upon the femur. It has a much weaker secondary role in restricting an element of internal tibial rotation; but this is by far it’s least consistent role compared to the former.

Question 3

Antero-lateral Ligament

Answer 3

• The anterolateral ligament is another crucial ligament to be aware of.
  
  • This ligament originates from the lateral femoral condyle, and inserts into the lateral tibial condyle.
  • Its main role is to prevent internal rotation of the tibia.
    What we sometimes see in practice is that ACL rupture patients who have had an anterolateral ligament injury, may fail in their recovery if the anterolateral ligament injury is not addressed as there may now be more stress going through the ACL when a patient has excessive internal tibial rotation.

Question 4

Terrible Triad Injury

Answer 4

• Occurs when it is the anterior cruciate ligament, medial collateral ligament, and medial meniscus which are all injured in the same trauma.
  
  • Could be due to less support on the anterior-medial aspect of the knee compared to the posterior-lateral aspect.
  • Could be injured through a lateral force causing a valgus mechanism

Question 5

Mechanism of Injury - when do they occur?

Answer 5

• These injuries occur when the knee is unable to sufficiently restrict anterior tibial translation.
  
  • Trauma - most commonly in a sporting environment.
  • 70% of these are non-contact injuries.
  • Pivoting injury - cutting, twisting, decelerating.
  • Uncontrolled landings
    Hyperextension (when you get hyperextension, the posterior aspect of the femur slides further backwards than the tibia. Anatomy of ACL shows the distance between the origin and insertion of the ACL is lengthened putting strain on the ACL and can cause the rupture).

Question 6

Mechanism of injury - how do they occur?

Answer 6

• Previous thinking was that this injury specifically occurred when there was excessive valgus forces applied to the knee joint.
  
  • Videos of individuals injuring the ACL would often occur with a valgus knee position which is why this was suggested.
  • It was proposed that a planted foot would lead to the tibia being internally rotated, with the femur remaining in a neutral or even externally rotation position.
  • It was suggested that as a result, the ACL would get torn specifically due to the valgus movement.
  • However, there has been a lot of controversy about this in recent years.
  • “Axial loading is the primary force responsible for a non-contact ACL injury” or “valgus alignment likely compounds the effect of an axial compressive load (downward force) on ACL disruption”.
  • However, recent research from groups such as Boden and Sheehan now suggest that the main reason that the ACL gets torn is when these injuries occur, the axial compression going down through the knee joint pushes the ACL forward, because there is less supporting structures to the anterior of the knee compared to posteriorly.
  • Their research suggests that this axial loading is the primary force responsible for a non-contact ACL injury, but that a valgus alignment at the knee compounds the effect of the axial loading. This still gives credit to the fact that a valgus knee position appears to be a clear feature of many ACL injuries.

Question 7

Mechanism of injury - does it actually matter?

Answer 7

• The exact mechanics of how the injury occurs may be important for future research particularly in female sports where the rate of ACL injuries is much higher than in male sports.
  This is crucial for protecting athletes, and perhaps if we better understand the mechanisms, we can create prehab plans that get the athletes ready to be able to withstand the axial loads that will go through their knee during sports.

Question 8

Subjective Assessment - For any knee trauma patient?

Answer 8

• Tell me what happened - may even have a video. This will better help your understanding of the mechanism of injury the patient has had.
  
  • Ok … so just so I’m clear = and then you act it out to clarify the above point.
  • Did you have an X-Ray? Always important if there is swelling to rule out injuries such as a fracture. Could have a silent tibial-plateau fracture. Sometimes patients can do a little bit of weight-bearing with fracture.
    Have you injured this knee before? It is important to help us recognise if there may have been inherent instability in the knee prior to their injury e.g., previous meniscal tear. If this patient has previously injured their ACL, it raises the suspicion they may have done it again. If they have already injured before, you are more likely to refer on for further investigations with less symptoms.

Question 9

Key Follow Up Questions - ACL Specific?

Answer 9

• Swelling - quick and significant swelling (0-60 minutes). We know this is a very common feature of ACL injuries that differentiates it from many other non-ACL injuries. Most ACL injuries with “balloon” within 10 minutes. Other injuries like fracture or extensor mechanism injury can swell. Some meniscal injuries swell because outer layer of meniscus has good supply, but inner layer doesn’t have good blood supply.
  
  • Noise or pop sensation - not always present. This may not always be a feature of ACL injuries, but if the patient explains that there was a noise or pop sensation, we consider it to be an ACL injury until an ACL injury can be ruled out.
  • Locking - commonly refers to the inability to extend the knee. Commonly associated with meniscal tear. ACL can sometimes cause locking through ACL stump injury (the ACL folds into the tibial and femoral bit when it tears; the tibial aspect of the ACL can get stuck in the joint which can prevent the knee extending). If there is true locking, would refer on to further investigations.
  • Unable to play on (pain, swelling, unable to weight bear). The vast majority of individuals who rupture their ACL are unable to play on after the injury. If they are able to play on, does this reduce the likelihood of a serious injury? ACL injuries are incredibly painful.
    Ongoing instability (“feels as if it buckles”) - naturally ongoing instability is consistent with a potential ligament injury as the key role of ligaments like the ACL is to prevent instability. Sometimes when people get a sudden sharp pain they say “its given way” but that is not a true giving way.

Question 10

Subjective History

Answer 10

• Consider diagnosing an ACL injury like completing a jigsaw puzzle.
  
  • When constructing a jigsaw puzzle, we will always start by finding the biggest pieces, the ones that are most clearly linked to an ACL injury, which will help us set the scene for the rest of the puzzle.
  • So for example, if you hear that your patient had a non-contact, pivotting injury, with immediate and significant swelling, this will certainly raise your index of suspicion that the patient is likely to have had an ACL injuries, as these are “big pieces”.
  • Then we may explore other pieces, which might be smaller and suggestibly less obvious in nature such as a pop sensation, or a noise sensation during the injury. These pieces may be considered as smaller pieces because they are not always a feature of ACL injuries.
  • So ultimately, you may not have every piece of the puzzle in the patient’s history, but if you have enough big pieces, perhaps combined with a few smaller pieces, you may well be able to work out most of the puzzle, which leads you to suspect that your patient has had an ACL injury.
    Always remember, if you have sufficient pieces in your puzzle, we must consider that our patient has had an ACL injury, until we can fully rule an ACL injury out.

Question 11

Objective Examination

Answer 11

• We say many clinicians rely purely on their objective assessment to diagnose an ACL injury. However, this is commonly difficult especially when the patient has significant swelling, lots of pain, or lots of guarding.
  
  • As a result, always use your subjective assessment to make a preliminary diagnosis of an ACL injury! With the specific signs we went through in the last section, many of these markers alone are enough to lead you to refer this patient on for further investigations.
  • Instead, we can use our objective examination to see if we can fully confirm the diagnosis, following our previous suspicions in the subjective history.
  • Observation and palpation - observe how your patient enters the clinic room. Are they using crutches? Are they fearful of movement? Are they in a significant amount of pain? Are they weight-bearing? How are they moving? Are they confident in putting their foot on floor? We can also palpate the medial and lateral joint line to look for signs of a potential meniscal injury.
  • Swelling / Joint Effusion - here we can use a tape measure to check the circumference around the knee and compare it to the other side. We can also use a Sweep Test where we sweep up the medial side of the knee to enter the medial patella pouch of fluid, and then sweep down the lateral side of the knee to see if fluid re-enters the pouch.
  • Grading of Sweep Test :
    1. Grade 0 - no wave of fluid with downstroke.
    2. Trace - small wave on the medial knee with downstroke.
    3. Grade 1 - large bulge of fluid on medial knee with downstroke.
    4. Grade 2 - effusion returns automatically on medial knee before downstroke.
    5. Grade 3 - so much fluid that it is not possible to move effusion with upstroke.
  • Range of Movement - there is no specific range of movement presentation that precisely tells us that your patient has an ACL injury. However, there are considerations we need to look at: your patient will commonly have reduced flexion if you are seeing them in the early phases, but the degree of flexion deficit can largely vary. Looking at knee extension is always important, as we do need to act on this. Common causes of a lack of extension include: its too painful for the patient given swelling and trauma, potential bucket handle meniscal tear, potential ACL stump injury which is preventing movement. If patient has a locked knee it could be due to being too painful, or could be a possible bucket handle meniscal tear (see if you can passively extend the knee) or could a possible ACL stump / cyclops lesion. Important to check if patient has knee extension.
  • Check the PCL! - It’s always important to rule out a PCL injury for these patients, because if we don’t, we may mistake any excessive laxity during our special tests. For example, if your patient has significant laxity in your Lachman’s test, you may presume this is due to an ACL injury. But as a result, you may be missing a PCL injury as this injury will also create excessive tibial laxity on testing. Could do PCL Sag Sign Test to see whether one tibia has sagged down compared to the other. If patient has PCL rupture, you may feel excessive movement and think its an ACL rupture, but its actually a PCL injury as the tibia is sitting further backwards.
  • Anterior Draw Test
  • Lachman’s Test
  • Pivot Shift Test
  • Lelli’s Test / Lever Sign

Question 12

Anterior Draw Test

Answer 12

• Sensitivity 83%
  
  • Specificity 85%
  • Sit on the patient’s foot with knee flexed to 90degrees.
  • Place hands around the anterior proximal tibia with thumbs on the joint line.
  • Slowly lean back and feel for excessive movement of the tibia on the femur.
  • Positive result - excessive anterior translation of the tibia upon the femur compared to unaffected side. OR a soft or lack of end feel compared to the other side.
    You can use forearm and hand on the joint line in order to utilise the hands to feel and control the test in a better way.

Question 13

Lachman’s Test

Answer 13

• Sensitivity 81%, specificity 85%
  
  • Place your knee underneath the patient’s knee, so that it brings their knee into 20-30degrees of flexion.
  • From their fix your upper hand around the patella so that your finger and thumb can sit on the joint line feeling for movement.
  • Place your thumb on the tibial tuberosity and fingers around the calf, and draw the tibia anteriorly.
    Positive result - excessive anterior translation of the tibia upon the femur compared to unaffected side OR a soft or lack of end feel compared to the other side.

Question 14

Pivot Shift Test

Answer 14

• Sensitivity 55%, specificity 94%.
  
  • Internally rotate the leg, and then bring the patient’s leg into approximately 30degrees of hip flexion
  • Bring the patient’s knee into a valgus position to see if it creates a clunk where the tibia appears to reduce or sublux on the femur.
  • Positive result - the test creates a clunk where the tibia appears to reduce on sublux on the femur.

Question 15

Lelli’s Test / Lever Sign

Answer 15

• Sensitivity 83%, specificity 91%.
  
  • Place your fist underneath the proximal 1/4 of your patient’s calf
  • Push down firmly on the distal femur and see what happens to the heel
  • The heel should lift off the bed because you have created a lever point.
    Positive result - the heel stays in place on the bed and does not lift up where instead there may be an anterior translation of the tibia on the femur.

Question 16

Next Steps

Answer 16

• Education - your suspicions and plan. Answer any questions. “I’m worried about your ACL. I think we need to investigate your anterior cruciate ligament”.
  
  • Onward referral - orthopaedics, MRI scan
    Immediate Rehab - gait re-education, basic exercises. If no X-RAY, get an X-Ray done first to check there is no fracture.