In this episode, Austin covers the highlights of the 2017 Knee Ligament Sprain CPG, including diagnosis, outcomes, and treatments. He also covers the Ottawa Knee Rules, which are bound to show up on the OCS exam.
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Hello and welcome back to the OCS Field Guide podcast. Today we are single leg hopping into the knee beginning with knee ligamentous injury. In this episode we are covering the most need to know information from the 2017 update of the knee ligament sprain CPG while pulling in useful information from other sources, as usual, to give you the most complete picture of what you need to know.
We’ve got a lot to cover, so let’s dive right in to our discussion of knee ligament function. I’ll cover this section by describing the ligament, giving any important facts to know about that ligament, and then covering information on testing the ligament. Let’s begin with the ligament that gets the most attention, and is most commonly injured, the anterior cruciate ligament. The ACL is the primary restraint against anterior translation of the tibia, and is most commonly injured during acceleration or deceleration with an uncontrolled valgus moment at the knee with the knee in slight flexion combined with tibial external or internal rotation. The ACL is made up of two main bundles, the anteromedial bundle, and the posterolateral bundle. The more robust posteriolateral bundle is most taut in full extension and is the primary restraint to anterior translation of the tibia from 20 deg of flexion to full extension. The smaller anteromedial bundle gets more taught as the knee bends and thus limits anterior translation of the tibia in a flexed knee. So, if you are testing the ACL with an anterior drawer test, you are likely biasing the anteromedial bundle. Thus if you have an isolated AM bundle tear, you could get a positive test while getting a negative lachman’s test, which primarily tests the larger posterolateral bundle. How do you remember which is which? Well, if you know those two tests, which I would hope that you do if you have a PT licence, its easy. The ANTERIOR drawer test, which is done at 90 deg knee flexion, tests the ANTEROmedial bundle, so the anteromedial bundle must be the one that is taut in knee flexion, while the posteroLateral bundle is tested primarily by the Lachman’s test, which is done in about 20-30 deg knee flexion, so the PL bundle must be the one that is taut in extension. There are three main clinical tests for ACL tear including the anterior drawer, lachman’s, and the pivot shift test. The anterior drawer test is the least reliable test, having a sensitivity of 49% and specificity of 58% for acute ACL injuries, which is likely due to the increased ability for the hamstring to guard and limit anterior translation of the tibia during this test. The best clinical test for ACL deficiency is the Lachman’s test, which has a pooled sensitivity of 85% and specificity of 94%. The Pivot shift is a little less common, so I’ll describe it. This test is performed by applying a valgus force and axial load to the knee while bringing it from extension into flexion with the tibia being forced into internal rotation. A positive test is when the tibia subluxes anteriorly, and then a “shift” is felt as the tibia slides back into position as the knee reaches about 25-30 deg extension. The pivot shift has poor clinical sensitivity at 24%, but high specificity at 98%. However, under anesthesia, it is a much better test with sensitivity of 81.8% and specificity of 98.4%. This is why it is such a common test to be performed by surgeons with the patient under anesthesia before proceeding with ACL reconstruction. Still, the best overall clinical test for ACL deficiency is the Lachman’s test. Some relevant risk factors for ACL injury that the knee ligament sprain CPG mentions are the following: Dry weather conditions and articial turf surface are potential risk factors for noncontact ACL injuries. Female sex, narrow intercondylar femoral notch size, lesser concavity depth of the medial tibial plateau, greater anterior/posterior tibiofemoral joint laxity, prior ACL reconstruction, and familial predisposition are associated with increased risk of ACL injury risk. The knee ligament sprain CPG recommends diagnosis with ACL injury when a patient presents with the following clinical findings: mechanism of injury consisting of deceleration or acceleration motions with noncontact valgus load occurring at or near full knee extension, hearing or feeling a “pop” at the time of injury, hemarthrosis within 0-12 hours of injury, history of giving way, positive lachman's test with soft end feel or increased anterior tibial translation compared to the opposite side, and positive pivot shift test.
The posterior cruciate ligament is the primary restraint to posterior movement of the tibia on the femur, especially between 30 and 90 degrees. It is most often commonly torn with a hyperflexion injury, or an external posteriorly directed force on the tibia, such as in a dashboard injury. It does have two bundles, which are named opposite of the ACL bundles, the anterolateral bundle and the posteromedial, but all you probably need to know is that the anterolateral is the largest and most important, making up 95% of the ligament. The PCL is best isolated for testing at 90 deg flexion with the posterior drawer test because at 90 deg, the other secondary restraints such as the posterolateral capsule, popliteus, and MCL are too lax to contribute at that range. As a secondary support for external rotation of the tibia, a PCL deficient knee may also have increased laxity into tibial external rotation at 90 degrees of knee flexion. The three main tests for PCL injury are the posterior drawer, the posterior sag sign, and the quadriceps activation test. The posterior drawer has pretty good stats with sensitivity of 90% and specificity of 99%. Its performed with the patient in hooklying with the knee at 90 degrees. The tibial plateau is grasped and forced posteriorly--a positive test would be a soft end feel or increased posterior tibial translation compared to the other side. This test can also evaluate the posterolateral corner by externally rotating the tibia and performing the test again. If posterior translation is unchanged the diagnosis is still PCL injury, but if it is increased in tibial external rotation, the posterolateral corner must be evaluated further, we’ll come back to the posterolateral corner in just a minute. The posterior sag sign is observed in the same position as the posterior drawer but with the opposite knee aligned beside it. The patient is instructed to relax and the clinician observes the knees from the lateral perspective and notes a “Sagged” or posterior positioning of the tibia compared with the other side. The quadriceps activation test is a continuation of this test where the patient is then instructed to activate their quad, or push the ankle into the clinician’s hand and the clinician looks for anterior translation of the tibia, or in other words, reduction of the posteriorly subluxed tibia. The posterior sag and anterior translation tests are the most specific tests for PCL at 100% specificity each, so if this is seen, you can be pretty confident in ruling IN PCL injury. They also have good sensitivity with the posterior sag at 79% and the quadriceps activation test at 97%.
The posterolateral corner is comprised of the arcuate ligament, LCL, popliteal tendon, the lateral head of the gastrocnemius, and is reinforced by the biceps femoris tendon. The posterolateral corner is often injured along with the PCL, but can be injured in isolation as well with a direct blow to the proximal tibia or a hyperextension injury . Testing for posterolateral corner injury can be a little confusing. First, the posterior drawer test can be completed at 30 degrees and 90 degrees. If there is increased posterior translation at 30 degrees, but normal motion at 90 degrees, this indicates isolate posterolateral corner injury, but if increased at both, you likely have concomitant PCL injury. The most specific test for posterolateral corner injury is the dial test. The dial test, or prone external rotation test, is performed with the patient prone and the knee bent to 30 degrees. The tibia is brought into maximal external rotation, and this measure is compared with the opposite side. The test should be repeated at 90 degrees. A positive test is considered a 10 degree or greater difference in one side to the other. A positive test at 30 degrees but not 90 degrees indicates isolated posterolateral corner injury, while increased laxity at both 30 and 90 degrees should indicate further testing of the the PCL. Furthermore, a positive at 90 deg, but not 30 degrees, could indicate isolated PCL, but you should rely on the more sensitive and specific tests for the PCL that we have already talked about.
Let’s move on the collateral ligaments. The MCL is a wide, capsular ligament. It is divided up into superficial and deep ligaments. The superficial portion runs from the posterior aspect of the medial condyle and attaches below the pes anserine and is the primary restraint to valgus force at the knee. The deep portion attaches to the medial meniscus from the tibia and the femur, and its primary function is more to support the medial meniscus and also limits anterior translation of the tibia. An MCL tear should be suspected and tested for with a history of trauma by a force to the lateral aspect of the leg, an uncontrolled valgus force, or a rotational trauma. Fun fact though, the medial meniscus actually has excellent blood supply, which makes it often able to heal on its own without surgical intervention. The LCL on the other hand is a cord-like, extracapsular ligament arising from the lateral epicondyle and attaching in a common attachment with the biceps femoris on the fibular head. It is the primary restraint to varus moments at the knee and provides secondary restraint to external rotation of the tibia. Injury to the LCL is suspected and tested for when a patient presents with a varus trauma, localized swelling over the LCL, and tenderness to the LCL and its attachments. Let’s talk about testing, with both collateral ligaments it’s important to note that both the ACL and PCL provide restraint to valgus and varus moments at the knee especially at full extension, so deficiency in either can cause some varus or valgus laxity. A positive valgus stress at 0 degrees indicates need to evaluate the ACL and PCL, while the valgus stress test at 30 deg isolates the MCL. Pain at the MCL and/or laxity of greater than 5mm when tested at 30 degrees is considered positive for MCL injury. There are distinct values for the sensitivity and specificity for pain and laxity with the valgus stress test. For pain, the sensitivity is 78% and for laxity it is 91%--so pretty sensitive overall. The specificity is not so great for pain or laxity though, with 67% and 49% respectively. So, a negative test for pain or laxity of the MCL can pretty confidently rule out MCL injury, and a positive test for pain has some utility for ruling in MCL injury. However, with 49% specificity for laxity with the valgus stress test, positive laxity doesn’t really tell you much, but it’s the best we have. The varus stress test may be positive in full extension with LCL, PCL, or ACL injury, but the LCL is preferentially tested in 30 degrees of flexion. The varus stress test at 30 degrees is considered positive for LCL injury if pain or increased laxity compared to the other side is noted. The CPG doesn’t include sensitivity or specificity information for the varus stress test, so I don’t think you need to know it.
Some other important ligaments to be aware of are the oblique popliteal ligament and the posterior oblique ligament which bother reinforce the posteromedial knee joint capsule; and the arcuate ligament, which has medial and lateral branches, the medial attaching to the oblique popliteal ligament, and the lateral attaching to the posterior aspect of the fibular head and thus providing support to the posterolateral knee joint capsule.
I know, lot’s of information covered there, but it’s important to know the ligaments of the knee well because you may well get a case on the OCS that describes an injury to the knee and subsequent testing information and asks you to decide on a intervention or asks you what else might have been injured, or what other test needs to be done to rule in or out a certain ligamentous injury.
While we are on the topic of examining knees that have just experienced trauma, it's a good time to go over the Ottawa knee rules for radiographs following acute knee injury. If any of the following 5 factors are true, a patient who has just experienced an acute knee injury should be referred for radiographs: 1. Age greater than 55; 2. Isolated tenderness of the patella with no other bony tenderness; 3. Tenderness to the fibular head; 4. Inability to flex the knee to 90 degrees; and 5. Inability to bear weight both immediately and in emergency room.
Let’s turn now to focus on what you most need to know from knee ligament sprain CPG from the examination and intervention sections. Let’s start with outcome measures. The two self-reported outcome measures recommended for assessment of knee symptoms and function are the IKDC 2000 and the knee injury and osteoarthritis outcome score, or the KOOS. The CPG doesn’t the MCIDs for either, so I wouldn’t worry about knowing them. I’d recommend you give each a once over, and remember that both are rated from 0-100 and are measures of function, meaning that a higher score means better function. For Activity level, The Tegner scale and Marx activity rating scale are both recommended. The Tegner scale is rated 0-10, and the Marx scale is rated 0-16, and in both of these scales, a higher number means a higher activity level.
For physical performance measures, the CPG recommends the following, quote, “Clinicians should administer appropriate clinical or field tests, such as single-leg hop tests (eg, single hop for distance, crossover hop for distance, triple hop for distance, and 6-meter timed hop)” end quote. For impairment measures, they recommend evaluating measures of knee laxity/stability, lower limb movement coordination, thigh muscle strength, knee effusion, and joint range of motion. spoiler alert, these hop tests, quad strength, and outcome measures should be 90% or better of the uninvolved side before considering return to sport.
Now for what you’ve probably been waiting for, intervention.
As you know, 2017 knee stability and movement coordination impairments CPG is an update of the 2010 CPG, so you’ll note that in most cases both the 2010 and 2017 recommendations are listed, but in a lot of cases the 2017 recommendations either strength or negate the 2010 recommendations, in those cases I’ll just tell you the most up to date recommendation. Also, I’ve reorganized the recommendations for you based on the condition. First let’s go over the recommendations for treatment following ACL reconstruction. There is C level recommendation for use of continuous passive motion machine immediately post op to decrease postoperative pain. There is C level recommendation for early weightbearing as tolerated within one week of ACL reconstruction, and there is B level recommendation for immediate mobilization within one week in order to increase ROM, reduce pain, and reduce risk of loss of ROM. There is also B level recommendation for immediate postoperative bracing, and B level recommendation for use of cryotherapy to reduce postop pain following ACL reconstruction. There is B level recommendation for supervised rehabilitation that incorporates in clinic exercise as well as a home exercise program that is monitored and progressed by the therapist. The two A level recommendations are for therapeutic exercise and for neuromuscular electrical stimulation. For ther-ex, They recommend weightbearing and non-weightbearing, concentric an eccentric exercise to be implemented within 4-6 weeks, 2-3 times per week for 6-10 months to increase thigh muscle strength and functional performance after ACL reconstruction. For NMES, there have been two new high quality systematic reviews since the 2010 guideline which have strengthened the recommendation from B to A level recommendation. They recommend NMES be used for 6-8 weeks to augment muscle strenghteninging exercises in patients after ACL reconstruction to increase quadriceps muscle strength, and enhance short-term functional outcomes. Finally, there is D level recommendation for functional knee bracing after ACL reconstruction. The 2017 update recommends ascertaining patient preference to aid in the decision for or against functional knee bracing after ACL reconstruction. For patients with ACL deficiency, however, there is C level recommendation FOR the use of functional bracing. Bracing has not been studied significantly in patients with other ligamentous injuries, but they do give a level F, or expert opinion, recommendation for using appropriate bracing for individuals following Acute PCL, severe MCL, or posterolateral corner injury. The remaining recommendations are more general in scope for all patients that can be classified as having knee stability and movement coordination impairments AKA anyone with a knee sprain whether operative or non-operative. There is B level recommendation for a supervised treatment program, pretty much identical to the recommendation for post-op ACLr patients; A level recommendation for ther-ex including weightbearing and non-weightbearing strengthening; and A level recommendation for the use of neuromuscular re-education training.
To summarize the intervention recommendations: for patients post-op ACLr, you SHOULD use therapeutic exercise and NMES, strongly consider using immediate mobilization, post-op bracing, cryotherapy, and a supervised rehab program; and if you like, you may use early weightbearing within one week and continuous passive motion if that floats your boat too. You can take or leave functional knee bracing for patients with reconstructed ACLs, but may want to use it for ACL deficient patients. Overall for anyone with a knee ligament sprain, you should absolutely use therapeutic exercise, neuromuscular re-education, and you should use a supervised exercise program.
Let’s finish out this episode with a practice question.
A 17 year-old female soccer player presents to an outpatient clinic reporting that in a game last week she was slide tackled and was struck in the front of her L knee. She reports feeling like her knee hyperextended and she was taken from the game. She was evaluated by the athletic trainer immediately after who told her that her ACL did not feel torn. She reports having iced her knee twice/day since then since she has had some mild swelling and that she has tried to rest the knee otherwise. She reports pain in the knee with going from sitting to standing and when going up stairs. Objective examination reveals the following:
● L knee ROM: 5 degrees short of extension to 130 degrees of knee flexion with posterior pain noted at end range
● 1+ effusion in the L knee
● 4/5 strength in L quadriceps and 4-/5 strength in L hamstrings, which reproduced posterior knee pain
● Crisp endfeel with L lachman’s test
● Firm end feel with L posterior drawer at 90 degrees, but slight increased laxity at 30 degrees compared to the R side.
Which of the following exam findings would increase suspicion of a posterolateral corner injury
A. Increased tibial external rotation with knee at 90 degrees
B. Increased anterior tibial translation with anterior drawer in external rotation
C. Increased laxity with varus stress at 30 degrees
D. Increased tibial external rotation at 30 degrees
Answer A is incorrect, as increased tibial external rotation with knee at 90 degrees flexion would be indicative of PCL injury. Answer B is incorrect, as it describes a variation of the anterior drawer test which would indicate compromise of medial knee structures along with the ACL. Answer C is incorrect as the varus stress test at 30 degrees is the variant that most isolates the LCL. Finally answer D is correct, as this describes the Dial test, which most isolates the posterolateral corner at 30 degrees of knee flexion. This also fits with her clinical picture as posterolateral corner injuries are commonly caused by a hyperextension injury or a blow to the anterior knee. Familiar pain reproduced with resisted hamstring testing also makes sense for posterolateral corner injury as the biceps femoris provides support to the posterolateral compartment and attaches to the fibular head along with the lateral band of the arcuate complex.
That wraps up this episode covering the ligaments of the knee and the 2017 knee ligament sprain CPG update.