FPT Cruciate ligament injuries (ACL/PCL)

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x Cruciate Ligament Disorders JB (3).docx

 

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Cruciate Ligament Disorders

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The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) connect the femur to the tibia and stabilize the knee joint, primarily in the sagittal plane (i.e., resisting anterior and posterior forces, respectively). Of the two, it is the anterior cruciate ligament that is more frequently injured, either in isolation or with associated injuries to the meniscus, articular cartilage or collateral ligaments. Tears of the ACL typically occur when a person abruptly changes direction or decelerates with the foot planted.    The less common PCL injury usually occurs when the tibia is forced when the knee is flexed. The classic mechanism is an automobile accident in which the flexed knee strikes the dashboard after collision. The anterior cruciate ligament has very little healing potential, whereas the posterior cruciate ligament can occasionally repair itself.

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Figure 1: The anterior (green) and posterior (red) cruciates seen in the intra-condylar notch. The ACL courses from the lateral femur medially to insert on the tibia.

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Figure 2: A lateral view showing the anterior (green) and posterior (red) cruciates. Note that ligaments are mostly vertical (which is not advantageous in terms of resisting anterior/posterior translation) to allow the knee to flex and extend. Note also that the ACL inserts on the top of the tibia (the plateau) whereas the PCL inserts about 1 cm below the joint line.

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Figure 3: An MRI sagittal slice within the notch showing the aAnterior cruciate (green) and a small piece of the posterior cruciate (faint red line). [MF1] Because Because the ACL courses lateral (femur)  to medial (tibia) and the PCL vice versa, it is rare to see both ligaments simultaneously on one single MRI image (from https://radiopaedia.org/images/20228493)

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The ACL has been described having two bundles: the anteromedial bundle and the posterolateral bundle. This distinction is somewhat arbitrary as the boundary between bundles is not stark. A better way to think about it, perhaps, is that there are different regions of the ligament, with the anteromedial aspect more taut in flexion and the posterolateral aspect more taut during extension.  

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The most sensitive physical exam maneuver for detecting a torn ACL is the Lachman test, where the femur is stabilized while the tibia is pulled forward (Figure 4). A positive test is signified by excessive forward translation without a firm endpoint, indicating disruption to the ACL.   Because the test is assessed via the quality of the endpoint – whether the examiner perceives a sudden stop of anterior translation by the intact ACL – the test is somewhat operator dependent: more experienced examiners will perform it better.

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Figure 4: Lachman Test: The examiner stands next to the supine patient and grasps the lateral thigh just above the knee with the upper (contralateral) hand to exert resistance (blue line). The examiner holds the tibia medially with the lower (ipsalateralipsilateral) hand,  flexes the knee to 30 degrees and then gently yet suddenly applies a force to the tibia in an attempt to subluxate it forward (blue arrow). As shown, this will place tension on the ACL (drawn in red).

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The anterior drawer test (simply assessing whether there is an abnormal amount of anterior displacement when a force is applied to the flexed knee) is another physical exam maneuver that is similar to the Lachman test but is less accurate. That is because a varying degree of anterior translation is normal, and whether what the examiner is perceiving represents an abnormal amount may be difficult to tell.

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The Lachman test can be falsely negative if there is a displaced fragment of either bone or cartilage in the knee or if the hamstrings are resisting the examiner. Also, as noted, the fluid in the knee? may stabilize it somewhat and therefore if there is a tense effusion the Lachman test may be falsely negative as well.

 

 It may be diagnostically and therapeutically helpful to aspirate the knee. Removing the volume of fluid will make the patient more comfortable. Also, merely assessing the color of the fluid helps with diagnosis (red, meaning blood, signifies a clinically important injury in approximately 90% of cases). In addition, by draining the knee, a more reliable physical examination can be performed.

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Figure 5: An MRI showing a torn ACL (red arrow) (from https://radiopaedia.org/articles/anterior-cruciate-ligament-tear)

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On sagittal view, absence or discontinuity of ACL fibers would indicate an ACL injury.

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A young male patient may present with both an effusion and a history of knee pain after playing sports but the two may not be related. Rather, the joint fluid in this case may actually be caused by gonorrhea.   This can be assessed by a short question about urethral symptoms.

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Treatment for either ACL or PCL injury include both non-operative options to surgical repair. [MF2MF1] 

 

Patients with less severe ACL injury or willingness to modify their activities may be successfully treated with physical therapy and some degree of immobilization (e.g. use of a brace while playing sports).  

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The first consideration when contemplating surgical repair of PCL injuries is the degree of injury. If not torn completely, the PCL has particularly high potential to heal with immobilization and then therapy.   These exercises can assist with stability of the knee, particularly by strengthening the quadriceps muscles which have an anterior-directed vector in their normal action.

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Figure 6: : aArthroscopic view of ACL reconstruction graft (arrow) in the notch. The white fibers of the PCL are seen to the right of the graft (“P”) (from commons.wikimedia.org/wiki/File:Anterior_cruciate_ligament_repair_2.jpg)

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Autografts are generally favored over allografts in patients 25 years old or younger, given the lower rate of re-tears as compared to allografts in this population.

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Prevention of either injury relies upon strengthening of the muscles that stabilize the knee joint and promote endurance.   It is not uncommon to see ACL tears later in the day on the sky ski slopes, which may reflect the loss of hamstring stabilization due to muscle fatigue. That is, if the hamstrings are tired and weak, they may not be able to hold on to the tibia, which then exposes the ACL to greater forces. Teaching proper landing technique may also reduce risk of ACL injury.

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Examination of cruciate ligament injuries to the knee.

 

 

 


 [MF1]Barely visible [MF2]Remove platitudes per Joe