The Case

A 19-year-old college athlete is brought to the emergency department (ED) for evaluation of her right knee. During a game, she collided with another player who fell into the outside of her right knee. She felt a pop when she was hit, her knee immediately began to swell, and she was unable to bear weight. She was assessed courtside and had questionable valgus laxity and tenderness along the medial aspect of her joint, so she was sent to the ED for further evaluation. She denied any open wounds, paresthesia, weakness, or skin discoloration of the affected extremity and also denied any other injuries.

Her physical exam was notable for tenderness to palpation over the medial aspect of her right knee joint with diffuse swelling. She had significantly limited range of motion, including extension, of her knee due to pain. There was no obvious instability, but pain was easily exacerbated with valgus stress. Otherwise, her exam was unremarkable with normal vital signs and no change in neurovascular status.

X-rays were ordered to rule out fracture. In the meantime, a point-of-care ultrasound of the affected knee was performed to evaluate for medial collateral ligament injury, joint effusion, and quadriceps and patellar tendon tear.

POCUS Findings

There is a joint effusion primarily seen in the suprapatellar recess and concern for a partial MCL tear. The quadriceps, patellar, and lateral collateral ligaments appear intact.

Case continued:

X-rays showed no bony abnormalities. Given her mechanism of injury, clinical presentation, and POCUS findings, there was high suspicion for ligamentous injury. She was placed in a knee immobilizer, provided with crutches, and advised to rest, ice, compress, and elevate her knee. She was instructed to follow up with orthopedic surgery for further evaluation and management. She ultimately underwent an outpatient MRI which confirmed MCL sprain and also found a partial ACL tear.

Medial Collateral Ligament Injury

Figure 1. Illustration of the bony and soft tissue components of the knee joint

Overview

The medial collateral ligament (MCL) originates at the anterolateral aspect of the medial femoral condyle and inserts 4.5 cm distal to the joint line on the proximal tibia (see Figure 1). There are superficial and deep portions of the MCL that work in conjunction to stabilize the knee joint against valgus stress [1].

Common Mechanism

MCL injury is the most common ligamentous injury to the knee; ligamentous injuries account for 42% of all knee injuries [2]. The typical mechanism involves direct valgus force to the lateral side of the knee. This injury is often associated with a popping sensation, swelling, and pain along the medial joint line [1]

Physical Exam Findings

MCL injuries typically have medial joint line tenderness and pain or laxity with valgus stress to the knee (see Figure 2). Any ligamentous injury to the knee can lead to effusion and swelling [3]

Figure 3: Stieda fracture - avulsion fracture of the medial femoral epicondyle where the proximal MCL attaches [4]

Diagnostic Imaging

X-rays should be obtained to assess for associated fracture. While rare, there are two fractures associated with MCL injury. A Stieda fracture is an avulsion fracture of the medial femoral epicondyle where the proximal MCL attaches [4] - see Figure 3. A reverse Segond fracture is associated with avulsion injury to the deep fibers of the MCL involving the medial proximal tibia. [5]

MRI is the gold standard. However, MRI is costly and often difficult to obtain in an ED setting [6-7]. Point-of-care ultrasound is a promising imaging modality to quickly evaluate for ligamentous injury [6,9].

Treatment

MCL tears are often treated nonoperatively depending on the severity and grading of the tear (which is based on degree of laxity with valgus stress at 30° flexion of the knee). Surgical intervention may be necessary in the setting of avulsion fracture, multiple ligamentous injuries, or joint instability.

Treatment is based on grading of MCL tear:

Grade I: Rest, Non-steroidal anti-inflammatory drugs (NSAIDs), physical therapy
Grade II/III: Rest, NSAIDs, bracing, and early physical therapy [2]

Knee Ultrasound Crash Course

Common focused questions you should ask yourself when using POCUS to assess knee injury:
- Is there evidence of tendon tear?
- Is a joint effusion present?
- Is there evidence of bony abnormality (fracture, dislocation)? [8]
Additionally, POCUS is an excellent tool to assess for ligamentous and meniscal injuries [6,9]

Since our patient had an MCL injury with effusion, we’ll focus primarily on these, as well as the quadriceps and patellar tendon, assessments

Figure 4: Placement of ultrasound probe for proper MCL evaluation [10]

MCL Assessment

Position the patient so that the medial aspect of the knee is well-exposed (i.e. supine with hip externally rotated and knee slightly flexed).
Palpate the medial joint line and place the high frequency linear array transducer in the coronal plane of the medial knee.
Identify the medial meniscus, which appears as a hyperechoic structure between the femur and the tibia. Superficial to the medial meniscus you will find the MCL.
The normal appearance of the MCL in long axis is an echogenic fibrillar structure, extending from the medial femoral condyle to the proximal tibia [6-10].
Once the MCL is identified, the probe should be turned 90 degrees to assess the MCL in short axis, scanning through the whole length of the ligament. In this view you can also assess for effusion in the medial recess of the joint [10]

Ligamentous Injury

Ultrasound findings include disruption, irregularity or heterogeneity with hypoechoic changes, or thickening of fibers, along with surrounding edematous changes [7-9]. See Figure 6 and Figure 7, in addition to our patient’s image above.
A recent observational cross-sectional blinded study by Elshimy et al found ultrasound to have sensitivity of 92.3% and a specificity 100% in diagnosing MCL tear compared with MRI which had a sensitivity of 88.5% and a specificity of 97.1% [6]. Another study in 2022 by Ahmadi et al, also comparing POCUS with MRI, yielded slightly lower sensitivity and specificity but still relatively high overall. This further supporting the utility of POCUS as a diagnostic modality with some advantages over MRI [9].

Figure 8. Suprapatellar longitudinal view of the quadriceps tendon and suprapatellar recess/joint space with an effusion

Knee Effusion Assessment

POCUS can be used to quickly and effectively assess for fluid collection within the joint space of the knee.
Place the probe over the suprapatellar space and evaluate for fluid in the suprapatellar recess (potential space between the quadriceps tendon and prefemoral fat pad). Evaluate for fluid in this space, superior to inferior and medial to lateral. Slight flexion can increase the sensitivity of your effusion assessment.
Effusions can be secondary to trauma, infection, autoimmune/inflammatory process and as such may require diagnostic arthrocentesis for characterization. If this is indicated, ultrasound guidance should be considered [1,8,10].

Quadriceps & Patellar Tendon Assessment (brief overview)

Quadriceps tendon — place the probe in the anterior midline in the suprapatellar region. Identify the fibrillar appearance of the tendon (in long axis).
Patellar tendon — place the probe over the caudal aspect of the patella and find the patellar tendon’s attachment. It, too, has a classic fibrillar appearance in a long axis view. Slide the probe caudally, visualizing the entire tendon to its attachment on the proximal tibia.
For each, look for any disruption of the tendon fibers, edema, tendon thickening, similar to findings seen with ligament tears. Evaluate in both long and short axis [1,8,10].

Take Home Points

POCUS is great initial diagnostic modality for patients presenting to the ED for knee injuries, including those concerning for MCL injury. This may be especially useful if the exam is equivocal or limited.
Look for disruption, irregularity, hypoechoic changes, or thickening of a ligament or tendon, as well as surrounding edema and joint effusions
While POCUS may not significantly change ED management, it can provide useful diagnostic information and has the advantage of being more time- and cost-effective compared to MRI.

POST BY: DR. SHAUNA COMBS (R1)

FACULTY EDITING BY: DR. LAUREN MCCAFFERTY

References

Alves TI, Girish G, Brigido MK, Jacobson JA. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016; 36(6):1759-1775
Friedman Eric R. Ligamentous Injuries of the Knee. In: Mattu A and Swadron S, ed. CorePendium. Burbank, CA: CorePendium, LLC. https://www.emrap.org/corependium/chapter/recxBlk7CeDb8TESV/Ligamentous-Injuries-of-the-Knee#h.dfarphhsn5of. Updated April 8, 2022. Accessed September 18, 2022.
Calmbach WL, Hutchens M. Evaluation of patients presenting with knee pain: Part I. History, physical examination, radiographs, and laboratory tests. Am Fam Physician. 2003;68(5):907-12.
Reddy S, Murphy A. Stieda fracture. Reference article, Radiopaedia.org. (accessed on 19 Sep 2022) https://doi.org/10.53347/rID-26300
Feger, J., Knipe, H. Medial collateral ligament injury (knee). Reference article, Radiopaedia.org. (accessed on 18 Sep 2022)
Elshimy A, Osman AM, Awad MES, Abdel Aziz MM. Diagnostic accuracy of point-of-care knee ultrasound for evaluation of meniscus and collateral ligaments pathology in comparison with MRI. Acta Radiol. 2021:2841851211058280.
Ghosh N, Kruse D, Subeh M, Lahham S, Fox JC. Comparing Point-of-care-ultrasound (POCUS) to MRI for the Diagnosis of Medial Compartment Knee Injuries. J Med Ultrasound. 2017;25(3):167-172.
Dewitz A (2014). Musculoskeletal, Soft Tissue, and Miscellaneous Applications. In OJ Ma, JR Mateer, RF Reardon, SA Joing (eds), Ma and Mateer’s Emergency Ultrasound (3rd ed). McGraw-Hill Education. pp 503-568.
Ahmadi O, Heydari F, Golshani K, Derakhshan S. Point-Of-Care Ultrasonography for Diagnosis of Medial Collateral Ligament Tears in Acute Knee Trauma; a Diagnostic Accuracy Study. Arch Acad Emerg Med. 2022;10(1):e47.
Hall, Mederic M, Rajasekaran S. “Musculoskeletal Ultrasound of the Knee.” UpToDate. 18 May 2022, https://www.uptodate.com/contents/musculoskeletal-ultrasound-of-the-knee/print?topicRef=13807&source=see_link.
https://silo.tips/download/ultrasound-evaluation-of-most-common-knee-patology
https://www.ultrasoundcases.info/medial-collateral-ligament-2746/

Intern Ultrasound of the Month: Medial Collateral Ligament Injury in the Emergency Department