By Sean Schowalter, M.D.

Learning Objectives:

  1. Be able to list major structures in the anterior, medial, lateral and posterior compartments of the knee
  2. Learn components of a basic ultrasound of the knee
  3. Understand the current literature involving ultrasound for detection of meniscal tears

Anterior compartment

-Quadriceps tendon

-Suprapatellar joint recess

-Patellar tendon

-Patella

-Prepatellar & infrapatellar bursitis

Medial Compartment

-MCL

-Medial Meniscus (incompletely visualized)

-Pes Anserinus

Lateral Compartment

-IT Band

-LCL

-Lateral Meniscus (incompletely visualized)

Posterior Compartment

-Baker cyst

-Popliteal neurovascular bundle

Anterior compartment Start with the patient in supine position and the knee slightly flexed (figure 1). Place the probe in the sagittal plane just proximal to the patella, along the long axis of the quadriceps tendon. Evaluate the complete quadriceps tendon, medial to lateral, in both the long and short axes (figures 2, 3). The tendon can be follow proximally to evaluate its four muscular components: rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius (figure 4). Just deep to the quadriceps tendon is the suprapatellar recess (figure 6). Positioning the knee in slight flexion preferentially drives fluid into this recess, making it a sensitive area to evaluate for knee effusions. From here, the transducer is moved inferiorly in the sagittal plane, just distal to the patella until the patellar tendon is identified. Again evaluate the entire tendon in longitudinal and transverse orientations. This region is also evaluated for bursal fluid superficial to the patella (prepatellar bursa), and anterior to the patellar tendon (infrapatellar tendon). Remember to use light pressure in order to avoid displacing and missing fluid in this area. Lastly flex the knee to 90° and evaluate the femoral trochlear cartilage by placing the probe in a transverse orientation. The cartilage should appear hypoechoic and of uniform thickness.

Figure 1. Probe/knee positioning for evaluation of anterior knee. Knee should be flexed 20-30°.
Figure 2. Quadriceps tendon longitudinal. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 3. Quad tendon transverse – VM is vastus medialis. C is Femoral trochlear cartilage. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 4. Quadriceps muscles. VM is vastus medialis. RF is rectus femoris, VI is vastus intermedius, VL is vastus lateralis.Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 5. Patellar Tendon longitudinal. HF is hoffa fat pad. TT is tibial tuberosity. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 6. Simple joint effusion in suprapatellar recess, deep to quadiceps tendon.Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.

Medial Knee

Evaluation is begun in coronal plane by finding the MCL along the medial aspect of the joint line. Evaluate the entire extent of the MC in long & short axes. The medial meniscus can also be seen deep to the MCL, between the femur and tibia (figure 8). The medial meniscus should appear triangular and hyperechoic. The probe can then be moved anteriorly and posteriorly to evaluate the anterior & posterior horns of the meniscus. Finally, evaluate the pes anserine tendons by moving distally along the MCL to about 4-5cm beyond the joint line and slightly anteriorly (figure 9). Here the insertions of the pes anserine tendons (sartorius, gracilis, and semitendinosus) can be evaluated, as well as the bursal fluid below them. The sartorius is the most anterior tendon, the semitendinosus is the most posterior tendon, and the gracilis is between the two.

Figure 7. Position the leg in external rotation and slightly flex knee (Line represents probe position)
Figure 8. MCL Longitudinal. MM is medial meniscus. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 9. Pes Anserine tendons in longitudinal, superficial to MCL. Appears as single entity at this level but can be followed proximally to see demarcation of the different tendons. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.

Lateral Knee

Start on the patellar tendon in long axis and move probe laterally. The first longitudinal structure will be the IT band (figure 11). Follow the IT band proximally, focal thickening or surrounding fluid at the distal femur can indicate IT band friction syndrome. Once evaluation of the IT band is finished, the transducer can be moved further laterally in the coronal plane until the LCL is visualized (figure 13). Along the joint line the lateral meniscus should also be visualized. Move the probe anteriorly and posteriorly to observe the anterior and posterior horns. As with the medial meniscus, the lateral meniscus should appear triangular and hyperechoic.

Figure 10: Position the leg in internal rotation and slightly flex knee (Rectangle represents probe position). Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 11. T band longitudinal view. Just lateral to patella. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 12. Probe placement for LCL evaluation. Proximal end of transducer at popliteal groove (surface of lateral femoral condyle where popliteus muscle originates)

Figure 13. LCL in longitudinal. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 14. Probe position for peroneal nerve – In transverse, just posterior to the fibula. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.

Figure 15. Peroneal nerve (circled) coursing posteriorly to fibula. Should be hypoechoic as pictured. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.

Posterior Knee

Place the transducer in the transverse plane of the midcalf, identifying the deep soleus and superficial medial/lateral heads of the gastrocnemius. Trace the medial head of the gastrocnemius until the semimembranosus tendon is identified. If a baker cyst is present, it will be located between the medial head of the gastrocnemius and semimembranosus tendon (figures 16, 17).

Figure 16. Probe position for baker cyst. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 17. Star represents expected location for baker cyst between medial head of gastric (MG) and semimembranosus tendon (SM).Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.
Figure 18. Make sure to be perpendicular to tendon. Anisotropy of tendons at shallower angles causes the tendon to be hypoechoic and may be mistaken for a baker’s cyst. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.

Figure 19. Probe position for popliteal neurovascular bundle – knee slightly flexed
Figure 20. Popliteal neurovascular bundle. A-artery, V-Vein, oval-nerve, F-femoral condyles. Image from Alves et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016.

Ultrasound for Meniscal Tears– The Literature

Study 1:

Accuracy of hand-held ultrasound scanning in detecting meniscal tears

The Bone & Joint Journal. A. A. Shetty, A. J. Tindall, K. D. James, J. Relwani, K. W. Fernando

August 2008

  • Compared ultrasound vs MRI, final outcome was determined at arthroscopy.
  • 35 patients with a mean age of 47 years.
  • Ultrasound: sensitivity 86.4% (95% (CI) 75-97.7%), specificity of 69.2% (53.7-84.7%), PPV 82.6% (70-95.2%) and NPV 75% (60.7-81.1%)
  • MRI: sensitivity 86.4% (75-97.7%), specificity 100.0%, PPV 100.0% and NPV 81.3% (74.7-87.9).

Study 2:

The Value of Ultrasonography in the Detection of Meniscal Tears Diagnosed

by Magnetic Resonance Imaging

American Journal of Physical Medicine & Rehabilitation. Gi-Young Park, Jong-Min Kim, Sung-Moon Lee, Michael Lee.

January 2008

  • Twenty-seven knees with meniscal tears and 14 knees without tears on MRI were prospectively evaluated with ultrasound. MRI was used as the reference standard.
  • Ultrasonography showed a sensitivity of 86.2%, specificity 84.9%, PPV 75.8%, and positive and negative predictive values of 91.8% for meniscal tears.

Ultrasound for Meniscal Tear Conclusions:

  • Good sensitivity for detecting meniscal tears, means ultrasound could be useful as a screening tool
  • However, accuracy is user dependent, and these studies involved operators with prior experience in detailed knee ultrasound
  • Can’t completely visualize the deeper aspects of the meniscus, and less good at picking up degenerative meniscal tears
  • Take away: Use as screening tool in younger patients with TRAUMATIC meniscal tears.

References

1.        Alves TI, Girish G, Kalume Brigido M, Jacobson JA. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016;36(6):1759-1775. doi:10.1148/rg.2016160019