Knee



Knee


Thomas Magee

Jeffrey J. Peterson

Thomas H. Berquist



▪ SKELETAL TRAUMA: OSTEOCHONDRAL FRACTURES


KEY FACTS



  • Fractures involving the joint surface result from direct blows or shearing forces.


  • Fractures may be subtle, requiring computed tomography (CT) or magnetic resonance imaging (MRI) for detection.


  • Osteochondral patellar fractures are commonly associated with dislocation.


  • Associated soft tissue injury is common.






FIGURE 4-1. Patellar view demonstrates subluxation after reduction of a patellar dislocation. There is a displaced osteochondral fragment (arrow) laterally.



SUGGESTED READING

Capps GW, Hayes CW. Easily missed injuries about the knee. Radiographics. 1994;14:1191-1210.

Dezell PB, Schils JP, Recht MP. Subtle fractures about the knee: innocuous-appearing yet indicative of internal derangement. Am J Roentgenol. 1996;167:699-703.



▪ SKELETAL TRAUMA: PATELLAR FRACTURES


KEY FACTS



  • Patellar fractures account for 1% of all skeletal fractures.


  • The mechanism of injury is direct trauma (motor vehicle accidents 28% and falls 68%) or indirect trauma (4%), such as quadriceps contraction.


  • Types of patellar fracture: Transverse or oblique 34%; comminuted 16%; longitudinal 28%; apical or basal 28%.


  • A bipartite patella most commonly involves the upper outer quadrant. It is usually often bilateral and should not be confused with a fracture.


  • Routine radiographs (anteroposterior [AP], lateral, and patellar views) are usually diagnostic.


  • Treatment includes reduction with internal fixation for displaced fractures. Fractures with less than 2 to 3 mm of displacement and articular surface congruency can be treated conservatively (casting). Badly comminuted fractures may require partial or complete patellectomy.


  • Complications



    • Osteoarthritis


    • Nonunion






FIGURE 4-2. Anteroposterior (AP) (A) and lateral (B) radiographs of a bipartite patella (arrow).







FIGURE 4-3. Anteroposterior (AP) (A) and lateral (B) radiographs of a comminuted displaced patellar fracture.







FIGURE 4-4. Lateral (A) and patellar (B) views after reduction with K-wires and tension band. The articular surface is reduced.



SUGGESTED READING

Bostrom A. Fracture of the patella. Acta Orthop Scand Suppl. 1972;143:1-80.

Walker CW, Moore TE. Imaging of skeletal and soft tissue injuries in and around the knee. Radiol Clin North Am. 1997;35(3):631-653.



▪ SKELETAL TRAUMA: SUPRACONDYLAR FRACTURES


KEY FACTS



  • Supracondylar fractures involve the distal 9 cm of the femur. Fractures of the distal femur account for 7% of all femoral fractures. Open injuries account for 5% to 10%.


  • Intra-articular extension is common. These complex fractures are difficult to manage.


  • Associated tibial plateau fractures are common.


  • Mechanisms of injury include minor trauma to the flexed knee in elderly patients and high-velocity forces applied to the anterolateral, lateral, or medial aspect of the knee.


  • Routine radiographs (AP and lateral) are diagnostic.


  • Treatment may be conservative (casting or traction) or operative to reduce and achieve restoration of the joint and leg length.


  • Complications:





















    Early

    Late


    Vascular injury

    Infection


    Infection

    Nonunion


    1% of closed

    Malunion


    20% of open

    Osteoarthritis


    Failed reduction







FIGURE 4-5. Orthopedic Trauma Association Classification. Type A: extra-articular, simple (A) or comminuted (B). Type B: partial articular, one condyle involved (C). Type C: complete articular, both condyles involved with “Y” pattern (D) or severely comminuted (E).







FIGURE 4-5. (continued)







FIGURE 4-6. Anteroposterior (AP) (A) and lateral (B) radiographs of a severely comminuted complete articular fracture. Note the loss of length and posterior rotation (arrow) of the distal fragment in (B).







FIGURE 4-7. Ipsilateral fractures of the tibia, fibula, and femur. Type I: tibial and femoral fractures without knee involvement (71% of cases). Type IIA: femoral fracture with tibial articular involvement (16.5% of cases). Type IIB: femoral articular involvement and proximal tibia and fibular fractures. Type IIC: both articular surfaces involved (8% of cases).



SUGGESTED READING

Fraser RD, Hunter GA, Waddle JP. Ipsilateral fractures of the femur and tibia. J Bone Joint Surg. 1978;60B:510-515.

O’Brien P, Meek RN, Blachut PA, et al. Fractures of the distal femur. In: Bucholz RW, Heckman JD, eds. Rockwood and Green’s Fractures in Adults. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2001:1731-1773.

Orthopedic Trauma Association Committee on Coding and Classifications. Fractures and dislocations compendium. J Orthop Trauma 1996;10(suppl):41-45.



▪ SKELETAL TRAUMA: PROXIMAL TIBIAL FRACTURES


KEY FACTS



  • Proximal tibial fractures may be extra-articular or articular (tibial plateau or condylar fractures).


  • Tibial plateau (condyle) fractures account for 1% of all fractures and 8% of fractures in the elderly. The majority (55% to 70%) of plateau fractures involve the lateral plateau. Isolated medial plateau factures occur in 10% to 23% of cases, and medial and lateral fractures occur in 10% to 30% of cases.


  • Mechanism of injury is motor vehicle accidents (54%) or falls (46%) leading to vertical compression (T and Y fractures) varus and valgus forces (medial and lateral plateau fractures, respectively).


  • Ligament and meniscal injuries are common with varus, valgus, or twisting forces.


  • AP and lateral radiographs are usually diagnostic for displaced fractures.


  • CT and MRI are frequently indicated to evaluate fragment position, articular surface congruity, and associated soft tissue injury.


  • Management is based on four key factors: degree of articular depression, degree of fragment separation, degree of comminution, and extent of soft tissue injury.


  • Depression of 4 to 8 mm and separation of fragments 4 mm or more generally indicate a need for internal fixation.


  • Complications include infection, nonunion, and arthropathy.


  • Ipsilateral, femoral, and tibial condylar fractures are not uncommon and have the following significant associated injuries:



    • Abdominal and chest injuries 20%


    • Open injury to leg 60%


    • Neurovascular injury 7%






FIGURE 4-8. Hohl classification of tibial plateau fractures: I, undisplaced fracture (24%); II, central depression (26%); III, split compression, usually with fibular fracture (29%); IV, total condylar depression (11%); V, comminuted bicondylar fractures (10%).







FIGURE 4-9. A: Tibial plateau fracture with splitting and separation laterally. B: Tibial plateau fracture reduced with buttress plate and screws to restore joint congruency.







FIGURE 4-10. Computed tomography (CT) images in the axial (A), sagittal (B), and coronal (C) planes demonstrate a minimally depressed fracture with minimal articular displacement.



SUGGESTED READING

Hohl M. Tibial condylar fractures. J Bone Joint Surg. 1967;49A:1455-1467.

Walker CW, Moore TE. Imaging of skeletal and soft tissue injuries in and around the knee. Radiol Clin North Am. 1997;35(3):631-653.



▪ SKELETAL TRAUMA: MISCELLANEOUS FRACTURES


KEY FACTS



  • Other tibial and femoral fractures include avulsion fractures, tibial spine fractures, tuberosity fractures, physeal fractures, stress fractures, and bone bruises.


  • Subtle osseous injury may be initially detected by the presence of a lipohemarthrosis on cross-table lateral radiographs.


  • Physeal fractures about the knee account for only 0.5% to 3% of physeal injuries. Femoral physeal fractures are more common because of the ligament support of the knee. Most injuries are Salter-Harris Types I and IV.


  • The Segond fracture is an avulsion injury at the insertion of the anterolateral ligament (ALL) on the upper lateral tibia. Anterior cruciate ligament (ACL) tears are associated with 75% to 100% of cases.


  • Stress fractures of the tibia and femur are subtle early radiographically. MRI has replaced radionuclide scans for more effective and specific early diagnosis.


  • Bone bruises are usually not evident on radiographs, but easily detected with MRI. Associated meniscal and/or ligament injuries are common and also easily appreciated on magnetic resonance (MR) images.






FIGURE 4-11. Ligament support about the knee. A: The tibial physis is within the ligament support, and the femoral physis is proximal resulting in greater risk for fracture (B, C).







FIGURE 4-12. Anteroposterior (AP) (A), lateral (B), and stress views (C) of a Salter-Harris Type III femoral fracture.







FIGURE 4-13. Anteroposterior (AP) radiograph of a Segond fracture (arrow).







FIGURE 4-14. Lateral radiograph of a tibial tuberosity avulsion.







FIGURE 4-15. Tibial spine-anterior cruciate ligament (ACL) avulsion. Fluid sensitive coronal (A) and sagittal (B) magnetic resonance (MR) images demonstrate the ACL avulsion fracture at its attachment upon the tibial spine.







FIGURE 4-16. Axial computed tomography (CT) demonstrates a lipohemarthrosis indicating an intra-articular fracture.







FIGURE 4-17. A: Anteroposterior (AP) radiograph is normal. B: Coronal T1-weighted image clearly demonstrates the stress fracture (arrow).







FIGURE 4-18. Bone contusion involving the medial femoral condyle clearly demonstrated on the sagittal T2-weighted magnetic resonance (MR) image resulting from varus injury.



SUGGESTED READING

Claes S, Luyckx T, Vereecke E, et al. The Segond fracture: a bony injury of the anterolateral ligament of the knee. Arthroscopy. 2014;30(11):1475-1482.

Dezell PB, Schils JP, Recht MP. Subtle fractures about the knee: innocuous-appearing yet indicative of internal derangement. Am J Roentgenol. 1996;167:699-703.



▪ MENISCAL LESIONS: MENISCAL TEARS


KEY FACTS



  • Meniscal tears are the most common cause of knee pain and instability.


  • Patients present with pain, locking, or “giving way.”


  • Tears may be the result of acute trauma or repetitive trauma with progressive degeneration.


  • The lateral meniscus is C-shaped and less firmly attached to the capsule (separated posteriorly by popliteus tendon sheath). The medial meniscus is more firmly attached, and the posterior horn is larger (see Fig. 4-19).


  • MRI has replaced other imaging techniques for diagnosis of meniscal tears. Tears are most easily identified on spin-echo proton density images. Conventional spin-echo sequences are 93% sensitive compared with 80% for fast spin-echo sequences. Sagittal, coronal, and axial image planes should all be evaluated to properly characterize the type of tear.






    FIGURE 4-19. Meniscal appearance (medial and lateral) with the knee in different degrees of rotation. Note the posterior horn of the medial meniscus (arrow) is larger. The popliteus tendon (pt) sheath separates the lateral meniscus from the capsule posteriorly.



  • Meniscal tears are described by configuration and location. The posterior horn is most commonly involved.


  • MR criteria for classifying meniscal tears have been clearly defined (see Fig. 4-21).


  • Treatment depends on the location (peripheral vs. central) and type of tear. Peripheral tears may heal or be repaired as in the vascular zone. Displaced fragments may be removed arthroscopically.






FIGURE 4-20. A: Types and appearances of meniscal tears. B: Meniscal tears seen in the axial and coronal planes.







FIGURE 4-21. Magnetic resonance (MR) classification of meniscal tears. Normal low signal intensity. Grade 1: globular increased signal intensity that does not communicate with the articular surface. Grade 2: linear increased signal intensity that does not communicate with the articular surface. Grade 3: linear increased signal intensity that communicates with the articular surface, a true tear. Grades 3a and b: more extensive articular involvement. Grade 4: complex tears with distortion of the meniscus.






FIGURE 4-22. Sagittal proton density-weighted image of a normal low-intensity meniscus.







FIGURE 4-23. Gradient echo sagittal image of a linear tear (arrowheads) in the posterior medial meniscus.







FIGURE 4-24. Coronal fat-suppressed T2-weighted image (A) of a bucket-handle tear of the medial meniscus. Note truncated meniscus (arrow) and displaced fragment (arrowhead). Sagital proton density image (B) shows the “double posterior cruciate ligament” (PCL) sign (arrow).







FIGURE 4-25. Axial (A) and sagittal (B) illustrations of a flipped meniscal fragment. Sagittal proton density image (C) demonstrates a small posterior meniscal remnant and a large flipped meniscal fragment anteriorly (arrow).



SUGGESTED READING

Blackman GB, Majors NM, Helms CA. Comparison of fast spin-echo versus conventional spin-echo MRI for evaluation of meniscal tears. Am J Roentgenol. 2005;184:1740-1743.

Crues JV III, Murk J, Levy TL, et al. Meniscal tears of the knee: accuracy of MR imaging. Radiology. 1987;164:445-448.

De Smet AA. How I diagnose meniscal tears on knee MRI. Am J Roentgenol. 2012;199(3):481-499.

Lance V, Heilmeier UR, Joseph GB, et al. MR imaging characteristics and clinical symptoms related to displaced meniscal flap tears. Skeletal Radiol. 2015;44(3):375-384.

Magee T. Three-Tesla MR imaging of the knee. Radiol Clin North Am. 2007;45(6):1055-1062.

Nguyen JC, De Smet AA, Graf BK, et al. MR imaging-based diagnosis and classification of meniscal tears. Radiographics. 2014;34(4):981-999.



▪ MENISCAL LESIONS: POSTOPERATIVE MENISCUS


KEY FACTS



  • Menisci may be partially or completely resected or repaired.


  • Image features applied to diagnosis of meniscal tears (increased signal intensity extending to the articular surface and displaced fragments) can be applied after repair.


  • Intra-articular gadolinium may improve accuracy for evaluating the postoperative meniscus. Intra-articular gadolinium is 92% accurate for detection of retear.


  • Arthroscopy is most useful in complex or equivocal cases.






FIGURE 4-26. A: Coronal image from a magnetic resonance (MR) arthrogram shows changes in a near-complete meniscectomy of the body of the medial meniscus (arrowhead). B: Sagittal image from an MR arthrogram shows changes in a prior meniscal repair (arrow) with no contrast extending into the meniscus to suggest retear. C: Sagittal image from an MR arthrogram shows changes in a prior partial meniscectomy with abnormal contrast extending into the substance of the medial meniscal remnant compatible with retear (arrow).







FIGURE 4-26. (continued)



SUGGESTED READING

Davis KW, Tuite MJ. MR imaging of the postoperative meniscus of the knee. Semin Musculoskelet Radiol. 2002;6(1):35-45.

Lum PS, Schweitzer ME, Bhatea M, et al. Repeat tear of postoperative meniscus: Potential MR imaging signs. Radiology. 1999;210:183-188.

Magee TH. Accuracy of 3-Tesla MR and MR arthrography in diagnosis of meniscal retear in the post-operative knee. Skeletal Radiol. 2014;43(8):1057-1064.

Sciulli RL, Boutin RD, Brown RR, et al. Evaluation of the postoperative meniscus of the knee: a study comparing conventional arthrography, conventional MR imaging, MR arthrography with iodinated contrast material, and MR arthrography with gadolinium-based contrast material. Skeletal Radiol. 1999;28(9):508-514.



▪ MENISCAL LESIONS: MENISCAL CYSTS


KEY FACTS



  • Meniscal cysts are reported in 1% of patients undergoing meniscectomy.


  • They are most common anterolaterally but can occur medially.


  • Meniscal tears are usually present and may be the basis for cyst formation.


  • Patients present with tenderness and joint-line swelling.


  • Meniscal cysts can be diagnosed with arthrography, but MRI is preferred.


  • Treatment requires decompression of the cyst and meniscal repair.


  • MR features include



    • Well-defined high signal intensity lesion adjacent to or partially including the meniscus on T2-weighted sequences.


    • Cysts may be septated (47%) and up to 5 cm in size.


  • Ganglion cysts and cruciate ligament cysts may be confused with meniscal cysts.






FIGURE 4-27. Meniscal cyst (curved arrow) seen on a sagittal T2-weighted image arising from a tear of the medial meniscus (arrow).



SUGGESTED READING

Anderson JJ, Connor GF, Helms CA. New observations on meniscal cysts. Skeletal Radiol. 2010;39(12):1187-1191.

Burk DL, Dalinka MK, Kanal E, et al. Meniscal and ganglion cysts of the knee: MR evaluation. Am J Roentgenol. 1988;150:331-336.

Campbell SE, Sanders TG, Morrison WB. MR imaging of meniscal cysts: incidence, location, and clinical significance. Am J Roentgenol. 2001;177:409-413.

De Smet AA, Graf BK, del Rio AM. Association of parameniscal cysts with underlying meniscal tears as identified on MRI and arthroscopy. Am J Roentgenol. 2011;196(2):W180-W186.



▪ MENISCAL LESIONS: DISCOID MENISCI


KEY FACTS



  • Discoid menisci are reported in 1.5% to 15.5% of lateral and 0.1% to 0.3% of medial menisci.


  • Discoid menisci are broad and disk shaped, and more prone to meniscal tears. Meniscal tears are more difficult to evaluate with discoid menisci because of degeneration and the high incidence of multiple tears.


  • The transverse diameter of a normal meniscus is 10 to 11 mm. A discoid meniscus projects farther into the joint and therefore appears larger on coronal and sagittal MR images (visible on three or more 4-mm-thick sagittal images).







FIGURE 4-28. Discoid meniscus. Sagittal proton density-weighted images using 4-mm-thick sections demonstrate meniscus on four contiguous images (A-D). Coronal image (E) shows the meniscus extending into the joint (arrow) near the tibial spine.



SUGGESTED READING

Ryu KN, Kim IS, Kun EJ, et al. MR imaging of tears of discoid menisci. Am J Roentgenol 1998;171:963-967.

Samoto N, Kozuma M, Tokuhisa T, et al. Diagnosis of discoid lateral meniscus of the knee on MR imaging. Magn Reson Imaging. 2002;20(1):59-64.



▪ LIGAMENT AND TENDON INJURIES: BASIC CONCEPTS


KEY FACTS



  • Complete evaluation of the ligaments, tendons, and capsule is difficult with conventional techniques, including CT and arthrography.


  • MRI offers the ability to evaluate all supporting structures of the knee.


  • Key anatomic structures for image evaluation include



    • ACL: oblique course with anteromedial and posterolateral bands. Extends from the lateral femoral condyle to the tibial plateau.


    • Posterior cruciate ligament (PCL): thicker than ACL. Extends from medial femoral condyle to posterior intercondylar region of the tibia.


    • Medial collateral ligament (MCL): three layers. The first layer is composed of fascia covering the quadriceps, the second layer includes the MCL, and the third layer is the capsular ligament. The MCL extends from the medial femoral condyle to attach on the tibia approximately 5 cm below the joint line.


    • Lateral collateral ligament (LCL): also known as the fibular collateral ligament. Extends from lateral femoral condyle to the fibular head. Separate from capsule.


    • Quadriceps tendon: formed by four muscles of quadriceps group, resulting in layers until it attaches to the patella.


    • Patellar tendon: extends from the patella to the tibial tuberosity.


    • Popliteus tendon: extends from the lateral femoral condyle passing between the lateral meniscus and capsule to join the muscle origin on the posterior tibia.






FIGURE 4-29. Ligament and tendon anatomy of the knee seen from posterior (A), lateral (B), and axial (C) planes.







FIGURE 4-29. (continued)



SUGGESTED READING

Berquist TH. MRI of the Musculoskeletal System. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2006:303-429.



▪ LIGAMENT AND TENDON INJURIES: ANTERIOR CRUCIATE LIGAMENT—ACUTE (PRIMARY FEATURES)


KEY FACTS

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Sep 22, 2018 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Knee

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