AUTHOR AND EDITOR INFORMATION

Section 1 of 9  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

INTRODUCTION

Section 2 of 9  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

Background

MRI has revolutionized the evaluation of musculoskeletal soft tissue injuries. Nowhere is this more evident than in the evaluation of internal derangements of the knee. MRI is an accurate and cost-effective means of evaluating a wide spectrum of knee injuries ranging from cruciate-collateral ligament injuries to cartilage deficiencies. For interpreting radiologists and clinicians, evaluation of an injured knee using MRI requires knowledge of the proper imaging techniques, normal and aberrant anatomy, and clinical significance of detected abnormalities.

For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education articles Knee Injury and Magnetic Resonance Imaging (MRI).

Pathophysiology

Both the medial and lateral supporting structures of the knee are complex arrangements of ligaments, fascial layers, and tendon insertions. For this reason, injuries can range from isolated single-element injuries to combined multiple-element injuries. In addition, injuries can range from strains or partial tears to complete disruptions.

Isolated medial collateral ligament (MCL) injuries result from a valgus stress without a rotary component. Biomechanical studies indicate that the primary function of the MCL as a limit to valgus is crucial only during flexion; therefore, most injuries occur when the knee is flexed.

MCL tears rarely are isolated. More commonly, they are associated with other soft tissue injuries of the knee, such as anterior cruciate ligament (ACL) tears and medial meniscal tears (O'Donoghue's unhappy triad). Of complete MCL tears, 73% are associated with additional significant knee injuries, usually an ACL tear. Other associations include meniscocapsular separations and bone bruises.

Isolated injuries of the lateral collateral ligament (LCL) result from an abnormal varus stress placed on an internally rotated knee. Posterior lateral corner (PLC) injuries can occur as a result of both direct and nondirect forces that cause hyperextension or hyperextension and external rotation. Similar to MCL tears, isolated injuries of the LCL are uncommon and typically occur in association with ACL or posterior cruciate ligament (PCL) tears. Injuries of the lateral compartment are complex, usually with injuries to multiple components, and often are more disabling than injuries of the medial structures because of the greater forces to which lateral structures are subjected during normal gait.

The grading system for classifying both MCL and LCL tears is the same as that used for other ligaments evaluated by MRI as follows:

• Grade 1 - Microscopic tears
• Grade 2 - Partial tears
• Grade 3 - Complete tears

Frequency

United States

The MCL is the weakest of the 3 primary stabilizers of the knee (ACL, LCL, MCL); therefore, it is injured most commonly. Disruption of the MCL has been reported in as many as 61% of skiing injuries and to occur commonly during the clipping injury of football.

Injury of the LCL occurs significantly less commonly than injury of the MCL.

Mortality/Morbidity

MCL tears are not associated with significant morbidity. Most MCL tears heal uneventfully with functional rehabilitation.

Chronic LCL and PLC tears can result in chronic instability, leading to buckling into hyperextension and subsequent injuries to additional ligaments. LCL and PLC instability eventually results in degenerative changes of the joint.

Anatomy

The MCL is a ligament measuring approximately 8-11 cm long by 10-15 mm wide. The MCL arises 5 cm above the joint from the medial femoral epicondyle and inserts 6-7 cm below the joint on the medial tibial metaphysis. Its insertion onto the tibia is covered by the muscle group of the pes anserinus. The MCL is considered to be a composition of the 2 deepest layers of the 3 layers forming the medial supporting structures of the knee.

The 3 layers include (1) layer I or the superficial layer consisting of crural fascia, (2) layer II or the intermediate layer consisting of what classically is considered the superficial MCL, and (3) layer III or the deep layer consisting of the medial capsular ligament and meniscofemoral/meniscotibial ligaments. Fibrofatty tissue and a small bursa are interposed between layers II and III. Layers I and II fuse anteriorly to form the medial patellar retinaculum. Layers II and III fuse posteriorly to form the posterior oblique ligament (POL) component of the MCL (see Image 1). The MCL has 2 components including an anterior vertical component (layer II) and a POL component (fused layers II and III; see Image 2).

The LCL is 5-7 cm long, extracapsular, and free from meniscal attachments. It arises from the lateral epicondyle and inserts conjointly with the biceps femoris tendon onto the fibular head. The LCL is considered to be a layer II structure. The lateral supporting structures of the knee can be divided into anterior, middle, and posterior thirds as well as classified into superficial, intermediate, and deep layers I-III, respectively. Layer I is composed of the iliotibial band anteriorly and the biceps femoris muscle posteriorly. Layer II is composed of the patellofemoral ligaments anteriorly and the LCL posteriorly (LCL is considered a layer II structure despite its envelopment by a portion of layer III). Layer III is composed of the lateral joint capsule, including lateral meniscal attachments, and meniscofemoral and meniscotibial components.

The lateral supporting structures of the knee can be subdivided further into more functionally anatomic divisions that include a group of structures commonly and collectively referred to as the PLC or posterior lateral arcuate complex. The PLC includes the LCL, popliteus tendon, lateral head of the gastrocnemius, arcuate ligament and, occasionally, popliteofibular and fabellofibular ligaments.

The popliteus muscle/tendon arises from the posterior aspect of the tibia, extends laterally and superiorly deep to the LCL, traverses the popliteal hiatus, and inserts onto the popliteal groove of the lateral femoral condyle (see Image 3). The arcuate ligament is a Y-shaped thickening of the capsule in which the medial limb curves over the popliteus muscle and tendon to join the oblique popliteal ligament, and the lateral limb ascends to blend with the capsule near the lateral gastrocnemius muscle insertion (see Image 4).

Clinical Details

Individuals with MCL tears often report feeling a pop after a direct lateral blow to the knee. Clinicians should suspect concomitant cruciate ligament tears if the mechanism of injury was indirect. MCL tears can be classified according to physical examination.

• Grade I tears are not characterized by laxity, only by tenderness upon palpation of the MCL.
• Grade II tears demonstrate some laxity upon valgus stress but have a firm endpoint.
• Grade III tears demonstrate increased laxity and no identifiable endpoint.

Grade I, grade II, and isolated grade III tears are treated nonsurgically and are limited to functional rehabilitation. Grade III tears with associated ACL tears are treated surgically by repairing the ACL only.

Individuals with LCL tears rarely report feeling a pop, since their symptoms usually are dominated by associated and more severe injuries. A hyperextension varus stress is the most common mechanism of isolated LCL tears, while hyperextension and external rotation is a common mechanism of PLC injuries. Patients present with instability, buckling into hyperextension, and posterior lateral pain. The LCL is a completely extracapsular structure; therefore, isolated injuries have little swelling and no effusions. Treatment of injuries to the lateral supporting structures remains controversial, but surgical reconstruction is favored in athletes with significant instability or if an avulsion fracture of the fibular head is present.

Preferred Examination

MRI is the preferred examination for both MCL and LCL injuries. Detection of associated internal derangements of the knee makes MRI superior to ultrasonographic imaging; however, with isolated injuries, ultrasound has demonstrated accuracy comparable to MRI.

Limitations of Techniques

The usual limitations of MRI pertain to MRI evaluation of the MCL and LCL. Limitations include patient claustrophobia, patients who are obese, presence of a pacemaker, or an artifact created by nearby orthopedic hardware. Open as well as dedicated extremity units have decreased the incidence of patient exclusion because of claustrophobia or obesity.

DIFFERENTIALS

Section 3 of 9  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

Other Problems to be Considered

MCL tear
Medial meniscal tears
Medial tibial plateau or medial femoral condyle bone bruises/fractures
Pes anserinus bursitis/avulsions
Medial plica syndrome
MRI differential diagnosis (limited to interlayer [between layers II and III] bursitis)

LCL or PLC tear
Lateral meniscal tears
Lateral tibial plateau or medial femoral condyle bone bruises/fractures
Iliotibial band syndrome
MRI differential diagnosis (limited to iliotibial band syndrome)

RADIOGRAPH

Section 4 of 9  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

Findings

Calcification, particularly in its proximal portion, can be seen in chronic tears of the MCL and is termed Pellegrini-Stieda disease (see Image 5).

Avulsions of the fibular head or of the lateral tibial metaphysis can be seen with injuries of the LCL/biceps femoris tendon or lateral capsule respectively (see Image 6).

Capsular avulsion of the lateral tibial metaphysis is termed a Segond fracture and is highly associated with ACL tears (see Image 7).

CT SCAN

Section 5 of 9  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

Findings

Findings similar to those observed on plain radiographs can be seen on CT. In addition, soft tissue injuries of the MCL and LCL can be detected, although not with the accuracy or contrast resolution of MRI.

MRI

Section 6 of 9  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

Findings

Routine MRI sequences for evaluation of the knee vary among institutions and scanners. The knee should be imaged in all 3 planes, sagittal, coronal, and axial. At a minimum, scans should include sequences to define anatomy, edema, and cartilage.

Sequences for anatomic definition include spin-echo (SE) and fast spin echo (FSE) proton density (PD) sequences. Fluid-sensitive sequences, such as SE/FSE PD fat-suppressed or short tau inversion recovery (STIR), detect edema. Cartilage can be characterized by fat suppressed FSE PD sequences, fat-suppressed gradient-echo (GRE) sequences, or spoiled gradient fat-suppressed sequences.

Coronal images with anatomy defining and fluid-sensitive sequences demonstrate the medial and lateral supporting structures optimally. Additional useful information can be gleaned from sagittal and axial images of these structures.

Both the anterior vertical component and the posterior oblique component of the MCL are depicted consistently on coronal T1-weighted or SE/FSE T2-weighted sequences. The MCL is seen as a thin, taut, well-defined, low T1/T2-signal structure extending from the medial femoral epicondyle to the medial tibial metaphysis. Surrounded by high T1-weighted signal fibrofatty tissue throughout its full extent, it is parallel to and closely applied to the medial femoral epicondyle and medial tibial metaphysis. The anterior vertical or superficial component is visualized best at the level of the intercondylar notch in the vicinity of the distal insertion of the ACL (see Image 8).

MRI appearance of acute MCL tears depends on the degree of tearing as follows:

• Grade I or microscopic ligamentous tears demonstrate an intact ligament of normal thickness surrounded to a variable degree by intermediate T1-weighted and high T2-weighted signals indicative of surrounding edema. The ligament remains closely applied to the underlying cortical bone (see Images 9-10).
• Grade II tears demonstrate thickening and/or partial disruption of the fibers of the MCL with an increased amount of surrounding intermediate T1-weighted and high T2-weighted signals indicative of increased edema and concomitant hemorrhage (see Images 11-12).
• Grade III tears demonstrate complete disruption of the ligament with corresponding surrounding hemorrhage and edema (see Images 13-15).

The difficulty lies in distinguishing between MRI grade II and grade III tears. Clinical evaluation of the presence (grade II) or absence (grade III) of an end point to valgus laxity is helpful. As discussed earlier, the presence of a concomitant ACL tear is suggestive of a complete disruption of the MCL.

A chronic MCL tear is seen as an ill-defined thickened ligament with both low T1-weighted and T2-weighted signals. Occasionally, the MCL ossifies and normal bone marrow signal can be seen within its proximal portion (see Image 16). Healing subacute tears demonstrate a thickened low T1/T2-signal ligament that reaches approximately 50% original strength at 12 months (see Image 17).

To include the LCL, the lateral supporting structures are depicted consistently on both posterior coronal and far lateral sagittal T1-weighted or SE/FSE T2-weighted sequences. The arcuate popliteofibular and fabellofibular ligaments are visualized inconsistently. Because of its posterior course, the entire LCL rarely is visualized on a single coronal image. Specialized coronal oblique (parallel to typical course of normal LCL) and sagittal 1-mm 3-dimensional volume-rendered sequences depict the LCL and PLC structures particularly well. The LCL is seen as a thin, taut, well-defined, low T1/T2-signal structure extending laterally and posteriorly from the lateral femoral epicondyle to the fibular head (see Images 18-19).

Unlike MCL tears, MRI appearance of an LCL tear depends less on the degree of tearing. The LCL is extracapsular; therefore, it excludes accumulated extravasated joint fluid and, as a result, does not demonstrate the high surrounding T2-weighted signal seen with MCL tears. In contrast to MCL tears, an acute LCL tear is seen as a serpiginous or lax ligament with discontinuous fibers (or avulsed fibular head), often without significant thickening of the ligament (see Image 20-21). As previously discussed, LCL tears rarely are isolated, and an LCL tear becomes more likely as associated PLC and cruciate ligament injuries increase in severity (see Image 22).

A chronic LCL tear appears as a thickened low T1/T2-weighted signal ligament (see Image 24).

Degree of Confidence

The degree of confidence is high with MRI of tears of the collateral ligaments and rises with increasing grade of the tear. A prospective study of normal knees and knees with surgically verified grade III LCL injuries demonstrated a sensitivity, specificity, and accuracy of 94.4%, 100%, and 95%, respectively. Sensitivity, specificity, and accuracy of MRI for MCL injuries is less well established because of the nonsurgical nature of the injury but can be assumed to be similar to that of the LCL.

False Positives/Negatives

Loose high T1-weighted areolar tissue interposed between the 2 layers of the MCL is a normal finding that may mimic disease.

ULTRASOUND

Section 7 of 9  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

Findings

The normal MCL appears as two parallel hyperechoic bands with loose hypoechoic areolar tissue imposed between them. Its thickness varies from approximately 2-4 mm along its length in the average individual.

An MCL tear appears as a thickened ligament with decreased echogenicity. A complete disruption can be seen as a discontinuity in the ligament.

The normal LCL appears as a single hyperechoic band just deep to the biceps femoris tendon. Similarly, tears appear as a discontinuity in the ligament or as thickening and loss of echogenicity.

Degree of Confidence

Sonography is approximately 94% sensitive for MCL tears.

MULTIMEDIA

Section 8 of 9  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

Media file 1:  Coronal drawing shows the 3 layers of the medial supporting structures of the knee, including the medial collateral ligament.
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Media file 2:  Sagittal drawing of the medial supporting structures of the knee shows the anterior vertical and posterior oblique ligament components of the medial collateral ligament and their relationship to the pes anserinus and semimembranosus tendon.
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Media file 3:  Sagittal drawing of the lateral supporting structures of the knee including the lateral collateral ligament.
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Media file 4:  Coronal drawing of the lateral supporting structures of the knee demonstrating the arcuate ligament's relationship to the popliteus muscle and lateral collateral ligament.
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Media file 5:  Calcification of the proximal portion of the medial collateral ligament (arrow) consistent with a chronic medial collateral ligament tear and Pellegrini-Stieda disease.
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Media type:  X-RAY

Media file 6:  Fibular head avulsion fracture (arrow).
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Media file 7:  Lateral, tibial-metaphyseal, capsular avulsion fracture termed a Segond fracture (white arrow). Segond fractures are highly associated with anterior cruciate ligament tears. Note the avulsion of the tibial spines (black arrow), indicating an anterior cruciate ligament injury.
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Media type:  X-RAY

Media file 8:  Proton density coronal image shows the anterior vertical portion of the medial collateral ligament as a thin, taut, well-defined, low-signal structure extending from the medial femoral epicondyle to the medial tibial metaphysis (straight arrows). Distal insertion of the anterior cruciate ligament is visualized (curved arrow).
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Media file 9:  Grade I medial collateral ligament tear with surrounding intermediate signal consistent with edema (straight arrows) on a coronal proton density sequence. Note the normal thickness and signal of the medial collateral ligament and continued close apposition to the femoral and tibial cortices.
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Media type:  MRI

Media file 10:  Corresponding fast spin-echo inversion recovery image demonstrates surrounding edema (white arrows).
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Media file 11:  Grade II medial collateral ligament tear seen on a coronal proton density image shows slight thickening of the medial collateral ligament and separation from the underlying cortices (arrows).
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Media file 12:  Corresponding coronal fast spin-echo inversion recovery image shows surrounding edema (small arrows). Note bone bruise of the lateral tibial plateau (large arrow), another sequela of the valgus stress.
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Media type:  MRI

Media file 13:  Grade III medial collateral ligament tear on a coronal fast spin-echo T2-weighted image demonstrates a disrupted ligament that is thickened and retracted with surrounding edema (black arrow).
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Media file 14:  Acute grade III tear with a folded ligament (arrow) and surrounding edema on a coronal proton density image.
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Media file 15:  Corresponding coronal fast spin-echo inversion recovery image.
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Media file 16:  Coronal proton density image demonstrating ossification of the proximal portion of the medial collateral ligament as evidenced by normal bone marrow signal within (arrow; same patient as Image 5).
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Media file 17:  MRI 7 months following functional rehabilitation demonstrating a thickened scarred medial collateral ligament without surrounding edema (same patient as Image 12).
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Media file 18:  Coronal proton density image demonstrating the lateral collateral ligament in its entirety, from the femoral condyle origin to the fibular head insertion.
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Media file 19:  Peripheral sagittal proton density image demonstrates the lateral collateral ligament as an obliquely oriented low-signal structure (white arrows). Note its insertion onto the fibular head conjointly with the biceps femoris tendon (black arrow).
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Media type:  MRI

Media file 20:  Acute tear of the proximal portion of the lateral collateral ligament is seen on this coronal proton density image (white arrow). Note the associated grade II medial collateral ligament tear (black arrows).
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Media file 21:  Corresponding coronal fast spin-echo inversion recovery image. Note the relative lack of accumulated edema/free fluid around the lateral collateral ligament tear compared to the associated grade II medial collateral ligament tear.
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Media file 22:  The lateral collateral ligament is lax and its fibers are interrupted at its origin (white arrow) on this coronal fast spin-echo T2-weighted image. Note the associated anterior cruciate tear (black arrow).
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Media file 23:  Coronal (A), sagittal (B), proton density, and coronal fast spin-echo inversion recovery (C) images demonstrating an acute fibular head avulsion fracture (arrows; same patient as Image 5).
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Media file 24:  Chronic lateral collateral ligament tear appearing as a thickened low-signal ligament on coronal fast spin-echo T2-weighted image (arrowheads).
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Media type:  MRI

REFERENCES

Section 9 of 9

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Multimedia
• References

• Chan K M, Hsu C Y. Cartilage and ligament injuries in sports injuries. In: Renstrum PA, ed. London: Oxford University Press;1993:54-70.
• De Maeseneer M, Van Roy F, Lenchik L. Three layers of the medial capsular and supporting structures of the knee: MR imaging-anatomic correlation. Radiographics. Oct 2000;20 Spec No:S83-9. [Medline].
• Deutsch AL, Mink JH, Fox JM. Peripheral meniscal tears: MR findings after conservative treatment or arthroscopic repair. Radiology. Aug 1990;176(2):485-8. [Medline].
• Irizarry JM, Recht MP. MR imaging of the knee ligaments and the postoperative knee. Radiol Clin North Am. Jan 1997;35(1):45-76. [Medline].
• Jakob RP, Hassler H, Staeubli HU. Observations on rotatory instability of the lateral compartment of the knee. Experimental studies on the functional anatomy and the pathomechanism of the true and the reversed pivot shift sign. Acta Orthop Scand Suppl. 1981;191:1-32. [Medline].
• LaPrade RF, Gilbert TJ, Bollom TS. The magnetic resonance imaging appearance of individual structures of the posterolateral knee. A prospective study of normal knees and knees with surgically verified grade III injuries. Am J Sports Med. Mar-Apr 2000;28(2):191-9. [Medline].
• Lee JI, Song IS, Jung YB. Medial collateral ligament injuries of the knee: ultrasonographic findings. J Ultrasound Med. Sep 1996;15(9):621-5. [Medline].
• Lee JK, Yao L. Tibial collateral ligament bursa: MR imaging. Radiology. Mar 1991;178(3):855-7. [Medline].
• Loredo R, Hodler J, Pedowitz R. Posteromedial corner of the knee: MR imaging with gross anatomic correlation. Skeletal Radiol. Jun 1999;28(6):305-11. [Medline].
• Mink JH, Reicher MA, Crues JV, Duetsch AL. The cruciate and collateral ligaments. In: MRI of the Knee. 2nd ed. Raven Press;1993.
• Muller W, Biedert R, Hefti F. OAK knee evaluation. A new way to assess knee ligament injuries. Clin Orthop. Jul 1988;(232):37-50. [Medline].
• Nicholas JA. Acute and chronic lateral instability of the knee: diagnosis, characteristics and treatment. AAOS Symposium of Reconstructive Surgery of the Knee;1978:187-206.
• Ptasznick, R. Ultrasound in acute and chronic knee injury. Radiol Clin North Am. 1999;37(4):797-830.
• Recondo JA, Salvador E, Villanua JA. Lateral stabilizing structures of the knee: functional anatomy and injuries assessed with MR imaging. Radiographics. Oct 2000;20 Spec No:S91-S102. [Medline].
• Reider B. Medial collateral ligament injuries in athletes. Sports Med. Feb 1996;21(2):147-56. [Medline].
• Ruiz ME, Erickson SJ. Medial and lateral supporting structures of the knee. Normal MR imaging anatomy and pathologic findings. Magn Reson Imaging Clin N Am. Aug 1994;2(3):381-99. [Medline].
• Schweitzer ME, Tran D, Deely DM. Medial collateral ligament injuries: evaluation of multiple signs, prevalence and location of associated bone bruises, and assessment with MR imaging. Radiology. Mar 1995;194(3):825-9. [Medline].
• Stoller DW, Cannon WD, Anderson LJ. The knee. In: Magnetic Resonance Imagin in Orthopaedics and Sports Medicine. 2nd ed. Lippincott Williams & Wilkins;1997.
• White AA 3rd, Raphael IG. The effect of quadriceps loads and knee position on strain measurements of the tibial collateral ligament. An experimental study on human amputation specimens. Acta Orthop Scand. 1972;43(3):176-87. [Medline].

Article Last Updated: Sep 30, 2005