- The document proposes a mechanism-based classification system for complex knee injuries seen on MRI. It divides injuries into 10 categories based on the knee position, direction of force, and presence of rotation. - Different injury mechanisms produce predictable patterns of injury to primary and secondary stabilizing knee structures. For example, hyperextension injuries often involve the posterior cruciate ligament and produce bone fractures, while flexion injuries are more likely to involve meniscal tears. - Understanding the injury mechanism can help radiologists detect all injuries present and assist surgeons in predicting instability and surgical needs. The classification system aims to improve evaluation and management of complex knee injuries on MRI.

2. ‫كثير‬ ‫أبى‬ ‫بن‬ ‫يحي‬ ‫قال‬‫كثير‬ ‫أبى‬ ‫بن‬ ‫يحي‬ ‫قال‬

3. Mechanism-based PatternMechanism-based Pattern
Approach to ClassificationApproach to Classification
of Complex Injuries of theof Complex Injuries of the
Knee Depicted at MRKnee Depicted at MR
ImagingImaging
Dr Wafik Ebrahim AliDr Wafik Ebrahim Ali
Lecturer of radiodiagnosis faculty of medicieLecturer of radiodiagnosis faculty of medicie
Alazhar universityAlazhar university

4.  Complex injuries of the knee are common,Complex injuries of the knee are common,
resulting from accidents or sports mishapsresulting from accidents or sports mishaps
at all levels of competition. These injuriesat all levels of competition. These injuries
often occur as a result of multiple forcesoften occur as a result of multiple forces
applied to the knee.applied to the knee.
 It is widely known that certain forcesIt is widely known that certain forces
predictably produce specific individual orpredictably produce specific individual or
combined patterns of injury.combined patterns of injury.

5. A comprehensive classification systemA comprehensive classification system
based on mechanisms of injury would bebased on mechanisms of injury would be
useful because:useful because:
((a) an understanding of the causativea) an understanding of the causative
mechanism in a given case may improvemechanism in a given case may improve
detection of the complete constellation ofdetection of the complete constellation of
injuries.injuries.
((b) appreciation of the mechanism of injuryb) appreciation of the mechanism of injury
may help predict both immediate andmay help predict both immediate and
delayed instability and need for surgery.delayed instability and need for surgery.

6.  Acquisition of a precise history of theAcquisition of a precise history of the
mechanism may be difficult, however, as ismechanism may be difficult, however, as is
performance of an accurate physicalperformance of an accurate physical
examination in the setting of acute injury.examination in the setting of acute injury.
 Magnetic resonance (MR) imaging is widelyMagnetic resonance (MR) imaging is widely
used to assess knee injuries moreused to assess knee injuries more
completely. Radiologists are accurate atcompletely. Radiologists are accurate at
detecting individual injuries anddetecting individual injuries and
combinations of injuries. However, littlecombinations of injuries. However, little
attention has been paid to the use of MRattention has been paid to the use of MR
imaging to classify knee injuries intoimaging to classify knee injuries into
mechanismbased categories.mechanismbased categories.

7. Functional AnatomyFunctional Anatomy
 The bones of the knee contribute little to theThe bones of the knee contribute little to the
stability of the joint. Both the static andstability of the joint. Both the static and
dynamic stability of the knee are dependentdynamic stability of the knee are dependent
on its supportingon its supporting soft tissues. Menisci,soft tissues. Menisci,
ligaments, tendons,ligaments, tendons, muscles, and fascia allmuscles, and fascia all
make contributions to knee stability.make contributions to knee stability.
 Dynamically, the supporting structures canDynamically, the supporting structures can
be divided by location: anterior, medial,be divided by location: anterior, medial,
lateral, posterior, and central.lateral, posterior, and central.

8. Figure 1. Diagram of functional anatomy ofFigure 1. Diagram of functional anatomy of
the knee jointthe knee joint

9.  Two areas in the knee are critical for stability: theTwo areas in the knee are critical for stability: the
posteromedial and posterolateral corners.posteromedial and posterolateral corners.
 Both corners are major resistors of rotational andBoth corners are major resistors of rotational and
translational stresses, particularly in extension.translational stresses, particularly in extension.
 Traumatic loss of one corner may allow unstableTraumatic loss of one corner may allow unstable
rotation of the knee joint, with a pivoting out aroundrotation of the knee joint, with a pivoting out around
the other corner.the other corner.
 Injury at the posterolateral corner, in particular, mayInjury at the posterolateral corner, in particular, may
lead to severe disability.lead to severe disability.
 Therefore, recognition of injuries to these structures isTherefore, recognition of injuries to these structures is
critical in any MR imaging evaluation of the injuredcritical in any MR imaging evaluation of the injured
knee.knee.

10. Impaction versus Avulsion InjuryImpaction versus Avulsion Injury
PatternsPatterns
 In general, forces acting on the knee produceIn general, forces acting on the knee produce
an impaction injury at the entry site of thean impaction injury at the entry site of the
force and a distraction injury, or avulsion, atforce and a distraction injury, or avulsion, at
the opposite, or exit, site of the force.the opposite, or exit, site of the force.
 Bone injuries caused by impaction tend to beBone injuries caused by impaction tend to be
broad, compared with smaller, more focalbroad, compared with smaller, more focal
areas of bone marrow edema associated withareas of bone marrow edema associated with
ligament avulsions on the distraction side.ligament avulsions on the distraction side.

11. Illustration of impaction bone bruiseIllustration of impaction bone bruise
pattern and avulsion bone bruisepattern and avulsion bone bruise
pattern. valgus forcepattern. valgus force

12. Impactions may be further divided into:Impactions may be further divided into:
 Contiguous,“kissing,” injuriesContiguous,“kissing,” injuries
 or noncontiguous injuries, which are produced byor noncontiguous injuries, which are produced by
the abrupt translation of two bones that occurs afterthe abrupt translation of two bones that occurs after
ligamentous rupture.ligamentous rupture.
The direction and type of force may be inferred fromThe direction and type of force may be inferred from
the patterns of bone marrow edema and soft tissuethe patterns of bone marrow edema and soft tissue
injury.injury.
Direct blows result in bone contusions and soft-tissueDirect blows result in bone contusions and soft-tissue
injury at the impaction site only.injury at the impaction site only.

13. Mechanism-based ClassificationMechanism-based Classification
System of Knee InjuriesSystem of Knee Injuries
On the basis of information from theOn the basis of information from the
injury patterns to primary andinjury patterns to primary and
secondary stabilizing structures, plussecondary stabilizing structures, plus
bone injury patterns, complex kneebone injury patterns, complex knee
injuries are classified into 10injuries are classified into 10
categories, according to the kneecategories, according to the knee
position (flexion, extension), directionposition (flexion, extension), direction
of force, and presence or absence ofof force, and presence or absence of
rotationrotation

14. Diagram illustrates the direction of injury-producing forcesDiagram illustrates the direction of injury-producing forces
acting on the knee.acting on the knee.

15. Forces Responsible for Knee Injuries and Supporting StructuresForces Responsible for Knee Injuries and Supporting Structures
Responsible for Primary and Secondary Resistance to Those ForcesResponsible for Primary and Secondary Resistance to Those Forces
Force Primary
resistance
Secondary
resistance
Anterior translation (displaces tibia anteriorly) ACL MCL, LCL
Posterior translation (displaces tibia posteriorly) PCL None
Varus (medial to lateral) LCL ACL, PCL
Valgus (lateral to medial) MCL ACL, PCL
Internal rotation (femur fixed) LCL ACL, capsule
External rotation (femur fixed) MCL PCL, capsule
Hyperextension PCL ACL, posterior
capsule

16. Hyperextension injuryHyperextension injury
 Hyperextension injuries, by virtue of theHyperextension injuries, by virtue of the
greater forces exerted on the extended orgreater forces exerted on the extended or
“locked” knee, produce more pronounced“locked” knee, produce more pronounced
bone injury patterns, often with frankbone injury patterns, often with frank
fractures. Severe distraction injuries on thefractures. Severe distraction injuries on the
posterior, exit side of the joint are commonposterior, exit side of the joint are common
with this pattern. These injuries arewith this pattern. These injuries are
particularly serious in that they involve theparticularly serious in that they involve the
critical posteromedial and/or posterolateralcritical posteromedial and/or posterolateral
corners of the knee.corners of the knee.

17. HyperextensionHyperextension

18. HyperextensionHyperextension

19. Pure hyperextensionPure hyperextension

20. Hyperextension with varusHyperextension with varus

21. Hyperextension with varusHyperextension with varus

22. Hyperextension with valgusHyperextension with valgus

23. Hyperextension with valgusHyperextension with valgus

24. Flexion injuryFlexion injury
 Flexion injuries, unless combined withFlexion injuries, unless combined with
significant axial load, tend to show fewsignificant axial load, tend to show few
contiguous impaction bone injuries but havecontiguous impaction bone injuries but have
a greater tendency to produce injury due toa greater tendency to produce injury due to
internal or external rotation.internal or external rotation. NoncontiguousNoncontiguous
impaction bone bruises areimpaction bone bruises are usually found, asusually found, as
well as smaller avulsion bone bruises. Wewell as smaller avulsion bone bruises. We
have observed that flexion injuries withhave observed that flexion injuries with
rotation show a greater association withrotation show a greater association with
meniscal tears than do hyperextensionmeniscal tears than do hyperextension
injuries.injuries.

25. Flexion with valgus andFlexion with valgus and
internal rotationinternal rotation

26. Flexion with valgus andFlexion with valgus and
internal rotationinternal rotation

27. Flexion with varus andFlexion with varus and
internal rotation injuryinternal rotation injury

28. Hyperflexion injury withHyperflexion injury with
posterior tibialposterior tibial
translationtranslation

29. Hyperflexion injury withHyperflexion injury with
posterior tibialposterior tibial
translationtranslation

30. Patellar dislocationPatellar dislocation
 Dislocation of the patella is typicallyDislocation of the patella is typically
produced by combined flexion, valgus, andproduced by combined flexion, valgus, and
internal rotation of the femur on a fixed tibia.internal rotation of the femur on a fixed tibia.
In theory, this is very similar to flexion,In theory, this is very similar to flexion,
valgus, and external rotation (tibia on fixedvalgus, and external rotation (tibia on fixed
femur),femur),

31. Flexion with internal feroralFlexion with internal feroral
rotation on fixed tibiarotation on fixed tibia

32. Transient patellarTransient patellar
dislocationdislocation

33. Lateral patellarLateral patellar
dislocationdislocation

34. Valgus and varus forceValgus and varus force
 Pure valgus and the rare pure varusPure valgus and the rare pure varus
categories are characterized by acategories are characterized by a
simple “coup-contrecoup” pattern ofsimple “coup-contrecoup” pattern of
impaction bone injuries andimpaction bone injuries and
oppositesided distraction ligamentoppositesided distraction ligament
injuries.injuries.

35. Pure valgus injuryPure valgus injury

36. Pure varus injuryPure varus injury

37. Direct traumaDirect trauma
 Direct trauma is characterized byDirect trauma is characterized by
broad bone contusions locatedbroad bone contusions located
beneath the site of impaction.beneath the site of impaction.
Typically, there are no injuries on theTypically, there are no injuries on the
opposite side of the knee. Directopposite side of the knee. Direct
anterior trauma, which causes patellaranterior trauma, which causes patellar
and trochlear groove contusions, andand trochlear groove contusions, and
lateral or medial blows are mostlateral or medial blows are most
common.common.

38. Direct traumaDirect trauma

40. Thank YouThank You
Wafik EbrahimWafik Ebrahim