1. KNEE
Dr. Michael P. Gillespie

2. KNEE: GENERAL CONSIDERATIONS
The knee consists of lateral and medial compartments at the tibiofemoral joint and the patellofemoral joint.
Motion of the knee occurs in two planes:
Flexion and extension
Internal and external rotation
Two-thirds of the muscles that cross the knee also cross either the ankle or the hip. This creates a strong functional association within the joints of the lower limb.
Stability of the knee is based primarily on its soft-tissue constraints rather than on its bony configuration.
Dr. Michael P. Gillespie

3. KNEE: BIOMECHANICAL FUNCTIONS
During the swing phase of walking, the knee flexes to shorten the functional length of the lower limb, thereby providing clearance of the foot from the ground.
During the stance phase, the knee remains slightly flexed allowing for shock absorption, conservation of energy, and transmission of forces through the lower limb.
Dr. Michael P. Gillespie

4. OSTEOLOGY
Dr. Michael P. Gillespie

5. BONES AND ARTICULATIONS OF THE KNEE
Dr. Michael P. Gillespie
FIGURE 13-1.   Radiograph showing the bones and associated articulations of the knee.

6. DISTAL FEMUR
At the distal end of the femur are the large lateral and medial condyles (Greek kondylos, knuckle).
Lateral and medial epicondyles project from each condyle. These serve as attachment sites for the collateral ligaments.
Intercondylar notch – passageway for the cruciate ligaments.
Femoral condyles fuse anteriorly to form the intercondylar (trochlear) groove. This groove articulates with the patella.
Lateral and medial facets – formed from the sloping sides of the intercondylar groove.
Lateral and Medial grooves are etched into the cartilage that covers the femoral condyles and the edge of the tibia articulates with these grooves.
Dr. Michael P. Gillespie

7. OSTEOLOGIC FEATURES OF THE DISTAL FEMUR
Lateral and medial condyles
Lateral and medial epicondyles
Intercondylar notch
Intercondylar (trochlear) groove
Lateral and medial facets (for the patella)
Lateral and medial grooves (etched in the cartilage of the femoral condyles)
Popliteal surface
Dr. Michael P. Gillespie

8. PATELLA, ARTICULAR SURFACES OF DISTAL FEMUR & PROXIMAL TIBIA
Dr. Michael P. Gillespie
FIGURE 13-2.   Osteology of the right patella, articular surfaces of the distal femur, and proximal tibia.

9. FIBULA
The fibular has no direct function at the knee; however, it splints the lateral side of the tibia and helps to maintain its alignment.
The head of the fibula is an attachment for biceps femoris and the lateral collateral ligament.
Proximal and distal tibiofibular joints attach the fibula to the tibia.
Dr. Michael P. Gillespie

10. PROXIMAL TIBIA
The proximal end of the Tibia flares into medial and lateral condyles which articulate with the femur.
Tibial plateau – the superior surfaces of the condyles.
Intercondylar eminence – separates the articular surfaces of the proximal tibia.
Tibial tuberosity – anterior surface of the proximal shaft of the tibia. Attachment point for the quadriceps femoris, via the patellar tendon.
Soleal line – posterior aspect of tibia.
Dr. Michael P. Gillespie

11. OSTEOLOGIC FEATURES OF THE PROXIMAL TIBIA AND FIBULA
Proximal Fibula
Head
Proximal Tibia
Medial and lateral condyles
Intercondylar eminence (with tubercles)
Anterior intercondylar area
Posterior intercondylar area
Tibial tuberosity
Soleal line
Dr. Michael P. Gillespie

12. RIGHT DISTAL FEMUR, TIBIA, AND FIBULA
Dr. Michael P. Gillespie
FIGURE 13-3A-B.   Right distal femur, tibia, and fibula. A, Anterior view. B, Posterior view. Proximal attachments of muscles are shown in red, distal attachments in gray. The dashed lines show the attachment of the joint capsule of the knee.

13. LATERAL VIEW RIGHT KNEE
Dr. Michael P. Gillespie
FIGURE 13-4.   Lateral view of the right knee. Note the curved articular surface of the lateral femoral condyle. Proximal attachments of muscles and ligaments are shown in red, distal attachments in gray.

14. PATELLA
The patella (Latin, “small plate”) is embedded within the quadriceps tendon.
The largest sesamoid bone in the body.
Part of the posterior surface articulates with the intercondylar groove of the femur.
Dr. Michael P. Gillespie

15. OSTEOLOGIC FEATURES OF THE PATELLA
Base
Apex
Anterior surface
Posterior articular surface
Vertical ridge
Lateral, medial, and “odd” facets
Dr. Michael P. Gillespie

16. PATELLA Dr. Michael P. Gillespie
FIGURE 13-5.   Anterior and posterior surfaces of the right patella. The attachment of the tendon of the quadriceps muscle is indicated in gray; the proximal attachment of the patellar tendon is indicated in red. Note the smooth articular cartilage covering the posterior articular surface of the patella.

17. ARTHROLOGY
Dr. Michael P. Gillespie

18. GENERAL ANATOMIC AND ALIGNMENT CONSIDERATIONS
The shaft of the femur angles slightly medial due to the 125-degree angle of inclination of the proximal femur.
The proximal tibia is nearly horizontal.
Consequently, the knee forms an angle of about 170 to 175 degrees on the lateral side. The normal alignment is referred to as genu valgum.
Excessive genu valgum – a lateral angle less than 170 degrees or “knock-knee”.
Genu varum – a lateral angle that exceeds 180 degrees or “bow-leg”.
Dr. Michael P. Gillespie

19. FRONTAL PLANE DEVIATIONS
Dr. Michael P. Gillespie
FIGURE 13-6A-B-C.   Frontal plane deviations of the knee. A, Normal genu valgum. The normal 125-degree angle of inclination of the proximal femur and the longitudinal axis of rotation throughout the entire lower extremity are also shown. B and C illustrate excessive frontal plane deviations.

20. CAPSULE AND REINFORCING LIGAMENTS
The fibrous capsule of the knee encloses the medial and lateral compartments of the tibiofemoral joint and patellofemoral joint.
Five regions of the capsule
Anterior capsule
Lateral capsule
Posterior capsule
Posterior-lateral capsule
Medial capsule
Dr. Michael P. Gillespie

21. LIGAMENTS, FASCIA, AND MUSCLES THAT REINFORCE THE CAPSULE OF THE KNEE
Region of the Capsule
Connective Tissue Reinforcement
Muscular-Tendinous Reinforcement
Anterior
Patellar Tendon
Patellar retinacular fibers
Quadriceps
Lateral
Lateral collateral ligament
Lateral patellar retinacular fibers
Iliotibial band
Biceps femoris
Tendon of the popliteus
Lateral head of gastrocnemius
Posterior
Oblique popliteal ligament
Arcuate popliteal ligament
Popliteus
Gastrocnemius
Hamstrings, especially the tendon of semimembranosus
Posterior-Lateral
Tendon of popliteus
Medial
Medial patellar retinacular fibers
Medial collateral ligament
Thickened fibers posterior-medially
Expansions from the tendon of the semimembranosus
Tendons from sartorius, gracilis, and semitendinosus
Dr. Michael P. Gillespie

22. ANTERIOR VIEW RIGHT KNEE: MUSCLES & CONNECTIVE TISSUES
Dr. Michael P. Gillespie
FIGURE 13-7.   Anterior view of the right knee, highlighting many muscles and connective tissues. The pes anserinus tendons are cut to expose the medial collateral ligament and the medial patellar retinaculum.

23. LATERAL VIEW RIGHT KNEE: MUSCLES & CONNECTIVE TISSUES
Dr. Michael P. Gillespie
FIGURE 13-8.   Lateral view of the right knee shows many muscles and connective tissues. The iliotibial band, lateral head of the gastrocnemius, and biceps femoris are cut to better expose the lateral collateral ligament, popliteus tendon, and lateral meniscus.

24. POSTERIOR VIEW RIGHT KNEE: MUSCLES & CONNECTIVE TISSUES
Dr. Michael P. Gillespie
FIGURE 13-9.   Posterior view of the right knee that emphasizes the major parts of the posterior capsule: the oblique popliteal and arcuate popliteal ligaments. The lateral and medial heads of the gastrocnemius and plantaris muscles are cut to expose the posterior capsule. Note the popliteus muscle deep in the popliteal fossa, lying partially covered by the fascial extension of the semimembranosus.

25. MEDIAL VIEW RIGHT KNEE: MUSCLES & CONNECTIVE TISSUES
Dr. Michael P. Gillespie
FIGURE    Medial view of the right knee shows many muscles and connective tissues. The tendons of the sartorius and gracilis are cut to better expose the superficial part of the medial collateral ligament and the posterior-medial capsule.

26. SYNOVIAL MEMBRANE, BURSAE, AND FAT PADS
The internal surface of the capsule is lined with a synovial membrane.
The knee has as many as 14 bursae.
These bursae form inter-tissue junctions involving tendon, ligament, skin, bone, capsule, and muscle.
Some bursae are extensions of the synovila membrane and others are formed external to the capsule.
Fat pads are often associated with the suprapatellar and deep infrapatellar bursae.
Dr. Michael P. Gillespie

27. EXAMPLES OF BURSAE AT VARIOUS INTER-TISSUE JUNCTIONS
Ligament & Tendon
Bursa between lateral collateral ligament & tendon of biceps femoris
Bursa between the medial collateral ligament and tendons of pes anserinus (i.e. gracilis, semitendinosus, sartorius)
Muscle & Capsule
Unnamed bursa between medial head of gastrocnemius and medial side of the capsule
Bone & Skin
Subsutaneous prepatellar bursa between the inferior border of the patella and the skin
Tendon & Bone
Semimembranosus bursa between the tendon of the semimembranosus and the medial condyle of the tibia
Bone & Muscle
Suprapatellar bursa between the femur and the quadriceps femoris (largest of the knee)
Bone & Ligament
Deep infrapatellar bursa between the tibia and patellar tendon
Dr. Michael P. Gillespie

28. KNEE PLICAE
Plicae or synovial pleats appear as folds in the synovial membrane.
Plicae may reinforce the synovial membrane of the knee.
Three most common plicae:
Superior or suprapatellar plica
Inferior plica
Medial plica (goes by about 20 names including alar ligament, synovialis patellaris, and intra-articular medial band).
Plicae that are unusually large or thickened due to irritation or trauma can cause knee pain.
Inflammation of the medial plica may be confused with patellar tendonitis, torn medial meniscus, or patellofemoral pain.
Treatment includes: rest, anti-inflammatory agents, PT, and in severe cases arthroscopic resection.
Dr. Michael P. Gillespie

29. TIBIOFEMORAL JOINT
Articulation between the large convex femoral condyles and the nearly flat and smaller tibial condyles.
The large articular surface area of the femoral condyles permits extensive knee motion in the sagittal plane.
There is NOT a tight bony fit at this joint.
Joint stability is provided by muscles, ligaments, capsule, menisci, and body weight.
Dr. Michael P. Gillespie

30. SUPERIOR SURFACE OF TIBIA
Dr. Michael P. Gillespie
FIGURE    A, The superior surface of the tibia shows the menisci and other cut structures: collateral, cruciate, and posterior meniscofemoral ligaments, as well as muscles and tendons. (This specimen does not have an anterior meniscofemoral ligament.) B, The superior view of the right tibia marks the attachment points of the menisci and cruciate ligaments within the intercondylar region.

31. POSTERIOR VIEW: DEEP STRUCTURES RIGHT KNEE
Dr. Michael P. Gillespie
FIGURE    Posterior view of the deep structures of the right knee after all muscles and the posterior capsule have been removed. Observe the menisci, collateral ligaments, and cruciate ligaments. Note the popliteus tendon, which courses between the lateral meniscus and lateral collateral ligament.

32. MENISCI: ANATOMIC CONSIDERATIONS
The medial and lateral menisci are crescent-shaped, fibrocartilaginous structures located within the knee joint.
They transform the articular surfaces of the tibia into shallow seats for the large femoral condyles.
Coronary (meniscotibial) ligaments anchor the external edge of each meniscus.
The transverse ligament connects the menisci anteriorly.
Several muscles have secondary attachments to the menisci.
Blood supply to the menisci is greatest near the peripheral border. The internal border is essentially avascular.
Dr. Michael P. Gillespie

33. MENISCI: FUNCTIONAL CONSIDERATIONS
The menisci reduce compressive stress across the tibiofemoral joint.
They stabilize the joint during motion, lubricate the articular cartilage, provide proprioception, and help guide the knee’s arthrokinematics.
Compression forces at the knee reach 2.5 to 3 times the body weight when one is walking and over 4 times the body weight when one ascends stairs.
The menisci nearly triple the area of joint contact, thereby significantly reducing the pressure.
With every step, the menisci deform peripherally.
The compression force is absorbed as circumferential tension (hoop stress).
Dr. Michael P. Gillespie

34. MENISCI: COMMON MECHANISMS OF INJURY
Tears of the meniscus are the most common injury of the knee.
Meniscal tears are often associated with a forceful, axial rotation of the femoral condyles over a partially flexed and weight-bearing knee.
The axial torsion within the compressed knee can pinch and dislodge the meniscus.
A dislodged or folded flap of meniscus (often referred to as a “bucket-handle tear”) can mechanically block knee movement.
The medial meniscus is injured twice as frequently as the lateral meniscus. Axial rotation with a valgus stress to the knee can cause this.
Dr. Michael P. Gillespie

35. OSTEOKINEMATICS AT THE TIBIOFEMORAL JOINT
Two degrees of freedom:
Flexion & extension in the sagittal plane
Provided the knee is slightly flexed, internal and external rotation.
Dr. Michael P. Gillespie

36. TIBIOFEMORAL JOINT: FLEXION AND EXTENSION
The healthy knee moves from 130 to 150 degrees of flexion to about 5 to 10 degrees beyond the 0-degree (straight) position.
The axis of rotation for flexion and extension is not fixed, but migrates within the femoral condyles.
The curved path of the axis is known as an “evolute”.
With maximal effort, internal torque varies across the range of motion.
External devices attached to the knee rotate about a fixed axis of rotation. A hinged orthosis can cause rubbing or abrasion against the skin. Goniometric measurements are more difficult. Place the device as close as possible to the “average” axis of rotation.
Dr. Michael P. Gillespie

37. SAGITTAL PLANE MOTION AT THE KNEE
Dr. Michael P. Gillespie
FIGURE    Sagittal plane motion at the knee. A, Tibial-on-femoral perspective (femur is stationary). B, Femoral-on-tibial perspective (tibia is stationary).

38. “THE EVOLUTE” Dr. Michael P. Gillespie
FIGURE    The flexing knee generates a migrating medial-lateral axis of rotation (shown as three small circles). This migration is described as “the evolute.”

39. TIBIOFEMORAL JOINT: INTERNAL AND EXTERNAL (AXIAL) ROTATION
Internal and external rotation of the knee occurs about a vertical or longitudinal axis of rotation.
This motion is called axial rotation.
The freedom of axial rotation increases with greater knee flexion.
A knee flexed to 90 degrees can perform about 40 to 45 degrees of axial rotation.
External rotation generally exceeds internal rotation by a ratio of nearly 2:1.
Once the knee is in full extension, axial rotation is maximally restricted.
The naming of axial rotation is based on the position of the tibial tuberosity relative to the anterior distal femur.
External rotation of the knee is when the tibial tuberosity is located lateral to the anterior distal femur.
This does not stipulate whether the tibia or femur is the moving bone.
Dr. Michael P. Gillespie

40. INTERNAL AND EXTERNAL (AXIAL) ROTATION OF THE RIGHT KNEE
Dr. Michael P. Gillespie
FIGURE    Internal and external (axial) rotation of the right knee. A, Tibial-on-femoral (knee) rotation. In this case the direction of the knee rotation (internal or external) is the same as the motion of the tibia; the femur is stationary. B, Femoral-on-tibial rotation. In this case the tibia is stationary and the femur is rotating. The direction of the knee rotation (external or internal) is the opposite of the motion of the moving femur: external rotation of the knee occurs by internal rotation of the femur; internal rotation of the knee occurs by external rotation of the femur.

41. ARTHROKINEMATICS AT THE TIBIOFEMORAL JOINT: EXTENSION OF THE KNEE
Tibial-on-femoral extension
The articular surface of the tibia rolls and slides anteriorly on the femoral condyles.
Femoral-on-tibial extension
Standing up from a deep squat position.
The femoral condyles simultaneously roll anterior and slide posterior on the articular surface of the tibia.
Dr. Michael P. Gillespie

42. ARTHROKINEMATICS OF KNEE EXTENSION
Dr. Michael P. Gillespie
FIGURE 13-16A-B.   The active arthrokinematics of knee extension. A, Tibial-on-femoral perspective. B, Femoral-on-tibial perspective. In both A and B, the meniscus is pulled toward the contracting quadriceps.

43. ARTHROKINEMATICS AT THE TIBIOFEMORAL JOINT: “SCREW-HOME” ROTATION KNEE
Locking the knee in full extension requires about 10 degrees of external rotation.
It is referred to as “screw-home” rotation.
It is a conjunct rotation. It is mechanically linked to the flexion and extension kinematics and cannot be performed independently.
The combined external rotation and extension maximizes the overall contact area. This increases congruence and favors stability.
Dr. Michael P. Gillespie

44. “SCREW-HOME” LOCKING MECHANISM
Dr. Michael P. Gillespie
FIGURE 13-17A-B.   The “screw-home” locking mechanism of the knee. A, During terminal tibial-on-femoral extension, three factors contribute to the locking mechanism of the knee. Each factor contributes bias to external rotation of the tibia, relative to the femur. B, The two arrows depict the path of the tibia across the femoral condyles during the last 90 degrees of extension. Note that the curved medial femoral condyle helps to direct the tibia to its externally rotated and locked position.

45. ARTHROKINEMATICS AT THE TIBIOFEMORAL JOINT: FLEXION OF THE KNEE
For a knee that is fully extended to be unlocked, it must first internally rotate slightly.
This internal rotation is achieved by the popliteus muscle.
Dr. Michael P. Gillespie

46. ARTHROKINEMATICS AT THE TIBIOFEMORAL JOINT: INTERNAL AND EXTERNAL (AXIAL) ROTATION OF THE KNEE
The knee must be flexed to maximize independent axial rotation between the tibia and femur.
The arthrokinematics involve a spin between the menisci and the articular surfaces of the tibia and femur.
Dr. Michael P. Gillespie

47. MEDIAL AND LATERAL COLLATERAL LIGAMENTS: ANATOMIC CONSIDERATIONS
The medial (tibial) collateral ligament (MCL)
A flat, broad structure that crosses the medial aspect of the joint.
Superficial part
Deep part
Attaches to the medial meniscus
The lateral (fibular) collateral ligament
A round, strong cord that runs nearly verticle between the lateral epicondyle of the femur and the head of the fibula
Does NOT attach to the lateral meniscus
The popliteus tendon crosses between these two structures
Dr. Michael P. Gillespie

48. MEDIAL AND LATERAL COLLATERAL LIGAMENTS: FUNCTIONAL CONSIDERATIONS
The function of the collateral ligaments is to limit excessive knee motion within the frontal plane.
The MCL provides resistance against valgus (abduction) force.
The lateral collateral ligament provides resistance against varus (adduction) force.
Produce a general stabilizing tension for the knee throughout the sagittal plane range of motion.
Dr. Michael P. Gillespie

49. ANTERIOR & POSTERIOR CRUCIATE LIGAMENTS: GENERAL CONSIDERATIONS
Cruciate, meaning cross-shaped, describes the spatial relation of the anterior and posterior cruciate ligaments as they cross within the intercondylar notch of the femur.
The cruciate ligaments are intracapsular and covered by extensive synovial lining.
Together, they resist the extremes of all knee movements.
The provide most of the resistance to anterior and posterior shear forces.
They contain mechanoreceptors and contribute to proprioceptive feedback.
Dr. Michael P. Gillespie

50. ANTERIOR CRUCIATE LIGAMENT: ANATOMY AND FUNCTION
The anterior cruciate ligament (ACL) attaches along an impression on the anterior intercondylar area of the tibial plateau.
It runs obliquely in a posterior, superior, and lateral direction.
The fibers become increasingly taut as the knee approaches and reaches full extension.
The quadriceps is referred to as an “ACL antagonist” because contraction of the quadriceps stretches (or antagonizes) most fibers of the ACL.
Dr. Michael P. Gillespie

51. ANTERIOR CRUCIATE LIGAMENT: COMMON MECHANISMS OF INJURY
The ACL is the most frequently totally ruptured ligament of the knee.
Approximately half of all ACL injuries occur in persons between the ages of 15 and 25.
Landing from a jump
Quickly and forcefully decelerating, cutting, or pivoting over a single planted limb
Hyperextension of the knee while the foot is planted firmly on the ground
Dr. Michael P. Gillespie

52. POSTERIOR CRUCIATE LIGAMENT: ANATOMY AND FUNCTION
The posterior cruciate ligament (PCL) attaches from the posterior intercondylar area of the tibia to the lateral side of the medial femoral condyle.
The PCL is slightly thicker than the ACL.
The “posterior drawer” test evaluates the integrity of the PCL.
The PCL limits the extent of anterior translation of the femur relative to the fixed lower leg.
Dr. Michael P. Gillespie

53. POSTERIOR CRUCIATE LIGAMENT: COMMON MECHANISMS OF INJURY
Most PCL injuries are associated with high energy trauma such as an automobile accident or contact sports.
Falling over a fully flexed knee with the ankle plantar flexed
“Dashboard” injury – the knee of a passenger in an automobile strikes the dashboard subsequent to a front-end collision, driving the tibia posterior relative to the femur.
Often after a PCL injury the proximal tibia sags posterior relative to the femur when the lower leg is subjected to the pull of gravity.
Dr. Michael P. Gillespie

54. GENERAL FUNCTIONS OF ANTERIOR & POSTERIOR CRUCIATE LIGAMENTS
Provide multiple plane stability to the knee, most notably in the sagittal plane
Guide the natural arthrokinematics, especially those related to the restraint of sliding motions between the tibia and femur
Contribute to the proprioception of the knee
Dr. Michael P. Gillespie

55. ANTERIOR & POSTERIOR CRUCIATE LIGAMENTS
Dr. Michael P. Gillespie
FIGURE    The anterior and posterior cruciate ligaments. A, Lateral view. B, Anterior view. The two fiber bundles within the anterior cruciate ligament are evident in A.

56. MUSCLE CONTRACTION AND TENSION CHANGES IN ANTERIOR CRUCIATE LIGAMENTS / ANTERIOR DRAWER TEST
Dr. Michael P. Gillespie
FIGURE 13-20A-B.   The interaction between muscle contraction and tension changes in the anterior cruciate ligaments. A, Contraction of the quadriceps muscle extends the knee and slides the tibia anterior relative to the femur. Knee extension also elongates most of the anterior cruciate ligament (ACL), posterior capsule, hamstring muscles, collateral ligaments and adjacent capsule (the last two structures not depicted). Note that the quadriceps and ACL have an antagonistic relationship throughout most of the terminal range of extension. (The angle-of-insertion between the patellar tendon and the tibia is indicated by α). B, The anterior drawer test evaluates the integrity of the ACL. Note that spasm in the hamstring muscles places a posterior force on the tibia, which can limit the tension on the ACL.

57. KNEE FLEXION & POSTERIOR CRUCIATE LIGAMENTS / POSTERIOR DRAWER TEST
Dr. Michael P. Gillespie
FIGURE 13-22A.   A, Contraction of the hamstring muscles flexes the knee and slides the tibia posterior relative to the femur. Knee flexion elongates the quadriceps muscle and most of the fibers within the posterior cruciate ligament (PCL). B, The posterior drawer test evaluates the integrity of the PCL. Tissues pulled taut are indicated by thin black arrows.

58. TISSUES THAT PROVIDE PRIMARY & SECONDARY RESTRAINT IN FRONTAL PLANE
Valgus Force
Varus Force
Primary Restraint
Medial collateral ligament, especially superficial fibers
Lateral collateral ligament
Secondary Restraint
Posterior-medial capsule (includes semimembranosus tendon)
Anterior and posterior cruciate ligaments
Joint contact laterally
Compression of the lateral meniscus
Medial retinacular fibers
Pes anserinus (i.e. tendons of the sartorius, gracilis, and semitendinosus)
Gastrocnemius (medial head)
Arcuate complex (includes lateral collateral ligament, posterior-lateral capsule, popliteus tendon, and arcuate popliteal ligament)
Iliotibial band
Biceps femoris tendon
Joint contact medially
Compression of the medial meniscus
Gastrocnemius (lateral head)
Dr. Michael P. Gillespie

59. FUNCTIONS OF KNEE LIGAMENTS & COMMON MECHANISMS OF INJURY
Structure
Function
Common Mechanism of Injury
Medial collateral ligament (and posterior-medial capsule)
Resists valgus (abduction)
Resists knee extension
Resists extremes of axial rotation (especially knee external rotation)
Valgus-producing force with foot planted
Severe hyperextension of the knee
Lateral collateral ligament
Resists varus (adduction)
Resists extremes of axial rotation
Varus-producing force with foot planted
Posterior capsule
Oblique popliteal ligament resists knee external rotation
Posterior-lateral capsule resists varus
1. Hyperextension or combined hyperextension with external rotation of the knee
Dr. Michael P. Gillespie

60. FUNCTIONS OF KNEE LIGAMENTS & COMMON MECHANISMS OF INJURY
Structure
Function
Common Mechanism of Injury
Anterior cruciate ligament
Most fibers resist extension (either excessive anterior translation of the tibia, posterior translation of the femur, or a combination thereof)
Resists extremes of varus, valgus, and axial rotation
Large valgus-producing force the foot firmly planted
Large axial rotation torque applied to the knee, with the foot firmly planted
The above with strong quadriceps contraction with the knee in full or near-full extension
Severe hyperextension of the knee
Posterior cruciate ligament
Most fibers resist knee flexion (either excessive posterior translation of the tibia or anterior translation of the femur, or a combination thereof)
Falling on a fully flexed knee (with ankle fully plantar flexed) such that the proximal tibia first strikes the ground
Any event that causes a forceful posterior translation of the tibia (i.e. “dashboard” injury) or anterior translation of the femur
Large axial rotation or valgus-varus applied torque
Severe hyperextension of the knee causing a large gapping of posterior aspect of joint
Dr. Michael P. Gillespie

61. FEMORAL-ON_TIBIAL EXTENSION WITH ELONGATION OF FIBERS
Dr. Michael P. Gillespie
FIGURE    Medial view of the knee shows the relative elongation of some fibers of the medial collateral ligament, oblique popliteal ligament, posterior capsule, and components of the anterior cruciate ligament (ACL) during active femoral-on-tibial extension. A, In knee flexion the structures are shown in a relatively slackened (or least taut) state. B, The structures are pulled relatively taut as the knee actively extends by contraction of the quadriceps. Note the “screw-home” rotation of the knee during end-range extension. The combined external rotation and extension on the knee specifically elongate the posterior-medial capsule and oblique popliteal ligament (within the posterior capsule).


62. PATELLOFEMORAL JOINT
The patellofemoral joint is the interface between the articular side of the patella and the intercondylar (trochlear) groove of the femur.
The quadriceps muscle, the fit of the joint surfaces, and passive restraint from retinacular fibers and capsule all help to stabilize this joint.
Abnormal kinematics of this joint can lead to anterior knee pain and degeneration of the joint.
As the knee flexes and extends, a sliding motion occurs between the articular surfaces of the patella and intercondylar groove.
Dr. Michael P. Gillespie

63. PATELLOFEMORAL JOINT KINEMATICS
The patella typically dislocates laterally.
There is an overall lateral line of force of the quadriceps muscle.
Dr. Michael P. Gillespie

64. POINT OF MAXIMAL CONTACT OF PATELLA ON FEMUR DURING EXTENSION
Dr. Michael P. Gillespie
FIGURE 13-23A-B.   The kinematics at the patellofemoral joint during active tibial-on-femoral extension. The circle depicted in A to C indicates the point of maximal contact between the patella and the femur. As the knee extends, the contact point on the patella migrates from its superior pole to its inferior pole. Note the suprapatellar fat pad deep to the quadriceps. D and E show the path and contact areas of the patella on the intercondylar groove of the femur. The values 135, 90, 60, and 20 degrees indicate flexed positions of the knee.

65. POINT OF MAXIMAL CONTACT OF PATELLA ON FEMUR DURING EXTENSION
Dr. Michael P. Gillespie
FIGURE 13-23C.   The kinematics at the patellofemoral joint during active tibial-on-femoral extension. The circle depicted in A to C indicates the point of maximal contact between the patella and the femur. As the knee extends, the contact point on the patella migrates from its superior pole to its inferior pole. Note the suprapatellar fat pad deep to the quadriceps. D and E show the path and contact areas of the patella on the intercondylar groove of the femur. The values 135, 90, 60, and 20 degrees indicate flexed positions of the knee.

66. PATH OF CONTACT OF PATELLA ON INTERCONDYLAR GROOVE
Dr. Michael P. Gillespie
FIGURE 13-23D.   The kinematics at the patellofemoral joint during active tibial-on-femoral extension. The circle depicted in A to C indicates the point of maximal contact between the patella and the femur. As the knee extends, the contact point on the patella migrates from its superior pole to its inferior pole. Note the suprapatellar fat pad deep to the quadriceps. D and E show the path and contact areas of the patella on the intercondylar groove of the femur. The values 135, 90, 60, and 20 degrees indicate flexed positions of the knee.

67. MUSCLE AND JOINT INTERACTION
Dr. Michael P. Gillespie

68. INNERVATION OF THE MUSCLES
The quadriceps femoris is innervated by the femoral nerve (one nerve for the knee’s sole extensor group).
The flexors and rotators are innervated by several nerves from both the lumbar and sacral plexus, but primarily the tibial portion of the sciatic nerve.
Dr. Michael P. Gillespie

69. SENSORY INNERVATION OF THE KNEE
Sensory innervation of the knee and associated ligaments is supplied primarily by spinal nerve roots from L3 to L5.
The posterior tibial nerve is the largest afferent supply of the knee.
The obturator and femoral nerve also supply some afferent innervation to the knee.
Dr. Michael P. Gillespie

70. MUSCULAR FUNCTION AT THE KNEE
Muscles of the knee are described as two groups:
Knee extensors (quadriceps femoris)
Knee flexor-rotators
Dr. Michael P. Gillespie

71. ACTIONS & INNERVATIONS OF MUSCLES THAT CROSS THE KNEE
Plexus
Sartorius
Hip flexion, external rotation, and abduction
Knee flexion and internal rotation
Femoral nerve
Lumbar
Gracilis
Hip flexion and abduction
Obturator nerve
Quadriceps
Rectus Femoris
Vastus Group
Knee extension and hip flexion
Knee extension
Popliteus
Tibial nerve
Sacral
Semimembranosus
Hip extension
Sciatic nerve (tibial portion)
Dr. Michael P. Gillespie
The actions involving the knee are shown in bold. Muscles are listed in descending order of nerve root innervations.

72. ACTIONS & INNERVATIONS OF MUSCLES THAT CROSS THE KNEE
Plexus
Semitendanosus
Hip extension
Knee flexion and internal rotation
Sciatic nerve (tibial portion)
Sacral
Biceps femoris (short head)
Knee flexion and external rotation
Sciatic nerve (common fibular portion)
Biceps femoris (long head)
Gastrocnemius
Knee flexion
Ankle plantar flexion
Tibial nerve
Plantaris
Dr. Michael P. Gillespie
The actions involving the knee are shown in bold. Muscles are listed in descending order of nerve root innervations.

73. EXTENSORS OF THE KNEE
Quadriceps femoris
Dr. Michael P. Gillespie

74. QUADRICEPS FEMORIS: ANATOMIC CONSIDERATIONS
Rectus femoris
Vastus lateralis
Vastus medialis
Vastus intermedius
Contraction of the vastus group produces about 80% of the extension torque at the knee. They only extend the knee.
Contraction of the rectus femoris produces about 20% of the extension torque at the knee. The rectus femoris muscle extends the knee and flexes the hip.
The inferior fibers of the vastus medialis exert an oblique pull on the patella that help to stabilize it as it tracks through the intercondylar groove.
Dr. Michael P. Gillespie

75. QUADRICEPS CROSS-SECTION
Dr. Michael P. Gillespie
FIGURE    A cross-section through the right quadriceps muscle. The arrows depict the approximate line of force of each part of the quadriceps: vastus lateralis (VL), vastus intermedius (VI), rectus femoris (RF), vastus medialis longus (VML), and vastus medialis obliquus (VMO). Much of the vastus medialis and vastus lateralis muscles originate on the posterior side of the femur, at the linea aspera.

76. QUADRICEPS FEMORIS: FUNCTIONAL CONSIDERATIONS
The knee extensor muscles produce a torque that is about two thirds greater than that produced by the knee flexor muscles.
Isometric activation – stabilizes and protects the knee
Eccentric activation – controls the rate of descent of the body’s center of mass during sitting and squatting. Provides shock absorption at the knee.
Concentric activation – accelerates the tibia or femur toward knee extension. Used in raising the body’s center of mass during uphill running, jumping, or standing from a seated position.
Dr. Michael P. Gillespie

77. EXTERNAL TORQUE DEMANDS AGAINST QUADRICEPS
During tibial-on-femoral knee extension, the external moment arm of the weight of the lower leg increases from 90 to 0 degrees of knee flexion.
During femoral-on-tibial knee extension (as in rising from a squat position), the external moment arm of the upper body weight decreases from 90 to o degrees of knee flexion.
Dr. Michael P. Gillespie

78. EXTERNAL (FLEXION) TORQUES
Dr. Michael P. Gillespie
FIGURE    The external (flexion) torques are shown imposed on the knee between flexion (90 degrees) and full extension (0 degrees). Tibial-on-femoral extension is shown in A to C, and femoral-on-tibial extension is shown in D to F. The external torques are equal to the product of body or leg weight times the external moment arm (EMA). The increasing red color of the quadriceps muscle denotes the increasing demand on the muscle and underlying joint, in response to the increasing external torque. The graph shows the relationship between the external torque–normalized to a maximum (100%) torque for each method of extending the knee–for selected knee joint angles. (Tibial-on-femoral extension is shown in black; femoral-on-tibial extension is shown in gray.) External torques above 70% for each method of extension are shaded in red.

79. QUADRICEPS WEAKNESS: PATHOMECHANICS OF “EXTENSOR LAG”
People with significant weakness of the quadriceps often have difficulty completing the full range of tibial-on-femoral extension of the knee.
They fail to produce the last 15 to 20 degrees of extension.
This is referred to as “extensor lag”.
Swelling or effusion of the knee increases the likelihood of an extensor lag.
Swelling increases intra-articular pressure.
Passive resistance from hamstring muscles can also limit full knee extension.
Dr. Michael P. Gillespie

80. FUNCTIONAL ROLE OF THE PATELLA
The patella acts as a “spacer” between the femur and the quadriceps muscle, which increases the internal moment arm of the knee extensor mechanism.
Torque is the product of force and its moment arm.
The patella augments the extension torque at the knee.
Dr. Michael P. Gillespie

81. USE OF PATELLA TO INCREASE THE INTERNAL MOMENT ARM
Dr. Michael P. Gillespie
FIGURE    The quadriceps uses the patella to increase its internal moment arm (thick black line). The axis of rotation is shown as the open circle near the lateral epicondyle of the femur.

82. PATELLOFEMORAL JOINT KINETICS
The patellofemoral joint is exposed to high magnitudes of compression force.
1.3 times body weight during walking on level surfaces
2.6 times body weight during performance of a straight leg raise
3.3 times body weight during climbing of stairs
7.8 times body weight during deep knee bends
The knee flexion angle influences the amount of force experienced at the joint.
Both the compression force and the area of articular contact on the patellofemoral joint increase with knee flexion, reaching a maximum between 60 and 90 degrees.
Dr. Michael P. Gillespie

83. TWO INTERRELATED FACTORS ASSOCIATED WITH JOINT COMPRESSION FORCE ON THE PATELLOFEMORAL JOINT
1. Force within the quadriceps muscle
2. Knee flexion angle
Dr. Michael P. Gillespie

84. COMPRESSION FORCE WITHIN THE PATELLOFEMORAL JOINT
Dr. Michael P. Gillespie
FIGURE    The relationship between quadriceps activation, depth of a squat position, and the compression force within the patellofemoral joint is shown. A, Maintaining a partial squat requires that the quadriceps transmit a force through the quadriceps tendon (QT) and the patellar tendon (PT). The vector addition of QT and PT provides an estimation of the patellofemoral joint compression force (CF). B, A deeper squat requires greater force from the quadriceps owing to the greater external (flexion) torque on the knee. Furthermore, the greater knee flexion (B) decreases the angle between QT and PT and consequently produces a greater joint force between the patella and femur.


85. FACTORS AFFECTING THE TRACKING OF THE PATELLA ACROSS THE PATELLOFEMORAL JOINT
If the patellofemoral joint has less than optimal congruity, it can lead to abnormal “tracking” of the patella.
The patellofemoral joint is then subjected to higher joint contact stress, increasing the risk of degenerative lesions and pain.
This can lead to patellofemoral pain syndrome and osteoarthritis.
Excessive tension in the iliotibial band or lateral patellar retinacular fibers can add to the natural lateral pull of the patella.
Dr. Michael P. Gillespie

86. ROLE OF QUADRICEPS MUSCLE IN PATELLAR TRACKING
As the knee is extending, the quadriceps muscle pulls the patella superior, slightly lateral, and slightly posterior in the intercondylar groove.
Vastus lateralis has a larger cross sectional area and force potential.
The quadriceps angle (Q-angle) is a measure of the lateral pull of the quadriceps.
Q-angles average about 13 to 15 degrees.
Dr. Michael P. Gillespie

87. QUADRICEPS PULL & Q-ANGLE
Dr. Michael P. Gillespie
FIGURE    A, The overall line of force of the quadriceps is shown as well as the separate line of force of each of the muscular components of the quadriceps. The vastus medialis is divided into its two predominant fiber groups: the obliquus and the longus. The net lateral pull exerted on the patella by the quadriceps is indicated by the Q-angle. The larger the Q-angle, the greater the lateral muscle pull on the patella. B, The line of force of several of the muscular components is observed from a medial view, emphasizing the posterior pull of the oblique fibers of the vastus medialis.

88. LOCAL FACTORS THAT NATURALLY OPPOSE THE LATERAL PULL OF THE QUADRICEPS ON THE PATELLA
The lateral facet of the intercondylar groove is normally steeper than the medial facet which blocks or resists the approaching patella.
The oblique fibers of the vastus medialis balance the lateral pull.
Medial patellar retinacular fibers are oriented in medial-distal and medial directions (referred to as the medial patellofemoral ligament). Often ruptured after a complete lateral dislocation of the patella.
Dr. Michael P. Gillespie

89. LOCALLY PRODUCED FORCES ACTING ON THE PATELLA
Dr. Michael P. Gillespie
FIGURE    Highly diagrammatic and idealized illustration showing the interaction of locally produced forces acting on the patella as it moves through the intercondylar groove of the femur. Each force has a tendency to pull (or push in the case of the raised lateral facet of the intercondylar groove of the femur) the patella generally laterally or medially. Ideally, the opposing forces counteract one another so that the patella tracks optimally during flexion and extension of the knee. Note that the magnitude of the lateral bowstringing force is determined by the parallelogram method of vector addition (see Chapter 4). In theory, if the line of force of the quadriceps is collinear with the patellar tendon force, the lateral bowstringing force would be zero. Vectors are not drawn to scale.


90. GLOBAL FACTORS
Factors that resist excessive valgus or the extremes of axial rotation of the tibiofemoral joint favor optimal tracking of the patellofemoral joint.
Excessive genu valgum can increase the Q-angle and thereby increase the lateral bowstring force on the patella. Increased valgus can occur from laxity or injury to the MCL.
Weakness of the hip abductors (coxa vara) can allow the hip the slant excessively medial, which in turn places excessive stress on the medial structures of the knee.
Excessive internal rotation of the knee, which is related to excessive pronation of the subtalar joint during walking.
Dr. Michael P. Gillespie

91. BOWSTRING FORCE ON THE PATELLA
Dr. Michael P. Gillespie
FIGURE 13-31A-B.   A, Neutral alignment of knee, showing the characteristic lateral bowstringing force acting on the patella. B, Excessive knee valgus and knee external rotation can increase the Q-angle and thereby increase the lateral bowstringing force on the patella. Blue arrows indicate bone movement that can increase knee external rotation, and purple arrows indicate an increased valgus load placed on the knee. Note that the increased external rotation of the knee can occur as a combination of excessive internal rotation of the femur and external rotation of the tibia.


92. PATELLOFEMORAL PAIN SYNDROME
Patellofemoral pain syndrome (PFPS) is one of the most common orthopedic conditions encountered in sports medicine outpatient settings.
It accounts for about 30% of all knee disorders in women and 20% in men.
Diffuse peripatellar or retropatellar pain with an insidious onset.
Aggravated by squatting, climbing stairs, or sitting with knees flexed for a prolonged period of time.
Pain or fear of repeated dislocations may be severe enough to significantly limit activities.
Abnormal movement (tracking) and alignment of the patella within the intercondylar groove.
Dr. Michael P. Gillespie

93. CAUSES OF EXCESSIVE LATERAL TRACKING OF THE PATELLA
Structural of Functional Cause
Specific Examples
Bony Dysplasia
Dysplastic lateral facet of the intercondylar groove of the femur (“shallow” groove)
Dysplastic or “high” patella (patella alta)
Excessive laxity in periarticular connective tissue
Laxity of medial patellofemoral ligament
Laxity or attrition of medial collateral ligament
Laxity or reduced height of the medial longitudinal arch of the foot (overpronation of the subtalar joint)
Excessive stiffness or tightness in periarticular connective tissue and muscle
Increased tightness in the lateral patellar retinacular fibers or iliotibial band
Increased tightness of the internal rotator or adductor muscles of the hip
Dr. Michael P. Gillespie

94. CAUSES OF EXCESSIVE LATERAL TRACKING OF THE PATELLA
Structural of Functional Cause
Specific Examples
Extremes of bony or joint alignment
Coxa varus
Excessive anteversion of the femur
External tibial torsion
Large Q-angle
Excessive genu vlagum
Muscle weakness
Weakness or poor control of
Hip external rotator and abductor muscles
The vastus medialis (oblique fibers)
The tibialis posterior muscle (related to overpronation of the foot)
Dr. Michael P. Gillespie

95. TREATMENT PRINCIPLES FOR ABNORMAL TRACKING AND CHRONIC DISLOCATION OF THE PATELLOFEMORAL JOINT
Reduce the magnitude of the lateral bowstring force on the patella.
Strengthen hip abductor and external rotator muscles.
Strengthen the oblique fibers of the vastus medialis.
Strengthen the medial longitudinal arch of the foot.
Stretch tight periarticular connective tissues of the hip and knee.
Mobilize the patella.
Use a patellar brace or using a foot orthosis to reduce excessive pronation of the foot.
Patellar taping to guide the patella’s tracking.
Dr. Michael P. Gillespie

96. KNEE FLEXOR-ROTATOR MUSCLES
With the exception of the gastrocnemius, all muscles that cross posterior to the knee have the ability to flex and to internally or externally rotate the knee.
Flexor-rotator group
Hamstrings
Sartorius
Gracilis
Popliteus
The flexor-rotator group has three sources of innervation
Femoral
Obturator
Sciatic
Dr. Michael P. Gillespie

97. KNEE FLEXOR-ROTATOR MUSCLES: FUNCTIONAL ANATOMY
The hamstring muscles have their proximal attachment on the ischial tuberosity.
The hamstrings extend the hip and flex the knee.
In addition to flexing the knee, the medial hamstrings (semimembranosus and semitendanosus) internally rotate the knee.
The biceps femoris flexes and externally rotates the knee.
The sartorius, gracilis, and semitendinosus attach to the tibia using a common, broad sheet of connective tissue known as the pes anserinus. The “pes muscles” are internal rotators of the knee.
Dr. Michael P. Gillespie

98. KNEE FLEXOR-ROTATOR MUSCLES: GROUP ACTION
Dr. Michael P. Gillespie

99. KNEE AS A PIVOT POINT – AXIAL ROTATION
Dr. Michael P. Gillespie
FIGURE 13-32A-B.   A, Several muscles are shown controlling the rotation of the head, neck, trunk, pelvis, and femur toward the approaching ball. Because the right foot is fixed to the ground, the right knee functions as an important pivot point. B, Control of axial rotation of the right knee is illustrated from above. The short head of the biceps femoris contracts to accelerate the femur internally (i.e., the knee joint moves into external rotation). Active force from the pes anserinus muscles in conjunction with a passive force from the stretched medial collateral ligament (MCL) and oblique popliteal ligament (not shown) helps to decelerate, or limit, the external rotation at the knee.

100. POPLITEUS MUSCLE “KEY TO THE KNEE”
The popliteus muscle is an important internal rotator and flexor of the knee joint.
As the extended and locked knee prepares to flex, the popliteus provides an important internal rotation torque that helps to mechanically unlock the knee.
The popliteus has an oblique line of pull.
This muscle has the most favorable leverage of all of the knee flexor muscles to produce a horizontal plane rotation torque on an extended knee.
Dr. Michael P. Gillespie

101. CONTROL OF TIBIAL-ON-FEMORAL OSTEOKINEMATICS
An important action of the flexor-rotator muscles is to accelerate or decelerate the lower leg during the swing phase of walking or running.
Through eccentric action, the muscles help to dampen the impact of full knee extension.
They shorten the functional length of the lower limb during the swing phase.
Dr. Michael P. Gillespie

102. CONTROL OF FEMORAL-ON-TIBIAL OSTEOKINEMATICS
The muscular demand needed to control femoral- on-tibial motions is generally larger and more complex than that needed for most tibial-on- femoral knee motions.
The sartorius may have to simultaneously control up to five degrees of freedom (i.e. two at the knee and three at the hip).
Dr. Michael P. Gillespie

103. ABNORMAL ALIGNMENT OF THE KNEE: FRONTAL PLANE
In the frontal plane the knee is normally aligned in about 5 to 10 degrees of valgus.
Deviation from this alignment is referred to as excessive genu valgum or genu varum.
Dr. Michael P. Gillespie

104. GENU VARUM WITH UNICOMPARTMENTAL OSTEOARTHRITIS OF THE KNEE
During walking across level terrain, the joint reaction force at the knee is about 2.5 to 3 times body weight.
The ground reaction force passes just lateral to the heel, then upward to the medial knee.
In some individuals this asymmetric dynamic loading can lead to excessive wear of the articular cartilage and ultimately to medial unicompartmental osteoarthritis.
Thinning of the articular cartilage and meniscus on the medial side can lead to genu varum, or a bow-legged deformity, which will further increase medial compartment loading.
Dr. Michael P. Gillespie

105. GENU VARUM (BOW-LEG) Dr. Michael P. Gillespie
FIGURE 13-35A.   Bilateral genu varum with osteoarthritis in the medial compartment of the right knee. A, The varus deformity of the right knee is shown with greater joint reaction force on the medial compartment. B, An anterior x-ray view with subject (a 43-year-old man) standing, showing bilateral genu varum and medial joint osteoarthritis. Both knees have a loss of medial joint space and hypertrophic bone around the medial compartment. To correct the deformity on the right (R) knee, a wedge of bone will be surgically removed by a procedure known as a high tibial osteotomy. C, The x-ray film shows the right knee after the removal of the wedge of bone. Note the change in joint alignment compared with the same knee in B. (Courtesy Joseph Davies, MD, Aurora Advanced Orthopedics, Milwaukee.)


106. GENU VARUM (BOW-LEG) / HIGH TIBIAL OSTEOTOMY
Dr. Michael P. Gillespie
FIGURE 13-35B-C.   Bilateral genu varum with osteoarthritis in the medial compartment of the right knee. A, The varus deformity of the right knee is shown with greater joint reaction force on the medial compartment. B, An anterior x-ray view with subject (a 43-year-old man) standing, showing bilateral genu varum and medial joint osteoarthritis. Both knees have a loss of medial joint space and hypertrophic bone around the medial compartment. To correct the deformity on the right (R) knee, a wedge of bone will be surgically removed by a procedure known as a high tibial osteotomy. C, The x-ray film shows the right knee after the removal of the wedge of bone. Note the change in joint alignment compared with the same knee in B. (Courtesy Joseph Davies, MD, Aurora Advanced Orthopedics, Milwaukee.)


107. EXCESSIVE GENU VALGUM
Several factors can lead to excessive genu valgum or knock-knee.
Previous injury, genetic predisposition, high body mass index, and laxity of ligaments.
Coxa vara or weak hip abductors can lead to genu valgum.
Excessive foot pronation
Standing with a valgus deformity of approximately 10 degrees greater than normal directs most of the joint compression force to the lateral joint compartment.
This increased regional stress may lead to lateral unicompartmental osteoarthritis.
Dr. Michael P. Gillespie

108. GENU VALGUM Dr. Michael P. Gillespie
FIGURE    Excessive genu valgum of the right knee. In this example the valgus deformity is assumed to be the result of abnormal alignment or muscle weakness at either the proximal or distal end of the lower limb. The pair of vertical arrows representing force vectors at the knee indicates the greater compression force on the lateral compartment.


109. “WIND-SWEPT” DEFORMITY / GENU VALGUM & GENU VARUM
Dr. Michael P. Gillespie
FIGURE 13-37A.   Bilateral frontal plane malalignment in the knees of an 83-year-old woman. A, The classic “wind-swept” deformity, with excessive genu valgum on the right and genu varum on the left. B and C are the x-ray films of the patient in A, before and after bilateral knee replacement. Note in B, the hypertrophic bone formation in areas of increased stress. With excessive genu valgum, the stress is greater on the lateral compartment; with genu varum, the stress is greater on the medial compartment. (Courtesy Joseph Davies, MD, Aurora Advanced Orthopedics, Milwaukee.)

110. “WIND-SWEPT” DEFORMITY BEFORE & AFTER KNEE REPLACEMENT
Dr. Michael P. Gillespie
FIGURE 13-37B-C.   Bilateral frontal plane malalignment in the knees of an 83-year-old woman. A, The classic “wind-swept” deformity, with excessive genu valgum on the right and genu varum on the left. B and C are the x-ray films of the patient in A, before and after bilateral knee replacement. Note in B, the hypertrophic bone formation in areas of increased stress. With excessive genu valgum, the stress is greater on the lateral compartment; with genu varum, the stress is greater on the medial compartment. (Courtesy Joseph Davies, MD, Aurora Advanced Orthopedics, Milwaukee.)

111. SAGITTAL PLANE: GENU RECURVATUM
Full extension with slight external rotation is the knee’s close-packed, most stable position.
The knee may be extended beyond neutral an additional 5 to 10 degrees.
Hyperextension beyond 10 degrees of neutral is called genu recurvatum (Latin genu, knee, + recurvare, to bend backward).
Chronic, overpowering (net) knee extensor torque eventually overstretches the posterior structures of the knee.
Due to poor postural control or neuromuscular disease (i.e. polio). That causes spasticity and / or paralysis of the knee flexors.
Dr. Michael P. Gillespie

112. GENU RECURVATUM Dr. Michael P. Gillespie
FIGURE    Subject showing severe genu recurvatum of the left knee secondary to polio. In addition to sporadic muscle weakness throughout the left lower extremity, the left ankle was surgically fused in 25 degrees of plantar flexion. A, When the subject stands barefoot, the body weight acts with an abnormally large external moment arm (EMA) at the knee. The resulting large extensor torque amplifies the magnitude of the knee hyperextension deformity. B, Subject is able to reduce the severity of the recurvatum deformity by wearing tennis shoes with a built-up heel. The shoe tilts her tibia and knee forward (indicated by the green arrow), thereby reducing the length of the deforming external moment arm at the knee.