Structure and Function of the Bones and Noncontractile Elements of the Knee

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1 Structure and Function of the Bones and Noncontractile Elements of the Knee

2 Any Questions Going over today: Bones around the knee Menisci LCL/MCL ligaments Biomechanics of knee extension/flexion-is it really just extending your knee? Gross injuries of the knee Thurs: Muscles

3 Shaft and Distal Femur Linea aspera gives rise to quadriceps. Flatten into supracondylar ridges End in condyles, joined anteriorly and separate posteriorly Condyles differ from one another

4 MEDIAL CONDYLE Extends farther distally, contributing to oblique alignment of shaft Articular surface differs from lateral and influences tibiofemoral motion. Radius of curvature is greatest distally, smaller posteriorly.

5 LATERAL CONDYLE Lies closer to sagittal plane Flattest distally

6 DISPARITY BETWEEN THE TIBIAL AND FEMORAL SURFACES Moving limb must undergo more complex motion than just rolling.

7 Tibiofemoral Motion Knee exhibits threedimensional motion. Medial rotation of femur accompanies knee extension or lateral rotation with flexion.

8 Also need translation- Appox >2cm during flexion in anterior direction and > 2cm with extension in posterior direction.

9 Small anterior-posterior translation occurs in flexion and extension. Relative motion of tibia and femur are the same in open- and closed-chain movements.

10 Knee has six degrees of freedom (DOFs) around 3-axis. What are they: Rotation Flex/extension translation

11 Closed Chain vs Open Chain

12 Why would the restoration of knee extension be more complex than Pg. 715 meets the eye??

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14 Largest sesamoid bone Three facets on articular surface Protects quadriceps from excessive friction Increases angle of application of quadriceps Patella

15 Patella and Patellar Tracking Chondromalacia sx: pain underneath the patella with possible popping or crepitus especially in the degree ROM. Direct pressure may elicit the pain; lateral patellar play, stairs and prolonged sitting are also problems. Causes include large Q angles (we will measure this on Thurs), laterally riding or subluxating patella's, overuse, and mm imbalance. Problems

16 Subluxating patella sx: giving way sensation, popping, local tenderness and a positive apprehension test. Causes include contraction of quad with a medial blow or externally rotated foot, small lateral condyle, tight lateral retinaculum. Dislocating patella sx: if the patella is out, the knee is severely deformed, painful, flexed, and patella is normally on the lateral side of the knee. Causes are the same as above.

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18 ARTICULAR STRUCTURES OF THE KNEE Tibiofemoral joint is synovial, modified hinge. Patellofemoral joint is synovial, gliding.

19 Menisci-STRUCTURE Fibrocartilaginous discs, covering more than 50% of tibial articular surface More coverage by lateral meniscus Firmly attached to tibia, medial more so than lateral Pg 718-avascular area

20 Most of the meniscus is avascular, meaning no blood vessels go to it. Only its outer rim gets a small supply of blood. Doctors call this area the red zone. The ends of a few vessels in the red zone may actually travel inward to the middle section, the redwhite zone. The inner portion of the meniscus, closest to the center of the knee, is called the white zone. It has no blood vessels at all. Although a tear in the outer rim has a good chance of healing, damage further in toward the center of the meniscus will not heal on its own.

21 FUNCTION OF THE MENISCI Joint lubrication, stabilization, stress reduction Approximately doubles contact area

22 Motion of the Menisci on the Move with rolling femoral condyles, posteriorly in flexion, anteriorly in extension Menisci deform during flexion and extension.? meniscetomy Tibia

23 Knee Injury Pathology

24 MENISCAL LESIONS Susceptible to injury because of position between two longest bones, attached to tibia, distortion during knee motion

25 Medial and lateral menisci in the knee may be pathological producing locking, catching, swelling, weakness and pain. Types of tears -bucket handle-transverse - peripheral -beak tear Special tests- McMurray, Apley's compression - hyper flexion or squat test

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28 Bucket handle tear of MM with a free fragment in the notch

29 Noncontractile Supporting Structures Capsule and ligaments work together to support the knee.

30 ARTICULAR CAPSULE OF THE KNEE JOINT Largest joint capsule Reinforced anteriorly by patellar retinaculi Synovial and fibrous layers separate posteriorly Anterior expansion of synovial layer is suprapatellar pouch Folds in synovial layer are plicae

31 COLLATERAL LIGAMENTS Medial is larger than lateral, with deep and superficial layers. Medial withstands valgus stresses, lateral, varus stresses. Knee position alters stretch of collateral ligaments.

32 Terrible Triad

33 CRUCIATE LIGAMENTS Each consists of at least two segments. Anterior cruciate ligament (ACL) limits anterior glide of tibia on femur. Effects of ACL tear depends on knee position during test, portion of ligament torn, force of test, and integrity of other tissues.

34 ACL ACL is tightest in knee extension and limits hyperextension range of motion (ROM). ACL limits rotation, depending on knee position.

35 PCL Posterior cruciate ligament (PCL) also has a complex stabilizing role. PCL limits posterior glide of tibia, maximum knee flexion, varus, valgus, and rotation

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37 Ligamentous Injuries

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40 CONCLUSIONS REGARDING THE CONNECTIVE TISSUE SUPPORT OF THE KNEE Collaterals are primary medial lateral supports, but cruciates add support. Cruciates are primary anterior-posterior support, but collaterals aid in support. Rotary stability is added by all four ligaments. Menisci and articular surfaces also stabilize the knee.