Clinical Biomechanics of the Knee pdf

Functional Joint Classification=

• Hinge Diarthrodial Joint

Bi-condylar joint

Condyles are smooth surface area at the end of the bone

Epicondyles are rounded protuberance found at the end of the bone

Joined y the articulation of 3 bones

• femur

• Tibia

• Patella

2 separate joints formed at the knee

• patellofemoral joint

  • Femoral condyles joint anteriorly to form the trochlear groove

    • This groove articulates with the posterior side of the patella, forming the patellofemoral joint

  • Trachlear groove is concave from side to side and slightly convex from front the back

  • The sloping sides of the trochlear groove form lateral and medial facets

  • The steeper slope of the lateral facet helps to stabilize the patella within the groove ring knee movement

• Tibiofemoral joint

  • Modified hinge synovial joint between the distal femur and the proximal tibia

  • The articulation occurs between the medial and lateral femoral condyles and the medial and lateral facets fo the tibial condyles

  • The medical and lateral menisci increase the depth and stability and comprehensive force bearing and absorption of the joint

  • The joint capsule consists of a thin fibrous sheath which attaches at the distal femur and joins at the proximal tibia enclosing the synovial fluid

Stability of the knee is based primarily on its soft-tissue constrains rather than on its bony configuration

• the femoral condyles are held in place by extensive ligaments, joint capsule and menisci and large muscles

Menisci:

• Crescent-shaped structures are composed of fibrocartilage

• Roots attaches to the intercondylar region of the tibia

• Lateral and Anterior horns of the menisci are vascularized as well as the periphery of the menisci

• Functions:

  • Increases joint stability

  • Shock absorption

  • Reduces friction

  • Distributes force by increasing surface area

  • Reduce hoop stress

• Injury:

  • Most common mechanism of injury is forceful axial rotation of the femur on a partially flexed knee that is weight-bearing

  • Medial menisci is 3X thicker than the lateral menisci

    • Can accept increased loads

  • Medial is injured more

  • Ligament injury often occurs concurrently or is a predisposing factor to meniscal injury

  • Tears in the body of the menisci for not heal, but the body will accommodate and pain can decrease

  • Surface area decreases by 50% without the menisci

  • Load on femoral condyles are 2X

  • Load of tibial condyles increases 6-7X

  • Friction in the joint increases by 20%

Frontal plane Alignment issues:

• Excessive Genu Valgum (knock-knee)

• Genu Varum (bow-leg)

Q angle of the knee:

• aka Quadriceps Angle

• The measurement between the quadriceps muscles and the patellar tendon

• Measured by drawing two lines that intersect while the knee is flexed at 25* angle

• Normal angle =

  • Males: 13*

  • Females: 18*

• Standing vs Sitting (Static) 1st measurement:

  • ASIS down through the kneecap

  • Midpoint kneecap through the tibia tuberosity

• Moving (Dynamic) 1st measurement

  • If larger while in motion, can indicate potential injury including ACL tears and patellofemoral pain

  • More useful than Static

Dynamic Q angle:

• when a person is landing from a jump or cutting really quick, the Q-angle becomes larger than usual

• This extra stress presents a large opportunity for injury to occur

Genu Valgum:

• Knock knees

• a condition hat cause the knees to angle inward and touch each other when the legs are straightened, while the ankles remain apart

• Common lower leg abnormality that’s usually first seen in late toddlerhood and its most severe by age 3

• Slightly more common in girls than boys and often resolves on their own by age 7-8

Genu Varum:

• Bow legs

• When the legs curve outward at the knees while the feet and ankles touch

• Infants and toddlers have bow legs

• Creates a wider space than normal between the knees and lower legs

• When your child stands with his or her feet and ankles together, the knees stay wide apart, legs look like they bow

  • Especially happened when they walk

• Most common cause is rickets or any condition that prevents bones from forming properly

Kinematics

• ROM

  • Walking= 0-60*

  • Climbing stairs= 0-82*

  • Going downstairs= 0=90*

  • Tying shoes= 0-107*

  • Lifting= 0-117*

• Flexion

  • ROM = 125-145*

  • Tibia causes posterior roll and glide

  • Femur causes posterior roll and posterior glide

• Extension

  • ROM = 0-5*

  • Tibia causes anterior Rolland anterior glide

  • Femur causes anterior roll and posterior glide

• Rotation

  • The axis of rotation does not stay static

  • This location is dependent of the shape of the articular surfaces and the relative tension in the Cruciate the and other ligaments

  • Axial rotation of the knee is greater in knee flexion than knee extension

“Screw Home” mechanism

• full extension of the knee requires ~10* of external rotation

• This is a true coupled motion, meaning it is obligatory with knee extension

• Conversely, internal rotation of the knee is needed to go from full knee extension into a flexion range of motion

  • As the knee extends, femoral movement occurs longer on the medial condyle due to its larger size

  • Medial gliding and rolling continues

  • Spinning occurs at the lateral condyle resulting in a locking of the joint

• Passive tissue contribution

  • Note the location of the tension developed in the passive restraints of the knee

  • This facilitates a slight external rotation while also tensioning these ligaments, which adds stability

Cruciate ligament mechanics:

• ACL & PCL and Multiplanar stabilizers of the knee

• ACL is the most important stabilizer to anterior translation of the tibia

• PCL is major stabilizer for posterior tibial translation

• ALC has two bundles:

  • Anteromedial (AMB)

  • Posterolateral (PLB)

• ACL becomes taut as knee extends, especially PLB

ACL injury:

• most are non-contact injuries (70%)

• Young individuals are at increased risk

• Common injury mechanism

  • Strong quad activation

  • Valgum load

  • Knee rotation (usually external rotation)

PCL injury:

• much less common than ACL

• High energy trauma:

  • Motor vehicle accident

  • American football

• Falling on fully flexed knee

Patellofemoral joint Kinematics:

• patella follows tibial tuberosity during knee flexion

• During knee etc tension, the pul of the quadriceps had a larger effect

• The Trochlear groove plays a role in both flexion and extension

• At 135* of flexion, patella contact the femur near its superior pole

• At 90* of flexion, contact of patella is more on midpoint

• At 20* of flexion, primary patellar contact point is now toward the inferior patellar pole

• @ full extension, patella is coated proximal o the femoral trochlear

Knee extensor muscle activation:

• knee extensor muscles produce about 2/3 more torque at the knee than knee flexor muscles

• Isometric activation - stabilizing force

• Eccentric estimation - control descent (squat) and absorb impact loads

• Concentric activation - extend knee by accelerating rotation of tibia relative to femur

External vs internal Torque

• External torque is the rotational force generated by gravity or load acting on the knee

• Internal torque is generated by muscles acting on that joint

• Both occur at the same time

• Muscle activation also loads the knee joint and associated structures

• You can vary loads depending on the patient’s needs

Internal torque relationship to joint angle:

• high torque potential of the quadriceps occurs though a large range of motion

• Internal torque potential decreases significantly at flexion angles

• External torques for femoral-on-tibial motion decrease significantly during the last 45-70* of knee extension

Knee extension limitations:

• ACL, PCL, MCL, LCL,

• Hamstring & Gastrocnemius ROM

• Joint capsule tautness

Knee Flexion limitations:

• soft tissue approximation

• Rectus femoris length

• Joint capsule tautness

Patellar Function:

• increases the internal moment arm of the knee extensor mechanism

• Centralize distraction forces within the extensor mechanism

3 factors that affect the internal moment arm:

• Depth of sulcus

• Height of lateral femoral condyle wall

• Shape of patella

Patellofemoral pain syndrome:

• most common cause of knee pain in adults

• Diffuse anterior knee Ian described as periptellar or retropatellar

• Wide spectrum of this disorder

  • Mild pain to subluxation/dislocation to Chondromalacia

  • Exact cause in unknown, but biomechanical factors are implicated

  • Abd normal patellar tracking

Patellofemoral joint Kinematics

• High compressive forces occur across the patellofemoral joint

• The magnitude of compressive force is affected by

  • Force of quad contraction

  • Knee flexionangle

• Area of contact will modulate the stresses

Patellar motion:

• media/lateral tilt

• Superior/inferior glide

• Medial/lateral glide

Factors affecting patellar tracking:

• Q-angle

  • A line representing the overall line of force of the quadriceps muscles

  • Usually about 13-15*

  • Demonstrates a laterally directed Compton tenet of the quadriceps force

Potential Patellar injuries:

• bony dysplasia

  • Shallow trochlear groove

  • High-riding patella (patella Alta)

• Lax or damaged stabilizing connective tissues

  • Lax/injured medial patellofemoral ligament

  • Lax/injured medial collateral ligament

  • Decreased medial longitudinal arch of the foot

• Tight or stif peri articular connective tissues

  • Tight stiff lateral patella Retinaculum or ITB

  • Tight/stiff internal hip rotators or adductors of the hip

Functional considerations:

• Popliteus

  • Externally rotate femur relative to tibia

  • Dynamic stabilizer to assist MCL, posteromedial jint capsule, andACL

• Pes Anserine group:

  • Dynamic medial collateral ligament spares posteromedial joint capsule and ACL

Knee flexion Torque

• hamstrings have their greatest flexor moment arm at 50-90* of knee flexion