The Knee Complex

The Knee Complex

A. General Structure & FunctionB. Structure & Function of Specific JointsC. Muscular Considerations

General Structure

Joints of the Knee Complex

General Function Provides very mobile link in an otherwise

stable lower extremity Transmits loads from tibia/fibula to femur

Knee Complex Movements

Sagittal plane• Flexion, extension

Transverse plane• Medial and lateral

rotation

Knee Complex Movements Frontal plane

Varus, valgus Anteroposterior translation Mediolateral translation

The Knee Complex

A. General Structure & FunctionB. Structure & Function of Specific JointsC. Muscular Considerations

Structure & Function of Specific Joints

1. Tibiofibular Joint2. Patellofemoral Joint 3. Tibiofemoral Joint

Tibiofibular Joint: Bony Structure

Amphiarthrodial membranous syndesmosis joint

Structure & Function of Specific Joints

1. Tibiofibular Joint2. Patellofemoral Joint 3. Tibiofemoral Joint

Purpose of Patella Increase leverage of QF Protect joint during knee flexion ↓ pressure and distribute forces on femur Prevent Fcompression on PT in resisted knee

flexion Disadvantage: ANT shear of QF

Patella Structure Medial facet Lateral facet Odd facet (30%)

ML

PF Articular Surfaces Largest sesamoid bone Least congruent joint Articular cartilage Vertical ridge Facets

ML

PF Articular Surfaces Largest sesamoid bone Least congruent joint Articular cartilage Vertical ridge Facets Angle of femoral sulcus

Patellar Motion INF & SUP Sliding Patellar tilt

11 MT as KN FL

MedLat

Patellar Motion Lateral rotation

ACC MR of femur 6 through KN FL

Medial rotation ACC LR of femur

Patellalectomy ↓ MA of QF (↓ strength 49%) Q tendon friction compressive stress on groove by Q tendon Most evident in closed chain EXT

ECC QF in CC Coupled w/ & assisted by hip & ankle movement QF not needed in erect posture of CC

Little effect overall

Extension

Noticeable weakness

Slight Flexion

Noticeable weakness

Extreme Flexion

From 0° to 60° of Knee Flexion

0-60 Contact area MA of QF; 60 ANT shear of QF

0-60 Facet contact at 20

From 60° to 140° of Knee Flexion

60-140 contact area MA of QF No leverage in full FL

Overall Medial facet most contact Odd facet least contact

During Full Extension

Full EXT MA of QF QF length Patella very unstable

PF JRF Amount of knee FL Strength of QF contraction

PF Compressive ForcesDescending stairs 4000 NMax isometric extension 6100 NKicking 6800 NParallel squat 14,900 N (7-8X BW)Isokinetic knee extension 8300 NRising from chair 3800 NRunning/jogging 5000 N (3-4X BW)Ascending stairs 1400 NWalking 840-850 N (0.5-1.5X BW)Cycling 880 N

Compensatory Mechanisms for Compressive Force Distribution Contact area with knee flexion Medial facet contact from 30-70

Thickest hyaline cartilage in body

Compensatory Mechanisms for Compressive Force Distribution Contact area with knee flexion Medial facet contact from 30-70

Thickest hyaline cartilage in body Largest QF MA 30-70

QF torque as MA decreases QF tendon contacts condyles 70-90

Normal Patella Tracking

Maintains maximum congruence

Passive restraints Active restraints

Abnormal Patella Tracking ↓ congruence Stretches capsule & retinacula ↓ contact area

Lateral Medial

Causes of Abnormal Tracking Skeletal abnormalities Strength imbalance in QF Strength imbalance in fibrous tissues Compensatory movements in knee due to

abnormal foot movement

Causes of Abnormal Tracking Skeletal abnormalities Strength imbalance in QF Strength imbalance in fibrous tissues Compensatory movements in knee due to

abnormal foot movement

Skeletal Abnormalities: Q-angle

Skeletal Abnormalities: Genu Varum & Genu Valgum

Q angle w/ age Varum common in

very young children Valgum seen in

growing children Menisectomy effects

Skeletal Abnormalities: Patella Alta & Patella Baja

Index of Insall & Salviti LT/LP Normal = 1.0 Patella alta = 0.8 Patella baja = 1.2 Women ratio

Skeletal Abnormalities: Patella Surface Lateral Border

Appositional forces ↓ in full extension

Prominence of lateral border prevents lateral displacement

Underdevelopment common in children as growing

Skeletal Abnormalities: Femoral & Tibial Torsion

Lateral tracking

Causes of Abnormal Tracking Skeletal abnormalities Strength imbalance in QF Strength imbalance in fibrous tissues Compensatory movements in knee due to

abnormal foot movement

QF Strength Imbalance

Causes of Abnormal Tracking Skeletal abnormalities Strength imbalance in QF Strength imbalance in fibrous tissues Compensatory movements in knee due to

abnormal foot movement

Fibrous Tissue Strength Imbalance

IT

Causes of Abnormal Tracking Skeletal abnormalities Strength imbalance in QF Strength imbalance in fibrous tissues Compensatory movements in knee due to

abnormal foot movement

Compensatory Movement

Pronation of foot accompanied by medial rotation of tibia medial rotation & medial translation of patella

Pronation coupled w/ forceful quadriceps femoris leads to anterior tilt

EX: jumping, landing, running

Summary