The Knee Complex

The Knee Complex General Structure & Function Structure & Function of Specific Joints 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

Transverse plane Medial and lateral rotation Sagittal plane Flexion, extension

Knee Complex Movements Frontal plane Varus, valgus Anteroposterior translation Mediolateral translation

The Knee Complex General Structure & Function Structure & Function of Specific Joints Muscular Considerations

Structure & Function of Specific Joints Tibiofibular Joint Patellofemoral Joint Tibiofemoral Joint

Tibiofibular Joint: Bony Structure Amphiarthrodial membranous syndesmosis joint

Structure & Function of Specific Joints Tibiofibular Joint Patellofemoral Joint 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 Increase leverage of QF Protect joint during knee flexion ↓ pressure and distribute forces on femur Prevent Fcompression on PT with resisted knee flexion as in deep knee bends

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

PF Articular Surfaces Largest sesamoid bone Least congruent joint Articular cartilage Vertical ridge Facets M L Largest sesamoid bone Least congruent joint in body Posterior surface covered with articular cartilage Vertical ridge on posterior, typically in center but can be situated more medially 30% of patellae have a second vertical ridge toward medial border, creating the odd facet on the extreme medial edge Angle of femoral sulcus (angle formed by medial & lateral facets of femur) averages 138° but varies widely (116° -151°)

PF Articular Surfaces Largest sesamoid bone Least congruent joint Articular cartilage Vertical ridge Facets Angle of femoral sulcus Largest sesamoid bone Least congruent joint in body Posterior surface covered with articular cartilage Vertical ridge on posterior, typically in center but can be situated more medially 30% of patellae have a second vertical ridge toward medial border, creating the odd facet on the extreme medial edge Angle of femoral sulcus (angle formed by medial & lateral facets of femur) averages 138° but varies widely (116° -151°)

Patellar Motion INF & SUP Sliding Patellar tilt 11 MT as KN FL Med Lat Sliding during knee flexion – enters sulcus at 20° of knee flexion Patellar tilt rotation about vertical axis to medial side of 11° occurs as knee flexion occurs

Patellar Motion Lateral rotation Medial rotation ACC MR of femur 6 through KN FL Medial rotation ACC LR of femur Lateral rotation of patella (around AP axis) with medial rotation of femur on tibia (top of patella goes with femur (7° - most by 60 ° of knee flexion) Medial rotation of patella (around AP axis) with lateral rotation of femur on tibia Failure to slide, tilt, or rotate will lead to restriction of knee joint ROM, instability of PF joint, or pain due to erosion of PF surfaces

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

Extension Little effect overall

Slight Flexion Noticeable weakness

Extreme Flexion Noticeable weakness

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 Collinear pull of patella tendon (inferior) and quadriceps tendon (superior) results in little or no contact with femur in full extension Justification for use of straight-leg raises to improve quad strength without creating or exacerbating PF problems With knee flexion, the pull of these tendons create a compressive force on patella into femur (Fig. 11.35) (occurs with active or passive mechanism due to elasticity of tendon) FQ and FP are generally not equal – depend on knee joint angle (Fig. 6.2) Creates JRF (magnitude of JRF depends on magnitude of active and passive pulls, and degree of knee flexion) JRF during gait at foot contact (10° -15° of knee flexion) is 50% of body weight In running, JRF may increase to 3.3X (60° of knee flexion & more vigorous muscle contraction) 7.8X BW (130° of knee flexion with strong muscle contraction) in deep knee bends Lack of congruency at this joint results in this force distribution occurring over smaller area – more stress/pressure Medial facet bears the brunt of this, but there are mechanisms to minimize this Lowest at knee flexion < 30 degrees

PF Compressive Forces Descending stairs 4000 N Max isometric extension Kicking 6800 N Parallel squat 14,900 N (7-8X BW) Isokinetic knee extension 8300 N Rising from chair 3800 N Running/jogging 5000 N (3-4X BW) Ascending stairs 1400 N Walking 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