Joint Biomechanics - Knee Flashcards
Knee Complex
Most injured in the body.
Supports the body’s weight during static erect posture.
Two distinct articulations within a single joint capsule:
- Tibiofemoral joint
- Patellofemoral joint
Tibiofemoral Joint
Double condyloid joint between the medial and lateral condyles of the femur (convex) and the tibial condyles (concave).
Tibiofemoral Joint - OKC vs CKC
Open kinetic chain: Tibia gliding on femur
Closed kinetic chain: Femur gliding on tibia
When the knee is flexed, rotation occurs through a vertical axis.
Anatomical Axis of the Femur
Oblique, directed inferiorly and medially from its proximal to its distal end.
Anatomical Axis of the Tibia
Directed almost vertically.
Femoral and tibial longitudinal axis are normally in angle of 180°-185°.
Mechanical Axis/Weight Bearing Line
In a normally aligned knee, it will pass through the center of the joint between the intercondylar tubercles.
- Simplification of the ground reaction force as it travels up the lower extremity (absorbs the force).
Middle of the thigh.
Genu Valgum
Tibiofemoral angle (between femoral and tibial longitudinal axis') is more than 185°. Compression forces present on lateral side of knee, distraction (tensile) forces on medial side of knee. Knees pointing inwards.
Genu Varum
Tibiofemoral angle is less than 175°.
Distraction (tensile) forces on lateral side.
Compression forces on the medial side.
Knees pointing outwards.
Range of Motion of Tibiofemoral Joint
Knee flexion (hip flexed/hip extended): 140/160° Knee extension: 0-5°(can be up to -3° because of laxity in PCL and hamstrings) Knee external rotation: 25-45° Knee internal rotation: 10-25° More knee flexion allows for greater rotation, less knee flexion reduces rotation due to tightness of collateral + cruciate ligaments and knee joint capsule.
Arthrokinematics of the Knee Joint
Flexion OKC: concave tibia gliding on convex femoral condyles, antero-posterior (front to back).
Extension OKC: concave tibia gliding on convex femoral condyles, postero-anterior (back to front).
Flexion CKC: convex femur gliding on concave tibia, postero-anterior (back to front).
Extension CKC: convex femoral gliding on concave tibia, antero-posterior (front to back).
Limitation of Knee Flexion
Contact of the thigh and calf muscles.
Agonists and Synergists of Knee Flexion
Agonist: Biceps femoris, semitendinosus, semimembranosus.
Synergist: None
Hamstrings
Knee flexors and hip extensors.
As the hip flexes, distance between the hamstrings attachments increases as they wrap around the ischial tuberosity.
Difficult to keep knee fully extended with hip flexion because of tension of hamstrings.
Hamstrings lose some of their efficiency with hip extension.
Agonists and Synergists of Knee Extension
Agonist: Rectus femoris, vastus lateralis, vastus medialis and vastus intermedialis.
Synergist: None.
Agonists and Synergists of Knee External Rotation
Agonist: Biceps femoris and popliteus (knee extension)
Synergist: None
Agonists and Synergists of Knee Internal Rotation
Agonist: Semitendinosus and semimembranosus.
Synergist: Gracilis and sartorius.
More limited because of muscle strength and tibias ability to rotate on the femur.
Menisci
Tibiofemoral congruence is improved by the menisci, forming concavities into which the femoral condyles sit.
Crescent shaped fibrocartilaginous structures located between the femur and tibia.
Important for:
- Joint stability
- Shock absorption
- Load distribution across the joint
- Joint lubrication
Medial Menisci
Semi-circular shape (D)
Anterior horn attaches to the anterior part of intercondylar area of tibia (anterior to ACL).
Posterior horn attaches to posterior part of intercondylar between PCL and posterior horn of lateral menisci.
Entire periphery attached to the capsule.
Lateral Menisci
Circular shape (4/5 of a circle). Two horns attached close together. Anterior horn attaches to intercondylar eminence, posterolateral to ACL. Posterior horn attaches posteriorly to intercondylar eminence, anterior to posterior horn of medial menisci.
Meniscal Movements - Knee Extension to Flexion
Both menisci move posteriorly.
Medial menisci moves much less than lateral menisci.
Reason why medial is more prone to injury.
Lateral moves 2x more posteriorly to improve surface area.
Meniscal Movements - Knee Rotation
Both menisci follow the movement of femoral condyles.
During lateral rotation: medial menisci pulled forwards over the tibia while lateral is drawn posteriorly.
During medial rotation: Lateral menisci pulled forwards over the tibia while medial is drawn posteriorly.
Roles of the Ligaments of the Knee
- Limits excessive extension
- Limit varus and valgus stress
- Prevent anterior or posterior displacement of tibia on the femur
- Control medial or lateral rotation of tibia on femur
- Prevent combinations of anteroposterior displacements and rotations of the tibia (known as rotatory stabilization of the tibia)
Anterior Cruciate Ligament
Origin: Anterior intercondylar area of the tibia.
Insertion: Posterior and medial surface of the lateral condyle of the femur.
(medial tibia to lateral femur)
Role: Avoid extreme anterior displacements of the tibia on the femur.
High injury rate.
Consists of two bands:
- Anteromedial band (tightens with increased flexion)
- Postero-lateal band (taut in full extension)
Resists force better in full extension.
Which ligaments keep the femoral condyles in contact with tibial condyles during movements of the tibiofemoral joint?
ACL
PCL
Posterior Cruciate Ligament
Origin: Posterior intercondylar area of the tibia
Insertion: Anterior and lateral surface of the medial condyle of the femur
Role: Prevent extreme posterior displacements of the tibia on the femur
More adept at restraining motion with the knee flexed.
Absorbs 93% of posterior load on tibia with a fully extended knee.
The Cruciate Ligaments
Not prone to injury in full flexion and full extension.
ACL most vulnerable at 5° flexion.
PCL most vulnerable at 30° flexion.
Most injuries happen in a knee flexion doing rotational movements (changing direction).
Medial Collateral Ligament
Origin: Medial femoral condyle
Insertion: Medial tibial condyle + medial meniscus, medial surface of the capsule and tibial shaft
Role: Stability of the knee in the frontal plane, resists valgus stress
Lateral Collateral Ligament
Origin: Lateral femoral condyle
Insertion: Fibular head
Role: Limits varus stress
Stability of the Knee
Primarily by the collateral and cruciate ligaments.
Reinforced by the musculotendinous ties crossing the joint.
No danger of tearing collateral ligaments while running or walking because of side to side stress unless they are accompanied by the application of a violent
transverse force.
Screw-Home Mechanism of the Tibiofemoral Joint
During extension, the tibia rotates externally (OKC)
During flexion, the tibia rotates internally (OKC)
All ligaments tighten in this position (into
extension)
About 10° of rotational movement, due to unequal articular surface sizes
Occurs during final 20-30° of extension
Provides position of maximal stability in the joint (able to support body weight without quads activation)
Which muscle unlocks the knee extension?
Popliteus
Patellofemoral Joint
Diarthrodial plane joint between posterior surface patella and intercondylar groove or trochlear surface of the distal anterior femur.
The lateral facet of the femur is larger and extends more proximally to provide a bony buttress to improve patella stability.
Sulcus Angle
Angle between the lateral and medial femoral condyle.
- Greater angle: trochlea dysplasia (less depth of the trochlea) increases the likelihood of patella subluxation.
Dislocation of the Patella
More common on the lateral side because it has a greater contact area which means easier to slide.
Functions of the Patella
Act as an anatomic pulley for the quadriceps as the patella changes the direction of the extension force throughout knee ROM.
- Critical in the last 30° of extension
- At full knee extension, provides 31% of total knee extension torque, 13% at 90-120° flexion.
Bony shield for the anterior trochlea.
Reduce friction between the quadriceps femoris tendon and the femoral condyles.
In which position is the patella most mobile?
Full extension, because it has minimal contact with femur.
Q Angle
- One line runs from the tibial tuberosity to the center of the patella.
- Other line runs from the center of the patella to the anterior superior iliac spine.
Measures the lateral angle of pull of the quads on the patella. - Normal Q angle in men: 10-13°
- Normal Q angle in women: 15 -17°
Increased Q angle pulls the patella laterally.
Muscles Acting on the Patella
- Vastus medialis controls medial movement.
- Vastus lateralis controls lateral movement.
Crucial for balancing the central position of the patella during knee flexion/extension activities. If medialis is weak, patella can move laterally from greater lateralis pull.
Movement of the Patella - Extension/Flexion
Extension: Patella glides superiorly
Flexion: Patella glides inferiorly
Movement of the Patella - Articular Surface
Articulating surface of patella changes through the knee range of motion.
Contact area increases with increased knee flexion.
Serves to distribute joint forces over a greater surface area.
Wight-bearing (CKC) vs Non Weight-bearing (OKC) Exercises
Less force is on the patella in OKC.
Weight is behind the knee cap in CKC, creating more force on the patella.
