Biomechanics Final *Knee* Flashcards by Richie S

What is the normal alignment of the knee in the frontal plane?

A slight valgus is normal

> ~20° is abnormal

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What are excessive frontal plane deviations for the knees?

Excessive Genu Valgum (Knock Knee) is <~165°

Genu Varum (Bow-leg) is >~180°

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What is Q Angle?
(Q is for Quads)

Another measurement of Valgus
- The Mechanical axis of the LE and combined vector of all 4 heads of the quadriceps.

(A line connecting the center of the ankle, knee, and hip. This is approximated by line parallel to patellar ligament)

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What are normal and abnormal Q Angles?

Normal: 10-15°

Abnormal: More than 20°

These are important factors in Patellofemoral joint pathologies

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What are the structures that the Anterior region of the joint capsule reinforces in connective tissue and Muscular-tendinous?

Connective Tissue Reinforcement :
- Patellar Tendon
- Patellar Retinacular Fibers

Muscular-Tendinous Reinforcement:
- Quadriceps

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What are the structures that the Lateral region of the joint capsule reinforces in connective tissue and Muscular-Tendinous?

Connective Tissue Reinforcement :
- LCL
- Lateral Patellar Retinacular fibers
- IT band

Muscular-Tendinous Reinforcement:
- Bicep Femoris
- Tendon of Popliteus
- Lateral Head of Gastrocnemius

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What are the structures that the Posterior region of the joint capsule reinforces in connective tissue and Muscular-Tendinous?

Connective Tissue Reinforcement :
- Oblique Popliteal Lig.
- Arcuate Popliteal Lig.

Muscular-Tendinous Reinforcement:
- Popliteus
- Gastrocnemius
- Hamstrings, especially semimembranosus tendon

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What are the structures that the Posterior-Lateral region of the joint capsule reinforces in connective tissue and Muscular-Tendinous?

Connective Tissue Reinforcement :
- Arcuate Popliteal Lig.
- LCL
- Popliteofibular Lig.

Muscular-Tendinous Reinforcement:
- Tendon of Popliteus

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What are the structures that the Medial region of the joint capsule reinforces in connective tissue and Muscular-Tendinous?

Connective Tissue Reinforcement :
- Medial Patellar Retinacular Fibers
- MCL
- Thickened Fibers posterior-medially

Muscular-Tendinous Reinforcement:
- Expansions from tendon of the semimembranosus
- Tendons of Sartorius, Gracilis, Semitendinosus (Pes Anserine)

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What happens to the Capsule and Ligaments of the knee when the knee is in flexion and extension?

When the knee is in flexion the ligaments and capsule as a whole are in slack

They are taut in extension

(Rotation in the transverse plane is only available when the knee is in flexion)

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What is Plica?

Embryonic folds in capsule

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What happens with the Medial Plica when the knee flexes and extends?

The plica unfolds during flexion and folds during extension

The fold can be pinched between tibia and femur
May mimic medial meniscus pathology
This is often palpable

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What is the role of the Menisci?

They reduce localized compressive stress
- increases concavity of tibial condyle (Joint stability)
- Weight distribution
- Reduces friction
- Not a Shock absorber; muscles absorb shock
Also gets nutrition through movement through diffusion and osmosis

Provides proprioception via tension on coronary ligs. and muscular attachments (Popliteus attaches lateral meniscus ; Semimembranosus attaches medial meniscus)

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Which meniscus is damage more frequently? What is the MOI? what is the classic presentation?

The medial meniscus is damaged more frequently

The MOI is usually un-controlled movement of femur on tibia in a closed kinematic chain, this causes pinching and tearing. Classic presentation is “Locking” of the knee.

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What happens if a meniscus injury is not repaired?

“Its the beginning of the end of your knee”
- There will be an increased of localized pressure (Compressive stress)

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How much Osteokinematic movement at the Tibiofemoral Joint with Flexion?

0 - 140°

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How much Osteokinematic movement at the Tibiofemoral Joint with Hyperextension?

WNL: 5 - 10°

> 10 is Genu Recurvatum

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How much Osteokinematic movement at the Tibiofemoral Joint with Internal and External Rotation?

At full knee extension, there is no rotation that occurs

At ~90° of knee flexion (Most rotation of tibia)
–40 - 45° total axial rotation

(External Rotation has more rotation than Internal Rotation; it s 2:1 Ratio)

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How much Osteokinematic movement at the Tibiofemoral Joint with Abduction and Adduction?

Total movement is ~6°
Passive only

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What is the Arthrokinematics movement at the Tibiofemoral joint during Open Chain Knee Extension?

The Tibia is moving on the Femur; Concave on Convex

During Knee Extension, the Tibia rolls and Glides Anteriorly

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What is the Arthrokinematics movement at the Tibiofemoral joint during Open Chain Knee Flexion?

The Tibia is moving on the Femur;Concave on Convex

During Knee Flexion, the Tibia rolls and Glides Posteriorly

What is the Arthrokinematics movement at the Tibiofemoral joint during Closed Chain Knee Extension?

The Femur is moving on the Tibia; Convex on Concave

During Knee Extension, the Femur Rolls anteriorly and glides posteriorly

What is the Arthrokinematics movement at the Tibiofemoral joint during Closed Chain Knee Flexion?

The Femur is moving on the Tibia; Convex on Concave

During Knee Flexion, the Femur rolls posteriorly and glides anteriorly

What does the ACL limit? When is it elongated?

Anterior Glide of Tibia
Posterior Glide of Femur
(The ACL is elongated during Extension)

What does the PCL limit? When is it elongated?

- Posterior Glide of Tibia - Anterior Glide of Femur (The PCL is elongated during Flexion)

What motion elongates both the ACL and PCL?

Rotation in the transverse plane

With the Screw Home Mechanism, what is required for Maximal Congruence?

Lateral Rotation is required for maximal congruence

With the Screw Home Mechanism, where does the Line of Gravity (LOG) fall?

The LOG falls anterior to a fully extended knee in normal posture

Why is the Screw Home Mechanism important?

- It allows for maintenance of the knee extension without muscular effort in normal standing effort. - It minimizes need for quad contraction at heel-off during normal gait

What motion does the MCL restrict? When is the MCL Taut?

- Valgus - Extension - Axial Rotation (Especially knee ER) - MCL is taut in Full Extension

What motion does the LCL restrict? When is the LCL taut?

- Varus - Extension - Axial Rotation - LCL is taut in Full Extension

How can the interaction with the quads affect the ACL?

Contraction of the quads extends the knee and slides the tibia anterior relative to the femur.

How can the interaction with the hamstrings affect the ACL?

Hamstring activation can limit anterior glide and tension on the ACL. (Because the hamstings place a posterior force on the tibia. - If the hamstrings are activated during the Anterior Drawer Test, it can result in a False-Negative

What is a common MOI for the MCL?

- Valgus producing force with foot planted - Severe hyperextension

What is a common MOI for LCL?

- Varus producing force with foot planted - Severe hyperextension

What is a common MOI for the Posterior Capsule?

- Hyperextension or combined hyperextension with external rotation

What is a common MOI of the ACL?

- Large valgus producing force with the foot firmly planted - Large axial rotation torque applied to knee with the foot firmly planted - Severe hyperextension

What is a common MOI of the PCL?

- Falling on a fully flexed knee (w/ ankle fully plantarflexed) - Any event that causes a forceful posterior translation of the tibia or anterior translation of the femur, especially while the knee is flexed - Large axial rotation or valgus-varus applied torque to the knee with the foot firmly planted, especially while the knee is flexed. - Severe hyperextension of the knee causing a large gapping of the posterior side of the joint

What is the Arthrokinematics with the Patellar-Femoral joint during extension?

There is a proximal glide during extension *Also as the knee angle changes, the contact areas change*

What are Major Pathologies linked to abnormal tracking?

- Chondromalcia (Abnormal growth of cartilage) - DJD Most Common: Excessive Lateral Knee Tracking secondary to Large Q-Angle

T/F: As the knee flexion increases, compressive forces increases?

True

What are the two interrelated factors associated with joint compressive force on the Patelleofemoral Joint?

- Force within the quad muscle - Knee flexion angle

What functional causes lead to excessive lateral tracking of the patella?

- Adhering of the IT band on Vastus Lateralis - Tightness of quads - Weakness of the hip abductors and external rotators

What structural causes lead to excessive lateral tracking of the patella?

- Genu Valgus - Femoral Anteversion - External Tibial Torsion

With abnormal forces on the Patellofemoral joint ("Excessive lateral tracking"), what is associated with chondromalcia?

- Excessive compressive force on lateral P-F - Insufficient compressive foce on medial P-F --Cartilage develops abnormally due to poor nutrition

Why is the Pes Anserinus group important?

*Sartorius, Gracilis, Semitendinosis* - All limit valgus and ER - At least on is activated when weight-bearing because of their actions at the hip joint

What are the forces on the Tibiofemoral joint with Genu Valgum?

- The medial structures are under tension - The lateral structures get shortened and tight over time - There is an increase of compression on the lateral condyle - Medial knee pain due to injuries to lig. and capsule - Lateral knee pain due to injury to meniscus and articular damage Will get DJD sooner on medial side Most like to injure LCL

What are the forces on the Tibiofemoral joint with Genu Varum?

- Lateral structures are under tension - The Medial structures get shortened and tight over time - There is an increase of compression on the medial condyle - Lateral knee pain due to injuries of lig. and capsule - Medial knee pain due to injury to meniscus and articular damage Will get DJD sooner on lateral side Most likely to injure MLC

What is a way to minimize risk of ACL tear?

With motor control training Ex. How to land from a jump

How happens if a person has weakness in the knee extensors?

- If the knee begins to flex or buckle, the muscles cannot stop it, so we choose to stay in extension - Over time, can develop Genu Recurvatum (Hyperextended Knee)