Updated: 10/16/2018

Knee Biomechanics

Topic
Review Topic
0
0
Questions
7
0
0
Evidence
4
0
0
Videos
1
Cases
2
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Introduction
  • The knee is comprised of 2 joints
    • tibiofemoral joint
    • patellofemoral joint
Patellofemoral Articulation
  • Function
    • transmits tensile forces generated by the quadriceps to the patellar tendon 
    • increases lever arm of the extensor mechanism
      • patellectomy decreases extension force by 30%
  • Biomechanics
    • patellofemoral joint reaction force 
      • up to 7x body weight with squatting 
      • 2-3x body weight when descending stairs
  • Motion
    • "sliding" articulation
      • patella moves 7cm caudally during full flexion
    • maximum contact between femur and patella is at 45 degrees of flexion
  • Stability
    • passive restraints to lateral subluxation
      • medial patellofemoral ligament 
        • primary passive restraint to lateral translation in 20 degrees of flexion
        • 60% of total restraining force
      • medial patellomeniscal ligament
        • 13% of total restraining force
      • medial retinaculum
        • 10% of total restraining force
    • dynamic restraint
      • quadriceps muscles
    • Q angle
      • definition
        • line drawn from the anterior superior iliac spine --> middle of patella --> tibial tuberosity
      • normal Q angle
        • in extension
          • males
            • 13 degrees
          • females
            • 18 degrees
        • in flexion
          • 8 degrees
      • pathology
Tibiofemoral Articulation
  • Function
    • transmission of body weight from femur to tibia
  • Biomechanics
    • tibiofemoral joint reaction force
      • 3x body weight with walking
      • 4x body weight with climbing
  • Motion in sagittal plane
    • range of motion
      • 3 degrees of hyperextension to 155 degrees of flexion
      • thigh-calf contact is usually the limiting factor to full flexion
      • normal gait requires ROM from 0 to 70 degrees
  • Rotation
    • instant center of rotation
      • definition
        • point at which the joint surfaces are in direct contact
      • relevance
        • posterior rollback
          • as the knee flexes, the instant center of rotation on the femur moves posteriorly
          • allows for increased knee flexion by avoiding impingement
    • "screw home" mechanism
      • definition
        • tibial externally rotates 5 degrees in the last 15 degrees of extension
      • cause
        • medial tibial plateau articular surface is longer than lateral tibial plateau
      • relevance
        • "locks" knee decreasing the work performed by the quadriceps while standing
  • Stability
    • varus stress
      • lateral collateral ligament
    • valgus stress
      • superficial portion of medial collateral ligament
    • anterior translation
      • anterior cruciate ligament
        • attachments
          • origin
            • semicircular area on the posteromedial aspect of lateral femoral condyle
          • insertion
            • just anterior to and between the intercondylar eminences of the tibia
        • components
          • anteromedial bundle
            • tight in flexion
          • posterolateral bundle
            • tight in extension
        • function
          • primary static restraint to anterior translation
          • also plays a roll in axial rotation
    • posterior translation
      • posterior cruciate ligament
        • attachments
          • origin
            • anterolateral medial femoral condyle
          • insertion
            • tibial sulcus below articular surface
        • components
          • anterolateral
            • tight in flexion
          • posteromedial
            • tight in extension
        • function
          • primary static restraint to posterior translation
    • external rotation
      • posterolateral corner is the primary stabilizer of external tibial rotation
 
 

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Questions (7)

(SAE07SM.88) Significant anterior tibial translation occurs during which of the following rehabilitation exercises? Review Topic

QID: 8750
1

Terminal weight-bearing knee extension

18%

(10/55)

2

Terminal non-weight-bearing knee extension

35%

(19/55)

3

Terminal weight-bearing knee flexion

29%

(16/55)

4

Terminal non-weight-bearing knee flexion

7%

(4/55)

5

Mid-range weight-bearing knee flexion

9%

(5/55)

N/A

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(SAE07SM.74) What is the most accurate description of the relationship between gender and knee loading during landing while playing basketball? Review Topic

QID: 8736
1

Males have greater total valgus knee loading.

0%

(0/95)

2

Females have greater total valgus knee loading.

86%

(82/95)

3

Males have greater total varus knee loading.

2%

(2/95)

4

Females have greater total varus knee loading.

11%

(10/95)

5

There is no gender difference in total varus or valgus knee loading.

1%

(1/95)

ML 1

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PREFERRED RESPONSE 2
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(OBQ12.115) Which of the following best describes normal tibio-femoral joint kinematics ? Review Topic

QID: 4475
1

The femur undergoes internal rotation with knee flexion

8%

(397/4783)

2

The lateral femoral condyle remains stationary on the lateral tibia plateau during knee flexion from 0 to 120 degrees

2%

(116/4783)

3

The tibia undergoes internal rotation with knee flexion

58%

(2797/4783)

4

The medial femoral condyle moves posteriorly on the medial tibial plateau during knee flexion from 0 to 120 degrees

24%

(1140/4783)

5

Beyond 120 degrees of flexion only the lateral femoral condyle participates in femoral rollback

6%

(299/4783)

ML 4

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(OBQ06.32) Which of the following motions shows the greatest difference between a normal and ACL deficient knee? Review Topic

QID: 143
1

Posterior femoral translation at 30° flexion

49%

(606/1238)

2

Posterior femoral translation at 60° flexion

10%

(123/1238)

3

Axial rotation in full extension

9%

(112/1238)

4

Axial rotation at 50° flexion

28%

(352/1238)

5

Varus angulation at 30 ° flexion

3%

(38/1238)

ML 5

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PREFERRED RESPONSE 4
ARTICLES (9)
VIDEOS (1)
CASES (2)
Topic COMMENTS (16)
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