| Knee Biomechanics |
- Biomechanic Definitions
- Joint reaction force (R)
- tibiofemoral joint
- three times body weight with walking
- four times body weight with climbing
- patellofemoral joint
- up to 7 times body weight with squatting
- 2-3 times body weight descending stairs
- thickest aricular cartilage in body
- note: with patellectomy extension force decrease by 30%
- Instant center of rotation
- simultaneous triplanar motion makes analysis impossible
- posterior rollback of femur on tibia with maximal knee flexion
- "screw home" mechanism lead to internal rotation of femur with last 15° of extension
- tibia EXternal rotates on femur as the knee EXtends
- caused by size and convexity of the medial femoral condyle (MFC)
- axis of rotation is in the MFC
- ACL deficient knees
- Similar pattern of posterior femoral translation during progressive knee flexion with decreased axial rotation pattern after 30° of knee flexion
- TKA knee
- Reduced magnitudes of both posterior femoral translation and axial rotation and an increased incidence and magnitude of paradoxical anterior femoral translation
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Qbank (1 Questions)
TAG
(OBQ06.32)
Which of the following motions shows the greatest difference between a normal and ACL deficient knee?
Review Topic
DISCUSSION:
The study by Dennis et al, found a different axial rotation pattern in ACL deficient (ACL-D) knees compared to normal knees after 30° of knee flexion. Axial rotation was the same between the two groups in less than 30° of flexion. They also found normal and ACL deficient (ACL-D) knee patients demonstrated a similar pattern of posterior femoral translation during progressive knee flexion (0-120°). Additionally, the study showed increased variability in knee kinematic patterns observed in ACL-D knees as compared to the normal knees. Posterior femoral translation is substantially greater laterally than medially in both normal and ACL deficient patients, creating a medial pivot type of axial rotation pattern. With knee flexion, the normal tibia typically internally rotates relative to the femur and conversely, externally rotates with knee extension (i.e., screw home mechanism)
REFERENCES:
1.
Dennis DA, Mahfouz MR, Komistek RD, Hoff W. In vivo determination of normal and anterior cruciate ligament-deficient knee kinematics. J Biomech. 2005 Feb;38(2):241-53
PMID:15598450 (Link to Abstract)
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Please Rate Educational Value!
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1.0
q-143
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Average 1.0 of 28 Ratings
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Level of Evidence 5 and Other Journal Articles (includes Case Reports, Expert Opinions,
Personal Observations, and Biomechanic Studies)
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Dennis DA, Mahfouz MR, Komistek RD, Hoff W. In vivo determination of normal and anterior cruciate ligament-deficient knee kinematics. J Biomech. 2005 Feb;38(2):241-53
PMID:15598450 (Link to Abstract)
Textbooks
- Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
- AAOS Comprehensive Orthopaedic Review, Jay R. Leiberman. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2009
- Orthopaedic Knowledge Update 10, John M Flyn. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2011
- Hoppenfeld SP. Surgical Exposures in Orthopaedics: The Anatomic Approach. Lipponcott, Williams, and Wilkins, Philadelphia, PA, Copyright 2009
- Orthopaedic In-training Examination (OITE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
- Self-Assessment Examination (SAE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
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