Knee Anatomy Biomechanics

What are the functions of the LCL?

• Checks varus stress of knee.

• Limits ER of tibia (OKC)

• Limits IR of femur (CKC)

What are the functions of the MCL?

• Checks valgus stress at full extension and 25° extension and anterior translation

When is the anterior and posterior bundle of the ACL taut?

• Anterior: taut through flexion

• Posterior: taut in extension to 20* of flexion

Lachman test is more posterior bundle

Anterior drawer is more anterior bundle

Why is open chain movements not favored over closed chain movements for ACL rehab, especially in the first 6-8 weeks?

40°-0° of resisted knee extension puts largest strain on ACL

When is the anterior lateral and posterior medial bundles of the PCL taut?

• Anterior lateral: taut in flexion

• Posterior medial: taut in extension

When is the PCL as a whole most taut?

Full knee flexion

Which parts of the meniscus is considered the “red zone” and which is considered the “white zone?” Why is it called this?

• Red zone (lateral 1/3rd): good blood supply allows for better prognosis

• White zone (medial 2/3rd): poor blood supple leads to poor healing

What part of the medial meniscus attaches to the ACL and PCL respectively?

• Anterior horn of medial meniscus attaches to ACL

• Posterior horn attaches to PCL

Explain the asymmetry of the femoral condyles.

• Lateral condyle is more anterior

• Medial condyle extends further inferiorly

Which side of the patella is the add facet located?

Medially, contact with full flexion

What is patella baja and alta?

• Patella baja: lower than normal patella position

• Patella alta: higher placement of patella than normal.

  • Less efficient mechanically.

Function of the IT band?

• Assists ACL to prevent posterior displacement of femur on tibia in terminal extension

• Additional connections to patella which adds lateral force to patella

High Q angle has a higher risk for what?

Lateral patellar subluxations

Increased Q angle will cause what things?

• genu valgum

• Increased femoral anteversion

• external tibial torsion

• Right lateral retinaculum

How does the tibia rotate during swing/stance phase of gait?

• Tibia IR in swing phase

• Tibia ER in stance phase

Explain the screw home mechanism of the tibia in OKC and CKC.

• OKC: tibia laterally rotates on femur during extension

• CKC: femur medially rotates on tibia during extension

What is the main stabilizer of the patella that prevents in from moving outwards?

Medial patellofemoral ligament (MPFL)

Where in knee ROM is the greatest area of contact between the patella and femur?

Between 90 and 60° of flexion

What is seen upon examination of a pt with quad tendon rupture?

• Acute knee pain, swelling, palpable defect at location of tear

• Loss of active extension and stability

• Unable to perform SLR with varying degrees of extension of lag depending on size of tear

What is found upon exam of a pt with patellar fx?

• Hematoma, edema, pain around involved area

• Ottawa and Pittsburg Rules for determining appropriateness for radiographs

• Tuning for test (significant pain)

What are the Ottawa and Pittsburg rules?

What would you see if a DVT is present?

• Discoloration, warmth, swelling, and tenderness of the affected extremity