The knee complex

Tibiofemoral- condyloid joint (primary in one motion but has some secondary movement) [true knee joint]

Patellofemoral- gliding joint, patella largest sesamoid bone in body

Joints:

  • ligaments provide static stability

  • quads and hamstrings provide dynamic stability

  • articulating cartilage surfaces on the femur and tibia

  • medial and lateral menisci- menisci form cushions between bones, the menisci moves when we flex and extend the knee

Bones:

  • Tibia bears most of the weight

  • fibula serves most as muscular and ligament insertion

  • Intercondylar fossa is attachment sight for PCL and ACL

Proximal Tibia: second longest bone in body, flat tibia plateaus

Patella: largest sesamoid bone, inbedded tendon of quadriceps, increases moment arm and angle of pull to be more efficient at the knee, reduce friction at knee joint

proximal fibula: not much for knee joint function, it is the attachment site for joint knee structures

Menisci: receptacles for large menisci condyles, moves with the femur by rolling and gliding, primarily avascular but the outer portion has the most blood supply, lateral meniscus is smaller and more mobile

menisci function: increase stability, decrease friction, increase contact area, minimal shock absorption

menisci injury: deep rotation is the most common knee injury think of deep squat with rotation, outer portion of menisci has blood flow so may fix itself but inner portion doesn’t so tear there may not heal

Joint will have bursae (help reduce friction in highly mobile areas) sacks, more then 10 sacks!

MCL: medial tibial collateral ligament

LCL: lateral fibular collateral ligament

MCL (medial resist valgus) and LCL (lateral resist varus) is in the frontal plane.. MCL sprain in isolation can usually heal itself…LCL less likely to get hurt, typically not under stress

Unhappy triad: ACL, MCL, meniscus, it is rare that only one part gets hurt

Cruciate ligaments: named for tibial attachments, cross through joint capsule

ACL (anterior crucial ligament): has multiple bundles, resist anterior translation, happens from plant and turn injuries for the most part, why we need muscle balance in quads and hamstrings

PCL (posterior crucial ligament): resist posterior glide of tibia on femur, tension increases as knee flexes, this is the car crash ligament (think sitting in car getting hit head-on tibia is pushed back a good amount and PCL breaks)

Knee alignments:

q- angle: angle created by two lines, 1. anterior superior spine of the ilium to middle of patella, 2. middle of patella to the tibial tuberosity

higher q angle means higher chance of knee injury, Males: 10-14 deg, Females 15-17 deg

abnormal q angles can be bad, small q angle is genu varum bowlegged, too high q angle means knock knees genu valgum

genu recurvatum is hyperextension of the knee, increased stress on acl

transverse plane- how tibia sits under femur, lateral verison: toe out, medial version: tow in

Screw home mechanism- femoral condyles and flat tibial plateaus, there has to be some rotation to sit into maximum contact position, 6 deg to 30 deg of internal rotation of tibia on femur occurs through 90 deg knee flexion

patella femoral articulations can be put in so many position

patella alta- increased distance between tibia and patella (high riding patella on femur)

patella baja (infera)- decreased distance between tibia and patella (low riding patella on femur)

Muscles of knee