Download KNEE - University of Kansas Medical Center

KNEE
Tibiofemoral Joint
Modified hinge joint.
 Articulating surfaces:

Femoral condyles:
Convex and asymmetric.
Medial condyle is larger than the lateral.
Condyles are separated anteriorly by
patellar groove.
Condyles are separated posteriorly by
intercondylar fossa.
Tibiofemoral Joint

Articulating surfaces:
Tibial plateaus:
Concave and asymmetric.
Articular surface of medial plateau is
50% larger than that of lateral.
Separated by intercondylar tubercles.
Menisci
Wedge-shaped fibrocartilage discs.
 Ends of menisci = horns:

Attached to intercondylar tubercles.

Coronary ligaments:
Attach menisci to rims of plateaus.

Anterior transverse ligament:
Joins menisci and allows them to move
together.
Menisci

Medial meniscus:
Larger of the two.
More securely attached.
Also attached to medial collateral ligament
and to semimembranosus muscle.
More often injured than lateral.
Menisci

Lateral meniscus:
Attached to posterior cruciate ligament:
Via meniscofemoral ligament.
Attached to popliteus muscle.
Menisci

Functions:
Enhance stability of knee:
Deepen articular surfaces.
Distribute weight.
Reduce friction between articular surfaces.
Menisci

Movement:
Medial meniscus moves posteriorly during
flexion:
Due to tension in semimembranosus muscle.
Medial meniscus drawn forward during
extension:
Due to tension in anterior capsular fibers.
Menisci

Movement:
Lateral meniscus moves posteriorly during
flexion:
Drawn by tension in popliteal expansion.
Distorts more than medial meniscus.
Joint Capsule
Large and lax.
 Deficient on lateral condyle:

For passage of popliteal tendon.
Anterior wall replaced by quadriceps
tendon.
 Excludes cruciate ligaments.
 Commonly communicates with synovial
bursae.

Bursae

Suprapatellar:
Upward expansion of synovial cavity
between femur and quadriceps muscle and
tendon.
Proximally receives insertion of articularis
genus muscle.
Bursae

Prepatellar:
Lies between superficial surface of patella
and skin.

Deep Infrapatellar:
Lies between patellar ligament and tibia.
Bursae

Subpopliteal.

Gastrocnemius:
Under medial head of gastrocnemius.
Bursae

Anserine bursa:
Between pes anserinus and tibial collateral
ligament.
Note: pes anserinus = combined tendons of
semitendinosus, gracilis, and sartorius.
Ligaments

Collaterals:
Medial (tibial):
Attachments:
Medial femoral condyle.
Proximal tibia.
Partly continuous with adductor magnus
tendon.
Attached to medial meniscus.
Distally separated from tibia by genicular
vessels and nerves.
Ligaments

Collaterals:
Lateral (fibular):
Splits tendon of biceps femoris muscle.
Separated from lateral meniscus by popliteal
tendon.
Ligaments

Anterior cruciate:
Weakest of cruciates.
Slack during flexion and taut during
extension.
Prevents backward sliding of femur on tibia.
Prevents hyperextension of knee.
Ligaments

Posterior cruciate:
Taut during flexion and slack during
extension.
Prevents forward sliding of femur on tibia.
Prevents hyperflexion of knee.
Movements

Flexion:
First part (0 to 25 degrees):
Posterior rolling and spinning.
Anterior sliding of femoral condyles on tibial
plateaus.

Extension:
First part:
Femoral condyles roll anteriorly and slide
posteriorly.
Followed by rolling and spinning of condyles.
Movements

Lateral-medial rotation of tibia:
At 90 degrees of knee flexion:
Up to 40 degrees of lateral rotation.
Up to 30 degrees of medial rotation.
Greater than 90 degrees of flexion:
Medial and lateral rotation ROM decreases.
Locking at Full Extension

During final few degrees of extension:
Femur rotates medially on tibia.
(Note that tibia would also rotate laterally on
femur.)
Knee is brought into close-packed position:
Tibial tubercles are lodged in intercondylar notch.
Menisci are tightly interposed between tibial and
femoral condyles.
= Locked or screw-home mechanism.

Popliteus laterally rotates femur for unlocking at
beginning of knee flexion.
Axes

Mechanical axis:
From head of femur to head of talus.
Almost equivalent to anatomic axis of tibia.

Anatomic axis:
Extends along femoral shaft.
Axes

Physiologic valgus:
Normal angle at knee where femoral and
tibial axes meet:
170 – 175 degrees.
Axes

Genu valgum:
Lateral deviation of tibia.
Less than 170 degrees.
Results in “knock knees.”
Axes

Genu varum:
Medial deviation of tibia.
Greater than 170 degrees.
Results in “bow legs.”
Patellofemoral Joint

During knee flexion/extension:
Central ridge of patella slides along central
groove of femur.
Patellofemoral Joint

During flexion:
Tibia moves posteriorly.
Ligamentum patellae pulls patella distally
and posteriorly:
Causes patella to remain firmly in apposition
to femur.
Patellofemoral Joint

During extension:
Patella is pulled proximally by quadriceps.
Vastus lateralis tends to pull patella laterally.
Vastus medialis oblique counteracts vastus
lateralis.
Patellofemoral Joint

Q-angle:
Formed by vector of quadriceps:
From ASIS to middle of patella.
And vector of pull of ligamentum patellae:
From tibial tubercle to middle of patella.
15 degrees.