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: Distribute weight. 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: Deep Infrapatellar: 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: Splits tendon of biceps femoris muscle. 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: Extension: 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: Anatomic axis: Extends along femoral shaft. 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.