Chapter 6 The Knee

Introduction Little bony support Tibiofemoral and patellofemoral joints rely on soft tissue structures to control forces transmitted through the joints Femur and lower leg = body’s longest lever arms

Clinical Anatomy Tibiofemoral joint – tibia, menisci, and femur Patellofemoral joint must also function properly Bones & Bony Landmarks Figure 6-1, pg 186, Figure 6-2, pg 187 Femur Linea aspera Medial and lateral condyles Medial and lateral epicondyles

Clinical Anatomy Tibia Patella Fibular head Medial and lateral tibial plateaus Tibial tuberosity Patella Fibular head Proximal tibiofibular syndesmosis

Articulations and Ligamentous Support Double condyloid articulation 2 planes of motion: flexion/extension and internal/external rotation Accessory motions: valgus/varus and anterior/posterior glide

Joint Capsule Figure 6-3, pg 187 Fibrous capsule surrounds circumference of knee jt Medial, anterior, and lateral aspect Capsule arises superior to femoral condyles and attaches distal to tibial plateau Posterior aspect Capsule arises from the posterior margins of femoral condyles above joint line and attaches to posterior tibial condyle Reinforcement from ligaments and muscles

Joint Capsule Synovial capsule lines articular portions of fibrous joint capsule Medially, anteriorly, and laterally Surrounds condyles of femur and tibia Posteriorly Runs anteriorly along femur's intercondyler notch and tibia’s intercondyler eminences, excluding the cruciate ligaments

Collateral Ligaments Figures 6-4, pg 188 MCL - Primary medial stabilizer of knee Deep layer: thickening of joint capsule and attaches to medial meniscus Superficial layer: separated from deep layer by a bursa, arises just below adductor tubercle and inserts 7-10 cm below joint line Protects knee against valgus stress Secondarily against external rotation of tibia and anterior translation of tibia on femur, especially in absence of intact ACL

Collateral Ligaments Figures 6-5, pg 188 LCL No attachment to meniscus or capsule Arises from lateral femoral epicondyle and inserts on proximal aspect of fibular head Protects knee against varus stress when knee is between full extension and 30o of flexion Secondarily against internal and external rotation of tibia

Cruciate Ligaments ACL Figures 6-6, pg 189 Arises from anteromedial intercondyler eminence of tibia, travels posteriorly, passes lateral to PCL and inserts on medial wall of lateral femoral condyle Stabilizes against: Anterior translation of tibia on femur, internal and external rotation of tibia on femur, and hyperextension of tibiofemoral joint

Cruciate Ligaments ACL has two segments that change positions as the knee flexes, causing the ACL to wind upon itself Anteromedial bundle Posterolateral bundle Figure 6-7, pg 189 Strain placed on ACL PROM vs. AROM vs. RROM

Cruciate Ligaments PCL Arises from posterior aspect of tibia and takes a superior and anterior course, passing medially to ACL, and attaches to lateral portion of femur’s medial condyle Stronger, wider than ACL; primary stabilizer of knee Provides restraint against: Posterior displacement of tibia on femur and external tibial rotation

Cruciate Ligaments Posterior support also from popliteus complex and posterior capsule Full extension – popliteus, posterior capsule, and other joint structures Midrange (40-120 degrees of flexion) – anterolateral bundle of PCL Beyond 120 degrees of flexion – posteromedial bundle of PCL

Arcuate Ligament Complex Figure 6-9, page 190 Arcuate ligament complex Arcuate ligament, LCL, oblique popliteal ligament, popliteus tendon, & lateral head of gastrocnemius Provides support to posterolateral joint capsule Assists in controlling posterolateral rotary instability; injury to area results in increased external rotation of tibia on femur

Proximal Tibiofibular Syndesmosis More stable than distal syndesmosis Superior anterior and posterior Tibiofibular ligaments Anterior displacement is blocked by bony outcrop of tibia Fibular instabilities tend to occur posteriorly, affecting peroneal nerve

The Menisci Fibrocartilaginous medial and lateral menisci Menisci serve to: Deepen articulations of knee joint; increasing load transmission over a greater percentage of surface Improve lubrication for articulating surfaces Provide shock absorption Increase stability of joint

The Menisci Figure 6-10, page 191 Wedged shaped, thick outer borders Knee is more stable in weight bearing Each menisci is divided into anterior, middle, and posterior thirds Vascular vs. avascular zones Medial (C-shaped) vs., lateral (O-shaped)

The Menisci Coronary ligament Transverse ligament Attaches menisci at their peripheries to the tibia Transverse ligament Joins anterior horns of each menisci Patellomeniscal ligaments Connects menisci to patella tendon Ligament of Wrisberg and ligament of Humphrey

The Menisci Knee extension Early flexion Later ROM Patellomeniscal ligaments pull lateral meniscus anteriorly, distorting its shape Early flexion Popliteus pulls lateral meniscus posteriorly Later ROM Meniscofemoral ligament pulls posterior horn medially and anteriorly

Muscles of the Knee Table 6-1, pages 192-193 Primarily serve to flex and extend Anterior muscles Figure 6-11, page 191 Posterior muscles Figure 6-12, page 194 Popliteal fossa, figure 6-13, page 195

Muscles of the Knee Pes Anserine muscle group Iliotibial Band Figure 6-14, page 195 The Screw Home Mechanism Unequal sizes of femoral condyles and the tightening of the cruciate ligaments as they wind upon themselves during flexion necessitates a locking mechanism as the knee nears its final degrees of extension