Functional anatomy of the knee

Knee structure and function

Hinge joint connecting the upper and lower leg; primarily allows flexion and extension with small amounts of rotation and side to side movement; transfers forces during weight bearing and depends on the feet, ankles, hips, and pelvis for stability

Planes of knee movement

Sagittal plane: flexion and extension; frontal plane: side to side movement; transverse plane: rotation

Knee ligaments and tendons

Quadriceps tendon connects the quadriceps to the patella; patellar ligament connects the patella to the tibia; MCL connects femur to tibia and LCL connects femur to fibula for side to side stability; ACL and PCL cross inside the knee to prevent excessive forward and backward tibial movement

Patella and femoral groove

Patella is the kneecap that glides over the femoral groove, which guides its movement; proper tracking prevents excessive pressure and irritation

Menisci

Medial and lateral cartilage structures between the femur and tibia that absorb shock and provide cushioning

Iliotibial band (IT band)

Dense connective tissue along the lateral thigh; originates from gluteus maximus fibers and inserts into the lower leg; helps decelerate internal rotation, and excessive tension from weak gluteus maximus can cause pain

Quadriceps group and individual muscles

Includes vastus lateralis (outer thigh), vastus intermedius (deep beneath rectus femoris), vastus medialis (inner thigh), and rectus femoris (crosses the hip and knee)

Quadriceps origin, insertion, and actions

Attach to the patella through the quadriceps tendon and tibia through the patellar ligament; extend the knee and stabilize the patella

Quadriceps function during movement

Lengthen and create tension during knee flexion to guide and stabilize the patella; decelerate knee bending during ground contact and squats; shorten during extension, with pressure on the patella decreasing as the knee straightens

Quadriceps bungee cord effect

Store elastic energy while lengthening under tension to help produce force during knee extension

Gluteus maximus structure and attachments

Large superficial muscle on the back of the hips and pelvis; originates from the posterior pelvis, sacrum, coccyx, and thoracolumbar fascia; inserts into the upper femur and IT band

Gluteus maximus actions and function

Extends the hip and externally rotates the leg; decelerates hip flexion and internal rotation to control knee and pelvic alignment

Gluteus maximus during walking and weakness

Slows internal rotation and prevents inward knee movement; weakness can contribute to valgus, overpronation, tracking problems, and increased IT band tension

Hamstring group and individual muscles

Includes semimembranosus and semitendinosus on the medial thigh and biceps femoris on the lateral thigh

Hamstring origins, insertions, and actions

Run from the pelvis down the back of the thigh and attach to either side of the lower leg; flex the knee, extend the hip, and assist with internal rotation of the lower leg when the knee is bent

Hamstring function during movement

Lengthen to decelerate knee extension and hip flexion; control forward bending during toe touching and stabilize the hips, pelvis, and lower back during weight bearing

Hamstrings and knee alignment

Act as guide ropes controlling side to side knee movement and helping prevent valgus, especially when the hip is flexed and the leg is relatively straight

Adductor group and individual muscles

Includes adductor magnus, adductor longus, and adductor brevis; located on the inner thigh, with magnus also assisting hip extension

Adductor origins, insertions, and actions

Individual attachment points are not listed in the slides; adduct the leg toward the midline and assist with hip flexion and extension

Adductor function during movement

Decelerate the leg as it moves away from the midline; lengthen to slow hip extension and internal rotation during walking and control the pelvis during weight transfer

Bungee cord effect

Muscles lengthen under tension to decelerate movement and store elastic energy that assists the next movement

Knee muscle stabilization

Muscles stabilize, decelerate, and accelerate movement in all three planes; gluteus maximus and adductors control side to side displacement, quadriceps guide patellar tracking, and hamstrings control knee alignment

Knee alignment deviations

Valgus occurs when the knee collapses inward toward the midline and is the most common deviation; varus occurs when the knee moves outward away from the midline

Knee valgus consequences

Can pull the patella laterally, disrupt tracking, contribute to overpronation, and increase pressure and irritation beneath the kneecap

Patellar tracking problems

Occur when the patella does not glide smoothly over the femoral groove during flexion and extension; can cause increased pressure, chronic irritation, inflammation, and dysfunction

Knee tracking and multiple planes

Although flexion and extension occur in the sagittal plane, the femur, tibia, and fibula also move slightly side to side and rotate, making frontal and transverse plane control important

Overpronation

Excessive inward rolling of the foot that can contribute to internal rotation of the leg and inward knee displacement

Chronic knee alignment problems

Repeated alignment problems can eventually become noticeable during static activities such as standing