KNEE JOINT

When a person gets up from sitting position the femur internally (medially) rotates on the fixed tibia.

When the knee extends, the tibia descends down and then ascends along medial femoral condyle, which is about 1.5 cm longer than the lateral condyle. Along with this movement, the tibia also rotates externally.

Ref: Campbell’s Operative Orthopaedics, 11th Edition, Page 2416; Functional Soft-Tissue Examination and Treatment By Manual Methods, Warren I. Hammer, Part II, Extremities and Lumbar Spine, Page 312

Tensor fasciae latae extends from iliac crest to iliotibial tract.

It is involved in medial rotation of hip, abduction of hip, and stabilises knee during flexion and extension. 

Tensor fascia latae is innervated by the superior gluteal nerve, L4, L5, and S1.

The basic functional movement of tensor fascia latae is walking.

The tensor fascia lata is heavily utilized in horse riding, hurdling and water skiing. 

Quadriceps femoris extends the leg (rectus femoris and the vastus muscles) and helps flex the hip (rectus femoris). It is innervated by the femoral nerve, which is made from the contributions of L2, 3, and 4 in the lumbar plexus. If a patient could not adduct at the hip, the adductor muscles might be damaged. These are supplied by the obturator nerve,which also comes from L2, 3, and 4 in the lumbar plexus.

If a patient could not extend at the hip or flex the leg, the hamstring muscles might be damaged. These muscles are supplied by the tibial nerve, a branch of the sciatic nerve. If a patient could not rotate the knee medially, popliteus might be injured. This muscle, which is innervated by the tibial nerve, allows the knee to twist and unlock from a fully extended position, as in erect stance.

Popliteus rotates the tibia medially on the femur or, when the tibia is fixed, rotates the femur laterally on the tibia. At the beginning of flexion of the fully extended knee, lateral femoral rotation by popliteus muscle unlocks the joint.

A. i.e. Rectus femoris 

C. i.e. Quadriceps femoris 

C. i.e. Posterior horn of menisci move more than anterior

Ans. is. d. a and b both

Locking of knee joint (i.e. joint held in flexion) is seen in meniscus tear, loose body (d/t osteochondral fracture) and fractures of tibial spine 

Mechanism of Locking

Normally the medial meniscus or at least its anterior movable portion glides slightly backwards towards the interior of joint as the knee is flexed.

If the tibia is at the same time abducted (valgus) and the medial compartment of the knee thus opened up, the mobility of the meniscus is still further increased.

Sudden medial rotation of femur on the fixed tibia forces the medial meniscus towards back of joint and causes medial ligament to become taut and it may undergo variety of transverse or oblique tear.

The inner fragment slips into the interior of the joint and when , extension is attempted and the knee begins to screw home’ the fragment is nipped between the condyles and the joint is ‘locked’ i.e. held in flexion.

Ans. C: Popliteus

Popliteus muscle

Origin: Lateral surface of lateral condyle of femur

Insertion: Posterior surface of shaft of tibia above soleal line

Nerve supply: Tibial nerve L4, 5; S1

Action: Flexes leg at knee joint; unlocks knee joint by lateral rotation of femur on tibia and slackens ligaments of joint

The Muscle Shown is Biceps femoris responsible for Lateral Rotaion of Flexed Knee Joint

Biceps femoris:

·         Origin: Long head-upper part of ischial tuberosity

·         Short head-from the lateral lip of linea aspera, upper 2/ 3rd of lateral supra – condylar line Insertion: To head of the fibula

·         Nerve supply: Long Head -Tibial part of sciatic nerve; Short Head- Common Peroneal part of sciatic nerve

Movements at Knee Joint

Popliteus

Popliteus is a deep muscle of posterior compartment of leg.

Features of popletius are –

Origin

• Lateral surface of lateral condyle of femur, origin is intracapsular.
• Outer margin of lateral meniscus of knee.

Insertion

• Posterior surface of shaft of tibia above soleal line.

Nerve supply

• Tibial nerve

Action

• Ulocks knee joint by lateral rotation of femur on tibia prior flexion.
• Accessory flexor of knee.