Knee Anatomy

This joint is a hinge joint with movements of flexion and extension. Secondary movements consist of slight rotation both medial and laterally.

Also referred to as the tibial collateral. Crossed by the tendons of the sartorius, gracilis and semitendinous muscles. This ligament lies more posteriorly than anteriorly on the medial aspect of the knee. It has 2 layers - these being the deep and superficial.

A. Superficial = strong broad triangular shaped strap. It starts distal to the adductor tubercle and extends to approx. 6 cm below the joint line where it blends with the posterior medial capsule. It is separated from the capsule and meniscus by a small bursae.

B. Deep = this portion is actually a thickening of the capsule and attaches to the medial meniscus

The ligament is tight throughout the entire r.o.m. However, the anterior fibers are tightest on flexion, the posterior fibers in the mid range, and all of the fibers in full extension.


Medial View of Knee	Lateral View of Knee

Also called the fibular collateral. Extends from the lateral condyle of the femur to the fibular head. The tendon of the biceps femoris inserts just behind the ligament. The ligament is rounded. It is not attached to the lateral meniscus and is separated from it by a small fat pad. It should not be overlooked that the I.T. band and the tendon of the biceps femoris provide a portion of the lateral joint stability.

These ligaments bear a name, which means, " to cross". They are the primary rotary stabilizers of the knee. They are named for their attachments into the tibia. While they lie in the intracapsular space, they are extra synovial.

The ACL prevents anterior movement of the tibia on the femur. It checks external rotation of the tibia in flexion and to a degree checks hyperextension of the knee. It has 2 portions or bundles; the anterior medial and the posterolateral. The ant med bundle is tight in both flexion and extension, while the posterolateral is tight only upon extension. The least stress is placed on the ligament when the knee is positioned between 30 and 60 degrees of flexion.

The PCL is a strong fan shaped ligament that is the strongest in the body. It is the primary stabilizer against posterior movement of the tibia on the femur and it helps check the knee in extension. It also functions as the central axis of rotation and helps the ACL guide the knee into the screw home position. The bulk of the fibers are tight at 30 degrees of flexion, but the posterolateral fibers are loose in early flexion at approx. a position of 10 degrees of flexion.

The coronary, transverse, and the ligament of Wrisberg attach the meniscus together and tie them down.

The oblique and arcuate portions, along with the tendons of the semimembranous provide added posterior support of the knee joint.

The vastus medialis is connected to the medial ret. And the lateral vastus lateralis muscle is attached to the lateral ret. These structures help to stabilize the patella.

The articular surfaces between the femur and tibia are not congruent. They are closest in full extension. However this space must be filled by the meniscus.

The medial meniscus is "c" shaped and is thicker posteriorly than anteriorly.
The lateral meniscus is "o" shaped and generally of equal thickness.

Both menisci are thicker at their periphery and thinner towards the middle. They both move in flexion and extension. The lateral meniscus moving further posteriorly than the medial. The lateral meniscus is also not firmly attached to the collateral ligament. Or to the tibia as is the medial meniscus. Thus, it is less prone to distortion and injury.

The menisci are relatively avascular towards their inner 2\3's and somewhat vascular in their outer 1\3. They are held in place by the coronary ligaments.

A. Lubrication
B. Nutrition
C. Shock absorbers
D. Spread stress
E. Decrease articular cartilage wear
F. Make joint spaces more congruent
G. Prevent hyperextension

The menisci possess no nerves, thus there is no pain unless a coronary ligament has been damaged. There is seldom a bloody effusion, however, you might find synovial swelling.

Modified plane joint with the lateral articular surface being wider than the medial. It (the patella) also has the thickest layer of articular cartilage in the body.

The "Odd" facet is the one most frequently affected by chondromalacia. During the flexion and extension movement phases the different parts/facets of the patella articulate with the femoral condyles. Incorrect alignment of the patellofemoral joint can lead to premature arthralgia (degenerative changes). The patella improves the efficiency of extension during the last 30 degrees of extension. The patella also functions to:

A. Guide the quad tendon
B. Decrease friction
C. Control capsular tension
D. Act al bony shield
E. Improve aesthetic appearance of knee

Muscles

Muscles: Quadriceps
Vastus lateralis
Vastus intermedius
Vastus femoris
Vastus medialis

Semimembranosus
Semitendinosus
Biceps femoris long head [ the short head is only a 1 joint muscle ]

Pes Anserine muscle attachment is into the medial tibia.It consists of the sartorius semitendinosus and gracilis.

Bursae: water-filled sacs which provide a cushioning and a lubricating effect for soft tissues over bone.

Anterior:
Prepatellar bursae which lies between the patella and skin.
Infrapatellar bursae between the tibia and patella ligament.

Medial:
Lies between the head of gastroc and the articular capsule. Under the Pes Anserine and between the medial collateral ligament and the muscles and the muscles and skin.

Lateral:
Lies between the lateral collateral ligament and the biceps femoris muscle. There are more than 18 separate bursae in and around the knee.

This movement is executed by the biceps femoris, semitendinous, semimembranosus, gracilis, sartorius, gastrocnemius, popliteus, and plantaris.

This movement is executed by the quadriceps group consisting of the vastus medialis, vastus lateralis, vastus intermedius, and the rectus femoris.

Internal rotation: 10 degrees - Controlled by the semimembranous, sartorius, and gracilis.

Rotation of the tibia is limited and can only occur when knee is flexed. Several things occur to the knee structures as the joint is flexed, extended, or rotated.

Rotation is the partial result of the greater length of the medial condyle of the femur which rolls forward more than the lateral. The medial meniscus becomes distorted during this twisting due to the tibial attachment.

At the time of full extension, the lateral condyle of the femur becomes "set" on the tibia, while the medial condyle continues forward to a position of slight external rotation. This final movement is referred to as the screw home movement. The final muscles responsible for this motion are the vastus medialis oblique which extends the knee, but the popliteus muscle rotates the tibia to complete the screw home action.