Presentation on theme: "DISSECTION OF THE KNEE JOINT As you begin your dissection of the knee, keep in mind the characteristics associated with a typical synovial joint."— Presentation transcript:
DISSECTION OF THE KNEE JOINT As you begin your dissection of the knee, keep in mind the characteristics associated with a typical synovial joint.
Marieb; Fig. 8.3
How do you know these bones are from a right patellofemoral articulation? Note this ‘notch’ on this femoral condyle? That is one of the signs used to identify a lateral femoral condyle. You cannot tell from this view but the medial condyle probably projects further distally than the lateral condyle, which accounts for the typical valgus seen with most knees. Also, when viewing the tibial condyles, the medial one is the condyle with the greater anterior to posterior diameter.
1. Make an incision along the inguinal crease. 2. Next, make a midline incision from the center of cut #1 extending inferiorly over the center of the patella, then over the anterior portion of the leg, and over the center of the dorsum of the foot. 3. Next make transverse circumferential incisions at (a) the level of the infrapatellar border, (b) just superior to the malleoli, and (c) at the level of the metatarsal heads. SKIN INCISIONS
Then, reflect the skin from the midline, taking care not to damage the superficial structures (veins, and nerves) that lie immediately deep to it. Next, remove the superficial fascia and identify the deep fascia which surrounds the muscles of the thigh and leg. Remember that in the thigh, the deep fascia is called the fascia latae. The fascia lata thickens to form the strong iliotibial tract on the lateral side of the thigh.
As you begin your dissection, the knee may require considerable cleaning. For example, the knee on the left needs to end up looking comparable to the knee on the right. superficial veins But, as usual, try your best to protect the superficial veins, such as the short or lesser saphenous vein, and the great saphenous vein.
Great saphenous v. Small, or lesser, saphenous v. Great saphenous v.
The great saphenous vein lies posterior to the medial aspect of the knee, and then lies along the medial aspect of the thigh.
Identify the saphenous nerve located on the anterior and medial aspect of the leg. This nerve (which is a continuation of the femoral nerve) pierces the fascia lata superior to the knee and then generally accompanies the great saphenous vein on the medial aspect of the leg.
On the medial side of the knee, the saphenous n. passes anterior to the tendon of the adductor magnus m. and pierces the deep fascia between the tendons of the sartorius muscle and gracilis muscle.
Tibial (medial) collateral ligament Iliotibial tract Patellar tendon Sartorius m. Gracilis m. Semitendinosus m. Tibialis anterior m. It is important to recall many tendon and ligament attachment sites as you dissect the knee joint.
So, as you begin dissecting with the intention of finding the lateral collateral ligament, identify other major structures that cross the knee joint laterally. For example, find the iliotibial tract and its insertion onto the anterior portion of the lateral tibial condyle. Identify the tendon of the biceps femoris m. as it inserts onto the head of the fibula, which is also the distal attachment site for the lateral collateral ligament. Iliotibial tract Biceps femoris m.
Though I do NOT want you to cut the tendon of the biceps femoris (or the iliotibial tract), you should now be able to find the lateral collateral ligament. It originates from the lateral femoral condyle and inserts on the fibular head. It is a very thin ligament, being described as almost “strawlike” in appearance.
Now as you intend to find the medial collateral ligament, identify major structures that cross the knee joint medially, most importantly the tendons of the semitendinosus m., the gracilis m., and the sartorius m.. The medial collateral ligament will lie deep to, and slightly anterior to, these tendons. Semitendinosus m. Gracilis m. Sartorius m.
Semitendinosus m. tendon Gracilis m. tendon Sartorius m. tendon Medial collateral ligament
The medial collateral ligament originates at the adductor tubercle and then fans out as it attaches onto the tibial condyle. It is sometimes described as having a superficial and a deep layer, with the deep layer attached to the medial meniscus.
On one of the cadavers, we want to keep the capsule of the knee relatively intact. But remember that the keen capsule is deficient anteriorly.
But on the other knee, we want to be able to look into the cavity of the knee joint. This requires that the quadriceps tendon be cut transversely. The patella can then be reflected distally.
Once this is done, you can observe the articular surfaces of the patella, a significant amount of the articular surface of the femur, and you can also see portions of the synovial membrane. Note the significant degeneration of the articular surface of this femur.
As you look deeper into the joint, you can see the menisci and cruciate ligaments.
The medial meniscus is the larger of the two menisci. It has an attachment to the medial collateral ligament, so these two structures are often injured together.
The lateral meniscus is much more mobile than the medial meniscus.
The lateral meniscus is NOT attached to the lateral collateral ligament. In fact, the tendon of the popliteus muscle passes deep to the lateral collateral ligament. But by virtue of the attachment of the medial meniscus to the medial collateral ligament, this meniscus has a stronger attachment to the knee capsule and so exhibits less excursion than the lateral meniscus. These anatomical points should be visible in your dissection of this region.
Anterior cruciate ligament
Posterior cruciate ligament
View with both cruciate ligaments cut – do NOT do this cut unless you are asked to do so.