Reading resources:
Moore and Agur, pp 247-250, 268-272
Objectives:
After the laboratory sessions you should be able to:
- Identify the bony and ligamentous features of the knee joint
- Identify the boundaries of the popliteal fossa
- Demonstrate the contents of the popliteal fossa
- Identify the muscles that act across the knee joint
On the femur (N 455) identify:
- linea aspera
- medial and lateral condyles
- medial and lateral epicondyles
- adductor tubercle
- intercondylar fossa
- popliteal surface
- Also, identify the patella, the tibia, fibula (N 476, 478)
On the tibia (N 478 – 479) identify:
- superior articular surface
- tuberosity
- shaft
- medial malleolus
- Posterior thigh and popliteal fossa
Identify again the following mucles in your specimens: semimembranosus, semitendinosus, and biceps femoris. Semimembranosus, semitendinosus, the long head of the biceps, and a component of the adductor magnus make up the group of muscles referred to as the hamstrings. These muscles originate from the ischial tuberosity. They act across two joints, the hip joint and the knee joint. They extend the thigh and flex the leg at the knee joint.
Using the atlas (Netter, 481) identify the muscular boundaries of the poplitealfossa, the diamond shaped space behind the knee. Superiorly the biceps femoris forms the lateral boundary while the medial boundary is formed by the semimembranosus and semitendinosus muscles. Inferiorly the boundaries of the popliteal fossa are formed by the medial and lateral heads of the gastrocnemius muscle. The floor of the popliteal fossa is formed by the popliteal surface of the femur, posterior part of the fibrous capsule of the knee joint, the oblique popliteal ligament, and the fascia of the popliteus muscle.
Trace the tibial and common peroneal nerves (N 482) into the fossa and clean the poplitealartery and poplitealvein (N 482) noting that they enter the fossa through an opening in adductor magnus called the adductor hiatus (Netter, 467). Note that the vein is more superficial than the artery.
Various arteries contribute to anastomoses around the knee. These include the genicular branches of the popliteal artery, a genicular branch of the femoral, and recurrent branches of the tibial (Netter, 477). You may not see the genicular arteries in your specimens at this time. Do not spend a lot of time looking for them, but understand that there are several pathways of collateral blood flow to the leg in the case in which the popliteal artery is occluded at the adductor hiatus.
You should be able to identify two branches of the popliteal artery in the popliteal fossa, the anterior tibial artery and the posteriortibial artery (N 483). The popliteal artery divides into anterior and posterior tibial arteries just below the popliteus muscle.
Knee joint
Identify the bony features contributing to the articulating surfaces of the knee joint are: the medial and lateral femoral condyles, the medial and lateral tibial condyles, and the patella.
Identify the fibrous capsule of the knee joint. It is attached to the margins of the femoral condyles and the tibial condyles posteriorly (N 476). It is strengthened by several ligaments. Identify the lateral collateral ligament (fibular collateral ligament) and the medial collateralligament (tibial collateral ligament). The fibular collateral ligament is a cord like structure between the lateral epicondyle and the head of the fibula. It is well separated from the joint capsule. The tibial collateral ligament is broad band that for the most part blends with the joint capsule. The tendon of the semimembranosus muscle expands to form the oblique popliteal ligament (N 476) which strengthens the joint capsule posteriorly.
Find a specimen in which the joint capsule has been opened. Note that the joint cavity is continuous with the suprapatellar bursa (N 476).
You have already identified two ligaments that attach the femur to the bones of the leg, the medial and lateral collateral ligaments. Now identify the anterior cruciate ligament and the posteriorcruciateligament (N 475). The anterior cruciate ligament attaches the anterior part of the intercondylar part of the tibia to the medial surface of the lateral condyle of the femur. The posterior cruciate ligament attaches the posterior part of the intercondylar part of the tibia to the medial condyle of the femur. The anterior cruciate ligament limits hyperextension and prevents backward displacement of the femur on the tibia. The posterior cruciate ligament limits forward displacement of the femur on the tibia. Both ligaments contribute stability to the knee joint.
(To find out how a damaged anterior cruciate ligament is repaired surgically check out the following internet link, http://www.scoi.com/aclrecon.htm)
Identify the medial and lateral menisci or semilunar cartilages (N 474, 476) which cover the articular surfaces of the tibia. Note that the medial collateral ligament is attached to the medial meniscus. The menisci deepen the articular surfaces of the tibia and function as shock absorbers.
Muscles that act across the knee joint
Quadriceps femoris* extension
tensor fascia lata maintaining extension
gluteus maximus maintaining extension
sartorius flexion
semimembranosus* flexion
semitendinosus* flexion
gracilis* flexion
biceps femoris* flexion
gastrocnemius flexion
plantaris flexion (weak)
popliteus flexion
On the front of the knee joint observe the ligamentum patellae and the attachments of the rectus femoris and the 3 vasti muscles via the quadriceps tendon into the patella. The quadriceps femoris is the major extensor of the leg at the knee joint.
On the lateral side of the knee identify the insertion of the iliotibialtract (N 472, 473) into the lateral condyle of the tibia. You may recall that the gluteus maximus muscle and the tensor fascia latae muscle insert into the iliotibial tract.
These muscle help to maintain the leg in extension by their insertion into the iliotibial tract.Also on the lateral side of the knee, identify the insertion of the bicepsfemoris muscle on to the head of the fibula. The biceps femoris is one of the muscle that contribute to flexion of the leg at the knee joint.
On the medial side of the tibia, above the tibial tuberosity, identify the insertion of the semitendinosus tendon, the tendon of gracilis, and the tendon of sartorius (N 472). Also observe the insertion of the semimembranosus tendon on the medial condyle of the tibia. These muscle also contribute to flexion of the leg at the knee (although sartorius is a weak flexor at the knee).
On the posterior surface of the joint (N 476) identify the two heads of the gastrocnemius, the plantaris and the popliteus muscle. The medial head of the gastrocnemius originates from the femur, superior to the medial condyle; the lateral head originates from lateral condyle of the femur. The plantaris muscle originates from the femur, superior to the origin of the lateral head of the gastrocnemius (N 476). The gastronemius inserts into the calcaneus tendon (Achilles tendon) (N 481) along with a muscle deep to the gastrocs, the soleus muscle. Identify the plantaristendon. It also inserts into the calcaneus tendon. This muscle is very small and functionally not as important as flexors of the foot. The plantaris tendon however can be used to surgically repair damaged ligaments or other tendons.
Now identify the popliteus muscle (N 476, 483). This muscle takes origin from the lateral femoral condyle within the joint capsule, deep to the lateral collateral ligament. It extends down and medially to attach to the tibia. The part of the capsule that arches over the popliteus as it emerges through the joint capsule is called the arcuate poplitealligament.
When the popliteus contracts it causes lateral rotation of the femur on the tibia. This motion is facilitated by the fact that the two femoral condyles are shaped somewhat differently – the lateral condyle is shorter. This lateral rotation of the femur functions to ‘unlock’ the knee joint prior to flexion.
The gastrocnemius, plantaris and politeus (as well as the muscles of the posterior compartment of the leg) are all innervated by the tibial nerve.
Review questions
- What three structures in the knee joint are most likely to be damaged during injuries resulting from rotation of the body when the leg is fixed (as in many football injuries).
- Why are the cruciate ligaments referred to as anterior and posterior?
- What is the function of the anterior cruciate ligament?
- What is the anterior drawer sign?
- Which of the cruciate ligaments would be more likely to be damaged by a severe blow to the tibia in a car accident.
- Why is the medial meniscus damaged more often during knee injuries than the lateral meniscus.
- What are the chief flexors of the knee?
- What is the function of the popliteus muscle?
- What is a ‘Charley horse’?
Answers
- The anterior cruciate ligament, the medial meniscus and the medial collateral ligament.
- They attach to the anterior and posterior part of the tibia.
- The anterior cruciate ligament limits hyperextension and prevents backward displacement of the femur on the tibia.
- A test for a rupture of the anterior cruciate ligament consists of attempting to displace the tibia anterior. Abnormal anterior displacement of the tibia in this test is an ‘anterior drawer’ sign.
- The posterior cruciate ligament.
- Because the medial meniscus is attached to medial collateral ligament.
- Semimembranosus, semitendinosus, biceps femoris, gracilis.
- When the popliteus contracts it results in lateral rotation of the femur on the tibia; it functions to ‘unlock’ the knee joint prior to flexion.
- Contusion and tearing of muscle fibers sufficient to result in a hematoma. The term is often used to describe damage to the quadriceps muscle.
Revised: July, 2000
