Primary Lab Objectives:
- Dissect the joint that was assigned to your table (see table list posted on Bluedocs).
- In addition to your assigned joint, dissect ONE more joint from the following list:
- View dissections of remaining joints at other tables.
Each table should dissect two joints. First, you will dissect the joint that was assigned to your table. Then, consult with the lab instructors to choose one of the remaining joints for dissection and demonstration to fellow students. Make sure that you view dissections of the remaining joints at other tables.
General note for whole lab: These dissections will involve carefully moving the musculature, vasculature and nerves away from the areas immediately surrounding the joint that you are dissecting. This will take a little finesse. Get advice from your instructors on how to preserve structure when possible. At the back of the knee, for example, this will be a challenge but many structures can be pulled to one side to when you open the capsule. In the same way, for the wrist or ankle, muscles transected above or below those joints can be easily preserved. And, of course, remember that not all tables dissect the same joints. As a result you can examine muscles and nerves and vessels intact on cadavers on which other dissections were performed.
1. Knee Joint Objectives and Goals (PLAY MOVIE -courtesy of Dr. Tom Gest. Note that they cut and reflect much more of the quadriceps than is necessary, so you should only use this video as a guide to the anatomy. For your actual dissection, please follow the specific instructions below.)
- Examine the bones that contribute to the knee joint.
- Review the muscles that cross the knee joint.
- Examine the posterior aspect of the knee.
- Examine the medial and lateral portions of the joint capsule, and dissect the medial and lateral collateral ligaments.
- Open the knee and find the cruciate ligaments.
- Examine the menisci of the knee on the tibia.
1. BONES OF THE KNEE JOINT
- Examine the bones of the knee: the femur, tibia, and patella.
The patella is a sesamoid bone that develops in the tendon of the quadriceps muscle. It is considered part of the knee joint complex as it provides the quadruceps muscle with greater leverage as it acts across the knee, but the patella plays no role in weight bearing or force transmission at the joint.
- On the distal end of the femur, identify the medial and lateral condyles, the intercondylar fossa,and the patellar groove.
- On the proximal tibia, identify the medial and lateral condyles and the intercondylar eminence.
2. MUSCLES OF THE KNEE JOINT
- Review the muscles that cross the knee joint (using the manual from the previous day for the details):
- Anterior: quadriceps
- Lateral: iliotibial tract (IT band), and biceps femoris
- Medial: sartorius, gracilis, and semitendinosus
- Posterior: popliteus, gastrocnemius, and plantaris
3. POSTERIOR KNEE
- Find the popliteus muscle. The popliteus is a small triangular muscle that stabilizes the knee by resisting medial rotation of the femur. It may also aid in unlocking an extended knee by rotating the femur laterally on the fixed tibia.
- Reflect the popliteus and the adjoining muscles.
NOTE: The posterior aspect of the knee joint and the synovial capsule are exposed above the popliteus muscle. The posterior capsule is reinforced by an extension from the tendon of the semimembranosus muscle, and the oblique popliteal ligament. Note the popliteus muscle passing into the fibrous capsule on the lateral side to insert on the lateral aspect of the lateral femoral condyle of the femur.
4. LATERAL AND MEDIAL KNEE
- Locate the tibial collateral ligament on the medial aspect of the knee joint.
NOTE: The tibial or medial collateral ligament (MCL) is a broad, flat structure about 1 inch wide and 4-5 inches in length that blends in with the joint capsule. It has superficial and deep portions. The deep portion has an attachment to the medial meniscus inside the joint capsule. The MCL can be better appreciated when the joint capsule has been opened.
Like all hinge joints, the knee joint displays collateral ligaments developed in the sides of the fibrous capsule to limit rotation and lateral excursion (adduction or abduction). Since the tibial and fibular collateral ligaments attach to the femur posterior to the joint axis of flexion and extension, they become taut in full extension and help to prevent hyperextension of the joint.
- Cut the tendon of insertion of the biceps femoris muscle and reflect it downwards to expose the fibular (or lateral) collateral ligament (LCL).
NOTE: The fibular or lateral collateral ligament (LCL) lies partially under the insertion of the biceps femoris muscle. The LCL is a short, round, cord-like ligament running from the lateral femoral condyle to the head of the fibula. It is outside the joint capsule and does not attach to the lateral meniscus. The tendon of the popliteus muscle lies between this ligament and the joint capsule.
5. INTERIOR OF KNEE
- Cut the quadriceps femoris tendon above the patella.
- Continue the cuts medial and lateral, stopping at the collateral ligaments.
- Reflect the patella and patellar ligament distally.
- Open the fibrous capsule of the knee joint from the front.
NOTE: The first structure you will see in the joint interior is the infrapatellar synovial fold. The anterior cruciate ligament is deep to this fold.
FUNCTIONAL ANATOMY: The anterior and posterior cruciate ligaments restrict dorsoventral sliding of the femur. The anterior cruciate ligament (ACL) attaches to the anterior medial portion of the intercondylar area. The posterior cruciate ligament (PCL) attaches to the posterior portion of the intercondylar area. The two cruciate ligaments cross in the intercondylar fossa of the femur. Note that the cruciate ligaments lie outside the synovial capsule (as do other elements of the fibrous capsule), while the menisci project into the synovial cavity (as do the articular discs in other synovial joints).
- Abduct the leg away from the thigh at the knee.
- Put your finger on the medial collateral ligament (MCL) and notice how it tightens when the leg is abducted.
- Cut the MCL slightly above the joint line.
- Continue to abduct the leg and note how the ACL becomes tight.
- Move the joint back into normal position and attempt to pull the tibia forward with the knee bent 90 degrees.
- Note how much the tibia can slide across the femur.
- Abduct the leg away from the thigh.
- Cut the ACL, but leave the PCL intact.
- Put the joint back into normal position with the knee bent 90 degrees and pull the tibia forward while holding the femur.
- Note how much movement there is now in the joint.
- Open the knee joint again and examine the two menisci sitting on top of the tibia.
2. SHOULDER JOINT (PLAY MOVIE-courtesy of Dr. Tom Gest)
Before you begin please refer to the articulated bones of the upper limb in your bone box, the model room, or a skeleton in the lab.
1. BONES OF THE SHOULDER JOINT
- Identify the following joints and bony landmarks:
- The sternoclavicular and acromioclavicular joints, both part of the shoulder joint complex.
- The shoulder joint (Consider both the humeral and the scapular components. Consider the interface between the glenoid fossa and the humeral head, and the ligaments and tendons that cross this joint).
- The anatomical neck of the humerus (separating the head from the shaft).
- The surgical neck of the humerus (on the shaft).
- The bicipital groove and the greater and lesser tubercles.
2. MUSCLES OF THE SHOULDER JOINT
- To begin the shoulder dissection, place the cadaver in the supine position.
- Remove the coracobrachialis muscle and the short head of the biceps brachii muscle from the coracoid process.
- Examine the insertion of the subscapularis on the humerus and leave this muscle intact.
- Turn the cadaver over into the prone position.
- Observe that the tendons of the supraspinatus, infraspinatus, and teres minor muscles blend with the joint capsule and provide structural support.
- Cut the tendons of these muscles and reflect them proximally.
- Cut the long head of the triceps muscle from the scapula and reflect it distally.
The fibrous capsule of the shoulder joint should now be exposed.
The shoulder joint (glenohumeral joint) is a multiaxial ball and socket type synovial joint with a wide range of motion. The shoulder joint has a greater degree of freedom of movement than any other joint in the body. By necessity, this freedom of movement requires laxity of the joint capsule, and as a result, there is relative joint instability. As you will see below this is especially true for the inferior (caudal) part of the joint.
Functional stability of the shoulder joint depends largely on the labrum and the surrounding muscles and tendons, particularly the muscles of the rotator cuff (subscapularis, supraspinatus, infraspinatus, and teres minor).
3. FIBROUS CAPSULE
- With the fibrous capsule now exposed (except in front where the subscapularis muscle remains intact), verify that the capsule is attached to the glenoid cavity slightly proximal to and encompassing the labrum.
- Verify that the capsule attaches around the anatomical neck of the humerus.
- Use a scalpel to open the posterior aspect of the joint capsule.
- Using a chisel, remove the head of the humerus as close as possible to the anatomical neck.
- Pull out the head of the humerus with your fingers, forceps, or hemostats.
4. SYNOVIAL CAVITY
- Explore the extent of the synovial cavity and identify the following structures:
- Glenoid cavity: around its margin, note a fibrocartilaginous rim; the glenoid labrum.
- Three bands reinforcing the front of the joint capsule (as seen from the posterior aspect): the glenohumeral ligaments. They converge on the supraglenoid tubercle.
- Tendon of long head of biceps brachii muscle.
Note that the joint capsule is relatively thin and does not provide stability by itself.
The capsule is reinforced internally in a number of interesting ways:
- Around the rim of the glenoid, there is a fibrocartilaginous rim called the glenoid labrum. The labrum increases the surface area and, like the knee menisci, may help distribute pressure. It also provides stability by encompassing more of the humeral head. The tendon of the long head of the biceps attaches at the supraglenoid portion of the labrum, and the excessive contraction of this muscle or rapid acceleration of the humerus away from the glenoid can tear the labrum.
- There are also three bands reinforcing the ventral side of the joint capsule (as seen from the posterior aspect). These are the glenohumeral ligaments. They have a superior, middle, and inferior portion arising near the anatomical neck and converging on the supraglenoid tubercle.
There are strong external supports as well:
- The coracoacromial ligament from the coracoid process to the acromion together with the acromion and the coracoid process forms a continuous ligamentous and bony protection, a kind of “roof” for the joint capsule that is sometimes called the coracoacromial arch. It prevents upward displacement of the head of the humerus.
- Cranially, posteriorly, and anteriorly the joint capsule is reinforced by rotator cuff muscles that produce a kind of half-wall on the front and back of the joint.
- Another powerful reinforcing structure is the tendon of the long head of the biceps brachii muscle that runs through the superior part of the capsule. This is clearly visible in this dissection.
3. Elbow joint
1. BONES OF THE ELBOW JOINT
- Examine the bones of the elbow joint: the humerus, radius, and ulna.
All three bones share one synovial capsule.
2. LIGAMENTS OF THE ELBOW JOINT
- Clean off the muscles surrounding the elbow joint.
- On the medial side of the joint, identify the ulnar collateral ligament.
- On the lateral side of the joint, identify the radial collateral ligament running from the lateral epicondyle of the humerus to the anular ligament surrounding the head of the radius.
- Note that the radius can freely rotate within the anular ligament.
The anular ligament prevents the radius from being pulled downward and dislocated while allowing rotation associated with supination and pronation. Before you cut any ligaments as instructed below, perform the motion of pronation and supination with your cadaver.
3. SYNOVIAL CAVITY
- Open the elbow joint by making a transverse cut through the anterior surface of the joint capsule between the ulnar and radial collateral ligaments.
- Use a probe to explore the extent of the synovial cavity.
4. Wrist joint
1. BONES OF THE WRIST JOINT
- Explore the wrist joint (radiocarpal joint).The radiocarpal joint is the articulation between the distal end of the radius and the proximal carpal bones.
- Note that the distal end of the radius articulates with only two carpal bones: the scaphoid and the lunate.
2. LIGAMENTS OF THE WRIST JOINT
- Remove all the tendons and soft tissue structures that cross the wrist.
- Note that the anterior and posterior surfaces of the wrist joint are reinforced by the radiocarpal ligaments.
- On the anterior surface of the joint capsule, cut transversely through the radiocarpal ligaments.
- This cut should be made proximal to the flexor retinaculum. Leave the hand attached to the forearm by the posterior part of the joint capsule.
Notice that the scaphoid and lunate bones must transmit forces from the hand to the forearm. Therefore, these carpal bones are the ones most commonly fractured in a fall on the outstretched hand. Also note that the many ligaments of the wrist help stabilize the carpal bones, although the lunate still often gets displaced.
3. FIBROCARTILAGINOUS DISK
- Examine carefully the fibrocartilaginous disk attaching the radius to the ulna.
- Perform supination and pronation with the cadaver and examine the ways in which that disk gets stretched and guides movement.
- Use the dissected specimen to perform movements at the wrist joint: flexion, extension, adduction, abduction, and circumduction.
- Observe the articular surfaces during these movements.
NOTE: A large part of the flexion and extension possible at the wrist occurs between the proximal and distal rows of carpals.
4. CARPOMETACARPAL JOINT OF THE THUMB
NOTE: The carpometacarpal joint of the thumb is a saddle joint between the trapezium and the first metacarpal bone.
- Remove the soft tissue structures covering the carpometacarpal joint of the thumb.
- Open the joint capsule posteriorly and examine the articular surfaces.
- Use the dissected specimen to perform movements at the carpometacarpal joint of the thumb: flexion, extension, adduction, abduction, rotation, and opposition.
- Observe the articular surfaces during these movements.
NOTE: Abduction and adduction occur at right angles to the plane of the palm, while flexion and extension take place in a plane parallel to the palm.
5. Ankle joint (PLAY MOVIE- courtesy of Dr. Tom Gest)
1. BONES OF THE ANKLE JOINT
- Review the bones and the bony landmarks of the ankle joint.
- The lateral malleolus is on the distal end of the fibula; the medial malleolus is on the distal end of the tibia.
- Distally the fibula and tibia cup around the trochlea of the talus. No muscle attach to the talus.
2. MUSCLES OF THE ANKLE JOINT
- On the anterior side of the lower leg and ankle, carefully cut the tendons, nerves and vessels that are crossing the ankle.
- Behind the medial malleolus, identify the tendons for the tibialis posterior, flexor digitorum longus, and flexor hallucis longus.
- Cut the tendon of the flexor digitorum longus.
- Leave the tibialis posterior tendon intact, but slide it forward over the mallelous.
- Leave the flexor hallucis longus in place.
3. LIGAMENTS OF THE ANKLE JOINT
- Identify the components of the deltoid ligament of the ankle. From back to front, it has four components:
- The posterior tibiotalar ligament
- The tibiocalcaneal ligament
- The tibionavicular ligament
- The anterior tibiotalar ligament
HINT: It is hard to see the parts of the deltoid ligament. It really is one very robust ligament. If the ankle is hypereverted it is more likely that the medial malleolus will fracture than that the deltoid ligament will tear.
- Identify the plantar calcaneonavicular (spring) ligament beneath the deltoid ligament.
- This ligament runs from the sustentaculum tali of the calcaneus to the tuberosity of the navicular.
- Anteriorly, the plantar calcaneonavicular ligament blends with fibers of the deltoid ligament.
- Turn the foot to work on the lateral side of the ankle.
- Identify the tendons of the fibularis longus and brevis muscles.
- Cut through the superior and inferior fibular retinacula, which are binding the fibularis longus and brevis tendons to the bone.
- Reflect the tendons of fibularis longus and brevis anteriorly to reveal the lateral ligaments of the ankle joint.
- Identify the three parts of the lateral ligament of the ankle, which supports the lateral side of the ankle:
Identify the anterior and posterior tibiofibular ligaments.
Using your cadaver, study the movements that occur at the ankle:
- The posterior talofibular ligament
- the calcaneofibular ligament
- the anterior talofibular ligament
- Dorsiflexion and plantarflexion are the primary movements that occur at the ankle joint.
- Inversion and eversion are possible at the subtalar joint.
The anterior talofibular ligament is the most commonly injured ligament at the ankle. This occurs when the foot is plantarflexed and inverted. Move the foot into that position and examine which ligaments are slack and which are tight.
- Sever the deltoid ligament so you can see the interior of the ankle joint.
- Examine the articulations of the fibula, tibia, and talus in the talocrural joint.
- Further consider the subtalar joint between the talus and the calcaneus.
Pulling the tibia forward while holding the femur in place is known as the anterior drawer test and is used clinically to determine if the ACL is torn. The posterior drawer test - pushing the tibia backward while holding the femur in place- is the equivalent test for a PCL tear.
Rotator Cuff Injury
The coracoacromial ligament runs between the coracoid process and the acromion, forming the coracoacromial arch. The space beneath the arch is the subacromial space. The supraspinatus muscle and subacromial bursa are in the subacromial space. Normally, the greater tubercle of the humerus, supraspinatus, and subacromial bursa fit comfortably beneath the coracoacromial arch during abduction. However, if the supraspinatus tendon is torn and becomes inflamed, or if the bursa is swollen, then the supraspinatus tendon will get pinned beneath the bony acromion during abduction, causing sever and chronic pain. This impingement phenomenon is similar to that which occurs in carpal tunnel, tarsal tunnel, or anterior compartment syndrome.
The shoulder joint is reinforced cranially, anteriorly, and posteriorly by the rotator cuff muscles that produce a kind of half wall on the front and back of the joint. In addition, the coracoacromial ligament provides a roof for the joint capsule, preventing upward displacement of the head of the humerus. Thus, the weak part of the shoulder joint is the inferior part of the capsule. Although this is rarely a problem, an abducted, rotated, and flexed humerus can bring this weak portion into a ventral position. If the humerus is levered forward by pressure on the distal half, the humeral head can dislocate through this space.