# Lecture 16: Surface Anatomy and Clinical Procedures ## Unit 1.3: Human Gross Anatomy I - Musculoskeletal System --- ## Learning Objectives By the end of this lecture, students will be able to: 1. Identify key surface anatomy landmarks of the trunk and limbs 2. Describe the anatomical basis for common clinical procedures 3. Demonstrate proper techniques for physical examination 4. Identify safe anatomical approaches for injections and aspirations 5. Correlate surface anatomy with underlying structures 6. Apply anatomical knowledge to emergency and routine clinical procedures --- ## Lecture Content ### I. Surface Anatomy of the Back and Trunk #### Posterior Surface Landmarks The vertebra prominens, the spinous process of C7, represents the most prominent cervical spinous process and is readily palpable at the base of the neck at the cervicothoracic junction. Moving inferiorly, the root of the spine of the scapula lies at the level of T3 when the arms are at the sides. The inferior angle of the scapula corresponds to T7, though this landmark moves with arm position. The inferior border of the twelfth rib lies at the L2-L3 level, marking the approximate location of the kidneys. The highest point of the iliac crest is palpable and corresponds to the L4 vertebral level, serving as a crucial landmark for lumbar puncture. The posterior superior iliac spines lie at the S2 level and are often marked by the dimples of Venus, small depressions visible in many individuals. The sacral hiatus, located at S4-S5, provides access for caudal epidural injections. #### Anterior Surface Landmarks The suprasternal notch, also called the jugular notch, is palpable at the superior border of the manubrium at the base of the neck, corresponding to the T2-T3 vertebral level. The sternal angle marks the junction of the manubrium and body of the sternum at the T4-T5 level. This landmark indicates the attachment of the second rib, providing the key reference for counting ribs. The xiphoid process lies at T9-T10 at the inferior end of the sternum. The umbilicus lies at approximately L3-L4, though this varies with body habitus. The anterior superior iliac spine is palpable at the anterior extremity of the iliac crest and marks the lateral attachment of the inguinal ligament. The pubic symphysis lies in the midline anteriorly, and the pubic tubercle, palpable lateral to the symphysis, marks the medial attachment of the inguinal ligament. Panel A: Posterior torso view showing vertebra prominens (C7), spine of scapula root (T3), inferior scapular angle (T7), and 12th rib (L2-3) with vertebral level reference bar. Panel B: Posterior torso continued with iliac crest (L4), PSIS with dimples of Venus (S2), and sacral hiatus (S4-5) as landmarks for lumbar puncture and caudal epidural. Panel C: Anterior torso view showing jugular notch (T2-3), sternal angle (T4-5) with rib 2 indicator, and xiphoid process (T9-10). Panel D: Anterior torso continued with umbilicus (L3-4), ASIS, pubic symphysis, and pubic tubercle with inguinal ligament between ASIS and pubic tubercle indicated. --- ### II. Surface Anatomy of the Upper Limb #### Shoulder Region The acromion forms the tip of the shoulder and represents the lateral-most bony prominence, palpable as a flat surface at the lateral end of the spine of the scapula. The entire length of the clavicle is subcutaneous and palpable from the sternoclavicular joint to the acromioclavicular joint. The coracoid process lies deep to the anterior fibers of the deltoid muscle and can be palpated by pressing deeply inferior to the lateral third of the clavicle while the patient relaxes the shoulder. The greater tubercle lies immediately below the acromion and represents the attachment site of the rotator cuff muscles. The deltopectoral groove, the depression between the deltoid and pectoralis major muscles, contains the cephalic vein and marks the anterior boundary of the deltoid. The axilla is bounded by the anterior and posterior axillary folds and contains the neurovascular bundle to the upper limb. #### Arm and Elbow The biceps muscle is prominent on the anterior arm, becoming more defined with elbow flexion against resistance. The biceps tendon is palpable at the elbow crease, entering the cubital fossa. The medial epicondyle of the humerus is easily palpated at the medial elbow and is commonly called the funny bone because the ulnar nerve passes behind it in a superficial position. The lateral epicondyle serves as the common origin of the extensor muscles. The olecranon, the proximal projection of the ulna, forms the posterior prominence of the elbow and receives the insertion of the triceps tendon. The cubital fossa, the triangular depression anterior to the elbow, contains from lateral to medial the biceps tendon, brachial artery, and median nerve. #### Forearm and Hand The radial styloid process forms the lateral bony prominence at the wrist, lying slightly more distal than the ulnar styloid. The ulnar styloid marks the medial side of the wrist at the distal ulna. The anatomical snuffbox, the depression between the tendons of extensor pollicis longus medially and abductor pollicis longus and extensor pollicis brevis laterally, overlies the scaphoid bone and radial artery. Tenderness here suggests scaphoid fracture. The flexor tendons are visible on the anterior wrist, with palmaris longus, when present, being the most superficial and medial to it lies flexor carpi radialis. The thenar eminence, the muscular mass at the base of the thumb, contains the thenar muscles. The hypothenar eminence at the base of the little finger contains the hypothenar muscles. Peripheral pulses in the upper limb include the radial pulse at the lateral wrist, palpated lateral to the flexor carpi radialis tendon. The ulnar pulse lies medial, lateral to the flexor carpi ulnaris tendon. The brachial pulse is located medial to the biceps tendon at the elbow crease. Panel A: Shoulder landmarks showing acromion at shoulder tip, clavicle palpable along entire length, coracoid process deep to deltoid, greater tubercle below acromion, and deltopectoral groove with cephalic vein. Panel B: Elbow landmarks showing medial epicondyle (ulnar nerve posterior), lateral epicondyle, olecranon, and cubital fossa triangle with contents labeled (biceps tendon, brachial artery, median nerve). Panel C: Wrist and hand landmarks showing radial and ulnar styloids, anatomical snuffbox between EPL and APL/EPB tendons with scaphoid underneath, and thenar and hypothenar eminences. Panel D: Pulse points at radial (lateral to FCR), ulnar (lateral to FCU), and brachial (medial to biceps tendon) locations marked with finger positioning technique. --- ### III. Surface Anatomy of the Lower Limb #### Hip and Thigh The greater trochanter is the most lateral prominence of the hip, palpable approximately a hand's breadth below the iliac crest. The anterior superior iliac spine marks the anterior end of the iliac crest and serves as the lateral attachment of the inguinal ligament as well as the origin of sartorius. The inguinal ligament extends from the anterior superior iliac spine to the pubic tubercle, forming the superior boundary of the femoral triangle. The femoral triangle lies below the inguinal ligament and contains the femoral nerve, artery, and vein from lateral to medial, with the femoral pulse palpable here. The adductor muscles form the bulk of the medial thigh. The quadriceps muscles form the anterior thigh mass. The iliotibial tract is palpable as a fibrous band along the lateral thigh. #### Knee The patella is the most prominent anterior knee structure and moves with knee extension. The patellar ligament connects the patella to the tibial tuberosity and is palpable as a taut structure when the quadriceps is contracted. The tibial tuberosity lies distal to the patella at the patellar ligament insertion. The medial and lateral joint lines are palpable as depressions between the femoral and tibial condyles, best felt with the knee flexed; tenderness along these lines suggests meniscal pathology. The popliteal fossa is the diamond-shaped depression behind the knee, where the popliteal pulse lies deep against the posterior surface of the tibia. The head of the fibula is palpable on the lateral leg just below and posterior to the knee joint line; the common peroneal nerve wraps around this structure and is vulnerable to compression here. #### Leg and Foot The tibial shaft is subcutaneous along its entire anteromedial surface, making it readily palpable. The gastrocnemius muscle forms the bulk of the calf. The Achilles tendon, the strongest tendon in the body, is palpable from the gastrocnemius-soleus muscle mass to its insertion on the calcaneus. The medial malleolus is the distal projection of the tibia on the medial ankle. The lateral malleolus, the distal fibula, lies slightly more distal and posterior than the medial malleolus. The dorsalis pedis pulse is palpable on the dorsum of the foot, lateral to the tendon of extensor hallucis longus. The posterior tibial pulse is palpable behind and below the medial malleolus. The calcaneus forms the heel and is readily palpable. Panel A: Hip and thigh landmarks showing greater trochanter as lateral prominence, ASIS with inguinal ligament to pubic tubercle, femoral triangle with NAVL contents and femoral pulse point. Panel B: Knee region showing patella, patellar ligament, tibial tuberosity, medial and lateral joint lines with finger palpation technique, popliteal fossa diamond with deep pulse location, and fibular head with common peroneal nerve vulnerability. Panel C: Ankle landmarks showing medial malleolus (tibia) and lateral malleolus (fibula, more distal and posterior), Achilles tendon, and calcaneus. Panel D: Lower limb pulse points including dorsalis pedis (lateral to EHL tendon) and posterior tibial (behind and below medial malleolus) with palpation technique shown. --- ### IV. Physical Examination Techniques Physical examination of the musculoskeletal system follows a systematic approach beginning with inspection. The examiner observes for symmetry between sides, swelling or deformity, skin changes including bruising, erythema, or scarring, and muscle wasting indicating chronic disuse or denervation. Palpation assesses temperature differences suggesting inflammation, point tenderness localizing pathology, swelling character distinguishing soft tissue from bony enlargement, crepitus indicating roughened articular surfaces or fracture fragments, and pulse quality assessing vascular integrity. Range of motion testing evaluates joint function. Active range of motion performed by the patient tests the motor system including nerve, muscle, and joint function together. Passive range of motion performed by the examiner isolates joint and soft tissue contributions. Comparing sides helps identify subtle limitations. Special tests evaluate specific structures. At the shoulder, the empty can test assesses supraspinatus integrity by having the patient resist downward pressure with arms elevated and internally rotated. The Neer impingement sign elicits pain by passively forward flexing the shoulder, compressing the rotator cuff against the acromion. The apprehension test for anterior instability places the shoulder in abduction and external rotation, producing apprehension in patients with recurrent dislocation. At the elbow, valgus and varus stress tests assess collateral ligament integrity. Tinel's sign at the elbow, tapping over the cubital tunnel, reproduces tingling in the ulnar nerve distribution with ulnar neuropathy. At the hand and wrist, Finkelstein's test for de Quervain's tenosynovitis produces pain over the radial styloid when the thumb is held in the palm and the wrist is ulnarly deviated. Phalen's test for carpal tunnel syndrome reproduces paresthesias in the median nerve distribution when the wrists are held in flexion. Tinel's sign at the wrist produces similar symptoms when tapping over the carpal tunnel. Allen's test evaluates arterial supply by having the patient make a fist while the examiner occludes both radial and ulnar arteries, then releasing one at a time to assess hand perfusion through each vessel. At the hip, the FABER test positions the hip in Flexion, ABduction, and External Rotation, producing groin pain with hip pathology or sacroiliac pain with sacroiliac joint dysfunction. The Trendelenburg test assesses abductor strength by having the patient stand on one leg; dropping of the contralateral pelvis indicates weakness of the stance-side abductors. The Thomas test detects hip flexion contracture by fully flexing one hip to flatten the lumbar spine, then observing whether the contralateral thigh rises off the table. At the knee, the anterior drawer test assesses anterior cruciate ligament integrity by pulling the tibia forward with the knee flexed to ninety degrees. The Lachman test is more sensitive for ACL injury, performed with the knee in slight flexion. The posterior drawer test evaluates the posterior cruciate ligament. McMurray's test for meniscal tears combines flexion, rotation, and extension, eliciting pain or a click with meniscal pathology. Valgus stress tests the medial collateral ligament while varus stress tests the lateral collateral ligament. At the ankle, the anterior drawer test assesses the anterior talofibular ligament. Thompson's test evaluates Achilles tendon integrity by squeezing the calf with the patient prone; absence of passive plantarflexion indicates tendon rupture. Panel A: Lachman test positioning with one hand stabilizing femur and other pulling tibia forward in slight knee flexion to assess ACL integrity. Panel B: McMurray test showing rotation during extension with meniscus compression mechanism, positive when pain or click elicited. Panel C: Thompson test with calf squeeze showing expected plantarflexion response (normal) versus absent response indicating ruptured Achilles tendon. Panel D: Ankle anterior drawer showing examiner hand position and talus translation to assess anterior talofibular ligament integrity with positive finding indicator. --- ### V. Common Injection Sites #### Intramuscular Injections The deltoid muscle serves as the preferred site for most vaccinations due to accessibility and adequate muscle mass. The injection site is located two to three finger-breadths below the acromion in the central portion of the deltoid. This location avoids the circumflex humeral vessels and axillary nerve, which lie more inferiorly. The ventrogluteal site represents the safest location for gluteal intramuscular injections. The technique involves placing the palm of the hand on the greater trochanter with the index finger pointing toward the anterior superior iliac spine and the middle finger extending toward the iliac crest. The injection is given between these two fingers into the gluteus medius muscle. This site avoids the sciatic nerve and major blood vessels. The dorsogluteal site, traditionally described as the upper outer quadrant of the buttock, carries higher risk of sciatic nerve injury and is currently less favored. If used, the injection must remain well within the upper outer quadrant to avoid the nerve. The vastus lateralis on the lateral thigh provides a safe injection site for all ages, including infants, because of its distance from major neurovascular structures. The injection is given into the middle third of the outer thigh. Panel A: Deltoid injection site showing two-three finger measurement below acromion with injection point marked and danger zone inferiorly where axillary nerve and circumflex vessels lie. Panel B: Ventrogluteal site showing hand landmark technique with palm on greater trochanter, index finger to ASIS, and middle finger to iliac crest with injection between fingers into gluteus medius. Panel C: Vastus lateralis injection showing middle third of lateral thigh with safe zone marked due to distance from major neurovascular structures. Panel D: Underlying muscle cross-sections for each site showing needle depth and target muscle tissue with safe approach angles. --- #### Joint Injections and Aspirations General principles for joint procedures include strict sterile technique to prevent septic arthritis. Landmarks should be marked before skin preparation because antiseptic solutions obscure them. Tendons should be avoided to prevent damage. Entry through extensor surfaces when possible minimizes neurovascular risk. Shoulder glenohumeral joint injection can be performed through posterior or anterior approaches. The posterior approach enters approximately two centimeters medial and inferior to the posterolateral corner of the acromion, directing the needle toward the coracoid process. The anterior approach uses the coracoid process as a guide, entering just lateral and inferior to it. Elbow injection uses a lateral approach targeting the soft spot, the triangular depression bounded by the radial head, lateral epicondyle, and olecranon tip. With the elbow flexed to ninety degrees, this space becomes palpable and provides direct access to the joint. Knee injection commonly uses the superolateral approach. The needle enters superior and lateral to the patella, directed slightly posteriorly and inferiorly into the suprapatellar pouch. Alternative approaches include superomedial and direct lateral at the level of the inferior patellar pole. The superolateral approach is most commonly used due to accessibility and lower risk of cartilage damage. Ankle injection uses an anterior approach between the tibialis anterior and extensor hallucis longus tendons, just medial to the dorsalis pedis artery. The joint space is entered with the ankle in slight plantarflexion to open the anterior joint. Panel A: Shoulder posterior approach with entry point two centimeters medial and inferior to posterolateral acromion, needle trajectory toward coracoid, and cross-sectional view avoiding rotator cuff. Panel B: Elbow lateral soft spot triangle bounded by radial head, lateral epicondyle, and olecranon with needle positioned in center at 90-degree flexion. Panel C: Knee superolateral approach with entry superior and lateral to patella, needle directed into suprapatellar pouch for aspiration or injection. Panel D: Ankle anterior approach between tibialis anterior and EHL tendons medial to dorsalis pedis artery with foot in plantarflexion to open joint space. --- ### VI. Emergency Procedures #### Cricothyrotomy Emergency surgical airway access is performed through the cricothyroid membrane when other airway management techniques have failed. The cricothyroid membrane is located between the thyroid cartilage superiorly and the cricoid cartilage inferiorly in the anterior neck. The membrane is palpable as a soft depression between these two cartilages. A horizontal incision through the membrane provides rapid access to the airway. #### Needle Thoracentesis Tension pneumothorax requires emergent decompression. The standard approach uses the second intercostal space at the midclavicular line. The needle is inserted perpendicular to the chest wall immediately above the third rib to avoid the neurovascular bundle running in the costal groove of the second rib. An alternative site is the fifth intercostal space at the midaxillary line. #### Chest Tube Insertion Chest tube placement for pneumothorax or hemothorax typically uses the fourth or fifth intercostal space at the midaxillary line, within the safe triangle. This triangle is bounded anteriorly by the lateral border of the pectoralis major muscle, posteriorly by the anterior border of the latissimus dorsi muscle, and inferiorly by a horizontal line at the level of the fifth rib or nipple. The tube is inserted immediately above the rib to avoid intercostal neurovascular structures. Blunt dissection through the muscle layers and parietal pleura confirms entry into the pleural space before tube advancement. #### Lumbar Puncture Lumbar puncture for cerebrospinal fluid sampling or spinal anesthesia is performed below the level of the conus medullaris, which terminates at approximately L1-L2 in adults. The patient is positioned in either lateral decubitus with spine flexed or sitting and leaning forward. The iliac crest serves as the key landmark, corresponding to the L4 spinous process. The puncture typically targets the L3-L4 or L4-L5 interspace. The needle enters in the midline through the supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, and dura mater to reach the subarachnoid space. #### Central Venous Access Internal jugular vein cannulation approaches the triangle formed between the sternal and clavicular heads of the sternocleidomastoid muscle. The needle is directed toward the ipsilateral nipple, entering lateral to the carotid artery pulse. Subclavian vein access enters inferior to the clavicle at the junction of the middle and lateral thirds. The needle is directed toward the sternal notch, passing deep to the clavicle. Risks include pneumothorax from pleural puncture and arterial puncture. Femoral vein access enters below the inguinal ligament. The key relationship is NAVL from lateral to medial: Nerve, Artery, Vein, Lymphatics. The needle enters medial to the femoral arterial pulse, accessing the vein while avoiding arterial puncture. Panel A: Cricothyrotomy showing anterior neck anatomy with thyroid cartilage, cricothyroid membrane target, and cricoid cartilage in sagittal and surface view with horizontal incision line; needle thoracentesis at second intercostal space midclavicular line with needle above third rib. Panel B: Chest tube insertion showing safe triangle boundaries (pectoralis major, latissimus dorsi, fifth rib line) with insertion above rib through blunt dissection. Panel C: Lumbar puncture in lateral decubitus position with spine anatomy, iliac crest at L4 level, and needle path through supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, and dura to subarachnoid space. Panel D: Central venous access showing internal jugular approach between SCM heads toward ipsilateral nipple, subclavian approach below clavicle toward sternal notch, and femoral approach with NAVL relationship. --- ### VII. Dermatomes and Myotomes Reference #### Upper Limb The C5 dermatome covers the lateral arm over the deltoid region. The C5 myotome includes the deltoid muscle for shoulder abduction. The biceps reflex tests C5-C6. The C6 dermatome extends down the lateral forearm to the thumb and index finger. The C6 myotome includes the biceps for elbow flexion and the wrist extensors. The brachioradialis reflex tests C6. The C7 dermatome covers the middle finger. The C7 myotome includes the triceps for elbow extension and wrist flexors. The triceps reflex tests C7. The C8 dermatome covers the medial forearm and extends to the ring and little fingers. The C8 myotome includes finger flexors. The T1 dermatome covers the medial arm. The T1 myotome includes the intrinsic hand muscles for finger abduction and adduction. #### Lower Limb The L2 dermatome covers the anterior upper thigh. The L2 myotome includes hip flexors. The L3 dermatome covers the anterior thigh to the knee. The L3 myotome includes the quadriceps for knee extension. The L4 dermatome covers the medial leg and extends to the great toe. The L4 myotome includes knee extensors and ankle dorsiflexors. The patellar reflex tests L4. The L5 dermatome covers the lateral leg and dorsum of the foot. The L5 myotome includes great toe extensors and hip abductors. The S1 dermatome covers the lateral foot, sole, and posterior calf. The S1 myotome includes plantarflexors and hip extensors. The Achilles reflex tests S1. Panel A: Anterior and posterior body outline showing upper limb dermatome distributions: C5 lateral arm, C6 lateral forearm to thumb, C7 middle finger, C8 medial forearm to small finger, T1 medial arm. Panel B: Lower limb dermatome distributions: L2 anterior upper thigh, L3 anterior thigh to knee, L4 medial leg, L5 lateral leg and dorsum of foot, S1 lateral foot and posterior calf. Panel C: Upper limb myotome testing positions: deltoid abduction (C5), biceps flexion (C6), triceps extension (C7), finger flexion (C8), finger abduction (T1) with reflex hammer icons for biceps, brachioradialis, and triceps. Panel D: Lower limb myotome testing positions: hip flexion (L2), knee extension (L3-4), ankle dorsiflexion (L4), great toe extension (L5), plantarflexion (S1) with patellar and Achilles reflex icons. --- ### VIII. Clinical Correlations #### Anatomical Considerations in Procedures Successful and safe procedures require thorough knowledge of underlying anatomy. Identifying surface landmarks before intervention allows accurate localization of target structures and avoidance of vulnerable neurovascular bundles. Understanding three-dimensional relationships prevents inadvertent injury to deep structures. Procedure-related complications often result from anatomical errors. Intramuscular injection into the lower medial quadrant of the buttock risks sciatic nerve injury because the nerve courses through this region. Subclavian line placement risks pneumothorax because the apex of the lung lies near the insertion site. Thoracentesis below the rib damages the intercostal neurovascular bundle running in the costal groove. Lumbar puncture above L1-L2 risks spinal cord injury because the conus medullaris extends to this level. Femoral line placement medial to the artery results in arterial puncture rather than venous access. Safe approaches minimize complications. Knowledge of anatomy must guide every procedure. Ultrasound guidance when available improves accuracy and safety by visualizing target structures and avoiding vessels and nerves in real time. Marking landmarks before skin preparation ensures accurate localization. Maintaining sterile technique prevents infectious complications. Panel A: Dorsogluteal injection showing upper outer quadrant safe zone versus danger zone where sciatic nerve courses, and subclavian line showing lung apex proximity with pneumothorax risk zone. Panel B: Intercostal procedure showing safe insertion above rib versus dangerous insertion below rib with neurovascular bundle injury from incorrect approach. Panel C: Lumbar puncture showing safe entry below L2 versus dangerous entry above where conus medullaris is present, risking spinal cord injury. Panel D: Femoral access showing correct venous access medial to arterial pulse versus arterial puncture from incorrect lateral placement, with NAVL relationship emphasized. --- ### IX. Practical Surface Anatomy Skills #### Spine Palpation Sequence Systematic spine examination begins at the external occipital protuberance, the midline bump at the base of the skull. The examiner follows the nuchal ligament inferiorly to the vertebra prominens at C7. Thoracic spinous processes angle inferiorly and may be difficult to palpate individually in the mid-thorax. Lumbar spinous processes are more horizontal and prominent. The sacral crests and coccyx complete the examination. #### Upper Limb Palpation Sequence The clavicle is palpable along its entire length from the sternoclavicular joint to the acromioclavicular joint. The acromion and spine of scapula provide shoulder landmarks. The greater tubercle lies immediately below the acromion. The biceps and triceps muscles define the arm compartments. The medial and lateral epicondyles and olecranon establish elbow orientation. The radial and ulnar styloids mark the distal forearm. The anatomical snuffbox overlies the scaphoid. #### Lower Limb Palpation Sequence The anterior superior iliac spine and iliac crest establish pelvic landmarks. The greater trochanter marks the lateral hip. The patella and patellar ligament define the anterior knee. The tibial tuberosity lies at the ligament insertion. The medial and lateral joint lines indicate the articular surfaces. The fibular head lies at the lateral knee. The medial and lateral malleoli mark the ankle. The Achilles tendon and calcaneus complete the posterior examination. Panel A: Spine palpation sequence showing examiner finger placement from external occipital protuberance through cervical spinous processes to vertebra prominens (C7) with vertebral level indicators. Panel B: Spine continued through thoracic and lumbar spinous processes to sacral crests and coccyx with palpation technique for each region. Panel C: Upper limb palpation sequence from clavicle and shoulder landmarks (acromion, greater tubercle) through elbow (epicondyles, olecranon) to wrist (styloids, anatomical snuffbox). Panel D: Lower limb palpation sequence from pelvis (ASIS, iliac crest) through hip (greater trochanter) to knee (patella, joint lines, fibular head) and ankle (malleoli, Achilles tendon, calcaneus). --- ## Summary - Surface anatomy provides the foundation for physical examination and guides safe performance of clinical procedures - Key vertebral landmarks include C7 as the vertebra prominens, T4 at the sternal angle where the second rib attaches, and L4 at the iliac crest level - Peripheral pulse points include radial, ulnar, and brachial in the upper limb, and femoral, popliteal, dorsalis pedis, and posterior tibial in the lower limb - Safe intramuscular injection sites require knowledge of underlying neurovascular structures to avoid injury - Emergency procedures including cricothyrotomy, needle thoracentesis, chest tube placement, and lumbar puncture depend on accurate landmark identification - Dermatomal and myotomal patterns help localize neurological lesions to specific spinal levels - Correlating surface anatomy with underlying structures enables safe and effective clinical practice --- ## Key Terms | Term | Definition | |------|------------| | Vertebra prominens | C7 spinous process; most prominent cervical spinous process palpable at base of neck | | Sternal angle | Manubriosternal junction at T4-T5 level; landmark for the second rib | | Anatomical snuffbox | Depression between EPL and APL/EPB tendons; overlies scaphoid and radial artery | | McBurney's point | Appendix landmark at one-third distance from ASIS to umbilicus in right lower quadrant | | Safe triangle | Chest tube insertion zone bounded by pectoralis major, latissimus dorsi, and fifth rib line | | Ventrogluteal | Preferred gluteal injection site using hand landmark technique; avoids sciatic nerve | --- *This content is subject to the [MIT License](https://opensource.org/licenses/MIT). © 2024–2026 Hibbert School of Medicine.*