Regional Anesthesia: Bony Landmarks

Introduction

• Accurate identification of anatomical surface landmarks remains fundamental to safe and effective regional anesthesia, even as ultrasound has become widely adopted.¹
• Bony and fixed landmarks provide consistent reference points that enhance needle guidance, reduce complications, and support reliable block performance across diverse clinical settings.²
• These principles are emphasized throughout contemporary regional anesthesia education and practice, where landmark proficiency complements image-guided techniques to optimize patient outcomes.³

Head and Neck Blocks

Overview

• Anatomical surface landmarks play an essential role in head and neck blocks. The mastoid process, occipital protuberance, and C6 tubercle (Chassaignac’s tubercle) are reliable, fixed references that do not shift with body habitus or edema.^4-5 These landmarks enable accurate blockade of various nerves and plexuses, even when ultrasound is unavailable.⁶

Cervical Plexus Blocks

• A superficial cervical plexus block anesthetizes the cutaneous branches of the plexus that supply sensation to the anterolateral neck, clavicle, and auricle. In contrast, a deep cervical plexus block provides a more extensive distribution by targeting the nerve roots themselves, providing anesthesia to both the superficial cervical territory and deeper neck and shoulder structures.^4-5

Superficial Cervical Plexus Block

• Landmarks include the posterior border of the sternocleidomastoid (SCM) muscle and the mastoid process.² The block is performed along the posterior SCM border at the midpoint between the mastoid and clavicle.^4,5

Deep Cervical Plexus Block

• The mastoid process and the transverse process of C2 (occasionally palpable) are the key landmarks.^2,4 A line between the mastoid process and Chassaignac’s tubercle helps approximate needle entry points for the C2–C4 roots.4-5 Needle insertion is directed to contact the cervical transverse processes, then slightly withdrawn to inject.^4,6

Stellate Ganglion Block

• The landmark-based stellate ganglion block is done by retracting the SCM muscle, carotid artery, jugular vein, and vagus nerve.⁴ The cricoid cartilage is palpated to establish the C6 level. The anterior tubercle of the C6 transverse process or Chassaignac’s tubercle can then be felt and used as a landmark to advance the needle towards the lateral part of the vertebral body.^1-3

Greater Occipital Nerve Block

• The classic landmark-based greater occipital nerve block is located at approximately two-thirds the distance on a line drawn from the center of the mastoid to the external occipital protuberance along the superior nuchal line, where it lies medial to the occipital artery.^2,4-5

Upper Extremity Blocks

Overview

• Bony landmarks play an essential role in performing upper extremity nerve blocks, particularly when ultrasound is unavailable or when used to complement ultrasound guidance.^1-3
• For commonly performed blocks, such as brachial plexus blocks (interscalene, supraclavicular, infraclavicular, axillary), and peripheral nerve blocks at the elbow and wrist, accurate needle placement can be guided by well-defined osseous landmarks.^2,4-6
• As with most procedures, however, anatomical variability must be considered when relying on surface anatomy.⁷

Interscalene Block

• The clavicle, SCM muscle, and interscalene groove between the anterior and middle scalene muscles are the principal surface landmarks.^2,4 The groove is palpated lateral to the SCM and above the clavicle, corresponding to the transverse processes of the lower cervical vertebrae, particularly C6 (Chassaignac’s tubercle).^4-5
• When surface landmarks are difficult to define, the underlying cervical spine anatomy can help conceptualize the needle trajectory.⁵

Supraclavicular Block

• The clavicle is the primary landmark.^2,4 The needle is inserted just superior to the midpoint of the clavicle, lateral to the lateral border of the SCM, targeting the region where the brachial plexus trunks are compact as they cross over the first rib.⁵
• Variability in first-rib depth and plexus position may influence the success of the block.⁷

Infraclavicular Block

• For the coracoid approach to the infraclavicular block, the coracoid process is the principal bony landmark.^2,4 The needle is inserted just inferior and medial to the coracoid process, directed toward the cords of the brachial plexus as they surround the axillary artery.^5,8

Axillary Block

• In the axilla, the medial aspect of the humerus and the axillary artery are used as key landmarks.^2,4 The artery is palpated high in the axilla against the humerus, and the needle is directed toward the neurovascular bundle adjacent to the humeral shaft.⁵

Peripheral Nerve Blocks at the Elbow and Wrist

• At the elbow, the medial epicondyle and olecranon define the ulnar groove, aiding ulnar nerve localization.^2,4 The medial and lateral epicondyles and the humeral condyles help orient approaches to the median and radial nerves, with final positioning guided by tendon and vascular landmarks.^5,8
• At the wrist, the styloid processes of the radius and ulna provide orientation for radial and ulnar nerve blocks, with soft-tissue structures refining needle placement.²

Lower Extremity Blocks

Overview

• Bony landmarks are especially helpful for lower extremity nerve blocks, where deep or variable nerve courses can make surface anatomy challenging, and in situations where ultrasound may not always be available.^1,2
• Key osseous structures, including the spine, pelvis, femur, and malleoli, provide reliable reference points for identifying neural pathways and guiding needle placement for lumbar plexus, femoral, sciatic, obturator, and ankle-level blocks.^2-4
• Anatomic variability should always be considered when relying on surface landmarks.⁷

Lumbar Plexus Block

• Landmarks for the psoas compartment block include spinous processes to define midline, the iliac crests to form the perpendicular intercristal line, and the posterior superior iliac spine (PSIS). The needle is inserted 4 cm lateral to the midline along the intercristal line.

Femoral Nerve Block

• The anterior superior iliac spine (ASIS) and pubic tubercle define the inguinal ligament, beneath which the femoral nerve, artery, and vein course. The nerve lies just lateral to the femoral artery at the inguinal crease.^2,3 A landmark-guided femoral block is typically performed 1-2cm lateral to the femoral pulse, just inferior to the ligament.^2,4

Obturator Nerve Block

• The pubic tubercle and the tendon of the adductor longus serve as key landmarks.2,3 The needle is introduced just inferior and lateral to the pubic tubercle, directed toward the adductor muscle group to access the anterior and posterior branches of the obturator nerve.^3,4

Posterior Sciatic Block

• The greater trochanter and PSIS are the primary landmarks for the classic Labat sciatic approach.^2,3 The confirmatory line of Winnie is drawn from the greater trochanter to the sacral hiatus, and the perpendicular bisector of the first line is drawn to the confirmatory line of Winnie. A further furrow line has been described, which is defined by the medial edge of the gluteus maximus and the long head of the biceps femoris and marks the course of the sciatic nerve toward the lower leg. The triangle formed by these markings, creates the needle insertion point.^3,4,11

• In the subgluteal approach, the greater trochanter and the ischial tuberosity serve as the key references. At the midpoint, another line is drawn perpendicularly and extended 4 cm in the caudal direction to identify the needle insertion point.³

Ankle Blocks

• The medial and lateral malleoli serve as key bony landmarks for distal nerve blocks.^2,3 The posterior tibial nerve is blocked posterior to the medial malleolus, immediately posterior to the posterior tibial artery.^3,4 The deep peroneal block lies lateral to the dorsalis pedis artery between the anterior tibial and extensor digitorum longus tendons. The sural nerve is blocked by subcutaneous injection between the cephalad border of the lateral malleolus to the Achilles tendon. The superficial peroneal is blocked by subcutaneous infiltration between the anterior tibia and the lateral malleolus. The saphenous nerve is blocked by subcutaneous injection from the anterior tibia to the posterior border of the medial malleolus.^2,3

Truncal Blocks

Overview

• Bony landmarks also play an essential role as an adjunct to ultrasound or as the sole basis for landmark-based techniques. The iliac crest, spinous and transverse processes, pubic tubercle, and ASIS give fixed, palpable references that can help guide needle placement for numerous truncal blocks.^3-4

Transversus Abdominis Plane (TAP) Block

• The landmark-guided TAP block involves needle insertion at the triangle of Petit, which is defined by the latissimus dorsi muscle posteriorly, the external oblique muscle anteriorly, and the iliac crest inferiorly. The needle is inserted perpendicular to all planes, and the plane is reached following two “pops.”^5,12

Ilioinguinal-Iliohypogastric Block

• The ASIS is the defining landmark for this block. From the ASIS, measure 2 cm medial and 2 cm inferior to determine the needle insertion site. Using this technique, there is one (and sometimes two) distinct pop through the external and internal oblique fascia to reach the target layer.⁹

Thoracic Paravertebral Block

• The thoracic spinous and transverse processes provide the primary bony orientation for paravertebral blocks.^2,4 The target level is identified by palpating the spinous processes, and the needle is inserted 2.5–3 cm lateral to midline to contact the transverse process at the chosen thoracic vertebra.^3,4
• After contacting bone, the needle is “walked off” the superior or inferior edge of the transverse process to enter the paravertebral space.^4,6 These vertebral landmarks offer consistent depth and orientation cues, making thoracic paravertebral blocks one of the few truncal techniques where bone contact is an integral part of confirming needle position.³

Erector Spinae Plane Block

• The transverse process of the targeted vertebral level is the key bony landmark for ESP blocks.^4-5 The spinous processes are palpated to identify the correct vertebral segment, and the needle is inserted 2–3 cm lateral to midline until firm contact with the transverse process is made.^4,6 Local anesthetic is deposited in the fascial plane deep to the erector spinae muscle, allowing spread over multiple dermatomes.⁵ This is one of the few truncal blocks in which bone contact serves as a reliable confirmation of correct needle depth.^4,6

Neuraxial Blocks

Overview

• Bony landmarks are fundamental for neuraxial procedures, which are still often done with landmark based techniques. The targets for neuraxial techniques can be difficult to identify using ultrasound. Surface anatomy is supplemented by knowledge of vertebral anatomy to complete these techniques.^5,7

Lumbar Epidural/Spinal Block

• The iliac crests are the most reliable bony landmarks, forming the intercristal (Tuffier’s) line, which typically corresponds to the L4 vertebral level (L4–L5 interspace).^3,6 Palpation of the spinous processes confirms midline. Needle insertion is directed either midline or paramedian using the interspinous spaces between lumbar vertebrae, identified by counting upward or downward from the intercristal line.^3,4,6

Thoracic Epidural Block

• Thoracic spinous processes are angled caudally, narrowing the interspinous spaces.3 The scapular spine (approximate T3 level) and inferior angle of the scapula (approximate T7 level) provide orientation.³ Counting vertebrae from these landmarks helps identify the entry level for thoracic epidural placement.^3,6

Caudal Epidural Block

• The sacral hiatus is the central landmark, bounded by the palpably firm sacral cornua.^3,4 The PSIS form a triangle with the sacral hiatus. The needle is directed through the sacrococcygeal ligament into the caudal epidural space.2 This approach remains one of the most anatomically landmark-dependent neuraxial techniques.⁶