Rib Level Identification

This article is still missing information.

Anterior Rib Counting

Landmark Guidance

The sternal angle (Angle of Louis) is the key for counting anteriorly. This is the ridge at the junction of the manubrium and sternal body, and it corresponds to the attachment of the 2nd costal cartilage (second rib). Because the 1st rib is hidden behind the clavicle and is not palpable, you need to start the count from rib 2.

1. Find the Sternal Angle: Palpate the sternum upwards from the manubrium until you feel the transverse prominence of the sternal angle (located roughly 5 cm below the suprasternal notch). This indicates the level of the 2nd rib
2. Identify the 2nd Rib: At the sternal angle, move fingers laterally to feel the 2nd rib where it attaches. The second costosternal joint can be felt here, making it a convenient starting point
3. Count Ribs Downward: Continue palpating downwards, counting ribs 3, 4, 5, and so on. It is recommended to palpate just lateral to the sternum (along the parasternal or mid-clavicular line) to feel the bony rib contours, since near the sternum the costal cartilages can be hard to distinguish. Each successive rib can be traced and counted until you reach the level of tenderness.
4. Note Lower Ribs: Ribs 7–10 join the costal margin, and ribs 11–12 are “floating.” By the time you reach the costal margin (the arc of cartilage from the 7th to 10th ribs), you may need to adjust hand position laterally or use other landmarks to continue counting accurately. If needed, you can switch to counting from the bottom (12th rib upward) as described below.

Ultrasound Guidance

1. Probe Position at Sternal Angle: Place the transducer near the sternum at the level of the manubriosternal joint (around where the 2nd rib joins). The probe can be oriented in a longitudinal (vertical) orientation alongside the sternum or in a transverse orientation to capture rib cross-sections. The goal is to locate the 2nd rib under ultrasound. Because the 2nd costal cartilage attaches at the sternal angle, scanning just lateral to the sternum at this level will show the transition from cartilage to bone. Move the probe laterally until you visualize a rib appearing as a bright line with shadow – this should correspond to the second rib. (Costal cartilage is less echo-dense, but the bony rib will produce a clear shadow once in view.)
2. Identify and Label the Rib: Confirm the identified structure is a rib (it will have a curved contour and cast a dark acoustic shadow deep to it). Use Doppler or observation to ensure it’s not an artifact; ribs are static and have a characteristic shape. Once confident, mentally label this as “Rib 2.
3. Count Ribs Sequentially: From the second rib, slide the probe inferiorly to find the third rib. This can be done by moving the probe down one intercostal space at a time along the mid-clavicular or mid-axillary line. Each downward movement will bring the next rib into view. Ensure the probe remains perpendicular to the chest wall to keep ribs visible as distinct structures. Count out loud or in your mind as you move: e.g. “next rib down is 3, next is 4,” etc., until reaching the level of tenderness. Keeping the rib in the center of the ultrasound image (“elongating” the rib in view) helps to not lose track of which level you are on.
4. Verify with Adjacent Landmarks: If uncertainty arises (for example, at the level of the costal margin where cartilages converge), the clinician can cross-check by scanning laterally to see the rib’s posterior portion or use the liver/diaphragm as a reference (e.g. the diaphragm typically attaches around the 10th rib at the mid-axillary line). In the case of very high or very low ribs, consider switching to a curvilinear probe for better penetration or using the posterior approach (described next) for confirmation.

In a study comparing traditional verses ultrasound guidance for thoracostomy, the traditional technique was 0.88 rib spaces away compared to only 0.09 rib spaces away for ultrasound.

Posterior Rib Counting

Landmark Guidance

On the posterior chest, rib counting relies on different landmarks because the upper ribs are obscured by musculature (and the scapula), and the first rib cannot be directly palpated from behind. Common posterior landmarks and techniques include the below, none of which are perfect. Hence posterior rib counting is less reliable than anterior. Many of the pitfalls are described in the article Vertebral Level Identification

• Vertebra Prominens (C7) and T1: The patient’s neck is flexed to locate the prominent spinous process of C7 at the base of the neck. Just below it is the T1 spinous process, which corresponds roughly to the level of the 1st rib’s attachment In practice, however, directly feeling the 1st rib is difficult due to the shoulder girdle.
• Inferior angle of the scapula: The scapula can guide rib counting. When the patient’s arms are folded across the chest or raised, the scapula shifts laterally, exposing more of the rib cage. The inferior angle of the scapula is classically described as lying approximately over the 7th rib. This again has many pitfalls and is not particularly accurate at all. For example the 8th rib is the most common not the 7th, but there is a wide range.
• Spine of the scapula (the horizontal ridge at the upper scapula) aligns with the T3 vertebra, which is near the level of the 3rd or 4th ribs. And the scapula’s superior angle sits around the 2nd rib level (at T1 vertebral level) in normal posture.
• Twelfth Rib Method: Another method is to start from the bottom. The 11th and 12th ribs are “floating” and can often be palpated in the back (the 12th rib’s tip is felt in the mid-back/flank area). The clinician can locate the free end of the 12th rib and then count ribs upward (12th to 11th to 10th, etc.) until reaching the area of interest.

It’s also helpful to have the patient sit upright with arms crossed or elevated, which moves the scapulae off the back and makes the ribs more accessible to palpation.

Remember that each thoracic vertebra’s spinous process is at the level of the rib numbered one higher (due to the downward slope of the spinous processes), so vertebral level and rib level may differ slightly (e.g. the T4 spinous is around the level of the 5th rib). Clinically, though, identifying a known rib (7th via scapula or 12th rib) and counting from it is the preferred method.

Ultrasound - Posterior and Lateral

A posterior or lateral ultrasound approach is often employed when the area of interest is on the back or side of the chest. This approach may use a lower-frequency curvilinear probe if deeper penetration is needed (e.g. near the spine in larger patients), or a linear probe for more superficial lateral scanning. There are two main ultrasound strategies: counting from the bottom (caudal-to-cephalad) and counting from the top (cephalad-to-caudal). Evidence suggests the bottom-up method is more reliable for ultrasound rib counting on the back. A typical protocol for the lateral chest (such as for regional anesthesia or rib fracture assessment) is as follows:

• Patient Positioning: Position the patient to maximize access to the posterior-lateral chest. For example, in a lateral decubitus position (patient lying on the side) with the side to be scanned uppermost and the arm raised above the head. This position moves the scapula out of the way and thins out the musculature over the ribs In a sitting position, the patient can also fold arms forward to laterally displace the scapula.
• Probe Orientation and Start Point: Place the ultrasound transducer in a coronal (vertical) orientation along the mid-axillary line at the lowest rib margin. Essentially, start around the flank where you expect the 11th or 12th rib to be. For example, one method marks the lowest palpable rib in the mid-axillary line (often the 11th) and centers the probe. The 11th rib will appear as a curved echogenic line with shadow. Since the 11th and 12th are floating ribs, the 11th rib can be traced until it “disappears” anteriorly (where it ends), confirming its identitypmc.ncbi.nlm.nih.gov. By sliding the probe slightly posteriorly, the tip of the shorter 12th rib can sometimes be visualized as well.
• Count Ribs Upward: Once the 11th rib is identified, move the probe upward (cranially) in the coronal plane to find the 10th rib, then 9th, and so on. You will see each successive rib come into view as a bright shadow-casting line. It can help to keep a mental count (e.g. “now 10, now 9…”) as you slide the transducer. Muscular landmarks can assist: around the 8th–9th rib level in the mid-axillary line, the serratus anterior muscle will appear overlaying the ribs (since serratus attaches to the first 9 ribs). Further posterior, the latissimus dorsi muscle comes into view covering the lower ribs. These muscular landmarks confirm you are in the proper plane (for instance, seeing the serratus anterior indicates you’re at roughly ribs 5–9 region). Continue sliding upward until you reach the axilla. By the time the probe is at the apex of the axilla, you should visualize the 2nd rib (with its adjacent intercostal artery and vein often visible by Doppler). Scanning slightly beyond that brings the shadow of the lateral clavicle into view, which tells you that the 1st rib lies just deep to it (the first rib is often difficult to visualize directly from a lateral approach).
• Alternative Posterior Approach: Another technique is to approach from the back (paramedian). The transducer can be placed just lateral to the spine (paraspinal area) and moved in a longitudinal orientation, counting ribs as they articulate with transverse processes. In this method, one might identify the 12th rib at the costovertebral angle under ultrasound and then count up, or identify C7/T1 and count down. A study comparing these two tactics found that counting upward from the 12th rib under ultrasound was significantly more accurate than counting downward from the C7 level. In that study, using the 12th rib as a starting landmark led to correct identification of target thoracic levels ~84% of the time, whereas starting from C7 led to correct identification only ~57% of the time. In practice, a posterior paramedian scan will show each rib’s head and transverse process junction as you move cranially; by counting those, you determine the rib number at the transducer position.