The scapula, or shoulder blade, is a flat triangular bone that sits against the back of the rib cage and serves as the anchor point for much of the shoulder’s movement. Its bony landmarks are the ridges, bumps, notches, and surfaces that give the scapula its distinctive shape and provide attachment sites for more than a dozen muscles. These landmarks include three borders (medial, lateral, and superior), three angles (superior, inferior, and lateral), the spine of the scapula with its acromion, the coracoid process, the glenoid cavity, and several fossae and notches. Understanding what each landmark is and where it sits is more than an anatomy exercise, since clinicians, surgeons, and therapists rely on these reference points every day to assess shoulder health, plan operations, and guide rehabilitation.
Borders, Angles, and Surfaces
The scapula has two broad surfaces. The front surface, which lies against the ribs, is the costal (or anterior) surface and forms a wide, shallow depression called the subscapular fossa. The back surface, the dorsal (or posterior) surface, is divided into two unequal parts by a prominent horizontal ridge called the spine of the scapula. Above the spine sits the supraspinous fossa, and below it the larger infraspinous fossa. Each fossa houses a rotator cuff muscle: the supraspinatus above, the infraspinatus below.
Three borders frame the triangle. The medial (or vertebral) border runs roughly parallel to the spine and is the longest of the three. It is where muscles like the rhomboids and serratus anterior attach. The lateral (or axillary) border runs from the glenoid cavity down to the inferior angle and is thicker because it bears more mechanical load. The superior border is the shortest, running from the superior angle to the base of the coracoid process, and it features the suprascapular notch near its lateral end.
The three angles serve as orientation points. The superior angle sits where the medial and superior borders meet, near the second rib. The inferior angle, where the medial and lateral borders converge, sits near the seventh rib and is the most easily felt bony landmark on the scapula. The lateral angle is where the glenoid cavity lives, forming the shallow socket that articulates with the head of the humerus.
The Spine, Acromion, and Coracoid Process
The spine of the scapula is probably the single most recognizable landmark. It starts as a low, flat ridge near the medial border (called the root of the spine) and becomes progressively taller as it sweeps laterally across the back of the bone. At its lateral end, it flattens and broadens into the acromion, the bony shelf you can feel at the tip of your shoulder. The acromion is the highest point of the shoulder, and it forms the roof of the space through which the rotator cuff tendons must pass.
The coracoid process projects forward from the upper part of the scapula like a bent finger. You can sometimes palpate it by pressing just below the outer third of the clavicle and slightly inward. It serves as an attachment point for the pectoralis minor, the short head of the biceps, and the coracobrachialis, and it anchors several important ligaments that stabilize the shoulder joint. The coracoid’s position relative to the acromion helps define the coracoacromial arch, a bony and ligamentous roof over the rotator cuff.
The Glenoid Cavity
The glenoid cavity is a shallow, slightly concave oval on the lateral angle of the scapula. It is the socket half of the shoulder’s ball-and-socket joint. Compared to the hip socket, the glenoid is remarkably shallow and covers only about a third of the humeral head’s surface, which is why the shoulder trades bony stability for extraordinary range of motion. A rim of fibrocartilage called the labrum deepens the socket somewhat.
Several landmarks cluster around the glenoid. Just above it sits the supraglenoid tubercle, where the long head of the biceps tendon originates. Just below it, the infraglenoid tubercle gives rise to the long head of the triceps. The glenoid’s tilt, both in the up-down and front-back planes, has clinical significance: the angle of its inclination is strongly correlated with the critical shoulder angle, a measurement that predicts susceptibility to rotator cuff tears and glenohumeral osteoarthritis.
Palpating the Landmarks Through Skin
Several scapular landmarks are easily felt through the skin, making them indispensable reference points for physical therapists and clinicians assessing posture, scapular position, and shoulder alignment. Research has shown that surface palpation is a reliable way to locate key bony points. In one study using cadavers, the difference between a surface palpation point and the actual bony location was less than about 7 mm for the root of the spine, under 10 mm for the acromial angle, and less than 5 mm for the inferior angle.1PubMed. Scapular position: the validity of skin surface palpation That level of accuracy is good enough for most clinical assessments.
Two common methods for measuring scapular position use these palpable landmarks. One measures the vertical distance from the C7 spinous process (the bump at the base of your neck) to the upper medial corner of the scapular spine. The other measures from the T8 spinous process to the inferior angle. Both methods have been shown to be reliable between testers, with the T8-to-inferior-angle method performing slightly better in terms of consistency and validity.2Physical Therapy. Reliability and Validity of the Measurement of Scapular Position Using the Protractor Method – Section: Results These measurements help clinicians track whether one scapula sits noticeably higher, lower, or more tilted than the other, which can indicate muscle imbalances or nerve injuries.
Muscular Attachments Along the Medial Border
The medial border of the scapula is a busy stretch of bone. Three muscles, the levator scapulae, the rhomboid minor, and the rhomboid major, attach here in a stacked arrangement from top to bottom. These muscles anchor the scapula to the cervical and thoracic spine and are responsible for retracting (pulling back) and elevating the shoulder blade. On the other side of the border, the serratus anterior wraps around from the front of the rib cage and attaches to the costal surface.
Cadaveric dissection has revealed that the attachments of these muscles are more complex than typical anatomy diagrams suggest. The levator scapulae and rhomboid minor have double-fold attachment patterns, with one layer attaching to the dorsal surface of the medial border and another to the costal surface. The rhomboid major attaches along the medial border opposite the infraspinous fossa and extends almost to the inferior angle. All three muscles overlap the serratus anterior fascia by about three centimeters.3PubMed. Muscular attachments along the medial border of the scapula The serratus anterior itself wraps around both the superior and inferior angles, attaching to both surfaces of the bone at those points. This overlapping arrangement matters clinically because injury or paralysis of any one of these muscles changes the position and movement of the scapula in characteristic ways.
Scapular Winging and What It Reveals
When the muscles that pin the scapula to the rib cage fail, the bone lifts away from the back in a phenomenon called scapular winging. The pattern of winging tells you which nerve or muscle is involved. If the serratus anterior is paralyzed, usually due to damage to the long thoracic nerve, the medial border lifts off the rib cage and the inferior angle shifts toward the midline, producing what is called medial winging. If the trapezius or rhomboids are paralyzed instead, the scapula wings laterally, with the medial border shifting outward.4PubMed Central. Scapular winging: anatomical review, diagnosis, and treatments
Winging is usually visible on inspection, especially when you push against a wall with your arms extended. It dramatically alters how the shoulder blade moves during arm elevation and can cause pain, weakness, and reduced overhead function. Recognizing the direction of winging, medial versus lateral, is a practical diagnostic shortcut rooted directly in knowing which muscles attach to which landmarks along the medial border.
The Suprascapular Notch and Its Variations
The suprascapular notch is a small indentation on the superior border, just medial to where the coracoid process begins. The suprascapular nerve passes through this notch beneath the superior transverse scapular ligament on its way to supply the supraspinatus and infraspinatus muscles. The shape of this notch varies considerably between people, and those variations have real clinical consequences.
A study of 138 scapulae found that about half had a U-shaped notch, roughly a fifth had a V-shaped notch, and about a tenth had a J-shaped notch. Smaller fractions had incomplete notches, absent notches, double foramina, or the unusual W-shaped variant.5PubMed Central. Anatomical Variations of the Suprascapular Notch and its Importance in Suprascapular Entrapment Neuropathy The shape matters because a narrow, deep notch (V-shaped or type I in some classification systems) places the nerve closer to sharp bony walls, increasing the risk of compression. In some people, the ligament that bridges the notch ossifies completely, converting the notch into a bony foramen. This complete ossification has been found more frequently in males, which may partly explain why suprascapular neuropathy is diagnosed more often in men.6PubMed Central. Variation in morphology of suprascapular notch as a factor of suprascapular nerve entrapment
Suprascapular neuropathy causes deep, aching shoulder pain and progressive weakness of the external rotators. It is often misdiagnosed as a rotator cuff tear because the symptoms overlap. Knowing that the anatomy of the notch itself can predispose someone to this problem helps explain why some overhead athletes or laborers develop nerve compression without an obvious injury.
Acromial Shape and Rotator Cuff Tears
The acromion is not the same shape in everyone, and its morphology has been linked to shoulder impingement and rotator cuff damage. In a widely used classification, acromia are sorted into flat (type I), curved (type II), hooked (type III), and convex (type IV). The hooked type III acromion has drawn the most clinical attention because it narrows the space beneath the acromion where the supraspinatus tendon runs. In a study of 423 dried scapulae, bony spurs at the ligament attachment site (enthesophytes) were significantly more common in type III acromia, and the combination of a hooked acromion with enthesophytes was particularly associated with impingement and rotator cuff tears.7Clinical Anatomy. Correlation between the four types of acromion and the existence of enthesophytes: A study on 423 dried scapulas and review of the literature
Beyond the simple classification, more detailed measurements of acromial geometry have proven useful. A low lateral acromial angle and greater lateral extension of the acromion are both associated with higher rates of impingement and cuff tears. Research has found that an extremely hooked anterior acromion with a slope greater than 43 degrees and a lateral acromial angle below 70 degrees occurred only in patients with rotator cuff tears, not in healthy shoulders.8PubMed Central. Correlation of acromial morphology with impingement syndrome and rotator cuff tears This is partly why surgeons sometimes shave down the undersurface of the acromion during shoulder surgery, a procedure called subacromial decompression, to give the rotator cuff tendons more room.
The Critical Shoulder Angle
One of the more useful measurements derived from scapular landmarks is the critical shoulder angle (CSA), which combines the lateral tilt of the acromion with the inclination of the glenoid into a single number measured on a standard shoulder X-ray. It captures the combined geometry of two landmarks, the acromion and the glenoid, to predict mechanical forces acting on the rotator cuff and the joint surface.
The relationship between the CSA and shoulder pathology has been confirmed across multiple studies. A systematic review found that a greater CSA significantly increased the likelihood of chronic, full-thickness rotator cuff tears.9Arthroscopy. The Relationship Between the Critical Shoulder Angle and the Incidence of Chronic, Full‐Thickness Rotator Cuff Tears and Outcomes After Rotator Cuff Repair: A Systematic Review At the other end of the spectrum, smaller CSAs have been associated with glenohumeral osteoarthritis.10PubMed Central. The Critical Shoulder Angle as a Diagnostic Measure for Osteoarthritis and Rotator Cuff Pathology The glenoid inclination itself differs between these groups: shoulders with massive rotator cuff tears had an average glenoid inclination of roughly 14 degrees, while osteoarthritic shoulders averaged around 5 to 8 degrees depending on the measurement method.11PubMed. Correlation between glenoid inclination and critical shoulder angle: a radiographic and computed tomography study – Section: RESULTS
What makes the CSA clinically appealing is that it is easy to measure on a plain X-ray and captures the net mechanical environment of the shoulder. A surgeon evaluating someone with early rotator cuff symptoms can use the CSA to gauge how much the patient’s own bony anatomy is stacking the odds against tendon survival. It does not determine treatment by itself, but it adds context to clinical decision-making.
The Coracoacromial Arch and Subacromial Space
The coracoacromial arch is the functional ceiling over the rotator cuff, formed by the coracoid process in front, the acromion behind and above, and the coracoacromial ligament spanning between them. Variations in the shape and dimensions of this arch directly affect the space available for the supraspinatus tendon to slide beneath it during arm elevation. Three-dimensional modeling of shoulders has shown that the supraspinatus outlet, the gap between the arch and the humeral head, was about 22.5 percent smaller in shoulders with rotator cuff tears compared to intact shoulders.12Journal of Shoulder and Elbow Surgery. The influence of coracoacromial arch anatomy on rotator cuff tears
The angle between the scapular plane and the spine of the scapula also plays a role. Shoulders with rotator cuff tears had a smaller angle between these two features (averaging about 47 degrees) compared to intact shoulders (about 58 degrees), meaning the spine was oriented differently relative to the rest of the bone. A flat yet curved acromion combined with an acromioclavicular joint sitting above the top of the glenoid was identified as a significant risk factor for cuff damage.13PubMed. The influence of variations of the coracoacromial arch on the development of rotator cuff tears These findings underline that rotator cuff disease is not just about overuse or age; the geometry of the scapula’s bony landmarks sets the stage.
Landmarks in Shoulder Replacement Surgery
When a shoulder joint wears out enough to need replacement (total shoulder arthroplasty), the surgeon must position the artificial glenoid component precisely to avoid loosening and early failure. Getting the angle right depends on accurately identifying scapular landmarks, both on preoperative CT scans and during the operation itself. Modern 3D planning software reconstructs the scapula from a CT scan and uses landmarks on the glenoid surface and the scapular body to calculate ideal implant placement.14Shoulder & Elbow. Variability in total shoulder arthroplasty planning software compared to a control CT-derived 3D printed scapula
During the actual operation, computer-assisted navigation systems track the orientation of the glenoid in real time using three surface landmarks on the glenoid. This approach provides the surgeon with feedback while they ream and seat the component, reducing errors in version and inclination compared to freehand technique.15PubMed. Improved accuracy of computer assisted glenoid implantation in total shoulder arthroplasty: an in-vitro randomized controlled trial – Section: METHODS Errors of even a few degrees in glenoid component tilt can alter load distribution across the implant, accelerating wear. The precision of the entire procedure ultimately rests on the surgeon’s ability to define scapular landmarks reliably, both in imaging and on the exposed bone.
Development and Ossification of the Scapula
The scapula does not start out as a single solid bone. It begins as cartilage and ossifies through multiple centers over the course of childhood and adolescence. The main body of the scapula ossifies from a single primary center that appears during fetal development, roughly around the eighth week of gestation. A separate primary center for the coracoid process appears between three and four months after birth, and a growth plate (physis) persists between the coracoid center and the main scapular body until late adolescence.16PubMed. Radiology of postnatal skeletal development. VII. The scapula
Additional secondary ossification centers appear during puberty at the acromion, the inferior angle, the medial border, and the tip of the coracoid. These fuse with the rest of the scapula by the early to mid-twenties. Awareness of this timeline matters in pediatric radiology because an unfused ossification center can mimic a fracture on an X-ray, and in adolescent sports medicine because the growth plates at the acromion or coracoid can be vulnerable to stress injuries in young overhead athletes.
Sex Estimation From Scapular Shape
In forensic anthropology, when skeletal remains need to be identified, the scapula is a useful bone for estimating biological sex. Males and females differ in overall scapular size and in subtler aspects of shape. A geometric morphometric study found that scapular shape alone correctly classified over 91 percent of females and 95 percent of males.17PubMed. A geometric morphometric study into the sexual dimorphism of the human scapula In a separate study of a Japanese population using CT-derived 3D measurements, stepwise analysis of scapular dimensions achieved sex prediction accuracy rates between 93 and 95 percent.18PubMed. Sex estimation based on scapula analysis in a Japanese population using multidetector computed tomography
These accuracy rates are high enough that the scapula can serve as a reliable alternative when more commonly used bones like the pelvis or skull are damaged or missing. The measurements that drive the discrimination include overall length and breadth, spine length, and glenoid dimensions. Because these dimensions are anchored to specific bony landmarks, consistent identification of those landmarks is the foundation of the entire method.
What the Scapula Tells Us About Human Evolution
The shape of the scapula has shifted over the course of human evolution, and those shifts are written into the same landmarks anatomists use today. A study of fossil hominin shoulder blades found that a sustained change in scapular shape occurred from an African ape-like ancestor toward the modern human form, with the modern configuration first appearing in our genus, Homo.19Proceedings of the National Academy of Sciences. Fossil hominin shoulders support an African ape-like last common ancestor of humans and chimpanzees In living apes, the scapula sits higher on the back with a more cranially (upward) oriented glenoid, suited to climbing and hanging. In modern humans, the glenoid faces more laterally, reflecting a shift toward tool use and throwing.
Comparative analysis of scapular landmarks across primates has shown that the orientation of the scapular spine and the relative sizes of the supraspinous and infraspinous fossae largely reflect spine orientation rather than independent changes in fossa size.20PubMed. Evolution of the hominoid scapula and its implications for earliest hominid locomotion – Section: RESULTS In other words, one landmark’s geometry drives the apparent proportions of others. Across mammals more broadly, scapular shape tracks habitat and locomotion: species adapted to climbing in forests tend to have broader scapulae with differently angled spines and longer acromion and coracoid processes than species adapted to running in open terrain.