Surgical Neck of Humerus: Fractures and Axillary Nerve Risk

The surgical neck of the humerus is a slightly narrowed zone of the upper arm bone located just below the two bony bumps (the greater and lesser tuberosities) near the shoulder. It earned the name “surgical” because fractures here are so common that surgeons historically encountered them more than any other proximal humerus break. The region sits at a transition point where the wider, cancellous bone of the humeral head meets the denser cortical shaft, creating a mechanical weak spot that is especially prone to failure in older adults with thinning bones. Understanding this anatomy matters because it connects to decisions about treatment, the risks of nearby nerve and blood vessel injury, and what recovery realistically looks like.

Where Exactly the Surgical Neck Sits

If you picture the top of your upper arm bone, the very top is the smooth, rounded humeral head that fits into the shoulder socket. Just below it is a shallow groove called the anatomical neck, which marks where the joint cartilage ends. Below that, two bony projections jut outward: the greater tuberosity on the outer side and the lesser tuberosity on the front. The surgical neck lies immediately beneath these tuberosities, forming a circumferential ring around the bone. It is not a sharp line but a zone, typically a centimeter or so wide, where the cross-section of the humerus narrows before continuing down the shaft.

This narrowing is what makes it biomechanically vulnerable. Above the surgical neck, the bone is mostly spongy (cancellous) tissue designed to distribute compressive loads through the joint. Below, the bone transitions into a thicker cortical tube designed for bending and torsion. The surgical neck is the transitional zone between those two architectures, and transitional zones in engineering tend to concentrate stress. A fall that drives force up through the arm or directly onto the side of the shoulder often channels that energy right through this region.

How Surgical Neck Fractures Happen

The classic scenario is an older adult falling onto an outstretched hand. The impact travels up the arm and concentrates at the surgical neck. But direct blows to the shoulder also cause fractures, and the pattern of the break differs depending on the mechanism. In a cadaveric study simulating both types of impact, a direct hit to the shoulder most often produced undisplaced head-split fractures, while a fall-on-outstretched-hand mechanism (sometimes called the “parachute reflex”) predominantly created shield-type injuries and displaced greater tuberosity fractures.

In younger people, surgical neck fractures usually require high-energy trauma like a car crash or a sports collision. In adults over 50, a simple ground-level fall is enough. Proximal humerus fractures in general are among the most common fractures in older populations, with women disproportionately affected. One large database study found that among patients aged 50 to 64, men were actually less likely than women to undergo surgery for a proximal humerus fracture, and treatment patterns shifted further once patients passed age 65.

An interesting finding from the research on bone quality is that bone mineral density alone does not reliably predict how severe a proximal humerus fracture will be. One study specifically tested whether lower bone density or a local bone-quality index predicted more complex fracture patterns and found no relationship. Weak bone may contribute to fracture risk overall, but the severity of the break seems to depend on multiple factors beyond bone density alone, including the direction and energy of impact.

Why the Muscles Pull the Fracture Apart

Once the surgical neck breaks, the fragments rarely stay neatly aligned. The shoulder is surrounded by powerful muscles that immediately begin pulling the pieces in different directions. The rotator cuff muscles attach to the tuberosities above the fracture line, while the pectoralis major and deltoid attach to the shaft below it. This tug-of-war is a major reason surgical neck fractures displace and deform.

A cadaveric biomechanical study quantified how individual muscles distort the fracture. Unbalanced pull from the supraspinatus (the muscle running along the top of the shoulder blade to the greater tuberosity) produced the most varus tilt, angling the humeral head inward by about 35 degrees on average. The subscapularis, which attaches to the front of the lesser tuberosity, caused the greatest backward angulation and twisting of the head fragment.

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These muscle forces also matter for non-operative treatment. If you are wearing a sling after a surgical neck fracture, the position of your arm affects how much tension the pectoralis major places across the fracture. A cadaveric study of immobilization positions found that externally rotating the arm (turning it outward) from a fully internally rotated position to neutral significantly increased pectoralis major tension, with the clavicular head of the muscle generating roughly four times the force at neutral compared with a more internally rotated position. The more external rotation, the greater the pull across the break.

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This is why most protocols immobilize surgical neck fractures with the arm in some degree of internal rotation (hand across the belly inside a sling) rather than letting it hang in a neutral or externally rotated position. The goal is to minimize the forces pulling the fragments apart during the early weeks of healing.

The Axillary Nerve and Blood Supply at Risk

The surgical neck is a neighborhood crowded with important structures. The axillary nerve wraps around the humerus just below the surgical neck, traveling through a space called the quadrilateral space before curving forward around the bone underneath the deltoid muscle. A fracture at the surgical neck, or the swelling that follows, can stretch or compress this nerve. When it is injured, the deltoid muscle (the main muscle that lifts your arm out to the side) weakens or stops working, and a patch of skin over the outer shoulder may go numb.

The posterior circumflex humeral artery travels alongside the axillary nerve in this area. An anatomical study mapping the branches of both structures found that most branches of the axillary nerve were concentrated about 4 to 6 centimeters below the bony point of the shoulder (the acromion), while the artery’s branches clustered slightly lower, around 6 to 8 centimeters below.

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This proximity means that displaced surgical neck fractures can injure both the nerve and the artery simultaneously, though that combination is rare. A case report described a 71-year-old man who presented with a displaced surgical neck fracture alongside both a blocked axillary artery and complete axillary nerve paralysis. After urgent vascular repair and later a reverse shoulder replacement, he regained good overhead motion at one year, though some deltoid weakness lingered.

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Most axillary nerve injuries from surgical neck fractures are stretch injuries (neuropraxias) that recover on their own over weeks to months. But surgeons need to keep the nerve in mind during operative treatment too. A study of the deltoid-splitting surgical approach found that retraction of the soft tissues during the procedure progressively stretched the axillary nerve, causing measurable microscopic damage to the nerve’s myelin sheaths and axons.

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Despite that laboratory finding, a clinical comparison of the two main surgical approaches for plating proximal humerus fractures (the deltopectoral approach, which goes between the deltoid and pectoralis, versus the deltoid-splitting approach) found no significant differences in outcomes, operative time, blood loss, or rates of nerve abnormalities on electrical testing.

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Classifying the Fracture and the Reliability Problem

Surgeons typically classify proximal humerus fractures using the Neer system, which counts the number of displaced “parts” (humeral head, greater tuberosity, lesser tuberosity, and shaft). A two-part surgical neck fracture means the break is at the surgical neck and the shaft fragment has displaced away from the head, while the tuberosities remain attached to the head. More complex patterns with three or four parts involve additional displaced tuberosity fragments.

The problem is that surgeons frequently disagree about how to classify a given fracture. A survey of orthopedic shoulder specialists found that respondents agreed with the originally published classification only about 55% of the time, and when they disagreed, they tended to underestimate the number of parts. The overall agreement among the 138 surgeons surveyed was only fair.

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Even when a simplified version of the Neer system is used that focuses specifically on distinguishing two-part surgical neck fractures from more complex multi-part fractures, agreement between observers is only moderate. One study measuring this specific task found interobserver reliability that was substantial on plain X-rays but dropped when using CT scans alone.

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Advanced imaging helps in some situations. When upper-extremity specialists used 3D CT reconstructions, their agreement on fracture classification was significantly higher than with plain X-rays, particularly for complex four-part fractures.

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Agreement on the actual treatment plan may also vary by imaging method. One small study comparing X-ray, CT, and 3D-printed models found that agreement on treatment indications was lower with X-ray alone than with CT or 3D models, where raters reached perfect agreement on treatment decisions.

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Non-Operative Treatment and When It Works

Most two-part surgical neck fractures are treated without surgery. If the fragments are minimally displaced or can be reduced into acceptable alignment, a sling, early gentle motion, and progressive rehabilitation often produce good results. A long-term follow-up study of patients managed non-operatively for surgical neck fractures found no clinically relevant difference in function between the injured shoulder and the uninjured opposite shoulder. Patients reported acceptable function, good quality of life, and few radiological complications over time.

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That said, not every non-operatively managed fracture heals without problems. The main worry is nonunion, where the bone fails to knit together. A large study of over 1,800 patients with a head-shaft angle of 140 degrees or less identified that about 12% developed nonunion. The risk was not evenly distributed. Patients whose fracture angle was greater than 90 degrees and whose fragments were translated less than 50% had only about a 1% nonunion rate. But patients with more severe angulation (90 degrees or less) and more than 50% translation faced a dramatically higher rate, above 80%. Smoking independently increased the risk in both groups.

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So the decision about whether to skip surgery depends heavily on how displaced the fracture is, how much angulation is present, and patient factors like smoking status. If the geometry looks favorable, non-operative treatment works well for most people. If the numbers push into the high-risk zone, surgery becomes a more serious conversation.

Surgical Options for Displaced Fractures

When surgery is needed, the two main fixation methods for surgical neck fractures are locking plates (metal plates screwed into the bone) and intramedullary nails (rods inserted down the center of the bone). Both achieve satisfactory shoulder function, and no clear winner has emerged in head-to-head comparisons. A review of the evidence concluded that the choice should be tailored to the individual patient based on fracture type, age, bone quality, and functional expectations.

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For more complex, multi-fragment fractures (not just two-part surgical neck breaks), intramedullary nailing may offer practical advantages. One study found that while functional outcomes and complication rates were similar between the two methods, nailing involved shorter operative time and less blood loss.

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In elderly patients specifically, cement-augmented locking plates (where bone cement is injected through the screws to improve grip in weak bone) have been compared with intramedullary nails for two-part surgical neck fractures. At two years, the plate group showed modestly better functional scores on some measures, though overall results were similar and revision rates were identical at about 7% in each group.

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Reverse Shoulder Replacement for Older Patients

For elderly patients with severely displaced or complex fractures, reverse total shoulder arthroplasty (a type of joint replacement where the ball-and-socket relationship is flipped) has become an increasingly popular alternative to plates and nails. A multicenter randomized trial comparing reverse shoulder replacement to plate fixation in patients over 65 with displaced fractures found that the replacement group had significantly better function at two years, with a mean Constant score about 13 points higher than the plate group. The advantage was even more pronounced in the most complex fractures.

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Reverse replacement also appears to carry a lower reoperation risk compared with plate fixation. A pooled analysis found that revision rates were roughly 70% lower with reverse replacement than with plates, while complication rates and overall function were otherwise comparable.

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A network meta-analysis that ranked multiple treatment strategies for elderly proximal humerus fractures placed standard reverse replacement at the top, though the high variability in the pooled data meant no single comparison reached statistical significance. That ranking should be read as a trend favoring replacement rather than proof that it is always the best choice.

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Rehabilitation After a Surgical Neck Fracture

Whether your fracture was treated in a sling or with surgery, rehabilitation follows a broadly similar staged progression. A systematic review of published rehab protocols found consistent patterns across dozens of treatment groups. Most protocols used a sling for about three weeks, started gentle pendulum exercises (letting the arm swing passively) on the first day after treatment, and introduced passive range-of-motion exercises within the first few days. Active-assisted motion (you help move the arm with your other hand or a pulley) typically started around three weeks. Unrestricted motion and strengthening exercises were generally allowed at about six weeks.

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The balance between protecting the fracture and getting the shoulder moving is the central tension in rehab. Too much immobilization leads to stiffness, which is the most common complication after proximal humerus fractures. Too aggressive movement too early risks displacing the fracture. Most modern protocols lean toward earlier motion than was historically standard, particularly pendulum and passive exercises, because the evidence suggests early gentle movement improves outcomes without increasing displacement risk.

Pain, Function, and What to Expect Long Term

One of the most useful things to know after a surgical neck fracture is what the trajectory of pain and function actually looks like. A systematic review of quality-of-life data after proximal humerus fractures in elderly patients (average age about 75, roughly three-quarters women) found that pain scores decreased steadily over the first year regardless of treatment type, with average pain ratings at 12 months ranging from mild to low-moderate. Quality-of-life indices improved after the first six to eight weeks and then plateaued, with no significant differences between surgical and non-surgical treatment.

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That finding echoes a theme running through the proximal humerus literature: for many fracture patterns, especially minimally displaced surgical neck fractures, non-operative and operative treatment converge on similar long-term outcomes. Surgery tends to offer faster early improvement and better results for the most displaced fractures, but the gap narrows over time. The practical implication is that unless the fracture geometry is clearly unfavorable, a well-managed non-operative approach is not a compromise. It is a legitimate first-line treatment with evidence to back it up.

Avascular Necrosis of the Humeral Head

One feared complication of proximal humerus fractures is avascular necrosis, where part of the humeral head loses its blood supply and the bone dies. The blood supply to the humeral head enters through small vessels that travel along the surgical neck region, which is why fractures here can disrupt it. However, the clinical reality is more reassuring than the anatomy might suggest. Although certain fracture patterns correlate with loss of blood flow at the time of injury, the humeral head has a capacity to revascularize, and most fractures do not progress to full-blown avascular necrosis. Newer surgical techniques that provide more stable fixation also appear to reduce this risk.

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For isolated two-part surgical neck fractures, avascular necrosis is uncommon because the tuberosities (which carry much of the blood supply) remain attached to the head. The risk rises sharply with three- and four-part fractures where tuberosities are displaced, because more of the vascular pathways are interrupted. This is one reason why complex fractures in older patients are increasingly treated with joint replacement rather than attempted fixation: if the blood supply is likely already compromised, fixing the native bone carries a higher risk of the head eventually collapsing.