A humeral shaft fracture is a fracture of the humeral diaphysis between the surgical neck and the supracondylar ridge. Most closed humeral shaft fractures unite in a functional brace, and the radial nerve is the structure the ST3 interviewer wants you to examine, document and manage under the December 2021 BOAST on peripheral nerve injury.
Key takeaways
- Functional bracing unites the large majority of humeral shaft fractures: Sarmiento's series of 922 patients reported nonunion in under 2% of closed and 6% of open fractures.
- Radial nerve palsy complicates 11.8% of humeral shaft fractures (532 of 4,517), and 88.1% recover; spontaneous recovery reached 70.7% in those treated expectantly (Shao 2005).
- The FISH trial (JAMA 2020) found no significant difference in DASH at 12 months between plating and bracing, but 30% of the braced arm crossed over to surgery and 25% developed nonunion.
- The December 2021 BOAST on peripheral nerve injury requires a documented nerve examination at first contact, after every manipulation or cast, and before and after any operation.
- Surgery is for open fractures, vascular injury, polytrauma, a floating elbow, pathological fracture and failure of closed treatment, not for the fracture pattern alone.
What is a humeral shaft fracture and how is it classified?
A humeral shaft fracture is classified by the AO/OTA system as bone 12: type A simple, type B wedge, and type C multifragmentary, with a location in the proximal, middle or distal third.
In practice the panel wants a description, not a code: closed or open, the third involved, transverse, oblique, spiral or comminuted, and the degree of displacement and angulation.
The Holstein-Lewis fracture is a spiral fracture of the distal third of the humeral shaft associated with radial nerve palsy, and naming it correctly signals that you know the anatomy.
Humeral shaft fractures follow two populations: low-energy falls in older patients with osteoporotic bone, and high-energy road traffic collisions or sport in younger patients.
How does the radial nerve relate to the humeral shaft?
The radial nerve lies against the posterior humeral shaft in the spiral groove, then pierces the lateral intermuscular septum to run anterior to the lateral epicondyle. That is why humeral shaft fractures put it at risk.
Research by Shao and colleagues, a systematic review of 4,517 humeral shaft fractures, found palsy was significantly more common with fractures of the middle and middle-distal thirds.
The same review found transverse and spiral humeral shaft fractures were more likely to injure the radial nerve than oblique or comminuted patterns.
Clinically a radial nerve palsy after a humeral shaft fracture presents as wrist drop, loss of finger and thumb extension, and numbness over the first dorsal web space.
How should you assess a humeral shaft fracture in the emergency department?
Assessment of a humeral shaft fracture starts with ATLS if the mechanism was high energy, then the limb: skin, compartments, distal pulses and a full, documented neurological examination.
The December 2021 BOAST on peripheral nerve injury states that an examination of all the functions of a peripheral nerve should be carried out and recorded at the first opportunity after injury.
The same standard requires that examination to be repeated after any intervention to the limb, such as manipulation or application of a cast, and recorded in enough detail to compare later.
Radiographs of a humeral shaft fracture must include the shoulder and the elbow, because an associated proximal or distal injury changes the plan.
NICE NG38 states that adults with suspected long bone fractures of the humerus should receive oral paracetamol for mild pain and intravenous paracetamol with titrated intravenous morphine for severe pain.
What is the initial management of a humeral shaft fracture?
Initial management of a closed humeral shaft fracture is analgesia, a coaptation splint or above-elbow cast with a collar and cuff, and a repeat documented nerve examination afterwards.
In Sarmiento's series the limb was stabilised in an above-elbow cast or coaptation splint for an average of nine days before the prefabricated functional brace was applied.
An open humeral shaft fracture follows the December 2017 BOAST on open fractures: intravenous antibiotics ideally within one hour of injury, photograph and cover the wound, and plan orthoplastic debridement.
Any new nerve deficit after a manipulation is a trigger, under the BOAST, to loosen bandages, split the cast to skin, reposition the limb and seek advice immediately if that fails.
When does a humeral shaft fracture need surgery?
A humeral shaft fracture needs surgery when the injury or the patient makes bracing unsafe: open fracture, vascular injury, polytrauma, an ipsilateral forearm fracture (floating elbow), or a pathological fracture.
Other accepted indications are bilateral humeral shaft fractures, failure to hold an acceptable reduction in a brace, and body habitus that makes a brace impossible to fit.
That said, the fracture pattern alone is not an indication. The panel wants to hear that surgery is chosen for the patient in front of you, not for the radiograph.
Where a humeral shaft fracture with a nerve injury is going to be fixed, the BOAST states formal advice should be sought before surgery as part of multidisciplinary care.
What does the evidence say about bracing versus plating a humeral shaft fracture?
The evidence says both work and both have costs. Sarmiento's 2000 series of 922 braced humeral shaft fractures reported nonunion in under 2% of closed and 6% of open fractures.
In that series 87% of humeral shaft fractures healed in under 16 degrees of varus and 81% in under 16 degrees of anterior angulation, and 98% of patients had 25 degrees or less of shoulder restriction.
The FISH randomised trial (Rämö, JAMA 2020) allocated 82 adults with closed displaced humeral shaft fractures to plate fixation or functional bracing.
At 12 months the mean DASH was 8.9 after surgery and 12.0 after bracing, a difference of -3.1 points (95% CI -9.6 to 3.3), which was not significant against a 10-point MCID.
However, 13 of the 44 braced patients (30%) crossed over to surgery to promote healing and 11 (25%) developed nonunion, while 3 of the 38 surgical patients (8%) had a temporary radial nerve palsy.
In practice the answer is shared decision-making: bracing avoids an operation and an iatrogenic nerve palsy, plating avoids a one-in-four nonunion risk in this trial population.
How should a radial nerve palsy with a humeral shaft fracture be managed?
A primary radial nerve palsy with a closed humeral shaft fracture is managed expectantly: document it, splint the wrist, protect the skin and follow the BOAST pathway for advice.
Shao's review found no significant difference in final outcome between palsies managed expectantly and those explored early, concluding that expectant treatment avoids many unnecessary operations.
The December 2021 BOAST states formal advice should be sought within 24 hours for any peripheral nerve injury where operative management of the fracture is not indicated.
A palsy that appears after a manipulation or after surgery on a humeral shaft fracture is different: the BOAST asks for immediate advice once loosening measures have failed.
An open humeral shaft fracture with a palsy is explored at the time of debridement, because the nerve may be lacerated, and the BOAST requires advice within 24 hours for a penetrating injury with deficit.
What are the complications of a humeral shaft fracture?
The complications of a humeral shaft fracture are nonunion, malunion, stiffness of the shoulder or elbow, radial nerve palsy (primary or iatrogenic) and, after surgery, infection and implant failure.
Nonunion is the complication that drives the surgical debate: under 2% for closed fractures in Sarmiento's braced series, but 25% in the braced arm of the FISH trial.
Iatrogenic radial nerve palsy after plating is real: 8% of the surgical arm in FISH, all temporary. The BOAST requires the nerve's relationship to any implant to be recorded in the operation note.
Malunion after bracing is usually tolerated; Sarmiento described the residual deformities as functionally and aesthetically acceptable, though no guideline sets a numerical limit you can quote.
What is the interviewer listening for on humeral shaft fractures?
The interviewer is listening for a documented radial nerve examination before and after everything you do to a humeral shaft fracture, and for a plan that names the BOAST.
They want to hear that a primary palsy is watched and a secondary palsy is escalated, that bracing is the default for a closed fracture, and that you can quote why (Sarmiento, FISH).
A strong candidate can say the FISH numbers both ways: no significant functional difference, but 30% crossover and 25% nonunion with bracing, and 8% temporary nerve palsy with surgery.
What are the common mistakes with humeral shaft fractures?
The commonest mistake with a humeral shaft fracture is a neurovascular examination recorded as "NVI" with no detail, which the BOAST specifically says is not enough to compare later.
Others are imaging the shaft without the shoulder and elbow, exploring every primary radial nerve palsy, and treating a secondary palsy after manipulation as something to review tomorrow.
Candidates also over-operate: a transverse midshaft pattern in a fit adult is not an indication on its own, and the panel will ask you to justify the theatre trip.
How this comes up at the ST3 interview
A humeral shaft fracture arrives at the ST3 T&O clinical station as a radiograph and a one-line stem: a 34-year-old cyclist with a spiral midshaft fracture and a wrist drop.
The follow-ups are predictable: how do you examine the radial nerve, what do you document, would you explore it, what does the BOAST say, and what would make you operate on the fracture.
orthointerview's question bank turns this into station-style questions with model answers and AI-marked spoken practice, across 782 questions and 100 scenarios, so the answer is rehearsed out loud before the day.