Humeral Shaft (Diaphyseal) Fractures

Introduction

Diaphyseal fractures of the humerus account for approximately 3 percent of all adult fractures, with a bimodal age distribution reflecting both high-energy trauma in young men and low-energy fragility fractures in elderly women. The humerus is remarkable among the long bones for its high inherent capacity for union with non-operative management — the muscular envelope, the predominantly cancellous diaphyseal bone, and the absence of weight-bearing demands together produce union rates that approach or exceed those of operative fixation in most series. The functional brace, popularized by Augusto Sarmiento beginning in the 1970s, has remained the cornerstone of management of humeral shaft fractures for half a century, and the modern evolution of management has been incremental rather than revolutionary. The dominant clinical concerns are the high rate of radial nerve injury that accompanies humeral shaft fracture (the highest of any long bone) and the increasing recognition that certain fracture patterns benefit from operative fixation despite the generally favorable non-operative trajectory. This chapter draws principally on Rockwood and Green’s Fractures in Adults, AO Principles of Fracture Management, Apley & Solomon’s, and Miller’s Review of Orthopaedics.

Surgical Anatomy

The humeral shaft extends from the surgical neck proximally to the supracondylar region distally. The cross-section transitions from a roughly circular proximal third through an oval mid-shaft to a triangular distal third, with the apex pointed posteriorly. The medullary canal is relatively narrow at the isthmus (typically located in the mid-third, with diameter 8 to 12 mm in adults) and tapers gradually proximally and distally. The cortical thickness is greatest at the mid-shaft and diminishes toward both metaphyses. The principal muscular attachments shape fracture displacement patterns. The deltoid insertion on the deltoid tuberosity, at the junction of the proximal and middle thirds, abducts the proximal fragment in fractures distal to its insertion. The pectoralis major insertion proximal to this, on the lateral lip of the bicipital groove, adducts the proximal fragment in fractures between its insertion and the deltoid insertion. The combined effect produces characteristic displacement: fractures proximal to the pectoralis major are abducted and externally rotated by the rotator cuff; fractures between the pectoralis and deltoid insertions are adducted and medially displaced by the unopposed pectoralis; fractures distal to the deltoid are abducted and proximally displaced by the deltoid. The neurovascular relationships are critical. The radial nerve passes posteriorly behind the humerus in the spiral groove, descending obliquely from medial to lateral across the posterior surface of the bone in the mid-shaft region, then passing anteriorly through the lateral intermuscular septum at the junction of the middle and distal thirds of the humerus. The nerve is anatomically intimate with the bone in the spiral groove region (with literature estimating it lies within 5 mm of the periosteum), placing it at high risk of injury in mid-shaft and distal-third fractures and during surgical exposure. The brachial artery descends along the medial aspect of the arm, accompanied by the median nerve; both are

typically protected from injury by their medial position, except in transverse or oblique fractures of the middle and distal third where penetrating displacement can occur. The ulnar nerve descends along the medial aspect of the arm posterior to the brachial artery, passing posterior to the medial epicondyle at the elbow.

Classification

The AO/OTA classification for humeral shaft fractures (region 12) is the most widely used system. Type A is a simple fracture with two main fragments: A1 spiral, A2 oblique (>30 degrees), A3 transverse (<30 degrees). Type B is a wedge fracture with intact bridging contact between the main fragments after wedge reduction: B1 spiral wedge, B2 bending wedge, B3 fragmentary wedge. Type C is complex fracture with no contact between main proximal and distal fragments after reduction: C1 spiral complex, C2 segmental, C3 irregular comminuted. This morphological grading correlates roughly with treatment intensity and outcome. A useful clinical descriptive classification subdivides fractures by location (proximal third, middle third, distal third), by mechanism (low- versus high-energy), and by configuration (transverse, spiral, oblique, comminuted, segmental, butterfly). The Holstein-Lewis fracture, described by Holstein and Lewis in 1963, is a spiral oblique fracture of the distal third of the humerus with characteristic displacement that puts the radial nerve at particular risk of injury — the most clinically important of the named patterns.

Clinical Assessment

The patient presents with pain, swelling, and gross deformity of the arm after trauma. The mid-arm is shortened and angulated; abnormal motion and crepitus are demonstrable but should not be deliberately elicited. Neurovascular examination is mandatory and must specifically document radial nerve function — wrist and finger extension, thumb abduction (extensor pollicis longus), and sensation over the first dorsal webspace of the hand. The median and ulnar nerves are also examined. Radial pulse is checked; vascular injury is uncommon but is more frequent in penetrating injuries and in low transverse fractures with significant displacement. Plain radiographs in two orthogonal planes (AP and lateral) with the shoulder and elbow joints included are mandatory. CT is rarely needed for diaphyseal fractures unless there is intra-articular extension into the proximal or distal humerus.

Radial Nerve Injury

The radial nerve is injured in approximately 8 to 16 percent of humeral shaft fractures, the highest rate among the long bones. The classical association is with distal-third fractures, particularly the Holstein-Lewis spiral oblique pattern, where the radial nerve passes through the lateral intermuscular septum and is tethered relative to the displacing distal fragment. However, the majority of radial nerve injuries are neurapraxic — a stretching or contusion of the nerve without loss of continuity — and recover spontaneously, typically beginning within 3 to 4 weeks of injury and reaching maximum recovery by 4 to 6 months.

The management of the radial nerve palsy associated with closed humeral shaft fracture has been debated for decades. The expectant approach — observation with serial clinical examination and electrophysiological studies, with surgical exploration reserved for failure of recovery by 4 to 6 months — is supported by the high spontaneous recovery rate (~75 to 90 percent) and is the standard for closed injuries without other indications for operative fracture management. The early exploration approach — surgical exploration of the radial nerve at the time of fracture surgery in patients undergoing operative fixation for other indications, or in patients with open fractures — is reserved for the operative cohort. Secondary radial nerve palsy (palsy that develops after fracture reduction or manipulation) is more concerning than primary palsy and is generally considered an indication for surgical exploration, on the grounds that the nerve may have been entrapped between fragments during reduction. Electrophysiological studies (electromyography, nerve conduction studies) are typically performed at 6 weeks and again at 3 to 4 months if recovery has not occurred. The first electrophysiological signs of recovery are typically motor unit potentials in the brachioradialis (the most proximal radial-innervated muscle), advancing distally to the wrist and finger extensors and finally the thumb extensor. Failure of clinical and electrophysiological recovery by 4 to 6 months is an indication for surgical exploration with neurolysis, nerve grafting, or tendon transfer (pronator teres to ECRB, FCR to EDC, palmaris longus to EPL — the standard radial nerve palsy transfer pattern) as appropriate.

Non-Operative Management — The Sarmiento Functional Brace

The functional brace for humeral shaft fractures, described by Augusto Sarmiento beginning in 1977 and continually refined through the following decades, has remained the standard non-operative treatment for closed humeral shaft fractures. The principle is the use of a circumferential thermoplastic brace that applies hydrostatic compression to the soft tissues of the arm, restraining angulation while permitting joint motion at the shoulder and elbow and avoiding the immobilization-related complications of casting. The brace allows immediate range of motion of the shoulder and elbow once swelling has subsided (typically by 1 to 2 weeks), with progressive rehabilitation continuing throughout the healing period. The protocol begins with a coaptation splint (a U-shaped plaster slab from the medial axilla, around the elbow, to the deltoid region) at presentation, with the arm dependent in a sling. The coaptation splint provides initial stability and allows soft-tissue swelling to subside. At approximately 7 to 14 days, the functional brace is applied, and the patient is encouraged to begin pendulum and gentle range-of-motion exercises. The brace is worn continuously for approximately 8 to 12 weeks, with weekly radiographic follow-up initially to monitor alignment. Acceptable alignment criteria are remarkably forgiving in the humerus, reflecting both the limited functional impact of moderate malunion in this non-weight-bearing bone and the substantial soft-tissue camouflage of any residual deformity. The classical Sarmiento criteria are: anterior angulation up to 20 degrees, varus angulation up to 30 degrees (or some authors say 20 degrees in females and 30 in males because of breast-related

obstruction), rotation up to 15 to 20 degrees, and shortening up to 2 to 3 centimeters. Within these limits, functional outcomes are uniformly good. The reported union rate with functional bracing ranges from 85 to 95 percent in classic series, with the principal risk factors for failure being proximal-third fractures (where adequate brace fit is difficult), transverse fractures (which are biomechanically less favorable than spiral patterns), and significant initial displacement. The recent HUSTLE trial (Rämö et al., 2020) and the FISH trial (Matsuura et al., 2019) have raised some questions about the actual union rate of functional bracing in contemporary practice, with reported nonunion rates of 15 to 25 percent in some recent series — substantially higher than the historical figures. The disparity may reflect more rigorous adjudication of nonunion in modern trials, the difficulties of bracing in increasingly obese populations, and patient compliance issues.

Operative Management — Indications

Despite the favorable biology of the humeral shaft, operative fixation is indicated in a substantial minority of patients. Recognized indications include: • Polytrauma — patients with multiple injuries who require upper-extremity weight- bearing for crutch ambulation, or in whom prolonged supine positioning is required, benefit from rigid fixation. • Open fractures requiring debridement, where the need for repeat surgical access makes fixation efficient. • Vascular injury requiring repair, where fracture fixation precedes or accompanies vascular reconstruction. • Pathological fractures or impending pathological fractures, where biological union may not occur. • Floating elbow — combined humeral and forearm fracture in the same limb — where rigid fixation of at least one component allows rehabilitation. • Bilateral humeral fractures, by similar logic. • Segmental fractures, where bracing is mechanically inferior. • Fractures with extensive soft-tissue injury or burns precluding brace application. • Obese patients in whom brace fit cannot be reliably achieved. • Failure of conservative management — nonunion or delayed union after a trial of bracing. • Patient preference for early return to work or activity in younger patients with appropriate counseling regarding risks and benefits. The HUSTLE and FISH trial data and more recent meta-analyses have shifted some practice toward more liberal use of primary operative fixation for displaced fractures, particularly in younger active patients, but the evidence remains mixed and many centers continue to favor primary functional bracing as the default.

Operative Techniques

Plate Fixation Open reduction and internal fixation with a plate is the most common operative technique. The approach is typically the anterolateral approach (developing the interval between brachialis and brachioradialis, with identification and protection of the radial nerve in the distal third) for proximal- and middle-third fractures, or the posterior approach (Henry posterior, with triceps-splitting or paratricipital exposure and explicit identification of the radial nerve in the spiral groove) for middle- and distal-third fractures. A 3.5-mm or 4.5-mm dynamic compression plate (DCP, LC-DCP) or locking compression plate (LCP) is applied with the principles of anatomical reduction for simple patterns (compression plating) or bridge plating for comminuted patterns. The plate length should provide at least three to four cortical screws (six to eight cortices) on each side of the fracture. The recently described dual mini-fragment plating technique applies two smaller plates at 90 degrees to each other and may improve construct stability and reduce hardware prominence; outcomes are reported as comparable to single large plate fixation. The principal complications of plate fixation include iatrogenic radial nerve injury (the most feared complication, with reported rates of 5 to 15 percent in posterior approaches; the nerve must be identified and protected throughout the procedure), infection (1 to 3 percent), nonunion (2 to 8 percent), and hardware-related symptoms. Removal of hardware is sometimes required for symptomatic prominence but should be deferred for at least 18 to 24 months and accompanied by patient counseling regarding refracture risk. Intramedullary Nailing Intramedullary nailing of the humerus, using antegrade or retrograde nails, has its proponents and offers the theoretical advantages of indirect reduction, smaller exposures, and load-sharing fixation. The historical results have been somewhat variable, with concerns about shoulder pain after antegrade nailing (from the proximal insertion site through the rotator cuff or with prominence under the acromion), elbow stiffness after retrograde nailing, and technical difficulties with reduction and locking screw placement, particularly proximally where the axillary nerve is at risk. Modern straight humeral nails with multiplanar locking and improved insertion techniques have improved outcomes. The most appropriate indications for nailing include segmental fractures, pathological or impending pathological fractures (where the nail provides protection of the entire length of the bone), and selected diaphyseal fractures in patients with poor soft-tissue conditions for plating. The MIRTH trial (2014) and the Singisetti meta-analysis (2010) suggest broadly comparable outcomes between nailing and plating in selected cohorts, but plating remains the predominant technique in most centers.

External Fixation External fixation has a limited role in humeral shaft fracture, primarily as temporary stabilization in damage-control settings, open fractures with extensive soft-tissue compromise, and severely contaminated open fractures with bone loss. Definitive

treatment with external fixation alone is uncommon because of pin-related complications and the long duration of treatment required.

Special Considerations

Pathological Fractures The humerus is the second most common site (after the femur) of metastatic disease and is a frequent site of pathological fracture in cancer patients. The Mirels scoring system for impending pathological fracture (covered in Topic Orth-3) applies; prophylactic stabilization is indicated for scores of 8 or higher. For established pathological fractures, the principles include rigid stabilization to allow immediate pain-free use of the limb, fixation of the entire length of the bone (typically by intramedullary nailing) to prevent subsequent fracture distal to the construct, and adjuvant local treatment (radiation, cementation) as indicated by the underlying pathology. Pediatric Humeral Shaft Fractures Pediatric humeral shaft fractures heal reliably with non-operative management because of the periosteum integrity and the considerable remodeling potential of the growing skeleton. Acceptable alignment limits are even more permissive than in adults. Birth- related humeral shaft fractures in the newborn (typically associated with difficult delivery and brachial plexus injury) heal reliably with simple immobilization to the chest with a soft binder. Older children with humeral shaft fractures are treated by sling or brace; the rare indication for operative management is the open fracture or the older adolescent with severely displaced segmental fractures. Floating Elbow The combination of humeral and forearm fractures in the same limb (the “floating elbow”) creates a biomechanical situation in which closed treatment is difficult because adjacent joint motion translates directly to motion at both fracture sites. Operative fixation of at least one component (typically the more severe) is the standard approach, with the second component often managed by closed means after stabilization of the first. Nonunion and Delayed Union Despite the favorable healing characteristics, humeral shaft nonunion is a recognized problem and is more common than was historically appreciated. Risk factors include transverse fracture patterns (which are biomechanically less favorable), distraction at the fracture site, fracture gap, obesity, smoking, and inadequate immobilization. Treatment requires conversion to operative fixation, typically by plating with bone graft, with high success rates (>90 percent) for the standard reconstruction.

Summary and Take-Home Points

Humeral shaft fractures are characterized by a uniquely favorable healing biology, with the Sarmiento functional brace remaining the cornerstone of non-operative management for half a century. The historical union rates of 85 to 95 percent have been challenged by more

recent data suggesting somewhat higher contemporary nonunion rates, perhaps reflecting changing patient populations and methodological rigor in modern trials. Acceptable alignment is forgiving — 20 degrees of anterior angulation, 30 degrees of varus, 15 to 20 degrees of rotation, 2 to 3 cm shortening — and reflects the non-weight-bearing role of the bone. The radial nerve is injured in 8 to 16 percent of humeral shaft fractures, with the Holstein- Lewis distal third spiral oblique pattern the classical association. The majority of primary radial nerve injuries are neurapraxic and recover spontaneously, with expectant management appropriate for most closed injuries and observation for 4 to 6 months before considering exploration. Secondary radial nerve palsy after manipulation is more concerning and is an indication for exploration. Operative fixation is indicated in polytrauma, open fractures, vascular injury, floating elbow, segmental fractures, pathological fractures, and selected other circumstances. Plate fixation through anterolateral or posterior approach is the predominant technique, with intramedullary nailing offering a useful alternative in selected indications and providing particular advantages in pathological fractures and segmental injuries. The iatrogenic radial nerve injury in posterior plating approaches remains the principal feared complication and demands explicit identification and protection of the nerve throughout the procedure. The chapter that follows turns to the elbow, where the radial nerve continues to be a structural consideration and where the principles of articular fracture reconstruction at the elbow joint introduce a different set of concerns from the diaphyseal management considered here.