Stress fractures of the humeral shaft

INTRODUCTION — Humeral stress fractures seldom occur, but there are case reports, particularly among overhead athletes, weightlifters, gymnasts, and rowers. The management of stress fractures of the humeral shaft will be reviewed here. Nonstress humeral fractures are discussed separately. (See "Midshaft humerus fractures in adults" and "Proximal humeral fractures in adults".)

CLINICAL ANATOMY — The humerus is the largest bone in the upper extremity (figure 1 and figure 2). The proximal humerus articulates with the glenoid of the scapula to form the shoulder joint. The distal humerus articulates with the radius and ulna at the elbow (figure 3). Shoulder anatomy is complex and discussed in greater detail separately. (See "Evaluation of the adult with shoulder complaints", section on 'Anatomy and biomechanics'.)

The greater tuberosity, located lateral to the humeral head on the proximal humerus, provides the attachment for three of the rotator cuff muscles: supraspinatus, infraspinatus, and teres minor (figure 4). The lesser tuberosity, located on the anterior surface of the proximal humerus, provides the attachment for the subscapularis muscle. For the purposes of fracture classification, the lesser tuberosity marks the boundary between the proximal humerus and the midshaft.

The humeral shaft supplies the attachment for a number of powerful muscles (figure 5). The pectoralis major muscle inserts on the proximal shaft, while the deltoid muscle attaches to the midshaft. The biceps brachii and triceps muscle groups attach distally.

The tendon of the long head of the biceps brachii muscle passes between the lesser and greater tuberosities as it courses from its origin on the superior portion of the glenoid to its insertion on the proximal radius (figure 6).

Stress injuries along the humerus are often due to increased stress on the bone from internal and external rotary forces. The main external rotators of the humerus are the deltoid, supraspinatus, infraspinatus, and teres minor muscles; the main internal rotators are the pectoralis major, latissimus dorsi, and subscapularis muscles.

The blood supply to the humeral shaft is supplied by branches of the axillary and brachial arteries (figure 7). The brachial artery moves anteriorly from the medial humerus at the bone's distal portion, just before it branches to form the radial and ulnar arteries distal to the elbow joint. The vascular supply can be disrupted if there is significant displacement of shaft fragments.

The radial nerve traverses the posterior humeral shaft (figure 8). Radial nerve injuries can occur with significant displacement of mid to distal shaft fractures. The median and ulnar nerves travel along the medial humerus, adjacent to the brachial artery, and are rarely injured.

EPIDEMIOLOGY AND MECHANISM OF INJURY — Upper limb stress fractures account for approximately 3 to 8 percent of all stress fractures. Overhead throwing is the most common mechanism, but violent muscle contraction during activities such as arm wrestling or weightlifting accounts for some number as well [1-4]. Humeral stress fractures are reported most often in baseball and tennis, but also occur during sports like swimming and rowing or while forcefully throwing an object, such as a shot put, snowball, javelin, or hand grenade [2,4-7]. As with other stress fractures, a sudden increase or change in activity often precedes the injury [2]. Osteoporosis can lead to humeral stress fractures, which typically involve low velocity trauma. (See "Overview of stress fractures".)

Although the mechanism is not completely understood, humeral stress fractures likely result when the extreme torque created by forceful overhead throwing or heavy lifting places excessive stress on immature or unconditioned bone. Tremendous torsional stresses are exerted upon the mid and distal humerus at the point between the late cocking and early acceleration phase of baseball pitching when the external rotators are still contracting and the internal rotators and flexors start to contract as well (figure 9) [6,8]. A retrospective study of 90 recreational baseball players with midshaft humeral fractures concluded that these fractures occur during the acceleration phase of throwing and can develop in any recreational athlete attempting to throw hard [6]. The axial loads generated by the biceps and triceps muscles during pitching protects the humerus from torsional stress during throwing. Thus, muscle fatigue from repetitive throwing and poor conditioning likely contributes to the development of stress fractures [7]. Complete fractures are more common in recreational athletes because of their irregular muscular activity [6,9].

In tennis, the mechanism of injury is also thought to involve rotational stress. During the acceleration phase of the serve, the humerus is brought into extreme internal rotation, while valgus force at the elbow exerts medial and posterior stress [10,11]. In arm wrestling, humeral stress fractures are thought to occur from torsional, bending, and axial compressive forces exerted upon the humerus simultaneously [12]. Fractures from weight lifting are likely caused by forceful opposing muscle contractions [13].

CLINICAL PRESENTATION AND EXAMINATION — Patients with humeral stress fractures often present with focal pain in the mid or distal shaft of the humerus that increases with activity. Pain occurs with throwing, lifting, or when pushing off with the injured arm, and increased gradually over weeks. Pain may also occur at rest. In contrast, complete fractures present with acute severe pain in the mid humerus and are often associated with a “pop.”

Examination can reveal a deformity, focal tenderness and increased pain with strength testing. Complications are rare, but peripheral vascular and nerve function (particularly of the radial nerve) should be assessed.

Humeral stress fractures are often missed initially or are found during a workup for a different presumptive diagnosis. Suspect the injury in patients who are involved in repetitive overhead sports or heavy lifting and present with mid or distal humeral bone pain without a clear history of injury. Several case reports of "spontaneous" humeral shaft fractures while throwing describe a prodrome of milder, chronic pain with focal tenderness preceding the acute injury [1,2,6,7]. Most likely, a stress fracture was preexistent. Such "throwing fractures" of the humerus are generally mid to distal shaft spiral fractures that are minimally displaced. They are treated like standard humeral fractures. (See "Midshaft humerus fractures in adults" and "Proximal humeral fractures in adults".)

DIFFERENTIAL DIAGNOSIS — Stress fractures of the humeral shaft are difficult to diagnose. The diagnosis should be considered in overhead athletes and patients who repetitively lift heavy objects. A number of problems in the shoulder, humerus, and elbow can present in a similar fashion. Often a humeral stress fracture is diagnosed after failed treatment for one or two more common problems. A differential diagnosis is provided below.

●Shoulder impingement or rotator cuff tendinopathy or tear – Referred pain to the deltoid or upper arm is extremely common with impingement or rotator cuff pathology. Rotator cuff tears present with pain at the shoulder joint, which may refer to the humerus. Weakness is present with resisted shoulder movement. Shoulder impingement and rotator cuff tendinopathy present gradually with pain at the shoulder joint that may refer to the humeral shaft, but there is no focal tenderness. Both passive movement and active, resisted movement cause symptoms. In contrast, humeral shaft stress fractures develop insidiously. There is focal tenderness over the humerus but shoulder joint pain is rare. While there is pain with active and resisted shoulder movement, there is no weakness or pain with passive motion or impingement testing. Advanced imaging provides a definitive diagnosis, when needed. (See "Subacromial (shoulder) impingement syndrome" and "Rotator cuff tendinopathy" and "Presentation and diagnosis of rotator cuff tears".)

●Muscle strain and tendinopathy – Acute anterior arm pain can be caused by a biceps muscle or tendon injury, while posterior pain may be caused by comparable triceps pathology. Overuse tendinopathy of the biceps tendon or triceps tendon can cause insertional pain or pain referred to the humeral shaft. Muscle strains and tendon tears usually occur acutely and are often associated with swelling. Tendinopathies present with a gradual onset of pain, which increases with eccentric stretching or active and resisted movement. Focal tenderness is present only near the tendon insertion. Humeral stress fractures develop insidiously and do not cause swelling. While resisted movement may elicit pain, eccentric stretching does not. Advanced imaging provides a definitive diagnosis, when needed. (See "Biceps tendinopathy and tendon rupture" and "Throwing injuries of the upper extremity: Clinical presentation and diagnostic approach".)

●Ligament injury – Ulnar collateral ligament (UCL) sprains or partial tears can present with acute or chronic medial elbow pain. Typically, there is pain with throwing and examination reveals focal tenderness at the medial elbow along the insertion of the UCL and laxity with valgus stress testing of the elbow. In contrast, the pain of humeral stress fractures is generally proximal and diffuse. While throwing and valgus stress testing may elicit pain, so do many other resisted movements involving the shoulder and elbow. Advanced imaging provides a definitive diagnosis, when needed. (See "Throwing injuries of the upper extremity: Clinical presentation and diagnostic approach", section on 'Ulnar collateral ligament (UCL) injury'.)

●Physeal injuries – In skeletally immature patients, stress injuries to the proximal humeral physis (little league shoulder) or distal humeral physis (little league elbow) are more common than humeral shaft stress fractures. All stress fractures present with a gradual onset of pain worsened by throwing. Physeal injuries manifest focal tenderness over the proximal or distal physis of the humerus, while humeral shaft stress fractures manifest tenderness at the shaft. (See "Throwing injuries of the upper extremity: Clinical presentation and diagnostic approach", section on 'Proximal humeral epiphysiolysis (Little League shoulder)' and "Elbow injuries in active children or skeletally immature adolescents: Approach", section on 'Little League elbow'.)  

●Nerve entrapment – Referred pain originating from the cervical spine, brachial plexus, or peripheral nerves can present with pain along the humerus. Neck, clavicular, or scapular pain may also be present, and referred pain may extend to the forearm or hand. Numbness, tingling, weakness, or muscle atrophy (if nerve injury is long-standing) may be present. In contrast, stress fractures of the humerus do not present with pain proximal or distal to the humerus, and symptoms and signs associated with neurologic injury, such as numbness or tingling, are absent. (See "Clinical features and diagnosis of cervical radiculopathy" and "Overview of upper extremity peripheral nerve syndromes".)

●Thoracic outlet syndrome (TOS) – Neurogenic or vascular TOS can cause pain along the humerus. The pain is often positional and associated with neurologic or vascular symptoms. Clavicular or scapular pain may be present, and referred pain may extend to the forearm or hand. In contrast, stress fractures of the humerus do not present with pain proximal or distal to the humerus, and do not have associated neurologic or vascular symptoms or signs. (See "Overview of thoracic outlet syndromes".)

●Axillary-subclavian vein thrombosis – Thrombosis of the axillary-subclavian vein (Paget-Schroetter syndrome) is associated with repetitive activity involving the affected upper extremity. The condition presents with acute swelling and pain of the upper extremity after exertion. Humeral stress fractures do not present with vascular symptoms, and swelling is only present if there is a complete fracture. Advanced imaging provides a definitive diagnosis, when needed. (See "Primary (spontaneous) upper extremity deep vein thrombosis".)

●Neoplasm – Malignant and benign bone and soft tissue tumors can develop in the upper extremity causing pain in the region of the humerus. Malignant tumors may be associated with constitutional symptom, such as fever, chills, or weight loss, or with pain that is worse at night. But such symptoms and signs are not consistently present. As the presentation of stress fractures and benign bone tumors can be similar, imaging studies, starting with plain radiographs, should be obtained if either is suspected, and advanced imaging (eg, CT or MRI) may be necessary. (See "Bone tumors: Diagnosis and biopsy techniques", section on 'Clinical presentation'.)

RADIOGRAPHIC FINDINGS — Humeral stress fractures occur most commonly in the mid or distal humerus, in a spiral orientation [14]. As with other stress fractures, plain radiographs are the initial study obtained and are helpful if a fracture is present. However, their sensitivity is low and a negative plain film does not rule out the diagnosis. If plain radiographs are negative but suspicion remains, we prefer to obtain an MRI because of its ability to detect other pathology. If a stress fracture exists, MRI reveals a linear zone of decreased signal intensity of the cortex of medullary cavity on T1-weighted images, and increased signal of the medullary cavity on T2-weighted images [14]. The degree of periosteal and bone marrow edema correlates with fracture severity [15,16]. A detailed discussion of imaging for stress fractures is found separately. (See "Overview of stress fractures", section on 'Imaging studies'.)

INDICATIONS FOR ORTHOPEDIC CONSULTATION OR REFERRAL — Humeral stress fractures rarely develop complications, and the majority is amenable to conservative management by primary care clinicians. Patients with a complete humeral fracture should be referred to an orthopedist. Although such complications are rare, any evidence of neurologic or vascular injury mandates immediate orthopedic referral. Patients who do not improve with conservative management should also be referred.

INITIAL TREATMENT — Initial management consists of reducing pain. Acetaminophen may be used. For patients with significant pain at rest, opiates and a sling may be helpful. Ice may be helpful if there is local inflammation. The effect of nonsteroidal antiinflammatory drugs (NSAIDs) on fracture healing is discussed separately. (See "Overview of COX-2 selective NSAIDs", section on 'Possible effect on fracture healing'.)

It is important to emphasize to the patient the need to refrain from any inciting activities during the recovery period. (See "Overview of stress fractures", section on 'Pain control'.)

FOLLOW-UP CARE — Unless symptoms worsen or the patient is engaged in an aggressive rehabilitation program, there is no need for follow-up evaluations during the initial three weeks of recovery. Thereafter, reassessment should be made every two to three weeks while the patient participates in a gradual, progressive rehabilitation program to regain strength and motion (see "Overview of stress fractures", section on 'Treatment concepts'). Patient symptoms provide the basis for deciding whether activity should be advanced.

Although we typically repeat radiographs at four to six weeks to assess potential healing, radiographic evidence of such healing may lag. Otherwise, repeat radiographs are unnecessary unless symptoms worsen, raising concern about a possible complete fracture.

Once pain has resolved, we suggest physical therapy for all athletes to help them improve core and shoulder girdle strength, thereby reducing the risk of reinjury. Treatment generally starts after four to six weeks of rest. If possible, a biomechanical evaluation of the patient should be done, especially in "overhead" athletes (eg, baseball, tennis, swimming); poor technique can contribute to humeral stress fractures and should be corrected [4,6].

COMPLICATIONS — Stress fractures of the humerus rarely have complications. Nonunion is possible. A far more common scenario, based upon case reports, is for a complete humeral shaft fracture to occur because an underlying stress fracture was not diagnosed. Complete fractures are more frequently complicated by nonunion and by radial nerve injuries [9]. (See "Midshaft humerus fractures in adults".)

RETURN TO SPORTS AND WORK — Patients with uncomplicated stress fractures should refrain from activities that might exacerbate their injury until they are pain free (usually about four weeks), and follow this with a slow, progressive rehabilitation program and gradual return to sport over a subsequent one- to six-month period [2,17]. A full return to sport is allowed after the patient is symptom-free and preinjury levels of motion and strength have been regained, generally four to six months following the injury. A biomechanical evaluation for throwing or "overhead" athlete (eg, tennis, swimming) is recommended to help prevent reinjury.

Workers with sedentary jobs may return to work immediately, assuming pain is reasonably well controlled. Those with jobs involving lifting or extensive use of the arm should not work until pain is resolved and strength and motion have been regained.

ADDITIONAL INFORMATION — Several UpToDate topics provide additional information about fractures, including the physiology of fracture healing, how to describe radiographs of fractures to consultants, acute and definitive fracture care (including how to make a cast), and the complications associated with fractures. These topics can be accessed using the links below:

●(See "General principles of fracture management: Bone healing and fracture description".)

●(See "General principles of fracture management: Fracture patterns and description in children".)

●(See "General principles of definitive fracture management".)

●(See "General principles of acute fracture management".)

●(See "General principles of fracture management: Early and late complications".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: General fracture and stress fracture management in adults" and "Society guideline links: Fractures of the skull, face, and upper extremity in adults" and "Society guideline links: Acute pain management".)

SUMMARY AND RECOMMENDATIONS

●Stress fractures of the humeral shaft, and the complete fractures that may subsequently develop from them (ie, "ball thrower's fracture"), are uncommon and typically occur with overhead throwing, most often in baseball, and occasionally with violent muscle contraction (eg, arm wrestling). The great majority are well managed with conservative methods by primary care physicians.

●Patients with stress fractures of the humeral shaft can present with focal pain that increases with activity but may also be present at rest. They often complain of pain with throwing, lifting, or pushing off with the injured arm. Examination can reveal focal tenderness around the fracture site and increased pain with strength testing. Peripheral nerve function, particularly of the radial nerve, should be assessed. The diagnosis of a true stress fracture of the humerus is often missed. Case reports of "spontaneous" humeral shaft fractures describe a prodrome of milder, chronic pain with focal tenderness that precedes an acute injury sustained while throwing. (See 'Clinical presentation and examination' above.)

●Plain radiographs are the initial study obtained and are helpful if a fracture is present. However, their sensitivity is low and a negative plain film does not rule out the diagnosis. If there is significant clinical suspicion, we suggest obtaining an MRI to determine the presence of a fracture or other pathology. (See 'Radiographic findings' above.)

●Orthopedic referral is rarely needed, but any neurologic or vascular injury and any concern over nonunion warrants immediate referral. (See 'Indications for orthopedic consultation or referral' above.)

●In the absence of controlled trials, we suggest the following general approach for managing humeral stress fractures (Grade 2C):

•Control pain with analgesics, ice, and a sling.

•Refrain from inciting activities during initial healing (approximately four weeks).

•Follow-up every two to three weeks, beginning after the initial three to four-week healing period (earlier and more frequent follow-up is needed for patients who participate in early, aggressive rehabilitation programs).

•Participate in a gradual, progressive rehabilitation program, once the initial healing period is complete, to regain strength and motion.

•Perform a biomechanical evaluation for throwing and overhead athletes. This may correct poor throwing technique, which can predispose to injury. (See 'Initial treatment' above and 'Follow-up care' above.)

●We suggest the patient not return to full athletic activity until symptom-free and preinjury levels of motion and strength have been regained, generally four months following the injury. (See 'Return to sports and work' above.)

●Complications are rare and include nonunion and nerve injury. (See 'Complications' above.)