1 Introduction

Sternal fractures are most commonly caused by direct trauma. Spontaneous fractures of the sternum are rare. Our case involves a healthy young man with sternal pain without any preceding trauma, caused by microtrauma to unfused sternebrae of a previous asymptomatic congenital bony deformation.

2 Case report

A 22-year-old man presented to our orthopaedic outpatient clinic with complaints of anterior chest pain for a period of 3 years. There was no history of trauma. The pain was described as sharp and was located in the center of the chest. The pain had started while performing strenuous physical labor on a fish farm. Initially, physical movements did not provoke any complaints. Subsequently, the patient noticed a direct relationship between physical effort and the intensity of pain. Because of these complaints, he quit his job and quit exercising for a period of two months. Nonetheless, the pain in his chest never fully subsided during this time. The patient worked as an electrician and gasfitter for following two years. The chest pain was especially aggravated by performing horizontal shoulder abduction. Resting and hunching over temporarily reduced the complaints. Over the last few years, the pain gradually increased, and conservative treatment (non-steroid anti-inflammatory drugs and physical therapy) did not give sufficient relief. His medical history was not remarkable, nor had he undergone surgery in the past. The patient did not experience fevers, nocturnal sweating, weight loss, shoulder pain, neck pain, or radiculopathy. He had never used corticosteroids. None of his family members were familiar with spontaneous fractures, nor were there any known congenital disorders.

3 Clinical findings

Physical examination revealed a slender young man with a minor pectus excavatum. Palpation over the sternum was slightly painful, although he was able to exactly point out the punctum maximum of the pain. At the moment of examination, his symptoms were mild. No excessive thoracic kyphosis was observed. There was no muscle atrophy. Bilateral shoulder range of motion and strength testing were normal. There were no clinical signs of cardiovascular or pulmonary disease.

4 Diagnostic assessment

Chest X-rays did not show any abnormalities. A technetium bone scan plus single-photon emission computer tomography (SPECT) of the thorax showed increased osteoblastic activity in the midline of the thorax (Fig. 1). Furthermore, there was suspicion of a sclerotic disruption of the cortical bone on the dorsal side of the sternum. This was confirmed by additional conventional computer tomography (CT), which revealed an image suggestive of a sternum fracture with a sclerotic reaction (Fig. 2).

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Fig. 1 Bone scintigraphy (A), low diagnostic CT (B) and SPECT (C) of the thorax showed increased activity in the sternum. The dorsal side of the sternum showed sclerosis with suspection of cortical dis-ruption.

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Fig. 2 Sagittal (A) and coronal (B) views of CT of sternum showing the sternomanubrial joint (black arrows) and the transverse cleft of the sternal body(white arrows).

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5 Differential diagnosis (if any)

There is a wide range of orthopedic differential diagnoses for sternal pain, such as sternal fracture, costochondritis, sternoclavicular osteoarthritis, costal fracture, pectoralis major tendon rupture, osteomyelitis, and congenital abnormalities.¹,²

Incomplete development of the sternum, resulting in unfused sternebrae, may gradually become symptomatic after repetitive stress and can mimic a stress fracture. A symptomatic unfused sternum is a very rare cause of sternal pain. Most causes of sternal pain can easily be differentiated from a symptomatic unfused sternum by conventional diagnostic modalities such as X-rays, sonography, bone scintigraphy, and/or CT. In contrast, a stress fracture of the sternum can fully mimic a symptomatic unfused sternum and be mistakenly regarded as the cause of the pain.

6 Therapeutic intervention

To our knowledge, no prior studies have examined the management of a symptomatic unfused sternal body. The more commonly described isolated stable sternal fracture with minimal dislocation usually does not require invasive treatment and heals spontaneously over the average course of 10 weeks.³ The management of other symptomatic unfused bony segments in the body, such as os acromiale or os trigonum is often invasive and includes simple excision or operative fixation.

As our patient currently only experienced mild symptoms, and had experienced a variable degree of severity over the course of multiple years, invasive treatment was undesirable.

Although a true fracture is different in nature than a symptomatic unfused bony segment, as the unfused sternal body was previously asymptomatic we decided that initial treatment should be similar to management of a sternal stress fracture.

Our patient initially reduced his physical effort while working.

7 Follow-up and outcomes

Nine months after load reduction the patient reported that he experienced little to no pain and was satisfied with the result of the treatment. In the future, open reduction and internal fixation may still be a viable option if complaints return and repeated conservative treatment would prove insufficient.

8 Discussion

8.1

8.1 Anatomy and development of the sternum

The adult sternum can be divided into three segments connected by cartilaginous joints: the manumbrium, mesosternum, and xiphoid process.

The development of the sternum starts during early gestation, when the cartilaginous precursor of the sternum is formed from a pair of longitudinal mesenchymal bars. These sternal bars migrate to the midline and eventually fuse, starting cranially and gradually progressing to the caudal end. Fusion is finished around the 9th week of gestation.⁴

The sternebrae, the ossification centers formed by the fusion of both sides of the sternal bars, continue to merge until early adulthood, eventually shaping the adult sternum, as seen in Fig. 3. By the age of 25 years, the calcification and fusion of the sternum is usually completed.

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Fig. 3 Schematic representation of the development of the sternum. A. unfused infant sternum with (partially fused) ossification centers forming sternebrae. B. adult sternum with fused sternebrae. C. adult sternum with unfused bar in the middle of the sternal body.

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Failure in the process of fusion of the sternal bars results in longitudinal sternal abnormalities, such as foramina, clefts, tubercles, and bifid-xiphioid process, which have been previously described.⁵ These anatomical variations of the sternum are relatively frequent, usually asymptomatic, and often detected incidentally.

Credit author statement

JR and EZ were directly involved in patient care and wrote the report with input of all authors. WZ and PR were overseeing patient care and revised and approved the final version to be published.

Financial support and sponsorship

None.

Informed consent

Patient consented for images and other clinical information relating to his case to be reported in a medical publication.

Authors contribution

JR and EZ were directly involved in patient care and wrote the report with input of all authors. WZ and PR were overseeing patient care and revised and approved the final version to be published.

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