Spontaneous sternal fracture due to multiple myeloma requiring extensive surgical repair

Abstract

Spontaneous sternal fracture is a well-known complication of multiple myeloma due to osteolytic bone lesions. The possibility of a multiple myeloma should be thoroughly investigated in patients presenting with a spontaneous sternal fracture. This work up should go beyond protein electrophoresis alone as a monoclonal paraprotein is not always present. In some cases, the myeloma plasma cell clone produces only the free light chain (κ or λ) or may even be non-secretory. The underlying plasma cell dyscrasia is treated with chemotherapy and, if needed, local radiotherapy. However, for patients with a fracture causing persistent pain and physical discomfort, internal fixation may be additionally required. We present a case of a patient who presented with a displaced pathological sternal fracture. She was treated with chemotherapy, radiotherapy and an open reduction and internal fixation with a Locking Compression Plate (LCP). This technique offers a feasible option for rigid fixation of pathological fractures.

Background

Osteolytic bone disease is a common feature of multiple myeloma and causes a risk for pathological fractures. In patients with bone lesions, these are usually multifocal and may affect any skeletal segment.¹ We describe a case of a patient with multiple myeloma presenting with severe chest pain and shortness of breath due to a pathological sternal fracture for which she received surgery and local radiotherapy in addition to systemic chemotherapeutic treatment.

Case presentation

A 53-year-old woman visited our hospital, with progressive dyspnoea and thoracic pain. She had a recent history of pain in the lower back and chest, which had been aggravated after a minor fall on the right side of her chest. Physical examination revealed no respiratory distress and normal breath sounds. During palpation, tenderness of the right hemithorax was noted.

Investigations

X-ray investigations showed fractures of multiple ribs (VI, VII & VIII), and lumbar and thoracic vertebrae (loss of height of various vertebrae, most notably Th-VI and Th-IX). To exclude a pulmonary embolism,  CT scan (CT-scan) was performed, which documented a displaced sternal fracture (figure 1). A (99 m)Tc-MDP bone scintigraphy confirmed the fractures, as mentioned above, and demonstrated multiple osteolytic lesions in the arms, femur and pelvis. A protein electrophoresis did not show any aberrancies. However, a thoracic vertebral bone biopsy showed the presence of a plasmacytoma, consistent with a diagnosis of multiple myeloma given the multifocal bone lesions. A repeated protein electrophoresis was again negative, but a free light chain assay showed increased serum κ light chain concentration with an abnormal κ/λ free light chain ratio. Complete blood count, renal function and plasma calcium levels were normal.

Figure 1.

CT scan of the dislocated sternal fracture (lateral view).

Treatment

The patient was diagnosed with multiple myeloma and treated with induction chemotherapy consisting of bortezomib, cyclophosphamide and dexamethasone. Despite rapidly achieving a complete haematological response during induction chemotherapy cycles, the patient experienced worsening dyspnoea and upper chest pain due to the sternal fracture. Progressive dislodgement of the sternal components was observed. A surgical consultation was obtained to consider surgical correction of the sternal dislocation. Informed consent was given and the patient was taken to theatre to perform an open reduction and internal fixation. The patient received general anaesthesia and standard preoperative cefazoline. The patient was placed in a supine position. A midline longitudinal incision was made from the manubrium of the sternum to the xiphoid process. Dissection was performed down to the periosteum of the sternum and the sternal fracture (figure 2A). The fracture site was carefully debrided. A manual reduction of the fractures with length traction and two-bone reduction forceps (figure 2B) was performed. Subsequently, a 10-hole small fragment Locking Compression Plate (LCP) (figure 2C) was placed and fixated with locking screws. A 1 mL syringe was used to prevent bicortical drilling and to protect the mediastinal structures (figure 2D). The wound was irrigated and closed with vicryl sutures (figure 2E). The total operation time was 95 min and total intraoperative blood loss was 200 mL.

Figure 2.

Operative repair of sternal fracture. Peroperatively, the pathological sternal fracture was exposed (A). The sternal fracture was relocated with reposition forceps and traction (B) and fixated using an eight hole small fragment LCP plate (C). A 1.0 mL syringe was used to prevent bicortical damage (D). Postoperatively, the sternal line was restored (E). LCP, Locking Compression Plate.

Outcome and follow-up

Postoperative complications did not occur and the patient was discharged on day three postoperatively. Four weeks postoperatively, adjuvant radiotherapy was given on the sternum with a total dose of 20 Gy divided into five fractions. The patient's symptoms of chest pain and dyspnoea dramatically improved. However, a significant restrictive pulmonary function remained due to the kyphosis caused by the sternal and vertebral injury (figure 3A, B). Therefore, the patient was considered ineligible for consolidating therapy with high-dose melphalan and autologous stem cell transplantation. As an alternative, the patient continued with a consolidating regimen of bortezomib, low-dose oral melphalan and prednisone.

Figure 3.

Lateral X-rays made pre- and postoperatively (A and B, respectively). Note the combination of vertebral fractures causing aggravated kyphosis and sternal fracture causing dislocation and further loss of stability with collapsing thoracic space.

Discussion

Multiple myeloma is estimated to account for 10% of all haematological malignancies and 2% of deaths from all malignancies in the world.² Although chemotherapy response rates are high, the disease cannot be cured. Median overall survival ranges from 29 to 66 months depending on the International staging system.³ The disease is characterised by the neoplastic proliferation of a plasma cell clone that produces a monoclonal immunoglobulin, often referred to as ‘paraprotein’.⁴ Symptoms of multiple myeloma may include increased plasma calcium levels, renal insufficiency, anaemia and bone lesions.⁵

A negative protein electrophoresis: diagnostic pitfall in multiple myeloma

The paraprotein is an immunoglobulin produced in excessive concentrations making it detectable on protein electrophoresis analysis when the immunoglobulin has retained its normal structure consisting of two light chains and two heavy chains. However, some malignant plasma cell clones do not produce an intact immunoglobulin, but secrete only one of the two immunoglobulin light chains (κ or λ).⁶ As in our case, increased free light chains may not be detectable on regular protein electrophoresis and require quantification using a specific assay. Free light chains are produced in small concentrations by normal plasma cells and are therefore detectable in every individual in approximately equal concentrations. When a malignant plasma cell clone is present, this causes an overproduction of one of the two light chain types with alteration of the free light chain ratio. In patients with symptoms suggesting the presence of multiple myeloma, such as unusual bone fractures as a sternal fracture, it is important to appreciate that a negative protein electrophoresis does not rule out multiple myeloma. The free light chain assay may provide biochemical evidence of the presence of a malignant plasma cell clone, although there are even rare cases of non-secretory myeloma that can only be detected by tumour biopsy.

Sternal fractures

Sternal fractures are mostly associated with a history of trauma. Metastatic tumours and pathological fractures of the sternum are rare. However, spontaneous sternal fractures are usually associated with a malignancy. Sternal fractures are a well-known complication of multiple myeloma; this has been documented in several studies.^7–9 The imaging of myeloma-related bone injury classically relied on plain radiographs, although there is increasing use of whole body low-dose CT (WBLDCT) for this purpose. In a recent study of WBLDCT findings in a cohort of myeloma patients, 10 sternal fractures were observed in 78 patients displaying pathological bone lesions from a total cohort of 134 with multiple myeloma.¹⁰ Sternal dissemination may also occur due to metastases of malignancies of the breast, lung or thyroid gland. The tumour is most often situated in the body of the sternum (95%). The manubrium is rarely a metastatic site (5%). Pathological fractures are more likely to cause deformation than are traumatic sternal fractures, and have a higher tendency to poor healing, as well.¹¹ The sternum is considered to be the ‘fourth vertebral column’.¹² Watkins et al¹³ exposed multidirectional flexibility tests to 10 human cadaveric thoracic spines and rib cages with intact as well as fractured sternums. This study showed that a sternal fracture significantly decreases the stability of the thorax and thoracic spine. Therefore, the concomitant presence of a sternal fracture may further compromise the stability of the spine when vertebral fractures are present, and restoration of sternal stability may prevent progressive deformity.¹²

Surgical fixation of sternal fractures

There is no consensus regarding the surgical approach for a sternal fracture. This is probably due to the rarity of sternal fractures and scarcity of reports of long-term postoperative patient outcomes.¹⁴ Some authors have therefore chosen to accept sternal deformity.¹⁵ Available studies on sternal fractures are mainly performed on patients with trauma.^{14 16–18} Most sternal fractures are treated conservatively. However, surgery can be a good option in severely displaced sternal fractures and in patients suffering uncontrollable pain and physical discomfort. Sternal fractures can be repaired with stainless steel wiring but a more compound fracture needs a more rigid fixation with plate and screws.^19–21 Steel wiring is less costly, less likely to cause discomfort and easier to remove. A systematic review by Harston and Roberts¹⁴ showed a lower rate of sternal steel wire removal (8.3%) compared to rigid plate fixation removal (15%). However, a rigid fixation with plate and screws requires minimal dissection of soft tissue and gains closer approximation of the bone. A case series by Kivioja et al²² in patients with fractures due to multiple myeloma, showed that various surgical methods are used to repair pathological fractures without any particular method showing a superior outcome. Harston and Roberts¹⁴ noted that using wires in osteopaenic bone entails the risk of cutting through bone. On the other hand, when using a plate and screws, drilling potentially causes damage to the mediastinum. It is important to secure surgical safety of the mediastinal structures when drilling the sternal bore holes. We used a syringe as protection in bicortical drilling, however, Schulz-Drost et al²⁰ also described a safe technique with a low-profile titanium locking plate. They used direct thickness measurement by dissecting the sternal edge. This secured limited depth drilling. Owing to lack of evidence, the choice of fixation type should be based on the experience and discretion of the surgeon.

Learning points.

• In patients with sternal fracture occurring spontaneously or after minor trauma, metastatic disease and particularly multiple myeloma should be considered as the underlying cause.

• Protein electrophoresis is a useful screening tool for the presence of a clonal plasma cell disorder, but is limited in its sensitivity, which can be improved by addition of a free light chain assay.

• Surgical fixation of sternal fractures is a relatively uncommon procedure. The majority of these fractures will heal without surgical intervention. Severely displaced sternal fractures causing pain and discomfort are valid indications for fixation. Stainless steel wiring or a Locking Compression Plate (LCP) can be used to fixate the fracture.

• Patients with multiple myeloma presenting with a displaced sternal fracture due to osteolytic bone lesions, might require a more rigid fixation with a plate and screws. As presented, an LCP plate might be a good option, however, the choice of therapy should be made on an individual basis depending on the aimed goal for the patient, and the experience and discretion of the surgeon.