Prior to the invention of radiography, in 1891, the German physician Dr. Hermann Kummell had reported on delayed vertebral collapse following minor trauma.1, 2) Such delayed kyphotic deformity after trauma was named Kummell's disease, and many reports and studies are now available on its diagnosis and treatment.3, 4, 5, 6) However, there is still ambiguity on whether the clinical entity described in Kummell's initial report over a century ago aligns precisely with the conditions that are currently defined as Kummell’s disease. In contemporary literature, terms such as Kummell’s disease, delayed post-traumatic vertebral collapse, osteoporotic vertebral compression fracture with delayed collapse, and nonunion after compression fracture are used interchangeably. This begs the question whether these conditions are indeed distinct or if they represent the same entity originally reported by Kummell. At present, there is a lack of a clear definition, the diagnostic criteria, the pathophysiology, and treatment guidelines for Kummell's disease. Therefore, it is imperative to establish a definitive understanding of this condition by examining its diagnosis, pathophysiology, and therapeutic approaches.

Before the 1891 report by Kummell on four cases of delayed vertebral collapse and recurrence of clinical symptoms following improvement in patients with post-traumatic symptoms, Dr. Schede had described delayed vertebral collapse due to softening of the vertebral body in 1881. Further, Dr. Konig had suggested a link between this variant and spinal tuberculosis.1) In 1892, Verneuil presented a case of pain and vertebral collapse occurring after spinal fracture, attributing it to abdominal muscle and visceral rheumatism.7) In 1911, Kummell's disciple Schulz reported 21 cases, attributing the condition to post-traumatic spondylitis, and named it Kummell's disease (Kummellsche Krankheit).2) In 1951, Steel divided the clinical manifestations of this condition into five stages (initial injury insult, posttraumatic period, latent interval, recrudescent stage, and terminal stage) and stated that a diagnosis of Kummell’s disease could be made only when these stages were present. Additionally, while Kummell primarily reported occurrences in the third and eighth thoracic vertebrae, Steel noted a predominance in the thoracolumbar transition zone.1)

Radiographically, the intravertebral cleft sign (IVC) that is observed as a characteristic shadow within the collapsed vertebral body, was identified as a pathognomonic sign of Kummell’s disease.8, 9, 10) However, the definition of Kummell’s disease has expanded over time, with many reports diagnosing it solely based on the presence of the IVC. Considering the importance of the original definition of delayed post-traumatic vertebral collapse, relying solely on the observation of the IVC from radiographic data may be problematic. The IVC is identified as a low-density shadow within the compressed vertebral body on a plain radiograph and has expanded in terms of diagnostic significance with the use of magnetic resonance imaging (MRI). It is characterized by a double-line sign on T2-weighted images, with low-intensity signals in the surrounding areas and high-intensity signals internally along with fat-suppression images, which are known to be helpful for confirmation (Fig. 1).9, 11) While the IVC was initially considered to be indicative of benign lesions, particularly osteoporotic compression fractures, recent reports have also associated it with bone marrow infiltration diseases, including multiple myeloma.9)

Fig. 1
Magnetic resonance imaging (MRI) illustrating the intravertebral cleft (IVC) sign. (A) T2-weighted MRI reveals fluid signals within the cleft and surrounding hypointensity line (arrow), termed the “double-line sign,” indicative of an IVC. (B) T1-weighted MRI and (C) T2-weighted axial MRI depicting the air and fluid contents within the cleft.

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Computed tomography (CT) can be used to confirm bone margins more clearly than X-ray and MRI, allowing confirmation of the cortical breakage and integrity of the posterior wall. Additionally, nonunion due to avascular osteonecrosis can be estimated through the intravertebral vacuum, which appears as a black signal within the vertebral body in CT (Fig. 2).

Fig. 2
Intravertebral vacuum confirmed via computed tomography. (A) Coronal and (B) sagittal images.

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Internal shadows in images may appear differently depending on the timing and posture during photography; in some cases, these may appear as air or fluid shadows. The etiology of IVC is believed to be nonunion at the fracture site or findings related to ischemic necrosis, with some researchers arguing that air shadows may result from the influx of air from the adjacent intervertebral discs due to destruction of the vertebral endplate.10, 11) There is controversy regarding its clinical significance, and in most reports, shadowing within the vertebral body is observed as early as 3 weeks after trauma, with most cases presenting between 1 and 3 months after trauma. According to a prospective observational study, symptom relief was observed over time in 66.7% of patients, and disappearance of symptoms was observed in follow-up plain radiographs in 26.7% of patients.8) As such, observation of the IVC during imaging is considered a necessary but insufficient factor for the diagnosis of Kummell’s disease.

In addition to IVC, other radiographic findings can aid in the diagnosis, such as dynamic mobility confirming nonunion of fractures and progressive kyphotic changes.12) Confirming such dynamics requires lateral radiographs in both upright and supine positions to assess the changes at the fracture site. The observation of mobility and IVC that are not evident in flexion positions but visible in extension positions can be instrumental to diagnosis (Fig. 3).

Fig. 3
Image of the dynamic mobility of the fractured vertebra. (A) Lateral radiographs during flexion and (B) extension reveal an intravertebral cleft in the L1 vertebral body; the dynamic mobility is evident as the patient changes position (white arrow). (C) Intravertebral empty space identified during surgery.

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Considering the early reports by Kummell and recent advances in imaging-based findings, the diagnosis of Kummell’s disease, which is defined as delayed post-traumatic vertebral collapse, is characterized by evolving clinical presentation, radiographic observation of the IVC, dynamic mobility at the fracture site, and progressive kyphotic deformity. While the original reports by Kummell and Steel did not describe any association with osteoporotic compression fractures, current literature suggests that Kummell’s disease is more of a complication arising from nonunion- or trauma-induced osteonecrosis that is associated with osteoporotic compression fractures. However, there have been reports of rare cases occurring in younger individuals and association with the use of steroid medications, necessitating consideration of these factors in the broader context.4)

Kummell’s disease clinically manifests as back pain caused by low-energy trauma or as an osteoporotic compression fracture that occurs without trauma in elderly patients with osteoporosis. In the beginning, there may be no or mild symptoms, but severe pain and neurological symptoms due to fracture instability or cord compression can manifest over time.13) In most cases, it is discovered through a test performed because of gradual worsening of the symptoms without any specific test or treatment, and the most frequent site is the thoracolumbar junction.14) This osteoporotic compression fracture initially begins with damage to the anterior column alone and shows a progressive pattern, with damage to the middle and posterior columns if the nonunion continues. When the posterior wall of the vertebral body collapses, there may be compression of the spinal cord and subsequent neurological complications, so it is important to suspect, diagnose, and commence appropriate treatment at an early stage.

The pathophysiology of Kummell’s disease was initially considered as a result of multiple minor traumas that cause damage to the bone and soft tissues in the cancellous bone of the vertebral body. Subsequently, Benedeck and Nicholas proposed vascular causes to explain the healing process of the fractures of the vertebral body. They attributed the challenges in the healing process of the fractures to circulatory disturbances during the later stages of healing, despite the absence of early radiographic evidence of trabecular bone injury.13) Studies supporting this hypothesis have been reported, among which research on the vascular distribution in the vertebral body has provided further substantiation. In terms of the vascular distribution in the vertebral body, the anterior–superior and anterior–inferior portions have relatively limited vascularity. The anterior part of the vertebral body that branches directly from the aorta into segmental arteries experiences insufficient lateral circulation. In contrast, the posterior region of the vertebral body, involving anastomosis between the superior and inferior segmental branches, is suggested to have relatively abundant lateral circulation. This anatomical distinction is considered to be relevant to the pathophysiology.15, 16) Furthermore, the characteristic occurrences of IVC predominantly in the anterior–superior and anterior–inferior portions of the vertebral body support this theory. Hasegawa et al. conducted histological observations by collecting components within the cleft and the membrane surrounding the cleft during bone grafting for IVC, with dynamic instability following osteoporotic vertebral fractures; they asserted that nonunion during the healing process of fractures is a cause of Kummell's disease.17) Thompson et al. observed the age-related changes in the microstructure of the vertebral body and reported that the decrease in trabecular thickness is more prominent in the vertebral endplate region than the central portion; they argued that such changes contribute to limitations in the healing of osteoporotic vertebral fractures.18) In the initial report by Kummell, there was no mention of an association with osteoporosis in the context of aging. However, most subsequent reports describe Kummell's disease as occurring after vertebral fractures associated with osteoporosis. The currently accepted pathophysiological mechanism involves vascular causes and pseudoarthrosis due to nonunion. However, there is lack of research on which of the risk factors for osteoporotic vertebral fractures are related to progression to this condition.19) Some suggest a correlation between the fracture location and radiological findings, but more research is needed in this regard. The analysis and identification of such risk factors are crucial for predicting and treating the progressive complications of osteoporotic vertebral fractures.

If we define Kummell’s disease as the occurrence of delayed post-traumatic kyphosis with IVC and dynamic instability, then nonunion after osteoporotic fractures and collapse of the vertebral body due to ischemia are the primary causes in most cases. When clinical symptoms manifest from conditions related to dynamic instability of the affected vertebral body, kyphotic deformity, and neurologic symptoms resulting from nerve compression and damage due to posterior displacement of the compressed bone fragments, these constitute the indications for treatment. The presence of IVC based on radiographic examination alone is not sufficient to determine the need for treatment. Some reports have indicated resolution of IVC and clinical improvement with certain conservative treatments as well as the use of bone-forming agents.20) However, these treatments are limited, and surgical intervention is required in most cases where instability and nerve compression due to nonunion are confirmed.

Since the occurrence of these conditions is mostly associated with advanced age, various factors must be considered when deciding on surgical treatment. Satisfactory results have been reported with relatively less invasive surgical treatments, including vertebral cement augmentation procedures such as vertebroplasty and balloon kyphoplasty.6, 21) Some reports have noted dislodgment of the injected cement due to the characteristic IVC lesion in Kummell's disease, expressing skepticism about the efficacy of vertebroplasty for progressive osteoporosis cases accompanied by IVC.22) There is a report on treating failed vertebral augmentation through balloon kyphoplasty; however, this is a limited case report, whose follow-up period was restricted.23) Traditionally, removal and reconstruction through the anterior approach have been utilized for anterior lesions of the vertebral body. However, this is also limited by secondary collapse from loss of fixation of the implant caused by weakened bone integrity because of osteoporosis. Accordingly, various methods involving additional posterior fixation using pedicle screws or hooks have been reported for reinforcement.24) Cement augmentation can increase fixation force when inserting a pedicle screw and prevent early failure.25) However, Lee et al. reported that this technique may increase degeneration of the adjacent disc segment.26) There is no disagreement regarding assessment of the most appropriate therapeutic approach, considering the benefits of surgical treatment and potential for complications associated with surgery, especially in elderly patients with concomitant systemic conditions. For these reasons, new surgical treatment methods have been attempted, including removal of the vertebral body and reconstruction through the posterior approach or posterior fixation after cement insertion through the pedicle.27, 28, 29) However, these reports are based on limited case numbers and preferences of the surgeon in terms of the treatment method. Additionally, the limited follow-up period is an inadequacy of all these reports for acceptance as surgical treatment. However, the generally accepted surgical principle in most of these reports is the necessity of removal and reconstruction of the anterior lesions, along with the need for additional posterior fixation to maintain stability.

Kummell’s disease, which was first reported through clinical observations over a century ago, seems to be reasonably understood not as a specific disease but rather a form of progressive osteoporotic compression fracture that occurs following an osteoporotic vertebral compression fracture, leading to sustained collapse and subsequent deformity. This condition is radiologically characterized by observation of the IVC and dynamic instability of the vertebral body, leading to axial pain and neurological symptoms. Conservative approaches have been attempted in the treatment of this condition, along with medical treatments including the use of bone-forming agents. However, if these medical treatments fail or result in neurological complications, surgical intervention may be considered. Although there are numerous reports on various surgical treatments, selection of an appropriate treatment requires analysis of the patient's overall condition and state of the spine to determine the most suitable therapeutic approach.