Transitional lumbosacral vertebrae in children with pelvic fractures: frequency of diagnosis and distribution of types and subtypes

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BACKGROUND

Current scientific data on various aspects of transitional lumbosacral vertebrae in children and adolescents are limited. As this is a congenital condition, it could most probably be diagnosed during childhood [1]. However, this is usually not the case; signs of the condition are often incidentally detected during imaging studies conducted for other reasons, most commonly for traumatic injuries to the spine or pelvis [2]. In addition, delayed transitional vertebrae diagnosis is frequently associated with numbering errors [3] or decreased attention from medical personnel when interpreting imaging results [4]. The relevance of this issue is further emphasized by the fact that the prevalence of this condition across pediatric populations remains unknown [5]. Clinical symptoms observed in adults are often mechanically extrapolated to growing patients without considering the anatomical and physiological characteristics of the developing spine [6]. Moreover, there is no standardized approach to effective treatment, especially for adequate pain management for L₅ radiculopathy [7].

These challenges are critical from a research perspective and in improving the quality of life for children with transitional lumbosacral vertebrae, who were unaware of their congenital lumbosacral anomaly before sustaining pelvic bones injuries [8].

The work aimed to determine the prevalence and distribution of transitional lumbosacral vertebrae in children with pelvic fractures.

METHODS

This study included longitudinal observations of 41 children aged 5–18 years who sustained pelvic fractures between 2022 and 2024. As part of a comprehensive diagnostic workup, including computed tomography (CT), transitional lumbosacral vertebrae were found in 10 of the 41 patients (24.4% ± 6.7%). These 10 children formed the study’s focus group. The mean age of the patients was 13.6 ± 2.8 years. The cohort included four boys (40.0% ± 15.5%) and six girls (60.0% ± 15.5%). The scope of the investigation was standard for trauma patients: recording of complaints and medical history, clinical examination conducted by relevant specialists, and comprehensive radiological assessment, with mandatory pelvic CT.

Pelvic fractures were classified using the Tile/AO system [9]. The classification by Judet et al. was used to assess acetabular fractures [10]. Transitional lumbosacral vertebrae were categorized into types and subtypes based on the classification by Castellvi et al. [11].

Statistical analysis involved calculating the relative value of each indicator as a percentage (P) and the standard error of representativeness (±m).

RESULTS

Clinical and radiological assessment of the injured children allowed for identifying the nature of the pelvic injuries. The pelvic trauma in eight clinical cases (80.0% ± 6.2%) was classified as type “a” according to accepted classification systems. In two patients (20.0% ± 6.2%), the fractures—specifically, acetabular fractures—were classified as type “b” injuries.

In evaluating pelvic imaging findings, particularly 3D CT scans, special attention was given to assessing the lumbosacral junction and sacrum for the presence of transitional lumbosacral vertebrae. When such vertebrae were detected, the type and subtype of the anomaly were determined using axial CT slices (scans). Table 1 presents the results of the CT analysis of the lumbosacral junction in 10 injured patients with diagnosed transitional vertebrae.

Table 1. Frequency of diagnosed types and subtypes of transitional vertebrae in children with pelvic fractures

The data in Table 1 indicates that in half of the clinical cases (50.0% ± 15.8%), the diagnosed condition of the lumbosacral junction corresponded to type II, subtype a, according to the Castellvi classification (Fig. 1).

Fig. 1. Three-dimensional reconstruction (a) and CT scan (b) of the lower thoracic and lumbar spine, pelvic bones, and hip joints of a 16-year-old female patient. Subtype IIIb injury of the left side of the pelvis (acetabular and iliac wing fractures). Transitional lumbosacral vertebra, subtype IIa.

The subtype IIa presented in Fig. 1 is characterized by an enlarged transverse process (either left, as in this case, or right) of the vertebra above the sacrum, which articulates with the sacral ala via a pseudoarticulation [11].

The second most common subtype of the diagnosed transitional vertebrae was subtype IIIb, which was observed in 30.0% ± 14.5% of the clinical cases (Fig. 2).

Fig. 2. Three-dimensional reconstruction (a) and CT scan (b) of the lower lumbar spine and sacrum of a 16-year-old female patient. Type a sacral injury (right iliac wing fracture). Transitional lumbosacral vertebra, type III, subtype b.

Analysis of the CT scans shown in Fig. 2 focused on the sacrum, which exhibits five pairs of sacral foramina. Normally, five sacral vertebrae fuse by the age of 22–24 years to form the sacrum (os sacrum), which has four pairs of sacral foramina [12]. A sacrum with five pairs of sacral foramina, as revealed by 3D reconstruction, is an indicator of transitional vertebrae type III or IV [11].

Subtypes Ia and IIb each accounted for 10.0% of the clinical cases. The radiological characteristics of these subtypes were typical: hypertrophy of one of the transverse processes of the vertebra above the sacrum (in subtype Ia) and bilateral pseudoarticulations between the hypertrophied transverse processes of the lowest lumbar vertebra and sacral alae (in subtype IIb).

Avulsion fractures of the cartilaginous pelvic structures, such as the anterior superior iliac spines and anterior inferior iliac spines, are classified as pediatric-specific injuries [13]. In the study group, a 13-year-old girl sustained an avulsion fracture of the right iliac crest after falling from a horse. Comprehensive assessment confirmed the avulsion fracture and presence of a transitional lumbosacral vertebra (Fig. 3).

Fig. 3. Three-dimensional reconstructions (a, b, and c) and CT scan (d) of the lower lumbar spine, pelvic bones, and hip joints of a 13-year-old female patient. Avulsion fracture of the right iliac crest (a and b). Transitional lumbosacral vertebra, type II, subtype b (а, c, and d).

The presence of a transitional vertebra was first indicated by the sacrum with five pairs of sacral foramina (Fig. 3a–c). Further analysis of the radiological findings revealed that, unlike the clinical case shown in Fig. 2, the two cranial vertebrae were separated by pseudoarthrosis at the level of the sacral wings on the left and right sides, classifying this clinical case as subtype IIb (Fig. 3d).

A critical finding of the present study was none of the 10 patients diagnosed with transitional vertebrae during evaluation for pelvic injuries had reported any complaints related to the spine or sacrum prior to the trauma. This was confirmed by the parents of the injured children.

DISCUSSION

The term transitional lumbosacral vertebrae was introduced by Durr over 160 years ago. In 1860, he published an article in the German journal Zeitschrift für rationale Medizin, where he proposed this term to describe vertebrae that had “adopted” the shape and functions of two adjacent spinal regions. The modern interpretation of transitional lumbosacral vertebrae is reflected in the classification proposed in 1984 by a group of American orthopedic surgeons led by Castellvi, which has remained widely accepted among specialists. Fig. 4 shows a schematic representation of the classification by Castellvi et al. [11].

Fig. 4. Schematic representation of different types and subtypes of transitional lumbosacral vertebrae according to Castellvi.

The Castellvi classification is based on the analysis of the size of the transverse processes of the lowest lumbar vertebra and type of contact (pseudarthrosis or synostosis) between these processes (or one of them) and the sacral wings on one or both sides. This condition originates in utero, between weeks 4 and 6 of gestation [14].

Scientific data indicate that the prevalence of transitional vertebrae in the general population greatly varies, ranging from 4% [15] to 36% [16]. According to Vaidya et al. [17], this variation is due to differences in the study populations, imaging techniques used, and interpretation of the findings.

Currently, CT is considered the most effective method for objectively diagnosing transitional vertebrae. In a scientific publication, Hanhivaara et al. [18] used the phrase “superior diagnostic efficacy” to describe the capabilities of this imaging modality.

As previously noted, in 50.0% ± 6.7% of the clinical cases in our cohort, transitional vertebrae of type II, subtype a were diagnosed. These findings are consistent with the results of a previous analysis conducted by the authors, which examined the prevalence of different types and subtypes of transitional vertebrae. That analysis was based on data from 17 scientific research studies across Europe, Asia, and the Americas. Collectively, these studies analyzed the radiological data of 5090 patients of various ages with transitional lumbosacral vertebrae. Ranking of disease types and subtypes revealed that clinical cases corresponding to subtype IIa ranked first in diagnostic frequency, with 26.9% ± 0.6% of cases [5].

Scientific data reveal that subtype IIa is the most frequently associated with vertebrogenic pain localized in the lumbosacral region [19]. The average intensity of the pain syndrome typically corresponds to 6 points on the visual analog scale [20]. The main cause of pain in patients with transitional vertebrae is extraforaminal stenosis at the lumbosacral junction [21], which significantly increases the risk of L₅ and S₁ nerve root impingement [22]. In addition, García López et al. [23] noted that transitional vertebrae induce abnormal rigidity (as described in the article) in the lumbosacral junction, which negatively affects the spine’s shock-absorbing function. These structural abnormalities at the lumbosacral junction progress as skeletal ossification advances during growth [24]. This may explain the absence of low back pain in 10 pediatric patients analyzed in the current study despite the presence of pathognomonic radiological signs of transitional vertebrae. Interestingly, when characterizing patients with transitional vertebrae, Tsoupras et al. [25] use the term “skeletally immature subjects.”

The absence of low back pain in children and adolescents with transitional vertebrae is further confirmed by another study conducted by the authors of the present study. In 19 children with uncomplicated lumbar vertebral fractures who also exhibited reliable radiological signs of transitional vertebrae, no vertebrogenic pain was reported prior to trauma [26]. Moreover, the possibility of low back pain has been reported in pediatric patients with transitional vertebrae [27]. In some cases, the duration, intensity, frequent recurrence, and limited efficacy of conservative pain treatment may be indications for surgical intervention, as in adult patients with the same condition [28]. In adolescents, surgery generally involves pseudoarthrectomy of the hypertrophied transverse process of the lumbosacral transitional vertebra [29].

CONCLUSION

The aim of the study was successfully achieved: The frequency and distribution of lumbosacral transitional vertebrae were determined in a pediatric cohort with pelvic bone fractures. It was found that the diagnostic frequency of lumbosacral transitional vertebrae in the studied cohort was 24.4% ± 6.7% of clinical cases. Subtype IIa was the most prevalent, accounting for 50.0% ± 15.8% of cases. Subtype IIIb ranked second, being diagnosed in 30.0% ± 14.5% of patients. Subtypes Ia and IIb were each found in 10.0% ± 9.4% of cases. No cases of subtypes Ib and IIIa and type IV transitional vertebrae were identified. A key distinguishing feature of the clinical presentation in children was the absence of the primary symptom, namely, pain in the lumbosacral region, despite the fact that the radiological features of all detected subtypes were identical to those observed in adult patients.

The study results confirm that lumbosacral transitional vertebrae are a widespread condition in the general population, including in pediatric patients. The alarmingly high detection rate of this condition during imaging examinations performed for various injuries to the axial skeleton indicates the need for focused radiological assessment of the lumbosacral junction. In cases wherein developmental anomalies of the lumbosacral region are identified, patients and their parents should be informed of the condition and counseled regarding its possible clinical manifestations in the near future. This is particularly crucial, as pain potentially caused by transitional vertebrae may be misinterpreted as a consequence of pelvic fractures, leading to diagnostic errors and hindering the selection of an appropriate treatment strategy.

ADDITIONAL INFORMATION

Author contributions: E.G. Skryabin: conceptualization, methodology, investigation, formal analysis, writing—original draft; A.Yu. Krivtsov: investigation, formal analysis, writing—original draft. All authors approved the version of the manuscript to be published and agree to be accountable for all aspects of the work, ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Ethics approval: The study was approved by the Local Ethics Committee of Tyumen State Medical University (approval protocol No. 187/06.1 dated April 2, 2025). The study and its protocol were not registered.

Consent for publication: Written informed consent was obtained from the patient for the publication of personal data in a scientific journal. The scope of the published data (results of pelvic imaging) was approved by the patients’ legal representatives.

Funding sources: The authors declare no external funding was received for conducting the study or publishing the article.

Disclosure of interests: The authors have no relationships, activities, or interests for the last three years related to for-profit or not-for-profit third parties whose interests may be affected by the contents of the article.

Statement of originality: No previously published material (text, images, or data) was used in this work.

Data availability statement: All data generated during this study are available in this article.

Generative AI: No generative artificial intelligence technologies were used to prepare this article.

Provenance and peer-review: This paper was submitted unsolicited and reviewed following the standard procedure. The review process involved two in-house reviewers.

About the authors

Evgeni G. Skryabin

Author for correspondence.
Email: skryabineg@mail.ru
ORCID iD: 0000-0002-4128-6127
SPIN-code: 4125-9422

MD, PhD, Dr. Sci. (Medicine), Professor

Alexey Yu. Krivtsov

Email: krivtsov4444@gmail.com
ORCID iD: 0009-0007-2343-4791
Russian Federation, Tyumen

References

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2. Fig. 1. Three-dimensional reconstruction (a) and CT scan (b) of the lower thoracic and lumbar spine, pelvic bones, and hip joints of a 16-year-old female patient. Subtype IIIb injury of the left side of the pelvis (acetabular and iliac wing fractures). Transitional lumbosacral vertebra, subtype IIa.

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3. Fig. 2. Three-dimensional reconstruction (a) and CT scan (b) of the lower lumbar spine and sacrum of a 16-year-old female patient. Type a sacral injury (right iliac wing fracture). Transitional lumbosacral vertebra, type III, subtype b.

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4. Fig. 3. Three-dimensional reconstructions (a, b, and c) and CT scan (d) of the lower lumbar spine, pelvic bones, and hip joints of a 13-year-old female patient. Avulsion fracture of the right iliac crest (a and b). Transitional lumbosacral vertebra, type II, subtype b (а, c, and d).

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5. Fig. 4. Schematic representation of different types and subtypes of transitional lumbosacral vertebrae according to Castellvi.

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