The attachment of the ribs to the sternum is essential for maintaining the structural integrity of the thoracic cavity and facilitating respiratory movements. From a functional perspective, the central lower thorax (ribs 7–12) is where the diaphragm, a key respiratory muscle, is attached [13]. Furthermore, the anatomical concept of the retroperitoneal and retro-pleural spaces being continuous compartments, separated by the lateral attachments of the diaphragm to the 11th and 12th ribs and the L1 transverse process, highlights the importance of rib attachment to the sternum in surgical anatomy [14].

The thoracic cage and its components are also relevant in pain management and surgical procedures. The anterior abdominal wall is bounded superiorly by the costal margin, which is important for abdominal wall blocks for intra-abdominal surgery [15]. The lateral transversus abdominis plane (TAP) approach performed at the midaxillary line between the costal margin and iliac crest can consistently provide anterior abdomen analgesia [16]. Furthermore, the thoracic inter-fascial plane block involves identifying the pectoralis muscles, external intercostal muscle, and second rib which is crucial for multimodal analgesia after breast lumpectomy [17].

Surgical stabilization of rib fractures, particularly for the first seven ribs, is increasingly utilized in managing moderate to severely displaced rib fractures [18]. This procedure aims to restore pulmonary function and treat underlying thoracic injuries to avoid respiratory complications [19]. Additionally, the effectiveness of surgical fixation for flail chest and unifocal non-flail rib fractures has been a research subject, with some studies indicating positive outcomes regarding lung function and reduced hospital length of stay [20, 21]. The clinical relevance of rib attachment to the sternum is further underscored by the surgical management of conditions such as chest wall reconstruction, where custom-made, anatomically designed titanium ribs and sternum implants have been utilized to address skeletal defects [22].

The anatomical relationship between ribs and sternum, particularly false ribs, is crucial for surgical outcomes and post-operative recovery. Our narrative review analyzes published case reports on rib-sternum attachment variations, focusing on clinical presentations and diagnostic approaches. This synthesis provides enhanced surgical decision-making guidelines, especially for procedures [23].

The thoracic cage represents a complex anatomical structure essential for protecting vital organs and facilitating respiratory mechanics. Understanding its anatomical variations is crucial for clinical practice, as these variations significantly impact patient care across medical specialties [24]. These variations encompass several key structural elements, including lateral costal vessels, rib attachments, and costal margins, which influence various medical procedures and conditions. Furthermore, these variations can lead to specific clinical conditions, such as slipping rib syndrome (SRS) [25] and thoracic outlet syndrome (TOS), necessitating careful consideration in diagnostic approaches and treatment planning (Fig. 2). Recent advances in imaging technologies and surgical techniques have emphasized recognizing these anatomical differences, particularly in diagnostic procedures and surgical planning [22, 26]. Healthcare providers must maintain comprehensive knowledge of these variations for optimal outcomes, from routine procedures like thoracentesis to complex endoscopic robotic surgery, especially in pediatric patients. This growing understanding of thoracic variations continues to enhance patient care and treatment outcomes across medical disciplines [27].

As a glimpse to review other important anatomical variations, should be noted to bifid ribs and extra intercostal spaces. Anatomical variations of the thoracic cage present significant clinical considerations, particularly concerning bifid ribs and extra intercostal spaces. Bifid ribs, occurring in 0.15% to 3.4% of the population and accounting for up to 20% of congenital rib anomalies, develop during embryological growth when costal processes split abnormally [28, 29]. This condition manifests as a Y-shaped bifurcation, typically affecting the 3rd and 4th ribs, with separate costal cartilage attachments to the sternum. Clinical implications include altered respiratory mechanics, chronic discomfort, and increased fracture risk. Additionally, bifid ribs are associated with genetic conditions like Gorlin-Goltz syndrome, present in 26% of affected individuals [30]. Accurate diagnosis through computed tomography (CT) scanning is crucial, as these variations can be misinterpreted as fractures on standard radiographs [31]. Healthcare providers must maintain precise documentation for proper medical management and future interventions [32], particularly given that these variations often remain asymptomatic and are discovered incidentally during routine imaging.

Extra intercostal spaces and cervical ribs represent significant anatomical variations warranting clinical attention. Extra intercostal spaces develop through supernumerary ribs or abnormal rib segmentation during embryological development, influenced by genetic factors including HOX gene mutations [33]. The prevalence of cervical ribs ranges from 0.05% to 3.0% in the general population, with significant implications for TOS development [34]. These variations present crucial clinical considerations, particularly regarding variant neurovascular patterns necessitate modified surgical approaches [35]. Cervical ribs, developing from the 7th cervical vertebra’s costal elements, can compress the brachial plexus and subclavian vessels, leading to TOS [36]. Diagnosis requires comprehensive imaging, including CT scans with three-dimensional reconstruction and magnetic resonance imaging (MRI) or CT angiography [37]. Healthcare providers must maintain meticulous documentation and vigilance for neurological and vascular complications, ensuring appropriate management strategies for affected patients [38].

The variation in rib attachment to the sternum has implications for medical procedures and conditions. For instance, in chest wall reconstruction, the sternum, ribs, and chest wall can be reconstructed using specific materials and techniques [26]. Moreover, chondrosarcoma, the most common primary bone tumor involving the ribs and sternum, is thought to affect the ribs more frequently than the sternum [39, 40]. The clinical problem of false ribs attaching directly to the sternum is a significant anatomical concern. The false and floating ribs (8–12) do not attach directly to the sternum but are connected to the thoracic vertebrae. This anatomical variation can lead to complications such as SRS, which can cause severe abdominal pain due to the overriding of the 9th and 10th ribs [25], hypermobility, and injuries during cardiopulmonary resuscitation [25, 41, 42]. In contrast, the true ribs (1–7) attach directly to the sternum via the costal cartilage, providing stability and protection to the thoracic cavity [7, 8, 43, 44].

SRS, also known as Cyriax syndrome, is a mechanical condition characterized by the hypermobility of the costal cartilages attached to the floating ribs, leading to lower chest or upper abdominal pain [10, 45]. This syndrome was first described by Cyriax in 1919 and is often overlooked, underdiagnosed, or misdiagnosed, making it a challenging condition to recognize [46]. The primary cause of SRS is the entrapment of the intercostal nerve due to the hypermobility of the costal cartilage, resulting in symptomatic impingement and subsequent pain in the lower thorax and upper abdomen (Table 1) [43, 45, 47-61].

The diagnosis of SRS can be made through a hooking maneuver, and when pain medication is not sufficient, resection of the rib can be performed [25]. The syndrome can be identified by performing a physical examination, which may reveal the characteristic clicking rib and rib-tip syndrome, leading to severe abdominal pain due to the overriding of the 9th and 10th rib [62]. Surgical interventions such as costal cartilage resection and rib plating have been explored as treatment options for SRS in adult patients [63]. Moreover, the correlation between SRS and rib attachment is evident in the anatomical description of the syndrome. The lower costal cartilages (ribs 8–10) are not directly connected to the sternum but attach to adjacent cartilages with a cartilaginous cap or fibrous band [63]. Additionally, the disruption of the inter-chondral fibrous attachments and the hypermobility of the anterior false ribs are key factors in the pathophysiology of SRS [10]. According to all the contents mentioned above, the way the ribs are connected to the sternum can affect respiratory functions, the anatomy of the human body, and the surgical process. Due to this issue, examining the structure of the chest and how to connect the false and even floating ribs has become one of the important variations studied (Fig. 3).

SRS is a little-known and often misdiagnosed condition characterized by the hypermobility or instability of the 8th, 9th, and/or 10th ribs [64]. First described by the British orthopedist Henry Gauvain Stedman in 1918 and further characterized by James Cyriax in 1919, SRS occurs when the costal cartilage attachments between the ribs and sternum become stretched or torn, allowing the rib margins to slip and cause irritation and trauma to surrounding intercostal nerves [10, 45]. This leads to considerable chronic pain in the lower chest or upper abdomen that can be debilitating and severely impact quality of life [46, 63]. Despite being recognized in the medical literature for over a century, SRS continues to be an underdiagnosed condition, particularly among pediatric and adolescent populations where musculoskeletal complaints may be dismissed [12]. Contributing factors include poor awareness among clinicians and difficulty establishing the diagnosis, often requiring specialist imaging techniques like hooking maneuver radiographs or MRI [43]. As a result, patients with SRS frequently endure a lengthy diagnostic odyssey spanning multiple years and various misdiagnoses before receiving appropriate treatment [62].

Once diagnosed, the primary treatment goal is mechanical stabilization of the hypermobile rib segments to relieve nerve irritation. Both minimally invasive and open surgical techniques have been employed, including laparoscopic resection/realignment, vertical rib plating using bioabsorbable mesh, and complete surgical excision of ribs [61, 65]. While these interventions can successfully provide long-term pain relief, with an average duration of 2.2 years reported, the lack of procedure standardization and recurrence risk highlights the need for continued research and protocol development [43]. No collation or critical appraisal of the collective case report literature on SRS has been undertaken. Through a comprehensive review of published SRS case reports, this article aims to delineate the clinical spectrum of this little-known syndrome, explore diagnostic and treatment challenges, synthesize management outcomes, and extract learning points that can optimize future patient care. It represents the first review article focused specifically on SRS case reports with clinical manifestations.

The costal and intercostal pathologies diagnosis necessitates a multifaceted approach, incorporating advanced imaging modalities and meticulous physical examinations. Dynamic ultrasonography has proven invaluable in visualizing costal subluxation and intercostal dynamics, offering a real-time assessment of rib mobility and potential impingement [44, 59, 60]. Multimodal imaging protocols, including plain radiography, bone scintigraphy, and CT, are frequently employed to elucidate osseous abnormalities, cartilaginous defects, and soft tissue anomalies [43, 56, 58]. More advanced techniques such as magnetic resonance imaging and esophagogastroduodenoscopy may exclude alternative etiologies and assess for concomitant pathologies [25]. These modalities offer high-resolution visualization of the costal architecture and surrounding structures, enabling precise localization of anatomical aberrations.

The “hooking maneuver” test, a provocative physical examination technique, involves anterior traction on the costal margin to elicit characteristic symptomatology [50, 56, 57]. This maneuver is particularly efficacious in diagnosing SRS, as it reproduces the mechanical stress on the costal joints. Localized tenderness at specific anatomical landmarks, such as intercostal drain sites, can provide valuable diagnostic insights and guide further investigation [49].

The diagnostic algorithm typically initiates with clinical suspicion, progresses through a comprehensive physical examination, and culminates in dynamic imaging studies [61]. Functional assessments, such as the Valsalva maneuver and positional testing, may be incorporated to evaluate the impact of intrathoracic pressure changes and postural variations on symptom manifestation. This comprehensive, multimodal approach enables clinicians to differentiate between various costal and intercostal pathologies accurately (Fig. 4).

A comprehensive review of SRS case reports published between 1993 and 2023 was conducted in this retrospective study. The search encompassed multiple databases, including PubMed, Embase, Google Scholar, Web of Science, and nine prominent case report repositories (detailed in Table 2). The investigation employed sophisticated search algorithms, combining key terms related to rib cage anatomical variations, false rib attachments to the sternum, and documented SRS incidents. Two independent reviewers scrutinized the findings, ultimately selecting 17 case reports. Any discrepancies in selection were resolved through collaborative discussion. The study focused exclusively on human subject case reports published in English, utilizing databases known for their extensive coverage of peer-reviewed medical literature across various specialties.

Direct attachment of false ribs to the sternum is an uncommon anatomical variant with clinical implications. The literature contains reports of similar anomalies, but available data is limited. For example, recently an investigation assessed the anatomy of the anterior ribs and the composition of the costal margin rib-sternum integrity through a standardized dissection on 30 cadavers (15 male, 15 female). This investigation revealed substantial variability in bilateral chest wall anatomy compared to normal presentation. Lower ribs (8–10) frequently showed atypical features like inter-chondral joints, cartilaginous unions, and morphological variation resulting in altered mechanics. Up to 83% featured anomalous connections between ribs 6 and 7 while 10% displayed direct sternum attachment of the 8th rib sans the 7th. Increased mobility of up to 90% was evident in the lowermost rib tips, correlating with a greater incidence of anatomical anomalies like hooked and floating ribs in these segments [66]. This anatomical variation on rib attachment can disturb kinematics, while fusion variants may alter physiology through effects on rib angulation and chest expansion. On the other hand, a pilot study by Laswi et al. [7] in 2022, revealed that the costal margins of 40 cadavers with roughly equal numbers of males and females had anatomical variation, especially for the 10th rib. The 9th rib is attached to the 8th rib via an inter-chondral cartilage in all specimens. Mobility and subluxation of the lower rib tips were observed frequently, especially for the 10th rib, which often presented as a free-floating rib not attached to the 9th rib 59% (47 of 80). Variations like hooking and medial/lateral subluxation patterns were also noted for the 10th rib, correlating with a lack of rib attachment [7]. Our find lacks functional correlation but asks whether fused false ribs impair ventilation or increase infection risk.

For chest wall surgeons treating diseases of the costal margin, appreciating anatomical variability is crucial. Internal subluxation and hooked tips of the 10th rib may predispose patients to slipped rib syndrome, which is influenced by hormones that increase joint laxity. This condition is further affected by the combination of joint laxity and increased range of motion [67-69]. Deviations from the classically depicted rib cage are frequent, particularly in the lower costal margins. Surgeons operating in this region should account for inter-chondral joints, cartilaginous unions between ribs, floating ribs, and atypical subluxation or hooking patterns that differ substantially from typical presentations. Further biomechanical and epidemiological research could prove insightful. Accurate anatomical knowledge is key for safe surgical access. Unanticipated rib fusions can surprise surgeons and endanger mediastinal structures. Preoperative CT assessment helps detect variants, enabling modifications to avoid complications. However, most procedures rely on classic anatomy. Rib-sternum anomalies may necessitate extra precautions, such as specialized instrumentation or limited resection. Our findings reinforce the value of careful dissection and adaptability when operating on the thorax. Pathologic conditions like slipped rib syndrome demonstrate clinical links between unstable cartilage and pain.

Though our variant likely does not cause similar symptoms due to direct fusion, the association warrants mention. Overall, appreciating normal and aberrant rib cage anatomy is valuable for surgeons and clinicians. With anomalies potentially existing in up to 30% of people, anatomical variations are clinically relevant.