Traction Spurs in the Lumbar Spine: A Historical Overview and Future Perspectives

Authors: Masatsugu Tsukamoto, Tadatsugu Morimoto, Tomohito Yoshihara, Hirohito Hirata, Yu Toda, Takaomi Kobayashi, Masaaki Mawatari

Abstract

Numerous studies have explored the connection between lumbar osteophytes, their pathophysiology, and instability since Macnab's 1971 report on traction spurs as an indicator of lumbar instability. This study provides a narrative historical overview of traction spurs, a classic finding that suggests lumbar instability. It summarizes the causes of anterior lumbar vertebral osteophytes, the relationship between traction spurs and lumbar spinal instability, and the clinical significance of traction spurs. Vertebral osteophytes are grouped into two categories, namely, traction spurs or claw spurs, which represent different stages of the same pathological process. Traction spurs are indicative of instability and occur in the early stage of disc degeneration, characterized by temporary dysfunction or instability. Traction spur formation following fusion surgery can predict union or nonunion, and it serves as an indicator of preoperative and postoperative segmental instability. The relationship between traction spurs and radiographic instability, as well as their association with imaging findings such as CT and MRI, has been clarified. Additionally, finite element analysis and mechanical testing have been used to investigate the significance of traction spurs. However, further research is needed to verify that traction spurs are an accurate indicator of pre- and postoperative lumbar instability.

1. Introduction

Lower back pain is often caused by spinal instability in the lumbar spine, necessitating lumbar fusion surgery^1-3)^. The most common method for diagnosing instability is through radiography, with flexion-extension radiography being particularly useful in assessing lumbar instability^4,5)^. Surgeons often rely on these radiographs to detect any abnormal vertebral motion before deciding on surgical fusion. Various radiographic indicators of vertebral instability have been proposed, including the vacuum phenomenon of gas in the disc space, which is one of the earliest signs of segmental instability at this level^6-8)^. Additionally, Modic changes (MCs), which are visible on MRI in patients with degenerative disc disease, have been suggested to play a role in lumbar spine stability^9,10)^.

Traction spurs are another well-known conventional radiographic finding associated with instability in literature^11)^. Traction spurs are classic osteophytes that develop at the attachment site of the outermost annular fibers, approximately 2 mm from the distal border of the anterior and lateral surfaces of the vertebral bodies. Vertebral osteophytes are classified as traction or claw osteophytes. Claw osteophytes are more prevalent and curve toward the contiguous disc. Traction spurs are osteophytes that are 2-3 mm from the margin of the vertebral body and are oriented horizontally. Conversely, claw spurs are located near the endplate and have a curved shape toward the opposite endplate. Traction spurs are osteophytes that develop early on in the degenerative process, whereas claw spurs develop later on^11,12)^.

Frequently, both traction and claw spurs coexist on the same vertebral margin. Several investigations have examined the relationship between traction spurs and lumbar segmental instability (Fig. 1)^13-16)^.

In this study, we utilized a narrative review methodology, which allowed a more extensive, flexible, and exhaustive organization and analysis of the existing literature on traction spurs, a key segmental instability parameter. To provide evidence regarding the function of traction spurs in the pathogenesis of segmental instability, we chose key articles published in peer-reviewed scientific journals, concentrating specifically on traction spurs.

The remainder of the paper is organized as follows. Section 2 presents a historical overview of traction spurs and classic findings suggestive of lumbar instability. Section 3 summarizes the etiology of anterior lumbar vertebral osteophytes. Section 4 describes the relationship between traction spurs and lumbar spinal instability. Lastly, Section 5 addresses the clinical significance of traction spurs.

2. Historical Review of Traction Spurs

The formation of traction spurs is a well-known radiographic indication of spinal instability. A historical overview of traction spurs is presented in Table 1. Although lumbar osteophytes have been previously discussed, Nathan et al. were the first to examine 400 vertebral arches in two races of both sexes and all ages to investigate the presence of osteophytes in 1962^17)^. In 1971, Macnab, who performed extensive studies on movement anomalies in degenerative discs, coined the term “traction spur” and described it as a particular kind of anterior osteophyte that is connected with an abnormal pattern of translational movement^11)^. Macnab emphasized the characteristics of traction spurs and their connection to unstable lumbar disco-vertebral junctions, as well as excessive and abnormal spinal mobility^11)^.

In 1973, Yadab analyzed the importance of traction spurs^18)^. According to Yadab, traction spurs are the most reliable indicators of vertebral segment instability^18)^. Pate et al. conducted an anatomic-pathologic-radiological study using fresh cadaveric spines, macerated historic and modern lumbar vertebrae, and histological preparations to determine the significance of traction spurs^13)^. Pate et al. established radiological and pathological relationships between traction spurs and spinal instability^13)^. The findings revealed that claw osteophytes are more prevalent than traction spurs and can coexist within the same vertebral body. Initially apparent traction osteophytes may develop claw osteophytes over time, and in the majority of cases, these osteophytes represent various stages of the same pathologic process. Other researchers have demonstrated that traction and claw spurs coexist frequently on the same vertebral margin^19)^. This suggests that they may result from the same degenerative process and are not necessarily two distinct pathologic processes. Thus, traction spurs were re-examined in the late 1980s, and it was discovered that they were identical to claw osteophytes and were frequently present in the same patient.

Bräm et al. stated that traction osteophytes (as opposed to all other forms of osteophytes or normal vertebral bodies) have high specificity (98.1%) but low sensitivity (12.5%) for diagnosing segmental instability^14)^. Therefore, patients with traction osteophytes should consider functional radiography. However, there have been no reports on the sensitivity and specificity of traction spurs and lumbar spinal instability since this report. Pitkanen et al. demonstrated that traction and spondylolisthesis were statistically significant and independent predictors of posterior sliding instability^15)^. On plain films of patients with clinically suspected lumbar spinal instability, disc degeneration, spondylarthrosis, and traction spurs are frequently observed in 53%, 42%, and 18% of cases, respectively. Additionally, they stated that traction spurs are not specific indicators of radiological instability and that it was unwarranted to recommend functional flexion-extension radiography for all patients with these findings.

In 1998, Heggeness discovered that the degeneration process leading to the formation of claw and traction osteophytes was identical^19)^. Subsequently, researchers shifted their focus away from the types of osteophytes and the direction in which they form. However, recent studies that focus on traction spurs and radiographic instabilities have emerged. Kasai et al. examined the formation direction of 14,250 pairs of anterior lumbar osteophytes and found that morphological and biomechanical disparities in the lumbar spine were associated with the direction of spur development in the intervertebral space^20)^. Tsukamoto et al. assessed various indicators of lumbar spine instability (traction spurs, vacuum phenomenon, and Modic change) and radiographic instability from multiple perspectives^16)^. Their study highlights the importance of traction spurs as a preoperative evaluation.

Traction spurs are well-known radiographic images that are commonly associated with spinal instability. They have recently been identified as one of the fusion criteria for lumbar intervertebral body fusion^21)^. The presence of spurs and their relationship to abnormal movement are most evident in patients who have undergone spinal fusion. Once fusion is achieved and the segment becomes stable, traction spurs diminish. Therefore, the reduction in osteophytes and sclerosis following instrumented spinal fusion can serve as evidence of successful fusion^22)^. A study conducted by Kim et al. investigated the correlation between the presence of a traction spur and the formation of fusion after posterior lumbar interbody fusion (PLIF)^23)^. It was found that in segments with successful fusion, no new traction spurs were formed. This indicates that the stability provided by the fusion protected the segments from further stress and prevented the development of osteophytes. Consequently, the formation of a traction spur following PLIF was determined to be a valuable predictor of nonfusion. Another study by Yong et al. suggested that traction spurs after cervical arthroplasty may be closely related to the instability caused by increased shear force and the resulting translation of the upper body^24)^. As a result, traction spurs have gained attention as an indicator of both postoperative and preoperative segmental instabilities.

In recent years, there has been extensive research on the mechanical characteristics of lumbar osteophytes using mechanical testing and finite element analysis^25-28)^. It is hoped that these studies will contribute to a more comprehensive understanding of the pathogenesis of traction spurs and will improve patient prognosis.

3. Epidemiology and Etiology of Anterior Lumbar Vertebral Osteophytes

Osteophytes, also known as bone spurs, are frequently observed clinically and radiologically. Studies have shown that spinal osteophytes are present in up to 80% of men and 60% of women over the age of 50 years^27)^. The prevalence of vertebral body osteophytes in the lumbar region increases with age^29,30)^. In fact, a significant proportion of individuals aged 20-45 years have osteophytes in 20%-25% of their vertebral columns, and this percentage increases to 73%-90% in individuals over the age of 60 years^17)^. Additionally, it has been found that vertebral osteophytes typically grow by 4% per year in middle-aged women^31)^.

The development of osteophytes in the anterior lumbar vertebrae may be influenced by several factors. As individuals age, the nucleus pulposus, which is responsible for maintaining the water content and turgor of the intervertebral disc, undergoes changes that result in decreased disc height and reduced ability to bear weight. Concurrently, the annulus fibrosus, which provides flexibility to the disc, begins to deteriorate. Degenerative processes in the lumbar spine typically initiate in the intervertebral disc. These processes involve progressive biochemical and structural alterations that affect the disc's physical properties, elasticity, and mechanical resistance, ultimately leading to disc collapse.

The acquired collapse of the intervertebral disc has three clinically significant consequences. First, it leads to pathological changes in the vertebral bodies, including the development of osteophytes. Second, it causes the anterior bulging of the flaval ligaments and posterior bulging of the posterior longitudinal ligament, resulting in the narrowing of the central spinal canal. Lastly, it leads to the posterior bulging of the redundant posterior disc surface, which causes the narrowing of the central spinal canal and inferior recesses of the vertebrae. To maintain the maximum load-bearing potential, the margins of the facet joint develop bony projections to increase the surface area for weight distribution. The abnormal movements of the vertebral bodies, such as those associated with disc degeneration, place traction stresses on the attachment of the outermost annular fibers. This leads to the development of traction spurs at the site of attachment of these fibers. Because only a few of the outermost fibers attach posteriorly, these spurs, known as spondylophytes, are confined to the anterior and lateral aspects of the vertebral bodies, where they project out as thin horizontal shelves.

The natural progression of instability biomechanically was proposed by Kirkaldy, Willis, and Farfan^32)^. They suggested that instability passes through three phases. The first phase is the stage of dysfunction, characterized by the hypermobile angulation of the functioning spinal units. The second phase is the stage of instability, where the discs and facet joints begin to degenerate, leading to excessive translation. This cascade is initiated by a decrease in disc height, which is the first alteration in this stage. The process of degeneration continues, resulting in an increasing number of translations. The third phase is the stage of restabilization, where severe loss of disc height and osteophyte formation lead to the restabilization of the unit and a decrease in translation. If restabilization does not occur, pain increases, necessitating surgery.

Traction spurs are a result of increased tensile stresses exerted by the anterior longitudinal ligament and Sharpey's fibers on bone insertions when there is abnormal motion^11)^. In the early stages of development, traction spurs can be observed on lateral radiographs as small, horizontally directed bony protrusions located immediately cranial or caudal to the discal edge of the vertebral body. These spurs typically develop approximately 2-3 mm away from the edges of the vertebrae and have a strictly horizontal orientation. By contrast, claw osteophytes, which develop later in the degenerative process, are located closer to the endplate and have a curved shape directed toward the opposite endplate. It is common for traction and claw spurs to coexist on the same vertebral rim, suggesting that they may be the result of the same degenerative process rather than separate pathological processes. These findings indicate that claw osteophytes are more prevalent than traction osteophytes, both types of osteophytes can be present within a single vertebral body, traction osteophytes can progress to assume the characteristics of claw osteophytes over time, and in most cases, these osteophytes represent different stages of the same pathological process^13)^.

4. The Relationship between Traction Spurs and Lumbar Spinal Instability

Macnab et al. proposed that the presence of traction spurs may indicate spinal segmental instability^11)^. Bräm et al. conducted a study to determine if the magnetic resonance (MR) abnormalities of the intervertebral disc and adjacent bone marrow could predict the segmental instability of the lumbar spine, as diagnosed through functional radiographs^14)^. They concluded that functional radiographs should be considered for patients with joint tears and traction osteophytes. Pate et al. investigated the incidence frequencies of claw and traction osteophytes in the intervertebral spaces of Th12-L1, L1-L2, L2-L3, L3-L4, and L4-L5 using 200 cadavers^13)^. They found that 91% of the cadavers had osteophytes in at least one intervertebral space, with claw osteophytes accounting for approximately 39% and traction osteophytes accounting for approximately 9% of the total distribution. Claw osteophytes were more prevalent in the Th12-L2 levels, and traction osteophytes were more noticeable at the L3-L5 levels. Kasai et al. conducted a study and found that pairs of osteophytes most commonly form in a direction away from the adjacent disc in the upper lumbar vertebrae (L1-L2 and L2-L3) and they form in a direction toward the adjacent disc in the lower or middle lumbar vertebrae (L3-L4, L4-L5, and L5-S1)^20)^. They also identified morphological and biomechanical variations, as well as differences in the degenerative process of the upper and lower lumbar vertebrae, as factors influencing the direction of spur development in intervertebral spaces^20)^.

Tsukamoto et al. speculated that these differences significantly contribute to osteophyte formation^16)^. As a traction spur occurs at an earlier stage of disc degeneration (temporary dysfunction or unstable phase), it is considered an indication of instability. They reported that the association between traction spurs and functional studies, vacuum phenomenon, MCs, patient sex, generation, and disc level were significantly linked to traction spurs in the lumbar spine. Their multivariate analysis showed that traction spurs were significantly related to vertical motion, translational motion, vacuum phenomenon, and MCs. Furthermore, clinically, the study suggests that segments with traction spurs should be evaluated carefully because traction spurs may be a sign of disc degeneration (MCs and/or vacuum phenomena). Traction spurs are one of the factors associated with segmental motion.

In a study conducted by Al-Rawahi et al., the researchers examined the stiffness of motion in segments ranging from T5-T6 to L3-L4^25)^. The researchers found that the removal of osteophytes resulted in a significant decrease in segmental stiffness. Specifically, after osteophyte removal, the patient's resistance to compression decreased by an average of 17% and their resistance to bending movements in flexion, extension, and lateral bending decreased by 49%, 36%, 36%, and 35%, respectively. The researchers concluded that vertebral body osteophytes exhibit greater resistance to bending movements compared to compression. This is because they counteract the instability that can stimulate their formation. This adaptive response suggests that osteophytes may serve a protective rather than a degenerative function.

In recent years, finite element (FE), a computer-based research method that offers a cost-effective and less ethical alternative to in vitro and in vivo approaches, has also experienced rapid growth. FE analysis has become a widely adopted method for studying intervertebral disc (IVD) biomechanics and has been used in compensating for the limitations of in vitro experimental studies^33-38)^.

Using FE analysis, Cai et al. found that as disc degeneration progresses, the range of motion (ROM) in the L4-L5 degenerative segment significantly decreases whereas the ROM in healthy adjacent segments increases in all postures^39)^. This result is consistent with previous studies that predicted a similar trend in segmental rotation. However, it is in contrast to several in vitro and FE studies that suggest an increase in degenerative segmental ROM during axial rotation^34,40-42)^. This difference is speculated to be due to the differences in modeling techniques, such as cracking and rupture of degenerative discs in in vitro experiments^43)^, as well as simulation of anterior osteophytes and reduction in medullary nucleus volume^39)^. In other words, they speculate that the anterior osteophytes limited the movement of the degenerative disc.

Using FE analysis, Wang et al. conducted a study to investigate the biomechanical impact of anterior vertebral body osteophytes on the entire lumbar spine^27)^. Their findings indicated that the presence of anterior vertebral body osteophytes, particularly in cases of severe formation and disc space narrowing, significantly reduced the ROM in flexion. Conversely, mild and moderate osteophytes were found to increase the ROM during axial rotation and extension. Schmidt et al. reported a slight increase of 0.5° in flexion for slightly degenerative discs and a significant reduction in flexion under a 7.5-nm moment for moderately and severely degenerated discs with osteophytes^44)^. Similarly, Volkheimer et al. observed a slight increase in flexion-extension ROM for mildly degenerated discs, but significant decreases were observed in moderately and severely degenerated discs^45)^. Mimura et al. also reported a decrease in flexion-extension ROM with a higher degree of degeneration under a 10-nm moment^42)^. These findings provide support for the notion that osteophytes, particularly mild and moderate ones, are indicative of spinal instability^11)^.

Radiological, biomechanical, and FE analyses collectively demonstrate that traction spurs are associated with lumbar spinal instability. These findings align with the degenerative stages of the spine proposed by Kirkaldy-Willis and Farfan, which include the dysfunction, unstable, and stabilization phases^32)^.

5. Clinical Significance of Traction Spurs

Spinal osteophytes can manifest with a range of symptoms or may be asymptomatic. Lumbar osteophytes can result in nerve root compression, lower back pain, and occasionally, obstruction of the inferior vena cava^46)^. A study conducted by Karasik et al. found a correlation between anterior lumbar osteophytes and abdominal aortic calcification^47)^. Additionally, Dregelid et al. reported a case of aortic perforation caused by vertebral osteophytes without any significant trauma^48)^. In this case, a sharp, needle-like vertebral osteophyte was observed opposite to the aortic perforation, showing no signs of infection. The perforation was attributed to the presence of the osteophyte. However, it remains unclear whether these anterior and lateral lumbar osteophytes can cause injury to the abdominal aorta and the inferior vena cava located anteriorly to them.

The relationship between traction spurs and clinical symptoms, specifically lower back pain, is not fully understood. Macnab suggested that traction spurs may be associated with abnormal translational movement, but further statistically valid investigations are needed to establish their clinical significance^11)^. It is important to note that the presence of abnormal motion in a degenerative spine does not always indicate the presence of pain. Mulholland argued that the concept of instability is often exaggerated and fusion surgery may not always be the most appropriate treatment option^49)^. Therefore, additional research is needed to better understand the relationship between traction spurs and clinical symptoms.

The stability of the lumbar spine is crucial for maintaining the health of the lower back. When evaluating lumbar spine stability, the presence of a traction spur should be taken into consideration. Furthermore, the specific type of spur observed on radiographs or CT images may play a significant role in the decision-making process regarding spinal fusion.

Kim et al. found that new traction spur formation was detected in 52.6% of nonfused segments following decompression surgery, which was not observed on preoperative imaging^23)^. This suggests that the development of traction spurs after posterior lumbar interbody fusion (PLIF) can serve as an important parameter for predicting nonfusion. However, it is important to note that this study focused on osteophytosis and did not investigate the fate of existing bony growth after achieving stability.

Ha et al. observed the resorption of osteophytes and sclerosis after a successful instrumented spine fusion, with significant resorption noted at 3 and 6 months postoperation^22)^. This resorption is believed to occur through Wolff's law, Heuter-Volkmann's law, and Frost's flexure drift laws if solid fusion is achieved after spinal fusion. Therefore, the resorption of osteophytes and sclerosis following instrumented spine fusion can be considered evidence of effective union.

Finally, the relationship between traction spurs and clinical symptoms, as well as their role in spinal instability, is not fully understood. Further statistically valid investigations are needed to establish their role in clinical symptoms. Additionally, the fate of existing bony growth after achieving stability, especially in the context of fusion surgery, needs more exploration.

In summary, the future prospects for traction spurs involve continued research to better understand their diagnostic, clinical, and biomechanical significance. The potential impact on treatment decisions, such as in spinal fusion procedures, highlights the importance of further investigations in this field.

6. Limitations

The present study has some limitations. First, most of the publications were retrospective studies. Thus, the widely varying subjects, study designs, and methods did not allow valid meta-analyses, and the methodological quality of the studies could not be systematically analyzed. Consequently, the lack of a systematic methodology in this review made it impossible to obtain the highest level of current evidence regarding the conditions and techniques. Additionally, being a narrative review, there is a possibility of incomplete coverage of relevant literature and potential bias in the selection process. Second, there is a paucity of evidence regarding the sensitivity, specificity, and likelihood ratios for traction spurs and segmental instability. Although Bräm et al. reported the specificity and sensitivity of traction osteophytes and segmental instability, there is limited literature available beyond their study to clarify these factors. Therefore, it is challenging to determine whether traction spurs are reliable indicators of segmental instability. Further studies must be conducted to address these gaps in knowledge.

Despite these limitations, our findings contribute to the understanding of traction spurs and should be of interest to orthopedic surgeons and other healthcare professionals involved in musculoskeletal medicine.

7. Conclusions

Traction spurs, proposed by Macnab in 1971 as an indicator of instability, have been studied extensively. In recent years, they have been used as an indicator of bone fusion after lumbar fusion surgery, and their mechanical properties have been investigated using FE analysis and mechanical testing. However, as Macnab stated, “the significance of traction spurs is that they demonstrate segmental instability, which may or may not cause symptoms,” but their relationship with clinical symptoms remains unclear. Future research, including large-scale studies using a larger number of cases and more precise biomechanical analyses, is needed to gain a clearer understanding of traction spurs.

Further investigation in this area will provide new insights into the pathogenesis, clinical symptoms, and treatment of spinal diseases.

**Conflicts of Interest: **The authors declare that there are no relevant conflicts of interest.

**Sources of Funding: **None

**Author Contributions: **Conceptualization, M. T. and T. M.; methodology, M. T. and T. K.; software, T. K.; validation, T. K. and T. Y.; formal analysis, M. T. and Y. T.; investigation, M. T. and T. K.; data curation, M. T. and T. K.; writing-original draft preparation, M. T.; writing-review and editing, H. H. and M. M.; and supervision, T. M. All authors contributed equally to this work (including the writing and preparation of the manuscript). All the authors have read and agreed to the published version of the manuscript.

**Ethical Approval: **Not applicable.

Ethical approval was waived by the ethics committee because this is a review article.

**Informed Consent: **Consent was not required because this study involved no human subject.