The prevalence of spondylolysis and intervertebral disc degeneration in male pole vaulters

Abstract

BACKGROUND:

The lower back is the most common injury location in pole vaulters, but the prevalence of lumbar spondylolysis and intervertebral disc degeneration is not known.

OBJECTIVE:

This study aimed to determine the prevalence of lumbar spondylolysis and intervertebral disc degeneration in pole vaulters.

METHODS:

This cross-sectional study was conducted in the Tokai area of Japan and included 21 pole vaulters (mean $\pm$ standard deviation [range]: age, 22.2 $\pm$ 3.2 [18–28] years; height, 172.2 $\pm$ 4.7 [165.0–182.0] cm; body weight, 67.6 $\pm$ 7.3 [54.0– 80.0] kg). The majority of pole vaulters were collegiate athletes. We performed anterior, lateral, and oblique radiography at 45 ${}^{\circ}$ and magnetic resonance imaging in the sagittal and coronal planes of the lumbar spine. The evaluation was performed independently of whether the athletes had lower back pain (LBP). Moreover, we investigated the duration of pole-vaulting experience and history and current presence of LBP using a questionnaire.

RESULTS:

The prevalence of lumbar spondylolysis and intervertebral disc degeneration was 28.6% (6/21) and 38.1% (8/21), respectively. Herniation was found in six discs in four vaulters (19.0%). All athletes had a history of LBP. The prevalence of lumbar spondylolysis was high (28.6%).

CONCLUSIONS:

Sport-specific movements performed by pole vaulters may be a risk factor for lumbar spondylolysis.

Keywords

Lumbar vertebra spondylolysis intervertebral disc degeneration track and field

1. Introduction

Lumbar spondylolysis (LS) and intervertebral disc degeneration (DD) occur in athletes and are frequently reported to be associated with occurrence of lower back pain (LBP). Spondylolysis is considered a stress fracture that is frequently reported in adolescent athletes. Sport movements requiring lumbar hyperextension and/or rotation are considered risk factors for the development of lesions. Sakai et al. [1] reviewed the incidence of LS in the Japanese population and reported an incidence of 5.9% in the general population, with the highest incidence (20.5%) of LS in rugby and American football players. In addition, Hangai et al. [2] reported that the prevalence of DD was significantly higher among Japanese collegiate baseball players (59.7%) and swimmers (57.5%) than among non-athletes (31.4%). Thus, it is conceivable that stress on the intervertebral discs varies depending on the type of sport-specific movements.

Pole vaulting is a track-and-field event, in which an athlete clears a height using a pole. Rebella [3] found that the lumbar region was the most common injury location. In collegiate pole vaulters, 83% of lumbar spine injuries and 100% of spondylolysis cases occurred during the plant/takeoff phase of vaulting. In addition, the study stated that pole vaulters may be particularly susceptible to spondylolysis because the plant/takeoff places the spine in a forced hyperextension position as the athlete drives forward off the ground. Gainor et al. [4] analyzed the vaulting of three athletes who have spondylolysis and indicated that the maximum angular acceleration occurred during takeoff when these vaulters had planted the pole and the spine had hyperextended. Previous studies have focused on the LBP associated with LS; however, it is suspected that pole vaulters encounter several types of LBP due to the motion of the spine. Pole vaulters may have a time-dependent load placed on the lower back that causes degenerative changes. However, the prevalence of LS and DD in pole vaulters remains unclear. It is difficult to include a large sample size of pole vaulters in a single study because it is rare for a large number of pole vaulters to belong to one institution; therefore, current research on the injuries of pole vaulters is insufficient.

This study aimed to determine the prevalence of LS and intervertebral DD in pole vaulters. The results of this study are expected to provide basic data and a foundation for future research on LBP in pole vaulters.

2. Methods

2.1 Participants

This was a cross-sectional study that took place in the Tokai area of Japan and included 21 male pole vaulters (mean $\pm$ standard deviation [range]; age, 22.2 $\pm$ 3.2 [18–28] years; height, 172.2 $\pm$ 4.7 [165.0–182.0] cm; body weight, 67.6 $\pm$ 7.3 [54.0–80.0] kg). The inclusion criteria were athletes who were $\geqslant$ 18 years of age as of March 2019 who also participated in a game organized or co-sponsored by The Inter-University Athletic Unions of Tokai or Central Japan Industrial Track and Field Association in 2019, and male pole vaulters with no metal in their body. Although there were 30 athletes who met the inclusion criteria, consent for this study could not be obtained from nine athletes. The majority of the included pole vaulters were collegiate athletes. The evaluation was performed independently of whether the athletes had LBP. All participants provided written informed consent. This research was approved by the Chukyo University Research Ethics Committee (2019-004) and was conducted in accordance with the Declaration of Helsinki.

2.2 Assessment of LS and DD

Radiographic and magnetic resonance imaging (MRI) was used to analyze the lumbar spine of all athletes. We took an X-ray of the lumbar spine from the front, side, and oblique planes at 45 ${}^{\circ}$ . MRI of the lumbar spine was performed using a flexible quadrature detection body coil at 3.0T (Vantage Galan ${}^{\text{TM}}$ 3T, Canon Medical Systems, Tochigi, Japan). T2-weighted and T2-weighted fat saturation (repetition time, 4000 ms; echo time, 90 ms) images in the sagittal plane as well as T1-weighted (repetition time, 2300 ms; echo time, 15 ms) and T2-weighted Dixon (repetition time, 4500 ms; echo time, 100 ms) images in the coronal plane were used to evaluate the characteristic MRI findings. The slice thicknesses of the sagittal and coronal views were 4.0 mm (sagittal view: matrix, 352 $\times$ 256; field of view 300 mm $\times$ 24 mm; T1-weighted image of the coronal view: matrix, 416 $\times$ 288; field of view 320 mm $\times$ 24 mm; T2-weighted Dixon image of the coronal view: matrix, 416 $\times$ 256; field of view 320 mm $\times$ 24 mm). The interval gaps for both views were 0.8 mm. Both X-ray and MRI were used to evaluate LS, and only MRI was used to evaluate lumbar DD. The imaging data were analyzed by one orthopedic specialist who had more than 25 years of clinical experience and had also operated as a spine surgeon at one point in his career. This study assessed the morphological changes of the intervertebral disc using the Macnab classification [5] and the degree of degeneration using the Pfirrmann classification [6]. The presence of lumbar disc herniation was defined as grade II or higher, based on the Macnab classification. The degree of degeneration was graded on the basis of the Pfirrmann classification, with degeneration defined as grade III or higher. Degeneration at $\geqslant$ 1 disc was regarded as DD.

Table 1
Proportions (%) of lumbar spondylolysis

Location	Number of athletes	Proportion	Laterality (%)
			Bilateral	Takeoff leg side	Lead leg side
L1	0	0.0	–	–	–
L2	0	0.0	–	–	–
L3	0	0.0	–	–	–
L4	1	4.8	4.8	0.0	0.0
L5	5	23.8	9.5	9.5	4.8
Total	6	28.6	14.3	9.5	4.8

Table 2

Proportions (%) of disk degeneration

Location	Number of athletes	Proportion	Grade (%)
			III	IV	V
L1/2	0	0.0	–	–	–
L2/3	0	0.0	–	–	–
L3/4	1	4.8	4.8	0.0	0.0
L4/5	5	23.8	23.8	0.0	0.0
L5/S1	4	19.0	14.3	4.8	0.0
DDPs	8	38.1	42.9	4.8	0.0

DDPs, the participants who had disk degeneration at 1 or more disk levels.

2.3 Questionnaire

Using a questionnaire, we investigated the height, body weight, age, personal best pole vaulting record, duration of pole vault experience, history of LBP, and presence of chronic and current LBP. Participants who answered “Yes” to the question “Do you often feel LBP?” were assigned to the chronic LBP group. History of LBP was defined as an event that “caused the athlete to cease participation that day or miss a subsequent practice/competition.” We also determined the takeoff leg using a questionnaire. We defined the takeoff leg as the leg used during vaulting. The opposite leg was termed the lead leg.

2.4 Statistical analysis

The prevalence of spondylolysis and intervertebral DD was calculated. We used SPSS version 23 (IBM Corp., Armonk, NY, USA) for data analyses. The participants were divided into the athletes with LS group when LS was confirmed and the Control group when it was not confirmed. The participants were similarly divided into two groups (athletes with DD group and Control group) according to the presence of lumbar DD. The normality of all basic data was analyzed using a Shapiro-Wilk test. Differences in normally distributed data between the groups were analyzed using an unpaired $t$ -test, and differences in non-normally distributed data were analyzed using a Mann-Whitney U test. The results of basic data are expressed as the mean $\pm$ standard deviation (95% confidence interval). $P$ -values $<$ 0.05 were considered statistically significant.

3. Results

Six pole vaulters had LS (28.6%; Table 1). Three vaulters (14.3%) had bilateral spondylolysis, two vaulters (9.5%) had unilateral spondylolysis on the takeoff-leg side, and one vaulter (4.8%) had unilateral spondylolysis on the lead-leg side. Three pole vaulters (14.3%) had lumbarization of the S-1 vertebra.

Eight pole vaulters had lumbar DD (38.1%; Table 2). Based on the Pfirrmann classification, nine intervertebral discs were evaluated as grade III and one intervertebral disc was evaluated as grade IV. Lumbar herniation was found in six discs in four vaulters (19.0%). In one vaulter, both LS and lumbar DD were observed.

All vaulters had a history of LBP, and 12 vaulters (57.1%) had chronic LBP. In addition, five vaulters had current LBP. Two vaulters with LS (2/6 vaulters; 33.3%) and two vaulters with DD (2/8 vaulters; 25.0%) had current LBP. There were no significant differences in all basic data between the groups (athletes with LS vs. control, and athletes with DD vs. control; Tables 3 and 4).

Table 3
Difference of basic data between athletes with and without lumbar spondylolysis

Variable	Athletes with lumbar spondylolysis ( $n=$ 6)				Athletes without lumbar spondylolysis ( $n=$ 15)
	Mean	$\pm$ SD	95% CI		Mean	$\pm$ SD	95% CI
Age (year)	22.5	$\pm$ 3.4	18.9	–26.1	22.1	$\pm$ 3.3	20.3	–23.9
Height (cm)	170.5	$\pm$ 3.7	166.6	–174.4	172.9	$\pm$ 5.0	170.1	–175.7
Body weight (kg)	69.0	$\pm$ 5.1	63.6	–74.4	66.4	$\pm$ 7.8	62.1	–70.7
Personal record (m)	5.0	$\pm$ 0.4	4.6	–5.4	4.8	$\pm$ 0.5	4.5	–5.1
Duration of pole vault (year)	10.5	$\pm$ 3.0	7.4	–13.6	9.5	$\pm$ 2.3	8.2	–10.8
Age at the start of pole vault (year)	12.0	$\pm$ 0.9	11.1	–12.9	12.6	$\pm$ 1.9	11.5	–13.7

Table 4

Difference of basic data between athletes with and without disk degeneration

Variable	Athletes with disk degeneration ( $n=$ 8)				Athletes without disk degeneration ( $n=$ 13)
	Mean	$\pm$ SD	(95% CI)		Mean	$\pm$ SD	(95% CI)
Age (year)	22.5	$\pm$ 4.2	19.0	–26.0	22.0	$\pm$ 2.6	20.4	–23.6
Height (cm)	171.9	$\pm$ 4.7	168.0	–175.8	172.3	$\pm$ 4.9	169.3	–175.3
Body weight (kg)	63.9	$\pm$ 7.0	58.0	–69.8	69.1	$\pm$ 6.7	65.1	–73.1
Personal record (m)	4.9	$\pm$ 0.3	4.6	–5.2	4.9	$\pm$ 0.5	4.6	–5.2
Duration of pole vault (year)	9.9	$\pm$ 3.1	7.3	–12.5	9.7	$\pm$ 2.1	8.4	–11.0
Age at the start of pole vault (year)	12.6	$\pm$ 2.2	10.8	–14.4	12.3	$\pm$ 1.4	11.5	–13.1

4. Discussion

This study was the first to investigate the prevalence of LS and DD in pole vaulters. The prevalence of LS and DD were 28.6% (6/21) and 38.1% (8/21), respectively. All vaulters had a history of LBP, and 12 vaulters (57.1%) had chronic LBP.

Previous studies have reported the prevalence of spondylolysis in athletes who were $\geqslant$ 18 years of age [7, 8, 9, 10, 11, 12, 13, 14, 15]. Iwamoto et al. [9] investigated abnormalities of the lumbar spine using radiography in Japanese athletes who played American football and reported prevalences of spondylolysis of 11.1% and 10.4% in high school and collegiate athletes, respectively. Kulling et al. [12] reported a prevalence of spondylolysis of 20.7% in beach volleyball athletes. In addition, Soler and Calderon [15] investigated abnormalities of the lumbar spine using radiography in Spanish elite athletes. A high prevalence of spondylolysis was reported in 26.7% (12/45) of throwing athletes in track-and-field events and 20.0% (3/15) of bobsledders. Compared to previous studies, the prevalence of spondylolysis in this study (28.6%) was considered high. As previously shown, the lower spinal levels (L4 and L5) were more frequently affected [9, 15]. Moreover, Rebella [3] reported that spondylolysis occurred during the plant/takeoff phase, which places the spine in a forced hyperextension position as the athlete drives the body forward off the ground. Thus, the results of this study suggested that pole vaulting is a risk factor for LS. We believe that the motion of the spine during pole vaulting causes the lumbar spine to rotate during takeoff, resulting in the development of LS on the lead-leg side. However, the prevalence of LS on the lead-leg side was not high in this study. Hence, the extension of the lumbar spine may be greater than the rotation of the lumbar spine during pole vaulting.

Hangai et al. [2] reported the proportion of participants with DD among college students and found the highest prevalence in baseball players (59.6%) and swimmers (57.5%). The sport-specific movements of baseball players and swimmers that frequently rotate the trunk were considered risk factors of DD that resulted in this high prevalence. The study reported that 31.4% of non-athletes and 25.6% of running athletes had DD. Another study [16] reported that 30% of non-athletic first-year high school students had DD. The prevalence of DD in this study was 38.1% (8/21 vaulters). This result was similar to the prevalence found in non-athletes and running athletes in previous studies and was considered to be lower than that in other sports. Therefore, pole vaulting may contribute to a low risk for DD.

Shimozaki et al. [17] reported that the prevalence of lumbar DD increased from 16.7% to 83.3% in a two-year follow-up study on weightlifters. In addition, Nagashima et al. [18] reported risk factors for lumbar DD and disc herniation in high school American football players. Thus, it is considered that stressors such as pressure on the spinal column and lifting of heavy weights are related to lumbar DD, whereas there are no such stressors in pole vaulting.

All vaulters in this study had a history of LBP, and 12 vaulters (57.1%) had chronic LBP. In addition, two vaulters with LS (25.0%) and two vaulters with DD (33.3%) had current LBP. Wilson et al. [19] reviewed studies of LBP prevalence and reported that no consistent associations were found between imaging findings and LBP in athletes. Athletes with degenerative changes do not always experience concurrent LBP; when assessing LBP, it is necessary to evaluate both clinical and imaging findings to determine the cause. Pole vaulters are prone to LBP and may require preventive interventions.

4.1 Limitations

This study has several limitations. The sample size was limited, and only male pole vaulters were studied. Therefore, the prevalence of degenerative changes is unknown in female pole vaulters and may higher than real prevalence. In particular, there were only six patients with LS in the present study; therefore, the statistical analysis may have been underpowered. This evaluation was performed independently of whether the athlete had LBP. Therefore, computed tomography scans were not performed because of the high radiation exposure. This ethical consideration may have resulted in an underestimation of LS.

5. Conclusion

In conclusion, this cross-sectional study on 21 pole vaulters revealed spondylolysis in six vaulters (28.6%) and DD in eight vaulters (38.1%) via analysis of X-ray and MRI examinations. There may be a higher prevalence of LS in male pole vaulters when compared to previous studies that investigated the LS and DD in each sport. Therefore, it is possible that the sport-specific movements of pole vaulting are risk factors for LS but not for DD. Because there was no association with current LBP, it is possible that the LS occurred in the past, before the athletes became college students. Adequate range of motion of the joints adjacent to the lumbar spine (e.g., hip, shoulder, and thoracic vertebra) should be obtained to avoid causing compensatory movements of the lumbar spine, especially in adolescent athletes. Future studies with continuous observations from the start of an athlete’s pole vaulting career are required.

Footnotes

Conflict of interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

Funding

This study was funded by a grant from the Chukyo University Research Institute in 2018 and 2019.

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