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INCREASED PREVALENCE OF FEMOROACETABULAR IMPINGEMENT ANATOMY AMONG ATHLETES WHO TREAD WATER 
Joanna Lind Langner1, Marianne Black1, James MacKay2, Kimberly Hall3, Marc Safran3, Feliks Kogan1, and Garry Gold1
1Radiology, Stanford University, Stanford, CA, United States, 2Cambridge University, Cambridge, United Kingdom, 3Stanford University, Stanford, CA, United States

Synopsis

Femoroacetabular impingement (FAI) is a disorder that causes hip pain and disability in young patients, particularly athletes. Treading water leads to increased stress on the hip, the effects of which are poorly understood. In this study, we used MRI to identify the prevalence of FAI anatomy in elite aquatic athletes that tread water. The prevalence of cam FAI was higher than that previously reported for any other sport. This study demonstrates that synchronized swimmers and water polo athletes are at increased risk of cam FAI, more than other sports.

INTRODUCTION

Femoroacetabular impingement (FAI) is a disorder that causes hip pain and disability in young patients, particularly athletes, and may lead to eventual hip osteoarthritis [1][2]. Increased stress on the hip due to continued rotational motion, like the egg-beater kick done while treading water, could put an individual at risk of FAI anatomy. Water polo and synchronized swimming require extensive egg-beater kicking to effectively participate in these activities (Figure 1A-1D). The goal of this study was to use MR imaging to identify whether athletes who tread water have an increased prevalence of FAI anatomy.

METHODS

20 NCAA Division 1 varsity water polo players and synchronized swimmers (15 female, 5 male), ages 18-23 (mean 20.7 ± 1.4), underwent non-contrast MRI scans of both hips using a whole-body 3T MRI scanner (GE Healthcare) with a large, 16 channel flexible phased-array-receive-only coil (Table 1). The presence of abnormal cam/pincer anatomy and labral tears were identified. An oblique T1 FSE sequence was used to evaluate the alpha angle for cam identification. A coronal 3D ZTE image was fused with a water-only coronal PD IDEAL FSE image to evaluate the lateral center edge angle (CEA) for pincer identification. Alpha angles greater than 55° and CEA greater than 39° were considered abnormal [3][4][5]. RadiAnt DICOM viewer software was used for all angles (Figure 2). Labral tears were identified by an experienced musculoskeletal radiologist. These were scored using the Scoring Hip Osteoarthritis Using MRI (SHOMRI) semiquantitative grading scale [6]. Participants completed the 33-item International Hip Outcome Tool (iHOT-33) which is a patient-reported measure designed to evaluate hip-related quality of life [7]. Correlations were calculated between the angles and the estimated number of lifetime hours participants treaded water. A correlation was also done between iHOT-33 and SHOMRI. A Wilcoxon Rank Sum Test was used to compare the different groups split by sport, gender, and symptoms to look for differences in alpha angles, CEA, and iHOT-33 scores. The prevalence of FAI anatomy in this cohort was compared to published research on asymptomatic, symptomatic, and athletic cohorts.

RESULTS

In our subjects, 70% (14/20) reported having pain in their hips yet only 15% (3/20) sought evaluation or treatment for hip pain. Cam deformity was identified in 97.5% (39/40) of hips while 22.5% (9/40) demonstrated pincer deformity. Additionally, 53% (21/40) of hips had evidence of a labral tear. Every participant had at least 1 hip with FAI anatomy (Table 2). This study found a higher prevalence of cam FAI anatomy in water polo players and synchronized swimmers compared to prior studies of athletes (Table 3). These trends were not seen for CEA or labral tears. No statistically significant differences between sport or gender was found on the basis of angles, iHOT-33, or labral tears. The exception is for iHOT-33 scores where there was a statistically significant difference for male versus female (p=0.043), with males having a mean value of 81.0 (±10.0) and females having a mean value of 90.3 (±16.4). No observed correlations were found between treading water and the measured outcomes. The correlation between iHOT-33 scores and SHOMRI (r=0.008) was not significant (p=0.963).

DISCUSSION

Water polo players and synchronized swimmers have a high prevalence of cam FAI anatomy, indicating that treading water may be a risk factor for cam FAI. Cam FAI is often thought to be the result of abnormal forces on the femoral head physis, and this study would suggest that rotational forces associated with treading water may be the cause, as there is no ground contact in these sports. Pincer FAI and labral pathology were not greater than the prevalence reported for other athletes in other sports. We did not find a correlation with lifetime hours of treading water and measurements of FAI, though more detailed analysis of larger numbers of athletes may still be warranted. As would be expected, athletes who reported hip symptoms had a statistically significantly lower iHOT-33 score than the asymptomatic group. This validates the use of the iHOT-33 as being able to distinguish between symptomatic and asymptomatic hips. However, iHOT-33 scores were not correlated with SHOMRI scores, indicating that structural changes as seen on MRI may not correlate well with patient symptoms, but requires further analysis.

CONCLUSION

This study demonstrates that synchronized swimmers and water polo athletes are at increased risk of cam FAI, more than other sports. Further, this study sheds some more light on the etiology of cam FAI, which contributes to our understanding of the development of FAI and the development of preventative treatments.

Acknowledgements

The authors would like to thank the Stanford Athletics varsity water polo and synchronized swimming teams and coaches for allowing us to use them as subjects. This work was supported by a Major Grant from the Stanford University Vice Provost for Undergraduate Education as part of the Human Biology Honors Program. Research support also came from GE Healthcare, and grants NIH EB002524 and NIH AR06206.

References

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Figures

Figure 1: An NCAA Division 1 varsity women’s water polo player treading water. The four images (1A-1D) represent the different phases of the egg-beater kick and shows the extreme range of motion in the hip joint. Used with permission, KE Hall (unpublished data, 2019).

Figure 2: 2A. Axial oblique T1-weighted image of the central slice from the right hip used to determine the alpha angle. 2B. Coronal image of a fusion of fat and water-only IDEAL-FSE scans from the left hip used to determine the CEA.

Table 1: MRI protocol information with parameters.

Table 2: Percent of participants with FAI anatomy and labral tears, and average alpha angles, CEA’s, iHOT-33 scores, and lifetime hours treading water (TR) found (with standard deviations) for different groups. Women’s water polo (WWP), men’s water polo (MWP), and synchronized swimming (Synchro). * indicates the average angle is abnormal and signifies FAI anatomy.

Table 3: Prevalence of FAI anatomy based on cam and pincer deformity, and labral tears, in all participants compared to estimates from past research on athletes, asymptomatic, symptomatic, and mixed groups.

Proc. Intl. Soc. Mag. Reson. Med. 28 (2020)
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