Cam morphology in Japanese adolescent male football player: a prospective study with 3-year follow-up

Abstract

Background

Cam morphology developed during adolescent increases the risk of hip osteoarthritis by 4.3-6.2-fold over 5 and 10 years. Although cam morphology are believed to occur during the growth period, when significant physical changes take place, no studies have examined the relationship with physical maturation indicators.

Aim

The aim of this study was twofold: (1) to examine the prevalence of cam morphology in Japanese adolescent football players.; (2) to investigate if cam morphology development is associated with peak height velocity age(PHVA) status.

Methods

Fifty-seven adolescent male football players (114 hips) were prospectively 1enrolled. Hip morphology was assessed using dual-energy X-ray absorptiometry at baseline and at 1- and 2-year follow-up. Participants with missing data, longitudinal height records required for estimating peak height velocity age (PHVA), were excluded. Consequently, 47 participants (94 hips) were included in the final analysis. Cam morphology on these time points was defined as: (A) visual scores of the anterior head-neck junction, classified as: (1) normal, (2) flattening, and (3) prominence. We calculated the years from age at PHV of each participant by subtracting the chronological age from the age at PHV to determine the period until the peak of growth.

Results

Cam morphology based on visual scores was found in 79 of 94 hips(84.0%, 39 kicking leg, 40 shaft leg)at in 2-year follow-up. non-association between cam morphology development based on visual scores and PHVA status (OR = 1.08, 95% CI 0.81–1.52, p = 0.517).

Conclusion

Although previous studies have suggested a lower prevalence of cam morphology in East Asian football players than in Western populations, we observed a relatively high hip-level prevalence of DXA-defined cam morphology, increasing from 53.2% (50/94 hips) at baseline to 84.0% (79/94 hips) at the 2-year follow-up, in this cohort of 47 Japanese adolescent football players. In addition, cam morphology developed both before and after peak height velocity age (PHVA), indicating that its development is not confined to a specific stage of biological maturation.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s13102-026-01862-y.

Introduction

Cam morphology prevalence is known to be increased by participation in high-impact sports such as soccer [1]. The development of cam morphology is considered to be influenced by multiple factors. Among these factors, sport-specific mechanical loading during skeletal growth is considered to play a central role, together with biological predisposition and cultural or lifestyle factors[2]. The interaction among these factors is thought to contribute to the development of cam morphology. Longitudinal studies have shown that cam morphology developed during adolescent increases the risk of hip osteoarthritis by 4.3-6.2-fold over 5 and 10 years [3, 4]. It is also reported to increase the risk of groin pain by a factor of 5-fold [5]. Therefore, identifying the timing of cam morphology development is important because it may facilitate the implementation of targeted preventive strategies during skeletal maturation.

The study of cam morphology prevalence by ethnic among male professional soccer players found that East Asians had significantly lower prevalence rates, with 66.6% of whites, 63.6% of blacks, and 49.2% of East Asians, and East Asians had a 0% prevalence of the prominent cam morphology [6]. However, the East Asian subgroup in that study was relatively small, and football exposure during skeletal growth was not consistent among participants. Therefore, it was difficult to determine whether the observed differences reflected ethnicity or sport-specific mechanical loading. Consequently, the prevalence and developmental characteristics of cam morphology in Japanese adolescent football players remain unclear. A previous study demonstrated that acetabular coverage was significantly smaller in Japanese individuals than in British individuals. [7]. Another study reported acetabular coverage in Koreans, suggesting that Japanese hip morphology is distinct even among closely related ethnic groups. [8]. Furthermore, acetabular dysplasia has been reported to be a risk factor for premature closure of the femoral head growth plate during growth [9], and the timing of cam morphology in Japanese patients may differ from previous reports. Therefore, given the distinct hip and pelvic morphology of Japanese individuals, determining the prevalence of cam morphology in this population is warranted. The primary aim of this study was to assess the prevalence of cam morphology in Japanese soccer players, in line with previous research. However, to appropriately interpret such longitudinal changes, it is essential to consider the timing of cam morphology development in relation to skeletal growth and maturation.

In growing footballers, cam morphology first becomes visible at approximately 10–12 years of age and gradually increases during skeletal maturation [10]. However, chronological age alone does not adequately reflect individual and ethnical differences in biological maturation because substantial variation exists in growth velocity, skeletal maturation, and the timing of physeal closure during adolescence [11, 12]. Peak height velocity age (PHVA), defined as the age at which the maximum rate of statural growth occurs, is a well-established indicator of biological maturity. Unlike chronological age, PHVA reflects each individual’s developmental tempo and has been widely used to investigate growth-related musculoskeletal disorders and to guide injury prevention strategies in youth athletes [11–13]. Therefore, PHVA may provide a more biologically meaningful framework for investigating the timing of cam morphology development.

Despite these findings, no longitudinal study has investigated whether cam morphology development is associated with biological maturation assessed using PHVA. Furthermore, although previous longitudinal studies have described the development of cam morphology in adolescent football players, they were conducted predominantly in Western populations. Japanese individuals have distinct hip morphology, including relatively reduced acetabular coverage compared with Western populations [7, 8], and it remains unclear whether the developmental pattern of cam morphology is similar in this population.

The aim of this prospective study was to characterize cam morphology in Japanese adolescent football players by determining its prevalence, identifying the timing of its development, and investigating its association with biological maturation assessed using PHVA.

Methods

Participants

Participants were recruited through a sports medical check-up conducted for a community football club in Tokyo. All participants had competed at the regional level and had participated in organized football for at least two years before enrollment. The team trained five or six times per week and played approximately 30 official matches and 45 unofficial matches per year. A total of three hip morphometry measurements were assessed at baseline (April 2022), 1-year follow-up (April 2023), and 2-year follow-up (March 2024), with 57 participants (114 hips). 10 participants were excluded from the final analysis because their height history data, required for the calculation of peak height velocity age (PHVA), were incomplete. Demographic data is presented in Table 1. The age at baseline of the analyzed footballers was between 11 and 14 years. In accordance with the regulations of the Ethics Committee, written informed consent was obtained from the parents or legal guardians of all participants, as all participants were younger than 18 years of age. The study was approved by the ethics committee of Waseda University (2021 − 218).

Table 1.

Demographic date of baseline, 1-year follow-up and 2-year follow-up

	Baseline		1-year		2-year
Age, y	12.9±	0.8	13.3±	0.6	14.3±	0.6
Month age, m	159.9±	8.3	165.7±	8.0	177.1±	7.4
Height, cm	160.6±	8.8	163.4±	7.8	167.0±	6.9
Weight, kg	51.9±	10.2	54.5±	11.6	58.6±	10.7
Years from PHVA	0.0±	1.2	0.5±	1.1	1.5±	1.1

Data are presented as mean ± SD

Imaging the hip

Frontal view of bilateral hip joints was acquired using dual X-ray absorptiometry (DXA) scanning (Hologic; Horizon-QDR). Participants were examined in the supine position with the pelvis aligned parallel to the scanning table, and both feet were secured in the manufacturer’s positioning device to maintain approximately 15° of internal hip rotation. Cam morphology has traditionally been evaluated using conventional radiographs and CT or MRI [10–14]. However, previous studies have demonstrated that DXA provides a valid method for assessing hip morphology, showing good agreement with radiographic assessment while substantially reducing radiation exposure [15]. Furthermore, recent studies, including our recent Online First study, have successfully used DXA to evaluate hip morphology across different age groups and sporting populations [16–18]. One of the main advantages of hip DXA images is the lower radiation burden of 0.36–70 µSv compared to hip or pelvic radiographs with an effective dose of 600–700 µSv [15]. In addition, comparison of DXA and MRI images obtained from the same participant in our cohort demonstrated comparable coronal femoral head–neck morphology (Supplementary Figure S1), further supporting the utility of DXA-based visual assessment. Nevertheless, because DXA provides only a two-dimensional anteroposterior projection, anterior or posterior femoral head–neck prominences may not be fully visualized. Therefore, DXA-based assessment may underestimate the true prevalence of cam morphology.

Quantification of morphology

The α-angle is often used to quantify cam morphology but is difficult to assess during skeletal maturation because the femoral head is often non-spherical rather than circular. Accordingly, we followed the methods of Agricola et al. (2014) and van Klij et al. (2019), who used a three-grade visual scoring system to assess cam morphology in adolescent football players [14, 19]. Cam morphology was therefore assessed using the visual scores and definitions described in these previous studies. Although quantitative measurements such as the α-angle facilitate comparison across studies, the visual scoring system is considered more appropriate for evaluating morphological changes during skeletal maturation.

Visual scores and definition of cam morphology

• 0.Normal: slight symmetric concavities of the anterior head-neck junction with respect to the posterior head-neck junction.
• 1.Flattening: moderate decrease in the anterior head-neck offset with respect to the posterior head-neck junction.
• 2.Prominence: convexity in the anterior head-neck junction, as opposed to concavity.

Cam morphology was independently assessed by two experienced raters: an experienced orthopaedic surgeon and a researcher specializing in hip morphology using the previously described three-grade visual scoring system. All DXA images were anonymized, and the raters were blinded to participant information, assessment time point, and laterality. Interobserver agreement was evaluated using an unweighted Cohen’s kappa coefficient and was excellent (κ = 0.88, 95% CI 0.81–0.94). In cases of disagreement, the assessment of the experienced orthopaedic surgeon was adopted as the final classification. Cam morphology development was defined as an increase in visual score and was assessed by pairwise comparisons between baseline and the 1-year follow-up and between baseline and the 2-year follow-up (Fig. 3). Transitions in visual scores between consecutive assessment time points (baseline to 1-year and 1-year to 2-year follow-up) were summarized in supplementary transition tables. An increase in visual score was considered to represent cam morphology development.

Fig. 3.

Cam morphological development based on visual scores. Case 1; Cases that developed into Cam morphology before PHVA by DXA image. Case 2; Case that developed into Cam morphology before and after PHVA by DXA image. Case 3; case that developed into Cam morphology after PHVA by DXA image. Case 4; Cases that developed prominently after PHVA by DXA image

PHVA

Historical height records obtained from elementary school health examinations were collected for each participant. Height had been measured annually using a standard stadiometer according to the school health examination protocol. PHVA was estimated using the AUXAL 3.1 program (Scientific Software International Inc., Skokie, IL, USA) based on longitudinal height records from 6 years of age until the height measurements obtained in the present study. Participants with incomplete height history required for PHVA estimation were excluded from the analyses. The years from PHVA (PHVA offset) were calculated by subtracting the age at PHVA from the chronological age at each assessment, with negative values indicating measurements obtained before PHVA and positive values indicating measurements obtained after PHVA [19].

Statistics

Participant baseline to 1 and 2-year characteristics is presented as mean ± standard deviation. Cam morphological prevalence was described separately for the kicking leg and the shaft leg in football. Development of cam morphology is analyzed blinded on hips of participants who attended at least two time points. Cam morphology development was analysed visual score in 294 hip images, which included repeated measurements. Generalized estimating equations (GEE) with a binomial distribution and logit link function were used to evaluate the association between PHVA and cam morphology development while accounting for repeated observations. The dependent variable was cam morphology development (yes/no), defined as an increase in visual score between consecutive assessments. PHVA was entered as a continuous variable. Analyses were performed at the hip level, with participant ID specified as the clustering variable and assessment interval (baseline to 1-year and 1-year to 2-year follow-up) specified as the repeated factor using an exchangeable working correlation structure. Robust (sandwich) standard errors were used to estimate regression coefficients. The statistical evaluation was performed using SPSS V.27.0 (Windows).

Results

Cam morphology prevalence

Prevalence by visual score during follow-up is shown in Fig. 1. At the hip level, cam morphology was identified in 50 of 94 hips (53.2%, 95% CI 43.2–63.0) at baseline, 78 of 94 hips (83.0%, 95% CI 74.1–89.2) at the 1-year follow-up, and 79 of 94 hips (84.0%, 95% CI 75.3–90.1) at the 2-year follow-up. At the participant level, cam morphology was present in 33 of 47 participants (70.2%) at baseline, 43 of 47 (91.5%) at the 1-year follow-up, and 44 of 47 (93.6%) at the 2-year follow-up. Bilateral cam morphology was observed in 17, 34, and 35 participants at baseline, the 1-year follow-up, and the 2-year follow-up, respectively.

Fig. 1.

Prevalence of cam morphological development based on visual scores. In both A and B there is a decreasing trend in Normal and an increasing trend in Prominace as the follow-up progresses

PHVA status

The proportion of participants who had not yet reached their estimated PHVA was 57.4% (27/47) at baseline, 31.9% (15/47) at the 1-year follow-up, and 6.4% (3/47) at the 2-year follow-up.

Association between cam morphology development and PHVA

A total of 94 unique hips were followed longitudinally, generating two consecutive observation intervals (baseline to 1-year follow-up and 1-year to 2-year follow-up). Overall, 54 of the 94 hips (57.4%) demonstrated progression in visual score during the follow-up period. Transitions in visual scores between consecutive assessments are summarized in Supplementary Table S1. Changes in Visual score against month of age and PHVA are shown in Fig. 2. Cam morphology development based on visual scores was observed in 37 of 94(39.4%, 22 kicking leg, 15 shaft leg)hips at baseline to 1-year and 53 of 94༈56.4%, 31 kicking leg, 22 shaft leg༉hips at 1-year to 2-year. Of these 90 hips, 35 had development from normal to flattening and from flattening to prominence during follow-up. Of these 90 hips, 18 had not exceeded and 72 had exceeded PHVA. There was no significant association between PHVA status and cam morphology development based on visual scores (OR = 1.08, 95% CI 0.81–1.52, p = 0.517), as portrayed in Fig. 3.

Fig. 2.

Cam morphology development at age and PHVA. In A and B an increase in visual scores is observed between the ages of 12 and 15 years. In C and D, an increase in visual scores was observed before and after PHVA, but the distribution was more variable after PHVA

Disscussion

Owing to the prospective design, we were able to longitudinally investigate the development of cam morphology throughout adolescence with sufficient follow-up.

This prospective study demonstrated a relatively high prevalence of DXA-defined cam morphology in a cohort of Japanese adolescent male football players. Together with our recent findings demonstrating a high prevalence of cam morphology in Japanese male collegiate long-distance runners and a non-athletic population, the present findings suggest that cam morphology may be more prevalent in Japanese males than previously recognized[17]. In addition, this study extends previous cross-sectional findings by characterizing the longitudinal development of cam morphology during adolescence. Because the present study employed a DXA-based visual scoring system, the reported prevalence should be interpreted with caution when compared with studies using radiographic α-angle definitions or different imaging modalities. Nevertheless, the use of the same visual scoring system as previous longitudinal studies enables comparison of developmental patterns during skeletal maturation. Furthermore, using peak height velocity age (PHVA), no apparent association with skeletal development was observed. We also believe that the use of DXA in the follow-up of cam morphology can be much less invasive for the participants than exposure to CT or X-rays [10–14].

Prevalence cam morphology of Japanese(East Asian)football player

This is the first study to report the prevalence of cam morphology in growing Japanese football players, suggesting a higher-than-expected prevalence in an East Asian population [6]. Although previous studies have primarily assessed cam morphology using the α-angle [6], visual scoring has also been widely adopted in longitudinal studies of adolescent athletes [10, 14]. Therefore, the use of the same visual scoring system as previous longitudinal studies facilitates comparison of developmental patterns during skeletal maturation, although comparisons of absolute prevalence should be interpreted with caution because of differences in imaging modalities and diagnostic criteria. It was also found that the prevalence of cam morphology in growing elite male footballers reported to date is generally comparable to that observed in the present study. Cam morphology development factors include internal factors such as hip morphology, and environmental factors such as participation in high-intensity sporting activity. Football, in which the subjects in this study participate, is known to be the activity with the highest prevalence of cam morphology [1], and may be one factor contributing to the higher prevalence. However, previous studies have demonstrated that the prevalence of cam morphology in adolescent soccer players is similar to that in adolescent runners [17]. In general, the prevalence of cam morphology in runners outside Japan is lower than that in soccer players, and is reported to be 10–19%, comparable to that observed in non-athletic populations [1]. Taken together, these findings suggest that, in Japan, the development of cam morphology may be influenced not only by environmental factors discussed in previous studies but also substantially by intrinsic factors.

The Japanese population contributing to cam morphology development

The development of cam morphology is thought to be caused by mechanical loading during physical activity in the growth period, when the growth plate is present, leading to alterations in the orientation of the growth plate [14, 20]. Although it is considered important to implement sports activities with consideration of skeletal development during growth, previous studies have suggested that a reduced acetabular width, analogous to acetabular dysplasia, may also be a significant factor increasing mechanical loading at the femoral head–neck junction [21]. A study comparing children with acetabular dysplasia and those with normal hips demonstrated that intra-articular pressure was approximately twofold higher in the dysplasia group than in the normal group [22]. The prevalence of acetabular dysplasia is higher in Japan than in other countries, and it is well known that the Japanese population is characterized by a relatively reduced acetabular width [7, 8]. Therefore, the high prevalence of cam morphology in Japan, compared with other East Asian populations, may be attributable to differences in acetabular morphology related to ethnic variation. These findings indicate that longitudinal studies in non-athletic populations in Japan are also needed. Although the present findings suggest that factors other than football-specific mechanical loading may contribute to the high prevalence of cam morphology in Japanese males, the present study did not directly assess intrinsic factors or quantify environmental exposures. Therefore, the relative contributions of these factors remain speculative and should be investigated in future studies.

No association between PHVA and cam morphology development

PHVA is defined as the age at which the rate of height growth reaches its maximum during adolescence and is widely used as an indicator of biological maturation. In the present study, no association was observed between PHVA and cam morphology development, suggesting that biological maturation assessed by PHVA alone may not explain the timing of cam morphology development. Cam morphology was already observed in participants as young as 11 years of age. Previous studies have suggested that cam morphology predominantly develops before proximal femoral physeal closure, although a small number of cases have also been reported after physeal closure [9]. Because proximal femoral physeal status was not directly assessed in the present study, our findings cannot be directly compared with those studies. Future longitudinal studies incorporating direct assessment of proximal femoral physeal status, rather than relying solely on PHVA, may provide a more accurate understanding of the relationship between skeletal maturation and cam morphology development.

Timing of cam morphology development in the Japanese population

Comparison of the timing of cam morphology development in the present study with reports from Western populations revealed that the period of increasing prevalence was largely consistent [10]. Comparisons between studies reporting growth patterns in Western populations and those examining skeletal development in Japan indicate that the timing of peak increases in bone and muscle mass, both at the whole-body level and in the upper and lower limbs, shows similar trends [23, 24]. Although direct ethnic differences cannot be determined due to comparisons across separate studies, the absence of substantial differences in growth patterns suggests that the timing of increases in cam morphology prevalence may also be similar. In summary, these findings suggest that differences in growth and development are less likely to account for the higher prevalence of cam morphology in Japan than differences in bone morphology related to ethnic variation [25].

Limitation

Several limitations of this study should be acknowledged. First, the primary analysis did not include a control group other than soccer players. Therefore, direct and definitive comparisons of hip morphology with the general population are limited. This limitation may affect the interpretation of the high prevalence observed in this study, as well as hypotheses regarding potential population-specific factors. Future studies including appropriate control groups are needed to validate these findings and clarify the underlying mechanisms. Second, DXA provides a two-dimensional anteroposterior projection and therefore may not fully visualize anterior or posterior femoral head–neck prominences. Consequently, some cases of cam morphology may remain undetected, potentially leading to an underestimation of its true prevalence. However, previous studies have demonstrated the validity of DXA for assessing hip morphology, and our recent study further supports its applicability for evaluating hip morphology in athletes. In addition, comparison of DXA and MRI images obtained from the same participant showed comparable coronal femoral head–neck morphology (Supplementary Figure S1). Nevertheless, MRI and CT remain the reference standards for comprehensive three-dimensional evaluation of hip morphology. Third, although the interobserver reliability of the visual scoring system was high (κ = 0.88), visual assessment is inherently subjective and may have resulted in misclassification, particularly in borderline cases. Furthermore, because cam morphology was evaluated using a qualitative visual scoring system rather than quantitative measurements such as the α-angle, direct comparison of prevalence with studies using different diagnostic criteria should be interpreted with caution. Nevertheless, the visual scoring system adopted in the present study has been widely used in previous longitudinal studies of adolescent football players, allowing comparison with these landmark investigations. Finally, several potential confounding factors, including years of football participation, cumulative training load, playing position, and family history, were not collected and therefore could not be included in the present analyses. These factors may influence the development of cam morphology and should be considered in future longitudinal studies to better clarify its determinants.

Conclusion

Although previous studies have suggested a lower prevalence of cam morphology in East Asian football players than in Western populations, we observed a relatively high hip-level prevalence of DXA-defined cam morphology, increasing from 53.2% (50/94 hips) at baseline to 84.0% (79/94 hips) at the 2-year follow-up, in this cohort of 47 Japanese adolescent football players. In addition, cam morphology developed both before and after peak height velocity age (PHVA), indicating that its development is not confined to a specific stage of biological maturation.

Authors' contributions

Ryota Yamamoto, Wataru Sakamaki, Toshiharu Tsutsui, and Suguru Torii contributed to data collection, analysis, and interpretation. Ryota Yamamoto, Toshiharu Tsutsui, and Suguru Torii contributed to the writing of the manuscript. Ryota Yamamoto, Toshiharu Tsutsui, and Suguru Torii contributed to the critical revision of the manuscript. All authors read and approved the manuscript and consented to the submission of the final version.

Funding

This work was supported by JST SPRING, Grant Number JPMJSP2128.

Data availability

All data supporting the findings of this study are available within the paper.

Declarations

Ethics approval and consent to participate

The study was approved by the ethics committee of Waseda University (2021 − 218). All participants or their legal guardians provided online informed consent prior to completing the questionnaire. The collected data were anonymized to ensure confidentiality.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.