Abstract
Background:
Femoroacetabular impingement (FAI) morphology may contribute to abnormal loading of the adductor–rectus abdominis (RA) aponeurosis and development of core muscle injury (CMI) in cutting-pivoting athletes. It is unclear whether CMI with combined RA and adductor longus (RA-AL) symptoms has a higher prevalence of FAI morphology than CMI with AL symptoms alone.
Purpose/Hypothesis:
The purpose was to determine (1) whether athletes with CMI with RA-AL or isolated AL symptoms differ in prevalence of FAI syndrome (FAIS) and (2) whether prevalence or severity of FAI morphology differs between these groups. It was hypothesized that athletes with RA-AL symptoms will have a higher prevalence of FAIS and more severe FAI morphology than those with AL symptoms alone.
Study Design:
Case series; Level of evidence, 4.
Methods:
Athletes who underwent surgical treatment of a CMI between 2021 and 2025 at a single center were identified. Patients were categorized as RA-AL or AL based on symptoms and physical examination findings. FAIS status was determined by symptomatic impingement morphology and treated with hip arthroscopy and core muscle surgery. Impingement anatomy was assessed on radiographs via lateral center-edge angle, crossover ratio, ischial spine sign, head-neck offset ratio, anterior center-edge angle, and α angle.
Results:
A total of 65 athletes with CMI were included (median age 21 years; IQR 18-43; 97% male); 42 (65%) had RA-AL and 23 (35%) had AL symptoms. No baseline demographic differences were identified between groups. The prevalence of symptomatic FAIS was 38% (25/65) overall and was lower (29%; 12/42) in the RA-AL group than the AL group (57%; 13/23) (P = .03). Almost all athletes with CMIs (98%; 64/65) demonstrated FAI morphology, irrespective of symptoms; 95% (62/65) had cam-type, 40% (26/65) had pincer-type, and 38% (24/65) had mixed impingement morphology. No differences in radiographic measurements or impingement type were found between groups (P > .05).
Conclusion:
There is a very high prevalence of FAI morphology, particularly femoral cam morphology, in both RA-AL and AL symptomatic athletes with CMI, suggesting a likely role of FAI morphology in CMI development. Symptomatic FAI is more common in athletes with isolated AL symptoms versus RA-AL symptoms. Type and degree of radiographic FAI morphology were not associated with specific CMI symptom patterns.
Core muscle injury (CMI), also commonly referred to as athletic pubalgia or sports hernia, is a significant source of disability in athletes who engage in cutting-pivoting, rapid lateral movement, and sudden acceleration or deceleration, particularly in soccer, hockey, rugby, and American football players.10,27 Trunk hyperextension and/or hip hyperabduction can also lead to increased tension in the pubic region, increasing the likelihood of injury. 27 These injuries typically present as isolated adductor longus (AL) pain or a combination of rectus abdominis and AL (RA-AL) pain, with the latter often indicating a more severe or higher-grade injury. 8 The RA-AL CMI presentation has been associated with prolonged recovery times and a greater likelihood of requiring surgical intervention. 9 Consistent with prior studies evaluating CMI treatment, the present investigation specifically focuses on athletes who underwent surgical intervention following unsuccessful conservative management, representing a more treatment-refractory subset of patients with CMI. Despite advances in diagnosis and treatment, the underlying biomechanical factors contributing to the severity of CMI remain incompletely understood.
Femoroacetabular impingement (FAI) morphology is frequently observed in athletes with CMIs, raising questions about its potential role in injury pathogenesis. 29 FAI is characterized by abnormal contact between the femoral head-neck junction and acetabulum, and it is common in athletes who perform repetitive rotational movements. 7 While some studies suggest that FAI may exacerbate CMIs by altering pelvic biomechanics and increasing stress on the pubic symphysis and surrounding soft tissue, there are no definitive conclusions.7,15 Notably, 86% of athletes with CMI appear to demonstrate radiographic evidence of FAI, 7 yet it remains unclear whether more severe FAI morphology or symptomatic FAI morphology (FAI syndrome [FAIS]) are associated with a higher likelihood of RA involvement.
FAI has been increasingly implicated as a contributing factor in the development of CMI, particularly in athletic populations. In athletes with cam or pincer morphology, restricted hip flexion and internal rotation can lead to compensatory pelvic motion to achieve sport-specific demands such as cutting, pivoting, and kicking.13,22 This altered biomechanics increases shear and torsional stress across the pubic symphysis and the RA–adductor complex, predisposing individuals to pubalgic injuries.13,22 Studies have demonstrated that reduced hip range of motion is associated with later development of groin-related pathology, supporting this biomechanical link. 13 Additionally, altered neuromuscular recruitment patterns and obligatory posterior pelvic tilt in the setting of constrained hip motion may further overload core and pelvic stabilizers.13,22 Conceptual frameworks now recognize CMI as a potential downstream compensatory injury in the setting of underlying FAI morphology, underscoring the importance of evaluating and managing both pathologies concurrently when present.
The purpose of this study was to determine (1) whether athletes with CMI with RA-AL or isolated AL symptoms have differing prevalence of FAIS and (2) whether there is a difference in the prevalence or severity of FAI morphology in athletes with CMI with RA-AL symptoms or isolated AL symptoms. We hypothesize that (1) athletes with RA-AL symptoms will have a higher prevalence of FAIS than athletes with AL symptoms alone and that (2) athletes with CMI with RA-AL symptoms will have a higher prevalence and more severe FAI morphology than patients with AL symptoms alone.
Methods
Patient Selection
This study was approved by the institutional review board of Indiana University. This retrospective study of prospectively collected data included patients who were diagnosed with a CMI and underwent subsequent outpatient surgical treatment by a single surgeon (J.S.E.) between January of 2021 and April of 2025. Inclusion criteria were (1) diagnosis of CMI, (2) regular sports participation, and (3) complete medical records, including available radiographic images. Exclusion criteria were (1) history of any hip surgery prior to diagnosis of CMI and (2) history of pediatric hip condition treated nonoperatively, including but not limited to hip dysplasia or Legg-Calve-Perthes disease. Basic demographic data, primary sport type, and level of sport competition was self-reported preoperatively by each patient on the day of surgery. Primary sports were categorized as either cutting and pivoting or non–cutting and pivoting sports, given that the former group is associated with a higher risk of CMI. 11 Cutting and pivoting sports included American football, soccer, basketball, hockey, and lacrosse. All other patient-reported sports and activities were considered non–cutting and pivoting sports (examples include but are not limited to track/running, walking, weight lifting, and cycling). Primary sport level of participation was broken up into professional, collegiate, competitive (level below collegiate participation including youth club sports and high school sports), and recreational.
Group Classification
Eligible patients were then placed into 1 of 4 groups: (1) CMI with RA-AL symptoms and without FAIS, (2) CMI with isolated AL symptoms and without FAIS, (3) CMI with RA-AL symptoms and FAIS, and (4) CMI with isolated AL symptoms and FAIS. Patients were categorized into CMI group based on physical examination findings and patient-reported pain location. All physical examinations were performed by the primary operating orthopaedic surgeon (J.S.E.) in the study. RA-AL CMI is defined as the presence of pubic or lower abdominal pain exacerbated by cutting, twisting, or heavy lifting activities, and reproducible pain with resisted sit-up testing on physical examination. In contrast, isolated AL CMI is defined as medial proximal thigh or pubic pain without abdominal symptoms during cutting, twisting, or heavy lifting activities and pain that was reproducible on palpation of the proximal adductor and/or resisted hip adduction, but not with resisted sit-up. For the purpose of this study, FAI was defined as femoroacetabular impingement morphology without hip impingement symptoms, while a diagnosis of FAIS was only included if the patient had both bony impingement morphology and clinical symptoms related to the impingement, specifically, anterior hip pain reproduced with flexion, adduction, and internal rotation (FADIR) testing. In cases where symptoms were ambiguous or not clearly reproducible on physical examination, a diagnostic ultrasound guided intra-articular injection of local anesthetic was used to confirm the hip joint as the primary pain generator prior to proceeding with arthroscopic surgery.
All included patients with RA-AL symptoms underwent RA repair with AL lengthening using a previously described surgical technique. 26 Patients with isolated AL symptoms underwent isolated AL lengthening. Patients with concomitant FAIS underwent hip arthroscopy with correction of underlying FAI morphology (femoroplasty and/or acetabuloplasty) either concurrently with the core muscle surgery or in a staged fashion. Labral repair was performed in all cases with a labral tear or if a labral takedown was performed in order to complete an acetabuloplasty.
Radiographic Measures
The radiographic images of all patients were reviewed, and measurements were taken to evaluate for radiographic evidence of FAI. The measurements used in this study were lateral center-edge angle (LCEA), crossing sign ratio, presence of ischial spine sign, head-neck offset, anterior center-edge angle (ACEA), and α angle (Figure 1). All of these measurements are standardized and have existing data to support cutoffs for the diagnosis of FAI (as described below). Measurements for LCEA, head-neck offset, ischial spine sign, crossing sign, and crossing sign ratio were taken on weightbearing anteroposterior (AP) radiographs, ACEA was assessed on weightbearing false profile radiographs, and α angle measurements were assessed on supine radiographs utilizing a Dunn view. After receiving training in each radiographic measurement under the supervision of the primary surgeon, 2 medical students (A.A., A.J.D.) independently performed the measurements while blinded to patient symptom status. Interobserver variances were calculated.
Radiographic measurements of acetabular and femoral bony morphology. (A) Lateral center-edge angle; (B) anterior center-edge angle; (C), crossover sign, crossover ratio, and ischial spine sign (green arrow); (D) femoral head-neck offset; and (E) alpha angle.
The LCEA was measured using the Ogata method, with values >39º indicating overcoverage of the femoral head by the acetabulum.5,24 Similarly, ACEA values >39º were considered indicative of pincer-type acetabular overcoverage.5,14 A positive crossing sign was used to identify acetabular retroversion and while there are few data supporting a cutoff value for crossover ratio compared with other measurements of FAI, current literature suggests that ratio of >20% is a significant indicator of acetabular retroversion. 6 Ischial spine sign was assessed as present or absent. All assessments for crossing and ischial spine sign were limited to radiographs meeting pelvic tilt quality control criteria defined as images where the tip of the coccyx was above and within 2 mm of the center of the pubic symphysis on AP radiographs. 5 A head-neck offset <9 mm was used to define cam-type impingement. 1 Finally, an α angle >50º on Dunn view radiographs was used as the threshold for identifying cam-type impingement morphology.19,28
Statistical Analysis
Statistical analysis was performed with a standard software package (JMP 17.2; SAS Institute). An a priori power analysis was performed for the primary outcomes of interest. A minimum sample size of 45 CMI patients (30 RA-AL group and 15 AL group) were needed to detect a 40% difference in prevalence of FAI morphology and FAIS between groups with 80% power and α of .05. A 40% difference in FAIS prevalence was selected as a clinically meaningful effect size, reflecting a threshold large enough to justify differing symptom-based treatment approaches. This estimate was chosen conservatively given the wide variability in reported FAIS prevalence and the lack of an established minimal clinically important difference. Descriptive statistics were generated for the entire sample and with stratification by study group. Bivariate analyses of categorical data between groups were performed with use of likelihood-ratio chi-square test or Fisher exact test as appropriate in the case of low (<5) cell counts. Bivariate analyses of continuous data between groups was performed by 1-way analysis of variance for all data with normal distributions and by nonparametric Kruskal-Wallis testing for all nonnormally distributed data. Multivariate regression analyses were then performed with exposures and outcomes of interest with correction, as needed, for age, race, insurance, type, surgical side, history of prior surgery for CMI, tobacco use, and body mass index. A forward selection method was utilized with inclusion of any potential confounder, in decreasing order of effect size, with significance <.05 as a predictor of the outcome of interest. Ultimately, no significant confounders were identified utilizing this method, and reported results therefore include bivariate analyses alone.
Results
Demographics
A total of 65 CMI patients were included in the current study, 64 of whom underwent primary treatment of their CMI while 1 underwent revision core muscle surgery after a prior mesh-based laparoscopic repair. A total of 42 patients (65%) had RA-AL symptoms and 23 (35%) had isolated AL symptoms. The cohort was predominantly male (63/65; 97%) with a median age of 21 years old (IQR 18-43) (Table 1). The majority of athletes (60%) participated in cutting and pivoting sports, most commonly at the recreational level (40%). The 3 most frequently reported sports were soccer (28%), football (20%), and track and field (17%). There were no statistically significant differences between groups in baseline demographic characteristics, primary sport classification, or level of sport participation (P > .05 for each comparison).
Study Group Characteristics a
Data are presented as n (%) unless otherwise indicated. AL, adductor longus; BMI, body mass index; CMI, core muscle injury; FAIS, femoroacetabular impingement syndrome; NSAID, nonsteroidal anti-inflammatory drug; RA-AL, rectus abdominis and adductor longus.
Prevalance of FAIS by CMI Symptom Pattern
The prevalence of symptomatic hip impingement was 38% overall (25/65 patients) and differed significantly between CMI subgroups. FAIS was present in 57% (13/23) of patients with isolated AL symptoms and only 29% (12/42) of patients with RA-AL symptoms (P = .03). Multivariate analysis confirmed that no demographic variables were confounding factors for the association between CMI symptom pattern (RA-AL vs AL) and prevalance of FAIS.
Relationship Between Radiographic FAI Measures and CMI Symptom Pattern
Radiographic signs of FAI were highly prevalent across all CMI patient subgroups with 98% (64/65) of patients demonstrating ≥1 radiographic finding diagnostic of hip impingement (Table 2). Interclass correlation coefficient values for all measures ranged from 0.75 to 1.00, indicating good to excellent interobserver reliability. 17 There were no differences in any radiographic parameters tested (LCEA, crossing sign, crossover ratio, ischial spine sign, head-neck offset, ACEA, or α angle) between patients with RA-AL symptoms versus those with isolated AL symptoms (Table 3). Cam-type impingement, as determined by head-neck offset and α angle measurements, was the most common impingement morphology overall, presenting in 62/65 (95%) patients. There was no significant difference in the prevalence of cam, pincer, or mixed-type cam and pincer impingement patterns between groups (Table 2).
Number of Patients With Cam or Pincer Hip Morphology a
Data are presented as n (%). AL, adductor longus; FAIS, femoroacetabular impingement syndrome; RA-AL, rectus abdominis and adductor longus.
Radiographic Measurements a
Data are presented as mean ± SD or n (%) unless otherwise indicated. AL, adductor longus; FAIS, femoroacetabular impingement syndrome; RA-AL, rectus abdominis and adductor longus.
Counts for ischial spine sign only include patients with pelvic radiographs that met quality control measures for pelvic tilt that allow accurate assessment of this measure.
Discussion
CMI and FAI often coexist in athletes, likely due to overlapping anatomical and biomechanical stressors at the hip-pelvic interface. In this cohort, the vast majority of athletes with CMI demonstrated radiographic evidence of FAI morphology, most commonly cam-type features, regardless of their specific CMI symptom pattern. However, less than half of these athletes also met clinical criteria for FAIS (anterior hip pain reproduced with FADIR testing), with a higher likelihood of symptomatic impingement in athletes with isolated adductor symptoms of CMI versus CMI with RA-AL symptoms. Notably, the presence and severity of FAI morphology, regardless of impingement symptoms, did not differ significantly between athletes with CMI with RA-AL symptoms and those with isolated AL symptoms.
Hips with FAI morphology have been shown to have a significant decrease in hip flexion (105° compared with 122°), internal rotation at 90° of hip flexion (11.1° compared with 35.2°), and abduction (51.7° compared with 63.3°) compared with controls. 18 When the hip is internally rotated, as seen in cutting-pivoting sports, the cam lesion contacts the rim of the acetabulum earlier in the arc of motion, restricting further rotation.18,25 This loss of internal rotation in the presence of cam-type morphology results in a compensatory increase in motion at the pubic symphysis2,12 and has been linked to an increased incidence of groin injury and osteitis pubis. 29 A cadaveric study conducted by Birmingham et al 4 found that presence of a cam lesion resulted in up to 35% more rotation of the pubic symphysis with internal rotation of the hip compared with a native noncam hip at every level of torque. Increased motion at the pubic symphysis leads to secondary increased strain of the muscles that originate adjacent to the pubic symphysis, including the AL and RA muscles. 13 Over time, this increased strain can lead to weakness and increased propensity for CMI. 18 Taken together, these findings may help explain the high prevalence of FAI morphology observed across both isolated AL and RA-AL CMI symptom groups, regardless of the presence of symptomatic FIAS.
Notably, FAIS was more frequently diagnosed in patients with isolated AL symptoms compared with those with combined RA-AL symptoms. Clinically, this represents an absolute difference of 28% in FAIS prevalence between groups (57% in isolated AL vs 29% in RA-AL), suggesting that symptom pattern alone may meaningfully influence the likelihood of concurrent hip-directed evaluation and treatment. These findings were contrary to our initial hypotheses, indicating that greater core muscle symptom complexity does not necessarily correspond to a higher prevalence of symptomatic FAIS or more severe hip joint pathology. One potential explanation for these findings is that CMI and FAIS represent related but distinct clinical phenotypes arising from similar abnormal loading patterns at the hip-pelvis interface. In one phenotype, abnormal hip joint mechanics may predominate, resulting in earlier presentation with hip-dominant symptoms and clinically apparent FAIS, while limiting the degree of RA involvement. In another phenotype, abnormal loading may be preferentially transferred to the core musculature, resulting in RA-AL predominant symptoms despite similar underlying impingement morphology. Individual patient factors, such as relative core strength or neuromuscular control, may influence which phenotype manifests clinically. Athletes with weaker core stabilizers may be more susceptible to RA-AL involvement under similar biomechanical demands, whereas those with relatively preserved core strength may present earlier with hip-dominant symptoms and isolated AL pathology.
In the presence of FAIS and CMI, treatment of only 1 of the symptomatic pathologies can lead to a suboptimal result. 27 Addressing the CMI alone demonstrated a 25% return to the previous level of sport, whereas arthroscopic treatment of FAIS alone resulted in a 50% return to the previous level based on 1 study. 20 However, when both conditions were surgically managed simultaneously or in a staged manner, 89% of patients were able to return to sports without limitations. 20 Similar results were noted in a series of professional athletes, except that no athlete was able to return following core muscle repair alone. 12 In the aforementioned study, Hammoud et al, 12 investigated the incidence of CMIs in professional athletes with FAIS and found that 11 athletes (29%) presenting with FAIS had previously undergone core muscle repair alone, though it was not reported whether or not these patients had radiographic FAI morphology at the time of their initial core muscle repair. An additional 12 (32%) athletes with a combined diagnosis of CMI and FAIS first underwent surgery for core muscle repair alone followed by a trial period of return to play. None of the athletes were able to return to previous level of competition after core muscle repair alone; however, following staged hip arthroscopy to address FAIS, all 12 patients returned to previous level of play in a mean time of 5.9 months. 12 In our practice, only patients with symptomatic FAIS are considered for femoroacetabular osteoplasty to address the FAI morphology, but these results beg the question as to whether FAI morphology should be addressed regardless of symptomatology in the treatment of CMIs. These findings underscore the need for future research comparing outcomes of CMI repair with and without concurrent femoroacetabular osteoplasty to determine if clinically meaningful long-term differences exist between treatment approaches.
In our study, we found no significant difference in age, sex, or mean α angle between our various groups. Importantly, differences between our reported prevalence of FAI morphology and those in prior studies should be interpreted primarily in the context of population selection rather than as true differences in disease characteristics, as many prior studies focused on elite athletic cohorts, whereas the present study reflects an all-comers surgical CMI population. In order to determine whether our population was representative of patients with CMI, we turned to the literature. We looked at all comers with CMI regardless of level of activity. In comparing the prevalence of FAI morphology in our patient population with that of athletes, a systematic review of approximately 60 studies that reported on 1389 hips in 958 athletes noted radiographic evidence of cam impingement in 66.4% of athletes and pincer impingement in 51.2% of athletes. 21 This is compared with our CMI patients, in which we found cam impingement in 95% and pincer impingement in 40%. In keeping with our higher prevalence of cam impingement morphology, our population overall had a mean α angle of 63.1° as compared with 55.7° in the athlete population. 21 In a study out of Drexel by Meyers et al 23 looking at 3 different academic institutions as well as in locker rooms and training facilities of various sports teams from 1986 to 2008, the authors reported a temporal shift in their patient population, with the proportion of elite athletes among those presenting with CMI decreasing from 100% of CMI diagnoses in the mid-80s, compared with 91.1% in the mid-90s and 76.9% in the early 2000s. This shift suggests that, over time, a broader spectrum of individuals beyond elite athletes began to be recognized with CMI, supporting the representativeness of our all-comers surgical cohort. This broader recognition may also help explain the differences in cam and pincer impingement prevalence compared with studies focused solely on elite athlete populations.
Additionally, Meyers et al 23 reported a rising prevalence of female patients presenting with CMI, increasing from 0% in the mid-1980s to 8% in the mid-1990s and early 2000s. 23 Consistent with this trend and the previously reported male predominance, our study included 2/65 (3%) women. The observed male predominance in CMI likely reflects a multifactorial interplay of factors, including higher male rates of hip/groin injury in cutting sports, sex-specific differences in pelvic anatomy and load distribution, and hormonal influences on tissue stiffness and injury patterns.3,16,30 While these mechanisms are biologically plausible, direct evidence for a protective role of female anatomy or hormones in CMI specifically remains limited. Finally, the mean age of patients in the Meyers cohort increased over time from 24.7 years in the mid-80s, to 26.3 years in the mid-90s, to 28.6 years in the early 2000s. 23 The mean age of patients in our study was 30, consistent with this trend and other published data. 12 These data suggest that our patient population is consistent with previous reports and is likely representative of all patients with CMI.
Limitations
This study had several limitations. Patients were included regardless of level of athletic participation, which makes the findings of this study more broadly applicable, but they may not be as specific to high-level athletes. Similarly, only patients who underwent surgical repair of CMI were included, limiting generalizability for conservatively treated patients with CMIs. Not all patients had radiographs that passed quality control measures for pelvic tilt to evaluate for crossover and ischial spine sign. Additionally, hip impingement is a dynamic process involving multiple structures and it is possible that a small percentage of patients lacking impingement anatomy at the acetabulum or proximal femur may have actually had dynamic impingement due to factors such as femoral torsion that were not assessed in the current study. Further, although individual measures of impingement morphology were not associated with CMI injury patterns in the current study, it is unknown whether there is also no association between CMI injury pattern and degree of in vivo impingement during sport-specific movements. Additionally, the physical examination findings used to classify CMI and FAIS subtypes are subject to interexaminer variability and subjectivity, which may introduce observer bias.
Conclusion
There is a very high prevalence of FAI morphology, particularly femoral cam morphology, in both RA-AL and AL symptomatic athletes with CMI, suggesting a likely role of FAI morphology in the development of CMI. Symptomatic FAI is more common in athletes with CMI with isolated AL symptoms versus RA-AL symptoms. Type and degree of radiographic FAI morphology were not associated with a specific CMI symptom pattern.
Footnotes
Final revision submitted January 14, 2026; accepted January 21, 2026.
The authors declared that there are no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
Ethical approval for this study was obtained from Indiana University (protocol No. 22175).
