Concomitant sacroiliac joint abnormalities in patients with femoroacetabular impingement

Despite the exponential rise in hip arthroscopy in patients with femoroacetabular impingement syndrome (FAI), the role of specific patient characteristics on the pathophysiology of FAI remains unclear [1, 2]. FAI is characterised by the presence of hip pain, restricted range of motion of the hip and abnormal morphology on imaging of the hip joint [3, 4]. Consequently, it has now been recognised as a significant risk factor for the onset of progressive degenerative changes and the development of early osteoarthritis (OA) in the non-dysplastic hip [3, 5, 6]. While hip arthroscopy is the established treatment of choice, not all patients with FAI benefit equally from this procedure [7]. For some patients, hip arthroscopy may not only fail to alleviate symptoms but could potentially lead to complications [8, 9] or unnecessary surgical intervention. This lack of universal success highlights a critical gap in our understanding of FAI and its management. Importantly, the focus on FAI morphology may sometimes overshadow other underlying conditions that could be the true source of a patient’s hip pain. Therefore, it is crucial to investigate factors contributing to the variability in treatment outcomes [10]. Recent findings suggest that the aetiology of hip pain in FAI may be more complex than previously thought, potentially involving systemic factors beyond local joint mechanics, with emerging research exploring connections to conditions such as axial spondyloarthritis (axSpA) [11‐13].

AxSpA is a chronic and progressive inflammatory condition which generally affects young individuals, typically starting in late adolescence. A diagnosis of axSpA is commonly considered in the presence of chronic back pain [14] and is associated with progressively worsening stiffness, pain, and impaired physical function [15]. A hallmark feature of axSpA is inflammation of the sacroiliac (SI) joints, which can lead to significant pain and structural changes in these joints over time. It is important to note that in axSpA, large joints including the hip can be affected by the inflammatory process itself, with or without FAI morphology. The prevalence of hip involvement in axSpA has been reported to range from 24 to 36% across various studies, emphasising the importance of distinguishing between inflammatory hip disease and mechanical impingement in these patients. As with axSpA FAI most commonly affects young adults, though through different mechanisms. Patients with FAI typically present with painful clicking, locking or instability but may also present with symptoms that overlap with other musculoskeletal conditions of the hip, pelvis, and lumbar spine [16]. Anterior groin pain is a predominant feature of FAI and often affiliated with intra-articular pathology and labral tears, however, posterior hip pain in these patients is associated with SI joint abnormalities [17, 18]. There are several patients presenting with clinical features of FAI and concomitant low back pain [19, 20] which may well be secondary to axSpA. It is therefore crucial to investigate factors responsible for outcomes not being universally good and to consider a broader differential diagnosis before proceeding with surgical intervention.

Nonetheless, a further in-depth scrutiny of the relationship between axSpA and FAI is required. Therefore, the purpose of this scoping review was to evaluate the relationship between FAI and SI joint abnormalities and FAI and axSpA.

The scoping review was performed as per the methodological framework proposed by Arksey and O’Malley and Levac et al. [21, 22] and was guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) scoping review extension checklist [23]. A scoping study methodology was chosen to specifically map the existing research on this topic and identify knowledge gaps in the literature to accurately guide future research.

The initial query of the Medline, Embase, and Cochrane databases resulted in 120 articles. After duplicates were removed and two additional publications were added through manual searching, there were 101 studies. The titles, abstracts, and keywords of the remaining articles were reviewed to determine initial relevancy, and 23 articles remained. Full-text reviews of the remaining articles were conducted, and 8 of these articles met the inclusion criteria. Figure 1 provides a detailed illustration of the study identification and selection process, adhering to the PRISMA guidelines.

The main findings of this scoping review reveal that the prevalence of SI joint abnormalities can be as high as 25–28% in patients with FAI. Furthermore, the prevalence of FAI morphology in patients with axial spondyloarthritis can be as high as 20–37%. Finally, patients undergoing hip arthroscopy for FAI with axSpA and/or SI joint abnormalities have lower postoperative outcome scores reported in comparison with those patients who do not have these comorbidities.

A large portion of the literature examined the prevalence of these conditions. Radiological SI joint abnormalities were present in 25.2–28.6% of patients with FAI [18, 24]. Whilst SI joint abnormalities can be found in up to 65% of asymptomatic adults in the general population [29], the patient population in these papers was younger, with mean ages of 32.3 and 44.6 years respectively [18, 24], in contrast to the general population where SI joint abnormalities typically increase with age and are more common in older adults [29]. The prevalence of radiographic FAI morphology in patients with axSpA ranged from 20.3 to 36.7% [11, 13], which needs consideration against the background of axSpA’s male predominance, given that radiographic FAI morphology is found in 20–30% of healthy young adults and up to 60% in male athletic populations [30, 31]. Of note, 77% of patients with SI joint pain exhibited at least one radiological abnormality consistent with FAI [26]. These findings suggest the need for sex and activity-matched controlled studies to determine whether these relationships have clinical significance beyond background prevalence rates. Regarding outcomes, while limited data suggests patients with concomitant FAI and SI joint changes demonstrated lower postoperative clinical scores following hip arthroscopy, specific outcomes for FAI patients with axSpA could not be determined from this review.

Hip arthroscopy has emerged as a less invasive alternative to open hip surgery for treating FAI, offering reduced morbidity and faster recovery [32‐34]. However, patient selection remains crucial for optimal outcomes, and identifying reliable predictive factors is essential for setting realistic expectations and guiding rehabilitation. While numerous patient characteristics have been linked to poor outcomes after arthroscopic surgery for FAI, including osteoarthritis, older age, and longer symptom duration [10, 35], and lateral joint space width [36], the influence of underlying inflammatory pathologies like axSpA has been less extensively studied. Exploring the relationship between FAI and inflammatory conditions is a critical step in understanding how these factors interact and affect surgical outcomes. This may necessitate a shift in focus toward new areas of FAI research beyond traditional athletic populations [37] to better serve the broader patient population.

The consistency in reporting elevated prevalence rates across these studies suggests a relationship between FAI and axSpA and/or SI joint involvement. This focus on prevalence in the literature underscores a tangible link between these conditions, establishing a foundation for further investigation. It also highlights the necessity of evaluating SI joint symptoms in patients diagnosed with FAI who are considering arthroscopic treatment.

Assessment of SI joint involvement should include standard history-taking and physical examination, with attention to both subjective indications of SI pain reported by patients and objective tenderness upon SI joint palpation (Fig. 3). SI joint pain can be distinguished from lower back pain if both the thigh thrust and distraction tests are positive, or if one of these tests is positive followed by a positive compression test [26]. While a detailed description of these clinical tests is beyond the scope of this review, their importance in differential diagnosis cannot be overstated. Radiological assessment of SI joint pathology typically follows the New York Criteria [38].

While both FAI and axSpA can affect the hip joint, they do so through distinct mechanisms. FAI represents a mechanical condition characterised by morphological variations in the femoral head-neck junction or acetabulum that lead to abnormal articular contact during hip motion. In contrast, axSpA manifests as a systemic inflammatory disease with the potential to affect large joints through immune-mediated pathways, independent of mechanical factors. This fundamental pathophysiological distinction has significant clinical implications, particularly in diagnostic approaches and therapeutic decision-making. The mechanical impingement in FAI typically produces movement-dependent symptoms and specific patterns of cartilage and labral damage, whilst inflammatory arthritis associated with axSpA presents with characteristic morning stiffness, systemic features, and a different pattern of joint involvement. Understanding these distinct disease patterns becomes crucial in clinical practice, as it influences both diagnostic strategies and treatment algorithms. This understanding underscores the importance of comprehensive evaluation in patients presenting with hip pain, particularly when considering surgical intervention. The presence of inflammatory markers, HLA-B27 status, and specific imaging features can help differentiate between mechanical and inflammatory aetiologies, guiding appropriate specialist referral and treatment selection.

The morphological observations reported by Seth et al. merit particular attention in the context of phenotypic variations across different patient populations. Their identification of a distinct cam morphology in paediatric patients with inflammatory conditions, characterised by a ‘sharp-edged’ head-neck junction, negative femoral offset, and increased alpha angles, represents a potentially significant radiological finding. This unique morphological pattern may serve as an important diagnostic indicator when evaluating young patients with hip pain, particularly in the context of concurrent inflammatory conditions. While the pathophysiological basis for these distinct morphological features remains to be elucidated, their recognition contributes to our understanding of the heterogeneous manifestations of hip pathology and underscores the importance of comprehensive radiological assessment in different patient subgroups.

Perhaps of most relevance to contemporary practice are the clinical outcomes. Our scoping review identified only two studies that specifically explored clinical outcomes in patients with both FAI and SI joint involvement. Horner et al. compared 70 patients with SI joint pain to 150 matched controls undergoing hip arthroscopy for FAI. Although both groups showed significant functional improvement, those with SI joint pain had lower postoperative PRO scores, with HOS-ADL, mHHS, and iHOT-12 scores were reduced compared to controls. In contrast, Krishnamoorthy et al., analysing 743 cases, found that patients with FAI and SI joint abnormalities on imaging had notably poorer outcomes, with a 30% lower success rate at a minimum of 2 years postoperatively compared to those without SI joint changes.

Horner et al. focused on SI joint pain, while Krishnamoorthy et al. examined SI joint changes on imaging, which may not always correlate with symptomatic presentation. This distinction highlights the need for standardised criteria in future studies to define and assess SI joint involvement in patients with FAI. These studies collectively suggest that the presence of SI joint pathology alongside FAI might lead to suboptimal postoperative results following hip arthroscopy, even in the absence of apparent SI joint related symptoms. These findings are further supported by a recent systematic review by Lee et al. [20], which examined the impact of low back pain on hip arthroscopy outcomes. Their review, encompassing 14 studies, found that over 50% of the studies reported worse outcomes after hip arthroscopy in patients with low back pain compared to those without. These findings have important clinical implications, emphasising the need for comprehensive evaluation and careful patient selection for hip arthroscopy in individuals with FAI and potential SI joint involvement.

Our review identified methodological variations in how these conditions were studied. FAI-focused studies primarily examined SI joint abnormalities or sacroiliitis as isolated findings, as demonstrated by Krishnamoorthy et al. and Horner et al. [12, 15]. Studies of axSpA cohorts included assessments of FAI morphology [16, 36], though without adjusting for demographic factors such as age and sex distribution. This heterogeneity in study approaches limits our ability to draw robust conclusions about relationships between these conditions. Future research would benefit from prospective cohort studies employing standardised diagnostic criteria, appropriate demographic matching, and comprehensive outcome measures to better understand the clinical implications of concurrent FAI and SI joint pathology.

Over a quarter of patients with FAI may have concurrent SI joint abnormalities. This underscores the importance of assessing the spine and excluding SI joint pathology, axSpA, and other sources of pain in patients presenting with FAI. The potential for poorer post-operative outcomes in patients with concomitant SI joint abnormalities emphasises the need for refined surgical selection criteria and careful management of patient expectations.