Hip capsular thickness correlates with range of motion limitations in femoroacetabular impingement
Femoroacetabular impingement (FAI) is a clinical entity of the hip causing derangements in range of motion, pain, gait, and function. Computer-assisted modeling and clinical studies suggest that patients with FAI have increased capsular thickness compared to those without.A retrospective chart review was performed to assess relationships between capsular thickness, hip range of motion, and demographic factors in patients with FAI.
Local Research Ethics Board approval was obtained to extract electronic medical records for 188 patients at a single institution who had undergone hip arthroscopy. Procedures were performed from 2009 to 2017 by a single, fellowship-trained, board-certified sports medicine orthopaedic surgeon. Inclusion criteria were preoperative hip range of motion testing, positive clinical impingement testing, and magnetic resonance imaging (MRI) of the affected hip. Patient demographics, hip range of motion, and time to surgery were recorded. MRIs were reviewed by a board-certified musculoskeletal radiologist blinded to clinical data. Maximum thickness of the anterior hip capsule was measured in axial, axial oblique, and sagittal oblique sequences. Anterior capsular thickness was also measured at the level of the femoral head–neck junction in axial sequences (axial midline).
Axial midline capsular thickness was negatively correlated with hip flexion (r = − 0.196, p = 0.0042) and internal rotation (r = − 0.143, p = 0.0278). Significant differences were seen between genders in axial midline thickness (5.3 ± 1.4 mm males/4.8 ± 1.3 mm females, p = 0.0079), flexion (113° ± 18° males/120° ± 17° females, p = 0.0029), and internal rotation (23° ± 13° males/29° ± 12° females, p = 0.0155). Significant differences also existed between side affected in flexion (116° ± 17° right/119° ± 17° left, p = 0.0396) and internal rotation (26° ± 12° right/29° ± 13° left, p = 0.0029). Positive correlation was observed between axial oblique capsular thickness and flexion (r = 0.2345) (p = 0.0229).
Increased anterior hip capsular thickness at the femoral head–neck correlates with limitations in hip range of motion in FAI. The strength of this relationship may be affected between pathologies, genders, and affected side. Pathologic thickening of the hip capsule may contribute to restricted hip mobility on clinical examination, and elucidation of this relationship may provide guidance into capsular management during hip arthroscopy.
Level of evidence
4, retrospective case series.
KeywordsImpingement Hip Capsule MRI Arthroscopy Femoroacetabular Mobility Surgery
KZ performed the data collection and analysis, created figures and tables, and drafted the manuscript. DdS aided in drafting the manuscript, as well as contributing to conception of the study purpose, coordination, and design. HY contributed to data collection and analysis, and aided in drafting the manuscript. HNC analyzed and collected radiographic data, and contributed to the initial study design. NS was consulted for statistical analysis and contributed to initial study design. ORA conceived of the study, provided access to patient data, participated in its design and coordination, and helped to draft the manuscript. All authors read and approved the final manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
Ethics approval for this retrospective study was granted following review by the Hamilton Integrated Research Ethics Board (HiREB) in affiliation with McMaster University, Hamilton, Canada (reference number 2017-3490-C).
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