PURPOSE: To systematically review factors affecting hip capsule thickness. METHODS: The review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The terms "hip," "arthroscopy," "capsule," "capsular," and "thickness" were used to search the PubMed, Ovid [MEDLINE], Cochrane Database, and EMBASE databases from inception to January 15, 2024. RESULTS: The initial search identified 1,735 studies. Twenty-three studies were included in the systematic review. Eight reported the relationship between sex and capsule thickness. Seven reported that capsule thickness was significantly lower in women. Of the 4 studies reporting the relationship between capsular laxity and capsule thickness or Beighton test score (BTS), 4 studies showed the association of lower capsule thickness in patients with capsular laxity or BTS ≥4. Of the 6 studies reporting the relationship between arthroscopic surgery and capsular thickness, 2 showed significantly greater capsule thickness after capsulotomy with repair and 2 found significantly decreased postoperative capsule thickness without repair. One study illustrated that anterior capsule thickness was significantly smaller in patients with femoral torsion angle >
20°. One study showed that neck-shaft angle was negatively corelated with anterior capsule thickness. Of the 3 studies that examined lateral central edge angle, 2 reported that lower angle correlated with thinner capsule thickness
one study reported the opposite result. Hip inflammatory disease was associated with thicker hip capsule. CONCLUSIONS: Female sex, capsular laxity, BTS ≥4, greater femoral torsion angle, and greater neck-shaft angle were associated with a thinner hip capsule. Hip inflammatory disease and capsule repair after arthroscopic surgery were associated with a thicker capsule. LEVEL OF EVIDENCE: Level IV, systematic review of Level I-IV studies.