What Are the Biomechanical Features and Metrics for Native Hip Instability? Consensus Statements From a Scoping Review and an International Multidisciplinary Delphi Study.

Abstract

Native hip instability encompasses a spectrum of abnormal pathomechanics under physiological loading and is associated with pain, dysfunction, and soft tissue damage. The condition spans a continuum-from developmental hip dysplasia to femoroacetabular impingement and even instability in the absence of bony deformities, as can be the case in patients with connective tissue disorders or soft tissue deficiencies. Despite advances in understanding this condition, biomechanical definitions, thresholds, and metrics remain inconsistent. We therefore sought to conduct a meeting with an international panel of experts to map available evidence on the biomechanical features of native hip instability, to identify knowledge gaps, and to explore whether current biomechanical metrics can reliably differentiate various degrees of severity of instability. In this scoping review and structured consensus document, we asked: (1) What are the biomechanical or pathomechanical features of native hip instability? (2) What are the biomechanical metrics of hip instability? (3) Can biomechanical metrics differentiate between hip microinstability versus conventional (bony) instability? A consensus study using the modified Delphi technique was conducted in accordance with the Accurate Consensus Reporting Document (ACCORD) guideline. The consensus meeting was held during the 15th Symposium on Joint Preserving and Minimally Invasive Surgery of the Hip, which took place in Québec City, Québec, Canada, in June 2025. The process involved a multidisciplinary steering committee and a diverse panel of 100 international participants representing 13 countries. Following a rapid scoping review, statements related to biomechanical or pathomechanical features of native hip instability and metrics of hip instability and hip microinstability were developed and sent to participants 1 week prior to the meeting. Participants voted on these statements across two Delphi rounds during the meeting, with consensus defined as ≥ 75% agreement. The anatomic features of instability were identified as follows: bony morphology, static soft tissue stabilizers of the labrum and joint capsule, and muscles as dynamic stabilizers. Reported metrics for instability included femoral head translation, with translation < 3 mm considered normal by consensus. There was insufficient evidence to differentiate between microinstability (ligamentous) and conventional (structural bony) instability. Biomechanically, native hip instability is characterized by an unpredictable femoral head path of motion influenced by bony morphology, capsulolabral integrity, and muscular stabilization. Femoral head translation was the most consistently supported metric, with translation < 3 mm considered physiological by consensus. Current biomechanical methods do not allow reliable differentiation between microinstability and structural instability. Standardized, reproducible in vivo measurements of three-dimensional hip motion are needed to establish clinically meaningful thresholds and guide patient care. Clinically, this study sets a biomechanical benchmark defining native hip instability, enabling researchers to better distinguish between physiological laxity and pathologic instability. By defining biomechanical features of hip instability-most notably femoral head translation > 3 mm-this work contributes to a more standardized approach for defining joint stability, integrating bony morphology, capsulolabral integrity, and muscular stabilization. Such biomechanical insights guide surgical decision-making regarding capsular management and soft tissue repair and inform targeted rehabilitation strategies aimed at restoring hip stability.