Functional Anatomy of the Hip Joint

Area of Science:

• Orthopedics
• Biomechanics
• Radiology

Background:

• The functional anatomy of the osteoarthritic hip joint in the sagittal plane remains undefined.
• Understanding hip joint biomechanics is crucial for managing osteoarthritis.

Purpose of the Study:

• To define the functional anatomy of the hip joint in the sagittal plane.
• To utilize clinical and radiographic analyses for hip anatomy definition.

Main Methods:

• Analysis of 320 preoperative standing and sitting lateral spine-pelvis-hip X-rays.
• Radiographic measurements included pelvic incidence (PI), sacral slope (SS), anteinclination (AI), and pelvic femoral angle (PFA).
• Development of a triangle model to illustrate hip functional motion during postural changes.

Main Results:

• Pelvic motion (ΔSS) and acetabular motion (ΔAI) demonstrated a 1:1 ratio coordination.
• Femoral motion (ΔPFA) exhibited an inverse 1:1 ratio relationship with pelvic motion (ΔSS).
• The triangle model confirmed coordinated motion: ΔSS, ΔPT, and ΔAI changed in a 1:1:1 ratio, with inverse femoral motion.

Conclusions:

• A triangle model visually represents the functional anatomy of the hip joint.
• Coordinated pelvic and acetabular motion contrasts with inversely changing femoral motion.
• This coordinated mobility clarifies limitations of the acetabulum-exclusive Lewinnek safe zone.