Variation in functional pelvic tilt in patients undergoing total hip arthroplasty.
OBJECTIVE
The pelvis rotates in the sagittal plane during daily activities. These rotations have a direct effect on the functional orientation of the acetabulum. The aim of this study was to quantify changes in pelvic tilt between different functional positions.


METHODS
Pre-operatively, pelvic tilt was measured in 1517 patients undergoing total hip arthroplasty (THA) in three functional positions - supine, standing and flexed seated (the moment when patients initiate rising from a seated position). Supine pelvic tilt was measured from CT scans, standing and flexed seated pelvic tilts were measured from standardised lateral radiographs. Anterior pelvic tilt was assigned a positive value.


RESULTS
The mean pelvic tilt was 4.2° (-20.5° to 24.5°), -1.3° (-30.2° to 27.9°) and 0.6° (-42.0° to 41.3°) in the three positions, respectively. The mean sagittal pelvic rotation from supine to standing was -5.5° (-21.8° to 8.4°), from supine to flexed seated was -3.7° (-48.3° to 38.6°) and from standing to flexed seated was 1.8° (-51.8° to 39.5°). In 259 patients (17%), the extent of sagittal pelvic rotation could lead to functional malorientation of the acetabular component. Factoring in an intra-operative delivery error of ± 5° extends this risk to 51% of patients.


CONCLUSIONS
Planning and measurement of the intended position of the acetabular component in the supine position may fail to predict clinically significant changes in its orientation during functional activities, as a consequence of individual pelvic kinematics. Optimal orientation is patient-specific and requires an evaluation of functional pelvic tilt pre-operatively. Cite this article: Bone Joint J 2017;99-B:184-91.
The University of Sydney, School of Aerospace, Mechanical and Mechatronic Engineering, Building J07, Sydney NSW 2006, Australia and Optimized Ortho, 17 Bridge Street, Pymble NSW 2073, Australia.
J
J
Pierrepont
Malabar Orthopaedic Clinic, 43 The Avenue, Windsor, VIC 3181, Australia.
G
G
Hawdon
Optimized Ortho, 17 Bridge Street, Pymble NSW 2073, Australia.
B P
BP
Miles
Optimized Ortho, 17 Bridge Street, Pymble NSW 2073, Australia.
B O'
BO
Connor
Melbourne Orthopaedic Group, 33 The Avenue, Windsor, VIC 3191, Australia.
J
J
Baré
Peninsula Orthopaedics, 812 Pittwater Rd, Dee Why, NSW 2099, Australia.
L R
LR
Walter
Peninsula Orthopaedics, 812 Pittwater Rd, Dee Why, NSW 2099, Australia.
E
E
Marel
Sydney Orthopaedic Specialists, Suite 29, Prince of Wales Private Hospital, Randwick NSW 2031, Australia.
M
M
Solomon
Monash University, 43 The Avenue, Windsor VIC 3181, Australia.
S
S
McMahon
Monash University, 43 The Avenue, Windsor VIC 3181, Australia and Melbourne Orthopaedic Group, 33 The Avenue, Windsor, VIC 3191, Australia.
A J
AJ
Shimmin
D000077:Acetabulum / Q000000981:diagnostic imaging / Q000503:physiopathology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000503:physiopathology* / Q000601:surgery; D010384:Pelvic Bones / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011187:Posture / Q000502:physiology*; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D055815:Young Adult
Component orientation; Dislocation; Implant positioning; Pelvic tilt