Surgeons' Accuracy in Achieving Their Desired Acetabular Component Orientation.
BACKGROUND
Wide variability in cup orientation has been reported. The aims of this study were to determine how accurate surgeons are at orientating the acetabular component and whether factors such as visual cues and the side of operating table improved accuracy.


METHODS
A pelvic model was positioned in neutral alignment on an operating table and was prepared as in a posterior approach. Twenty-one surgeons (9 trainers and 12 trainees) were tasked with positioning an acetabular component in a series of target orientations. The orientation of the component was measured using stereophotogrammetry, and the difference between the achieved orientation and the target orientation was calculated. Tasks included stating the surgeon's preferred orientation and thereafter placing the cup in that orientation, reproducing visual cues (transverse acetabular ligament and alignment guide), altering orientation by 10°, and estimating orientation while on the assistant's side.


RESULTS
The preferred inclination was 42° and the preferred anteversion was 21°. On average, surgeons decreased the inclination by 4° and increased the anteversion by 11° when tasked with replicating their desired orientation. The variability (defined as 2 standard deviations) in achieving a target orientation was 14°. The use of visual cues, such as the transverse acetabular ligament or the alignment guide, significantly improved accuracy to 1° for anteversion (p < 0.001) and -3° for inclination (p = 0.003). In addition, the use of an alignment guide reduced the variability by one-third. Trainees and trainers had similar accuracy and variability. There was greater variability in assessing cup inclination when standing on the assistant's side compared with the surgeon's side of the table, which has implications for training.


CONCLUSIONS
Surgeons overestimate operative inclination and underestimate anteversion, which is of benefit, as this, on average, helps to achieve the desired radiographic cup orientation. Although the use of visual cues helps, conventional techniques result in a large variability in acetabular component orientation. New and better guides and methods for training need to be developed.
Nuffield Orthopaedic Centre, Oxford, United Kingdom Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, Headington, Oxford, United Kingdom george.grammatopoulos@ndorms.ox.ac.uk.
George
G
Grammatopoulos
Nuffield Orthopaedic Centre, Oxford, United Kingdom Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, Headington, Oxford, United Kingdom.
Abtin
A
Alvand
Nuffield Orthopaedic Centre, Oxford, United Kingdom Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, Headington, Oxford, United Kingdom.
A Paul
AP
Monk
Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, Headington, Oxford, United Kingdom.
Stephen
S
Mellon
Nuffield Orthopaedic Centre, Oxford, United Kingdom Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, Headington, Oxford, United Kingdom.
Hemant
H
Pandit
Nuffield Orthopaedic Centre, Oxford, United Kingdom Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, Headington, Oxford, United Kingdom.
Jonathan
J
Rees
Department of Mechanical Engineering, University of Bath, Bath, United Kingdom.
Harinderjit S
HS
Gill
Nuffield Orthopaedic Centre, Oxford, United Kingdom Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, Headington, Oxford, United Kingdom.
David W
DW
Murray
D000077:Acetabulum / Q000601:surgery*; D019644:Arthroplasty, Replacement, Hip / Q000379:methods* / Q000592:standards; D002983:Clinical Competence; D006621:Hip Joint / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D056888:Patient Positioning; D025321:Surgery, Computer-Assisted / Q000379:methods / Q000592:standards