Hip offset in total hip arthroplasty: quantitative measurement with navigation.
BACKGROUND
Offset in THA correlates to abductor muscle function, wear, and impingement. Femoral offset after THA is not independent of the cup center of rotation (COR) so hip offset, a combination of femoral offset and change in hip COR, becomes the important measurement.


OBJECTIVE
We therefore asked whether hip offset in arthritic hips would correlate with cup COR; whether offset could always be balanced within 6 mm of contralateral normal hips; and whether hip length could also be kept within 6 mm.


METHODS
We compared hip offset of arthritic and contralateral normal hips on radiographs in 82 patients (82 hips) who had THA. We used computer navigation in all patients with the aim of reconstructing the hip offset and to compare hip offset change to the quantitative change of the hip COR.


RESULTS
The preoperative radiographic change to equalize the offset ranged from -12 to +21 mm (mean, 1.5); postoperatively the change was 1.4 ± 6.4 mm and was within ± 6 mm in 78 of 82 hips. As COR displaced superiorly from 3 to 6+ mm the offset had to be substantially increased. Only with COR 0-3 mm superior and 0-5 mm medial was offset always within 5 mm.


CONCLUSIONS
Hip offset reconstruction was directly related to the position of the hip COR, and navigation allowed quantitative control of offset and hip length.
Dastane
Manish
M
The Arthritis Institute at Good Samaritan Hospital, 637 S Lucas Avenue, 5th Floor, Los Angeles, CA 90017, USA.
Dorr
Lawrence D
LD
Tarwala
Rupesh
R
Wan
Zhinian
Z
D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D001696:Biomechanical Phenomena; D005260:Female; D006621:Hip Joint / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D007870:Leg Length Inequality / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D011859:Radiography; D016059:Range of Motion, Articular; D020127:Recovery of Function; D012399:Rotation; D025321:Surgery, Computer-Assisted