In all, 145 of 160 hips (90%) were considered safe from impingement. Patients with highest risk are those with biological or surgical spinal fusion; patients with dangerous spinal imbalance can be safe with correct acetabular component position. The clinical relevance of the study is that it correlates acetabular component position to spinal pelvic mobility which provides guidelines for total hip arthroplasty. Cite this article: Bone Joint J 2017;99-B(1 Supple A):37-45.
Background:
The spine-pelvis-hip interaction during postural change should be considered in the functional anatomy of the hip. The component parts of this anatomy and how they influence hip function are important to know. Pelvic incidence (PI) is one of these components. We studied if PI was preoperatively predictive of impingement risk and if it postoperatively influences hip position, which could cause outliers from the functional safe zone of hip replacement.
Methods:
This was a prospective radiographic study of 187 consecutive patients (200 hips) who had lateral spinopelvis-hip radiographs before and after primary total hip arthroplasty with measurements of the component factors that influence mobility and position of the functional anatomy. The predictive value of PI for risk of impingement of the hip and its postoperative relationship to functional safe-zone outliers were assessed. Forty-one dislocations from our clinical practice were also reviewed.
Results:
Of 200 hips, the PI was normal in 145 hips (73%), low in 18 hips (9%), and high in 37 hips (19%). Eighty-two hips had spinopelvic imbalance: 12 (67%) of the 18 hips with low PI, 56 (39%) of the 145 hips with normal PI, and 14 (38%) of the 37 hips with high PI. Low-PI hips was the most predictive of the risk of impingement and postoperatively these hips had the most outliers from the functional safe zone.
Conclusions:
PI is an anatomical component that is predictive of both impingement risk and functional safe-zone outliers. Preoperative risk, based on factors such as the Lewinnek zones and combined anteversion, is an established guide in determining cup position in hip replacement. Low-PI hips that have the “terrible triad” of a posteriorly tilted pelvis, stiff pelvic mobility, and increased femoral flexion therefore have no functional safe zone.
Level of Evidence:
Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.
Computer-assisted orthopedic surgery improves mechanical alignment and the accuracy of surgical cuts in the context of total knee arthroplasty (TKA). A simplified, navigation-enhanced instrumentation system was assessed to determine whether the same effects could be achieved with a less intrusive system. Two cohorts of surgeons (experienced and trainees) performed a series of TKA cuts using models with and without navigation-enhanced instrumentation. The accuracy of each system was determined via the rate of outliers, measured as any cut that deviated from the planned cut by more than 2° or 2 mm. The effect of experience level was limited, with only the outlier rate for tibial varus or valgus measurement showing a significant difference between user groups with conventional instrumentation (
P
=.004). The use of navigation-enhanced instrumentation significantly reduced the total outlier rate compared with conventional instrumentation from 35% to 4% for experienced users (
P
<.001) and from 34% to 10% for trainees (
P
<.001). These results suggest that navigation-enhanced instrumentation is a viable alternative to conventional instrumentation to reduce outlier rates and improve cut accuracy. This trial also showed that additional experience may not correlate with improved surgical accuracy. Outliers may not reflect individual surgical ability as much as limitations of the instrumentation or other unidentified factors. [
Orthopedics
. 2021;44(1):54–57.]
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