Correlation of Spinopelvic Parameters and Acetabular Cup Orientation



Status:Recruiting
Conditions:Arthritis, Osteoarthritis (OA)
Therapuetic Areas:Rheumatology
Healthy:No
Age Range:Any
Updated:10/5/2018
Start Date:February 2016
End Date:December 2019
Contact:Grant Sutter, MD
Email:grant.sutter@dm.duke.edu

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Measurement and Quantitative Correlation of Spinopelvic Parameters and Acetabular Cup Orientation Between Standing and Sitting to Define a Better Functional Anteversion Safe Zone in Total Hip Arthroplasty

In total hip arthroplasty, cup anteversion is an important factor in stability. Lewinnek's
safe zone and functional anteversion are often used to assess appropriate orientation.
However, these approaches do not consider the effect of the spinopelvic chain and lumbar
mobility when in the seated position. This study will measure functional anteversion when
standing and sitting with patient-specific computer models and define a quantitative
relationship between the change in functional anteversion and spinopelvic parameters. This
will challenge the historical paradigm of the safe zone and provide a tool to define
anteversion based on a patient's mechanics and reduce risk of dislocation.

In total hip arthroplasty (THA), incorrect cup orientation markedly increases the risk of
dislocation, wear, and impingement. The primary method of cup placement is based on the
surgeon's interpretation of orientation within a "safe zone" defined by Lewinnek almost 40
years ago. This approach has undergone little change despite consistent dislocation rates and
a large proportion of dislocations occurring in patients with cups within the safe zone. One
reason for this may be that it does not account for a patient's natural pelvic posture, which
affects the functional cup anteversion. Some modern techniques of cup placement assess a
functional anteversion based on supine and others on standing orientation. However, these
methods do not account for lumbar mobility and the effects on spinopelvic mechanics when in
the seated position, the most common position in which dislocation occurs. The investigators
have shown that patients with lumbar fusion have a higher rate of THA dislocation. This risk
also correlated with length of fusion construct. This suggests that decreased lumbar
mobility, whether a result of arthrodesis, disease or age related degeneration, may play an
important role in the risk of THA dislocation. Some studies have measured change in pelvic
orientation and cup anteversion between sitting and standing. Others have used modeling to
estimate change in functional anteversion based on pelvic tilt. Presently, however, there are
no studies that have investigated the quantitative relationship, in vivo, between
patient-specific changes in spinopelvic parameters and cup anteversion between sitting and
standing. Within this exploration, identification of an appropriate safe zone in individuals
with mobility restrictions of the lumbar spine is not possible.

The investigators will test the hypothesis by addressing the aims presented below. These aims
will be approached by directly measuring the spinopelvic parameters on standing and seated
radiographs in 100 patients who have undergone primary THA. Computer models of cups and
pelvises generated from patient-specific pelvis CTs will be manipulated based on the measured
changes in pelvic alignment. The change in functional cup anteversion will then be directly
measured from each patient's model.

Specific Aim #1: To quantify the relationship between the change in pelvic tilt and
functional acetabular cup anteversion between the standing and sitting positions in patients
who have undergone primary THA. The investigators hypothesize that there will be a directly
proportional relationship between the increase in pelvic tilt and increase in functional
anteversion. The investigators anticipate that Aim #1 will identify the importance of
functional anteversion in the seated position and support its consideration when defining a
patient-specific cup safe zone. This data will serve as the foundation for development of a
clinical tool used in pre-operative planning and post- operative rehabilitation that accounts
for spinopelvic mechanics to maintain safe cup orientation when in the vulnerable seated
position.

Specific Aim #2: To quantify the relationship between the change in lumbar lordosis and
functional acetabular cup anteversion between the standing and sitting positions in patients
who have undergone primary THA. The investigators hypothesize that there will be a directly
proportional relationship between the decrease in lumbar lordosis and increase in functional
anteversion and that patients with history of lumbar immobility will have decreased change in
functional anteversion. The data obtained in Aim #2 can be used to identify those at
increased risk of dislocation. It will also provide insight into, and a basis for further
study of, the relationship between seated functional anteversion and specific etiologies of
lumbar immobility (spinal fusion, ankylosing spondylitis, flat back syndrome, degenerative
changes, etc.) that may affect THA dislocation.

The overall objective of this study is to define a clinically relevant and applicable
quantitative correlation between the change in spinopelvic parameters and change in
functional anteversion between the standing and seated positions and challenge the historical
safe zone paradigm. The central hypothesis is that the change spinopelvic mobility correlates
with the change in functional anteversion. The investigators believe that this quantitative
relationship will provide the clinician a tool to identify at-risk THA candidates and make
appropriate patient-specific modifications to cup anteversion and post-operative
rehabilitation.

Inclusion Criteria:

-All patients who have undergone THA with the appropriate pre-operative CT for planning and
those who are candidates for primary THA for osteoarthritis will be contacted for
recruitment.

Exclusion Criteria:

- inflammatory arthritis

- neuromuscular disorders

- revision surgery
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Durham, North Carolina 27703
Phone: 919-668-4373
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