CT-based Automated Preoperative Planning of Acetabular Cup Size and Position using Pelvis-cup...

Copyright © Osaka Univ., Kobe Univ. 2009

CT-based automated preoperative planning of acetabular cup size and position using pelvis cup integrated

statistical shape model

Itaru OTOMARUa ， Kazuto Kobayashia ， Toshiyuki OKADAb ，

Masahiko NAKAMOTOb ， Masaki TAKAOb ， Nobuhiko SUGANOb ， Yukio TADAa and Yoshinobu SATOb

a Graduate School of Engineering, Kobe Universityb Graduate School of Medicine, Osaka University


Outline1. Introduction

2. Methods1. Cup planning of mildly and severely diseased

pelvises

2. Construction of pelvis-cup integrated statistical shape model

3. Automated planning procedure

3. Experimental results

4. Discussions and future direction


Outline1.1. IntroductionIntroduction


pelvises






Surgical CAD/CAM is one of common frameworks of CAOS. The CAM system ensure accurate execution of preoperative

plans prepared using the CAD system.

Image acquisition

Preoperative planning Intraoperative assistance

CAD CAM

Surgical CAD/CAM

Therefore, the quality of preoperative planning is becoming more critical.


Image acquisition

Preoperative planning Intraoperative assistance

In this framework, a large number of surgical data and preoperative plans are accumulated in some of the hospitals.

The feedback of these past planning can potentially improve the future planning.

Atlas-based closed-loop surgery

Database of 3D/4D Patient & Surgical Data

Statistical Surgical Atlas

Statistical Analysis

Patient’s dataPre-op plans

Surgical logIntra-op data

Atlas based preoperative planning


Objective Our objective is to automate the preoperative

planning to reduce its time consuming nature by utilizing the accumulated past planning data.

To achieve this, we construct a statistical atlas which models the expertise of the experienced surgeons.

We target acetabular cup planning for total hip arthroplasty.


Outline1. Introduction2.2. MethodsMethods

1.1. Cup planning of mildly and severely diseased Cup planning of mildly and severely diseased pelvisespelvises

2.2. Construction of pelvis-cup integrated statistical Construction of pelvis-cup integrated statistical shape modelshape model

3.3. Automated planning procedureAutomated planning procedure




Cup planning of mildly and severely diseased pelvises: Our problem

Mildly diseased case Severely diseased case

• In cup planning, it is somewhat difficult to predict the original anatomy for severely diseased acetabulum due to its severe deformation and shift.


Pelvis-cup statistical shape model (PC-SSM)

Pelvis-cup statistical shape modelTraining datasets

We embed spatial relations between pelvis and cup, which are regarded as expertise of the surgeon, into SSM.

Principal Principal component component analysisanalysis


Pelvis-cup statistical shape model (PC-SSM)

Given training datasets of cup plans prepared by experienced surgeon, merger of pelvis and cup surfaces of each plan is considered as one shape to construct SSM.

Principal Principal component component analysisanalysis

Pelvis-cup statistical shape modelTraining datasets


Automated planning procedure

1. The statistical shape model is roughly registered to the segmented patient’s pelvis.

White: Patient’s pelvis

Yellow: Pelvis part of statistical atlas

Red: Cup part of statistical atlas



2. Shape parameter of the statistical atlas is optimized so as to the difference between the pelvis part of the statistical atlas and the patient’s pelvis shape is minimized.






3. Cup size and position are estimated using determined cup surface.





Outline

1. Introduction


pelvises



3.3. Experimental resultsExperimental results



Conditions 28 cases (used for actual THA surgery via a navigation

system) were used for atlas construction and evaluation.

Leave-one-out cross validation was used for evaluation.

We compared with the previous method [CAOS 2004] which was based on user-specified constraints obtained from surgeon’s interview.

Error was defined as the difference between the automated plan and the surgeon’s plan.


Results

• Mean size error: 1.4 mm (proposed), 2.1 mm (previous)• Mean positional error: 4.2 mm (proposed), 4.3 mm (previous)• Number of cases of penetration: 4 (proposed), 0 (previous)

Mean size error was smaller in the proposed method. However, cup penetration occurred in four cases.


Results of illustrative case

Same size was selected in the proposed method as the surgeon’s plan while the size error of the previous method was 8 mm.

Previous ProposedSurgeon’s

Size 58 Size 50 Size 50


Outline

1. Introduction


pelvises




4.4. Discussions and future directionDiscussions and future direction


Discussions The proposed method shows better performance for

size selection than the previous method.

Statistically derived constraints could be successfully incorporated and are shown to be useful.

On the other hand, statistical constraints are insufficient to avoid the cup penetration.

To avoid the penetration, we will add the constraints based on residual bone thickness between pelvis and cup.


In principle, given a sufficient number of planning datasets that a surgeon planned, the method is applicable to various implants for different bones.

We are planning to apply the method to the femoral stem.

Future direction

Femur-stem combined statistical atlas


Thank you for your attention

This research was supported in part by Stryker Japan K. K. and Biovisiq Japan, Inc.

CT-based Automated Preoperative Planning of Acetabular Cup Size and Position using Pelvis-cup...

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