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Surgical and Radiologic Anatomy ISSN 0930-1038 Surg Radiol AnatDOI 10.1007/s00276-013-1172-7

An evaluation of CT-scan to locate thefemoral head centre and its implication forhip surgeons

Anthony Viste, Franck Trouillet,Rodolphe Testa, Laurence Chèze,Romain Desmarchelier & Michel-HenriFessy

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ORIGINAL ARTICLE

An evaluation of CT-scan to locate the femoral head centreand its implication for hip surgeons

Anthony Viste • Franck Trouillet • Rodolphe Testa •

Laurence Cheze • Romain Desmarchelier •

Michel-Henri Fessy

Received: 20 April 2013 / Accepted: 9 July 2013

� Springer-Verlag France 2013

Abstract

Purpose The aim of this preliminary study was to

determine the accuracy of CT-scan to locate the femoral

head centre.

Methods Eleven dried femurs were included for study.

Three techniques were compared to determine femoral head

centre (FHC) location: CT-scan, Motion Analysis and Faro-

Arm. Markers were stuck on each femur to create a system of

coordinates. Femurs lied on their posterior parts (bicondylar

plane). Several points around the femoral head were palpated

(Motion Analysis and Faro-Arm) or determined (Amira

software for CT-scans). By a least-square regression method,

the FHC location in 3D was defined for each technique.

Results The results of the FHC location determined by

the CT-scan technique were compared with those measured

by the faro-arm and the Motion Analysis techniques. The

coordinates (X, Y, Z) of the FHC were compared between

the three methods, and no statistical difference was found

(p = 0.99). In a 3D plot, this gave a mean difference of

1.3 mm. The mean radius of the femoral head was of

22.5 mm (p = 0.6).

Conclusions CT-scan is as accurate and reliable as gold-

standard techniques (motion and faro-arm). Locating FHC

before and after hip arthroplasty would allow hip surgeons

to determine and compare 3D orientation of the upper-end

of femur: offset, height and anteversion.

Keywords CT-scan � Femoral head centre �Orientation � Total hip replacement

Introduction

Since Sir Charnley and his ‘‘low-friction arthroplasty’’ in

1962, total hip arthroplasty has become a common proce-

dure nowadays [11]. It is now used for the treatment of

osteoarthritis of the hip and in case of femoral neck frac-

tures. The major complications that may occur after this

procedure remain dislocation [9, 14] and loosening [4].

Optimization in component positioning [10] can prevent

from those pitfalls.

Several radiological methods were described to calcu-

late cup positioning [1, 8, 13, 16, 18] but very few on the

femoral side [15, 20]. The morphology of femurs was

studied in order to create best-fit implants [5, 7] but stem

3D orientation was underestimated until the concept of

combined (cup ? stem) version [2] emerged. Stem posi-

tioning and restoration of femoral anatomy [12] is essential

to avoid lower limb discrepancy, tendinopathy of abductors

or limp [3, 19] and dislocation of the device.

A. Viste � M.-H. Fessy

Faculte de Medecine Lyon-Sud Charles Merieux, Laboratoire

d’Anatomie, 165 Chemin du Petit Revoyet, BP 12,

69921 Oullins Cedex, France

A. Viste (&) � R. Desmarchelier � M.-H. Fessy

Hospices Civils de Lyon, Centre Hospitalier Lyon-Sud, Service

Chirurgie Orthopedique, Traumatologique et Medecine du Sport,

165 Chemin Grand Revoyet, 69495 Pierre Benite Cedex, France

e-mail: anthony.viste@chu-lyon.fr

A. Viste � R. Testa � L. Cheze � M.-H. Fessy

Universite de Lyon, Lyon, France

A. Viste � R. Testa � L. Cheze � M.-H. Fessy

IFSTTAR, UMRT_9406, LBMC, Universite Lyon1,

Villeurbanne, France

F. Trouillet

Hospices Civils de Lyon, Hopital de la Croix-Rousse, Centre

Albert Trillat, 103 Grande Rue de la Croix-Rousse, 69004 Lyon,

France

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Surg Radiol Anat

DOI 10.1007/s00276-013-1172-7

Author's personal copy

Femoral head centre (FHC) position must be restored for

anatomical reconstructions of the hip [6]. FHC location in

3D would allow us to simultaneously know if offset,

version and height of the femoral head have been well

re-established after surgery.

Our hypothesis was that CT-scan could be routinely

used to study FHC before and after total hip replacement

and so being aware of 3D orientation of the proximal

femoral component. We performed a comparative ana-

tomical study between CT-scan, Motion AnalysisTM and

Faro-arm to know if CT scan was a reliable and accurate

technique for determining 3D FHC position.

Methods

Eleven dried femurs (6 right and 5 left) were included for

study. Three passive markers were glued on each bone to

create the bone reference. They were placed on the medial

epicondyle, the lateral epicondyle and the greater

trochanter of each femur. Femurs were positioned on a

support, so they could lie on their three more posterior

points, which defined the posterior bicondylar plane.

FHC was then determinated using three different

methods: Motion AnalysisTM, Faro-Arm and CT-scan. The

same system of coordinates was used for all the methods to

compare the results: origin (O) on the lateral epicondyle,

Y-axis between O and the greater trochanter and X-axis

between O and medial epicondyle and Z-axis perpendicular

to X and Y (Fig. 1). A surgeon used the Motion Analysis

and Faro-Arm techniques and another the CT-scan tech-

nique. An engineer and a professor of biomechanics

effectuated the calculations and the definitions of coordi-

nates system.

Motion analysisTM (Fig. 2)

Measurements were obtained with an optoelectronic sys-

tem with the help of the passive markers. Six EagleTM

cameras (1.3 Mpx) were piloted by EVaRT 5.0TM soft-

ware. Static and dynamic calibrations were effectuated.

System errors were below 0.2 mm. The sampling fre-

quency of the cameras was 100 Hz. A Butterworth filter

was used (low pass, order 5, cut-off frequency 6 Hz) to

correct the 3D path of the markers. Three markers were

glued on the support to define the bi-condylar plane. The

BrainLabTM tracking sensor (dimensions known from

manufacturer) defined by three markers was used to palpate

3,000 peripheral points around femoral head. EVaRT

5.0TM software calculated the 3D coordinates of the

tracking markers at a main static reference point, which

was determined during calibration of the device. The

SkeletonBuilderTM module integrated into the software

was used hierarchically to define the objects being studied.

We calculated the theoretical FHC by a least-square

regression method.

Fig. 1 System of coordinates (O, X, Y, Z): O origin on the lateral

epicondyle, X-axis transversal axis between O and medial epicondyle,

Y-axis between O and greater trochanter and Z-axis: perpendicular to

X and Y

Fig. 2 Palpation of femoral head with BrainLab sensor (Motion

AnalysisTM)

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Faro arm (Fig. 3)

Measurements were effectuated with the help of the Faro-

Arm (Faro technologies, Lake Mary, FL), at IFSTTAR

(Bron, France). Calibration was obtained, while palpating a

metallic head of a known diameter. The same method was

used than with motion.

CT-scan (Figs. 4, 5)

Femurs lied on their bicondylar planes. The slice width was

of 0.67 mm. With the help of Amira� software, the coor-

dinates of the markers were extracted. Then ten points were

chosen around the femoral head. A least square regression

method allowed us to define the coordinates of the FHC.

Statistical analysis

It was performed using JMP 7.0. Comparison tests between

groups with continuous variables were effectuated with

non-parametric Mann–Whitney and Kruskal Wallis tests.

The significance threshold was of 0.5.

Results (Table 1)

The results of the FHC location determined by the CT-scan

technique were compared with those measured by the Faro-

Arm and the Motion Analysis techniques. The coordinates

(X, Y, Z) of the FHC were compared between the three

methods, no statistical difference was found (p = 0.99).

Then we calculated the mean distance between FHC as

measured by each method. In a 3D plot, this gave a mean

difference of 1.3 mm. The mean radius of the femoral head

was of 22.5 mm (p = 0.6). The mean difference between

femoral head radius was compared for each method.

Discussion

The aim of this preliminary study was to prove the accu-

racy and reliability of CT-scan to define 3D position of the

FHC. CT-scan was as reliable and accurate as Motion

Analysis and Faro-Arm (gold standard) for determining

FHC localization: the difference between CT-scan and the

two other methods corresponded of an error about 2 pixels.

This is the first study to determine FHC location in order to

compare it before and after surgery. So this preliminary

Fig. 3 Palpation with Faro-Arm�

Fig. 4 Frontal view of CT-scan with Amira�

Fig. 5 3D view of the femoral head with Amira�

Table 1 Comparison of results between the three techniques

Comparison

Faro vs. Motion

Comparison

Faro vs. CT

Comparison

CT vs. Motion

X-axis 0.015 ± 0.5 0.22 ± 0.6 0.21 ± 0.6

Y-axis 0.83 ± 0.7 0.09 ± 0.7 0.74 ± 0.7

Z-axis 0.67 ± 1.3 0.41 ± 0.5 0.27 ± 1.5

Distance FHC 1.53 ± 0.6 0.99 ± 0.4 1.43 ± 0.9

Radius 0.86 ± 0.4 0.43 ± 0.3 1.29 ± 0.6

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study is necessary before its introduction into clinical

practice.

Working on isolated femurs is clearly not the same than

patients in practice, but it allowed us to confirm the feasi-

bility of the CT-scan technique. The strength of this study

was the comparison made with the gold standards: Motion

Analysis and Faro-Arm. The number of femurs can be

considered as sufficient because the results were very sim-

ilar with a 1-mm precision. However, due to our small

group, though we found no significant differences, it does

not mean that these three techniques are equivalent in terms

of precision. But for our study, the results were statistically

not significantly different. We chose native femoral heads

instead of metallic ball to study FHC because we thought

that it would have been more difficult to determine FHC in

variable bony structures. But it will be interesting to com-

pare these three techniques using a metallic ball to confirm

the accuracy of CT-scan (errors due to metallic artefacts).

The reproducibility and repeatability ([0.9) of the mea-

surements to determinate 3D coordinates of the FHC were

found excellent for each method.

Until now, some studies only deal with femoral ante-

version [21], other works assessed offset [19] but knowing

FHC position will allow us to simultaneously be aware of

three essential parameters for hip surgeons [17]. The ori-

entation of the femoral upper end, before and after hip

arthroplasty, can be defined from the position of the FHC.

The 3D position of the FHC allows us to compare femoral

anatomy before and after surgery in terms of anteversion/

retroversion, medialization/lateralization and height. The

version deals with dislocation risk, the offset with the

strength of abductors [19] and the height with the limb

discrepancy.

This study confirms the accuracy of the bicondylar plane

[15] as system of coordinates for assessing orientation of

the proximal part of femur. It is essential to use a repro-

ducible plane, whatever the position of the subject, to

define the FHC location. Because the goal of this work is to

be reproducible on patients, so this bicondylar plane seems

accurate and reliable.

Conclusions

FHC location can reliably and accurately be assessed by

CT-scans. It could be used to compare 3D position of the

FHC before and after total hip arthroplasty. This pre-

liminary, but necessary, study will allow us to calculate and

determine FHC before and after surgery using our

cementless stem.

Conflict of interest None.

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