hip pelvic position and movement during hip replacement€¦ · > lateral), procedure (hip...

876 THE BONE & JOINT JOURNAL

HIP

Pelvic position and movement during hip replacement

G. Grammatopoulos,H. G. Pandit,R. da Assunção,A. Taylor,P. McLardy-Smith,K. A. De Smet,D. W. Murray,H. S. Gill

From Nuffield Orthopaedic Centre, Oxford, United Kingdom

G. Grammatopoulos, MRCS, DPhil, Orthopaedic Trainee H. G. Pandit, DPhil, FRCS(Orth), Honorary Senior Clinical Lecturer D. W. Murray, MD, FRCS (Orth), Professor Of Orthopaedic SurgeryUniversity of Oxford, NDORMS, Windmill Road, Headington, Oxford, OX3 7LD, UK.

R. da Assunção, FRCS (Tr&Orth), Consultant Orthopaedic and Trauma SurgeonWestern Sussex Hospitals NHS Foundation Trust, Lyndhurst Rd, Worthing BN11 2DH, UK.

A. Taylor, FRCS (Tr&Orth), Consultant Orthopaedic Surgeon P. McLardy-Smith, FRCS, Consultant Orthopaedic SurgeonOxford University Hospitals, Nuffield Orthopaedic Centre, Windmill Road, Headington, OX3 7LD, UK.

K. A. De Smet, MD, Consultant Orthopaedic SurgeonANCA Clinic, Xavier de Cocklaan 68/1, 9831 Sint-Martens-Latem, Deurle, Belgium.

H. S. Gill, BEng, DPhil, Professor of Healthcare EngineeringUniversity of Bath, Dept of Mechanical Engineering, Claverton Down, Bath BA2 7AY, UK.

Correspondence should be sent to Mr G. Grammatopoulos; e-mail: [email protected]

©2014 The British Editorial Society of Bone & Joint Surgerydoi:10.1302/0301-620X.96B7.32107 $2.00

Bone Joint J2014;96-B:876–83.Received 18 April 2013; Accepted after revision 31 March 2014

The orientation of the acetabular component is influenced not only by the orientation at which the surgeon implants the component, but also the orientation of the pelvis at the time of implantation. Hence, the orientation of the pelvis at set-up and its movement during the operation, are important. During 67 hip replacements, using a validated photogrammetric technique, we measured how three surgeons orientated the patient’s pelvis, how much the pelvis moved during surgery, and what effect these had on the final orientation of the acetabular component. Pelvic orientation at set-up, varied widely (mean (± 2, standard deviation (SD))): tilt 8° (2SD ±32), obliquity –4° (2SD ±12), rotation –8° (2SD ±14). Significant differences in pelvic positioning were detected between surgeons (p < 0.001). The mean angular movement of the pelvis between set-up and component implantation was 9° (SD 6). Factors influencing pelvic movement included surgeon, approach (posterior > lateral), procedure (hip resurfacing > total hip replacement) and type of support (p < 0.001). Although, on average, surgeons achieved their desired acetabular component orientation, there was considerable variability (2SD ±16) in component orientation. We conclude that inconsistency in positioning the patient at set-up and movement of the pelvis during the operation account for much of the variation in acetabular component orientation. Improved methods of positioning and holding the pelvis are required.

Cite this article: Bone Joint J 2014; 96-B:876–83.

Wide variations in the orientation of the acetab-ular component in total hip replacement (THR)are invariably reported, with measurements ofinclination and anteversion having standarddeviations (SD) of up to 10° and ranges of up to60°, even in high-volume centres.1-3 The quanti-fication of variability is difficult, as rangeincludes extreme outliers and standard devia-tion includes only about 68% of cases. Toaddress this, we have defined variability as ±2 SD,which includes about 95% of cases. With thisdefinition, the reported variability in acetabularcomponent orientation is about ±20°. This var-iability is the result of many factors such as theposition of the pelvis at the time of implanta-tion, the orientation the surgeon wants toachieve and the way that orientation is assessedpost-operatively.

The position of the pelvis at implantationdepends on the position the pelvis is placed atthe beginning of the operation and theamount of intra-operative movement. In gen-eral before commencing surgery, surgeonsaim to position the pelvis in a ‘neutral’ orien-tation relative to the operating table, so thatthe axes of the pelvis are parallel to those ofthe operating table. The patient supports are

then supposed to maintain the pelvis in thisposition during the procedure. At the time ofimplantation, the surgeon assumes the pelvisis still in a ‘neutral’ position. During non-nav-igated procedures, the precise orientation ofthe pelvis at implantation is not known andany deviation from ‘neutral’ will affect theorientation of the component that is assessedpost-operatively. If the pelvis is tilted (rota-tion around transverse axis) or rotated (rota-tion around longitudinal axis) this willprimarily influence the anteversion of thecomponent, whereas if the pelvis is oblique(rotation around antero-posterior axis), thiswill mainly influence its inclination.4 Pelvicorientation is known to vary widely both indifferent patients and situations. For exam-ple, in the physiologically supine position, thepre-operative pelvic tilt has been reported tohave a range from –24° to 10° among arthriticpatients.5

Our aims were to determine the variationin pelvic orientation as the surgeon positionsthe patient on the operating table, and toascertain the amount of pelvic movementthat takes place between set-up and introduc-tion of the acetabular component.

PELVIC POSITION AND MOVEMENT DURING HIP REPLACEMENT 877

VOL. 96-B, No. 7, JULY 2014

Patients and MethodsBetween October 2010 and November 2011, we prospec-tively recruited 67 patients to this study which had receivedethical approval from two centres (Nuffield OrthopaedicCentre, Oxford, United Kingdom and ANCA Medical Cen-tre, Ghent, Belgium). Inclusion criteria were primary sur-gery for osteoarthritis (OA), absence of fixed deformities ofthe hip and an American Society of Anaesthesiologist (ASA)grade I or II.6 Patient demographics and anthropometricparameters (weight, height and body mass index (BMI)) aredetailed in Table I. The majority of patients (n = 52, 78%)underwent THR, whereas the remaining 15 (22%) under-went hip resurfacing (HR). All patients were operated on inthe lateral decubitus position. The procedures were per-formed by three surgeons (KADS, PMS and RdA). SurgeonA was a senior clinical fellow who had performed 300THRs via the posterior approach and his target orientationof the acetabular component (inclination/anteversion) was40°/20°. Surgeon B had performed over 7000 hip replace-ments, including over 3500 HRs via the posteriorapproach, and his target inclination/anteversion was 45°/20°. Surgeon C had performed over 13 000 hip replace-ments via the lateral approach and his target inclination/anteversion was 40°/15°.

The surgeons used the same support posteriorly over thesacrum (Fig. 1) but different supports anteriorly. Surgeon Broutinely used a single support over the pubic symphysis(pubis only), surgeons A and C used a single support overthe operated anterior superior iliac spine (ASIS) (ASISx1).For the last 12 operations (six each) enrolled in the study(ASISx2) surgeons A and C were invited to place an addi-tional support over the contralateral ASIS. Details of surgi-cal practice, including prostheses used and size ofacetabular component, are included in Table I.

Intra-operative measurements. Stereophotogrammetry(SPG) allows the spatial measurement of three-dimensional(3D) objects from a pair of images.7 Common points areidentified on each image, and if the location of each camerarelative to the image plane is known, the 3D co-ordinatesand thus the location, can be determined. The 3D locationsof specific pelvic landmarks and of a guide wire drilled intothe pelvis, were captured. The position of the landmarkswere used to determine the pelvic orientation at set-up, andthe movement of the wire during surgery was used to assesssubsequent pelvic movement.

Two Logitech Webcam Pro 9000 HD cameras (Log-itech, Romanel-sur-Morges, Switzerland) were mountedon the theatre’s laminar air-flow hoods orientated atapproximately 90° to each other and arranged so that theoperating field was fully captured. All three surgeons posi-tioned patients on the operating table in the manner rou-tine to their practice, aiming to orientate the pelvisneutrally relative to the table using the frontal planedefined by the two ASISs and the pubis. The table waspositioned in the middle of the operating theatre space, asdefined by the laminar-flow hood. A calibration object,consisting of 12 spherical markers, was placed over thepatient and aligned with the operating table. Stereoscopicimages were captured using the cameras; this initial ste-reo-pair of images was used to calibrate the measurementvolume. All subsequent measurements were made in a co-ordinate frame aligned to the operating table. A customsoftware application, Fotop, written in Matlab (R2011,The MathWorks, Natick, Massachusetts) was developedto perform the measurements.

Surgeons were then asked to locate, using a wand, thespecific anatomical landmarks that they had used to alignthe pelvis and a stereo-pair of images were captured. The

Table I. Cohort demographics (means with ranges as appropriate) and surgical details for patients undergoing total hipreplacement (THR) and hip resurfacing (HR) (ASIS, anterior superior iliac spine)

Cohort (n = 67)

Type of hip surgery

THR (n = 52) HR (n = 15) p-value*

GenderMale 24 15 9 0.03Female 43 37 6 0.03

Age (years) 67.1 (41.4 to 86.8) 70.2 (46.2 to 86.8) 56.5 (41.4 to 69.1) < 0.001Height (m) 1.7 (1.5 to 1.9) 1.7 (1.5 to 1.9) 1.8 (1.7 to 1.9) 0.01Weight (kg) 72.4 (47.1 to 123.6) 72.5 (47.1 to 123.6) 72.0 (50.0 to 88.0) 0.76BMI (kg/m2) 25.5 (17.5 to 38.6) 26.0 (17.5 to 38.6) 23.2 (17.9 to 28.0) 0.07Cup size (mm) 53.5 (46 to 60) 52.8 (46 to 60) 56.3 (52 to 60) 0.001Supports

Pubis 31 16 15 < 0.001ASISx1 24 24 - < 0.001ASISx2 12 12 - < 0.001

ApproachLateral 17 17 - 0.01Posterior 50 35 15 0.01

*Mann–Whitney U test and Chi Square for supports and approach

878 G. GRAMMATOPOULOS, H. G. PANDIT, R. DA ASSUNÇÃO, A. TAYLOR, P. MCLARDY-SMITH, K. A. DE SMET, D. W. MURRAY, H. S. GILL

THE BONE & JOINT JOURNAL

landmarks captured were the two ASISs, the pubic symph-ysis (PS) and the lumbosacral junction (LSJ) (Fig. 2). Thewand was manufactured with such specifications (pointedend and length) as to allow its placement between patient’ssupports/bony landmarks and capture, even when pointingat the non-operated side. The orientation of the pelvis wasdetermined from the positions of the landmarks. In threecases, surgeons were asked to identify the pelvic landmarkstwice, with an interval of five minutes between measure-ments. Good repeatability was found with the difference inmeasurement of tilt, obliquity and rotation being 1° (SD 3°),1° (SD 2°) and 1° (SD 3°) respectively.

Patients were prepared and draped. Prior to skin inci-sion, a wire was inserted into the iliac wing of the operatedhemipelvis and a pair of images was captured, from whichthe location of the wire at the beginning of the operation(t0) could be determined. Surgery was carried out and a pairof images was captured following implantation of the ace-tabular component, with the introducer still attached andthe retractors in place, in order to measure the location ofthe wire at the time of implantation (t1). Radiographic orientation measurements. Radiographic meas-urements of the orientation of the acetabular component weremade from standardised post-operative, supine anteroposte-

rior (AP) pelvic and lateral hip radiographs. The Ein-Bild-Roentgen-Analysis (EBRA) software,8 a validated method ofestimating radiographic orientation, was used to calculateradiographic inclination (RI) and anteversion (RA) of the ace-tabular component from the AP radiographs.9,10 Measure-ments were performed independently by two observers (GG,HGP) blinded to other parameters, with excellent intra- andinter-observer correlations (inter-class correlation coefficients> 0.95, p < 0.001, 95% confidence interval (CI): 95.6 to 98.1).The mean differences in the measurements of inclination andanteversion were 0.1° (SD 1) and 0.3°(SD 2) respectively. Anal-ysis of a second set of radiographs obtained at follow-upfor 20 patients revealed an intra-subject difference of 1° (SD 1)(-1 to 3)/2° (SD 2) (-5 to 7) for inclination and anteversion ofthe acetabular component, respectively. Data analysis. From the position of the pelvic landmarksmeasured after the patient was positioned, we calculatedthe orientation of the pelvis relative to the operating theatretable. From this we determined the variability (defined as2SD) in pelvic orientation at set-up in all three planes (tilt/obliquity/rotation).

We calculated the angular pelvic movement that takesplace during the operation between set-up and implanta-tion of the orientation by capturing the wire’s orientation at

Fig. 1c

Images showing different types of support used in this study, placed according to the surgeon’s discretion. Of note, the posterior support was thesame for all cases. Figure 1a – support placed over the pubic symphysis only (pubis only). Figure 1b – support placed over the anterior superior iliacspine (ASIS) on the operated side (ASISx1). Figure 1c – support placed over both ASISs (ASISx2).

Fig. 1a Fig. 1b


VOL. 96-B, No. 7, JULY 2014

set-up (t0, prior to skin incision), and at implant impaction(t1) (Fig. 3). In addition, we investigated the effect of type ofsupport (pubis only versus ASISx1 versus ASISx2), proce-dure (HR versus THR), approach (posterior versus lateral)and surgeon on the amount of pelvic movement.

In order to determine how accurately surgeons achievedtheir desired target, we calculated Δinclination andΔanteversion for each patient as defined below:

Δinclination = Surgeon-specific inclination target – RIachieved

Δanteversion = Surgeon-specific anteversion target – RAachieved.

In addition, we determined whether surgeons hadachieved orientation within their target zone (personal ori-entation target ± 10°).Statistical analysis. Variability was defined as two standarddeviations (SD). Non-parametric statistical tests (Mann–Whitney U, Kruskal-Wallis, Spearman’s rho) were used.The chi-squared test was used for cross-tabulated data.Correlation was characterised as poor (0.00 to 0.20), fair(0.21 to 0.40), moderate (0.41 to 0.60), good (0.61 to0.80), or excellent (0.81 to 1.00). Statistical significancewas defined as p < 0.05. Statistical analyses were performed

with IBM SPSS Statistics version 19, (IBM, Chicago,Illinois).

ResultsA wide scatter of pelvic orientations at set-up was detectedfor the whole cohort, as detailed in Table II and Figure 4. Thevariability was much greater for pelvic tilt (2SD ±32°) thanpelvic rotation (2SD ±14°) and obliquity (2SD ±12°). Therewere significant differences between surgeons in the posi-tioning of the pelvis at set-up for pelvic tilt and rotation (p <0.001), but not for pelvic obliquity. For example the meantilt for surgeon B was 5º (2SD ±18), whereas for surgeon C itwas -21º (2SD ±30).

The mean amount of movement of the wire and thus ofthe pelvis that took place between set-up and implantationwas 9° (2SD ±12, (0° to 28°)). Wire movement was not influ-enced by anthropometric factors. The following surgicalfactors had a significant effect on wire movement: surgeon(p < 0.001, Kruskal–Wallis) (Fig. 5), pelvic supports(p = 0.004, Kruskal–Wallis), approach (p < 0.001, Mann–Whitney U test) and procedure type (p = 0.02, Mann–Whit-ney U test) (Fig. 5). Wire movement had a moderate correla-tion (rho = 0.45, p < 0.001) with pelvic tilt at set-up.

Fig. 2c

Photographs showing a stereo-pair of images calibrating theatre space (a and b). The surgeon identifies the bony landmark of the operated anteriorsuperior iliac spine (ASIS) (c and d) among the bony landmarks (ASISs, pubis, lumbosacral junction) (e). The wand is an aluminium rod 40 cm longon which two 10 mm diameter retro-reflective spherical markers were mounted.

Fig. 2a Fig. 2b

Fig. 2d Fig. 2e



The mean RI inclination of the acetabular componentwas 43° (2SD ±12, (28° to 55°)), and the mean RA was 19°(2SD ±14, (4° to 35°)). The mean difference between wherethe surgeon aimed to place the acetabular component and -where it ended up was 1° (2SD ±12, (–10° to 17°)) forΔinclination and 0° (2SD ±14, (–15° to 12°)) forΔanteversion. None of the anthropometric or surgical fac-tors influenced Δinclination. No anthropometric factorinfluenced Δanteversion. However, two surgical factorsinfluenced Δanteversion: type of pelvic support (p = 0.03,Kruskal–Wallis) and procedure (p = 0.006, Mann–WhitneyU test) (Tables II, III and IV). In 80% of cases, the orienta-tion of the acetabular component ended up within the sur-geon’s target zone.

To date, at a mean follow-up of 58 months (37 to 71),none of the patients have had any complications; none havereturned nor are due to return to theatre for any reason.

DiscussionWe have demonstrated a wide variation in both pelvic posi-tioning at set-up (2SD between ±12º and ±32° in differentdirections) and pelvic movement (2SD ±12º) during hipreplacement. This would lead to great variability in pelvic

orientation at implantation, and therefore variability infinal orientation of the acetabular component. Althoughthe desired target zone orientation was achieved in 80%(n = 57) of cases, there was considerable variability in bothinclination (2SD ±12°) and anteversion (2SD ±14º).

The wide variation in pelvic orientation is due to bothpatient and surgical factors. The greatest variability in pel-vic orientation was in tilt (rotation around the transverseaxis). Our measured pelvic tilt angles were higher than havebeen previously reported.5,11,12,13 This may be because tiltangles have typically been measured with the patient inphysiological positions such as supine, standing or sitting.Surgeon B positioned the pelvis closest to neutral, with theleast amount of pelvic tilt and had the least variability. Thisis probably because he was the only surgeon who assessedthe position of the pubic symphysis as well as both ASISs,all of which have to be identified to determine pelvic tilt. Hedid this as he was the only surgeon to use a support over thepubis symphysis. We therefore recommend that during set-up, surgeons should routinely assess for pelvic tilt by pal-pating both ASISs and the symphysis pubis. The position ofthe posterior support in the cranio-caudal direction alongthe lumbosacral spine varies amongst surgeons, and influ-

Stereo-pair images demonstrating the amount of pelvic movement that occurs between set-up (a and b) and implantation of the acetabular compo-nent (c and d)

Fig. 3a Fig. 3b Fig. 3c Fig. 3d

Table II. Pelvic orientation at set-up, amount of pelvic movement during surgery, radiographic orientations of the acetabular compo-nent and Δinclination / anteversion for the whole cohort and per surgeon (data presented as mean, standard deviation (SD) and range)

Cohort (n = 67) mean/SD (range)

Surgeons

Surgeon A (n = 19) mean/SD (range)

Surgeon B (n = 31) mean/SD (range)

Surgeon C (n = 17) mean/SD (range) p-value*

Pelvic tilt (°) –8/16 (–50.0 to 29) –16/10 (–35 to –3) 5/9 (–18 to 29) –21/15 (–50 to –2) < 0.001Pelvic obliquity (°) –4/6 (–19 to 8) –4/6 (–13 to 5) –2/4 (–11 to 8) –6/7 (–19 to 7) 0.09Pelvic rotation (°) –8/7 (–27 to 4) –7/6 (–17 to 0) –5/5 (–18 to 4) –13/6 (–27 to –3) < 0.001Wire movement (°) 9/6 (0 to 28) 8/5 (2 to 22) 13/6 (5 to 28) 4/3 (0 to 11) < 0.001Radiographic inclination (°) 43/6 (28 to 55) 40/6.0 (28 to 49) 46/4 (36 to 55) 39/6 (28 to 47) < 0.001Radiographic anteversion (°) 19/7 (34 to 35) 22/7 (12 to 35) 19/6 (8 to 35) 14/8 (4 to 30) 0.009Δinclination (°) –0/5 (–10 to 17) 0/6 (–8 to 12) –1/4 (–10 to 10) 1/6 (–7 to 17) 0.67Δanteversion (°) 0.0/7 (–15 to 12) –2/7 (–15 to 9) 1/6 (–15 to 12) 1/8 (–15 to 11) 0.24Within individual target zone n (%) 57 (80) 14 (74) 29 (94) 14 (82) 0.15

* Kruskal–Wallis for scale, chi-squared for categorical


VOL. 96-B, No. 7, JULY 2014

ences pelvic tilt. By adjusting its position, surgeons shouldbe able to minimise pelvic tilt.

The operated hemipelves tended to be externally rotatedat set-up. This was most pronounced with the single ASISsupport (–11°, 2SD ±12º) compared with the double ASIS(–7°, 2SD ±14º) or the pubis only (–5°, 2SD ±10º) supports(p = 0.02). This is not surprising, as a single support overthe operated ASIS used in combination with a posteriorsupport over the lumbosacral spine would tend to exter-nally rotate the pelvis. It is therefore recommended that asingle ASIS support is not used.

A considerable change in pelvic position intra-opera-tively was detected, similar to previous findings of Asayamaet al,14 who reported that internal rotation is the primarymovement that takes place during THR. Although patientfactors did not influence pelvic movement, surgical factors

did, in particular pelvic support, approach and type of pro-cedure. Although these factors are interrelated and surgeondependent, significant differences were identified evenwhen these factors were uncoupled. The support with theleast constraint anteriorly, i.e. the pubis-only support, dem-onstrated the greatest amount of pelvic movement amongstTHRs. In contrast, the use of supports over both the ASISsanteriorly significantly reduced the amount of movementthat takes place. We therefore recommend that surgeonsconsider having at least two supports anteriorly, therebyachieving three-point stabilisation and increasing pelvicconstraint. Like Ezoe et al,15 we identified significantlymore intra-operative movement with the posteriorapproach (mean 9°) than with the lateral approach (mean4°) in THR. During the posterior approach, the intactstrong anterior capsule and iliofemoral ligament, coupled

25

15

5

-5

15

-25

-35

-45

-55

Am

ou

nt

(°)

Tilt Obliquity RotationPelvic Axis

40

20

0

-20

-40

-60

Pelv

ic t

ilt/ (

°)

Surgeon A Surgeon B Surgeon C

10

5

-10

-5

-10

-15

-20

Pelv

ic o

blii

qu

ity/

(°)


10

0

-1

-20

-30

Pelv

ic r

ota

tio

n/ (

°)


Fig. 4a

Box plots showing the scatter of pelvic orientations for pelvic tilt, obliquity and rotation for the whole cohort (a), and analysis of each orientationaccording to surgeon (b, c and d).

Fig. 4c Fig. 4d

Fig. 4b



with the strong retraction and the leg-twisting manoeuvre,probably apply an increased torque to the pelvis.

We also found that the type of procedure influenced theamount of intra-operative pelvic movement. Analysing theprocedures of surgeon B only, (hence eliminating factorsrelating to surgeon, approach and supports), we found asignificantly greater amount of intra-operative pelvic move-ment for HRs than for THRs (means, 16° versus 10°)(p = 0.02). This is not surprising, as in HRs the intact fem-oral head and neck obscure the acetabulum, and hencegreater retraction is needed for an adequate view.

The variability in orientation of the acetabular compo-nent (±12° to ±14°) was similar to the variability in pelvicrotation and obliquity at set-up (±12° to ±13°), but wasmuch less than the variability in tilt (±32°). This consistencyin terms of tilt is an encouraging finding, demonstratingthat surgeons are able to account in part for pelvic tilt dur-

ing the operation. It is not clear how they do this. Surgeonstend to set the pelvis up with different amounts of tilt, pre-sumably because they position their supports differently. Byreviewing their post-operative radiographs, they probablylearn how to implant the components so as to optimise theorientation for their setup. They may also use intra-opera-tive landmarks such as the transverse acetabular ligament(TAL) to aid component positioning.

This study has certain limitations. First, the pelvic orien-tation was determined by surgeons identifying landmarks,which may not be accurate. However the repeatabilitystudy suggests that the errors introduced by this amountedto about ±5°, which is much less than the variability in pel-vic position. Second, although the software (Fotop) wasable to calculate the angular movement of the pelvis, it wasnot able to determine the 3D direction of movement basedon measurements from a single wire.

30

20

10

0

Wir

e m

ovem

ent

(sta

rt t

o im

pla

nta

tio

n)/

(°)


Fig. 5a

a) Box and whisker plot showing the amount of pelvic movement measured for the different surgeons, b) showing the amount of pelvic move-ment measured for the different supports (pubis only, only one anterior superior iliac spine (ASISx1) and ASISx2 (both), c) showing the amountof pelvic movement measured for the different approaches (posterior and lateral), d) showing the amount of pelvic movement measured for thedifferent procedures (total hip replacement (THR) and hip resurfacing (HR). The box demonstrates the inter-quartile range (IQR) and the bandis the median. Ends of the whiskers represent the lowest and highest datum within 1.5 IQR of the lower and upper quartiles respectively (TukeyBoxplots).

30.00

20.00

10.0

0Wir

e m

ovem

ent

(sta

rt t

o im

pla

nta

tio

n)/

(°)

One x ASIS 2 x ASIS Pubis only

30

20

10

0

Wir

e m

ovem

ent

(sta

rt t

o im

pla

nta

tio

n)/

(°)

Posterior Lateral

30

20

10

0

Wir

e m

ovem

ent

(sta

rt t

o im

pla

nta

tio

n)/

(°)

THR HR

Fig. 5b

Fig. 5c Fig. 5d


VOL. 96-B, No. 7, JULY 2014

In conclusion, this study demonstrated wide variations inpelvic orientation, particularly tilt, at set-up for any givensurgeon and between surgeons. Also substantial amountsof pelvic movement occurred during surgery. These findingsexplain, at least in part, the variation seen in post-operativeorientations of acetabular components. In order to mini-mise this variability, we recommend that surgeons carefullyposition the pelvis at set-up, taking particular note of tiltassessed by the relative position of the symphysis pubis andASISs. We also recommend the use of improved supportsand increased care with retraction and leg twisting duringthe posterior approach and hip resurfacing, in order to min-imise pelvic movement during surgery.

Supplementary materialA detailed explanation of planes defined, calcula-tions made, validation of technique, and a mathe-

matical analysis quantifying possible inaccuracies due towand misplacement, is available with the electronic versionof the article at www.bjj.boneandjoint.org.uk.

The authors wish to thank V. Flanagan, J. Brown and B. Marks for their assis-tance with this study. Financial support was received from Stryker, UK. DWMwas in receipt of an NIHR Senior Investigator Award.

Although none of the authors has received or will receive benefits for per-sonal or professional use from a commercial party related directly or indirectlyto the subject of this article, benefits have been or will be received but will bedirected solely to a research fund, foundation, educational institution, or othernon- profit organisation with which one or more of the authors are associated.

This article was primary edited by D. Rowley and first proof edited by G. Scott.

References1. Callanan MC, Jarrett B, Bragdon CR, et al. The John Charnley Award: risk factors

for cup malpositioning: quality improvement through a joint registry at a tertiary hos-pital. Clin Orthop Relat Res 2011;469:319–329.

2. Grammatopoulos G, Pandit H, Glyn-Jones S, et al. Optimal acetabular orienta-tion for hip resurfacing. J Bone Joint Surg [Br] 2010;92-B:1072–1078.

3. Langton DJ, Joyce TJ, Jameson SS, et al. Adverse reaction to metal debris fol-lowing hip resurfacing: the influence of component type, orientation and volumetricwear. J Bone Joint Surg [Br] 2011;93-B:164–171.

4. Murray DW. The definition and measurement of acetabular orientation. J Bone JointSurg [Br] 1993;75-B:228–232.

5. Babisch JW, Layher F, Amiot LP. The rationale for tilt-adjusted acetabular cupnavigation. J Bone Joint Surg [Am] 2008;90-A:357–365.

6. Dripps SR. New classification of physical status. Anesthesiol 1963; 24:111.7. Linder W. Digital Photogrammetry - A practical course. Vol. 1, Third ed. Dusseldorf:

Springer Berlin Heidelberg, 2009:220.8. Krismer M, Bauer R, Tschupik J, Mayrhofer P. EBRA: a method to measure

migration of acetabular components. J Biomech 1995;28:1225–1236.9. Langton DJ, Sprowson AP, Mahadeva D, et al. Cup anteversion in hip resurfac-

ing: validation of EBRA and the presentation of a simple clinical grading system. JArthroplasty 2010;25:607–613.

10. Wilkinson JM, Hamer AJ, Elson RA, Stockley I, Eastell R. Precision of EBRA-Digital software for monitoring implant migration after total hip arthroplasty. JArthroplasty 2002;17:910–916.

11. DiGioia AM, Hafez MA, Jaramaz B, Levison TJ, Moody JE. Functional pelvic ori-entation measured from lateral standing and sitting radiographs. Clin Orthop RelatRes 2006;453:272–276.

12. Nishihara S, Sugano N, Nishii T, Ohzono K, Yoshikawa H. Measurements ofpelvic flexion angle using three-dimensional computed tomography. Clin Orthop RelatRes 2003;411:140–151.

13. Zhu J, Wan Z, Dorr LD. Quantification of pelvic tilt in total hip arthroplasty. ClinOrthop Relat Res 2010;468:571–575.

14. Asayama I, Akiyoshi Y, Naito M, Ezoe M. Intraoperative pelvic motion in total hiparthroplasty. J Arthroplasty 2004;19:992–997.

15. Ezoe M, Naito M, Asayama I, Ishiko T, Fujisawa M. Pelvic motion during totalhip arthroplasty with translateral and posterolateral approaches. J Orthop Sci2005;10:167–172.

Table III. The effect of different surgical factors on pelvic movement intra-operatively and inclination/anteversion (I and A) (ASIS, anterior supe-rior iliac spine; SD, standard deviation)

Wire movement (°) mean/SD (range) p-value

∆I (°) mean/SD (range) p-value ∆A (°) mean/SD (range) p-value

Approach Lateral (n = 17) 4/3 (0 to 11) < 0.001 1/6 (–7 to 17) 0.54 1/8 (–14 to 11) 0.59Posterior (n = 50) 11/6 (2 to 28) < 0.001 –1/5.0 (–10 to 12) 0/6 (–15 to 12) 0.59

Supports Pubis (n = 31) 7/5 (0 to 22) < 0.001 1/6 (–8 to 17) 0.42 1/6 (–15 to 12) 0.03ASISx1 (n = 24) 13/6 (5 to 28) < 0.001 –1/4 (–10 to 10) 0.42 -3/7 (-15 to 10) 0.03ASISx2 (n = 12) 5/3.0 (0 to 12) < 0.001 –1/5 (–8 to 6) 0.42 3/6 (–10 to 11) 0.03

Table IV. Pelvic measurements and those of orientation of the component for total hip replacements (THRs) and hipresurfacings (HRs) performed by surgeon B (SD, standard deviation)

Procedure THR (n = 16) mean/ SD* (range) HR (n = 15) mean/SD (range) p-value*

Wire movement (°) 10/1 (5 to 17) 16/7 (7 to 28) 0.02Radiographic inclination (°) 46/5 (36° to 55) 46/4 (40 to 52) 0.91Radiographic anteversion (°) 22/6.0 (12 to 35) 16/4 (8 to 21) 0.002Δinclination (°) –1/5 (–10 to 10) –1/4 (–7 to 5) 0.9Δanteversion (°) –2/6 (–15 to 8) 4/4 (–1 to 12) 0.003Within individual target zone n (%) 15 (94) 14 (93) 0.9

hip pelvic position and movement during hip replacement€¦ · > lateral), procedure (hip...

Documents