The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

1

A Patient-Specific Predictive Model Increases Preoperative Templating

Accuracy in Hip Arthroplasty.

Amir Pourmoghaddam, PhD; Marius Dettmer, PhD; Adam M. Freedhand, MD; Brian C.

Domingues, BSc.; Stefan W. Kreuzer, MD, MSc.

Affiliation:

Memorial Bone & Joint Research Foundation, Department of Orthopaedic Surgery, The

University of Texas Health Science Center at Houston – Medical School

1140 Business Center Drive, Suite 101

Houston, TX 77043

This is author’s version. For publisher version please visit:

http://www.arthroplastyjournal.org/article/S0883-5403(14)00897-3/abstract

Abstract:

Application of digital radiography during preoperative templating has shown potential to reduce

complications in total hip arthroplasty. Digital radiography has significantly improved this process.

In this study, we aimed to further improve the digital templating by using a predictive model built

on patients’ specific data. The model was significant in improving the accuracy of templating

within +/-1 size of acetabular component (2(1, 𝑁 = 468) = 19.314, p<0.0001, =0.604, and

odds-ratio: 7.750 (95% CI 2.740-30.220)). We successfully achieved a 99% accuracy within +/- 2

of templated size. Additionally, patient demographics, such as height and weight, have shown

significant effects on the predictive model. The outcome of this study may help reducing the costs

of health care in the long term by minimizing implant inventory costs for each patient.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

2

Introduction:

Preoperative planning in total hip replacement is an essential part of the procedure [1,2] because

it prepares the surgical team and significantly reduces the surgical time by minimizing potential

complications [3]. The utilization of digital radiography in clinical settings has grown significantly

in the past few years. This technique is being used more commonly as a financially sound

alternative compared to analogue radiography, as it provides the opportunity to store an unlimited

number of images while reducing the costs of film storage and the need for recycling [4]. In

addition, advanced computer programs have been developed to analyze the obtained digital

information [5].

Historically, templating accuracy, particularly when utilizing analog radiography, has been

reported to be relatively low; recently, the literature shows that digital templating can be successful

in identifying the implant size within +/- 2 implant sizes [3–13]. In this study, we aimed to further

improve the accuracy of predicting the implant size in total hip replacement by considering some

anthropometric characteristics of the patient.

In today’s digital world, due to the costs associated with expanding implant options and inventory

management, digital templating could be of great benefit for surgical preparation and for reducing

inventory in the field, thereby decreasing the overall cost of THA. Proper surgical preparation,

including digital templating, can reduce surgical time and potential complications, but digital

templating is rarely utilized to manage inventory flow in the field. Accurate templating requires

proper patient positioning and standardized X-ray techniques to generate images of sufficient

quality. A major concern with templating, particularly computer-assisted, image-processing

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

3

software, is the issue of “inaccurate magnification ratio.” Generally with computer-assisted

templating, an initial 20% magnification of the image is assumed. This ratio can be affected by

patient-related factors, such as obesity and body habitus, or technical factors, such as the distance

of the X-ray tube to the joint being X-rayed. Traditional preoperative planning utilizes a tube-to-

film a distance of 48 inches for X-ray imaging, resulting in an estimated magnification of 20%

compared to the actual size. However, the accuracy of such magnification has been questioned and

can vary widely [4]. Traditional templates provided by implant manufacturers come in different

magnifications and are overlaid on standard X-rays to provide the templated implant size. A similar

concept is utilized in digital radiography, in which the digital radiographs are adjusted for

magnification by utilizing a magnification marker or a constant magnification ratio and software

is used to create digital overlays of implant sizes to select the appropriate size and orientation of

the component. Error! Reference source not found. summarizes some of the recent studies

conducted in different institutions representing the relationship between the preoperative

templating and the actual implant sizes used for the patients. Although many of the previous studies

indicated high accuracy, other studies have raised concerns about relying on the outcome of

templating. Efe et al. reported that, in approximately 9% (15 out of 169) of their cases, the

intraoperative implant size could not be predicted, even within 2 sizes [14]. These concerns have

inspired our research to find other factors that might facilitate and improve the accuracy of

preoperative templating. Thus, the main goal of this study was to improve accuracy of preoperative

templating by using a predictive model that includes patient-specific demographics (i.e., height,

weight, Body Mass Index (BMI). Thus, the purpose of this study was to develop a prediction model

to enhance the accuracy of preoperative digital templating by considering a multitude of patient

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

4

variables, such as height, age, sex, BMI, etc. We hypothesized that anthropometric variables

impact the accuracy of the preoperative templating size of acetabular and femoral components.

Table 1 – Examples of previous studies investigating the accuracy of preoperative templating of femoral and

acetabular components.

Study Exact Size (%) ± 1 size (%) ± 2 size (%)

Total Femoral Acetabular Femoral Acetabular Femoral Acetabular

Whiddon et. al (2011) –

Digital

51 61 39 90 78 96 96

Whiddon et. al (2011) –

Manual measurement

51 33 31 82 67 100 88

Shaarani et. al(2013) 100 38 36 80 75 98 98

Maratt (2012) 20 NA NA 75 73 93 96

Maratt (2012) – Acetate 20 NA NA 93 63 98 86

Methods:

A retrospective review of preoperative radiographs for 468 individuals (224 females/ 244 males)

who received total hip arthroplasty was conducted. The preoperative templated sizes were

compared to actual implant sizes used at the time of surgery. The data was collected from August

2012 to December 2013 at a single institution.

The average age was 59.96 ±12.50 years, 436 diagnosed with osteoarthritis, 53 with avascular

necrosis, 13 with failed THA, 2 with infection, 4 post trauma, and 13 with failed hemi arthroplasty.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

5

All patients underwent direct anterior total hip arthroplasty. The level of the femoral osteotomy

was performed based on preoperative templating. Acetabular reaming and cup impaction was

performed in standard fashion. Supplemental screw fixation was utilized when needed. The final

acetabular component size was selected based on the final reamer size and a quality press fit in the

bleeding bone. An attempt was made to restore the native hip center of rotation in all cases. During

the study period, two different implant manufacturers for the acetabular component (Stryker

Orthopedics and Corin Inc.) were utilized. Acetabular reaming was performed according to the

manufacturers’ recommendation to achieve a solid interference fit.

All preoperative radiographs were taken with a standardized X-ray source-to-image distance of 1

m when the patients were at the standing position. All radiographs were taken by a single team of

radiology technicians. However, no magnification marker was used in these radiographs for the

purpose of referencing.

For THA templating in the anteroposterior view the pelvis image was centered over the pubic

symphysis, while the hip was internally rotated between 10° to 15°. Figure 1 depicts a sample of

the templated joints that was used in predicting the implant size. The digital radiographs were all

analyzed utilizing the TraumaCadTM software system (TraumaCad, BRAINLAB, Westchester, IL,

USA) [15]. The initial implant model was adjusted and magnified by a factor of 120% to provide

an acceptable overlay on the hip joint. All intraoperative data was collected prospectively using

online, web-based, data-entry software from an IRB-approved joint registry (IRB # HSC-GEN-

09-0143), including the final implant sizes selected by the surgeon.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

6

Figure 1 – A sample of templated hip joints by using TraumaCadTM

Statistical model

A multiple regression model was used to develop the predictive model and to investigate the

contribution of each factor to the model to predict the actual size of the implant from the

preoperative measurements. These variables included, preoperative acetabular size, preoperative

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

7

femoral size, body mass index (BMI), age, gender, height, and weight. In each model, a backward

stepwise algorithm was used to identify the variables, resulting in significant model demonstration.

This algorithm initially enters all variables into the model but systematically removes the

predictors that do not have significant contribution in defining the changes in the model. In

addition, we used a multiple regression model that include all the variables of interest in this study

to explore their effects as well and provide a more standardized equation for future studies. Finally,

to assess the improvement in the accuracy of the templating we used a nonparametric McNemar’s

test to compare the binomial accuracy outcome (i.e., Yes vs. No) between the templating alone

method versus utilizing the model. The effect size and odds ratio of the McNemar’s test was

calculated for the significant differences. In the cases in which the number of cells in the

McNemar’s test was less than 5 we used an exact McNemar’s test. A significance level of .05 was

assumed in this study. The analysis was conducted by using SPSS 21.0.0 (SPSS Inc., Chicago,

Illinois, USA).

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

8

Results:

Table 2 includes the demographics of the individuals who participated in this study.

Table 2- patients’ preoperative and intraoperative measurements.

Average SD

Age (years) 61.01 12.50

Height (cm) 172 10.67

Weight (kg) 84.83 20.13

BMI 28.5 5.26

Tempalated Acetabulum size (mm) 54.63 4.07

Tempalated Femoral size (mm) 4.73 1.81

Actual Acetabulum size (mm) 55.61 3.77

Actual Femoral size (mm) 4.82 1.77

The Acetabular component

The backward stepwise model has demonstrated that, for the acetabular component size, four

significant predictors were achieved, which were templated acetabulum size, height, BMI, and

templated femoral size. This model had the 𝑅2 = .0.797 with Adjusted 𝑅2 = .795 with standard

error of (𝑆𝐸 = 1.726). Gender and weight were not significant factors in this model. The outcome

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

9

of a full regression model is demonstrated in the acetabular model, in which gender and weight

are also included in the prediction.

Acetabular component model

𝐴𝑐𝑡𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 = 4.532 + 0.661 × 𝐴𝑐𝑡𝑇𝑒𝑚𝑝 + 0.202 × 𝐹𝑒𝑚𝑇𝑒𝑚𝑝 + 0.067 × 𝐻𝑒𝑖𝑔ℎ𝑡 − 0.024 × 𝑊𝑒𝑖𝑔ℎ𝑡

+ 0.138 × 𝐵𝑀𝐼 +

In which 𝐴𝑐𝑡𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 is the estimated size of acetabulum cup, 𝐴𝑐𝑡𝑇𝑒𝑚𝑝 is the preoperative

templated acetabulum size from digital radiography, 𝐹𝑒𝑚𝑇𝑒𝑚𝑝 is the preoperative templated

femoral size, and is the residual error term. Gender is defined as a binomial variable (Female =

0 and Male = 1).

This model resulted in an estimated acetabular size of 54.96 ±3.41 mm. This model was significant

overall to predict the acetabular size (Mean Square = 1331.40, F(6,461) = 302.338, p <.0001).

The Femoral component

The backward stepwise model indicated that the femoral component size could only be

significantly determined by the preoperative femoral component measurements. This model had a

𝑅2 = .727 with Adjusted 𝑅2 = .723 and standard error of (SE=0.935). Femoral component model

was developed based on a fully factored model, including the preoperative measurements of the

patients to develop a prediction model for estimating the femoral size.

Femoral component model

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

10

𝐹𝑒𝑚𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 = 3.387 + 0.016 × 𝐴𝑐𝑡𝑇𝑒𝑚𝑝 + 0.814 × 𝐹𝑒𝑚𝑇𝑒𝑚𝑝 − 0.018 × 𝐻𝑒𝑖𝑔ℎ𝑡 + 0.018 × 𝑊𝑒𝑖𝑔ℎ𝑡

− 0.061 × 𝐵𝑀𝐼 +

In which 𝐹𝑒𝑚𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 is the estimated size of the femoral stem.

This model resulted in an estimated femoral size of 4.82 ±1.51 mm. This model was significant

overall to predict the femoral size (Mean Square = 178.32, F(6,460) = 204.152, p <.0001).

Figure 2 – The accuracy of the model to retrospectively predict the implant sizes in the current study. The femoral

component size was predicted accurately in 97.2% of cases of within ±2 size and more than 99.1% for acetabular

component size within ±2 size.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

11

For the acetabular component, two cases were predicted within +/- 3 size and two cases were

predicted within +/-4 size. However, for the femoral component, the model predicted with less

accuracy, and in 11 cases the implant size was correctly predicted in +/- 3 size and in two cases

within +/- 4 size as depicted in Figure 3.

Figure 3 – The distribution of the prediction error for both Acetabulum cup size and femoral stem size.

Accuracy improvements

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

12

The results of the McNemar’s test and McNemar’s exact test are summarized in Appendix 1. The

outcomes suggest that using the model overall improved accuracy of the templating as summarized

in

Table 3. The improvement in accuracy was significant in the acetabular component within +/- 1 size

(2(1, 𝑁 = 468) = 19.314, p<0.0001, =0.604, and odds-ratio: 7.750 (95% CI 2.740-30.220)).

The details of the test and cross-tab tables are presented in the Appendix.

Discussion:

The use of digital radiography and preoperative templating is increasingly common and can

improve the success of joint replacement surgery [3]. Pre-surgical planning is critical in the

performance of joint replacement surgery and should be used to optimize patient outcomes. Pre-

surgical planning can also be used to enhance OR efficiency and implement cost savings through

inventory and supply chain management. Operating room efficiency depends on a coordinated

team effort, the use of specialized equipment, and the shared knowledge of pertinent patient

information. We routinely use preoperative templating to streamline our surgical efforts, minimize

the use of unnecessary equipment, optimize patient outcomes, and minimize cost.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

13

In this study we used a multiple regression model to identify factors that would allow us to predict

component size during hip replacement surgery to within +/- 1 size. For the acetabulum, the

significant factors were the templated acetabular size, templated femoral size, weight, and height.

For the femoral component, the preoperative femoral templating was the only significant factor.

In our retrospective review of 468 patients, the exact acetabular implant size was identified by the

model with an accuracy of 48.93%, which was slightly higher than results achieved by using only

preoperative digital templating size to predict the exact acetabular cup size (i.e., 48.08%).

Application of the model was further justified when the gap between the accuracy of identifying

proper acetabular cup within +/- 1 size of the actual implant was improved significantly by utilizing

the model. This statistically significant increase was a more than 5% improvement (27 cases in

this study). The high effect size of the findings (indicated by >0.4) and the significance of the

improvement suggest that utilizing the model will enhance the accuracy of preoperative

templating.

Table 3 depicts the improvement in accuracy of identifying the appropriate acetabular size while

using the model. Similar outcome was found in predicating the actual femoral stem size, and the

application of the model improved the accuracy of identifying the proper size (

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

14

Table 3).

Our results resemble the findings of Della Valle et al., who reported 99% prediction within one

size for the acetabular component and 99% within two sizes for the femoral component [16]. Our

results were similar to previous studies, including those conducted with TraumaCad [10].

Table 3 depicts the differences between the predicted model versus the actual implant size

(acetabular and femoral). The error is larger in the acetabular cup size. This may be due to the

limited number of commercially available acetabular cup sizes.

Table 3 – The accuracy of the identifying the proper implant component size while utilizing the model versus the

preoperative templating size. Total number of cases was 468.

Acetabular component size

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

15

Method Exact ±1 size ±2 size

N % N % N %

Model 229 48.93 437 93.38 464 99.13

Preop Size 225 48.08 410 87.60 462 98.70

Change 4 0.85 27 5.77 2 0.43

Femoral Component Size

N % N % N %

Model 216 46.15 415 88.74 462 98.7

Preop Size 209 44.65 414 88.52 460 98.48

Change 5 1.07 1 0.22 2 0.44

In our study we were limited by the total number of personnel who performed the preoperative

templating; hence, we were not able to evaluate the interrater reliability factor and measure

potential errors that may be added to the model if different evaluators are used such as those

reported by Maratt et al. [8]. However, our assumption in the current study was that the

employment of digital radiography and application of standard templating techniques could

minimize this potential error. Future studies may focus on retrospectively estimating

preoperative implant sizes by using different trained technicians. Another limitation is in the

difficulty in templating patients with severe bone loss or proximal femoral or acetabular

deformity. We analyzed the patients whose predicted model was more than +/- 2 sizes different

from the actual implant size used at the time of surgery and found that, in each case, there was

severe distortion of the hip anatomy that made templating difficult and subsequently inaccurate.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

16

An example of such case is depicted in

Figure 4. These cases typically required preoperative CT scan to assess the anatomy, assess bone

stock for implant fixation, and identify specific component needs (i.e., augments, cages, revision

stems, and the need for bone grafting). Thus, employing preoperative templating should be used

with caution in more complex cases in which the hip anatomy is severely distorted.

All cases were templated the week before the actual procedure. Single instrument trays were

prepared, consisting of a basic set of surgical tools in addition to the specifically sized implants

and size-matched tools. Only specifically required instruments were standard components of the

tray. Additionally, there was a general backup set in case of significantly inaccurate templating

results (size according to templating off by more than two sizes). However, there was a 99%

success rate using the templating technique, which meant the backup was rarely required.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

17

Figure 4 – Anterior-posterior view X-ray of an example case that was not templated within 2 implant sizes. The

margins of the acetabulum and femoral head are not clearly shown in the X-ray due to severe deformity of the limb.

In conclusion, this study presented a prediction model to better estimate the actual size of implants.

We routinely use this information to create patient-specific trays to simplify patient care, improve

OR efficiency, and optimize patient outcomes. This practice can also produce significant cost

savings in the delivery of joint replacement care.

Acknowledgements

The authors would like to thank Mr. David Balderree for his assistance with preparing the collected

data. We would also like to thank Mr. Brian Caballero and Ms. Lauren Hennecke for their

assistance with pre and post-operative data collection. Finally, we are grateful to Dr. Ashish Arya

for assistance with editing this manuscript and providing insightful comments.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

18

Appendix

Femoral

Exact Size

Model

Accurate

No Yes

Templated

Acc

ura

cy

No 235 24

Yes 17 192

(2(1, 𝑁 = 468) = 0.878, p=0.3487)

+/- 1 Femoral Size

Model

Accurate

No Yes

Templated

Acc

ura

cy

No 48 6

Yes 5 409

Exact McNemar’s test results indicated that the two-sided probability was p=.5 thus in +/- 1 size no

significant improvement was provided by the model.

𝑝 = 2 × (116

) × 0.52 × 0.50 = 0.45

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

19

+/- 2 Femoral Size

Model

Accurate

No Yes

Templated A

ccura

cy

No 6 2

Yes 0 460

Exact McNemar’s test results indicated that the two-sided probability was p=.5 thus in +/- 2 size no

significant improvement was provided by the model.

𝑝 = 2 × (22

) × 0.52 × 0.50 = 0.5

Acetabular

Exact Size

Model

Accurate

No Yes

Templated

Acc

ura

cy

No 198 45

Yes 41 184

(2(1, 𝑁 = 468) = 0.105, p=7463)

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

20

+/- 1 Size

Model

Accurate

No Yes

Templated A

ccura

cy

No 27 31

Yes 4 406

(2(1, 𝑁 = 468) = 19.314, p<0.0001, =0.604, and odds-ratio: 7.750 (95% CI 2.740-30.220))

+/- 2 Acetabular Size

Model

Accurate

No Yes

Templated

Acc

ura

cy

No 2 4

Yes 2 460

Exact McNemar’s test results indicated that the two-sided probability was p=.5 thus in +/- 2 size no

significant improvement was provided by the model.

𝑝 = 2 × (64

) × 0.52 × 0.50 = 0.47

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

21

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

22

Reference

[1] Valle A Della. Preoperative planning for primary total hip arthroplasty. J Am …

2005;13:455–62.

[2] Eggli S, Pisan M, Müller ME. The value of preoperative planning for total hip

arthroplasty. J Bone Joint Surg Br 1998;80:382–90.

[3] Davila J a, Kransdorf MJ, Duffy GP. Surgical planning of total hip arthroplasty: accuracy

of computer-assisted EndoMap software in predicting component size. Skeletal Radiol

2006;35:390–3. doi:10.1007/s00256-006-0106-4.

[4] Pullen WM, Whiddon DR. Accuracy and reliability of digital templating in primary total

hip arthroplasty. J Surg Orthop Adv 2013;22:148–51.

[5] Shaarani SR, McHugh G, Collins D a. Accuracy of digital preoperative templating in 100

consecutive uncemented total hip arthroplasties: a single surgeon series. J Arthroplasty

2013;28:331–7. doi:10.1016/j.arth.2012.06.009.

[6] Iorio R, Siegel J, Specht LM, Tilzey JF, Hartman A, Healy WL. A comparison of acetate

vs digital templating for preoperative planning of total hip arthroplasty: is digital

templating accurate and safe? J Arthroplasty 2009;24:175–9.

doi:10.1016/j.arth.2007.11.019.

[7] Whiddon DR, Bono J V, Lang JE, Smith EL, Salyapongse AK. Accuracy of digital

templating in total hip arthroplasty. Am J Orthop (Belle Mead NJ) 2011;40:395–8.

[8] Maratt JD, Srinivasan RC, Dahl WJ, Schilling PL, Urquhart AG. Cloud-based

preoperative planning for total hip arthroplasty: a study of accuracy, efficiency, and

compliance. Orthopedics 2012;35:682–6. doi:10.3928/01477447-20120725-05.

[9] Steinberg EL, Eitan S. Pre-operative Planning Using the Traumacad TM Software System.

US Radiol 2010;2:87–90.

[10] Steinberg EL, Shasha N, Menahem A, Dekel S. Preoperative planning of total hip

replacement using the TraumaCadTM system. Arch Orthop Trauma Surg 2010;130:1429–

32. doi:10.1007/s00402-010-1046-y.

[11] Wedemeyer C, Quitmann H, Xu J, Heep H, von Knoch M, Saxler G. Digital templating in

total hip arthroplasty with the Mayo stem. Arch Orthop Trauma Surg 2008;128:1023–9.

doi:10.1007/s00402-007-0494-5.

The Journal of Arthroplasty

Available online 26 November 2014 doi:10.1016/j.arth.2014.11.021

23

[12] Hossain M, Lewis J, Sinha a. Digital pre-operative templating is more accurate in total hip

replacement compared to analogue templating. Eur J Orthop Surg Traumatol

2008;18:577–80. doi:10.1007/s00590-008-0356-z.

[13] Gamble P, de Beer J, Petruccelli D, Winemaker M. The accuracy of digital templating in

uncemented total hip arthroplasty. J Arthroplasty 2010;25:529–32.

doi:10.1016/j.arth.2009.04.011.

[14] Turgay E, ZAyAT B El. Precision of preoperative digital templating in total hip

arthroplasty. Acta Orthopædica … 2011;77:616–21.

[15] King RJ, Makrides P, Gill J a, Karthikeyan S, Krikler SJ, Griffin DR. A novel method of

accurately calculating the radiological magnification of the hip. J Bone Joint Surg Br

2009;91:1217–22. doi:10.1302/0301-620X.91B9.22615.

[16] González Della Valle A, Slullitel G, Piccaluga F, Salvati E a. The precision and usefulness

of preoperative planning for cemented and hybrid primary total hip arthroplasty. J

Arthroplasty 2005;20:51–8. doi:10.1016/j.arth.2004.04.016.