escanometria

137

Scanometry of lower extremities: revisiting Dr. Juan Farill

Radiol Bras 2007;40(2):137–141

Radiology Education

SCANOMETRY OF LOWER EXTREMITIES: REVISITING

DR. JUAN FARILL*

Henrique Zambenedetti Werlang1, Gabriel Antônio de Oliveira2, Ana Maria Tamelini3,

Ben Hur Madalosso1, Francisco da Silva Maciel Júnior4

Orthoradiographic measurement employing the “Farill technique” is a routine study in the majority of radio-

logical services. For more than half a century, this method has been widely utilized by specialists in several

areas for both measuring and treating differences in length between lower extremities. Nevertheless, tech-

nical procedural details during examination and measurements evaluation have usually been neglected or

ignored, affecting the final results and consequently the effectiveness of this method. The present study is

aimed at publicizing the details standardized by the authors, restoring accuracy to the technique, besides

discussing it in comparison with other methods.

Keywords: Farill; Orthoradiographic measurement; Lower extremities; Difference.

Escanometria dos membros inferiores: revisitando Dr. Juan Farill.

A escanometria pelo “método de Farill” é exame rotineiro na maioria dos serviços radiológicos. Ela perma-

nece, há mais de meio século, como um método amplamente utilizado para diagnóstico da diferença entre

os membros inferiores e seu respectivo tratamento pelos especialistas de diversas áreas. Contudo, detalhes

na técnica do exame e na avaliação das medidas costumam ser ignorados ou negligenciados, comprometendo

o resultado final. Este trabalho tem por objetivo divulgar os detalhes preconizados pelo autor, restaurando a

precisão do método, bem como discuti-lo em relação aos demais métodos.

Unitermos: Farill; Escanometria; Membros inferiores; Diferença.

Abstract

Resumo

* Study developed at Centro de Diagnóstico por Imagem (CDI)

and at Hospital Infantil Nossa Senhora da Glória (HINSG), Vitó-

ria, ES, Brazil.

1. Titular Members of Colégio Brasileiro de Radiologia e Diag-

nóstico por Imagem (CBR), MDs, Residents at Centro de Diag-

nóstico por Imagem (CDI)/Hospital Universitário Cassiano Antô-

nio de Moraes (HUCAM)/Hospital Infantil Nossa Senhora da Glória

(HINSG), Vitória, ES, Brazil.

2. Titular Member of Colégio Brasileiro de Radiologia e Diag-

nóstico por Imagem (CBR), MD, Radiologist at Hospital Infantil

Nossa Senhora da Glória (HINSG), Preceptor in Pediatric Radio-

logy at Centro de Diagnóstico por Imagem (CDI)/Hospital Univer-

sitário Cassiano Antônio de Moraes (HUCAM)/Hospital Infantil

Nossa Senhora da Glória (HINSG), Vitória, ES, Brazil.


nóstico por Imagem (CBR), MD, Radiologist and Preceptor in

Radiology at Centro de Diagnóstico por Imagem (CDI)/Hospital

Universitário Cassiano Antônio de Moraes (HUCAM)/Hospital

Infantil Nossa Senhora da Glória (HINSG), Vitória, ES, Brazil.


nóstico por Imagem (CBR), MD, Radiologist and Chief of Medi-

cal Residence at Centro de Diagnóstico por Imagem (CDI)/Hos-

pital Universitário Cassiano Antônio de Moraes (HUCAM)/Hospi-

tal Infantil Nossa Senhora da Glória (HINSG), Vitória, ES, Brazil.

Mailing address: Dr. Gabriel A. de Oliveira. Rua Sagrado Cora-

ção de Maria, 220, Praia do Canto. Vitória, ES, Brazil, 29055-

770. E-mail: [email protected]

Received September 22, 2005. Accepted after revision Oc-

tober 17, 2005.

surement of the difference between the twodistances, the elimination of equal seg-ments from both distances does not changethe final result. Since it is an easy-to-per-form method and does not require any spe-cific equipment, it is routinely performedin any general Radiology service. However,few specialists had the opportunity to readthe original article of Dr. Juan Farill; theyhave almost always learned the methodwith someone who also has not read it.Consequently, the measuring method is notstandardized and incorrect results are ob-tained, affecting the patient’s treatment,which varies according to the type and de-gree of deformity observed(4). This method,likewise others is limited, and is contrain-dicated in some cases.

The objective of the present study is torestore and divulge the measurement tech-nique recommended by the author, as wellas to compare its efficiency with the othermethods available (scanography with mil-limetric ruler, panoramic radiography andcomputed tomography).

SCANOGRAPHY (TECHNIQUE)

The examination is performed in twostages. In the first one, with the patient ly-ing in supine position on a Potter-Buckytable, his/her feet are placed together withtheir longest axes forming an angle of ap-proximately 90º with the table (Figure 1);the longitudinal, central axis of the collima-tor is aligned in a way that it passes exactly

INTRODUCTION

The most accurate way to evaluate thedifference in length between lower ex-tremities is by means of imaging studies(1).Scanography was first described by Merrillin 1942(2). In 1953, Dr. Juan Farill describeda practical technique for measuring differ-ences in length between the lower limbs(3).The principle is very simple: in the mea-

Figure 1. Sites of collimation of the x-ray beams for performance of scanography. The result is shown on

Figure 5.

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Radiol Bras 2007;40(2):137–141

Figure 4. Positioning adopted for balancing in cases of feet deformity.

Figure 2. Before the x-ray imaging is initiated, the

x-ray tube must be moved to assure that the cen-

tral beam axis passes exactly between the feet and

the pubic symphysis, with no need for the patient

to be moved.

Figure 3. Positioning for x-ray imaging of the foot height. The result is shown on Figure 6.

between the ankles and the pubic symphy-sis of the individual (Figure 2). The patientmust remain still until the examination iscompleted. With two lead plates, the filmis divided into three segments, which areseparately radiographed: in the first one,the hip x-ray is performed; in the secondone, the knees; in the third one, the ankles.The numbering device at the patient’s right,indicates the side. Between images acqui-sitions, only x-ray-drawers can be moved.In no hypothesis should the chassis be re-moved from the drawer until the three ex-posures are completed.

In a second stage, the study proceeds tomeasure the feet height. With the feet in-ternally rotated about 30º on a wood plat-form whose posterior surface is coveredwith lead, the chassis is positioned imme-diately behind the feet, and an anteropos-terior x-ray view from the ankles is made.This positioning determines a dissociationof malleolus, allowing a total visualizationof the tali. For an adequate imaging the footsoles must be totally resting on the platform(Figure 3). In case this is not possible be-cause of any deformity, for example, to-wards or backwards inclination should betried, as necessary, until an appropriatepositioning is achieved (Figure 4).

This second stage usually is neglectedbecause of unawareness or because most oftimes there are no significant differencesbetween feet height. However, there are

situations where this may happen (congeni-tal lesions, poliomyelitis sequelae, osteo-cartilaginous destruction by inflammatoryor surgical processes, etc.).

Contraindications of the method

The most important aspect is the impos-sibility of a complete contact of all the sur-faces of the lower limb with the table sur-face, because flexed positions distort boneimages on x-ray films. This occurs whenexternal fixators are utilized(5), in femurand tibia deformities on sagittal plane orcontractures with flexion of hip or knee.

Pronounced valgus, varus or equinusdeformities hinder a reliable evaluation ofthe differences between foot heights.

SCANOMETRY (MEASUREMENTS)

The first measurement is performed inthe scanography, between the highest pointon the femoral head and the projection ofthe center of the intercondylar notch on aline touching the femoral condyles (Figure5a). The same procedure is performed inthe contralateral limb (Figure 5a’); the dif-ference between these two measurementsrepresenting the femoral shortening.

The second measurement is the distancefrom the same point on the line between thefemoral condyles up to the lowest point onthe tibial articular surface, in the ankle (Fig-ure 5b). This measurement is repeated forthe contralateral bone (Figure 5b’); the dif-ference between these two measurementsrepresents the tibial shortening.

The third measurement is performeddirectly from the highest point on the femo-ral head up to the lowest point on the tibialarticular surface (Figure 5c). This proce-dure is repeated for the contralateral limb(Figure 5c’); the difference between thesetwo measurements was named functionalshortening by Farill.

Finally, the fourth measurement con-cerns the foot height; it is performed fromthe lowest point of the talus, on the tibio-tarsal joint surface, up to the line resultingfrom the lead plate on the posterior surfaceof the wood platform (Figure 6d); thismeasurement is repeated for the contralat-eral foot (Figure 6d’). The difference be-tween these two measurements corre-sponds to the foot shortening.

Calculation and discrepancies analysis

Lower limbs length discrepancy may

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Radiol Bras 2007;40(2):137–141

basically be due to three types of alter-ations: The first one is bones with differ-ent lengths in relation to their contralateral;the second, is a patient with varus devia-tion or valgus asymmetry, that is, when alimb presents a greater curvature than itscontralateral; the third one is isometric fe-murs and tibias and discrepant foot heights.Overlapping of such alterations is fre-quently found, so these measurementsshould be evaluated as whole.

Initially, the right functional measure-ment must be added to the right foot height.This calculation is repeated for the left side.Then, one measurement is subtracted fromthe other, so the functional discrepancybetween the lower limbs is found. This isthe discrepancy that must be mentioned in

Femur (cm)

Tibia (cm)

Total femur + tibia (cm) (indirect measurement)

Femorotibial distance (functional) (cm)

Foot height (cm)

Total shortening (cm) (functional × foot height)

Right

23.4

15.2

38.6

38.6

9.2

Left

23.4

14.7

38.1

38.1

9.2

Shortening

—

0.5 < at left

0.5 < at left

0.5 < at left

—

Example 1

The left lower limb is 0.5 cm < than the right

lower limb (shortening due tibial discrepancies

– the differences between indirect measure-

ments is equal the direct measurements)

Figure 5. Sites of measurements for calculation of femurs and tibias shortening.

Figure 6. Sites of measurements for calculation of feet shortening.

the medical report, the indirect measure-ments being utilized only for analyzing thedeformity.

So, once the discrepancy between lowerlimbs is found, we must perform a com-parative analysis of the indirect (Figures 5a

+ 5b; Figures 5a’ + 5b’) and direct measure-ments (Figure 5c; Figure 5c’). The resultswill be:

– The lower limbs length discrepancy isthe same both for direct and indirect mea-surements. This means that the shorteningis real, i.e., femurs and/or tibias presentdifferent lengths (example 1);

– Indirect measurements indicate limblength equality, and direct measurementsindicate limb length discrepancy. This in-dicates that the shortening is probably dueto a varus or asymmetrical valgus deformity(example 2);

– Both the direct and indirect measure-ments indicate a discrepancy betweenlower limbs. In this case, there is summa-tion of these deformities (actual shortening+ varus/valgus deformity)(example 3).

Although the indirect measurement isaimed only at defining whether the limbsshortening is real or is due to a varus/val-gus deviation, this analysis should be al-ways performed, since it may affect directlythe therapy of the patient.

As regards the feet, the evaluation of thediscrepancy between heights provides es-sential information. Some times femursand tibias may present lengths equality anda discrepancy between foot heights; if thisdiscrepancy is significant and we fail toperform this part of the examination, we arelikely to fail in diagnosing an asymmetryin the total lower limbs length. On the otherhand, a discrepancy between femurs and/or tibias could be balanced by an oppositeasymmetry in foot heights; in this case, atreatment for the functional measurementsdiscrepancy would be contraindicated (ex-ample 4). The Farill technique does not takeinto consideration the highest point fromthe iliac crest to the acetabulum – Figure7). However, this measurement might to be

Indirect measurements Direct measurements

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Werlang HZ et al.

Radiol Bras 2007;40(2):137–141

performed with the same objective of thefoot height measurement(6).

In the cases where there are knees dys-plasias, and a line cannot be drawn betweenfemoral condyles, Farill recommends thatonly direct measurements are utilized inconjunction with the foot height measure-ments.

In cases of hip or ankle dysplasias, theauthor does not mention alternatives; forthese cases, we suggest the method em-ployed by Terry et al.(7), where the measure-ment is performed directly from the ante-rior superior iliac spine to the outermostpoint of the lateral malleolus. For this pur-pose a film with only two exposures is nec-

essary, with each exposure including theanatomical points of reference (anterosupe-rior iliac spine and lateral malleolus). Evenso, it is our understanding that the footheight as well as the iliac wings measure-ments should be performed and included inthe discrepancies calculation.

In our opinion, the Bell-Thompsonmethod (with a millimetric ruler), althoughbeing recommended by some authors(8,9),does not offer any substantive advantagesover the Farill technique. As the ruler re-mains positioned on the chassis, it does notfollow the magnification of the long bonesin the radiographic imaging, which couldresult in measurement errors(10). Addition-

ally, for demanding a strict immobilizationof the patient, it is very difficult to employthis method in children(8).

The panoramic x-ray of lower limbs isa very accurate method and presents as anadvantage the possibility of being per-formed in orthostasis(10). However, it pre-sents the inconvenience of not beingwidely available, besides the high cost.Also, it does not measure appropriately feetand iliac wings heights, and must becomplemented by x-rays appropriate forsuch measurements.

The measurement of lower limbs dis-crepancy by means of CT topogram is men-tioned by some authors as the most accu-rate method for diagnosis of lower limbsasymmetry(5,11). This is true, mainly in thecases where a complete resting of the footsoles on the platform is not achieved (de-formities, utilization of external fixators,etc.); in these cases, it is necessary to per-form a lateral topogram with the measure-ments on this view(5). Additionally, amongstthe methods analyzed in the present study,this is the method with lowest radiationdose(5,10,11), and is the method of choice foryoung patients who need serial studiesduring the therapy management. But, be-sides not being widely available, presentshigh cost(10).

In summary, considering the low cost,high availability and reasonable accuracy,we recommend the Farill technique, comple-

Femur (cm)

Tibia (cm)



Foot height (cm)

Total shortening (cm)

Right

23.4

15.2

38.6

38.6

9.2

Left

23.4

14.7

38.1

37.6

9.2

Shortening

—

0.5 < at left

0.5 < at left

1.0 < at left

—

Example 3

The left lower limb is 1.0cm < than the right

lower limb (0.5cm due the tibial shortening,

and 0.5cm due the varus or valgus shorten-

ing)

Femur (cm)

Tibia (cm)



Foot height (cm)


Right

23.4

14.7

38.1

38.6

9.2

Left

23.4

14.7

38.1

38.1

9.2

Shortening

—

—

—

0.5 < at left

—

Example 2

The left lower limb is 0.5 cm < than the right

lower limb (shortening due the difference of

varus or valgus deviation)

Femur (cm)

Tibia (cm)



Foot height (cm)


Right

23.4

15.2

38.6

38.6

8.7

Left

23.4

14.7

38.1

38.1

9.2

Shortening

—

0.5 < at left

0.5 < at left

0.5 < at left

0.5 < at right

Example 4

There is no difference between the lower

limbs, since the discrepancy between femurs

+ tibias is balanced by the inverted differ-

ence between feet.

Figure 7. Sites of iliac measurements.

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Radiol Bras 2007;40(2):137–141

mented with an iliac wing measurement. Incases where there is a contraindication, werecommend a panoramic x-ray or computedtomography.

REFERENCES

1. Lampe HI, Swierstra BA, Diepstraten AF. Mea-surement of limb length inequality. Comparisonof clinical methods with orthoradiography in190 children. Acta Orthop Scand 1996;67:242–244.

2. Merrill OE. A method for roentgen measurementof the long bones. Am J Roentgenol Radium TherNucl Med 1942;48:405–406.

3. Farill J. Orthoradiographic measurement of short-ening of the lower extremity; technic. Med Ra-

diogr Photogr 1953;29:32–38.4. Dahl MT. Limb length discrepancy. Pediatr Clin

North Am 1996;43:849–865.5. Aaron A, Weinstein D, Thickman D, Eilert R.

Comparison of orthoroentgenography and com-puted tomography in the measurement of limb-length discrepancy. J Bone Joint Surg Am 1992;74:897–902.

6. Badii M, Shin S, Torreggiani WC, et al. Pelvicbone asymmetry in 323 study participants receiv-ing abdominal CT scans. Spine 2003;28:1335–1339.

7. Terry MA, Winell JJ, Green DW, et al. Measure-ment variance in limb length discrepancy: clini-cal and radiographic assessment of interobserverand intraobserver variability. J Pediatr Orthop2005;25:197–201.

8. Lebouchard R, Denis JP, Trope J, Duranteau Mme.Mensuration radiologique osseuse par la méthodede Bell Thompson. J Radiol Electrol Arch ElectrMedicale 1956;37:108–110.

9. Delouvrier JJ, Nahum H. Longueur des membres.Précision des méthodes orthoradiographiques. JRadiol 1981;62:647–651.

10. Machen MS, Stevens PM. Should full-lengthstanding anteroposterior radiographs replace thescanogram for measurement of limb length dis-crepancy? J Pediatr Orthop B 2005;14:30–37.

11. Aitken AG, Flodmark O, Newman DE, KilcoyneRF, Shuman WP, Mack LA. Leg length determi-nation by CT digital radiography. AJR Am JRoentgenol 1985;144:613–615.

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