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2010;92:2319-2327. doi:10.2106/JBJS.I.01150 J Bone Joint Surg Am.Kyoung Min Lee, Chin Youb Chung, Moon Seok Park, Sang Hyeong Lee, Jae Hwan Cho and In Ho Choi

Varus and ValgusReliability and Validity of Radiographic Measurements in Hindfoot

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Reliability and Validity of RadiographicMeasurements in Hindfoot Varus and Valgus

By Kyoung Min Lee, MD, Chin Youb Chung, MD, Moon Seok Park, MD,Sang Hyeong Lee, MD, Jae Hwan Cho, MD, and In Ho Choi, MD

Investigation performed at the Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Sungnam,and the Department of Orthopaedic Surgery, Seoul National University Children’s Hospital, Seoul, South Korea

Background: Clinical decision-making in the treatment of foot deformities is based primarily on the results of thephysical examination and the radiographic findings. The purpose of this study was to determine the validity and reliabilityof commonly used radiographic measurements of hindfoot valgus and varus deformities.

Methods: Seventy-two patients with hindfoot deformity (thirty-six hindfoot valgus, mean age 15.5 years; thirty-six hind-foot varus, mean age 30.2 years) were evaluated. Nine representative indices on weight-bearing radiographs wereassessed. Three examiners measured the radiographic indices at two sessions, and intraobserver and interobserverreliability was determined. Discriminant validity of the radiographic measurements between hindfoot valgus and varus wasevaluated. The correlation with pedobarographic findings in evaluating the distribution of foot pressure during gait wasassessed for convergent validity.

Results: Naviculocuboid overlap, anteroposterior talonavicular coverage angle, anteroposterior talus-first metatarsalangle, calcaneal pitch angle, and lateral talus-first metatarsal angle showed excellent reliability. Naviculocuboidoverlap, anteroposterior talonavicular coverage angle, and anteroposterior talus-first metatarsal angle showed excel-lent discriminant validity (in terms of effect-size r) and convergent validity (in terms of correlation coefficients withpedobarography).

Conclusions: Naviculocuboid overlap, anteroposterior talonavicular coverage angle, and anteroposterior talus-firstmetatarsal angle are reliable and valid measures for the evaluation of hindfoot valgus and varus deformities.

Level of Evidence: Diagnostic Level III. See Instructions to Authors for a complete description of levels of evidence.

Valgus and varus hindfoot deformities are commondeformities in both children and adults. Many of thesefoot deformities require orthopaedic intervention, and

the treatment goal is to address all of the aspects of the de-formity and achieve a painless plantigrade foot. In general,clinical decision-making for foot deformities is based onphysical examination and radiographic findings.

Radiographs of the foot are commonly used to evaluatefoot deformities, and the weight-bearing anteroposterior andlateral views are used to obtain the standard measurementsnecessary for evaluation of the foot. In addition to qualitativeassessment, specific radiographic indices have been used toquantify hindfoot deformity, and the reliability of these indicesin normal subjects or subjects with specific diseases has beenreported1,2. However, there are concerns that these measure-ments cannot explain all of the facets of foot deformity. For

example, the subtalar joint is not horizontal, and hindfootvalgus or varus does not occur simply in one plane. We hy-pothesized that the radiographic indices in hindfoot defor-mities may not be as reliable as previous reports have impliedand that the anteroposterior or lateral projection of the footmay not always reflect the amount of actual deformity. That is,some of the indices may not be valid in the evaluation ofhindfoot deformities.

There are no gold standards for measuring foot defor-mities. Therefore, measurement validity relies on the con-struct validity. This study examined the radiographic footmeasurements in terms of both reliability and validity, asfollows: (1) reliability, as assessed by the interobserver andintraobserver reliability in the radiographic measurements ofhindfoot valgus and varus; (2) discriminant validity3, as de-termined by the differences in the measurements between

Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a memberof their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

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COPYRIGHT � 2010 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED

J Bone Joint Surg Am. 2010;92:2319-27 d doi:10.2106/JBJS.I.01150

different groups (varus and valgus), which is one aspect ofconstruct validity; and (3) convergent validity, as determinedby the correlation between the radiographic indices and pe-dobarographic measurements, which is another aspect ofconstruct validity.

Materials and Methods

This study was approved by the institutional review boardat our hospital, which waived informed consent. The

patients were randomly selected from a review of the medicalrecords. The inclusion criteria were as follows: (1) clinicallydiagnosed hindfoot deformity (hindfoot valgus or varus)between January 2004 and May 2009. The diagnosis wasbased on the clinical information, including the patient’shistory, underlying diseases, and physical examination. Theangle between the long axis of the calf and vertical axis of theheel in the weight-bearing position was assessed to diagnosethe hindfoot valgus and varus qualitatively4; (2) availability of

Fig. 1-A

Figs. 1-A, 1-B, and 1-C The radiographic measurements for hindfoot varus (left side of each figure) and hindfoot valgus (right side of each

figure). Fig. 1-A On the lateral weight-bearing radiographs, the calcaneal pitch angle (CP) is the angle between a line drawn along the edge of the

plantar soft-tissue shadowand a line drawn along the lower margin of the calcaneus. The lateral talocalcaneal angle (TC) is the angle between a

line drawn along the lower margin of the calcaneus and a line drawn through the midpoints of the talar head and neck. The tibiocalcaneal angle

(TibioCalc) is the angle between a line drawn along the lower margin of the calcaneus and a line bisecting the long axis of the tibia. The lateral

talus-first metatarsal angle (Talo-1MT) is the angle between a line bisecting the long axis of the first metatarsal bone and a line drawn through

the midpoints of the talar head and neck. The metatarsal stacking angle (MT stacking) is the angle between a line drawn at the lower margin of

the fifth metatarsal and a line drawn from the fifth metatarsal base to the first metatarsal head.

Fig. 1-B

On the lateral weight-bearing radiographs, the naviculocuboid overlap (A/B) is the overlapped portion of the navicular and cuboid divided by the vertical

height of the cuboid. The medial-lateral column ratio (C/D) is the distance between the distal tip of the first metatarsal head and the proximal margin of

the posterior talar dome divided by the distance between the most proximal margin of the posterior aspect of the calcaneus and the distal-most margin of

the fifth metatarsal head.

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TH E J O U R N A L O F B O N E & JO I N T SU R G E RY d J B J S . O R G

VO LU M E 92-A d NU M B E R 13 d O C T O B E R 6, 2010RE L I A B I L I T Y A N D VA L I D I T Y O F RA D I O G R A P H I C

ME A S U R E M E N T S I N HI N D F O O T VA R U S A N D VA L G U S

the weight-bearing foot radiographs (both anteroposteriorand lateral views). Foot radiographs were made with use of aUT 2000 x-ray machine (Philips Research, Eindhoven, The

Netherlands) at a source-to-image distance of approximately100 cm and set to 50 kVp and 5 mAs, with the patient in thestanding position. The patients were radiographed barefoot;

Fig. 1-C

On the anteroposterior weight-bearing radiograph, the talonavicular coverage angle (TN) is the angle between a line bisecting the anterior articular surface

of the talus and another line bisecting the proximal articular surface of the navicular. The anteroposterior talus-first metatarsal angle (Talo-1MT) is defined

as the angle between a line bisecting the anterior articular surface of the talus and a line bisecting the long axis of the first metatarsal.

TABLE I Patient Demographics*

Hindfoot Valgus Group Hindfoot Varus Group

Age ± standard deviation (yr) 15.5 ± 4.2 30.2 ± 18.0

Sex (M:F) 21:15 20:16

Causes of deformities (no. of cases) Idiopathic planovalgus (27) Cerebral palsy (14)

Cerebral palsy (9) Residual poliomyelitis (10)

HMSN (3)

Guillain-Barre syndrome (1)

Peroneal nerve injury (2)

Congenital clubfoot (2)

Unknown cause (4)

*HMSN = hereditary motor sensory neuropathy.

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and (3) performance of pedobarography. All radiographicmeasurements were performed with use of a picture ar-chiving and communication system (PACS) (IMPAX; AgfaHealthCare, Mortsel, Belgium) software. Patients with ahistory of prior foot surgery or a severe equinus deformitywho could not achieve toe-to-heel contact on the groundwere excluded.

Selecting the Items of Radiographic MeasurementsPrior to the study, the radiographic measurements to be as-sessed were selected from literature reviews and consensus bythe orthopaedic surgeons. Previous studies were reviewed1,2,5-10,and one of the authors (K.M.L.) selected the items that webelieved would be relevant to measure hindfoot valgus andvarus. Items were chosen on the basis of a consensus amongfour orthopaedic surgeons, who constituted a consensusdevelopment panel3. We intended to include as many ra-diographic measurements as possible. Radiographic mea-surements were selected by eliminating redundant methodsand those not used frequently. The four panelists (C.Y.C.,M.S.P., S.H.L., and K.M.L.) were orthopaedic surgeons withtwenty-one, nine, eight, and six years of experience, two ofwhom specialized in pediatric orthopaedic surgery and twoin adult foot and ankle surgery. One of the authors (M.S.P.)was a moderator, and each item was chosen by consensus bythe panel. The discussion focused mainly on the clinicalrelevance and importance of each measurement. Overall,nine measurements were chosen for evaluation.

The following seven items were measured on the lateralfoot radiographs: calcaneal pitch angle8, lateral talocalcanealangle5, tibiocalcaneal angle5, lateral talus-first metatarsal an-gle5, metatarsal stacking angle1, naviculocuboid overlap1, and

medial-lateral column ratio1. Two items were measured on theanteroposterior foot radiographs, the talonavicular coverageangle10 and the anteroposterior talus-first metatarsal angle5

(Figs. 1-A, 1-B, and 1-C).

Intraobserver and Interobserver ReliabilityThree examiners (a pediatric orthopaedic surgeon [S.H.L.], afoot and ankle surgeon [K.M.L.], and an orthopaedic surgeryresident [J.H.C.], with eight, six, and three years of ortho-paedic experience, respectively) were used to assess the in-traobserver and interobserver reliability of the radiographicmeasurements. A prior sample size estimation by precisionanalysis indicated that a minimum of thirty-six feet should beassessed for both the hindfoot valgus and hindfoot varusgroups. The measurements were performed by the three ex-aminers in two sessions, with a three-week interval betweensessions11. Each examiner was blinded to the other measure-ments and to all patient data. All measurements were collectedby a research assistant who did not otherwise participate inthe study.

Discriminant ValidityDiscriminant validity is one facet of construct validity. It is theability to detect relevant differences between various subgroupsof subjects or patients. In this study, Cohen’s d and effect-size rwere assessed between the hindfoot valgus and hindfoot varusgroups.

Convergent ValidityConvergent validity, which is another type of construct validity,occurs when the scales of a measurement correlate as expectedwith the related scales of another measurement. In this study,

TABLE II Summary of the Radiographic and Pedobarographic Measurements* �

Hindfoot Valgus Group (mean ± SD [range]) Hindfoot Varus Group (mean ± SD [range])

Lateral radiographs

CP (�) 9.3 ± 4.9 (–9.0 to 18.6) 15.2 ± 6.7 (1.9 to 29.5)

LatTC (�) 47.2 ± 10.6 (21.0 to 68.0) 44.5 ± 13.1 (14 to 75.8)

TibioCalc (�) 75.2 ± 6.7 (61.6 to 91.0) 69.5 ± 8.1 (53.3 to 90.5)

Lat talo-1MT (�) 20.5 ± 11.0 (2.3 to 42.0) –2.8 ± 13.5 (–36.8 to 21.7)

MT stacking (�) 5.5 ± 6.7 (–27.6 to 13.1) 8.2 ± 6.4 (–16.8 to 19.2)

NC overlap (%) 68.6 ± 17.3 (30 to 100) 7.3 ± 9.5 (0 to 33)

ML column ratio 0.97 ± 0.04 (0.86 to 1.03) 0.97 ± 0.06 (0.85 to 1.10)

Anteroposterior radiographs

AP TN coverage (�) 31.6 ± 13.7 (3.6 to 62.8) –13.8 ± 15.9 (–45.4 to 15.9)

AP Talo-1MT (�) 27.0 ± 11.1 (6.3 to 47.5) –18.8 ± 16.8 (–48.5 to 13.0)

Pedobarographs

Valgus/varus index 0.33 ± 0.28 (–0.55 to 0.79) –0.25 ± 0.39 (–0.87 to 0.51)

*SD = standard deviation, CP = calcaneal pitch angle, LatTC = lateral talocalcaneal angle, TibioCalc = tibiocalcaneal angle, Lat talo-1MT =

lateral talus-first metatarsal angle, MT stacking = metatarsal stacking angle, NC overlap = naviculocuboid overlap, ML column ratio = medial-lateral column ratio, AP TN coverage = anteroposterior talonavicular coverage angle, AP Talo-1MT = anteroposterior talus-first metatarsalangle.

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the radiographic measurements were compared with pedo-barographic measurements.

The pedobarographic measurements were obtainedwith use of a high-resolution pressure assessment system(Tekscan, South Boston, Massachusetts). The system con-sisted of a 2180-cm2 pressure-sensitive floor mat containing3.9 pressure-sensing cells/cm2. The foot pressures were re-corded at a rate of 50 Hz. The examination began with thepatient standing 2 m away from the floor mat, which was nothidden in the floor. Each patient was instructed to lookahead and begin walking at a self-selected speed. The pres-sure readings were collected with the foot completely on thepressure surface before, during, and after the stance phase.After the pressure readings were obtained, the informationthat was collected was processed with use of software spe-cifically designed for research with the Tekscan system. Thearea of measurement was divided into equal anterior,middle, and posterior thirds, and into equal medial andlateral halves. This produced the following five sections:medial forefoot (MFF), lateral forefoot (LFF), medial midfoot

(MMF), lateral midfoot (LMF), and the heel. The peakpressure and pressure-time integral were retrieved for eachof the five segments of the foot, and these data were pro-cessed to produce the valgus/varus index, which is definedas ((MMF 1 MFF) 2 (LMF 1 LFF))/(MMF 1 MFF 1 LFF 1

LMF) (Fig. 2)12. The foot-pressure measurement index wascalculated by one of the authors (K.M.L.), and the corre-lation between the radiographic measurements and valgus/varus index was assessed to determine the convergentvalidity.

Statistical MethodsA prior sample-size analysis was carried out to determine theminimum number of patients required. In this study, the re-liability was calculated with use of intraclass correlation coef-ficients13 at a target value of 0.8. The 95% confidence intervalwas set to 0.2, and the minimum sample size was thirty-six feetwith a Bonett approximation14. For the purpose of statisticalindependence, only the data from a single foot in each patientwere included for statistical analysis.

P Value Normal Alignment1 (mean ± SD [range]) Definition of Larger Value1

<0.001 17 ± 6.0 (5 to 32) Dorsiflexion

0.324 49 ± 6.9 (36 to 61) Valgus and abduction

0.002 69 ± 8.4 (44 to 86) Plantar flexion

<0.001 13 ± 7.5 (1 to 35) Midfoot planus

0.084 8 ± 2.9 (1 to 13) Supination

<0.001 47 ± 13.8 (22 to 85) Pronation

0.453 0.9 ± 0.1 (0.8 to 1.1) Longer medial column

<0.001 20 ± 9.8 (5 to 39) Abduction

<0.001 10 ± 7.0 (–3 to 28) Abduction

<0.001 Not available Lateral pressure

TABLE II (continued)

TABLE III Discriminant Validity of Radiographic Measurements*

Lateral RadiographsAnteroposterior

Radiographs

CP LatTC TibioCalcLat

Talo-1MTMT

StackingNC

OverlapML Column

RatioAP TN

CoverageAP

Talo-1MT

Cohen’s d 1.00 0.24 0.77 1.89 0.42 4.47 0.18 3.06 3.22

Effect-size r 0.45 0.12 0.36 0.69 0.20 0.91 0.09 0.84 0.85

*CP = calcaneal pitch angle, LatTC = lateral talocalcaneal angle, TibioCalc = tibiocalcaneal angle, Lat Talo-1MT = lateral talus-firstmetatarsal angle, MT stacking = metatarsal stacking angle, NC overlap = naviculocuboid overlap, ML column ratio = medial-lateralcolumn ratio, AP TN coverage = anteroposterior talonavicular coverage angle, AP Talo-1MT = anteroposterior talus-first metatarsalangle.

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In this assumption, thirty-six feet for each group wererepresentative of the radiographic measurements (i.e., the caseswere considered to be random factors) from a population withhindfoot deformities.

The intraclass correlation coefficients and their 95%confidence intervals were used to summarize the intraobserverand interobserver reliability and were calculated in the settingof a two-way random-effect model, assuming a single mea-surement and absolute agreement. An intraclass correlationcoefficient of 1 indicates perfect reliability, and an intraclasscorrelation coefficient of >0.8 indicates excellent reliability15.

A Kolmogorov-Smirnov test was used to identify thenormality of the variables. An independent sample t test and acalculation of effect-size r with Cohen’s d16 were used to presentthe discriminant validity of the measurements.

The Pearson correlation coefficients were used to deter-mine the convergent validity of the weight-bearing radiographmeasurements regarding a specific foot deformity. In this study,the Pearson correlation coefficient and the intraclass correla-tion coefficient were characterized as poor (0.00 to 0.20), fair

(0.21 to 0.40), moderate (0.41 to 0.60), good (0.61 to 0.80), orexcellent (0.81 to 1.00)17. A p value of <0.05 was consideredsignificant.

Source of FundingThere was no external funding source for this investigation.

Results

Of the 301 patients with weight-bearing foot radiographs andpedobarographs, seventy-two patients with a foot deformity

(thirty-six with hindfoot valgus and thirty-six with hindfootvarus) were selected randomly (i.e., a single foot from each pa-tient was selected randomly to ensure statistical independence).The mean age and standard deviation of the patients withhindfoot valgus was 15.5 ± 4.2 years (range, twelve to thirty-oneyears), and the mean age of the patients with hindfoot varus was30.2 ± 18.0 years (range, eight to sixty-seven years). There weretwenty-one male subjects and fifteen female subjects in thehindfoot valgus group, and twenty male subjects and sixteenfemale subjects in the hindfoot varus group (Table I).

Fig. 2

The pedobarograph was divided into five segments: the heel, medial midfoot (MMF), lateral

midfoot (LMF), medial forefoot (MFF), and lateral forefoot (LFF). The image on the left

depicts left hindfoot varus, and the image on the right depicts right hindfoot valgus.

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Calcaneal pitch angle, tibiocalcaneal angle, lateral talus-firstmetatarsal angle, naviculocuboid overlap, anteroposterior talona-vicular coverage angle, anteroposterior talus-first metatarsal angle,and valgus/varus index showed significant differences between thehindfoot valgus group and the hindfoot varus group (Table II).

Measurement of the calcaneal pitch angle and naviculo-cuboid overlap, the talonavicular coverage angle, and the antero-posterior talus-first metatarsal angle showed satisfactory overallreliability. Most of the radiographic measurements showed good-to-excellent reliability for clinical use (see Appendix).

In terms of discriminant validity, the naviculocuboidoverlap showed the highest Cohen’s d and effect-size r and wasthe most valid method for discriminating between a hindfootvalgus deformity and a hindfoot varus deformity, followed bythe anteroposterior talus-first metatarsal angle and the antero-posterior talonavicular coverage angle (Table III).

In terms of convergent validity, naviculocuboid overlapshowed the highest correlation coefficient (r = 0.639, p < 0.001)with the valgus/varus index as determined by pedobarography.The anteroposterior talus-first metatarsal angle and the antero-posterior talonavicular coverage angle were also found to havea significant correlation with the valgus/varus index (r = 0.628,p < 0.001; and r = 0.613, p < 0.001, respectively), and the medial-lateral column ratio had the lowest correlation coefficient withthe valgus/varus index (r = 20.023, p = 0.855) (Table IV).

Discussion

We believe that the reliability and validity of many footradiographic measurements have not been clarified, al-

though such measurements are used frequently. In this study,the naviculocuboid overlap, the anteroposterior talus-firstmetatarsal angle, and the talonavicular coverage angle werefound to be reliable and valid methods for discriminatinghindfoot valgus and varus deformities, reflecting pressuredistribution in the foot during walking.

Some limitations of this study should be addressed be-fore discussing these findings in detail. First, the diagnosis offoot deformities was simplified as either hindfoot valgus orhindfoot varus. Although these deformities are common inclinical situations, the study results may not be applicable to

various other foot deformities. Second, the two groups in thisstudy had a substantial difference in patient age, which mighthave confounded the results due to age-related changes inhindfoot anatomy, and the degree of ossification in the osseouslandmarks could have affected the reliability of the test results.Third, the radiographic measurements were compared withthe pedobarographic valgus/varus index for convergent va-lidity. Some might argue that pedobarographic measurementis inaccurate; however, although pedobarographic measure-ment is not a gold standard, it is believed to be a relevant toolthat has been used in many studies for surgical outcome as-sessment18-22. Therefore, we assumed that convergent validityof the radiographic measurements could be assessed by cor-relation with the pedobarographic index. Fourth, subjectswith a severe equinus deformity who could not achieve totalplantar contact during gait were excluded because the radio-graphic and pedobarographic measurements for those sub-jects might be distorted or not defined properly. The studyresults therefore cannot be generalized, as a considerable pro-portion of foot deformities are associated with an equinusdeformity. Fifth, for severely deformed feet, the hindfoot andforefoot cannot be evaluated appropriately with use of a singlelateral radiographic image and should instead be evaluatedwith use of two separate images focusing on the forefoot andhindfoot, respectively. However, in this study, all feet wereevaluated on a single radiographic image made perpendicularlyto the long axis connecting the heel center and the secondmetatarsal head. Sixth, ankle deformities were not consideredin the inclusion and exclusion criteria; however, severe hind-foot deformities often coincide with ankle deformities andtherefore some of the foot deformities could have been sec-ondary to an ankle deformity. This group of patients mayhave had different characteristics from those of patients withprimary hindfoot deformities, and these differences mighthave affected the study results. Seventh, although a period ofthree weeks between repeated measurements has previouslybeen used to determine intraobserver reliability11, this periodis somewhat short and may have increased the measured in-traobserver reliability. However, our results also showed com-parable interobserver reliability, which is independent of recall.

TABLE IV Convergent Validity of Radiographic Measurements Presented as Correlation Coefficients with Valgus/Varus

Index in Pedobarography*

Lateral RadiographsAnteroposterior

Radiographs

CP LatTC TibioCalcLat

Talo-1MTMT

StackingNC

OverlapML Column

RatioAP TN

CoverageAP

Talo-1MT

r –0.146 0.110 0.138 0.386† –0.337† 0.639† –0.023 0.613† 0.628†

p 0.240 0.374 0.266 0.001 0.005 <0.001 0.855 <0.001 <0.001

*CP = calcaneal pitch angle, LatTC = lateral talocalcaneal angle, TibioCalc = tibiocalcaneal angle, Lat Talo-1MT = lateral talus-firstmetatarsal angle, MT stacking = metatarsal stacking angle, NC overlap = naviculocuboid overlap, ML column ratio = medial-lateralcolumn ratio, AP TN coverage = anteroposterior talonavicular coverage angle, AP Talo-1MT = anteroposterior talus-first metatarsal angle.†p < 0.05.

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The diagnostic criteria for a foot deformity, includinghindfoot valgus and hindfoot varus, are clinical and depend ona visual inspection. The diagnosis in this study population wasbased primarily on the gross appearance of the foot. We believethat the results from our study may be useful when trying toclarify a diagnosis or when attempting to objectively quantifythe severity of a foot deformity.

The calcaneal pitch angle measurement is widely used inthe evaluation of foot deformities because it is intuitive and easyto understand and because defining the landmarks on a lateralfoot radiograph is a relatively simple process. Despite its relativelyhigh reliability, however, it has been shown to be a less validmethod for discriminating hindfoot valgus and varus defor-mities. Therefore, it is important to reevaluate the value of thisradiographic measurement for clinical use. The medial-lateralcolumn ratio showed the lowest reliability of the radiographicmeasurements. This low reliability is believed to be caused by theoverlap of the five metatarsals, which makes it difficult to identifythe distal margin of the metatarsal head. The naviculocuboidoverlap measurement was found to be a valid method for dis-criminating between hindfoot valgus and varus deformities. Inour study, the minimum value of this measurement in hindfootvalgus was 30%, and the maximum value of this measurement inhindfoot varus was 33%. However, by definition, the naviculo-cuboid overlap measurement does not consider the direction ofoverlap. For example, both severe varus, in which the cuboid islocated below the navicular on the lateral radiograph, and severevalgus, in which the cuboid is located above the navicular on thelateral radiograph, would result in a naviculocuboid overlap ofzero, though there was no case in which the cuboid was above thenavicular in this study. Furthermore, this radiographic mea-surement does not discriminate between the severity of a severe

varus or valgus deformity. Nineteen of the thirty-six varus feetin this study showed a naviculocuboid overlap of zero, althoughthe severity of the varus deformity varied among the nineteen.This represents a floor or ceiling effect of this measurement andthus does not reflect the degree of the deformity in severe varusor valgus feet. Therefore, although naviculocuboid overlap is auseful method for discriminating between hindfoot valgus andvarus deformities, care should be taken when applying thismethod to severe deformities. The talonavicular coverage angleand the anteroposterior talus-first metatarsal angle showedexcellent reliability and favorable discriminant validity. Initially,we believed that these measurements would not reflect hindfootvalgus and varus deformities; however, the two measurements onthe anteroposterior radiographs were reliable and valid methodsfor differentiating between hindfoot valgus and varus defor-mities. These results appear to reflect the complicated nature ofhindfoot valgus and varus deformities and suggest that hindfootvalgus and varus are not isolated coronal plane deformities.

It is believed that pressure measurements of the footduring gait would be more relevant than radiographic mea-surements because they could possibly reflect the pressureexerted on the plantar surface, which could help to identifypathologic biomechanics and subsequently localize the cause offoot pain19,23-26. Therefore, this study evaluated the convergentvalidity of the radiographic measurements by comparing themwith the valgus/varus foot pressure distribution index. Navi-culocuboid overlap, anteroposterior talonavicular coverageangle, and anteroposterior talus-first metatarsal angle showedgood convergent validity. A higher discriminant validity was ob-tained with these measurements than with the valgus/varus index.

In summary, the results of this study are in concurrencewith those of two previous studies1,2 in terms of the reliability of

TABLE V Clinical Relevance of Each Radiographic Measurement*

Reliability (ICC)Discriminant Validity

(effect-size r)Convergent Validity

(correlation r)

Lateral radiographs

CP wwwww www NS

LatTC wwww w NS

TibioCalc wwww ww NS

Lat talo-1MT wwwww wwww ww

MT stacking wwww w ww

NC overlap wwwww wwwww wwww

ML column ratio www w NS

Anteroposterior radiographs

AP TN coverage wwwww wwwww wwww

AP talo-1MT wwwww wwwww wwww

*Stars indicate level of significance: w = 0 to 0.2, ww = 0.2 to 0.4, www = 0.4 to 0.6, wwww = 0.6 to 0.8, wwwww = 0.8 to 1.0; ICC =

intraclass correlation coefficient; CP = calcaneal pitch angle; NS = not significant; LatTC = lateral talocalcaneal angle; TibioCalc = tibiocalcanealangle; Lat talo-1MT = lateral talus-first metatarsal angle; MT stacking = metatarsal stacking angle; NC overlap = naviculocuboid overlap; MLcolumn ratio = medial-lateral column ratio; AP TN coverage = anteroposterior talonavicular coverage angle; AP Talo-1MT = anteroposterior talus-first metatarsal angle.

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the radiographic indices. In the present study, however, we alsoexamined each radiographic measurement in terms of its dis-criminant and convergent validity, and we believe that the re-sults add an objective diagnostic guideline (Table V) to thecurrent vague criteria used to evaluate hindfoot valgus andvarus deformities.

AppendixTables showing the results of the reliability tests areavailable with the electronic version of this article on our

web site at jbjs.org (go to the article citation and click on‘‘Supporting Data’’). n

NOTE: The authors thank Mi Seon Ryu for data collection and support.

Kyoung Min Lee, MDChin Youb Chung, MDMoon Seok Park, MDSang Hyeong Lee, MDJae Hwan Cho, MDDepartment of Orthopaedic Surgery,Seoul National University Bundang Hospital,300 Gumi-Dong, Bundang-Gu, Sungnam,Kyungki 463-707, South Korea.E-mail address for M.S. Park: [email protected]

In Ho Choi, MDDepartment of Orthopaedic Surgery,Seoul National University Children’s Hospital,28 Yeongon-Dong, Jongno-Gu, Seoul 110-744, South Korea

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