The Foot 15 (2005) 91–94

Weight bearing ankle dorsiflexion range of motion in idiopathicpes cavus compared to normal and pes planus feet

Joshua Burns∗, Jack CrosbieSchool of Physiotherapy, University of Sydney, Lidcombe, NSW, Australia

Received 3 August 2004; accepted 8 March 2005

Abstract

Background: Various factors are considered influential in the development of pes cavus. Short tendo-Achilles is one factor that has beenhypothesised as a deforming mechanism of ‘idiopathic’ pes cavus.Objective: To measure tendo-Achilles length in subjects with idiopathic pes cavus, compared to normal and pes planus feet, and to examinethe relationship between tendo-Achilles length and foot type.Method: Fifty-three healthy volunteers (34 female, 19 male) were recruited to encompass a wide range of foot types, varying in degree ofcavoid, normal and planus features. Foot type was measured weight bearing using the Foot Posture Index (FPI). The length of the tendo-AchilleswR the study.L nwC s planusf©

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as also measured weight bearing using the lunge test.esults: Twenty-four subjects with pes cavus, 24 subjects with a normal foot type and five subjects with pes planus completedunge angle in the pes cavus group was significantly less than the normal and pes planus groups (P< 0.001). A strong, positive correlatioas identified between tendo-Achilles length and foot type (r = 0.757,P< 0.001;r2 = 57.3%).onclusion:Distinct differences exist in tendo-Achilles length in individuals with a pes cavus foot type, compared to normal and pe

eet. A strong positive relationship between tendo-Achilles shortness and pes cavus severity has been identified.2005 Elsevier Ltd. All rights reserved.

eywords:Foot type; Ankle joint; Tendo-Achilles; Biomechanics

. Introduction

While much attention has been given to the plight of theathological pes planus, little is known about the other ex-

reme in foot type, pes cavus. Pes cavus is characterised byn excessively high medial longitudinal arch, occurs in ap-roximately 15% of the population[1] and is associated with

oot pain in 60% of cases[2]. Various factors are consid-red influential in the development of pes cavus, such asuscle weakness and imbalance in peripheral neuropathy

3], residual effects of congenital clubfoot[4], and post-raumatic malformation[5]. However, the majority of pesavus cases are termed ‘idiopathic’ because their aetiology isnknown.

∗ Corresponding author. Tel.: +61 2 8230 1131; fax: +61 2 9968 1527.E-mail address:jbur2522@mail.usyd.edu.au (J. Burns).

Short tendo-Achilles is one factor considered influenin the development of idiopathic pes cavus[6]. Dickson andDiveley, in 1939, hypothesised that “a short heel cordraising the os calcis, throws the major part of the burdeweight bearing on the ball of the foot. This in turn, appareexcites a response in the intrinsic muscles of the foot, andhaps the long muscles of the leg as well, to meet the abnoweight demand. Such increased muscle activity brings atightening up of all of the joints, shortening of the ligamecrowding together of the bones of the foot and elevation olongitudinal arch”[6]. While many authors have since cithis theoretical mechanism producing pes cavus[7–11], noempirical exploration of the hypothesis has been condu

Prompted by this lack of experimental data, the aimsstudy were to measure tendo-Achilles length in subjectsidiopathic pes cavus, compared to normal and pes pfeet, and to examine the relationship between tendo-Achlength and foot type.

958-2592/$ – see front matter © 2005 Elsevier Ltd. All rights reserved.oi:10.1016/j.foot.2005.03.003

92 J. Burns, J. Crosbie / The Foot 15 (2005) 91–94

2. Methods

Fifty-three healthy volunteers (34 female, 19 male) wererecruited to the study and gave informed consent in accor-dance with the University Human Ethics Committee beforetesting commenced. The sample was constructed to encom-pass a wide range of foot types, varying in degree of cavoid,normal and planus features. Potential subjects were excludedif they were suffering acute foot injuries, had undergone pre-vious osseous foot surgery or were diagnosed with inflam-matory arthritis, diabetes mellitus, congenital defects or neu-romuscular disease. In subjects with pes cavus, a standardbattery of clinical neurological tests were also performed toexclude subjects with overt neurological signs. An assump-tion was made that in the absence of neurological, congenitalor post-traumatic causes of pes cavus, those subjects selectedcould be reasonably classified as having idiopathic pes cavus.

Foot type was measured using the Foot Posture Index(FPI), which provides a composite score of eight weight bear-ing clinical measures[12,13], A Foot Posture Index of≤−2was categorised as pes cavus, a Foot Posture Index between+2 and +8 was categorised as normal and a Foot Posture In-dex of >+11 was considered pes planus. The length of thetendo-Achilles is a reflection of gastrocnemius-soleus mus-cle compliance and can be determined by measuring anklejoint dorsiflexion[14]. Ankle joint dorsiflexion was measuredw ctw andtp um

angle of ankle joint dorsiflexion was reached without the heellifting. Subjects were able to hold onto the wall for balanceand the contra lateral leg was placed in a comfortable posi-tion. Pronation and supination of the subtalar and midtarsaljoints was restricted by ensuring the foot was positioned per-pendicular to the wall and the subject lunged directly over themidline of the foot. To measure the angle of ankle joint dorsi-flexion in degrees, a digital inclinometer (Baseline®, Fabrica-tion Enterprises Inc, New York, U.S.A.) was aligned with themidline of the tendo-Achilles. This protocol was consideredthe most appropriate method of measuring tendo-Achilleslength as it is routinely used in a clinical setting, is time effi-cient, non-invasive and has the advantage of being performedin a weight bearing (i.e. functional) position.

Prior to using the Foot Posture Index and the lunge test,intrarater reliability was determined during a pilot study of31 healthy subjects with a range of foot types across 2-weeks. The intrarater reliability of the Foot Posture Index wasfound to acceptable (intraclass correlation coefficient (ICC)3, 1 = 0.83, 95% Confidence Interval (CI) 0.68–0.91). Theintrarater reliability of the lunge test was also found to beacceptable (ICC 3, 1 = 0.93, 95% CI = 0.86–0.97).

2.1. Statistical analysis

One foot only was analysed for each subject, in order tos lysis[ ighth nce,i e ofs pesc lanuss weres (SPSSI rac-t erea or’sc h theL met-r dif-f eighta t-hocc -m one-w onsw e an-g ethera foott isticalt

3

ted;

eight bearing using the lunge test[15], whereby the subjeas required to place their foot perpendicular to a wall

o lunge their knee toward the wall (Fig. 1). The foot wasrogressively moved away from the wall until the maxim

Fig. 1. Measurement of tendo-Achilles length using the lunge test. 2 x

atisfy the independence requirement for statistical ana16]. This method also aims to minimise the bias that mave originated with observer (and subject) limb domina

mproved skill acquisition and any other unknown causystematic error. The more supinated foot from eachavus subject, the more pronated foot from each pes pubject and a random foot from each normal subjectelected. In the statistical analysis package SPSS 12.0nc, Chicago, IL.), descriptive statistics were used to chaerise the study sample. Normality of data distribution wssessed using the Kolmogorov-Smirnov test with Lillieforrection and homogeneity of variance was tested witevene statistic. The appropriate parametric or nonparaic statistic was subsequently employed. To determineerences between groups for Foot Posture Index, age, hnd mass, a Kruskal–Wallis test was applied and posomparisons made using Mann–WhitneyU-test. To deterine differences between groups for the lunge test, aay analysis of variance with Tukey post-hoc comparisas used. To examine the relationship between the lungle and the Foot Posture Index, and to determine whny other variables (age, height or mass) were related to

ype, a series of correlational analyses were used. Statests were considered significant ifP< 0.05.

. Results

Three distinctly different foot type groups were collec4 subjects with pes cavus (mean Foot Posture Inde−4

J. Burns, J. Crosbie / The Foot 15 (2005) 91–94 93

Table 1Physical characteristics of the sample

Subject group Age (years), mean (S.D.) Height (metres), mean (S.D.) Mass (kg), mean (S.D.)

Normal foot (n= 24) 33.5 (11.6) 1.77 (0.11) 71.1 (6.9)Pes cavus (n= 24) 29.3 (10.9) 1.73 (0.10) 77.4 (18.7)Pes planus (n= 5) 28.0 (8.7) 1.66 (0.14) 60.6 (8.9)

Note:no statistically significant differences between groups (P< 0.05).

(S.D., 2), 24 subjects with a normal foot type (mean Foot Pos-ture Index +4 (S.D., 2) and five subjects with pes planus (meanFoot Posture Index +12 (S.D., 1) (H= 42.866,P< 0.001).Groups were comparable for age (H= 3.076, P= 0.251),height (H= 3.038,P= 0.219) and mass (H= 4.912,P= 0.086)(Table 1).

There were significant differences between foot typegroups for the lunge test (F(2, 50) = 20.623,P< 0.001). Post-hoc comparisons indicated that the lunge angle in the pescavus group (26.2 (S.D., 5.3) degrees) was significantly lessthan the normal foot type group (31.8 (S.D., 6.0) degrees)(P= 0.003), which was significantly less than the pes planusgroup (42.8 (S.D., 1.9) degrees) (P< 0.001).

The relationship between tendo-Achilles length and foottype is shown inFig. 2. Examination of the scatter plot revealsa curvilinear pattern indicating a nonlinear relationship. Intu-itively, values for the lunge test should be transformed froman angular to a linear value to better represent elongation ofthe tendo-Achilles. Thus, in the linear regression model, thelunge angle was represented by the cosecant of the angle [i.e.1/cos(Lunge angle)]. Pooling all data to test for a predictablerelationship between the Foot Posture Index and this trigono-metric function, a strong, positive correlation was identified:

Foot Posture Index= 42.98

cos(Lunge angle)− 49.06

w st Noo cor-r

F t Pos-t

4. Discussion

The first purpose of our study was to measure tendo-Achilles length in subjects with idiopathic pes cavus, com-pared to normal and pes planus feet. Subjects with id-iopathic pes cavus demonstrated 21–63% shorter tendo-Achilles length than subjects with normal or pes planus feet,respectively. Interestingly, some authors have described anassociation between a short tendo-Achilles and pes planus[17–19]. Our results gave no indication of such a link. Infact, our small group of subjects with clinically detectablepes planus, demonstrated a 35% greater than normal tendo-Achilles length, a finding concurrent with a study of 1047veterans with diabetes[20].

The second purpose of our study was to examine the re-lationship between tendo-Achilles length and foot type. As-suming that ankle range of dorsiflexion is indicative of tendo-Achilles length, our results show that tendo-Achilles length isclosely related to weight bearing foot type. Specifically, pescavus severity was closely related to tendo-Achilles short-ness (Fig. 2). Coefficient of determination (r2) indicated that57% of the variation in foot type could be explained by differ-ences in the tendo-Achilles length. By measuring the lungeangle, we have 57% of the information we would need tomake an accurate prediction of foot type. However, the cavusfoot is complex and multifactorial in nature. Some other un-k sucha rthe-l be-i lesl avusd

sona eredi ,t ucesp rtheri onalM mit-t is di-r ougha usl softt rch[ shortt rchm ry ofh nsis-

ith r = 0.757 (P< 0.001);r2 = 57.3%. This correlation showhat tendo-Achilles length is closely related to foot type.ther variables (age, height or mass) were significantlyelated with the Foot Posture Index (r < 0.193,P> 0.16).

ig. 2. Regression analysis of the relationship between foot type (Fooure Index (FPI) and tendo-Achilles length (lunge angle)).

nown factors must account for the remaining variance,s bony architecture or environmental influences. Neve

ess, this level of correlation is generally regarded asng “high” [21,22] therefore we believe that tendo-Achilength is a substantial explanatory of the degree of ceformity.

Our results fit the theoretical model proposed by Dicknd Diveley, whereby a short tendo-Achilles is consid

nfluential in the development of pes cavus[6]. Howeverhe exact mechanism of how a short tendo-Achilles prodes cavus is less certain. Recent studies may provide fu

nsight into this deforming mechanism. Three-dimensiRI reconstructions have shown that when force is trans

ed to the calcaneus from a loaded tendo-Achilles, forceected via a pulley system towards the plantar fascia thrseries of highly organized trabeculae[23]. Such an osseo

ine of force transmission complements the continuousissue link that helps maintain the medial longitudinal a23,24]. When there is excessive tendon load, such as aendo-Achilles, heightening of the medial longitudinal aay result as the plantar fascia also shortens. This theoow a short tendo-Achilles may produce pes cavus is co

94 J. Burns, J. Crosbie / The Foot 15 (2005) 91–94

tent with previous reports describing plantar fascia shortnessin patients with pes cavus[25].

While the lunge test is a clinically relevant and reliablemethod to measure ankle joint dorsiflexion, it may be limitedin that it can not differentiate between a soft tissue and os-seous block. In pes cavus, the forefoot is often plantarflexedon the rearfoot resulting in compensatory ankle joint dorsi-flexion just to establish a plantar grade position of the foot.This compensation may use all of the available ankle dor-siflexion causing talar neck impingement with the anteriortibial plafond (pseudo-equinus)[25]. More invasive and ex-pensive examination such as radiography, fluoroscopy andfunctional MRI were not appropriate in this study, but mayprove definitive in future studies. Furthermore, the cross-sectional design of our study is also limited in that we wereunable to establish causality. Does limited ankle dorsiflex-ion, caused by a short tendo-Achilles, produce pes cavus ordoes pes cavus produce limited ankle dorsiflexion by ‘jam-ming’ the tibiotalar mortise. Further research, prospectivelytracking tendo-Achilles length and foot type in young chil-dren, where pes cavus is rare and pes planus is common[26],would be necessary to clarify this cause-effect relationshipin adulthood.

5. Conclusion

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[2] Burns J, Crosbie J, Ouvrier R, Hunt A. The effect of pes cavuson foot pain and plantar pressure. In: Woodburn J, editor. Emedscientific meeting, 2004 July 29–August 1; Leeds, UK. 2004.p. 18.

[3] Burns J, Redmond A, Crosbie J, Ouvrier R. Quantification of musclestrength and imbalance in neurogenic pes cavus, compared to healthycontrols, using hand-held dynamometry. Foot Ankle Int; in press.

[4] Pandey S. Neglected clubfoot. Foot 2002;12:123–41.[5] Horne G. Pes cavovarus following ankle fracture. A case report. Clin

Orthop 1984:249–50.[6] Dickson FD, Diveley RL. Functional disorders of the foot.. 2nd ed.

Philadelphia: J.B. Lippincott Company; 1939.[7] Brewerton D, Sandifer P, Sweetnam D. “Idiopathic” pes cavus: an

investigation into its aetiology. BMJ 1963;2:659–61.[8] Dwyer FC. The present status of the problem of pes cavus. Clin

Orthop 1975:254–75.[9] Gudas CJ. Mechanism and reconstruction of pes cavus. J Foot Surg

1977;16:1–8.[10] Samilson RL, Dillin W. Cavus, cavovarus, and calcaneocavus. An

update. Clin Orthop 1983:125–32.[11] Yale AC, Hugar DW. Pes cavus: the deformity and its etiology. J

Foot Surg 1981;20:159–62.[12] Redmond A, Burns J, Ouvrier R, Crosbie J, Peat J. An initial ap-

praisal of the validity of a criterion based, observational clinicalrating system for foot posture. J Orthop Sports Phys Ther 2001;31:160.

[13] Yates B, White S. The incidence and risk factors in the developmentof medial tibial stress syndrome among naval recruits. Am J SportsMed 2004;32:772–80.

[14] Moseley AM, Crosbie J, Adams R. Normative data for passive ankleplantarflexion-dorsiflexion flexibility. Clin Biomech 2001;16:514–21.

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The question of how much a pes cavus foot type isonsequence of joint moments precipitated by tendo-Achhortness, and how much is architectural (subtalar andarsal joint linkages) is complex. This study shows distifferences in tendo-Achilles length of individuals with pavus, compared to normal and pes planus feet. A strongtive relationship between tendo-Achilles shortness andavus severity has been identified. An understanding oelationship may provide insight into the deforming mecism producing ‘idiopathic’ pes cavus.

onflict of Interest

None

cknowledgements

Financial support: The Prescription Foot Orthotic Labory Association (PFOLA), U.S.A., The Australian Podiaducation and Research Foundation (APERF).

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