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The Foot 19 (2009) 7–21

Cross-sectional study to evaluate radiological parameters inhallux rigidus

P. Beeson ∗, C. Phillips, S. Corr, W.J. RibbansDivision of Podiatry, School of Health, The University of Northampton, Park Campus, Boughton Green Road, Northampton NN2 7AL, United Kingdom

Received 9 April 2008; received in revised form 3 July 2008; accepted 17 July 2008

Abstract

Backgound: Hallux rigidus (HR) is a common condition with X-rays used to evaluate its pathology, grade joint changes and to informtreatment.Method: A cross-sectional study was undertaken to evaluate radiological foot parameters in HR. In 110 subjects (180 feet) aged 18–70 years(mean 52 years) standard weight-bearing X-rays were examined using dorsal plantar and lateral views.Results: Seventy (64%) subjects had bilateral HR and 73 (66%) were female. The mean onset of HR (denoted by first metatarsophalangeal(MTP) joint restriction/pain) was 44 (14–68 years) years and median HR duration was 6 years (1–33 years). Flat or chevron-shaped metatarsalheads presented in 131 (73%) feet and a history of first MTP joint trauma in 22% (74% of whom had unilateral HR). In 74% of feet halluxabductus interphalangeus angle (HAI◦) was greater than normal (≤10◦). Correlations between first MTP joint narrowing and sclerosis (r = 0.76,p = 0.01) and increased HAI◦ and first MTP joint narrowing (r = 0.34, p = 0.01) was found. The mean hallux equinus angle of 11◦ was outsidethe normal range (16–18◦). Abnormal sesamoid morphology presented in 117 (65%) feet (30% irregular or hypertrophic). Proximal sesamoiddisplacement was greater than that seen in non-HR. Metatarsus primus elevatus was within normal range (≤8 mm) in 160 (89%) feet. Thefirst metatarsal was longer than the second metatarsal in 66 (37%) feet although the first metatarsal was longer than the third metatarsal in131 (73%) feet and may be responsible for altered forefoot function in HR.Conclusions: HR was associated with female gender, bilateral involvement, older age groups, flat or chevron-shaped metatarsal head, longerproximal phalanx, increased HAI◦ and a first metatarsal longer than the third metatarsal. For radiological parameters to be considered validfor inclusion in a classification of HR their content validity needs to be established by formal research.© 2008 Elsevier Ltd. All rights reserved.

Keywords: Hallux rigidus; Radiological; Parameters; X-ray

1. Introduction

Hallux rigidus (HR) describes the clinical and radi-ological findings of both limited motion and associateddegenerative arthritis of the first metatarsophalangeal (MTP)joint. Objective measurements form the basis of the sci-entific process and are critical to the understanding of apathological change [1]. The most common objective eval-uation of HR has been by radiological measurement [1].The magnitude and pattern of first MTP and metatarso-sesamoid joint wear in HR differ from other first MTPjoint pathologies such as hallux valgus due to the differ-

∗ Corresponding author. Tel.: +44 1604 735500.E-mail address: [email protected] (P. Beeson).

ent kinematic patterns and overall biomechanical properties[2].

This study aimed to identify the radiological parametersassociated with HR evaluated from dorsal plantar (DP) andlateral views of the foot in order to determine radiologicalcontent validity (how comprehensively a system evaluates theproblem it is assessing) for HR. In addition to the first MTPjoint a variety of other radiological foot parameters linked toHR were examined.

2. Methods

An observational, cross-sectional study was undertaken.This involved a quantification of specific variables applied

0958-2592/$ – see front matter © 2008 Elsevier Ltd. All rights reserved.doi:10.1016/j.foot.2008.07.002


8 P. Beeson et al. / The Foot 19 (2009) 7–21

Table 1Exclusion criteria

Hallux valgus-rigidus (intermetatarsal angle ≥12◦)Severe multiple forefoot deformitiesSignificant trauma sustained to foot/leg in previous 12 monthsNeuropathyFirst ray/forefoot surgery (including digital/excluding soft tissue)Morton’s neuroma affecting any inter-metatarsal spaceSeptic arthritis of first MTP jointInflammatory arthritidesNeuromuscular disordersInsulin-dependent Diabetes MellitusHypermobility syndromesLong-term steroid useHistory of severe peripheral vascular diseaseMetabolic bone disease

to a sample of subjects with varying severity. It was under-taken to evaluate radiological parameters in HR subjects(age range 18–70 years) with varying degrees of restrictedfirst MTP joint dorsiflexion <65◦ (measured with a standardfull-circle plastic goniometer, calibrated to 1◦ increments)with either pain, deformity or both. 180 standard pre-operative weight-bearing X-rays were randomly selected andexamined (94 plain, 86 digital). DP and lateral views ofboth feet (exclusion criteria permitting) were used. Ethicalapproval (Leicestershire, Northants, Rutland) was obtained,subjects gave informed consent and a pilot study was under-taken.

Careful preliminary examination of subjects’ clinicalnotes was undertaken to remove those possessing criteria ofexclusion (Table 1). An invitation letter and study informationsheet was sent to suitable subjects giving them time for con-sideration prior to inclusion in the study. Detailed exclusioncriteria were used to reduce unwanted variables.

The body mass index (BMI) for each subject was docu-mented to determine its effect on the radiological parameters.

2.1. Radiological technique

To ensure the best possible comparability of X-rays, stan-dard weight-bearing views were taken and rigid protocoladherence was followed.

The technique used followed guidelines laid down by theResearch Committee of the American Orthopaedic Foot andAnkle Society [3]. Positioning of the feet and tube-head anglewere the same for individual and bilateral X-rays (a standardradiological protocol was used). The only parameter that dif-fered was where the X-ray beam was centered in the tarsus.For DP views the X-ray beam was directed at 15◦ from thevertical (craniocaudal angled) and aimed centrally betweenthe feet, centred on the navicular. On individual feet it wascentered on the intermediate cuneiform [4]. In each case thefeet were parallel, side by side and in line. Angle and baseof gait was not used. It was considered that this may varybetween subjects and it was considered that these differentpositions may introduce unwanted variables between sub-

jects making comparison between feet difficult. Film focusdistance was 100 cm; the kilovoltage and milliamperage wereset at 55 and 6.3, respectively [5,6]. For lateral views a hor-izontal tube-head angulation of 90◦, mediolateral-directedbeam, centered on lateral cuneiform with the film verticallyplaced, parallel to the second metatarsal [5].

2.2. Radiological evaluation

X-rays were evaluated and interpreted using one of twostandardized methods:

(1) A film marker and plastic goniometer (1◦ increments forangles, 1 mm increments for length) on plain film with aclear acetate sheet to protect it.

(2) A digital workstation with high-resolution monitor com-puter picture archiving communication system (PACS)using a web image browser (Visage) to display losslessJPEG images for diagnostic interpretation.

Computerized X-ray measurement was undertaken in twocentres while hand measured X-rays were evaluated in oneother. The use of two methods enabled evaluation and com-parison of the techniques.

2.3. Radiological parameters

These were evaluated (Table 2) by one examiner to elim-inate inter-observer error.

2.4. Radiological protocol

2.4.1. First MTP joint widthTwo methods were used:

(1) Joint space narrowing between bone end plates (notosteophyte bridging) was objectively graded as: none,

Table 2Radiological measurements

Area assessed Radiological criteria

First MTP joint Narrowing, symmetry, presence and severity ofosteophytes, subchondral sclerosis, subchondralcysts, loose bodies

Hallux Proximal/distal phalanx length ratio, HAI◦, IPJ OA,equinus◦

Sesamoids Type and shape, metatarsal/sesamoid joint space.Distance between metatarsal head and proximaledge of sesamoids. Inter-sesamoid distance

First metatarsal Head shape. Length compared to second and thirdmetatarsals. First metatarsal/proximal phalanxlength ratio. Sagittal plane position, first M-C jointposition/angle/joint sag

General features MAA, lateral talus–first metatarsal angle.Transverse plane angulation second MTPJ, N-Cjoint sag, medial/intermediate cuneiform diastasisand gross alterations in tarsal morphology

HAI◦ = hallux abductus interphalangeus angle, M-C = metatarso-cuneiform,MAA = metatarsus adductus angle, N-C = navicular-cuneiform.


P. Beeson et al. / The Foot 19 (2009) 7–21 9

Fig. 1. (A) DP view and (B) lateral view.

definitely narrowed, severely narrowed or joint fusion atone point at least.

(2) Summation method using six separate measurements.Three points were placed along corresponding joint sur-faces of each view (Fig. 1A and B). A perpendicular lineconnecting each pair of corresponding points was used tomeasure joint width in millimeters. Average joint widthwas calculated.

First MTP joint symmetry (symmetrical, medial or lat-eral narrowing), periarticular subchondral sclerosis (none,minimal, moderate or severe); osteophyte location andseverity (minimal, moderate or severe) were documented.The presence of loose bodies and bone cysts was alsodocumented.

2.4.2. HalluxUsing two metaphyseal–diaphyseal reference points the

longitudinal axis of the proximal and distal phalanges were

Fig. 2. Method of measuring length of hallucal phalanx.

charted then measured in millimeters using the methoddescribed by Munuera et al. [7] (Fig. 2).

The hallucal length ratio was calculated by dividingproximal by distal phalanx length. The hallux abductus inter-phalangeus (HAI) angle was formed by intersection of thelongitudinal bisections of the hallucal phalanges and gradedas: absent, mild (>5◦), moderate (>10◦), severe (>15◦). Thehallux equinus angle was measured using lateral longitudi-nal bisections of the proximal phalanx and first metatarsal(Fig. 3). Hallux equinus is defined as <15◦.

2.4.3. SesamoidsSesamoid morphology was documented as: normal, irreg-

ular/hypertrophic, cystic, osteopaenic or bi/tri/quadripartite.The distance between the sesamoids (distal end) andmetatarsal head (DP view) was calculated. A line tangentialto the distal articular surface of the first metatarsal head andperpendicular to its longitudinal axis was drawn. A line wasdrawn at the articular surface of the first metatarsal headperpendicular to its longitudinal axis. The distance fromthis line to the distal end of each sesamoid was measured

Fig. 3. Hallux equinus angle.



Fig. 4. Sesamoid distance from metatarsal head and ISD.

in millimeters and the inter-sesamoidal distance (ISD) wascalculated as the shortest distance between the sesamoids,to the closest 0.5 mm (Fig. 4).

2.4.4. First metatarsal head morphologyThis was documented as: oval, chevron or flat (Fig. 5A–C).

If flat, the degree of flatness was graded as: minimal, moderateor severe.

2.4.5. First metatarsal lengthThe longitudinal bisection line was measured in millime-

ters using the method described by Munuera et al. [7] (Fig. 6).The first metatarsal/proximal phalanx length ratio was calcu-lated by dividing first metatarsal by proximal phalanx length.

Fig. 6. Method for measuring first metatarsal length.

2.5. First metatarsal length compared to second andthird metatarsals

Relative metatarsal measurement (protrusion distance)is a comparative measurement where the lengths of themetatarsals are compared with a specified point in the tarsus.

Fig. 5. (A) Oval, (B) chevron and (C) flat.



Fig. 7. Relative metatarsal protrusion measurement.

The method was used as it is not influenced by increased1–2 intermetatarsal angle or metatarsus adductus. The samemethod cannot be reproduced by computer software so anabsolute (complete) metatarsal measurement was requiredfor digitized X-rays.

Plain X-rays (relative measurement): a modified Hardyand Clapham [8] method was used. A transverse tarsalline was made by bisecting the lateral base calcaneocuboidjoint and medial base talonavicular joint. The longitudi-nal axis of the second metatarsal was marked using twometaphyseal–diaphyseal reference points. The point wherethe second metatarsal axis intersected with the transversetarsal line acted as the center of rotation for the axis. Theaxis line was rotated (using a compass) and three arcsdrawn, at the most distal extent of the first, second andthird metatarsal heads. This enabled the protrusion distance(relative measurement) between the first and second, andfirst and third metatarsals to be measured in millimetersusing a perpendicular line drawn between the three arcs(Fig. 7). A positive value indicates a longer first metatarsalrelative to the second and third metatarsals and a negativevalue indicates a shorter first metatarsal. Length measure-ments within 1 mm of each other were considered to beequal.

Digital X-rays (absolute measurement): the methoddescribed by Munuera et al. [7] (Fig. 8) was used.

A perpendicular line was drawn between the respectivehorizontal lines and measured in millimeters to calculate thedifference in lengths between the first and second and firstand third metatarsals. A positive value indicates a longerfirst metatarsal relative to the second and third metatarsalsand a negative value indicates a shorter first metatarsal.

Fig. 8. Measurement of absolute metatarsal length.

Measurements within 1 mm of each other were consideredequal.

2.5.1. First metatarsal sagittal plane positionThe sagittal plane position of first metatarsal relative to

the second metatarsal was made. The difference between thedistal dorsal metaphyseal cortex (head–neck junction) of thefirst and second metatarsals (lateral X-ray) was measured. Aperpendicular line was drawn between the two dorsal cortices,and the difference measured in millimeters (Fig. 9). A positivevalue indicated a more elevated first metatarsal.

2.5.2. First metatarsal declination angleThe lateral longitudinal axis of the first metatarsal (using

mid-metaphyseal–diaphyseal reference points) relative to theplantar surface of the foot was used (Fig. 9 Angle A). Theline representing the plantar surface of the foot (on support-ing surface) used intersecting reference points on the plantarcalcaneus and medial sesamoid. Normal range = 19–25◦.

Fig. 9. First metatarsal sagittal plane position.



Fig. 10. Talar declination angle.

2.5.3. Talar declination angleThe lateral talus–first metatarsal (talar declination) angle

formed between bisections of the talus and first metatarsalwas measured (Fig. 10). Normal = 0◦, where the midline axisof the talus and first metatarsal are in line.

2.5.4. First metatarsal-cuneiform (M-C) jointFirst M-C joint morphology and angle were documented.

The angle was represented by intersection of the firstmetatarsal longitudinal bisection with a line perpendicularto the medial cuneiform distal articular surface (Fig. 11).

2.5.5. First M-C joint and navicular-medial cuneiform(N-MC) joint sagging

The presence of first M-C joint and N-MC joint sagging(sagittal plane) was documented (lateral view). Normal jointpositions were denoted by parallel dorsal cortices of the bones

Fig. 11. First M-C joint angle.

Fig. 12. FF reference line.

either side of the joint. A difference in height between thetwo bones dorsally with plantar joint gapping representedsagging.

2.5.6. General featuresMetatarsus adductus (MA) was measured. A line par-

allel to the articular surface of the intermediate cuneiformbase (Fig. 12) represented the forefoot (FF) reference line. Aline perpendicular to the forefoot reference line was drawn.The angle formed between the intersections of this per-pendicular line and a longitudinal bisection of the secondmetatarsal represented the degree of MA (Fig. 13), andgraded: absent, mild (16–19◦), moderate (20–25◦), severe(>25◦).

Transverse plane angle deviation of the second MTPjoint was measured. The angle formed between the bisection(proximal and distal metaphyseal–diaphyseal junctions) ofthe proximal phalanx second toe and the longitudinal bisec-tion of the second metatarsal shaft (Fig. 14). Lateral deviationof the second toe was denoted as negative and medial devia-tion positive. Normal value = 7◦ lateral.

The presence of medial/intermediate cuneiform diastasisand gross alterations in tarsal morphology were also docu-mented.

3. Results

Descriptive and comparative statistical analyses were per-formed using SPSS for Windows version 15.0 (SPSS Inc.,Chicago, IL, USA). Standard chi-squared analysis (χ2) wasperformed on categorical data. Pearson and binary correla-tion coefficients were used to evaluate the non-continuous



Fig. 13. MA angle.

data. Differences were considered to be significant when theP-value was ≤0.05.

3.1. Demographic findings

The findings of the current study demonstrate that HRwas associated with increased female prevalence, bilateralinvolvement and older age of subjects (Tables 3 and 4),agreeing with the findings of previous research [9]. Few sub-

Fig. 14. Transverse plane angle deviation second MTP joint.

Table 3Sample characteristics

Subjects (feet) 110 (180)

GenderFemale 73 66%Male 37 34%

Age (years)Mean (range) 52 (23–70)Median 55

Age of onset, mean (range) 44 (14–68)Duration of symptoms years (range) 6 (1–33)

BMI (kg/m2), mean (range) 25.93 (19.53–37.26)Male 26.48Female 25.70

Trauma history (feet) % (39) 22%Unilateral 74%Bilateral 26%

Table 4Age groups

Years 18–30 31–40 41–50 51–60 61–70% 5.7 10.7 18.6 37.1 27.9F:M ratio 7:1 7:1 1:1 2:1 3:1

jects in this study had adolescent onset. Overall subjectswere marginally overweight, indicated by a mean BMI of25.93 kg/m2 (19.53–37.26) but with no gender difference forthis variable (Table 3).

The mean age of onset of symptoms (first MTP joint defor-mity or restriction/pain) was 44 years. This is eleven yearsprior to the median age of presentation at a foot and ankleclinic (55 years) and supports the concept that this conditionmay be one of insidious development. Foot biomechanics,footwear type and activity levels may have some bearing onthe development of symptoms and subsequent progression ofdisease. Epidemiological studies show that the pathologicalprocess of OA takes place several years before radiologicaldetection is possible [10], so the prevalence of first MTP jointradiological change presented here is an underestimate of theactual prevalence of cartilage degeneration.

3.2. Radiographic

Table 5 shows general radiographic findings andTables 6 and 7 data-specific to each radiological parameter.The confidence interval (CI) illustrates the range of measuresdrawn from the study sample.

Table 5X-ray data

Mode ofevaluation

Bilateral(subjects) %

Unilateral(subjects) %

Analog Digitized (70) 64% (40) 36%; L(18) 45%; R(22) 55%

94 (52%) 86 (48%)



Table 6Mean Radiographic findings (Based on 180 feet)

Radiological parameters (counts*) Mean ±S.D. 95% CI Range

Lower Upper

First MTP joint width 1.1 mm 0.79 0.93 1.41 0–3Hallucal length ratio 1.20 0.16 1.16 1.26 1–1.80Hallux abductus interphalangeus 18.2◦ 2.00 14.6 22.8 5–30◦Hallux equinus angle 11.10◦ 3.68◦ 10.01 12.20 2–18◦

Sesamoid distanceTibial 7.2 mm 2.75 6.41 8.05 1–15Fibular 8.7 mm 2.97 7.97 9.74 1–17

Inter-sesamoidal distance 1.36 mm 0.86 1.10 1.62 0–4First metatarsal length 60.3 mm 6.0 58.54 62.02 50–76First metatarsal length ratio 2.09 0.19 2.03 2.15 1.61–2.8First met length compared to second: shorter (69), equal (45), longer (66) 0.08 mm 3.01 −0.22 0.97 −5 to 10First met length compared to third: shorter (26), equal (23), longer (131) 4.73 mm 3.90 3.57 5.88 −4 to 15MPE 4.96 mm 2.02 4.35 5.56 0–11First metatarsal declination angle 21.14◦ 2.14 20.5 21.78 16–26◦Lateral talus–first metatarsal angle 1.30◦ 2.08 0.67 1.89 0–9◦First M-C joint angle: 9.68◦ 6.93 7.58 11.74 0–26◦

Male 9.7◦ – – – –Female 9.1◦ – – – –

Transverse plane angle second MTPJ 3.93◦ 4.09 2.72 5.15 0–21◦

* = nominal data, SD = Standard deviation, MPE = metatarsus primus elevatus, M-C = metatarso-cuneiform.

Loose bodies were found in 23 (13%) first MTP joints,subchondral bone cysts in only 45 (25%) metatarsal headsand 38 (21%) proximal phalanx bases. Hallucal IPJ OA wasrarely associated with HR and only present in 19 (11%) feet.

Differences in tarsal morphology (Table 8) are presentedin 32 feet (18%).

4. Discussion

4.1. Radiographic findings

In this study bilateral involvement presented in 70 (64%)subjects (Table 5), which may reflect the predominance ofolder subjects (Table 4) rather than the true incidence as, withthe passage of time, a higher percentage of patients are likelyto exhibit bilateral disease. It may also reflect the type ofclinic (surgical) from which subjects were taken. Conserva-tive management may delay attendance for a surgical opinionby which time, although only one side is severe enoughto warrant surgery, the patient may present with bilateralinvolvement.

In the current study analysis was undertaken at the pointof referral.

4.1.1. First MTP jointAll subjects were clinically diagnosed with HR and pre-

sented with varying degrees of severity. A loss of first MTPjoint width (Table 6) was found in 78% of feet with a mean of1.1 mm (0–3 mm) with 35% severely narrowed. The remain-ing 22% of subjects with no loss of joint space representearly clinical stage HR in which no radiological joint changes

were present. As pathological process precedes radiologicaldetection [10] (subchondral bone changes precede loss ofjoint space) a stage in clinical HR may exist which precedesradiological joint space loss. A strong correlation was foundbetween first MTP joint space narrowing on the DP and lateralviews (r = 0.98, p = 0.01). This was an interesting observationbearing in mind that the first MTP joint is not a ball and socketjoint and that joint space may differ between views becauseof variations in metatarsal head shape between the transverseplane (DP view) and frontal plane (lateral view).

Normal joint space symmetry was found in 102 (57%) feet.It was expected that asymmetrical joint changes would bemore commonly associated with more severe hallux rigidusor hallux valgus-rigidus. In this study concurrent presentationof hallux valgus and hallux rigidus was not common.

χ2-Analysis of joint space narrowing and halluxabductus interphalangeus revealed a significant finding(p = 0.005 < 0.05) whereas for joint space narrowing and jointspace symmetry there was no statistical significance. Whilethese findings indicate a relationship between the parametersthis is not necessarily a causal relationship.

Assessment of periarticular subchondral sclerosis wassubjective and difficult to quantify. The severity of firstMTP joint sclerosis increased with loss of MTP joint space(Table 7) with 67 (37%) of feet having moderate sclerosis.There was a strong correlation between sclerosis and loss ofjoint space (r = 0.76, p = 0.01) but this was not statisticallysignificant. A weak correlation between sclerosis and MPE(r = 0.29, p = 0.01) was found, this concurs with Coughlinand Shurnas [9] who also found a weak correlation (r = 0.5,p = 0.01) which was not significant. In some cases sclero-sis of the proximal phalanx base was an artifact, i.e. due to



Table 7Categorical and nominal radiological findings (based on 180 feet)

Radiological parameters Count Percentage

First MTP joint spaceNone 39 22Definitely narrowed 40 22Severely narrowed 63 35Joint fusion 1 point 38 21

First MTP joint symmetry:Symmetrical 102 57Medial narrowing 32 18Lateral narrowing 46 25

Subchondral sclerosisNone 22 12Minimal 62 34Moderate 67 37Severe 29 16

First MTP joint osteophtyesNone 30 17Lateral only 22 12Dorsal only 7 4%Lateral + dorsal 70 39Medial + dorsal 7 4Lateral + medial 27 15Lateral + medial + dorsal 17 9

Osteophyte severityMinimal 56 31Moderate 84 47Severe 40 22

Metatarsal head shapeOval 49 27Flat 61 34Chevron 70 39

Severity of flatness where flatMild 51 29Moderate 79 43Severe 50 28

Sesamoid changesNormal 63 35Irregular/hypertrophic 54 30Cystic 28 15Bi/tri/quadripartite 23 13Atrophic 12 7

First M-C joint positionFlat 57 32Angled 123 68First M-C joint sag 7 5Second metatarsal-intermediate cuneiformjoint OA

22 12

Metatarsus adductusAbsent 97 54Mild (16–19◦) 42 23Moderate (20–25◦) 25 14Severe (>25◦) 16 9Medial/intermediate cuneiform diastasis 101 56

superimposition of bones (plantar flexed proximal phalanx)or osteophytosis.

Osteophytes were predominantly found on the lateral anddorsal aspects of the first MTP joint in 70 (39%) feet and were

Table 8Differences in tarsal morphology

Radiological feature Count Percentage

Enlarged medial cuneiform 2 1.1

Accessory navicularType I 1 0.5Type II 4 2.2Type III 10 5.5

Os supra naviculare 3 1.7Os peroneum 2 1.1Hallucal IPJ accessory ossicle 3 1.7Talonavicular OA 4 2.2Spurred facet first metatarsal lateral base 3 1.7

Total 32 17.7

moderately severe in 84 (47%) feet (Table 7). The severity offirst MTP joint osteophytes were correlated with a loss of jointspace (r = 0.50, p = 0.01) but this was not statistically signifi-cant.χ2-Analysis of severity of osteophytes and HAI revealedno significant finding (0.234 > p > 0.05) but there was a signif-icant relationship between severity of osteophytes and jointspace narrowing (p = 0.002 < 0.05). This relationship is notnecessarily causal.

Loose bodies were only found in 18 (13%) first MTPjoints. This is comparable with other researchers’ results 17%[1,9].

In this study the incidence of subchondral cysts was low:36 feet (25%) had metatarsal head cysts and 30 feet (21%)proximal phalanx cysts. This was lower than expected con-sidering the profile of subjects but may suggest a differentprocess of subchondral bone change in HR compared to otherforms of OA.

4.2. Hallux and IPJ

In this study the proximal phalanx was found to be longerthan the distal phalanx (mean hallucal length ratio of 1.20).Another study has found similar results when comparingHR with non-HR subjects [7]. A few of our subjects pre-sented with a radiologically short proximal phalanx. Thiswas considered to be an artifact due to proximal phalanxplantar flexion secondary to flexor hallucis brevis (FHB)spasm in subjects with early joint changes or elevation of thefirst metatarsal in those with more advanced joint changes.The overall length of the hallux may be a factor contribut-ing to HR and is supported by others who have comparedHR with non-HR subjects and found a longer hallux inthe HR group [7]. It was concluded that where there isincreased length a proportional increase in girth (squaring)of the proximal phalanx base is likely. If this is combinedwith a metatarsal head with flat morphology it may playsome part in restricting first MTP joint dorsiflexion in HR[7].

The hallux abductus interphalangeus angle averaged18.2◦. In 133 feet (74%) the HAI◦ was greater than normal



(where normal ≤10◦). There was a strong correlationbetween an increased HAI◦ and first MTP joint space reduc-tion (r = 0.84, p = 0.05). It is hypothesized that the presenceof HAI indicates a more progressive HR process and thatwith increased first MTP joint damage the first metatarsalhead becomes flatter and more resistant to transverse planemovement, thus predisposing to an increased HAI.

As 131 (73%) of feet had a flat or chevron-shapedmetatarsal head this may also contribute to resistance to trans-verse plane movement. A correlation between an increasedHAI◦ and diminished hallux valgus or intermetatarsal anglewas found by one author [9] who used the theory of trans-verse plane resistance to explain this. χ2-Analysis of jointspace symmetry and HAI revealed no significant finding(0.40 > p > 0.05).

The mean hallux equinus angle 11◦ (2–18◦) was wellbelow the normal range (16–18◦) [11]. This is a useful radi-ological measure of HR as it documents the amount ofproximal hallucal plantar flexion generated by soft tissuespasm (capsular and FHB).

4.3. Sesamoids

Sesamoid morphology was found to be abnormal in117 (65%) feet with 54 (30%) presenting as irregular orhypertrophic. These sesamoid changes contribute to thepathological process in HR but are not a cause of it. Increasedsesamoid length in HR was found, this finding concurs withother researchers [12–14]. Abnormal sesamoid morphologyand increased length is attributed to excessive traction exertedby the retracted FHB and is likely to restrict first metatarsalplantar flexion contributing to reduced first MTP joint exten-sion, quality of motion and pain.

Proximal sesamoid displacement in HR may be due toFHB spasm (guarding response to pain) or contracture sec-ondary to joint stiffness. Logically this may be more prevalentin the later phase of HR, i.e. in older subjects where the con-dition has developed over time and is more advanced. Oursample was more likely to be influenced by such findingsas the older age range predominated. The tibial and fibu-lar sesamoid distance from the metatarsal head was used tomeasure proximal sesamoid displacement. Yoshioka et al.[15] (without giving specific values) and Munuera et al. [14],found that the tibial sesamoid is closer to the metatarsalhead than the fibular sesamoid. Yoshioka et al. [15] pro-posed that this is because the tibial sesamoid is usually larger,more elongated and has a shorter sesamophalangeal liga-ment [15]. The findings of this study concur, in that, themean tibial sesamoid distance was 7.2 ± 2.75 mm (1–15) andfibular 8.7 ± 2.97 mm (1–17). This is greater than that foundby Prieskorn et al. [4] who evaluated 100 paired feet with-out foot pathology (tibial sesamoid distance 4.9 ± 1.8 mm,fibular sesamoid distance 7.6 ± 1.9 mm). The findings of thecurrent study are comparable with Roukis et al. [1] whofound a mean tibial sesamoid distance 5.8 ± 1.8 mm (range2–9 mm) and mean fibular sesamoid distance 8.0 ± 1.8 mm

(range 0–12 mm) and Munuera et al. [14] who found amean tibial distance 4.7 ± 1.8 mm and mean fibular distance6.2 ± 1.7 mm. The difficulty in comparing our findings withstudies examining normal feet is the methodology used wasnot comparable. It is not possible to draw firm conclusions asmeasurement of sesamoid distance from the first metatarsalhead is influenced by the first metatarsal length. For exam-ple, a sesamoid located 10 mm from the joint space in ametatarsal measuring 60 mm would not have the same sig-nificance as in one that measures 50 mm. By expressing themeasurement as a percentage of the first metatarsal lengththis factor could be taken into account. The findings of thisstudy do not concur with Munuera et al. [14], this may be dueto the different age profile between the studies with muchyounger subjects (mean age 23 years) used by Munuera etal. [14]. Proximal sesamoid displacement appears to be alate effect. The value of this radiological measurement needsfurther investigation. Evaluating sesamoid position in early-stage HR and monitoring its evolution in the same patientsover time to observe how sesamoid distance increases withseverity.

Inter-sesamoidal distance was found to be difficult to mea-sure due to merging of the inner edge of the sesamoidswith the first metatarsal head trabeculae and also sesamoidosteopaenia due to immobility or fusion with the metatarsalhead. The reliability of this measurement could not be guar-anteed.

4.4. Metatarsal head shape

Of the 180 feet 49 (27%) had an oval metatarsal headshape, 70 (39%) chevron and in 61 (34%) it was flat. Forindividual subjects, joint shapes were the same on both feetand thus 140 (78%) had a flat or chevron-shaped metatarsalhead. In this study an association between a flat or chevron-shaped metatarsal head and HR presented. Of those witha flat metatarsal head, 79 feet (43%) had moderate sever-ity of flatness with the remainder being equally distributedbetween minimally and severely flat. While these findingsconcur with other researchers [9], and the general hypoth-esized assumption that an association exists between HRand a flat or chevron-shaped metatarsal head [16,17] firmconclusions cannot be made as the incidence of occurrencein the general population is unknown. Obviously with timeand increasing severity of HR, joint flattening and widening(attributed to osteophytes formation) will occur [3,16–21].It is suggested that such joint shapes resist transverse planedeformity, predisposing to sagittal plane deformity and HR.Flat metatarsal head morphology can be seen in a healthy jointbut such a joint shape can predispose to HR [13]. A strongcorrelation between an increased HAI◦ and first MTP jointspace reduction (r = 0.84, p = 0.05) was found. With increasedfirst MTP joint damage the first metatarsal head becomes flat-ter, leading to a lack of sagittal plane MTP joint movement,which may result in increased transverse plane IPJ movementand subsequent deformity, i.e. HAI.



A small proportion of the unilateral HR subjects had X-rays of the asymptomatic foot. In these cases it was apparentthat first metatarsal head shape differed between the HR andnon-HR foot and that metatarsal head shape was oval in casesof hallux valgus. Consequently different first metatarsal headshape may result in different biomechanical joint function.Although these findings suggest a trend the numbers of sub-jects where such a comparison was possible was too small toenable definitive conclusions to be drawn.

Changes in metatarsal head trabecular pattern wereobserved and may reveal valuable information about func-tion. A long first metatarsal with respect to the lessermetatarsals may constrain first metatarsal plantarflexion atpropulsion promoting changes in first metatarsal head pres-sure. In addition if the joint is stable in the transverse plane(flat or chevron morphology) excessive joint compressionmay be generated at propulsion. These pathological changesin bone pressure during function may modify its trabecularpattern. Further research of this finding in HR is indicated.

4.5. Absolute or relative first metatarsal length andcomparative length to second metatarsal

The mean first metatarsal length ratio of 2.09 demon-strates that, in most cases, the first metatarsal is about twicethe length of the proximal phalanx. The relevance of firstmetatarsal length in HR is unclear. Multiple pathologies of thefoot caused by metatarsal parabola malalignment (excessiveshortness or length) of one or more metatarsals have been pre-viously reported [22–26]. A long first metatarsal [27–29] hasbeen implicated in the development of HR, with the incidencevarying between 0 and 60% [7,20,21,30,31]. The method ofmeasurement appears to influence the reported incidence ofa long first metatarsal [7,9]. The method used by Hardy andClapham [8] was used in this study as it was not found tobe influenced by metatarsus adductus or an increased 1–2intermetatarsal angle. Some studies have actually reportedon the comparative length of the first and second metatarsals[7,9,21,30,32–34] and no studies have reported on the com-parative length of the first and third metatarsals.

This study demonstrated a shorter first metatarsal (38%),equal metatarsal length (25%) and longer first metatarsal(37%) when compared to the second metatarsal. The inci-dence of a long first metatarsal in HR was no more commonthan that found by Harris and Beath [35] who examined7167 asymptomatic military recruits. Coughlin and Shur-nas [9] found a smaller proportion of feet (28%) with along first metatarsal. In the current study there was no sig-nificant difference in the relative metatarsal length of HRsubjects unlike that found by other studies [7,20,21,30,31] norwas there any correlation between increased first metatarsallength and severity of HR. This concurs with the findingsof other researchers [7,34] but differs from a study wherenon-HR feet were measured (using Hardy and Clapham’smethod) where it was found that the first metatarsal relativeto the second metatarsal had a mean protrusion of +1.88 mm

[22] (second metatarsal protrusion relative to third metatarsalwas −4.72 mm [22]). The sample characteristics, i.e. non-HR and mean age (22 years) may have been responsible forthis. A later study [7] which examined early hallux limitus(mean age 23 years) concluded that increased first metatarsallength presented in younger subjects and that in older sub-jects with more advanced HR the metatarsal length could bealtered (shortened) by degenerative first MTP joint changesand metatarsal head flattening [7]. A different pathogenesisbetween young HR and old HR may be responsible.

One disadvantage of using digitized X-rays was that theavailable computer software was not able to measure the rel-ative metatarsal lengths. An alternative method was adoptedwhere absolute values were measured. Although measure-ment of individual absolute metatarsal length has been shownto be reliable [7] it does not allow for the effects of metatarsusadductus or increased 1–2 intermetatarsal angle.

Increased first metatarsal/proximal phalanx girth wasobserved. This was not measured in this study but furtherresearch of such findings in HR is indicated.

4.6. Biomechanical considerations of first metatarsalrelative to third metatarsal length

It is hypothesized that in a normal metatarsal parabolathe first metatarsal is equal in length to the third metatarsalwith the second metatarsal longer than both [36]. In thecurrent study, the comparative lengths of the first and thirdmetatarsals revealed that the first metatarsal was longer in 131(73%) feet (mean 4.73 mm). It is hypothesized that the rela-tive length differential between the first and third metatarsalsmay predispose to HR due to altered forefoot biomechanicalfunction. It is determined that the second metatarsal acts asa fulcrum with weight transferring from the lateral to medialforefoot around the second metatarsal fulcrum [36]. For thisto occur efficiently the first metatarsal should be the samelength as the third with the second longer than both. It is pos-tulated that an abnormal metatarsal parabola may result indisruption of weight-bearing through the forefoot with jam-ming of the first MTP joint. The mechanism for this pathologymay be explained by the work of Bojsen-Moller [36] whodescribed two axes within the foot. The oblique axis (lowgear) represented by a line passing through the second tofifth MTP joints and the transverse axis (high gear) repre-sented by a line passing through the first and second MTPjoints.

During propulsion through first and second MTP joints(high gear); the plantar fascia tightens and first MTP joint dor-siflexes. This supports the windlass mechanism of Hicks [37]who, like Bojsen-Moller [36], found that when the plantar fas-cia tightened, the first metatarsal would plantarflex against theground under the stabilizing influence of the peroneus longustendon. During propulsion through second to fifth MTP joints(low gear); the plantar fascia fails to become taught mediallyand the first metatarsal dorsiflexes as the stabilizing effect ofthe windlass mechanism and peroneus longus is lost, while



the hallux plantarflexes to provide some stability at finalpropulsion to the medial side of the foot. This concurs withaspects of the centre of pressure and sagittal plane facilitationtheories [38–40]. Where the first metatarsal is long, high geartoe-off is impossible to achieve because there is only one axisextending from the first MTP joint through to the fifth. More-over, the first metatarsal cannot plantarflex because its lengthmeans it cannot rotate over the ground but instead is jammedinto dorsiflexion. In this study only 38% of feet had a secondmetatarsal longer than the first while 131 (73%) feet had afirst metatarsal that was longer than the third metatarsal thusmodifying the low gear axis and subsequent forefoot func-tion. The implication is that the relative length differentialbetween the first and third metatarsals may be of consid-erable aetiological significance in HR however, we cannotmake firm conclusions as we do not know the incidence ofoccurrence in the general population. Further research wouldbe required to compare foot function in a group of HR withnon-HR subjects using dynamic in-shoe analysis to determinehow metatarsal length influences function.

4.7. Metatarsus primus elevatus (MPE)

The importance of MPE in HR was first proposed byLambrinudi in 1938 [41] and endorsed by later reports[21,28–31,42–46] but more recently radiographic evidenceto the contrary has been reported [9,34,47,48]. In this studyMPE, first metatarsal declination angle and lateral talus–firstmetatarsal angle were used as measures of first metatarsalsagittal plane position. It was found that 89% of subjects hadradiographic measurements for MPE that were within a nor-mal range (≤8 mm) [48] with a mean MPE 4.96 ± 2.02 mm(0–11). There were only 10 cases of up to 11 mm of MPEidentified. The findings of this study concurs with otherauthors [9,48–50] and suggests that MPE is a secondarychange resulting from an arthritic MTP joint and that as HRprogresses so does first ray elevation (analogous with theincreased intermetatarsal angle associated with increasingseverity of hallux valgus) [9]. Surprisingly a weak corre-lation was found between MPE and severity of first MTPjoint narrowing lateral view (r = −0.29, p = 0.05) and DP view(r = −0.28, p = 0.05) unlike others [9] who found a strongercorrelation (r = 0.5, p = 0.01). The mean first metatarsal dec-lination angle was 21.14 ± 2.14◦ (16–26◦) which falls withinthe normal range (19–25◦) [34]. This finding concurs withseveral researchers [9,34,47,48]. The mean lateral talus–firstmetatarsal angle was 1.3 ± 2.08◦ (0–9◦) also within the nor-mal range (0–4◦). A good correlation was found between firstmetatarsal declination angle and MPE (r = 0.59, p = 0.01),similar to the findings of one author [9] (r = 0.60, p = 0.03).No correlation between MPE and metatarsus adductus wasfound, again this concurs with other researchers [1,9].

The theory of functional hallux limitus, a reduction offirst MTP joint dorsiflexion with simulated loading of thefoot compared to passive MTP joint dorsiflexion; has beenproposed as a cause of HR [38,39,50]. In this study and that of

other researchers [9] the mean MPE and mean first metatarsaldeclination angles fall within normal limits. These findingstherefore question the concept of functional hallux limitusas reported in the literature which remains theoretical con-jecture and a subjective diagnosis [51], conceived to explainabnormalities seen on in-shoe pressure readings and visualgait assessments [52]. Some [9] hypothesize that functionalhallux limitus represents the residual elevatus occasionallynoted on dorsiflexion stress X-rays in severe HR. It may bea consequence of tenosynovitis of the FHL tendon whichlimits its excursion and subsequently that of first MTP jointdorsiflexion on foot loading [53].

4.8. Tarso-metatarsal and inter-tarsal joints

The first M-C joint position was found to be angled in131 feet (73%) with a mean joint angle of 9.68◦ (±6.93).The mean angle was possibly not a good representation ofthe data as the standard deviation was found to be large.This angle increased with age from a mean of 6.9◦ in theyoungest age group (18–30 years) to 10.57◦ in the oldest(61–70 years). Hyer et al. [54] found a similar trend withincreasing age. In the current study the mean angle in males(9.7◦) was marginally greater than females (9.1◦). Hyer et al.[54] found a greater mean angle in females but their methodwas not comparable as it consisted of measurements takenfrom (77) dry bone samples.

In conclusion the first M-C joint angle was difficult tointerpret due to overlapping contours on the DP view, a find-ing also reported by Dykyj et al. [55]. In addition the positionof the first ray on this view may have created the appearanceof an increased angle of obliquity, a finding supported byother researchers [56,57]. It is anticipated that bigger first M-C joint angles would be associated with hallux valgus. FirstM-C joint OA was seen in 11 (8%) feet. First M-C joint sagwas only found in a few feet 7 (5%). This concurs with Jack[30] who describes the first M-C joint as a flat stable jointwith a small range of movement which never gives way.

Using lateral weight-bearing X-rays Jack [58] describedthree anatomical types of flat foot based on the level ofthe joint break within the medial column (talar-navicular,navicular-cuneiform or both). The navicular-cuneiform (N-C) joint sag was the commonest seen [58]. In this study 55(31%) feet presented with N-C joint sag. The significanceof this finding in HR is supported by recent research linkinghindfoot valgus with first MTP joint OA [59]. No measure-ment of N-C joint sag angle was made because it was revealed(pilot study) that difficulty in defining bones resulted in sig-nificant variation in angular measurements.

Second metatarsal cuneiform joint OA was found in 22(12%) subjects in this study. It has been suggested [23] thatpatients with a functionally short first ray (or a function-ally long second ray) have radiographic evidence of overloadstresses on the second metatarsal segment consisting of thick-ening of the cortices and/or shaft or a gap between the firstand second cuneiforms. These stresses may accumulate over



time and result in arthrosis. In this study 38% of feet werefound to have a second metatarsal longer the first metatarsal.Davitt [60] suggests a clear association between midfootarthrosis and a long second metatarsal and suggests a possiblemechanical aetiology.

Metatarsus adductus was absent in 97 (54%) of feet but42 (23%) had a mild metatarsus adductus angle (MAA) of16–19◦ (normal = 15◦). In 25 (14%) of feet the MAA wasbetween 20 and 25◦ and only 16 (9%) feet had a severeMAA (>25◦). There was no statistically significant associa-tion between HR and MAA; however, the overall percentageof subjects with metatarsus adductus 83 (46%) was greaterthan that seen in the general population (0.1%) [61].

The method described by Coughlin and Shurnas [13] formeasuring MAA was used in the pilot study but found to beinconsistent. The four tarsal reference points could not beconsistently identified on all X-rays; however, the interme-diate cuneiform base was more easily identified and so thismethod (a modification of that used by Engel et al. [62]) wasapplied in the current study.

It is speculated that metatarsus adductus may increasemedial transverse plane pressure at the first MTP jointincreasing the risk of HR. Further evaluation using in-shoeand force plate studies comparing metatarsus adductus withcontrols are indicated.

4.9. Transverse plane angle second MTP joint

Transverse plane angulation of the second MTP joint waspresent in 58% of feet (mean 3.93◦) and a strong correla-tion found between second MTP joint transverse plane angleand direction (r = 0.72, p = 0.01). Medially deviated secondMTP joints were seen in 44 (31%) with 38 (27%) later-ally deviated and the remaining 61 (43%) rectus. Transverseplane drift of the second MTP joint is considered a subtleindicator of first ray hypermobility and can be promoted byflatfoot or medial column instability (N-C joint sag). Thiscan lead to second MTP joint synovitis with attenuationof the lateral collateral ligament, allowing unopposed pullof the first lumbricale, thereby creating medial angulationof the second toe. In subjects presenting with an asymp-tomatic second MTP joint the second toe angulation mayresult from forceful contraction of FDL in an attempt to pro-vide medial column stability. This concurs with Roukis etal. [1] who demonstrated increased medial angulation of thesecond toe with increasing severity of HR. In the currentstudy a moderate correlation was found between subjects withincreased metatarsus adductus and increased second MTPjoint transverse plane angle (r = 0.42, p = 0.01) but this wasnot significant.

4.10. Medial/intermediate cuneiform diastasis andtarsal morphology

Medial/intermediate cuneiform diastasis (MICD) was firstreported by Jack [30] as a common feature in HR. MICD may

be a result of increased transverse plane movement in com-pensation for reduced first MTP joint sagittal plane motion.In this study it presented in 101 (56%) of feet (Table 7). It hasalso been associated with a functionally short first ray (or afunctionally long second ray) [23]. It is a difficult feature toassess and its presence is influenced by foot position. Medialcuneiform rotation may present as a diastasis? Without nor-mal values for comparison there is a temptation to condemnany gap as being abnormally wide.

Gross alterations in tarsal morphology presented in 32(18%) of subjects (Table 8) but these differences were notperceived to be significant.

It is recognized that difficulties and limiting factors asso-ciated with radiological evaluation of the foot, where theX-ray beam was centered in the tarsus and foot positioncould influence findings [63]. Previous publications may haveunwittingly introduced unwanted variables by using angleand base of gait rather than a standardized foot position.Comparison with these studies has taken such factors intoaccount.

This study supports the inclusion of the followingradiological parameters in a classification of HR to aidsurgical decision-making and their statistical relevance(Table 9).

5. Conclusion

The purpose of this cross-sectional study was to documentthe key radiological parameters associated with HR. In doingthis a number of difficulties and limiting factors associatedwith radiological evaluation and assessment of the foot werehighlighted [63]. Digitized X-rays provide an easier formatfor evaluation and interpretation of the radiological featuresof HR [63].

Only certain radiological parameters were useful to eval-uate HR. The incidence of some features was low andtherefore represented no significant association with HR,while others were either too time-consuming, too difficult tomeasure, or the reliability of their measurement [64,65] (par-ticularly angular measurements) were in doubt [54]. Futureassessment of frontal plane sesamoid rotation using a weight-bearing axial sesamoid view may provide a more reliablemethod [66].

The findings of this research are based on the defined studypopulation. HR was associated with female gender, bilateralinvolvement, older age groups (a condition which developsover time), flat or chevron-shaped metatarsal head, longerproximal phalanx (with increased sized base), increased HAIangle and a first metatarsal longer than the third metatarsal.Unilateral involvement was more commonly associated withtrauma. In bilateral cases a positive family history could notbe concluded, however, a properly constructed family studymay prove such an association. Metatarsus adductus wasmore common in HR than in the general population but a sig-nificant correlation was not found with HR severity. HR was



Table 9Useful radiological parameters to include in classification of HR

Radiological parameter Statistical relevance in thisstudy

First MTPJJSN JSN in 78% feetJSS Asymmetrical joint space

(43%)Sclerosis JSN and sclerosis (r = 0.76,

p = 0.01)Osteophytes Osteophyte severity and JSN

(p = 0.002 < 0.05)

HalluxProximal phalanx (PP) length 78% long PP and increased

base sizeHAI◦ 74% HAI◦ > 10◦. Chi-square

JSN and HAI(p = 0.005<0.05)

Equinus◦ Mean hallux equinus angle11◦ (normal range: 16–18◦)

SesamoidMorphology 65% abnormal morphology

(30% of which hypertrophicor irregular)

Displacement Proximaldisplacement > non-HR.Mean tibial sesamoid distance7.2 ± 2.75 mm (1–15) andfibular 8.7 ± 2.97 mm (1–17)

Metatarsal head morphology 73% flat or chevron-shapedFirst metatarsal length (relative to

third met)73% first metatarsal longerthan third met (mean4.73 mm)

N-C joint sag 31% N-C joint sagMetatarsus adductus (MA) MA in 46%. More common

in HR than general population(0.1%) [61] but no significantcorrelation with HR severity

Second MTPJ deviation 58% (mean 3.93◦).Correlation between secondMTP joint transverse planeangle and medial direction(r = 0.72, p = 0.01)

Medial/intermediate cuneiformdiastasis

56%

not associated with MPE, increased first metatarsal length rel-ative to second metatarsal and there were few subjects withadolescent onset.

For radiological parameters of the foot to be consideredvalid for inclusion in a classification of HR their contentvalidity needs to be firstly established by formal research[65]. The purpose of this research study was to establish suchvalidity.

Conflict of interest

All authors were fully involved in the preparation of themanuscript and the material within has not been and will notbe submitted for publication elsewhere.

Acknowledgement

The authors wish to thank Mr Chris Kemp for his helpwith the line diagrams.

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Author's personal copy Cross-sectional study to evaluate radiological parameters in hallux rigidus

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