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Published online before print December 10, 2003, 10.1148/radiol.2302021543
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(Radiology 2004;230:493-497.)
© RSNA, 2003

Musculoskeletal Imaging

Variations in Calcaneonavicular Morphology Demonstrated with Radiography1

John T. Lysack, MD, MSc and Paul V. Fenton, MD, FRCPC

1 From the Department of Diagnostic Radiology, Queen’s University, Kingston General Hospital, 76 Stuart St, Kingston, ON, Canada K7L 2V7. From the 2002 RSNA scientific assembly. Received November 27, 2002; revision requested January 22, 2003; final revision received May 28; accepted June 25. Address correspondence to J.T.L. (e-mail: 3jtl@qlink.queensu.ca).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To determine and classify radiographically demonstrated variations in calcaneonavicular morphology and to estimate prevalence in a clinically relevant patient population.

MATERIALS AND METHODS: Retrospective review was performed of foot radiographs obtained during diagnostic evaluation of 460 consecutive patients who presented to the emergency department with acute foot pain. Variations in calcaneonavicular morphology depicted on the medial oblique view (obtained at a 45° angle) were classified into four groups according to morphologic type (types 1–4), and the prevalence of each type was calculated. {chi}2 analysis was used to compare the prevalence of each type in male patients and in female patients. One-way analyses of variance were used to compare mean ages of patients for each type and mean calcaneonavicular gaps for each type.

RESULTS: The prevalence of morphologic types 1, 2, and 3 was 94.3%, 2.8%, and 2.8%, respectively. The combined prevalence of types 2 and 3 (calcaneonavicular coalitions produced by synchondrosis and syndesmosis, respectively) was 5.6% (95% CI: 3.5%, 7.8%). There were no patients with type 4 morphology (synostosis). The numbers of male patients and female patients with morphologic types 1–3 were approximately equal (P = .9), and there was no statistically significant correlation between any of these three morphologic types and patient age (P = .2). The calcaneonavicular gap was significantly narrower in types 2 and 3 than in type 1 (P = .01), which was characterized as the normal morphology.

CONCLUSION: The general prevalence of calcaneonavicular coalition (synchondrosis and syndesmosis) may be greater than previously reported, but further research is needed to prove the validity of this hypothesis.

© RSNA, 2003

Index terms: Bones, radiography, 464.11 • Calcaneus, 4648.143 • Navicular, 4648.143


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Calcaneonavicular coalition (CNC) is defined as abnormal coalescence of the calcaneus with the tarsal navicular bone (1). CNC may be described as osseous (synostosis) or nonosseous (ie, either cartilaginous [synchondrosis] or fibrous [syndesmosis]), but it is probably best to consider these categories as points in a histopathologic continuum (2). In general terms, the normal morphologic relationship of the calcaneus with the navicular bone can be described as a slender gap between the two articulated bone structures. This morphology occurs in a statistically normal distribution in the general population, while a wider gap between the two (nonarticulated) structures occurs in individuals at one end of the continuum and completely continuous osseous fusion occurs in individuals at the opposite end.

To date, the scientific literature about calcaneonavicular morphology has been based primarily on retrospective findings of association between radiographically or surgically proved CNC in particular patients and a previously defined clinical syndrome in those patients. The association of CNC with peroneal spastic (rigid) flat foot, in particular, has led to more effective management of an important cause of chronic foot pain. However, because of the selection biases inherent in such retrospective analyses, the general understanding of the clinical importance of an incidental finding of abnormal calcaneonavicular morphology remains limited (3). Because only symptomatic CNC has been extensively studied to date and the prevalence of asymptomatic CNC remains unknown, the positive predictive value of radiographic findings for diagnosis of CNC has likely been overestimated (3,4). The purpose of the present study was to determine and classify radiographically demonstrated variations in calcaneonavicular morphology and to estimate prevalence in a clinically relevant patient population.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Subjects
We retrospectively reviewed 673 consecutive emergency department cases that included radiographs obtained at our institution during diagnostic evaluation of patients with acute foot pain and with eventual discharge diagnosis of (a) sprain or strain of the foot or (b) dislocation or (c) fracture of one or more tarsal bones, metatarsal bones, or phalanges of the foot. Because ossification does not consistently occur in CNC until the age of 12 years (1,5), 25 cases involving patients 11 years of age and younger were excluded from the study. Another 188 cases were excluded because the records did not include a 45° medial oblique radiographic view of the foot. The remaining 460 cases were included in the analysis. Of 460 patients, 218 were male (mean age, 33 years; range, 12–85 years) and 242 were female (mean age, 40 years; range, 12–90 years). The study was approved by our institutional review board. Patient informed consent is not required by our institutional review board for the review of medical images and records.

Image Evaluation
Foot radiographs were evaluated by both authors, who were blinded to all other information. The calcaneonavicular gap, defined as the least distance between the cortical surfaces of the calcaneus and navicular depicted on 45° medial oblique radiographic views, was measured with calipers on the radiographs by one of the authors (J.T.L.). Variations in calcaneonavicular morphology were classified by consensus into four groups (types 1–4) according to their appearance on medial oblique radiographs. Type 1 morphology (Fig 1) was characterized by a wide calcaneonavicular gap and smooth, rounded, and well-defined calcaneal and navicular cortices. Type 2 morphology (Fig 2) was characterized by a narrow calcaneonavicular gap, flattening and widening of the calcaneus where it approaches the navicular, and smooth, regular, and well-defined cortical surfaces. Type 3 morphology (Fig 3) was characterized by a narrow calcaneonavicular gap, flattening and widening of the calcaneus where it approaches the navicular, and rough, irregular, and poorly defined calcaneal and navicular cortices. Type 4 morphology (Fig 4) was characterized by a completely continuous osseous structure spanning the calcaneus and navicular. If one describes the morphologic relationship between the calcaneus and the navicular as a histopathologic continuum, type 1 represents one extreme (a wide gap between nonarticulated bone structures) and type 4 represents the other extreme (completely continuous osseous fusion). The two intermediate morphologic types, both of which had radiographic features that indicated articulation, were radiographically differentiated according to whether articulation was smooth (type 2) or irregular (type 3).



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  		Figure 1. Type 1 calcaneonavicular morphology. Medial oblique radiograph obtained in a 22-year-old man shows minimally distracted avulsion fracture at the base of the fifth metatarsal bone (arrowhead). Note the wide calcaneonavicular gap (solid arrow) and the smooth, rounded, and well-defined calcaneal (C) and navicular (N) cortices (open arrows).

 


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  		Figure 2. Type 2 calcaneonavicular morphology. Medial oblique radiograph obtained in a 60-year-old woman shows undisplaced fracture at the base of the fifth metatarsal bone (white arrowhead). Note the narrow calcaneonavicular gap (solid arrow), the flattening and widening of the calcaneus where it approaches the navicular (black arrowhead), and the smooth, regular, and well-defined calcaneal (C) and navicular (N) cortices (open arrows).

 


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  		Figure 3. Type 3 calcaneonavicular morphology. Medial oblique radiograph obtained in an 18-year-old woman with foot sprain. Note the narrow calcaneonavicular gap (solid arrow), the flattening and widening of the calcaneus where it approaches the navicular (arrowhead), and the rough, irregular, and poorly defined calcaneal (C) and navicular (N) cortices (open arrows).

 


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  		Figure 4. Type 4 calcaneonavicular morphology. Medial oblique foot radiograph from author’s teaching file shows completely continuous osseous structure spanning the calcaneus (C) and navicular (N) (arrowheads).

 
Statistical Analysis
The prevalence of each morphologic type was calculated as the ratio of the number of cases (feet) in which the specific morphology was demonstrated to the total number of cases (feet) reviewed. A {chi}2 analysis was used to compare the prevalence of each type in males versus females. A one-way analysis of variance was used to compare the mean age of patients with each morphologic type. A one-way analysis of variance with Bonferroni correction was used to compare the mean calcaneonavicular gaps for each type.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Most cases (94.3%) showed type 1 morphology (Table). Types 2 and 3 (synchondrosis and syndesmosis, respectively) were depicted in 13 cases each, indicating a 2.8% prevalence for each type and a combined prevalence of 5.6% for both types. No case of type 4 morphology was found in the study sample. Males and females were equally affected by morphologic types 1–3 (P = .9), and there was no statistically significant relationship between morphologic type and mean patient age (P = .2). The calcaneonavicular gap was significantly narrower in types 2 and 3 than in type 1 (P = .01), by definition.


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  		Prevalence Characteristics of Calcaneonavicular Morphology Types

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
REFERENCES
 
The anatomy of CNC was described by Cruveilhier (6) in 1829, nearly a century before its clinical relationship to peroneal spastic (rigid) flat foot was radiographically demonstrated by Slomann (7) in 1921. Several decades later, in 1948, Harris and Beath (8) renewed interest in tarsal coalition with a publication that focused on new diagnostic radiographic techniques. It is from the data reported in that article, which were based on their earlier work (9), that the often-cited (1–4,10,11) prevalence of 0.03% (one of 3,619) for CNC was first derived. The perpetuation of this statistic is unfortunate, however, because a review of the original study clearly shows that the value of 0.03% is only a rough estimate of the prevalence of calcaneonavicular synostosis alone and does not include either syndesmosis or synchondrosis, which also contribute to CNC. In an attempt to show that CNC "is not a rare entity, although a review of the literature might lead one to think this to be the case," Vaughan and Segal (12) retrospectively reviewed approximately 2,000 cases of patients with foot pain and found radiographically confirmed CNC (of all types) in nine (0.45%). Because the diagnostic radiographic criteria used in their study are unclear from their report, however, one cannot determine either the validity or the generalizability of this result.

CNC is most often diagnosed by using three standard radiographic views of the foot (2,13,14). Because CNC can be overlooked on anteroposterior and lateral views, the diagnostic radiographic series must include a 45° medial or lateral oblique view (13,15,16), which is considered optimal for the radiographic detection of CNC (1,2,5,13). Osseous CNC is clearly demonstrated as a continuous bony structure bridging the calcaneus and navicular. Nonosseous CNC is demonstrated by proximity of the calcaneus to the navicular, flattening and widening of the calcaneus where it approaches the navicular, and, possibly, eburnation or sclerosis of the two approximated cortical surfaces (1,2,5,11,13,17). In contrast to talocalcaneal coalition, in which computed tomography (CT) or magnetic resonance (MR) imaging is usually necessary to achieve diagnosis, CNC is typically diagnosed radiographically (1,13). CT or MR imaging may be employed for further characterization and preoperative planning in selected cases (2). Although what constitutes a diagnostic finding at CT and MR imaging in CNC is disputed, both CT and MR imaging can depict subtle changes that may be missed at conventional radiography (2,10,11,14,18–21).

The initial treatment of symptomatic CNC is conservative and includes orthotic therapy to limit motion across the calcaneonavicular joint (1,22). If conservative therapy fails, surgery is indicated. Surgery is eventually performed in most cases (3). The procedure of choice is resection of the CNC and interposition of the extensor digitorum brevis (23). Long-term follow-up studies indicate that although this procedure is reasonably successful in reducing symptoms in most cases, one-third of patients ultimately consider their surgery a failure (10,24–28). The reasons for perceived failure of surgery in a substantial percentage of patients are unclear, but it is hypothesized that CNC may not have been the cause of symptoms in these patients.

It must be emphasized that the purpose of the present study was not to determine the prevalence of abnormal calcaneonavicular morphology per se, but simply to determine variations in radiographically demonstrated calcaneonavicular morphology in a clinically relevant patient population. The definition of normal versus abnormal calcaneonavicular morphology, as for any feature of interest within a given population, is determined by choices that are somewhat arbitrary (eg, whether the upper and lower limits of normal morphology are defined by {alpha} of 1.25%, 2.5%, or 5%). Care must be taken not to equate a statistically abnormal finding with a clinically pathologic finding, because the two may not be related in the given situation.

In this study, the prevalence of calcaneonavicular morphology of types 1, 2, and 3 was shown to be 94.3%, 2.8%, and 2.8%, respectively. No type 4 morphology was demonstrated. The clinical relevance of these observations lies in the definitions of the four morphologic types. Type 1 was defined as a wide calcaneonavicular gap with smooth, rounded, and well-defined calcaneal and navicular cortices. Given this definition, we propose that type 1 morphology has no association with CNC and that it be described as normal morphology. Type 2 morphology was defined as a narrow calcaneonavicular gap with flattening and widening of the calcaneus where it approaches the navicular, and with smooth, regular, and well-defined cortical surfaces. Given that this is also the radiographic definition of calcaneonavicular synchondrosis (ie, the cartilaginous union of two bones) provided in the literature (1,2,5,11,13,17) and that previously published images of calcaneonavicular synchondrosis (2,5,29,30) show radiographic features similar to those on the image included in this article (Fig 2), we propose that radiographically demonstrated morphologic type 2 be considered indicative of calcaneonavicular synchondrosis. Type 3 morphology was defined as a narrow calcaneonavicular gap with flattening and widening of the calcaneus where it approaches the navicular, and with rough, irregular, and poorly defined cortical surfaces. Given that this is also the radiographic definition of calcaneonavicular syndesmosis (ie, the fibrous union of two bones) provided in the literature (1,2,5,11,13,17) and that previously published images of syndesmosis (2–4,8,12–17,29–32) show radiographic features similar to those on the image of type 3 morphology included in this article (Fig 3), we propose that radiographically demonstrated type 3 morphology be considered indicative of calcaneonavicular syndesmosis. Type 4 morphology was defined as a completely continuous osseous structure spanning the calcaneus and navicular. Given that this is also the radiographic definition of calcaneonavicular synostosis that is provided in the literature (1,2,5,11,13,17), we propose that radiographically demonstrated type 4 morphology be considered diagnostic for calcaneonavicular synostosis.

It is important to note that the degree of obliquity at imaging, which affects the radiographic appearance of the calcaneonavicular gap, could lead to overestimation of the prevalence of nonosseous CNC. To minimize this potential limitation, particularly with regard to detection of type 2 morphology, emphasis should be placed on any observation of flattening and widening of the anterior calcaneus where it approaches the navicular. The presence of eburnation or sclerosis of the two approximated cortical surfaces also would support a diagnosis of CNC (type 2 or type 3 morphology).

Our data indicate a 5.6% prevalence (95% CI: 3.5%, 7.8%) of nonosseous CNC (syndesmosis and synchondrosis) in a clinically relevant patient population. We concede that radiographic-pathologic correlation is needed to definitively prove or disprove the validity of these results. It is unfortunate that such a correlation could not be accommodated in the cross-sectional descriptive design of the present study. However, we believe that our study cohort is similar to the patient population encountered by most physicians and is a reasonable representation of the general adult population. This belief is supported by the excellent agreement between our results and those of the exquisitely detailed morphologic study of 425 feet, reported by Pfitzner (33), in which a 4.5% prevalence of "concrescentia calcaneonavicularis" (including calcaneonavicular syndesmosis and synchondrosis but not synostosis) was found. We consider that result the best estimate to date of the prevalence of CNC in the general population.

In conclusion, using radiographic definitions of CNC that are published in the literature, we found a prevalence of radiographically indicated CNC (syndesmosis and synchondrosis in roughly equal proportions) many times greater than that suggested by previous investigators. Because there is solid evidence that many cases (20%–75%) of radiographically demonstrated CNC involve patients who are completely asymptomatic (1,3–5,8,17,29), we know that many of these should not require further evaluation. Regardless of the debate surrounding the diagnostic standard for CNC, the questions with ultimate relevance are the following: What is the clinical importance of incidental radiographic findings of CNC? Which patients require further evaluation with CT or MR imaging? Which patients might benefit from surgery? Further research is necessary to determine what combination of clinical and diagnostic imaging findings (from radiography, fluoroscopy, CT, MR imaging, or scintigraphy, or a combination of these) is predictive of a positive surgical outcome.


   FOOTNOTES
 
Abbreviation: CNC = calcaneonavicular coalition

Author contributions: Guarantor of integrity of entire study, J.T.L.; study concepts and design, J.T.L., P.V.F.; literature research, J.T.L.; clinical studies, J.T.L., P.V.F.; data acquisition and analysis/interpretation, J.T.L., P.V.F.; statistical analysis, J.T.L.; manuscript preparation, definition of intellectual content, editing, revision/review, and final version approval, J.T.L., P.V.F.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 

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