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Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph
G Model FAS 1397 No. of Pages 4
Foot and Ankle Surgery xxx (2019) xxx–xxx
Contents lists available at ScienceDirect
Foot and Ankle Surgery journal homepage: www.elsevier.com/locate/fas
Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph Dong-Oh Lee* , Joo-Hak Kim, Sang-Heon Song, Hyung-In Cho, Jongwoong Lee Department of Orthopedic Surgery, Myongji Hospital, Hanyang University College of Medicine, 697-24 Hwajung-dong, Deokyang-gu Goyang-si, Gyeonggi-do, 10475, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Article history: Received 15 March 2019 Received in revised form 18 November 2019 Accepted 16 December 2019 Available online xxx
Background: Subtle cavus foot (SCF) is an entity characterized by mild cavus. However, few studies have examined whether a SCF may be a risk factor for chronic ankle instability (CAI). Methods: This study included 116 patients who underwent lateral ankle ligament repair (modified Broström operation) for CAI and 105 controls. We used the standing lateral radiograph, so compared calcaneal pitch angle, Meary’s angle, heights of the first and fifth metatarsal bases, and fibular positions between groups. Additionally, two observers subjectively rated the standing lateral radiographs for the presence of SCF. Results: There were no significant intergroup differences in any of the radiographic angles. The prevalence of SCF was 20.7% in the CAI group and 18.1% in the control group according to observer 1 versus 21.6% and 28.6% (CAI group and control group, respectively) according to observer 2. There were no significant intergroup differences in the proportion of SCF between the two observers (p = 0.105 and 0.211, respectively). Conclusion: SCF was not a significant risk factor for CAI when judging by standing lateral radiograph, and the detection of SCF seems to require considerable experience. Thus, care should be taken when determining whether to perform corrective osteotomies when treating CAI patients with SCF. Level of evidence: III, case control © 2019 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.
Keywords: Subtle cavus foot Chronic ankle instability Risk factor Prevalence
1. Introduction Ankle sprain, one of the most common injuries, responds well to conservative management. Regardless, chronic lateral ankle instability (CAI) is progressed in an estimated 30–40% of patients with ankle sprain [1]. Potential complications of CAI include pain, giving way, peroneal tendon injury, synovitis, osteoarthritis, and so on [2]. Thus, risk factors of CAI have been the topics of many studies, several of which suggested that structural features such as fibular position and talus translation would affect CAI [3,4]. Subtle cavus foot (SCF) is an entity characterized by mild heel varus and a plantarflexed first ray [5]. SCF has been shadowed by prudent cavus or flatfoot deformity because that can be underdiagnosed compared to the other deformities
* Corresponding author. E-mail addresses: [email protected] (D.-O. Lee), [email protected] (J.-H. Kim), [email protected] (S.-H. Song), [email protected] (H.-I. Cho), [email protected] (J. Lee).
for several reasons [6]. Although it is estimated that 25% of the population has SCF, there are few studies of its actual incidence [7]. Anecdotally, SCF is much more commonly encountered at outpatient clinics than cavus since it is a mild form of cavus and even considered a normal variant [2,5,8]. However, information about SCF is sparse. Although the body of literature regarding SCF has recently grown, most relevant studies were not quite distinguishable from traditional studies of cavus because there is no definite criteria available for diagnosing SCF [2,5,6,8]. Nevertheless, it is important to determine whether a mild deformity such as SCF may also be a risk factor for CAI as such cavus when counseling patients or determining surgical plans. Therefore, we sought to identify whether SCF is also a risk factor of CAI. This study aimed to: (1) determine the prevalence of SCF among patients who underwent lateral ankle ligament repair for CAI; and (2) compare it with the prevalence of SCF in the control group. Our hypothesis was that the proportion of SCF in the CAI patient group would be higher than that in the control group.
https://doi.org/10.1016/j.fas.2019.12.001 1268-7731/© 2019 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: D.-O. Lee, et al., Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph, Foot Ankle Surg (2019), https://doi. org/10.1016/j.fas.2019.12.001
G Model FAS 1397 No. of Pages 4
2
D.-O. Lee et al. / Foot and Ankle Surgery xxx (2019) xxx–xxx Table 1 Demographics of patient with chronic ankle instability (CAI) and control group.
Sex (male:female) Age (years) Concomitant surgery or disease
CAI group (n = 116)
Control group (n = 105)
P-value
58:58 41.0 8.5 Microfracture 17 OATS* 5 Peroneal repair 9 os subfibulare/old
62:43 42.8 11.4 Cellulitis 18 Contusion 31 Wart 7 Mass 18 Neuralgia 12 Neuroma 14 Foreign body 5
0.224 0.303 N/A
2. Materials and methods This retrospective study included patients who were admitted to or visited our hospital between 2005 and 2016. During that period, a total of 261 patients underwent lateral ankle ligament repair (modified Broström operation). Their symptoms such as persistent pain and/or complaint of instability were unresponsive to conservative treatment for at least 3 months. CAI had been diagnosed by history taking, physical examination including evaluation of heel alignment, and stress radiographs. A standing radiograph was available for 221 of our patients. Two patients underwent revision surgery of the lateral ankle ligament repair due to primary surgical failure. Exclusion criteria were: (1) having undergone open reduction and internal fixation for fracture proximal to the metatarsus; (2) age less than 20 years or more than 60 years; and (3) congenital disease or rheumatoid arthritis that can affect the bony structures. As a result, a total of 116 patients were finally included in the CAI group. The control group also included patients who visited or were admitted to our hospital. Inclusion criteria for control group were: (1) having undergone simple soft tissue surgery such as mass excision, (2) medical treatment for simple presentation such as cellulitis or contusion. Exclusion criteria were: (1) having undergone all other surgeries including open reduction and internal fixation for fracture of the lower extremities; (2) chronic disease such as diabetic foot or rheumatoid arthritis that could affect the bone structure; (3) patients with osteoarthritis, especially with varus or planovalgus deformity; (4) age less than 20 years but greater than 60 years. Thus, 105 patients were finally included in the control group. The patient demographics and concomitant surgeries/diseases are listed in Table 1.
previous study (Fig. 1) [3]. We screened the data and repeated the measurements if two values differed by more than 5 or 2 mm [10,11]. Two weeks later, the two observers reassessed the lateral radiographs in a random order. In addition to second radiographic measures, they classified the radiographs into three categories: cavus, SCF, and other for observers’ subjective judgement of SCF. Interobserver reliability of the first measurement and intraobserver reliability was evaluated with intraclass correlation coefficients (ICC) because all parameters were continuous data. An ICC greater than 0.8 indicated excellent reliability; absent to poor (0 to 0.24), low (0.25 to 0.49), fair to moderate (0.50 to 0.69), good (0.80 to 0.89) [12,13]. In addition to overall comparison of all radiographic measures, SCF portion was additionally compared by presumptive criteria because there are no definite radiographic criteria available for discriminating SCF from the others. Referring the previous literature, we presumed specific range of each radiographic measurement for the detection of SCF; (1) Calcaneal pitch angle is between 25 and 30 , (2) Meary angle is between 0 to 5 , (3) difference in the heights of the first and fifth metatarsal bases is between 10 and 15 mm, and (4) fibular position is between 0.6 and 0.7 [3,5]. For the estimation of the portion of SCF among each group, at first we selected cases exceeding upper limit of each measures; (1) Calcaneal pitch angle is more than 30 , (2) Meary angle is more than 5 , (3) difference in the heights of the first and fifth metatarsal bases is more than 15 mm, and (4) fibular position is more than 0.7. Then, we transferred them to cavus category. Among the rest of them, we then estimated the number of SCF from two groups in every cases meeting from 1 to 4 criteria above.
2.1. Assessing radiographs For the detection of cavus or SCF, all ankles were classified into three categories based on standing lateral views of the foot: cavus, SCF, and other [5,9]. We assessed radiographs by (1) radiographic measures and (2) subjective analysis. To analyze those with the first method, we compared the radiographic measures between the groups. The standing lateral foot reportedly reveals three highlighted features of SCF [5]. First, it shows an increased arch height defined by the distance from the base of the first metatarsal to the base of the fifth metatarsal on a lateral view of the foot. Second, Meary’s angle may be positive, depicting a plantarflexed first ray in cases of SCF. Third, the fibula may be overlying the posterior one third of the tibial shadow. Two observers, orthopedic surgeons with 8 years (observer 1) and 2 years (observer 2) of experience, measured four radiographic markers when assessing the standing lateral radiographs in a randomly sorted order: calcaneal pitch angle, Meary’s angle, difference in the heights of the first and fifth metatarsal bases, and fibular position defined in a
Fig. 1. Radiographic markers for SCF. (a) Calcaneal pitch angle; (b) Meary’s angle; (c) Difference in height between the first and fifth metatarsal bases; and (d) fibular position (e/f).
Please cite this article in press as: D.-O. Lee, et al., Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph, Foot Ankle Surg (2019), https://doi. org/10.1016/j.fas.2019.12.001
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Table 2 Overall comparison of radiographic angles between patient with chronic ankle instability (CAI) and control group. (mean standard deviation).
Calcaneal pitch Meary angle Difference of 1st–5th metatarsal base Fibular position
CAI group (n = 116)
control group (n = 105)
P-value
20.7 4.7 0.67 5.7 4.9 3.7 0.56 0.08
21.8 4.8 0 6.0 5.7 4.2 0.54 0.1
0.075 0.390 0.132 0.161
Table 3 The proportion change of SCF among each group by four presumptive radiographic criteria. Cases 1 2 3 4 5 6 7 8 9 10 11 12 13 14 a b
Calcaneal pitch
Meary angle
Oa O O
O O O O
O O O
Diff 1–5th MT baseb
Fibular position
O O O O
O O O
O O O
O O O
O O O O
O
Portion of SCF, n (%) CAI
Control
P-value
0 0 0 1 6 0 0 2 6 1 10 30 2 2
2 2 1 2 4 2 4 4 8 2 15 35 4 4
0.207 0.240
Means that each radiographic marker is within the range of SCF provided in the main text. Means Difference of 1st–5th metatarsal base.
Finally, we analyzed which radiographic features affected the observers’ subjective assessments of SCF on the lateral radiographs. 2.2. Statistical analysis The sex ratios of the groups, analysis by presumptive criteria, and the subjective assessments of the two observers were analyzed using the Chi-square test. Intergroup comparisons of age and all radiographic angles were performed using an independent two-sample Student’s ttest. A multiple regression analysis with backward elimination was performed to determine the effect of each radiographic marker on each observer’s assessment. Statistical significance was considered at p values < 0.05. All analyses was performed using SPSS software (version 20; IBM Inc., New York, NY, USA). 3. Results Sex ratios and mean age did not differ significantly between the two groups (Table 1). A total of 116 patients who underwent modified Broström operation simultaneously underwent several procedures: 22 os subfibulare or old avulsion fragment excisions, 17 microfracture for osteochondral lesion of the talus, 5 osteochondral autograft transfers, and 9 peroneal repair or
Table 4 Subjective assessment of each observer.
tenosynovectomy (Table 1). The various diagnoses of the control group are also shown in Table 1. The interobserver reliability for Calcaneal pitch, Meary angle, the difference of 1st and 5th metatarsal base, and fibular position of the first measure was excellent or good (ICC = 0.95, 0.83, 0.89, 0.81, respectively). The intraobserver reliability of two observers was excellent (ICC, 0.91, 0.86, respectively). Table 2 shows the mean measurement of each radiographic angle in each group. In overall comparison, there were no significant intergroup differences. According to our presumptive criteria, the portion of SCF was calculated shown as Table 3. As a result of statistical analysis on two cases more than 10, there was no significant difference of SCF portion between two groups (Table 3). In the subjective assessment, according to observer 1, the prevalence of SCF was 20.7% in the CAI group and 18.1% in the control group. According to observer 2, the prevalence of SCF was 21.6% and 28.6%, respectively. There were no significant intergroup differences in the proportion of SCF between the two observers (p = 0.105, 0.211, respectively; Table 4). All four radiographic markers affected observer 1’s assessments (p < 0.001). However, interestingly, only calcaneal pitch affected observer 2’s assessments (p < 0.001). The other markers did not affect his decision; Meary’s angle (p = 0.091), the difference in height between the 1st and 2nd metatarsal bases (p = 0.502), or fibular position (p = 0.248). 4. Discussion
CAI group (n = 116)
control group (n = 105)
p
Observer1
Others SCF Cavus
83 (71.6%) 24 (20.7%) 9 (7.8%)
84 (80%) 19 (18.1%) 2 (0.9%)
0.105
Observer2
Others SCF Cavus
89 (76.7%) 25 (21.6%) 2 (1.7%)
75 (71.4%) 30 (28.6%) 0 (0%)
0.211
Our study found that SCF is not a risk factor for CAI and that considerable experience may be required to detect SCF on lateral standing radiographs because the radiographic features of SCF are subtle. Patients with SCF are known to have long-standing mild symptoms, lateral column pain, peroneal tendon subluxation, and even chronic fifth metatarsal stress fracture [5]. These features do not differ from the traditional knowledge of cavus. Meanwhile,
Please cite this article in press as: D.-O. Lee, et al., Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph, Foot Ankle Surg (2019), https://doi. org/10.1016/j.fas.2019.12.001
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D.-O. Lee et al. / Foot and Ankle Surgery xxx (2019) xxx–xxx
another study reported that pure cavus, not the heel varus component, causes few symptoms and rarely requires surgical treatment [2]. Similarly, the proportion of SCF in the CAI group did not differ significantly from that in the control group. Several studies reported bony alignment or morphologies in patients with CAI [3,14,15]. Some studies debated whether cavus would be a risk factor for CAI [4,14,16–18]. Larsen et al. reported that cavovarus foot was more common in patients with ankle instability [16]. However, they compared 95 patients with a relatively small 34-patient control group and even used nonweightbearing radiographs. Moreover, several studies showed no significant correlation between leg and foot alignment and the risk of injury [17,19,20]. Other studies reported that patient satisfaction with the clinical outcome of cavus correction surgery was not proportionally related to radiographic measures [21–24]. Some authors divided cavus deformity into hindfoot-, forefoot-, and mixed-driven cavus [8]. Hindfoot-driven cavus, which is characterized by a high calcaneal pitch greater than 30 degrees, is typically seen in cases of secondary cavus caused by poliomyelitis or cerebrovascular accident [8]. These patients, who do not have features of SCF considered a normal variant, were not included in this study. Accordingly, cavus or SCF with a secondary cause can be a still risk factor for CAI. Our study had several limitations. First, diagnosing SCF is challenging because there are no definite criteria for it and it is a relatively recently introduced entity. Thus, the proportion of SCF in our results may vary among observers; in other words, interobserver variation may be unavoidable. However, we tried to minimize this error by detecting SCF using two methods and two observers. Actually, there was no interobserver difference in the detected proportion of SCF in this study. Second, we had no radiographic data showing objective heel alignment because this study had a retrospective design based on the review of medical records and radiographs. However, patients with prominent varus heel requiring corrective osteotomy were already excluded from this study because we routinely performed physical examinations because we did osteotomy only to severe cavovarus feet when the patient’s symptoms are related to cavus, such as intractable painful keratosis, plantar discomfort. In addition, the reliability for measuring heel alignment angle is known to be low overall, especially in cases of low-grade varus of the heel, and there is no known radiographic SCF feature from a standing heel alignment view because it can be very difficult to discriminate [5]. No simple clinical sign is widely recognized to identify SCF [6]. Thus, we suspect that the absence of a hindfoot analysis affected the outcome of this study. In conclusion, SCF was not a significant risk factor for CAI when judging on the standing lateral radiograph, and detecting SCF seems to require considerable experience. Thus, we should consider other factors when performing any component of a limited cavus reconstruction to patients with subtle cavus and lateral instability. Conflict of interest
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There is nothing to disclose for all authors.
Please cite this article in press as: D.-O. Lee, et al., Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph, Foot Ankle Surg (2019), https://doi. org/10.1016/j.fas.2019.12.001
Foot and Ankle Surgery xxx (2019) xxx–xxx
Contents lists available at ScienceDirect
Foot and Ankle Surgery journal homepage: www.elsevier.com/locate/fas
Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph Dong-Oh Lee* , Joo-Hak Kim, Sang-Heon Song, Hyung-In Cho, Jongwoong Lee Department of Orthopedic Surgery, Myongji Hospital, Hanyang University College of Medicine, 697-24 Hwajung-dong, Deokyang-gu Goyang-si, Gyeonggi-do, 10475, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Article history: Received 15 March 2019 Received in revised form 18 November 2019 Accepted 16 December 2019 Available online xxx
Background: Subtle cavus foot (SCF) is an entity characterized by mild cavus. However, few studies have examined whether a SCF may be a risk factor for chronic ankle instability (CAI). Methods: This study included 116 patients who underwent lateral ankle ligament repair (modified Broström operation) for CAI and 105 controls. We used the standing lateral radiograph, so compared calcaneal pitch angle, Meary’s angle, heights of the first and fifth metatarsal bases, and fibular positions between groups. Additionally, two observers subjectively rated the standing lateral radiographs for the presence of SCF. Results: There were no significant intergroup differences in any of the radiographic angles. The prevalence of SCF was 20.7% in the CAI group and 18.1% in the control group according to observer 1 versus 21.6% and 28.6% (CAI group and control group, respectively) according to observer 2. There were no significant intergroup differences in the proportion of SCF between the two observers (p = 0.105 and 0.211, respectively). Conclusion: SCF was not a significant risk factor for CAI when judging by standing lateral radiograph, and the detection of SCF seems to require considerable experience. Thus, care should be taken when determining whether to perform corrective osteotomies when treating CAI patients with SCF. Level of evidence: III, case control © 2019 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.
Keywords: Subtle cavus foot Chronic ankle instability Risk factor Prevalence
1. Introduction Ankle sprain, one of the most common injuries, responds well to conservative management. Regardless, chronic lateral ankle instability (CAI) is progressed in an estimated 30–40% of patients with ankle sprain [1]. Potential complications of CAI include pain, giving way, peroneal tendon injury, synovitis, osteoarthritis, and so on [2]. Thus, risk factors of CAI have been the topics of many studies, several of which suggested that structural features such as fibular position and talus translation would affect CAI [3,4]. Subtle cavus foot (SCF) is an entity characterized by mild heel varus and a plantarflexed first ray [5]. SCF has been shadowed by prudent cavus or flatfoot deformity because that can be underdiagnosed compared to the other deformities
* Corresponding author. E-mail addresses: [email protected] (D.-O. Lee), [email protected] (J.-H. Kim), [email protected] (S.-H. Song), [email protected] (H.-I. Cho), [email protected] (J. Lee).
for several reasons [6]. Although it is estimated that 25% of the population has SCF, there are few studies of its actual incidence [7]. Anecdotally, SCF is much more commonly encountered at outpatient clinics than cavus since it is a mild form of cavus and even considered a normal variant [2,5,8]. However, information about SCF is sparse. Although the body of literature regarding SCF has recently grown, most relevant studies were not quite distinguishable from traditional studies of cavus because there is no definite criteria available for diagnosing SCF [2,5,6,8]. Nevertheless, it is important to determine whether a mild deformity such as SCF may also be a risk factor for CAI as such cavus when counseling patients or determining surgical plans. Therefore, we sought to identify whether SCF is also a risk factor of CAI. This study aimed to: (1) determine the prevalence of SCF among patients who underwent lateral ankle ligament repair for CAI; and (2) compare it with the prevalence of SCF in the control group. Our hypothesis was that the proportion of SCF in the CAI patient group would be higher than that in the control group.
https://doi.org/10.1016/j.fas.2019.12.001 1268-7731/© 2019 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: D.-O. Lee, et al., Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph, Foot Ankle Surg (2019), https://doi. org/10.1016/j.fas.2019.12.001
G Model FAS 1397 No. of Pages 4
2
D.-O. Lee et al. / Foot and Ankle Surgery xxx (2019) xxx–xxx Table 1 Demographics of patient with chronic ankle instability (CAI) and control group.
Sex (male:female) Age (years) Concomitant surgery or disease
CAI group (n = 116)
Control group (n = 105)
P-value
58:58 41.0 8.5 Microfracture 17 OATS* 5 Peroneal repair 9 os subfibulare/old
62:43 42.8 11.4 Cellulitis 18 Contusion 31 Wart 7 Mass 18 Neuralgia 12 Neuroma 14 Foreign body 5
0.224 0.303 N/A
2. Materials and methods This retrospective study included patients who were admitted to or visited our hospital between 2005 and 2016. During that period, a total of 261 patients underwent lateral ankle ligament repair (modified Broström operation). Their symptoms such as persistent pain and/or complaint of instability were unresponsive to conservative treatment for at least 3 months. CAI had been diagnosed by history taking, physical examination including evaluation of heel alignment, and stress radiographs. A standing radiograph was available for 221 of our patients. Two patients underwent revision surgery of the lateral ankle ligament repair due to primary surgical failure. Exclusion criteria were: (1) having undergone open reduction and internal fixation for fracture proximal to the metatarsus; (2) age less than 20 years or more than 60 years; and (3) congenital disease or rheumatoid arthritis that can affect the bony structures. As a result, a total of 116 patients were finally included in the CAI group. The control group also included patients who visited or were admitted to our hospital. Inclusion criteria for control group were: (1) having undergone simple soft tissue surgery such as mass excision, (2) medical treatment for simple presentation such as cellulitis or contusion. Exclusion criteria were: (1) having undergone all other surgeries including open reduction and internal fixation for fracture of the lower extremities; (2) chronic disease such as diabetic foot or rheumatoid arthritis that could affect the bone structure; (3) patients with osteoarthritis, especially with varus or planovalgus deformity; (4) age less than 20 years but greater than 60 years. Thus, 105 patients were finally included in the control group. The patient demographics and concomitant surgeries/diseases are listed in Table 1.
previous study (Fig. 1) [3]. We screened the data and repeated the measurements if two values differed by more than 5 or 2 mm [10,11]. Two weeks later, the two observers reassessed the lateral radiographs in a random order. In addition to second radiographic measures, they classified the radiographs into three categories: cavus, SCF, and other for observers’ subjective judgement of SCF. Interobserver reliability of the first measurement and intraobserver reliability was evaluated with intraclass correlation coefficients (ICC) because all parameters were continuous data. An ICC greater than 0.8 indicated excellent reliability; absent to poor (0 to 0.24), low (0.25 to 0.49), fair to moderate (0.50 to 0.69), good (0.80 to 0.89) [12,13]. In addition to overall comparison of all radiographic measures, SCF portion was additionally compared by presumptive criteria because there are no definite radiographic criteria available for discriminating SCF from the others. Referring the previous literature, we presumed specific range of each radiographic measurement for the detection of SCF; (1) Calcaneal pitch angle is between 25 and 30 , (2) Meary angle is between 0 to 5 , (3) difference in the heights of the first and fifth metatarsal bases is between 10 and 15 mm, and (4) fibular position is between 0.6 and 0.7 [3,5]. For the estimation of the portion of SCF among each group, at first we selected cases exceeding upper limit of each measures; (1) Calcaneal pitch angle is more than 30 , (2) Meary angle is more than 5 , (3) difference in the heights of the first and fifth metatarsal bases is more than 15 mm, and (4) fibular position is more than 0.7. Then, we transferred them to cavus category. Among the rest of them, we then estimated the number of SCF from two groups in every cases meeting from 1 to 4 criteria above.
2.1. Assessing radiographs For the detection of cavus or SCF, all ankles were classified into three categories based on standing lateral views of the foot: cavus, SCF, and other [5,9]. We assessed radiographs by (1) radiographic measures and (2) subjective analysis. To analyze those with the first method, we compared the radiographic measures between the groups. The standing lateral foot reportedly reveals three highlighted features of SCF [5]. First, it shows an increased arch height defined by the distance from the base of the first metatarsal to the base of the fifth metatarsal on a lateral view of the foot. Second, Meary’s angle may be positive, depicting a plantarflexed first ray in cases of SCF. Third, the fibula may be overlying the posterior one third of the tibial shadow. Two observers, orthopedic surgeons with 8 years (observer 1) and 2 years (observer 2) of experience, measured four radiographic markers when assessing the standing lateral radiographs in a randomly sorted order: calcaneal pitch angle, Meary’s angle, difference in the heights of the first and fifth metatarsal bases, and fibular position defined in a
Fig. 1. Radiographic markers for SCF. (a) Calcaneal pitch angle; (b) Meary’s angle; (c) Difference in height between the first and fifth metatarsal bases; and (d) fibular position (e/f).
Please cite this article in press as: D.-O. Lee, et al., Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph, Foot Ankle Surg (2019), https://doi. org/10.1016/j.fas.2019.12.001
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Table 2 Overall comparison of radiographic angles between patient with chronic ankle instability (CAI) and control group. (mean standard deviation).
Calcaneal pitch Meary angle Difference of 1st–5th metatarsal base Fibular position
CAI group (n = 116)
control group (n = 105)
P-value
20.7 4.7 0.67 5.7 4.9 3.7 0.56 0.08
21.8 4.8 0 6.0 5.7 4.2 0.54 0.1
0.075 0.390 0.132 0.161
Table 3 The proportion change of SCF among each group by four presumptive radiographic criteria. Cases 1 2 3 4 5 6 7 8 9 10 11 12 13 14 a b
Calcaneal pitch
Meary angle
Oa O O
O O O O
O O O
Diff 1–5th MT baseb
Fibular position
O O O O
O O O
O O O
O O O
O O O O
O
Portion of SCF, n (%) CAI
Control
P-value
0 0 0 1 6 0 0 2 6 1 10 30 2 2
2 2 1 2 4 2 4 4 8 2 15 35 4 4
0.207 0.240
Means that each radiographic marker is within the range of SCF provided in the main text. Means Difference of 1st–5th metatarsal base.
Finally, we analyzed which radiographic features affected the observers’ subjective assessments of SCF on the lateral radiographs. 2.2. Statistical analysis The sex ratios of the groups, analysis by presumptive criteria, and the subjective assessments of the two observers were analyzed using the Chi-square test. Intergroup comparisons of age and all radiographic angles were performed using an independent two-sample Student’s ttest. A multiple regression analysis with backward elimination was performed to determine the effect of each radiographic marker on each observer’s assessment. Statistical significance was considered at p values < 0.05. All analyses was performed using SPSS software (version 20; IBM Inc., New York, NY, USA). 3. Results Sex ratios and mean age did not differ significantly between the two groups (Table 1). A total of 116 patients who underwent modified Broström operation simultaneously underwent several procedures: 22 os subfibulare or old avulsion fragment excisions, 17 microfracture for osteochondral lesion of the talus, 5 osteochondral autograft transfers, and 9 peroneal repair or
Table 4 Subjective assessment of each observer.
tenosynovectomy (Table 1). The various diagnoses of the control group are also shown in Table 1. The interobserver reliability for Calcaneal pitch, Meary angle, the difference of 1st and 5th metatarsal base, and fibular position of the first measure was excellent or good (ICC = 0.95, 0.83, 0.89, 0.81, respectively). The intraobserver reliability of two observers was excellent (ICC, 0.91, 0.86, respectively). Table 2 shows the mean measurement of each radiographic angle in each group. In overall comparison, there were no significant intergroup differences. According to our presumptive criteria, the portion of SCF was calculated shown as Table 3. As a result of statistical analysis on two cases more than 10, there was no significant difference of SCF portion between two groups (Table 3). In the subjective assessment, according to observer 1, the prevalence of SCF was 20.7% in the CAI group and 18.1% in the control group. According to observer 2, the prevalence of SCF was 21.6% and 28.6%, respectively. There were no significant intergroup differences in the proportion of SCF between the two observers (p = 0.105, 0.211, respectively; Table 4). All four radiographic markers affected observer 1’s assessments (p < 0.001). However, interestingly, only calcaneal pitch affected observer 2’s assessments (p < 0.001). The other markers did not affect his decision; Meary’s angle (p = 0.091), the difference in height between the 1st and 2nd metatarsal bases (p = 0.502), or fibular position (p = 0.248). 4. Discussion
CAI group (n = 116)
control group (n = 105)
p
Observer1
Others SCF Cavus
83 (71.6%) 24 (20.7%) 9 (7.8%)
84 (80%) 19 (18.1%) 2 (0.9%)
0.105
Observer2
Others SCF Cavus
89 (76.7%) 25 (21.6%) 2 (1.7%)
75 (71.4%) 30 (28.6%) 0 (0%)
0.211
Our study found that SCF is not a risk factor for CAI and that considerable experience may be required to detect SCF on lateral standing radiographs because the radiographic features of SCF are subtle. Patients with SCF are known to have long-standing mild symptoms, lateral column pain, peroneal tendon subluxation, and even chronic fifth metatarsal stress fracture [5]. These features do not differ from the traditional knowledge of cavus. Meanwhile,
Please cite this article in press as: D.-O. Lee, et al., Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph, Foot Ankle Surg (2019), https://doi. org/10.1016/j.fas.2019.12.001
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another study reported that pure cavus, not the heel varus component, causes few symptoms and rarely requires surgical treatment [2]. Similarly, the proportion of SCF in the CAI group did not differ significantly from that in the control group. Several studies reported bony alignment or morphologies in patients with CAI [3,14,15]. Some studies debated whether cavus would be a risk factor for CAI [4,14,16–18]. Larsen et al. reported that cavovarus foot was more common in patients with ankle instability [16]. However, they compared 95 patients with a relatively small 34-patient control group and even used nonweightbearing radiographs. Moreover, several studies showed no significant correlation between leg and foot alignment and the risk of injury [17,19,20]. Other studies reported that patient satisfaction with the clinical outcome of cavus correction surgery was not proportionally related to radiographic measures [21–24]. Some authors divided cavus deformity into hindfoot-, forefoot-, and mixed-driven cavus [8]. Hindfoot-driven cavus, which is characterized by a high calcaneal pitch greater than 30 degrees, is typically seen in cases of secondary cavus caused by poliomyelitis or cerebrovascular accident [8]. These patients, who do not have features of SCF considered a normal variant, were not included in this study. Accordingly, cavus or SCF with a secondary cause can be a still risk factor for CAI. Our study had several limitations. First, diagnosing SCF is challenging because there are no definite criteria for it and it is a relatively recently introduced entity. Thus, the proportion of SCF in our results may vary among observers; in other words, interobserver variation may be unavoidable. However, we tried to minimize this error by detecting SCF using two methods and two observers. Actually, there was no interobserver difference in the detected proportion of SCF in this study. Second, we had no radiographic data showing objective heel alignment because this study had a retrospective design based on the review of medical records and radiographs. However, patients with prominent varus heel requiring corrective osteotomy were already excluded from this study because we routinely performed physical examinations because we did osteotomy only to severe cavovarus feet when the patient’s symptoms are related to cavus, such as intractable painful keratosis, plantar discomfort. In addition, the reliability for measuring heel alignment angle is known to be low overall, especially in cases of low-grade varus of the heel, and there is no known radiographic SCF feature from a standing heel alignment view because it can be very difficult to discriminate [5]. No simple clinical sign is widely recognized to identify SCF [6]. Thus, we suspect that the absence of a hindfoot analysis affected the outcome of this study. In conclusion, SCF was not a significant risk factor for CAI when judging on the standing lateral radiograph, and detecting SCF seems to require considerable experience. Thus, we should consider other factors when performing any component of a limited cavus reconstruction to patients with subtle cavus and lateral instability. Conflict of interest
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There is nothing to disclose for all authors.
Please cite this article in press as: D.-O. Lee, et al., Is subtle cavus foot a risk factor for chronic ankle instability? Comparison of prevalence of subtle cavus foot between chronic ankle instability and control group on the standing lateral radiograph, Foot Ankle Surg (2019), https://doi. org/10.1016/j.fas.2019.12.001