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Lee SY et al. Is there a Relationship … Int J Sports Med 2016; 37: 1080–1086

Is there a Relationship between Bone Morphology and Injured Ligament on Imaging Studies and Laxity on Ankle Stress Radiographs?

Authors S. Y. Lee1, S.-S. Kwon2, M. S. Park3, M. K. Chung3, K. B. Kim4, S. Koo5, K. M. Lee3

Affiliations Affiliation addresses are listed at the end of the article

Introduction▼Lateral ankle sprain is one of the most common sports injuries [16, 44]. Although ankle sprains can result in limitations of daily activity due to pain following the acute injury [24], they are often regarded as benign injuries that will resolve quickly with limited treatment [17, 42]. However, ankle sprain may be associated with an incidence of ankle instability up to 50 % [41]. Because ankle instability is known to be a cause of early osteoar-thritic changes [22, 30, 39], surgical repair or reconstruction of ankle ligaments has been per-formed to treat severe ankle instability [12, 15, 21]. Currently, among patients with functional insta-bility in whom conservative treatment failed, talar tilt greater than 15 degrees on varus stress anteroposterior (AP) view and an anterior drawer greater than 1 cm on anterior drawer lateral view are generally considered positive indications for surgery [14].With the introduction of magnetic resonance imaging (MRI) to evaluate ankle ligament injuries and ankle instability, clinicians are able to iden-

tify the specific ligaments injured [17]. While MRI demonstrates high sensitivity and specific-ity for the detection of ligament tears [8], it is limited for the evaluation of ankle instability because it cannot evaluate the dynamic status of the ankle. Therefore, both MRI and ankle stress radiographs are generally performed for the pre-operative evaluation of ankle instability, although ankle stress radiograph is an indirect and 2-dimen-sional examination. However, only a few studies have been conducted on the relationship between the degree of ligament injury and laxity on ankle stress radiographs [2, 25]. A previous study reported that isolated anterior tibiofibular liga-ment (ATFL) injury caused only small laxity changes, but a pronounced increase in laxity was observed after a combined calcaneofibular liga-ment (CFL) and ATFL injury [2]. In addition, sev-eral studies revealed that ankle stress radiographs correlated poorly with the degree of ligamentous disruption on MRI [9, 34]. Ankle stress radio-graphs also showed great variability and lack of consistency according to degree of ligament injury [8, 20, 29]. On the contrary, a previous

accepted after revision March 29, 2016

BibliographyDOI http://dx.doi.org/ 10.1055/s-0042-106300 Published online: September 27, 2016Int J Sports Med 2016; 37: 1080–1086 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622

CorrespondenceDr. Kyoung Min LeeOrthopaedic Surgery Seoul National University Bundang Hospital 300 Gumi-Dong Sungnam Korea, Republic of Tel.: + 82/31/787 7205 Fax: + 82/31/787 4056 oasis100@empal.com

Key words●▶ ankle stress radiographs●▶ lateral ankle instability●▶ anterior talofibular ligament●▶ bimalleolar tilt●▶ tibiotalar tilt angle●▶ fibular position

Abstract▼This study aimed to investigate the relationship between bone morphology and injured liga-ments on imaging studies and laxity on ankle stress radiographs in patients with lateral ankle instability. In total, 115 patients who had under-gone ankle MRI, ankle radiography, and stress radiography were included. Distal tibial articular surface angle, bimalleolar tilt, medial and lateral malleolar relative length, medial malleolar slip angle, anterior inclination of the tibia, and fibular position were measured on ankle radiographs. Tibiotalar tilt angle and anterior translation of the talus were measured on ankle stress radiographs. Degree of ligament injury was evaluated on ankle

MRIs. Multiple regression analysis was performed using the following independent variables: age, sex, and factors significantly associated with ankle stress view on univariate linear regression analysis. Age (p = 0.041), sex (p = 0.014), degree of anterior talofibular ligament injury (p < 0.001), and bimalleolar tilt (p = 0.016) were correlated with tibiotalar tilt angle. Fibular position and degree of posterior talofibular ligament injury were factors significantly related to anterior translation of the talus. Differences in patient characteristics might predispose ankle stress radiograph results. Comparison of both ankles on stress radiographs is superior to applying fixed numerical values to the injured side in order to reduce the influence of patient factors.

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study that compared ankle stress radiographs with surgical find-ings showed that radiological instability could be observed in patients with ATFL injury only [33]. However, these previous studies did not consider patient factors such as bony constraint and age. Furthermore, because the degree of ligament injury cannot be evaluated directly before surgery and most physicians have used both MRI and ankle stress radiographs to assess ankle instability, the correlation between degree of ligament injury to the ankle and stress radiographs and determinants on ankle stress radiographs should be evaluated.One cause of variability in ankle stress radiographs may be uni-dentified determinants. A previous study reported that females showed a 1.5 ° larger tibiotalar tilt angle than males, and the angle decreased 0.05 ° per 1-year increase in age [25]. However, this study did not consider the influence of the bony configura-tion of the ankle. The ankle joint has a ‘mortise’ configuration. Because differences in the bony configuration of the ankle may predispose the outcome of an inversion injury to a fracture or sprain [26], they may also affect ankle stress radiographs. It can be hypothesized that an ankle with greater bony constraint may be fractured rather than undergo ligament injury under the same external stress. In other words, injury severity on ankle stress radiographs can be underestimated in patients who have greater bony constraint on the ankle joint because the bony structure can block movement of the talus under external stress.Knowledge of determinants can help physicians more accurately determine ankle laxity on ankle stress radiographs. We hypoth-esized that the bony configuration of the ankle could also be associated with ankle stress radiographs, in addition to ligament injury of the ankle. Therefore, the aim of this study was to inves-tigate the relationship between bone morphology and injured ligament of the ankle on imaging studies and laxity of the ankle on ankle stress radiographs in patients evaluated for lateral ankle instability. Univariate and multiple regression analyses were used to evaluate the correlation between the findings of ankle stress radiographs and structural factors such as the bony configuration and degree of ligament injury around the ankle joint.

Materials and Methods▼This retrospective study was approved by the institutional review board of our hospital. Informed consent was waived because of the retrospective nature of the study. We have read and understood the International Journal of Sports Medicine’s ethical standards document [23].We reviewed the medical records of consecutive patients who visited our institution between May 2003 and November 2014 for recurrent ankle sprain (inversion injury), subjective symp-toms of ankle instability (giving way, unstable ankle, or localized ankle weakness), or positive physical examination (tenderness over the ATFL, ankle swelling, crepitus, and a positive anterior drawer and inversion test) [19]. Patients at least 20 years old who underwent ankle MRI and radiography in the AP view, AP varus stress view, lateral view, anterior drawer lateral view, and mortise view were included. The exclusion criteria were as fol-lows: (1) acute pain following less than 6 weeks of ankle inver-sion injury [25]; (2) conditions that could affect normal ankle anatomy such as fracture, os subfibulare, congenital anomaly, tumor, or previous ankle surgeries; and (3) inadequate radio-graphs that showed more than 3 mm of superimposition of the

talar trochlear surface on the lateral ankle view. To compare the measurements on radiographs in ankle instability patients, 274 consecutive patients who were diagnosed with lateral malleolar fracture in our institution between May 2003 and November 2014 were screened. All patients were at least 20 years old and underwent bilateral ankle radiography. Ankle radiograph of the contralateral side of the fracture was included for measurement. Contralateral radiography is performed routinely at our institute to evaluate other possible injuries such as syndesmosis injury.Ankle radiographs were taken with a UT 2000 X-ray machine (Philips Research, Eindhoven, The Netherlands) at a source-to-image distance of approximately 110 cm. The radiograph set-tings were 60 kVp and 6.3 mAs. Using a telometer device (Daiseung Medics, Seoul, South Korea), varus stress radiographs were taken with the patients in the supine position, while exert-ing 15 daN of varus force on the ankle. Anterior drawer radio-graphs were taken with 15 daN of anterior drawing force on the ankle at 10 degrees of plantar flexion using a telometer device (Daiseung). All conventional radiographic images were digitally acquired using a picture archiving and communication system (PACS; Infinitt, Seoul, South Korea), and measurements were subsequently carried out using PACS software.All subjects underwent ankle MRI using a 1.5-T system (Gyros-can NT Intera, Philips Healthcare) and dedicated ankle coil (C4 circular surface coil with an 80-mm diameter or SENSE Flex-M coil, Philips Healthcare). The parameters of the coronal T1-weighted (TR/TE, 502–630/20–25) and sagittal T2-weighted sequences (3 224–4 049)/90–100) were as follows: (1) 3-mm slice thickness and 0.3-mm interval, (2) 140- to 170-mm2 field of view, and (3) 256 × 512 imaging matrix. Axial T1-weighted (400–600/15–22) and T2-weighted (4 427–6 074/80–100) images were obtained with a 100- to 130-mm2 field of view. All MR images were also digitally acquired using a PACS (Infinitt), and MRI was subsequently carried out using PACS software. The angle and distance were measured to 2 decimal places. All meas-urements were rounded off to the nearest hundredths.

Consensus building and measurements6 orthopedic surgeons with 30, 14, 12, 10, 9, and 8 years of orthopedic experience held a consensus-building session before measuring radiographs. Previous studies were reviewed [6, 26, 27, 36, 38], and 7 items relevant to measuring bony con-straints of the ankle joint were identified: distal tibial articular surface angle, bimalleolar tilt, medial malleolar relative length, lateral malleolar relative length, and medial malleolar slip angle on AP radiograph, and anterior inclination of the tibia and fibu-lar position on lateral radiograph ( ●▶ Fig. 1). The distal tibial articular surface angle is formed by the distal tibial articular sur-face and the longitudinal axis of the tibia [6]. Bimalleolar tilt is formed by the longitudinal axis of the tibia and a line connecting the tips of the lateral and medial malleoli [38]. Medial (or lat-eral) malleolar relative length is the ratio of the length of the medial (or lateral) malleolus to the width of the talar dome, and medial (or lateral) malleolar length is the perpendicular dis-tance of the medial (or lateral) malleolar tip to the continuous line of the distal tibial articular surface [27]. The medial malleo-lar slip angle is formed by the line parallel to the medial malleo-lar articular surface and the distal tibial articular surface [26]. The anterior inclination of the tibia is formed by the longitudinal axis of the tibia and the anterior and posterior margins of the tibial plafond [6]. The fibular position was the relative position of the fibular center on a line between the anterior and posterior

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margins of the tibial plafond [26]. The tibiotalar tilt angle on the AP varus stress view and the anterior translation of the talus on the anterior drawer lateral view were measured [36]. The tibio-talar tilt angle on the anteroposterior varus stress view was measured between the distal tibial articular surface and talar dome ( ●▶ Fig. 2a). The anterior translation of the talus on the anterior drawer lateral view was defined as the length of the shortest interval between the posterior lip of the distal tibial articular surface and the articular surface of the talus ( ●▶ Fig. 2b). On ankle MRI, ATFL was assessed on axial images, and CFL, pos-terior talofibular ligaments (PTFL), and deltoid ligaments were evaluated on coronal images. Ligament injuries were classified as intact, partial injury, or complete injury [25]. The presence of ankle joint effusion was also recorded. All radiographs were assessed by a surgeon with 8 years of orthopedic experience, and all MR images were assessed by a musculoskeletal specialist with 16 years of radiographic experience. Reliability testing was conducted for each measurement on the radiographs. Intra- and interobserver reliabilities were determined using intraclass cor-relation coefficients (ICCs) for 3 surgeons with 10, 9, and 8 years of orthopedic experience, respectively. These 3 surgeons meas-ured the radiographs independently without knowledge of the

other surgeons’ measurements. 4 weeks after the measurements were taken by all 3 surgeons, one surgeon who measured all radiographs repeated the measurements to evaluate intraob-server reliability.

Statistical analysisThe symptomatic ankle of each patient was included in data analysis. In bilateral cases, for the purpose of statistical inde-pendence, only data from the right ankle of each patient were included [32]. The Kolmogorov-Smirnov test was used to verify the normality of distribution of continuous variables. Descrip-tive statistics included mean ± SD and proportion. In the present study, reliability was assessed using ICCs and a 2-way random effects model, assuming a single measurement and absolute agreement [37]. Using an ICC target value of 0.8, Bonett’s approx-imation was used, setting 0.2 as the width of 95 % confidence intervals [7]. The minimal sample size was calculated to be 36. Univariate and multiple analyses were performed using tibiota-lar tilt angle and anterior translation of the talus as response variables and age, sex, various radiograph measurements, and MRI findings as explanatory variables. For multiple regression analysis, independent variables were age, sex and the factors

a b Fig. 1 a Distal tibial articular surface angle (DTAS), bimalleolar tilt (BT), medial malleolar relative length (a/c), lateral malleolar relative length (b/c), medial malleolar slip angle (MMSA). b anterior inclination of the tibia (AI), and fibular position (d/e).

a b Fig. 2 Tibiotalar tilt angle on anteroposterior varus stress view a. Anterior translation of the talus on anterior drawer lateral view b.

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found to be significantly associated with ankle stress view on univariate linear regression analysis. Statistical analyses were conducted with R (version 3.0.1) (R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.r-project.org) using the stats package [10, 43]. All statisti-cal tests were 2-tailed, and p-values < 0.05 were considered sig-nificant.

Results▼A total of 401 patients met the inclusion criteria. After imple-mentation of the exclusion criteria, 115 ankles from 115 patients were ultimately included in this study ( ●▶ Fig. 3). Patients’ mean age at the time of examination was 37.5 ± 13.5 years (range, 20–74 years). There were 66 male and 49 female patients ( ●▶ Table 1).The summary of radiographic measurements is shown in ●▶ Table 2. Of the 115 ankles, 87 demonstrated anterior tibiofibular liga-ment injury, 53 calcaneofibular ligament injury, and 26 poste-rior tibiofibular ligament injury on MRI. There were 43 ATFL-only and 2 CFL-only injuries on MRI. 33 ankles demonstrated both AFTL and CFL injury and 17 ankles showed ATFL, CFL, and PTFL injury on MRI. There was no PTFL-only injury. 31 ankles demon-strated deltoid ligament injury, and 43 ankles showed joint effu-sion on MRI ( ●▶ Table 2). In terms of reliability, all measurements on the radiographs showed good to excellent reliability ( ●▶ Table 3).On univariate linear regression analysis, the tibiotalar tilt angle on AP varus stress view was associated with patients’ sex, bimalleolar tilt, lateral malleolar relative length, and degree of ATFL and deltoid ligament injury. Bimalleolar tilt, lateral malleo-lar relative length, fibular position, and degree of PTFL injury were also associated with the anterior translation of the talus on the anterior drawer lateral view. Joint effusion was not a deter-minant for the anterior translation of the talus and tibiotalar tilt ankle on the ankle stress radiographs ( ●▶ Table 4).

After adjusting for patients’ age and sex, multiple regression analysis was performed with the factors that were found to be significantly associated with the ankle stress view on univariate linear regression analysis. Age (p = 0.041), sex (p = 0.014), degree of ATFL injury (p < 0.001), and bimalleolar tilt (p = 0.016) were significantly associated with tibiotalar tilt angle on the AP varus stress view ( ●▶ Table 4). Younger patients demonstrated a larger tibiotalar tilt angle than older patients, and the angle decreased by 0.07 ° per year of age. Tibiotalar tilt angle in female patients was 2.2 ° larger than that in male patients. Fibular position and degree of PTFL injury were factors significantly associated with anterior translation of the talus on the anterior drawer lateral view ( ●▶ Table 5).

Discussion▼Several factors could affect ankle stress radiographs in patients with lateral ankle instability, such as age and sex, in addition to ligament injury on MRI [25]. Therefore, we performed this study to investigate the influence of the relationship between bone morphology and the injured ligament of the ankle on imaging studies and laxity of the ankle on ankle stress radiographs in patients evaluated for lateral ankle instability. We found that younger and female patients demonstrated larger tibiotalar tilt angle compared with older and male patients. Tibiotalar tilt angle increased as bimalleolar tilt angle increased. Relative pos-terior position of the fibula demonstrated larger anterior trans-lation of the talus on the ankle stress radiograph. Tibiotalar tilt angle and anterior translation of the talus on the stress view increased by 2.6 ° and 1.6 ° respectively as the degree of anterior talofibular ligament and posterior talofibular ligament injury worsened.In the present study, there was no significant difference in radio-graphic measurements between ankle instability patients and controls except fibular position. The fibula was more posteriorly

401 patients were screened

Chronic ankle instabilityMay 2003 – November 2014

Age ≥ 20Ankle MRI

Ankle stress radiographsSimple ankle radiographs

286 patients were excluded

32103151

115 ankles from 115 patients wereincluded

Acute pain (< 6 weeks)Abnormal anatomyInadequate radiograph

Fig. 3 Inclusion and exclusion criteria.

Table 1 Patient demographics.

Parameter Value

Patient Control

No. of subjects (male/female) 115 (66/49) 274 (138/136)Laterality (right/left) 65/50 150/124Age at examination (years) 37.5 ± 13.5

(range, 20.0–74.0)44.6 ± 14.3 (range, 20.0–69)

Age at examination is presented as mean ± standard deviation

Table 2 Summary of measurements.

Radiographic measurements Value

Patients Control p-value

Distal tibial articular surface angle

91.1 ± 2.6 ° 91.1 ± 2.8 0.638

Bimalleolar tilt 103.5 ± 2.8 ° 104.7 ± 3.3 ° 0.210 Medial malleolar relative length 0.52 ± 0.07 0.51 ± 0.06 0.108 Lateral malleolar relative length 0.86 ± 0.09 0.88 ± 0.08 0.850 Medial malleolar slip angle 110.6 ± 7.3 ° 112.8 ± 7.4 ° 0.791 Anterior inclination of tibia 82.5 ± 3.1 ° 81.1 ± 3.1 ° 0.758 Fibular position 0.65 ± 0.10 0.57 ± 0.13 0.012Ankle stress radiograph Tibiotalar tilt angle 7.8 ± 5.1 ° Anterior talar translation 7.5 ± 2.3 mmMRI evaluations ATFL (intact/partial/complete

injury)14/73/28

CFL (intact/partial/complete injury)

62/53/0

PTFL (intact/partial/complete injury)

89/25/1

Deltoid ligament (intact/ partial/complete injury)

84/31/0

Presence of effusion 43MRI = magnetic resonance image, ATFL = anterior talofibular ligament, CFL = calcane-ofibular ligament, PTFL = posterior talofibular ligament

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positioned in patients with ankle instability compared with the control group, which supported the hypothesis that a posteri-orly positioned fibula predisposes to ankle instability [3]. Tibio-talar tilt angle and anterior translation of the talus on the ankle stress radiographs were similar with those of previous studies that addressed the relationship between ankle stress radio-graphs and the lateral ligament injury of the ankle joint [1, 5, 11, 40]. The patients who were included in this study showed a mean tibiotalar tilt angle of 7.8 ° and a 7.5-mm ante-rior translation of the talus on the ankle stress radiographs. Pre-vious studies that compared the results of ankle stress radiographs with surgical findings, demonstrated various nor-mal ranges (< 5–10 ° in tibiotalar tilt angle and < 4–6 mm in ante-rior translation of the talus) on the ankle stress radiographs [1, 5, 11, 40]. Although these angles and distances were similar to those of our patients, we believe that direct comparison of the measurements between the studies might be limited because various patient factors such as age and sex are not adjusted.Ankle stress radiographs including tibiotalar tilt angle and ante-rior translation of the talus have been used as surgical indica-tions for lateral ankle instability [14] regardless of patients’ age, sex, and anatomical characteristics. The effects of age and sex on ligament laxity have been controversial [13, 18, 26, 44]. In the present study, bony anatomical characteristics were identified as factors associated with ankle stress radiographs in addition to age, sex, and injury of ligaments. Physicians should be aware of

Measurements Intraobserver reliability Interobserver reliability

ICC 95 % CI ICC 95 % CI

Distal tibial articular surface angle 0.809 0.656–0.898 0.811 0.694–0.892Bimalleolar tilt 0.886 0.789–0.940 0.783 0.660–0.874Medial malleolar relative length 0.664 0.432–0.814 0.693 0.528–0.818Lateral malleolar relative length 0.898 0.810–0.947 0.789 0.667–0.877Medial malleolar slip angle 0.968 0.939–0.984 0.820 0.712–0.896Anterior inclination of tibia 0.941 0.888–0.969 0.841 0.727–0.913Fibular position 0.880 0.777–0.937 0.819 0.712–0.896Tibiotalar tilt angle 0.997 0.993–0.998 0.991 0.985–0.995Anterior talar translation 0.996 0.992–0.998 0.977 0.949–0.989ICC = intraclass correlation coefficient; CI = confidence interval

Table 3 Intra- and interobserver reliability of measurements.

Tibiotalar tilt angle Anterior translation of talus

Estimate SE p-value Estimate SE p-value

Age − 0.037 0.036 0.299 0.006 0.016 0.721Sex (female) 2.230 0.952 0.021 0.469 0.435 0.284Radiographic measurements * Distal tibial articular surface angle 0.142 0.187 0.451 0.055 0.084 0.511 Bimalleolar tilt 0.503 0.165 0.003 0.160 0.076 0.037 Medial malleolar relative length − 4.684 6.679 0.485 − 0.968 2.999 0.747 Lateral malleolar relative length 11.909 5.448 0.031 4.911 2.450 0.047 Medial malleolar slip angle 0.103 0.065 0.116 0.032 0.029 0.278 Anterior inclination of tibia 0.093 0.222 0.678 − 0.008 0.102 0.936 Fibular position 6.238 7.127 0.385 6.889 3.148 0.033MRI evaluations†

Degree of ATFL injury 3.080 0.761 < 0.001 0.579 0.361 0.112 Degree of CFL injury 1.270 0.960 0.189 0.585 0.430 0.176 Degree of PTFL injury 1.708 1.074 0.115 1.137 0.475 0.018 Degree of Deltoid ligament injury 2.167 1.067 0.045 0.427 0.486 0.381 Presence of effusion − 0.500 0.996 0.617 0.111 0.447 0.805SE = standard error, MRI = magnetic resonance image * increase in degree or ratio† a degree increase

Table 4 Factors affecting ankle stress radiographs by univariate analysis.

Table 5 Factors affecting ankle stress radiographs by multiple regression analysis.

Estimate SE p-value Adjusted R2

Tibiotalar tilt angle 0.51 Age –0.068 0.033 0.041 Sex (female) 2.244 0.895 0.014 BT * 0.386 0.158 0.016 Degree of ATFL injury * 2.601 0.733 < 0.001 Degree of deltoid

ligament injury * 1.692 0.973 0.085

Anterior translation of talus 0.50 Age –0.013 0.026 0.625 Sex (female) 0.181 0.666 0.787 BT * 0.111 0.140 0.432 LMRL† 1.263 4.762 0.792 FP† 6.824 3.189 0.038 Degree of PTFL injury * 1.620 0.785 0.044SE = standard error, BT = bimalleolar tilt, ATFL = anterior talofibular ligament, LMRL = lateral malleolar relative length, FP = fibular position, PTFL = posterior talofibu-lar ligament * increase in degrees† increase in ratio

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differences in these patient factors during the interpretation of ankle stress radiographs. We believe that comparison of both ankles on stress radiographs is superior to applying fixed numerical values to the injured side in order to reduce the influ-ence of patient factors when assessing surgical indications. After the surgery, these determinants may affect the result of the open ligament reconstruction. According to our results, we may assume that younger female patients, who showed greater bimalleolar tilt angle and more posterior position of the fibula, had a poorer prognosis after ligament reconstruction. Namely, patient-specific postoperative rehabilitation programs and braces may be required according to the patient’s risk factors after the surgery. Further study regarding the relationship between patient characteristics and prognosis of the surgery is required.Ankle instability is one of the causes of posttraumatic arthritis [4]. Excessive motion of the ankle joint can result in cartilage damage over time. In the present study, degree of ATFL injury and PTFL were determinants of excessive motion on the coronal and sagittal plane, respectively. Hence, the location and condi-tion of the cartilage damage on the ankle joint could differ according to the injured ligament in patients with ankle instabil-ity. Bimalleolar tilt angle and fibular position were also associ-ated with ankle motion. The larger bimalleolar tilt angle and fibular position ratio in some patients may result in different conditions of cartilage damage compared to patients with a sim-ilar degree of ligament injury. To the best of our knowledge, this study is the first to investigate the influence of both of bone mor-phology and injured ligament of the ankle on ankle stress radio-graphs in patients evaluated for lateral ankle instability. Based on the present study, we believed that future research regarding the relationship between ankle arthritis and specific ligament injury and bony configuration is warranted. Future research is expected to help physicians to develop patient-specific braces and surgical implants for the prevention and treatment of osteo-arthritis.Anterolateral rotation of the ankle joint is normally restrained by the CFL, and anterior translation of the talus in relation to the tibia is normally prevented by the ATFL [20, 28]. However, a pre-vious study also showed that the tibiotalar tilt angle and ante-rior translation of the talus were affected by AFTL injury and PTFL injury, respectively [25]. These findings are consistent with the present study. However, PTFL-only injury is rare. Although 26 PTFL injuries (25 partial and 1 complete) were included in this study, all PTFL injuries were associated with another liga-ment injury. In the present study, ATFL and CFL injury were adjusted during analysis to assess the effect of PTFL injury. Namely, ATFL and/or CFL injury can be also speculated when an increased anterior translation of the talus is found on the ante-rior drawer view.MRI is widely used to assess the ligamentous condition of joints. Although our results were based on MRI findings of the ankle joint and not confirmed surgically, ankle MRI shows good to excellent sensitivity and specificity for detecting ligament inju-ries [11, 31]. In addition, the use of MRI to assess ligamentous condition enabled patients who did not require surgery due to mild lateral ankle instability to be included in the study.7 items relevant to measuring the bony constraint of the ankle joint on radiographs were selected in a consensus-building ses-sion. These measurements showed good to excellent reliability and these results were consistent with a previous study [26]. Among these, bimalleolar tilt and fibular position were found to

be factors significantly associated with tibiotalar angle and ante-rior translation on ankle stress radiographs, respectively. A larger bimalleolar tilt might represent relatively less bony con-straint in the medial ankle joint, which is believed to contribute to the increase of the tibiotalar tilt angle on the varus stress view. Fibular position has been reported as a determinant lead-ing to lateral ankle instability [3, 35], and the current study sup-ports these results. A previous study suggested that the more posteriorly the fibula is located, the wider the anterolateral space of the ankle joint becomes, which provides more space for the talus to subluxate anterolaterally [26]. We also believe that the anterolateral subluxation of the talus resulted in anterior translation of the talus on anterior drawer on lateral view. Future 3-dimensional biomechanical studies of the ankle joint will pro-vide more comprehensive evidence concerning the influence of bone morphology on lateral ankle instability.This study has clinical importance in that the bony constraint was included in evaluating ankle instability in addition to the conventional ligament injuries. A patient could have an unstable ankle without mechanical instability shown on the ankle stress radiograph. The diagnosis and treatment should depend on patients’ subjective symptoms and the physician’s insight, and no concrete surgical indications have been defined. More unknown factors should be included when defining ankle insta-bility, such as subjective degree of pain and individual variation of flexibility, although the present study reveals that bone mor-phology can a play role in mobility of the ankle joint on the ankle stress radiograph. Further study regarding various patient factors should be required to develop personalized treatment.Some limitations of this study should also be addressed. First, the study was retrospective in nature. All subjects were patients diagnosed with lateral ankle instability who visited our institu-tion to manage their ankle problems. Because our institution is a tertiary referral center for ankle disease, patients who suffered mild symptoms might not have been included in this study. Sec-ond, pain and subjective symptoms were not quantitatively eval-uated. Ankle pain might have affected stress radiographs by involuntary contraction of muscles around the ankle. Third, sev-eral radiographic measurements were used to assess the influ-ence of bone morphology on ankle stress radiographs in patients with lateral ankle instability. Due to the complex 3-dimensional nature of the ankle joint, 2-dimensional radiograph measure-ments may be limited in explaining the effect of bone morphol-ogy on ankle stress radiographs. Further investigation employing a 3-dimensional anatomical approach is required. However, sim-ple radiographs are widely used as a basic clinical examination, and thus we believed that anatomical assessment using simple radiographs is helpful for physicians in terms of accessibility. Fourth, we did not use a calibration ruler in the radiographs. Unlike the angle on the radiographs, the length on radiographs might have an effect on the results were a calibration ruler to be used. However, all lengths on the radiographs, except the ante-rior translation of the talus on the anterior drawer lateral view, were converted to ratios for analysis. Therefore, we believe that the error was minimal.In conclusion, although ankle stress radiographs have been widely used in patients with lateral ankle instability, various potential determinants including bony morphology of the ankle joint have been overlooked during interpretation of the meas-urements. Based on our study, age, sex, degree of ATFL injury, and bimalleolar tilt were found to be factors significantly associ-ated with tibiotalar tilt angle on the varus stress view, and the

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Lee SY et al. Is there a Relationship … Int J Sports Med 2016; 37: 1080–1086

degree of PTFL injury and fibular position were factors signifi-cantly associated with anterior translation of the talus on the anterior drawer view. These results suggest that differences in patient factors including age, sex, and bony anatomical structure of the ankle joint might predispose the outcomes of ankle stress radiographs. We conclude that comparison of both ankles on stress radiographs is superior to applying fixed numerical values to the injured side in order to reduce the influence of patient factors when assessing surgical indications.

Conflictofinterest: The authors have no conflict of interest to declare.

Affiliations1 Orthopaedic Surgery, Ewha Womans University Mokdong Hospital, Seoul,

Korea, Republic of2 Department of Mathematics, College of Natural Science, Ajou University,

Suwon, Korea, Republic of3 Orthopaedic Surgery, Seoul National University Bundang Hospital,

Sungnam, Korea, Republic of4 Department of Orthopaedic Surgery, Seoul National University Bundang

Hospital, Sungnam, Korea (the Republic of)5 School of Mechanical Engineering, Chung-Ang University, Seoul, Korea (the

Republic of)

References1 Ahovuo J, Kaartinen E, Slatis P. Diagnostic value of stress radiography

in lesions of the lateral ligaments of the ankle. Acta Radiol 1988; 29: 711–714

2 Bahr R, Pena F, Shine J, Lew WD, Lindquist C, Tyrdal S, Engebretsen L. Mechanics of the anterior drawer and talar tilt tests. A cadaveric study of lateral ligament injuries of the ankle. Acta Orthop Scand 1997; 68: 435–441

3 Berkowitz MJ, Kim DH. Fibular position in relation to lateral ankle instability. Foot Ankle Int 2004; 25: 318–321

4 Blankenhorn B, Saltzman C. Ankle arthritis. In: Coughlin M, Saltzman C, Anderson R (eds.). Mann’s Surgery of the Foot and Ankle. Philadel-phia: Elsevier; 2014: 1041

5 Blanshard KS, Finlay DB, Scott DJ, Ley CC, Siggins D, Allen MJ. A radio-logical analysis of lateral ligament injuries of the ankle. Clin Radiol 1986; 37: 247–251

6 Bonasia DE, Dettoni F, Femino JE, Phisitkul P, Germano M, Amendola A. Total ankle replacement: why, when and how? Iowa Orthop J 2010; 30: 119–130

7 Bonett DG. Sample size requirements for estimating intraclass correla-tions with desired precision. Stat Med 2002; 21: 1331–1335

8 Breitenseher MJ, Trattnig S, Kukla C, Gaebler C, Kaider A, Baldt MM, Haller J, Imhof H. MRI versus lateral stress radiography in acute lateral ankle ligament injuries. J Comput Assist Tomogr 1997; 21: 280–285

9 Cardone BW, Erickson SJ, Den Hartog BD, Carrera GF. MRI of injury to the lateral collateral ligamentous complex of the ankle. J Comput Assist Tomogr 1993; 17: 102–107

10 Chambers J. Linear models. In: Chambers J, Hastie T (eds.). Statistical models in S. Boca Raton: Chapman & Hall/CRC; 1992

11 Chandnani VP, Harper MT, Ficke JR, Gagliardi JA, Rolling L, Christensen KP, Hansen MF. Chronic ankle instability: evaluation with MR arthrography, MR imaging, and stress radiography. Radiology 1994; 192: 189–194

12 Chen CY, Huang PJ, Kao KF, Chen JC, Cheng YM, Chiang HC, Lin CY. Sur-gical reconstruction for chronic lateral instability of the ankle. Injury 2004; 35: 809–813

13 Chesworth BM, Vandervoort AA. Age and passive ankle stiffness in healthy women. Phys Ther 1989; 69: 217–224

14 Clanton T, Waldrop N III. Athletic injuries to the soft tissues of the foot and ankle. In: Coughlin M, Saltzman C, Anderson R (eds.). Mann’s Sur-gery of the Foot and Ankle. Philadelphia: Elsevier; 2014: 1531–1687

15 Coughlin MJ, Schenck RC Jr, Grebing BR, Treme G. Comprehensive recon-struction of the lateral ankle for chronic instability using a free gracilis graft. Foot Ankle Int 2004; 25: 231–241

16 DeHaven KE, Lintner DM. Athletic injuries: comparison by age, sport, and gender. Am J Sports Med 1986; 14: 218–224

17 Doherty C, Delahunt E, Caulfield B, Hertel J, Ryan J, Bleakley C. The incidence and prevalence of ankle sprain injury: a systematic review and meta-analysis of prospective epidemiological studies. Sports Med 2014; 44: 123–140

18 Ericksen H, Gribble PA. Sex differences, hormone fluctuations, ankle stability, and dynamic postural control. J Athl Train 2012; 47: 143–148

19 Ferkel R, Dierckman B, Phisitkul P. Arthroscopy of the foot and ankle. In: Coughlin M, Saltzman C, Anderson R (eds.). Mann’s Surgery of the Foot and Ankle. Philadelphia: Elsevier; 2014: 1770–1829

20 Frost S, Amendola A. Is stress radiography necessary in the diagnosis of acute or chronic ankle instability? Clin J Sport Med 1999; 9: 40–45

21 Hamilton WG, Thompson FM, Snow SW. The modified Brostrom proce-dure for lateral ankle instability. Foot Ankle 1993; 14: 1–7

22 Harrington KD. Degenerative arthritis of the ankle secondary to long-standing lateral ligament instability. J Bone Joint Surg Am 1979; 61: 354–361

23 Harriss DJ, Atkinson G. Ethical standards in sports and exercise science research: 2016 update. Int J Sports Med 2015; 36: 1121–1124

24 Kerkhoffs GM, Rowe BH, Assendelft WJ, Kelly K, Struijs PA, van Dijk CN. Immobilisation and functional treatment for acute lateral ankle liga-ment injuries in adults. Cochrane Database Syst Rev 2002; CD003762

25 Lee K, Chung C, Kwon S, Chung M, Won S, Lee S, Park M. Relationship between stress ankle radiographs and injured ligaments on MRI. Skel-etal Radiol 2013; 42: 1537–1542

26 Lee KM, Chung CY, Sung KH, Lee S, Kim TG, Choi Y, Jung KJ, Kim YH, Koo SB, Park MS. Anatomical predisposition of the ankle joint for lateral sprain or lateral malleolar fracture evaluated by radiographic meas-urements. Foot Ankle Int 2015; 36: 64–69

27 Magerkurth O, Frigg A, Hintermann B, Dick W, Valderrabano V. Fron-tal and lateral characteristics of the osseous configuration in chronic ankle instability. Br J Sports Med 2010; 44: 568–572

28 Marder R. Current methods for the evaluation of ankle ligament inju-ries. Instr Course Lect 1995; 44: 349–357

29 Martin DE, Kaplan PA, Kahler DM, Dussault R, Randolph BJ. Retrospec-tive evaluation of graded stress examination of the ankle. Clin Orthop Relat Res 1996; 328: 165–170

30 McKinley TO, Rudert MJ, Koos DC, Brown TD. Incongruity versus insta-bility in the etiology of posttraumatic arthritis. Clin Orthop Relat Res 2004; 423: 44–51

31 Park HJ, Cha SD, Kim SS, Rho MH, Kwag HJ, Park NH, Lee SY. Accuracy of MRI findings in chronic lateral ankle ligament injury: comparison with surgical findings. Clin Radiol 2012; 67: 313–318

32 Park MS, Kim SJ, Chung CY, Choi IH, Lee SH, Lee KM. Statistical consid-eration for bilateral cases in orthopaedic research. J Bone Joint Surg Am 2010; 92: 1732–1737

33 Raatikainen T, Putkonen M, Puranen J. Arthrography, clinical exami-nation, and stress radiograph in the diagnosis of acute injury to the lateral ligaments of the ankle. Am J Sports Med 1992; 20: 2–6

34 Schneck CD, Mesgarzadeh M, Bonakdarpour A. MR imaging of the most commonly injured ankle ligaments. Part II. Ligament injuries. Radiol-ogy 1992; 184: 507–512

35 Scranton PJ, McDermott J, Rogers J. The relationship between chronic ankle instability and variations in mortise anatomy and impingement spurs. Foot Ankle Int 2000; 21: 657–664

36 Seligson D, Gassman J, Pope M. Ankle instability: evaluation of the lateral ligaments. Am J Sports Med 1980; 8: 39–42

37 Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reli-ability. Psychol Bull 1979; 86: 420–428

38 Sugimoto K, Samoto N, Takakura Y, Tamai S. Varus tilt of the tibial plafond as a factor in chronic ligament instability of the ankle. Foot Ankle Int 1997; 18: 402–405

39 Valderrabano V, Hintermann B, Horisberger M, Fung TS. Ligamen-tous posttraumatic ankle osteoarthritis. Am J Sports Med 2006; 34: 612–620

40 van Dijk CN, Mol BW, Lim LS, Marti RK, Bossuyt PM. Diagnosis of liga-ment rupture of the ankle joint. Physical examination, arthrography, stress radiography and sonography compared in 160 patients after inversion trauma. Acta Orthop Scand 1996; 67: 566–570

41 van Rijn R, van Os A, Bernsen R, Luijsterburg P, Koes B, Bierma-Zeinstra S. What is the clinical course of acute ankle sprains? A systematic lit-erature review. Am J Med 2008; 121: 324–331

42 Wilkerson GB, Horn-Kingery HM. Treatment of the inversion ankle sprain: comparison of different modes of compression and cryother-apy. J Orthop Sports Phys Ther 1993; 17: 240–246

43 Wilkinson G, Rogers C. Symbolic description of factorial models for analysis of variance. J Appl Stat 1973; 22: 392–399

44 Yeung MS, Chan KM, So CH, Yuan WY. An epidemiological survey on ankle sprain. Br J Sports Med 1994; 28: 112–116

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