Fibular Malalignment in Subjects with Chronic Ankle Instability

Transcription

1 Fibular Malalignment in Subjects with Chronic Ankle Instability Takumi Kobayashi 1,2, Eiichi Suzuki 3, Naohito Yamazaki 3, Makoto Suzukawa 4, Atsushi Akaike 4, Kuniaki Shimizu 4, Kazuyoshi Gamada 1. 1 Hiroshima International University, Higashihiroshima, Japan, 2 Hokkaido Chitose Institute of Rehabilitation Technology, Chitose, Japan, 3 Kanagawa Prefectural Shiomidai Hospital, Yokohama, Japan, 4 Yokohama Sports Medical Center, Yokohama, Japan. Disclosures: T. Kobayashi: None. E. Suzuki: None. N. Yamazaki: None. M. Suzukawa: None. A. Akaike: None. K. Shimizu: None. K. Gamada: 6; Nippon Sigmax Corp.. Introduction: Chronic ankle instability (CAI) is caused by either mechanical ankle instability (MAI) or functional ankle instability (FAI). MAI, by definition, involves ligament laxity, whereas FAI may be caused by the other functional components including proprioceptive deficits, neuromuscular deficits, postural control deficits, and muscle weakness [1]. However, there is continuing controversy as to the contributing factors for CAI. Instability of the distal tibiofibular joint is commonly associated with lateral ankle sprain (LAS) or ankle syndesmosis injury [2]. Assessment of this instability was commonly performed by radiography [3] or horizontal computed tomography (CT) [4], and their accuracy and repeatability were consistently poor. In addition, most studies assessed the fibular alignment in the CAI joints two-dimensionally and no study examined it three-dimensionally. The objective of this study was to determine threedimensionally if fibular malalignment exists in subjects with CAI. Previous studies reported inconsistent anteroposterior fibular alignment in the CAI joints, while no study even measured mediolateral fibular alignment [5, 6]. We hypothesized that the fibula of the CAI joints are in posterior and lateral to the contralateral healthy ankles. Methods: Seventeen males with unilateral CAI (21.0 ± 2.4 years; mean ± standard deviation) were enrolled in this IRB-approved, cross-sectional study after signing the informed consent form. Selection criteria were; (a) multiple episodes of unilateral LAS with no history of injuries to the contralateral ankle, (b) no history of other medical or rheumatologic conditions, (c) at least five reported episodes of giving-ways and a reported ongoing tendency for the previously injured ankle to give way during sporting activities. (d) no history of LAS in the last 6 weeks, (e) reported no swelling or feeling severe pain in the last 3 months, and (f) not involved in formal rehabilitation program including balance exercise to the involved ankle. All subjects underwent stress radiograph (anterior drawer / talar tilt) as a screening for mechanical instability. Subjects underwent CT scan at 1.0 mm slice pitch spanning distal one-third of the lower leg and the distal end of the calcaneus. Geometric bone models of the tibia, fibula and talus were created using 3D-Doctor software (Able Software Corp., MA). Anatomical coordinate systems were embedded in each bone model [7]. In the virtual space, the left tibia was horizontally flipped around the sagittal plane of the tibia and was superimposed with the right tibia using a best-fit algorithm of the Geomagic studio software (Geomagic, NC), which provided a transformation matrix (Figure 1). Then, the same transformation matrix was applied to the flipped left fibula and displacements between the right fibula and the transformed left fibula was computed to display separation of two fibular surfaces by a 49-stage color-coded map. The exact displacement at given location can be determined by moving the cursor to that location (Figure 2). The displacements were determined at the level of the most prominent point laterally of the lateral malleolus, and at 5 and 10 cm proximally from the distal tip of the fibula. Paired t-test was used to compare fibular alignment of the CAI and contralateral healthy ankles in each reference point. Effect sizes were calculated to provide clinical meaningful difference according to Cohen [8]. Differences were considered statistically significant where p <.05. Results: The fibula of the CAI joints demonstrated significant lateral translation compared to that of the healthy ankles at all reference points. The effect sizes of the mediolateral displacement were medium. There was no statistical difference in anteroposterior fibular displacement between the healthy and CAI joints (Table 1-3). Discussion: The objective of this study was to determine if the fibular malalignment exist in the CAI joints. The fibula in the CAI joints demonstrated significant lateral translation comparing to that of the healthy ankles, and no statistical difference was detected in the anteroposterior direction. Previous studies indicated lateral displacement of the fibula after ankle syndesmosis injury [4]. In our study, the patients with CAI who had repeated LAS demonstrated lateral displacement of the fibula. This may be caused by the damages of the anterior tibiofibular ligament and/or interosseous membrane that are suffered in LAS [2]. Therefore, the CAI joints may involve distal tibiofibular instability and enlarged width between the lateral and medial malleoli. It may reduce the bony stability of the talus and mortise structure, further causing unstable talocrural joint. The anatomical coordinate systems used in this study had very small inter-/intra-observer differences [9]. The analysis of fibular alignment was automated. Thus, we believe this study was carried out with high reliability. As for the external validity, since the

2 samples in this study were young, healthy males without osteoarthritic changes in the ankle, these results may not be applicable to females or elderly people with osteoarthritis. The limitations of this study were inclusion of four subjects with positive stress radiography and the CT scanning was performed in the non-weightbearing, static condition. In conclusion, the distal fibula in CAI joints is translated laterally to the healthy ankles in the non-weightbearing condition, which may contribute to chronic instability and frequent giving-way. Significance: Fibular malalignment in the CAI joints may require further attention in preventing and\or treating LAS. This information will be useful in future studies involving treatment or prevention of CAI. Acknowledgments: This study was funded by Nippon Sigmax Corp. References: [1] Hertel J, [2] Gerber JP, [3] Harper MC, [4] Gardner MJ, [5] Hubbard TJ, [6] Scranton PE, [7] Kobayashi T, [8] Cohen J, [9] Yamaguchi S,

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