Arthroscopic assessment of syndesmotic instability: Are we pulling correctly in the coronal plane?
Introduction
Syndesmotic instability is a multiplanar phenomenon, occurring in the coronal, sagittal and translational planes [1], [2], [3], [4], [5]. Recognizing such instability can be challenging, especially when subtle. When undiagnosed or untreated, syndesmotic instability can result in significant and potentially irreversible patient morbidity [6]. Prior studies have highlighted that destabilization of the syndesmosis requires injury to all three syndesmotic ligaments (AITFL, IOL, and PITFL), but that partial syndesmotic injuries to the AITFL and IOL can be rendered unstable by deltoid involvement [5], [6], [7], [8]. Contrastingly, isolated AITFL injury does not render the syndesmosis unstable [9]. However, because of the obliquity of the anterior and posterior syndesmotic ligaments, there is the potential for syndesmotic diastasis under stress examination if a lateral hook test (LHT) is performed at variable angles [7], [8]. Prior study by Ogilvie-Harris et al. [10] demonstrated that there is 50% less resistance to lateral translation in the presence of partial syndesmotic injuries (AITFL and IOL), which can result in joint instability.
Arthroscopic evaluation of the syndesmotic joint is considered the gold standard to diagnose and treat syndesmotic instability. It allows surgeons to directly visualize the distal tibiofibular space as well as assess stability in multiple planes under manual stress [7], [8], [11], [12], [13]. The LHT performed 5 cm above the ankle joint under 100 N of lateral force has been shown to be an effective technique for diagnosing an unstable syndesmosis in the coronal plane [7], [14], [15]. Previous cadaveric studies have shown that using the bone hook to apply 100 N of lateral force with no angulation is sufficient to reveal complete distal tibiofibular instability in the coronal plane both radiographically and arthroscopically [7], [13], [14], [16]. However, the impact of angulation on coronal plane measurements of the distal tibiofibular articulation during the hook test remains unknown.
Thus, the primary aim of the study was to determine if changing the direction of the force while performing the hook test impacts the amount of coronal displacement that occurs in subtle syndesmotic instability. We hypothesized that different directions of force application while evaluating distal tibiofibular joint would generate different degrees of diastasis at the distal tibiofibular articulation.
Section snippets
Specimen preparation
Ten non-paired fresh-frozen human cadaveric specimens (mean age at the time of death, 60 years; range, 42–74) amputated 15 cm above the knee were used. Based on pre-sectioning arthroscopic and radiographic evaluation (OrthoScan FD Pulse C-Arm, OrthoScan, Scottsdale, AZ), no specimen had signs of previous trauma or ankle osteoarthritis. Soft tissues were maintained to simulate in vivo conditions. Before testing, specimens were thawed at room temperature and the tibia was fixed to board by using
Results
Ten cadaveric specimens were included in the study, of which five were from males, and five were from females. The means and standard deviations of the coronal space as measured along the anterior and posterior margins of the incisura in the intact state and following ligament sectioning is presented in Table 1, Table 2 respectively.
Discussion
Accurate diagnosis of subtle syndesmotic instability is critical as it has been associated with prolonged disability when not treated properly. Therefore, even with the evolution of more advanced imaging modalities such as WBCT and dynamic ultrasound, the use of arthroscopy to directly visualize the distal tibiofibular articulation remains an evaluative mainstay [11], [12]. Conventionally, assessment of syndesmotic instability in the coronal plane has been the diagnostic benchmark, spanning
Conclusion
Angulation of the applied force ranging from 15 degrees anteriorly to 15 degrees posteriorly during the intraoperative LHT has no effect on coronal plane measurements in patients with subtle syndesmotic instability. On the other hand, posteriorly directed forces result in more sizable diastasis, potential increasing their sensitivity.
Funding
This study was supported by a grant from the Arthroscopy Association of North America (grant 2017D009573). In addition, the author(s) received research support from Arthrex Inc.
Level of evidence
Biomechanical cadaveric study.
Conflict of Interest
The authors declare that there are no conflict of interests.
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