Innovative Smartphone Technology for Assessment of Ankle Proprioception in Chronic Ankle Instability

<p dir="ltr">Chronic ankle instability (CAI) is a leading cause of chronic musculoskeletal impairment affecting the lower limbs. It is characterised by impaired locomotor function and reduced ankle proprioception, which can heighten the injury risk in lower-limb-dominant sports activities; decrease individuals’ physical activity levels and overall quality of life. Function-oriented rehabilitation is acknowledged as a first-line intervention for managing CAI, underscoring the crucial role of functional assessments for validated and reliable measurement to guide monitoring and personalised treatment interventions that mitigate re-injury. However, a major gap exists regarding the clinical applicability of existing functional assessments for CAI populations. Although numerous assessments targeting ankle mobility and motor-task performance are used, their measurement properties have not been thoroughly validated in CAI. Furthermore, deficits in ankle proprioception have been identified as a key factor contributing to the development and persistence of CAI, highlighting the need for comprehensive evaluation and targeted intervention. Despite this, most proprioception assessments are restricted to laboratory settings and depend on bulky, expensive equipment, limiting their clinical utility. Therefore, this thesis aims to evaluate the use of function-oriented assessments for individuals with CAI, with particular emphasis on advancing the clinical evaluation of ankle proprioception.</p><p dir="ltr">This research begins with a bibliometric analysis, followed by three experimental studies designed to evaluate the clinometric properties of existing functional tests and a newly developed device for measurement of ankle proprioception assessment in individuals with and without CAI. The bibliometric analysis presented in Chapter 1 part B based on CAI-related literature published up to the end of 2023, revealed several key findings: first, research interest in CAI is increasing globally; second, authors and institutions based in the United States dominate both publication volume and academic influence; third, there is a clear shift in research focus from structural to functional concerns; and fourth, future research directions are likely to emphasise epidemiological studies involving diverse cohorts and the adoption of emerging diagnostic and therapeutic technologies. This review provides the necessary background and developmental trajectory for focusing on function-oriented assessment in CAI, thereby strengthening the rationale of this thesis.</p><p dir="ltr">Following this, the study presented in Chapter 2 evaluated the test-retest reliability and known-group validity of a battery of function-oriented tests in a CAI population. Twenty-four participants with unilateral CAI were recruited. Both symptomatic and asymptomatic ankles of each participant were tested three times. Assessments included ankle dorsiflexion range of motion (DFROM) measured with a goniometer under non-weight-bearing conditions, the weight-bearing lunge test (WBLT), dynamic balance assessed by the three-direction star excursion balance test (SEBT), and ankle proprioception evaluated through the active movement extent discrimination assessment (AMEDA). The study found that test-retest reliability was influenced by CAI pathology, with the asymptomatic side showing generally higher intraclass correlation coefficients (ICCs), compared to the symptomatic side across testing sessions. WBLT and SEBT demonstrated good to excellent reliability on both sides, supporting their use for assessing ankle dorsiflexion mobility and dynamic balance clinically. In contrast, AMEDA showed only moderate reliability for the symptomatic side and good reliability for the asymptomatic side, with no difference in proprioceptive performance detected between the two sides. This characteristic complicates the establishment of clinical benchmarks based on the unaffected contralateral side in unilateral CAI patients. Furthermore, unlike the other assessments which are more clinically accessible, AMEDA typically requires bulky, customised, and costly equipment, limiting its feasibility in clinical practice. Hence, the clinical applicability of AMEDA-based apparatus is considered low.</p><p dir="ltr">Acknowledging the potential of smartphone technology to enhance clinical assessment due to its portability, popularity, and cost-effectiveness, this thesis addresses the current shortcomings of smartphone-based ankle proprioception assessments in methodology and clinical accessibility, which remain in an exploratory stage with theoretical and practical concerns. Based on the principle of movement extent discrimination, an innovative smartphone application called Smartphone Proprioception for Ankle Navigation (SPAN) was designed and developed. In Chapter 4, the test-retest reliability of SPAN and the influence of a new concept; position exposure time (PET), i.e. the required duration for holding a preset movement terminal in each trial, on ankle proprioception performance was investigated in a cohort of healthy adults. Twenty-four participants underwent SPAN testing under four PET conditions—0.25s, 0.5s, 0.75s, and 1.0s—and were retested within one week. The results showed associations between PET, proprioceptive performance, and SPAN reliability, with ICCs ranging from 0.473 to 0.897. Notably, the shortest PET (0.25s) yielded near-excellent reliability but the lowest proprioception accuracy. The prolongation of PET improved proprioceptive performance but also increased variability across sessions. These findings suggest the feasibility of SPAN as an ankle proprioception assessment tool and highlight its sensitivity to temporal parameters.</p><p dir="ltr">To further validate the use of SPAN in a clinical CAI population, the study presented in Chapter 5 conducted between-day test-retest and cross-sectional comparisons involving 24 unilateral CAI patients paired with 24 healthy controls. Testing was performed under two PET conditions (0.25s and 1.0s). The study found that the ankle proprioception measured under the 1.0s PET condition demonstrated moderate to good test-retest reliability, effectively discriminated symptomatic ankles from asymptomatic ones both from the same individuals and the healthy controls, and showed significant positive correlation with perceived severity of ankle instability. These results further support SPAN’s utility as a portable proprioception assessment instrument and indicate that proprioceptive deficits in CAI are PET-related, providing insight for rehabilitation strategies. Specifically, neuromuscular training that incorporates position-holding may be critical for restoring proprioceptive function in CAI patients.</p><p dir="ltr">In summary, this thesis provides a scholarly contribution to the valid and reliable assessment of individuals with CAI that may also inform personalised intervention and rehabilitation by (1) establishing clinical benchmarks of reliability and validity for existing functional assessments in CAI populations and (2) introducing and validating a novel, smartphone-based proprioception assessment tool—SPAN—that offers a practical, scalable solution for clinical evaluation. Collectively, these findings underscore the importance of integrating reliable, accessible, and patient-centred assessment tools into CAI rehabilitation. Future research should investigate SPAN’s clinical responsiveness in CAI rehabilitation, expanding its application to other lower-limb musculoskeletal disorders, and exploring its potential use as a training or biofeedback device within proprioception-focused protocols.</p>