This is a long-term research registry for patients with Achilles tendon disorders (like tears, chronic pain, or ruptures) as well as healthy adults without tendon problems. The goal is to collect detailed information over time to understand which treatments work best for different people, identify risk factors for injury, and improve overall care. Adults over 18, both with and without Achilles tendon conditions, are eligible to join. Participants will attend several assessment visits at the Prince of Wales Hospital over the first year (at the start, 6 weeks, 3, 4, 6, and 12 months) for physical tests, ultrasounds, and questionnaires. After the first year, follow-up continues with annual online questionnaires for up to five years. The main measure is a standard questionnaire about tendon pain and function (VISA-A). The study aims to use this information to guide better, more personalized rehabilitation strategies, improve patient outcomes, and reduce long-term disability. All participation is voluntary and requires written consent.

This is a prospective, longitudinal Achilles Tendon Registry study. The registry is conceived as a foundational cohort study designed to systematically address critical evidence gaps in the management of Achilles tendon pathologies. The Achilles tendon, while robust, is susceptible to a spectrum of disorders including acute ruptures and chronic tendinopathies, often summarized colloquially as the "Achilles heel." Current clinical management strategies for these conditions are characterized by heterogeneity, largely due to a paucity of high-quality, longitudinal comparative effectiveness data. This registry aims to mitigate this gap by creating a centralized repository of standardized, prospective data, thereby enabling rigorous evaluation of treatment outcomes, prognostic factors, and long-term sequelae.

The primary objective is to establish a comprehensive, prospectively enrolled cohort of individuals with Achilles tendon disorders, complemented by a cohort of asymptomatic controls, to facilitate comparative and predictive analyses. The study is explicitly designed to answer three pivotal research questions. First, it will investigate the prognostic influence of baseline structural and vascular status of the tendon, as quantified by ultrasonographic and elastographic metrics, on functional recovery. Second, it will assess whether a pre-existing diagnosis of Achilles tendinopathy constitutes a significant risk factor for subsequent acute tendon rupture. Third, it will analyze differential treatment responsiveness, aiming to identify which patient subgroups, defined by specific baseline characteristics, demonstrate optimal outcomes with specific treatment modalities.

The study methodology is that of a prospective, single-center cohort study to be conducted at the Prince of Wales Hospital in Hong Kong. The target sample size is a minimum of 500 participants, to be consecutively enrolled from 2025 to 2028. The participant pool will include adults over the age of 18 with a diagnosis of an Achilles tendon disorder, as well as asymptomatic control participants without tendon pathology. Key exclusion criteria encompass any comorbid physical or psychological condition that would impair the ability to complete study assessments or provide informed consent, and concomitant diseases that severely affect lower limb function (e.g., severe osteoarthritis, prior amputation, active inflammatory arthritis, or paralysis).

The follow-up protocol is structured into intensive initial and long-term phases. All participants will undergo comprehensive in-person assessments at baseline, 6 weeks, 3 months, 6 months, and 1 year post-enrollment. These assessments constitute the core data collection points and encompass a multi-modal battery of outcome measures. Following the initial 1-year follow-up, the protocol transitions to long-term monitoring, wherein all self-reported outcome measures will be collected annually via online questionnaires at years 2, 3, 4, and 5.

The primary outcome measure is the Victorian Institute of Sports Assessment-Achilles (VISA-A) questionnaire, a validated, disease-specific patient-reported outcome tool scored from 0 to 100. A comprehensive suite of secondary outcome measures will be collected to provide a holistic assessment. These include patient-reported outcomes such as the Numeric Pain Rating Scale (NPRS) and the Foot and Ankle Outcome Score (FAOS). Functional and physical performance measures are integral and consist of the Achilles Tendon Resting Angle (ATRA), calf muscle strength quantified via hand-held dynamometry, the heel raise endurance test, and a one-legged counter-movement jump test performed on a pressure mat. Biomechanical analysis includes foot pressure distribution assessment and treadmill-based gait analysis using a Zebris system.

A central and rigorous component of the assessment protocol is ultrasonographic evaluation, performed at all in-person time points using a standardized imaging protocol. Key sonographic parameters include tendon thickness and cross-sectional area, neovascularity scored via the Öhberg scale, and tendon elasticity quantified by shear wave elastography (SWE) to measure stiffness in kilopascals. Supplementary advanced imaging modalities may be employed in subsets of participants, including photoacoustic ultrasound (PAUS) for quantifying tendon oxygenation and vascularity, and infrared thermography for measuring superficial tendon temperature.

Data management and security are paramount. All collected data, including personally identifiable information and consent forms, will be stored under strict physical and electronic security protocols. Physical documents will be kept in locked cabinets, and electronic data on password-protected computers. Data entry will employ a double-entry method with range checks to ensure accuracy. The final analysis dataset will be de-identified. Access to identifiable data is restricted to authorized trial team members. De-identified data may be shared with external researchers upon reasonable request, execution of a data sharing agreement, and following approval by the relevant ethics committee.

Statistical analysis will be performed using SPSS software (version 28.0) with a two-sided alpha level of 0.05. Analytical strategies are tailored to the research questions. Multivariable linear or logistic regression will evaluate associations between baseline metrics and outcomes (Q1). Cox proportional hazards or logistic regression models will assess the risk of rupture associated with pre-existing tendinopathy (Q2). To identify differential treatment effects (Q3), regression models will incorporate interaction terms between patient subgroups and treatment types, with subsequent stratified analysis if interactions are significant. Missing data will be handled using multiple imputation techniques, and sensitivity analyses will be conducted. An interim analysis for safety monitoring will be performed after 20% of participants complete the 1-year follow-up.

The study will be overseen by a Trial Steering Committee comprising the Principal Investigator, orthopaedic surgeons, research assistants, and a biostatistician from the research team. The committee is responsible for monitoring study progress, participant recruitment, and data collection. An independent annual audit of trial conduct will be performed by an auditor from the Joint Chinese University of Hong Kong - New Territories East Cluster Clinical Research Ethics Committee. All protocol amendments will require prior ethics committee approval and will be communicated to participants and registered publicly.

The study is conducted under the auspices of the Department of Orthopaedics and Traumatology, Faculty of Medicine, The Chinese University of Hong Kong. No external funding sources or sponsors have been declared at this protocol stage. All investigators have declared no competing interests. Participants will not receive financial incentives. Provisions for harm are established: any participant experiencing an adverse effect directly attributable to the study procedures will receive appropriate medical care at the Prince of Wales Hospital at no additional cost, with compensation handled per institutional and ethical guidelines.

Inclusion Criteria:

• Adults (>18 years of age)

Exclusion Criteria:

• Any physical or psychological comorbidity that would impair the ability to complete study assessments (e.g., significant neurological deficits) or preclude the provision of informed consent.
• Concomitant diseases that severely affect lower limb function or assessment (e.g., severe osteoarthritis of the knee or hip, prior lower limb amputation, peripheral vascular disease, active rheumatoid arthritis, lower limb paralysis, etc.)

Hong Kong Residents