Achilles tendon rupture pilot protocol: comparing the feasibility of a criterion-based experimental protocol against standardised care

A criteria based rehabilitation protocol developed as the experimental group intervention. Physical handouts: Participants and physiotherapists will be provided a digital / physical (as per preference) exercise and education sheet for each session. The patient sheet will have all their prescribed exercises and immobilisation requirements. The physiotherapist sheet is a comprehensive version of the patient sheet, with further explanation of how to prescribe all the education and exercises to the patient. Intervention descriptions: Each participant of each group will receive 13 fortnightly in-person consultations as part of their intervention. The initial consultation will be 60 minutes and the 12 follow-up consultations will be 30 minutes. All consultations and treatments will be provided by a registered and trained physiotherapist at Centaur Institute (Richmond, Victoria, Australia). The optimised standard care protocol will be the accelerated Achilles rehabilitation protocol by Willits et al., (2010). This protocol is 12 weeks in length, plus additional time on following weaning of the controlled ankle motion (CAM) walker. It is time-based, permitting progression to the next phase once enough time has elapsed. The type of immobilisation device and wedges the participant is initially prescribed will remain the same throughout their involvement. Clinicians will be given guidelines around how to tailor the intervention to the individual participant. The Willits protocol may be found in the supplementary files of the 2010 publication (Willits et al., 2010). The experimental protocol implements a criterion-based approach. Participants will be immobilised in 30-degrees of plantarflexion. This may be in a plaster cast, a CAM-walker with heel wedges, or a 30-degree strut in the VACOped boot (OPED GmbH, Oberlainderm, Germany). If the participant is prescribed shelf wedges, they will instead be given custom made triangular wedges. The first 2 weeks will be non-weight bearing with two forearm crutches to protect the tendon. After 2 weeks, participants will gradually increase weight bearing and reduce wedge height. Exercise interventions include variations of seated and standing single and double leg calf raises, upper and lower body general strength programs, and stationary cycling for cardiovascular health. Graduation from one phase to the next is permitted once criteria are met. The internal Achilles tendon load will be the criterion metric to graduate to the next phase. This load is calculated via a custom-made calculator. It considers Achilles tendon load (L), total body mass (TBM), shank mass (SM), the external mass (E), Achilles tendon moment arm (ATMA), external moment arm (EMA), a maximal voluntary isometric contraction (MVIC) adjustment, an Achilles tendon displacement adjustment (AM), and a cosine adjustment to the external moment arm (cos(theta)) (Byron et al., 2026). The equation below shows the process to calculate an external mass to achieve a pre-specified Achilles tendon load. When a participant is able to consistently lift the external mass required to reach a pre-specified Achilles tendon load, they may then progress to the next phase. E=(L×TBM×((AM×MVIC×ATMA)/(EMA×cos(theta))))-SM A simplified version of the protocol is shown below. The intervention criteria have built in contingency alterations based on participants that are delayed in meeting the progression criteria. Delayed patients will be kept in higher wedges, restricted weight bearing, and a step-to pattern for longer. Adherence: Behavioral change strategies will be suggested and discussed in both groups to assist with exercise completion and protocol adherence. The key strategy for protocol adherence is regular appointments with the treating physiotherapist. It is expected that face to face meetings and tailored modifications of the program will assist with maintaining close program adherence (Bishop et al., 2015; Chester et al., 2023; Room et al., 2021; Teo et al., 2022). Suggested behavioural change strategies include scheduling and timing of exercises, building the program into a daily planner, keeping a personal diary of exercises completed, and setting electronic calendar alerts (Chester et al., 2023; Cinthuja et al., 2022). During fortnightly in-person sessions, physiotherapists will also provide feedback on exercise technique. Participants find value and reassurance in feedback, which may increase adherence (Bishop et al., 2015; Chester et al., 2023; Jónsdóttir et al., 2023). Fidelity: The intervention fidelity will be monitored at regular intervals (every 10-13 sessions) by the chief investigator (PM). The chief investigator will not be involved in data collection or analysis, but will be involved in experimental group intervention delivery. Physiotherapists delivering the treatment will be provided feedback and strategies to improve fidelity as required. All physiotherapists will be provided a script for each appointment with their patients. Patient consent for review of the appointment script and clinician notes will be sought and analysed to measure delivery fidelity. Observation of at least one session of each participant by the chief investigator.