Effects of immobilization angle on tendon healing after achilles rupture in a rat model

Abstract

Conservative (non‐operative) treatment of Achilles tendon ruptures is a common alternative to operative treatment. Following rupture, ankle immobilization in plantarflexion is thought to aid healing by restoring tendon end‐to‐end apposition. However, early activity may improve limb function, challenging the role of immobilization position on tendon healing, as it may affect loading across the injury site. This study investigated the effects of ankle immobilization angle in a rat model of Achilles tendon rupture. We hypothesized that manipulating the ankle from full plantarflexion into a more dorsiflexed position during the immobilization period would result in superior hindlimb function and tendon properties, but that prolonged casting in dorsiflexion would result in inferior outcomes. After Achilles tendon transection, animals were randomized into eight immobilization groups ranging from full plantarflexion (160°) to mid‐point (90°) to full dorsiflexion (20°), with or without angle manipulation. Tendon properties and ankle function were influenced by ankle immobilization position and time. Tendon lengthening occurred after 1 week at 20° compared to more plantarflexed angles, and was associated with loss of propulsion force. Dorsiflexing the ankle during immobilization from 160° to 90° produced a stiffer, more aligned tendon, but did not lead to functional changes compared to immobilization at 160°. Although more dorsiflexed immobilization can enhance tissue properties and function of healing Achilles tendon following rupture, full dorsiflexion creates significant tendon elongation regardless of application time. This study suggests that the use of moderate plantarflexion and earlier return to activity can provide improved clinical outcomes. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res

Diminishing effects of mechanical loading over time during rat Achilles tendon healing

“…The histological analysis showed that unloaded tendons improved significantly between 1 and 4 weeks, again proposing that loading influences primarily the first weeks of tendon healing. The improved collagen orientation due to mechanical loading has been reported by other researchers (Hillin et al 2019), but to our knowledge no other studies have used SAXS to characterize tendon healing.…”

Gastrocnemius muscle remodeling explains functional deficits three months following Achilles tendon rupture

“…10 Clinical treatment is targeted at minimizing tendon elongation following rupture, which can be targeted with early ankle motion 5 and avoiding immobilization in dorsiflexion. 26 Conversely, high velocity training stimulates longer muscle fascicles in a bipedal bird model. 27 However, both tendon elongation and fascicle remodeling appear to occur during the weeks following the initial injury, limiting the potential efficacy of restoring muscle structure after the tendon is fully healed in an elongated position.…”

Effects of Pulsed Electromagnetic Field Therapy on Rat Achilles Tendon Healing

“…Testing included preloading (0.1 N), preconditioning (0.5–1.5% strain at 0.25 Hz for 30 cycles), stress relaxation (6% strain), dynamic frequency sweeps (0.125% strain amplitude, at 0.1, 1, 5, and 10 Hz for 10 cycles each), a ramp at 2% strain/s to 35 N (used to calculate quasistatic parameters), and fatigue cycling (5–35 N at 2 Hz; which corresponds to 10–70% of ultimate failure load) until failure. During loading, force and displacement data were acquired using the WaveMatrix (Instron, Norwood, MA) data acquisition software and analyzed using custom MATLAB code . Images were acquired during testing to track strain optically.…”

“…Testing included preloading (0.1 N), preconditioning (0.5-1.5% strain at 0.25 Hz for 30 cycles), stress relaxation (6% strain), dynamic frequency sweeps (0.125% strain amplitude, at 0.1, 1, 5, and 10 Hz for 10 cycles each), a ramp at 2% strain/s to 35 N (used to calculate quasistatic parameters), and fatigue cycling (5- and analyzed using custom MATLAB code. 13,14,22,23 Images were acquired during testing to track strain optically. Fatigue parameters were calculated at 5, 50, and 95% of fatigue life (defined by the corresponding percentage of cycles to failures) to describe the three phases of fatigue behavior.…”