Ankle joint proprioception and passive mechanical properties of the calf muscles after an Achilles tendon rupture: a comparison with matched controls

Abstract

Objective. To examine if ankle joint proprioception, passive stiffness, and torque relaxation responses of the involved and uninvolved limbs of persons with a previous history of an Achilles tendon rupture were different from matched controls.

Design. Quasi-experimental mixed design.

Background. The influence of an Achilles tendon rupture on the proprioceptive and kinetic performance of the involved and uninvolved ankle is not known.

Methods. Twenty persons (mean age, 44.8 years) with a unilateral rupture and 20 matched controls (mean age, 44.2 years) volunteered. Proprioception was tested with a position-matching protocol from which absolute errors were quantified. A dynamometer was used to measure ankle joint angle and passive torque from which stiffness and torque relaxation were calculated.

Results and conclusions. Proprioception absolute errors for the involved and uninvolved limbs of the experimental group were 27% and 31% greater respectively, than values for the control group. Torque relaxation values were greater in the involved limb versus the uninvolved limb or the control group (P=0.003–0.04). In conclusion, participants with a previous history of an Achilles tendon rupture display proprioception deficits in both limbs and greater torque relaxation in the involved limb in comparison to matched controls.
Relevance

Bilateral deficits in ankle joint proprioception, as reported in this study, suggest the uninvolved limb may not serve as an effective control and because proprioception deficits influence some functional tests, Achilles tendon rupture patients may benefit from proprioception training.

Introduction

An Achilles tendon rupture is a devastating injury that leaves the patient with various acute limitations and chronic adaptations such as weakness in the calf muscle-tendon unit and decreased functional ability (Bressel and McNair, 2001; Moller et al., 2002). Some research has indicated the injury occurred more frequently among athletes and middle-aged individuals but the exact cause (etiology) of rupture remains elusive (Leppilahti and Orava, 1998; Leppilahti et al., 1996; Maffulli, 1999). While researchers have recognized the cause of rupture is multifaceted, they have proposed a “degeneration” theory and a “mechanical” theory to help explain the etiology (Leppilahti and Orava, 1998; Waterston et al., 1997).

The premise of the degeneration theory is that repeated micro trauma to the tendon weakens vascular elements and causes structural and material changes to the collagen and cellular matrix of the tendon (Jozsa and Kannus, 1997; Maffulli et al., 2000a), predisposing the tendon to spontaneous rupture. In support of this theory, researchers have reported that newly ruptured Achilles tendons and repaired animal tendons after long term healing contain a greater proportion of type III rather than type I collagen (Coombs et al., 1980; Eriksen et al., 2002; Jozsa et al., 1984; Russell and Manske, 1990), which in various animal tendons has displayed reduced stiffness, strength, and viscoelastic measures compared to controls (Liu et al., 1995; Woo et al., 1994). With these latter findings in mind, we hypothesized in a prior investigation that persons who had sustained an Achilles tendon rupture would exhibit different biomechanical behaviors between the involved and uninvolved limb (Bressel and McNair, 2001). It was observed that biomechanical measures, which reflect structural and material changes of tendon (i.e., passive stiffness and torque relaxation), were not different between limbs. A limitation of the study may have been that a separate control group was not included as recent histological evidence (Maffulli et al., 2000b) suggests the uninvolved limb may also experience abnormal healing in response to repeated micro trauma that alters its biomechanical behavior.

The premise of the mechanical theory is that healthy Achilles tendons, with no degeneration, may spontaneously rupture if select mechanical conditions are present such as a forceful uncoordinated muscle action that loads the tendon in an oblique manner (Leppilahti and Orava, 1998; Maffulli, 1999). The work of Barfred (1973) has demonstrated the Achilles tendons of anaesthetized rats are more susceptible to rupture when a maximal asymmetric versus symmetric load is applied to the tendons. Some researchers have indicated that such loading or muscle activity may be more prevalent in persons with inadequate sensory feedback (Inglis and Sculco, 1981; Leppilahti and Orava, 1998). Inadequate sensory feedback from mechanoreceptors in the ankle joint region distorts a person’s perception of foot position (i.e., proprioception) during movement (Simoneau et al., 1996) that may increase the risk of an injurious oblique load to the Achilles tendon. Proprioception deficits may be inherent, for instance, in individuals with less coordination (Radin et al., 1991) or may be a function of injury (Friden et al., 1997) or inactivity (Inglis and Sculco, 1981). Ankle joint proprioception in an Achilles rupture population is not well understood.

A study that examines biomechanical and proprioceptive measurements of both limbs of persons who have ruptured their Achilles tendon will contribute to a better understanding of the lasting effect of the Achilles tendon rupture. Our hypothesis was that ankle joint proprioception, passive ankle joint stiffness, and torque relaxation of the involved and uninvolved limbs of persons with previous Achilles tendon ruptures are different than that for matched controls. The purpose of the study was to examine this hypothesis.