Biomechanical and neuromuscular impairments in individuals with gluteal tendinopathy

Abstract

Gluteal Tendinopathy (GT) is a typically chronic, recalcitrant cause of lateral hip pain most commonly seen in women aged 40 to 70 years. The condition involves pathology of the gluteus minimus and/or gluteus medius tendons at or above their insertion into the greater trochanter of the femur. Clinically, symptomatic GT presents as pain around the greater trochanter, aggravated during single leg loading in walking and stair climbing, and can have a major impact on function. Based on clinical observation it has been hypothesized that individuals with GT exhibit altered biomechanics and neuromuscular control during single leg loading tasks; specifically increased pelvic drop and hip adduction, which might modify gluteal tendon loading at the greater trochanter contributing to the development and/or perpetuation of the condition. However, despite clinical assessment and treatment for GT often being based on these presumed impairments, little is known about the biomechanical or neuromuscular impairments in individuals with GT.

Given evidence of muscle weakness in other lower limb tendinopathies, and that strengthening exercise appears to be an effective management strategy for tendinopathy, Study 1 aimed to establish whether individuals with GT exhibit hip abductor muscle strength deficits when compared to pain-free controls. Interestingly, not only did Study 1 identify hip abductor weakness of the symptomatic hip when compared to the asymptomatic hip and to controls, bilateral hip abductor weakness was identified in individuals with GT when compared to controls.

The primary functional role of the hip abductor muscles is to maintain alignment of the pelvis in the frontal plane during single leg loading. Given that single leg stance (SLS) is often assessed visually by clinicians to evaluate hip abductor function, Study 2 aimed (1) to quantify trunk, pelvic and hip kinematics in preparation for, and during, a SLS task in those with and without GT, and (2) evaluate the effect of hip abductor muscle strength on these kinematics. Results from Study 2 showed that in contrast to pain-free controls, individuals with GT exhibit greater lateral translation of the pelvis and hip adduction in preparation for SLS; and more hip adduction and less pelvic elevation during SLS. Hip abductor strength appeared to be a key determinant of these kinematic differences, as when adjusting for strength in our analysis only between-group differences in lateral pelvic shift persisted.

As altered kinematics of the hip and pelvis were identified in SLS, and walking is a typically provocative functional single leg loading task for those with GT, Study 3 aimed to evaluate kinematics and kinetics of the trunk, hip and pelvis during walking gait. This was the first study to evaluate walking kinematics and kinetics in individuals with GT using three-dimensional gait analysis. Results showed that, in contrast to pain-free controls, individuals with GT exhibited a greater external hip adduction moment throughout the stance phase of walking as well as greater contralateral trunk lean at the time of the first peak hip adduction moment and greater contralateral pelvic drop at the time of the second peak hip adduction moment. Contralateral pelvic drop was significantly correlated with the first and second peak hip adduction moments, and hip adduction angle with the second peak hip adduction moment in those with GT, providing some insight into potential modifiable kinematic patterns underpinning their greater external hip adduction moment. Finally, post-hoc analysis identified two subgroups with opposite trunk and pelvic strategies within the GT group. Taken together, these findings suggest that evaluation of the trunk and pelvis during clinical observation of gait is warranted in order to identify specific maladaptive gait patterns.

A greater external hip adduction moment, identified in Study 3, infers a greater demand on the hip abductor muscles, including the gluteus medius and minimus muscles and the overlying muscles that insert into the iliotibial band (ITB). On this basis Study 4 aimed to evaluate the independent and synergistic characteristics of hip abductor muscle activation during walking using electromyography (EMG). This study highlighted altered muscle activity in the posterior gluteus minimus and middle gluteus medius muscle segments during stance phase in individuals with GT, characterized by greater activity continued into mid-stance, compared to controls. Further to this, individuals with GT exhibited less within-participant variability of the posterior gluteus minimus and less between-participant variability in the anterior gluteus minimus and medius segments and upper gluteus maximus when compared to controls. For both groups, synergy analysis identified two muscle synergies during the stance phase of gait. However, differing levels of contribution from the tensor fascia lata muscle to each synergy was observed between those with and without GT. Taken with a greater external hip adduction moment, modified distribution of activity within the gluteal muscle segments and the tensor fascia lata, which generates tension in the ITB via it’s insertion, has the potential to modify gluteal tendon loading. Compressive forces from the tension in the overlying ITB and the greater trochanter below on the gluteal tendons could have potentially negative tendon effects.

Lastly, Study 5 investigated kinematics and kinetics of the trunk, hip and pelvis during a step up task. Similar, to the findings of Study 3, parameters of the external hip adduction moment were consistently greater in those with GT during the stance phase of stair ascent. Based on the patterns of the external hip adduction moment, three subgroups were identified in both the GT and control groups, with individuals with GT 4.5 times more likely to have an external hip adduction moment characteristic of a large impulse, greater lateral pelvic translation and less pelvic obliquity at heel strike than the subgroup most likely to contain controls.

The studies outlined in this thesis are the first to report strength, kinematic, kinetic and EMG findings in individuals with symptomatic GT in contrast to pain-free controls. Differences were identified in: hip abductor strength; kinematics during SLS, gait and step up tasks; kinetics during walking and step up; and neuromuscular control of the hip abductor muscles during walking. These findings imply that the gluteal tendons might be experiencing modified tensile and compressive loads in those with GT, with implications for tendon health. Given the cross-sectional study design it is not possible to determine whether these differences preceded or followed GT, but it is possible that restoration of muscle strength and normal kinematics may be beneficial for recovery. However future research is needed to determine whether altered muscle activity, kinematics and kinetics can be changed with conservative treatment and subsequent effects on patient outcomes.