Gait Parameters and Muscle Activation Patterns At

Gait analysis was performed on 20 patients with unilateral hip prosthesis (3, 6 and 12 months postoperatively) and 20 controls to investigate their gait characteristics and muscle activation patterns. One year after the intervention, patients still walked with a higher percentage of “atypical” cycles, a 2 prolonged heel contact, a shortened flat foot contact, a reduced hip dynamic range of motion and abnormal timing in the muscle activation patterns of tibialis anterior, gastrocnemius lateralis, biceps femoris and gluteus medius, with respect to the control group. Although the gait velocity and the knee range of motion improved from 3 to 6 months post-surgery, the above mentioned parameters did not improve from 6 to 12 months. THA patients failed to obtain normal gait one year after surgery. INTRODUCTION Total hip arthroplasty (THA) is a surgical procedure indicated for patients affected by severe osteoarthritis of the hip [1]. Despite a surgeon’s ability, THA inevitably damages muscles and periarticular tendons and brings forth a loss of joint proprioceptors [2]. Literature reports that the surgical insult, deconditioning and compensatory mechanisms adopted by the patient in the rehabilitation period may result in residual impairment, with a decline of hip abductor function [34] and gait symmetry [5]. Gait analysis is increasingly used to quantitatively assess a patient’s functional improvement and to evaluate hip surgery procedures [6-8] and implant types [9-12]. Some studies considered surface electromyography (EMG) as an adjunctive tool that complements gait analysis by monitoring muscle activity during gait [12-15]. However, these studies limited the EMG analysis to a few gait cycles for each assessment session. This prevented researchers from analyzing the different muscle activation patterns of human gait. These patterns can be reliably observed by recording a subject’s gait for at least 2-3 minutes, thus collecting a sufficiently large number (100-200) of consecutive strides for applying a statistical approach to data analysis. ‘Statistical gait analysis’ was developed to obtain gait parameters and muscle activation patterns by analyzing a large number of strides in a user independent manner [16-18]. The present study tests the null hypothesis that there are no gait differences between the control group and THA patients one year after surgery. 3 MATERIALS AND METHODS An a priori power calculation was performed to estimate the minimum sample size required for the study using data from the literature [13][19]. The hip dynamic range of motion (ROM) was chosen as the primary outcome measure for comparing the THA and control groups through a 1-tailed Student t-test, at a significance level α = 0.05 and power = 0.9. The test was chosen 1-tailed because we expected THA patients to show a hip dynamic ROM not greater than that of controls. We obtained a minimum sample size ranging from 7 to 10 patients, with an equal number of controls (allocation ratio 1:1). Participants This study analyzed 20 patients and 20 healthy controls. Patients were recruited from the Rehabilitation and Functional Recovery Unit at the Ivrea Hospital, Torino (Italy), between 2007 and 2009. They were enrolled in the study after the end of their (standard) rehabilitation protocol. Patients with bilateral coxoarthrosis, neurological problems and/or other orthopedic problems compromising gait were excluded from this study. We screened a total of 25 unilateral THA patients (see Fig.1): 3 were excluded because they did not match the inclusions criteria (1 presented a reimplant, 1 was unable to cooperate due to cognitive deficits, 1 had a fracture in the contralateral acetabulum). Two patients declined to participate after the first gait test. Patients originally suffered from hip osteoarhtrosis and had surgery for primary unilateral THA, with posterior-lateral incision. After surgery, patients underwent joint and muscular rehabilitation. All patients received the same rehabilitation protocol. The load of the operated limb was gradually restored instructing the patients to first use two crutches, then partially loading the limb removing one crutch, and finally gaining full load. The whole rehabilitation program lasted 2 months. More specifically, patients were hospitalized 8-10 days for surgery, then they spent from 2 to 3 weeks in the Rehabilitation Unit, and, finally, they followed a one-month rehabilitation program at their home. Controls were