Assessment of changes in gait parameters and vertical ground reaction forces after total hip arthroplasty

The principal objectives of arthroplasty are relief of pain and enhancement of range of motion. Currently, postoperative pain and functional capacity are assessed largely on the basis of subjective evaluation scores. Because of the lack of control inherent in this method it is often difﬁcult to interpret data presented by different observers in the critical evaluation of surgical method, new components and modes of rehabilitation. Gait analysis is a rapid, simple and reliable method to assess functional outcome. This study was undertaken in an effort to evaluate the gait characteristics of patients who underwent arthroplasty, using an Ultraﬂex gait analyzer. Materials and Methods: The study was based on the assessment of gait and weight-bearing pattern of both hips in patients who underwent total hip replacement and its comparison with an age and sex-matched control group. Twenty subjects of total arthroplasty group having unilateral involvement, operated by posterior approach at our institution with a minimum six-month postoperative period were selected. Control group was age and sex-matched, randomly selected from the general population. Gait analysis was done using Ultraﬂex gait analyzer. Gait parameters and vertical ground reaction forces assessment was done by measuring the gait cycle properties, step time parameters and VGRF variables. Data of affected limb was compared with unaffected limb as well as control group to assess the weight-bearing pattern. Statistical analysis was done by‘t’ test. Results: Frequency is reduced and gait cycle duration increased in total arthroplasty group as compared with control. Step time parameters including Step time, Stance time and Single support time are signiﬁcantly reduced ( P value <.05) while Double support time and Single swing time are signiﬁcantly increased ( P value <.05) in the THR group. Forces over each sensor are increased more on the unaffected limb of the THR group as compared to the control group. Vertical ground reaction force variables are Conclusion: Signiﬁcant changes ( P value <.05) in gait parameters and vertical ground reaction forces show that gait pattern is not normalized after THR and weight-bearing is not equally shared by both hips. Patient walks with residual antalgic gait even after surgery, which results in abnormal loading around hip joints and the integrity of the prosthesis ﬁxation could be compromised.

T he principal objectives of arthroplasty are relief of gait, would be of great value. pain and enhancement of range of motion. Previous studies on arthroplasty have focused either on surgical Gait analysis is simply a measurement system that allows technique, postoperative management or radiographic the user to monitor and analyze human locomotion. assessment but not on its functional outcome. Most of the Quantification of human motion by the measurement of patients postoperatively are satisfactorily relieved from joint motion, electromyography activity of muscle and the also altered.
pain as well as have acceptable improvement in functions and mobility. But evaluation of these subjective variables is questionable and accurate assessment is difficult. Joint motion is a functional variable of the hip, which returns to normal after months postoperatively. Continued atypical joint motion leads to abnormal loading and further osteoarthritis. Thus another objective method, which is a reliable indicator for functional assessment of a patient's forces both created by and acting upon the body can be precisely recorded and evaluated. These measurements may be coordinated in time to allow comparison between modes of evaluation, creating an accurate assessment of patients' ambulatory ability.
Measures determined from gait parameters and vertical ground reaction forces have been used to quantify abnormal limb loading for individuals after hip arthroplasty. 1-3 Gait parameters and vertical ground reaction forces provide indirect information about internal joint loading because peak ground reaction forces coincide with the timing of peak loads on the femur and hip joint during gait. 4,5 The purpose of the study was to compare the selected MMF MLF MMM MLM MMR MLR measures from vertical ground reaction force variables and gait parameters of hip replacement patients to a normal healthy age and sex-matched control group. It was hypothesized that there would be no significant differences between normal individuals and hip replacement subjects for gait parameters and vertical ground reaction forces and weight-bearing would be equally shared by the both hips. Measurements unit: The ultraflex unit is a portable

MATERIALS AND METHODS
measurement unit that records normal ground reaction forces while walking. All measurement data will be Twenty pain-free individuals (mean age-51.6 years), stored in to the memory card while conducting a new measurement. operated by posterior approach for total hip arthroplasty ( THA) were included in the study. The control group subjects were randomly selected from the general population and Ultraflex Optical link cable: It is glass fiber cable. Its were age and sex-matched to the subjects in the Total main function is for high-speed data transfer.
Arthroplasty group so that the control group would exhibit Cords: Used to connect ultraflex measurement unit to the a comparable gait pattern to that age group. All the subjects were at least six-month post surgery (range 6-51 computer used for data analysis. months) and had completed their prescribed rehabilitation Straps: Used to fix the cord to the body so that patients have no problem in walking.
Subjects with a medical condition that would compromise

Method of data collection
their ability to walk were excluded from the study. Only Each subject was made to wrap an ultraflex unit around individuals with unilateral degenerative hip disease the waist and a pair of CDG shoes of approximate size was participated. Secondary involvement of the lower limb put on the feet. The subjects were then given two minutes joint was ruled out based on a clinical assessment using the of familiarization time. After the familiarization time the guidelines for Osteoarthritis classification of the American College of Rheumatology. 6,7 subjects were made to walk at a natural speed, straight, in a ten-meter corridor. Data was than taken for 20 seconds.

Procedures
The recorded data were than transferred to a processor Ultraflex (Gait analysis system) by Infrotronics Medical by link cables and were analyzed from the fifth to the 15 th Industrial Engineering was used for data collection. It has seconds of gait as it was supposed to represent natural gait CDG Computer Dynography. The complete ultraflex gait pattern [ Figure 2].
analysis system consists of the following parts: Gait parameters and vertical ground reaction forces CDG Shoes with sensors: CDG shoes are designed to assessment is done by measuring the following data: measure and record the normal forces under the foot while walking. Each shoe contains 8-load sensor at the sole. Cable attached to shoes transfers the normal forces data to the ultraflex unit for recording [ Figure 1].
regimen. Step time Parameter: Single support time, Double support time, Stance time, Step time and Single swing time.
Vertical ground reaction forces variables: Include first and second peak forces (f1, f2), time to first and second peak force (t1, t2), Loading rate (calculated as magnitude of first peak force divided by the time at which it occurred) Shrivastava P, et al.: Gait characteristics after hip arthroplasty Step  Table c]. Data reduction and analysis: All data was reduced to mean pressure in each sensor by the software in CDG. Only Ground reaction forces variables measures: The step time parameter and vertical ground reaction forces magnitude of the first and second peak forces was measures obtained by force graphics and histogram were significantly reduced on the affected limb of the arthroplasty meticulously noted. Now mean of each group data was group when compared against the data of either their calculated and comparison done. For statistical significance unaffected leg or control group. There were no differences 't' value and 'P' value was calculated. Changes were in the peak forces values between the unaffected side of considered significant when 'P' value was <. 05.
the hip arthroplasty subject and control group. The first peak force occurs at a significantly later time in the stance phase on the affected limb although there were no timing All data was noted and comparison was done between differences between the unaffected and control group. The affected limb of total arthoplasty group and unaffected second peak force occurs at a similar time on both legs in limb and control group on the basis of gait cycle properties, the total arthroplasty group and control group. Loading step time parameters and vertical ground reaction forces rate was significantly greater on the unaffected leg of the variables obtained by histogram and force graphics.
hip replacement subjects when compared to their affected leg and that of the control group. The push-off rate was There were a number of significant differences for gait cycle greater on the affected leg of the total arthroplasty group properties and vertical ground reaction forces between the as compared to the control group [ Table d]. arthroplasty group and the control group.

DISCUSSION
Gait cycle properties: Frequency was reduced in total arthroplasty group (99.4) as compared to the control Previous studies on total hip arthroplasty (THA) have focused group (110.9) while Gait cycle duration increased in total on surgical technique and postoperative management or arthoplasty group (1.3145 sec) as compared with control. radiographic assessment and not on functional outcome.   Assessment of gait parameters clearly shows that the walking ability is reduced in postreplacement patients and they also avoid weight-bearing on the affected limb.
Unequal limb loading was measurable from the ground reaction force curves. The asymmetries can be quantified when the affected and the unaffected legs of the hip replacement subjects are compared against each other and against healthy control subjects.
Both the first and the second vertical force peaks were less on the affected leg when compared with their unaffected The time to first peak force occurred significantly later on Loading rate (N / Sec) 5.22 6.21 5.00 Push-off rate (N / Sec) 6.12 6.44 6.69 Loading rate was less and push-off rate was more on the This study demonstrates that though there was considerable affected limb, which shows that patient, switch over to improvement in all gait parameters, the patients did not the unaffected leg as quickly as possible. Although the improve to a level that would be considered normal for their patients in the arthroplasty group were pain-free, they age group. Gait analysis was done only after six months were favoring their affected limb by not putting as much because it was proved by previous studies that the greatest force on it and not as quickly, during the weight acceptance improvement of gait symmetry and of both temporal and phase of walking. Adriacchi 8 hypothesized that individuals spatial gait parameters (such as stride length and double with a joint pathology adopt a gait reprogramming their support time) occurred within the first six months after movement patterns. unilateral THA.
The current study ascertains that in hip replacement subjects Frequency measured denotes that the walking ability hip strength 9 and hip range of motion 1,9,10 improve after is reduced in the postreplacement group. Gait cycle surgery but do not reach normal level and subjects walk duration denotes the time elapsed in single gait cycle.
with a residual antalgic gait well after surgery. Increment in gait cycle duration signifies that the patient is doing more postural adjustment while walking. This also Although the subjects in the hip arthroplasty group were results in reduced frequency. Walking ability after total hip pain-free, they were favoring their affected limb by not arthroplasty, suggested that although hip movements are putting as much force on it and not as quickly, during pain-free in postreplacement cases they are not normalized the weight acceptance phase of walking; this results in according to their age group. This supports our study.
additional stress on the unaffected leg eventually leading Symmetry of left to right foot parameters is not maintained to development of osteoarthritis in that leg. 11-14 because both hips do not equally share weight-bearing, degeneration on the healthy contralateral limb seen which is clearly obtained by assessing the step time by Arsever and Bole 11 and Suter and coworkers 14 Joint was parameters.
Step time parameters show both weight-bearing duration of a particular limb as well as duration when the limb is off the ground. Single support time, step time and statue time are reduced on the affected limb in both groups while single swing time and double support time increased. This shows that patients avoid weight-bearing on the affected limb and most of the time keep the limb off the ground. Increase in double support time shows that when the patient bears weight on the affected side the contralateral limb also supports it. These changes are significant (P value < 0.05).
attributed to increased limb loading. Dekel et al. 12 and Radin 13 also noted severe articular cartilage degeneration of the knee in the presence of limb overloading.
Prosthetic joints' designs are based on studies of normal gait pattern. If the individual walks with an abnormal gait, this unexpected pattern of wear and tear may lead to mechanical failure of implant. So it is advisable to train these individuals to walk with equal force distribution on both legs. No preoperative data was collected on these subjects. It is therefore unknown if this pattern of walking may be attributed to a residual antalgic gait adopted when these subjects had severe, painful arthritis in the joint.