The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 94, Issue 9

Scientific Articles | May 02, 2012

Functional Limitations Associated with End-Stage Ankle Arthritis

Ava D. Segal, MS^a; Jane Shofer, MS^a; Michael E. Hahn, PhD^a; Michael S. Orendurff, MS^b; William R. Ledoux, PhD^a; Bruce J. Sangeorzan, MD^a

^a Department of Veterans Affairs, RR&D Center, 1660 South Columbian Way, Mail Stop 151, VA Medical Center, Seattle, WA 98108. E-mail address for A.D. Segal: avasegal@gmail.com
^b Orthocare Innovations, Inc., 6405 218th Street S.W., Suite 301, Mountlake Terrace, WA 98043-2180

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Investigation performed at the Department of Veterans Affairs, VA Medical Center, Seattle, Washington, and the Departments of Mechanical Engineering and Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington

J Bone Joint Surg Am, 2012 May 02;94(9):777-783. doi: 10.2106/JBJS.K.01177

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Abstract

Background:

Ankle arthritis, like hip and knee arthritis, has a substantial impact on patient function. Understanding the functional limitations of ankle arthritis may help to stratify treatment strategies.

Methods:

We measured the preoperative demographic characteristics, physical function, and self-assessed function of patients with end-stage ankle arthritis and identified correlations among these metrics. Participants wore a StepWatch 3 Activity Monitor for two weeks and completed the Musculoskeletal Function Assessment and Short Form-36 surveys. Gait kinematics and kinetics were also measured as participants walked at a self-selected pace.

Results:

Musculoskeletal Function Assessment and Short Form-36 scores revealed reduced perceived function for patients with end-stage ankle arthritis compared with healthy controls. These patients also took fewer total steps per day, took fewer high-intensity steps, and chose to walk at a slower walking speed. Gait analysis revealed reduced ankle motion, peak ankle plantar flexor moment, peak ankle power absorbed, and peak ankle power generated for the affected limb compared with the unaffected limb. High-intensity step count was also correlated with both survey scores, walking speed, step length, peak ankle plantar flexor moment, and peak ankle power generated. Walking speed, step length, and ankle motion were correlated with peak ankle plantar flexor moment and power generated.

Conclusions:

Generally, patients with end-stage ankle arthritis have reduced physical and perceived function compared with healthy individuals. Additionally, high-intensity step count was a better indicator of physical and perceived function compared with total steps per day for this population.

Clinical Relevance:

Functional impairments related to ankle arthritis are substantial. In addition, significant associations among perceived function, sustained high-intensity step count, and certain gait variables can further define the utility of these outcome measurements in this patient population.

Figures in this Article

Introduction

Ankle arthritis is a debilitating condition present in approximately 6% of the population¹ and has an impact on patient function comparable with that of osteoarthritis of the hip, knee, and back^2,3. Yet data related to this disorder are limited compared with data for other joints. Studies of self-reported function and health-related quality of life based on surveys have shown that patients with end-stage ankle arthritis score consistently two standard deviations below the general population with regard to physical function, pain, and mental effects^2,3. Most patients with end-stage ankle arthritis (>70%) are posttraumatic, more than seven times the proportion seen in hip or knee arthritis^2,4,5. Posttraumatic arthritis is frequently due to residual misalignment of the limb following injury, rather than to an intrinsic joint problem^1,6, and often affects younger patients⁴. The presence of end-stage ankle arthritis in younger patients is problematic because the current surgical treatments lack proven longevity. Ankle arthrodesis, traditionally considered the gold standard of treatment for end-stage ankle arthritis⁶, usually relieves pain but is known to cause gait alterations as well as arthritic changes in the subtalar and other distal foot joints^7-10. Also, long-term follow-up of ankle arthrodesis (an average of eight years) has shown that further challenges and compensations exist during some activities of daily living^9-11. Ankle arthroplasty is an alternative treatment option for end-stage ankle arthritis that may allow a patient to maintain functional ankle motion^12,13 and minimize the need to compensate at other joints. However, a three-year follow-up of the functional results of the contemporary prostheses has demonstrated satisfactory but not outstanding results¹⁴. Therefore, establishing preoperative patient characteristics related to health status and function may be used to predict postoperative outcomes, as has been suggested for patients with end-stage hip arthritis¹⁵.

There are currently few clear, objective criteria defining patients with end-stage ankle arthritis¹⁶. To aid in the development of these criteria, this population needs to be better characterized and stratified. One important element is an objective assessment of patient function and the underlying cause for gait abnormalities, which can be measured with gait analysis¹⁷. Also, the quantity of gait measured with average step count per day can be used to distinguish between healthy and mobility-impaired subjects^18-21. Examining the correlations between these objective measures and how they relate to perceived function and health through subjective surveys will demonstrate the relationship between the quality and quantity of gait and the quality of life, helping to establish criteria for treatment.

The gait measurements that we chose to examine have been reported in the literature to assess activity limitations associated with impairment of patients with end-stage ankle arthritis^19,22. When compared with patients with no ankle pathology, end-stage ankle arthritis patients have shown a decrease in temporal-spatial gait parameters, including walking speed, cadence, and stride length^19,22. Patients with end-stage ankle arthritis also have experienced a loss of motion in the affected ankle compared with the unaffected ankle^19,22, as well as decreased peak ankle moment and power²². Although functional limitations associated with gait have been demonstrated in the laboratory, few objective data have been reported on the daily physical activity of patients with end-stage ankle arthritis. On the basis of a count of steps per day, previous studies have shown decreased activity levels for patients with knee and hip arthritis compared with those of a normal population^20,21. Brandes et al.²⁰ reported that although quality of life as measured with the Short Form-36 (SF-36) survey and quantity of gait as measured with step count were correlated, quality of gait as measured with gait analysis and quantity of gait as measured with step count were not correlated in subjects with knee and hip arthritis. In addition, Kennedy et al.²³ found little correlation between perceived and objective function in candidates for hip and knee arthroplasty. In contrast, Britt et al.²⁴ examined subjects with ankle arthritis and reported a significant correlation between the Musculoskeletal Function Assessment (MFA) overall survey score and the average daily step count. However, it remains unknown if step count and survey scores are correlated with gait measurements for patients with end-stage ankle arthritis. Identifying a correlation between quantitative gait analysis and daily step count could facilitate long-term follow-up assessment, as step count data can be collected without a visit to the laboratory.

The purpose of this study was to provide pretreatment data on patients with end-stage ankle arthritis who were scheduled for surgery. This study also assessed the correlations among gait biomechanics (as measured with gait analysis), daily physical activity (as measured with step counts), and perceived function (as measured with survey scores).

Materials and Methods

Participants

Thirty-seven participants who were scheduled to have ankle surgery (either tibiotalar arthrodesis or arthroplasty) for the treatment of end-stage ankle arthritis were recruited from three area medical centers. The study group included sixteen male and twenty-two female patients with an average height (and standard deviation) of 1.69 ± 0.1 m, an average weight of 88.0 ± 16.6 kg, and an average age of 56.7 ± 11.5 years. Twenty-three of the patients had a traumatic etiology. The remaining fourteen patients did not fit neatly into a particular group but had a broad range of etiologies, including recurring ankle sprains, varus and valgus malalignment, and inflammation. All patients gave informed written consent to participate in this institutional review board-approved study. Subject inclusion criteria were an age of eighteen years or older, primary diagnosis of ankle arthritis, failure to respond to nonoperative care, candidacy for either ankle arthrodesis or arthroplasty based on pain and radiographic measurements, and ability to walk without an assistive device. Exclusion criteria were any recent (<1 year) lower-extremity surgical procedures or neurological disorders that would alter gait characteristics, previous arthroplasty or arthrodesis that now required revision, prescribed surgical interventions that would require multiple corrections, or the presence of rheumatoid arthritis.

Functional Assessments

Questionnaires

Participants completed two questionnaires. The MFA is a general arthritis functional assessment consisting of 100 yes or no questions that measure how the subject’s musculoskeletal disorder affects the subject’s ability to function in activities of daily living (e.g., household chores, walking in the community). This survey was validated in a similar posttraumatic population and has been shown to meet the standards for test-retest reliability, internal consistency²⁵, criterion validity, and content validity²⁶. Higher scores indicate reduced function. The SF-36 (Medical Outcomes and Trust, Boston, Massachusetts) is a multipurpose, generic, short-form health survey with thirty-six questions broken into eight specific categories²⁷. In contrast to the MFA, higher scores indicate increased function. The SF-36 has passed tests for consistency, validity, and reliability²⁸. United States population norms are 50 ± 10 points for all categories³. This study only presents three categories (Physical Function, Bodily Pain, and Mental Health), which were deemed most relevant in relation to the other functional outcomes and have been shown to have a high correlation with the MFA total score in other impaired populations²⁹.

Step Count

To measure the preoperative functional level of our subject population, we fit each participant with a StepWatch 3 Activity Monitor (Orthocare Innovations, Mountlake Terrace, Washington). The StepWatch is a small, lightweight, plastic device the size of a standard pager (70 × 50 × 20 mm; 38 g) that contains a sensor to record the number of steps that a subject takes over an extended period of time. The device has been shown to be accurate³⁰ at a range of walking speeds and weights^31,32 and has high test-retest reliability^33,34. The StepWatch was mounted to the participant’s ankle with an elastic attachment strap and worn for a mean of 12.6 ± 2 days. Step data were collected in one-minute intervals. Data were downloaded with use of a docking station and the total number of steps per day was recorded. Three additional step intensity categories were also examined similar to previous research²⁰: low (<15 strides per minute), medium (fifteen to forty strides per minute), and high (>40 strides per minute). These categories were thought to represent activity similar to moving within a room, moving from one room to another, and continuous activity, respectively. To compare our results with those of studies that have used other pedometers, we multiplied our step count by two to obtain the total steps per day for both limbs.

Gait Analysis

Anthropometric measurements were performed for each individual according to the requirements for static and dynamic modeling recommended by the manufacturer of the gait analysis system (Vicon, Centennial, Colorado). Thirty-five 14-mm reflective markers were placed on each participant at locations consistent with the Plug-In Gait full-body model (Vicon). Raw marker trajectories were collected with use of a twelve-camera MX system (Vicon) at a sampling frequency of 120 Hz and filtered with the Woltring quintic spline algorithm (Vicon) with a mean-square-error value of 20. Ground reaction forces were collected with four embedded force plates (two FP4060-NC plates; Bertec, Columbus, Ohio; and two BP400600 plates; AMTI, Watertown, Massachusetts) at a sampling frequency of 1200 Hz. Participants walked barefoot along a 10-m walkway at a self-selected walking speed for five repeated trials. Timing lights that were placed 2 m apart in the center of the 10-m walkway were used to determine the average walking speed for each trial.

Statistical Methods

Ankle joint kinematics were calculated with use of the Plug-In Gait model (Vicon). Standard inverse dynamic techniques³⁵ were used to calculate net internal ankle joint forces, moments, and powers with use of Nexus software (Vicon). All kinetic data were normalized to subject body weight.

The following discrete gait parameters were extracted with use of the Event Analyzer (Vaquita Software, Zaragoza, Spain) for both the affected and unaffected limbs for each trial: sagittal plane ankle range of motion (the difference between maximum plantar flexion and maximum dorsiflexion during the stance phase of gait), peak plantar flexor moment (positive values indicate an internal joint moment), and peak power absorbed (negative) and generated (positive). Walking speed, step length (distance in the direction of progression between heel markers at heel-strike of the designated limb), and step width (the mediolateral distance between heel markers at heel-strike of the designated limb) were also calculated.

Statistical Analysis

Questionnaire, step activity monitor, and biomechanical measures were summarized with use of means and standard deviations with biomechanical measures being averaged across trials. Differences between the affected and unaffected limbs for the biomechanical variables were tested with use of linear mixed effects regression with a biomechanical variable as the dependent variable, the limb as the independent fixed effect, and random effects for subject and subject times limb interaction (the latter term to adjust for variability in differences by limb across subject).

Associations among step count and questionnaire variables were assessed with use of Pearson correlation coefficients with simple linear regression to determine significance. Pearson correlation coefficients were also computed to describe the association between biomechanical variables and step count or questionnaire variables. However, because of the repeated measures structure of the biomechanical data, significance of these associations was assessed with use of linear mixed effects regression with the biomechanical variable as the dependent variable, the step count or questionnaire variable as the independent fixed effect, and the subject as a random effect. Because of right skewness in the high-intensity step count distribution, this variable was log-transformed for analysis. This analysis rescales the data to allow for a more normal distribution and, therefore, less influence from just a few outlying data points. Significance was set at p < 0.05, with moderate correlations designated as p < 0.01 and weak correlations designated as 0.01 < p < 0.05. Analyses were carried out with use of R 2.9.1 (R Foundation for Statistical Computing, Vienna, Austria)³⁶.

Source of Funding

This work was supported by the Department of Veterans Affairs, Rehabilitation Research and Development Service grants (A4513R and A4843C). Funds from both grants were used, in part, to support salaries, supplies, and participant reimbursements.

Results

The demographic characteristics, step counts, and questionnaire scores for all patients are presented in Table I. Of the total steps per day, 32% ± 10% were low-intensity steps, 53% ± 28% were medium-intensity steps, and 15% ± 13% were high-intensity steps.

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TABLE I Demographic Characteristics, Step Activity, and Questionnaire Scores for All Patients (N = 37)*†

Demographic characteristics
Age (yr)	56.7 ± 11.5
Height (m)	1.69 ± 0.1
Weight (kg)	88.0 ± 16.6
Body mass index (kg/m2)	30.7 ± 5.1
No. of female patients‡	22 (60%)
Step activity (no. of steps per day)
Total steps	8647 ± 3578
Low-intensity steps	2770 ± 838
Medium-intensity steps	4613 ± 2416
High-intensity steps	1300 ± 1092
Questionnaire scores (points)
SF-36
Physical Function	40.2 ± 20.4
Bodily Pain	36.2 ± 15.1
Mental Health	75.0 ± 12.4
MFA	38.8 ± 12.3

* General population values for the MFA (9.3 ± 8.9 points)^2,26, SF-36 (50 ± 10 points)³, and total number of steps per day (13,232 ± 4774 steps per day)²⁰ from the literature demonstrated an overall reduction in function for our patients with end-stage ankle arthritis as compared with healthy controls.
†The values are given as the mean and the standard deviation unless otherwise specified.
‡The value is given as the number of patients, with the percentage in parentheses.

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TABLE I Demographic Characteristics, Step Activity, and Questionnaire Scores for All Patients (N = 37)*†

Demographic characteristics
Age (yr)	56.7 ± 11.5
Height (m)	1.69 ± 0.1
Weight (kg)	88.0 ± 16.6
Body mass index (kg/m2)	30.7 ± 5.1
No. of female patients‡	22 (60%)
Step activity (no. of steps per day)
Total steps	8647 ± 3578
Low-intensity steps	2770 ± 838
Medium-intensity steps	4613 ± 2416
High-intensity steps	1300 ± 1092
Questionnaire scores (points)
SF-36
Physical Function	40.2 ± 20.4
Bodily Pain	36.2 ± 15.1
Mental Health	75.0 ± 12.4
MFA	38.8 ± 12.3

All participants had reduced values for ankle motion, peak ankle plantar flexor moment, peak ankle power absorbed, and peak ankle power generated when the affected limb was compared with the unaffected limb (with the values on the affected side being 33%, 12%, 28%, and 34% less than those on the unaffected side, respectively; p < 0.001 for all) (Fig. 1 and Table II). The unaffected step length (measured at heel-strike) of the unaffected limb was slightly (average, 4%) shorter than that of the affected limb (p = 0.022). The average walking speed was 0.98 ± 0.2 m/s.

Fig. 1

Line graph showing the average sagittal plane ankle angle (°), moment (Nm/kg), and power (W/kg) across the gait cycle for the affected and unaffected limbs for patients with end-stage ankle arthritis (n = 37). Significant differences (p < 0.05) between the affected and unaffected limbs of the following discrete variables are designated with asterisks (*): ankle range of motion, peak plantar flexor moment, and peak power absorbed and generated. Peak power values are reduced compared with Table II averages because of variability in the timing of the peak; however, the relationships are maintained.

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TABLE II Comparison of Biomechanical Variables of Affected Limbs with Those of Unaffected Limbs

Gait Variables	Affected Limb*	Unaffected Limb*	P Value†
Step length (mm)	518 ± 79	499 ± 78	0.022
Step width (mm)	130 ± 45	127 ± 47	0.6
Ankle range of motion (°)	17.0 ± 4.6	25.4 ± 6.9	<0.001
Peak ankle plantar flexor moment (Nm/kg)	1.17 ± 0.23	1.33 ± 0.20	<0.001
Peak ankle power absorbed (W/kg)	–0.49 ± 0.23	–0.68 ± 0.29	<0.001
Peak ankle power generated (W/kg)	1.90 ± 0.86	2.90 ± 0.97	<0.001

*The values are given as the average and the standard deviation.
†The level of significance was set at p < 0.05.

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TABLE II Comparison of Biomechanical Variables of Affected Limbs with Those of Unaffected Limbs

Gait Variables	Affected Limb*	Unaffected Limb*	P Value†
Step length (mm)	518 ± 79	499 ± 78	0.022
Step width (mm)	130 ± 45	127 ± 47	0.6
Ankle range of motion (°)	17.0 ± 4.6	25.4 ± 6.9	<0.001
Peak ankle plantar flexor moment (Nm/kg)	1.17 ± 0.23	1.33 ± 0.20	<0.001
Peak ankle power absorbed (W/kg)	–0.49 ± 0.23	–0.68 ± 0.29	<0.001
Peak ankle power generated (W/kg)	1.90 ± 0.86	2.90 ± 0.97	<0.001

*The values are given as the average and the standard deviation.
†The level of significance was set at p < 0.05.

Moderate correlations (p < 0.01) were found among the MFA score and both the SF-36 (Physical Function) and SF-36 (Mental Health) scores (Table III). The SF-36 (Physical Function) score was also moderately correlated with the SF-36 (Bodily Pain) score and weakly correlated with ankle motion (Table III). The log transform of the high-intensity step count was moderately correlated and weakly correlated with the SF-36 (Physical Function) and MFA scores, respectively (Table III) (see Appendix). The log transform of the high-intensity step count was also moderately correlated with walking speed, peak ankle plantar flexor moment, and peak ankle power generated and was weakly correlated with step length (Table III). After adjustment for speed, however, only the association with peak ankle power generated remained significant (speed adjusted, p = 0.01). Other weak correlations existed among peak ankle power generated and total steps per day, medium-intensity steps, and MFA score, as well as among peak ankle power absorbed and total steps per day. In addition, all but one of the identified significant correlations among gait variables were moderate (Table IV). Specifically, walking speed, step length, and ankle motion were correlated with both peak ankle plantar flexor moment and peak ankle power generated. Ankle motion was not correlated with any of the temporal gait variables.

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TABLE III Pearson Correlation Coefficients to Illustrate the Relationships Among Questionnaire, Step Count, and Gait Variables

					SF-36
	Total Steps	Low-Intensity Steps	Medium-Intensity Steps	High-Intensity Steps*	Physical Function	Bodily Pain	Mental Health	MFA
Step count and questionnaires
SF-36
Physical Function	0.07	–0.1	–0.01	0.46†
Bodily Pain	–0.14	–0.12	–0.25	0.11	0.58†
Mental Health	0.16	0.06	0.13	0.34	0.33	0.24
MFA	0.03	0.25	0.06	–0.38‡	–0.62†	–0.34‡	–0.47†
Gait variables
Walking speed	0.29	0.04	0.25	0.47†	0.21	–0.03	0.07	–0.19
Step length	0.07	–0.05	0.01	0.31‡	0.05	–0.09	–0.06	–0.11
Step width	–0.12	–0.16	–0.08	–0.07	–0.05	0.01	0.01	–0.12
Ankle range of motion	–0.11	–0.18	–0.11	–0.04	–0.21‡	–0.14	–0.03	0.06
Peak ankle plantar flexor moment	0.15	–0.01	0.11	0.31†	0.15	0.05	0.05	–0.21
Peak ankle power absorbed	–0.22‡	–0.16	–0.21	–0.13	–0.08	–0.07	0.02	0.06
Peak ankle power generated	0.28‡	–0.04	0.27‡	0.45†	0.2	–0.04	0.15	–0.25‡

*Log scale.
†P < 0.01 (moderate correlation).
‡P < 0.05 (weak correlation).

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TABLE III Pearson Correlation Coefficients to Illustrate the Relationships Among Questionnaire, Step Count, and Gait Variables

					SF-36
	Total Steps	Low-Intensity Steps	Medium-Intensity Steps	High-Intensity Steps*	Physical Function	Bodily Pain	Mental Health	MFA
Step count and questionnaires
SF-36
Physical Function	0.07	–0.1	–0.01	0.46†
Bodily Pain	–0.14	–0.12	–0.25	0.11	0.58†
Mental Health	0.16	0.06	0.13	0.34	0.33	0.24
MFA	0.03	0.25	0.06	–0.38‡	–0.62†	–0.34‡	–0.47†
Gait variables
Walking speed	0.29	0.04	0.25	0.47†	0.21	–0.03	0.07	–0.19
Step length	0.07	–0.05	0.01	0.31‡	0.05	–0.09	–0.06	–0.11
Step width	–0.12	–0.16	–0.08	–0.07	–0.05	0.01	0.01	–0.12
Ankle range of motion	–0.11	–0.18	–0.11	–0.04	–0.21‡	–0.14	–0.03	0.06
Peak ankle plantar flexor moment	0.15	–0.01	0.11	0.31†	0.15	0.05	0.05	–0.21
Peak ankle power absorbed	–0.22‡	–0.16	–0.21	–0.13	–0.08	–0.07	0.02	0.06
Peak ankle power generated	0.28‡	–0.04	0.27‡	0.45†	0.2	–0.04	0.15	–0.25‡

*Log scale.
†P < 0.01 (moderate correlation).
‡P < 0.05 (weak correlation).

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TABLE IV Pearson Correlation Coefficients to Illustrate the Relationships Among Gait Variables

Gait Variables	Step Length	Step Width	Ankle Range of Motion	Peak Ankle Plantar Flexion Moment	Peak Ankle Power Absorbed	Peak Ankle Power Generated
Walking speed	0.7*	–0.26	0.02	0.51*	–0.16	0.64*
Step length		–0.18†	0.09	0.42*	–0.1	0.37*
Step width			0.08	–0.19	–0.15	–0.14
Ankle range of motion				0.35*	–0.23*	0.53*
Peak ankle plantar flexor moment					–0.31*	0.71*
Peak ankle power absorbed						–0.42*

*P < 0.01 (moderate correlation).
†P < 0.05 (weak correlation).

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TABLE IV Pearson Correlation Coefficients to Illustrate the Relationships Among Gait Variables

Gait Variables	Step Length	Step Width	Ankle Range of Motion	Peak Ankle Plantar Flexion Moment	Peak Ankle Power Absorbed	Peak Ankle Power Generated
Walking speed	0.7*	–0.26	0.02	0.51*	–0.16	0.64*
Step length		–0.18†	0.09	0.42*	–0.1	0.37*
Step width			0.08	–0.19	–0.15	–0.14
Ankle range of motion				0.35*	–0.23*	0.53*
Peak ankle plantar flexor moment					–0.31*	0.71*
Peak ankle power absorbed						–0.42*

*P < 0.01 (moderate correlation).
†P < 0.05 (weak correlation).

Discussion

Patients with end-stage ankle arthritis tend to be a young, functionally and pathophysiologically diverse group that makes outcome analysis challenging. Because minimal objective data exist that define patients with end-stage ankle arthritis, treatment choice is based primarily on a surgeon’s thoughtful judgment and patient preference. Therefore, establishing objective criteria of function prior to surgery could aid in assessing posttreatment efficacy, possibly leading to improved guidelines to facilitate a surgeon’s recommendation for treatment.

Our patients with end-stage ankle arthritis had an overall decrease in sagittal plane ankle motion, ankle plantar flexor moment, and ankle power for the affected limb compared with the unaffected limb, which is consistent with previous literature^10,12,22. They also demonstrated a shorter unaffected step length, which may be the result of reduced ankle motion of the affected limb during stance³⁷. In addition, our patients walked more slowly on average compared with what has been reported for healthy controls, which was consistent with other studies^{10,12,13,19,22}. With the exception of the Valderrabano study²², our patients walked faster on average (1.0 m/s) than patients with preoperative end-stage ankle arthritis reported in previous studies (overall average across studies, 0.73 ± 0.15 m/s).

The average number of steps per day for our patients was comparable with the average step count for patients with knee and hip osteoarthritis and was reduced compared with healthy controls²⁰. More than half of the total steps per day were categorized as medium-intensity steps (mean, 53% ± 28%), with fewer steps dedicated to high-intensity (15% ± 13%) and low-intensity (32% ± 10%) activities. Although somewhat variable across the population, this finding suggests that patients with end-stage ankle arthritis dedicate more steps throughout the day to moderate-intensity activities such as moving from one room to another than to more continuous or very short bouts of activity. Finally, compared with published norms for the healthy population (mean MFA score, 9.3 ± 8.9 points^2,26; mean SF-36 score, 50 ± 10 points³), self-perceived function was reduced in all patients. Although the MFA scores in our study were comparable with those in the literature², the SF-36 scores for physical function and mental health were higher on average in our study compared with those of other studies of patients with end-stage ankle arthritis³, suggesting that our subject population perceived themselves as more functional. This finding is consistent with the fact that our subjects walked faster compared with what has generally been reported for patients with end-stage ankle arthritis.

Our results demonstrated that in patients with end-stage ankle arthritis, high-intensity steps are a more sensitive measurement than total steps per day because of a higher correlation with gait variables and surveys. Both the SF-36 (Physical Function) score and the MFA score were correlated with a high-intensity step count, indicating that patients who were able to complete more steps at a higher-intensity level perceived themselves as having higher overall physical function. Brandes et al.²⁰ found a similar relationship in patients with knee and hip osteoarthritis. In addition, patients with end-stage ankle arthritis who could sustain longer periods of activity chose to walk faster, had a longer step length, and increased peak ankle plantar flexor moment and power generated in the late stance phase. After adjustment for speed, however, only the association with peak ankle power generated remained significant, which indicates that the peak ankle power generated had the strongest correlation with the number of longer walking periods regardless of walking speed. Although Brandes et al.²⁰ reported different step intensity levels for patients with hip and knee osteoarthritis, it is unclear if they used the different intensity levels in their correlation analysis, which showed no correlation between the number of daily gait cycles and the gait laboratory variables.

The SF-36 (Physical Function) score and SF-36 (Mental Health) score were correlated with the MFA score, although in a numerically inverse fashion, because a larger score for the SF-36 indicates increased function, whereas a larger score for the MFA indicates reduced function. Therefore, in general, patients with higher self-perceived physical function apparently also reported less bodily pain and improved mental health.

Increased ankle motion and peak ankle power tended to indicate increased perceived physical function. However, stronger correlations were found among high-intensity step count and increased peak plantar flexor moment, peak ankle power, walking speed, and step length. High-intensity step count was also correlated with both SF-36 (Physical Function) and MFA scores. Therefore, although the questionnaires and the gait variables appear to be generally assessing different aspects of physical function, the high-intensity step count may serve as a good predictor of general function, encompassing aspects of both questionnaire score and gait laboratory measurements. Furthermore, walking speed, step length, and ankle motion were predictive of an increased peak ankle plantar flexor moment and peak push-off power generated in late stance. These findings suggest that inadequate push-off power can affect the ability to walk in the community and at higher intensities, which leads to the perception of reduced physical function.

In conclusion, patients with end-stage ankle arthritis have reduced physical function based on deficiencies in ankle biomechanics, leading to reduced walking in the community and sustained higher-intensity walking with reduced self-perceived function. There are significant associations among survey score, high-intensity step count, and some gait variables in patients with end-stage ankle arthritis. In the future, this information can be applied to the assessment of postoperative outcomes and treatment efficacy in patients with end-stage ankle arthritis.

Appendix

A figure showing a scatterplot of the SF-36 (Physical Function) score compared with the raw high-intensity step count and the log scale of the high-intensity step count to demonstrate the effect of the log transform is available with the online version of this article as a data supplement at jbjs.org.

Acknowledgements

Note: This work was supported by the Department of Veterans Affairs, Rehabilitation Research and Development Service grants (A4513R and A4843C). Eric Rohr, Elise Wright, Hannah Sutton, Eric Whitaker, Marisa Benich, and Jacynda Wheeler were integral in subject recruitment, data collection, or data processing.

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Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, one or more of the authors has had another relationship, or has engaged in another activity, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Topics

gait ; ankle ; osteoarthritis of ankle

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Ava D. Segal, Jane Shofer, Michael E. Hahn, Michael S. Orendurff, William R. Ledoux, Bruce J. Sangeorzan; Functional Limitations Associated with End-Stage Ankle Arthritis. The Journal of Bone & Joint Surgery. 2012 May;94(9):777-783.

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