Background/Purpose: In a recent study, 14% of total hip arthroplasty (THA) patients were classified as nonresponders, using osteoarthritis (OA) treatment response criteria1. Identifying characteristics of responders and nonresponders could lead to better ways to identify and manage likely nonresponders. The purpose of this study was to test the hypothesis that responders have different preoperative and postoperative clinical and gait characteristics than nonresponders. A secondary goal was to evaluate the utility of the Harris hip score (HHS) for calculating response.
Methods: We identified 132 THA patients with pre- and one year postoperative gait and HHS data from our IRB-approved data repository. We calculated responder criteria in three ways based on the literature1: (i) Return to Normal (RTN): follow-up HHS ≥ 2 standard deviations above baseline; (ii) a modified version of OMERACT-OARSI responder criteria: relative change ≥ 20%; and (iii) Minimally Important Different (MID): follow-up HHS score ≥ 0.5 standard deviation above baseline. Gait variables of interest were self-selected normal walking speed, sagittal plane dynamic range of motion (ROM) and the 3D peak external moments. We used t-tests to compare pre- and postoperative gait variables for responders and nonresponders.
Results: 20%, 13% and 7% of patients were classified as nonresponders based on RTN, modified OMERACT-OARSI, and MID criteria, respectively. Using the modified OMERACT-OARSI criteria, baseline physical characteristics were similar for both groups (table). Preoperatively, nonresponders had 35% higher HHS (p<0.001) and 25% higher ROM (p=0.021) compared to responders. After surgery, nonresponders had significantly lower HHS compared to responders (p<0.001), as well as lower adduction and external rotation moments (p=0.038). Findings were similar when comparisons were done using the other responder criteria.
Conclusion: Although a different score was used, a similar proportion of THA patients were classified as nonresponders here as in a previous study1. This suggests that the HHS can be used to calculate response criteria if WOMAC scores are unavailable. HHS and ROM were initially higher in patients who would become nonresponders, but after surgery the nonresponders were left with lower mean HHS and lower adduction and external rotation moments. These gait moments reflect net activity of hip abductors. More work is needed to determine whether addressing the abductor impairment suggested by the biomechanical data would improve response. These results demonstrate that some patients who would appear to be more highly functioning before surgery may have both poorer responses and poorer final outcomes.
References: 1. Judge et al., Arthritis Care Res. 62:480-8, 2010.
Acknowledgement: Rush Research Mentoring Program Young Investigators Grant
Table. Characteristics of THA subjects classified as responders and nonresponders
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Responders (87%) |
Nonresponders (13%) |
p value |
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Baseline Physical Characteristics |
Age (yrs) |
60 ± 10 |
61 ± 10 |
0.868 |
|
BMI (kg/m2) |
29 ± 5 |
28 ± 4 |
0.475 |
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|
Sex |
58 F/57 M |
8 F/9 M |
0.795 |
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Clinical Characteristics |
*Preoperative HHS |
55 ± 13 |
74 ± 14 |
<0.001 |
|
*Postoperative HHS |
93 ± 8 |
80 ± 17 |
<0.001 |
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|
*Absolute Change |
39 ± 12 |
6 ± 8 |
<0.001 |
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|
*Relative Change (%) |
80 ± 44 |
9 ± 11 |
<0.001 |
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Preoperative Gait Biomechanics |
‘Normal’ walking speed (m/s) |
1.01 ± 0.24 |
1.02 ± 0.20 |
0.930 |
|
*Dynamic sagittal plane range of motion (degrees) |
16 ± 6 |
20 ± 6 |
0.021 |
|
|
Peak Flexion Moment (%Body Weight x Height) |
4.19 ± 1.49 |
4.97 ± 1.98 |
0.140 |
|
|
Peak Extension Moment (%Body Weight x Height) |
1.79 ±0.86 |
1.80 ± 0.67 |
0.954 |
|
|
Peak Adduction Moment (%Body Weight x Height) |
3.45 ± 1.02 |
3.23 ± 1.30 |
0.423 |
|
|
Peak Abduction Moment (%Body Weight x Height) |
1.60 ± 0.86 |
1.73 ± 0.75 |
0.548 |
|
|
Peak External Rotation Moment (%Body Weight x Height) |
0.33 ± 0.21 |
0.34 ± 0.26 |
0.818 |
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Peak Internal Rotation Moment (%Body Weight x Height) |
0.37 ± 0.22 |
0.37 ± 0.15 |
0.994 |
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Postoperative Gait Biomechanics |
‘Normal’ walking speed (m/s) |
1.19 ±0.19 |
1.13 ± 0.19 |
0.249 |
|
Dynamic sagittal plane hip range of motion (degrees) |
25 ± 6 |
25 ± 6 |
0.915 |
|
|
Peak Flexion Moment (%Body Weight x Height) |
5.91 ± 2.03 |
5.82 ± 2.17 |
0.852 |
|
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Peak Extension Moment (%Body Weight x Height) |
2.70 ± 1.10 |
2.82 ± 0.83 |
0.664 |
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*Peak Adduction Moment (%Body Weight x Height) |
3.54 ± 0.94 |
3.03 ± 0.91 |
0.038 |
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Peak Abduction Moment (%Body Weight x Height) |
1.88 ± 0.84 |
1.87 ± 0.97 |
0.921 |
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*Peak External Rotation Moment (%Body Weight x Height) |
0.43 ± 0.23 |
0.31 ± 0.21 |
0.038 |
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Peak Internal Rotation Moment (%Body Weight x Height) |
0.51 ±0.21 |
0.44 ±0.18 |
0.201 |
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*bold text indicates t-test or chi-square test p<0.05 |
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Disclosure:
G. Waldman,
None;
K. C. Foucher,
None.
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