ABSTRACT
Background:
The WISH-type S-form hip brace (WISH brace) has been shown to significantly improvehip function, functional mobility, and gait biomechanics in patients with hiposteoarthritis. The aim of the current study was to evaluate the effects of the WISHbrace over time on the strength of muscles around the hip and knee joints.
Methods:
A prospective short-term longitudinal study with a 6-month follow-up was conducted.Muscle strengths were measured using a handheld dynamometer.
Results:
The muscle strengths of hip flexion, hip abduction, and knee extension were lower inthe affected limb than in the unaffected limb, whereas hip adduction muscle strength wasreduced to the same extent in both the affected and unaffected limbs. This short-termlongitudinal study revealed that only hip adduction and knee extension exhibitedsignificant interaction between legs and time when measurement was performed without theWISH brace. Furthermore, the inherent hip abduction muscle strength of the affected limbwas improved by the WISH brace so that the strength became the same as the unaffectedlimb.
Conclusions:
Improvement in abduction muscle strength of the affected limb by daily walkingexercise with the WISH brace, which occurred with little interaction with the unaffectedlimb, may improve hip function.
Keywords: hand held dynamometer, hip brace, hip osteoarthritis, muscle strength, WISH-type
INTRODUCTION
Osteoarthritis (OA) is the most common form of arthritis.1) It is a joint disorder that results in joint painand stiffness2) and is theleading cause of disability in the elderly.2) The pain associated with OA of the hip is usually related todaily activities, such as climbing stairs, walking, and engaging in work.1) Clinical guidelines advocate acombination of conservative non-drug and drug therapies for optimal treatment of hipOA.3) However, the majorityof treatments currently available for OA involve drugs and/or surgery.4) Conservative treatments includeanalgesics, physical therapy, and bracing. The surgical approach of total hip arthroplasty(THA) provides reliable outcomes for patients with end-stage degenerative hip OA,specifically pain relief, functional restoration, and overall improved quality of life.However, major complications may occur following THA; these include dislocation,periprosthetic fracture, aseptic loosening, wound complications, and prosthetic jointinfection.5) For patientswith less severe OA, conservative treatments play an important role, especially for youngerpatients.
We previously developed a hip brace, the WISH-type S-form hip brace (WISH brace), andreported its effects on hip-functional responses of patients with unilateral6) and bilateral7) OA. Pain relief on gait was observedafter the initial use of the WISH brace.6) A series of studies has elucidated the biomechanical effectsof the WISH brace. For hip OA patients fitted with the WISH brace, the average time tocomplete the Timed Up & Go Test was significantly shorter than for those without thebrace, suggesting that the WISH brace improves hip function during external and/or abductionmovements at the turning phase.8) In the cross test, augmentation of the power output of theadductor and flexor muscles by the brace may support the moment required for resistanceagainst the upper body mass when leaning backward on the braced side, which may enableexcursions of the center of pressure to be altered.9) Gait analysis revealed that application of the WISH braceresulted in a stronger vertical reaction force at the first peak during the early stance,and an earlier switch between backward and forward reaction force vectors.10) Moreover, daily walking exercisemay also be associated with the improvement of hip function in patients with hipbraces.6,9) However, the mechanisms underlyingaugmentation of the power output in muscles around the hip joint with the use of the WISHbrace remain unclear.
Isometric hip abduction,11,12)adduction,11)flexion,11) and internalrotation12) strength werereduced in patients in the hip OA group when compared with a control group. However,isometric and isokinetic extension strength did not differ between thegroups.11) There were nosignificant differences between groups in external hip rotation.12) On the other hand, comparisonsbetween OA and healthy limbs in the patients, isometric hip extension,11,13) flexion,11,13) adduction,13) abduction,13) and knee extension13) strength were reduced in the OA limb as compared with thehealthy limb. Furthermore, neither adduction nor abduction strength values differed betweenthe affected and unaffected side in OA subjects.11) In patients with hip OA, the reduced hip abductor musclestrength mediates the relationship between avoidance of activity and limitations inactivities.14) Thus themuscle strength around the hip joint may affect hip functions and play an important role intheir improvement of those by the WISH brace.
In the present study, we examined the effects of the WISH brace on the strength of musclesaround the hip joint by using a hand-held dynamometer (HHD) in patients with hip OA. A HHDis a portable measurement device often used for assessing hip muscle function.15) A high intra-class correlationcoefficient was obtained for HHD measurements in patients with OA of the hip.9) In the current short-termlongitudinal study, the muscle strengths of affected and unaffected limbs were compared.
METHODS
Subjects
Between August 2011 and March 2013, patients with symptomatic unilateral OA of the hipwere referred to the outpatient clinic of Gunma University Hospital. Hip OA was definedaccording to the clinical criteria of the American College of Rheumatology.16) Patients in whom the hip paininduced by weight bearing during gait was notably reduced by manual pressure on thegreater trochanter were recruited for this study.
Subjects who were on a waiting list for hip replacement or had previously undergone hipreplacement were excluded. Subjects for whom a WISH brace was used for both hips were alsoexcluded. The radiological grade of OA was estimated according to the grading systemproposed by Crowe et al.,17)and patients with radiological grade III or IV were excluded.
The study was conducted after approval by the local Ethics Committee (Gunma University,Maebashi, Gunma, Japan), and informed consent for the study was received from eachindividual participating in the study.
Hip Brace
The WISH brace was based on the design concept of the Wakayama Medical College,18) and the effects of the WISHbrace were previously reported.6) The pelvic portion of the hip brace holds it at the correctposition against the pelvis to prevent rotation of the brace and provides a fulcrum forthe lever though a lateral bar, possessing two single joints, the combination of whichrestricts only hip adduction. The greater trochanter pad is fixed directly to the upperextended bar attached to the lower hip joint bar, producing medial pressure on standing.Furthermore, an S-form bar holding the thigh is made of co-polymer polypropylene materialwith continuity to the greater trochanter pad. The brace weighs approximately 0.9 kg.
Exercise Therapy
To strengthen the muscles around the hip joint required for gait, patients equipped withthe WISH brace were required to walk for at least 30 min every day. Home exercisesconsisting of hip muscle strengthening exercises with the use of a weight were suggested.Furthermore, gait exercise in water was additionally recommended.6)
Assessment of the Strength of Muscles Around the Hip
Muscle strength testing was performed with the patient lying on an examination tableaccording to the method described by Thouborg et al.15) using the Power Track II Commander HHD (JTECK Medical,Midvale, UT, USA). The HHD was calibrated on each test day, and all test procedures werestandardized. All strength tests were isometric strength tests. Each subject performed hipflexion (FLEX), abduction (ABD), adduction (ADD), and knee extension (K-EXT). FLEX andK-EXT were assessed in the sitting position, and ABD and ADD were assessed in the supineposition, corresponding to HF-SIP, HIR-SIP, HABD-SUP, and HADD-SUP, respectively, in thereport of Thouborg et al.15)The participants were asked to stabilize themselves by holding the sides of the table withtheir hands. The examiner applied resistance in a fixed position and the patient beingtested exerted a 5-s isometric maximum voluntary contraction against the dynamometer andthe examiner. In the present study, to avoid involvement of the knee joint, the examiner’shand was set just above the knee for the hip movements. To assess K-EXT, resistance wasapplied at the level of the malleoli. Each individual test was administered three times toreduce possible learning effects. There was a 30-s rest period between two consecutivetrials to avoid a decline in strength across trials due to fatigue in patients with spinalcord injury.19) The meanmaximal torque values were divided by the patient’s body weight to calculate the relativemuscle torque (Nm/kg).
Hip Function Assessments
Hip function was evaluated using the Harris Hip Score (HHS).20) The HHS was considered to be the primary outcomemeasure and consists of four variables: pain, functional capacity, range of motion, anddeformity. The maximum HHS score is 100, and a score of less than 70 reportedly reflectspoor functioning (poor category).20)
Statistical Analyses
To compare HHS over months 0, 1, 3, and 6, we used repeated-measures analysis of variance(ANOVA), followed by post hoc comparisons with the Bonferroni correction. The averagemuscle strength was compared between the affected and unaffected sides using the pairedt-test or the Wilcoxon signed-rank test after the Shapiro-Wilk test wasperformed to determine whether the data were normally distributed.
There were two within-group independent variables: one with four conditions (FLEX, ADD,ABD, and K-EXT) and the other with two conditions (affected/unaffected). To evaluate themuscle strength longitudinally, data analysis was conducted using two-way ANOVA withrepeated measures. The time effect, the leg × time interaction, and the leg effect weredetermined. In brief, the ANOVA procedure considered the with-brace and without-braceresults to depend on two within-subject factors: the type of muscle and the affected legor unaffected leg. One purpose of the ANOVA analysis was to establish whether the changein muscle strength between the affected and unaffected legs was dependent on each muscle.To single out individual effects of the muscle type and leg side, we considered whethersuch interactions were significant.
If the leg × time interaction was not significant, the characteristics of each leg(affected and unaffected leg) were analyzed using one-way ANOVA with repeatedmeasurements. Dunnet’s post hoc analysis was used to compare each group’s muscle strengthwith that before the brace intervention was started.21) P-values of less than 0.05 were considered to besignificant.
RESULTS
Patient Characteristics and Follow-up
A total of 10 patients, all female, were recruited (Table 1). The patients ranged in age from 36 to 65 years, and the average was51.6 years (SD, 9.5 years). Five patients had OA of the right hip and five patients had OAof the left hip. Seven patients were radiological grade I and three patients were gradeII.
Table 1. Patient characteristics.
| Patient number | Age | Sex | Radiographical gradea | Site of OA hip | HHS evaluated after use of the WISH brace | |||
| 0 monthsb | 1 month | 3 months | 6 months | |||||
| 1 | 49 | F | II | L | 50 | 70 | 73 | 76 |
| 2 | 38 | F | II | L | 47.7 | 77.7 | 94.7 | 82.7 |
| 3 | 54 | F | I | R | 65.7 | 75.7 | 95.7 | 95.7 |
| 4 | 51 | F | I | R | 66 | 76 | 81 | 94 |
| 5 | 36 | F | I | R | 63 | 73 | 85 | 75 |
| 6 | 57 | F | I | L | 61 | 73 | 73 | 69.0 |
| 7 | 65 | F | I | R | 59 | 76 | 72 | 72 |
| 8 | 52 | F | I | L | 76 | 76 | 76 | 91 |
| 9 | 50 | F | I | L | 76 | 93 | 91 | 91 |
| 10 | 64 | F | II | R | 62.7 | 75.7 | 95.7 | 91.7 |
| Mean±SD | 62.7±9.3 | 76.6±6.2* | 83.7±10* | 83.8±10.1* | ||||
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F female, R right, L left.
aRadiological grade was evaluated according to Crowe et al.17)
bMonths after start of brace intervention.
*Significantly different from 0 months (P<0.05).
Improvement of HHS after Application of the WISH Hip Brace
Eight hip joints had a poor hip function score (<70)20) on the first assessment. After the WISH bracewas used, HHS improved in all patients, as shown in Table 1. However, in one patient, hip function was poor again after 6 months.One factor influencing the score reduction in this patient was the requirement of a canewhen walking long distances. However, pain was improved at the 1-month follow-upassessment, and the pain improvement was maintained until the 6-month follow-upassessment. Significant improvements in the average HHS were observed at months 1, 3, and6 compared with the initial assessment.
Comparison of Muscle Strength Between Affected and Unaffected Limbs
Because application of the WISH brace directly and significantly altered the strength ofmuscles around the hip,9) inthe present study, longitudinal change in the affected and unaffected limbs was analyzedbased on the presence (Fig. 1) or absence (Fig. 2) of the WISH brace at assessment.
Fig. 1.
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Fig. 2.
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In paired tests, the muscle strengths of FLEX and K-EXT were lower in the affected limbthan in the unaffected limb for all evaluations whether measurement was performed with(Fig. 1) or without (Fig. 2) the WISH brace. The muscle strength of ABD without the WISHbrace was lower in the affected limb than in the unaffected limb before bracingintervention, i.e. month 0. Although a significant difference was also observed at month1, by month 3 the difference had disappeared (Fig.2). No significant difference was noted in the ADD muscle strength between theaffected and unaffected sides at any evaluation time with (Fig. 1) or without (Fig.2) the WISH brace.
The two-way ANOVA results are shown in Table2. For FLEX, ABD, ADD, and K-EXT, the unaffected limb had a significantly highermuscle strength whether measurements were performed with or without the WISH brace. Timeeffects were not observed. Significant leg × time interactions were observed for ADD(F3,27=3.055, P=0.045) and K-EXT (F3,27=3.481, P=0.029) musclestrength only when measurement was performed without the brace.
Table 2. Leg×time interaction evaluated by two-way ANOVA with repeated measures.
| Muscle | With brace | Without brace | ||
| F | P value | F | P value | |
| FLEX | 0.79 | 0.51 | 1.213 | 0.324 |
| ADD | 1.034 | 0.393 | 3.055 | 0.045* |
| ABD | 2.814 | 0.058 | 2.675 | 0.067 |
| K-EXT | 0.488 | 0.694 | 3.481 | 0.029* |
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* Significant difference (P<0.05).
The characteristics of each leg (affected and unaffected) were analyzed using one-wayANOVA with repeated measurements. There was a significant change in muscle strength in ABD(P=0.035) and K-EXT (P=0.029) when measurements were performed without the WISH brace.Dunnett’s post hoc analysis revealed a significant increase (P<0.05) in muscle strengthwithout the WISH brace at months 3 and 6 for ABD (Fig.2C), and at month 3 for K-EXT (Fig.2D).
DISCUSSION
This short-term longitudinal study evaluated the effects of the WISH brace on the strengthof muscles around the hip and knee joints. Consistent with previous studies, hip functionwas significantly improved by application of the WISH brace.6,8) It is uncertain why one patient (case 6) once again had poorhip function after 6 months. Patients equipped with the WISH brace were required to walk atleast 30 min every day to strengthen muscles around the hip joint required forgait.6) It is possible thatthis daily exercise routine may not have been closely adhered to by this patient.
The FLEX muscle strength was significantly lower in the affected limb than in theunaffected limb at all time points whether assessed with or without the WISH brace. Ingeneral, the mean hip isometric flexion strength was lower in OA patients than incontrols.11,22) Furthermore, the hip isokineticflexion strength was lower in OA patients than in controls. In OA patients, the hip flexionisometric strength was lower in the affected hip than in the unaffected hip.11,13) Furthermore, there was no significant leg × timeinteraction for FLEX with or without the WISH brace. Therefore, the FLEX muscle strength maybe lower in the affected limb than in the unaffected limb, and is not affected by the WISHbrace.
There was no significant difference between the affected and unaffected limbs in ADD musclestrength before WISH brace intervention, i.e., at month 0. These results are consistent witha previous report that adduction strength values did not differ between the affected andunaffected side in OA patients.11) In the same report, the mean hip isometric adduction strengthwas found to be lower in OA patients than in healthy controls.11) In contrast, another report showed that hipadduction strength was reduced in the OA limb relative to that of the healthylimb.13) The reason forthese inconsistent results is unclear at present. Reduction of the adduction strength wasobserved when hip forces were assessed in the standing position,13) but no significant reduction was observed when hipadductor torque was tested with the subject positioned supine on a table,11) as performed in the present study.Considerable variability in outcomes in the strength of muscles around the hip joint may beexplained by the difficulty in isolating specific muscles during testing or related to thechoice of testing positions.22)These results suggest that ADD muscle strengths on the affected and unaffected sides arereduced by equal amounts when the muscle strength is assessed by HHD with the subject in thesupine position on a table. However, repeated-measures ANOVA revealed a significant leg ×time interaction in unbraced ADD strength, but there was no significant leg × timeinteraction when the measurements were performed with the WISH brace. Moreover, there was nosignificant improvement in unbraced adduction strength during the evaluation period. Takentogether, ADD muscle strength may be reduced to the same extent in both affected andunaffected limbs in OA patients, and the reduced strength may be little improved by the WISHbrace.
The K-EXT muscle strength was significantly lower in the affected limb than in theunaffected limb before WISH brace intervention. Previous studies have shown that the meanhip isometric knee extension strength was lower in OA patients than in controls.22) Also, in OA patients, the kneeextension isometric strength was lower in the affected hip than in the unaffectedhip.13) In the presentstudy, a significant leg × time interaction was observed for K-EXT. Moreover, a significantincrease (P<0.05) in muscle strength was observed at month 3 in the unbraced K-EXT. Therewas a synergistic effect on K-EXT muscle strength in the affected and unaffected limbs.Therefore, the WISH brace temporarily improves the K-EXT muscle strength of the affectedlimb via interaction with the unaffected limb.
The ABD muscle strength was significantly lower in the affected limb than in the unaffectedlimb before WISH brace intervention when assessed without the WISH brace. However, there wasno significant difference after brace application, confirming the direct effects of thebrace on the output of muscle strength.9) The present result supports the finding that the ABD strengthwas lower in the OA limb than in the healthy limb.13) In contrast, Arokoski et al. demonstrated that theisometric hip abduction strength did not differ between the affected and unaffectedlimbs.11) However, in thatstudy, the sample size was low and there was a significant difference in isometric abductionstrength values between the radiographic OA subgroups.11) On the other hand, the mean hip isometric abductionstrength was lower in OA patients than in controls.11,12) In another study, patients with hip OA demonstrated 17% lesship abductor strength than healthy controls, but the difference was notsignificant.22) Patientswith hip OA also exhibited decreased hip abduction moments during the stance phase ofgait.23) These resultssuggest that the hip abduction muscle strength was significantly reduced, and the reductionwas significantly more marked in the affected limb than in the unaffected limb, at least inpatients with radiological grade I or II OA and an HHS of approximately 60.
Of note, a difference in ABD strength assessed without the WISH brace was observed usingone-way ANOVA with repeated measurements. Dunnett’s post hoc analysis revealed a significantincrease in muscle strength at months 3 and 6 for unbraced ABD in the affected limb.However, the significant difference between the affected and unaffected limbs haddisappeared at the 3-month and 6-month follow-up assessments. With this bracing approach,continuous daily walking exercise was associated with the final outcome of hip function,suggesting a virtuous cycle in which pain reduction by the hip brace increases the activeperformance of daily walking and vice versa.6) On the other hand, it should also be noted that the ABD musclestrength did not exhibit synergistic effects between the affected and unaffected limbs.These results suggest that the WISH brace may improve the inherent ABD muscle strength,which is reduced in the limb affected by hip OA, independently of the unaffected limb.Therefore, this improvement of abduction muscle strength may result in improvements in hipfunction,6)biomechanics,10) functionalmobility,8) and posturalcontrol.9)
One limitation of the present study is the relatively short evaluation period. Improvementof hip function and functional mobility is maintained for at least 12 months.6,8) Careful comparative examination of the time course of changein the strength of muscles around the hip joint and functional status would be useful toelucidate in detail the mechanisms underlying the beneficial effects of the WISH brace onhip OA. Another limitation is the measurement methods used to assess muscle strength. Toassess abduction muscle strength, for example, the supine position11) was used in the present study, whereas in otherstudies, the standing position13) and the side lying position12,22) were adopted. To discuss the effects of hip OA on musclestrength, the measurement method should be considered carefully.
CONCLUSION
As shown in Table 3, the FLEX, ABD, and K-EXTmuscle strengths were lower in the affected limb than in the unaffected limb and in thelimbs of control subjects without hip OA. The ADD muscle strength, however, was reduced tothe same extent in both the affected and unaffected limbs. The present study revealed thatonly the inherent ABD muscle strength was improved by the WISH brace, and after 3 months,the strength equaled that in the unaffected limb. This improvement in ABD muscle strengthmay lead to an improvement of hip function.
Table 3. Summary of muscle strengths measured without WISH brace equipment.
| FLEX | ADD | K-EXT | ABD | ||
| Before intervention (starting point of theintervention) | |||||
| Reduction against normal controla | + | + | + | + | |
| Reduction against unaffected limbb | + | – | + | + | |
| After intervention of WISH brace | |||||
| Improvement of muscle strengthc | – | – | + (temporary) | + | |
| Interaction between affected and unaffectedlimbsd | – | + | + | – | |
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aData from previous reports.11,12,22
bData from the present study and previous reports.11,13
cData from one-way ANOVA in the present study.
dData from two-way ANOVA in the present study.
ACKNOWLEDGEMENTS
This work was supported in part by a Grant-in-Aid for Young Scientists JP18K17710 (E.S.)from the Japan Society for the Promotion of Science.
Footnotes
CONFLICT OF INTEREST: All authors declare that there are no conflicts of interest.
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