CHANGES IN GAIT SYMMETRY, GAIT VELOCITY AND SELF-REPORTED FUNCTION FOLLOWING TOTAL HIP REPLACEMENT

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1 J Rehbil Med 2011; 43: ORIGINAL REPORT CHANGES IN GAIT SYMMETRY, GAIT VELOCITY AND SELF-REPORTED FUNCTION FOLLOWING TOTAL HIP REPLACEMENT Croline Hodt-Billington, MS 1, Jorunn L. Helbostd, PhD 2, Willemijn Vervt, MS 1, Turid Rognsvåg, MS 3 nd Rolf Moe-Nilssen, PhD 1 From the 1 Setion of Physiotherpy Siene, Fulty of Mediine nd Dentistry, University of Bergen, 2 Deprtment of Neurosiene, Norwegin University of Siene nd Tehnology nd St Olv University Hospitl, Trondheim nd 3 Kysthospitlet in Hgevik, Deprtment of Orthopedi Surgery, Hukelnd University Hospitl, Bergen, Norwy Objetive: To investigte the mgnitude of hnge t different time points in mesures of git symmetry, git veloity nd self-reported funtion following totl hip replement. Design: Longitudinl with test osions pre-surgery nd 3, 6 nd 12 months post-surgery. Subjets: Thirty-four ptients with hip osteorthritis (men ge 63 yers, stndrd devition 11 yers). Methods: Subjets wlked bk nd forth long 7-m wlkwy t slow, preferred nd fst speed. Anteroposterior, vertil nd mediolterl trunk symmetry ws ssessed by elerometry, while single support symmetry, step-length symmetry nd git veloity ws simultneously ssessed by n eletroni wlkwy. Self-reported funtion ws ssessed by Hip disbility nd Osteorthritis Outome Sore. Git symmetry dt were normlized for git veloity. Chnges between test osions were reported s effet size. Results: All mesures showed effet sizes > 0.30 from preopertive to 12-months postopertive ssessments, nd improvements were signifint (p < 0.05) in ll mesures, exept medio lterl symmetry. In generl, git symmetry nd git veloity improved most 6 nd 12 months postopertively, while self-reported funtion improved most 3 months postopertively. Conlusion: Erly improvements were seen in self-reported funtion, suggesting immedite relief from stiffness nd pin, while git symmetry nd veloity improved lter postopertively, suggesting tht git qulity nd performne require prolonged rehbilittion with postopertive guidne, musulr strengthening nd motor relerning. Key words: git nlysis; hip rthroplsty; linil ourse; reovery; outome mesures; effet size. J Rehbil Med 2011; 43: Correspondene ddress: Croline Hodt-Billington, Setion of Physiotherpy Siene, Deprtment of Publi Helth nd Primry Helth Cre, Fulty of Mediine nd Dentistry, University of Bergen, PO Box 7804, NO-5020 Bergen, Norwy. E-mil: roline.hodt@isf.uib.no Submitted September 3, 2010; epted My 31, 2011 INTRODUCTION Git symmetry is often gol for physiotherpy in ptients fter totl hip replement (THR), nd hs been dvoted when evluting git qulity fter disese or injury ffeting the lower limbs, suh s stroke nd hip osteorthritis (1, 2). However, git symmetry is not routinely ssessed s linil outome following THR. Evlution should inlude temporl nd sptil footfll movement s well s mesures of trunk movement (1), beuse ompenstory movements of the upper body re frequently seen in ptients with injury or disese in the hip (3, 4). At present, git veloity nd selfreported funtion re typilly reported s linil outomes fter THR (5 7). These mesures re esily dministrted. Git veloity is onsidered fundmentl mesure of git (3), while self-reported funtion hs been dvoted s supplement to other informtion on linil outome (8). In ontrst to mesures of git symmetry, git veloity nd selfreported funtion do not provide informtion tht relte esily to speifi movement strtegies, whih my in turn provide vluble informtion for the development of individully trgeted rehbilittion progrmmes. Most longitudinl studies on hnge in funtion following THR ssess funtion only one before nd fter surgery. Thus, informtion regrding the mgnitude of hnge in funtion t different points in time is not known. Better knowledge bout funtionl hnge following surgery my led to better trgeted rehbilittion progrmmes. The purpose of this study ws to investigte the mgnitude of hnge of git symmetry, git veloity nd self-reported funtion t different time-points during the first 12 months fter THR. MATERIAL AND METHODS Subjets A totl of 41 ptients with primry hip osteorthritis sheduled for hip replement surgery were reruited from two university hospitls. To reflet the popultion in need of THR, hosen inlusion riteri omprised both genders t wide rnge of ges (Tble I), 3 tegories of hip involvement (Tble II), different implnts nd 2 postopertive weight-bering regimes (Tble II). However, ll ptients were without other musuloskeletl ilments likely to influene wlking bility nd were ble to wlk t lest 10 m without ssistive devies t ll test osions. For inlusion in the finl nlysis, subjets hd to omply with postopertive instrutions from the 2 operting hospitls nd ttend t lest 3 test osions. In order to ompre outome mesures t ommon git veloity of 0.9 m/s, inluded ptients hd to hve this speed within the rnge of self-seleted git veloities t every test osion. Thirty-four ptients with men ge of 63 yers, stndrd devition (SD) 11 yers (Tble I) were inluded in the finl nlyses, 2011 The Authors. doi: / Journl Compiltion 2011 Foundtion of Rehbilittion Informtion. ISSN

2 788 C. Hodt-Billington et l. Tble I. Desriptive hrteristis of the ptients preopertively (pre) nd 3, 6, nd 12 months postopertively (post 3, 6, nd 12) Pre (n = 34) Men (SD) Post 3 (n = 34) Men (SD) Post 6 (n = 31 ) Men (SD) Post 12 (n = 31 ) Men (SD) Age, totl smple, yers 63 (10.8) Age, men, yers (n = 14) 60 (12.6) Age, women, yers (n = 20) 65 (9.3) Height, m 1.74 (0.09) 1.74 (0.09) 1.74 (0.09) 1.74 (0.09) Weight, kg 83.3 * (16.4) 83.4 (15.7) 83.9 (15.9) 86.3 (14.6) BMI b, kg/m * (4.9) 27.5 (4.7) 27.8 (4.7) 28.5 (4.5) Step ount 40 (9) 38 (7) 35 (5) 33 (6) * Signifint differene between preopertive nd 12 months postopertive ssessments (p = 0.05). Missing dt not imputed for desriptive hrteristis. b Indoor lothing, shoes nd equipment (body fixed sensor nd dt logger) inluded in the mesures of height nd weight. The totl number of steps used to lulte outome mesures t eh test osion. BMI: body mss index; SD: stndrd devition. fter the exlusion of one ptient due to postponed THR surgery, 2 due to postopertive omplitions, 2 beuse they missed 2 test osions, nd 2 beuse they wlked too slowly 3 months postopertively. All subjets reeived postopertive physil therpy during the hospitl sty, nd were enourged to void the extremes of hip rottion, flexion nd ddution. The Regionl Committee for Medil Reserh Ethis pproved the study, nd ll prtiipnts provided informed onsent. Mesurements Single support (% of stride time), step length (m), nd git veloity (m/s) were registered by n eletroni wlkwy (GAITRite Gold, CIR Systems In., NJ, USA). The GAITRite hs previously showed good to exellent test retest relibility of temporl sptil git prmeters (9 12), nd is regrded s vlid tool for ssessment of those prmeters (9, 10). Trunk elertion in nteroposterior (AP), vertil (V) nd mediolterl (ML) diretions ws simultneously registered by kg trixil, piezoresistnt elerometer (Logger tehnology HB, Mlmö, Sweden), whih provides relible nd vlid mesures of movement during git (13, 14). A omputerized stopwth ws synhronized to the elerometer nd registered time sequenes for eh wlk through photoeletri ells. The elerometer ws seured to the subjet s bk, pproximtely t the L3-level of the spine, by ustomized belt, nd onneted to 0.3 kg bttery-operted Personl Computer Memory Crd Interntionl Assoition rd dt-logger (Logger Tehnology HB, Mlmö, Sweden), lso worn by the subjets. The Hip disbility nd Osteorthritis Outome Sore questionnire (HOOS), Likert version (LK) 1.1, ws used to ssess self-reported symptoms nd funtionl limittions. HOOS is disese speifi nd ws developed to evlute self-reported problems of ptients with hip osteorthritis (15, 16). HOOS hs dequte mesurement properties of vlidity nd relibility (17), nd hs been reommended for use in the evlution of ptients with hip osteorthritis before nd fter totl hip replement (16). The questionnire is sored ording to the HOOS LK 1.1 User s Guide 2003 (18) with 39 items in 5 sub-sles: P = Pin; S = Other symptoms, inluding stiffness; ADL = Funtion in dily living; QOL = Hip-relted qulity of life; SP = Funtion in sport nd reretion. Dt from the SP subsle ws not registered t postopertive tests due to postopertive movement restritions. In eh subsle, no Tble II. Dignosti, opertionl nd postopertive weigth-bering desriptive hrteristi mong the ptients PWB (n = 15) n (%) b WBAT (n = 19) n (%) Totl (n = 34) n (%) Operted hip Left hip 6 (18) 9 (26) 15 (44) Right hip 9 (26) 10 (29) 19 (56) Totl 15 (44) 19 (56) 34 (100) Dignosti group (rdiogrphi imges) 1-sided osteorthritis 5 (15) 11 (32) 16 (47) 2-sided osteorthritis 1 st hip to be 4 (12) 5 (15) 9 (26) operted 2-sided osteorthritis 2 nd hip to be 6 (18) 3 (9) 9 (26) operted Totl 15 (44) 19 (56) 34 (100) Prosthesis; etbulum/ femur omponents Chrnley Ogee ement/chrnley ement 2 (6) 12 (35) 14 (41) Refletion ement/spetron ement 5 (15) 3 (9) 8 (24) d Refletion/Lndos Coril ement 5 (15) 5 (15) less Other brnds 3 (9) 1 (3) 4 (12) e Birminghm hip resurfing 3 (9) 3 (9) Totl 15 (44) 19 (56) 34 (100) PWB: prtil weight-bering. Ptients were instruted to llow mximum lod of kg on the operted leg nd to use ruthes 3 months post-opertively. Ptients operted with diret lterl pproh were dditionlly instruted to void tive hip bdution exerises 6 weeks post-opertively. b WBAT: weight-bering s tolerted, limited by pin. Ptients were instruted to use ruthes 6 weeks post-opertively. Diret lterl pproh. d Diret lterl pproh in 3 ptients nd dorsl pproh in 1 ptient. e Dorsl pproh. symptoms equl sore of 0, while 100 indites extreme symptoms, ording to the HOOS LK 1.1 User s Guide 2003 (18). Proedure To beome ustomed to the equipment nd void prtie effet, subjets wlked ross the wlkwy twie before dt olletion strted. Eh subjet then wlked 6 times long the 7-m wlkwy: 2 wlks t self-seleted slow speed, 2 wlks t self-seleted preferred speed, nd 2 wlks t self-seleted mximum sfe speed. Footfll nd trunk symmetry mesures were ssessed during the middle 4.3 m of the wlkwy, leving the rest of the wlkwy for elertion nd deelertion. The subjets wore their own shoes nd performed the tests without ny personl ssistne or wlking ids. Questionnires were posted to eh subjet less thn 1 week before test osions nd returned when subjets presented for testing. Dt nlysis The eletroni wlkwy s softwre (GAITRite3A) nd Mirosoft Exel ( ) were used in the lultions of footfll mesures nd git veloity. Anlogue signls from the elerometer were low-pss filtered t 55 Hz nd smpled t 128 Hz before digitl signls were trnsferred to lptop for off-line proessing in Mtlb 7.1 (The Mthworks In., Ntik, MA, USA). Aelertion signls were trnsformed to true horizontl vertil oordinte system, keeping the AP xis in the sgittl plne to eliminte unwnted grvity omponents used by inurte orienttion of the sensor (19).

3 Clinil outome mesures fter hip replement 789 Between-step nd between-stride trunk regulrity were ssessed by n utoorreltion proedure where yli elertion urve representing wlk ws orrelted to the sme urve t phse shift of one step nd one stride, respetively. In the mthemtil proedure proposed by Moe-Nilssen & Helbostd (20) nd dopted by Tur et l. (21), the generi unbised utoorreltion funtion, Ad(m), of the smple sequene x(i) is omputed using: 1 Ad(m) = N m x(i) x(i+m) N m i = 1 where, N is the number of smples nd m is the time lg expressed s number of smples. The first pek of Ad(m) represents between-step regulrity, while the seond pek of Ad(m) represents between-stride regulrity. Regulrity vlues pprohing 1.0 imply highly repetitive git or high git regulrity, while vlues pprohing 0.0 imply low git regulrity. Sores were imputed for ptients who missed one git ssessment. Chnges in group men vlues were lulted nd dded to the previous sore of the ptient with missing dt. While the totl number of sore ws 156 (4 test osions times 34 ptients) for eh outome mesure, 8 of these sores were missing nd thus imputed for eh of SL nd SS symmetry. For trunk symmetry nd git veloity mesures, the number of imputed sores ws 6 for eh mesure. Missing dt within eh subsle of the HOOS questionnire were repled by the men vlue for the subsle in question, s reported in previous studies (15). If more thn 2 items were missing, the subsle in question ws deleted from the nlysis. To evlute the inlusion of missing vlues, Friedmn s nlysis of vrine (ANOVA) ws performed with nd without the imputed vlues. All git symmetry mesures were heked for speed dependeny using dt from the 6 wlks performed by eh subjet preopertively. The grdients (b 1 ) of individul liner trend lines of symmetry mesure vs wlking speed were tested by one-smple t-tests for H 0 : b 1 = 0. The tests returned signifint liner reltionships for most symmetry mesures. Thus, ontrolling symmetry mesures for git veloity ws wrrnted. Dt from the 6 wlks were used to mke liner urve estimtes for eh subjet, nd dt t point estimte of 0.9 m/s were used in the nlysis. This speed ws within the rnge of git veloities for inluded subjets t ll test osions, exept for 1 ptient whose fstest veloity 3 months postopertively ws 0.84 m/s. To void overll exlusion of this ptient, liner urve estimtes of symmetry dt in reltion to speed were extrpolted to 0.9 m/s t this prtiulr osion, before symmetry dt were estimted. Symmetry indies (SI) were lulted for eh trunk nd footfll mesure. Step length nd single support symmetry rtio were used to desribe footfll symmetry: SI footfll = 1 (limb with lower vlue/limb with higher vlue) Trunk mesures re previously used to desribe git symmetry (1, 20, 21), nd symmetry indies were lulted seprtely for AP, V nd ML signls: SI trunk =between-stride regulrity between-step regulrity Absolute vlues of between-step trunk regulrity re used beuse the softwre displys ML between-step trunk regulrity with negtive vlues. Rtio lultions of trunk mesures re unsuitble beuse the between-step nd between-stride utoorreltions my pproh zero if regulrity between neighbouring steps or neighbouring strides is low. The number zero nnot be used s the denomintor. Hene, the symmetry indies of footfll nd trunk mesures re bsed on different lultions. However, t perfet symmetry, both indies equl 0, nd positive indies indite symmetri git. Sttistil nlysis Anthropometri dt re presented s men nd SDs, while pired smple t-tests were used to evlute hnge in these dt from preopertive to 12 months postopertive ssessments (Tble I). The outome mesures, git symmetry, git veloity nd self-reported funtion, re presented s medin with 25 th nd 75 th perentiles. Wiloxon rnk-sum test ws used to ssess possible differenes in outome mesures relted to differenes in gender, postopertive weight-bering restritions or operting hospitl. The Kruskl-Wllis test, followed by Wiloxon rnk-sum test when pproprite, ws used to ssess differenes in outome mesures relted to hip involvement. Chnge from preopertive to 12 months postopertive ssessment ws evluted with the Friedmn s ANOVA, while the Wiloxon signed-rnk ws used to ssess hnges between neighbouring ssessments. To orret for the number of tests in the Wiloxon signed-rnk nlysis, the Bonferroni orretions (α/number of omprisons) ws used to deide ritil vlues (22, p. 577). Effet size (ES) ws used to quntify funtionl hnge, s it is suited to ompre the mgnitude of hnge in mesures using different sles nd units of mesurements (23, 24). Reports were mde between neighbouring test osions, nd between preopertive nd 12 months postopertive tests. The Rosenthl (25) formul, lso z dopted by Field (22, p. 550); ES = N, lets Z equl the vlue of the observtion expressed in SD units, while N is the number of totl observtions on whih Z is bsed (22, p. 580). Smll, medium nd lrge mgnitude of hnge equl ES vlues bove respetively 0.1, 0.3 or 0.5, s suggested by Cohen (26), who further suggests tht medium effet is omprble to improvement visible to the eye (26). The level of signifine ws set t p < Sttistil nlyses were performed in Mirosoft Exel nd Sttistil Pkge for Soil Sienes (SPSS) Version 18. RESULTS Ptients inresed their body weight signifintly from preopertive to 12 months postopertive ssessments (Tble I). The men number of steps used to evlute git symmetry ws from 33 (SD 6) to 40 (SD 9) per test osion (Tble I). In generl, men wlked signifintly fster thn women t fst nd preferred git veloities throughout test osions (p = p = 0.042), exept for preferred git veloity preopertively, where the differene ws insignifint (p = 0.10). Ptients from one hospitl showed higher git symmetry, lower git veloity nd self-reported funtion. These differenes were insignifint t most test osions, exept in 3 HOOS subsles preopertively; symptoms (p = 0.035), ADL (p < 0.001) nd QOL (p = 0.046), AP symmetry 3 nd 12 months postopertively (p = 0.04 p = 0.03) nd ML symmetry 6 months postopertively (p = 0.02). Most outome mesures were unffeted by differenes in postopertive weight-bering restritions, exept for HQOL preopertively (p = 0.045), V symmetry 3 months postopertively (p = 0.007) nd ADL 12 months postopertively (p = 0.048). No differenes in outome mesures were relted to dignosti group, exept ADL 3 nd 6 months postopertively, where ptients with one-sided ffetion demonstrted better self-reported funtion thn ptients with respetively bilterl 1 st hip to be operted (p = 0.008) nd bilterl 2 nd hip to be operted (p = 0.011). All outome mesures, exept ML symmetry, showed signifint improvement from preopertive to 12 months postopertive ssessments (Tble III). The mgnitude of hnge between preopertive nd 12 months postopertive ssessments in symmetry mesures tht showed signifint improvement rnged from ES 0.33 to 0.52 (Tble III). Compring neighbouring test osions, the lrgest improvement in AP nd SS git symmetry ws seen from 3 to 6 months postopertively, in SL nd ML symmetry from

4 790 C. Hodt-Billington et l. Tble III. Friedmn s nlysis of vrine (ANOVA) (χ 2 ) sttistis of min effet with level of signifine (p-vlue), post-ho tests (Wiloxon signedrnk tests) with Bonferroni orretion of level of signifine p < (0.05/3) re pplied nd supplemented with effet sizes (ES) to evlute hnge between neighbouring ssessments Min effet p-vlue Pre-post 12 Pre-post 3 Post 3 6 Post 6 12 p-vlue ES b p-vlue ES b p-vlue ES b p-vlue ES b Symmetry indies AP < < < V < < ML SL SS < Veloity, m/s Fst < < < Pref < < Slow < < < HOOS P < < < S < < < < ADL < < < < QOL < < < < Min effet bsed upon χ 2 test (degrees of freedom = 3); b ES bsed upon Z-vlues; n = 33; ES vlues bove 0.1, 0.3 or 0.5 represent smll, medium nd lrge effets. AP: nteroposterior; V: vertil; ML: mediolterl; SL: step length; SS: single support; Git veloities: Fst, Preferred (pref) nd Slow; HOOS: Hip disbility nd Osteorthritis Outome Sore questionnire; P: pin; S: other symptoms, inluding stiffness; ADL: funtion in dily living; QOL: hiprelted qulity of live; SP: funtion in sport nd reretion. 6 to 12 months postopertively, while V showed the highest improvement between preopertive nd 3 months postopertive ssessments; however, ontinuous improvement (ES > 0.22) throughout test osions. In mesures of git veloity, the ES mgnitude of hnge from preopertive to 12 months postopertively rnged from 0.42 to Medin git veloity deresed insignifintly from preopertive to 3 months postopertively, while the inrese in git veloity ws lrgest from 3 to 6 months postopertively (Tbles III nd IV). The mgnitude of hnge from preopertive to 12 months postopertive test osions in self-reported funtion rnged from ES 0.61 to The lrgest improvement in self-reported funtion ws seen from preopertive to 3 months postoper- Tble IV. Medin vlues with 25 th nd 75 th perentiles (perentiles) of symmetry indies, git veloities nd HOOS subtegories (n = 34) preopertively (pre) nd 3, 6 nd 12 months postopertively (post 3, 6 nd 12) Mesure Pre Medin (perentiles) Post 3 Medin (perentiles) Post 6 Medin (perentiles) Post 12 Medin (perentiles) Symmetry indies AP 0.26 (0.10, 0.51) 0.15 (0.06, 0.47) 0.09 (0.06, 0.18) 0.09 (0.04, 0.14) V 0.15 (0.05, 0.28) 0.06 (0.02, 0.18) 0.04 (0.01, 0.12) 0.03 (0.00, 0.09) ML 0.13 (0.06, 0.28) 0.14 (0.05, 0.23) 0.12 (0.08, 0.19) 0.08 (0.03, 0.18) SL 0.05 (0.03, 0.09) 0.04 (0.02, 0.07) 0.04 (0.03, 0.09) 0.04 (0.01, 0.06) SS 0.08 (0.04, 0.13) 0.05 (0.03, 0.12) 0.04 (0.02, 0.07) 0.04 (0.01, 0.07) Veloity (m/s) Fst 1.50 (1.26, 1.83) 1.48 (1.28, 1.86) 1.57 (1.38, 1.96) 1.74 (1.42, 1.98) Pref 0.97 (0.87, 1.13) 0.96 (0.87, 1.11) 1.08 (0.95, 1.21) 1.18 (1.05, 1.30) Slow 0.49 (0.45, 0.59) 0.49 (0.43, 0.58) 0.54 (0.45, 0.68) 0.68 (0.62, 0.79) HOOS P 61.1 (52.8, 66.7) 13.9 (2.8, 27.8) 13.9 (5.6, 25.0) 5.6 (0, 19) S 57.5 (43.8, 70.0) 25 (15, 35) 20 (10, 31.3) 15 (5, 20) ADL 58.8 (48.9, 63.2) 29.4 (22.8, 35.3) 16.2 (8.1, 32.4) 10.3 (2.9, 21.3) QOL 75 (67.2, 82.8) 50 (43.8, 62.5) 37.5 (25, 51.6) 37.5 (25, 50) SP b 75 (68.8, 87.5) n = 33; b SP only reported preopertively, due to postopertive movement restritions. Git veloities: Fst, Preferred (pref) nd Slow; AP: nteroposterior; V: vertil; ML: mediolterl; SL: step length; SS: single support; HOOS: Hip disbility nd Osteorthritis Outome Sore questionnire; P = Pin, S = Other symptoms, inluding stiffness; ADL: funtion in dily living; QOL: hip-relted qulity of life; SP: funtion in sport nd reretion.

5 Clinil outome mesures fter hip replement 791 tively (Tbles III nd IV), lthough improvement ws high for most tegories throughout test osions. DISCUSSION The purpose of this study ws to investigte the mgnitude of hnge in mesures of git symmetry, git veloity nd selfreported funtion preopertively, nd 3, 6 nd 12 months postopertive to THR. A repeted mesures design ws hosen to llow identifition of periods with lrger nd smller mgnitudes of linil hnge. Overll, ll mesures showed postopertive improvement in funtion, but the period of lrgest hnge differed between mesures. While git symmetry nd git veloity mesures in generl showed the lrgest postopertive improvement towrds 6 nd 12 months postopertively (Fig. 1, 1b), self-reported funtion showed the lrgest improvement towrds 3 months postopertively. However, improvement in self-reported funtion ws lrge for ll test osions (Fig. 1). ) b) ) Fig. 1. ( ) Medin with 25 th nd 75 th perentiles for outome mesures ssessed preopertively (pre), nd 3, 6 nd 12 months (post, 3, 6, 12) fter totl hip replement surgery. () Anteroposterior (AP), vertil (V), mediolterl (ML) trunk symmetry indies, step length (SL) nd single support (SS) symmetry indies (0 = perfet symmetry). (b) Fst, preferred nd slow git veloity. () Hip disbility nd Osteorthritis Outome Sore questionnire (HOOS) with subsles: Pin, Other symptoms, inluding stiffness, Funtion in dily living (ADL), nd hip-relted qulity of life (QOL) (0 100 = best to worse sore).

6 792 C. Hodt-Billington et l. The lrgest improvement in most symmetry mesures ws observed t test osions 6 nd 12 months postopertively. The sme time-lgged postopertive improvement in git symmetry hs lso been reported previously (27, 28), nd my be explined by erly postopertive weight-bering restritions, time needed to reover from surgery nd the need for musulr strengthening nd motor relerning to hieve symmetril git. Chnge in ML symmetry differed somewht ompred with the other symmetry mesures, nd improvement ws sre t ssessments 3 nd 6 months postopertively. However, 12 months postopertively, ML symmetry showed lrgest improvement mong symmetry mesures, suggesting tht ML symmetry desribes different qulities of git ompred with other symmetry mesures. Unilterl musulr wekness of the hip bdutors hs been reported in ptients with osteorthritis (27, 29) nd hs lso been found to persist 2 yers fter THR (27). The wekness my led to the so-lled Trendelenburg git, where filure to stbilize the pelvis during stne my result in lterl devition of the trunk, hene ML trunk symmetry. The pttern of hnge in git veloity differed somewht ompred with the observed hnge in git symmetry nd self-reported funtion (Fig. 1), s ptients tended to wlk slightly slower fter 3 months thn they did preopertively. Therefter, git veloity inresed t 6 nd 12 months postopertive ssessments. The delyed inrese in git veloity my be explined by onsiousness nd wreness surrounding the effort to hieve symmetril git, but lso by postopertive inseurity in generl. vn den Akker-Sheek et l. (30) let the ptients use wlking ids t postopertive git ssessment nd found inresed git veloity s soon s 6 weeks postopertively. However, in greement with our findings, the lrgest improvement in git veloity ws seen 6 months postopertively. Self-reported funtion showed the lrgest overll mgnitude of hnge nd ES bove 0.58 s soon s 3 months postopertively nd bove 0.61 fter 12 months. This lrge nd erly improvement my be explined by the ptients experiene of immedite relief from stiffness nd pin, whih is lso previously reported fter THR (31). The hievement of git symmetry my be prerequisite to void lter disese or injury used by mislignment. Timeonsuming linilly guided exerises, long with musulr strengthening nd relerning, my be neessry to hieve git symmetry, nd nturlly led to improvement lter postopertively ompred with improvement in self-reported funtion. Our findings support previous findings tht highlight the importne of inluding objetive mesures in postopertive evlution nd rehbilittion strtegies (8). Self-reported mesures lone, or filure to lso inlude objetive mesures with unique properties, suh s properties suggested for mesures of ML symmetry in this study, my onel importnt funtionl qulities of git nd my lso dely rehbilittion fter THR. The low number of steps per wlk my represent limittion, but is linilly relevnt beuse of limited spe vilble t typil test lotions. However, dt were olleted from 6 wlks, with men of t lest 33 steps t ny of the 4 test osions (Tble I). A number of symmetry indies with known limittions hve been used previously to quntify git symmetry (32). The two indies used in this study were hosen beuse they relte esily to performne of limbs or movement qulities, nd rtio indies re previously dvoted for similr resons (33). ES re not lulted from min effet, but rther for the preopertive test ompred with 12 months postopertively, in ddition to neighbouring test osions, due to the limited possibility to lulte ES bsed on χ 2 sttisti with more thn 1 degree of freedom (22). Although our results suggest ontinuous improvement throughout the first yer following THR in ll reported mesures, ML symmetry seems to improve lter thn the other mesures evluted in this study. Longer follow-up periods or exerise progrmmes imed to strengthen nd stbilize the trunk nd pelvis, nd the hip bdutors in prtiulr, my revel to wht degree the observed hnge in ML symmetry reflets time-lgged reovery ompred with the other mesures. Future studies should implement disese-speifi exerise progrmmes before nd fter THR, nd evlute hnge over time mesured by different objetive nd self-reported linil outome mesures. Git symmetry is suggested s preferred mesure of git qulity. However, the vrition in time nd mgnitude of postopertive hnge found in this study supports the dditionl inlusion of git veloity nd self-reported funtion to provide omplete postopertive evlution fter THR. In onlusion, the results of this study showed improvement in git symmetry, git veloity nd self-reported funtion 1 yer fter THR. Only hnge in ML symmetry ws not signifint. The mgnitude nd time of improvement differed mong linil outome mesures. Lrge nd erly improvement ws seen in self-reported funtion, suggesting immedite relief from stiffness nd pin post-surgery. Git symmetry nd git veloity showed lter improvements, suggesting tht these funtions my require prolonged rehbilittion, with musulr strengthening nd motor relerning, possibly with postopertive guidne. A test-bttery inluding ssessment of git symmetry, git veloity nd self-reported funtion is suggested in postopertive evlution of THR. ACKNOWLEDGEMENTS The study ws funded by The Norwegin Fund for Post-Grdute Trining in Physiotherpy. We thnk the ptients who prtiipted in the study nd the stff t Oslo University Hospitl, Ullevl nd Bergen University Hospitl, Kysthospitlet in Hgevik for their help in the reruitment of ptients. 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