determinants of function knee arthroplasty

Determinants of Function AfterTotal Knee Arthroplasty

Background and Purpose. Decreasing hospital stays for patients withtotal knee arthroplasties (TKAs) have a direct effect on rehabilitation.The identification of modifiable determinants of postsurgical func-tional status would help physical therapists plan for discharge fromhospitals. The purpose of this study was to identify preoperativedeterminants of functional status after a TKA. Participants. Using acommunity-based, prospective cohort study, data were collected from276 patients who received a primary TKA in a Canadian health careregion. Data were collected in the month before surgery and 6 monthsafter surgery. Methods. Function was measured using the functionsubscale of a disease-specific measure—the Western Ontario andMcMaster Universities (WOMAC) Osteoarthritis Index—and a generichealth status measure—the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). Independent variables examinedincluded demographic variables (eg, age, sex), medical variables (eg,diagnosis, number of comorbid conditions, ambulatory status), surgi-cal variables (eg, type of implant, number of complications), and kneerange of motion. Results. At 6 months after surgery, the averageWOMAC physical function score was 70.5 (SD�18.2) and the averageSF-36 physical function score was 44.8 (SD�25.3). Using multipleregression analyses, baseline function, walking device, walking dis-tance, and comorbid conditions predicted 6-month function(WOMAC: R2�.20; SF-36 physical function: R2�.27). Discussion andConclusions. Patients who have lower preoperative function mayrequire more intensive physical therapy intervention because they areless likely to achieve similar functional outcomes similar to those ofpatients who have less preoperative dysfunction. [Jones CA, Voak-lander DC, Suarez-Almazor ME. Determinants of function after totalknee arthroplasty. Phys Ther. 2003;83:696–706.]

Key Words: Determinant, Function, Total knee arthroplasty.

C Allyson Jones, Donald C Voaklander, Maria E Suarez-Almazor

696 Physical Therapy . Volume 83 . Number 8 . August 2003

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The utilization rates of elective total knee arthro-plasties (TKAs) are steadily increasing with anaging population.1 Moreover, the trend towardearlier hospital discharge after TKA has meant

that patients are returning home during a more acutephase of recovery. These 2 factors have had directimplications for the rehabilitation of patients with TKA.

Elective TKA is, more often than not, the last effort inmanaging joint pain and dysfunction caused by arthritis.Extensive evidence indicates that the majority of patientswho have had a TKA report improvement in pain andfunction.2–4 Eighty-five percent to 90% of patients withTKA report pain relief after surgery, and 70% to 80%report functional improvement.4,5 The greatest amountof improvement is seen within 3 to 6 months aftersurgery, with more gradual improvements occurring upto 2 years after surgery.6–8 A meta-analysis of 130 studies4

indicated that these favorable results continue over time.

This meta-analysis showed that 89.3% of patientsreported good to excellent results at an averagefollow-up period of 4.1 years. The mean improvement inrange of motion in those studies in which preoperativeand postoperative range of motion of the knee wasmeasured was 8 degrees.4

Although the improvements following TKA can be dra-matic, the gains are typically less than the changesreported by patients who have had a total hip arthro-plasty.5,9–11 Long-term “technical failures” requiring revi-sion of the prosthesis (eg, loosening, fracture, or infec-tion) are low (less than 10% over 10 years),4,12 yet thelack of improvement is usually related to continuingpain and poor function. Approximately 15% to 30% ofpatients receiving TKA report little or no improvementafter surgery or are unsatisfied with the results after a fewmonths.5,13,14

CA Jones, PT, PhD, is Postdoctoral Fellow, Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Dentistry/Pharmacy Building,Room 2137, Edmonton, Alberta, Canada T6G 2N8 ([email protected]). Address all correspondence to Dr Jones.

DC Voaklander, PhD, is Associate Professor in Community Health, University of Northern British Columbia, Prince George, British Columbia,Canada.

ME Suarez-Almazor, MD, PhD, is Associate Professor in Medicine, Baylor College of Medicine, Houston, Tex.

All authors provided concept/research design, writing, and data collection. Dr Jones provided data analysis. Dr Voaklander and Dr Suarez-Almazorprovided project management, fund procurement, institutional liaisons, and consultation (including review of manuscript before submission). DrSuarez-Almazor provided facilities/equipment and clerical support. The authors thank Dr Karen Kelly and Sue Barrett for their assistancethroughout the study, as well as Lauren Beaupre and Dr DWC Johnston for their clinical expertise. They also are grateful to Dr Lynn Redfern andGordon Kramer for instigation of this project.

Ethics approval was obtained from the Health Research Ethics Board (University of Alberta Sciences Faculties, Capital Health Authority, and theCaritas Health Group).

This research was supported by grants from the Capital Health Authority Research and Grant Fund and the Edmonton Orthopaedic ResearchTrust. Dr Suarez-Almazor was supported by The Arthritis Society of Canada and the Alberta Heritage Foundation for Medical Research. Dr Joneswas supported, in part, by the Canadian Physiotherapy Foundation, the Royal Canadian Legion, and the Alberta Heritage Foundation for MedicalResearch.

This article was received July 5, 2002, and was accepted March 24, 2003.

Physical Therapy . Volume 83 . Number 8 . August 2003 Jones et al . 697

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For the physical therapist, rehabilitation of patients withTKA is often a challenge. One of the primary issues intreating patients with TKA is identifying those patientswho may require extensive rehabilitation. For thosehigh-risk patients, early rehabilitation is thought to pro-vide a benefit.15 Although much of the published clinicalwork has focused on recovery, little evidence exists ondeterminants of recovery from TKA. One group ofresearchers3 concluded that baseline pain and function(ie, pain and function on date of decision to proceedwith surgery) were the single best predictors of func-tional recovery at 6 months. Fortin and colleagues3

surmised that patients who reported greater pain anddysfunction prior to surgery were more likely to havemore pain and dysfunction after surgery than patientswho had less pain and dysfunction. In a prospectivecohort study,16 psychosocial factors such as motivationand social function were more influential than medicalfactors or initial function in predicting 3-month function

after TKA, accounting for 15% of thevariance. To date, no clear predictorsof functional recovery have been con-sistently reported in the literature.

Given the shortened length of stay inacute care hospitals for patients withTKA, we believe that it is importantfor the physical therapist to identifythose patient-related factors that willaffect functional independence. Ifmodifiable determinants of functioncould then be identified, patientswho require additional interventionsduring their recovery could be readilyidentified. The primary objective ofour study was to identify those demo-graphic, medical, and clinical factorsavailable to physical therapists thatpredict function at 6 months aftersurgery. A 6-month follow-up timewas selected because studies6 – 8 haveshown that the greatest change inpain and function occurs during thefirst 3 to 6 months after surgery.Moreover, we contend that short-term evaluation can provide usefulinformation on patient recovery andmay highlight the need for furthertherapy to augment recovery. Thisstudy was part of a larger study thatexamined the effect of waiting timesfor hip and knee arthroplasties on thesubsequent health-related quality oflife (HRQL) after this surgery.5,17

Method

ParticipantsOur study was a prospective, longitudinal study of aninception cohort of surgical candidates who receivedTKA in a Canadian health care region, Capital Health. Ahealth care region is a geographical area administeredby a regional health authority. Patients in this study wereselected based on time of placement on the regionaljoint arthroplasty waiting list rather than on the time ofsurgery. Waiting time for a TKA ranged from 7 to 487days, with a median wait of 78 days. All patients hadsurgery between February 1996 and February 1998.Patients were eligible for this study if they: (1) werescheduled for elective primary TKA, (2) were placed onthe joint arthroplasty waiting list at least 7 days beforesurgery (which would help to ensure that emergencysurgeries were excluded), (3) resided in the healthregion, (4) were 40 years of age or older, and (5) spoke

Table 1.Participant Characteristics

Characteristic n % X SD

Demographics (n�276)Age (y) 69.2 9.2Female 162 59Living alone 67 24

Medical statusOsteoarthritis (n�273) 257 94Previous arthroplasty (n�276) 68 25Comorbid conditions (n�276) 3.5 2.0Body mass index (kg/m2) (n�276) 31.6 5.9

Preoperative walking distance (n�253)Indoors 19 7�1 block 67 271–5 blocks 124 496–10 blocks 22 9Unlimited 21 8

Preoperative assistive walking devices (n�256)None 158 62Cane 86 33Walker 12 5

Preoperative knee range of motion (°) (n�259) 106 15

SurgicalImplant fixation (n�272)

Cementless 44 16Hybrid 156 57Cemented 72 27

In-hospital complications (n�272)None 183 67

Health services utilization (n�276)Hospital length of stay (d) 6.8 2Discharge directly home (n�272) 156 57Rehabilitation facility length of stay (d) 9.3 3.3Community therapy 129 47

698 . Jones et al Physical Therapy . Volume 83 . Number 8 . August 2003

English. Exclusion criteria included hemiarthroplastiesand revision and emergency arthroplasties.

Patients who resided in long-term care institutionsbefore being placed in the joint replacement waiting listalso were excluded. Rarely is any elective joint arthro-plasty performed in patients from long-term care facili-ties. We felt that patients from long-term facilities rep-resent a small unique group of this patient populationand are atypical of patients who receive elective kneearthroplasty. After meeting the selection criteria andagreeing to participate, each patient signed a consentform before participating in the study.

Of the 377 patients eligible to participate in the study, 53(14%) refused to participate, and 18 (5%) were lost tofollow-up. Another 30 patients (8%) had completedtheir preoperative assessments but had their surgeriescancelled for either medical reasons or personal choice.Of those patients who had their surgeries, the participa-tion rate was 79.5%. There were no differences betweenparticipants and nonparticipants with respect to age orsex.

Patient characteristics are shown in Table 1. Of the 276patients in our study, the majority of patients tended tobe elderly women with osteoarthritis. Sixty-seven percentof patients (n�186) reported unilateral joint involve-ment. Hypertension (39%) and back pain (26%) werethe 2 most commonly reported comorbid conditions.

ProcedureWhen the orthopedic surgeon and patient agreed that aTKA was necessary, the patient’s name was placed on thehealth care region’s joint arthroplasty waiting list. Nameswere retrieved from the joint arthroplasty waiting list ona weekly basis, and patients were contacted to requestparticipation in the study. When the patient agreed toparticipate, in-person interviews were completed within31 days before surgery and 6 months after surgery. Theinitial interview consisted of questions regarding demo-graphic information, joint pain, function and stiffness,HRQL, comorbid conditions, medical status, and ambu-latory status. During the interview, passive range ofmotion for the operated knee was measured with a largestandard universal goniometer with the patient in asupine position. The hip was placed in a comfortableflexed position (degree of hip flexion varied among thepatients), and the maximum amount of knee movement,as tolerated by patient, was measured. The reliability andvalidity of goniometric measurements of the knee havebeen reported by others.18,19 Rothstein and colleagues19

reported the intrarater reliability (r) of knee goniomet-ric measurements in the clinical setting to be .91 to .99,and interrater reliability of knee flexion was slightlylower (r �.88–.97). Assessments were completed by 1 of

3 health care professionals (a physical therapist and 2nurses) who were trained using a standardized studyprotocol and were not involved in the care of anyparticipants. We did not examine the reliability of theirgoniometric measurements.

All patients received a primary TKA and were managedusing a clinical pathway for TKA in an effort to ensurestandardized treatment of medical, pharmaceutical, andrehabilitation care over the 5- to 7-day hospital stay. Animportant part of the clinical pathway was early mobili-zation. The protocol for physical therapy interventionconsisted of commencing basic activities of daily livingwith assistance on postoperative day 1. Active-assistedrange-of-motion exercises were started on postoperativeday 2, after removal of the hemovac. Ambulation,assisted by a physical therapist, was started after post-operative day 1, with weight bearing as tolerated unlessotherwise stated. The discharge goal related to mobilitywas independent and safe ambulation with assistivewalking devices on a level surface between postoperativedays 5 and 7. Patients were discharged home with anexercise program and referral for community therapy asrequired. Only 10 patients (4%) were not seen by aphysical therapist during their hospital stay, and 257patients (93%) were seen by postoperative day 2. Noparticipants had simultaneous bilateral knee arthroplasties.

Standardized medical chart reviews were completed by 2health care professionals. The following surgical andperioperative data were extracted from the medicalcharts: implant fixation (cemented, hybrid, or cement-less), number and type of in-hospital complications(wound infection, dislocation, manipulation underanesthesia, cardiovascular/pulmonary complications,peripheral/central nervous system involvement, urinaryinfection, acute confusion, blood loss requiring transfu-sion after surgery), medical information (diagnosis,height, weight), and preoperative ambulatory status(walking distance and use of assistive walking devices).Rehabilitation received within the community wasretrieved from administrative databases and treated as adichotomous variable.

MeasuresThe interview included a disease-specific questionnaire,the Western Ontario and McMaster Universities(WOMAC) Osteoarthritis Index,20 which is a self-administered health questionnaire designed to measuredisability of the osteoarthritic hip and knee. TheWOMAC provides an aggregate score for each of the 3subscales: joint pain (5 items), physical joint function(17 items), and joint stiffness (2 items). The 5-pointLikert version of this measure was used in our study. Inthe calculation of each of the 3 subscale scores, therange of the subscale score was transformed to a range


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from 0 to 100 points, with a score of 100 indicating nopain or dysfunction. This type of transformation hasbeen used by others to allow an easier comparisonbetween the WOMAC and the Medical Outcomes Study36-Item Short-Form Health Survey (SF-36).21 TheWOMAC is a responsive instrument that yields reliableand valid measurements and that has been extensivelyused to evaluate this patient population.20,21

A multidimensional generic health measure, theSF-36,22–24 was used to measure HRQL. The SF-36 exam-ines 8 health dimensions: physical function, role limita-tion (physical), bodily pain, mental health, emotionalrole function, social functioning, vitality, and generalhealth perception. Scoring for each dimension rangesfrom 0 to 100, with higher scores representing betterhealth. There is no global score; however, 2 componentsummary measures—physical component summary(PCS) and the mental component summary (MCS)—have been derived from the 8 dimensions and standard-ized using norm-based methods. Summary measuresdescribe the overall changes in HRQL, but do notcapture the smaller changes within the specific dimen-sions. Reliability and validity have been extensively eval-uated in a variety of patient populations, includingpeople with total hip and knee arthroplasties andcommunity-dwelling elderly people.21,25–28

The types of comorbid conditions were recorded by thepatient or reported on the medical chart. Comorbiditieswere defined as differing from complications, in thatcoexisting medical conditions are chronic conditionsthat exist before surgical intervention or hospital admis-sion. Only those medical conditions identified at thetime of admission to the hospital were recorded. The list

of 23 comorbid conditions identified by the CharlsonComorbidity Index29 was used. The weighting of severityused with this index was not used in our study becausethe weights were not derived from function. The num-ber of comorbid conditions was treated as a summativescore.

Data AnalysisThe dependent variables, the 6-month function scores ofthe WOMAC and SF-36, were examined as continuousvariables given the normal distributions. Functionalimprovement from the baseline value was defined as a gainof at least 60% of the baseline standard deviation andwas considered a moderate effect.30 This equated toapproximately a 10-point gain (Tab. 2). This definitionposed a potential problem for patients with preoperativescores of 80 or greater because the WOMAC may have aceiling effect. Because the improvement at 6 months wasexpected to be large, the net difference preoperativelyand postoperatively may be artificially low for thosepatients with higher preoperative scores. To compensatefor this effect, we arbitrarily defined those patients withpreoperative scores of 80 or more who maintained a6-month score of at least 80 as having improved. If the6-month score dropped below 80 for those patients, itwas considered as no improvement.

Independent variables consisted of: (1) demographicvariables (age, sex), (2) baseline medical variables (diag-nosis, body mass index (BMI), number of comorbidconditions, previous joint arthroplasty, preoperativequality of life as measured by the SF-36, preoperativejoint function and pain as measured by the WOMAC,preoperative passive range of motion for the knee,preoperative ambulatory status, type of residence and

Table 2.Preoperative and 6-Month Health Statusa

Preoperative Health Status 6-Month Health Status

n X SD n X SD

WOMACPhysical function 275 42.8 17.4 270 70.5 18.2Pain 275 43.4 17.6 271 76.0 19.1Joint stiffness 275 39.7 21.5 271 63.3 22.0

SF-36Physical function 276 21.0 18.1 273 44.8 25.3Bodily pain 276 30.8 17.6 273 53.4 22.8Role–physical 276 12.0 24.7 271 35.2 40.0Social function 276 54.0 27.2 273 72.1 27.7Mental health 276 68.9 19.5 272 75.0 19.0Role–emotion 274 55.2 44.3 271 67.3 40.4Vitality 276 42.0 20.9 272 52.9 22.7Health perception 276 62.1 19.4 273 64.5 19.8Physical component summary 274 25.9 7.5 269 34.6 10.1Mental component summary 269 50.1 11.4 269 52.5 10.8

a Range of scores for both the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index subscales and Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) dimensions was 0 to 100, with better functional status represented by higher scores.


living arrangements), and (3) perioperative variables(the number of in-hospital complications, type ofimplant fixation, waiting times, and length of stay).Rehabilitation received during the 6 months after sur-gery within the community may have had a potentialconfounding effect and was examined.

Univariate linear regression analyses for each of thesevariables were examined on the dependent variables. Allindependent variables that met an initial statistical levelof less than .25 or were considered to be clinicallymeaningful were examined in the multivariate analysis.

Multiple linear regression using stepwise entry withseparate models was developed to examine those signif-icant variables associated with function of the knee andoverall function. Both joint function—as measured bythe WOMAC—and overall function—as measured by theSF-36 physical function dimension—were examinedbecause these measures examined slightly differentaspects of function. The SF-36 physical function exam-ined the overall function that could be influenced byother problems, whereas the WOMAC physical jointfunction measurement specifically examined how theknee affected function.

Stepwise forward model selection techniques were usedto obtain the final models. In addition, because age andsex were considered to be potential confounding vari-ables, they were forced into the final models. Modeldiagnostics, such as residual plots, were inspected toverify that the model assumptions of linearity were notviolated. Finally, multicollinearity was assessed by anexamination of correlation matrixes of all independentvariables.

All statistical testing was performed with 2-tailed testsand at a .05 level of significance unless otherwise stated.Statistical analyses were performed using the SPSS soft-ware version 11.01 for Windows.*

ResultsThe median length of stay in the acute care hospitals was7 days (range�3–20). All procedures for TKA used amedial peripatellar exposure with a midline skin inci-sion. Of the TKA procedures, 157 (58%) were hybrid, 73(27%) were cemented, and 42 (15%) were cementless.The hybrid prosthesis routinely involved a porous coatedfemoral component and a cemented tibial component.Twenty-nine percent of the patients (n�77) receivedpatellar components. Thirty percent of the patellae(n�79) were resurfaced. All patellar components werecemented, all-polyethylene (non–metal-backed)components.

Sixty-seven percent of the patients (n�183) did not havein-hospital complications; however, the primary types ofcomplications were urinary tract infection (n�18) anddeep venous thrombi or emboli (n�13). There were 2deaths due to pulmonary embolism within a month ofdischarge and another death at 3 months that wasunrelated to the knee arthroplasty.

More than half of the patients (n�156 [57%]) weredischarged directly home, and all patients returned tothe community within 6 months after surgery. Thosepatients who were discharged directly home tended tobe younger (mean age�66.2 years, SD�9.0) than thosepatients who were transferred to another facility (meanage�73.3 years, SD�7.9) (P � .001). Patients dischargeddirectly home also had better preoperative WOMACfunction scores (X�45.3, SD�18.0) than the patientswho were transferred to another facility (X�39.4,SD�16.4) (P�.006). A higher proportion of women(53%) than men (27%) were transferred to a rehabili-tation facility (P�.001); however, more women (32%)than men (13%) lived alone (P�.001). Within thecommunity, 129 patients (47%) received communityrehabilitation over the 6 months after their surgery.Forty-six percent of the patients (n�125) walked withoutany assistive devices 6 months after surgery. The meanpassive knee range of motion at 6 months was 99 degrees(SD�14).

Functional Status

WOMAC. The preoperative and 6 month scores of theWOMAC and SF-36 are shown in Table 2. The meanpreoperative physical joint function score reported was42.8 (SD�17.4); however, the 6-month score improved28% to 70.5 (SD�18.2). Despite the improvement, 53(20%) patients did not report an improvement fromtheir preoperative scores; that is, they did not report atleast a 10-point gain. In particular, questions that con-cerned domestic duties and stairs were rated difficult at6 months. Sixty-four percent of the patients (n�165)reported “moderate” to “extreme” difficulty for heavydomestic duties (eg, vacuuming), and 60% (n�160)reported moderate to extreme difficulty descendingstairs.

SF-36 physical function. Overall function as measuredby the SF-36 physical function subscale showed lessimprovement—24%. The mean preoperative score, 21.0(SD�18.1), improved to 44.8 (SD�25.3) at the 6-monthfollow-up; however, 77 patients (28%) did not report atleast a 10-point improvement from their preoperativescores. When matched for age and sex to the general USpopulation, the 6-month score was significantly less thanthe mean score reported for the general population—67.6 (SD�7.5) (P�.002).31 The overall physical compo-

* SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606-6307.


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nent is derived from the physical function, bodily pain,role–physical, and health perception dimensions and isstandardized using norm-based methods. The physicalcomponent score improved almost one standard devia-tion (9 points) from 25.9 (SD�7.5) to 34.6 (SD�10.1).

Multivariate Regression ModelsThe unadjusted regression coefficients of preoperativevariables that were not included in the final multivariatemodels are seen in Table 3. While many domains of theSF-36, BMI, and a diagnosis were significant in theunivariate analysis, they were not significant whenadjusted in the final model. A higher preoperative scoreof the SF-36 (bodily pain, role–physical, social function,mental health, vitality, and health perception), a lowerBMI, and a diagnosis of osteoarthritis rather than asystemic arthritis had an association of higher functionscores (WOMAC and SF-36 physical function).

The results of the multiple linear modeling for predic-tors of 6-month function are presented in Tables 4 and5. No strong correlations (r�.50) were noted betweenindependent variables; therefore, multicollearity did notaffect the regression analyses. Of the variables that metthe level of significance in the univariate analyses, 3variables met the level of significance and were includedin the final multivariate models (Tabs. 4 and 5).

To control for confounding effects, age and sex wereforce entered into both final models of joint functionand overall function. The amount of postoperative reha-bilitation may have had potential confounding effects,but this was not significant either in the preliminaryunivariate analyses or in the multiple linear regressionmodel. Therefore, rehabilitation after surgery was notincluded in the final model.

Preoperative joint function was a predictor of jointfunction (WOMAC) and overall function (SF-36 physicalfunction). This finding can be interpreted by theunstandardized coefficient; a 10-point increase in pre-operative WOMAC physical joint function scores wasassociated with a 3.0-point increase in WOMAC physicaljoint function scores at 6 months (Tab. 4) and with a3.9-point increase in SF-36 physical function scores(Tab. 5). The standardized beta coefficient indicatedthat preoperative joint function was the most influentialvariable in predicting both joint function (as deter-mined by WOMAC joint function scores) and overallfunction (as determined by SF-36 physical functionscores) at 6 months.

The type of walking devices used before surgery was alsoassociated with 6-month function. For instance, a patientwho ambulates independently will have a WOMAC

Table 3.Unadjusted Regression Coefficients Relating Preoperative Variables to 6-Month Physical Function for Both the Western Ontario and McMasterUniversities (WOMAC) Osteoarthritis Index and Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) Physical Function Scores

Baseline Variables

WOMAC Physical Function SF-36 Physical Function

UnstandardizedCoefficient P

UnstandardizedCoefficient P

Diagnosis (osteoarthritis) 12.4 .008 17.66 .007

Body mass index �0.65 �.001 �0.87 .001

Previous joint arthroplasty 2.78 .280 3.95 .269

SF-36 physical function 0.22 �.001 Not evaluatedBodily pain 0.30 �.001 0.47 �.001Role–physical 0.16 �.001 0.24 �.001Social function 0.21 �.001 0.32 �.001Mental health 0.22 �.001 0.27 .001Role–emotion 0.03 .213 0.01 .828Vitality 0.28 �.001 0.43 �.001Health perception 0.27 �.001 0.36 �.001

WOMAC pain 0.29 �.001 0.40 �.001

Knee range of motion 0.07 .328 0.14 .174

Walking distance 4.29 �.001 See Tab. 5

Living alone �2.38 .361 �4.85 .176

No. of in-hospital complications �0.32 .861 �0.03 .989

Implant fixation (cemented) �5.30 .075 2.74 .252

Waiting times �0.01 .531 0.01 .527

Length of stay in acute care setting �1.71 .004 �1.26 .125


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6-month score approximately 12 points higher than thatof a patient who ambulates with a walker before surgery.

Preoperative walking distance was predictive of overallfunction as determined by SF-36 physical function scores(ie, patients who were able to walk longer distancesbefore surgery were more likely to have better overallfunction at 6 months after surgery). Patients who reportthat they are able to walk more than 10 blocks beforesurgery are likely to have a score, that is, 26 points higherthan patients who are unable to ambulate.

Twenty percent of the variance in the 6-month WOMACjoint function scores was explained by age, sex, preop-erative joint function (WOMAC), comorbid conditions,and preoperative walking devices. Age, sex, preoperativewalking devices, walking distance, and joint function(WOMAC) explained 27% of the variance in the SF-36physical function scores.

DiscussionOur results indicate that preoperative joint function is apredictor of function at 6 months after TKA. Thosepatients who had lower preoperative functional statusrelated to knee arthritis functioned at a lower level at 6months than patients with a higher preoperative func-tional status. These findings concur with those of Fortinand colleagues,3 who reported not only that worsepreoperative function resulted in a worse postoperativefunctional status, but that these differences were morepronounced in patients with TKAs than in patients withtotal hip arthroplasties.

The variables in the final models accounted for 20% and27% of the variance seen in the 6-month WOMAC andSF-36 physical function scores, respectively. These vari-ances are comparable to those seen in other studies ofTKA3,16 as well as other studies that have examined riskfactors of total hip arthroplasties.32 We believe that thevariances seen in this study’s models are not unreason-able given the dependent and independent variables.

We believe the relationship between baseline functionand functional outcome has implications related to theissue of waiting times for TKA. Very few studies haveexamined the effect of waiting time on function,33–35 yetit is of interest in the present context. Earlier findings ofthis cohort reported minimal functional deteriorationwith longer waiting times.33 In light of the effect ofpreoperative function, one goal of rehabilitation wouldbe to maximize function while patients wait for surgery.A preoperative exercise program may help so that dete-rioration of function might be minimized while waitingfor surgery. Little quantitative evidence exists regardingthe effect of preoperative exercise programs for kneearthroplasties36–38; however, other researchers39 have

reported that exercise programs can produce pain reliefin patients with knee osteoarthritis. Further investigationmay be warranted given the implications of preoperativefunctional status on functional outcome, particularly forthose patients with poor preoperative function.

The relationship between initial function and functionaloutcome following TKA also has implications for identi-fying those patients who might require further inpatientrehabilitation. With the current trend toward early dis-charge, not all patients are suitable candidates for earlydischarge directly home. Munin and colleagues15

reported that older age, living alone, a greater numberof comorbid conditions, and function were predictive ofinpatient rehabilitation after a total joint arthroplasty.Patients who have lower levels of preoperative functionwill likely need further rehabilitation in addition to thetherapy received in the acute care setting. Althoughlimited research has compared different models of deliv-ery for rehabilitation of joint arthroplasty,40 furtherevidence is needed regarding the specific treatmentprotocols and the most appropriate settings to achievethese treatment goals for patients with high-riskcharacteristics.

Although we did not specifically address effectiveness ofrehabilitation for people with TKAs, we believe a moreproactive treatment plan for patients with poor preop-erative function should be planned before surgery. Atreatment plan may include more intensive physicaltherapy interventions during the 6 months after surgeryregardless of whether it is in a rehabilitation setting or acommunity setting.

Preoperative knee flexion was not a strong predictor for6-month function as may have been expected. Ourfindings, however, suggest that preoperative joint func-tion, comorbid conditions, preoperative walking dis-tance, and walking devices were more predictive offunction at 6 months than preoperative knee flexion.Thirteen percent of the patients (n�33) in our cohorthad less than 90 degrees of knee flexion prior to surgery.A minimum of 90 degrees of knee flexion is typicallyrequired for activities of daily living.41 We believe thatour cohort was representative of patients with TKA andreflected the preoperative knee range of motion seen inthis patient population because it was a community-based cohort, not restricted to one surgeon or center.Although these results did not show a significant rela-tionship between preoperative knee flexion and6-month functional status, we believe the measurementof knee flexion may be more informative to the therapistpostoperatively than preoperatively.

The 6-month follow-up used in this study could be seenas a limitation. We feel that the 6-month follow-up was


appropriate, given the objective of our study and sup-porting evidence from previous literature of pain andfunctional recovery after total joint arthroplasty. Thegreatest change with pain and function occurs duringthe first 3 to 6 months after surgery,9,42,43 with moregradual improvement occurring over 2 years.9,43 Alonger follow-up would provide information about thesuccess of the prosthesis, but we believe it most likelywould not change the functional outcomes we observedin our study. From a clinical perspective, evaluation overthe 6 months after surgery provides valuable practicalinformation to assist the therapists with management ofthe patient during the recovery phase.

Another limitation of our study concerns the accuracy ofself-report measurement of function. Both joint functionand overall function were evaluated with self-reportassessments. No performance-based functional measureswere used. Some authors44 have reported discrepanciesbetween self-report and performance-based measures ofactivities of daily living during hospitalizations whenfunctional status was changing. We feel that informationgained from self-report assessment of function for ourstudy was valid because function was assessed duringstable times (ie, within a month before surgery and 6months after surgery).

ConclusionDespite these limitations, findings from this study, alongwith others,3 present persuasive evidence that patientswith greater dysfunction prior to surgery will not attaincomparable functional outcomes as those patients withless preoperative dysfunction. Those patients who havelow preoperative function may require supplementalrehabilitation while waiting for surgery and furtherrehabilitation after discharge from the acute caresetting.

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