1. Research Report
Determinants of Function After
Total Knee Arthroplasty
Background and Purpose. Decreasing hospital stays for patients with
total 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 from
hospitals. The purpose of this study was to identify preoperative
determinants of functional status after a TKA. Participants. Using a
community-based, prospective cohort study, data were collected from
276 patients who received a primary TKA in a Canadian health care
region. Data were collected in the month before surgery and 6 months
after surgery. Methods. Function was measured using the function
subscale of a disease-specific measure—the Western Ontario and
McMaster Universities (WOMAC) Osteoarthritis Index—and a generic
health status measure—the Medical Outcomes Study 36-Item Short-
Form Health Survey (SF-36). Independent variables examined
included 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 knee
range of motion. Results. At 6 months after surgery, the average
WOMAC physical function score was 70.5 (SD 18.2) and the average
SF-36 physical function score was 44.8 (SD 25.3). Using multiple
regression 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 and
Conclusions. Patients who have lower preoperative function may
require more intensive physical therapy intervention because they are
less likely to achieve similar functional outcomes similar to those of
patients who have less preoperative dysfunction. [Jones CA, Voak-
lander DC, Suarez-Almazor ME. Determinants of function after total
knee 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

2. T
he utilization rates of elective total knee arthro- This meta-analysis showed that 89.3% of patients
plasties (TKAs) are steadily increasing with an reported good to excellent results at an average
aging population.1 Moreover, the trend toward follow-up period of 4.1 years. The mean improvement in
earlier hospital discharge after TKA has meant range of motion in those studies in which preoperative
that patients are returning home during a more acute and postoperative range of motion of the knee was
phase of recovery. These 2 factors have had direct measured was 8 degrees.4
implications for the rehabilitation of patients with TKA.
Although the improvements following TKA can be dra-
Elective TKA is, more often than not, the last effort in matic, the gains are typically less than the changes
managing joint pain and dysfunction caused by arthritis. reported by patients who have had a total hip arthro-
Extensive evidence indicates that the majority of patients plasty.5,9 –11 Long-term “technical failures” requiring revi-
who have had a TKA report improvement in pain and sion of the prosthesis (eg, loosening, fracture, or infec-
function.2– 4 Eighty-five percent to 90% of patients with tion) are low (less than 10% over 10 years),4,12 yet the
TKA report pain relief after surgery, and 70% to 80% lack of improvement is usually related to continuing
report functional improvement.4,5 The greatest amount pain and poor function. Approximately 15% to 30% of
of improvement is seen within 3 to 6 months after patients receiving TKA report little or no improvement
surgery, with more gradual improvements occurring up after surgery or are unsatisfied with the results after a few
to 2 years after surgery.6 – 8 A meta-analysis of 130 studies4 months.5,13,14
indicated that these favorable results continue over time.
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 (ajones@pharmacy.ualberta.ca). 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-Almazor
provided project management, fund procurement, institutional liaisons, and consultation (including review of manuscript before submission). Dr
Suarez-Almazor provided facilities/equipment and clerical support. The authors thank Dr Karen Kelly and Sue Barrett for their assistance
throughout the study, as well as Lauren Beaupre and Dr DWC Johnston for their clinical expertise. They also are grateful to Dr Lynn Redfern and
´
Gordon 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 the
Caritas Health Group).
This research was supported by grants from the Capital Health Authority Research and Grant Fund and the Edmonton Orthopaedic Research
Trust. Dr Suarez-Almazor was supported by The Arthritis Society of Canada and the Alberta Heritage Foundation for Medical Research. Dr Jones
was supported, in part, by the Canadian Physiotherapy Foundation, the Royal Canadian Legion, and the Alberta Heritage Foundation for Medical
Research.
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

3. Table 1. after TKA, accounting for 15% of the
Participant Characteristics variance. To date, no clear predictors
of functional recovery have been con-
Characteristic n % X SD sistently reported in the literature.
Demographics (n 276)
Age (y) 69.2 9.2 Given the shortened length of stay in
Female 162 59 acute care hospitals for patients with
Living alone 67 24 TKA, we believe that it is important
Medical status for the physical therapist to identify
Osteoarthritis (n 273) 257 94 those patient-related factors that will
Previous arthroplasty (n 276) 68 25
Comorbid conditions (n 276) 3.5 2.0
affect functional independence. If
Body mass index (kg/m2) (n 276) 31.6 5.9 modifiable determinants of function
Preoperative walking distance (n 253)
could then be identified, patients
Indoors 19 7 who require additional interventions
1 block 67 27 during their recovery could be readily
1–5 blocks 124 49 identified. The primary objective of
6–10 blocks 22 9 our study was to identify those demo-
Unlimited 21 8
graphic, medical, and clinical factors
Preoperative assistive walking devices (n 256) available to physical therapists that
None 158 62
Cane 86 33
predict function at 6 months after
Walker 12 5 surgery. A 6-month follow-up time
Preoperative knee range of motion (°) (n 259) 106 15
was selected because studies6 – 8 have
shown that the greatest change in
Surgical
Implant fixation (n 272)
pain and function occurs during the
Cementless 44 16 first 3 to 6 months after surgery.
Hybrid 156 57 Moreover, we contend that short-
Cemented 72 27 term evaluation can provide useful
In-hospital complications (n 272) information on patient recovery and
None 183 67 may highlight the need for further
Health services utilization (n 276) therapy to augment recovery. This
Hospital length of stay (d) 6.8 2 study was part of a larger study that
Discharge directly home (n 272) 156 57 examined the effect of waiting times
Rehabilitation facility length of stay (d) 9.3 3.3
Community therapy 129 47
for hip and knee arthroplasties on the
subsequent health-related quality of
life (HRQL) after this surgery.5,17
For the physical therapist, rehabilitation of patients with Method
TKA is often a challenge. One of the primary issues in
treating patients with TKA is identifying those patients Participants
who may require extensive rehabilitation. For those Our study was a prospective, longitudinal study of an
high-risk patients, early rehabilitation is thought to pro- inception cohort of surgical candidates who received
vide a benefit.15 Although much of the published clinical TKA in a Canadian health care region, Capital Health. A
work has focused on recovery, little evidence exists on health care region is a geographical area administered
determinants of recovery from TKA. One group of by a regional health authority. Patients in this study were
researchers3 concluded that baseline pain and function selected based on time of placement on the regional
(ie, pain and function on date of decision to proceed joint arthroplasty waiting list rather than on the time of
with surgery) were the single best predictors of func- surgery. Waiting time for a TKA ranged from 7 to 487
tional recovery at 6 months. Fortin and colleagues3 days, with a median wait of 78 days. All patients had
surmised that patients who reported greater pain and surgery between February 1996 and February 1998.
dysfunction prior to surgery were more likely to have Patients were eligible for this study if they: (1) were
more pain and dysfunction after surgery than patients scheduled for elective primary TKA, (2) were placed on
who had less pain and dysfunction. In a prospective the joint arthroplasty waiting list at least 7 days before
cohort study,16 psychosocial factors such as motivation surgery (which would help to ensure that emergency
and social function were more influential than medical surgeries were excluded), (3) resided in the health
factors or initial function in predicting 3-month function region, (4) were 40 years of age or older, and (5) spoke
698 . Jones et al Physical Therapy . Volume 83 . Number 8 . August 2003

4. English. Exclusion criteria included hemiarthroplasties 3 health care professionals (a physical therapist and 2
and revision and emergency arthroplasties. nurses) who were trained using a standardized study
protocol and were not involved in the care of any
Patients who resided in long-term care institutions participants. We did not examine the reliability of their
before being placed in the joint replacement waiting list goniometric measurements.
also were excluded. Rarely is any elective joint arthro-
plasty performed in patients from long-term care facili- All patients received a primary TKA and were managed
ties. We felt that patients from long-term facilities rep- using a clinical pathway for TKA in an effort to ensure
resent a small unique group of this patient population standardized treatment of medical, pharmaceutical, and
and are atypical of patients who receive elective knee rehabilitation care over the 5- to 7-day hospital stay. An
arthroplasty. After meeting the selection criteria and important part of the clinical pathway was early mobili-
agreeing to participate, each patient signed a consent zation. The protocol for physical therapy intervention
form before participating in the study. consisted of commencing basic activities of daily living
with assistance on postoperative day 1. Active-assisted
Of the 377 patients eligible to participate in the study, 53 range-of-motion exercises were started on postoperative
(14%) refused to participate, and 18 (5%) were lost to day 2, after removal of the hemovac. Ambulation,
follow-up. Another 30 patients (8%) had completed assisted by a physical therapist, was started after post-
their preoperative assessments but had their surgeries operative day 1, with weight bearing as tolerated unless
cancelled for either medical reasons or personal choice. otherwise stated. The discharge goal related to mobility
Of those patients who had their surgeries, the participa- was independent and safe ambulation with assistive
tion rate was 79.5%. There were no differences between walking devices on a level surface between postoperative
participants and nonparticipants with respect to age or days 5 and 7. Patients were discharged home with an
sex. exercise program and referral for community therapy as
required. Only 10 patients (4%) were not seen by a
Patient characteristics are shown in Table 1. Of the 276 physical therapist during their hospital stay, and 257
patients in our study, the majority of patients tended to patients (93%) were seen by postoperative day 2. No
be elderly women with osteoarthritis. Sixty-seven percent participants had simultaneous bilateral knee arthroplasties.
of patients (n 186) reported unilateral joint involve-
ment. Hypertension (39%) and back pain (26%) were Standardized medical chart reviews were completed by 2
the 2 most commonly reported comorbid conditions. health care professionals. The following surgical and
perioperative data were extracted from the medical
Procedure charts: implant fixation (cemented, hybrid, or cement-
When the orthopedic surgeon and patient agreed that a less), number and type of in-hospital complications
TKA was necessary, the patient’s name was placed on the (wound infection, dislocation, manipulation under
health care region’s joint arthroplasty waiting list. Names anesthesia, cardiovascular/pulmonary complications,
were retrieved from the joint arthroplasty waiting list on peripheral/central nervous system involvement, urinary
a weekly basis, and patients were contacted to request infection, acute confusion, blood loss requiring transfu-
participation in the study. When the patient agreed to sion after surgery), medical information (diagnosis,
participate, in-person interviews were completed within height, weight), and preoperative ambulatory status
31 days before surgery and 6 months after surgery. The (walking distance and use of assistive walking devices).
initial interview consisted of questions regarding demo- Rehabilitation received within the community was
graphic information, joint pain, function and stiffness, retrieved from administrative databases and treated as a
HRQL, comorbid conditions, medical status, and ambu- dichotomous variable.
latory status. During the interview, passive range of
motion for the operated knee was measured with a large Measures
standard universal goniometer with the patient in a The interview included a disease-specific questionnaire,
supine position. The hip was placed in a comfortable the Western Ontario and McMaster Universities
flexed position (degree of hip flexion varied among the (WOMAC) Osteoarthritis Index,20 which is a self-
patients), and the maximum amount of knee movement, administered health questionnaire designed to measure
as tolerated by patient, was measured. The reliability and disability of the osteoarthritic hip and knee. The
validity of goniometric measurements of the knee have WOMAC provides an aggregate score for each of the 3
been reported by others.18,19 Rothstein and colleagues19 subscales: joint pain (5 items), physical joint function
reported the intrarater reliability (r) of knee goniomet- (17 items), and joint stiffness (2 items). The 5-point
ric measurements in the clinical setting to be .91 to .99, Likert version of this measure was used in our study. In
and interrater reliability of knee flexion was slightly the calculation of each of the 3 subscale scores, the
lower (r .88 –.97). Assessments were completed by 1 of range of the subscale score was transformed to a range
Physical Therapy . Volume 83 . Number 8 . August 2003 Jones et al . 699

5. Table 2.
Preoperative and 6-Month Health Statusa
Preoperative Health Status 6-Month Health Status
n X SD n X SD
WOMAC
Physical function 275 42.8 17.4 270 70.5 18.2
Pain 275 43.4 17.6 271 76.0 19.1
Joint stiffness 275 39.7 21.5 271 63.3 22.0
SF-36
Physical function 276 21.0 18.1 273 44.8 25.3
Bodily pain 276 30.8 17.6 273 53.4 22.8
Role–physical 276 12.0 24.7 271 35.2 40.0
Social function 276 54.0 27.2 273 72.1 27.7
Mental health 276 68.9 19.5 272 75.0 19.0
Role–emotion 274 55.2 44.3 271 67.3 40.4
Vitality 276 42.0 20.9 272 52.9 22.7
Health perception 276 62.1 19.4 273 64.5 19.8
Physical component summary 274 25.9 7.5 269 34.6 10.1
Mental 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.
from 0 to 100 points, with a score of 100 indicating no of 23 comorbid conditions identified by the Charlson
pain or dysfunction. This type of transformation has Comorbidity Index29 was used. The weighting of severity
been used by others to allow an easier comparison used with this index was not used in our study because
between the WOMAC and the Medical Outcomes Study the weights were not derived from function. The num-
36-Item Short-Form Health Survey (SF-36).21 The ber of comorbid conditions was treated as a summative
WOMAC is a responsive instrument that yields reliable score.
and valid measurements and that has been extensively
used to evaluate this patient population.20,21 Data Analysis
The dependent variables, the 6-month function scores of
A multidimensional generic health measure, the the WOMAC and SF-36, were examined as continuous
SF-36,22–24 was used to measure HRQL. The SF-36 exam- variables given the normal distributions. Functional
ines 8 health dimensions: physical function, role limita- improvement from the baseline value was defined as a gain
tion (physical), bodily pain, mental health, emotional of at least 60% of the baseline standard deviation and
role function, social functioning, vitality, and general was considered a moderate effect.30 This equated to
health perception. Scoring for each dimension ranges approximately a 10-point gain (Tab. 2). This definition
from 0 to 100, with higher scores representing better posed a potential problem for patients with preoperative
health. There is no global score; however, 2 component scores of 80 or greater because the WOMAC may have a
summary measures—physical component summary ceiling effect. Because the improvement at 6 months was
(PCS) and the mental component summary (MCS)— expected to be large, the net difference preoperatively
have been derived from the 8 dimensions and standard- and postoperatively may be artificially low for those
ized using norm-based methods. Summary measures patients with higher preoperative scores. To compensate
describe the overall changes in HRQL, but do not for this effect, we arbitrarily defined those patients with
capture the smaller changes within the specific dimen- preoperative scores of 80 or more who maintained a
sions. Reliability and validity have been extensively eval- 6-month score of at least 80 as having improved. If the
uated in a variety of patient populations, including 6-month score dropped below 80 for those patients, it
people with total hip and knee arthroplasties and was considered as no improvement.
community-dwelling elderly people.21,25–28
Independent variables consisted of: (1) demographic
The types of comorbid conditions were recorded by the variables (age, sex), (2) baseline medical variables (diag-
patient or reported on the medical chart. Comorbidities nosis, body mass index (BMI), number of comorbid
were defined as differing from complications, in that conditions, previous joint arthroplasty, preoperative
coexisting medical conditions are chronic conditions quality of life as measured by the SF-36, preoperative
that exist before surgical intervention or hospital admis- joint function and pain as measured by the WOMAC,
sion. Only those medical conditions identified at the preoperative passive range of motion for the knee,
time of admission to the hospital were recorded. The list preoperative ambulatory status, type of residence and
700 . Jones et al Physical Therapy . Volume 83 . Number 8 . August 2003

6. living arrangements), and (3) perioperative variables Sixty-seven percent of the patients (n 183) did not have
(the number of in-hospital complications, type of in-hospital complications; however, the primary types of
implant fixation, waiting times, and length of stay). complications were urinary tract infection (n 18) and
Rehabilitation received during the 6 months after sur- deep venous thrombi or emboli (n 13). There were 2
gery within the community may have had a potential deaths due to pulmonary embolism within a month of
confounding effect and was examined. discharge and another death at 3 months that was
unrelated to the knee arthroplasty.
Univariate linear regression analyses for each of these
variables were examined on the dependent variables. All More than half of the patients (n 156 [57%]) were
independent variables that met an initial statistical level discharged directly home, and all patients returned to
of less than .25 or were considered to be clinically the community within 6 months after surgery. Those
meaningful were examined in the multivariate analysis. patients who were discharged directly home tended to
be younger (mean age 66.2 years, SD 9.0) than those
Multiple linear regression using stepwise entry with patients who were transferred to another facility (mean
separate models was developed to examine those signif- age 73.3 years, SD 7.9) (P .001). Patients discharged
icant variables associated with function of the knee and directly home also had better preoperative WOMAC
overall function. Both joint function—as measured by function scores (X 45.3, SD 18.0) than the patients
the WOMAC—and overall function—as measured by the who were transferred to another facility (X 39.4,
SF-36 physical function dimension—were examined SD 16.4) (P .006). A higher proportion of women
because these measures examined slightly different (53%) than men (27%) were transferred to a rehabili-
aspects of function. The SF-36 physical function exam- tation facility (P .001); however, more women (32%)
ined the overall function that could be influenced by than men (13%) lived alone (P .001). Within the
other problems, whereas the WOMAC physical joint community, 129 patients (47%) received community
function measurement specifically examined how the rehabilitation over the 6 months after their surgery.
knee affected function. Forty-six percent of the patients (n 125) walked without
any assistive devices 6 months after surgery. The mean
Stepwise forward model selection techniques were used passive knee range of motion at 6 months was 99 degrees
to obtain the final models. In addition, because age and (SD 14).
sex were considered to be potential confounding vari-
ables, they were forced into the final models. Model Functional Status
diagnostics, such as residual plots, were inspected to
verify that the model assumptions of linearity were not WOMAC. The preoperative and 6 month scores of the
violated. Finally, multicollinearity was assessed by an WOMAC and SF-36 are shown in Table 2. The mean
examination of correlation matrixes of all independent preoperative physical joint function score reported was
variables. 42.8 (SD 17.4); however, the 6-month score improved
28% to 70.5 (SD 18.2). Despite the improvement, 53
All statistical testing was performed with 2-tailed tests (20%) patients did not report an improvement from
and at a .05 level of significance unless otherwise stated. their preoperative scores; that is, they did not report at
Statistical analyses were performed using the SPSS soft- least a 10-point gain. In particular, questions that con-
ware version 11.01 for Windows.* cerned domestic duties and stairs were rated difficult at
6 months. Sixty-four percent of the patients (n 165)
Results reported “moderate” to “extreme” difficulty for heavy
The median length of stay in the acute care hospitals was domestic duties (eg, vacuuming), and 60% (n 160)
7 days (range 3–20). All procedures for TKA used a reported moderate to extreme difficulty descending
medial peripatellar exposure with a midline skin inci- stairs.
sion. Of the TKA procedures, 157 (58%) were hybrid, 73
(27%) were cemented, and 42 (15%) were cementless. SF-36 physical function. Overall function as measured
The hybrid prosthesis routinely involved a porous coated by the SF-36 physical function subscale showed less
femoral component and a cemented tibial component. improvement—24%. The mean preoperative score, 21.0
Twenty-nine percent of the patients (n 77) received (SD 18.1), improved to 44.8 (SD 25.3) at the 6-month
patellar components. Thirty percent of the patellae follow-up; however, 77 patients (28%) did not report at
(n 79) were resurfaced. All patellar components were least a 10-point improvement from their preoperative
cemented, all-polyethylene (non–metal-backed) scores. When matched for age and sex to the general US
components. population, the 6-month score was significantly less than
the 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.
Physical Therapy . Volume 83 . Number 8 . August 2003 Jones et al . 701

7. Table 3.
Unadjusted Regression Coefficients Relating Preoperative Variables to 6-Month Physical Function for Both the Western Ontario and McMaster
Universities (WOMAC) Osteoarthritis Index and Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) Physical Function Scores
WOMAC Physical Function SF-36 Physical Function
Unstandardized Unstandardized
Baseline Variables Coefficient P Coefficient 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 evaluated
Bodily pain 0.30 .001 0.47 .001
Role–physical 0.16 .001 0.24 .001
Social function 0.21 .001 0.32 .001
Mental health 0.22 .001 0.27 .001
Role–emotion 0.03 .213 0.01 .828
Vitality 0.28 .001 0.43 .001
Health 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
nent is derived from the physical function, bodily pain, To control for confounding effects, age and sex were
role–physical, and health perception dimensions and is force entered into both final models of joint function
standardized using norm-based methods. The physical and overall function. The amount of postoperative reha-
component score improved almost one standard devia- bilitation may have had potential confounding effects,
tion (9 points) from 25.9 (SD 7.5) to 34.6 (SD 10.1). but this was not significant either in the preliminary
univariate analyses or in the multiple linear regression
Multivariate Regression Models model. Therefore, rehabilitation after surgery was not
The unadjusted regression coefficients of preoperative included in the final model.
variables that were not included in the final multivariate
models are seen in Table 3. While many domains of the Preoperative joint function was a predictor of joint
SF-36, BMI, and a diagnosis were significant in the function (WOMAC) and overall function (SF-36 physical
univariate analysis, they were not significant when function). This finding can be interpreted by the
adjusted in the final model. A higher preoperative score unstandardized coefficient; a 10-point increase in pre-
of the SF-36 (bodily pain, role–physical, social function, operative WOMAC physical joint function scores was
mental health, vitality, and health perception), a lower associated with a 3.0-point increase in WOMAC physical
BMI, and a diagnosis of osteoarthritis rather than a joint function scores at 6 months (Tab. 4) and with a
systemic arthritis had an association of higher function 3.9-point increase in SF-36 physical function scores
scores (WOMAC and SF-36 physical function). (Tab. 5). The standardized beta coefficient indicated
that preoperative joint function was the most influential
The results of the multiple linear modeling for predic- variable in predicting both joint function (as deter-
tors of 6-month function are presented in Tables 4 and mined by WOMAC joint function scores) and overall
5. No strong correlations (r .50) were noted between function (as determined by SF-36 physical function
independent variables; therefore, multicollearity did not scores) at 6 months.
affect the regression analyses. Of the variables that met
the level of significance in the univariate analyses, 3 The type of walking devices used before surgery was also
variables met the level of significance and were included associated with 6-month function. For instance, a patient
in the final multivariate models (Tabs. 4 and 5). who ambulates independently will have a WOMAC
702 . Jones et al Physical Therapy . Volume 83 . Number 8 . August 2003

8. Table 4.
Multiple Linear Regression: Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index Function at 6 Months
Unadjusted Adjusted (R2 .20)
Unstandardized Standardized Unstandardized Standardized Partial
Variable Coefficient Coefficient CIa P Coefficient Coefficient r CI P
Intercept 41.59 (24.14, 59.05) .001b
Age 0.21 0.11 ( 0.03, 0.45) .08 0.35 0.18 .18 (0.10, 0.60) .005
Female 4.73 0.13 ( 9.15, 0.31) .04 0.26 0.01 .01 ( 4.85, 4.32) .91
Preoperative joint
function (WOMAC) 0.39 0.36 (0.27, 0.51) .001b 0.30 0.28 .28 (0.16, 0.43) .001b
Comorbid conditions 1.89 0.21 ( 2.98, 0.80) .001b 1.62 0.18 .19 ( 2.75, 0.49) .005b
Preoperative walking
devices 4.98 0.21 ( 7.94, 2.02) .001b 4.15 0.17 .17 ( 7.23, 1.06) .009b
a
CI 95% confidence interval.
b
Physical Therapy . Volume 83 . Number 8 . August 2003
Statistically significant at P .05.
Table 5.
Multiple Linear Regression: Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) Physical Function at 6 Months
Unadjusted Adjusted (R2 .27)
Unstandardized Standardized Unstandardized Standardized Partial
Variable Coefficient Coefficient CIa P Coefficient Coefficient r CI P
Intercept 5.51 ( 31.67, 20.65) .68
Age 0.07 0.03 ( 0.26, 0.40) .67 0.26 0.09 0.01 ( 0.06, 0.58) .12
b
Female 10.31 0.20 ( 16.34, 4.28) .001 2.63 0.05 0.19 ( 8.65, 3.40) .39
Preoperative joint
function (WOMAC)c 0.59 0.40 (0.43, 0.76) .001b 0.39 0.27 0.41 (0.21, 0.58) .001b
Preoperative walking
distance 9.28 0.36 (6.28, 12.27) .001b 5.29 0.21 0.38 (2.02, 8.57) .002b
Preoperative walking
devices 10.68 0.32 ( 14.64, 6.72) .001b 6.78 0.20 0.33 ( 10.99, 2.57) .002b
a
CI 95% confidence interval.
b
Statistically significant at P .05.
c
WOMAC Western Ontario and McMaster Universities Osteoarthritis Index.
Jones et al . 703

9. 6-month score approximately 12 points higher than that reported that exercise programs can produce pain relief
of a patient who ambulates with a walker before surgery. in patients with knee osteoarthritis. Further investigation
may be warranted given the implications of preoperative
Preoperative walking distance was predictive of overall functional status on functional outcome, particularly for
function as determined by SF-36 physical function scores those patients with poor preoperative function.
(ie, patients who were able to walk longer distances
before surgery were more likely to have better overall The relationship between initial function and functional
function at 6 months after surgery). Patients who report outcome following TKA also has implications for identi-
that they are able to walk more than 10 blocks before fying those patients who might require further inpatient
surgery are likely to have a score, that is, 26 points higher rehabilitation. With the current trend toward early dis-
than patients who are unable to ambulate. charge, not all patients are suitable candidates for early
discharge directly home. Munin and colleagues15
Twenty percent of the variance in the 6-month WOMAC reported that older age, living alone, a greater number
joint function scores was explained by age, sex, preop- of comorbid conditions, and function were predictive of
erative joint function (WOMAC), comorbid conditions, inpatient rehabilitation after a total joint arthroplasty.
and preoperative walking devices. Age, sex, preoperative Patients who have lower levels of preoperative function
walking devices, walking distance, and joint function will likely need further rehabilitation in addition to the
(WOMAC) explained 27% of the variance in the SF-36 therapy received in the acute care setting. Although
physical function scores. limited research has compared different models of deliv-
ery for rehabilitation of joint arthroplasty,40 further
Discussion evidence is needed regarding the specific treatment
Our results indicate that preoperative joint function is a protocols and the most appropriate settings to achieve
predictor of function at 6 months after TKA. Those these treatment goals for patients with high-risk
patients who had lower preoperative functional status characteristics.
related to knee arthritis functioned at a lower level at 6
months than patients with a higher preoperative func- Although we did not specifically address effectiveness of
tional status. These findings concur with those of Fortin rehabilitation for people with TKAs, we believe a more
and colleagues,3 who reported not only that worse proactive treatment plan for patients with poor preop-
preoperative function resulted in a worse postoperative erative function should be planned before surgery. A
functional status, but that these differences were more treatment plan may include more intensive physical
pronounced in patients with TKAs than in patients with therapy interventions during the 6 months after surgery
total hip arthroplasties. regardless of whether it is in a rehabilitation setting or a
community setting.
The variables in the final models accounted for 20% and
27% of the variance seen in the 6-month WOMAC and Preoperative knee flexion was not a strong predictor for
SF-36 physical function scores, respectively. These vari- 6-month function as may have been expected. Our
ances are comparable to those seen in other studies of findings, however, suggest that preoperative joint func-
TKA3,16 as well as other studies that have examined risk tion, comorbid conditions, preoperative walking dis-
factors of total hip arthroplasties.32 We believe that the tance, and walking devices were more predictive of
variances seen in this study’s models are not unreason- function at 6 months than preoperative knee flexion.
able given the dependent and independent variables. Thirteen percent of the patients (n 33) in our cohort
had less than 90 degrees of knee flexion prior to surgery.
We believe the relationship between baseline function A minimum of 90 degrees of knee flexion is typically
and functional outcome has implications related to the required for activities of daily living.41 We believe that
issue of waiting times for TKA. Very few studies have our cohort was representative of patients with TKA and
examined the effect of waiting time on function,33–35 yet reflected the preoperative knee range of motion seen in
it is of interest in the present context. Earlier findings of this patient population because it was a community-
this cohort reported minimal functional deterioration based cohort, not restricted to one surgeon or center.
with longer waiting times.33 In light of the effect of Although these results did not show a significant rela-
preoperative function, one goal of rehabilitation would tionship between preoperative knee flexion and
be to maximize function while patients wait for surgery. 6-month functional status, we believe the measurement
A preoperative exercise program may help so that dete- of knee flexion may be more informative to the therapist
rioration of function might be minimized while waiting postoperatively than preoperatively.
for surgery. Little quantitative evidence exists regarding
the effect of preoperative exercise programs for knee The 6-month follow-up used in this study could be seen
arthroplasties36 –38; however, other researchers39 have as a limitation. We feel that the 6-month follow-up was
704 . Jones et al Physical Therapy . Volume 83 . Number 8 . August 2003

10. appropriate, given the objective of our study and sup- 6 Kirwan JR, Currey HL, Freeman MA, et al. Overall long-term impact
porting evidence from previous literature of pain and of total hip and knee joint replacement surgery on patients with
osteoarthritis and rheumatoid arthritis. Br J Rheumatol. 1994;33:
functional recovery after total joint arthroplasty. The
357–360.
greatest change with pain and function occurs during
the first 3 to 6 months after surgery,9,42,43 with more 7 van Essen GJ, Chipchase LS, O’Connor D, Krishnan J. Primary total
knee replacement: short-term outcomes in an Australian population.
gradual improvement occurring over 2 years.9,43 A J Qual Clin Pract. 1998;18:135–142.
longer follow-up would provide information about the
8 Aarons H, Hall G, Hughes S, Salmon P. Short-term recovery from hip
success of the prosthesis, but we believe it most likely
and knee arthroplasty. J Bone Joint Surg Br. 1996;78:555–558.
would not change the functional outcomes we observed
in our study. From a clinical perspective, evaluation over 9 Rissanen P, Aro S, Sintonen H, et al. Quality of life and functional
ability in hip and knee replacements: a prospective study. Qual Life Res.
the 6 months after surgery provides valuable practical 1996;5:56 – 64.
information to assist the therapists with management of
10 Ritter MA, Albohm MJ, Keating EM, et al. Comparative outcomes of
the patient during the recovery phase.
total joint arthroplasty. J Arthroplasty. 1995;10:737–741.
Another limitation of our study concerns the accuracy of 11 Salmon P, Hall GM, Peerbhoy D, et al. Recovery from hip and knee
arthroplasty: patients’ perspective on pain, function, quality of life, and
self-report measurement of function. Both joint function well-being up to 6 months postoperatively. Arch Phys Med Rehabil.
and overall function were evaluated with self-report 2001;82:360 –366.
assessments. No performance-based functional measures
12 Rorabeck CH. Mechanisms of knee implant failure. Orthopedics.
were used. Some authors44 have reported discrepancies 1995;18:915–918.
between self-report and performance-based measures of
13 Mancuso CA, Salvati EA, Johanson NA, et al. Patients’ expectations
activities of daily living during hospitalizations when and satisfaction with total hip arthroplasty. J Arthroplasty. 1997;12:
functional status was changing. We feel that information 387–396.
gained from self-report assessment of function for our 14 Dickstein R, Heffes Y, Shabtai EI, Markowitz E. Total knee arthro-
study was valid because function was assessed during plasty in the elderly: patients’ self-appraisal 6 and 12 months postop-
stable times (ie, within a month before surgery and 6 eratively. Gerontology. 1998;44:204 –210.
months after surgery). 15 Munin MC, Kwoh CK, Glynn N, et al. Predicting discharge outcome
after elective hip and knee arthroplasty [published erratum appears in
Conclusion Am J Phys Med Rehabil, 1995:74(6), following table of contents]. Am J
Despite these limitations, findings from this study, along Phys Med Rehabil. 1995;74:294 –301.
with others,3 present persuasive evidence that patients 16 Sharma L, Sinacore J, Daugherty C, et al. Prognostic factors for
with greater dysfunction prior to surgery will not attain functional outcome of total knee replacement: a prospective study.
comparable functional outcomes as those patients with J Gerontol A Biol Sci Med Sci. 1996;51:M152–M157.
less preoperative dysfunction. Those patients who have 17 Kelly KD, Voaklander D, Kramer G, et al. The impact of health
low preoperative function may require supplemental status on waiting time for major joint arthroplasty. J Arthroplasty.
rehabilitation while waiting for surgery and further 2000;15:877– 883.
rehabilitation after discharge from the acute care 18 Gogia PP, Braatz JH, Rose SJ, Norton BJ. Reliability and validity of
setting. goniometric measurements at the knee. Phys Ther. 1987;67:192–195.
19 Rothstein JM, Miller PJ, Roettger RF. Goniometric reliability in a
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