Chapitre 3 Article

Table des matières



Madeleine Denis, PT1,2,3, Hélène Moffet, PT, PhD2,3, France Caron, PT1, Denise Ouellet, PT, MSc4, Julien Paquet, MD1, Lucie Nolet,BSc, Head nurse1

1 CHUQ-Hôtel-Dieu de Québec

2 Centre interdisciplinaire de recherche en réadaptation et intégration sociale (CIRRIS)

3 Université Laval

4 CHUQ-Saint-François d'Assise

This paper has been submitted to "Physical Therapy", Journal of the American Physical Therapy Association.

L'objectif de cet essai clinique randomisé était de comparer l’efficacité de trois programmes de réadaptation post-opératoire, avec ou sans mobilisation passive continue (CPM) chez des patients souffrant d'arthrose ayant subi une arthroplastie du genou (AG) primaire. Quatre-vingt-un patients ont été randomisés dans 3 groupes: 1) physiothérapie usuelle sans CPM, 2) physiothérapie usuelle avec CPM 35 minutes par jour, 3) physiothérapie usuelle avec CPM 2 heures par jour. Deux évaluations ont été réalisées: la première avant l'AG et la seconde 7-8 jours après l'AG, au départ de l'hôpital. La mesure principale était la flexion active maximale du genou après l'AG. Les mesures secondaires étaient l'extension active du genou, le questionnaire WOMAC, le "Timed up and go" et la durée du séjour hospitalier. Les trois groupes étaient comparables avant l'AG. Sept à 8 jours après l'AG, aucune différence significative n’a été mise en évidence dans la mesure principale et les mesures secondaires. Les résultats de cet essai clinique ne supportent pas l'utilisation du CPM en phase post-opératoire après une AG primaire puisque l’ajout d’applications de CPM à une intervention usuelle de physiothérapie ne favorise pas une meilleure mobilité du genou, une meilleure habileté fonctionnelle et ne contribue pas davantage à réduire la durée du séjour hospitalier.

This randomized clinical trial was conducted to compare the efficacy of three in-hospital rehabilitation programs with and without continuous passive motion (CPM) on knee flexion, functional ability and length of stay after a primary total knee arthroplasty (TKA). Eighty-one patients who underwent a TKA for a diagnosis of osteoarthritis were randomly assigned to three groups immediately after TKA: 1) control group (CTL): conventional physical therapy (PT) intervention only; 2) experimental group 1 (EXP1): conventional PT intervention and CPM applications for 35 minutes daily; 3) experimental group 2 (EXP2): conventional PT intervention and CPM applications for 2 hours daily. All patients were evaluated twice: once before TKA for baseline measurements and at discharge (7 to 8 days after TKA). The primary outcome measure was active knee flexion at discharge. Active knee extension, Timed Up and Go, results on the WOMAC questionnaire and length of stay were the secondary outcome measures. The characteristics and outcome measurements of patients in the three groups were similar at baseline. No significant difference between the three groups was demonstrated in primary and secondary outcomes at discharge. The results of this study do not support the use of CPM in post-primary TKA rehabilitation programs, as applied in this clinical trial, since it did not further improve knee impairments or disability, nor did it reduce length of hospital stay.

The biological concept of continuous passive motion (CPM) was introduced by R.B. Salter in the late seventies. He demonstrated that continuous passive movement on rabbit knees after cartilage injury enhanced cartilage healing and regeneration compared to prolonged articular rest.175,177Afterwards, his research focused on the effects of CPM on a variety of injuries in rabbits and in clinical applications on human subjects.178 Coutts19 first initiated CPM use immediately following total knee arthroplasty (TKA). His reasoning was based on Salter's research and the postulate that CPM enhanced collagen tissue healing with better fiber orientation, avoiding cross-linking and thus, generating better movement restoration.19,171

The efficacy of post-operative CPM applications has been studied in a large variety of protocols after TKA. Knee flexion was usually the primary outcome measure analyzed at the end of hospital stay (short term efficacy) and two to twelve months after TKA (long term efficacy). Most authors agree on long term CPM inefficacy on knee flexion;2-11 however, there is still a controversy regarding its short-term efficacy. Many studies conclude that CPM applications do not provide any additional gain on knee flexion at the end of hospital stay.1,3,4,6,12-17 In a large proportion of these studies, knee flexion exercises in the control group began when CPM applications were started in the experimental group.1,3,6,12,13,16 Other authors reported significant knee flexion gains between 7 to 22° as compared to the control groups,5,8-11,18-20 or faster knee flexion recovery during hospital stay.7,14,15,19,20 In the majority of these studies, patients’ knees in the control group were immobilized for 2 to 7 days, while patients in the experimental groups had early post-operative CPM applications.5,8,9,11,18-20 These results cannot be applied to contemporary practice since a long period of immobilization is no longer recommended after TKA, and early movement is always promoted in this population. In addition, description and standardization of knee flexion measurements have been neglected in many experiments and only few studies have provided detailed methodology.1,3,5,9,132

Besides knee flexion, length of stay (LOS) and function have also been used to measure CPM efficacy following TKA. In some studies, LOS was reduced by 2 to 5 days in groups with CPM applications. However, discharge criteria other than knee flexion were not always clear enough to make inferences about the influence of CPM on LOS.9,15,16,19,20,209 In some studies, function was measured with questionnaires at varying times between six weeks and two years following surgery. Comparable results on these questionnaires were observed in groups with and without CPM applications.1,4,5,8,10,17

The purpose of this single-blinded randomized clinical trial was to compare the efficacy of three in-hospital rehabilitation programs with varying intensities of CPM applications on knee flexion, functional ability and LOS after a primary total knee arthroplasty. The results are intended to determine whether or not to maintain CPM applications as part of the rehabilitation protocol following TKA in our clinical setting, particularly as these applications are time consuming and require the mobilization and effort of numerous staff members.

For each participant, anthropometric, personal and clinical characteristics were reported including gender, age, weight, height, social status, co-morbid conditions, previous disease or surgeries and time from the onset of symptoms. A questionnaire was also administered to measure the frequency and intensity of physical activity usually performed by patients.189 The same measurements were taken at baseline and at discharge. The primary outcome was maximal active knee flexion in a seated position. The secondary outcomes were: active knee extension, Timed Up and Go (TUG) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Assessments were performed by five experienced physical therapists who were blind with respect to group assignment at discharge. The theoretical and real LOS were also reported. All assessments at discharge were performed at the same time of day, that is, in the morning before physical therapy interventions, if those were still needed.

From February 2001 to February 2003, 82 patients were randomized: 27 were assigned to the control group (CTL), 26 to the group with 35-minute CPM applications (EXP1), and 28 to the group with 2-hour CPM applications (EXP2); one patient was excluded after being randomized inadvertently (Figure 3). For the main analysis (intention-to-treat principle), 81 patients were considered. Personal characteristics, co-morbid conditions, physical activity level and measurement outcomes at baseline were similar in the three groups (Table 2).

No significant difference was found between the three groups for surgery characteristics such as patella resurfacing (CTL: 85%; EXP1: 69%; EXP2: 64%; p=0.19) or postero-stabilized prosthesis (CTL: 22%; EXP1: 27%; EXP2: 7%; p=0.15).

Our results confirm that adding CPM applications of low or moderate intensity to conventional PT interventions has no short-term effect on active knee flexion. Moreover, CPM applications did not have any additional effect on secondary outcome measurements including active knee extension, TUG, WOMAC, and LOS.

Our results confirm those of other studies in which CPM applications did not have any additional effect on knee flexion.1,3,4,6,12-17 Agreement was also reached for the mean range of knee flexion at discharge. In some studies, this amplitude varied from 62.7° to 76.5°, seven to ten days after TKA, all groups taken into account.1,6,12 In studies supporting the efficacy of CPM applications, similar ranges of knee flexion (70° to 82°) were observed seven days after surgery.5,10,18,161,184 When the mean knee flexion amplitude was found to be greater (86° to 93°) at discharge, the LOS was also longer, attaining 15 to 20 days.7,9,11,14,15 In our clinical trial, the mean knee flexion amplitude at discharge for the whole population of our patients (n=81) was 80.8° (standard deviation, 11.5°) for a mean LOS of 8 days (standard deviation, 2).

One of the adverse effects that could occur with CPM applications is an increased lack of active or passive knee extension. However, only few studies reported a significant decrease in knee extension at discharge in the experimental group using CPM applications. In all these, duration of applications was 20 hours per day.6,8,10 In our study, active knee extension was not found to be decreased in groups with CPM applications (CTL: -8°, EXP1: -7°, EXP2: -6.5°). Nevertheless, in all three groups, there was a lack of knee extension of about 7.2° (standard deviation, 0.7°). Comparable amplitudes (-4° to -10°) have been observed at discharge (5-14 days after TKA) in other studies, regardless of study duration or the protocol used.1,3,5,13,20,184 Difficulties in performing knee extension might be explained by extensor muscle weakness, stiffness in flexor muscles, knee swelling, pain or a combination of these impairments considering the acute stage condition.

One could think that patients who received additional CPM applications would have decreased functional ability because they remained inactive during the duration of CPM interventions. To our knowledge, no study using CPM applications has measured functional ability at discharge. All assessments of functional ability were performed 6 weeks to 2 years after TKA. However, at these post-operative periods, no adverse effect of CPM applications on functional ability was found.1,4,5,8,10,17 In our study, functional ability, as measured by the TUG and WOMAC questionnaire, was comparable in the three groups at discharge. The mean duration of TUG for all patients in the three groups was 48.2 seconds (standard deviation, 27.2), three times longer than at baseline (16.8 seconds, standard deviation, 9.8). Furthermore, 81.5% of our patients (CTL: 85.2%, EXP1: 76%, EXP2: 88.9%) were using a walker for ambulating, thus, decreasing walking speed. In a previous study which did not use CPM applications, Walsh et al 149 evaluated functional performances at one week after TKA and their results showed that TUG duration was only twice that measured at baseline. However, patients in that study seemed to have greater pre-operative functional ability, as suggested by their superior performance on the TUG (12.9 seconds, standard deviation, 0.7). Also, the majority of their patients used a cane (78%) instead of a walker149. In the present study WOMAC questionnaire percentage scores were comparable in the three groups. However, it is important to note that the results may have been influenced by the withdrawal of five non-relevant items from the functional difficulty sub-scale since patients were not exposed to these during the acute post-operative stage. This methodological choice might have reduced the validity of the corresponding sub-scale and the total score of the WOMAC questionnaire. There is a need to develop and validate an appropriate functional outcome measure for the weeks immediately following TKA.

In the past ten years, pre-established discharge criteria have evolved concurrently with decreasing LOS, which now vary between 5 and 10 days after TKA.1,4,12,113,125,138,139 Therefore, the 90° knee flexion discharge criteria was modified to a lesser amplitude, and functional ability was emphasized to accelerate discharge.113,212 In many studies the mean knee flexion amplitude at discharge varied from 63° to 80° for a LOS between 5 and 10 days after TKA.1,4,12 In our study, one of our discharge criteria in addition to independence in functional activities was active knee flexion amplitude, which had to be around 75°. Eighty-three percent (83%) of our patients reached 75°± 5° (CTL: 81.5%, EXP1: 80.8%, EXP2: 86%). Others were allowed to return home because they had reached the functional independence goal, and they continued to be partially supervised for their exercises. All patients were discharged with home supervised physical therapy interventions. In our clinical trial, when all groups were taken into account, real and theoretical LOS was 8 days (standard deviation, 2) and 7.6 days (standard deviation, 1.6) after TKA, respectively. The slight difference between the two LOS measures was mostly due to delays in transportation for patients living in outlying regions.

Deep-vein thrombosis (DVT) can develop in 40 to 80% of patients after TKA. This proportion decreases with prophylactic anticoagulant therapy.29,96-98 There is a controversy concerning the effect of CPM on DVT. Many authors did not find any difference in DVT with CPM applications,1,8,11,132,186 while others found less DVT in CPM application groups, although, this may be due to the fact that their controls were immobilized.9,14,19,185 In our study, a large majority of patients received anticoagulo-therapy and the same very small proportion of side effects, including DVT, was observed in the three groups.

Our choice of CPM application duration could be criticized. Indeed, many protocols with varying CPM application durations have been studied, for instance: 1 hour 3 times a day,16 2 hours 3 times a day,1 comparison of moderate and intensive durations of 5 and 20 hours per day,132 mean applications between 4 and 8 hours,3 and applications as long as 20 hours a day for 1 to 6 days after TKA.4,6,17 None of these studies have demonstrated any additional effect of CPM applications on knee flexion. Compliance to CPM interventions has been reported in two studies and was less than the prescribed duration.1,3 For example, Beaupré et al,1 reported a compliance of 1.7 hours, 1.8 times per day, which was less than the prescribed applications of 2 hours, 3 times a day. In this case, 61% of subjects missed the morning session because of interference with other activities.1 In our study, the 35-minute duration in the EXP1 group corresponded to the usual length of CPM applications in our rehabilitation practice after TKA. The two-hour CPM application was added to the research protocol to explore the effect of a more intense, yet still feasible, CPM intervention. This second group (EXP 2) received CPM applications in the evening, thus avoiding interference with other post-operative activities routinely performed during the hospital stay. This 2-hour duration was chosen based on a consensus among the health professionals (orthopedic surgeons, physical therapists and nurses) involved in rehabilitation after TKA. We determined that CPM applications could not be any longer than 2 hours in the acute care context after TKA, since patients had daily conventional physical therapy interventions, occupational therapy visits, nursing care, X-rays and medical assessments. Furthermore, patients needed time to achieve all their rehabilitation goals, in addition to knee flexion, such as independence and security in transfers, and in walking with aids before being discharged and sent home.

Our study has many strengths. First, our three groups were comparable at baseline in terms of personal and clinical characteristics and outcome measurements. Second, there was a high degree of compliance to interventions. Only one patient in EXP1 (4%) and three patients in EXP2 (11%) did not received 75% of the planned CPM applications. Three patients in the CTL group (11%) and one in EXP1 (4%) did not received 75% of the conventional physical therapy interventions. Third, all patients in the three groups began CPM mobilization and knee flexion exercises at the same time after TKA, thus avoiding a delayed exposure to knee movement in the CTL group. Furthermore, the level of co-interventions was comparable between groups. Finally, a statistical power of 86% (alpha error = 5%) was established to detect a difference in active knee flexion ≥10º between our groups, which was determined as the minimum effect size needed to keep CPM applications in our rehabilitation protocol after TKA.

The conclusions of this study are limited to populations and CPM application protocols similar to those described in our clinical trial. In specific situations, such as when important restrictions in knee flexion are present before TKA surgery, or after knee manipulation, CPM application efficacy still needs to be tested.

Adding CPM applications to conventional PT interventions does not favor better knee flexion, and should not be routinely used during in-hospital rehabilitation programs after a primary TKA on patients with OA. Furthermore, CPM applications do not have any additional effect on knee extension, functional ability or LOS. The CPM modality was removed from our post-operative protocol for this population since conventional PT interventions alone contribute to reaching the same functional outcomes, including optimal active knee flexion, needed to perform activities of daily living at discharge.


The authors would like to thank the patients for participating in this project, the orthopaedic surgeons, the nurses for CPM device installations, the physical therapists for patient assessments and treatments, and all persons who helped carry out this study.

The “Ordre Professionnel de la Physiothérapie du Québec” (OPPQ), the Canada Physiotherapy Foundation (Alun Morgan Funds), and Hôtel-Dieu de Québec du CHUQ Orthopaedic surgeons funds contributed to financing this project.

Madeleine Denis is a physical therapist, master’s degree candidate, and Réseau Provincial de Recherche en Adaptation-Réadaptation (REPAR), OPPQ, Fonds de la recherche en Santé du Québec (FRSQ) and Canadian Institutes of Health Research (CIHR) fellow.

FIGURE 3 Patients' enrollment, distribution and participation to the study

FIGURE 4 Maximal active knee flexion and differences between groups at discharge

Graph in the upper part of the figure illustrating the mean and standard deviation of active knee flexion amplitude in each group at discharge. Bar graph in the lower part of the figure illustrating the 95% confidence interval (CI) of inter-group differences at discharge: 0° means no difference between groups; the dotted vertical lines illustrates the range of differences that is not considered clinically important.

FIGURE 5 Compliance to CPM interventions

Graph in the upper part of the figure illustrating the percentage of patients in each experimental group (EXP1, EXP2) who received CPM applications for each day of the clinical trial. Graph in the lower part of the figure illustrating the mean duration (in minutes) of daily CPM applications in each experimental group