Effectiveness of passive and active knee joint mobilisation following total knee arthroplasty: Continuous passive motion vs. sling exercise training.

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1 Effectiveness of passive and active knee joint mobilisation following total knee arthroplasty: Continuous passive motion vs. sling exercise training. Mau-Moeller, A. 1,2, Behrens, M. 2, Finze, S. 1, Lindner, T. 1, Mittelmeier, W. 1, Bruhn, S. 2 & Bader, R. 1 1 University Medicine Rostock, Department of Orthopaedics, Rostock, Germany 2 University of Rostock, Department of Exercise Science, Rostock, Germany Abstract Introduction: The randomized clinical study was conducted to compare the effectiveness of continuous passive motion (CPM) and active sling exercise training (ST) following total knee arthroplasty (TKA). It was hypothesized that a sling exercise training (ST) could have additional benefits on patient s recovery after TKA compared to CPM therapy. Methods: Thirty-eight patients undergoing primary TKA for osteoarthritis were randomly assigned to receive ST or CPM during hospital stay. Patients were evaluated before TKA (baseline), at each postoperative day during hospital stay and three months postoperatively. Knee flexion range of motion (ROM) was the primary outcome measure. Secondary outcome measures included knee extension ROM, pain, physical activity, postural control, length of hospital stay as well as functional and subjective outcomes (SF-36, HSS and WOMAC scores). Data were analyzed according to the intention-to-treat principle. Results: The patients characteristics and outcome measures were similar in both groups at baseline. The ST group revealed significantly higher active knee flexion ROM at 8-day and 9-day follow-up (4.8 ; 95% CI: 0.2, 9.4 and 5.3 ; 95% CI: 1.5, 9.1) and passive knee flexion ROM (5.9 ; 95% CI: 0.9, 11.0 and 5.3 ; 95% CI: 0.6, 9.9). No significant differences could be observed in secondary outcome measures. Conclusions: Active ST seems to have statistically significant beneficial short-term effects on knee flexion ROM compared to CPM. A clinically relevant difference could be detected for active knee flexion ROM at 9-day follow-up (d = 0.95; power = 0.81). The results of the study support the implementation of ST in rehabilitation programs following TKA. 1. Introduction The major objectives of rehabilitation after total knee arthroplasty (TKA) are early regaining of range of motion (ROM) and mobilization of the patient. Continuous passive motion (CPM) has been frequently used as part of the postoperative care regime following TKA with the aim to increase knee joint mobility and improve postoperative recovery despite little conclusive scientific evidence [1, 2]. A review of the recent literature on the effectiveness of CPM following TKA reported evidence for small short-term effects on active and passive knee flexion ROM [1]. ROM is directly related to function and a rapid regain of ROM is a primary indicator of a successful TKA [3]. Adequate knee flexion up to is required for activities of daily living such as sit to stand transfers and climbing stairs [3]. Nevertheless, a passive mobilization of the knee joint with CPM does not encourage the patients to actively participate in their rehabilitation. Active exercises require the activation of muscles which is supposed to have beneficial effects on recovery. Research on the effect of active ROM exercises added to standard physiotherapy during the short in-hospital period is lacking so far. Only three studies have investigated an adjunctive active motion therapy (slider board) by comparing it to patients treated with physiotherapy plus CPM and to patients treated only with physiotherapy [4, 5]. Group differences were not reported, indicating that an adjunctive active and passive ROM therapy in the early postoperative phase has no benefit for patients recovery. However, it should be taken into account that knee joint mobilization exercises using a CPM machine and slider board are guided movements and are therefore less functional. Hence, a prospective two arm parallel-group superiority randomized clinical study was conducted to compare an active sling-based in-hospital ROM exercise program with CPM therapy following TKA. Sling exercises are self-induced and non-guided movements with unstable support and higher demands on dynamic knee joint stabilization. Therefore, it was hypothesized that voluntary muscle activation and joint stabilization during sling exercise training (ST) might be advantageous for early recovery following TKA. Whether an early postoperative application of a new ST could be beneficial for postoperative ROM, pain, physical activity, postural control, length of hospital stay as well as functional and subjective outcomes compared to CPM therapy, were analyzed. 2. Methods Eligible participants were patients undergoing primary TKA for osteoarthritis aged 50 to 80 years with a body mass index (BMI) less than 40. Patients with contralateral TKA or total hip arthroplasty were included when the surgery was performed more than one year before the current TKA. Exclusion criteria were as follows: musculoskeletal and neurological disorders that limit physical function, any planned further joint surgery within 12 months and substantial pain or functional limitation which made the patients unable

2 to perform the study procedures. Prior to participation, written informed consent was obtained from all participants. The study was approved by the ethics committee of the University of Rostock (A ). Harvey et al. [1] suggested that a between-group difference in knee flexion ROM (primary outcome) of more than 5 is clinically meaningful. Effect sizes from Huang et al.[6] for a short-term effect of active knee flexion ROM (d = 0.736) and from Harms et al. [7] for passive knee flexion ROM (d = 0.619) were used for power analysis. Sample size calculation for active knee flexion ROM indicated that the number of participants required was 30 per group in order to detect a clinically relevant difference in ROM of 10 with a two-sided 5% level and a power of 80%. The calculation for passive knee flexion ROM indicated that a sample size of 42 per group would be needed to detect large effects. In considering an anticipated dropout rate of 10%, a total of 94 patients were needed for the trial. A 14-month recruitment period was assumed to enroll this number of participants. Eligible patients were randomly assigned to one of two treatment groups using blocked randomization by a computer-generated table of random numbers, a block size of ten and an allocation ratio of 1:1. Participants were sequentially allocated to the treatments in the order in which they were recruited. Intervention assignment was ascertained using sealed, opaque envelopes with consecutive numbering after the enrolled patients completed all baseline measurements. The investigator who opened the envelopes and carried out the implementation of assignments was not involved in the generation and allocation concealment. Outcome assessors and participants were blinded to the treatment at baseline measurements. Afterwards, participants and physiotherapists were aware of the group allocation due to the nature of the intervention. All patients underwent a standard surgical procedure by inserting the same total knee implant (Multigen Plus, Lima-Lto, San Daniele, Italy) with an identical surgical approach. Postoperatively they received same pain medication in accordance with the standard pain management protocol. The Multigen Plus implant is a non-constrained surface replacement consisting of symmetrical, cruciate-retaining, cemented metallic femoral and tibial components and fixed-bearing ultra-high molecular weight polyethylene liners. All patients underwent full-weight-bearing with two crutches beginning on the second postoperative day Interventions Eligible patients were either allocated to (a) the CPM group, which received physiotherapy and CPM application or (b) the ST group, which received physiotherapy and performed sling exercises. All patients participated in a standardized in-hospital physiotherapy which was carried out by physical therapists twice a day for 30 minutes each, starting on the first postoperative day. Physiotherapy consisted of active and passive ROM exercises, active isometric contractions of the quadriceps and exercises to improve activities of daily living like transfer from bed to chair, transition from sitting to standing, walking and climbing stairs. Exercise intensity was gradually increased according to pain and tolerance. Furthermore, patients received two 30 minutes CPM or ST applications each day from the second postoperative day until one day prior to discharge. The patients were shown the CPM or the ST exercises by a physiotherapist. The CPM protocol was started with 0 to the maximum tolerated flexion at the highest, adjustable speed. ROM was increased daily depending on tolerance. The CPM machines used were Kinetec OptimaTM S3 and S4 (AbilityOne Kinetec S.A., Tournes, France). Participants were instructed not to resist or actively support the motion of the device. The participants in the ST group performed active knee flexions and extensions in a sling while lying in a supine position (Fig. 1). The patient s leg was placed in a standard tubular bandage that was suspended from a cross brace fixed to the bed. The ST protocol was started with 0 to maximum tolerated flexion at a movement speed comparable to those used in the CPM protocol. Exercise progression was achieved by asking the patients to gradually increase the range of motion as tolerated. Figure 1. Sling exercise training. Patients were discharged when sufficiently mobile (i.e., at least 90 knee flexion and no need of personal care) and medically stable. After discharge, all patients participated in daily physical therapy for three weeks in a rehabilitation hospital.

3 2.2. Outcome Measures Participants were assessed before TKA for baseline measurement, at each postoperative day during hospital stay and three months after TKA. The primary outcome measure was the knee flexion ROM (active and passive). The primary endpoint was the knee flexion ROM at the end of the intervention at the 9- day follow-up. Secondary outcome measures included active and passive knee extension ROM, pain, physical activity, postural control with open and closed eyes, length of hospital stay and functional and subjective outcomes (i.e., SF-36, HSS and WOMAC scores). ROM and pain were assessed by the clinical staff during hospital stay. Any other outcomes were determined by the same investigator Statistical analysis Data analysis included all randomized patients according to their original treatment allocation (intentionto-treat analysis). Data were checked for normal distribution using the Kolmogorov-Smirnov test. Multiple imputation (5 imputed data sets) was used to account for missing data. Differences between the groups were tested for significance by the unpaired Student s t test or Mann-Whitney U test. The level of significance was established at P All data were analyzed using SPSS 20.0 (SPSS Inc., Chicago, IL, USA). Sample size requirements, Cohen s d effect sizes and power were calculated with the statistical software package G*Power (version ) [8]. 3. Results Thirty-eight participants were recruited from 125 available patients within the 14 month recruitment period. The recruitment of patients was stopped when the scheduled date of closure was reached. The minimum sample size (N = 94) required was not achieved. The patients demographic and clinical characteristics and all outcome measures were not found to be different between the two treatment groups at baseline. All patients received the allocated intervention and were analyzed for outcome measures. Both groups did not differ significantly in the number of physiotherapy, CPM and ST interventions and in the time to follow-up. No incidents of adverse effects or harm during the study could be observed Primary Outcome Active and passive knee flexion ROMs were consistently higher from the third to the ninth postoperative day in the ST group (Fig. 2). Significant between-group differences could be determined 8 and 9 days after surgery. Active knee flexion ROM was significantly higher by 4.8 (95% CI: 0.2, 9.4; P = 0.04; d = 0.71; power = 0.57) and 5.3 (95% CI: 1.5, 9.1; P = 0.01; d = 0.95; power = 0.81) at the 8-day and 9-day followups in the ST group (Fig. 2 A). Passive knee flexion ROM was likewise significantly increased by 5.9 (95% CI: 0.9, 11.0; P = 0.02; d = 0.78; power = 0.65) at 8-day follow-up and by 5.3 (95% CI: 0.6, 9.9; P = 0.03; d = 0.76; power = 0.63) at 9-day follow-up (Fig. 2 B). No differences in active and passive knee flexion ROM were documented at the 3-month follow-up (Fig. 2). Figure 2. The graphs show comparisons between the groups for (A) active knee flexion range of motion (ROM) and (B) passive knee flexion ROM. Data are means and standard error of the mean. * denotes a significant difference between the groups (* 0.05, ** 0.01) Secondary Outcomes No significant differences between the groups could be observed for any secondary outcome measure at different follow-up time points. A trend toward a decrease in time of achieving passive knee flexion ROM of 90 and in length of hospital stay could be documented for the ST group. Passive knee flexion ROM of 90 was achieved 1.6 days earlier (95% CI: -3.3, 0.1; P > 0.07; d = 0.61; power = 0.46) and length of hospital stay was 0.9 days shorter (95% CI: -1.9, 0.0; P > 0.06; d = 0.64; power = 0.45) in the ST group. 4. Discussion The objective of the present randomized clinical study was to compare the effectiveness of a new slingbased ROM therapy (ST) with the traditional CPM application as an adjunct to daily physiotherapy following TKA.

4 There is evidence that ST has significantly positive, short-term effects on knee flexion ROM of the operated knee joint. No significant differences between groups remained at the 3-month follow-up. Although we found significant differences in short-term knee flexion, the confidence intervals are fairly wide and do not rule out between-group differences of less than 1, which indicate no clinical relevance. However, the Cohen s d effect sizes suggest a medium to high practical significance [9]. A post-hoc power analysis for all significant variables revealed a low power (< 0.80) for active knee flexion ROM at 8-day follow-up as well as for passive knee flexion ROM which indicate that these differences are not clinically meaningful. However, a power of 81% could be detected for active knee flexion ROM at 9-day follow-up representing a medium effect at the 5% level of significance which indicates a clinical relevance [9]. This result suggests that an adjunctive ST therapy in the early postoperative phase seems to be advantageous for patients recovery following TKA. There were no significant beneficial effects of ST on active and passive knee extension ROM, pain, physical activity, postural control, length of hospital stay, health-related status, function or quality of life. Nevertheless, a trend toward earlier achievement of a passive knee flexion ROM of 90 as well as earlier discharge from hospital could be reported for the ST group. A post-hoc power analysis was conducted for all variables that did not reach statistical significance in order to rule in or to rule out inadequate power as a threat to the internal validity of the findings [10]. The post-hoc power coefficients are low (power < 0.80). Thus, the lack of power is an alternative explanation of the statistical non-significant findings possibly due to small sample size. A recent review on the effectiveness of adjunctive CPM therapy compared to physiotherapy alone reported short-term effects on active and passive knee flexion ROM by 3 and 2, respectively [1]. As an adequate ROM is required for performing physical activity[3], it could be claimed that even these minimal additional ranges are functionally important for early postoperative mobilization of the patient. Nevertheless, the authors suggested that these effects on ROM are too small to be clinically relevant. Taking into account the fact that the application of CPM is associated with high costs for the rental or acquisition of the device and additional technical and personnel efforts to set up and operate the machine, it was suggested that an additional ROM of more than 5 is required to justify its use [1]. Our present data demonstrated that an adjunctive ROM therapy using sling-based exercises revealed a significant and clinically relevant additional active knee flexion ROM of 5.3 at 9-day follow-up compared to CPM therapy. The knee joint mobilization in the sling required the activation of muscles which probably accounted for these beneficial effects. Furthermore, the unstable support during the performance of ROM exercises might have contributed to higher demands on muscle strength and muscle coordination. Moreover, ST is easy to carry out during hospital stays and less expensive than CPM therapy. Since the cost-effectiveness could be increased while even improving the quality of clinical results, the application of an ST therapy in the postoperative phase can be recommended as a part of the early post-operative rehabilitation management. However, our study was limited by the small sample size. The target number of participants was not achieved by the scheduled day of closure due to an unexpectedly low number of patients that met the inclusion criteria. The high proportion of ineligibility reduces the generalizability of the findings. It was not possible to extend the study to achieve adequate enrollment, as the date of termination of financial support of the project was reached. A second limitation was the 26% dropout rate at the 3-month follow-up which reduced precision and possibly introduced bias. However, none of the patients withdrew from the study for a reason related to the study treatment. A further limitation was the inability to blind the patients and practitioners, which was impossible due to the nature of the intervention. Although it would be appropriate, it was not possible to run a three arm trial including an arm with no additional ROM intervention because CPM combined with usual physiotherapy is the standard treatment following TKA in our department. Therefore, it was not considered appropriate to exclude ROM exercise from the postoperative physiotherapy. Despite these limitations, statistically significant positive results relating to the ST therapy could be presented for the primary outcome measure. Furthermore, there was a clinically relevant difference between groups regarding active knee flexion ROM at 9-day follow-up. Nevertheless, the study was underpowered for many outcome variables. It could be assumed that, if the study had been adequately powered we could have seen a greater number of statistically significant differences. 5. References 1. Harvey LA, et al. (2010). Cochrane Database Syst Rev, CD Grella RJ (2008). Phys Ther Rev, 13, Rowe PJ, et al. (2000). Gait Posture, 12, Beaupre LA, et al. (2001). Phys Ther, 81, Davies DM, et al. (2003). Can J Surg, 46, Huang D, et al. (2003). Chinese Journal of Clinical Rehabilitation, 7: Harms M, et al. (1991). Physiotherapy, 7, Faul F, et al. (2007). Behav Res Methods, 39, Cohen J (1988). Statistical Power Analysis for the Behavioral Sciences 10. Onwuegbuzie AJ, et al. (2004). Understanding statistics, 3,

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