The use of continuous passive motion (CPM) machines has become a component of some rehabilitation protocols following anterior cruciate ligament (ACL) reconstruction. Older protocols relied on early joint immobilization, which is now known to lead to several complications, including intra-articular adhesions, disuse osteopenia, muscle atrophy, and range of motion (ROM) deficits.1,2 Salter2 first reported the benefits of postoperative CPM use in animal models, suggesting that it improved medial collateral ligament repair strength and promoted healing. Proposed benefits of CPM use after ACL reconstruction now include improved ROM,3,4 reduced rates of intraarticular adhesions requiring manipulation under anesthesia (MUA),2,5–8 early clearance of postoperative hemarthrosis,8 improved articular cartilage nutrition and healing,5,9 decreased need for pain medications,6,10,11 reduced muscle atrophy,11 and improved ACL graft strength.6
Despite the intended benefits of CPM use, previous studies have generally failed to show that it significantly increases post-operative ROM in adult ACL reconstruction patients,11–16 although some evidence suggests it may modestly improve ROM at early time points during rehabilitation.3,4 This is in contrast to total knee arthroplasties, where CPM use has been shown to improve postoperative flexion at both discharge17 and 1-year follow-up.10
Research has failed to show that CPM use reduces pain during rehabilitation.11,13 Interestingly, few studies have examined the impact of CPM on postoperative limb strength. Although one animal study suggested that CPM might prevent muscle atrophy following ACL reconstruction,2 no similar findings have been reported in humans.15 However, research has shown that CPM use in adults after ACL reconstruction can reduce rates of MUA due to arthrofibrosis.5,16 Similar effects have also been found among patients after total knee arthroplasty10,17–19 as well as among patients following open reduction and internal fixation for tibial plateau fractures.20
To date, there has been no study of the effectiveness of CPM in reducing MUA rates or improving ROM after ACL reconstruction in a pediatric population. Therefore, the primary purpose of this study was to compare postoperative ROM and rates of MUA due to arthrofibrosis among pediatric ACL patients treated with or without a standard postoperative CPM protocol. Secondary goals included assessment of pain and limb strength during rehabilitation.
Materials and Methods
This was a retrospective cohort study of pediatric patients (age <20 years) who underwent primary ACL reconstruction at an urban tertiary care children's hospital between January 1, 2009, and June 30, 2015. After institutional review board approval, eligible patients were identified using the Current Procedural Terminology code for arthroscopic ACL reconstruction (29888). Manual review of electronic health records was done to apply inclusion and exclusion criteria. Owing to availability of follow-up ROM measures, only patients who received physical therapy (PT) within the authors' health care system were considered. Because ACL patients with meniscus repair at index surgery were routinely restricted to 90° of flexion (vs no limit for those without a meniscus repair), they were excluded. On the other hand, those with partial meniscectomies were included, as these patients have no stricter postoperative ROM restrictions than those with ACL reconstruction and no meniscus surgery.
Included ACL reconstructions were performed by 3 attending surgeons, each with more than 7 years of independent practice. Further chart review was done to determine CPM use, and patients were assigned to cohorts using an as-treated approach. Physical therapy records were further reviewed to document postoperative ROM, pain, limb strength, and insurance status. The study did not account for potential differences in PT and measurements across different sites, and reported measurements were used as recorded. Patients issued CPM were prescribed 2 hours 3 times a day for 3 weeks. They were further instructed to begin with a flexion endpoint of 30° and increase 10° per day as tolerated. Indications for CPM use were dependent on surgeon preference, insurance status, and patient preference. Range of motion data were obtained from PT records at 1 week, 1 month, 3 months, and 6 months after surgery. At the authors' institution, MUA for arthrofibrosis is generally performed by 4 months postoperatively. For assessing MUA rates in the cohorts, the sample was restricted to only those patients who had more than 6 months of clinical follow-up. Limb strength was analyzed at 3 months and 6 months after surgery using an isokinetic testing machine (System 4 Pro; Biodex Medical Systems, Shirley, New York). Patients are generally allowed to return to full activities only after full ROM (flexion equal to the contralateral side or reaching 120°) is acquired and strength deficits are less than 10% (compared with the contralateral leg) in extension and flexion. Statistical analysis was done using Stata version 14.2 software (Statacorp, College Station, Texas). Statistical significance was set at P≤.05 for all statistical tests.
The final dataset was composed of 163 patients who underwent ACL reconstruction (97 in the CPM cohort and 66 in the no-CPM cohort) (Table 1). The no-CPM group contained higher proportions of over-weight/obese individuals (P=.028) and was slightly older (P=.045). There was no statistically significant difference in the number of PT sessions between cohorts (P=.096).
No significant difference in ROM between the 2 cohorts was found at 1 week, 1 month, 3 months, and 6 months after surgery (P=.137, .695, .897, and .339, respectively) (Figure 1). Bivariate linear regression analysis revealed no consistent association between ROM and obesity status, age, number of PT sessions, Medicaid status, or surgeon.
Effect of use of continuous passive motion (CPM) on postoperative range of motion. Values represent degrees of flexion postoperatively. Student's t test found no significant difference between the cohorts at 1 week, 1 month, 3 months, and 6 months (P=.137, .695, .897, and .339, respectively).
Of the 163 patients, 137 had more than 6 months of follow-up (83 in the CPM cohort and 54 in the no-CPM group). Considering those with more than 6 months of follow-up, no patients in the CPM group required MUA (Table 2), while 4 patients in the no-CPM group (7.4%; 95% confidence interval, 2.1%–17.9%) required MUA for arthrofibrosis within 6 months of surgery (average, 59.5 days; range, 35–76 days). Fisher's exact test showed that this difference was statistically significant (P=.023). None of the 26 patients who were excluded from MUA analysis because of inadequate follow-up had a documented MUA. No patient in the overall dataset of 163 patients had MUA after 6 months postoperatively. None of the patients who received MUA were overweight or obese. Among the 137 patients with more than 6 months of follow-up, there was no statistically significant relationship between risk of MUA and surgeon (P=.381), patient age (P=.669), or Medicaid status (P=.965). Those who underwent MUA appeared to attend more PT sessions (median, 32 vs 29) than those who did not, although this was not statistically significant (P=.430).
Effect of Use of CPM on Need for Manipulation Under Anesthesia
Pain scores were compared between the overall cohorts using Mann–Whitney U tests, revealing no statistically significant differences 1 week, 1 month, 3 months, and 6 months after surgery (Figure 2). Strength deficits in the operative leg (as compared with the contralateral leg via isokinetic testing) are detailed in Table 3 for 3-month and 6-month postoperative time points. Hamstrings (flexion) and quadriceps (extension) isokinetic strength was evaluated at 180° per second and 300° per second. No statistically significant difference in hamstrings or quadriceps strength was found at either time point.
Effect of use of continuous passive motion (CPM) on postoperative pain scores. Values were obtained at physical therapy sessions and represent patient-identified pain levels on a scale of 0 to 10. Mann–Whitney U test found no significant difference between the cohorts at 1 week, 1 month, 3 months, and 6 months (P=.684, .623, .507, and 1.000, respectively).
Effect of Use of CPM on Postoperative Limb Strength
A lower proportion of Medicaid patients used CPM machines as compared with privately insured patients (46.8% vs 64.7%; P=.035; Table 1). Medicaid patients also attended fewer PT sessions (median, 22 vs 32; P<.001). The 3 surgeons treated similar proportions of Medicaid patients (P=.145; Table 4).
Proportion of Patients Insured by Medicaid Across Surgeons
Previous studies of the efficacy of CPM have largely failed to show that it improves postoperative ROM in adults after ACL reconstruction.11–16 Similarly, the current study of a pediatric population revealed no significant difference in ROM after surgery between CPM and no-CPM cohorts. In addition, CPM use did not affect postoperative pain or strength, consistent with findings from other studies in adult populations.11,13 The authors also found that CPM users and non-users attended similar numbers of PT sessions, which reduced the possibility that PT biased the findings regarding ROM outcomes. In all, it seems that CPM has little to no effect on postoperative ROM, pain, and strength in the rehabilitation of pediatric ACL patients.
Although research has yet to show an association between CPM use and postoperative ROM for ACL patients, some studies have suggested that CPM reduces the likelihood of needing MUA for arthrofibrosis in adults after ACL reconstruction.5,16 In this study of pediatric patients, the authors found that CPM use was associated with a lower rate of MUA to address arthrofibrosis in the first 6 months after ACL reconstruction. Although this finding supports the use of CPM protocols after pediatric ACL reconstruction, a thorough cost-benefit analysis should be performed. If CPM use reduces the risk of MUA by approximately 7% (as observed in this study), the number needed to treat to prevent 1 MUA would be approximately 14. A larger study might provide more precise estimates of MUA rates, allowing for a thorough financial analysis to further inform physicians' choices regarding the use of CPM. Furthermore, the data suggest that those who undergo MUA might attend more PT, adding additional financial and emotional cost to their care.
In this study, the authors also found that Medicaid patients were less likely to receive CPM machines as part of rehabilitation and attended fewer PT sessions. These findings could have important ramifications for the patients' well-being and the financial burden on the health care system. As CPM use is linked to a reduced need for MUA, the fact that Medicaid patients are less likely to receive CPM might place them at an increased risk of requiring MUA vs patients who are privately insured. This inequality may be worsened for patients who undergo MUA because they require more PT sessions, yet the authors found that Medicaid patients typically attend fewer PT sessions. The need for MUA and additional PT would almost certainly add undue stress to patients and their family, the consequences of which cannot be easily expressed in dollars. Unfortunately, this study was primarily powered to examine the effect of CPM use on postoperative ROM, strength, and pain and not the impact of insurance on these outcomes. Therefore, a thorough cost analysis examining the ramifications of CPM use regarding insurance status is warranted. However, the data may be useful in such an analysis because the use of CPM machines and PT for pediatric ACL patients in this series led to fewer instances of arthrofibrosis requiring MUA.
In this study, the authors showed that the use of a CPM machine after ACL reconstruction in a group of pediatric patients was associated with reduced rates of arthrofibrosis requiring MUA in the 6 months following surgery. However, practitioners' decisions regarding postoperative CPM use are likely influenced by many factors, including patient adherence rates and insurance reimbursement policies. Guidance on CPM use should be informed not only by studies like this investigating the efficacy of the intervention but also by studies detailing its cost-effectiveness.
Use of CPM was not associated with improved postoperative pain, ROM, or limb strength in this series. It was, however, associated with a reduced rate of MUA secondary to arthrofibrosis.
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|Obesity status, No.||.028a|
| Not overweight||71||36|
|Knee laterality, No.||.055a|
|Physical therapy visits, No.||.096b|
|Partial meniscectomy, No.||39||31||.392a|
Effect of Use of CPM on Need for Manipulation Under Anesthesia
|Manipulation Under Anesthesia||Group, No.|
|Yes||0 (0%)||4 (7.4%)|
Effect of Use of CPM on Postoperative Limb Strength
|Time and Strength||Percent Deficit, Group||P|
| Extension, 180°/s||22.205||24.513||.341|
| Flexion, 180°/s||9.779||12.787||.219|
| Extension, 300°/s||18.451||23.241||.056|
| Flexion, 300°/s||7.377||11.207||.137|
| Extension, 180°/s||10.115||14.693||.175|
| Flexion, 180°/s||4.427||5.907||.593|
| Extension, 300°/s||9.400||10.653||.716|
| Flexion, 300°/s||3.268||4.103||.775|
Proportion of Patients Insured by Medicaid Across Surgeons
|Surgeon||Total No. of Patients||Medicaid|