Abstract
Background
We sought to determine whether continuous passive motion (CPM) usage improves outcomes following arthroscopic hip surgery involving acetabular labral repair. Our hypothesis is that CPM usage reduces pain and pain medication use and improves quality of life in individuals who undergo hip arthroscopy.
Methods
We created a randomized controlled trial consisting of 54 patients who underwent arthroscopic acetabular labral repair. Patients were randomized to two groups, one with CPM use post-operatively and one without. Primary outcomes measured were pain level, patient satisfaction, and quality of life. Parameters used to measure these outcomes were self-reported pain scores on Likert scale, frequency of analgesic medication use, and self-reported scores on Hip Outcome Score Activity of Daily Living (HOS ADL). These parameters were compared between the two randomized groups using t-test for statistical analysis.
Results
There was no statistical difference between the treatment and control groups in terms of patient characteristics. There was no statistical difference between the two groups in terms of HOS ADL scores, although the patients in the control group demonstrated a trend toward higher HOS ADL scores. The patients in the CPM group had a statistically significant decrease in pain levels after surgery compared to patients in the control group. The total morphine equivalent dose consumed in the first two post-operative weeks was higher in the control group compared to the CPM group, although this difference was not statistically significant.
Conclusions
Use of CPM resulted in lower pain level scores in patients after hip arthroscopy. Although there is no statistical difference in quality of life or quantity of analgesics consumed post-operatively, patients who used CPM tended to have lower HOS ADL scores (which is desirable) and less consumption of pain medication. A study with a larger sample of patients might elucidate more differences between the two groups.
Level of Evidence
II, therapeutic.
Keywords: Continuous passive motion, Pain, Patient satisfaction, Quality of life, Hip arthroscopy
1. Introduction
Continuous passive motion (CPM) therapy was first introduced by Dr. Salter in the 1970s after his basic science research showed that CPM had no increased risk of wound healing complications and is well tolerated by patients after surgery involving intra-articular structures.1 CPM use was initially advocated in post-operative rehabilitation after joint surgery or trauma because rabbit models showed that it counteracted the pathologic stages of joint stiffness: bleeding, edema, granulation tissue, and fibrosis. Further animal studies showed positive results in reducing joint stiffness after intra-articular injury.2 However, these results have not been borne out in clinical studies involving patients after joint surgeries. CPM use after total knee arthroplasty has not been shown to have clinically significant effect on range of motion (ROM), pain, function, or quality of life to justify routine use.3,4
While effectiveness of CPM use after total knee arthroplasty is questionable, there is a paucity of literature on CPM use in the hip. One study from Italy showed that CPM use for three weeks post-operatively after open reduction and internal fixation of acetabular fractures may decrease risk of post-traumatic arthrosis of the hip.5 However, there are not much data regarding post-operative use of CPM in patients after hip arthroscopy.
The purpose of this study is to determine whether continuous passive motion usage improves outcomes following arthroscopic hip surgery involving acetabular labral repair. Our hypothesis is that CPM usage reduces pain and pain medication use and improves quality of life in individuals who undergo hip arthroscopy.
2. Methods
Prior to subject recruitment, the study protocol was approved by the Institutional Review Board (IRB). Fifty-four subjects undergoing primary hip arthroscopy for acetabular labral repair by one of the two orthopaedic surgeons at our institution were recruited and consented. All subjects were randomized into two groups: those who would receive a CPM machine and those who would not. Those subjects randomized to the CPM group were instructed to use it for 4–6 h daily throughout the first two postoperative weeks. Primary outcomes measured to determine the clinical effect of CPM usage were: 1) Pain control; 2) Pain medication consumption; and 3) Quality of life. During the outcome measurement period, both investigators and clinicians were blinded to minimize bias during data collection.
Inclusion criteria for the study included patients aged 14–50 undergoing primary arthroscopic hip surgery for labral repair. Patients were excluded from the study if they were pregnant, if they were undergoing a revision surgery, or if they were having surgery on bilateral lower extremities.
During the first two postoperative weeks, subjects were instructed to rate their pain from 0 to 10 on a Likert scale. They were also asked to record the number of oral analgesic tablets they took, the type of analgesic medication they used, and the frequency of analgesic tablet administration.
Reported medications included hydrocodone, oxycodone, hydromorphone, tramadol, acetaminophen, aspirin, meloxicam, ibuprofen, and naproxen. At 2 days, 7 days, and 14 days post-operatively, subjects recorded their CPM usage over the preceding days. The analgesic consumption, pain level, and CPM usage were recorded in a log book provided to the patient prior to surgery. In addition, subjects completed the HOS ADL scale preoperatively and at six weeks, twelve weeks, and six months postoperatively.
The aforementioned parameters for pain control, patient satisfaction, and quality of life were compared between the two groups via a two sample t-test. In the analysis, the morphine equivalent dose (MED) was computed for each subject's logged medications over the two week period. These doses were added together for each patient, and the sum MED was analyzed via t-test. In addition, each subject's reported pain scores were averaged over the two-week post-operative period while the HOS ADL scores were analyzed with a separate t-test at each time point—6 weeks, 12 weeks, and 6 months post-operatively.
3. Results
For the subjects with and without CPM usage, there was no significant difference in age, sex, BMI, or laterality of arthroscopic surgery between the two groups (Table 1).
Table 1.
Patient characteristics in treatment and control groups.
| CPM Group | No CPM Group | P-value | |
|---|---|---|---|
| Age | 36.2 | 29.5 | 0.06 |
| BMI | 27.5 | 25.1 | 0.21 |
| Sex (F:M Ratio) | 0.95 | 0.87 | 0.39 |
| Laterality of surgery (Left:Right ratio) | 0.42 | 0.43 | 0.93 |
Forty two of the 54 consented subjects (78%) had complete data sets. Forty-one of the forty-two patients (98%) completed the HOS-ADL for at least one of the time points post-operatively.
There was no statistically significant difference in the total morphine equivalent dose ingested in the first two weeks post-operatively between the CPM and control groups (239 MED vs 331 MED, p = 0.25). However, this gap widened when comparing only the first post-operative week, with the patients in the CPM group recording 66 fewer MED on average than those in the control group. However, this difference did not achieve statistical significance (p = 0.07). In almost all instances, the subjects’ medications included oxycodone and meloxicam.
The patients randomized to the CPM group recorded significantly lower pain scores at two weeks post-arthroscopy than the patients in the group without CPM use (2.94 vs 4.23, p = 0.04).
HOS ADL scores did not differ between the two groups at any time post-operatively (Table 2 below). Even though there was no statistical significance, the control group had a trend toward higher HOS ADL scores at each post-operative time point compared to the CPM group.
Table 2.
Primary outcome measures in treatment and control groups.
| CPM | CONTROL | P-VALUE | |
|---|---|---|---|
| HOS ADL PRE-OP | 47.1 | 62.7 | 0.67 |
| MED CONSUMED DURING FIRST 2 POSTOP WEEKS | 239 | 330 | 0.25 |
| MED CONSUMED DURING FIRST POSTOP WEEK | 120 | 186 | 0.07 |
| AVERAGE PAIN SCORES OVER FIRST 2 POSTOPERATIVE WEEKS | 2.94 | 4.23 | 0.04 |
| HOS ADL 6 WEEKS | 64.3 | 72.8 | 0.73 |
| HOS ADL 12 WEEKS | 76.3 | 81.5 | 0.87 |
| HOS ADL 6 MONTHS | 77.5 | 82.8 | 0.78 |
4. Discussion
There are abundant data available in the literature in terms of weight bearing status and return to sports after hip arthroscopy, but there are very few studies to date looking at the effectiveness of CPM in post-operative rehabilitation after hip arthroscopic surgery.6,7 Cunningham and colleagues showed in a prospective, observational study that patients who used CPM in addition to brace and compressive cooling devices had greater hip flexion (14° vs 4.5°) at 6 weeks post-operatively compared to those who did not after arthroscopic hip surgery.8
While we did not measure range of motion, our study results showed that patients who used CPM throughout the first two postoperative weeks reported lower pain levels throughout this period compared to patients who did not use CPM. This difference in pain scores was statistically significant. Taken together with previous studies that showed decrease in post-operative pain with CPM use after rotator cuff repair, our results suggest that CPM use in the early postoperative period may potentially reduce pain after arthroscopic surgery of any joint.9 This may be explained by the fact that in recent studies, CPM use was found to have anti-inflammatory properties. A biomechanical study in rabbit knees found that knees subjected to CPM use for 24–48 h had decreased expression of pro-inflammatory mediators MMP-1, COX-2, and IL-1β.10
While there was no statistical difference in the sum of analgesic MED consumed after arthroscopic hip surgery between those who used CPM and those who did not in the early post-operative period, there was a trend toward greater consumption of narcotics in the group without CPM use. This suggests that perhaps this trend might achieve statistical significance if the sample size were bigger. When we first began the study, our goal was to enroll 66 patients to achieve a power of 80%, accounting for 20% attrition rate (patients who drop out of the study). However, we were only able to enroll fifty-four patients with an observed attrition rate of 30%. Our study was likely underpowered to detect a difference in this outcome measure. Therefore, future studies with larger sample sizes may elucidate greater differences in post-operative narcotic consumption between the control and intervention groups.
We found that patients achieved similar HOS ADL score at 6-month follow up period regardless of CPM usage. The HOS ADL scale is a self-reported scale measuring the ease of performing activities of daily living like getting into a car, getting out of a bathtub, stepping down curbs, walking up steep hills, etc. While this indicates that CPM use might not have a clinical effect on long-term functional outcomes after hip arthroscopy, this does not reveal much about speed of recovery and time to return to prior activity level. Further clinical studies are needed to determine whether CPM use has any impact on time to return to work/sports.
4.1. Limitations
Some weaknesses of our study are that, as previously mentioned, it might have been underpowered to detect some of the differences between the CPM and control groups, specifically the quantity of analgesic medication consumed by patients. Another weakness of the study is its relatively narrow scope. Only the pain level, consumption of narcotics, and functional level after surgery were considered between the intervention and control groups. Other outcomes such as range of motion, strength, and need for manipulation under anesthesia could have been considered; in fact, these measures have all been shown to be affected by CPM use in joint arthroplasty literature.11
However, the narrow scope of the project is also a strength of the study as it allowed us to focus on three simple, measurable outcomes in this first-ever clinical study examining post-operative rehabilitation with CPM after hip arthroscopy. Because these results have shown that CPM usage may confer some clinical benefits in this specific patient population, a study with larger sample size and broader scope may be initiated to elucidate these benefits in more detail.
Another strength of the study was its design as a randomized, controlled trial with single-blind testing. This strategy circumvents most biases—selection and recall bias—inherent in retrospective studies and chart reviews.
Perhaps the biggest strength of the study is that it justifies use of CPM as another tool for managing post-operative pain after arthroscopic hip surgery in this era of opioid epidemic in the United States. Recent studies have illustrated that opioid analgesics are the cause of more deaths than suicide and motor vehicle crashes combined or cocaine and heroin use combined.12 As the nation and media have turned their attention to sales of opioid prescriptions, there has been increasing scrutiny of physicians' prescribing patterns. Appropriately treating patients’ post-operative pain while at the same time decreasing the number of therapeutic narcotics prescribed is a fine line that all physicians must learn to tread to help curb the opioid epidemic. CPM may be another tool orthopaedic surgeons can add to their armamentarium when it comes to managing post-operative pain after hip arthroscopy.
5. Conclusion
Use of CPM resulted in lower pain level scores in patients after hip arthroscopy. Although there is no statistical difference in quality of life or quantity of analgesics consumed post-operatively, patients who used CPM tended to have lower HOS ADL scores (which is desirable) and less consumption of pain medication. A study with a larger sample of patients might elucidate more differences between the two groups.
Ethical committee statement
This study was approved by the Biomedical Institutional Review Board of The Ohio State University.
Declaration of competing interest
The authors received no funding for this study and report no conflicts of interest.
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