The efficacy of continuous passive motion in the rehabilitation of anterior cruciate ligament reconstructions

The efficacy of continuous passive motion in the rehabilitation of anterior cruciate ligament reconstructions

Mark A. Rosen

The effects of immobilization on joints have been well documented and include adhesions, cartilage resorption and ulceration, capsular and pericapsular contracture, fibrofatty proliferation within the joint cavity, weakened ligament insertion, muscle atrophy, osteoporosis, and histologic and biochemical alterations.[1,5,10,15] Prior to the work of Salter et al.,[21,23] most knee ligament reconstructions were immobilized. The benefits of early motion on articular cartilage, muscle, and healing has been studied extensively in animal models.[9,17,19,27] Potential advantages attributed to the use of early motion and continuous passive motion (CPM) in knee surgery include diminishing the effects of immobilization by enhancing reabsorption of the hemarthrosis; decreasing the adhesions, pain, thrombophlebitis and muscle atrophy; and improving the cartilage nutrition, range of motion, and collagen orientation and strength.[2,6-8,11,12,17,20,22-26] The use of immediate active motion and continuous passive motion after ACL reconstruction raised concerns about deleterious loads or anterior tibial displacement altering the ultimate graft strength and anterior joint laxity. This study was undertaken to evaluate potential advantages or deleterious effects of continuous passive motion on stability and range of motion after ACL reconstruction.


Seventy-five patients with ACL deficiencies who underwent arthroscopically-assisted ACL autograft reconstruction were randomly assigned to one of three groups using a lottery system. All patients were evaluated preoperatively by history and physical examination. Standard weightbearing anterior-posterior lateral, notch, and Merchant patella view radiographs were obtained of the involved knee. Objective anterior laxity testing using the KT-1000 instrumented arthrometer (MEDMetric, San Diego, CA) was performed in the office and under general anesthesia immediately before and after surgery. The contralateral extremity was also tested to assess side-to-side measurements at each examination. Subsequent testing was performed at 2 months and at 6 months postoperatively.

All reconstructions were performed by the same surgeon using an autograft from the middle third of the patient’s ipsilateral patella tendon. Patients undergoing meniscal repair or extraarticular capsular procedures were excluded. Those with associated partial meniscectomy procedures were included. Office follow-up examinations were performed at 1 week after surgery and then at monthly intervals for 6 months. The International Knee Documentation Committee Evaluation Form (first draft) was used at the 6 month visit.

Postoperatively, all patients were placed in a hinged brace (DonJoy Range of Motion Splint, DonJoy Inc, Carlsbad, CA) locked at 10 [degrees] of flexion. The brace was removed on the 1st postoperative day for physical therapy, which included active range of motion, isometrics, and patella mobilization. Initially, touch-down weightbearing was allowed, progressing to full weightbearing at 4 weeks. The lateral femoral incision drain was removed on the 1st postoperative day. The patients were discharged when they had achieved independent motion on crutches and their pain was controlled with oral analgesics. There were 25 patients in each group.

Group A was an active-motion group that did not use CPM. After discharge, the brace was worn when sleeping and walking for 4 weeks. It was removed while sitting and to perform active range of motion exercises as directed by a physical therapist. Physical therapy was continued three times a week after discharge from the hospital and early hamstring strengthening, restoration of quadriceps tone, and closed chain loading of the lower extremity were stressed. Therapy was conducted with emphasis on the following areas:

1. During the initial treatment, patients were instructed in cocontraction (simultaneous quadriceps/harmstring exercises) to reduce anterior translation forces.

2. Active terminal knee extension was performed in a closed-action configuration by performing knee dips or short-range squats.

3. Patients were progressed to full weightbearing as soon as quadriceps control was reestablished and the patient’s extension was within 10 [degrees] of full.

4. Attention was directed to patellofemoral mobility.

5. Exercises tended to be in functional positions (i.e., stair master versus weight machines).

Formal physical therapy continued, three visits per week, until full range of motion was achieved. The patient progressed to an unsupervised strengthening program when they demonstrated an understanding of their recovery goals.

Group B patients had the same therapy as Group A, but they were also placed in a CPM device (Sutter Corp, San Diego, CA) in the recovery room. The initial settings were at 0 [degree] to 30 [degrees] and increased as tolerated to 0 [degree] to 90 [degrees] with a frequency of 0.5 cycles/minute. The CPM was used a minimum of 20 hours per day while the patient was hospitalized. The patients was otherwise treated exactly the same as the Group A patients while in the hospital.

After discharge, these patients continued to use the CPM device a minimum of 6 hours per day for 4 weeks. The CPM range of motion remained at 0 [degree] to 90 [degrees] with the same rate of 0.5 cycles/minute. Groups A and B received the same formal physical therapy three times per week. Formal physical therapy continued until a full range of motion was achieved and the patient demonstrated that an individual unsupervised strengthening program could be initiated.

Group C received the same initial in-hospital therapy as Groups A and B, including physical therapy for crutch training and instruction on active range of motion, isometrics, and patella mobilization. The CPM protocol used in Group B was also used in this group. However, they did not start outpatient physical therapy until 1 month after surgery.

Range of motion testing

Range of motion was assessed preoperatively in the office, at the time of surgery while under anesthesia, at discharge from the hospital, at 1 week, and then at monthly intervals for 6 months. Measurements were manually performed on the involved and uninvolved knee using a calibrated goniometer. Subjective evaluations by the hospital and outpatient physical therapists were performed regarding to ease with which motion and ambulatory status was regained. Those patients in which there was an absence of progression in the range of motion for 2 weeks and who were behind the expected range of motion for that period were taken to the operating room for manipulation under anesthesia and a video arthroscopic lysis of adhesions. A heel-height difference test was performed at the 6-month visit.[18]

Patient data

Data was collected so that comparisons could be made between the three subgroups with respect to age, length of hospital stay, tourniquet time, the amount of hemovac drainage, acute (3 weeks), weight, and associated knee joint changes.

Patient compliance

Documentation of CPM use was recorded in the computer portion of the device for each patient.

Subjective data

Each patient using CPM completed a form stating how many days and hours per day they used it. They commented on their preference for its use, if it helped, and its effect on their pain and recovery of their knee motion.



One patient did not feel that the CPM machine helped, but the other 49 were very enthusiastic about the machine. Seventeen percent of the patients complained about loss of sleep. In general, most patients believed their good results were attributable to the CPM.


The CPM machine has an internal clock that recorded the amount of time it was used. This varied from a low of 50 hours to a high of 429 hours per week (average, 204 hours). The average usage of 7.3 hours/day was more than the minimum 6 hours we suggested. Although the machine could have been running without the patient’s leg in it, it was our impression that home compliance was very good.

Objective data

Table 1 lists the mean and the standard deviation for each group in the following areas: age, sex, weight, height, acute ACL injury, dominant hand, tourniquet time, hemovac drainage, hospital stay, hours of CPM usage, and knee form scores. The data were analyzed using a one-way analysis of variance computed for each area using a personal computer and BMDP-7D Statistical Software (BMDP Statistical Software Inc, Los Angeles, CA). There were no areas with a P [is less than or equal to] 0.05. [Tabular Data Omitted]

Table 2 lists the range of motion mean of each group at each time period. At 1 month, 2 months, and 6 months, it appeared that the CPM Groups (B and C) had significantly more flexion. However, when the motion is corrected for the control (which also had slightly greater flexion), flexion was not significantly greater.


Degrees of knee motion

Group A Group B Group C

Control knee

Extension 0 -0.3 0

Flexion 141 145 140

Surgical knee

Preop extension 4 3 2

Preop flexion 121 126 128

Anesthetized extension 1 0 1

Anesthetized flexion 139 142 142

Hospital discharge extension 9.3 11 13

Hospital discharge flexion 59 67 57

1 week extension 10 9 10

1 week flexion 63 77 77

1 month extension 9 6 8

1 month flexion 99 112 105

2 months extension 5 3 5

2 months flexion 119 130 127

3 months extension 3 3 3

3 months flexion 131 135 132

4 months extension 2 3 2

4 months flexion 136 136 137

5 months extension 0 1 2

5 months flexion 141 140 140

6 months extension 1 1 1

6 months flexion 139 143 139

Table 3 lists the KT-1000 data for each of the three groups obtained prior to surgery, upon completion of the surgical procedure, at 2 months, and at 6 months after surgery. Occasionally, the KT-1000 data demonstrated some patients had less than 3 mm side-to-side difference on the manual maximum preoperatively. The lack of a large difference can occur when the patient has difficulty relaxing the thigh muscles, an abnormal control knee, a displaced bucket-handle meniscal tear, or, in a large patient, a heavy leg. [Tabular Data Omitted]


The analgesics used by the patients varied widely and included meperidine hydrochloride (intramuscular and intravenous), hydroxyzine pamoate (orally and intramuscular), morphine (intramuscular and intravenous), oxycodone, hydrocodone bitartrate, codeine, Darvon (Lilly Corp, Indianapolis, IN), and acetaminophen. Because of the wide variance in medication used, comparisons among the groups of the amount used on a mg/kg basis was not meaningful. However, the transfer to oral analgesics was the same for each of the three groups and the length of hospital stay was similar for each group.

Associated knee injuries

The associated intraarticular knee injuries were recorded at the time of arthroscopy. All patients with additional ligamentous injuries requiring surgery were excluded from the study. Twenty-two (29%) of the patients had no apparent associated intraarticular injuries. Thirty-one (41%) had a medial meniscal tear. Twenty-three (31%) had a lateral meniscal tear. If the meniscal lesion was felt to be repairable, the meniscus was sutured and the patient was excluded from the study. A partial meniscectomy was performed on non-repairable menisci. Sixteen (21%) had grade II or greater articular cartilage changes (chondromalacia) in the patellofemoral joint and seventeen (23%) had similar involvement of chondromalacia elsewhere in the joint.

Radiographic assessment

Radiographs were taken before surgery and compared with radiographs taken at 6 months after surgery. They were evaluated with respect to the medial tibial femoral joint, the lateral tibial femoral joint, and the patellofemoral joint and compared to the preoperative radiographs. At 6 months, there was no increase in degenerative changes.


At the end of the 6 months, four patients met our criteria for early manipulation under anesthesia and arthroscopy: two for lack of extension (Groups A and C), one for lack of flexion (Group A), and one for a cyclops lesion (Group B). A cyclops lesion is a nodule of fibrous tissue with a central region of granulation tissue usually found anterolateral to the tibial tunnel.[13] Three additional patients had surgery after the 6-month study period. Two patients had a cyclops lesion (Groups A and B) and one had loss of motion )Group B). Other frequent complaints were an area of numbness around the incision (100% of the patients at 6 months), inferior pole of the patella discomfort and tenderness to direct palpation in comparison to the uninvolved knee (80%), pain at the tibial tunnel, and pain at the tibial tubercle. There was no apparent clinical deep-venous thrombosis and no patellar fractures. Ligament testing demonstrated 16% of the reconstructions to have 3mm or greater side-to-side difference at 20 pounds.

Cost of therapy versus CPM rental

The cost of physical therapy for 1 month, based on three sessions a week for 4 weeks at $70 per session, was $840. The cost of CPM rental for 1 month was $1800.


This prospective study in patients undergoing intraarticular ACL reconstruction examined the effects of continuous passive motion and supervised active range of motion during the first 30 days after surgery. It did not address an ideal length of time spent in a CPM machine after ligament reconstruction. Our decision to use the machine full time while the patient was in the hospital and then 6 hours a day for 4 weeks after surgery was an arbitrary one. In this study, the range of motion did not correlate with the hours that the machine was in use and all three groups had similar results.

Three groups were chosen to study different rehabilitation approaches. Group A was the active motion group that received supervised physical therapy three times a week but no CPM. Group B received physical therapy and CPM. Group C received CPM, but no formal physical therapy after leaving the hospital. All groups received crutch training and instruction on active range of motion, isometrics, and patella mobilization while in the hospital and were encouraged to perform these activities on their own as outpatients. The groups represent various rehabilitation protocols. Group A and B differed significantly from Group C in that they received individualized instruction and followup as described earlier. Group A was chosen to determine the effects of a well-supervised physical therapy program. Group C was chosen to represent the results of using the CPM without a supervised physical therapy program. Group B was chosen to represent results from both physical therapy and CPM.

The role that CPM should play in knee ligament reconstructions has been questioned with differing conclusions. Burks et al.[4] reported on cadaver ACL reconstructions and found disruption of the fixation sites. Noyes et al.[14] studied 18 patients and did not find problems with the ligament stretching out or with the fixation site. Anderson and Lipscomb[3] studied five different rehabilitation protocols and found CPM to be better than immobilization, but not as effective as early motion.

The satisfaction rate in our patients using the CPM machine was 98%. Many of the patients were convinced that the machine was responsible for their end result. Many patients felt that it was substandard care not to have the machine, and two patients (both physicians) had to be excluded from the study because they demanded the CPM machine. The enthusiasm for the machine can put the physician in an awkward situation with patients who are convinced that it is beneficial. It is one of our duties as the treating physician to educate the patient. If one of the patient’s friends used a CPM machine after their surgery, the pressure to use them may be increased. We have found that patients generally talk to their friends, and they are often fairly well informed about the various postoperative regimens being used in their community.

There were 65 different areas that were analyzed for each patient. Although the differences between the groups were not statistically significant, Group B had more females (42% compared to 24% and 20%), they were lighter (156 pounds compared to 173 and 172 pounds), and they had 4 [degrees] more range of motion than the other two groups. The hemovac drainage, length of hospital stay, age, tourniquet time, acute versus chronic injury, and right and left distribution were remarkably similar between groups.

We feel a rehabilitation protocol must strike a balance between the deleterious effects of immobilization and the equally devastating effects of too rigorous a program that could result in loss of fixation, damage, or rupture of the graft. Over the last several years our rehabilitation program has become much more aggressive in reestablishing an early return to function. This trend toward earlier and more aggressive physical therapy has occurred across the country and has resulted in better outcome.

The timing of surgical reconstruction of the ACL has recently been discussed in the orthopaedic community. The suggestion has been made that patients with acute reconstruction have greater problems with motion than those done after 3 weeks. We found no difference in motion at any time period between those patients operated on acutely (3 weeks or less from the time of injury) and those who had their ACL reconstructed after 3 weeks. We feel it is important to reestablish a normal range of motion before surgery.

Complications seen after ACL reconstruction vary with the diligence with which they are sought. We were very attuned to loss of stability and loss of motion, but did not previously appreciate the numbness that occurred around the incision in almost 100% of the patients.

Pain at the graft site was common. Only 30% of the patients complained about it, but another 50% of the patients would acknowledge that they had pain if the area was palpated. There were no infections, symptomatic deep-venous thrombosis, patellar fractures, or tendon ruptures. Four patients were returned to surgery during the study (two in Group A and one each in Groups B and C) and another three (one in Group A and two in Group B) after the study ended. While this seems high, it in part reflects our philosophy that surgical manipulation and lysis of adhesions is better than placing someone in a cast or device that subjects the articular cartilage to increased pressures and abnormal loading.

Radiographs were obtained prior to surgery and at 6 months after surgery in accordance with International Knee Documentation Committee format. Six months is rather early to judge degenerative changes and the radiographs were more instructive of interference screw placement technique. The initial draft of the International Knee Documentation Committee knee evaluation form was used. This form evaluates swelling, stability, pain, return to work and sports, radiographic changes, and one-legged hop test, and includes a subjective evaluation.


The range of motion at discharge, 1 week, and at monthly intervals for 6 months obtained with CPM and with supervised active motion was not statistically different. The patients in the CPM device and those undergoing active motion did not have a deleterious effect on the stability of the knee joint after ACL reconstruction. Neither method altered the postoperative bleeding, usage of analgesics, or length of hospital stay. This study demonstrates that the use of CPM during the first 30 days after ACL reconstruction was similar to supervised active motion in reestablishing the range of motion, neither protocol had deleterious effects on stability. The CPM device did add an additional cost to the patient’s treatment.


The authors thank Tim Simon, Dennis Kunishima, and Andrew Einhorn for technical assistance and Sutter Corporation for partial research funding.


Kenneth E. DeHaven, MD, Rochester, New York: This paper by Doctors Rosen, Jackson, and Atwell is a good example of the type of clinical research needed to provide a more scientific basis for our treatment programs in sports medicine. The authors have carried out a prospective randomized study to answer a pertinent clinical question: does the addition of CPM to the postoperative rehabilitation protocol have any effect on stability or range of motion following ACL reconstruction?

In my opinion, the authors’ conclusions are supported by the data they have presented. The take-home message is that the routine use of postoperative CPM did not improve results compared to their protocol of early mobilization and supervised physical therapy. The fact that the supervised physical therapy was also cost effective compared to CPM is significant as we seek means to control the cost of health care without compromising quality.

It is important to emphasize, however, that this study also found that the use of CPM did not cause increased bleeding and had no deleterious effect on stability. This is reassuring for those who choose to use CPM in selected cases. I hope the authors will present their opinions about those specific circumstances in which they feel that the use of CPM is reasonable and might be expected to be beneficial.

Author’s Reply: In response to Dr. DeHaven’s request for specific circumstances in which we feel CPM is beneficial, we use it routinely in patients who undergo lysis of adhesions and intracondylar notch debridement after ACL reconstructions. These patients can be quite refractory and during the immediate postoperative period we feel CPM use has been beneficial.

The patient’s satisfaction with and perceived benefit from the use of CPM can not be underestimated. We had three physicians who refused to participate in this randomized study because they did not want to take the chance that they would be excluded from use of the CPM. The marketing and potential financial profit for the suppliers of these devices has resulted in considerable “hype” among patients. I have patients who come to the office planning to have an ACL reconstruction who want to know if I will be using a CPM postoperatively. They are using this aspect of their treatment to help select their surgeon. While we do not feel a CPM is detrimental to a well-placed graft, we do wish to point out there are still acceptable alternatives to achieve a successful outcome.


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