Benjamin Bell
ATTR 420-Modalities
Dr. Kevin Jones
April 29, 2013
Continuous Passive Motion in ACL Rehabilitation
Over many years, scientists have desired to find the appropriate treatment for post
operation on anterior cruciate ligament tears. Continuous passive motion (CPM) has been highly
regarded as an important implement for regaining range of motion in the tibiofemoral joint. Yet,
is this CPM the most effective tool for regaining the knee’s range of motion as compared to other
treatment devices or programs? How will the immediate usage of CPM affect patient’s range of
motion whom have just undergone ACL reconstruction surgery, verses other therapeutic
modalities.
Tears of the anterior cruciate ligament (ACL) are some of the most well-known and
catastrophic injuries known to the sports world. The ACL is one of the four major ligaments in
the knee and is located in the anterior compartment. The ACL originates in the distal femur and
inserts at the anterior portion of the tibial plateau. The basic purpose for the ACL is to prevent
excess anterior translation of the tibia on the femur, keeping the knee stable. The fibers of the
ACL fibers are unique relative to other knee ligaments in that they are the only one of the four
knee ligaments to have its own blood vessel. This is a concern when dealing with an ACL tear
but that will be discussed later (Shultz et al. 2005).
When an ACL is injured, the knee is usually extended beyond its normal limits, either
flexed or rotated. The typical mechanism of injury for an ACL tear is a quick change in direction
or cutting with the foot planted in the ground, landing on a straight leg after a jump with a
sudden slowing down, falling off from a tall height, or receiving a blow to the medial knee or
lateral knee as it is planted in a flexed position. Immediately following the injury, there is a
significant amount of pain at the posterior side of the knee, instability, and the feeling or hearing
of a “pop.” Within a few minutes or hours, the knee will begin to swell and there will be a
limited amount of knee movement because of the swelling. This swelling is caused by the
vascularity of ligament and the vessels are torn in the injury, releasing the blood into the synovial
capsule(Blahd 2010).
Immediate treatment for the injured knee includes ice and rest. The athlete must be taken
out of activity to avoid further damage to the knee. An athlete that sustains this kind of injury
will be out of activity for quite some time. The typical recovery time depends on each individual,
but will range from 6 to 8 months to return to normal activities, depending on the severity of the
tear. However, the athlete will have a decision to make, in regards to what he or she wants to do
to repair the injury. They can have an operation to repair the torn tissues or let the injury heal and
develop without the use of a surgery. The main purpose to having ACL surgery is to regain
previous injury level function of the knee and return the knee to proper stability, limit loss of
function in the knee, and prevent further harm or degeneration to any other knee structures.
Sometimes this can be achieved through a nonsurgical approach. This can be the case if you have
a minor tear in the ACL (that can heal with rehab and rest), are not active in sports, if medical
problems yield a risk from surgery, or decide to change lifestyles by not doing what you were
able to do previously. Both avenues are capable of producing a positive effect, but both have
some negatives to it. The main issue with the non-operative approach is the fact that the patient
will not gain the previous strength and stability of the knee as it was prior to the injury. In the
case of an athlete, it is probably well advised to have the ligament reconstructedin surgery(Blahd
2010).
If the patient chooses to go with the surgery route, a procedure on the ACL should be
conducted as soon as possible after the injury has occurred. Reconstructive surgery can be done
by either two methods: arthroscopic surgery or open surgery. Arthroscopic surgery is when small
incisions are made and a small arthroscope is inserted in one of the incisions to transmit images
onto a monitor, in order for the physician to see the knee in a bigger, clear image. Open surgery
is where the whole knee is opened up to get a full view of the joint. Arthroscopic surgery is
preferred to open surgery by physicians for quite a few reasons. Arthroscopic surgery is easier
for surgeons to see and work on the knee, it is less invasive than open surgery with its smaller
incisions, it can be used as a diagnostic tool instead of an MRI, and it has a fewer risks than an
open surgery. The ACL is usually reconstructed with a graft to replace the ligament. A graft isa
ligamentous tissue taken from another region of the body to replace the damaged ligament; this
ligament can be an autograft or an allograft. An autograft is when the ligament is usually
transferred from the patient’s hamstring tendon or patellar tendon. In this case, the surgeon must
make more incisions in the patient to access the ligament. An allograft is when surgeon transfers
the ligament from a donor or cadaver. With the allograft, there is a slight chance that the body
will reject the new tissue, potentially leading to more surgery. Sometimes the ACL can be still
intact, but the bone in which it attaches to has separated with a piece of the bone attached to it.
So the bone fragment with the ACL must be reattached to the bone (Blahd 2010).
Generally, ACL reconstruction surgery is safe, but there can always be possibilities for
complications. These problems are uncommon, but can still occur: numbness in the surgical scar
area, infection in the surgical incisions, damages to any of the nerves, blood vessels, or structures
around and in the knee, blood clots in the lower leg, and potential risks of anesthesia. Like with
the cadaver, the allograft could potentially be rejected or cause issues with stretching or
loosening.
Continuous Passive Motion (CPM) is a technique used on patients who have just gotten
out of a surgical procedure or trauma, like an ACL surgery. CPM involves a motorized device
that the patient applies to the treated joint and allows for movement through its full range of
motion at a controlled speed. This technique is the antithesis of immobilization. The device was
proposed for rehabilitation usage by Robert Salter, a Canadian physician who saw many
advantages on using CPM on synovial joints. The device is made to replicate the natural
movement of a joint and is implanted after the surgery as soon as possible. The implement
placed on the patient is a boot or a brace; the affected joint is stabilized above and below the
joint. Once it is on, the device will begin to move the joint passively through the range of
motion, extending and flexing the knee. It continues for a certain duration and speed. This could
increase over time as the joint becomes more mobile. It is essential to have early maintenance of
motion to ensure the joint’s long-term mobility (Driscoll 2010).
With CPM designs, three types of devices were made with a different style, some bearing
more advantages than others. The three styles are free linkage, anatomic design, and nonanatomic design. Free linkage is very poor with joint stability and controlling the joint’s range of
motion; yet, this style favors the patient in that it’s adjustable to comfortably fit them. So these
are not appropriate for unstable joints. Anatomic design is poor in patient comfortability and
multi-axis motion. However, it is very good with controlling the range of motion and getting the
joint through the range completely, as well as stabilizing the joint. This style is most preferred
for the knee. Non-anatomic design is an average style that doesn’t favor one characteristic but
only excels at getting a full range of motion (Driscoll 2000).
To sum up the basic physiological effect on CPM, Diehm SL states that “motion that is
never lost need never be regained. It is the regaining of movement that is painful” (Diehm 1989)
When CPM is used; gentle pressure is applied to the healing tissues. Alternate flexion and
extension of the joint by CPM raises and lowers the hydrostatic pressure in the joint and
periarticular tissues resulting in a "pumping effect" that forces fluid out of the joint and
periarticular tissues. The use of CPM is beneficial for three reasons. First, the articular
cartilage(which is an avascular tissue) that is damaged will receive nutrients from the synovial
capsule and its metabolic activity will be increased. Second, through the stimulation of tissue
remodeling, the articular cartilage will be able to regrow and become stronger. Finally, the
healing process of articular cartilage, tendons and ligaments will be expedited. Through these
three benefits, the joint will become enhanced and many other physiological effects are achieved.
For one, the range of motion will increase, if the treatment is applied early enough after
operation. As stated previously, the joint’s nutrition will be increased because of the synovial
fluid supplying the cartilage with nutrition. The meniscus absorbs the substances and is
nourished through expansion and compression. Elevating the injury while the joint is moving
reduces edema within the injury site. (Denegar 2006) Also, pain is reduced when movement of
the joint activates afferent nerves in the muscles and skin. In turn, this may help control the pain
via the gate mechanism. However, CPM is not designed for treating acute pain. Ligament
healing is also an enhancement received from this treatment. In some studies where CPM was
applied immediately following operation, the allograft’s biomechanical properties were increased
in a MCL reconstruction. Unfortunately, studies have also shown unpromising effects of
immediate CPM on post-ACL surgery (Starkey 1999).
Since the ACL is the most unique ligament of the knee’s four main ligaments, it doesn’t
receive the same effects as do the other three ligaments, the meniscus or the articular cartilage.
The ACL is covered with a synovial lining of its own and this prohibits the ligament from
receiving nutrients from the synovial fluid. So, the ligament must depend on the intrinsic blood
vessels (Starkey 1999).
The purpose of CPM is to maintain joint range of motion following trauma or surgery,
but in order to understand that, one must have an understanding of the pathophysiology of joint
stiffness. The initial purpose to using CPM is to reduce stiffness within the joint after surgery. If
a joint is immobilized after a traumatic surgery, the joint can become stiff and develops from
four main difficulties: bleeding, edema, granulation tissue, and fibrosis. Applying CPM early
affects the first two stages by pumping blood and fluid away from joint and the surrounding
tissues. This helps in reducing any potential swelling that would occur.
The first stage of joint stiffness is bleeding, which results in distension of the joint
capsule and the swelling of the periarticular tissues. This can sometimes occur within minutes or
hours following the surgery. Under typical circumstances, the joint is held in the position of
maximum articulation to minimize pain when stretching the joint capsule and pressure of the
hematoma.
The second stage of joint stiffness is the edema, which occurs within a few hours or days.
It is very similar to the bleeding stage except it progresses less rapidly. This edema is caused by
inflammatory mediators that are released from dead, injured cells and platelets. These mediators
cause vasodilation, producing plasma to leak out into the adjacent tissues. Once the joint has
become more swollen and less compliant, the joint becomes more physically difficult to move
and pain increases with movement. The fluid basically clogs up the intrastitial fluid and reduces
the knee’s ability to move effectively.
The third stage of joint stiffness is the formation of granulation tissue. This can occur
after a few days or weeks after the operation. Granulation is tissue that has become highly
vascularized and is loosely organized. The material is similar to a highly organized blood clot
and a loose areolar fibrous tissue. This tissue will eventually form into collagen and then forms a
scar tissue from its extracellular matrix. The fluid accumulation in the first two stages goes away
but the stiffness increases due to the solid extracellular matrix that is formed. This matrix has
thickened and the joint greatly loses its compliance. At this stage, the knee is amenable to
“manipulation” until a certain amount of force is exerted to overcome the blocked motion.
The fourth and final stage is called fibrosis. This is the stage where scar tissue is formed
from the mature granulation. It has a high concentration of collagen type I (slow twitch) fibers.
This formation can obliterate the structure of the underlying tissues, causing extreme pain when
the joint moves through the range of motion. The loss of motion sustained in this stage cannot be
overcome, even with manipulation. This is due to the high concentration of this dense,
collagenous scar tissue (Driscoll 2000).
As the joint goes longer and longer into post-operative time without forced motion of the
joint, the stiffer the joint will become. If the joint’s range of motion was tested 2 hours after the
surgery under anesthesia, the joint would not be able to swing through the full arc of motion due
to the accumulating blood in the knee. This causes distention of the periarticular tissues and the
loss of amenability. Yet, if this fluid was forced out of the periarticular surfaces, the knee’s
range of motion would not be hindered and would be restored. If the patient progressed further
without range of motion exercises, edema would form and the joint would in all likelihood not
move through the full range of motion. However, it is possible to remove the fluid from the
periarticular region with an excessive amount of “milking.” Yet, the range of motion is hindered
because of the delay in time and can’t return to normal. The joint will stiffen more and more the
longer the delay in doing range of motion exercises. Generally, people assume the stiffness
comes from the scar tissue weeks after the operation, which is true; but, it all comes down to the
initial blood fluid in the joint within the first few hours post-operation. If this is done
successfully, long term benefits will be achieved with immediately usage of CPM. With this
understanding of joint stiffness, it is important to act upon the joint as soon as possible (Salter
1993).
Although CPM is one of the utmost effective tools for regaining joint range of motion,
complications can arise from its application. Most are not serious or permanent. Increased
bleeding is the most common complication with CPM. Fortunately, this increased bleeding is not
common enough to have a sufficient amount of blood to require a transfusion. The major concern
with using CPM after major joint operations pertains to the wound itself. In a study conducted on
the elbow by the Veterans AffairsDepartment of Research and Development, the CPM was
applied to elbow joint and suggested that CPM did not have a negative impact on the wound’s
healing itself. However, there could have been a problem if there was still a good amount of
swelling within the joint. In that case, the CPM must take the joint through the full range of
motion till the swelling has curtailed. Some patients in their study sustained nerve compression
palsies due to the CPM’s local compressive; this can be fixed with proper fitting of the device on
the patient. Another issue that is of concern is deep vein thrombosis and pulmonary embolism,
relating more towards the lower extremity. While using the CPM, studies have shown an
increase in femoral vein flow with each cycle (Driscoll 2000).
With this given knowledge, the question arises as to whether CPM is the most
appropriate therapy to restore joint mobility. Physicians are more likely to choose CPM devices
because of their easy application and utilization. Studies have been conducted to determine what
type of treatment will be best in returning that patient from post-ACL surgery to increase their
range of motion. Other treatments such as non-CPM therapy, rehabilitative bracing,
neuromuscular stimulation, open verses closed kinetic chain exercises, early weight bearing, and
home versus supervised physical therapy are also available for use. A paper written by
researchers in the Physiotherapy Department at Norfolk and Norwich University compared CPM
to a non-CPM based rehabilitative approach. In the systemic review, they examined the data on
published studies dealing with CPM and covered a wide variety of aspects to their treatment. In
regards to range of motion, six papers were used to determine range of motion and five out of the
six studies determined that knee joint range of motion after ACL reconstruction was not
significantly different between CPM and non-CPM therapy (Smith & Davies 2006). However,
one of the reports stated that their subjects in the CPM group presented significantly greater
active and passive knee flexion than the non-CPM group (p<0.05) (Wright et al. 2008).
In one study, researchers wanted to assess hemovac, drainage, range of motion, swelling,
effusion, and subject pain by comparing a CPM group and a non-CPM group (a hinged knee
brace was used for this group). In the CPM group, they applied a Model 9000 CPM machine
immediately following surgery for at least 16 hours a day while in the hospital. Usually, they
were kept in the hospital for three days and were told to gradually increase their knee flexion to
90 degrees as tolerated. When they were not using the CPM, they were told to wear a PB
Sportlite hinged knee brace. The range of motion for the brace was set at 10 to 90 degrees. In the
non-CPM group, they were given the same knee brace. They wore the brace every all the time,
especially while on crutches. While in the hospital, “physical therapy was identical for both
groups; emphasizing isometric thigh exercise, patellar mobilization, active knee flexion as
tolerated and achieving full passive extension as soon as possible” (Yates et al. 1992). They
continued their rehabilitation programs at home until they were called in for a follow up 3 weeks
later. Before the physical therapy began, range of motion was documented before and after with
active flexion, passive flexion, and passive extension 3, 7 and 21 days postoperatively. The data
shows that after 3 days, active and passive flexion was higher in the CPM group than the nonCPM group. However, there was no significant difference in the passive extension of the CPM
and non-CPM group. Nothing was recorded in regards to active extension.After 7 days, range of
motion increased for both groups but the CPM group had a higher range and increase. After 21
days,similar results were recorded for the group.Then once released from the hospital’s
supervision, they were told to decrease their time to 6 hours a day for two weeks. The results
suggest that immediate CPM after ACL reconstruction is safe and facilitates early range of
motion by decreasing the amount of pain medication, effusion, and soft tissue swelling (Yates et
al 1992).
In a study that showed that CPM and a non-CPM techniqueswere comparable, patients
were all treated with a ACL reconstruction but some had be injured for over 3 months and some
had more acute injuries. In this sense, it’s not as a quality of comparable study**. The study
allocated at random two different groups with different rehab programs. One group used early
active range of motion with a brace fastened with Velcro straps with 10 degrees of flexion. They
were also given crutches with partial weight bearing. The active motion group underwent a
program focused on dynamic active knee flexion, and passive full extension, which was
supervised by a physical therapist. The training was conducted three times a day. The CPM
group had 6 hours a day of passive training using the CPM device, along with daily session of
active range of motion training with a physical therapist. This occurred for six days
postoperatively. After this six day rehab session was over, nothing was stated on any other rehab
conducted on the knee over a five week period. The examiners reevaluated the patients at six
weeks postoperatively. From the results of this study, range of motion for extension and flexion
was not significant postoperatively between the two groups. The reason for this sort of result, as
compared to the previous study (Yates et al. 1992), could be because of the study not containing
a suction of intrastitial fluid from the joint space and no application of pain medication. The
researchers recognize CPM and its benefits to the knee joint, but based on this study they do not
suggest because of its potentially harmful effects on the ACL. “CPM has documented positive
effect on the healing of articular defects. However, no benefit has been demonstrated after
ligament reconstruction. Using CPM can induce undesired strain on the healing graft compared
to active motion, which will reduce the strain on the graft.” (Engostrum). The study did not
appear to be high quality due to a very small number of references and short length. The paper
alsodid not go into enough detail about the rehab programs and how they were maintained
throughout the course a six-week period (Engostrum 1995).
In another comparable study, 60 patients with ACL ruptures were split into two groups.
The range of motion was observed preoperatively and postoperatively on the seventh day. One
group was given the CPM the first postoperative day after the drain had been removed. The other
group was given a CAM (continuous active motion) the first postoperative day. Both groups
were informed to use the device for 3 hours a day. They were allowed full flexion in their knee,
based on their pain level during the motion. Isometric strengthening exercises were performed
daily, as well as lymphatic drainage. This postoperative treatment was allotted for seven straight
days and the patients were given the capability to perform partial weight-bearing exercises for 2
weeks. Prior to the study, both groups had a similar scale on the knee’s range of motion. The
mean for CPM group was 137.5 degrees and 139.5 degrees for the CAM group. No deficits were
recorded in patient’s capacity to reach full knee extension. Postoperatively, full knee extension
was achieved in all the patients at the same time. For knee flexion, the CPM group was able to
flex the knee to an average of 95 degrees while the other group was able to flex the knee to 101
degrees. However, this was not significantly different (Freimertet al. 2006).
In conclusion to this examination of CPM, I have learned about the anatomy of the ACL
and how it is affected by the certain therapeutic devices after undergoing repair. CPM is a
frequently used a therapeutic device to help with range of motion and I have gathered that it is an
effective tool in increasing the knee’s range of motion. As stated from the studies gathered, CPM
can be effective but continuous active range of motion can do that same as well as using a brace
with specific therapeutic exercises. Even if CPM does not that effective increasing the range of
motion, it can severely decrease the amount of swelling within the joint. Also, pending on the
type of CPM used, it can be a useful device for decreasing pain, even though it is not meant for a
pain reducing device. However, I fear that it is not the greatest technique to use for gaining the
most range of motion immediately following surgery and further research is needed to conclude
this.
Works Cited
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