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REVIEW PAPER

The Value of Continuous Passive Motion in Rehabilitation Following Total Knee Replacement Jennifer naOnis

Key Words Continuous passive motion, total knee replacement. rehab- ilitation.

Summary Variable use is made of continuous passive motion (CPM) as a modality in rehabilitation after total knee replacement. The liier- ature regarding the value of using CPM in addition to exercise is reviewed. The claimed beneficial effects of CPM on reducing pain, helping wound healing, maintaining circulation, gaining range of motion, reducing length of hospital stay and reducing the need for manipulation under anaesthetic are discussed. Perceived disadvantages of CPM including cost and the devel- opment of extension lag are also considered, as is the issue of optimal duration of application of CPM. The results of the studies are inconclusive, but several trends are identified and their implications for rehabilition discussed.

Introduction Mechanical continvous passive motion (CPM) and the possibility of its use after total knee replacement (TKR) to assist in achieving range of movement (ROM) is widely known in ortho- paedic medicine and physiotherapy (Basso and Knapp, 1987). However, its use varies widely. In some hospitals it is not used at all; in some it is used only if the patients are unable to gain sufficient ROM by other means, while in others it is applied routinely to all patients who have undergone a m. This paper critically reviews studies into the effectiveness of CPM to ascertain whether the published literature provides any useful guidelines to the efficacy of this modality as a rehabilitation tool and, in the current cli- mate of health care, its value in reducing the risk of post-operative complications and shortening length of hospital stay. The concept of CPM was largely researched and developed by Salter and his colleagues. They experimented on rabbits and found benefits from the use of CPM on the healing of cartilage defects and intra-articular fractures, protection of articular cartilage in septic arthritis and heal-

ing of damaged knee extensor tendona (Coutta et al, 1984; Coutte, 1986; Salter ef al, 1980, 1981). CPM on humane hes been used in a num- ber of conditions and after various mrgical pro- cedures (Coutts et al, 1989), but possibly its most wideepread use is after TRR.

According to Coutts (1986), one of the main aims in rehabilitation after TKR is marimisation of ROM. The traditional post-operative manage- ment has been immobilisation of the joint for some time followed by active exercises (Coutte et al, 1984). It has been claimed, however, that joint stiffness is encouraged by immobilisation (Stap and WoodGn, 1986; Harme and Engstrom, 1991) and the current trend is moving away from immobilisation towarda early motion of the joint (Frank et d, 1984; Vice et ol, 1987).

CPM is only one method available to phydother- apists to help in achieving the desired ROM at the joint. Others include manual w i v e , active assisted and active motion. Coutta (1986) argues that, if passive motion is to be effective, it must be applied by a machine, because manual passive motion is inconsistent, causes more pain and does not last long enough, but he provides no justification for these claims. If CPM is to have a place in rehabilitation after TKR it must have proven value in addition or in preference to the other available methods.

It has been claimed that there are a number of areas in post-operative recovery and rehabilita- tion after TKR where CPM offers advantages over the use of just an exercise based rehabilita- tion programme (Frank et al, 1984; Gose, 1987; Johnson, 1990). These include: 0 Pain and need for analgesia. 0 Wound healing and infection. 0 Circulatory effects and post-operative complications like deep vein thrombosis and pulmonary embolus. 0 Early and later ROM. 0 Length of hospital stay. 0 Need for manipulation under anaesthetic (MA).

Each of thate! six aspects wil l be considered indi- vidually, but it must be remembered that many of these effects are interdependent. For example, less pain would result in less protective muscle spasm so more ROM could be gained. Achieving 90' of knee flexion is commonly a requisite for patient discharge, so if ROM is gained sooner, then length of hospital stay wil l be shortened.

Pain Relief and Need for Analgesia Frank et aZ(1984) state that the use of rhythmic movement of the joint has been shown to inhibit the pain spasm reflex. As the CPM machine pro- duces such motion it seems possible that its use would reduce pain and allow achievement of greater ROM more easily than if it were not applied. A number of other authors support this conclusion and state that the patients in their studies who were given CPM as well as an exer- cise programme needed less analgesia than the control group who were doing only the exercises (Coutts et uZ, 1983; Coutts, 1986; Ritter et a,?, 1989; Romness and Rand, 1988). None of these authors, however, used any measure of pain such as a visual analogue scale. Coutts et al(19841, Harms and Engstrom (1991) and Basso and Knapp (1987) did measure pain levels and demand for analgesia in the first few days following surgery. They found that, although there was less pain in the groups using CPM, the differences were not statistically sig- nificant. Significant results in favour of CPM as a means of pain relief were found by Woods et aZ (1987). In contrast, Davis (1984) found that patients on CPM required more analgesia on the day of surgery. However, on following days, the differences between the two groups were not statistically significant.

Wound Healing Probably the main reason why surgeons advo- cated immobilisation of the knee aRer TKR was concern that early movement would stress the wound and adversely affect healing (Harms and Engstrom, 1991). However, it is claimed that early motion actually helps wound healing. It is argued that, if the wound is immobilised, the influence of natural stresses is removed and collagen is laid down in a haphazard way and a weak repair resulta (Evans, 1980). Frank et al (1984) further claim that elongation of the wound is itself a specific stimulation for collagen production and, thus, a requirement for effective healing. Coutta et al (1984) refer to Salter's work and state that early joint mobilisation is imp- ortant as poor wound healing results in a contracted scar and adhesion formation which adversely affect ROM. None of these authors,

however, provides support for these claims.

Van Rooyen et aZ(1986) experimented on rabbits and concluded that the structural organieation of the collagen was much better in the legs moved by CPM than those immobilised. They claimed that their results were also valid in humans, but this statement was not invest- igated or supported in any way. The need for early mobilisation may not, in itself, justify the use of early CPM as some argue that use of this modality is possibly too aggres- sive at this stage. Johnson (1990) compared the effects on wound healing of CPM and immobili- sation in humans, applying it in the immediate post-operative period. He found that healing after TKR was delayed in the immobilised knees, although not Significantly. In the CPM group he found that oxygen tension levels in the wound edges were reduced during the first three post- operative days if flexion greater than 40" was set. After that time, flexion greater than 40" did not have similar effects. The patients on CPM did, however, gain significantly better ROM than the immobilised control group and the author concluded that the careful application of CPM was justified. Johnson also found that the use of CPM did not increase the incidence of infection. In fact, infection occurred more in the immobilised knees.

Harms and Engstrom (1991) agree that CPM promotes desirable patterns of wound healing, but cite Johnson and caution that care should be taken not to exceed 40" of flexion in the first few post-operative days.

Circulatory Effects and Postsperative Complications The effects of circulatory stasis after TKR, eg joint effision and deep vein thrombosis (DVT), interfere with achievement of ROM and also result in longer hospital stay if complications like DVT become clinically significant. CPM is claimed to help venous lymphatic drainage and thus reduce joint effision and lessen the risk of thrombus formation (Coutta, 1986). Harms and Engstrom (1991) found that wound drainage was unaffected by application of CPM, but did not measure joint oedema. In contrast, Romness and Rand (1988) found that wound drainage was significantly greater in the CPM group although blood loss and haemoglobin levels were similar in both groups. Davis (1984) also found greater wound drainage in the CPM group. Compared to the control groups which were immobilised for a few days and then began active movements, Coutts et aZ(1983,1984), and

Coutts (1986) found that the CPM groups had significantly less joint effusion and oedema. These findings are also supported by Ritter et al (1989). Basso and Knapp (1987) measured joint oedema and found no significant differences. However, they were comparing two CPM regimes, not a CPM regime and a control of immobilisation and exercises, so their results are not comparable with other studies. With regard to the potentially more serious cir- culatory complications. of DVT and pulmonary embolism (PE), Lynch et a2 (1988) found that the incidence of calf thrombosis was about 40% in both groups and that there was no incidence of PE in either group. Vince et a2 (1987) performed venograms on the CPM and control groups and found a much lower incidence of DVT in the CPM group. They concluded that CPM is effective in reducing the incidence of post-operative DVT. However, they did not state how many patients from each group actually presented with clinical signs and symptoms of DVT.

Range of Movement Two periods of time need to be investigated when considering whether CPM is effective in helping patients to achieve ROM, particularly knee flexion. The first is the length of time it takes patients to reach the degree of flexion required for discharge. The second is between six and 12 months after surgery when the ulti- mate ROM can be evaluated. Several studies have shown positive results in terms of ROM achieved in the first weeks after surgery. Coutts et a2 (1983, 1984) and Coutts (1986) found that the patients given CPM gained 90" flexion saoner than the controls and still had better knee flexion two weeks post-operatively. Similar results were also reported by Davis (1984) and Johnson (1990). Woods et a2 (1987) found that ROM at discharge was significantly greater in the CPM group and that this group also achieved independent straight leg raising sooner than the control group. Greater range of knee flexion was also achieved in the early post-operative period by the CPM group in the study made by Harms and Engstrom (1991). They also noted some other interesting and possibly important results. Patients with good pre-operative flexion did better post-operatively than those with poorer pre-operative ROM irrespective of which group they were in. Also, patients with rheumatoid arthritis did better than those with osteo- ar thr i t is throughout the time in hospital. This latter result regarding diagnosis was also found by Ritter and Stringer (1979).

Other authors found no staWcel difference in ROM between the two groups in the early &age6 of recovery (Ritter et a2, 1989; Romness and Rand, 1988; Young and Kroll, 1984). Vince et a2 (1987) reported that, although the patients given CPM reached 90" sooner than the control group, by the date of diecharge mean flexion in both groups waa almost identical. The time of discharge was not stated, but these results do raise the iseue of how long-lasting is any advantage gained by the w e of CPM.

With regard to the long term effects on ROM of the use of CPM, Coutts et a2 (19841, Coutte (1986) and Johnson (1990) all report that early gains in the CPM group were still present one year later. However, Woods et d (1987) found no statisti- cally significant difference between the two groups in their study. These findings are sup ported by Ritter et al(1989); Romness and Rand (1988) and Young and Kroll(1984).

Length of Hospital Stay It may seem logical to assume that, if diecharge is governed by patients gaining a required range of knee flexion, studies in which patients given CPM did better than controls would ale0 show that length of hospital stay would be shorter. In some studies this was the case (Coutts et al, 1983; Coutta, 1986, Woods d al, 1987; Johnson, 1990; Harms and Engstrom, 1991). Length of hospital stay was shorter by between one and six days. Davis (1984) and Romnesa and Rand (1988) ale0 reported shorter lengths of stay in hospital for the CPM patients, but did not state the differ- ences, only that they were not significant. Based on these studies, a coet-effective as well as rehabilitative argument could be made for the use of CPM.

However, in some papers, date of discharge did not always appear to be linked directly with achievement of desired ROM. This would imply that there may be other factore which influence length of hospital stay irrespective of absence of post-operative complications and gains in ROM, but these factors were not identified.

Need for Manipulation under Anaesthetic When immobilisation was the treatment of choice aRer TKR, manipulation under anaesthetic (MUA) was almost a routine requirement in order to break down adhesions and gain ROM (CouttS et a& 1984). The indication for MUA in studies which compared its incidence between

CPM and control group8 was failure to gain enough knee flexion by other means.

The majority of studies which considered MUA found that more patients in control groups needed manipulation than did those in groups receiving CPM (Coutts et al, 1984; Coutts, 1986; Woods et al, 1987; Vince et al, 1987; Romness and Rand, 1988). Only onqtudy found a higher incidence of MUA in the CPM group (Young and Kroll, 1984). The validity of drawing con- clusions from these findings is brought into doubt because no explanations were given as to why patients were not achieving required ROM. Factors like pre-operative ROM, pathology and patient age may well be valid indicators that post-operative ROM is unlikely to be good.

Considering the fact that MUA is still used on some patients after TKR, it is worth considering how effective MUA is as a method of gaining ROM. Fox and Poss (1981) looked at the ROM before and immediately aRer MUA and one year later and compared the results with those patients in their sample who had not undergone MUA. Results showed that, although MUA did achieve an immediate increase in ROM, this had not been maintained after one year. The authors raised the issue of whether MUA has any place in management of the knee after I K R if it provides no long-term gain in ROM and involves the patients undergoing further surgery with all its associated risks.

Duration of Use of CPM The length of time of application of CPM did not appear to have had any effect on whether results were positive or not in terms of wound healing, gains in ROM, or length of hospital stay. Gose (1987) applied CPM only three times a day for one hour while most other studies had applied it for much longer. His findings showed that the application of CPM, even for a short length of time, produced better results than if it was not used at all. However, when comparing his results with other studies he found that those which applied CPM for much longer peri- ods had even better results. He concluded that attention needs to be given to the optimal length of application of CPM and to the whole protocol of CPM use.

Basso and Knapp (1987) undertook such a study and compared two protocols. One group received CPM for a minimum of 20 hours daily and the other for five hours daily in addition to the same exercise programme. The results showed that, although there was a trend towards better knee ROM in the group receiving 20 hours of CPM,

there was no statistically significant difference between either group for ROM achieved, length of hospital stay, pain or joint oedema. The authors concluded that long applications of CPM produced no greater benefits than a shorter application. These results raise interesting issues, but insufficient research has been done for any definitive conclusions to be drawn.

Disadvantages of CPM Some authors claim tha t use of CPM tends towards development of an extension lag in patients. Coutts et a2 (1989) stated that this is a common problem, but provided no support for this claim. Harms and Engstrom (1991) found that problems with extension tended to occur if flexion was gained too quickly. They ascribed this to the possibility that the patients were focusing too much on gaining flexion and not giving enough time to extension exercises, but did not discuss the possibility that this problem might have been due to an extension lag resulting from use of CPM. According to Ritter et a2 (19891, who measured knee extension to test for extension lag, this problem occurred in patients undergo- ing only a programme of active exercises as well as in those also receiving CPM, but they argued that the lag was much more difficult to reverse in patients on CPM. Coutts et a2 (1989) believed that gains in knee flexion must not occur at the expense of quadriceps muscle length and strength and that, if CPM is going to be used, this must only be as an adjunct to active exercis- es and strengthening of all muscle groups. Ritter et a2 (1989) noted three problems which arose in their study. The first was tightness in the knee flexors of the patients on CPM. They ascribed this to the possibility that less active extension was being done by patients because of the amount of time spent on the machine. Secondly, the cost of CPM was felt to be high in terms of both purchase of the machine and the time needed by staff to set the equipment up correctly. In view of these costs, CPM should be proved to be effective if it is to be used. The third issue raised was that patients became bored when they were on the machine and resented the way their mobility was limited, and that compliance became poor. These patients were on the CPM machine for 20 hours a day so these complaints are understandable. In almost all the studies presented, the CPM was used for between 16 and 24 hours daily, but no other authors mentioned this problem. This does not mean that such a problem was not more widely present and again raises the question of optimal duration of application of CPM.

Discussion Although the results of these studies are not conclusive, some interesting points have been raised which may indicate trends which need to be accounted for when considering its use.

The majority of researchers found that use of CPM immediately or very soon after surgery does help patients gain ROM sooner than they would without mechanical assistance. Johnson’s findings (19901, however, suggest that the set- tings for flexion in the early stages should not be too high as wound healing may be jeopardised. Another important consideration is that the development of a n extension lag should be avoided. This could be achieved by the patient performing regular knee extension and inner range quadriceps exercises and not focusing too much on merely gaining flexion (Coutts et al 1989; Harms and Engstrom, 1991).

Fewer authors found that early gains in ROM after use of CPM were maintained in the long term. Patients who have not received CPM seem to ‘catch up’ in time and ultimate ROM seems to be very similar. This raises the question as to whether the use of CPM is justified and may be a reason why it is not used in some hospitals. However, the short-term gains resulting from the use of CPM may be justified from a cost- effectiveness point of view. If patients a re required to gain a certain ROM before they can be discharged and this ROM can be achieved sooner with the use of CPM, then the length of hospital stay is likely to be reduced (Coutts, 1986; Johnson, 1990; Harms and Engstrom, 1991). The savings made may justify the cost of using CPM.

In considering the whole post-operative rehabili- tation programme following TKR, the factors of pre-operative ROM and underlying pathology raised by Harms and Engstrom (1991) and Ritter and Stringer (1979) are worth considering. It is possible that patients who are not achieving the required ROM may not be able to, even with the help of CPM. A smaller ROM may be quite acceptable to these patients because they also have the added gains of removal of joint pain and some correction of deformity.

The literature does support early and sustained movement of the wound in order to produce a strong scar and little adhesion formation which would interfere with gaining functional ROM. It could be argued that such movement could be achieved with active and, possibly, manual passive motion, but appropriate use of CPM has the advantage of providing consistent oscillatory tension in soft tissue over a sustained length of time.

Conclusion The findings discussed in this review on the possible benefits of the use of CPM afbr TKR have proved inconclusive, although Borne trende in favour of CPM are preeent. Thew trends may not, however, be strong enough to justify its regular use and may explain why the inclueion of CPM in post-operative rehabilitation pro- grammes is so variable.

Author and Addm88 tor Jennifer Moms BA MCSP OipTP is a teadm at the school of Physiotherapy, Institute of Health Care Studies, University Hos- pital of Wales. Heath Park, Cardiff CF4 4XW.

This article was received on August 17,1994, and accepw W, March 9,1995.

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An Investigation Into the Effects of Low Level Therapy on Arterial Blood Flow in Skeletal Muscle

Denis James Martin DPhil BSc MCSP

Course: DPhil, Depaftment of Physiotherapy, University of Ulster at Jordanstown, 1994

Housed at: University of Ulster (at Jordanstown) Contact address: Department of Physiotherapy, Queen Margaret College, Leith Campus, Duke Street, Edinburgh EH6 BHF

While cellular, and to a lesser extent animal, research has supplied evidence that irradiation has biological effects, studies on humans have failed to provide unequivocal support for low level laser therapy (LUT). Arterial blood flow waa outlined as a major factor in the healing process and claims that low level laser irradi- ation has a vasodilator effect on skeletal muscle were investigated. Strain gauge plethysmography was chosen to measure blood flow. Having established the validity of etrain gauge plethysmography in the litera- tue, its reliability was confirmed in initial correlational &dies. Following preliminary atudies to determine the required period ofeatabliahed equilibrium of blood flow and the behaviour of blood flow under the controlled experimental environment, three different subject experimental studies tested the effecte of irradiation on the calf muscle area of healthy human volunteers in

supine lying using an Omega 3ML machine with a multi-diode cluster head. Treatment using a number of combinations of pulse repetition rate (PRR) and irradi- ation time showed no changes of therapeutic benefit, defined as being equivalent to the effects of light exer- cise. The combinations of PRR and irradiation time were as follows:

Experiment 1 PRR = 36.48 Hz; irradiation time = 6 minutes; n = 6 PRR = 5000 Hz; irradiation time = 6 minutes; n = 6 Control; no treatment; n = 6

PRR = 5000 Hz, irradiation time = 20 minutes; n = 8 Control; no treatment; n = 8

PRR = 2.28 Hz, irradiation time = 20 minutes PRR = 36.48 Hz; irradiation t i e = 20 minutes PRR = 5000 Hz, irradiation time = 20 minutes Controt no treatment; n = 6

Experiment 2

Experiment 3

Xrradiation at a PRR of 36.48 Hz for six minutes and also for 20 minutes produced consistent decreases in blood flow (p < 0.06). In the other groups changes were small and inconsistent among subjects. While the results suggest that PRR may be an important factor in LLLT the claimed vasodilator effects of low laser irradiation on skeletal muscle blood flow were not upheld and its therapeutic efficacy was questioned.