Yonsei Medical JournalVol. 43, No.5, pp. 621- 626, 2002

The Effect of Cold Air Application on Intra-Articular andSkin Temperatures in the KneeYoung-Ho Kim\ Seung-Sug Baek2

, Ki-Sub Choi2, Sang-Gun Lee2, and Si-Bog Park1

'Department of Medical Engineering, College of Health Science, Research Institute of Medical Engineering, Research Institutefor Medical Instrumentation and Rehabilitation Engineering, Yonsei University, Wonju, Korea;2Department of Rehabilitation Medicine, the Hospital for Rheumatic Diseases, Hanyang University College of Medicine, Seoul,Korea.

The present study was performed to investigate the effecton the skin and the intra-articular structures of 5-minutes ofcold air application. During and after 5 minutes of cold airapplication on 20 healthy subjects, the skin and intra-articulartemperatures were measured by means of an infraredthermogram and a digital k-wire probe, respectively. 1beresults showed that 1) Skin temperature dropped very rapidlyby a total of 22.1't after 5 minutes of cold air application.2) Intra-articular temperature dropped by 3.9'(; after 5 minutesof cold air application. 3) Two hours after the start of trearmentwith cold air, intra-articular temperatures had still not returnedto their baseline values (p <0.01). 4) The baseline skintemperature and the baseline intra-articular temperatnre weresignificantly correlated r=O.51 (p <0.05). However, there wasno significant correlation between the skin temperature changeand the intra-articular temperature change after 5 minutes andafter two hours of cold air application. Finally, 5) a significantcorrelation r={).72 (p <0.01) between the body mass indexand the baseline skin temperatures was found There was nosignificant correla1ion between the body mass index and thetemperature changes, at the skin or in the knee joint, eitherduring or after cryotherapy (p>O.05).

Key Words: Cryotherapy, skin temperature, intra-articulartemperature

Received March 9, 2000Accepted July 25, 2002This wf1I'k was supported by RRe Program of MOST and

KOSO-'.

Reprint address: requests to Dr. Young-He Kim, Departmentof Biomedical Engineering, College of Health Science, ResearchInstitute of Medical Pngineering, Research Institute for MedicalInstrumentation and Rehabilitation Engineering, Yonsei Univer-sity, 234 Maeji, Heungup, Wonju, 220-710, Korea. Tel: 82-33-760-2492, Fax: 82-33-760-2197, I-mail: yhkim@dragon.yonsei.

ac.kr

INTRODUCTION

Cryotherapy has been used as a method ofphysical therapy along with heat therapy for along time. It is a superficial treatment with botha conductive and a convective effect? 'The mostcommonly used cold therapies include the use ofice, cold water, chemical packs, vaporized liquidsand refrigeration units. Recently, cryotherapyunits using cold air have been developed, andhave been applied to the diseased area using acold air temperature of -30"C.

In general, heat or cold therapy on a localizedarea is known to be effective for arthritis.However, some investigators do not recommendits use, because of the fact that the associated in-crease in intra-articular temperature has a detri-mental effect, due to the resulting increase in thenumber of destructive articular enzymes.43 Coldtherapies on inflammatory joints and on the bursaresult in a decrease in edema, due to vasocon-striction. Although pain relief is achieved indi-rectly because of the resulting decrease in edema,it can also be accomplished by directly treatingthe nerve fiber. \lVhen sufficient cold therapy isperformed on the painful joint, the pain isreduced due to the increased pain threshold.4

In 1949, Horvath and HollanderS reported thatintra-articular temperature decreased when a hotpack was applied for four minutes, and increasedwhen an ice pack was applied for the same periodof time. In addition, Oosterveld and Raskero andOosterveld et a1? measured intra-articular tem-perature during heat and cold therapies for three

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622 Young-He Kim, et al.

hours, and reported that heat and cold therapiesresulted in increasing and decreasing intra-articu-lar temperatures, respectively.

The purpose of this study was to investigate theeffects of local cold air application all. the skin, tomeasure the associated intra-articular temperaturechanges and to observe the rebound temperaturechanges after cooling.

MATERIALS AND METHODS

The subjects for the present study were 20healthy volunteers for whom there was neitherevidence of disease or physical damage, nor ofinflammatory symptoms, including fever orswelling, and who agreed to participate in theexperiment (Table 1). As shown in Fig. 1, eachsubject was maintained in a supine position with

Table 1. Subject Characteristics

Mean ± SD

Number of subjects 20

33.8 .1 127 (23 - 68)

male IS/female 5

170.3 ± 6.5

66.9 ± 7.7

23.0 ± 2.2

Age (years)

Gender

Height (em)

Weight (kg)

Body mass index (kg/m')

Fig. 1. The measurement of intra-articular temperaturesduring cold air application.

Yonsei Med J Vol. 43, No.5, 2002

the knee flexed to 90 degrees, with the ambienttemperature kept between 26 and 28 ·C.The kneewas prepared using an aseptic technique, andanesthetized at the site of the needle thermometerprobe with 2% lidocaine. A 2CC spinal needle wasinserted using an anterior approach to the knee.Then, a thermometer probe, with a k-wire ther-mostat mounted on its tip, was inserted into theintra-articular cavity through the spinal needle.The intra-articular temperature was measuredwith an accuracy of ± 0.2 ·C using a digital ther-mometer (Bamant 90, Bamant Co, Barrington, IL,U.S.A.), and the skin temperature was measuredby means of an infrared thermogram (Thermovi-sion 900, Agema, Taby, Sweden). Cold air at -30"C,ejected from a CRAis (Century, Seoul, SouthKorea), was applied in a circular manner on thelateral aspect of the knee joint from a distance of10 em perpendicular to the skin surface for 5minutes. The skin and intra-articular temperatureswere measured simultaneously every 30 secondsduring the 5-minute cold air application, everyminute after cold air application, and every fiveminutes for two hours after the application. Fig.2 shows an example of the thermogram imageobtained following cold air application at the kneeusing the CRAis. The average skin temperaturewas measured at the two cold areas in the lateralaspect of the knee, which appeared dark in aninfrared thermogram image.

RESULTS

Skin and intra-articular temperatures

Statistical analysis was performed to determinethe statistical ::.ignificanceof the changes in skinand intra-articular temperatures after the cold airtherapy. Since the insertion of the spinal needle,required for the measurement of the intra-arti-cular temperature, failed all. two subjects, only 18subjects were included in the statistical analysis.We first applied the Kolmogorov-Smirnov nor-mality test, to check the normality assumptionwith a significance level 0.01, in order to deter-mine the appropriate statistical procedure toapply in each case. Based on the result of theKolmogorov-Srnimov test, we applied either the

Intra-Articular and Skin Temperatures with Cryotherapy

paired t-test or the Wilcoxon signed rank test fordetermining the statistical significance of thechanges in skin and intra-articular temperatures.

The baseline skin temperature was 31.8 ± 1.0 ·cbefore the application of the cold air (Table 2).After 5 minutes of cold air application, it droppedto 9.7 ± 2.9·C with a significant statistical dif-ference, compared with the baseline skin tem-perature (p <0.01) (Fig. 2). Two hours after theremoval of the cold air application, the skin tem-perature was 30.7 ± 1.3 ·c, which is still signifi-cantly lower than the baseline intra-articulartemperature (p <0.01).

The baseline intra-articular temperature wasinitially 33.9 ± 1.2t and then dropped to 30.0 ±1.8·C following the cold air application with asignificance (p <0.01). The intra-articular tempera-ture two hours after the removal of the cold airapplication was 31.4 ± 2.2·C, which is still signifi-cantly lower than the value observed at the onsetof the cold air application (p<O.Ol) (Table 2).

•ll!l> (lLSlllS-5!'il1 ~.~ • 74: I ~~IW »_4 C!C!:7JI orsc"1'\1)1 ~.7' Ul"'l ) 1Wi~~I'M »_7 c!i!i:iI.!I one:

623The skin temperature decreased dramatically

right from the onset of the cold air therapy,increased rapidly a few minutes after the removalof the cold air, and then slowly returned toequilibrium. It took 35.3 ± 31.5 minutes to attainthe minimal intra-articular temperature, and theintra-articular temperature remained low until 2hours after the cryotherapy (Fig. 3).

Body mass index and skin and intra-articulartemperatures

We investigated the relationship between bodymass index, skin temperature and intra-articulartemperature. A significant correlation r=0.51 wasfound between the baseline skin temperature andthe baseline intra-articular temperature (p< 0.05).However, the skin temperature changes do notcorrelate with the intra-articular temperaturemeasured after 5 minutes and after two hours ofcold air application (Table 3).

Fig. 2.. An example of thermography aftercold air application of knee using CRAis.

Table 2. Chmges in Skin Temperatures and Intra-articular Temperatures during and after Cold Air Application Using rnAis"

TemperaturesSites

B_Al C_A2Baseline(A) The lowest(B) After 2 hours(C)

Skin('C) 31.811.0 9.712.9 30.7 11.34 -22.1 1 3.1t -1.1 J. 1.1t

Intra-articular ("C) 33.9 + 1.2 30.0 ± 1.8 31.4 ± 2.22 -3.9 ± 1.1t -2.6± If'Values are the mean ± S.D. degrees centigrade.tp<O.Ol.11.:Baseline temperature, B: The lowest temperature during cold therapy, C: The temperature after 2 hours.l)paired t-test.2)Wilcoxon signed rank test.

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624 Young-He Kim, et al.

Intra-articular Skin A

Table 3. Correlation Coefficients for Changes in Skin and Intra-articular Temperatures

C-AB-A

D

E-D

F- D

r=0.51*

r=0.18

r=-0.28

*p<O.05.r Pearson correlation coefficient.A: Baseline skin temperature, B: The lowest skin temperature, C: the skin temperature after 2 hours,D: Baseline intra-articular temperature, E: The lowesl intra-articular temperature, F: The intra-articular temperature alter 2 hours.

There was a correlation (r=-O.72)between thebody mass index and the baseline skin tempera-ture (p<O.01). IIowever, there were no significantcorrelations between the body mass index and theskin or intra-articular temperature changes, eitherduring or after the cryotherapy (p >0.05) (Table 4).

DISCUSSION

Cold air therapy is used to reduce tissue edema,

in.f1anunation, hematoma formation and pain, aswell as for the treatment of arthritis.8.

10 In rheu-matoid arthritis and active osteoarthritis, destruc-tive enzymes are produced, which become moreactive as the temperature increases, resulting inthe destruction of the cartilage and other tissues.The destruction of cartilage increases rapidly at 35- 36°C, when the cartilage is in a state of activesynovitis, but at below 30"C the activity of theassociated enzymes may be negligible.2,,3·6.7There-fore, one way of reducing the synovitis might be

4

..-.lU~'-.,,;,

-""s-O)Q.

lil.,"'" !

f) 211 ~~ 60 $UIi ,••,(minutes)

1110Fig. 3. Mean skin temperatures andintra-articular temperatures of theknee, during and after cold airapplication using CRAis.

A B-A

Table 4. Correlation Coefficients Ior I3.M.I.* to Intra-articular and Skin Temperature

D E-D f-DC-A

B.M.!." r = _O.72t r= 0.19 r = 0.18 r =0.38 r =0.36r = -0.17

*lIody Mass lndex.t p<O.01.r Pearson correlation coefficient.A: Baseline skin temperature, B: The lowest skin temperature, C: the skin tempemture after 2 hours,D: Baseline intra-articular temperature, E: The lowest intra-articular temperature, F: The intra-articular temperature after 2 hours.

Yonsei Med J Vol. 43. No.5, 2002

lntru-Articular and Skin. Temperatures with Cryotherapy

to decrease the intra-articular temperature bymeans of cold air therapy.

Cryotherapy can be used to relieve pain bothindirectly by reducing muscle spasm, spasticity,swelling after trauma and inflammation, anddirectly by applying a low-threshold mcchano-rc-ceptor and a cold sensitivity unit or by extrudingendorphins.ll,12 Our results showed that when thebaseline skin temperature was high, the baselineintra-articular temperature was also high, whichimplies that there exists a correlation between thebaseline skin temperature and intra-articular tem-perature. However, changes in temperature indeep tissues take place relatively slowly whensubjected to cold air.2.13Since the vasoconstrictedsubcutaneous fat layer acts as an insulatingmaterial during the cryotherapy, the temperatureof th.e deeper structure changes very little.1,8

Therefore, the effects of cold therapy lasts longerthan those of heat therapy of equal strength. Inaddition, because vasoconstriction induced by thecryotherapy reduces blood flow, it takes longerfor the cold tissue to recover its original tempera-ture, in comparison with warmed tissue. Thepresent study also revealed that the intra-articulartemperature dropped much more slowly than theskin temperature. Furthermore, the intra-articulartemperature returned to its original level at aslower rate than did the skin temperature.

The body mass index was correlated with theskin baseline temperature, but not with thetemperature change at the skin or in the kneejoint. These results show that the body mass indexis related to both the skin temperature and theintra-articular temperature before the cryotherapy,but that during or after the cryotherapy it is notrelated to either of these temperatures. The bodymass index might not accurately reflect theamount of subcutaneous fat layer present, espe-cially in the vicinity of the knee joint. It may benecessary to measure the thickness of the subcu-taneous fat layer directly, and to determine itsrelationship with the changes in intra-articulartemperature. It has been reported that for a fewminutes during the cryotherapy, the superficialtissue is vasoconstricted, but that the intra-arti-cular temperature may increase due to the effectsof vasodilatation in the deep tissues. However, inthe present study no rise in temperature or

625vasodilatation was observed. This may be becauseany vasodilatation occurring in the deep tissue, asa result of the cryotherapy, would not be able todirectly influence the temperature rise. However,another theory is that the intra-articular tempera-ture dropped very slowly during the cryotherapyand continued to drop even after the cryotherapy.

Our results showed that the intra-articulartemperature, measured two hours after the coldair application, remained lower than the baselinetemperature when the subject's knee joint re-mained in the supine static position. Since jointmotion would tend to increase the intra-articulartemperature.i" gait training or other practicescould reduce the decrease intra-articular tempera-ture.

The present study investigated the changes inskin and intra-articular temperatures resultingfrom cold air application. The following conclu-sions can be drawn from our results:

1) After 5 minutes of cold air application, theskin and intra-articular temperatures drop-ped by 22.1°C and 3.9°C, respectively. Twohours after the start of the treatment withcold air, the intra-articular temperatures hadstill not returned to their baseline values (p <0.01). A significant correlation r = 0.51 wasfound between the baseline skin temperatureand the baseline intra-articular temperature(p<O.01).

2) The baseline skin temperature and the base-line intra-articular temperature arc signifi-cantly correlated r = 0.51 (p <0.05).However,there is no Significant correlation betweenthe skin temperature change and the intra-articular temperature change following coldair application by means of cryotherapy.

3) A significant correlation r = -0.72 (p <0.01)between the body mass index and the base-line skin temperatures was found. There wasno significant correlation between the bodymass index and the temperature changes, atthe skin or in the knee joint, either during orafter the cryotherapy (p >0.05).

4) No rise in intra-articular temperature wasobserved by the localized application of coldair. The rebound rise of the temperature, dueto reactive vasodilatation, did not occur inthe skin or in the knee joint cavity.

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626 Young-He Kim, et al.

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