In Vivo Arthroscopic Temperatures: A Comparison Between 2 Types of Radiofrequency Ablation Systems in Arthroscopic Anterior Cruciate Ligament Reconstruction—A Randomized Controlled Trial

Abstract

Purpose:
To compare a plasma ablation device with a standard ablation device in anterior cruciate ligament (ACL) reconstruction to determine which system is superior in terms of intra-articular heat generation and diathermy efficiency.

Methods:
This was a prospective, randomized controlled trial. The inclusion criteria were adult patients undergoing primary ACL reconstruction. Patients were randomized preoperatively to the standard ablation group or the plasma ablation group. A thermometer was inserted into the inferior suprapatellar pouch, and the temperature, time, and duration of radiofrequency ablation were measured continually.

Results:
No significant differences were found between the standard ablation system and the plasma ablation system for maximum temperature (29.77°C and 29.34°C, respectively; P = .95), mean temperature (26.16°C and 26.99°C, respectively; P = .44), minimum temperature (22.66°C and 23.94°C, respectively; P = .54), and baseline temperature (26.80°C and 27.93°C, respectively; P = .35). Similarly, no significant differences were found for operative time (82.90 minutes and 80.50 minutes, respectively; P = .72) and mean diathermy activation times (2.6 minutes for both systems; P = .90). The between-system coefficient of variation for the measured parameters ranged from 0.12% to 3.69%. No intra-articular readings above the temperature likely to damage chondrocytes were recorded. The mean irrigation fluid temperature had a significant correlation with the maximum temperature reached during the procedure (Spearman rank correlation, r = 0.87; P < .01).

Conclusions:
No difference in temperature was observed between the standard ablation and plasma ablation probes during ACL reconstruction. Temperatures did not exceed critical temperatures associated with chondrocyte death.

Level of evidence:
Level I, randomized controlled trial.

Full text

In Vivo Arthroscopic Temperatures: A Comparison
Between 2 Types of Radiofrequency Ablation
Systems in Arthroscopic Anterior Cruciate Ligament
ReconstructiondA Randomized Controlled Trial
Brent Matthews, M.B.B.S., Matthew Wilkinson, M.B.B.S., F.R.A.C.S.,
Peter McEwen, M.B.B.S., F.R.A.C.S., Kaushik Hazratwala, M.B.B.S., F.R.A.C.S.,
Kenji Doma, Ph.D., B.Sp.Exc.Sci.(Hons), Varaguna Manoharan, M.B.B.S.,
Zaid Bahho, M.B.B.S., and Shannon McEwen
Purpose: To compare a plasma ablation device with a standard ablation device in anterior cruciate ligament (ACL)
reconstruction to determine which system is superior in terms of intra-articular heat generation and diathermy efficiency.
Methods: This was a prospective, randomized controlled trial. The inclusion criteria were adult patients undergoing
primary ACL reconstruction. Patients were randomized preoperatively to the standard ablation group or the plasma
ablation group. A thermometer was inserted into the inferior suprapatellar pouch, and the temperature, time, and
duration of radiofrequency ablation were measured continually. Results: No significant differences were found between
the standard ablation system and the plasma ablation system for maximum temperature (29.77C and 29.34C, respec-
tively; P¼.95), mean temperature (26.16C and 26.99C, respectively; P¼.44), minimum temperature (22.66C and
23.94C, respectively; P¼.54), and baseline temperature (26.80C and 27.93C, respectively; P¼.35). Similarly, no
significant differences were found for operative time (82.90 minutes and 80.50 minutes, respectively; P¼.72) and mean
diathermy activation times (2.6 minutes for both systems; P¼.90). The between-system coefficient of variation for the
measured parameters ranged from 0.12% to 3.69%. No intra-articular readings above the temperature likely to damage
chondrocytes were recorded. The mean irrigation fluid temperature had a significant correlation with the maximum
temperature reached during the procedure (Spearman rank correlation, r¼0.87; P<.01). Conclusions: No difference in
temperature was observed between the standard ablation and plasma ablation probes during ACL reconstruction. Tem-
peratures did not exceed critical temperatures associated with chondrocyte death. Level of Evidence: Level I, ran-
domized controlled trial.
Arthroscopic anterior cruciate ligament (ACL)
reconstruction is a frequently performed surgical
treatment for ACL rupture. During the procedure,
radiofrequency (RF) ablation is used to debride the ACL
remnant and to define anatomic landmarks. These
landmarks are used to define the entry point for the
tibia and femoral tunnel positions for subsequent
placement of a hamstring tendon graft.
As a byproduct of RF ablation, heat is produced, with
the potential within the enclosed space of the knee joint
for temperatures to increase to levels at which damage
to sensitive tissues occurs. A temperature of 45C can
From the Orthopaedic Research Institute of Queensland (B.M., M.W., P.M.,
K.H., V.M., Z.B., S.M.); and James Cook University (K.D., S.M.), Townsville,
Australia.
The authors report the following potential conflict of interest or source of
funding: B.M., M.W., P.E., K.H., and V.M. receive support from Argo, Device
Technologies (Arthrex). S.M. receives support from Dr. Peter McEwen. This
project received no external funding grants. The project was funded entirely by
the Orthopaedic Research Institute of Queensland (ORIQL). ORIQL receives
annual funding from Argo and Device Technologies for its Arthroplasty
Fellowship Program. These fellowships support the research and contribute to
salary for the Research Assistant and Research Fellows.
Received December 8, 2015; accepted May 17, 2016.
Address correspondence to Brent Matthews, M.B.B.S., Orthopaedic
Research Institute of Queensland, 7 Turner St, Pimlico, Townsville 4817,
Australia. E-mail: drbrentmatthews@gmail.com
Ó2016 The Authors. Published by Elsevier Inc. on behalf of the Arthros-
copy Association of North America. This is an open access article under the CC
BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
0749-8063/151133
http://dx.doi.org/10.1016/j.arthro.2016.05.026
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol -,No-(Month), 2016: pp 1-8 1

damage muscle and nerve cells, whereas a temperature
of approximately 55C has been shown to cause
destruction of chondrocytes in vitro.
1
Both extra-articular RF ablation and intra-articular
RF ablation are generally considered safe; however,
case reports linking incidences of glenohumeral chon-
drolysis to RF ablation exist.
2
RF devices are developed
and tested in simulated clinical environments, often
using animal or cadaveric tissues. Although these mo-
dalities are reasonable surrogates, the characteristics of
these environments differ from the environment of
true, human intraoperative use. Recently, RF ablation
instruments have incorporated the use of a plasma
bubble to ablate tissue with the aim of more efficient
diathermy and reduction of temperature transmission
to surrounding tissue. We conducted a literature review
using PubMed, Ovid, and Medline. No studies involving
in vivo monitoring of joint fluid temperature during
ACL reconstruction were identified. Furthermore, no
robust data comparing intra-articular temperature dif-
ferences between standard ablation and plasma abla-
tion could be found.
The purpose of this study was to compare a plasma
ablation device with a standard ablation device in ACL
reconstruction to determine which system is superior in
terms of intra-articular heat generation and diathermy
efficiency. We hypothesized that the plasma ablation
group would operate at a lower temperature and more
efficiently, resulting in lower intra-articular tempera-
tures and reduced diathermy times intraoperatively.
We further hypothesized that by adhering to safe
diathermy practices as defined by Zoric et al.,
3
intra-
articular temperatures would be maintained below
45C for both systems.
Methods
Ethics committee approval was obtained from the
health region ethics committee (MHS20130806-02)
before commencement of the study, and the trial
was registered with the country of origin’s clinical
trials registry (Australian Clinical Trials Registry,
ACTRN12613000569707).
Trial Design
This trial was conducted in a prospective, randomized
manner, with 47 participants over the age of 18 years
and of both male and female gender enrolled.
Recruiting occurred between March 2014 and June
2015. The inclusion criteria were adult patients un-
dergoing primary arthroscopic ACL reconstruction by a
single bundle secured with double adjustable suspen-
sory loop fixation to an anatomically referenced ACL
footprint. Revision ACL reconstructions and/or ACL
reconstructions using boneepatellar tendonebone graft
were not eligible for inclusion. The exclusion criteria
were patients who were unable to provide informed
consent or unable to attend a 6-month follow-up visit.
All surgical procedures were performed by 1 of 3 or-
thopaedic consultants (P.M., K.H., M.W.), in private
practice, within a large regional hospital. All of the
surgeons are current members of the Australian Or-
thopaedic Association and hold an F.R.A.C.S.(Ortho).
They have 16, 9, and 6 years’experience since attaining
fellowship. The 2 most experienced surgeons (P.M.,
K.H.) specialize in lower limb surgery, with the most
senior (P.M.) specializing in surgery of the knee only.
At the time of recruitment, patients were randomly
assigned to either the standard ablation group, treated
with the Stryker SERFAS probe (Kalamazoo, MI), or
the plasma ablation group, treated with the ArthroCare
RF Wand Super TurboVac 90 IFS system (Austin, TX),
with a computer program used to generate a random
number list. The device to be used was concealed from
the surgeon until the time of surgery, when it was
revealed by the nursing staff under the direction of the
research assistant.
Intraoperatively, 1 or 2 medial portals and 1 lateral
arthroscopic portal were placed, and a Luxtron 812
thermometer (LumaSense Technologies, Santa Clara,
CA) connected to a LumaSense Technologies fiberoptic
temperature probe (STB Probe [part No. SQ10939L])
was inserted into the inferior aspect of the suprapatellar
pouch, percutaneously, independent of the ports. The
probe was positioned so that it was as close to the
working area of the RF ablation probe as possible without
interfering with the arthroscopic instrumentation. The
thermometer was connected to a computer running
Luxtron TrueTemp (version 2.0.0; LumaSense Tech-
nologies), and the temperature was recorded in real time
every 0.5 seconds. Subsequent analysis was performed
with SPSS software (version 20; IBM, Armonk, NY).
The surgical technique consisted of ACL reconstruc-
tion with a single-bundle semitendinosus graft in a
double adjustable suspensory configuration placed in
the anatomic ACL footprint. Normal saline solution
stored at room temperature was used for irrigation of
the joint, with the operating room temperature set at
21C. The fluid was delivered either by a gravity-fed
system that used two 3-L bags elevated to 1.85 m and
a hand pump or by a pressure-regulated electric pump.
The pressure of the gravity-fed irrigation system was
calculated by connecting the system to the arterial
blood gas manometer and was zeroed at the level of the
patient’s knee. This process was repeated 3 times and
returned an average reading of 80 mm Hg with both
bags full and open to the circuit. This figure has been
adopted in statistical calculations using this variable.
The pump pressure setting varied according to the
surgeon’s preference and ranged from 35 to 90 mm Hg.
An independent suprapatellar outflow portal was
created and connected to free drainage in cases in
which it was the surgeon’s preference to do so.
2B. MATTHEWS ET AL.

The RF ablation probes were used intermittently.
Suction was attached to the RF ablation wand when
requested by the surgeon. When suction was not
requested, free drainage was used.
We set a temperature of 45C as the maximum
acceptable temperature for the joint. The worthwhile
differences in the maximum temperature were deter-
mined according to a nomogram for the estimation of
the measurement repeatability error from the coeffi-
cient of variation (CV).
4
The worthwhile differences for
the current sample size (20 per group) and a hypo-
thetical sample size of 10 per group were determined
using linear regression equations (y¼0.7955xþ0.1284
and y¼1.1096x0.1132, respectively).
5
On the basis
of these calculations, the worthwhile differences of the
current sample size of 20 per group and a hypothetical
sample size of 10 per group were 0.93% and 1.32%,
respectively.
The plasma ablation device has an inbuilt thermom-
eter that was set to alarm at 45C. On occasion, the
inbuilt alarm would be triggered; however, there was
no change to the intra-articular temperature as
measured by the independent fiberoptic probe. When
the RF ablation tool was activated by the surgeon, the
time and duration of activation were measured with a
stopwatch operated by the research assistant. Times
were documented in Microsoft Excel. At the completion
of the case, the probe was removed and inspected for
damage before being sent to the institution’s central
sterilizing department for reprocessing.
The primary outcome measure was the intra-articular
temperature recorded every 0.5 seconds for the dura-
tion of the operation that involved RF ablation. The
secondary outcome measures were the duration of
application of RF ablation for each system and the total
operating time for each system.
As reported in the Results section, the total diathermy
time is defined as the total duration of the active RF
ablation within the intra-articular space during the
procedure, calculated by the sum of all individual
diathermy applications. The total temperature time is
defined as the total duration for which the temperature
probe was actively recording temperature during the
procedure. The temperature probe was removed during
the case once no further RF ablation was required to
mitigate the risk of probe damage or entanglement
during the passage of the graft. The total surgery time is
defined as the time from knife to skin until completion
of wound closure. A port is defined as a stab incision to
the skin for the passage of instruments, an accessory
outflow portal, or the arthroscope; the probe was
inserted using a cannulated needle and is not classified
as a port. Pressure, as reported in the Results section, is
as measured by a manometer at the end of the irriga-
tion tubing at knee-high level for the manual
pressureefed system or the setting for pressure control
pumps. The baseline mean temperature is defined as
the average temperature for the first 5 seconds after
probe insertion into the knee. The mean temperature is
defined as the average temperature of all readings
recorded during the procedure, and the maximum
temperature is the highest single reading recorded
during the case.
Statistics
All statistical analyses were conducted with SPSS
software (version 20). An a priori calculation was
conducted with an anticipated effect size of 0.8, an
a
level of .05, and a power of 0.8 (G*Power 3.1.9.2,
Heinrich-Heine-Universität, Düsseldorf, Germany) for
differences between 2 independent measures. The
sample size was based on 2 groups (standard ablation
and plasma ablation). According to these effects, a total
sample size of 40 was required.
On the basis of the Shapiro-Wilk test, the dependent
variables were not normally distributed and thus all
measures were log transformed (log
10
[x]) before ana-
lyses. The measures of central tendency and dispersion
are reported as mean standard deviation. By use of
the log10[x] data, the intersystem CV (% CV ¼Stan-
dard deviation 100/Mean) of the dependent variables
was calculated. Furthermore, differences in the
dependent variables between the Stryker and Arthro-
Care systems were determined using analysis of
covariance with 3 separate surgeons treated as a co-
variate. The correlations between dependent variables
were examined by use of the Pearson correlation co-
efficient for pooled data, as well as the correlations for
the Stryker and ArthroCare systems. The level of sig-
nificance was established at .05.
Results
A total of 47 patients were recruited into the study; 7
of these were excluded. Two participants withdrew
consent to have their temperatures recorded after
randomization but before surgery, and 1 patient was
deemed medically unfit for the procedure in the anes-
thetic holding bay and the procedure was cancelled.
The remaining 4 were withdrawn because of equip-
ment issues (laptop hardware or software failure) at the
time of data collection that resulted in incomplete data
collection during the procedure.
Of the remaining 40 patients, 19 were randomized to
the plasma ablation group and 21 to the standard
ablation group. ACL reconstruction was performed in
18 right and 22 left knees. Eight patients had an
accessory suprapatellar portal under free drainage; of
these, 4 were in the standard ablation group and 4 were
in the plasma ablation group. Twenty-three patients
had 2 medial portals and no suction attached to the
diathermy device; of these, 12 were in the standard RF
group and 11 were in the plasma ablation group.
IN VIVO ARTHROSCOPIC TEMPERATURES 3

During the course of the study, 3 temperature probes
required replacement as a result of the fiberoptic fila-
ment being kinked intraoperatively; this occurred at the
time the probe was removed through the skin. The
fiberoptic probe was noted to be particularly prone to
damage when not withdrawn directly perpendicular to
the skin surface.
The patient’s irrigation pressure was determined
intraoperatively by the surgeon. The pressure
was 35 mm Hg in 5 patients, 40 mm Hg in 4 patients,
45 mm Hg in 2 patients, 50 mm Hg in 1 patient, 55 mm Hg
in 1 patient, 60 mm Hg in 1 patient, 70 mm Hg in twelve
patients, 75 mm Hg in 1 patient, 80 mm Hg in 11 patients,
and 90 mm Hg in 2 patients.
For comparisons between the standard RF ablation
andplasmaRFablationsystems,nosignificant differ-
ences were found for any of the variables examined
(P>.05, Figs 1-3). The mean values (log
10
[x]) for the
maximum temperature in the standard ablation and
plasma ablation groups were 29.77C and 29.34C,
respectively (CV, 1.01%); the mean temperature was
26.16C and 26.99C, respectively (CV, 0.96%). The
operative times for the standard and plasma ablation
groups were 82.90 minutes and 80.50 minutes,
Fig 1. Log-transformed
maximum temperature,
minimum temperature, and
mean temperature for stan-
dard radiofrequency (RF)
ablationand plasma ablation.
Fig 2. Log-transformed to-
tal diathermy time, total
temperature time, and total
surgery time for standard
radiofrequency (RF) abla-
tion and plasma ablation.
4B. MATTHEWS ET AL.

respectively (CV, 2.08%). The mean diathermy acti-
vation time was 2.6 minutes for each group (CV,
1.91%).
No interaction effect was found between any of the
dependent variables with different surgeons as a co-
variate (P>.05). The intersystem CVs ranged from
1.2% to 3.6% (Table 1). For the correlation analyses of
the pooled data (i.e., standard RF and plasma RF sys-
tems combined), significant correlations were found
between a number of dependent variables (P<.05,
Table 2). The minimum temperature had a strong cor-
relation (r¼0.74, P<.001) with the maximum tem-
perature recorded for both systems combined. This
correlation was also seen when the 2 systems were
analyzed independently: r¼0.63 and P¼.005 for
standard ablation and r¼0.86 and P<.001 for plasma
ablation (Tables 3 and 4). The mean temperature for
both systems correlated with the maximum tempera-
ture (r¼0.86, P<.001); again, this was also seen when
both systems were analyzed independently: r¼0.85
and P<.001 for standard ablation and r¼0.91 and
P<.001 for plasma ablation.
At no time when the plasma RF probe’s inbuilt
thermometer alarmed at 45C was a temperature
change detected in the joint. All patients attended
6-month follow-up visits. Although not a defined
outcome measure, there were no presentations
consistent with chondrolysis, defined as complete
cartilage loss in 1 or more compartments, in any of the
patients. Because no patients had clinical symptoms
Fig 3. CONSORT (Consoli-
dated Standards of Report-
ing Trials) flow diagram.
(ACL, anterior cruciate
ligament.)
Table 1. Coefficients of Variation and Percentage Differences of Log-Transformed (log
10
[x]) Means of Dependent Variables
Parameter
Mean (log
10
[x])
CV, % PD, % PValue
*
Standard RF Ablation Plasma Ablation
No. of ports 2.95 (0.47) 2.95 (0.47) 0.12 0 .97
Pressure, mm Hg 65.71 (1.82) 62.37 (1.79) 3.69 1.25 .34
Surgery, min 82.90 (1.92) 80.50 (1.91) 2.08 0.67 .72
Temperature, min 47.9 (1.68) 47.6 (1.68) 0.44 0.16 .74
Diathermy, min 2.60 (0.41) 2.60 (0.41) 1.91 2.81 .90
Mean temperature, C 26.16 (1.42) 26.99 (1.43) 2.22 0.96 .44
Minimum temperature, C 22.66 (1.36) 23.94 (1.38) 2.89 1.73 .54
Maximum temperature, C 29.77 (1.47) 29.34 (1.47) 1.01 0.42 .95
Baseline temperature, C 26.80 (1.42) 27.93 (1.44) 2.93 4.1 .35
CV, coefficient of variation; PD, percentage difference; RF, radiofrequency.
*The level of significance was set at P<.05.
IN VIVO ARTHROSCOPIC TEMPERATURES 5

that warranted further investigation, no further radio-
graphs or magnetic resonance imaging scans were
performed to confirm this.
Discussion
Our study confirmed the safety of the 2 aforemen-
tioned types of RF ablation systems and showed no
difference in operative time or temperature generation
between standard RF ablation and plasma ablation in
ACL reconstruction. Furthermore, we found that the
mean intra-articular temperature correlated closely
with the maximum temperature reached in the joint, a
similar finding to that observed by Barker et al.
6
The use of appropriate-temperature irrigation fluid is
a key factor because it closely correlates with mean
temperature and maximum temperature intra-
articularly. Cheng et al.
7
showed in a rat model that
the intra-articular temperature changes according to
the temperature of the irrigation fluid and that the
magnitude of this change is related to the initial irri-
gation fluid temperature.
At no point in our study did the use of the standard
RF ablation device or the plasma RF ablation device
result in a temperature that exceeded the safe working
limit of 45C. These findings replicate those of Barker
et al.,
6
who examined intra-articular temperatures
during subacromial decompression. Barker et al.
confirmed that the heat generated by the probe escapes
through its drainage tube; at no time when the
ArthroCare system’s temperature probe alarmed at
Table 2. Spearman
r
Correlation Between Selected Parameters for Pooled Data (i.e., Standard and Plasma Ablation Systems
Combined)
Parameter Pressure Surgery Temperature Diathermy
Mean
Temperature
Minimum
Temperature
Maximum
Temperature
Baseline
Temperature
Ports r¼0.08
P¼.61
r¼0.40
P¼.01
r¼0.38
P¼.02
r¼0.01
P¼.95
r¼0.24
P¼.14
r¼0.12
P¼.45
r¼0.14
P¼.40
r¼0.21
P¼.21
Pressure dr¼0.34
P¼.03
r¼0.21
P¼.19
r¼0.02
P¼.90
r¼0.32
P¼.046
r¼0.47
P¼.006
r¼0.25
P¼.12
r¼0.06
P¼.72
Surgery ddr¼0.75
P<.001
r¼0.009
P¼.96
r¼0.25
P¼.13
r¼0.30
P¼.06
r¼0.16
P¼.33
r¼0.13
P¼.45
Temperature dd dr¼0.13
P¼.43
r¼0.30
P¼.06
r¼0.32
P¼.047
r¼0.28
P¼.08
r¼0.19
P¼.27
Diathermy dd d dr¼0.19
P¼.26
r¼0.05
P¼.76
r¼0.02
P¼.93
r¼0.18
P¼.31
Mean
temperature
dddddr¼0.88
P<.0001
r¼0.86
P<.001
r¼0.04
P¼.83
Minimum
temperature
ddddd dr¼0.74
P<.001
r¼0.03
P¼.92
Maximum
temperature
ddddd d dr¼0.02
P¼.92
NOTE. Pressure was measured in millimeters of mercury; surgery, temperature, and diathermy were measured in seconds; and mean, mini-
mum, maximum, and baseline temperatures were measured in degrees Celsius.
Table 3. Spearman
r
Correlation Between Selected Parameters for Standard Radiofrequency Ablation System
Parameter Pressure Surgery Temperature Diathermy
Mean
Temperature
Minimum
Temperature
Maximum
Temperature
Baseline
Temperature
Ports r¼0.313
P¼.17
r¼0.19
P¼.42
r¼0.23
P¼.33
r¼0.30
P¼.22
r¼0.18
P¼.43
r¼0.01
P¼.98
r¼0.09
P¼.70
r¼0.20
P¼.39
Pressure dr¼0.23
P¼.31
r¼0.09
P¼.70
r¼0.01
P¼.96
r¼0.05
P¼.84
r¼0.23
P¼.31
r¼0.01
P¼.96
r¼0.14
P¼.55
Surgery ddr¼0.71
P<.001
r¼0.04
P¼.87
r¼0.24
P¼.29
r¼0.37
P¼.10
r¼0.22
P¼.34
r¼0.04
P¼.22
Temperature dd dr¼0.12
P¼.63
r¼0.47
P¼.03
r¼0.48
P¼.03
r¼0.39
P¼.08
r¼0.21
P¼.35
Diathermy dd d dr¼0.39
P¼.10
r¼0.29
P¼.25
r¼0.05
P¼.84
r¼0.10
P¼.71
Mean temperature dd d d dr¼0.85
P<.001
r¼0.82
P<.001
r¼0.15
P¼.53
Minimum temperature dd d d d dr¼0.63
P¼.005
r¼0.08
P¼.75
Maximum temperature dddddddr¼0.13
P¼.57
NOTE. Pressure was measured in millimeters of mercury; surgery, temperature, and diathermy were measured in seconds; and mean, mini-
mum, maximum, and baseline temperatures were measured in degrees Celsius.
6B. MATTHEWS ET AL.

45C did we detect a change in the temperature of the
joint fluid being measured independently.
A cadaveric study by Zoric et al.
3
identified 3 primary
factors that influence the quantity and effect of heat
generated during RF ablation in arthroscopic shoulder
surgery. These are defined as follows: (1) the flow rate
of the irrigation fluid, (2) the duration of application of
RF ablation, and (3) the distance between the probe tip
and target tissue.
3
In their discussion Zoric et al. rec-
ommended that suction be applied to the RF ablation
device, that adequate irrigation fluid flow be main-
tained, that RF ablation be activated only intermit-
tently, and that the arthroscope be focused on the RF
probe tip at the time of application.
Flow is proportional to pressure and can be calculated
through the Hagen-Poiseuille relation. Variable pres-
sure was used in our study, ranging from a minimum of
35 mm Hg up to a maximum of 90 mm Hg. No signif-
icant correlation was found between inflow pressure
and intra-articular temperature; we assume that this is
because inflow pressure of 35 mm Hg is above the
threshold required to prevent heat build-up when
ablation is used.
Good et al.
2
were able to show temperatures of
greater than 45C in all arms of their cadaveric trial, in
which temperatures were recorded by a probe posi-
tioned 1 cm from the active diathermy area. High
temperatures in vicinity to the probe were, however,
not replicated in regions of the glenoid distant to the
site of diathermy activation. By design, RF ablation,
whether plasma based or noneplasma based, is the
controlled application of heat; it is therefore reasonable
to expect a transient temperature increase in proximity
to the target field. The theoretical advantage of plasma
ablation technology is that surrounding tissue is pro-
tected from heat, which is contained by the plasma
field. The amount of heat generated by RF ablation is a
function of the power output of the device, the design
of the electrode, and the duration of application; this
has been extensively examined in the field of tumor
ablation.
8
Nonetheless, thermal injury and, by association, the
use of RF frequency or intra-articular electrocautery
devices have the potential to cause intra-articular
temperatures that may lead to chondrolysis. A strong
association of chondrolysis of the knee with RF abla-
tion has not been established in the literature; it has
only been implicated in knee chondrolysis in 3 of the
24 international studies examined by Provencher
et al.
9
Limitations
Our study examined only 2 different manufacturers’
RF ablation systems. Given that we examined the RF
probes only in the knee joint, which is a larger joint
with higher fluid capacity than other joints, our find-
ings cannot be extrapolated to other joints. We concede
that we did not control the irrigation pressure, appli-
cation of suction, and number of arthroscopic ports
between the 2 groups. The potential bias from these
variables is minimized by randomization, and the study
design reflects the variability seen in orthopaedic
practice. In addition, the study was not designed or
powered to determine the effects of the different vari-
ables (use of suction, differences in inflow temperature,
or number of portals) on intra-articular temperature.
We did not measure the irrigation fluid temperature
before its infusion into the knee.
Conclusions
No difference in temperature was observed between
the standard ablation and plasma ablation probes
Table 4. Spearman
r
Correlation Between Selected Parameters for Plasma Radiofrequency Ablation System
Parameter Pressure Surgery Temperature Diathermy
Mean
Temperature
Minimum
Temperature
Maximum
Temperature
Baseline
Temperature
Ports r¼0.13
P¼.59
r¼0.71
P<.001
r¼0.58
P¼.01
r¼0.29
P¼.22
r¼0.29
P¼.21
r¼0.23
P¼.34
r¼0.18
P¼.46
r¼0.23
P¼.41
Pressure dr¼0.49
P¼.04
r¼0.30
P¼.22
r¼0.01
P¼.96
r¼0.56
P¼.01
r¼0.63
P¼.008
r¼0.50
P¼.03
r¼0.10
P¼.72
Surgery ddr¼0.76
P<.001
r¼0.04
P¼.89
r¼0.21
P¼.39
r¼0.18
P¼.45
r¼0.13
P¼.59
r¼0.32
P¼.25
Temperature dd d r¼0.14
P¼.57
r¼0.13
P¼.61
r¼0.19
P¼.44
r¼0.13
P¼.61
r¼0.61
P¼.02
Diathermy dd d dr¼0.05
P¼.83
r¼0.12
P¼.64
r¼0.11
P¼.64
r¼0.27
P¼.34
Mean temperature dd d d d r¼0.91
P<.001
r¼0.95
P<.01
r¼0.14
P¼.61
Minimum temperature dd d d d d r¼0.86
P<.001
r¼0.04
P¼.90
Maximum temperature dddddddr¼0.28
P¼.30
NOTE. Pressure was measured in millimeters of mercury; surgery, temperature, and diathermy were measured in seconds; and mean, mini-
mum, maximum, and baseline temperatures were measured in degrees Celsius.
IN VIVO ARTHROSCOPIC TEMPERATURES 7

during ACL reconstruction. Temperatures did not
exceed critical temperatures associated with chon-
drocyte death.
Acknowledgment
The authors thank A. Grant and L. Murphy for
manuscript proofreading assistance.
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