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Letter to the Editor |
Connective Tissue Biochemistry, Department of Orthopaedic Surgery, University Of California, San Diego, La Jolla, California
Dear Editor:
As I was perusing the July edition of AJSM, I read with great interest the article of Caffey et al, in which the investigators study the effect of radiofrequency (RF) energy on human articular cartilage ("Effects of Radiofrequency Energy on Human Articular Cartilage: An Analysis of 5 Systems," July 2005, pages 1035–1039). The study describes, in simulated operating room conditions, the testing of 5 commercially available RF probes attached to a customized jig to standardize a minimum contact pressure of each probe tip to 2.0 g on human articular cartilage.
As I have tested and published in Arthroscopy1 on the chondrocyte viability and metabolic activity after treatment of bovine articular cartilage with bipolar RF using the ACD-50 probe, I would like to rebut the experimental design and express the numerous weaknesses of the Caffey et al article. The data obtained by these investigators on articular cartilage testing are quite different than the data we have published.
The first issue I would like to address is that in our clinical experimental setting, the maximum cell death observed with the ACD-50 was 109.4 ± 22.1 µm at a power setting of 4. I see that the Caffey et al investigators chose a different power setting of 3 for the probe testing, which may affect cell death.
Another issue that seems misleading is the title, which expresses the effects of RF on human articular cartilage. The tissue tested by the investigators is listed as aged articular cartilage–osteoarthritic (OA) tissue. These testing samples were taken from patients undergoing total knee procedures who were aged 57 to 72 years. The cores obtained and tested from aged/OA patients have different structures compared to mature articular cartilage. In aged/OA patients, the calcified layer is quite different; the superficial layer lacks cell viability. It is well known that aged articular cartilage is hypocellular, with apoptotic cells present in the articular cartilage matrix.
The article of Caffey et al does not show histology or confocal microscopy of control specimens. No ablation of the tissue is described in their assessment of the application of the RF probe. A zone of ablation is generally seen with the majority of bipolar RF devices (see Figure 1).1
The list of references seems incomplete. The authors list only 1 reference in 2004, Liao et al. Why could they not continue the search and refer, within the same year, to the work of Amiel et al, which was also published in Arthroscopy? They could refer in the article to the numerous publications related to the positive effect(s) of RF treatment for chondral lesions.
In an attempt to simulate an arthroscopic environment with controls, the authors have chosen to use a nonphysiologic application, applying direct pressure without probe movement, which in no way is replicated during a normal surgical procedure. The specimens were placed in a metal container, and the only circulation that took place was with a motorized propeller. This does not replicate the normal physiologic flow of saline in juxtaposition to probe application and would obviously have significant implications in terms of the generation of heat. The results could only be applied to their experimental design and not to the clinical environment, where the probes used in arthroscopy are used in a free-hand technique. Control over duration of application and amount of pressure could only lie in the hands of the surgeon, and only the surgeon could have the determination and skill to apply these instruments.
REFERENCE
Los Angeles, California
We welcome the feedback from Dr Amiel at his Connective Tissue Biochemistry Lab with his letter to the editor of The American Journal of Sports Medicine. We do not feel that there are "numerous weaknesses" or "fundamental flaws" in our study as much as there is a difference of opinion about study design.
We defined a well-controlled model, under a room-temperature fluid medium similar to everyday arthroscopy, to precisely control energy delivery to human articular cartilage. Five common commercially available RF probes were investigated using the manufacturers’ recommended energy levels. Every model can have drawbacks, yet our experimental setup was one of the most precise methods used to date for the evaluation of RF heat transfer to human articular cartilage.
Dr Amiel did not like our cartilage source. As human tissue is difficult to come by, we were able to obtain human knee tissue with minimal degenerative changes (less than grade 3 or 4 by Outerbridge classification) that were macroscopically intact. We understand that these tissues can have age-related changes, yet we preferred this tissue over healthy animal articular cartilage and feel that this more closely represents the clinical human situation and provides valuable scientific information. Clearly, grade 3 cartilage demonstrated easy destruction and a much greater response to RF application. More important, we precisely measured and controlled the pressure of the RF wand application, an important variable for any RF experiment. In general, lack of control of potential sources of error is what constitutes a fundamentally flawed study. As stated, we observed a great variability in tissue changes when attempting "hand control" and determined that this error must be controlled by study design. Unfortunately, few studies have controlled for this variable. Dr Amiel found less cell death (around 109 µm) with his study. With "light touch" RF application, his uncontrolled energy application may have minimized thermal energy contact to his bovine tissue, resulting in the smaller penetration numbers in his published sample size of 12 specimens.
Dr Amiel did not like our confocal microscopy photograph. Our images were consistent, and this was a representative image from more than 120 specimens tested. Our controls show no effect with normal confocal surfaces. Histologic examination was not the focus of this study.
We disagree that any "numerous publications" in the literature demonstrate the positive effects of RF treatment in chondrol lesions. Actually, the literature consistently demonstrates poor study designs with poor control of thermal applications on animal cartilage with few human articular cartilage effects studied to date.
Our circulating bath was not meant to simulate the clinical environment. This was our chosen model, and although we recognize that the fluid environment has a documented effect, the fluid influences were not the focus of this study, and again, the fluid environment was well controlled from one experimental condition to the next. The thermal effects of 1 and 3 seconds of applications in this large basin of saline have minimal effects to the overall temperature of the bath setup. Probe movement, as controlled and investigated in other studies with longer times of thermal exposure, was not the purpose or design of our study of minimal energy application. We discussed this in our published article.
Overall, the purpose of our study was to raise the level of understanding to the orthopaedic surgeon who sees articular cartilage lesions on a daily basis. We attempted to control thermal application, which has not been adequately done to date. Treatment of articular cartilage lesions has become increasingly common, and a rigid scientific approach to evaluate the arthroscopic treatment of them is critical to our patients.
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