The Effect of Radiofrequency on Articular Cartilage

abstract & commentary

Synopsis: Although the new radiofrequency probes do not cause penetrating injury at time zero, the long-term effects on chondrocytes are not known.

Source: Kaplan L, Uribe JW. The acute effects of radiofrequency energy in articular cartilage: An in vitro study. Arthroscopy 2000;16(1):2-5.

Radiofrequency (rf) probes have become popular arthroscopic tools for soft tissue ablation and shrinkage. The indications for RF have been expanded to include chondroplasty or debridement of partial thickness articular cartilage lesions; however, the effects of RF on chondrocytes and the surrounding matrix have not been well studied.

Kaplan and Uribe examined the acute effects of RF on human articular cartilage harvested during total knee replacements. Six knees with unicompartmental osteoarthritis were used to harvest specimens from both intact and fibrillated areas. Cartilage specimens were placed in a simulated, arthroscopic, saline environment and treated with the Arthrocare bipolar RF probe. Low, medium, and high voltage settings each were delivered to the surface by lightly brushing the surface with the probe for three seconds. Specimens were then immediately fixed, decalcified, sectioned, and prepared with a variety of stains.

Kaplan and Uribe could not determine a difference between the three voltage settings histopathologically, so they considered the specimens together. The RF probe effectively removed the articular cartilage, leaving a smooth, scalloped surface, even for the fibrillated cartilage. Higher settings removed proportionately more cartilage. A thin, tan film on the surface represented coagulated tissue fragments. Both the matrix and the chondrocytes immediately adjacent to the treated borders appeared undisturbed. Because the chondrocytes appeared unchanged on histology, they were presumed to be viable. The fibrillar collagen pattern also appeared unaltered by polarized light microscopy. The only difference noted by Kaplan and Uribe was a decreased uptake of proteoglycan-specific stains such as Alcian blue adjacent to the treatment area.

Comment by David R. Diduch, MS, MD

Bipolar RF probes deliver thermal energy in a localized fashion at a relatively low temperature (100°-160°C) when compared to standard unipolar electrocautery (400°-600°C). As such, the depth of penetration, and presumed injury to adjacent tissue, is reduced. This has been an advantage over laser treatment that has been associated with an energy-dependent zone of necrosis with associated complications.1 Likewise, bipolar RF was shown to be superior to mechanical debridement with a rotary shaver in a sheep model by demonstrating less destruction of adjacent normal cartilage.2

While on the surface it would appear that these new bipolar RF probes were superior to other methods of cartilage debridement, a closer look at these studies warrants a word of caution. Kaplan and Uribe, as they acknowledged, examined the effects of RF at time zero on cartilage. No data are presented concerning how the thermal energy affects the surrounding chondrocytes and matrix over time. Histological inspection does not confirm viability of the chondrocytes. It is quite possible that the thermal energy may injure the chondrocytes, leading to a delayed death and subsequent loss of matrix. These chondrocytes initially would appear quite normal. Our own experience, with a limited number of secondlook arthroscopies, suggests that this may occur as we have noted progressive deepening of the treated area with time.

Kaplan and Uribe admit this shortcoming in their paper and state that they are examining this issue with other studies. To their credit, the paper is well constructed and, with the exception of the statement concerning chondrocyte viability, their conclusions well supported. They provide an excellent addition to the scant literature on the subject and address an issue not covered in the sheep study by Turner. That is, how do the effects on fibrillated cartilage differ compared to intact cartilage. Because the surface area is increased with fibrillations, it is possible that the thermal effects on the cells are more pronounced. Kaplan and Uribe demonstrate that, at least at time zero, there does not appear to be much difference in the remaining tissue surrounding the ablation area.

The visual assessment of the RF probe’s ability to contour the cartilage surface during chondroplasty is impressive. It would seem that these will be helpful additions to our arthroscopic tools. However, we should be cautious until we know the long-term effects of RF energy on the chondrocytes and whether the treated area changes over time. Likewise, these studies do not translate into clinical outcomes. That is another major gap in the literature on this subject.

References

1. Trauner KB, et al. Acute and chronic response of articular cartilage to holmium: YAG laser irradiation. Clin Orthop 1995;310:52-57.

2. Turner AS, et al. Radiofrequency (electrosurgical) ablation of articular cartilage: A study in sheep. Arthroscopy 1998;14:585-591.

The use of bipolar radiofrequency probes on articular cartilage has been shown to:

a. demonstrate minimal damage to surrounding cartilage at the time of treatment only.

b. be superior to mechanical debridement (shaving) in long-term clinical studies.

c. create a deep, thermal injury resulting in avascular necrosis.

d. not injure the surrounding chondrocytes, as demonstrated by long-term viability.