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Monopolar Radiofrequency Treatment of Partial-Thickness Cartilage Defects in the Sheep Knee Joint Leads to Extended Cartilage Injury

Max J. Kääb, MD, PhD^*,, Herman J. Bail, MD, Andreas Rotter, Pierre Mainil-Varlet, MD, PhD, Iolo apGwynn, PhD and Andreas Weiler, MD, PhD

From the Sports Traumatology and Arthroscopy Service, Center for Musculoskeletal Surgery, Charité, Campus Virchow, Humboldt University, Berlin, Germany, the Institute of Pathology, University of Bern, Bern, Switzerland, and the Institute of Biological Sciences, University of Wales, Aberystwyth, United Kingdom

^* Address correspondence to Max J. Kääb, MD, PhD, Center for Musculoskeletal Surgery, Charité, Humboldt University, Sports Traumatology and Arthroscopy Service, Schumannstrasse 20-21, D-10117 Berlin, Germany (e-mail: max.kaeaeb{at}charite.de).

Background: The application of radiofrequency energy to smooth and stabilize the cartilage surface has become increasingly controversial. There is little knowledge on extended-term effects, such as cartilage viability.

Purpose: To analyze the effect of radiofrequency treatment on artificially created partial-thickness defects in the femoral cartilage of sheep knee joints 24 weeks after surgery.

Study Design: Controlled laboratory study.

Methods: Grade II cartilage surface defects on the medial and lateral femoral condyles were artificially created in sheep for in vivo analysis. The cartilage lesions were treated alternately on the lateral or the medial condyle using a monopolar radiofrequency probe. Radiofrequency treatment was performed in a freehand technique until surface smoothing without change of cartilage color was seen. At 24 weeks after surgery, cartilage samples were harvested and were processed for macroscopic and histological evaluation. To analyze the effect of radiofrequency at time zero, samples of sheep femoral condyle cartilage with and without artificially created clefts were treated in vitro with radiofrequency. Evaluation was performed by scanning electron and confocal microscopy.

Results: At 24 weeks after surgery, grade IV cartilage defects were detected in all radiofrequency-treated samples. The histological findings showed a central ulcer and dead chondrocytes in the radiofrequency-treated regions. The radiofrequency-treated cartilage revealed partial surface irregularities with partial-defect repair. After radiofrequency treatment in vitro, samples at time zero showed smoothing of the artificially created clefts, as seen by scanning electron microscopy. Confocal microscopy showed necrosis of chondrocytes over approximately one fourth of the upper cartilage thickness.

Conclusion: Even if chondrocyte death is seen only in approximately one fourth of the upper cartilage layers in the sheep femur after in vitro application, radiofrequency treatment can cause damage to cartilage 24 weeks after application.

Clinical Relevance: Caution is recommended in the application of monopolar radiofrequency energy by visual control to partial-thickness cartilage defects. Irregular fronds of chondromalacia may be unattractive but represent viable articular cartilage. Using radiofrequency to obtain a more visually pleasing smooth surface may be counterproductive.

Key Words: radiofrequency (RF) energy • partial-thickness defect • articular cartilage • confocal microscopy

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