Quantification of laser-induced cartilage injury by confocal microscopy in an ex vivo model.
BACKGROUND
The application of lasers in orthopaedic surgery is increasing. However, some investigators have reported that osteonecrosis may occur after laser meniscectomy. The objective of the present study was to evaluate the effect of laser wavelength and energy on cartilage injury in an ex vivo model.


METHODS
Fresh bovine articular cartilage was exposed to either holmium:yttrium-aluminum-garnet (Ho:YAG) or erbium:YAG-laser (Er:YAG) irradiation. Both lasers were operated in a free-running mode and at a pulse-repetition rate of 8 Hz. The effect of laser treatment at several energy levels (Er:YAG at 100 and 150 mJ and Ho:YAG at 500 and 800 mJ) was examined. For each light source and energy level, ten cartilage samples were assessed by conventional histological analysis and by confocal microscopy. Thermal damage was assessed by determining cell viability.


RESULTS
The extent of thermal damage demonstrated by confocal microscopy was much greater than that demonstrated by histological analysis. The extent of thermal injury after Ho:YAG-laser irradiation was much greater than that after Er:YAG-laser irradiation, which was associated with almost no damage. In addition, the ablation depth was greater after treatment with the Er:YAG laser than after treatment with the Ho:YAG laser.


CONCLUSIONS
In the present study, histological analysis underestimated thermal damage after laser irradiation. In addition, our findings highlighted problems associated with use of high-power settings of Ho:YAG lasers during arthroscopic surgery.
Mainil-Varlet
P
P
Institutes of Pathology and Applied Physics, University of Bern, Switzerland. mainil@patho.unibe.ch
Monin
D
D
Weiler
C
C
Grogan
S
S
Schaffner
T
T
Züger
B
B
Frenz
M
M
D000818:Animals; D002358:Cartilage, Articular / Q000293:injuries*; D002417:Cattle; D007719:Knee Joint; D007834:Lasers / Q000009:adverse effects*; D018613:Microscopy, Confocal