Quantification of laser-induced cartilage injury by confocal microscopy in an ex vivo model

Temperature Profile Measurement From Radiofrequency Nasal Airway Reshaping Device

OBJECTIVE

Nasal airway obstruction (NAO) is caused by various disorders including nasal valve collapse (NVC). A bipolar radiofrequency (RF) device (VivAer®, Aerin Medical, Sunnyvale, CA) has been used to treat NAO through RF heat generation to the upper lateral cartilage (ULC). The purpose of this study is to measure temperature elevations in nasal tissue, using infrared (IR) radiometry to map the spatial and temporal evolution of temperature.

STUDY DESIGN

Experimental and computational.

METHODS

Composite porcine nasal septum was harvested and sectioned (1 mm and 2 mm). The device was used to heat the cartilage in composite porcine septum. An IR camera (FLIR® ExaminIR, Teledyne, Wilsonville, OR) was used to image temperature on the back surface of the specimen. These data were incorporated into a heat transfer finite element model that also calculated tissue damage using Arrhenius rate process.

RESULTS

IR temperature imaging showed peak back surface temperatures of 49.57°C and 42.21°C in 1 and 2 mm thick septums respectively. Temperature maps were generated demonstrating the temporal and spatial evolution of temperature. A finite element model generated temperature profiles with respect to time and depth. Rate process models using Arrhenius coefficients showed 30% chondrocyte death at 1 mm depth after 18 s of RF treatment.

CONCLUSION

The use of this device creates a thermal profile that may result in thermal injury to cartilage. Computational modeling suggests chondrocyte death extending as deep as 1.4 mm below the treatment surface. Further studies should be performed to improve dosimetry and optimize the heating process to reduce potential injury. Laryngoscope, 134:1063-1070, 2024.

Usefulness of Thulium-Doped Fiber Laser and Diode Laser in Zero Ischemia Kidney Surgery-Comparative Study in Pig Model

Background: The aim of this study was to evaluate the usefulness of a thulium-doped fiber laser and a diode laser in zero ischemia kidney surgery, by carrying out a comparative study in a pig model. Material and methods: Research was carried out on 12 pigs weighing 30 kg each. A thulium-doped fiber laser (TDFL) and a diode laser (DL) operating at wavelengths of 1940 and 1470 nm, respectively, were used. The cut sites were assessed both macroscopically and microscopically. The zone of thermal damage visible in the histopathological preparations was divided into superficial and total areas. Results: During partial nephrectomy, moderate to minimal bleeding was observed, which did not require additional hemostatic measures. All animals survived the procedure. On day 0, the total thermal damage depth was 837.8 µm for the TDFL and 1175.0 µm for the DL. On day 7, the depths were 1556.2 and 2301.7 µm, respectively. On day 14, the overall thermal damage depth for the DL was the greatest (6800 µm). The width of the superficial zone was significantly reduced on days 7 and 14 after TDFL application. Conclusion: Both lasers are suitable for partial wedge nephrectomy without ischemia in pigs. The TDFL produced similar or better hemostasis than the DL, with a smaller zone of thermal damage and, therefore, seems more suitable for application in human medicine.

Laser photobiomodulation for cartilage defect in animal models of knee osteoarthritis: a systematic review and meta-analysis

To review and assess the efficacy of laser photobiomodulation for cartilage defect in animal models of knee osteoarthritis (KOA). Medline, Web of Science, and EMBASE were searched. Studies were considered if the global quality score of cartilage were parallelly reported between laser and untreated control groups. The methodological quality of each study was assessed using a modified 10-item checklist. The effect size was estimated by standardized mean difference (SMD) and pooled based on the random-effects model. Stratified analysis and regression analysis were conducted to partition potential heterogeneity. An adjusted significant level of 0.01 was acceptable. Five hundred eight initial search recordings were identified, of which 14 studies (including 274 animals) were included for quantitative analysis. The global quality scores mostly weighted by the structural integrity and chondrocyte distribution were measured by different four scales including Histologic Histochemical Grading System (HHGS), Osteoarthritis Research Society International (OARSI), Pineda, and Huang. There were considerable variances on laser parameters and irradiation time among those included studies. Overall, a moderate level of methodological qualities was determined. The synthesis results indicated that the SMD effect size was significantly larger in HHGS (z = 2.61, P = 0.01) and Huang (z = 4.90, P < 0.01) groups. Stratified by irradiance, SMD of low (< 1 W/cm²) but not high (≥ 1 W/cm²) level estimated significant difference (z = 5.62, P < 0.01). Meta-regression identified a significant association for SMDs and irradiation time (P < 0.01). Yet, Egger's test detected small study effect (P < 0.01). No individual study with significant variance was found in homogeneity tests. The results demonstrated the positive effect of laser photobiomodulation for cartilage defect in animal models of KOA under proper irradiance and adequate irradiation time.

Ablation of porcine ligamentum flavum with Ho:YAG, q-switched Ho:YAG, and quadrupled Nd:YAG lasers

BACKGROUND AND OBJECTIVES

Ligamentum flavum (LF) is a tough, rubbery connective tissue providing a portion of the ligamentous stability to the spinal column, and in its hypertrophied state forms a significant compressive pathology in degenerative spinal stenosis. The interaction of lasers and this biological tissue have not been thoroughly studied. Technological advances improving endoscopic surgical access to the spinal canal makes selective removal of LF using small, flexible tools such as laser-coupled fiber optics increasingly attractive for treatment of debilitating spinal stenosis. Testing was performed to assess the effect of Ho:YAG, Q-switched Ho:YAG, and frequency quadrupled Nd:YAG lasers on samples of porcine LF. The objective was to evaluate the suitability of these lasers for surgical removal of LF.

STUDY DESIGN/MATERIALS AND METHODS

LF was resected from porcine spine within 2 hours of sacrifice and stored in saline until immediately prior to laser irradiation, which occurred within an additional 2 hours. The optical absorbance of a sample was measured over the spectral band from 190 to 2,360 nm both before and after dehydration. For the experiments using the Ho:YAG (λ = 2,080 nm, tp  = 140 µs, FWHM) and Q-Switched Ho:YAG (λ = 2,080 nm, tp  = 260 ns, FWHM) lasers, energy was delivered to the LF through a laser-fiber optic with 600 µm core and NA = 0.39. For the experiment using the frequency quadrupled Nd:YAG laser (λ = 266 nm, tp  = 5 ns FWHM), rather than applying the laser energy through a laser-fiber, the energy was focused through an aperture and lens directly onto the LF. Five experiments were conducted to evaluate the effect of the given lasers on LF. First, using the Ho:YAG laser, the single-pulse laser-hole depth versus laser fluence was measured with the laser-fiber in direct contact with the LF (1 g force) and with a standoff distance of 1 mm between the laser-fiber face and the LF. Second, with the LF remaining in situ and the spine bisected along the coronal plane, the surface temperature of the LF was measured with an IR camera during irradiation with the Ho:YAG laser, with and without constant saline flush. Third, the mass loss was measured over the course of 450 Ho:YAG pulses. Fourth, hole depth and temperature were measured over 30 pulses of fixed fluence from the Ho:YAG and Q-Switched Ho:YAG lasers. Fifth, the ablation rate and surface temperature were measured as a function of fluence from the Nd:YAG laser. Several LF staining and hole-depth measurement techniques were also explored.

RESULTS

Aside from the expected absorbance peaks corresponding to the water in the LF, the most significant peaks in absorbance were located in the spectral band from 190 to 290 nm and persisted after the tissue was dehydrated. In the first experiment, using the Ho:YAG laser and with the laser-fiber in direct contact with the LF, the lowest single-pulse fluence for which LF was visibly removed was 35 J/cm(2) . Testing was conducted at 6 fluences between 35 and 354 J/cm(2) . Over this range the single-pulse hole depth was shown to be near linear (R(2)  = 0.9374, M = 1.6), ranging from 40 to 639 µm (N = 3). For the case where the laser-fiber face was displaced 1 mm from the LF surface, the lowest single-pulse fluence for which tissue was visibly removed was 72 J/cm(2) . Testing was conducted at 4 energy densities between 72 and 180 J/cm(2) . Over this range the single-pulse hole depth was shown to be near linear (R(2)  = 0.8951, M = 1.4), ranging from 31 to 220 µm (N = 3). In the second experiment, with LF in situ, constant flushing with room temperature saline was shown to drastically reduce surface temperature during exposure to Ho:YAG at 5 Hz with the laser-fiber in direct contact with the LF. Without saline, over 1 minute of treatment with a per-pulse fluence of 141 mJ/cm(2) , the average maximum surface temperature measured 110°C. With 10 cc's of saline flushed over 1 minute and a per-pulse laser fluence of 212 mJ/cm(2) , the average maximum surface temperature was 35°C. In the third experiment, mass loss was shown to be linear over 450 pulses of 600 mJ from the Ho:YAG laser (212 J/cm(2) , direct contact, N = 4; 108 J/cm(2) , 1 mm standoff, N = 4). With the laser-fiber in direct contact, an average of 53 mg was removed (R(2)  = 0.996, M = 0.117) and with 1 mm laser-fiber standoff, an average of 44 mg was removed (R(2)  = 0.9988, M = 0.097). In the fourth experiment, 30 pulses of the Ho:YAG and Q-Switched Ho:YAG lasers at 1 mm standoff, and 5 Hz produced similar hole depths for the tested fluences of 9 J/cm(2) (151 and 154 µm, respectively) and 18 J/cm(2) (470 and 442 µm, respectively), though the Ho:YAG laser produced significantly more carbonization around the rim of the laser-hole. The increased carbonization was corroborated by higher measured LF temperature. In all tests with the Ho:YAG and Q-Switched Ho:YAG, an audible photo-acoustic affect coincided with the laser pulse. In the fifth experiment, with the frequency quadrupled Nd:YAG laser at 15 Hz for 450 pulses, ablation depth per pulse was shown to be linear for the fluence range of 0.18 - 0.73 J/cm(2) (R(2)  = 0.989, M = 2.4). There was no noticeable photo-acoustic effect nor charring around the rim of the laser-hole.

CONCLUSION

The Ho:YAG, Q-Switched Ho:YAG, and frequency quadrupled Nd:YAG lasers were shown to remove ligamentum flavum (LF). A single pulse of the Ho:YAG laser was shown to cause tearing of the tissue and a large zone of necrosis surrounding the laser-hole. Multiple pulses of the Ho:YAG and Q-Switched Ho:YAG lasers caused charring around the rim of the laser-hole, though the extent of charring was more extensive with the Ho:YAG laser. Charring caused by the Ho:YAG laser was shown to be mitigated by continuously flushing the affected LF with saline during irradiation. The Nd:YAG laser was shown to ablate LF with no gross visible indication of thermal damage to surrounding LF.

Regenerative and proliferative activities of chondrocyte based on the degree of perichondrial injury in rabbit auricular cartilage

Although the regeneration process for injured cartilage requires an intact perichondrium, few studies have addressed the importance of the intact perichondrial layer in the regeneration of damaged cartilage. In this study, we evaluated the role of the perichondrium on regenerative activities in injured cartilage according to different degrees of perichondrial injury. Auricular cartilage harvested from six New Zealand white rabbits was irradiated with a 1,460-nm diode laser at two different power settings (0.3 or 0.5 W). Irradiated cartilage was reimplanted into a subperichondrial pocket under three different conditions: non-injured perichondrium (NPI), unilaterally injured perichondrium (UPI), or bilaterally injured perichondrium (BPI). Rabbits were sacrificed at 1, 2, and 4 weeks after reimplantation and the auricular cartilage was reharvested. A histopathological study using hematoxylin and eosin staining, a live/dead viability assay, and immunohistochemical staining for proliferating cell nuclear antigen were performed to evaluate structural changes and regenerative and proliferative activities of the injured chondrocytes. A modified array and restored boundary of chondrocytes were observed in the NPI and UPI groups. Regeneration of chondrocytes was prominent in the NPI and UPI groups, but was not observed in the BPI group. Proliferative activity of chondrocytes was observed only when the perichondrium was preserved in the NPI and UPI groups. In contrast, proliferative activity was not observed until 4 weeks in the BPI group. The degree of perichondrial injury affected proliferation and regeneration in injured elastic cartilage. In the case of unilateral perichondrial injury, the surgeon should be careful to avoid damaging the other side of the perichondrium, because at least a unilateral perichondrial layer is needed for the regeneration of elastic cartilage.

Viability and Regeneration of Chondrocytes after Laser Cartilage Reshaping Using 1,460 nm Diode Laser

Objectives

Cartilage reshaping by laser irradiation is used to correct septal and auricular cartilage deformities. Chondrocyte viability following laser irradiation and reshaping has been well established. However, the regeneration process of chondrocyte after laser irradiation has not been revealed yet. The aims of this study were to determine the mechanism of cartilaginous thermal injury and the regenerative process of damaged cartilage following laser irradiation.

Methods

Laser irradiation was performed on human septal cartilage and rabbit auricular cartilage using a 1,460-nm diode laser. We observed change in the shape of cartilage and evaluated the extent of cartilage injury using live/dead cell assay via confocal microscopy. Hoechst and propidium iodide (PI) staining was used to evaluate the mechanism of chondrocyte injury after laser irradiation. To evaluate the regeneration of cartilage, laser irradiated cartilages were reimplanted into a subperichondrial pocket and were harvested at 1, 2, and 4 weeks after reimplantation for viability assessment and histologic examination.

Results

Laser irradiation using a 1,460-nm diode laser produced a marked shape change in both human septal and rabbit auricular cartilages. Thermal damage on cartilage was correlated with the exposure time and the laser power. Hoechst and PI staining showed that chondrocyte death by laser irradiation was due to mainly necrosis, rather than apoptosis. In lower power treatment group (0.3 W and 0.5 W), all the chondrocytes regenerated within 4 weeks, however, in 1 W treatment group, chondrocytes could not regenerate until 4 weeks.

Conclusion

Reshaping of cartilage using 1,460 nm diode laser was attained concurrently with the thermal injury to the chondrocytes. The extent of thermal damage on chondrocytes was dependent on the exposure time and the laser power and the damaged chondrocytes irradiated with lower level of laser power could be regenerated after reimplantation into subperichondrial pocket.

Effects of radiofrequency energy on porcine articular cartilage: higher-power settings in ablation mode show lower thermal radiation injury

PURPOSE

The purpose of this study was to compare the radiofrequency (RF) injury effect on cartilage in the different settings that are mostly used in clinical work under rigidly controlled laboratory conditions.

METHODS

Twelve fresh porcine knees were used in our study. Five treatment areas were created on the femoral condyles of each knee: the control group, coagulation (setting 2) group, coagulation (setting 7) group, ablation (setting 2) group, and ablation (setting 7) group. Hematoxylin/eosin staining, dual fluorescence staining, and the GAG content were observed to evaluate the histological cartilage changes, vacuolar cell rate of chondrocytes, depth of chondrocyte death, and detection of GAG content.

RESULTS

Vacuolar cell rates of chondrocytes in each experimental group were higher than that in the control group (P < 0.05); there was no significant difference in vacuolar cell rate among experimental groups. Dual fluorescent staining showed that the ablation (setting 7) group had a smaller depth of cell death than did the coagulation (setting 2) group (P < 0.05); the other experimental groups showed no statistically significant difference (n.s.). In addition, there was no significant difference in GAG content between the experimental groups and control group (n.s.).

CONCLUSIONS

The coagulation mode results in heavier thermal radiation injury to chondrocytes than does the ablation mode. Higher-power settings in the ablation mode result in lower thermal radiation injury and may be most suitable for cartilage debridement.

Survival of chondrocytes in rabbit septal cartilage after electromechanical reshaping

Electromechanical reshaping (EMR) has been recently described as an alternative method for reshaping facial cartilage without the need for incisions or sutures. This study focuses on determining the short- and long-term viability of chondrocytes following EMR in cartilage grafts maintained in tissue culture. Flat rabbit nasal septal cartilage specimens were bent into semi-cylindrical shapes by an aluminum jig while a constant electric voltage was applied across the concave and convex surfaces. After EMR, specimens were maintained in culture media for 64 days. Over this time period, specimens were serially biopsied and then stained with a fluorescent live–dead assay system and imaged using laser scanning confocal microscopy. In addition, the fraction of viable chondrocytes was measured, correlated with voltage, voltage application time, electric field configuration, and examined serially. The fraction of viable chondrocytes decreased with voltage and application time. High local electric field intensity and proximity to the positive electrode also focally reduced chondrocyte viability. The density of viable chondrocytes decreased over time and reached a steady state after 2–4 weeks. Viable cells were concentrated within the central region of the specimen. Approximately 20% of original chondrocytes remained viable after reshaping with optimal voltage and application time parameters and compared favorably with conventional surgical shape change techniques such as morselization.

Ablation of articular cartilage with an erbium:YAG laser: an ex vivo study using porcine models under real conditions-ablation measurement and histological examination

BACKGROUND AND OBJECTIVES

The use of an erbium:YAG laser in arthroscopic surgery has the advantage of a precise treatment of soft tissue. Due to the high absorption in water, the laser energy is perfectly matched to smoothing the hydrous, fibrillated articular cartilage surface. In minimal invasive surgery, the workspace is filled with aqueous liquids for enlargement. This appears contrary to the absorption characteristics of erbium:YAG laser radiation in water. The purpose of this study was to evaluate the ablated volume per pulse of cartilage lesions and the potential side effects including thermal damage and tissue necrosis.

STUDY DESIGN/MATERIALS AND METHODS

Twenty-four osteochondral specimens of porcine knee joints were irradiated with an Er:YAG laser completely submerged in water, with distances to the cartilage surface of 1, 3 and 5 mm and pulse durations of 75 and 100 microseconds. To keep a constant peak power of approximately 6 kW, pulse energies of 450 and 580 mJ were used at a pulse repetition rate of 15 Hz. After a histological preparation, ablated volumes, depths, and widths of the cuts were investigated. Additionally, laser protocols were correlated with different markers of cartilage tissue damage and apoptosis.

RESULTS

Ablation could be observed for every measurement. The influence of the distance showed a statistical significance (P < 0.001) for the volume, depth, and width of the cuts. For the pulse duration, statistical significance (P < 0.001) was found only for the volume and the depth. We observed no loss of proteoglycan or collagen type II. The total cell number, cell morphology, and number of apoptotic cells in an area close to the cutting edge and in a corresponding unaffected area of the same specimens revealed no differences regardless of the applied protocol.

CONCLUSION

The use of an Er:YAG laser demonstrates the successful application in liquid environments for cartilage removal without any damage of the surrounding tissue.

Thermoforming of tracheal cartilage: viability, shape change, and mechanical behavior

BACKGROUND AND OBJECTIVES

Trauma, emergent tracheostomy, and prolonged intubation are common causes of severe deformation and narrowing of the trachea. Laser technology may be used to reshape tracheal cartilage using minimally invasive methods. The objectives of this study were to determine: (1) the dependence of tracheal cartilage shape change on temperature and laser dosimetry using heated saline bath immersion and laser irradiation, respectively, (2) the effect of temperature on the mechanical behavior of cartilage, and (3) tissue viability as a function of laser dosimetry.

MATERIALS AND METHODS

Ex vivo rabbit trachea cartilage specimens were bent and secured around a cylinder (6 mm), and then immersed in a saline bath (45 and 72 degrees C) for 5-100 seconds. In separate experiments, tracheal specimens were irradiated with a diode laser (lambda = 1.45 microm, 220-400 J/cm(2)). Mechanical analysis was then used to determine the elastic modulus in tension after irradiation. Fluorescent viability assays combined with laser scanning confocal microscopy (LSCM) were employed to image and identify thermal injury regions.

RESULTS

Shape change transition zones, between 62 and 66 degrees C in the saline heating bath and above power densities of 350 J/cm(2) (peak temperatures 65+/-10 degrees C) for laser irradiation were identified. Above these zones, the elastic moduli were higher (8.2+/-4 MPa) than at lower temperatures (4.5+/-3 MPa). LSCM identified significant loss of viable chondrocytes within the laser-irradiation zones.

CONCLUSION

Our results indicate a change in mechanical properties occurs with laser irradiation and further demonstrates that significant thermal damage is concurrent with clinically relevant shape change in the elastic cartilage tissues of the rabbit trachea using the present laser and dosimetry parameters.

Viability of human septal cartilage after 1.45 microm diode laser irradiation

BACKGROUND AND OBJECTIVES

Chondrocyte viability following laser irradiation and reshaping has not been established for human nasal septal cartilage. Knowledge of the relationship between thermal injury and laser dosimetry is needed in order to optimize septal laser cartilage reshaping. The objective of this study was to determine the depth and width of thermal injury in human septal cartilage following laser irradiation.

STUDY DESIGN/MATERIALS AND METHODS

Excess fresh nasal septal cartilage sections from rhinoplasty or septoplasty operations were irradiated using a 1.45 microm diode laser 1.25-3.6 W (2.8 mm spot diameter) with 1 second fixed exposure time, and then at exposure times of 1-4 seconds for a fixed power of 1.25 W. An infrared camera recorded surface temperature profiles during irradiation, and the temperature data were incorporated into a rate process model to numerically estimate thermal damage. Calcein AM and ethidium homodimer-1 fluorescent dyes combined with confocal laser microscopy (CLM) were used to measure thermal damage.

RESULTS

CLM demonstrated clear demarcation between dead and living cells following irradiation. The extent of non-viable chondrocyte distributions increased with power and exposure time. The maximum depths of injury were 1,012 and 1,372 microm after 3.6 W 1 second and 1.25 W 4 seconds irradiation respectively. The damage predictions made by the rate process model underestimated thermal injury when compared with CLM measurements.

CONCLUSIONS

The assay system identified regions of non-viable chondrocytes in human septal cartilage and defined how thermal injury varies with dosimetry when using a 1.45 microm diode laser.

Magnetization transfer based contrast for imaging denatured collagen

PURPOSE

To study of the sensitivity of various NMR and MRI methods and parameters to the degree of thermal denaturation of collagen.

MATERIALS AND METHODS

Collagen type I powder was washed with methanol:chloroform to remove traces of lipids and then suspended in saline. Denaturation was carried out by heating the suspension for 5-120 minutes at a temperature range of 50-100 degrees C. The NMR methods tested were two T(2) filter methods: Goldman-Shen (GS) and Edzes-Samulski (ES); magnetization transfer contrast (MTC); double quantum filtering (DQF) and high resolution spectroscopy. MRI contrasts based on these methods were compared.

RESULTS

The following parameters were found to be sensitive to denaturation of collagen: 1) the amount of spins that experience high dipolar interactions as assessed by DQF; 2) MTR; 3) k(w)T(1w) (where k(w) is the magnetization transfer rate from water to collagen, and T(1w) is the water protons longitudinal relaxation time); and 4) aliphatic residues content. The contrast between native and denatured collagen was improved by all the tested methods, with ES and DQF producing the highest contrast.

CONCLUSION

Methods depending on T(2) filtering and DQF were found to be sensitive to the degree of thermal denaturation of collagen and improve the contrast between native and denatured collagen.

Reversal of suppressed metabolism in prolonged cold preserved cartilage

Chondrocytes in cold preserved cartilage are metabolically suppressed. The goal of this study was to address this metabolic suppression and seek ways to reverse it. Specifically, we examined the roles of rewarming protocols and nitric oxide (NO) in this metabolic suppression. Bovine and canine full-thickness articular cartilage explants were cultured under various temperature conditions, and NO production, proteoglycan (PG) synthesis, and cell viability were measured. Nitric oxide was shown to be negatively correlated with PG synthesis following abrupt rewarming of cold preserved osteochondral allografts. Gradual rewarming of the allograft tissue decreased NO production with higher PG synthesis. Inhibition of nitric oxide synthases (NOS) led to a decrease in NO production and a concomitant increase in PG synthesis. We were able to partially reverse metabolic suppression of cold preserved osteochondral allograft material with gradual rewarming and decrease NO production with NOS inhibition. Chondrocytes in cold preserved allograft material may be metabolically suppressed predisposing the graft to failure in vivo. Minimizing this loss of metabolic function by gradual graft rewarming and decreasing NO production by NOS inhibition at the time of graft implantation may have implications on graft survival in vivo.

Analysis of Nd:YAG laser-mediated thermal damage in rabbit nasal septal cartilage

BACKGROUND AND OBJECTIVES

Laser cartilage reshaping (LCR) involves the use of photo-thermal heating to reshape cartilage. Its clinical relevance depends on the ability to minimize thermal injury in irradiated regions. The present study seeks to understand the safety of LCR by determining shape change and resultant tissue viability as a function of laser dosimetry.

STUDY DESIGN/MATERIALS AND METHODS

Rabbit nasal septal cartilage were irradiated using a Nd:YAG laser (lambda = 1.32 microm, 5.4 mm spot diameter) with different exposure times of 4, 6, 8, 10, 12, and 16 seconds and powers of 4, 6, and 8 W. Temperature on the cartilage surface in the laser-irradiated region was collected using infrared thermography, this data was then used to predict tissue damage via a rate process model. A Live/Dead viability assay combined with fluorescent confocal microscopy was used to measure the amount of thermal damage generated in the irradiated specimens.

RESULTS

Considerable thermal injury occurred at and below the laser-reshaping parameters that produced clinically relevant shape change using the present Nd:YAG laser. Confocal microscopy identified dead cells spanning the entire cross-sectional thickness of the cartilage specimen (about 500 microm thick) at laser power density and exposure times above 4 W and 6 seconds; damage increased with time and irradiance. The damage predictions made by the rate process model compared favorably with measured data.

CONCLUSIONS

These results demonstrate that significant thermal damage is concurrent with clinically relevant shape change. This contradicts previous notions that there is a privileged laser dosimetry parameter where clinically relevant shape change and tissue viability coexist.

Postarthroscopic osteonecrosis of the knee

Little is known about the etiology of postarthroscopic osteonecrosis of the knee. Its prevalence is probably very low. The most important differential diagnosis is pre-existing and undiagnosed early-stage spontaneous osteonecrosis of the knee. From the medicolegal point of view, orthopaedic surgeons need to be aware of the diagnostic pitfalls in differentiating between postarthroscopic osteonecrosis of the knee and spontaneous osteonecrosis of the knee, and they must understand that both may be unpreventable conditions. The purpose of this report is to review the presumable pathophysiology and the clinical and radiographic features as well as the pitfalls in diagnosing postarthroscopic osteonecrosis of the knee.

Cartilage viability after trochleoplasty

Trochleoplasty is an established and accepted technique for the treatment of patellar instability because of a missing trochlear groove. In this technique, a flap of cartilage over the trochlea is carefully removed and a new trochlear groove is created in the underlying bone before the cartilaginous flap is reattached with sutures. The mid-term clinical and radiological results of this operation are promising but no information about the viability of the reattached cartilage has been reported. To evaluate cartilage viability and quality after trochleoplasty and to verify the healing process, two osteochondral biopsies were harvested from three patients 6, 8, and 9 months after trochleoplasty. One cylinder was evaluated histologically to assess cartilage, calcified cartilage (cc), and subchondral bone quality, while the other one was examined by confocal microscopy to evaluate cell viability. The histological examination showed a normal matrix and cell distribution of the cartilage, while the cc showed lacunae ingrowing from the underlying bone. The subchondral bone showed normal lamellae and histology, and the healing of the flap. Confocal microscopy showed almost exclusively viable chondrocytes. This demonstration of non-injured cartilage at short-term follow-up together with promising clinical and radiological 2- and 5-year follow-up results indicate a potential promising outlook for the long term, as further chondral damage is not expected. So trochleoplasty can be seen as a primary intervention for patellar instability because of trochlear dysplasia as the risk for cartilage damage is low.

Comparison of mechanical debridement and radiofrequency energy for chondroplasty in an in vivo equine model of partial thickness cartilage injury

OBJECTIVE

The purpose of this study was to develop a long-term model of cartilage injury that could be used to compare the effects of radiofrequency energy (RFE) and mechanical debridement as a treatment.

METHODS

Partial thickness fibrillation of patellar cartilage was created in 16 mature ponies. Three months after the initial surgery all injured patellae were randomly selected to receive one of the four treatments (n = 8/treatment): (1) control, (2) mechanical debridement with a motorized shaver, (3) TAC-CII RFE probe, and (4) CoVac 50 RFE probe. The ponies were euthanized 22 months after treatment. Macroscopic appearance of the cartilage surface was scored, vital cell staining was used to determine chondrocyte viability and light microscopy was used to grade the morphometric changes within the cartilage. Mechanical properties (aggregate modulus, Poisson's ratio and permeability) also were determined and compared to normal uninjured cartilage.

RESULTS

There were no differences in the cartilage surface scores among the treatment groups and control samples (P > 0.05). The maximum depth of cell death and the percentage of dead area in control and mechanical debridement groups were significantly less than those in both RFE groups. There were no significant differences in maximum depth and the percentage of dead area between the two RFE treatment groups. Histologic scores demonstrated better cartilage morphology for the control and mechanical debridement groups than those of RFE groups. However, even with full thickness chondrocyte death, the matrix in the RFE treated sections was still retained and the mechanical properties of the treated cartilage did not differ from the mechanical debridement group.

CONCLUSION

RFE caused greater chondrocyte death and more severe morphological changes compared to untreated degenerative cartilage and mechanical debridement in this model.

Effects of thermal energy on chondrocyte viability

OBJECTIVE

To determine the critical temperature that reduces chondrocyte viability and evaluate the ability of chondrocytes to recover after exposure to the critical temperature.

SAMPLE POPULATION

Cartilage explants obtained from the humeral heads of 30 sheep.

PROCEDURES

In a randomized block design, 318 full-thickness cartilage explants were collected from 30 humeral heads of sheep and cultured for up to 14 days. On the first day of culture (day 0), explants were subjected to temperatures of 37 degrees , 45 degrees , 50 degrees , 55 degrees , 60 degrees , or 65 degrees C for 5 minutes by heating culture tubes in a warming block. The ability for chondrocytes to recover after exposure to the critical temperature was determined by evaluating viability at days 0, 1, 3, 7, and 14 days after heating. Images were analyzed by use of confocal laser microscopy.

RESULTS

Analysis of images revealed a significant decrease in live cells and a significant increase in dead cells as temperature increased. Additionally, the deepest layer of cartilage had a significantly lower percentage of live cells, compared with values for the 3 most superficial layers. Chondrocytes did have some ability to recover temporarily after the initial thermal insult.

CONCLUSIONS AND CLINICAL RELEVANCE

A strong relationship exists between increasing temperature and cell death, with a sharp increase in chondrocyte death between 50 degrees and 55 degrees C. Chondrocytes in the deepest cartilage layer are most susceptible to thermal injury. The threshold of chondrocyte recovery from thermal injury is much lower than temperatures reached during chondroplasty by use of most radiofrequency energy devices.

Low-power laser stimulation of tissue engineered cartilage tissue formed on a porous calcium polyphosphate scaffold

BACKGROUND AND OBJECTIVE

Forming cartilage tissue in vitro that resembles native tissue is one of the challenges of cartilage tissue engineering. The aim of this study was to determine whether low-power laser stimulation would improve the formation of cartilage tissue in vitro.

STUDY DESIGN/MATERIALS AND METHODS

Bovine articular chondrocytes were seeded on the top surface of porous calcium polyphosphate substrates. After 2 days, laser stimulation was applied daily at a wavelength of 650 nm using a laser diode with energy densities of either 1.75 or 3 J/cm(2) for 4 weeks. Proteoglycan and collagen synthesis and matrix content were determined. Cartilage tissue morphology was evaluated histologically.

RESULTS

Histologically, there was no difference in the appearance or cellularity of the tissues that formed in the presence or absence of laser stimulation at either dosage. There were no differences in DNA content between treated and untreated constructs and live-dead assay confirmed that this treatment was not toxic to the cells. Laser stimulation at 3 J/cm(2) enhanced matrix synthesis resulting in significantly more tissue formation than laser stimulation at 1.75 J/cm(2) or untreated cultures.

CONCLUSION

Short exposures to low-power laser stimulation using a laser diode with 3 J/cm(2) dose improves cartilage tissue formation.

Development of partial thickness articular cartilage injury in an ovine model

The purpose of this study was to create a controlled partial thickness cartilage lesion in a sheep model, and to provide a foundation to study the natural history of the progression of this lesion. Twenty-eight sheep divided into four groups (1, 12, 24, and 52 weeks, n=7/group) were used in this study. In one stifle, a mechanical tool was used to create a 200 microm partial thickness lesion (1.5x1.5 cm2) on the medial femoral condyle via arthroscopy. Joint fluid was drawn presurgery and after euthanasia for analysis of collage II 3/4 C (long) (C2C). After euthanasia, the condyle was analyzed by gross appearance, confocal laser microscopy (CLM) for cell viability, scanning electronic microscopy (SEM) for surface roughness, Artscan for cartilage stiffness, and histology for cartilage morphology. The gross appearance of the treated area appeared rough, soft, and swollen compared to untreated control over time. CLM demonstrated that the depth of cell death increased to 590 microm at 52 weeks after surgery. SEM demonstrated that the treated area became more irregular over time. Stiffness of the treated area was significantly less than control by 12 weeks after surgery. Histologic analysis demonstrated that the 12, 24, and 52 week groups had significantly poorer histologic scores than the 1 week group. Joint fluid analysis demonstrated that the treatment group at 1 week had significant higher levels of C2C than the pretreatment baseline data. The results of this study demonstrated that partial thickness injury of cartilage continued to propagate and degenerate over time in this sheep model. Options for the prevention or treatment of this lesion may be tested using this model in the future.

Comparison of techniques for determination of chondrocyte viability after thermal injury

OBJECTIVE

To compare 2 methods of quantitating chondrocyte viability and to determine chondrocyte response to thermal injury over time.

SAMPLE POPULATION

108 stifle joints from 54 adult rats.

PROCEDURES

Cartilage from the distal aspect of the femur was treated ex vivo with radiofrequency energy at a probe setting that would result in immediate partial-thickness chondrocyte death; untreated sections served as controls. Explants were cultured, and cell viability was compared by use of lactate dehydrogenase (LDH) histochemical staining and calcein AM and ethidium homodimer-1 confocal laser microscopy (CLM) cell viability staining. Terminal deoxynucleotidyl transferase-mediated X-dUTP nick end labeling (TUNEL) was used to detect apoptosis. All labeling studies were performed 0, 1, 3, 7, 14, and 21 days after treatment.

RESULTS

In the treated tissues, a greater percentage of viable cells were found with CLM, compared with LDH staining. This result contrasted that of control tissues in which LDH staining indicated a greater percentage of live cells than CLM. The greatest number of TUNEL-positive chondrocytes was present at day 3, declining at later time intervals.

CONCLUSIONS AND CLINICAL RELEVANCE

CLM and LDH histochemistry techniques yield different absolute numbers of live and dead cells, resulting in differing percentages of live or dead cells with each technique. These differences may be related to the enzymes responsible for activation in each technique and the susceptibility of these enzymes to thermal injury. Results of TUNEL indicate that apoptosis contributes to chondrocyte death after thermal injury, with a peak signal identified 3 days after insult.

Long-term viability and mechanical behavior following laser cartilage reshaping

OBJECTIVE

To investigate the long-term in vivo effect of laser dosimetry on rabbit septal cartilage integrity, viability, and mechanical behavior.

METHODS

Nasal septal cartilage specimens (control and irradiated pairs) were harvested from 18 rabbits. Specimens were mechanically deformed and irradiated with an Nd:YAG laser across a broad dosimetry range (4-8 W and 6-16 seconds). Treated specimens and controls were autologously implanted into a subperichondrial auricular pocket. Specimens were harvested an average +/- SD of 208 +/- 35 days later. Tissue integrity, histology, chondrocyte viability, and mechanical property evaluations were performed. Tissue damage results were compared with Monte Carlo simulation models.

RESULTS

All laser-irradiated specimens demonstrated variable tissue resorption and calcification, which increased with increased dosimetry. Elastic moduli of the specimens were significantly either lower or higher than controls (all P<.05). Viability assays illustrated a total loss of viable chondrocytes within the laser-irradiated zones in all treated specimens. Histologic examination confirmed these findings. Experimental results were consistent with damage profiles determined using numerical simulations.

CONCLUSION

The loss of structural integrity and chondrocyte viability observed across a broad dosimetry range underscores the importance of spatially selective heating methods prior to initiating application in human subjects.

Mid-IR laser ablation of articular and fibro-cartilage: a wavelength dependence study of thermal injury and crater morphology

BACKGROUND AND OBJECTIVE

The aim of this study was to evaluate areas of collateral thermal injury and crater morphology for evidence of wavelength-dependent effects on the ablation of articular cartilage and fibro-cartilage (meniscus) using selected mid-IR wavelengths produced by a free electron laser.

STUDY DESIGN/MATERIALS AND METHODS

Two types of cartilage, articular cartilage and fibro-cartilage were used in the study. The wavelengths (lambda) evaluated were 2.79, 2.9, 6.1, and 6.45 microm generated by a free electron laser (FEL) using a 4 microseconds macropulse configuration. The zone of thermal injury and crater morphology produced by laser ablation were examined by light microscopy following standard histologic processing.

RESULTS

The zone of thermal injury and crater morphology created in cartilage by the FEL at selected mid-IR wavelengths were examined as a function of incident radiant exposure. Ablation using lambda = 6.1 microm provided the largest crater size for both articular and fibro-cartilage at all radiant exposures. For the zones of collateral thermal injury in articular cartilage, lambda = 6.1 microm produced the least thermal injury at the radiant exposure of 7.6 J/cm2. When the radiant exposure is increased to 20.4 J/cm2, both lambda = 6.1 and 6.45 microm produced less thermal injury than the ablation using lambda = 2.79 and 2.9 microm. The greatest amount of collateral thermal injury was produced by lambda = 2.79 microm for both tissue types.

CONCLUSIONS

The results demonstrate that crater depth and collateral thermal injury produced in articular cartilage and fibro-cartilage are wavelength-dependent with 6.1 microm providing the largest craters at all radiant exposures. The least amount of thermal injury was created in articular cartilage using lambda = 6.1 microm at the radiant exposure of 7.6 J/cm2. Both 6.1 and 6.45 microm wavelengths demonstrated similar amount of thermal injury at 20 J/cm2 that was less than lambda = 2.79 and 2.9 microm at similar fluences. These observations are explained based on the absorption by water and protein in the tissue types studied. It is further observed that the use of crater dimensions may not provide a reliable estimate for the amount of tissue removal provided by an ablation procedure.

Monopolar radiofrequency treatment of partial-thickness cartilage defects in the sheep knee joint leads to extended cartilage injury

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.

Effects of radiofrequency energy on human articular cartilage: an analysis of 5 systems

BACKGROUND

Previous radiofrequency work has not rigidly controlled energy application to the articular cartilage, giving uncertain results published to date.

HYPOTHESIS

At minimal settings, radiofrequency probes cause cell death in measurable areas when applied to human articular cartilage.

STUDY DESIGN

Controlled laboratory study.

METHODS

Simulating operating room conditions, 5 commercially available radiofrequency probes were attached to a customized jig to standardize a minimal contact pressure of each probe tip to 2.0 g. Keeping all variables the same, probes were placed on specific points of fresh grade II human cartilage with treatment times of 1 and 3 seconds at the manufacturer's recommended settings. Grade III cartilage was also tested with a treatment time of 3 seconds, and grade II cartilage was studied with the probe held 1 mm off the cartilage surface. Cartilage was blindly analyzed by confocal microscopy using a live/dead cell viability assay to determine the extent of cell death.

RESULTS

Radiofrequency probes produced significant cellular death in the form of a half-circle into the cartilage to variable depths. For treatment times of 1 and 3 seconds, cell death measurements ranged from 404 to 539 mum and 1034 to 1283 mum, respectively. One probe failed to show any effect, with minimal evidence of cell death or cartilage smoothing. When probes were kept a 1.0-mm distance above the cartilage, no cell death or cartilage smoothing was noted. Radiofrequency treatment of grade III cartilage penetrated to the subchondral bone. There was no statistically significant difference between the damage caused by monopolar and bipolar probes when tested under these rigidly controlled conditions.

CONCLUSION

These results showed significant cellular death at these minimal conditions to the underlying chondrocytes with radiofrequency probes. Surgeons using this technology need to be aware of the power and dangerous potential these probes can have on articular cartilage.

Prolonged-fresh preservation of intact whole canine femoral condyles for the potential use as osteochondral allografts

Defects in articular cartilage are often repaired with fresh osteochondral grafts. While fresh allografts provide viable chondrocytes, logistic limitations require surgical implantation within seven days of graft harvest. Here, we provide information on cold preservation of whole intact osteochondral materials that retains cartilage cell viability and function, and histologic and biochemical integrity for 28 days. Canine femoral condyles were obtained and stored at 4 degrees C for 14, 21 or 28 days. At the end of the storage period, cartilage was assessed for cell viability, 35S uptake, proteoglycan content and histologic parameters. The most noticeable histologic change was reduced Safranin-O near the cartilage surface with 14 days of cold preservation, but had recovered with 21 and 28 days. Cartilage thicknesses did not vary significantly. Cell viability was >95% at 14 days, 75-98% at 21 days and reduced to 65-90% at 28 days. Cell function measures showed that the level of 35SO4 incorporation was suppressed in samples stored at 4 degrees C. However, no significant differences were seen among groups at 14, 21 or 28 days of cold preservation. This data has implications for tissue banking protocols for osteochondral allograft material obtained for transplantation suggesting that cold preserved allograft material be implanted within 28 days.

Chondrocyte death associated with human femoral osteochondral harvest as performed for mosaicplasty

BACKGROUND

Autologous osteochondral transfer is an option for the treatment of articular defects. However, there are concerns about graft integration and the nature of the tissue forming the cartilage-cartilage bridge. Chondrocyte viability at graft and recipient edges is thought to be an important determinant of the quality of repair. The purpose of the present study was to evaluate early cell viability at the edges of osteochondral grafts from ex vivo human femoral condyles.

METHODS

Fresh human tissue was obtained from eleven knees at the time of total knee arthroplasty for the treatment of osteoarthritis. Osteochondral cylinders were harvested with use of a 4.5-mm-diameter mosaicplasty osteotome from regions of the anterolateral aspect of the femoral condyle that were macroscopically nondegenerate and histologically nonfibrillated. Plugs were assessed for marginal cell viability by means of confocal laser scanning microscopy.

RESULTS

The diameter of the cartilaginous portion of the osteochondral plugs was a mean (and standard error of the mean) of 4.84 +/- 0.12 mm (as determined on the basis of three plugs). This value was approximately 300 microm greater than the measured internal diameter of the osteotome. There was a substantial margin of superficial zone cell death (mean thickness, 382 +/- 68.2 microm), with >99% cell viability seen more centrally (as determined on the basis of five plugs). Demiplugs were created by splitting the mosaicplasty explants with a fresh number-11 scalpel blade. The margin of superficial zone cell death at the curved edge was significantly greater than that at the site of the scalpel cut (390.3 +/- 18.8 microm compared with 34.8 +/- 3.2 microm; p = 0.0286). Similar findings were observed when the cartilage alone was breached and the bone was left intact, with the margin of superficial zone cell death being significantly greater than that obtained in association with the straight scalpel incision (268 +/- 38.9 microm compared with 41.3 +/- 13.4 microm; p = 0.0286). The margin of superficial zone cell death showed no increase during the time-period between fifteen minutes and two hours after plug harvest. A mathematical approximation of the mosaicplasty region suggested that early cell death of this magnitude affects about one third of the superficial graft area.

CONCLUSIONS

The results of the present study suggest that mosaicplasty, while capable of transposing viable hyaline cartilage, is associated with an extensive margin of cell death that is likely to compromise lateral integration and articular reconstruction.

Ex vivo investigation of the use of hydrothermal energy to induce chondrocyte necrosis in articular cartilage of the metacarpophalangeal and metatarsophalangeal joints of horses

OBJECTIVE

To evaluate the use of hydrothermal ablation of articular cartilage for arthrodesis in horses through investigation of the effects of joint lavage with physiologic saline (0.9% NaCI) solution (80 degrees C) for various treatment times on chondrocyte viability in the articular cartilage of the metacarpophalangeal and metatarsophalangeal joints of cadaveric horse limbs. Sample Population-7 pairs of metacarpophalangeal and 8 pairs of metatarsophalangeal joints from 8 Thoroughbreds.

PROCEDURE

The horses were euthanatized for reasons unrelated to musculoskeletal disease. On a random basis, 1 joint of each pair underwent intra-articular lavage for 5, 10, or 15 minutes with heated saline solution (80 degrees C); the other joint underwent sham treatment of similar duration with saline solution at 22 degrees C (control). Cartilage samples from the distal articular surface of metacarpus III (or metatarsus III), the proximal surface of the proximal phalanx, and the lateral and medial proximal sesamoid bones were assessed for chondrocyte viability via confocal microscopy and viability staining following enzymatic digestion.

RESULTS

Compared with the control joints, findings of both viability assays indicated that the percentage of sites containing viable chondrocytes in heat-treated joints was decreased. Treatment hazard ratios of 0.048 (confocal microscopy) and 0.2 (digestion assay) were estimated. Histologically, periarticular soft tissues had minimal detrimental effects after heat treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Ex vivo intra-articular lavage with saline solution at 80 degrees C resulted in the death of almost all articular chondrocytes in the joint. This technique may be a satisfactory method for extensive cartilage ablation when performing arthrodesis by minimally invasive techniques.

Chondrocyte viability and metabolic activity after treatment of bovine articular cartilage with bipolar radiofrequency: an in vitro study

PURPOSE

Some controversy exists regarding the effects of radiofrequency (RF) probes on articular cartilage. To further elucidate these effects, we examined the chondrocyte viability and metabolic activity after treatment of fresh bovine articular cartilage with bipolar RF probes.

TYPE OF STUDY

In vitro assessment.

METHODS

Three fresh bovine knees served as a baseline control for chondrocyte viability, yielding 6 samples (1 from each medial femoral condyle and 1 from each lateral femoral condyle). After the baseline expected chondrocyte viability was determined, 3 additional bovine knees served as the experimental specimens for the study. Under sterile conditions, 2 different bipolar RF probes were used to treat the articular surface in a light contact mode, moving at a linear rate of 3 to 4 mm/s to provide tissue debridement. Full-thickness articular cartilage was then harvested from each of the treatment areas. Six samples per probe were then assessed for chondrocyte viability using fluorescent double-staining followed by confocal microscopy; 6 samples per probe were assessed for metabolic activity using an 35SO4 incorporation assay; and 12 additional untreated samples were obtained to serve as controls for viability (n = 6) and metabolic activity (n = 6).

RESULTS

The depth of chondrocyte death (mean +/- standard deviation) was 109.4 +/- 22.1 microm after treatment with the ACD-50 probe, and was 172.3 +/- 34.3 microm after treatment with the 2.5-mm/90 degrees probe. The 35SO4 uptake (mean +/- standard deviation) was 2584 +/- 1388 cpm/mg dry cartilage for the ACD-50 probe and 1995 +/- 852 cpm/mg of dry cartilage for the 2.5-mm/90 degrees probe. The 35SO4 uptake for the control was 2647 +/- 1380 cpm/mg dry cartilage.

CONCLUSIONS

The 2 probes tested created a well-controlled debridement with smooth edges and a defined margin of chondrocyte death that extended approximately 100 to 200 microm deep to the treatment area. There does not appear to be a significant effect on the metabolic activity of the chondrocytes adjacent to the treatment zone, but with the small sample size we lacked sufficient statistical power to definitively determine these effects.

CLINICAL RELEVANCE

The 2 bipolar radiofrequency probes tested created a well-controlled debridement in normal articular cartilage with smooth edges and a defined margin of chondrocyte death that extended approximately 100 to 200 microm into the treatment area.

Temperature requirements for altering the morphology of osteoarthritic and nonarthritic articular cartilage: in vitro thermal alteration of articular cartilage

BACKGROUND

Radiofrequency and laser thermal chondroplasty procedures are performed to debride and smooth fibrillated, articular cartilage.

HYPOTHESIS

Temperature requirements necessary to achieve morphological change will be lower in fibrillated arthritic cartilage as compared with nonarthritic articular cartilage.

STUDY DESIGN

Controlled laboratory study.

METHODS

A thermal cell-culture chamber was mounted on a stereoscopic microscope and coordinated with a custom temperature-control program. Nonarthritic and osteoarthritic articular cartilage specimens were sectioned into full-thickness slices. The articular sections were exposed to temperatures incrementally from 37 masculine C to 75 masculine C. Real-time, digital capture microscopy was used to visualize and analyze the morphological changes undergone by the articular cartilage specimens.

RESULTS

Arthritic articular cartilage displayed morphological change at 56.5 +/- 1.7 masculine C. Loss of fibrillation was the initial morphological change visualized. Continued thermal exposure caused a shrinkage effect of the entire tissue section that was similar to the change seen in nonarthritic sections. Nonarthritic cartilage displayed morphological change at 60.9 +/- 1.9 masculine C.

CONCLUSIONS

Consistent characteristic morphological changes were found at distinct temperatures in osteoarthritic and nonarthritic articular cartilage.

CLINICAL RELEVANCE

This information begins to establish the thermal parameters required for morphological change of osteoarthritic articular cartilage.

Hoechst 33342 is a useful cell tracer for a long-term investigation of articular cartilage repair

The repair process of a full-thickness osteochondral defect was observed in a rat model using Hoechst 33342 as a cell tracer. The osteochondral defect was created at the medial femoral condyle of the right knee joints of twelve 11 week old male rats. Three weeks after the surgery, Hoechst 33342 was injected into the same knee joints. Calcein, a marker of the mineralization front, was then injected subcutaneousely twice at seven days and one day before harvesting of the tissue. At six, ten, and fourteen weeks and one year after the surgery, femoral condyles were obtained from the operated knee joints, fixed by alcohol, and embedded in polymethylmethacrylate. The sections were examined by fluorescent and then light microscopy. In the lateral femoral condyle cartilage, Hoechst 33342 labeling of chondrocyte nuclei was observed in all layers of the intact cartilage, and the dye never infiltrated beneath the subchondral bone plate. At 6 weeks after the surgery, Hoechst 33342-positive cells were observed not only in the regenerated fibrous cartilage, but also in the newly formed mineralized tissue in the medial femoral condyle. Interestingly, Hoechst 33342 labeling remained undiminished even one year after the intra-articular injection. The findings of the present study suggest that intra-articular injection of Hoechst 33342 is a useful tracer for long-term investigations of chondrocyte differentiation in vivo.

Recovery of chondrocyte metabolic activity after thermal exposure

BACKGROUND

The relationship between temperature elevation and thermal exposure time during thermal chondroplasty has implications for cell viability and subsequent articular cartilage function.

PURPOSE

To characterize cartilage metabolic changes after exposure to thermal stress and to determine whether changes seen acutely are reversible.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human cartilage was exposed to a 45 degrees, 50 degrees, or 55 degrees C bath for up to 3 minutes. Untreated control specimens were analyzed with each group. Viability and metabolic capability of treated and untreated specimens were evaluated immediately or 1 week after thermal stress by using methylthiotetrazole conversion, (3)H-serine incorporation into protein, and (35)S-sulfate incorporation into newly synthesized proteoglycan.

RESULTS

Nonarthritic and arthritic articular cartilage metabolic activity declined with increasing thermal exposure. Articular cartilage displayed a recovery from thermal stress after exposure to the 50 degrees C but not the 55 degrees C bath. Arthritic cartilage displayed increased sensitivity with higher temperatures.

CONCLUSIONS

Understanding of the increased sensitivity to thermal stress of arthritic articular cartilage may be helpful in thermally based treatments.

CLINICAL RELEVANCE

Further correlation with the temperatures attained during thermal chondroplasty will be necessary to confirm the clinical relevance of these in vitro observations to the use of radiofrequency energy devices to treat partial-thickness chondral lesions.

The analysis of articular cartilage after thermal exposure: "Is red really dead?"

Partial-thickness articular cartilage (PARC) lesions have no propensity to heal. Surgical techniques have focused on halting their progression. Thermal chondroplasty procedures have become controversial with regard to the viability of the remaining cartilage. This controversy has expanded to the way that articular cartilage is evaluated after treatment. In this article, evaluation of articular cartilage viability is reviewed.

Laser-assisted chondroplasty

Laser-assisted chondroplasty is a controversial issue in arthroscopy. Some preliminary research has demonstrated that laser energy can stimulate DNA synthesis and matrix production in articular cartilage. Other studies cite the dangers of thermal energy with laser use on articular cartilage. Commonly used lasers and their current research are discussed in this chapter. It is unclear whether or not the laser will remain in the arthroscopists' arsenal for chondroplasty, and further research is warranted.

Complications of thermal energy in knee surgery--Part I

The use of thermal energy in knee surgery has many potentially exciting and useful applications. There is a growing body of literature that demonstrates the effects of these energy probes on different types of tissue. When contemplating the use of these surgical interventions in patients, it is important to recognize the potential limitations and complications that may arise.

The basic science of thermally assisted chondroplasty

Thermal chondroplasty provides a visually enticing effect on articular cartilage, but the long-term effects of thermal modification and injury to articular cartilage must be understood before the technology is applied to cartilage and chondrocytes in a clinical setting.

Complications of thermal energy in knee surgery--Part II

With the theoretical and reported complications of thermal energy use in the knee, an analysis of potential risks and benefits should be done on a case-by-case basis. Many of the basic science studies may not be directly applicable to clinical practice because they use normal (i.e., not diseased) tissues in animal models. Clinical studies are also dependent on surgical technique and equipment settings. With the benefits listed previously, however, it is likely that thermal energy will continue to play an important role in arthroscopic orthopedic surgery, and there are studies that strongly support its safety and efficacy. Janecki performed a retrospective review of 504 laser chondroplasties to determine safe parameters for Ho:YAG laser use in the knee [10]. In their series, they found an 88% patient satisfaction rate, no significant changes in the articular cartilage lesions in the failure group who underwent repeat arthroscopy, and no new cases of osteonecrosis. They concluded that the Ho:YAG laser was safe and recommended energy settings of less than or equal to 1 joule when performing chondroplasties, noncontact and tangential delivery of the laser beam, and maximizing laser spot size as methods for further decreasing complication rates. We agree with the above recommendations and with using the minimal power settings required to afford the desired surgical result. More studies are required to fully define the indications and consequences of thermal energy use in the knee.

In vitro model for the study of necrosis and apoptosis in native cartilage

Apoptosis plays a role in everything from early development to ageing and in a host of disease states. Studying this important process in the in vivo state is critical, to understand its varied role and to open further avenues of therapeutic intervention. The present paper presents an ex vivo bovine articular cartilage model to study apoptotic and necrotic processes following acute injury. Ex vivo bovine articular cartilage was assessed 1, 3 and 6 days following holmium : YAG laser treatment (780 mJ). Markers to visualize cell viability, caspase-3 activity, changes in mitochondrial membrane potential and the degree of DNA fragmentation (TUNEL assay) were used alone or in various combinations. Standard histology and transmission electron microscopy (TEM) were also performed for a more comprehensive assessment. A significant progression (p < 0.05) of ethidium/caspase-3-positive signal depth at day 3 preceded a significant increase (p < 0.05) in TUNEL signal depth by day 6. The mitochondrial matrix marker CMXRos was shown to provide an alternative to calcein-AM for assessing cell viability. The identification of chondrocyte apoptosis morphology by TEM was not conclusive. Nevertheless, TEM revealed that cells which were clearly necrotic also stained positively for TUNEL, thus indicating the risk of using TUNEL alone for the assessment of apoptosis. The model described here allows the rapid, spatial and temporal determination of cell viability and of apoptotic and necrotic processes in whole-tissue specimens after acute injury, and permits study of the balance between these events. The assessment of healthy and diseased cartilage and of the effects of surgical, pharmaceutical or in vitro intervention are immediate applications of these protocols. Moreover, this model may be useful for the study of key mechanisms involved in apoptosis or for the establishment of other markers of apoptosis.

Lavage solution temperature influences depth of chondrocyte death and surface contouring during thermal chondroplasty with temperature-controlled monopolar radiofrequency energy

BACKGROUND

Although radiofrequency energy can smooth and contour cartilage surface, it has deleterious effects on chondrocyte viability.

HYPOTHESIS

Monopolar thermal chondroplasty in a 37 degrees C lavage solution, as compared with a 22 degrees lavage solution, will reduce chondrocyte death and result in greater smoothing of the articular cartilage surface.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixteen chondromalacic samples from patients undergoing total knee arthroplasty were divided into two groups: 22 degrees C and 37 degrees C lavage solution. Each sample was divided into two equal parts and half of each group was treated for 10 seconds and the other half for 15 seconds.

RESULTS

Confocal laser microscopy demonstrated that the depth of chondrocyte death in the 37 degrees C lavage solution group was significantly less (range, 200 to 340 microm) than that in the 22 degrees C solution group for both 10- and 15-second treatment times. Scanning electron microscopy demonstrated that the cartilage surface in the 37 degrees C lavage solution group was smoother than that in the 22 degrees C solution group for the 10-second treatment time. Energy delivery power in the 37 degrees C lavage solution group was significantly lower than in the 22 degrees C solution group for both treatment times.

CONCLUSIONS

Thermal chondroplasty with 37 degrees C lavage solution resulted in less depth of chondrocyte death and produced smoother surfaces than with 22 degrees C solution for 10 seconds of treatment.

CLINICAL RELEVANCE

Less chondrocyte death would permit increased use of thermal chondroplasty.

Articular cartilage repair: basic science and clinical progress. A review of the current status and prospects

OBJECTIVE

To review the basic scientific status of repair in articular cartilage tissue and to assess the efficiency of current clinical therapies instigated for the treatment of structural lesions generated therein as a result of trauma or during the course of various diseases, notably osteoarthritis (OA). Current scientific trends and possible directions for the future will also be discussed.

DESIGN

A systematic and critical analysis is undertaken, beginning with a description of the spontaneous repair responses in different types of lesion. Surgical interventions aimed at inducing repair without the use of active biologics will then be considered, followed by those involving active biologics and those drawing on autogenic and allogeneic tissue transplantation principles. Cell transplantation approaches, in particular novel tissue engineering concepts, will be critically presented. These will include growth-factor-based biological treatments and gene transfection protocols. A number of technical problems associated with repair interventions, such as tissue integration, tissue retention and the role of mechanical factors, will also be analysed.

RESULTS

A critical analysis of the literature reveals the existence of many novel and very promising biologically-based approaches for the induction of articular cartilage repair, the vast majority of which are still at an experimental phase of development. But prospective, double-blinded clinical trials comparing currently practiced surgical treatments have, unfortunately, not been undertaken.

CONCLUSION

The existence of many new and encouraging biological approaches to cartilage repair justifies the future investment of time and money in this research area, particularly given the extremely high socio-economic importance of such therapeutic strategies in the prevention and treatment of these common joint diseases and traumas. Clinical epidemiological and prospective trials are, moreover, urgently needed for an objective, scientific appraisal of current therapies and future novel approaches.

Thermometric determination of cartilage matrix temperatures during thermal chondroplasty: comparison of bipolar and monopolar radiofrequency devices

PURPOSE

To compare cartilage matrix temperatures between monopolar radiofrequency energy (mRFE) and bipolar RFE (bRFE) at 3 depths under the articular surface during thermal chondroplasty. We hypothesized that cartilage temperatures would be higher at all cartilage depths for the bRFE device than for the mRFE device.

TYPE OF STUDY

Randomized trial using bovine cartilage.

METHODS

Sixty osteochondral sections from the femoropatellar joint of 15 adult cattle were used for this study. Using a custom jig, fluoroptic thermometry probes were placed at one of the following depths under the articular surface: 200 microm, 500 microm, or 2,000 microm. RF treatment was performed either with fluid flow (F) (120 mL/min) or without fluid flow (NF) (n = 5/depth/RFE device/flow; total specimens, 60). Irrigation fluid temperature was room temperature (22 degrees C). Thermometry data were acquired at 4 Hz for 5 seconds with the RF probe off, for 20 seconds with the RF probe on, and then for 15 seconds with the RF probe off. During RF treatment, a 0.79-cm2 area (1.0-cm diameter) of the articular surface centered over the thermometry probe was treated in a paintbrush manner in noncontact (bRFE) or light contact (mRFE).

RESULTS

Thermal chondroplasty with bRFE resulted in higher cartilage matrix temperatures compared with mRFE for all depths and regardless of fluid flow. Bipolar RFE resulted in temperatures of 95 degrees C to 100 degrees C at 200 microm and 500 microm under the surface, with temperatures of 75 degrees C to 78 degrees C at 2,000 microm. Fluid flow during bRFE application had no effect at 200 microm. Monopolar RFE resulted in temperatures of 61 degrees C to 68 degrees C at 200 microm, 54 degrees C to 70 degrees C at 500 microm under the surface, and 28 degrees C to 30 degrees C at 2,000 microm below the surface. A significant effect of fluid flow during mRFE application occurred at 200 microm (NF, 61 degrees C; F, 63 degrees C) and 500 microm (NF, 53 degrees C; F, 68 degrees C).

CONCLUSIONS

In this study, we found significant differences between bRFE and a temperature-controlled mRFE device with regard to depth of thermal heating of cartilage in vitro. Bipolar RFE resulted in matrix temperatures high enough (>70 degrees C) to kill cells as deep as 2,000 microm under the articular surface. Fluid flow during thermal chondroplasty had the effect of significantly increasing cartilage matrix temperatures at 200 and 500 microm with the mRFE device. During thermal chondroplasty, bRFE creates greater matrix temperature elevations at equivalent depths and treatment duration than does mRFE. Excessive temperatures generated deep within the cartilage matrix could cause full-thickness chondrocyte death, in vivo.

Laser solder welding of articular cartilage: tensile strength and chondrocyte viability

BACKGROUND AND OBJECTIVE

The surgical treatment of full-thickness cartilage defects in the knee joint remains a therapeutic challenge. Recently, new techniques for articular cartilage transplantation, such as mosaicplasty, have become available for cartilage repair. The long-term success of these techniques, however, depends not only on the chondrocyte viability but also on a lateral integration of the implant. The goal of this study was to evaluate the feasibility of cartilage welding by using albumin solder that was dye-enhanced to allow coagulation with 808-nm laser diode irradiation.

STUDY DESIGN/MATERIALS AND METHODS

Conventional histology of light microscopy was compared with a viability staining to precisely determine the extent of thermal damage after laser welding. Indocyanine green (ICG) enhanced albumin solder (25% albumin, 0.5% HA, 0.1% ICG) was used for articular cartilage welding. For coagulation, the solder was irradiated through the cartilage implant by 808-nm laser light and the tensile strength of the weld was measured.

RESULTS

Viability staining revealed a thermal damage of typically 500 m in depth at an irradiance of approximately 10 W/cm(2) for 8 seconds, whereas conventional histologies showed only half of the extent found by the viability test. Heat-bath investigations revealed a threshold temperature of minimum 54 degrees C for thermal damage of chondrocytes. Efficient cartilage bonding was obtained by using bovine albumin solder as adhesive. Maximum tensile strength of more than 10 N/cm(2) was achieved.

CONCLUSIONS

Viability tests revealed that the thermal damage is much greater (up to twice) than expected after light microscopic characterization. This study shows the feasibility to strongly laser weld cartilage on cartilage by use of a dye-enhanced albumin solder. Possibilities to reduce the range of damage are suggested.