Collagen shortening. An experimental approach with heat

Monopolar radiofrequency energy for arthroscopic treatment of shoulder instability in the athlete

Monopolar radiofrequency energy is increasingly being used in the treatment of shoulder instability. Basic science studies and early clinical results have shown that application of thermal energy can result in successful shrinkage of the shoulder capsule. This procedure is useful in treating certain traumatic and recurrent instability conditions of the shoulder especially in the athlete where range of motion is preserved, recovery is faster than with open procedures, and there, is little disruption or alteration of inherent anatomy. The procedure is technically easy to perform, and the complication rate is low. Success, however, depends on proper patient selection, attention to the rehabilitation program, and patient compliance. Long-term follow-up will be necessary to determine if results for this procedure will deteriorate over time, especially in patients with multidirectional instability.

The healing effects on the biomechanical properties of joint capsular tissue treated with Ho:YAG laser: An in vivo rabbit study

PURPOSE

The objective of this study was to evaluate the healing response, after thermal treatment with a Ho:YAG laser, on the biomechanical properties of capsular soft tissue.

TYPE OF STUDY

Before and after trial.

METHODS

Forty-five New Zealand white rabbits were used in this study. A medial peripatellar retinacular thermal capsuloplasty using a Ho:YAG laser and a lateral peripatellar retinacular release was performed on 1 knee of each rabbit. The contralateral knee served as a control and had a lateral release of the retinaculum only. The temperature of the medial retinaculum was maintained at 55 degrees C +/- 5 degrees C during treatment. The medial peripatellar retinaculum was evaluated at 0, 6, and 12 weeks postoperatively. Tensile testing of the medial retinaculum and a biomechanical assessment evaluating the structural and material properties were performed.

RESULTS

The ultimate load (force) of the medial retinaculum was 70%, 56%, and 84% of control at 0, 6, and 12 weeks, respectively, after the procedure. The stiffness (force/deformation) of the medial retinaculum was 83% of control at 0 weeks, 54% at 6 weeks, and 85% at 12 weeks. The ultimate stress (force/area) of the medial retinaculum also showed a significant reduction at 0 and 6 weeks postoperatively, 63% and 62% of control, respectively. By 12 weeks, the ultimate stress was 83% of control.

CONCLUSIONS

Thermal treatment of the medial retinaculum with a Ho:YAG laser results in soft tissue with significantly diminished biomechanical properties after treatment. The results of this study suggest that a 12-week period of minimal stress on the capsular tissues should follow a thermal capsuloplasty procedure.

Histologic signatures of thermal injury: applications in transmyocardial laser revascularization and radiofrequency ablation

BACKGROUND AND OBJECTIVE

Cardiac treatments such as transmyocardial laser revascularization and radiofrequency ablation cause thermal injury. We sought to provide quantitative histologic methods of assessing such injury by using the inherent birefringence of cardiac muscle and collagen; specifically, to exploit the connection between thermal injury and the loss of birefringence.

STUDY DESIGN/MATERIALS AND METHODS

We quantified tissue birefringence changes in vitro for temperatures up to 130 degrees C. This information was used to assess thermal injury associated with myocardial channels made in vitro. We then measured in vivo cardiac injury 30 minutes and 3 days after radiofrequency exposure.

RESULTS

Birefringence decreased above 60 degrees C for muscle and above 70 degrees C for collagen. Temperatures above 80 degrees C were associated with collagen fiber straightening and above 95 degrees C with little muscle birefringence. Injury adjacent to laser channels was greatest parallel to cell orientation. In vivo, muscle with reduced birefringence was surrounded by cells exhibiting focal birefringence increases (contraction bands). Early injury assessment marked by birefringence changes corresponded to lesion size at 3 days.

CONCLUSION

Polarized light revealed histologic temperature signatures corresponding to irreversible muscle injury and collagen denaturation.

Temperature dependence of thermal damage to the sclera: exploring the heat tolerance of the sclera for transscleral thermotherapy

Thermal damage to the human sclera in relation to temperature and duration of exposure was studied in order to determine the heat tolerance of the sclera with respect to transscleral thermotherapy of choroidal melanoma. Samples of human sclera were submerged in saline for 10 sec to 10 min at temperatures of 37-100 degrees C. The effects of heat on the shape, weight and size of the samples were studied. Thermal damage of scleral collagen was examined by polarized light microscopy (LM) and electron microscopy (EM). The sclera was embedded in epoxy resin and stained with toluidine blue for LM and with uranyl acetate and lead citrate for EM. Thermal damage of scleral collagen on polarized LM was graded on a five point scale. Scleral damage was visible on macroscopic examination and on LM and EM in sclera heated at 65 degrees C for 20 sec or longer, at 70 degrees C for 10 sec or longer, and at higher temperatures. A sigmoidal function was used to define the relation between temperature and changes in diameter, thickness, and weight of scleral samples. Using fitted functions, the threshold temperature for thermal damage was estimated to be 59-61 degrees C when samples were heated for 10 min, 62-63 degrees C when heated for 1 min, and 66-67 degrees C when heated for 10 sec; the threshold exposure time at 60 degrees C was estimated to be 7-12 min. These results indicate a temperature of 60 degrees C for 1 min is well tolerated by human donor sclera; information of in vivo studies is required to validate whether this setting can be used in transscleral thermotherapy (TSTT) for choroidal melanoma.

Radiofrequency energy-induced heating of bovine capsular tissue: Temperature changes produced by bipolar versus monopolar electrodes

PURPOSE

To determine temperature changes associated with radiofrequency (RF) energy-induced heating of bovine capsular tissue using a bipolar RF electrode versus a temperature-controlled, monopolar RF electrode.

TYPE OF STUDY

In vitro laboratory investigation using bovine capsular tissue.

METHODS

Samples of bovine tissue were placed in a saline bath (37 degrees C) and RF energy was applied using bipolar and monopolar RF electrodes at manufacturer-recommended settings for tissue shrinkage. Fluoroptic thermometry was used to record temperatures on the tissue surface and at depths of 1 mm and 2 mm during continuous delivery of RF energy at 1, 2, 3, 4, 5, and 10 second time increments.

RESULTS

The highest mean temperatures were recorded on the tissue surface, as follows (mean +/- SD; *P <.05, value compared with baseline): 1 sec 2 sec 3 sec 4 sec 5 sec 10 sec Bipolar 40.1 +/- 1.0* 48.2 +/- 4.7* 62.8 +/- 6.9* 76.0 +/- 7.6* 84.7 +/- 5.7* 94.7 +/- 1.9* Monopolar 39.0 +/- 0.7* 48.2 +/- 4.3* 67.7 +/- 7.0* 86.6 +/- 6.1* 93.8 +/- 2.7* 59.5 +/- 2.6* For the bipolar RF electrode, there was a strong linear relationship (R =.926) between mean surface temperatures versus time. The temperature-controlled, monopolar RF electrode did not appear to properly regulate the delivery of RF energy to maintain tissue temperatures at the selected level (i.e., 65 degrees C). The bipolar RF electrode produced a smaller temperature gradient (average difference, 9.2 degrees C) at the 1-mm tissue depth compared with the monopolar RF electrode (average difference, 14.6 degrees C). Temperature profiles at the 2-mm tissue depth were comparable for both types of RF electrodes.

CONCLUSIONS

These data provide basic information pertaining to the temperature profiles produced by bipolar and monopolar RF electrodes applied to collagen-based tissue.

Electrothermal shrinkage reduces laxity but alters creep behavior in a lapine ligament model

Thermal denaturation of collagen in ligament tissue has the potential to enhance arthroscopic shoulder stabilization. Previous studies have shown that laser energy produces significant capsular shortening without alteration of viscoelastic properties, but little information is available on the effects of radio frequency electrothermal energy. We assessed the acute effects of radio frequency shrinkage with use of the lapine medial collateral ligament model, in which the tibial insertion was shifted proximally to produce abnormal laxity. Thermal treatment resulted in restoration of laxity from 3.33 +/- 0.25 mm to 0.66 +/- 0.31 mm, which was not significantly different from medial collateral ligaments replaced anatomically (0.50 +/- 0.34 mm). When tested at 4.1 megapascals, cyclic and static creep strains were increased twofold to threefold in thermally-treated ligaments (P <.01), and partial failure occurred in 2 of 8 cases. We conclude that radio frequency electrothermal shrinkage is effective at reducing laxity but significantly alters viscoelastic properties, posing a risk of recurrent stretching-out at "physiological" loads.

Thermally induced shrinkage of joint capsule

Thermal shrinkage of collagen currently is being used in orthopaedic surgery to treat ligamentous laxity. Understanding the kinetics of collagen shrinkage is key to revealing the events that take place during application of thermal energy. To elucidate the thermokinetic properties of collagen, punch biopsies of bovine joint capsule were immersed in a heated saline bath at temperatures between 20 degrees and 90 degrees C for periods up to 60 minutes. The resulting tissue thermal shrinkage was measured by the change in the cross-sectional area of the specimens. Only a small amount of shrinkage occurred at temperatures below 63 degrees C, and increasing amounts and rates of shrinkage were seen at temperatures between 63 degrees and 72 degrees C. The denaturation kinetics of bovine knee collagen, which could be described by a first order reaction rate, had an activation energy of 2.3 x 10(5) kJ/mol.

The effect of monopolar radiofrequency treatment pattern on joint capsular healing. In vitro and in vivo studies using an ovine model

The purpose of this study was to compare joint capsular healing after two delivery patterns of monopolar radiofrequency energy: 1) uniform treatment of the joint capsule (paintbrush pattern) and 2) multiple single linear passes (grid pattern). First, an in vitro study was performed to compare the percent shrinkage of these two treatment patterns using the femoropatellar joints (stifles) of six sheep. Monopolar radiofrequency energy (settings, 70 degrees C/15W) was applied to the lateral joint capsule; the treated area was approximately 10 x 10 mm. There was no significant difference in shrinkage between the grid (27% +/- 8.7%) and paintbrush (29% +/- 7.9%) patterns. In the in vivo study, stifles of 24 sheep were randomly assigned to the paintbrush or the grid pattern groups and treatment was performed arthroscopically. Sheep were sacrificed immediately after surgery, or at 2, 6, or 12 weeks after surgery. At 6 weeks after surgery, confocal microscopy demonstrated that treated areas had almost completely repaired in the grid group; some nonviable areas were still present in the paintbrush group. Mechanical testing at 6 weeks indicated that joint capsule in the grid group had better mechanical properties than capsule in the paintbrush group. This study revealed that radiofrequency treatment of joint capsule in a grid pattern allowed faster healing than tissue treated in a paintbrush pattern.

Thermal modification of connective tissues: basic science considerations and clinical implications

Thermal modification (shrinkage) of capsular connective tissue has gained increasing popularity as an adjunctive or even a primary procedure in the arthroscopic treatment of shoulder instability. Although the physical effects of heat on collagenous tissues are well known, the long-term biologic fate of these shrunken tissues is still a matter of debate. The temperatures required to alter the molecular bonding of collagen and thus cause tissue shrinkage (65 degrees C to 70 degrees C) are also known to destroy cellular viability. Therefore, thermally modified tissues are devitalized and must undergo a biologic remodeling process. During this remodeling, the mechanical properties of the treated tissues are altered (decreased stiffness) and can be at risk for elongation if the postoperative rehabilitation regimen is too aggressive. Although anecdotal reports suggest that thermal capsular shrinkage does have a beneficial effect, the exact mechanism responsible for this clinical improvement has yet to be fully defined. The reported improvement could be due to the maintenance of initial capsular shrinkage, secondary fibroplasia and resultant thickening of the joint capsule, a loss of afferent sensory stimulation due to the destruction of sensory receptors, or a combination of all three. The clinical role for thermal modification of connective tissues has not yet been defined, but it appears that it may prove most useful as a stimulant for inducing a biologic repair response.

Endovenous management of saphenous vein reflux. Endovenous Reflux Management Study Group

PURPOSE

This study assessed clinical outcomes of two catheter-based endovenous procedures to eliminate or greatly mitigate saphenous vein reflux.

MATERIALS AND METHODS

A computer-controlled, dedicated generator and two catheter designs were used to treat 210 patients at 16 private clinic and university centers in Europe. The Closure catheter applied resistive heating over long vein lengths to cause maximum wall contraction for permanent obliteration; the Restore catheter induced a short subvalvular constriction to improve the competence of mobile but nonmeeting leaflets.

RESULTS

Closure treatment caused acute obliteration in 141 (93%) of 151 limbs; Restore treatment, shrinking one or more valves, acutely reduced reflux to less than 1 second in 41 (60%) of 68 limbs. Closure treatments were associated with early recanalization (6%), paresthesias (thigh, 9%; leg, 51%; P <.001), 3 skin burns, and 3 deep-vein thrombus extensions, with 1 embolism. Restore treatments were thrombogenic (16%) despite prophylactic anticoagulation, and treated valves enlarged over 6 weeks, becoming less competent. Clinical Efficacy Assessment Project clinical class was significantly improved after both treatments, up to 1 year. At 6 months, 87% of 53 Closure patients were class 0 or 1, 75% were symptom-free, and 96% of 55 treated limbs were completely free of reflux. Fourteen of 31 Restore patients (45%) had no symptoms, but 55% were class 2 or lower and only 19% had less than 1-second reflux.

CONCLUSION

Closure treatment is clinically effective, albeit with offsetting complications and early failures; these are being addressed through four procedural modifications. Restore valve shrinking, although conceptually attractive, is too problematic to be competitive with Closure treatment or saphenectomy.

Multiquadrant digital analysis of shoulder capsular thickness

PURPOSE

Nonablative thermal capsular shrinkage has been developed in an attempt to address the plastic capsule deformation thought to cause increased rates of recurrent instability following arthroscopic stabilization procedures. Although the temperature required to optimize collagen shrinkage is known, a safe depth of thermal penetration, in various locations about the shoulder capsule, has not been defined. The purpose of this study was to measure shoulder capsule thickness by quadrant and circumferentially from the glenoid to the humerus so that thermal energy in shoulder procedures can be more precisely applied to limit possible injury to pericapsular structures.

TYPE OF STUDY

This is an anatomic study using a cadaveric shoulder specimens.

MATERIALS AND METHODS

Soft tissue was dissected from 8 fresh cadaveric shoulders to isolate intact glenohumeral joint capsules. The humeral insertion was released and the capsule was cut into 6 longitudinal quadrants around the glenoid. The capsule specimens were then flash frozen and stored at -80 degrees C. Quadrant tissue was cut into longitudinal sections 14 to 16 microm wide and stained with hematoxylin and eosin. The specimens were then digitized under a dissecting microscope and measured using computer imaging software at approximately 4-mm intervals. Two-way analysis of variance (ANOVA) was performed on the measurements of the intact capsule specimens 2.5 cm off the glenoid. Humeral insertion data were recorded separately.

RESULTS

A total of 248 separate measurements were made throughout the capsule in 8 specimens. Capsular thickness increased from an average of 2.42 mm anteriorly to 2.80 mm in the inferior capsular pouch and again thinned to 2.22 mm posteriorly. Global shoulder capsule thickness ranged from 1.32 to 4.47 mm. When analyzed by position, from glenoid to humerus, a general thinning was noted with a mean thickness of 3. 03 mm at the glenoid to 2.17 mm at the humeral insertion. Two-way ANOVA showed a significant thickness variation along the specimen (P <.05), a nearly significant thickness variation with regard to quadrant (P <.03), and no significant interaction (P >.07) when applied to specimen measurements approximately 2.5 cm off the glenoid.

CONCLUSIONS

The thickness of the shoulder capsule ranges from 1.32 to 4.47 mm, with a significant thinning laterally from the glenoid to the humerus. Further, capsule thickness ranges from 2.76 to 3.18 mm in the regions in closest proximity to the axillary nerve. These data may help determine the proper amount of thermal penetration necessary when performing shrinkage procedures and provide safety guidelines to limit the depth of thermal penetration to avoid possible injury to pericapsular structures.

Electrothermally-assisted capsulorrhaphy (ETAC): a new surgical method for glenohumeral instability and its rehabilitation considerations

Knowledge of current surgical procedures and the effect they have on healing tissue is important when developing rehabilitation guidelines. Recently, clinicians have been asked to treat patients who have undergone Electrothermally-Assisted Capsulorrhaphy (ETAC) for shoulder instability. The ultimate tensile strength of the tightened capsule is unknown during various timeframes following surgery. The use of thermal energy to shrink the shoulder joint capsule initially causes weakness of the collagen ultrastructure. Rehabilitation following ETAC includes a period of relative immobilization, followed by controlled range of motion exercises. Exercises to strengthen shoulder muscles must be done in a manner that minimizes stress on the surgically treated capsule. This article provides a brief review of capsuloligamentous repair; describes the surgical procedure, its indications, contraindications, and the effect ETAC has on the healing tissue; and provides guidelines for rehabilitation following ETAC based on the evidence available and the authors clinical experience.

Arthroscopic management of glenohumeral instability

There has been substantial development of techniques for performing arthroscopic surgery of the shoulder over the past 20 years. A multitude of arthroscopic techniques have been developed in an attempt to manage the unstable glenohumeral joint while decreasing surgical morbidity. The results obtained with arthroscopic stabilization have been widely variable. This review will examine the current status of arthroscopic management of glenohumeral instability. The techniques and results of arthroscopic stabilization for primary anterior glenohumeral instability, recurrent anterior instability, and multidirectional instability will be discussed. A brief discussion on thermal capsulorrhaphy is included.

Comparative effects of laser and radiofrequency energy on joint capsule

The study compared the effects of laser and monopolar radiofrequency energy on thermal and architectural properties of joint capsular tissue in an in vitro ovine model. Sheep glenohumeral joint capsular specimens were treated with laser (5, 10, 15 W) or radiofrequency energy (55 degrees, 65 degrees, 75 degrees C) (n = six per group). Energy application caused significant tissue shrinkage and decreased surface area in all laser and radiofrequency treatment groups. Tissue thickness significantly increased in all treatment groups except for radiofrequency 55 degrees C. Tissue shrinkage, surface area, and thickness each correlated significantly with the delivered laser energy per tissue area or mean radiofrequency probe temperature. There were no significant differences among laser 10 W, laser 15 W, and radiofrequency 75 degrees C treatment groups for these three architectural parameters. Tissue temperature was elevated significantly in the laser 10 W, laser 15 W, radiofrequency 65 degrees C, and radiofrequency 75 degrees C groups when compared with the control. Tissue temperature changes between the laser 10 W and radiofrequency 75 degrees C groups were similar; however, laser treatment produced a steeper temperature increase accompanying its peak temperature. Despite different mechanisms, laser and radiofrequency energy can achieve similar and predictable tissue modification, which is temperature dependent. Additional in vivo studies must be performed to evaluate the applicability of these techniques to clinical use.

Radio frequency heating of chronic ovine infarct leads to sustained infarct area and ventricular volume reduction

OBJECTIVE

Myocardial infarct expansion and subsequent left ventricular remodeling are associated with increased incidence of congestive failure and mortality. Collagen is known to denature and contract when heated above 65 degrees C. We therefore tested the hypothesis that radio frequency heating of myocardial infarct tissue with application of a restraining patch causes a sustained reduction in myocardial infarct area and left ventricular volume.

METHODS

Thirteen male Dorset sheep underwent surgical coronary artery ligation. At least 14 weeks later, animals were randomized to either radio frequency infarct heating (95 degrees C) with application of a restraining patch or a sham operation. Before treatment, after treatment, and 10 weeks later, left ventricular volume was measured with transdiaphragmatic echocardiography and myocardial infarct area was measured with an array of sonomicrometry crystals.

RESULTS

Radio frequency infarct heating causes an acute decrease of 34% (-215 +/- 82 mm(2); P =.0002) in infarct area at end-diastole that is maintained at 10 weeks (-144 +/- 79 mm(2); P =.0002). Radio frequency infarct heating causes a downward trend in end-diastolic left ventricular volume measured by echocardiography of 20% (-15.7 +/- 6.3 mL; P = no significant difference) and end-systolic left ventricular volume of 32% (-17.1 +/- 9.8 mL; P =.09), which are significantly decreased at 10 weeks (-13.6 +/- 22.3 mL; P =.007 and -15.3 +/- 21.9 mL; P =.008, respectively). Radio frequency infarct heating causes an acute improvement in systolic function (P <.001), a sustained increase in left ventricular ejection fraction (+0.11%; P =.06), and preserved stroke volume.

CONCLUSION

Radio frequency heating of chronic left ventricular myocardial infarct causes a sustained reduction in infarct area and left ventricular volume. This technique may beneficially reverse infarct expansion and left ventricular remodeling after myocardial infarction.

Arthroscopic monopolar radiofrequency thermal stabilization for chronic lateral ankle instability: a preliminary report on 10 cases

This study represents a preliminary review of 10 patients having undergone arthroscopic monopolar thermal stabilization for ankle instability from October 1996 to June 1998. All patients in this study expressed mild to moderate chronic ankle instability complaints and were dissatisfied with their attempts at conservative care. Subjective clinical results were evaluated in all patients having undergone this procedure utilizing a modified version of the American Orthopedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Scale. In addition, eight of these patients underwent pre- and postoperative stress radiographs. The average age of the patient population in this study was 34.5 +/- 9.26 years. The preoperative AOFAS scores averaged 58.3 +/- 8.96 and the postoperative were 88.1 +/- 11.09 points. Patients returned to full activities on the average of 3 months. Postoperative ankle varus stress test reduced on the average of 2.8 degrees +/- 2.77 degrees, while the anterior drawer measurements reduced 4.8 +/- 1.83 mm. The reduction in anterior drawer test amounted to an approximate 60% decrease in talar excursion postoperatively. All patients who underwent this procedure achieved ankle stability and commented that they would undergo the procedure again.

Temperature changes associated with radiofrequency energy-induced heating of bovine capsular tissue: evaluation of bipolar RF electrodes

SUMMARY

This in vitro study determined the temperature changes associated with radiofrequency (RF) energy-induced heating of bovine capsular tissue using bipolar RF electrodes. Tissue samples were placed in a saline bath (37 degrees C) and RF energy was applied using 2 different types of bipolar electrodes (VAPR T End Effect and Vapor T Side Effect; Mitek, Westwood, MA). Each electrode was activated for 3 seconds at 10 W, 16 W, and 20 W, for 6 separate data acquisitions. Fluoroptic thermometry designed to be unperturbed by RF fields was used to record temperatures on the tissue surface and at depths of 2 mm, 4 mm, and 5 mm, at 1-second intervals before (5 seconds), during (3 seconds), and after (7 seconds) the application of RF energy. The highest mean temperatures were recorded at the tissue surfaces for the different power settings for each RF electrode type, as follows: End Effect: 48.9 degrees C (10 W), 57.0 degrees C (16 W), and 67.3 degrees C (20 W). Side Effect: 51.5 degrees C (10 W), 62.1 degrees C (16 W), and 71.2 degrees C (20 W). All recorded surface temperatures were within the range known to be acceptable for tissue shrinkage. Gradient effects (i.e., higher-to-lower) were observed for the tissue temperatures measured at the different depth positions. None of the temperatures recorded at the different depths were excessive, suggesting that sensitive anatomic structures should not be damaged by RF energy-induced heating under the conditions described above.

Multidirectional instability of the shoulder in the female athlete

Multidirectional instability (MDI) of the shoulder is a complex entity, characterized by symptomatic global laxity of the glenohumeral joint. Because symptoms vary widely, making the diagnosis of MDI is not always straightforward. In addition, relatively few series of patients with this disorder have been reported. Thus, precise definition, causes, and treatment remain elusive. This article reviews the current literature regarding anatomy, biomechanics, clinical diagnosis, and treatment of MDI that are relevant to care of the female athlete.

The mechanism of joint capsule thermal modification in an in-vitro sheep model

The purpose of this study was to understand the mechanism responsible for joint capsule shrinkage after nonablative laser application in an in-vitro sheep model. Femoropatellar joint capsular tissue specimens harvested from 20 adult sheep were treated with one of three power settings of a holmium:yttrium-aluminum-garnet laser or served as a control. Laser treatment significantly shortened the tissue and decreased tissue stiffness in all three laser groups, whereas failure strength was not altered significantly by laser treatment. Transmission electron microscopic examination showed swollen collagen fibrils and loss of membrane integrity of fibroblasts. A thermometric study revealed nonablative laser energy caused tissue temperature to rise in the range of 64 degrees C to 100 degrees C. Electrophoresis after trypsin digestion of the tissue revealed significant loss of distinct alpha bands of Type I collagen in laser treated samples, whereas alpha bands were present in laser treated tissue without trypsin digestion. The results of this study support the concept that the primary mechanism responsible for the effect of nonablative laser energy is thermal denaturation of collagen in joint capsular tissue associated with unwinding of the triple helical structure of the collagen molecule.

Monopolar radiofrequency energy effects on joint capsular tissue: potential treatment for joint instability. An in vivo mechanical, morphological, and biochemical study using an ovine model

The purpose of this study was to evaluate the thermal effect of monopolar radiofrequency energy, a potential treatment means for joint instability, on the mechanical, morphologic, and biochemical properties of joint capsular tissue in an in vivo ovine model. The energy was applied arthroscopically to the synovial surface of the femoropatellar joint capsule of 24 sheep. The sheep were sacrificed at 0, 2, 6, and 12 weeks after surgery (6 per group). Monopolar radiofrequency energy initially caused a significant decrease in tissue stiffness and an increase in tissue relaxation properties, followed by gradual improvement in the tissue's mechanical properties by 6 weeks after surgery. Microscopic examination illustrated that radiofrequency energy initially caused collagen hyalinization and cell necrosis, followed by active tissue repair. Biochemical analysis revealed that treated collagen was significantly more trypsin-susceptibile than untreated collagen at 0 and 2 weeks after surgery, indicating early collagen denaturation. This study demonstrated that this treatment initially caused a significantly deleterious effect on the mechanical properties of the joint capsule, which was associated with partial denaturation of joint capsular tissue. This was followed by gradual improvement of the mechanical, morphologic, and biochemical properties of the tissue over time.

Laser-mediated reversal of cardiac expansion after myocardial infarction

BACKGROUND AND OBJECTIVES

A complication of transmural myocardial infarction is infarct expansion, which can lead to the development of heart failure. However, the necrotic muscle is replaced by collagen, a material known to shrink when heated. Thus, the hypothesis was that thermally-induced scar shrinkage could reverse infarct expansion.

STUDY DESIGN/MATERIALS AND METHODS

Four weeks after transmural infarcts were produced by coronary occlusion, rats were randomized to control or treatment with a neodymium:yttrium-aluminum-garnet laser. The epicardial scar surface was irradiated until shrinkage was observed. Thirty minutes later, hearts were excised and fixed at a distending pressure of 15 mm Hg, left ventricular cavity volume was measured, and histologic analysis was performed.

RESULTS

Cavity volume was reduced by laser treatment (0.72 +/- 0.07 ml vs. 0.54 +/- 0.05 ml; P= 0.044). In addition, treatment resulted in thicker scars, a leftward shift of the heart's electrical axis, and straightening of collagen fibers.

CONCLUSION

Laser treatment resulted in thermally-mediated scar shrinkage, which reversed infarct expansion and reduced cavity volume.

The effects of laser-induced collagen shortening on the biomechanical properties of the inferior glenohumeral ligament complex

The purpose of this study was to determine the effects of laser-induced collagen shortening on the biomechanical properties of the inferior glenohumeral ligament complex. Fifty-seven bone-ligament-bone specimens underwent uniaxial tensioning to 10% strain. Approximately half of the specimens then underwent 10% shortening by lasing using a holmium:yttrium-aluminum-garnet laser. Both groups were again tensioned to 10% strain, and then loaded to failure. Ultimate strain and yield strain were significantly higher in the lased specimens than in the nonlased specimens. No significant difference was found for ultimate stress, yield stress, or elastic modulus between the two groups. Failure of the ligament did not appear to occur in the lased areas. The load-to-failure results suggested that the strength of the ligament complex was not significantly compromised by this lasing protocol.