1.1.1.

Joint instability and treatment

The glenohumeral (shoulder) joint has the greatest range of motion of any joint in the human body. Functional shoulder stability is controlled by joint geometry, intraarticular pressure, ligamentous constraints, and muscle forces.^27-29 Shoulder instability, which is defined as excessive glenohumeral translation that produces symptoms of instability or pain, is an important clinical problem in medicine.³⁰ The maintenance of glenohumeral stability is dependent upon an intact capsulo-ligamentous complex and labrum (static stabilizer) as well as a neuromuscularly intact rotator cuff (dynamic stabilizer). Multidirectional and unidirectional glenohumeral instability (GHI) secondary to ligamentous laxity, capsular redundancy, and excessive joint volume are common occurences.^6-11 The three typical situations where capsular redundancy can develop are atraumatic instability with minimal or no trauma, repetitive microtrauma as might occur in athletes who perform activities with the arm overhead, and acute trauma resulting in severe disruption of capsular tissues, possibly resulting in dislocation.³¹ The development of GHI is multifactorial and due to intrinsic and extrinsic factors. The pathologic feature common to all forms of GHI is interstitial damage, plastic deformation, and redundancy of the shoulder ligaments and capsule.

Successful treatment of GHI relies upon the identification of the direction of the instability pattern and the pathologic features which contribute to the development of a given instability pattern. The treatment of instability includes both nonoperative and operative means. Exercise programs that aim to strengthen the rotator cuff and scapular muscles are often the primary treatment for instability. The nonoperative management of instability relies upon an intensive exercise program which strengthens the dynamic muscular glenohumeral and scapulothoracic stabilizers. It would appear that rehabilitation of shoulder instability has a limited capacity to accommodate capsular redundancy or ligamentous laxity which results in excessive joint volume and multidirectional instability. Operative repairs are presently performed using both open techniques and arthroscopy. The open operative treatment of GHI involves procedures that historically fall into 1 of 4 groups: capsulorrhaphy,^32,33 bone block procedures,^34,35 subscapular muscle advancement,^36,37 and osteotomies of the glenoid and humerus.^38,39 The magnitude of these surgical procedures which significantly derange the local glenohumeral anatomy leads to significant morbidity. Pain, loss of motion, nerve injury, and osteoarthritis have been reported as common complications associated with these procedures.¹⁰ Recent open surgical treatments for glenohumeral instability have focused upon a more anatomic repair of the unstable shoulder, however, these procedures remain technically demanding and morbid.^6,8,33,40-43 Following these open procedures, the joint regains stability, however, shoulder stiffness continues to be a problem and less than 5% of athletes who perform activities with the arm overhead appear to be able to achieve their previous level of pre-injury function.^6,8,33,40 In addition, the postoperative rehabilitation is lengthy and expensive in these patients.

Citing the obvious morbidity and complications associated with open shoulder repairs and reconstructions for GHI, numerous arthroscopic techniques have been developed as an alternative treatment. Current arthroscopic techniques include: metal staples,^44,45 bio-absorbable tacks,⁴⁶ suture techniques,^47,48 and suture anchor techniques.⁴⁹ The reported benefits of arthroscopic shoulder treatments include better postoperative range of motion, less risk of neurovascular injury, and accelerated rehabilitation. However, the recurrence rate of glenohumeral instability ranges from 0 to 44% and appears to be extremely technique-dependent.^44-48 Additionally, the rehabilitation needs for patients remain considerable and athletes frequently require 6 to 12 months of therapy before returning to their activity. The most common pathologic feature cited to contribute to residual or recurrent glenohumeral instability following arthroscopic repair is that of capsular redundancy and excessive joint volume.^{11,33,43,46,50-53} The technical difficulties associated with trying to arthroscopically treat multidirectional and unidirectional instability secondary to capsular redundancy has led many authors to state that arthroscopic reconstruction of this select patient population is contraindicated.^5,6,12,43,47

1.1.2.

Thermal properties of collagen

Glenohumeral joint stability is maintained by a capsulo-ligamentous complex (joint capsular tissue) that is comprised of joint capsule surrounding the shoulder joint and capsular ligaments (glenohumeral ligaments) that are thickened bundles embedded within the joint capsule. The primary function of these tissues is to limit joint translation over the normal range of motion. Joint capsular tissue (joint capsule and ligaments) is mainly composed of fibrillar collagen (type I).

Collagen, an extracellular matrix component, is the most abundant protein in the human body. Type I collagen is the main constituent of joint capsule and ligament, and these highly ordered dense collagen fibers provide these tissues with their mechanical stiffness and strength. It is a well known phenomenon that collagenous tissue shrinks when it is heated. The thermal properties of collagen have been extensively studied in a variety of experimental models in the field of physical chemistry.^21-23,54-56 In the 1950s, Flory et al. described that thermal shrinkage of collagen is brought about by transition between the crystalline and amorphous phases of collagen.^21,23 A number of studies have demonstrated a molecular structural transition from the triple helix to a random coil during heating; a process that is described as degradation to gelatin or as denaturation.^20,54-56 More recently, shrinkage of collagen was proposed to be secondary to unwinding of the triple helix with maintenance of heat-stable intermolecular crosslinks, where each step in the unwinding process is highly sensitive to temperature.¹⁹ The thermal properties of collagen also vary with the species of the animal, the age of the animal, and the environmental condition in which the animal lives.^26,57 Rosenbloom et al. reported that hydroxyproline content determines the denaturation temperature of collagen using a chick tendon model.⁵⁷ Hogan et al. reported a strong correlation between the thermal properties of tendon and the concentration of non-reducible crosslinks.²⁶ A number of different methods have been used to study this characteristic, including differential scanning calorimetry, ultraviolet difference spectroscopy, isometric tension measurement, and isotonic contraction measurement.^19,26,54-56 To date, the thermal properties of collagen have been explained mainly in terms of the identity, position, and ionization state of charged residues of the amino acids of collagen and collagen’s crosslinks.^58,59

1.1.3.

Tissue modification using thermal effect of laser energy

The first functional ruby laser was developed by Maiman in 1960.⁶⁰ Subsequent to the development of the ruby laser, numerous lasers in the infrared, visible-light, and ultraviolet light spectrum have been developed. When laser energy is directed at any material, the material can reflect the light, scatter it, or absorb it. The optical properties of the material govern the effectiveness of a laser by controlling the interaction between the light and the material. In biological tissues, mid-infrared and far-infrared lasers, such as the CO₂ laser at 10.65 μm and the Ho:YAG laser at 2.14 μm, are mostly absorbed by water. Near-infrared and visible-light lasers, such as the neodymium:YAG (NdtYAG) laser at 1.06 μm and the argon laser at 515 nm, are absorbed relatively poorly by water but are absorbed rapidly by pigments such as hemoglobin and melanin. This optical property makes these lasers effective in the ablation of tissues which have abundant pigment, such as those in the retina, gastric mucosa, and pigmented cutaneous lesions; however, the absence of pigment in musculoskeletal connective tissues such as joint capsule, ligament, and cartilage makes these lasers less effective in most orthopedic applications. Ultraviolet-light lasers are absorbed by specific components of protein molecules, which vary with the wavelength of the laser. The absorption is due to a photochemical mechanism in which the molecular bonds of tissue proteins are broken apart.

The potential applications of laser energy in surgery and medicine have been evaluated in a variety of specialties. The interactions of laser energy and tissue are based on photothermal, photochemical, photomechanical, and photoacoustic effects.^61,62 These effects are used for a wide variety of applications in medicine and surgery, including ablation or vaporization, coagulation, incisional application, interstitial hyperthermia, tissue welding, selective photothermolysis, photodynamic therapy, lithotripsy, and biostimulation.^15,62 Laser applications in surgery have mainly focused on the tissue ablative action of laser energy which is primarily caused by the photothermal effect of laser energy. The nonablative application of laser energy to tissue also has been evaluated in a variety of experimental models, mainly in thermokeratoplasty, tissue welding, and skin resurfacing.

The concept of thermokeratoplasty arose from studies which demonstrated that corneal stromal collagen shrinks to approximately 1/3 of its original length when heated to a temperature of 60 to 65°C.⁶³ Seiler et al. used a pulsed Ho:YAG laser to steepen corneas.⁶⁴ Laser tissue welding has been evaluated in a variety of experimental models including blood vessels, skin, nerves, and bile ducts.^65-69 Laser welding offers several potential advantages over conventional suture technique such as faster healing, less inflammatory response, and higher threshold for infection.⁷⁰ These studies indicate that long-lasting alteration of collagenous architecture can be achieved by nonablative application of laser energy with minimal or no concomitant inflammatory response. Clinically, over the last 5-10 years, the application of controlled thermal laser energy to denature collagen and achieve a therapeutic effect has gained tremendous popularity in applications such as skin resurfacing (wrinkle ablation, or exfoliation (“peel”))^71-73 and thermokeratoplasty (curvature correction).^17,64 Although the mechanisms behind these treatments are still being critically evaluated, clinical results generally have been excellent with ensuing tissue regeneration free of inflammation and scar formation.

1.2.1.

Impact of shoulder joint instability

The magnitude of shoulder instability-related problems is reflected by the incidence of shoulder dislocation in the general population. Glenohumeral instability (GHI) affects between 2 and 8% of the population and represents 1/3 of all shoulder-related emergency room visits.^30,74,75 In many series, shoulder dislocations are more common than all other joint dislocations combined.⁷⁶ If one considers the spectrum of shoulder instability to include transient subluxation which produces activity-related pain, then the true incidence of glenohumeral instability is grossly under-reported. Shoulder instability is a disease of the young and numerous studies have reported that the recurrence rate of instability is inversely proportional to the age of the patient at the time of the injury.^77-80 Thus, young individuals affected by shoulder instability are afflicted by a disability that is recurring and which severely limits their capacity to work, to participate in athletics, or to perform their activities of daily living. In general, individuals with shoulder-related instability tend to decrease their level of activity to accommodate their degree of functional instability.

1.2.2.

Need for a new treatment modality

Glenohumeral instability is a common and recurring problem that current closed, open, and arthroscopic treatments do not satisfactorily address. Closed treatment has an unacceptably high recurrence rate in the young and athletic individual. Open techniques are morbid, require prolonged rehabilitation, and return a minority of overhead athletes back to their pre-injury level of activity. Arthroscopic procedures have a higher rate of failure, require extreme technical expertise, and may be contraindicated in cases of capsular redundancy-related shoulder instability. Whether a non-operative or operative treatment is chosen, prolonged physical therapy ranging from 3 months to 12 months is routinely employed. With increasing pressures to drive down the cost of medicine, many health care plans are severely restricting either the access to physical therapy or the total number of visits available for patient treatment. Thus, considering the shortcomings of the current treatment armamentarium, there appears to be a need for a simply performed, low morbidity procedure that eliminates capsular redundancy, diminishes joint volume, and helps stabilize shoulders of patients, allowing individuals to return to their previous level of activity or performance.

2.2.1.

Effect of nonablative laser energy on joint capsular tissue

Schaefer et al. (1997) reported significant shrinkage (approximately 7%) of patellar tendon by Ho:YAG laser energy applied at 10 watts in saline solution using an in vitro rabbit model, with the mean depth of laser energy’s penetration approximately 1 mm.⁸⁴ Hayashi et al. (1995, 1996) evaluated the effect of laser energy at three nonablative levels (5 watts (5W), 10 watts (10W), and 15 watts (15W)) on the mechanical, biochemical, histologic, and ultrastructural properties of joint capsular tissue in an in vitro rabbit femoropatellar joint capsular model.^81-83 The application of laser energy resulted in 9%, 26%, and 36% reduction in capsular tissue length for the 5W, 10W, and 15W groups, respectively. Tissue shrinkage was significantly and strongly correlated with energy density.⁸¹ Laser energy caused a significant decrease in the tissue’s tensile stiffness in the 10W and 15W groups. Despite the significant decrease in the tissue stiffness, the loads required to return specimens to their original lengths were significantly higher for the 10W and 15W groups compared to control and 5W groups. Histologic examination of the tissue revealed evidence of thermal damage of the tissue at all laser energy densities, which was characterized by hyalinization of collagen and pyknotic nuclear changes in fibroblasts. Each subsequently higher laser energy caused significantly greater morphologic changes over a larger area.⁸³ Transmission electron microscopy revealed alteration of collagen architecture, with significantly increased fibril cross-section for each of the treated groups compared to controls.⁸² The fibrils began to lose their distinct edges and their periodical cross-striations at higher energy densities. Biochemical analysis indicated that application of laser energy did not cause significant alteration of collagen content and non-reducible crosslinks at any energy density.⁸³

These studies demonstrated that significant capsular shrinkage can be achieved with the application of nonablative Ho:YAG laser energy, although at higher energy densities, laser energy did lessen capsular stiffness properties. Application of laser energy did not cause significant alteration of biochemical parameters evaluated in this study, however, histologic/ultrastructural analysis revealed significant thermal changes in the tissue.

2.2.2.

Heating musculoskeletal tissues: Temperature profile and shrinkage

Pilot experimental studies suggested that the effect of nonablative laser energy is predominantly caused by the thermal effect of laser energy. To investigate “pure” thermal effects, several experimental studies have been performed evaluating the effect of heating on collagenous tissues.^85-88 These studies have described the relationship between tissue behavior, temperature, and duration of treatment, utilizing tissue samples treated in temperature controlled tissue baths. Although the tissue response to thermal treatment (e.g., amount of tissue shrinkage) varied widely depending on the experimental conditions and therefore the results were not completely comparable, all studies demonstrated significant tissue shrinkage with heat. Wall et al. (1999) studied the effect of temperature and time on shrinkage and mechanical properties of bovine extensor tendons, reporting that tissue shrinkage was sensitive to temperature changes and mechanical properties decreased with increase shrinkage.⁸⁸ Vangsness et al. (1997) reported a sharp increase in shrinkage to approximately 70% of resting length at approximately 70°C using fresh frozen human Achilles tendon in saline solution.⁸⁷ Naseef et al. (1997) evaluated the effect of temperature and time (duration of thermal exposure) on tissue shrinkage using bovine stifle joint capsule in saline solution, and demonstrated approximately 50% shrinkage at 65, 70, and 75°C with thermal exposures of 1 minute or greater.⁸⁶

Using human glenohumeral joint capsule/ligament specimens, Hayashi et al. (1997) evaluated the effect of temperature on shrinkage and histological properties of this tissue.⁸⁵ In this study, the entire joint capsule was detached from the glenoid and humerus and seven regions of interest were collected from the superior, middle, inferior (anterior band, axillary pouch, posterior band), and posterior (inferior, superior portion) glenohumeral ligament/capsule. Specimens were treated with one of seven temperature settings (37, 55, 60, 65, 70, 75, 80°C) under a constant load (0.098 N). Treatments with 37, 55, and 60°C tissue baths did not cause significant changes in tissue length, whereas temperature treatments at or above 65°C caused significant shrinkage when compared to 37, 55, and 60°C groups. Post-treatment lengths in 70, 75, and 80°C groups were significantly less than pre-treatment lengths. Shrinkage of the tissue started immediately after the temperature treatment and reached maximum shrinkage within 3 min in 75 and 80°C groups. There was no significant effect of tissue region on tissue shrinkage. Histological analysis revealed significant thermal alteration of the tissue, characterized by hyalinization of collagen in 65, 70, 75, and 80°C groups. These histologic properties were similar to the changes caused by nonablative energy.

These studies demonstrated that thermal heating of joint capsule, ligament, and tendon resulted in significant shrinkage that is both temperature and time dependent.^85-88 The degree of tissue modification (shrinkage) is influenced by the quality of the tissue (e.g., collagen content, crosslinks) and direction of the collagen fibers. Despite the differences in experimental conditions, all these studies reported a very similar trend of tissue behavior, demonstrating 65-75°C as the “critical temperature range” for the thermal modification of dense collagenous tissues.

2.2.3.

Mechanism of thermal modification

To understand the mechanism responsible for thermal modification of joint capsular tissue, Hayashi et al. (1999) evaluated the effect of nonablative laser energy on the thermal, ultrastructural, and molecular properties of femoropatellar joint capsular collagen.⁸⁹ A thermometric study revealed that nonablative laser energy caused tissue temperature to rise in the range of 64 to 100°C. Transmission electron microscopic examination showed swollen collagen fibrils, and the biochemical study revealed partial denaturation of collagen. This study support the concept that the primary mechanism responsible for the joint capsular modification is thermal denaturation of collagen in joint capsular tissue associated with unwinding of the triple helical structure of the collagen molecule.

2.4.1.

Tissue heating by radiofrequency energy

Radiofrequency (RF) energy is a form of electromagnetic energy that can produce controlled tissue heating through the mechanism of electrolyte oscillation and consequent molecular movement. RF generators are economic heat sources with a high degree of safety that have been used in numerous clinical applications, including cardiology,⁹⁰ oncology,⁹¹ neurosurgery,⁹² urology,⁹³ and thermokeratoplasty.⁹⁴ In all clinical procedures, the goal of RF energy application is to produce a well-defined area of tissue heating that undergoes controlled tissue cutting with coagulation, ablation, or volume reduction. Based on the initial success of thermal modification of joint capsular tissue by laser energy (laser assisted capsular shift procedure), a RF system was developed for arthroscopic use by modifying a RF generator used for prostate ablation (Oratec Interventions, Inc, Menlo Park, CA). This monopolar RF system has several advantages over Ho:YAG laser including substantial cost benefit, ease of use, increased safety to operator, and temperature control. For thermal modification, this monopolar RF system can produce the critical temperature range (65 to 75°C) in joint capsular tissue. Currently, “monopolar” and “bipolor” probes are available for arthroscopic use by several manufactures. The principle of RF heating with a monopolar probe utilizes an alternating current between the application probe and the grounding plate. This ionic current density produces molecular friction in tissue which results in tissue heating. In contrast, energy produced by bipolar probe follows the path of least resistance through the conductive irrigating solution between probe tips.

2.4.2.

Effect of radiofrequency energy on joint capsular tissue

Experimental studies were performed to evaluate whether monopolar RF energy can produce tissue heating that is required for joint capsular shrinkage and joint stabilization. Obrzut et al. (1998) evaluated the effect of monopolar RF energy on the length of glenohumeral joint capsule in an in vitro sheep study.⁹⁵ Post-treatment lengths of tissues treated at 65, 70, 75, and 80°C RF settings were significantly shorter than pre-treatment lengths. Lopez et al. (1998, 1999) evaluated the effect of monopolar RF energy on the mechanical, histologic, and ultrastructural properties of femoropatellar joint capsular tissue in an in vitro sheep study.^96,97 Monopolar RF treatment caused significant tissue shrinkage at 45, 65, and 85°C RF settings, however, tissue stiffness significantly decreased at 65 and 85°C RF settings. Histologic changes consisted of thermal tissue damage characterized by a fused and homogenized appearance of collagen and fibroblastic nuclear pyknosis at all application temperatures. Ultrastructural alterations included a general increase in cross-sectional fibril diameter and loss of fibril size variation with increasing treatment temperature. Biomechanical, histologic, and ultrastructural alterations by monopolar RF energy application were similar to those observed with nonablative laser energy. These studies provided basic information on temperature settings and tissue shrinkage following monopolar RF treatment, and demonstrated monopolar RF’s ability to produce controlled and predictable thermal energy delivery and tissue modification.

3.1.1.

Comparison of laser and radiofrequency energy application

Initially, Ho:YAG laser was used for thermal modification of glenohumeral joint capsular tissue. Subsequently, RF energy was introduced clinically to achieve joint capsular shrinkage. Laser and radiofrequency treatment methods use very different methods of heating tissue. The laser achieves tissue heating based on a photothermal effect. In contrast, tissue heating by monopolar RF energy is achieved as a result of ionic agitation within the tissue because of a high frequency alternating current that flows between the probe tip and the grounding plate. Because of the different mechanisms involved, there are likely varying effects in tissue response between these two techniques, including the amount of shrinkage, depth of penetration, and the degree and distribution of thermal damage. Currently, both treatment methods have been used clinically for joint capsular shrinkage. To compare the effects of laser and RF energy, joint capsular tissues were treated with laser (5, 10, 15 W) or RF energy (settings at 55, 65, 75°C) in an in vitro ovine model.⁹⁸ Energy application caused significant tissue shrinkage and decreased surface area in all laser and RF treatment groups. Tissue thickness significantly increased in all treatment groups except for RF set at 55°C. There were no significant differences among laser at 10 W, laser at 15 W, and RF set at 75°C treatment groups for these three architectural parameters. Despite different mechanisms, laser and RF energy can achieve similar and predictable tissue modification.

A few potential clinical advantages of using monopolar RF treatment are that the generator can be purchased for substantially less cost than a Ho:YAG laser, has less safety concerns, is physically much smaller than the laser, and has greater versatility because the application probe can be flexed. A potential disadvantage of monopolar RF energy is the inadvertent thermal modification of too much tissue at too great a depth by using a high power setting. Advantages of laser energy include the ability to ablate, coagulate, and shrink tissue with one probe by varying the distance from the probe tip to the tissue. Laser energy induces a brisk and immediate visible shrinkage of the treated tissue, whereas monopolar RF energy application results in smoother and slower shrinkage.

This study did not evaluate the effect of bipolar RF energy, an additional energy modality that is available for arthroscopic use and has been used clinically for thermal stabilization of joints. Although monopolar and bipolar RF devices use molecular friction caused by alternating current for tissue heating, the mechanism of action and resultant tissue effects by these two energy applications are completely different. Therefore, no relevant information on bipolar RF application could be deduced from this study. Bipolar RF devices heat the irrigating solution around the application probe and the tissue nearby, producing tissue effects such as shrinkage, ablation, vaporization, and cauterization. Thermal energy created by bipolar RF can shrink joint capsular tissue when the device is used at the manufacturers’ recommended settings (unpublished data). However, the solution around the probe tip is intensively boiling, indicating that the temperature around the probe tip is at least 100°C. In addition, overheating characterized by charring of the tissue is commonly observed. Therefore care must be taken when using bipolar RF for modification of tissue. To date, no peer-reviewed studies have been reported on the effect of bipolar RF energy on joint capsular tissue.

3.1.2.

Amount of shrinkage to be achieved

There is no information available regarding what percentage of shrinkage is therapeutic for return of normal joint stability, and this probably varies among individuals and is dependent on their abnormality. Selecky et al. (1999) and Ferrara et al. (1999) recommended 10% shrinkage because this amount of shrinkage of human glenohumeral ligament did not significantly alter failure strength.^99,100 Clinically, 5 to 10% shrinkage seems to be sufficient to reduce glenohumeral translation and to regain stability (McMahon PJ, Lee TQ, personal communication) although this goal has not yet been validated experimentally. To date, there is no guideline regarding the amount of energy that should be delivered to achieve therapeutic effects in a clinical situation.

3.1.3.

Effect of thermal modification on human shoulder joint

Previous in vitro experimental studies utilized joint capsular specimens from various animal models, which provided only limited information regarding the effect of joint capsular modification on the human shoulder joint. Selecky et al. (1999) investigated the effect of Ho:YAG laser energy on the biomechanical properties of the human inferior glenohumeral ligament complex using cadaveric shoulders.⁹⁹ The shoulder capsule and its glenohumeral ligaments are significant restraints to shoulder dislocation. In particular, the inferior glenohumeral ligament complex has been shown to be the primary static restraint to anterior-inferior shoulder instability. This study demonstrated that the strength of the ligament complex was not significantly altered and the ultimate strain of the lased specimens was 23% greater than that of the nonlased specimens when tissue underwent 10% shortening with laser energy applied at 10 watts. The authors concluded that the lased specimen was able to sustain a greater amount of stretch before failure and the strength of the inferior glenohumeral ligament complex were not significantly compromised by this lasing protocol. Ferrara et al. (1999) reported a similar result using monopolar radiofrequency energy.¹⁰⁰

Deutsch et al. (1999) studied the biomechanical effects of thermal capsulorrhaphy on resulting multidirectional translation and rotation of the human glenohumeral joint.¹⁰¹ RF energy (set at 40 watts/65°C) was applied to the axillary pouch, inferior glenohumeral ligament complex, middle glenohumeral ligament, rotator interval, and posterior capsule in fresh cadaveric shoulders. The capsular shrinkage procedure resulted in reduction in joint volume (approximately 35%) and in anterior, posterior, and inferior translation, with only a small reduction in rotation. This study demonstrated the significant effect of the capsular shrinkage technique in reducing capsular volume and multidirectional joint translation.

Tibone et al. (1998) evaluated changes in anterior and posterior glenohumeral translation after arthroscopic thermal capsulorrhaphy using nonablative laser energy in human cadaveric shoulders.¹⁰² Thermal capsulorrhaphy by Ho:YAG laser energy at 20 watts applied tangential to the anterior glenohumeral joint capsular tissue resulted in a significant reduction in anterior and posterior translation, with approximately 34% decrease in anterior translation and approximately 38% decrease in posterior translation. Similarly, another study by Tibone et al. (1998) demonstrated that thermal capsulorrhaphy using monopolar RF energy also resulted in a significant decrease in anterior and posterior translation.¹⁰³ The percent reduction in translation was similar in both anterior and posterior directions regardless of which device was used to apply the thermal energy. These results confirm that thermal capsulorrhaphy can be used to decrease glenohumeral joint translation and may be effective for the treatment of glenohumeral instability.

3.1.4.

Biological response to thermal modification of joint capsular tissue: Healing process

Previous in vitro studies have indicated that thermal treatment using laser or RF energy causes collagen denaturation, cell necrosis, and deleterious effects on the tissue’s mechanical properties.^81-83,89 Therefore, in vivo studies to investigate the tissue’s biologic response to the thermal damage must be performed to verify the validity and safety of these treatments before they can be used clinically. Hayashi et al. (1999) evaluated the healing process of collagenous tissue after thermal treatment in a sheep model.¹⁰⁴ Femoropatellar joint capsule was treated with either laser energy or RF energy under arthroscopic guidance and treated joint capsular specimens were harvested at 0, 1, 2, 4, 8, 12, and 24 weeks after surgery. Stiffness of laser treated tissue at 0 and 1 week after surgery was significantly lower than control, however at 2 weeks and beyond, stiffness were not significantly different from control. Failure strength tended to be lower than the control at 1 and 2 weeks after laser treatment. RF energy caused a significant decrease in tissue stiffness at 0 and 2 weeks after surgery. Failure strength had a trend to be lower than the control at 2 weeks after radiofrequency treatment.

Histology following both treatment modalities demonstrated immediate collagen hyalinization and cell necrosis, followed by an active cellular reparative response characterized by extensive fibroblast migration and capillary sprouting, and subsequent tissue maturation. Histologic examination of treated samples at time 0 revealed hyalinization of collagen with nuclear karyorrhexis of fibroblasts following both laser and RF energy application. In the laser treated tissue, histologic alterations were limited to the directly treated regions, whereas RF treated tissue demonstrated a more uniform thermal effect throughout the joint capsular tissue. For both laser and RF groups, reactive fibroblasts and vascular responses were significantly increased around the treated region at 2 weeks after surgery. Interestingly, subcapsular muscle necrosis caused by the thermal effect of RF energy at high power settings induced a severe inflammatory response, whereas inflammation was not evident in ligamentous regions of the capsule. Hyalinized regions were gradually reduced and replaced with cellular fibrous tissue at 4 weeks after laser treatment and at 6 weeks after RF treatment. Although cellularity remained elevated in both laser and RF treated tissue, joint capsular tissue regained its organized fibrous appearance at 12 weeks after surgery. Transmission electron microscopy revealed that the treated region was infiltrated with fibroblasts and replaced with fine collagen fibrils by 12 weeks post surgery. Tissue culture studies demonstrated that collagen synthetic activity of laser treated tissue was 64% of control at day 0, however collagen synthesis increased significantly at 1 week (196%) and 2 weeks (197%) after treatment. The biochemical analysis of collagen revealed that thermal treatment initially caused denaturation of joint capsular collagen, which over time then regained its native structure.

This study illustrated an active and prompt tissue response to the tissue modification, with concomitant improvement of mechanical properties by 6 weeks after surgery. Treatment by laser and RF energy induced similar cellular responses after thermal modification of joint capsular tissue. This study revealed that thermally modified joint capsular tissue was actively repaired and returned to pre-treatment mechanical properties by 6 weeks after surgery, although histologic return to normalcy required 12-24 weeks and the treated tissue had not returned to a completely normal ultrastructural appearance at 6 months after treatment. Thermal treatment did cause cell necrosis, collagen denaturation, and an initial deleterious effect on mechanical properties, therefore the joint should be protected during this healing phase by limiting motion for 6 to 12 weeks after surgery.

3.1.5.

Maintenance of shrinkage over time and effect of joint immobilization

The in vivo study by Hayashi et al. described above (3.1.4) did not examine whether significant shrinkage was maintained over time in vivo. Schaefer et al. (1997) showed in a rabbit patellar tendon model that despite significant immediate shrinkage after laser application, the patellar tendon stretched out within 4 weeks after surgery when subjected to immediate physiological loading after surgery.⁸⁴ This study demonstrated that significant tendon shrinkage (6.6 %) occurred after Ho:YAG laser energy application (10 W), however, tendon length increased significantly beyond the immediate postlaser length at 4 weeks and beyond its original length by 8 weeks after surgery. At 8 weeks, the lased tendons were significantly less stiff with significantly greater cross-sectional areas than contralateral controls. The authors concluded that after initial shrinkage, laser-modified tissues demonstrate a loss of tensile stiffness and can stretch out to beyond preshrinkage length when exposed to normal physiologic load. Using the identical animal model, Schlegel (1999) evaluated the effect of postoperative immobilization on the healing of thermally modified tissue using monopolar RF.¹⁰⁵ Rabbit patellar tendon was treated with monopolar RF energy and the limb was either not immobilized, immobilized for 2 weeks, or immobilized for 4 weeks (8 week survival time for all animals). Immobilization for 4 weeks resulted in a significant decrease in tissue elongation when compared to non-immobilized and 2 week immobilized groups at 8 weeks. All treatment groups demonstrated a significant decrease in tissue tensile stiffness when compared to normal controls. The authors concluded that early activity can lead to stretching of the thermally shortened tissue and postoperative immobilization is important following thermal modification of joint capsular tissue.

Wallace et al. (1999) reported that shrinkage induced by RF energy was maintained for 12 weeks using a rabbit medial collateral ligament model.¹⁰⁶ In this study, abnormal laxity was experimentally created by elevating and shifting the tibial insertion of the medial collateral ligament. Monopolar RF energy was applied to the midsubstance of the shifted ligament. Laxity of the ligament was significantly reduced with thermal treatment at time 0, with stability maintained for up to 12 weeks after surgery. However, the tissue’s viscoelastic properties (creep behavior) were significantly altered by thermal modification of the ligament. This study indicated that although laxity may be reduced, there is a potential risk of recurrent elongation during early loading of the tissue.

3.1.6.

Potential mechanisms of postoperative joint stabilization

Studies have demonstrated that thermal energy can be used to produce controlled tissue modification such as shrinkage, and both laser and RF energy can create predictable thermal effects in the tissue. Despite the immediate thermal damage to the tissue, thermal modification of joint capsular tissue does not lead to permanent tissue injury, as a residual population of fibroblasts repairs the tissue by replacing denatured collagen with new collagen. A critical aspect of this treatment is that the application of thermal energy to achieve joint stability relies on both an initial effect (shrinkage) and the tissue’s healing response to regain the tissue’s mechanical properties while maintaining its shorter length. It is also possible that shrinkage alone is not the reason for clinical effectiveness of thermal treatment. Schaefer et al. (1997) demonstrated increased cross-sectional area in healing tendon after laser thermal modification.⁸⁴ Wallace et al. (1999) also reported increased cross-sectional area in healing ligament after monopolar RF thermal modification.¹⁰⁶ Hayashi et al. (1999) described an active healing process of joint capsular tissue following laser and monopolar RF thermal modification, which is characterized by repair of the thermally treated tissue with thicker fibrous tissue.¹⁰⁴ Therefore, we believe that induction of active repair (fibrosis) and joint capsular thickening, concomitant with tissue remodeling and maturation regulated by functional demand are essential factors for successful outcome of thermal modification of joint capsular tissue. Arnoczky (1999) proposed the following mechanisms as the reasons for clinical effectiveness of the thermal joint stabilization: (1) initial shrinkage, (2) secondary cicatrix formation and collagen deposition, and/or (3) thermal denervation in joint capsular tissue.¹⁰⁷

3.2.1.

Histologic evaluation of glenohumeral joint capsular tissue after thermal modification

Hayashi et al. (1999) evaluated histologic properties of glenohumeral joint capsular tissues obtained from 42 patients who had undergone an arthroscopic laser-assisted capsular shift (LACS) procedure.¹⁰⁸ A total of 53 samples from the anterior inferior glenohumeral ligament of the joint capsule were collected before and at various times after the LACS procedure (range, time 0 to 38 months post-surgery). Despite glenohumeral instability, joint capsule of the patients before LACS showed no significant histologic lesions. Laser treatment significantly altered histologic properties of the tissue characterized by hyalinization of collagen and necrotic cells (time 0). Tissues sampled during 3-6 months after the surgery demonstrated fibrous connective tissue with reactive cells and vasculature. Collagen and cell morphology returned to normal in the post-operative period between 7 to 38 months, while the number of fibroblasts remained elevated. Six patients experienced mild stiffness after the LACS procedure. Joint capsule collected from these shoulders showed persistent synovial, cellular, and vascular reaction even after one year post-operatively. This study revealed histologic evidence of robust tissue healing and maturation after thermal treatment by the LACS procedure. The incidence of arthrofibrosis (stiff shoulder) following the LACS procedure is estimated to be less than 1% of all LACS-treated patients and these patients improved after therapeutic manipulation, however, the cause of arthrofibrosis in these patients is unclear. This result indicated that further follow-up studies in this area are needed.

3.2.2.

Clinical results of laser and monopolar radiofrequency thermal capsulorrhaphy

Frogameni et al. (1999) reported the clinical outcome of laser-assisted capsular shift (LACS) procedure for symptomatic multidirectional glenohumeral instability in 41 patients with a minimum of two year follow up.¹⁰⁹ The LACS procedure was performed using a Ho:YAG laser set at 10 watts applied to the inferior glenohumeral complex and advanced anteriorly or posterioirly depending on the pathology. All patients were followed for a minimum of two years and underwent a subjective and objective examination. Overall, 84% of the shoulders had a satisfactory outcome. Six patients who demonstrated primary posterior, inferior multidirectional instability had only 50% success. Five of the 41 patients experienced recurrent episodes of instability. Savoie et al. (1999) reported the result of the LACS procedure for symptomatic multidirectional shoulder instability in 33 patients with mean of 25.5 months.¹¹⁰ Only 1 of the 33 patients had recurrent instability after the LACS procedure. The author concluded that the LACS procedure is superior to arthroscopic capsular shift.

Fanton (1999) reported clinical results of thermal capsulorrhaphy using monopolar RF energy in 54 patients.¹¹¹ At 2 years follow up, the success rate was over 90% (with good or excellent results). All patients maintained excellent post-operative range of motion. Five of the 54 patients demonstrated fair or poor results, which the author concluded were due to insufficient joint protection or other pathology such as a large Hill-Sachs lesion that should be considered a contraindication to arthroscopic stabilization. There have been 2 complications in this 54 patient population. One patient developed adhesive capsulitis that required prolonged physical therapy to regain range of motion, and at 26 months post-operatively the patient was fully active with no residual pain or instability. One patient developed a temporary sensory axillary neuritis post-operatively, although symptoms completely resolved at 4 weeks and the patient had an excellent result at 2 years after surgery.

Andrews (1999) reported short term results of thermal capsular shrinkage using monopolar RF energy in 46 throwing athletes, with excellent rates of return to competition and excellent subjective post-operative scores, and very low incidence of complications.¹¹² The author stated that SLAP legions signify more severe shoulder pathology and decrease the odds of return to the same level of competition regardless of treatment method. D’Alessandro (1999) reported improvement of shoulder score from 43 to 87 after monopolar RF thermal capsulorrhaphy in 33 shoulder with multidirectional glenohumeral instability.¹¹³ Warren (1999) reported combined result of thermal capsulorrhaphy by laser and monoploar RF energy in 68 patients with dislocation, subluxation, or multidirectional instability, with improvement of shoulder scores from 40 to 80 postoperatively.¹¹⁴

These early clinical results have demonstrated clinical efficacy of thermal modification of joint capsular tissue as a treatment for shoulder joint instability and related clinical problems at approximately 2 years follow up. Complications were infrequent and minor. Sensory axillary neuritis was observed as a postoperative complication, which was mild and temporary. Postoperative shoulder stiffness (feeling tight) may be due to over-treatment or idiopathic hyperreaction of the tissue. Post-operative insufficient stabilization may be due to under-treatment or pre-existed pathology such as abnormal collagen. Non-responsiveness to thermal treatment was probably due to pathology other than capsular redundancy. Fanton (1999) stated that patients with multidirectional instability seem to be more resistant to thermal treatment compared to patients with unidirectional instability.¹¹¹ Warren had an impression that thermal capsulorrhaphy by laser caused more stiff shoulders compared to monopolar RF energy. Although there is no formal guideline for post-operative care, it is generally recommended that the joint be immobilized for 2 to 3 weeks before physical therapy is initiated. At 5 to 6 weeks strengthening and endurance exercise are permitted within the limited range of motion, and sports activity may be started at 12 weeks post-operatively. All authors stated that careful patient selection and postoperative rehabilitation protocols are essential for the successful outcome of thermal capsulorrhaphy.