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

Comparison of Electrothermal Ablation and Electrolyte Plasmalization Devices Based on the Mechanical Properties of Anterior Cruciate Ligament Femoral Attachment Following Partial Debridement: A Biomechanical Study Using a Porcine Model

Purpose This study aimed to clarify whether differences in ablation devices used in the knee joint during partial debridement of the proximal end of the femoral attachment of the anterior cruciate ligament (ACL) affect the mechanical properties of the femur-ACL-tibia complex. Methods Electrothermal ablation was generated from Vulcan for the left knees, and radiofrequency ablation was generated from Werewolf Flow 50 Wand for the right knees. The probes were set to the default setting of 120 W and 150 W for Vulcan and Werewolf Flow 50 Wand, respectively. To mimic partial debridement in remnant tissue-preserving (RTP) ACL reconstruction, the bipolar ablation mode and serpentine movements were employed while in contact with the femoral fan-like extension fibers of the ACL. To simulate the arthroscopic environment, the model was immersed in a saline solution. The probes were applied for 60 s, and their biomechanical properties were evaluated. Results A significant difference was observed in the upper yield load between the two groups (Vulcan group, 107.1 ± 93.4 N; Werewolf group, 177.9 ± 108.8 N; P = 0.045). However, no significant differences were noted in linear stiffness (Vulcan group, 47.6 ± 30.9 N/mm; Werewolf group, 50.1 ± 30.5 N/mm; P = 0.85), maximum load (Vulcan group, 276.2 ± 171.8 N; Werewolf group, 397.7 ± 150.8 N; P = 0.26), or elongation at failure (Vulcan group, 6.1 ± 0.9 mm; Werewolf group, 11.6 ± 10.4 mm; P = 0.20) between the two groups. Conclusion The mechanical properties of the ACL after partial ACL femoral attachment debridement for RTP-ACL reconstruction were better when an electrolyte plasmalization device was used. When performing RTP-ACL reconstruction, surgeons must consider that the device used for partial femoral ACL stump debridement may affect the mechanical properties of the ACL remnant tissue. Clinical relevance When performing RTP-ACL reconstruction, surgeons must consider that the device used for partial femoral ACL stump debridement may affect the mechanical properties of the ACL remnant tissue.

Photobiomodulation therapy increases collagen II after tendon experimental injury

A tendon is a mechanosensitive tissue that transmits muscle-derived forces to bones. Photobiomodulation (PBM), also known as low-level laser therapy (LLLT), has been used in therapeutic approaches in tendon lesions, but uncertainties regarding its mechanisms of action have prevented its widespread use. We investigated the response of PBM therapy in experimental lesions of the Achilles tendon in rats. Thirty adult male Wistar rats weighing 250 to 300 g were surgically submitted to bilateral partial transverse section of the Achilles tendon. The right tendon was treated with PBM, whereas the left tendon served as a control. On the third postoperative day, the rats were divided into three experimental groups consisting of ten rats each, which were treated with PBM (Konf, Aculas - HB 750), 780 nm and 80 mW for 20 seconds, three times/week for 7, 14 and 28 days. The rats were sacrificed at the end of the therapeutic time period. The Sca-1 was examined by immunohistochemistry and histomorphometry, and COLA1, COLA2 and COLA3 gene expression was examined by qRT-PCR. COLA2 gene expression was higher in PBM treated tendons than in the control group. The histomorphometric analysis coincided with increased number of mesenchymal cells, characterized by Sca-1 expression in the lesion region (p<0.001). PBM effectively interferes in tendon tissue repair after injury by stimulating mesenchymal cell proliferation and the synthesis of collagen type II, which is suggested to provide structural support to the interstitial tissues during the healing process of the Achilles tendon. Further studies are needed to confirm the role of PBM in tendon healing.

History of surgical stabilization for posterior shoulder instability

Background

Posterior shoulder instability is common in young athletes. Although the posterior shoulder instability literature is less robust than its anterior counterpart, many surgical procedures have been developed and refined over the past several centuries to address this condition.

Materials and methods

This article represents a retrospective historical analysis of the most common procedures used to treat posterior shoulder instability after sports injuries. A systematic approach to obtain published information on posterior shoulder instability was performed using the PubMed/MEDLINE database, manual searches of high–impact factor journals, and conference proceedings and books.

Results

A wide array of both soft tissue–based and bone-based procedures have been developed for the treatment of posterior shoulder instability, ranging from procedures addressing the soft tissue alone (capsular shift, labral repair, reverse Putti-Platt) or bone-based procedures (glenoid and/or humeral osteotomy, glenoid bone block) to a combination of both bone and soft-tissue procedures (modified McLaughlin procedure).

Discussion

Over the past several centuries, a number of procedures have been developed to address posterior shoulder instability, particularly as this pathology has become better understood. Future work is required not only to continue to advance these procedures but also to assess their outcomes. An understanding of the historical perspective of posterior shoulder instability procedures is essential as surgeons continue to modify these procedures in an effort to best help their patients.

Thermal shrinkage for shoulder instability

Thermal capsular shrinkage was popular for the treatment of shoulder instability, despite a paucity of outcomes data in the literature defining the indications for this procedure or supporting its long-term efficacy. The purpose of this study was to perform a clinical evaluation of radiofrequency thermal capsular shrinkage for the treatment of shoulder instability, with a minimum 2-year follow-up. From 1999 to 2001, 101 consecutive patients with mild to moderate shoulder instability underwent shoulder stabilization surgery with thermal capsular shrinkage using a monopolar radiofrequency device. Follow-up included a subjective outcome questionnaire, discussion of pain, instability, and activity level. Mean follow-up was 3.3 years (range 2.0-4.7 years). The thermal capsular shrinkage procedure failed due to instability and/or pain in 31% of shoulders at a mean time of 39 months. In patients with unidirectional anterior instability and those with concomitant labral repair, the procedure proved effective. Patients with multidirectional instability had moderate success. In contrast, four of five patients with isolated posterior instability failed. Thermal capsular shrinkage has been advocated for the treatment of shoulder instability, particularly mild to moderate capsular laxity. The ease of the procedure makes it attractive. However, our retrospective review revealed an overall failure rate of 31% in 80 patients with 2-year minimum follow-up. This mid- to long-term cohort study adds to the literature lacking support for thermal capsulorrhaphy in general, particularly posterior instability.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s11420-010-9187-7) contains supplementary material, which is available to authorized users.

Shoulder instability in patients with joint hyperlaxity

Generalized ligamentous hyperlaxity and glenohumeral joint instability are common conditions that exhibit a spectrum of diverse clinical forms and may coexist in the same patient. No single diagnostic test can confirm the presence of these disorders, and a careful clinical assessment is important. Unlike patients with traumatic shoulder instability, patients with hyperlaxity and instability are more likely to experience episodes of recurrent subluxation than they are to have recurrent dislocation. They are more likely to have instability in more than one anatomic plane, and they usually do not have the soft-tissue and osseous lesions associated with traumatic instability. Shoulder symptoms in a patient with hyperlaxity are not always due to instability; other pathological conditions may coexist, with rotator cuff impingement being the most common. Most patients with hyperlaxity have a reduction in instability symptoms after nonoperative treatment, including physical therapy, activity modification, and additional psychological support when necessary. Operative treatment provides reproducibly good results for patients with hyperlaxity who do not respond to a prolonged program of nonoperative measures. Open inferior capsular shift remains the gold standard of operative treatment, although arthroscopic capsular shift and plication procedures are now producing comparable results. Thermal capsulorrhaphy is associated with unacceptably high failure rates and postoperative complications and cannot be recommended as a treatment.

The effect of postoperative immobilization on the healing of radiofrequency heat probe modified tissue: assessment of tissue length, stiffness, and morphology

The effect of postoperative immobilization on the length, stiffness, and structure of connective tissue after radiofrequency probe shrinkage was examined in a rabbit patellar tendon model. Tendon lengths were measured before, immediately following, and 2, 4, and 8 weeks following heat application, with the contralateral tendon as a control. The animals were randomly assigned to three groups. In Group I, the controls, the animals were allowed free caged activity for 8 weeks. In Groups II and III, the experimental limb was immobilized at 15 degrees of knee flexion for 2 and 4 weeks, respectively, after which the animals were allowed 6 and 4 weeks of free caged activity. Changes in tendon length, stiffness, and cross-sectional area were compared using repeated measures ANOVA and differences between groups examined using Tukey's post-hoc analysis. Patellar tendon lengths were increased in all 3 groups at 8 weeks (P< .001). Tissue elongation was less extensive in group III compared to group I at 8 weeks (P< .001), while tissue cross-sectional area was decreased in both groups II and III compared to group I at 8 weeks (P< .001). All groups demonstrated decreases in tensile strength when compared to controls (P< .001). These findings suggest that postoperative immobilization is important following thermal shrinkage of connective tissue, as early activity can lead to stretching of the heat-modified tissue.

Mechanical changes induced by thermal stimulation in collagenous tissue

Radiofrequency thermal stimulation is used as a therapeutic procedure for joint laxity, but its thermal effects are still controversial. Although collagen shrinkage may be expected, this conclusion is empirical and not universally accepted. The purpose of this study was to investigate the mechanical response of collagen to thermal stimulation. A longitudinal cut was made in rabbit Achilles tendons previously marked with monofilament sutures. The distance between the sutures was measured before the cut, just after it was made, and after 8 weeks. The results did not show any shrinkage or significant change in tendon resistance to traction 8 weeks after thermal stimulation; however, comparison with the opposite, normal tendon revealed a statistically significant increase in tendon stiffness.

A structural, kinetic model of soft tissue thermomechanics

A structure-based kinetic model was developed to predict the thermomechanical response of collagenous soft tissues. The collagen fibril was represented as an ensemble of molecular arrays with cross-links connecting the collagen molecules within the same array. A two-state kinetic model for protein folding was employed to represent the native and the denatured states of the collagen molecule. The Monte Carlo method was used to determine the state of the collagen molecule when subjected to thermal and mechanical loads. The model predictions were compared to existing experimental data for New Zealand white rabbit patellar tendons. The model predictions for one-dimensional tissue shrinkage and the corresponding mechanical property degradation agreed well with the experimental data, showing that the gross tissue behavior is dictated by molecular-level phenomena.

Incidence of the anterior meniscofemoral ligament: an arthroscopic study in anterior cruciate ligament-deficient knees

PURPOSE

The purpose of this study was to arthroscopically determine the incidence of the anterior meniscofemoral ligament of Humphry in anterior cruciate ligament (ACL)-deficient knees.

METHODS

One hundred forty knees were prospectively evaluated during arthroscopic ACL reconstruction procedures. The mean patient age was 30 years (range, 16 to 45 years), and there were 93 male and 47 female patients. In 69 patients, the right knee was evaluated, and in 71, the left. Inclusion criteria were skeletally mature patients aged under 45 years with isolated ACL injuries. Exclusion criteria were degenerative articular changes, external meniscus injuries, insufficiencies of ligaments other than the ACL, and previous knee surgery.

RESULTS

The anterior meniscofemoral ligament of Humphry was present in all of the knees evaluated.

CONCLUSIONS

It has been proposed that traumatic and degenerative changes may explain the variation of the reported incidence of the meniscofemoral ligament. In our study in young patients with no degenerative changes, no meniscal injuries or surgery, and no ligament disruption except from the ACL, the anterior meniscofemoral ligament presented as a constant structure.

CLINICAL RELEVANCE

Given the high incidence of the appearance of the anterior meniscofemoral ligament, this structure should be preserved during meniscus and ligament surgeries at least until its function and clinical relevance are determined.

Treatment of ligament laxity by electrothermal shrinkage or surgical plication: a morphologic and mechanical comparison

Capsular plication or thermal shrinkage can be used to enhance surgical joint stabilization. We compared mechanical or morphologic properties of the medial collateral ligament of the rabbit knee treated by either bipolar radiofrequency electrothermal shrinkage or surgical plication. After 12 weeks, the medial collateral ligaments were procured from treated and contralateral knees to undergo viscoelastic (creep) testing, quantitative transmission electron microscopy, and immunohistochemistry. Creep strain in thermal (1.85% +/- 0.32%) and plicated (1.92% +/- 0.36%) ligaments was almost twice that of the control group (1.04% +/- 0.15%), although there was no difference between treatment modalities. The morphologic parameters of all 3 groups were significantly different (P < .001). The thermal ligaments demonstrated predominantly small fibrils, whereas the plicated group displayed an intermediate distribution of heterogeneous fibrils, suggesting a different pattern of remodeling. Viscoelastic properties are similar after thermal shrinkage or plication, though inferior to those of intact ligaments.

Thermal medial retinaculum shrinkage and lateral release for the treatment of recurrent patellar instability

PURPOSE

To study a technique of medial retinacular thermal shrinkage and evaluate the clinical effectiveness of this technique.

TYPE OF STUDY

Nonrandomized prospective case series.

METHODS

A consecutive series of patients with recurrent patellar instability treated with arthroscopic lateral release and medial thermal retinaculum shrinkage using a monopolar radiofrequency probe was assessed subjectively by visual analog scale and both preoperatively and postoperatively by physical examination and Lysholm and Fulkerson knee scores.

RESULTS

We evaluated 53 knees with an average follow-up of 53 months (range, 24 to 88 months). The mean Lysholm and Fulkerson scores improved from 45 and 41 to 81 and 82, respectively. Subjectively, 48 of 53 knees (90%) were reported as excellent or good. The average visual analog scale score was 8 out of 10. Five patients failed because of recurrent dislocation (9% recurrence). Additional stabilization procedures were performed in 4 patients.

CONCLUSIONS

Medial shrinkage using monopolar thermal energy is effective in treating recurrent patellar instability. Our results were comparable with prior studies using suture plication. The technique avoids additional incisions and decreases operative time.

LEVEL OF EVIDENCE

Level IV, therapeutic prospective cohort study.

Radiofrequency energy effects on the mechanical properties of tendon and capsule

PURPOSE

To compare the mechanical properties of tendon and capsule after radiofrequency (RF) energy treatment.

TYPE OF STUDY

An in vitro study.

METHODS

RF energy was applied to ovine extensor tendon and human cadaveric glenohumeral capsule varying in the treatment wattage and time (5, 10, or 20 W for 10 or 30 seconds). The associated tissue length changes and dynamic and failure properties of the tissues were investigated using a materials testing machine.

RESULTS

Length changes in the 2 tissues were comparable across the range of treatment settings used with both increases in the treatment wattage and time increasing the amount of tissue shrinkage observed. However, tendon showed greater changes in its mechanical properties after RF treatment, with significant decreases in the failure properties of the tissue as well as the dynamic and static stiffness.

CONCLUSIONS

RF treatment shrinks collagenous tissues in a progressive manner correlated to the treatment wattage. However, it has different effects on the mechanical properties of tendon and capsule with the properties of tendinous tissues dramatically reduced.

CLINICAL RELEVANCE

RF treatment has been shown to effect the mechanical properties of different collagenous tissues differently; therefore, it must be used specifically and with caution around areas of mixed tissue origin.

Revision surgery for failed thermal capsulorrhaphy

BACKGROUND

With the failure of thermal capsulorrhaphy for shoulder instability, there have been concerns with capsular thinning and capsular necrosis affecting revision surgery.

PURPOSE

To report the findings at revision surgery for failed thermal capsulorrhaphy and to evaluate the technical effects on subsequent revision capsular plication.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Fourteen patients underwent arthroscopic evaluation and open reconstruction for a failed thermal capsulorrhaphy. The cause of the failure, the quality of the capsule, and the ability to suture the capsule were recorded. The patients were evaluated at follow-up for failure, which was defined as recurrent subluxations or dislocations.

RESULTS

The origin of the instability was traumatic (n = 6) or atraumatic (n = 8). At revision surgery in the traumatic group, 4 patients sustained failure of the Bankart repair with capsular laxity, and the others experienced capsular laxity alone. In the atraumatic group, all patients experienced capsular laxity as the cause of failure. Of the 14 patients, the capsule quality was judged to be thin in 5 patients and ablated in 1 patient. A glenoid-based capsular shift could be accomplished in all 14 patients. At follow-up (mean, 35.4 months; range, 22 to 48 months), 1 patient underwent revision surgery and 1 patient had a subluxation, resulting in a failure rate of 14%.

CONCLUSIONS

Recurrent capsular laxity after failed thermal capsular shrinkage is common and frequently associated with capsular thinning. In most instances, the capsule quality does not appear to technically affect the revision procedure.

Anterior capsulorrhaphy: an in vitro comparison of volume reduction--arthroscopic plication versus open capsular shift

PURPOSE

The purpose of this study was to objectively compare volume reduction after arthroscopic plication and open lateral capsular shift.

TYPE OF STUDY

Experimental cadaver study.

METHODS

Fifteen fresh-frozen human cadaver shoulders were assigned to 1 of 2 groups: arthroscopic plication (n = 7) or open lateral capsular shift (n = 8). Initial capsular volume was measured by repeated injection of a viscous fatty acid sulfate solution and recorded for each specimen. Repeated measurements were taken after the procedure to determine volume reduction.

RESULTS

Both procedures resulted in reduction of capsular volume. The arthroscopic plication resulted in a 22.8% volume reduction and the open lateral capsular shift resulted in a 49.9% volume reduction. Comparison of the 2 procedures revealed significant volume reduction after open lateral capsular shift compared with arthroscopic plication (P = .00001). Repeated measurements confirmed that the injection technique was valid and reproducible.

CONCLUSIONS

The lateral capsular shift resulted in significantly greater volume reduction compared with arthroscopic plication. Based on these results, we recommend an open lateral-based capsular shift for patients with multidirectional instability in which a larger capsular shift is required. However, additional plication sutures may allow for an even further reduction in volume. The amount of volume reduction required to eliminate instability still remains unknown for patients with shoulder instability caused by capsular laxity.

LEVEL OF EVIDENCE

Level IV Case Series, in vitro anatomic comparison of 2 surgical procedures.

The effects of thermal capsular shrinkage on the outcomes of arthroscopic stabilization for primary anterior shoulder instability

BACKGROUND

The effectiveness of arthroscopic thermal capsulorrhaphy in the prevention of recurrent instability in primary anterior stabilization is undetermined.

PURPOSE

To determine if patients with recurrent anterior shoulder instability who have labral repair plus arthroscopic thermal capsulorrhaphy have better outcomes than those with labral repair alone.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHOD

There were 72 patients who underwent arthroscopic anterior shoulder stabilization with Suretac II tacks (n = 32) during 1996 to 1999 or with Suretac II tacks plus arthroscopic radiofrequency capsular shrinkage (n = 40) from 1999 to 2002. Standardized patient-determined and examiner-determined outcome measures were obtained preoperatively and at 3, 6, 12, and 24 months postoperatively. Statistical analyses included a Kaplan-Meier analysis of time to recurrent instability.

RESULTS

Of the 72 patients, 66 had complete follow-up, including 28 patients treated with the Suretac stabilization and 38 patients with the Suretac plus radiofrequency shrinkage, for a mean follow-up of 58 and 30 months, respectively. All patients had a Bankart lesion. Both groups had similar results with respect to patient-determined and examiner-determined outcome measures. The only adverse outcome was postoperative recurrent instability in 6 of 28 cases in the Suretac group alone and 8 of 38 cases in the Suretac-plus -shrinkage group. Most recurrent instability occurred between 6 and 24 months. Kaplan-Meier analysis for time to recurrent instability showed no differences in the rate of instability recurrence between the 2 groups.

CONCLUSION

Arthroscopic thermal capsulorrhaphy neither enhanced nor impaired the outcomes of arthroscopic labral repair with biodegradable tacks in patients with primary recurrent anterior shoulder instability.

Neuronal regeneration after application of radiofrequency energy to collagenous tissue is affected by limb immobilization: an in vivo animal study

Despite widespread use of radiofrequency (RF)-shrinkage, there have been no studies on the influence of RF-energy on neural elements of collagenous tissue. The purpose of this study was to examine the effect of RF-shrinkage on neural structures of capsuloligamentous tissue and the recovery of neural elements under different postoperative treatment protocols. One patellar tendon of 46 New-Zealand-White rabbits was shrunk. Six rabbits were sacrificed immediately postoperative. Twenty rabbits were not immobilized, 10 were immobilized for 3 and 10 were immobilized for 6 weeks. A monoclonal antibody, specific against a neurofilament protein, was used to detect nerves and neural structures. Staining pattern of nerve fibres was significantly altered immediately postoperative. After 3 weeks the number of nerve fibres and bundles decreased significantly in immobilized and non-immobilized limbs. The loss of nerve fibres was significantly less in immobilized limbs. At 6 weeks the number of neural elements in immobilized limbs increased to the level of untreated control tissue. In non-immobilized limbs we found no recovery of neural elements 9 weeks postoperatively. At this time the number of nerve fibres and bundles was still significantly less compared to the untreated control limbs. RF-shrinkage causes significant alteration of neural elements. Under immobilization nerve fibres and bundles reach the level of normal untreated tissue. Careful rehabilitation is important after RF-shrinkage. Not only for biomechanical reasons, but also to allow the neural elements to recover, thermally modified tissue should be protected from normal physiologic loads.

Altered Mechanical Behavior of Epicardium Under Isothermal Biaxial Loading

Most soft tissues that are treated clinically via heating experience multiaxial states of stress and strain in vivo and are subject to complex constraints during treatment. Remarkably, however, there are no prior data on changes in the multiaxial mechanical behavior of a collagenous tissue subjected to isometric constraints during heating. This paper presents the first biaxial stress-stretch data on a collagenous membrane (epicardium) before and after heating while subjected to various biaxial isometric constraints. It was found that isometric heating does not allow the increase in stiffness at low strains that occurs following isotonic heating. Moreover, increasing the degree of stretch prior to heating increased the thermal stability of the tissue consistent with the concept that mechanical loading primarily affects the activation entropy, not the activation energy.

Thermal capsulorrhaphy

The initial wave of enthusiasm for thermal capsulorrhaphy has subsided. Long-term clinical data were lacking until D'Alessandro et al's prospective study indicated the results were not as promising as the previously reported short-term studies. Complications including obliteration or attenuation of capsular tissue, axillary nerve injury, and chondrolysis have all been reported in recent years further raising concern about the widespread use of this procedure. The inexact nature of how much "shrinkage" is being performed has led surgeons to further develop surgical technique in capsular plication, shift, or advancement. Although it remains to be seen if these techniques will lead to good clinical outcomes, it appears that they more closely resemble the original operative procedure-anterior capsular shift.

Immediate effect of thermal capsulorrhaphy on glenohumeral joint mobility

OBJECTIVES

To evaluate the effects of anterior thermal capsulorrhaphy of the glenohumeral joint by monitoring changes of magnitudes of the anterior and posterior displacements of the humeral head and ranges of motion of abduction and rotation in fresh cadaver shoulders.

DESIGN

Single session repeated-measures design.

BACKGROUND

Following thermal shrinkage anterior and posterior displacements of the head of humerus were decreased. However, no studies were focused on the ranges of motion of abduction and rotation of the shoulder joint immediately. The mobility of abduction and rotation are also important indexes for glenohumeral function.

METHODS AND MEASURES

Nine fresh frozen shoulder specimens were used. The dorsal and ventral displacements of humeral head and ranges of motion of abduction and rotation of glenohumeral joint before and after thermal capsulorrhaphy were performed and monitored. Changes after thermal treatment in these linear and angular displacement variables were calculated as outcome measures.

RESULTS

After anterior thermal capsulorrhaphy, significant (P < 0.001) decreases were found in displacements (-1.80 mm in dorsal direction and -1.24 mm in ventral direction), rotation range of motion (-3.93 degrees in lateral rotation and -2.60 degrees in medial rotation), and abduction range of motion (-3.15 degrees ).

CONCLUSIONS

The results from cadaveric experiments showed that anterior thermal capsulorrhaphy immediately reduced the dorsal and ventral displacements and ranges of abduction and rotation of glenohumeral joint by a small amount.

RELEVANCE

Radiofrequency electrosurgical system combined with arthroscopy has the potential to decrease the translations of the humeral head as well as the rotational range of motion of the glenohumeral joint.

Does immobilization after radiofrequency-induced shrinkage influence the biomechanical properties of collagenous tissue? An in vivo rabbit study

BACKGROUND

Despite widespread use of radiofrequency-induced shrinkage of collagenous tissue, there have been no animal studies on the effects of postoperative immobilization on the biomechanical behavior of shrunken tissue.

PURPOSE

To examine the role of postoperative immobilization after radiofrequency-induced shrinkage, with special emphasis on the biomechanical properties of shrunken collagenous tissue.

STUDY DESIGN

Controlled laboratory study.

METHODS

One patellar tendon of 66 New Zealand White rabbits was shrunk. Six rabbits were sacrificed immediately after surgery. Twenty rabbits were not immobilized, twenty were immobilized for 3 weeks, and twenty were immobilized for 6 weeks. The biomechanical parameters failure strength, stiffness, and relaxation were tested.

RESULTS

Nine weeks after surgery, biomechanical parameters were still low compared to control tendons. Shrunken tendons did not reach levels of normal tissue at any time after surgery, regardless of whether the animals had been immobilized. According to time-related development, all biomechanical parameters had the lowest levels 3 weeks after surgery. Immobilized tendons demonstrated a better and faster recovery than nonimmobilized tendons compared to the immediate postoperative level.

CONCLUSION

Postoperative immobilization supports recovery of biomechanical properties after shrinkage. Despite immobilization, biomechanical properties of shrunken tissue did not completely reach levels of normal tissue.

CLINICAL RELEVANCE

Careful rehabilitation is imperative after radiofrequency-induced shrinkage. This animal model supports an immobilization period of at least 6 weeks after surgery.

Comparative effects of monopolar radiofrequency energy and conservative management of mechanical properties of elongated lateral collateral ligament in rabbits: an experimental study

OBJECTIVE

We examined the biomechanical effects of shrinkage in elongated rabbit lateral collateral ligament.

DESIGN

This study was designed in an attempt to evaluate the energy effects of monopolar radiofrequency on strained but not ruptured ligaments.

BACKGROUND

In treatment of ligament injuries difficulty in reducing increased laxity after trauma and recurrence of instability are important factors for failure.

METHODS

Ligament elongation and laxity were achieved in operating room by applying varus stress for multiple times. In Group C ( n = 8 ), elongated lateral collateral ligaments were treated only with above-knee cast, while in Group S ( n = 8 ), they were treated with shrinkage and above-knee casts. The un-operated sides were labeled as control groups. At the 12th week after surgery the animals were sacrificed and hind limbs were disarticulated. Removing the other soft tissues around knee, only lateral collateral ligaments were left intact. Biomechanical analyses of the effects of two different treatment methods were compared by performing a pulling-out test.

RESULTS

Considering maximum load and stiffness, conservatively treated ligaments were stronger and stiffer than shrunken ligaments ( P < 0.05 ).

CONCLUSION

Biomechanical values were altered by both treatment methods. Reflecting an alteration in intra-molecular structure, the main alteration was the decrease of strength in shrunken ligaments. In ligament injuries, we concluded shrinkage not to be superior to conservative treatment.

Thermomechanical Analysis of Soft-Tissue Thermotherapy

Soft-tissue thermotherapy based on sub-ablative heating of collagenous tissues finds widespread application in medicine such as tissue welding, thermokeratoplasty, skin resurfacing, elimination of discogenic pain in the spine and treatment of joint instability. In this paper, heat-induced thermomechanical response characteristics of collagenous tissues are quantified by means of in vitro experimentation with a representative model tissue (New Zealand white rabbit patellar tendon). Three distinct heat-induced thermomechanical response regimes (defined by the rate of deformation and the variation of material properties) are identified. Arrhenius damage integral representation of collagenous tissue thermal history is shown to be adequate in establishing the master response curves for quantification of thermomechanical response for modeling purposes. The trade-off between the improved kinematical stability and compromised mechanical stability of the heated collagenous tissue is shown to be the major challenge hindering the success of subablative thermotherapies.

Altered mechanical behavior of epicardium due to isothermal heating under biaxial isotonic loads

Recent isothermal biaxial isotonic tests suggest that increasing the temperature hastens the rate of denaturation of epicardium whereas increasing the mechanical load during heating delays this process, findings that are consistent with prior uniaxial tests on tendons. Yet, contrary to uniaxial reports, a clear time-temperature-load equivalency was not found in this multiaxial setting. There is, therefore, a need to delineate multiaxial thermomechanical behavior in greater detail, and ultimately, to correlate changes therein with the underlying microstructure. Toward this end, we describe a new experimental approach for quantifying heating-induced changes in the multiaxial mechanical response of thin sheet-like specimens. Illustrative results are presented for bovine epicardium subjected to nine different thermomechanical loading protocols. Among other results, it is shown that thermal damage tends to increase the stiffness at low strains and that overall changes in extensibility correlate well with the degree of thermal damage independent of the specific thermomechanical protocol. Multiaxial changes in behavior are nevertheless complex, and there is a need for significantly more testing before constitutive relations can be formulated.

Influence of postoperative immobilization on tendon length after radiofrequency-induced shrinkage. An in vivo rabbit study

BACKGROUND

Despite the widespread use of radiofrequency-induced shrinkage of collagenous tissues, there have been no animal studies on the effects of postoperative immobilization after such treatment.

PURPOSE

To examine the effects of postoperative immobilization after radiofrequency energy treatment, with special emphasis on any tissue length increases.

STUDY DESIGN

Controlled laboratory study.

METHODS

The right patellar tendon of 60 New Zealand White rabbits was shrunk with a radiofrequency probe. Tendon length was measured intraoperatively before and after shrinkage and via radiographs immediately postoperatively and at 3, 6, and 9 weeks. Twenty rabbits were not immobilized, 20 were immobilized for 3 weeks, and 20 were immobilized for 6 weeks.

RESULTS

In the nonimmobilized limbs, the tendon length increased 34.9% at 3 weeks and another 2.5% at 6 weeks, versus 11.2% at 3 weeks and 6.6% at 6 weeks in the immobilized limbs. Ten of the 20 rabbits that were immobilized for 6 weeks were sacrificed at 9 weeks and were found to have a further length increase of 10.8%. At 9 weeks, the tendons of this group were no longer significantly shorter than the tendons from rabbits that had not been immobilized.

CONCLUSIONS

Careful postoperative rehabilitation is imperative after radiofrequency-induced shrinkage. Without protection, exposure to normal physiologic loads places the shrunken tissue at risk of stretching out beyond the preshrinkage length.

CLINICAL RELEVANCE

Shrunken tissue is at risk of stretching out after radiofrequency-induced shrinkage.

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.

Arthroscopic stabilization of anterior shoulder instability: a review of the literature

The treatment of anterior glenohumeral instability has been a topic of debate in the recent literature. Current surgical management of shoulder instability has included a variety of open and arthroscopic procedures. Open techniques for anterior reconstruction have been quite successful in preventing recurrent dislocations and continue to be the gold standard of care. In an attempt to address some of the disadvantages associated with open procedures, arthroscopic stabilization procedures have been developed. Arthroscopic capsuloligamentous repair presumably has clear advantages including better cosmesis, decreased perioperative morbidity, and a possible decrease in the loss of external rotation. Advances in arthroscopic instrumentation and improved arthroscopic techniques have increased the popularity of arthroscopic stabilization. The art of diagnosing the anatomic pathology associated with instability and proper patient selection continues to evolve. Most previous reports of arthroscopic stabilization have included small numbers of patients, variable patient pathology, and a variety of surgical techniques, making comparisons between stabilization procedures difficult. Arthroscopy can be valuable in both the confirmation of the degree and severity of the instability and to correct the pathoanatomy responsible for the instability.

Thermal treatment of anterior cruciate ligament injury and laxity with its imaging characteristics

The use of radiofrequency or laser to treat lax anterior cruciate ligaments is at its infancy. The imaging results of such treated ligaments using MRI are undocumented in the literature. This article reviews the basic science behind thermal treatment of ligaments and previously published and unpublished data on this therapy and its imaging implications.

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.