Sub-ablative thermal exposure is applied clinically to stabilize joints by taking advantage of the fact that such heating causes collagenous tissues to shrink. Unfortunately heating also generally causes tissue material properties to degrade, owing to the denaturation of the collagen network. The literature reveals that different modalities of heating such as laser and radio frequency modes create different amounts of shrinkage and varying levels of thermal damage (mechanical property degradation) within the target tissue. The relationship between shrinkage and denaturation is poorly understood, limiting the rational design of such thermal therapies. In the present research, a preliminary thermomechanical modeling capable of predicting the final state of a collagenous tissue undergoing sub-ablative heating is presented. The hybrid methodology utilized includes in-vitro experimentation and finite element analysis. It has been shown that the proposed methodology has excellent potential as a tool in simulating and determining the optimal responses of collagenous tissues when they are subjected to sub-ablative thermal treatments.
Heat-Assisted Capsular Shift (HACS) procedures are currently applied to treat shoulder (glenohumeral) instability. The therapy aims at thermally denaturing the collagenous framework, thus shrinking the surrounding soft tissues of the lax glenohumeral joint. The desired outcome of the therapy is restoring the kinematic stability of the joint without degrading its mechanical stability. Reports describing the outcome of HACS procedures reveal considerable variations, most likely due to utilization of different heat deposition modalities and the diversity of the thermal treatment protocols applied. The uncertainty of the outcome is also amplified by the post-heating recovery from shrinkage and the heat-induced degradation of mechanical stability. This study introduces a novel method designed to minimize the adverse effects of current therapies. A mechanical property enhancement technique in the form of an adjuvant chemical treatment is presented. In-vitro experiments performed on rabbit patellar tendons using a new arthroscopic fluid with thermal treatment indicate therapeutic improvement compared to therapies based on heating alone. A decrease in the strain recovery as large as 50% and an increase in stiffness as much as 100% have been produced in collagenous tissues without compromising strength. In summary, this work presents the initial results of an effort aimed at increasing the safety and reliability of currently applied HACS procedures by optimal manipulation of novel thermo-chemical treatments.