Capsular Shrinkage and Arthroscopy
Abstract & Commentary
Synopsis: Capsular shrinkage involves new technologies (laser, bipolar, monopolar) for the treatment of overhead throwing athletes. Early clinical results are limited but encouraging.
Source: Anderson K, et al. Thermal capsulorrhaphy: Where are we today? Sports Medicine and Arthroscopy Review 2000;7(2):117-127.
Although an explosion of arthroscopic procedures about the shoulder has occurred in the past 10 years, none is as controversial or as promising as thermal capsulorrhaphy (capsular shrinkage of collagen). Anderson and colleagues review the literature surrounding this new procedure, examining the energy types, commercial claims, and clinical results. Anderson et al note the well-described problem of shoulder instability in the throwing athlete: open procedures adequately stabilize the joint with a functionally limiting decrease in motion, whereas arthroscopic procedures, despite their motion preservation, have significantly higher failure rates. Anderson et al note these failures may result from neglect of the capsular laxity, hence the use of thermal shrinkage in arthroscopic management.
Three types of energy are currently used to create heat and resultant collagen or tissue shrinkage. The earliest use was that of laser and most commonly now the Ho:YAG laser, which involves an intense beam of light. Hydrated collagenous tissue absorbs this light, in turn heating the tissue and producing shrinkage. Radiofrequency probes work by producing electromagnetic energy and creating molecular oscillation and tissue heating. Monopolar radiofrequency (Oratec) creates an alternating current, which, when meeting a higher resistance (capsular tissue), creates heat. Bipolar radiofrequency (Arthrotec, Mitek) devices create a conduction arc through the arthroscopic fluid (saline) instead of through the tissue in producing heat and resultant shrinkage.
Optimal temperatures for the effect on collagenous tissues have been studied with a heated saline water bath model. The optimal temperature has been shown to be 67°, which produces a shrinkage of 15%. Higher temperatures lead to increased shrinkage (shortening), but there is increased loss of mechanical properties. The mechanism of tissue shortening has been shown to be ultrastructural collagen fibril alteration, thought to be due to the unwinding of the triple helix with maintenance of the intermolecular crosslinks. Depth of penetration is dependent upon the device, with the Ho:YAG laser creating an average depth of 1.12 mm (± 0.23 mm). Monopolar radiofrequency produces a depth of 4.75 mm (± 1.25 mm), with bipolar devices creating a depth of penetration between 0.55 mm and 1 mm.
Anderson et al note that long-term clinical studies have not yet been performed and the potential for stretching or failure of shrinkage is present. However, they note that early clinical results in the overhead athlete without gross multidirectional instability (MDI) are positive and future work will center around evaluating the maintenance of these results. Risks of heat injury to the axillary nerve and brachial plexus require careful application of this technology to the patient.
Comment by Robert C. Schenck, Jr., MD
This review is timely and useful for the practicing sports medicine specialist. Shrinkage despite its detractors has had great acceptance by the patient. Interestingly, in my experience, patients readily accept the increased failure rate of arthroscopic repairs in order to avoid open shoulder surgery. Clearly, application of radiofrequency technology requires careful patient selection and education. Patient education of the options and a clear explanation of surgical risks allow an informed and safe application of this increasingly popular technique of shoulder thermal capsulorrhaphy.
Capsular shrinkage about the shoulder is best defined ultrastructurally by:
a. collagen transition to an amorphous gel.
b. unwinding of the collagen triple helix.
c. disruption of intermolecular crosslinks.
d. reversal of the collagenous semicrystalline state.
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