Basic Science

What is old is new again. Capsular shrinkage was used by Hippocrates 2,400 years ago to stabilize dislocated shoulders. Luckily, anesthetic techniques and thermal delivery methods have improved during the past two millennia. Recently (comparatively speaking), the biology of capsular shrinkage has been extensively studied in animal models. These studies have shown that the triple helix of collagen “unwinds” and “shrinks” when heated to 60° C, maximum shrinkage being achieved between 65 and 75° C (Figures 15.1 and 15.2). The hydrogen bonds that maintain the 3D configuration of the type I collagen triple–helix rupture as the collagen is heated beyond 60° C. The denatured collagen can potentially shorten to 50% of the resting length of the untreated collagen. The shortened denatured collagen acts as scaffolding onto which new collagen is deposited.¹ The new collagen fibers maintain this shortened conformation, thus assuring the long–term maintenance of the shortening.

FIGURE 15.1 Thermally induced unraveling of collagen triple helix.

FIGURE 15.2 Shrinkage versus RF probe temperature.

Biomechanical studies have demonstrated that the tensile strength of heated collagen decreases rapidly and does not return to normal values for 12 weeks.² The tensile strength returns to nearly 80% normal by six weeks after heating (Figure 15.3). This transient loss of tensile strength would suggest that the application of stress to recently heated collagen is contraindicated. Premature loading of the shrunk collagen will lead to a lengthening of the collagen. This has been verified in an animal model.^3,4 Based on this data, it would seem reasonable to recommend at least six to eight weeks of joint immobilization after capsular shrinkage. Clearly heavy loading of the joint should be avoided for 12 weeks.

FIGURE 15.3 Post-shrinkage tensile strength versus time.

Indications and Contraindications

Capsular shrinkage can be used to treat mild forms of carpal instability. Patients with symptomatic Geissler type I and II scapholunate and mild midcarpal instability would be considered good candidates. Greater degrees of carpal instability associated with disruption or severe attenuation of the interosseous ligaments will not respond to capsular shrinkage. Lunotriquetral instability is the manifestation of a spectrum of pathology. The following are three possible LT instability scenarios.

The first two scenarios lend themselves to capsular shrinkage because the integrity of the LT stabilizers, although compromised, is maintained. Shrinkage in the third scenario will be ineffective due to the extensive disruption of the LT stabilizers.

Technique