The effects of thermal capsulorrhaphy and rotator interval closure on multidirectional laxity in the glenohumeral joint: a cadaveric biomechanical study.

PURPOSE: Arthroscopic rotator interval closure has been advocated to supplement the stabilization provided by thermal capsulorrhaphy for glenohumeral instability. However, no basic science study has examined the separate and combined effects of thermal capsulorrhaphy and rotator interval closure on the multiplane laxity of the glenohumeral joint. The purpose of this study was to measure the effects of isolated and combined thermal capsulorrhaphy and rotator interval closure on anterior, posterior, and inferior glenohumeral joint laxity in a cadaveric model.

TYPE OF STUDY: Anatomic biomechanical study.

METHODS: Ten cadaveric shoulders were fixed to a biomechanical testing apparatus and 5.5 lb (25 N) of force was applied to the humeral head in anterior, posterior, and inferior directions in a random order. Translation was measured in each direction on the untreated specimen (U), after arthroscopic rotator interval closure (R), after thermal capsulorrhaphy (T), and after combined rotator interval closure and thermal capsulorrhaphy (RT) with a transducer attached to a computer via data acquisition software and A/D board. Values for anterior, posterior, and inferior translation were thus obtained for U, R, T, and RT.

RESULTS: Average translations in the anterior direction for the U, R, T, and RT groups were 8.0 +/- 4.4 mm, 6.7 +/- 3.3 mm, 8.5 +/- 3.6 mm, and 7.8 +/- 2.2 mm, respectively. Average translations in the posterior direction were 6.9 +/- 3.3 mm (U), 5.9 +/- 3.4 mm (R), 7.9 +/- 4.7 mm (T), and 6.8 +/- 4.0 mm (RT). Average translations in the inferior plane were 4.9 +/- 4.7 mm (U), 3.6 +/- 3.7 mm (R), 3.7 +/- 3.3 mm (T), and 2.4 +/- 1.6 mm (RT). Rotator interval closure decreased anterior, posterior, and inferior translation by 17%, 15%, and 28%, respectively, versus the untreated subjects. Thermal capsulorrhaphy increased anterior and posterior translation by 5% and 13% and decreased inferior translation by 25% versus untreated subjects. Combined RT decreased anterior, posterior, and inferior translation by 4%, 2%, and 52%, respectively. Statistical analysis revealed that rotator interval closure significantly decreased laxity values in all planes, whereas thermal capsulorrhaphy did not significantly alter laxity values versus untreated subjects.

CONCLUSIONS: Isolated rotator interval closure decreased glenohumeral laxity in all directions tested, particularly inferior translation. Thermal capsulorrhaphy actually increased anterior and posterior translation in these subjects while decreasing inferior translation. We believe the trends seen reflect the clinical efficacy of rotator interval closure in the treatment of multidirectional instability. This procedure has the potential to provide improved stability versus thermal capsulorrhaphy alone, and may be considered as a supplement to or substitute for thermal capsulorrhaphy in patients with multidirectional instability.

CLINICAL RELEVANCE: When treating glenohumeral instability with arthroscopic techniques, rotator interval closure may enhance stability to a greater degree than thermal capsulorrhaphy without its associated risks.