The effect of the inferior capsular shift on shoulder intra-articular pressure: a cadaveric study.
BACKGROUND
The inferior capsular shift procedure is commonly performed for multidirectional instability of the shoulder with excellent clinical results.


OBJECTIVE
The mechanism of this procedure is to increase shoulder stability by changing the responsiveness of intra-articular pressure to downward loading.


METHODS
Controlled laboratory study.


METHODS
In 7 fresh-frozen cadaveric shoulders, inferior capsular shift was simulated by imbricating the anterior and posterior capsule using clamps. The position was monitored using an electromagnetic tracking device with the glenohumeral joint capsule intact, imbricated anteriorly, or imbricated anteriorly and posteriorly and with the inferior load of 0, 0.5, or 1.0 kg. Simultaneously, intra-articular pressure was monitored using a pressure transducer. Saline was injected into the glenohumeral joint to measure capsular volume. The capsule was vented, and the position was again measured.


RESULTS
Intra-articular pressure was -71 +/- 19, -221 +/- 70, and -366 +/- 73 cm H(2)O with 0, 0.5, and 1.0 kg of load, respectively, with the capsule intact. With anterior imbrication, intra-articular pressure decreased to -79 +/- 10, -274 +/- 103, and -460 +/- 135 cm H(2)O, respectively, and with anterior and posterior imbrication, intra-articular pressure further decreased to -87 +/- 16, -308 +/- 74, and -548 +/- 39 cm H(2)O, respectively. The volume of the intact shoulder (36 +/- 9 mL) significantly decreased to 27 +/- 7 mL (75%) with anterior imbrication and to 15 +/- 5 mL (42%) with anterior and posterior imbrications (P = .0001). Before venting the capsule, inferior displacement was 5% of the vertical length of the glenoid, even with 1.0 kg of load with any capsular conditions. After venting, the humeral head dislocated inferiorly in all shoulders, even after imbrications.


CONCLUSIONS
The inferior capsular shift procedure decreases joint volume and increases responsiveness of intra-articular pressure to downward loading.


CONCLUSIONS
Biomechanical data provide scientific background to the commonly performed procedures of inferior capsular shift and thermal capsular shrinkage.
Yamamoto
Nobuyuki
N
Division of Orthopedic Surgery, Department of Neuro and Locomotor Science, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan.
Itoi
Eiji
E
Tuoheti
Yilihamu
Y
Seki
Nobutoshi
N
Abe
Hidekazu
H
Minagawa
Hiroshi
H
Shimada
Yoichi
Y
Okada
Kyoji
K
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D006811:Humerus / Q000502:physiology; D007593:Joint Instability / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011312:Pressure; D012785:Shoulder Joint / Q000502:physiology* / Q000601:surgery