Distances to the subacromial bursa from 3 different injection sites as measured arthroscopically

The purpose of this study was to assess the distance for a standard needle to reach the subacromial bursa through 3 commonly used approaches.

Thirty patients without associated rotator cuff tears underwent arthroscopic evaluation of the shoulder. The bursa was entered without shaving or altering of the bursa. By use of standard arthroscopic portals, a spinal needle was inserted from an anterior, lateral, and posterior position and measured to define the distance to the subacromial bursa from the skin.

The mean distance with anterior needle placement was 2.9 +/- 0.6 cm. The mean distance with lateral needle placement was 2.9 +/- 0.7 cm. The mean distance with posterior needle placement was 5.2 +/- 1.1 cm. The mean body mass index for the group of patients was 27.5. The minimum was 18.7, and the maximum was 42.8.

The distance to the subacromial bursa from the anterior and lateral approaches appears to be consistent and within reach of a standard 22- or 25-gauge needle. The distance to the subacromial bursa from a posterior approach appears to be almost double that of the anterior and lateral approaches and may not be reachable by standard 22- and 25-gauge needles in all patients. There appears to be no correlation between distances to the subacromial bursa from the anterior, lateral, or posterior approaches and the patient's body mass index.

Given the relative distances measured to the subacromial bursa from the anterior, lateral, and posterior positions, clinicians may choose a longer needle to improve the accuracy of placement when approaching the subacromial bursa from a posterior position. Use of a standard-length needle will provide reasonable accuracy from the anterior and lateral positions.