Accuracy of measuring tape and vertebral-level methods to determine shoulder internal rotation

Abstract

BACKGROUND: Goniometers can be used to assess shoulder ROM with reasonable accuracy, but not internal rotation. Vertebral level, as determined by the hand-behind-the-back method, is used frequently but its reproducibility is questionable. We therefore devised a new measuring tape-based method for determining vertebral level.

QUESTIONS/PURPOSES: We (1) compared the accuracy of a measuring tape-based and conventional vertebral-level method; (2) determined whether BMI affects their accuracy; and (3) devised a formula for converting distances measured using a measuring tape to vertebral levels.

PATIENTS AND METHODS: We assessed internal rotation in 61 patients with shoulder pain. An electrode was taped to the skin where the thumb reached maximally behind the back. The vertebral-level method involved determining the vertebral level of the electrode by palpating bony landmarks whereas the measuring tape method involved measuring the distance between the C7 spinous process and the electrode. True vertebral levels of the electrode were confirmed by radiography.

RESULTS: In nonobese patients, the accuracies of the upper thoracic and lumbar-level measurements were better for the measuring tape method than the vertebral-level method (r = 0.861 and 0.700, respectively in upper thoracic; 0.913 and 0.710, respectively in lumbar). Patient BMI affected the accuracy of the vertebral-level method but not that of the measuring tape method. The distances obtained using the measuring tape method could be converted into vertebral-level units using the formula: estimated vertebral level = 0.031 × [distance between C7 spinous process and thumb behind back] - 0.044 × [patient height] + 7.277.

CONCLUSIONS: The measuring tape-based method reflected shoulder internal rotation with higher accuracy than the vertebral-level method, and unlike the vertebral-level method, the measuring tape method was not affected by obesity.

LEVEL OF EVIDENCE: Level II, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.