Clinical predictors of a positive response to guided diagnostic block into the subacromial bursa
Angela Cadogan, Mark Laslett, Wayne Hing, Peter McNair, Stephen Taylor
Objective: To compare the accuracy of combinations of clinical examination findings for predicting a positive response to injection of local anaesthetic into the subacromial bursa.
Design: Prospective, cohort, diagnostic validity design.
Subjects: Consecutive patients with shoulder pain recruited from primary care physiotherapy and general medical practices.
Methods: All subjects underwent a standardised clinical examination (index test) followed by a diagnostic injection of xylocaineTM into the subacromial bursa (reference standard test) performed under ultrasound guidance. Clinical examination variables associated with a positive anaesthetic response (≥ 80% post-injection reduction in pain intensity) were identified (p < 0.20) and diagnostic accuracy was calculated.
Results: Of the 196 subjects who received a subacromial bursa injection, 66 subjects (34%) reported a positive anaesthetic response. Strain injury (adjusted odds ratio (AOR) 2.3), anterior shoulder pain (AOR 2.3) and absence of pain with external rotation at 90º abduction (AOR 3.9) were the strongest clinical predictors of positive anaesthetic response. Clinical prediction model variables demonstrated 100% specificity (3 positive tests) but low sensitivity (maximum 40%) for a positive anaesthetic response. Combinations of 9 other clinical variables also demonstrated 100% specificity (7 or more positive tests), and improved sensitivity
(95 to 100%) for a PAR compared with clinical prediction model variables when less than two findings were present.
Conclusion: Combinations of these clinical tests may assist the clinician to differentiate subacromial pain from other shoulder conditions and guide selection of targeted pain management interventions. Additional diagnostic tests may be required when clinical criteria are not satisfied.