Original article
The Validity of the Lag Signs in Diagnosing Full-Thickness Tears of the Rotator Cuff: A Preliminary Investigation

Presented to the International Conference on Movement Dysfunction, September 25, 2005, Edinburgh, United Kingdom.
https://doi.org/10.1016/j.apmr.2007.10.046Get rights and content

Abstract

Miller CA, Forrester GA, Lewis JS. The validity of the lag signs in diagnosing full-thickness tears of the rotator cuff: a preliminary investigation.

Objective

To investigate whether the lag signs were valid tools in diagnosing full-thickness tears of the rotator cuff.

Design

A same-subject, correlation, double-blinded design was used. The results of the external rotation lag sign, drop sign, and internal rotation lag sign were compared with the criterion standard of diagnostic ultrasound to establish their accuracy.

Setting

A regional orthopedic hospital.

Participants

Consecutive subjects (N=37), 21 women and 16 men, with shoulder pain referred to a consultant orthopedic surgeon specializing in shoulder conditions were recruited for this investigation.

Interventions

Not applicable.

Main Outcome Measures

Sensitivity, specificity, and positive and negative likelihood ratios of the lag signs when using ultrasound as the reference test.

Results

The specificities of the drop sign and internal rotation lag sign were 77% and 84%, respectively, which, together with low positive likelihood ratios 3.2 (95% confidence interval [CI], 1.5–6.7) and 6.2 (95% CI, 1.9–12.0), indicate that a positive result was poor at recognizing the presence of full-thickness tears. The drop sign had a sensitivity of 73% with a negative likelihood ratio of .34 (95% CI, 0.2–0.8), suggesting that a negative test was fair at ruling out the presence of full-thickness tears. The sensitivity of the internal rotation lag sign (100%) supported by the negative likelihood ratio of 0 (95% CI, 0.0–2.5) suggests that a negative test will effectively rule out the presence of full-thickness tears of the subscapularis. A positive external rotation lag sign is the clinical test most likely to indicate that full-thickness tears of the supraspinatus and infraspinatus are present (specificity, 94%). However, the external rotation lag sign did demonstrate a low sensitivity score of 46% and negative likelihood ratio of .57 (95% CI, 0.4–0.9), which means that a negative test will not rule out the presence of full-thickness tears.

Conclusions

The findings of this investigation suggest that a clinical diagnosis of a full-thickness tear of the rotator cuff cannot be conclusively reached using one or more of the lag signs.

Section snippets

Study Design

A same-subject, correlational, double-blinded design was used in this study. Ethics approval was obtained from Coventry University and South Birmingham Ethics Committee before commencing the study. Subjects were informed of their rights, including the right to withdraw from the investigation at any stage without providing an explanation.

Study Sample

Thirty-seven subjects with shoulder pain referred to a consultant orthopedic surgeon specializing in shoulder conditions were recruited for this investigation.

Results

The final patient group recruited for the study was composed of 37 patients, 16 men and 21 women. The average patient age was 55.5 years (range, 20–86y), and the average length of time since onset of shoulder pain was 37.5 months (range, 4–120mo). Nine subjects presented with bilateral shoulder pain. Therefore, results from 46 symptomatic shoulders were analyzed. Fifteen of 46 of the shoulders assessed had a full-thickness tear on ultrasound, giving a symptomatic prevalence rate of 33%. Only 6%

Discussion

With the specificity of 94% for the external rotation lag sign, clinicians should have some confidence in interpreting a positive result as indicating the presence of full-thickness tears of both the supraspinatus and infraspinatus. This finding is supported by the positive likelihood ratio of 7.2 (95% CI, 1.7–31.0), which suggests a moderate increase in the likely presence of full-thickness tears.25 However, the poor lower end of the 95% CI together with the width of the CI strongly suggests

Conclusions

Diagnostic ultrasound has been shown to have a detection rate of full-thickness tears of the rotator cuff comparable to that of arthroscopy, which is considered to be the criterion standard reference test. In addition, ultrasound has the advantage of allowing a comparison of the clinical findings in a blinded manner, which for ethical and pragmatic reasons is not possible when clinical findings are compared with arthroscopy. Another benefit of ultrasound is that is allows a bilateral

Acknowledgments

We thank Marcus Green, MD, and Gina Allen, MD, for their assistance with this research. Thanks also to Catherine Elliott, MSc, MCSP, for her support.

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