Impingement / Instability Differentiation

Original Editor - Andrew Bucknor and Kevin McLaughlin as part of the Temple University EBP Project

Top Contributors - Kevin McLaughlin, Admin, Andrew Bucknor, Rachael Lowe, Kim Jackson, Scott A Burns, Alicia Fernandes, WikiSysop, Wanda van Niekerk and 127.0.0.1  

Introduction

The differentiation between shoulder impingement and instability refers to the process of distinguishing between these two conditions based on their symptoms, physical examination findings, and diagnostic tests. Both conditions affect the shoulder but have different underlying causes, presentations, and treatment approaches.

Purpose

The purpose of this article is to help healthcare providers differentiate between shoulder impingement and instability by utilizing the most current literature.

Shoulder Impingement

• Definition: Shoulder impingement occurs when the tendons of the rotator cuff muscles are compressed or "impinged" between the bones of the shoulder joint, particularly under the acromion .
• Symptoms: Pain when lifting the arm, especially overhead; pain that worsens at night; limited range of motion; weakness in the shoulder .
• Diagnosis: Diagnosed through special tests such as the Hawkins-Kennedy, Neer, and Painful Arc tests, which assess pain and range of motion  .
• Cause: Compression of tendons and soft tissues .

Shoulder Instability

• Definition: Shoulder instability occurs when the shoulder joint is loose and slides around too much in the socket, which can lead to partial or complete dislocation .
• Types: Instability can be anterior (front), posterior (back), or multidirectional .
• Symptoms: Sensation of the shoulder slipping out of place, pain during specific movements, recurrent dislocations, weakness, and a feeling of looseness in the shoulder .
• Diagnosis: Diagnosed through special tests such as the Apprehension Test, Relocation Test, and Anterior Drawer Test, which assess the stability and integrity of the shoulder joint  .
• Cause:  Excessive movement and lack of stability in the joint .

Impingement

Individual special tests for sub-acromial impingement have varying psychometric properties. For this reason, it is best to utilize special test clusters in order to diagnose this injury. Two special test clusters are provided below that can be used in order to diagnose sub-acromial impingement.

	Sensitivity	Specificity	Accuracy%	PPV%	NPV%
Hawkins-Kennedy	.92	.25	72.8	75.2	56.2
Neers	.89	.31	72.0	75.9	52.3
Horizontal-adduction	.82	.28	66.4	73.7	38.4
Speed	.69	.56	64.8	79.2	41.6
Yergason	.37	.86	51.2	86.8	35.6
Painful arc	.33	.81	46.4	80.5	32.5
Drop arm	.08	.97	33.6	87.5	29.9

A total of 5 positive special tests is indicative for subacromial impingement.

Positive tests	Sensitivity	Specificity	Accuracy%	PPV%	NPV%
All positive	.04	.97	31.2	80.0	29.1
≥6 positive	.30	.89	47.2	87.0	34.0
≥5 positive	.38	.86	52.0	87.1	36.0
≥4 positive	.70	.67	68.8	83.7	47.0
≥3 positive	.84	.44	72.8	72.8	44.4

Accuracy: The percentage of time that the result of the test reflects the true nature of the condition

A second cluster utilizes a slightly different set of special tests.

	Sensitivity	Specificity	Positive LR	Negative LR
Hawkins-Kennedy	.63	.62	1.63	.61
Neers	.81	.54	1.17	.35
Painful arc	.75	.67	2.25	.38
Empty can	.50	.87	3.90	.57
External rotation resistance	.56	.87	4.39	.50

Any combination of 3 or more positive tests are indicative of sub-acromial impingement

	Sensitivity	Specificity	Positive LR	Negative LR
3+ positive tests	.75	.74	2.93	.34

Instability

Test	Sensitivity	Specificity	+LR	-LR
Apprehension test	.72	.96	20.2	.29
Relocation test	.81	.92	10.4	.20
Anterior drawer test	.53	.85	3.57	.56

Instability can be categorized in a few different ways, including anterior, posterior and multidirectional instability. The 3 tests above focus on the diagnosis for anterior shoulder instability.

Positive tests	Sensitivity	Specificity	+LR	-LR
Apprehension, relocation and anterior drawer tests	.48	.99	39.1	.52
Apprehension and relocation tests	.81	.98	39.7	.19
Relocation and anterior drawer tests	.48	.96	18.0	.54
Apprehension and anterior drawer tests	.46	.98	23.1	.55

The above table represents a cluster to help rule in favor of an anterior shoulder instability diagnosis. With positive results of any 2 tests or more, you can be fairly confident ruling in favor of anterior shoulder instability. It should be noted that the apprehension test is only positive in the presence of apprehension and the relocation test is considered positive with the relief of apprehension. In addition, the anterior drawer test is positive when symptoms of instability are reproduced.

The tests below are additional diagnostic tests for instability which may assist you in your examination, however they are not a part of the above mentioned cluster.

	Sensitivity	Specificity	+LR	-LR
Anterior release test	.92	.89	8.6	.09

	Sensitivity	Specificity	+LR	-LR
Sulcus Sign	.17	.93	2.43	.89

+LR: describes how much the odds of impingement increase with a positive test
-LR: describes how much the odds of impingement decrease with a negative test