Injuries to the posterior labrum are less common and more difficult to diagnose compared to anterior labral pathology. This may be in part due to difficulties in preoperative diagnosis. Posterior labral injuries cause abnormal loading of the rotator cuff with subsequent weakness. Examination using the Modified O’Briens test tightens the posterior capsule and posteriorly translates the humeral head, stressing the labrum resulting in pain and weakness. A retrospective case controlled study of 74 patients diagnosed with a posterior labral tear at arthroscopy showed 55 to have subjective weakness on performing a Modified O’Briens test, a sensitivity of 83% and a positive predictive value of 90%. At present there is no single test diagnostic of posterior labral pathology. They can often be missed on MRI scanning and also at surgery if not specifically looked for. We believe that clinically demonstrated weakness on performing a Modified O’Briens test is sensitive, with a high positive predictive value for posterior labral pathology and can help guide further treatment.

1. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
Lennard Funk
Matt Owen
Thomas Boulter
Tanya Mackenzie
1

2. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
POSTERIOR INSTABILITY
2
• Posterior instability is a relatively rare condition in the shoulder
!
• Of all shoulder instabilities approximately 88-98% are anterior
instabilities
!
• Posterior instability can often be overlooked or missed
!
!
!
!
!
!

3. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
Lesions
3
ABER Tackle Direct Impact
Neurological Lesion 32% 15%
Soft tissue Bankart 79% 33%
Bony Bankart 26% 11%
Posterior Labral Tear 11% 50%
SLAP 7% 35%
Partial Cuff Tear 32% 12%
Collision shoulder injuries
Malone, Funk, Mohammed, Ball. Shoulder injury patterns in Rugby - the Collision Shoulder.
JBJS (Suppl). 2008.

4. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
4

5. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
5

6. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
TRADITIONAL TESTS
6
Specificity Sensitivity Notes Reference
Posterior
Drawer Test
No data
Load & Shift 100% 14% For Laxity Gerber &
Ganz. JBJSB.
1984
Posterior
Apprehensio
n
99% 20% Jia et al.
JBJSA. 2009
Jerk Test 85% 90% posteroinf.
labral tear
Kim et al.
AJSM. 2004
Kim Test 95% 80% posteroinf.
labral tear
Kim et al.
CORR. 1993

7. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
7
• The Jerk Test has only been shown to be selective
in detecting a postero-inferior labral lesion
!
!
• None of the others have been shown to have good
clinical diagnostic value

8. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
MODIFIED O’BRIEN’S TEST (MOB)
WRIGHTINGTON POSTERIOR INSTABILITY TEST (WPIT)
8

9. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
• Conducted in a similar manner to that initially described by
O’Brien
• Patient asked to forward flex the affected arm 90° with the
elbow in full extension.
• Adduct the arm fully, medial to the sagittal plane of the body.
• Internally rotate so that the thumb points downward.
• The examiner then applies a downward force to the arm being
resisted by the patient.
• The test is considered positive with objective weakness
observed by the examiner when downward force on the arm
resulted in loss of forward flexion from 90°.
9
MODIFIED O’BRIEN’S TEST (MOB)
WRIGHTINGTON POSTERIOR INSTABILITY TEST (WPIT)

10. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
10

11. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
MECHANISM:
11
MODIFIED O’BRIEN’S TEST (MOB)
WRIGHTINGTON POSTERIOR INSTABILITY TEST (WPIT)

12. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
AIMS
12
!
• How sensitive and specific is the new MOB test at correctly
diagnosing posterior instability?
!
• How does the new MOB test compare to the tests already
available?

13. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
METHODS
13
• Retrospective study
!
• 74 patients seen over a 3 year period with traumatic
instability
!
• All clinical tests recorded.
!
• The imaging and surgical findings were then recorded
and compared to the MOB test findings
!
• Patients with surgical findings consistent with a diagnosis
of posterior instability (according to the lesions previously
mentioned) and a positive MOB test formed the true
positive group and vice versa

14. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
RESULTS
• Included All arthroscopic stabilisations, incl. anterior
• n = 74
14
Post lesion
present
Post lesion
absent
MOB +ve 55 6 PPV 90%
MOB -ve 11 2 NPV 15%
Sensitivity
83%
Specificity
25%
N=74
Owen, Mackenzie, Boulter, Funk, 2014

15. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
DISCUSSION
15
• High sensitivity and PPV values shows that the test is
accurate at detecting the presence of posterior instability
!
• Unlikely to have a missed diagnosis, high confidence
in your diagnosis.
!
• Low specificity and NPV values however mean that the
test is unreliable in patients with no posterior instability
!
• Benefit is in conjunction with tests with high specificity
(i.e. Posterior Apprehension test)
!

16. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
POSTERIOR INSTABILITY TESTS
16
Specificity Sensitivity Notes Reference
Posterior
Drawer Test
No data
Load & Shift 100% 14% For Laxity Gerber &
Ganz. JBJSB.
1984
Posterior
Apprehension
99% 20% Jia et al.
JBJSA. 2009
Jerk Test 85% 90% posteroinf.
labral tear
Kim et al.
AJSM. 2004
Kim Test 95% 80% posteroinf.
labral tear
Kim et al.
CORR. 1993
MOB/WPIT 25% 83% Muscular
Athletes

17. AMSTERDAM / THE NETHERLANDS
www.esska-congress.org
CONCLUSIONS
17
MOB test has promise
!
MOB test could be used to help confirm a diagnosis of
posterior instability and better guide management from
there
!
This could mean that this test in combination with more
specific tests could be considered as a effective method of
diagnosing posterior instability clinically
!
!