[Dynamic anterior jerk of the shoulder. A new clinical test for shoulder instability. Preliminary study]

A new clinical test named "The shoulder anterior jerk test" is proposed to confirm the diagnosis of chronic shoulder anterior instability.

The test combines of a compression force and a translation force, applied along the arm between the humeral head and the glenoid cavity. In so doing, a subluxation of the humeral head is provoked and it is accompanied with a jerk recognised by the patient as his instability.

Three different populations of patients had been studied: Population A: 28 patients operated on for chronic anterior dislocation, uni or bilateral (32 shoulders), had been tested before the operation, without and under anesthesia. Population B: 100 patients without any problem at the shoulder, had been tested before and under anesthesia done for knee or hip surgery. Population C: 100 young sportive athletes with normal shoulder tested without anesthesia.

Population A: The 28 patients suffering from shoulder instability had all a positive shoulder jerk test under anesthesia. Without anesthesia the test had been positive only in 10 cases (30 per cent). The jerk is potentially present for all the patients, but it is disturbed by apprehension. Population B: Among the 200 shoulders tested, 26 shoulders (17 patients) had a positive test under anesthesia (13 per cent). 5 had positive jerk test without anesthesia. Population C: 5 among the 200 shoulders tested had a positive jerk test (2.5 per cent) Under anesthesia the test has a sensitivity of 100 per cent, a specificity of 87 per cent, a positive predictive value of 55 per cent and a negative value of 100 per cent. Without anesthesia, the test has a sensitivity of 31 per cent, a specificity of 97.5 per cent, a positive predictive value of 66 per cent and a negative predictive value of 90 per cent.

The instability which is shown by the jerk test is in relation with the anterior subluxation of the humeral head in front of the anterior edge of the glenoïd cavity. It reproducts, with a minimal amplitude, the clinical instability which is recognized by the patient. The test is always positive under anesthesia in case of chronic anterior instability, it may confirm pre-operative diagnosis just before the begining of the procedure and may orientate the choice of it. Apprehension is a major obstacle to the research of the jerk, but it is the same with the other classical clinical tests of the shoulder anterior instability.

The anterior jerk test of the shoulder is thus a test which is able to prove the diagnosis of an anterior instability. The future will permit to confirm its efficiency and will confirm if the test may differenciate anterior and inferior instability with variation of the abduction, as it has been shown in this preliminary study.