THE SHOULDER ANTERIOR JERK TEST - A NEW C LINICAL EXAMINATION TEST FOR SHOULDER ANTERIOR INSTABILITY - PRELIMINARY-REPORT

1) Purpose of study: A new clinical test named ''The shoulder anterior jerk test'' is proposed to confirm the diagnosis of chronic shoulder anterior instability. 2) Material: The test combines of a compression force and a translation force, applied along the arm between the humer al head and the glenoid cavity. In so doing, a subluxation of the hume ral head is provoked and it is accompagnied with a jerk recognised by the patient as his instability. 3) Methods: Three different population s 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. Popul ation B: 100 patients without any problem at the shoulder, had been te sted before and under anesthesia done for knee or hip surgery. Populat ion C: 100 young sportive athletes with normal shoulder tested without anesthesia. 4) Results: Population A: The 28 patients suffering from shoulder instability had all a positive shoulder jerk test under anest hesia. Without anesthesia the test had been positive only in 10 cases (30 per cent). The jerk is potentially present for all the patients, b ut it is disturbed by apprehension. Population B: Among the 200 should ers tested, 26 shoulders 17 patients) had a positive test under anesth esia (13 per cent). 5 had positive jerk test without anesthesia. Popul ation C: 5 among the 200 shoulders tested had a positive jerk (2.5 per cent) Under anesthesia the test has a sensitivity of 100 per cent, a specificity of 97.5 per cent, a positive predictive value of 55 per ce nt 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 po sitive predictive value of 66 per cent and a negative predictive value of 90 per cent. 5) Discussion: 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 glenoid cavity. It reproduct s, with a minimal amplitude, the clinical instability which is recogni zed by the patient. The test is always positive under anesthesia in ca se of chronic anterior instability, it may confirm pre-operative diagn osis just before the begining of the procedure and may orientate the c hoice of it. Apprehension is a major obstacle to the research of the j erk, but it is the same with the other classical clinical tests of the shoulder anterior instability. 6) Conclusion: 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 effici ency and will confirm if the test may differenciate antability. The fu ture will permit to confirm its efficiency and will confirm if the tes t may differenciate anterior and inferior instability with variation o f the abduction, as it has been shown in this preliminary study.