5% did not improve and declined further treatment.Of the 413 patients who improved, 74 had a recurrence of symptoms during the observation period and their symptoms responded to rest or after resumption of the exercise program.The Morrison study shows that the outcome of impingement symptoms varies with patient characteristics. Younger patients (20 years or less) and patients between 41 and 60 years of age, fared better than those who were in the 21 to 40 years age group. This may be related to the peak incidence of work, job requirements, sports and hobby related activities, that may place greater demands on the shoulder. However, patients who were older than sixty years of age had the "poorest results". It is known that the rotator cuff and adjacent structures undergo degenerative changes with ageing.The authors were unable to posit an explanation for the observation of the bimodal distribution of satisfactory results with regard to age. They concluded that it was "unclear why (those) who were twenty-one to forty years old had less satisfactory results". The poorer outcome for patients over 60 years old was thought to be potentially related to "undiagnosed full-thickness tears of the rotator cuff". References
Anderson, D., M, (2000), Dorland’s Illustrated Medical Dictionary, 29th ed, W.B. Saunders Company, Canada, 965-967. Buschbacher, R., M, Braddom, R., L. (1994). Sports medicine & rehabilitation: A sport-specific approach. Hanley and Belfus Inc, Philadelphia. Hartley, A. (1990). Practical joint assessment: A sports medicine manual, St Louis, Sydney. Further reading
Arend CF. Ultrasound of the Shoulder. Master Medical Books, 2013.
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van Holsbeeck M, Strouse PJ (1993). "Sonography of the shoulder: evaluation of the subacromial-subdeltoid bursa". AJR Am J Roentgenol. 160 (3): 561–4. doi:10.2214/ajr.160.3.8430553. PMID 8430553. Yanagisawa K, Hamada K, Gotoh M,  et al. (2001). "Vascular endothelial growth factor (VEGF) expression in the subacromial bursa is increased in patients with impingement syndrome". J. Orthop. Res. 19 (3): 448–55. doi:10.1016/S0736-0266(00)90021-4. PMID 11398859. S2CID 20098903.