The most important findings of this study are that dual rotator cuff PRP injection is safe and produces consistently beneficial results in patients with partial rotator cuff tears that have failed conservative treatment The results continued to show benefits at two years after the initial injection. None of the treated patients presented with an increase in symptoms that would indicate progression of rotator cuff pathology from partial to full thickness tear. This is the first study to show sustained improvement out to two years post injection. It is the first to report dual injection of the rotator cuff. In our opinion, this study helps establish PRP injection as the preferred treatment for partial rotator cuff tears that fail activity modification and physical therapy. Adverse events are essentially unknown and we saw none beyond short-term pain immediately after injection. The only impediment to care is that the patients must pay for the procedure since it is not reimbursed by commercial insurance, although some worker’s compensation boards will authorize payment.
Although this study did not use a control group, all patients failed initial conservative treatment including activity modification and physical therapy before being enrolled in this study. Although conservative treatment continued after treatment with PRP, because of this earlier failure to improve, the patients worked as their own control group. We feel that we can say with a good degree of confidence that the improvement seen after the PRP injection was related to the injection and not to the conservative treatment.
A weakness of the study is the use of global improvement scores to help determine improvement of patients after treatment. This score is self-reported by patients and due to the extended follow-up time, may be subject to some recall bias by patients. We have backed up these scores with the standardized VAS and Q-DASH scores, which demonstrate results that parallel the global improvement scores. Clinically, we have found the global improvement score to be a very simple yet useful measure to track patient improvement or lack of improvement to treatment.
An additional weakness of this study is that some of the patients received 1 or 2 additional PRP injections after the initial pair. PRP was only repeated in patients who were already showing improvement from the treatment but who desired a stronger improvement. Patients who had no improvement from the initial treatment were not injected a second time. So though repeat injection may have affected the duration or degree of improvement, it did not affect whether or not a patient had a positive response to treatment. Because of this, we felt that these patients should remain included in the study. The other major finding of our study was that the injections performed best in the more structurally damaged tendons. Severe partial tears, which we worried might not benefit, did quite well overall and had the best results of any group. Less severe partial tears also did well, as did full thickness tears. Treatment of these groups, all of which had significant structural damage to the tendon, produced results that were not significantly different from each other.
However, although patients who had inflammation with minimal or no structural damage had overall benefits, they were statistically significantly less than the patients with torn tendons. This was an unexpected result, as we expected the best results in the least damaged tendons. We cannot fully explain this finding. It may be that these tendinitis patients had pain from some source other than the rotator cuff: although none had frozen shoulder, significant arthrosis, AC joint inflammation or significant labral pathology. We think it is more likely that such patients simply have enhanced sensitivity to shoulder use. This would render them symptomatic at an earlier stage of tendon wear, and also less likely to benefit from treatment. This also parallels the finding that patients with more normal pre-operative radiographs do less well after joint replacement than patients with worse pathology. [32,33,34]
It is interesting also that the percentage of significantly improved patients were steady or improved in the > 50 % tear and full thickness tear group at 2 year follow-up, decreased a little in the < 50 % tear group and decreased more in the tendinitis group. This strengthens the relationship between structural damage and beneficial PRP effect. The < 50 % group may be a mix of significant structural damage and high signal inflammation whose results were in fact intermediate between the definitely significantly damaged > 50 % partial tear and full thickness tear groups excellent results on the one hand, and the non-structurally damaged tendinitis group’s less good results on the other. Interestingly, within the tendinitis cohort there was a significant decrease in the number of patients as a percentage of the total cohort who showed improvement from the one to two year follow-up times. However, the mean improvement went up substantially. Thus, the cohort bifurcated between a subgroup with excellent improvement from the first to the second year and a group which did not improve.
The tendinitis subgroup was also significantly younger in age, suggesting that the lower scores in the tendinitis group could be partially due to decreased age. However, since patients with tendinitis made up the majority (73 %) of patients in the youngest age group of < 35 years old, it is impossible to differentiate the effects of age from pathology.
It is also fortunate that the PRP performed best in the definitely structurally affected tendons since most of these patients (at least in the United States) would have progressed on to surgery if the PRP had not been successful. Surgery was thus successfully avoided in the patients who were most at risk to have surgery recommended, had the PRP treatment not been offered. This is also gratifying since surgery for partial tears is generally unreliable with a relatively high failure rate [3, 4, 6, 7]. The PRP patients were thus not only spared the risks of surgery, but spared the significant likelihood of an unsatisfactory surgical result.
The third finding of this study is that based on symptoms, patients did not appear to have progression of partial thickness to full thickness rotator cuff tears. This finding would have been strengthened by the performance of post-treatment MRI, which was not done. However, worsening symptoms is a strong indicator of worsening pathology. Although not all patients improved with treatment, none showed a strong worsening of symptoms that would be an indication of transition from partial to full-thickness rotator cuff tear. A followup study that included post-treatment MRI is recommended to verify this initial impression.
Our two year follow-up is the longest yet reported for PRP for rotator cuff pathology. Our results showing improvement are consistent with other studies, [12,13,14, 16,17,18, 20,21,22,23]. The next longest follow-up was reported by Mautner  who found 81 % of patients were improved significantly at an average of 15 months. Importantly, we found that results overall continued to improve from the one to the two year mark for both Q-DASH and VAS and were unchanged for the subjective global improvement rating. This finding makes it likely that the good two year results found are probably unlikely to deteriorate at even longer follow up.
Rotator cuff disease in patients without full-thickness tears is mainly a disease based on symptoms. In a study by Miniaci  MRI was performed on 30 shoulders of young volunteers (ages 17 to 49) who had no shoulder symptoms and no known abnormalities. None of the shoulders were rated as normal with all rated at least some signal and 23 % rated has having high grade changes. Based on this study, clinical symptoms, not MRI changes are the determining factor in diagnosing rotator cuff disease. From this point of view, PRP is not just palliative but in some measure potentially “curative” for rotator cuff disease. The fact that tendinous tissue is capable of healing and regenerating makes this possibility all the more possible. We wish to emphasize however, that we did not obtain routine post treatment MRI scans to evaluate this possibility since there was no clinical reason to obtain them except in isolated cases.
We wish to express that we believe very strongly that the management of the rotator cuff injured shoulder beyond the PRP treatment is critically important. Specifically, the activity modifications detailed in the methods sections are essential to maintaining both general rotator cuff health and specific improvements produced by injection of PRP. While some physicians may think these restrictions to be impractical, we have found them both extremely effective and acceptable to patients when time is taken to explain to them why these modifications are important.
Regarding the full thickness tears in this study, we do not know how much these tears have progressed over the duration of the study since we did not obtain follow-up MRI scans. Health permitting, we recommend to our patients that all full thickness tears undergo surgical repair in patients under 80 years of age. However, in unhealthy patients and patients over 80 years old, we do not perform repair, as we think the risks of even minor arthroscopic surgery generally exceed the benefits in this population. Our results from the small number of full thickness tears injected with overall very good results and enduring benefit to two years has caused us to recommended PRP as primary treatment for pain to older or more infirm patients who have failed physical therapy. We do not use corticosteroid injections in this population (or for any shoulder patient except some patients with frozen shoulder) due to the risk of adverse events, worsening of tendon damage, and the generally short duration of improvement [10, 18, 36].
A limitation of this study is the limited size of the full thickness rotator cuff tear cohort. However the uniformity of benefit in this cohort somewhat mitigates this limitation. The limited size of each subgroup also limits the reliability of sub-group comparisons. A strength of the study is the high follow up rate and follow up out to 2 years after treatment.