These authors investigated the safety and efficacy of a fully characterized allogeneic pure PRP injection into the subacromial space of patients with "rotator cuff disease" in comparison with corticosteroid injection. Inclusion criteria: ≥18 years ofd age, unilateral shoulder pain for at least 3 months, a Neer or Hawkins impingement sign, either a painful arc or a positive result on the Jobe test. Exclusion criteria included previous subacromial injections within the past 3 months, a history of shoulder trauma, a full-thickness rotator cuff tear as demonstrated with magnetic resonance imaging (MRI) or ultrasonography, and limitation of both active and passive movement of the glenohumeral joint of 25% in at least 2 directions as compared with the contralateral shoulder or with normal values.
60 patients with rotator cuff disease were randomly assigned to receive a subacromial injection of either 4 mL of allogeneic pure PRP or a 4-mL mixture of 1 mL of 40-mg/mL triamcinolone acetonide and 3 mL of 2% lidocaine under ultrasonographic guidance.
The authors concluded that " Constant score at 1 month did not significantly differ between the PRP and corticosteroid groups. At 6 months, the DASH (Disabilities of the Arm, Shoulder and Hand) score, overall function, and external rotation were significantly better in the PRP group than in the corticosteroid group, and the other clinical outcomes did not show significant differences. All pain measurements, the strength of the supraspinatus and infraspinatus, and 5 functional scores also improved slowly and steadily after injection, becoming significantly better at 6 months compared with those before the injection, whereas those in the corticosteroid group responded promptly but did not further improve. Allogeneic PRP injections for the treatment of rotator cuff disease are safe but are not definitely superior to corticosteroid injections with respect to pain relief and functional improvement during 6 months. The DASH score, overall function, and external rotation were significantly better in the PRP group than in the steroid group at 6 months. Generally, PRP slowly but steadily reduced pain and improved function of the shoulder until 6 months, whereas corticosteroid did not."
Comment: Let's take a look at the DASH data. Recalling that a lower DASH score is good, we can see that at later time points the average DASH scores for the available patients are lower (i.e. better).
In this study, we see that the average DASH score for the patients available at each time point after treatment is related to the percentage of patients lost to followup. The best (lowest) DASH score is at 6 months when 24% of the original patients were not included. The conclusion that the DASH improved with time is fragile because it is possible that the missing 24% could have had higher (worse) DASH scores at 6 months - we just don't know.
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