Platelet-Rich Plasma Augmentation of Rotator Cuff Repair: Letter

Dear Editor: Evidenced-based medicine has appropriately become the ‘‘gold standard’’ by which new procedures, technologies, and treatments are objectively evaluated and their merits judged. The pinnacle of these objective assessments is the Level of Evidence I studies, which incorporate a prospective, randomized, controlled study design. Therefore, as someone who has followed the platelet-rich plasma debate closely, I was eager to read the recent publication by Castricini and colleagues, which examined the effect of a platelet-rich fibrin matrix (PRFM) on the functional outcomes (Constant Score) and MRI appearance of rotator cuff repair in a randomized, controlled clinical study design. The authors concluded that PRFM had no effect on the Constant score or the MRI appearance of the tendon. However, in examining the statistical analysis of the MRI data for tendon thickness, size of the tendon footprint, and signal intensity, I am concerned that the authors may have unintentionally biased their results by the statistical methods chosen. Tendon thickness and footprint size are continuous data in which precise values can be determined. However, the authors have chosen to use an ordinal scale that lumps large segments of continuous data into 1 of 3 categories: tendon thickness is categorized into grade I, \50% of normal thickness; grade II, . 50% of normal thickness; and grade III, normal (100%) thickness. Tendon footprint coverage is similarly parsed into grades, with grade I being one-third of the coverage, grade II being two-thirds of the coverage, and grade III being 100% of the coverage. In this scheme, a patient with a tendon thickness of 55% of normal is considered the same as a patient with a tendon thickness of 95% of normal. A similar situation occurs with tendon footprint coverage. When parametric data are converted to a nonparametric format for statistical analysis (and this is a format that severely limits the ability to distinguish between such large degrees of variability), it is more likely that the statistical analysis will reveal no difference. The addition of the ‘‘semi-ordinal’’ scale for signal intensity (the scale used does not have an inherent logical, progressive order) to come up with a ‘‘total tendon score’’ further dilutes the validity of this statistical analysis. I do understand that MRI evaluations often report these grades of tendon thickness and footprint size. However, using such nondiscriminating grades to try to determine the potential significance of a ‘‘treatment effect’’ is questionable. Perhaps a more reasonable statistical examination of such generalized outcome metrics would involve an analysis based on the observation that footprint size, tendon thickness, and/or normal MRI signal intensity are either normal or not in PRFM versus non-PRFM–treated repairs. This would involve the use a simple binomial (2 3 2, yes/no) x test to compare each of these outcome variables. Using the data from Table 4 of the Castricini article and comparing only those individuals considered to have normal values in each MRI outcome measurement to all the rest, one finds that the use of a PRFM actually results in a statistically significant return to normal footprint area (P = .02) and MRI signal intensity (P \ .001) when compared with non-PRFM–treated individuals. While there is no significant difference (P = .09) in return to normal tendon thickness between PRFM and non-PRFM–treated groups, the lack of power analysis in this dataset could suggest a potential type II statistical error. Therefore, the conclusion presented by Castrinici et al that PRFM does not result in any significant difference in the MRI appearance is not entirely valid. It is likely that only through the use of a parametric analysis (t test) that is performed on more precise tendon thickness and footprint area measurements, and powered adequately, can the true effect of PRFM and non-PRFM treatment on these outcome metrics be determined. I would strongly encourage the authors to perform that analysis. It is ultimately up to each individual surgeon to determine what changes in outcome(s) (ie, footprint coverage, tendon thickness, MRI signal intensity, and/or Constant scores) are clinically significant enough to justify the use of PRFM in rotator cuff repairs. However, unless the conclusions are based on data that are presented and analyzed rigorously, and without the chance of unintended obfuscation, the reader may only get ‘‘part of the story. ’’ It is incumbent upon the AJSM to ensure that, in their desire to provide the readership of the journal with these much needed clinical studies in a timely manner, these studies represent a rigorous, complete, and accurate assessment of the data. While Level I studies remain the gold standard in evidence-based medicine, and will ultimately determine if a PRFM construct will have a role in rotator cuff repair, it must be realized that the conclusions of any prospective, randomized, controlled studies are only as valid as the strength and depth of their data analysis and interpretation.