Response to: Letter to editor regarding: OASIS 1: Retrospective analysis of four different microprocessor knee types by Campbell et al.

Abstract

Dear Editor, Thank you for the opportunity to address the comments recently submitted in response to our recently published analysis: “OASIS 1: Retrospective analysis of four different microprocessor knee types.” The letter clearly articulates five points of discussion to which we would address our response. First, regarding the assertion that we refer to the retrospective nature of our study as the most important aspect of the study design, this is incorrect. It is specifically the cross-sectional nature of the study design that is most salient. The letter notes “cross-sectional study designs assess outcomes at only one point in time and, thus, do not allow for any conclusions on causal relationships to explain the results.” We would submit that we are very clear to not note causality, and indeed pose many statements in hypothetical context. For example, regarding findings with mobility, we have deliberately noted that the data would ‘suggest that when improved mobility is considered a primary aim for MPK prescription’ clinicians could consider all models of knees. The suggestive language is preferred over stronger, more absolute language. The authors of the letter later comment on the potential for clinically meaningful differences with relation to the findings for injurious falls despite lack of statistical significance. They suggest we “neglected” these differences, and that we “stopped short of drawing the conclusion.” We agree with the emphasis on clinically meaningful differences. However, the two statements made in the letter are contradictory as initially the letter places emphasis on posing discussion points more as hypotheses needing further testing. The language throughout the manuscript is consistent, the data would ‘suggest that when stability and falls reduction is considered a primary aim for MPK prescription’, clinicians may consider the C-Leg or Orion. Regarding “absence of bias,” we are misquoted in the letter. The manuscript specifically states “absent of potential bias due to manufacturer funding or publication.” Nowhere within the manuscript do we state that the study is without bias. As mentioned within the manuscript, the study design carries inherent biases such as selection bias, and our falls questionnaire is subject to recall bias. There is also potential for observation bias with patients performing outcomes for their clinicians. We contend, while manufacturers certainly publish studies with attempts at minimizing bias, there will always be a need for additional studies that would not carry the same potential for confirmation bias, or pressure of publication bias. In the second point of the letter, it is noted that the “study was unable to control for a potential clinician bias in the selection of the different MPK.” We acknowledged selection bias in the manuscript, but there is great value in the increased ecological validity when examining the outcomes of more than 600 MPK users. The third point raised in the letter revolves around the term “parity.” The correspondents contend it to be a legal term and scientifically inadequate. We are unable to find where the term parity is noted as a legal term. The first definition of Merriam-Webster for parity is “the quality or state of being equal or equivalent,” and indeed nowhere within MerriamWebster’s definition does the term “legal” appear. Searches of other resources show similar definitions. However, while the term “equivalent” appears within the definition, the letter is correct in that we have