Letters to the Editor: Authors’ Response (original) (raw)

2016, Journal of Periodontology

We are writing to comment on "The Drop-Jump Screening Test: Difference in Lower Limb Control by Gender and Effect of Neuromuscular Training in Female Athletes" by Noyes et al (February 2005, pp 197-207), where methodological errors and bias undermine the validity of the study conclusions. Two experienced sports orthopaedic researchers (K.P.S. and L.S.M.) reviewed the paper using the evidence-based medicine systematic literature review worksheet recently published by Spindler et al in the Journal of the American Academy of Orthopaedic Surgeons. The drop-jump screening test study has subsequently been cited as a reliable and valid test of abnormal lower limb alignment in several papers, most of which were published by the authors of this study in The American Journal of Sports Medicine. While intraclass correlation coefficients (ICCs) demonstrated acceptable reliability, there is no evidence in this paper, or any of the subsequent papers, that the test is valid. In the study, the authors hypothesized that during a drop-jump: (1) females have decreased knee separation distances upon landing and acceleration; (2) male athletes have neutrally aligned lower limb positions upon landing and acceleration; and (3) a 6-week neuromuscular training program will significantly increase knee separation distance in female athletes. The main outcome variables were knee separation distance (gender difference), ankle separation distance (gender difference), and how the training regimen changes knee and ankle separation distances in females only. These distances were measured off of a video screen. They concluded that both females and males have valgus alignment and that the females had improved knee separation distance after training. Methodologically, while there is a comparison group in the study, the design is incomplete; the males were not trained, despite the fact that they had the same identified "abnormal" knee separation distances as the females. In addition, there are no reported data for what appears to have been a control population. Seventeen female subjects who did not undergo training underwent test-retest measurements of the jump-landing sequence taken 7 weeks apart (and ICCs were taken). Neither the test-retest reliability for the knee separation distance nor the data themselves were presented. They should have been. Consequently, the readers do not know if the differences seen in the trained female group are due to test-retest "learning" improvement, natural test-retest variation, or the training regimen. Several significant sources of potential bias undermine the credibility of this study. First, there was potential selection bias. The population was not stratified by sport or level of play. The female subject population was not randomized for control/treatment group inclusion. The authors state that the female population participated in the treatment group strictly on a voluntary basis. However, the fact remains that referral/recruitment bias most likely exists, because only 62 of 325 athletes participated in the training regimen. The authors state that all female participants tested were given information about the training program and 62 participated in the training. How were they selected? Were they offered the training program in exchange for their participation in the data collection procedures? Did the center pay the athlete? Did the athlete pay to participate in the training regimen? Second, there was potential exclusion/transfer bias. The authors do not mention why only certain subpopulations were chosen to