Introduction Patellar tendinopathy (PT) is a painful, sports related overuse injury of the patellar tendon3 with a high prevalence in sports that require a lot of jumping and landing, like volleyball and basketball.4 Since PT can be very persistent and treatments do not guarantee recovery1 it is important to identify risk factors for this injury that can be used for prevention. In 2008 in a cross-sectional study the following factors were identified that may be associated with the aetiology of PT: younger age, playing national, being male and playing volleyball (compared to playing basketball).2 However, due to the retrospective design of this study, nothing could be concluded about causal relations. The aim of the current study is to investigate if the factors identified in the previous study can also be prospectively recognised as predictors of symptomatic PT three years later.
Methods 926 asymptomatic Dutch non-elite and elite basketball and volleyball players who participated in the retrospective 2008-study were invited to complete again an online survey in 2011. Questions about respondent characteristics, sports participation, knee injuries and occupation were included in the survey. Diagnosis of PT was based on a self reported pain map and/or made by a physical therapists or physician. Using simple and multiple logistic regression analysis, it was investigated if variables from the 2008-survey could be identified as predictors of PT in 2011.
Results 385 athletes (290 volleyball and 90 basketball players) completed the questionnaire in 2011 and 51 (13%) of these participants developed PT since 2008 (18% male and 10% female). In the simple logistic regression analysis we found in the total group that males had increased odds to develop PT (OR 2.0 95% CI 1.1–3.5), this was also found in the volleyball players separately (OR 2.6 95% CI 1.3–5.2). In the volleyball players a trend was found for increased odds for those jumping at work (OR 2.4 95% CI 1.0–5.5) compared to not jumping at work and for those performing heavy physically demanding work compared to mentally demanding work (OR 2.6 95% CI 0.9–7.8), the latter variable showing also a trend in the total group in the multiple logistic regression analysis (OR 2.3 95% CI 0.9–6.3). In the basketball population we found a trend toward increased odds for a higher BMI as a risk factor for developing PT in the simple regression analysis (OR 1.2 95% CI 1.0–1.5).
Discussion In this first prospective cohort study investigating risk factors for symptomatic PT in a large group of non-elite and elite basketball and volleyball players it was shown that the most important factors were male gender and performing physically demanding work (whether or not involving jumping). There was some evidence in the relative small group of basketball players that a higher BMI increases the risk for PT. In contrast to the study of Van der Worp et al (2012), no specific sports related factors for PT were identified in this study. This can be caused by the smaller number of participants in this study and/or it might be that other sports-related factors that cannot be measured with an online survey (like jumping height or landing strategy) have more predictive power.
Implications for practice The findings from this study suggest that especially in males (with higher BMI) the activities at work should be taken into account when adjusting patellar tendon load for PT prevention purposes.
References 1 Gaida and Cook. Current Sports Medicine Reports. 2011;10:255–270
2 van der Worp, et al. Scand J Med Sci Sports. 2012;22:783–790
3 Warden, Brukner. Clin Sports Med. 2003;22:743–759
4 Zwerver, et al. Am J Sports Med. 2011;39:1984–1988