Feasibility and reliability of pain pressure threshold measurements in patellar tendinopathy

Patellar tendinopathy is a common and often difficult to treat overuse injury which is characterized by activity-related anterior knee and focal palpation tenderness of the patellar tendon. The clinical diagnosis is mainly based on clinical examination, in which the yardstick is a non-standardized manual palpation. To standardize this palpation procedure the use of an algometer seems applicable. The purpose of this study was to investigate the feasibility and reliability of the algometer in patellar tendinopathy. A cross sectional study was carried out.The algometer was applied to the patellar tendon in 20 asymptomatic volleyball players to measure the 'normal' pressure pain threshold. The inter-rater reliability was analyzed in 54 athletes with symptomatic patellar tendinopathy, the intra-rater reliability was analyzed in 48 athletes with symptomatic patellar tendinopathy. During the procedure difficulties were described, the SEM, intra class correlations and limits of agreement were determined using the Bland and Altman method. The feasibility of the algometer is adequate. The PPT of asymptomatic athletes differs significantly (p<.001) from athletes with a diagnosis of patellar tendinopathy. The inter-rater (ICC 0.93) and intra-rater (ICC 0.60) reliability of the pain pressure threshold are adequate to moderate. Although further research is warranted PPT algometry seems to be a feasible, reliable and useful tool in the diagnosis and treatment evaluation of athletes with patellar tendinopathy.