Infrapatellar Straps Decrease Patellar Tendon Strain at the Site of the Jumper’s Knee Lesion: A Computational Analysis Based on Radiographic Measurements

BACKGROUND: The impetus for the use of patellar straps in the treatment of patellar tendinopathy has largely been based on empirical evidence and not on any mechanistic rationale. A computational model suggests that patellar tendinopathy may be a result of high localized tendon strains that occur at smaller patella–patellar tendon angles (PPTAs). HYPOTHESIS: Infrapatellar straps will decrease the mean localized computational strain in the area of the patellar tendon commonly involved in jumper’s knee by increasing the PPTA. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty adult males had lateral weightbearing and nonweightbearing radiographs of their knees taken with and without 1 of 2 infrapatellar straps at 60° of knee flexion. Morphologic measurements of PPTA and patellar tendon length with and without the straps were used as input data into a previously described computational model to calculate average and maximum strain at the common location of the jumper’s knee lesion during a simulated jump landing. RESULTS: The infrapatellar bands decreased the predicted localized strain (average and maximum) in the majority of participants by increasing PPTA and/or decreasing patellar tendon length. When both PPTA and patellar tendon length were altered by the straps, there was a strong and significant correlation with the change in predicted average localized strain with both straps. CONCLUSION: Infrapatellar straps may limit excessive patella tendon strain at the site of the jumper’s knee lesion by increasing PPTA and decreasing patellar tendon length rather than by correcting some inherent anatomic or functional abnormality in the extensor apparatus. CLINICAL RELEVANCE: The use of infrapatellar straps may help prevent excessive localized tendon strains at the site of the jumper’s knee lesion during a jump landing.