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

Michael Lavagnino, Steven P. Arnoczky, Julie Dodds, and Niell Elvin. Sports Health: A Multidisciplinary Approach May/June 2011 vol. 3 no. 3 296-302
Infrapatellar straps are a common recommendation in the treatment of patellar tendinopathy. While some studies have indicated that infrapatellar straps can reduce anterior knee pain associated with certain causes the underlying mechanism remains unclear. A recent cadaveric study found that infrapatellar straps can reduce patellofemoral contact pressures but no study has evaluated the effect of these straps on patellar tendon (ligament) strain. Therefore, Lavagnino et al examined the effect of two commonly used infrapatellar straps on patella-patellar tendon angle (PPTA; angle between midline of patella and inferior patellar pole to tibial tuberosity) of 20 healthy male participants and then used these data in computer models. A sports medicine physician instructed the participants on how to apply the strap and the order of the two straps was randomized. Lateral knee x-rays were performed at 60 degrees of knee flexion (weight-bearing and nonweight-bearing) with and without the straps. The flexion angle was based on previous research that indicated that patellar tendon strain is highest at 60 degrees. Merchant (sunrise) view x-rays were also performed. X-ray outcome measures included PPTA, patellar tilt, and distance from patella to tibial tuberosity relative to the patella height (patellar tendon length). Overall, neither infrapatellar strap influenced patellar tilt. Both straps reduced the average patellar tendon length and increased the PPTA. The computer models indicated that both straps reduced the average and maximum strain on the patellar tendon (2.5 to 87.6% reduction for Donjoy Cross Strap, 0.9% to 62.5% reduction with Cho-Pat knee strap). Interestingly, the data indicated that 5 participants wearing the Donjoy Cross Strap and 4 participants wearing the Cho-Pat knee strap did not experience a reduction in patellar tendon strain (among these participants 3 had no reduction with both straps). The authors could not determine, based on the x-ray data, why these participants did not respond to the straps. Among the participants that had decreased patellar tendon strain, the data indicates that infrapatellar straps may help reduce excessive patellar tendon strain by reducing the patellar tendon length and increasing the PPTA.
This is one of those studies that finally verifies something that many of us have probably been telling patients or thinking for years: that these straps reduce patellar tendon strain.  This can be valuable information for clinicians when making clinical decisions as well as educating patients. It is important to note that this study only included healthy males and it is unclear if these findings can be applied to females or patients with anterior knee pain. It is important to keep in mind that some patients did not benefit from the straps. The authors could not determine why based on anatomical measures of x-ray (e.g., patellar tendon length, patella anatomy). The authors caution that while patients received standard instruction in applying the straps they did not standardize the strap tightness; which may be a reason for this finding but more research will be needed. It should be noted that previous studies of infrapatellar straps have also reported that a small but notable percentage of patients seem to be nonresponders. This may be a patient population that warrants further study. What are your experiences with these straps? Have you also found that some patients don’t respond? Have you noticed any patterns that characterize these nonresponders?
Written by: Jeffrey Driban
Reviewed by: Stephen Thomas
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