Patellar Tendon Load Progression during Rehabilitation Exercises: Implications for the Treatment of Patellar Tendon Injuries

Abstract

Purpose: This study aimed to evaluate patellar tendon loading profiles (loading index, based on loading peak, loading impulse, and loading rate) of rehabilitation exercises to develop clinical guidelines to incrementally increase the rate and magnitude of patellar tendon loading during rehabilitation.

Methods: Twenty healthy adults (10 females/10 males, 25.9 ± 5.7 yr) performed 35 rehabilitation exercises, including different variations of squats, lunge, jumps, hops, landings, running, and sports specific tasks. Kinematic and kinetic data were collected, and a patellar tendon loading index was determined for each exercise using a weighted sum of loading peak, loading rate, and cumulative loading impulse. Then the exercises were ranked, according to the loading index, into tier 1 (loading index ≤0.33), tier 2 (0.33 < loading index <0.66), and tier 3 (loading index ≥0.66).

Results: The single-leg decline squat showed the highest loading index (0.747). Other tier 3 exercises included single-leg forward hop (0.666), single-leg countermovement jump (0.711), and running cut (0.725). The Spanish squat was categorized as a tier 2 exercise (0.563), as was running (0.612), double-leg countermovement jump (0.610), single-leg drop vertical jump (0.599), single-leg full squat (0.580), double-leg drop vertical jump (0.563), lunge (0.471), double-leg full squat (0.428), single-leg 60° squat (0.411), and Bulgarian squat (0.406). Tier 1 exercises included 20 cm step up (0.187), 20 cm step down (0.288), 30 cm step up (0.321), and double-leg 60° squat (0.224).

Conclusions: Three patellar tendon loading tiers were established based on a combination of loading peak, loading impulse, and loading rate. Clinicians may use these loading tiers as a guide to progressively increase patellar tendon loading during the rehabilitation of patients with patellar tendon disorders and after anterior cruciate ligament reconstruction using the bone-patellar tendon-bone graft.

Figure 1.

Loading peak (maximum force), loading rate (maximum instantaneous change of force overtime), and loading impulse (area under the force-time curve) during a rehabilitation exercise.

Figure 2.

Patellar tendon loading index across 35 rehabilitation exercises, categorized as low (Tier 1), moderate (Tier 2), and high (Tier 3). Each loading index was determined with a 50% weight on loading peak (bodyweight), 30% weight on loading impulse (bodyweight * second), and 20% on loading rate (bodyweight / second).

Figure 3.

Patellar tendon loading during different variations of the squat exercise. Group averages are represented as solid or dashed lines and the standard deviation is represented as shades. Patellar tendon loading during self-selected pace walking and running are graphed in light gray solid and dashed lines, respectively. X-axis indicates normalized exercise time and y-axis indicates patellar tendon load normalized against body weight. BW, bodyweight; 1-Leg, single-leg; 2-Leg, double-leg.