Tibial and femoral articular cartilage exhibit opposite outcomes for T1ρ and T2* relaxation times in response to acute compressive loading in healthy knees.

Abnormal loading is thought to play a key role in the disease progression of cartilage, but our understanding of how cartilage compositional measurements respond to acute compressive loading in-vivo is limited. Ten healthy subjects were scanned at two timepoints (7 ± 3 days apart) with a 3 T magnetic resonance imaging (MRI) scanner. Scanning sessions included T1ρ and T2* acquisitions of each knee in two conditions: unloaded (traditional MRI setup) and loaded in compression at 40 % bodyweight as applied by an MRI-compatible loading device. T1ρ and T2* parameters were quantified for contacting cartilage (tibial and femoral) and non-contacting cartilage (posterior femoral condyle) regions. Significant effects of load were found in contacting regions for both T1ρ and T2*. The effect of load (loaded minus unloaded) in femoral contacting regions ranged from 4.1 to 6.9 ms for T1ρ, and 3.5 to 13.7 ms for T2*, whereas tibial contacting regions ranged from -5.6 to -1.7 ms for T1ρ, and -2.1 to 0.7 ms for T2*. Notably, the responses to load in the femoral and tibial cartilage revealed opposite effects. No significant differences were found in response to load between the two visits. This is the first study that analyzed the effects of acute loading on T1ρ and T2* measurements in human femoral and tibial cartilage separately. The results suggest the effect of acute compressive loading on T1ρ and T2* was: 1) opposite in the femoral and tibial cartilage; 2) larger in contacting regions than in non-contacting regions of the femoral cartilage; and 3) not different visit-to-visit.

Compliance and Fidelity With an Injury Prevention Exercise Program in High School Athletics.

BACKGROUND: Use of injury prevention programs (IPPs) by high school athletes has increased but their success in reducing injury depends on program compliance and fidelity of exercise performance. HYPOTHESIS: Compliance with the 11+ IPP and exercise performance fidelity by high school athletic teams depend on sex, sport, and level of play. STUDY DESIGN: Secondary analyses of data from a randomized controlled trial (RCT). LEVEL OF EVIDENCE: Level 2. METHODS: The 11+ IPP was implemented by 100 male and female high school athletic teams (American football, soccer, basketball, and lacrosse). Team compliance and fidelity with the program were evaluated by direct observation of warm-up routines and a weekly online survey completed by coaches. Differences in compliance and fidelity due to sport, sex, and level of play were assessed by analysis of variance. RESULTS: Coaches reported that their teams performed the full IPP an average of 1.45 times per week, and 28% of observed warm-ups included all exercises in the IPP. Compliance differed by sport but not by level of play or the athletes' sex. At the end of the season, cueing was observed 19% of the time and differed by sport. Good technique was observed 66% of the time and varied by level of play. CONCLUSION: Team compliance with the IPP varied by sport and was below the recommended number of sessions per week needed to reduce injury. Removal of implementation barriers and improved support from coaches are needed at all levels of play for IPPs to be effective. CLINICAL RELEVANCE: Clinical and sports practitioners intending to implement an IPP at the high school level should anticipate and address barriers that affect program compliance and fidelity of exercise performance. Frequent follow-up and instruction may be necessary for successful adoption of the IPP.