Tibial bone load during running: estimation methods and relationships to clinical measures

Abstract

Introduction: Tibial bone stress injuries (BSI) are an overuse injury in endurance runners, influenced by a complex set of risk factors including excessive mechanical loads. However, current methods for estimating these loads are not clinically accessible. It is important to establish surrogate measures of tibial bone load that are clinically accessible to identify runners who may be at risk of tibial BSI. Additionally, tibial loads are sensitive to methodology; however, models for quantifying tibial force specifically have yet to be compared. Therefore, the aims of this dissertation are as follows: Aim one: To evaluate the influence of different modeling methodologies on tibial force estimation during running. Aim two: To determine whether clinical measures can predict tibial loads during running in healthy and injured recreational running populations. Methods: For Aim one, a systematic review and meta-analysis was conducted to determine whether differences in peak tibial axial force during running exist between three modeling approaches. Additionally, methods for estimating Achilles tendon moment arm were compared to investigate how length differences influence plantarflexor and tibial force estimates during running. For Aim two, two studies were conducted to investigate relationships between strength, balance, and endurance assessments and tibial bone load during running in healthy and injured populations. Results: Model methodology accounted for 50% of the variability in tibial force estimates, with a static optimization model producing 3.45 BW greater forces than a distal model. Achilles tendon moment arm length was also method-dependent and influenced estimates of Achilles and tibial axial forces during running. Clinical measures of ankle strength, dynamic balance, and plantarflexor endurance cannot be used as surrogates for tibial bone force or other tibial load metrics during running. Preliminary results suggest that runners who have recently returned to running after tibial BSI exhibit decreased plantarflexor strength and endurance, along with increased impulse and cumulative load compared to healthy runners. Conclusions: Estimates of tibial bone load during running is method-dependent; model design and assumptions should be carefully considered when selecting methods. Study conditions such as speed, strike pattern, load carriage, surface grade, and step frequency contribute to variability in load estimates and should be accounted for in study design and analysis. Common clinical assessments of strength, dynamic balance, and endurance are not reliable surrogates for tibial bone load in healthy runners; however, injured runners present with deficits in these measures during the early return to run period following tibial BSI.