Humans have engaged in endurance running for millions of years, but the modern running shoe was not invented until the 1970s. For most of human evolutionary history, runners were either barefoot or wore minimal footwear such as sandals or moccasins with smaller heels and little cushioning relative to modern running shoes. We wondered how runners coped with the impact caused by the foot colliding with the ground before the invention of the modern shoe. Here we show that habitually barefoot endurance runners often land on the fore-foot (fore-foot strike) before bringing down the heel, but they sometimes land with a flat foot (mid-foot strike) or, less often, on the heel (rear-foot strike). In contrast, habitually shod runners mostly rear-foot strike, facilitated by the elevated and cushioned heel of the modern running shoe. Kinematic and kinetic analyses show that even on hard surfaces, barefoot runners who fore-foot strike generate smaller collision forces than shod rear-foot strikers. This difference results primarily from a more plantarflexed foot at landing and more ankle compliance during impact, decreasing the effective mass of the body that collides with the ground. Fore-foot- and mid-foot-strike gaits were probably more common when humans ran barefoot or in minimal shoes, and may protect the feet and lower limbs from some of the impact-related injuries now experienced by a high percentage of runners.

Competitive cross-country runners on a college team incur high injury rates, but runners who habitually rearfoot strike have significantly higher rates of repetitive stress injury than those who mostly forefoot strike. This study does not test the causal bases for this general difference. One hypothesis, which requires further research, is that the absence of a marked impact peak in the ground reaction force during a forefoot strike compared with a rearfoot strike may contribute to lower rates of injuries in habitual forefoot strikers.

Minimally shod runners are modestly but significantly more economical than traditionally shod runners regardless of strike type, after controlling for shoe mass and stride frequency. The likely cause of this difference is more elastic energy storage and release in the lower extremity during minimal-shoe running.

Objectives: The preferred method of fixation for posterior malleolus fractures remains controversial, and practices vary widely among surgeons. The purpose of this study was to compare anterior-to-posterior (AP) lag screws with posterior buttress plating for fixation of posterior malleolus fractures in a human cadaveric model. Methods: Posterior malleolus fractures involving 30% of the distal tibial articular surface were created in 7 pairs of fresh frozen cadaveric ankles. One specimen in each pair was randomly assigned to fixation with either 2 AP lag screws or a one-third tubular buttress plate without supplemental lag screws. Each specimen was then subjected to cyclic loading from 0% to 50% of body weight for 5000 cycles followed by loading to failure. Outcome measures included permanent axial displacement during each test cycle (axial displacement at no load), peak axial displacement during each test cycle (axial displacement at 50% body weight), load at 1-mm axial displacement, ultimate load, and axial displacement at ultimate load. Results: The buttress plate group showed significantly less peak axial displacement at all time points during cyclic loading. Permanent axial displacement was significantly less in the buttress plate group beginning at cycle 200. There were no significant differences between the 2 groups during load-to-failure testing. Conclusion: Posterior malleolus fractures treated with posterior buttress plating showed significantly less displacement during cyclical loading compared with fractures fixed with AP lag screws. Surgeons should consider these findings when selecting a fixation strategy for these common fractures. Further research is warranted to investigate the clinical implications of these biomechanical findings.

Critical bone defects pose a formidable orthopaedic problem in patients with bone loss. We developed a preclinical model based on the induced membrane technique using a synthetic graft to replace autograft for healing critical bone defects. Additionally, we used a novel osteoconductive scaffold coupled with a synthetic membrane to evaluate the potential for single‐stage bone regeneration. Three experimental conditions were investigated in critical femoral defects in rats. Group A underwent a two‐stage procedure with insertion of a polymethylmethacrylate (PMMA) spacer followed by replacement with a 3D printed polycaprolactone(PCL)/β‐tricalcium phosphate (β‐TCP) osteoconductive scaffold after 4 weeks. Group B received a single‐stage PCL/β‐TCP scaffold wrapped in a PCL‐based microporous polymer film creating a synthetic membrane. Group C received a single‐stage bare PCL/β‐TCP scaffold. All groups were examined by serial radiographs for callus formation. After 12 weeks, the femurs were explanted and analyzed with micro‐CT and histology. Mean callus scores tended to be higher in Group A. Group A showed statistically significant greater bone formation on micro‐CT compared with other groups, although bone volume fraction was similar between groups. Histology results suggested extensive bone ingrowth and new bone formation within the macroporous scaffolds in all groups and cell infiltration into the microporous synthetic membrane. This study supports the use of a critical size femoral defect in rats as a suitable model for investigating modifications to the induced membrane technique without autograft harvest. Future investigations should focus on bioactive synthetic membranes coupled with growth factors for single‐stage bone healing. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res

The preferred method of fixation for posterior malleolus fractures remains controversial, and practices vary widely among surgeons. The purpose of this study was to compare anterior-to-posterior lag screws to posterior buttress plating for fixation of posterior malleolus fractures in a cadaveric model. Methods: Posterior malleolus fractures were created in seven pairs of fresh frozen cadaveric ankles. One specimen in each pair was randomly assigned to fixation with either two anterior-to-posterior lag screws or a one-third tubular buttress plate without supplemental lag screws. Each specimen was then subjected to cyclic loading from 0% to 50% of body weight for 5,000 cycles followed by loading to failure. Failure was defined as 1mm of axial displacement. Results: The buttress plate group showed significantly less peak axial displacement at all time points during cyclic loading. Permanent axial displacement was significantly less in the buttress plate group beginning at cycle 200 (figure). There were no significant differences between the two groups during load to failure testing. Conclusion: Posterior malleolus fractures treated with posterior buttress plating showed significantly less displacement during cyclical loading compared to fractures fixed with anterior-to-posterior lag screws. Surgeons should consider these findings when selecting a fixation strategy for these common fractures. these biomechanical findings. Further research is warranted to investigate the clinical implications of