STUDY OBJECTIVES: Demonstrate equivalent clinical and radiologic outcomes to the "gold standard" (ABG) in a representative clinical model (hindfoot and ankle fusions)

STUDY HYPOTHESIS: GEM OS™1 is an equivalent bone grafting substitute to autologous bone graft in applications as shown by non-inferiority analysis

STUDY RATIONALE: Evaluate a fully synthetic growth-factor enhanced bone graft substitute to facilitate fusion in conditions or injuries requiring bone graft in a representative clinical fusion model and thus the opportunity to provide equivalent union rates as ABG without necessitating an additional invasive procedure to harvest the graft

REGULATORY PHASE: Investigational Device Exemption (IDE) for Premarket Approval (PMA) Application as a bone regeneration system, pivotal phase

Inclusion Criteria:

1) Bone defect in the hindfoot or ankle requiring fusion using open surgical technique with supplemental bone graft/substitute, requiring one of the following procedures:

• Ankle joint fusion
• Subtalar fusion
• Calcaneocuboid fusion
• Talonavicular fusion
• Triple arthrodesis (subtalar, talonavicular and calcaneocuboid joints)
• Double fusions (talonavicular and calcaneocuboid joints)

Exclusion Criteria:

1. Previous fusion surgery of the proposed fusion site.
2. The patient uses chronic medications known to affect the skeleton (e.g. glucocorticoid usage > 10mg/day).
3. Pregnant or a female intending to become pregnant during this study period.
4. Morbidly obese (BMI > 45 kg/m2)