A retracting two-piece cannula for distracting soft tissue from bone (e.g., the articular surface of a knee) to provide a surgical workspace for osteochondral repair. After inserting an outer cannula provided with a threaded outer surface into an incision (preferably widened by one or more dilators), the outer cannula is rotated to engage the threaded outer surface with the soft tissue to be distracted. An inner cannula is then inserted into the outer cannula and advanced until it contacts the articular surface. Further relative movement between the inner and outer cannulas causes the outer cannula to be drawn away from the articular surface, thereby retracting the soft tissue and establishing the workspace. The inner and outer cannula are then locked together to maintain the workspace, and an osteochondral core may be introduced through the inner cannula.