A tendon anchoring system, comprising: an anchor assembly having a sheath (111, 211, 411) with a threaded lumen formed therein, and a threaded expander screw (107, 207, 407) configured to threadably engage the threaded lumen in the sheath such that the expander screw (107, 207, 407) causes the sheath (111, 211, 411) to expand outward to engage a bone hole; and an inserter tool having an elongate outer shaft (109, 209, 409) having proximal and distal ends with an inner lumen extending therethrough, the distal end being configured to couple to a proximal end of the sheath, and an elongate inner shaft (103, 203, 301, 403) having a distal drive tip (105, 205, 305, 405) configured to engage a corresponding drive recess formed in a proximal end of the expander screw, the inner shaft (103, 203, 301, 403) being rotatable relative to the outer shaft (109, 209, 409) to thread the expander screw into the sheath, characterised by the inner shaft (103, 203, 301, 403) being prevented from rotating relative to the outer shaft, in the direction for threading the expander screw into the sheath, when the expander screw is fully threaded into the sheath to prevent over-insertion of the expander screw into the sheath, and wherein either: a) the inner and outer shafts include complementary abutting surfaces that are configured to contact one another when the expander screw is fully threaded into the sheath, or b) a distal end of the elongate inner shaft (103, 203, 301, 403) is configured to abut the proximal end of the sheath (111, 211, 411) when the expander screw is fully threaded into the sheath. an anchor assembly having a sheath (111, 211, 411) with a threaded lumen formed therein, and a threaded expander screw (107, 207, 407) configured to threadably engage the threaded lumen in the sheath such that the expander screw (107, 207, 407) causes the sheath (111, 211, 411) to expand outward to engage a bone hole; and a sheath (111, 211, 411) with a threaded lumen formed therein, and a threaded expander screw (107, 207, 407) configured to threadably engage the threaded lumen in the sheath such that the expander screw (107, 207, 407) causes the sheath (111, 211, 411) to expand outward to engage a bone hole; and an inserter tool having an elongate outer shaft (109, 209, 409) having proximal and distal ends with an inner lumen extending therethrough, the distal end being configured to couple to a proximal end of the sheath, and an elongate inner shaft (103, 203, 301, 403) having a distal drive tip (105, 205, 305, 405) configured to engage a corresponding drive recess formed in a proximal end of the expander screw, the inner shaft (103, 203, 301, 403) being rotatable relative to the outer shaft (109, 209, 409) to thread the expander screw into the sheath, characterised by the inner shaft (103, 203, 301, 403) being prevented from rotating relative to the outer shaft, in the direction for threading the expander screw into the sheath, when the expander screw is fully threaded into the sheath to prevent over-insertion of the expander screw into the sheath, and wherein either: a) the inner and outer shafts include complementary abutting surfaces that are configured to contact one another when the expander screw is fully threaded into the sheath, or b) a distal end of the elongate inner shaft (103, 203, 301, 403) is configured to abut the proximal end of the sheath (111, 211, 411) when the expander screw is fully threaded into the sheath. an elongate outer shaft (109, 209, 409) having proximal and distal ends with an inner lumen extending therethrough, the distal end being configured to couple to a proximal end of the sheath, and an elongate inner shaft (103, 203, 301, 403) having a distal drive tip (105, 205, 305, 405) configured to engage a corresponding drive recess formed in a proximal end of the expander screw, the inner shaft (103, 203, 301, 403) being rotatable relative to the outer shaft (109, 209, 409) to thread the expander screw into the sheath, characterised by the inner shaft (103, 203, 301, 403) being prevented from rotating relative to the outer shaft, in the direction for threading the expander screw into the sheath, when the expander screw is fully threaded into the sheath to prevent over-insertion of the expander screw into the sheath, and wherein either: a) the inner and outer shafts include complementary abutting surfaces that are configured to contact one another when the expander screw is fully threaded into the sheath, or b) a distal end of the elongate inner shaft (103, 203, 301, 403) is configured to abut the proximal end of the sheath (111, 211, 411) when the expander screw is fully threaded into the sheath. a) the inner and outer shafts include complementary abutting surfaces that are configured to contact one another when the expander screw is fully threaded into the sheath, or b) a distal end of the elongate inner shaft (103, 203, 301, 403) is configured to abut the proximal end of the sheath (111, 211, 411) when the expander screw is fully threaded into the sheath.