Reamer instruments and related methods
Reamer instruments and related methods are disclosed herein, e.g., for reaming bone to facilitate in situ assembly of a bone anchor. In some embodiments, the instrument can include a feedback mechanism configured to alert the user when sufficient bone has been removed to facilitate assembly of the bone anchor. The feedback mechanism can be triggered by a movable shaft of the instrument that is displaced by the shank portion of the bone anchor as the surrounding bone is reamed.
1. A surgical instrument, comprising:
an outer shaft having a cutting element at a distal end thereof and a central passage extending proximally from the distal end;
an inner shaft disposed within the central passage of the outer shaft, the inner shaft being configured to move longitudinally relative to the outer shaft as the cutting element is used to remove bone from around an implanted bone anchor shank; and
an indicator configured to generate user feedback when the inner shaft moves longitudinally relative to the outer shaft by a threshold distance;
wherein a distal end of the inner shaft includes a bearing surface configured to contact and slide across a proximal surface of the implanted bone anchor shank as the instrument is rotated axially and/or polyaxially articulated relative to the shank.
2. The instrument of claim 1 , wherein the threshold distance corresponds with an amount of clearance space needed to assemble a receiver member to an implanted bone anchor shank.
3. The instrument of claim 1 , further comprising a collection chamber in fluid communication with at least one of (a) a cannulation formed in the inner shaft and (b) a space defined between the inner and outer shafts, such that material removed by the instrument is collected in the chamber.
4. The instrument of claim 1 , wherein the cutting element comprises a plurality of longitudinally-extending flutes spaced about an outer perimeter of the outer shaft.
5. The instrument of claim 4 , wherein the flutes are at least one of (a) helical, (b) bi-directional, (c) interrupted along their length by one or more radial grooves, (d) have a non-zero rake angle, and (e) have distal-facing surfaces that are angled radially inwards.
6. The instrument of claim 1 , further comprising a driver shaft inserted through the inner shaft and configured to apply torque to a bone anchor shank.
7. The instrument of claim 6 , wherein the inner shaft includes a plurality of flexible and resilient fingers configured to grasp a head portion of a bone anchor shank.
8. A surgical method, comprising:
driving a shank of a bone anchor into bone;
positioning a reamer instrument over the implanted shank such that a cutting element at a distal end of an outer shaft of the reamer instrument at least partially surrounds the shank of the bone anchor and a distal end bearing surface of an inner shaft of the reamer instrument disposed within a central passage of the outer shaft contacts a proximal surface of the shank;
manipulating the reamer instrument relative to the shank to remove bone from around the shank, the distal end bearing surface of the inner shaft of the reamer instrument sliding across the proximal surface of the shank as the instrument is rotated axially and/or polyaxially articulated relative to the shank;
as bone is removed by the reamer instrument, advancing the outer shaft distally relative to the bone while the shank axially displaces the inner shaft in a proximal direction relative to the outer shaft; and
generating feedback indicative of a degree of bone removal using an indicator configured to trigger when the inner shaft moves relative to the outer shaft by a threshold distance.
9. The method of claim 8 , wherein said driving comprises rotating the shank relative to the bone using a driver shaft inserted through the inner shaft of the reamer instrument.
10. The method of claim 8 , wherein said positioning comprises inserting a head portion of the shank into an open distal end of the outer shaft of the instrument.
11. The method of claim 8 , wherein said manipulating comprises at least one of (a) rotating the outer shaft of the instrument relative to a head portion of the shank about a central longitudinal axis of the outer shaft and (b) polyaxially articulating the outer shaft of the instrument relative to the head portion of the shank.
12. The method of claim 8 , wherein the threshold distance corresponds with an amount of bone removal sufficient to assemble a receiver member to the implanted shank.
13. The method of claim 8 , further comprising separating the instrument from the shank and attaching a receiver member to the implanted shank.
14. The method of claim 8 , further comprising retaining the shank to the instrument by grasping the head of the shank between a plurality of fingers of the inner shaft.
15. The instrument of claim 1 , wherein the user feedback is at least one of audible, visual, and tactile feedback.
16. The instrument of claim 15 , wherein the indicator need not be contacted to convey the user feedback.
17. The instrument of claim 1 , wherein the indicator provides visual feedback.
18. The instrument of claim 17 , wherein the indicator provides visual feedback in a form selected from the group consisting of color, texture, and pattern.
19. The method of claim 8 , wherein the feedback generated by the indicator is at least one of audible, visual, and tactile feedback.
20. The instrument of claim 1 , wherein the bearing surface forms a negative of the proximal surface of the implanted bone anchor shank.
21. The instrument of claim 1 , wherein the bearing surface has a concave spherical shape.
22. The instrument of claim 1 , wherein the inner shaft is biased distally relative to the outer shaft.
23. The instrument of claim 1 , further comprising one or more stops to limit longitudinal movement of the inner shaft relative to the outer shaft.