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;
an inner shaft slidably disposed within 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
a feedback mechanism configured to generate user feedback when the inner shaft moves longitudinally relative to the outer shaft by a threshold distance.
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 , wherein the feedback mechanism is configured to prevent relative longitudinal movement between the inner and outer shafts when the feedback mechanism is triggered.
4. The instrument of claim 1 , wherein the feedback mechanism comprises an indicator configured to move into a relief to generate at least one of audible, visual, and tactile feedback when the inner shaft is moved longitudinally relative to the outer shaft by the threshold distance.
5. The instrument of claim 4 , wherein the indicator is movably coupled to the outer shaft and the relief is formed in the inner shaft.
6. The instrument of claim 4 , wherein the indicator is movably coupled to the inner shaft and the relief is formed in the outer shaft.
7. The instrument of claim 4 , wherein the indicator has an opening through which the inner shaft passes, the opening having a central axis.
8. The instrument of claim 7 , wherein the indicator is movable between:
a first position in which the central axis of the indicator opening is aligned with a central axis of the inner shaft such that relative longitudinal movement of the inner and outer shafts is not limited by the indicator; and
a second position in which the central axis of the indicator opening is offset from the central axis of the inner shaft and a portion of the indicator is received within the relief of the inner shaft, such that the indicator interferes with relative longitudinal movement of the inner and outer shafts.
9. The instrument of claim 1 , wherein the feedback mechanism comprises an indicator configured to move longitudinally relative to the outer shaft as the inner shaft moves longitudinally relative to the outer shaft, the indicator being visible through an opening formed in a proximal end cap of the instrument.
10. The instrument of claim 9 , wherein the indicator is flush with, protrudes from, or is recessed with respect to an outer surface of the instrument when the inner shaft moves longitudinally relative to the outer shaft by the threshold distance.
11. The instrument of claim 1 , wherein the distal end of the inner shaft has a bearing surface configured to contact and slide across a head portion of an implanted bone anchor shank as the instrument is used to remove bone from around the implanted bone anchor shank.
12. 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.
13. 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.
14. The instrument of claim 13 , 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.
15. The instrument of claim 1 , wherein the feedback mechanism comprises one or more markings of the inner shaft visible through a window formed in the outer shaft and one or more markings of the outer shaft, the markings of the inner and outer shafts providing a visual indication as to the degree of longitudinal movement of the inner shaft relative to the outer shaft.
16. 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.
17. The instrument of claim 16 , wherein the inner shaft includes a plurality of flexible and resilient fingers configured to grasp a head portion of a bone anchor shank.
18. A surgical method, comprising:
driving a shank of a bone anchor into bone;
positioning a reamer instrument over the implanted shank;
manipulating the reamer instrument relative to the shank to remove bone from around the shank, the reamer instrument having an inner shaft slidably mounted within an outer shaft;
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 a feedback mechanism of the reamer instrument, the feedback mechanism being configured to trigger when the inner shaft moves relative to the outer shaft by a threshold distance.
19. The method of claim 18 , wherein said driving comprises rotating the shank relative to the bone using a driver shaft inserted through the inner shaft of the reamer instrument.
20. The method of claim 18 , wherein said positioning comprises inserting a head portion of the shank into an open distal end of the outer shaft of the instrument and contacting the head portion with the inner shaft of the instrument.
21. The method of claim 18 , 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.
22. The method of claim 18 , wherein said generating feedback comprises axially moving an indicator as the inner shaft is displaced axially, the indicator being flush with, protruding from, or recessed with respect to an outer surface of the instrument when the inner shaft moves relative to the outer shaft by the threshold distance.
23. The method of claim 18 , wherein the threshold distance corresponds with an amount of bone removal sufficient to assemble a receiver member to the implanted shank.
24. The method of claim 18 , further comprising separating the instrument from the shank and attaching a receiver member to the implanted shank.
25. The method of claim 18 , further comprising retaining the shank to the instrument by grasping the head of the shank between a plurality of fingers of the inner shaft.