Fixed-handle tunnel drill bit for anterior cruciate ligament replacement surgery and tunnel building device

Abstract

The utility model discloses a fixed handle tunnel drill bit for anterior cruciate ligament replacement surgery and a tunnel building device, and belongs to the technical field of medical instruments, the fixed handle tunnel drill bit for anterior cruciate ligament replacement surgery comprises a drill rod main body, the middle part of the drill rod main body is provided with a center hole for a kirschner wire to penetrate through; a cutting edge is arranged at the front part of the drill rod main body; the rear portion of the drill rod body is provided with a fixed handle quick-insertion section which is used for being inserted into a drill power mobile phone and is in clearance fit with the drill power mobile phone, and the front portion of the fixed handle quick-insertion section is provided with an annular groove used for being matched with the drill power mobile phone to achieve axial positioning. A positioning boss used for being matched with a drilling power mobile phone to achieve circumferential positioning is arranged in the middle of the rear end face of the fixed handle quick insertion section. The fixed-handle tunnel drill bit further comprises a drill bit blocking needle used for being inserted into the center hole. The drill bit is convenient to install, small in run-out error and capable of preventing the center hole of the drill bit from being blocked.

Description

Technical Field

[0001] The utility model relates to the technical field of medical instruments, in particular to a fixed-shank tunnel drill bit and a tunnel building device used for anterior cruciate ligament replacement surgery. Background Art

[0002] The anterior cruciate ligament (ACL) is an important part of the knee joint anatomy. ACL injury is common in clinical practice. There have been many research reports on the treatment and rehabilitation of ACL injury in the knee joint at home and abroad. Currently, surgical treatment is the main treatment for ACL injury in clinical practice. The expansion of the femoral and tibial tunnels in ACL reconstruction / replacement surgery is particularly important and is closely related to the patient's postoperative knee joint stability and functional recovery, graft survival, etc.

[0003] In the ACL replacement surgery navigation system / navigation positioning system, a drill bit that can expand the prefabricated hole is needed. When such a drill bit is used in the navigation system, the drill bit should be able to be installed on a common slow-drilling power mobile phone, and the Kirschner wire should be able to pass through the center hole of the drill bit; when such a drill bit is used in the navigation positioning system, the drill bit should have a quick installation interface so that it can be easily installed on a customized slow-drilling power mobile phone without the help of other tools, and the drill bit should maintain a small runout error after installation, and bone chips should be prevented from filling the center hole of the drill bit during the expansion process, affecting its use. The existing technology is insufficient in these aspects and needs to be improved. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide a fixed-shank tunnel drill bit and a tunnel establishment device for anterior cruciate ligament replacement surgery, which are convenient to install, have small runout error and avoid clogging of the drill center hole.

[0005] In order to solve the above technical problems, the utility model provides the following technical solutions:

[0006] In one aspect, a fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery is provided, comprising a drill rod body, wherein:

[0007] A central hole for inserting a Kirschner wire is provided in the middle of the drill rod body;

[0008] The front portion of the drill rod body is provided with a cutting edge;

[0009] The rear part of the drill rod body is provided with a fixed handle quick-insertion section for being inserted into the drilling power mobile phone and having a clearance fit with the drilling power mobile phone, the front part of the fixed handle quick-insertion section is provided with an annular groove for cooperating with the drilling power mobile phone to realize axial positioning, and the middle part of the rear end surface of the fixed handle quick-insertion section is provided with a positioning boss for cooperating with the drilling power mobile phone to realize circumferential positioning;

[0010] The fixed shank tunnel drill bit also includes a drill stop pin for being inserted into the central hole.

[0011] Furthermore, the drill bit stopper needle comprises a needle body and a first limiting protrusion located at the upper end of the needle body, and a receiving groove for receiving the first limiting protrusion is provided in the middle of the positioning boss;

[0012] And / or, the tolerance of the clearance fit is 0.02 mm.

[0013] Further, the fixed-shank tunnel drill bit is a fixed-shank femoral tunnel drill bit, the axial length of the cutting edge is 0.5-1.5 cm, and the outer diameter of the cutting edge is greater than the outer diameter of the drill rod body;

[0014] And / or, the outer diameter of the drill rod body is smaller than the outer diameter of the fixed-shank quick-insert section.

[0015] Further, the fixed-shank tunnel drill bit is a fixed-shank tibial tunnel drill bit, the axial length of the cutting edge is 2-5 cm, and the outer diameter of the cutting edge is equal to the outer diameter of the drill rod body;

[0016] And / or, the outer diameter of the drill rod body is greater than the outer diameter of the fixed-shank quick-insert section.

[0017] On the other hand, a tunnel establishment device is provided, comprising a drilling power handpiece and the above-mentioned fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery.

[0018] Furthermore, the drilling power mobile phone includes a mobile phone body, wherein:

[0019] The front end of the mobile phone body is rotatably equipped with a transmission shaft, the front part of the transmission shaft extends out of the mobile phone body, the transmission shaft is provided with a drill bit plug-in hole for accommodating the fixed handle quick-insertion section, and the bottom surface of the drill bit plug-in hole is provided with a boss plug-in hole for accommodating the positioning boss;

[0020] The front sliding sleeve of the transmission shaft is provided with a drill chuck, a through hole is provided at a position on the transmission shaft corresponding to the annular groove, a steel ball is provided in the through hole, and a pushing part for pushing the steel ball into the annular groove is provided on the inner side of the middle part of the drill chuck.

[0021] Furthermore, a second limiting protrusion is provided on the inner side of the front portion of the drill chuck, and a retaining spring is provided on the transmission shaft to cooperate with the second limiting protrusion to prevent the drill chuck from falling out;

[0022] And / or, a third limiting protrusion is provided on the transmission shaft behind the pushing portion, and a spring is sleeved on the transmission shaft between the pushing portion and the third limiting protrusion.

[0023] Furthermore, a first bearing and a second bearing are provided at intervals on the portion of the transmission shaft located inside the mobile phone body, and silicone rubber and an outer spacer are provided in sequence on the portion of the transmission shaft between the first bearing and the second bearing.

[0024] Furthermore, a brushless motor is provided in the mobile phone body at the rear of the transmission shaft, and the brushless motor is driven and connected to the rear end of the transmission shaft through a reduction gearbox assembly.

[0025] Furthermore, the mobile phone body includes a front cap for accommodating the transmission shaft, a middle sleeve for accommodating the reduction box assembly, and a rear body for accommodating the brushless motor, which are threadedly connected in sequence from front to back.

[0026] The utility model has the following beneficial effects:

[0027] The utility model discloses a fixed-shank tunnel drill and a tunnel establishing device for anterior cruciate ligament replacement surgery. The fixed-shank tunnel drill is provided with a fixed-shank quick-insertion section that is clearance-matched with a drill power mobile phone. The front part of the fixed-shank quick-insertion section is provided with an annular groove for cooperating with the drill power mobile phone to achieve axial positioning. The middle part of the rear end surface of the fixed-shank quick-insertion section is provided with a positioning boss for cooperating with the drill power mobile phone to achieve circumferential positioning. In this way, the interface between the fixed-shank tunnel drill and the drill power mobile phone adopts a specific fixed-shank quick-insertion structure (clearance fit + annular groove + positioning boss). Compared with the traditional three-jaw chuck structure, the fixed-shank quick-insertion structure can be quickly installed without the aid of tools, and the interface form of the shaft hole matching can better ensure the coaxiality and circular runout error between the drill bit and the drill power mobile phone; and the drill stopper needle is inserted into the fixed-shank tunnel drill to prevent bone chips from entering the hollow part of the tunnel drill during the cutting process. This design can meet the needs of a set of hollow drill bits, which can be used in a navigation system (without a mechanical arm) in combination with a Kirschner wire, and can also be used in a navigation positioning system (with a mechanical arm). Therefore, the utility model is easy to install, has a small run-out error and can avoid clogging of the center hole of the drill bit. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of a fixed shank tunnel drill bit of the utility model;

[0029] Figure 2 It is a structural schematic diagram of another structural form of the fixed shank tunnel drill bit of the utility model;

[0030] Figure 3 This is a structural schematic diagram of the drill bit stopper in the utility model;

[0031] Figure 4 It is a schematic diagram of the cross-sectional structure of the tunnel building device of the present utility model. DETAILED DESCRIPTION

[0032] In order to make the technical problems to be solved, technical solutions and advantages of the present invention more clear, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0033] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0034] On the one hand, the utility model provides a fixed-shank tunnel drill bit 1 for anterior cruciate ligament replacement surgery, such as Figure 1-3 As shown, it includes a drill pipe body 11, wherein:

[0035] A central hole 111 for inserting a Kirschner wire is provided in the middle of the drill rod body 11;

[0036] The front of the drill pipe body 11 (such as Figure 1 A cutting edge 12 is provided at the portion (in the direction indicated by the middle arrow);

[0037] The rear part of the drill rod body 11 is provided with a fixed handle quick-insertion section 13 for being inserted into the drilling power mobile phone 2 and having a clearance fit with the drilling power mobile phone 2, the front part of the fixed handle quick-insertion section 13 is provided with an annular groove 131 for cooperating with the drilling power mobile phone 2 to achieve axial positioning, and the middle part of the rear end surface of the fixed handle quick-insertion section 13 is provided with a positioning boss 132 for cooperating with the drilling power mobile phone 2 to achieve circumferential positioning;

[0038] The fixed-shank tunnel drill bit 1 also includes a drill stopper needle 14 for being inserted into the center hole 111 to effectively block the center hole 111 of the drill bit and prevent bone chips from filling up the center hole 111 of the drill bit during the drilling process.

[0039] When used during surgery, the knee joint is flexed 90 degrees, and the doctor removes the damaged and torn anterior cruciate ligament according to conventional techniques. After the reconstruction / replacement position of the anterior cruciate ligament is determined, when used in a navigation system (without a mechanical arm), there is no need to use the drill stopper 14. The fixed handle quick-insertion section 13 of the drill rod body 11 can be directly inserted into the drill power mobile phone 2 and then used in conjunction with the Kirschner wire; when used in a navigation positioning system (with a mechanical arm), the drill stopper 14 can be first inserted into the center hole 111 of the drill rod body 11, and then the fixed handle quick-insertion section 13 of the drill rod body 11 can be inserted into the drill power mobile phone 2 for use. At this time, the annular groove 131 can cooperate with the drill power mobile phone 2 to achieve axial positioning, and the positioning boss 132 can cooperate with the drill power mobile phone 2 to achieve circumferential positioning, and the drill power mobile phone 2 can be started to expand the hole.

[0040] The utility model discloses a fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery, which is provided with a fixed-shank quick-insertion section that is clearance-matched with a drill power mobile phone, a front portion of the fixed-shank quick-insertion section is provided with an annular groove that is used to cooperate with the drill power mobile phone to achieve axial positioning, and a positioning boss that is used to cooperate with the drill power mobile phone to achieve circumferential positioning is provided in the middle portion of the rear end surface of the fixed-shank quick-insertion section. In this way, the interface between the fixed-shank tunnel drill bit and the drill power mobile phone adopts a specific fixed-shank quick-insertion structure (clearance fit + annular groove + positioning boss). Compared with the traditional three-jaw chuck structure, the fixed-shank quick-insertion structure can be quickly installed without the aid of tools, and the interface form of the axial hole fit can better ensure the coaxiality and circular runout error between the drill bit and the drill power mobile phone; and the drill stopper needle is inserted into the fixed-shank tunnel drill bit to prevent bone chips from entering the hollow part of the tunnel drill bit during the cutting process. This design can meet the needs of a set of hollow drill bits, and can be used in a navigation system (without a robotic arm) in combination with a Kirschner wire, and can also be used in a navigation positioning system (with a robotic arm). Therefore, the fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery of the utility model is easy to install, has a small run-out error and can avoid clogging of the center hole of the drill bit.

[0041] According to the specific structure of the fixed shank tunnel drill bit 1, it can have the following structural forms.

[0042] Structural form 1

[0043] like Figure 1 As shown, the fixed-shank tunnel drill bit 1 can be a fixed-shank femoral tunnel drill bit, and the axial length of the cutting edge 12 is 0.5-1.5 cm, for example, 0.8 cm, 1 cm, 1.3 cm, etc. Since an excessively long cutting edge 12 will scratch the periosteum and other soft tissues in the non-surgical part during the femoral drilling process, in this embodiment, reducing the length of the cutting edge 12 can better avoid this problem. At the same time, in order to ensure chip removal and cutting efficiency, it is necessary to reduce the diameter of the rod portion of the non-cutting edge portion, that is, the outer diameter of the cutting edge 12 can be larger than the outer diameter of the drill rod body 11, and the outer diameter of the drill rod body 11 can be smaller than the outer diameter of the fixed-shank quick-insert section 13.

[0044] Structural form 2

[0045] like Figure 2 As shown, the fixed-shank tunnel drill bit 1 can be a fixed-shank tibial tunnel drill bit, and the axial length of the cutting edge 12 is 2-5 cm, for example, 3 cm, 4 cm, 4.5 cm, etc. Since the preparation of the tibial bone tunnel will not cause damage to other non-surgical tissues by the blade, the cutting edge 12 can be made according to the length of the tibial bone tunnel; the outer diameter of the cutting edge 12 can be equal to the outer diameter of the drill rod body 11, and the outer diameter of the drill rod body 11 can be larger than the outer diameter of the fixed-shank quick-insert section 13, at this time, the use effect is best.

[0046] In the above-mentioned structural forms 1 and 2, the cutting edge 12 of the fixed-shank tunnel drill bit 1 can be spiral, and the diameter of the drill bit cutting edge 12 should meet the use requirements of conventional anterior cruciate ligament replacement surgery, that is, the diameter of the cutting edge 12 should have at least different specifications such as φ4.5, φ5, φ6, φ7, φ8, φ9, φ10, φ12, etc., and the length of the cutting edge 12 should meet the different cutting requirements of the tibia and femur.

[0047] like Figure 1-3 As shown, the drill needle stopper 14 may include a needle body 141 and a first limiting protrusion 142 located at the upper end of the needle body 141, and a receiving groove 133 for accommodating the first limiting protrusion 142 is provided in the middle of the positioning boss 132. Such a design can not affect the normal installation of the fixed-shank tunnel drill 1. The tolerance of the clearance fit between the fixed-shank quick-insertion section 13 and the drilling power mobile phone 2 can be 0.02mm (that is, the clearance between the two is guaranteed to be within 0.02mm through mechanical processing), so that the fixed-shank tunnel drill 1 will not shake in the radial direction. The smaller the radial runout error, the more ideal bone channel accuracy can be obtained.

[0048] On the other hand, the utility model provides a tunnel establishment device, including a drilling power mobile phone 2 and the above-mentioned fixed-shank tunnel drill bit 1 for anterior cruciate ligament replacement surgery. Since the structure of the fixed-shank tunnel drill bit 1 is the same as above, it will not be repeated here.

[0049] The tunnel establishment device of the utility model comprises a drilling power mobile phone and a fixed-shank tunnel drill bit. The fixed-shank tunnel drill bit is provided with a fixed-shank quick-insertion section which is clearance matched with the drilling power mobile phone. The front part of the fixed-shank quick-insertion section is provided with an annular groove for matching with the drilling power mobile phone to realize axial positioning. The middle part of the rear end surface of the fixed-shank quick-insertion section is provided with a positioning boss for matching with the drilling power mobile phone to realize circumferential positioning. In this way, the interface between the fixed-shank tunnel drill bit and the drilling power mobile phone adopts a specific fixed-shank quick-insertion structure (clearance match + annular groove + positioning boss). Compared with the traditional three-jaw chuck structure, the fixed-shank quick-insertion structure can be quickly installed without the aid of tools, and the interface form of the shaft hole matching can better ensure the coaxiality and circular runout error of the drill bit and the drilling power mobile phone; and the drill stopper needle is inserted into the fixed-shank tunnel drill bit to prevent bone chips in the cutting process from entering the hollow part of the tunnel drill bit. This design can meet the needs of a set of hollow drill bits, which can be used in a navigation system (without a mechanical arm) in combination with a Kirschner wire, and can also be used in a navigation positioning system (with a mechanical arm). Therefore, the utility model is easy to install, has a small run-out error and can avoid clogging of the center hole of the drill bit.

[0050] like Figure 4 As shown, the drilling power mobile phone 2 may include a mobile phone body 21, wherein:

[0051] The front end of the mobile phone body 21 is rotatably equipped with a transmission shaft 22, the front part of the transmission shaft 22 extends out of the mobile phone body 21, and a drill plug hole 221 for accommodating the fixed handle quick plug section 13 is provided in the transmission shaft 22 (the drill plug hole 221 and the fixed handle quick plug section 13 are clearance-matched), and a boss plug hole (not shown) for accommodating the positioning boss 132 is provided on the bottom surface of the drill plug hole 221;

[0052] A drill chuck 23 is provided on the front sliding sleeve of the transmission shaft 22. A through hole 222 is provided at a position corresponding to the annular groove 131 on the transmission shaft 22. A steel ball 223 is provided in the through hole 222. A pushing portion 231 is provided on the inner side of the middle part of the drill chuck 23 for pushing the steel ball 223 into the annular groove 131.

[0053] When in use, unlock the drill chuck 23, insert the fixed shank quick-insertion section 13 of the fixed shank tunnel drill bit 1 into the drill bit plug-in hole 221 of the transmission shaft 22, and make the positioning boss 132 of the fixed shank tunnel drill bit 1 be located in the boss plug-in hole of the transmission shaft 22, then move the drill chuck 23, so that the pushing part 231 of the drill chuck 23 pushes the steel ball 223 into and is stuck in the annular groove 131 of the fixed shank quick-insertion section 13 (that is, the drill chuck 23 is in a locked state), thereby ensuring that the fixed shank tunnel drill bit 1 is fixed in the axial direction.

[0054] In order to facilitate the limited installation of the drill chuck 23, a second limited protrusion 232 may be provided on the inner side of the front part of the drill chuck 23, and a retaining ring 233 (specifically, a shaft earless retaining ring) that cooperates with the second limited protrusion 232 to prevent the drill chuck 23 from coming out may be provided on the transmission shaft 22. A third limited protrusion 224 may be provided on the transmission shaft 22 behind the pushing portion 231, and a spring 225 is sleeved between the pushing portion 231 and the third limited protrusion 224 on the transmission shaft 22, so that the drill chuck 23 is automatically reset to a locked state, thereby improving the convenience of use.

[0055] A first bearing 226 and a second bearing 227 (both of which can be high-speed bearings) can be provided at intervals on the part of the transmission shaft 22 located inside the mobile phone body 21. Silicone rubber 228 and an outer spacer 229 are provided in sequence on the part of the transmission shaft 22 between the first bearing 226 and the second bearing 227. The first bearing 226 and the second bearing 227 can axially fix the transmission shaft 22 to ensure coaxial transmission while increasing transmission accuracy and rotation stability.

[0056] A brushless motor 211 may be provided behind the transmission shaft 22 in the mobile phone body 21. The brushless motor 211 is driven by a reduction gear assembly 212 to connect to the rear end of the transmission shaft 22. The use of the reduction gear assembly 212 can effectively reduce the rotation speed of the brushless motor 211 and increase the torque, thereby improving efficiency. Figure 4 The middle number 216 is an elastic retaining ring for the shaft, 217 is a cross countersunk screw, and 218 is a skeleton sealing ring.

[0057] The mobile phone body 21 may include a front cap 213 for accommodating the transmission shaft 22, a middle sleeve 214 for accommodating the reduction gearbox assembly 212, and a rear body 215 for accommodating the brushless motor 211, which are threadedly connected in sequence from front to back. The threaded connections of the various parts are convenient for disassembly and installation, and thus convenient for replacing damaged parts.

[0058] The above is a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery, characterized in that: It comprises a drill pipe body, wherein: A central hole for inserting a Kirschner wire is provided in the middle of the drill rod body; The front portion of the drill rod body is provided with a cutting edge; The rear part of the drill rod body is provided with a fixed handle quick-insertion section for being inserted into the drilling power mobile phone and having a clearance fit with the drilling power mobile phone, the front part of the fixed handle quick-insertion section is provided with an annular groove for cooperating with the drilling power mobile phone to realize axial positioning, and the middle part of the rear end surface of the fixed handle quick-insertion section is provided with a positioning boss for cooperating with the drilling power mobile phone to realize circumferential positioning; The fixed shank tunnel drill bit also includes a drill stop pin for being inserted into the central hole.

2. The fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery according to claim 1, characterized in that: The drill bit stopper needle comprises a needle body and a first limiting protrusion located at the upper end of the needle body, and a receiving groove for receiving the first limiting protrusion is provided in the middle of the positioning boss; And / or, the tolerance of the clearance fit is 0.02 mm.

3. The fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery according to claim 1, characterized in that: The fixed-shank tunnel drill bit is a fixed-shank femoral tunnel drill bit, the axial length of the cutting edge is 0.5-1.5 cm, and the outer diameter of the cutting edge is greater than the outer diameter of the drill rod body; And / or, the outer diameter of the drill rod body is smaller than the outer diameter of the fixed-shank quick-insert section.

4. The fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery according to claim 1, characterized in that: The fixed-shank tunnel drill bit is a fixed-shank tibial tunnel drill bit, the axial length of the cutting edge is 2-5 cm, and the outer diameter of the cutting edge is equal to the outer diameter of the drill rod body; And / or, the outer diameter of the drill rod body is greater than the outer diameter of the fixed-shank quick-insert section.

5. A tunnel establishment device, characterized in that: The invention comprises a drilling power mobile phone and a fixed-shank tunnel drill bit for anterior cruciate ligament replacement surgery as described in any one of claims 1 to 4.

6. The tunnel establishment device according to claim 5, characterized in that: The drilling power mobile phone comprises a mobile phone body, wherein: The front end of the mobile phone body is rotatably equipped with a transmission shaft, the front part of the transmission shaft extends out of the mobile phone body, the transmission shaft is provided with a drill bit plug-in hole for accommodating the fixed handle quick-insertion section, and the bottom surface of the drill bit plug-in hole is provided with a boss plug-in hole for accommodating the positioning boss; The front sliding sleeve of the transmission shaft is provided with a drill chuck, a through hole is provided at a position on the transmission shaft corresponding to the annular groove, a steel ball is provided in the through hole, and a pushing part for pushing the steel ball into the annular groove is provided on the inner side of the middle part of the drill chuck.

7. The tunnel establishment device according to claim 6, characterized in that: A second limiting protrusion is provided on the inner side of the front portion of the drill chuck, and a retaining spring is provided on the transmission shaft to cooperate with the second limiting protrusion to prevent the drill chuck from falling out; And / or, a third limiting protrusion is provided on the transmission shaft behind the pushing portion, and a spring is sleeved on the transmission shaft between the pushing portion and the third limiting protrusion.

8. The tunnel establishment device according to claim 6, characterized in that: The portion of the transmission shaft located in the mobile phone body is provided with a first bearing and a second bearing at intervals, and the portion of the transmission shaft between the first bearing and the second bearing is provided with silicone rubber and an outer spacer in sequence.

9. The tunnel establishment device according to claim 6, characterized in that: A brushless motor is arranged behind the transmission shaft in the mobile phone body, and the brushless motor is driven and connected to the rear end of the transmission shaft through a reduction box assembly.

10. The tunnel establishment device according to claim 9, characterized in that: The mobile phone body comprises a front cap for accommodating the transmission shaft, a middle sleeve for accommodating the reduction box assembly, and a rear body for accommodating the brushless motor, which are threadedly connected in sequence from front to back.

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