REAR-RETAINING STRUCTURE FOR DYNAMIC HIP SCREW
A rear-retaining structure for dynamic hip screw (DHS) includes a retaining block and a positioning element. The dynamic hip screw comprises a lag screw, a sideplate, a sleeve with a higher orifice and a lower orifice, and a compression screw. The retaining block of the rear-retaining structure is attached to the sideplate of the dynamic hip screw by the positioning element. A stopper portion of the retaining block is located opposite to the lower orifice of the sleeve. The height of the highest point of the stopper portion in the lower orifice is in inverse proportion to the distance that the lag screw and the compression screw are allowed to slip back in the sleeve from an implant position to the lower orifice; namely, the higher the height of the highest point of the stopper portion is in the lower orifice, the smaller the distance for the slip back.
1. Technical Field of the Invention
The present invention relates to a rear-retaining structure for dynamic hip screw (DHS). Especially, the present invention relates to a rear-retaining structure attached to a dynamic hip screw to stop the slip back or provide a limited macro-slip back of the lag screw and the compression screw of DHS.
2. Prior Arts
Clinically, proximal femoral fractures are common hip fractures. Internal fixation systems, such as DHS system and intramedullary fixation system are used in the current treatments. According to clinical implementations and researches, the therapeutic effect of DHS on the stable proximal femoral fracture has been affirmed.
As showed in
In the healing process of proximal femur fracture, there are some factors causing a lot of stress to the lag screw 1 and compression screw 4 of DHS, including the component force for neck inversion, weight pressure, shear forces from muscle stretches, external rotation force of lower limb, cyclical stress-strain changes occurring at the fracture, and axial micro-movement bearing at the ends of fracture. The stress may cause the lag screw 1 and compression screw 4 to produce an excessive sliding back phenomenon (referred to as “slip back”), as showed in
In some of the fracture healing process, allowing the lag screw 1 and compression screw 4 a limited sliding back, referred to as “macro slip back”, will reduce the shear and stress concentration at the fracture, and prevent the downward shift of proximal fracture bone and the formation of collapse, inversion and slumping of femoral neck angle. But in other fracture healing process, it is also beneficial for fracture healing to fix the lag screw 1 and compression screw 4 for blocking their slip back. Therefore, whether the lag screw 1 and compression screw 4 should be in fixation or macro slip back depends on the individual condition of fractures.
SUMMARY OF INVENTIONThe problem to be resolved in this invention is related to the excessive sliding back phenomenon of the lag screw and compression screw that occurred in conventional dynamic hip screw (DHS).
Accordingly, in one aspect, the present invention provides a rear-retaining structure for dynamic hip screw (DHS), which comprises a lag screw, a sideplate, a sleeve, and a compression screw, wherein the sleeve is obliquely connected to the top of the sideplate; the sleeve has an axial bore passing through the shaft axis of the sleeve, forming an upper orifice and a lower orifice at the two ends of the sleeve; the end of the lag screw enters the sleeve from the upper orifice, and the compression screw locks into the end of the lag screw from the lower orifice. The dynamic hip screw is to be fixed in the femoral neck fracture of the proximal femur.
The rear-retaining structure comprises a retaining block and a positioning element, wherein the positioning element mounts the retaining block on the surface of the sideplate at a position adjacent to the lower orifice of the sleeve; and the retaining block has a stopper portion opposite to the lower orifice. The height of the highest point of the stopper portion in the lower orifice is in inverse proportion to the distance that the lag screw and the compression screw are allowed to slip back in the sleeve from an implant position to the low orifice. In other words, the higher the height of the highest point of the stopper portion is in the lower orifice, the smaller the distance for the slip back.
In a first embodiment, the highest point of the stopper portion is located below the center of the lower orifice. There is a distance between the highest point of the stopper portion and the end surface of the compression screw at the implant site to allow the lag screw and the compression screw to slip back in the sleeve from the implant site to the low orifice. Preferably, the maximum range for slip back is controlled within about 10 mm.
In a further embodiment, the highest point of the stopper portion is located above the center of the lower orifice. There is no distance between the highest point of the stopper portion and the end surface of the compression screw at the implant site. The highest point of the stopper portion just withstands the end surface of the compression screw at the implant site to prevent the slip back of the lag screw and compression screw by fixing them at the implant position.
Effects of the InventionAccording to the present invention, after DHS is implanted into the position of a proximal femur fracture, the rear-retaining structure of the first embodiment allows the lag screw and compression screw of DHS for a limited macro slip back in response to the axial inching at the both sides of the fracture. The maximum range for slip back is controlled within about 10 mm. When the allowed macro-slip back distance is reached, the lag screw and compression screw will be stopped by the rear-retaining structure.
According to the rear-retaining structure of the present invention, the lag screw of DHS will allow a limited macro-slip back under a controlled condition. Therefore, a controlled fine axial inching at the both sides of the fracture is allowed to proceed for promoting callus formation and calcification, which can accelerate fracture healing. The rear-retaining structure of the present invention strengthens the dynamic compression effects of DHS to assist a faster healing of proximal femoral fracture.
According to the present invention, by the action of the rear-retaining structure, the lag screw and compression screw of DHS will allow a limited macro-slip back to fit the fine axial inching at the both sides of fracture. The axial inching will disperse the shear and stress, and reduce the probability of the collapse of the femoral neck angle caused by the downward shift of the proximal fracture fragment, and the cut out of lag screw to pierce from the femoral neck.
According to another embodiment of the present invention, after DHS is implanted into the position of a proximal femur fracture, the rear-retaining structure fixes the lag screw and compression screw of DHS at the implanted position to block the slip back of the lag screw and compression screw.
The rear-retaining structure of the present invention can not only stop the lag screw and compression screw, but also provide a function for supporting the lag screw and compression screw to reduce the bend or break of the lag screw caused by the concentrated stress.
Preferably, the rear-retaining structures according to the present invention are suitable for the fracture types 31-A1 to 31-C3 as defined in the AO Classification.
The other characteristics and advantages of the present invention will be further illustrated and described in the following examples. The examples described herein are used for illustrations, not for limiting the invention.
The elements or objects described in the following Embodiments are drawn according to the proportion, size, amount of deformation or amount of shift suitable for illustration, and might not to the scale of actual elements. Similar elements are represented by the same reference numerals.
The sideplate 2 is mounted outside the shaft of the femur 91 with bone screws (not showed). The compression screw 4 is inserted through the lower orifice 7 of the sleeve 3 and locked into the end of the lag screw 1. The tightening of the compression screw 4 will cause the lag screw 1 to lead the proximal end of the fracture outward and downward along the axis of the sleeve 3, resulting in the closing of the ends of the fracture onto each other, due to the functions of the sleeve 3 in supporting and preventing rotation of the lag screw 1. After confirming that the fracture has achieved the desired abutting, the lag screw 1 and compression screw 4 are positioned in the implant position, then a rear-retaining structure 8 is attached to the sideplate 2 of the DHS by way of screw locking.
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In the healing process of proximal femoral fractures, there are some factors causing a lot of stress to the lag screw 1 and the compression screw 4 of DHS, including the component force for neck inversion, weight pressure, shear forces from muscle stretches, external rotation force of lower limb, cyclical stress-strain changes occurring at the fracture, and axial micro-movement bearing at the ends of fracture. These factors will make the lag screw 1 slip back down along the sleeve 3. When the allowed limit of macro-slip back is reached, the nail head 401 of the compression screw 4 is stopped by the stopper portion 11 of the retaining block 10, as showed in
The allowance for the lag screw 1 and the compression screw 4 to produce a limited macro-slip back will allow the both sides of the fracture to proceed a controlled fine axial inching (referred micro-inching), which may promote callus formation and calcification, accelerate fracture healing, strengthen the dynamic compression effects of DHS to assist a faster healing of proximal femoral fracture, and will disperse the shear and stress to reduce the probability of the collapse of the femoral neck angle caused by the downward shift of the proximal fracture fragment and the cut out of lag screw to pierce from the femoral neck.
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In summary, whether the rear-retaining structure showed in
Claims
1. A dynamic hip screw (DHS) with a rear-retaining structure, comprising:
- a dynamic hip screw, which comprises a lag screw, a sideplate, a sleeve, and a compression screw, wherein the sleeve is obliquely connected to a top end of the sideplate; the sleeve has an axial bore passing through a first end of the sleeve to form a lower orifice and through a second end of the sleeve to form an upper orifice; a lower end of the lag screw enters the sleeve from the upper orifice, and the compression screw locks into the lower end of the lag screw from the lower orifice; and the sideplate has a fixation hole set at a position near the lower orifice of the sleeve, and
- a rear-retaining structure, which comprises: a retaining block, and a positioning element;
- wherein the positioning element is fixed in the fixation hole; the retaining block is mounted on an outer surface of the sideplate at a position adjacent to the lower orifice of the sleeve; the retaining block has a stopper portion opposite to the lower orifice, wherein the highest point of the stopper portion is located below the center of the lower orifice, and a gap exists between the highest point of the stopper portion and an end surface of a nail head of the compression screw at the implant site to allow the lag screw and the compression screw to slip back in the sleeve from the implant site toward the lower orifice; and when the dynamic hip screw is fixed in a femoral neck fracture of a proximal femur, the higher the stopper portion is in the lower orifice, the smaller is the distance that the lag screw and the compression screw are allowed to slip back in the sleeve from an implant position toward the lower orifice.
2. (canceled)
3. (canceled)
4. The dynamic hip screw with a rear-retaining structure of claim 1, wherein the highest point of the stopper portion is located above the center of the lower orifice.
5. The dynamic hip screw with a rear-retaining structure of claim 1, wherein the positioning element is integrally formed with the side of the retaining block.
6. The dynamic hip screw with a rear-retaining structure of claim 1, wherein the retaining block has a bore, the positioning element has a nail head and passes through the bore to be fixed into the fixation hole of the sideplate, and the nail head presses and positions the retaining block on the outer surface of the sideplate.
7. The dynamic hip screw with a rear-retaining structure of claim 1, further comprising a container housing tank set on the surface of the sideplate and located below the lower orifice of the sleeve, and a communicating part set between the lower orifice and the container housing tank, wherein the fixation hole is located in a slot base of the container housing tank; the retaining block is locked in the container housing tank by the positioning element; and the stopper portion is located opposite to a lower edge of the lower orifice by passing through the communicating part.
8. The dynamic hip screw with a rear-retaining structure of claim 1, wherein the stopper portion is a part of an upward-extending peripheral edge of the retaining block and has at least one concave portion at sides thereof; a container housing tank is set on the outer surface of the sideplate and located below the lower orifice of the sleeve; a communicating part is set between the lower orifice and the container housing tank; at least one protrusion is set on two opposite side walls of the communicating part; the fixation hole is located in a slot base of the container housing tank; the retaining block is fixed in the container housing tank by the positioning element, the stopper portion is located opposite to the lower edge of the lower orifice through the communicating part; and the at least one protrusion is embedded in the at least one concave portion respectively.
9. A dynamic hip screw (DHS) with a rear-retaining structure, comprising:
- a dynamic hip screw, which comprises a lag screw, a sideplate, a sleeve, and a compression screw, wherein the sleeve is obliquely connected to a top end of the sideplate; the sleeve has a axial bore passing through a first end of the sleeve to form a lower orifice and through a second end of the sleeve to form an upper orifice; a lower end of the lag screw enters the sleeve from the upper orifice, and the compression screw locks into the lower end of the lag screw from the lower orifice; and the sideplate has a fixation hole set at a position near the lower orifice of the sleeve, and
- a rear-retaining structure, which comprises: a retaining block, and a positioning element;
- wherein the positioning element is fixed in the fixation hole; the retaining block is mounted on an outer surface of the sideplate at a position adjacent to the lower orifice of the sleeve; the retaining block has a stopper portion opposite to the lower orifice; and the highest point of the stopper portion is located above the center of the lower orifice.
10. The dynamic hip screw with a rear-retaining structure of claim 9, wherein when the dynamic hip screw is fixed in a femoral neck fracture of a proximal femur, no gap exists between the highest point of the stopper portion and an end surface of a nail head of the compression screw at the implant site, such that the highest point of the stopper portion withstands the end surface of the compression screw at the implant site, and the lag screw and the compression screw are fixed at the implant position.
11. The dynamic hip screw with a rear-retaining structure of claim 1, wherein when the dynamic hip screw is fixed in a femoral neck fracture of a proximal femur, the shortest distance between the highest point of the stopper portion and the end surface of the nail head of the compression screw at the implant site is 10 mm.
Type: Application
Filed: Nov 24, 2014
Publication Date: May 26, 2016
Inventors: Yung-Fang Tsai (Taichung), Pei-Yuan Lee (Taichung), Tsung-Chen Liu (Taichung)
Application Number: 14/551,620