Why does the INTERTAN nail have a trapezoidal shape?
The smaller cross-section of the INTERTAN nail has the advantage of preserving the Gluteus Medius Tendon while at the same time not compromising the overall strength of the implant. The trapezoidal shape of the nail places more material at the lateral side of the implant where tensile forces are typically the strongest. In addition, the nail's trapezoidal profile also provides enhanced anatomical fit
and added rotational stability in the proximal femoral metaphysis similar to that offered by conventional hip stems.
What is an Integrated Interlocking Screw configuration and how will it help my patients?
The integrated interlocking screws of the INTERTAN system increase stability and resistance to both intra and post-operative fracture rotation about the implant by providing two points of fixation within the femoral neck and head. This directly reduces rotational instability and eliminates the possibility of implant failure due to Z-Effect. The integrated screw configuration is a fourth generation intramedullary nail concept combining the enhanced rotational stability of the TRIGEN Reconstruction Nail with the superior controlled sliding and compression of the IMHS™ implant. The INTERTAN system incorporates the best aspects of both devices by providing both single and dual integrated lag screws for the treatment of most major fracture patterns.
What is Z-Effect and how does INTERTAN solve it?
Z-Effect is an unfortunate by-product of most intramedually nails that utilize two screws placed up into the femoral neck and head. Typically, the superior screw is of smaller diameter than the inferior and bears a disproportionate amount of load during weight bearing. Excessive varus forces placed on the smaller screw at the lateral cortex cause it to toggle and either back out or migrate through the femoral head into the acetabulum. The larger inferior screw is neither keyed in rotation nor locked in place, and it too will either back out or migrate medially. The resultant Z-Effect where the two screws move in opposite directions is one mode of failure for the conventional two screw reconstruction device. The INTERTAN nail turns that construct upside down and integrates the two screws so that they act as one device to bear all load, enact all compression and prevent excessive medial or lateral migration thus negating the Z-Effect.
Why do I ream with a 16mm channel reamer and the nail size is larger?
Upon its initial insertion into the proximal femur, the INTERTAN nail exerts a small amount of press-fit within the canal by virtue of its trapezoidal cross-section. Once the correct degree of femoral neck anteversion has been determined, the nail can then be impacted into the proximal femoral metaphysis acting essentially as a broach to further enhance the initial press-fit. This has the distinct advantage of fixing the nail in correct orientation with respect to neck anteversion and preventing excessive rotation of the nail within the canal and possible soft tissue tethering/damage. The 17mm reamer is available to accommodate those instances when dense bone is encountered such that it precludes that initial press-fit.
Why does the short nail have a clothespin distal tip?
The clothespin distal tip of the INTERTAN short nail reduces the overall cross-sectional stiffness of the implant to minimize the risk of iatrogenic fracture during insertion, to ease the actual process of nail insertion and to offer enhanced rotational stability within the proximal femoral canal. As the distal tip of the INTERTAN nail encounters the AP bow of the proximal femur, it closes slightly changing the implant's straight profile to bent. This has the advantage of lessening point stresses about the distal tip of the nail and reducing the possibility of fracture due to a stress riser at that location.
If I only use the single subtrochanteric lag screw option does that create a stress riser at the empty inferior hole in the nail?
Fatigue testing was performed with the nail and single subtrochanteric screw construct undergoing a typical 10° adduction/flexion cycle. This is the same orientation used in the testing of femoral stems for total joint replacement. The INTERTAN nail was compared to the TAN nail in two screw reconstruction nail mode and was found to be equally as strong, completing 500,000 cycles at 350 lbs load without failure. This is representative of approximately six months implantation time at which fracture union should have occurred. Our mechanical testing data reveals no significant stress riser occurring at that point.
I have been using a single screw IM device for the last 20 years and have yet to have one cut out. Do I have to use the integrated screws?
Absolutely not. One of the advantages of the INTERTAN system is that it provides you with options to treat a wide variety of fracture patterns. However, you are probably well aware that approximately 25% of all hip fractures are unstable and one in five (20%) will actually fail due to implant cut out. Our designing surgeons feel that rotational instability is a major contributing factor to that failure rate and propose the INTERTAN nail as the solution to this dilemma. The problem lies in the fact that even implants that are keyed to prevent rotation can still experience rotation of the fragments about the axis of the lag screw. Placement of a secondary point of fixation into the femoral neck and head reduces the chances of rotation but adds the secondary concern of Z-Effect. The INTERTAN nail solves that problem by integrating two screws so that they function as one unit to prevent rotation and excessive screw migration. Mechanical testing of the two screw construct was stopped at 100,000 cycles with no evidence of implant cut out, further reinforcing the INTERTAN nail philosophy.
What is the lateral valgus offset of the INTERTAN nail?
The INTERTAN nail has a 4° valgus offset, allowing for an optimal insertion trajectory into the femoral canal. Excessively lateral nail insertion can cause damage to the abductor muscle group, the effects of which are not entirely clear. Recent literature (JOT Vol. 19, #10. November/December 2005 pp. 681- 685) states that a nail starting point at the tip or even just medial to the tip provides excellent fracture alignment results. A 4°, 5° or 6° valgus offset may not be of major clinical significance as stand alone variables. They must be examined relative to the location of the offset, the AP bow of the nail and the location of the nail entry point in both the AP and LM planes in order to get a complete picture.
How do I know when to use the integrated interlocking screws vs. the single subtrochanteric lag screw option with the INTERTAN nail?
Approximately 25% of proximal femur fractures are biomechanically unstable and one in five (20%) will fail due to femoral neck/head cut out. These fractures require enhanced fixation in order to maximize their postoperative stability, and single screw, keyed implants can still experience rotational instability about the lag screw. The INTERTAN integrated interlocking screws provide enhanced rotational stability and superior weight-bearing capability. The active linear compression driven by the integrated screws gives the surgeon clear visible and tactile confirmation of intraoperative fracture reduction. The dual screw option is ideal for unstable fractures or for those surgeons simply wanting enhanced confirmation of fracture reduction. Surgeons comfortable with the single subtrochanteric lag screw will appreciate the fact that the INTERTAN nail provides that as well.
Why does Smith & Nephew have two implants (INTERTAN nail & IMHS™ CP hip screws) that treat the same fractures?
No two fractures are exactly alike and so to say that one implant can adequately treat every injury is misleading. In as much, we need to look at the INTERTAN nail and IMHS CP hip screw as two very different stand- alone systems that complement one another. We want to appeal to as wide a customer base as possible and feel that we would be doing a disservice to our surgeons if we attempted to give them one nail to treat every fracture that walked through their clinic door. IMHS CP hip screws are proven in the literature to out-perform the Gamma-type device in postoperative controlled sliding. Its lower coefficient of friction facilitates superior sliding of the lag screw within the barrel of the nail relative to other single screw devices to promote fracture healing. The INTERTAN nail offers a two screw solution for enhanced rotational stability and active linear compression for visual and tactile compression of the fracture. The integrated interlocking screws provide superior life to cut out and so offer surgeons a viable treatment modality for highly unstable fracture patterns. Smith & Nephew is a solutions-based medical device company and as such we are geared to providing our surgeons with a wide variety of products for the treatment of their patients.
Why do I ream with a 16mm reamer and the nail size is larger?
Proximally, the width of the INTERTAN nail measures 16.25mm x 15.25mm. This trapezoidal cross-section allows a larger diameter nail to fit into a smaller hole thus reducing the total amount of bone removed. The nail's shape in association with the smaller entry portal give it enhanced rotational stability within the proximal femur. The trapezoidal vertices of the nail cause it to press-fit into the
femoral metaphysis and provide enhanced rotational control vs. a round geometry nail. This is important in the proximal femur where maintenance of correct femoral neck anteversion during lag screw placement is essential to the prevention of implant cut out. Should the surgeon encounter very dense bone during nail insertion, the 17mm reamer will over-ream the proximal femur and allow the nail to slide more freely into the canal. This does, however, negate the press-fit effect created by the nail's trapezoidal shape.
What is the length of the short INTERTAN nail?
The short INTERTAN nail is available in 18cm and 20cm lengths. Some surgeons feel that the longer 20cm nail provides enhanced interference fit within the femoral diaphysis thus preventing fracture rotation about the nail. Both implants have a straight profile, but the clothespin distal tip closes slightly as it encounters the AP bow in the femur in order to reduce point stresses about the nail tip. This has the advantage of reducing the likelihood of iatrogenic fracture of the femur at the nail tip due to a stress riser. The same clothespin distal tip characteristics are available in the more frequently implanted 18cm nail as well.