Expert Asian Femoral Nail (A2FN)

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Expert Asian Femoral Nail (A2FN)

Michael Wagner, Michael Schütz, Dean Lorich, Brent Norris, Sean Nork, Phil Kregor

Expert A2FN

The small statured/Asian anatomy was carefully assessed via CT scans and MRI data in terms of morphology and size, to assess the fit of nails to the intramedullary canal of the small stature/Asian patient. It was discovered that current femoral nails do not offer an optimal fit for small stature/Asian anatomy. Generally, the medial lateral bend of current nails is disproportionate, the proximal design of the nails is too long and challenges the surgeon to deliver locking or recon screws into the femoral head without having too much proximal protrusion of the nail itself. The lateral aspects of the nail may cause impingement on the lateral cortex of the small stature/Asian patient.

Details
Clinical Cases
Disclaimer

The A2FN has accommodated all these different aspects. In the proximal region of the nail, the relationship between the locking elements and the proximal nail end has been decreased to negate protrusion in the small stature/Asian patient. Optimum positioning of the recon screws has been accounted for and the length of the proximal end of the nail has been decreased to negate protrusion in the shorter patients. The entry point is at the greater trochanter (5) as this approach is preferred in Asia. The locking options are identical to the AFN except for an additional anteromedial (25) locking hole for more axial stability. The end cap has a longer unthreaded part for easier insertion. A special guide wire with hook engages with the end cap to facilitate a secured way through soft tissue. The nail comes in diameters of 914 mm and in lengths of 280460 mm. The nail is cannulated and available in a left and right version.

Dynamic 4-point bending test of Expert A2FN and AFN according to ASTM showed that the stress curve of the Expert A2FN is about 5% superior to that of the AFN. Dynamic strength of the Expert A2FN is about 30% above that of the AFN.

Impingement on the lateral cortex

Case 1: 22-year-old Asian male with multiple injuries after MVA at 160km/hthe car finally stopped in a front yard

Besides severe upper limb injuries, maxillofacial injuries, a lateral compression pelvic ring injury, and pulmonary contusions, the patient sustained a 32-C3 femur fracture right.

Case provided by Michael Schtz, Brisbane, Australia

After initial stabilization with an external fixator, the femur was nailed in a closed fashion stabilized with an AFN2 in static mode. The accurate length of the injured femur was contemplated from the uninjured leg.

9-month follow-up demonstrates that that the fracture is uniting.

Fig 1 Scene of the accident

Fig 2ab X-rays following the accident

Fig 3ab Initial stabilization

Fig 4ab Postoperative x-rays

Fig 5ac Follow-up x-rays

Case 2: A 76-year-old female underwent right total knee replacement 5 years ago and left total knee replacement 4.5 years ago

The patient underwent left L5S1 minimally invasive TLIF with pedicle screws 2 years ago for left lumbar 5th radiculopathy. At the same time she was put on fosamax for osteoporosis.

Case provided by Merng Koon Wong, Singapore, Singapore

Three weeks prior to her last admission, she complains of recurrent right thigh pain for which epidural analgesics were administered for presumed radiculopathy, however preliminary x-rays and even MRI of the thigh were also taken in view of her primary complaint regarding her right thigh. These investigations did not indicate the possibility of impending bisphosphonate related femur fracture. It is clear from the radiographs that she has an obvious anterolateral bow of her femur and a thickened lateral cortex in the lateral midshaft cortical bone, which may indicate a stress fracture (see Fig 3a-b).

No edema indicated a stress fracture (see Fig 4a-b).

Based on the negative MRI thigh and positive MRI lumbar spine of multiple levels of spinal stenosis, the patient underwent epidural analgesic injection. Patient sustained right femur midshaft periprosthetic fracture the next day after her epidural injection with no trauma.

Notice the fracture decrease the emphasis on the anterolateral bow of the femur (See Fig 5a-b).

Insertion of A2FN as patient may be suffering from a stress fracture related to long term (2.5 years) bisphosphonate use. My rationale against a plate is because bisphosphonate related fractures will heal extremely slowly. In our experience even despite bone grafting union may need up to 2 years. In that time, a plate will fail in less than a year even if the patient is only allowed very minimal weight bearing.

Note despite the increased in curvature compared to other nails in the market, there is still noticeable malreduction at the fracture site (see Fig 6a-b).

Patient was allowed and achieved immediate weight bearing and in 6 weeks callus is seen at the fracture site (see Fig 7a-b).

Fig 1ab Immediately post knee replacement x-rays. Note the anterolateral bow of the femur shaft

Fig 2ab Immediate post TLIF x-rays of lumbar spine

Fig 3ab Right femur x-rays 3 weeks before midshaft femur fracture

Fig 4ab MRIs of the right thigh 1 week before fracture. No edema to indicate stress fracture

Fig 5ab Midshaft fracture right femur

Fig 6ab Immediately postoperative x-rays of right femur

Fig 7ab X-rays 6 weeks postoperatively

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