OTA 2004 Posters
Scientific Poster #77 Femur / Knee / Hip
A Critical Analysis of the Eccentric Starting Point for Trochanteric Intramedullary Femoral Nailing
Purpose: Antegrade femoral nailing through a greater trochanter entry site using intramedullary nails with a proximal bend is gaining in popularity. Insertion sites differ according to manufacturer. "The tip of the trochanter" or "just lateral to the tip" are commonly used terms. "Slightly anterior to the midline" has also been described. The authors have noted subtrochanteric femur fractures reduced on a fracture table that become malreduced with the introduction of a trochanteric nail. The purpose of this study was to look at specific trochanteric entry sites to examine whether there is a "perfect" universal starting point. In addition, we examined the insertion angle, the trochanteric angle, the proximal bend, and the radius of curvature of four commonly used implants. Three different starting points were employed.
Methods: Nine matched pairs and one unmatched pair of cadaveric embalmed femurs (20 femora) were stripped of soft tissues and stored frozen until ready for use. This study was performed in an OSHA approved site. The femora were placed in neutral rotation, and they were radiographed with use of fluoroscopy. The trochanteric angle was calculated by drawing a line up the midpoint of the femoral shaft to exit proximal and connected to a line drawn from 3 mm lateral to the tip of the trochanter and bisecting at 3 cm distal to the lesser trochanter.
Four intramedullary trochanteric nails were employed: Trochanteric Antegrade Nail, (TAN, Smith & Nephew), GAMMA nail (2nd and 3rd generations, Howmedica/Osteonics), Trochanteric Fixation Nail (TFN, Synthes), and the Holland Nail (Biomet).The proximal bend on these nails and the radius of curvature were calculated. One of three entry points was used: at the tip of the trochanter and 2 to 3 mm medial and lateral to the tip. The starting point was determined by direct measurements off the greater trochanter and with fluoroscopy. The entry hole of 12 mm was made over a 3.2-mm guide wire. After reaming to 12.5 mm, a reverse obliquity osteotomy was made with an oscillating saw from the lesser trochanter to a point on the lateral cortex 4 cm distal. The Holland and TAN nails were inserted into the 12.5 mm entry site. The proximal entry site then was reamed to 17 mm prior to insertion of the TFN and the Gamma nails. The starting point was approximately in the midportion in the coronal plane. Fluoroscopic views in the anteroposterior and lateral planes were obtained. The displacement (gapping) and angulation were assessed after each nail insertion. The gap from the tip of the displaced fracture to the intact shaft was measured in millimeters. The angle of insertion was calculated by using the insertion wire and the midline of the femur bisecting at 3 cm below the lesser trochanter.
Results: The Holland nail had a bend of 10° and a radius of 300 cm. TAN was 5° and 350 cm; TFN was 6° and 150 cm; Gamma 2 was 4° and 300 cm, and Gamma 3 was 4° and 200 cm.
| Holland | Angulation (degrees) | Gapping (mm) |
| Lateral start | 1.25° varus (0-3° varus) | 5.9 (4-8) |
| Medial start | 9.75° valgus (9-11° valgus) | 3.7 (1-7) |
| Tip start | 2° varus (6° varus, 2° valgus) | 3.12 (0-6.4) |
| TAN | ||
| Lateral | 4.4° varus( 0-8° varus) | 4.54 (0-7) |
| Medial | 3.2° valgus ( (0-8° valgus) | 2.16 ( 0-4.8) |
| Tip | 1.2 ° varus (0-4° varus) | 2.28 (1-4) |
| Gamma | ||
| Lateral | 6.7° varus (6-10° varus) | 6.26 (4-9) |
| Medial | 2.3° valgus (2°varus-10° valgus) | 3.76 (0-9) |
| Tip | 2.3° varus (2° valgus-8° varus) | 3.12 (0-7) |
| TFN | ||
| Lateral | 6.6° varus (4-10° varus) | 8.04 (5.6-12) |
| Medial | 7.75° valgus (5-11° valgus) | 3.85 (2.6.4) |
| Tip | 0.3° varus ( 5° valgus-6° varus) | 3.56 (0-5.6) |
The trochanteric angle measured for 11 femurs averaged 10.45° (7-14°). The insertion angle measured on 17 femurs averaged 6° (1-14°). There was no correlation between trochanteric angle, insertion angle, and nail bend with the amount of angulation or gapping at the osteotomy site.
Conclusions: An analysis of four trochanteric intramedullary nails with different proximal bends and three different starting points in the greater trochanter showed no correlation. There was no correlation with the insertion angle or the trochanteric angle and osteotomy alignment, either. Moving the starting point 2 to 3 mm medial or lateral to the tip of the trochanter caused significant malalignment. Matching the starting point to the degree of lateral bend in the nail led to improved results. There is no universal starting point for trochanteric nailing of subtrochanteric femur fractures.