OTA 1997 Posters - Tibia Fractures

Poster #75

*Anatomical Considerations of Distal Interlocking of Tibial Nails: A Comparison of Two Directions of Distal Screw Insertion

Craig S. Roberts, MD, David King, MD, Mei Wang, PhD, David Seligson, MD, Mike Voor, PhD

University of Louisville, Louisville, Kentucky, USA

Purpose: Intramedullary nailing with proximal and distal interlocking is the procedure of choice for most displaced fractures of the tibial shaft. Distal interlocking is generally performed from a medial to lateral (ML) direction and appears to have a low incidence of iatrogenic neurovascular injury. We studied the distances of four anatomic structures from the two distal interlocking screws during distal interlocking from a medial to lateral (ML) direction and a lateral to medial (LM) direction. The purpose of our study was to compare the proximity of the neurovascular structures using these two modes of distal tibial interlocking.

Methods: Six nonembalmed matched cadaveric lower extremity specimens consisting of the calf-foot-ankle were obtained. Specimens were all male with an average age of 74 years (range 44-87). Specimens underwent reamed intramedullary nailing on a standard fracture table with the Alta tibial nail (Howmedica, Rutherford, New Jersey). The only surgical variable between sides of the matched pairs was the direction of distal screw targeting. All right legs underwent insertion of two distal screws (D1-more proximal and D2-more distal) using a "free-hand" technique from a LM direction and all left legs underwent screw insertion from a ML direction. All tibiae remained intact (unfractured) throughout.

After distal interlocking, anatomic dissection was performed immediately. Four neurovascular structures were dissected out: the anterior tibial neurovascular bundle (AT), the posterior tibial neurovascular bundle (PT), superficial peroneal nerve (SP), and the saphenous vein (SV). Distances were measured from these structures to the nearest end (tip or head) of each of the two distal screws. All measurements were made three times by the same investigator (D.K.) with calipers, rounded to the nearest tenth of a millimeter, and recorded. Descriptive statistics and paired student's t-test were calculated using the SPSS statistical package (SPSS Inc., Chicago, IL).

Results: Distal targeting from a LM direction showed increased distances from the PT and SP compared to targeting from the ML direction for both D1 and D2 (Table 1). There were no significant differences between LM and ML distal tibial interlocking in terms of distances of the screws to the AT or SV. Distances of D1 and D2 to AT and SV were rather small in both modes of interlocking (range 0.5-4.8 mm). None of the four anatomic structures was injured during distal screw insertion.

Discussion and Conclusion: Distal tibial interlocking involves screw insertion in close proximity to four neurovascular structures for both LM and ML techniques. Both LM and ML techniques involve small margins of safety from the AT and SV. Distances from the PT were large (greater than two centimeters) with both LM and ML locking. However, LM interlocking appears to offer a small anatomic advantage over ML interlocking in terms of distances from the SP and the PT. Further clinical studies are necessary prior to changes in clinical practice.

Table 1 Distances of Distal Screws from Anatomical Structures (mm)

 

 Distal Screw D1

 Distal Screw D2

 Structure  ML  Mean ± SEM  LM  ML  Mean ± SEM  LM
 AT  3.0 ± 1.0  NS  2.2 ± 0.8  4.0 ± 1.5  NS  4.8 ± 1.2
 PT  21.3 ± 1.0  p<0.04  25.1 ± 2.3  20.7 ± 1.2  p<0.05  24.8 ± 2.4
 SV  0.5 ± 0.2  NS  1.5 ± 0.6  1.7 ± 0.3  NS  3.5 ± 1.4
 SP  2.7 ± 0.8  P<0.01  7.8 ± 1.2  3.2 ± 0.8  P<0.01  9.0 ± 1.7