DCS Plating for Unstable Subtrochanteric Fractures

Paul Duffy, M.D, FRCSC
Calgary, AB

Accounting for between 7-34% of femoral fractures and classified as extending five centimetres below the lesser trochanter, this injury has a bimodal distribution with high energy mechanisms in the younger population and low energy in the elderly1.

The high concentration of deforming forces of flexion, abduction and external rotation must be considered in surgical planning and implant selection. The relative paucity of blood supply compared to the metaphyseal region and instability determined by the degree of comminution of the medial cortex also play a role.

Multiple classification systems exist for this fracture - each with a degree of interobserver variability. Much of the published literature data refers to the AO classification2. Whilst lesser trochanteric comminution is important biomechanically, it was previously considered that extension of the fracture into the greater trochanter or piriformis fossa precluded the use of an intramedullary device3. This point is emphasised in the Russel Taylor Classification but its importance has been questioned1. Many surgeons feel comfortable proceeding with intramedullary nailing despite fracture extension to the entry point.

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Historically, when the Dynamic Condylar Screw (DCS) was used for transverse and non-comminuted fractures, there was a reported 20% rate of complications including delayed union and failure of hardware4. This was likely caused by iatrogenic devascularisation of the posteromedial cortex. More recently, surgical techniques stress the use of indirect reduction, thus decreasing the amount dissection. Appropriate tensioning of the DCS coupled with the use of antibiotics lead to 100% union without hardware failure for type 2A and 2B fractures in one study4.

Biomechanical studies have shown that the femoral cortex in the postero-medial subtrochanteric region is subjected to the highest stresses in the body5. Restoration of the integrity of the posteromedial column then allows the DCS to act as a tension band along the lateral femoral cortex. However, if the column's integrity isn't restored, all implants are subjected to high bending stresses. It is in this situation that the cephalomedullary nail is subjected to lower bending moments as it is closer to the fracture. In comparing the DCS and cephalomedullary nail, successful fracture healing has been shown to be more dependent on the indirect reduction techniques which preserve blood supply rather than being related solely to the mechanical strength of the implant6. However, extensive biomechanical studies have shown inferior stiffness and lower load to failure for extramedullary devices compared to 2nd generation nails4.

Technical difficulties are common with the cephalomedullary nail. Fracture abduction may make finding the entry point difficult. Flexion of the proximal fragment, if not identified and corrected, could cause reaming of the posterior cortex and potential residual flexion after insertion of the nail. Some of these problems are reduced by performing the surgery with the patient in the lateral position and are less relevant when using a DCS.

The available literature comparing the two techniques is small. Schipper et al tried to perform a meta analysis but found themselves unable to do so as methodological considerations precluded analysis7. Many studies included both stable and unstable fracture patterns. Available studies are hampered by a lack of randomization, small samples and no power calculations.

Hardy et al showed there was a lower risk of implant-related problems, improved mobilization and less impaction of the fracture site with intramedullary devices8.

Sadowski et al set out to test the hypothesis that extramedullary fixation was acceptable for A1 and A2 fractures but not for A3. Comparing 19 DCS versus 20 PFN, they reported that the DCS took twice as long, was associated with greater blood loss, and was described as difficult in half the cases which resulted in a significantly longer hospital stay. At one year in the extramedullary group, five patients had screw cut out, one had plate fatigue and there was one case of nonunion with an intact implant. There were no complications in the cephalomedullary nail group9.

Although the literature supporting the cephalomedullary nail is strong, this does not preclude the use of a DCS for unstable subtrochanteric fractures. Successful outcome is dependent not only on implant selection but also heavily influenced by surgical skill and experience. Certain surgeons may be more comfortable and skilled with the use of a DCS and therefore achieve better results with this device in their practice. Care must be taken however to use this implant appropriately by minimizing dissection particularly the posterior medial cortex. Successful use of a DCS is also based on an understanding of fracture repair biomechanics. An intact posterior medial column adds significantly to the biomechanical stability of the DCS construct.

References

  1. Bedi, A. and T. Toan Le, Subtrochanteric femur fractures. Orthop Clin North Am, 2004. 35(4): p. 473-83.
  2. Muller, M.E., [Classification and international AO-documentation of femur fractures]. Unfallheilkunde, 1980. 83(5): p. 251-9.
  3. Pai, C.H., Dynamic condylar screw for subtrochanteric femur fractures with greater trochanteric extension. J Orthop Trauma, 1996. 10(5): p. 317-22.
  4. Blatter, G. and M. Janssen, Treatment of subtrochanteric fractures of the femur: reduction on the traction table and fixation with dynamic condylar screw. Arch Orthop Trauma Surg, 1994. 113(3): p. 138-41.
  5. Kummer, F.J., et al., Intramedullary versus extramedullary fixation of subtrochanteric fractures. A biomechanical study. Acta Orthop Scand, 1998. 69(6): p. 580-4.
  6. Nungu, K.S., C. Olerud, and L. Rehnberg, Treatment of subtrochanteric fractures with the AO dynamic condylar screw. Injury, 1993. 24(2): p. 90-2.
  7. Schipper, I.B., R.K. Marti, and C. van der Werken, Unstable trochanteric femoral fractures: extramedullary or intramedullary fixation. Review of literature. Injury, 2004. 35(2): p. 142-51.
  8. Hardy, D.C., et al., Use of an intramedullary hip-screw compared with a compression hip-screw with a plate for intertrochanteric femoral fractures. A prospective, randomized study of one hundred patients. J Bone Joint Surg Am, 1998. 80(5): p. 618-30.
  9. Sadowski, C., et al., Treatment of reverse oblique and transverse intertrochanteric fractures with use of an intramedullary nail or a 95 degrees screw-plate: a prospective, randomized study. J Bone Joint Surg Am, 2002. 84-A(3): p. 372-81.

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