The Hip: Preservation, Replacement and Revision

Subtrochanteric Frx: Anatomy and Factors in Healing

- Anatomy:
    - axis of femoral neck forms angle of approx 135 deg w/ femoral shaft, and is anteverted from the frontal plane by variable amount (- 4 to 36 deg, average 10 to 20 deg in Caucasians);
    - distinct cortex surrounds the cancellous bone of the neck, the center of which becomes progressively empty with age (Ward's triangle);
           - center of femoral head is most secure site for proximal fixation;
    - at femoral neck, there is transition from metaphysis to epiphysis, formed of cancellous bone that is most dense peripherally, esp medially & laterally where primary compression and primary tension trabecular streams are respectively situated;
    - calcar femorale is a condensed IM bony thickening that extends from posterior neck thru the posteromedial portion of intertrochanteric region, just anterior to lesser trochanter, & ends in posteromedial cortex of the proximal shaft;
         - it thus provides sig support to counteract large compressive stresses borne by this region;
         - its displacement, w/ large lesser troc frx fragment, renders unstable a fracture fragment in this region;
    - bending forces cause the medial cortex to be loaded in compression & lateral cortex to be in tension;
    - compressive forces are much greater than the tension forces, and therefore, it is manditory to restore medial cortical stability;
          - as little as 2 mm of separation of the medial cortex will lead to medial collapse and lateral plate bending;

- Factors in Healing:
    - major obstacles: non union and malunion;
    - factors responsible for slower rate of union or nonunion include:
        - large quantity of cortical bone, which is often comminuted in these frx;
             - cortical bone vascularity and fractures srufaces available for healing are less than in cancellous bone surfaces in intertrochanteric frx;
        - biomechanical stresses across frx may result in hardware failure;
             - stress on nail plate acting as tension band under any condition other than perfect reduction is highly sensitive to loading;
             - failure of nail plate devices in such situations is thus almost certain if early wt bearing is allowed

Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Wednesday, September 19, 2012 11:32 am