Abstract
Background Increasingly large segments of medial femoral condyle (MFC) corticocancellous flaps
have been harvested for transfer. Biomechanical evaluations demonstrated no osseous
stability impairment under axial loading regardless of flap size harvested. The purpose
of this study was to determine the donor site's response to torsional forces.
Methods Dual-energy X-ray absorptiometry (DEXA) scanning was performed on 16 pairs of cadaver
legs followed by removal of all soft tissues, except knee capsule and ligaments. Specimens
were randomly assigned to three groups with bone harvest defects measuring 3, 5, or
7 cm in length and a control group with no osseous resection. Torsional load was applied
until fracture or ligamentous failure.
Results Bone failure rates were 12.5, 12.5, 28.6, and 55.6% for control, 3, 5, and 7 cm groups,
respectively. Bone failure rate increased with increasing harvest size; the 7 cm group
demonstrated a significantly higher rate compared with the other groups combined (55.6
vs. 17.4%; p = 0.03). Failure torque was 45.5, 29.35, 27.4, and 30.83 Nm for the control, 3, 5,
and 7 cm groups, respectively (p = 0.11). Harvest of any size segment resulted in a significant decrease in failure
torque (p = 0.01). Bone mineral density (BMD) and Z-scores were no different among groups (p = 0.79 and 0.59, respectively). A direct relationship was identified between force
required for failure and BMD (p = 0.02) and Z-scores (p = 0.05) but not for failure location and BMD (p = 0.09) or Z-scores (p = 0.94).
Conclusion MFC corticocancellous flap harvest of any size decreases donor site failure torque.
Flap harvests > 7 cm demonstrate a higher frequency of iatrogenic fracture and therefore
warrant caution with torsional loading of the knee postoperatively. Routine preoperative
DEXA scans may not be warranted.
Keywords
donor site failure - medial femoral condyle flap - torsional loading
