Augmentation of posterior wall acetabular fracture fixation using calcium-phosphate cement: a biomechanical analysis.

OBJECTIVE

This study investigates if the use of calcium phosphate cement as an adjunct to internal fixation for posterior wall acetabular fracture will result in acute restoration of joint loading parameters to the intact condition.

METHODS

Ten fresh-frozen cadaveric pelves were used for this investigation. Simulated abductor mechanism was used to load the hip. Pressure-sensitive film was used to measure contact area and pressure within the anterior, superior, and posterior regions of the acetabulum for all experimental conditions. The hips were loaded under the following 4 conditions: 1) intact; 2) following posterior wall osteotomy; 3) following reduction and standard internal fixation; and 4) following reduction of the posterior wall using calcium phosphate cement, as a grout, in addition to internal fixation. A posterior wall fracture was created along an arc of 40-90 degrees about the acetabular rim. Extensometers were utilized to measure posterior wall fragment micromotion under conditions 3 and 4 above. Statistical analysis was performed using multivariate analysis of variance to assess the significance of the difference among and between conditions simultaneously for each region. Fragment motion data were analyzed using a 2-tailed t test.

RESULTS

Fragment micromotion was reduced to 78 microm superiorly and 46 microm inferiorly with the use of calcium phosphate cement (P < 0.05). Creation of a posterior wall defect resulted in increased load in the superior acetabulum (1201N) as compared to the intact condition (902N, P = 0.024). Following reduction and internal fixation, the load distributed to the superior acetabulum (1132N) was not statistically different from the displaced condition. Following the addition of calcium phosphate cement, the load seen at the superior region of the acetabulum (883N) was less than fixation without calcium phosphate cement and was not different from the intact state (P = 0.85).

CONCLUSION

The use of calcium-phosphate cement as a fracture grout with internal fixation resulted in a partial restoration of joint loading parameters toward the intact state. Further work will be needed to determine if similar types of augmented articular fixation may result in a clinical benefit.