An In Vitro Biomechanical Study on Ovine Rib Flexibility With Increasing Deconstruction-As an Alternative to Rib Resection for Costoplasty.

STUDY DESIGN

An in vitro biomechanical study into the effect of rib deconstruction on the flexibility in ovine ribs, using three-point bending.

OBJECTIVE

To examine the feasibility and possible effectiveness of a more conservative costoplasty using an in vitro animal model.

SUMMARY OF BACKGROUND DATA

Costoplasty remains useful in the treatment of adolescent idiopathic scoliosis, rib hump, and associated chest wall deformities. However, traditional costoplasty increases morbidity and blood loss.

METHODS

Ribs 2-10 were dissected from four fresh half ovine rib cages. The ribs were randomly allocated to Groups 1 to 4. The ribs underwent deconstruction, 10 mm from the lateral tubercle and 30 mm long, according to their group: Group 1 = control; Group 2 = convex cortical bone removed; Group 3 = convex cortical and cancellous bone removed; Group 4 = all but the ventral cortex is removed. Flexibility was tested by loading the concave side of each rib while fixed at the rib head and equidistant from the center of the resected area. The ribs were deformed at 0.5 mm/s up to a maximum load of 9.99 kg or fracturing. Load was plotted against displacement to find the load/displacement coefficient for each group. Statistical analysis was by an analysis of variance with Tukey's honestly significant difference post hoc testing.

RESULTS

The load/displacement coefficients were as follows: Group 1 = 131.93 (±27.52) N/mm, Group 2 = 93.36 (±40.71) N/mm, Group 3 = 88.66 (±25.84) N/mm, and Group 4 = 29.69 (±29.11) N/mm. Group 4 was significantly less stiff than Groups 1, 2, and 3 (p < .01). No ribs in Groups 1, 2, and 4 fractured. Five of 8 ribs in Group 3 fractured during loading.

CONCLUSIONS

Deconstructing the rib down to the concave side significantly increases the flexibility by approximately 4.5 times. Despite large removal of bone, it retains the ability to withstand 10 kg of load without fracture.