Influence of screw configuration on reduction and stabilization of simulated complete lateral condylar fracture in equine limbs.

OBJECTIVE: To determine the influence of screw configuration on the reduction and stabilization of simulated complete lateral condylar fracture. STUDY DESIGN: Randomized experimental crossover study. METHODS: A lateral condylar fracture was simulated in 18 cadaver limbs from nine horses. Each limb underwent repair with 4.5 mm diameter cortex screws, tightened to 4 Nm, in a linear and triangular configuration. Computed tomography (CT) of each repair was performed with the limbs in unloaded and loaded conditions. Fracture gaps were measured at the dorsal, palmar, and middle locations of the third metacarpal condyle. Fracture gap measurements were graded 0-4, based on voxels. Following descriptive analysis, a Bayesian network (BN) model was fitted to the data. RESULTS: The median fracture grade was 0 (range: 0-4) for unloaded linear repairs and 2 (0-4) for loaded linear repairs. The median fracture grade was 0 (0-3) for unloaded triangular repairs and 1 (0-3) for loaded triangular repairs. Bayesian network sensitivity analysis showed that the construct configuration reduced the uncertainty in the measured fracture outcome by 0.8%. CONCLUSION: Triangular screw configuration resulted in better fracture reduction and stability in comparison with linear screw configuration. However, the BN sensitivity analysis results showed that the effect of construct configuration on fracture outcome was weak. CLINICAL SIGNIFICANCE: These findings indicate a low probability that triangular repair of lateral condylar fracture will result in improved outcomes, when compared with linear repair.

Comparison of interfragmentary compression across simulated condylar fractures repaired using four techniques.

Introduction: Equine condylar fractures are commonly repaired using cortex screws applied in lag fashion. Inadequate interfragmentary compression can lead to post-operative complications. Methods: Lateral condylar fractures were simulated in 21 cadaver limbs (8 third metatarsals, 13 third metacarpals). In each limb, pressure-sensitive film (Prescale®, Fuji Photo Film Co.) was placed in each osteotomy prior to repair with 4.5 mm diameter cortex screws placed in lag fashion. Screws were placed in linear (L), triangular (T), linear plus a washer (LW) and sequentially tightened triangular configurations (TD1). All screws were tightened to a torque of 4 Nm. Pressure prints obtained were scanned using dedicated software (Fuji FPD-8010E, Fuji Photo Film Co.). A Bayesian Network (BN) model was developed to investigate the impact and interrelationship of each factor on interfragmentary compression. Sixty-three repairs (20*L, 24* T, 11*TD1, and 8*LW) performed on 21 limbs were included in the analysis. Results: The BN predicted mean contact area (±s.d.) for pressures within the operating range of the prescale film [≥2.5 Megapascals (MPa) ≤ 10 MPa] by L, T, TD1 and LW repairs were 403mm2 ± (140), 411 mm2 ± (120), 403 mm2 ± (120), and 366mm2 ± (70). The mean contact area (± s.d.) created by L, T, TD1 and LW repairs at pressures >10 MPa were 112 mm2 ± (48), 167 mm2 ± (67), 142 mm2 ± (50), and 100mm2 ± (27). When pressures ≥2.5 MPA to ≤10 MPa were considered, the construct (T or L), washer and screw tightening sequence variables had a very low effect on interfragmentary contact area. At pressures >10 MPa BN sensitivity findings were 16.3, 5.03, and 0.133% for construct, washer and screw tightening sequence. The BN model indicated that triangular repair configuration had a weak influence in the ≥2.5 MPa ≤ 10 MPa range and a moderate influence in the <10 MPa range, on interfragmentary compression. The addition of a washer and the screw tightening sequence had a weak influence on interfragmentary compression at all pressure ranges. Discussion: The results show that triangular repairs create larger interfragmentary contact areas at greater interfragmentary pressure in simulated condylar fractures, however it is unknown if this results in improved repair stability in the clinical scenario.