Sternal Plating for Primary and Secondary Sternal closure; Can it improve sternal stability?
Background and Purpose:
Sternal instability predisposes to post-operative mediastinitis. Biomechanical studies have shown the superiority of rigid plate fixation over wire cerclage in sternal healing. This study evaluates the mechanical stability of traditional or multifilament wire sternal closure compared to plate closure utilizing the Synthes Sternal Cable and Titanium Reconstruction Sternal Fixation System (West Chester, PA, USA) in a human cadaveric model.
Methods:
Midline sternotomy was performed in 18 human cadavers. Two sternal closure techniques were tested: (1) approximation with six interrupted steel wires (size No.5) or six multifilament wire (2) the same closure technique reinforced with a transverse locking 12 hole sternal plate (4 screws/side) at the sixth rib (Synthes Titanium Sternal Fixation System, Synthes CMF, West Chester, PA, USA). (3) Closure using 4 sternal plates alone one at the manubrium and at ribs 3 through 5. Screws were inserted into sternal bone rib cartilage as recommended.
Intrathoracic pressure was continuously measured using a calibrated pressure transducer as it was increased in a standardized fashion in all closure techniques using an inflatable rubber bladder placed beneath the anterior chest wall. Sternal separation was measured by three pairs of sonomicrometry crystals (Sonometrics Corporation, London, Ontario, Canada) fixed at the upper, middle and lower parts of the sternum. For the crystals, the accuracy is +/-0.04 mm (and the sampling rate is >1500/sec). Intrathoracic pressure in was increased until failure as defined by 2.0 mm of separation of any pair of crystals. Differences in distraction pressures were analysed using one-way repeated measures ANOVA and the Holm-Sidak test. Regression Coefficients were utilized to compare the groups.
Results:
Intrathoracic pressure required to cause sternal separation of 2.0 mm was significantly improved with plate fixation both single and multiple plates compared to both monofilament and multifilament wiring. Data is summarized in Table 1.
Discussion:
Variability of the specimens led to variable absolute measurements of sternal distraction pressure. However, a similar improvement in sternal stability was demonstrated in all the specimens with plating. The sequence of wiring which is tested was designed to mimic the clinical situation with failure of the sternal wires to preserve sternal stability. Our clinical experience in dehisced cases utilizing plates has suggested that this form of plate fixation restores sternal stability reliably in this situation. An unexpected finding is the improvement in sternal stability with wiring and a plate only at rib 6. Adding a sternal plate to primary closure might help reduce the risk of sternal dehiscence in high risk patients.
Conclusion:
Sternal stability is improved with sternal plating compared to wiring techniques. Adding a transverse plate to primary wire cerclage closure substantially improves stability of sternotomy closure in a human cadaver model.
Group | Mean ± SD | Median (IQR) | Unadjusted p value | Regression Coefficients (95% CI) |
| Wires/Cables (n=18) | 180.1 ± 117.6 | 149.5 (117.0) | --------- | Reference Group (---) |
| Wires/Cables + 1 Plate (n=18) | 301.3 ± 204.5* | 225.0 (95.0)* | P< .003 | 120.0 (47-194)** |
| 4 Plates (n=16) | 357.5 ± 209.8* | 325.0 (279.5)* | P= .0007 | 142.0 (66-219)** |
Table 1 . Summary Data. * - p<0.05 vs cables/wires ; SD = Standard Deviation; IQR = Interquartile Range; CI = Credible Intervals. * p< 0.05 when compared to cables/wires alone, ** Credible Intervals indicate significance when compared to cables/wires alone.
For the mean and STD data, a One-way repeated measures ANOVA was used (F=8.740, p < 0.001). For the multiple pairwise comparisons the Holm-Sidak method was used (p-values in the table). For cables/wires +1 plate vs 4 plates the unadjusted p = 0.601.