Measured sternal vibration transmittance data from mockups and cadavers
Description
Stability of bone splitting sternotomy is essential for normal healing after open cardiac surgery. Mechanical vibration transmittance may offer a means for early detection of separation of bone (diastasis) in the sternotomy and prevent further complications. An in-house built measurement system consisting of actuator, sensor, and main controller unit was designed and manufactured for clinical purposes. Three different test settings were studied in mockups (polylactide rods in ballistic gel) and in two human sterni: intact, stable wire fixation, and unstable wire fixation with a gap mimicking bone diastasis. The transmittance of vibration stimulus across the median sternotomy was measured. The technical solution is given. The vibration transmittance response to material cut and sternotomy was evident and detectable in the 20Hz - 2kHz band. The transmittance decreased 23% - 75%, 70% - 97%, and 61% - 89% in intact→stable, intact→unstable, and stable→unstable respectively.
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Steps to reproduce
Three mockups were manufactured to simulate intact, split and steel wire fixed, and split sterni. A 3D printed 20 mm x 5 mm x 200 mm PLA rod (PLA silver gray 2.85 mm filament by Ultimaker B.V., Geldermalsen, The Netherlands) modeled the rib-sternum-rib combination. The rods were embedded into 150 mm x 60 mm x 210 mm ballistic gel blocks (10 % ballistic gelatin by Clear Ballistics, Fort Smith, AR, USA) to a depth of 5 mm (Figure 3). The actuator to sensor distance was 6 cm. Five repeated measurements were made on the mockups. For each measurement the power in the 20 Hz - 2 kHz band was integrated. Two adult human cadavers were used to test the device in a realistic setting. The study consisted of three states of in situ sterni and modeled them before and after surgery: baseline (intact sternum), stable tight wire fixation closure (sternum bound tightly with surgical steel wires) and unstable wire fixation with a gap (wires slightly loose and sternal halves moving; mimicking a complication inducing sternal instability). The skin was covered with an adhesive plastic film. After each manipulation of the cadaver the soft tissue was closed by suturing. The sternal midline and costal cartilage level 3 were marked on the skin. The actuator and sensor were placed on the costal cartilage bilaterally 3 cm from the sternal midline and perpendicular to the skin. Five repeated measurements were recorded, and the measurement power calculated as above.