A novel instrumented retractor to monitor tissue-disruptive forces during lateral thoracotomy

Objective: Acute and chronic pain after thoracotomy, post-thoracotomy pain syndrome, is well documented. The mechanical retractors used for the thoracotomy exert significant forces on the skeletal cage. Our hypothesis was that instrumented retractors could be developed to enable real-time monitoring and control of retraction forces. This would provide equivalent exposure with significantly reduced forces and tissue damage and thus less post-thoracotomy pain. Methods: A novel instrumented retractor was designed and fabricated to enable real-time force monitoring during surgical retraction. Eight mature sheep underwent bilateral thoracotomy. One lateral thoracotomy was retracted at a standard clinical pace of 5.93 +/- 0.80 minutes to 7.5 cm without real-time monitoring of retraction forces. The other lateral thoracotomy was retracted to the same exposure with real-time visual force feedback and a consequently more deliberate pace of 9.87 +/- 1.89 minutes (P=.006). Retraction forces, blood pressure, and heart rate were monitored throughout the procedure. Results: Full lateral retraction resulted in an average force of 102.88 +/- 50.36 N at the standard clinical pace, versus 77.88 +/- 38.85 N with force feedback ( a 24.3% reduction, P = .006). Standard retraction produced peak forces of 450.01 +/- 129.58 N, whereas force feedback yielded peak forces of 323.99 +/- 127.79 N ( a 28.0% reduction, P =.009). Systolic blood pressure was significantly higher during standard clinical retraction ( P =.0097), and rib fracture occurrences were reduced from 5 to 1 with force feedback (P=.04). Conclusions: Use of the novel instrumented retractor resulted in significantly lower average and peak retraction forces during lateral thoracotomy. Moreover, these reduced retraction forces were correlated with reductions in animal stress and tissue damage, as documented by lower systolic blood pressures and fewer rib fractures.