COMPARISON OF INTRA-OPERATIVE RETRACTION PRESSURE BETWEEN A NOVEL RETRACTOR SYSTEM AND CONVENTIONAL RETRACTOR SYSTEM: A CADAVERIC STUDY

Abstract

Introduction: Anterior cervical spine surgeries are associated with high incidence (up to 60%) of early postoperative dysphagia and hoarseness of voice. These symptoms have been attributed to retraction injury on the larynx, trachea and oesophagus. Pressure from retractors producing ischaemia might explain the soft tissues complications following anterior cervical approach. Conventional retractor systems rely on the soft tissues for stability and create a vertical surgical channel but a novel system (Seex retractor) is fixed directly to the spine and rotates to allow an oblique approach. This may reduce retraction pressure by the Seex retractor on tissues This is the first investigation of retraction pressures using any two different retractor systems for anterior cervical spine surgery. The aims of this study were to measure the retraction pressure on the larynx, trachea and oesophagus during the anterior surgical approach to the cervical spine, in cadavers using conventional (Cloward) retractor and Seex retractor and to investigate the effect of flat or curved blades on retraction pressure

Methods: In a cadaveric model, through a standard anteriomedial approach simulated anterior cervical discectomy procedure was performed in cadavers at C3/4, C4/5, C5/6 and C6/7 levels using Cloward retractor with curved blade (Cervical Large Retractor Set. No. C50-1380: Cloward Instrument Corporation), Seex retractor with flat blade and Seex retractor with curved blade (Patent holder Dr. K. Seex, No PCT/AU05/001205). An online pressure transducer (Tekscan pressure measurement system) was applied between the retractor blade and medial tissues. Retraction pressures were recorded for all the retractors at each level on two separate occasions. Average retraction pressure (ARP), average peak retraction pressure (APRP), pressure distribution along the area of retraction, pressure difference at the edge and surface of the retractor blades, pressure variation with flat and curved blades were determined and compared.

Results: A total of 40 sets of pressure recordings were made from 5 cadavers. Cloward retractor system generated an ARP of 33 mmHg (range 16 – 66 mmHg). ARP of Seex retractor with curved blade was 20 mmHg (range 9 – 50 mmHg) and that of Seex retractor with flat blade was 25 mmHg (range 10 – 74 mmHg). At one level ARP was same for all the three retractors. At another level ARP was same for Cloward retractor and Seex retractor with flat blade but higher than that of Seex retractor with curved blade. At two other levels Seex retractor with flat blade showed higher ARP than others. At 36 levels Cloward retractor showed highest ARP. This was statistically significant with Pearson’s Chi-square test (X2=10.023, degree of freedom=1, p = 0.0015) and Fisher exact test, p = 0.0005. Cloward retractor system showed an APRP of 124 mmHg (37 – 255 mmHg). While that of the Seex retractor with curved blade was 69 mmHg (14 – 254 mmHg) and that of Seex retractor with flat blade was 94 mmHg (18 – 255 mmHg). Of the 40 sets of the recordings at 32 levels Cloward retractor system generated highest APRP. With the Seex retractor itself flat blade generated more APRP than curved blade in 31 sets of measurements; it was reverse in 3 sets and in 6 sets APRP was same. Only at one level curved blade generated higher ARP than flat blade, at 11 levels it was same. At 28 levels ARP was higher with flat blade.

Discussion: Cloward retractor generated significantly high retraction pressure (peak and average contact pressure) than Seex retractor in majority of the cases. Curved blades generate less retraction pressure than the flat ones. Based on these findings a prospective randomised study is underway in live patients.