Comparison of retraction pressure between novel and conventional retractor systems--a cadaver study

Sore throat, dysphagia, and dysphonia are very common after anterior cervical surgery; clinical studies show an incidence of up to 60% or more. Neural, mucosal, or muscular injuries during dissection or retraction are regularly discussed, but investigations are few. Retraction pressure causing ischemia might explain these complications. A new anterior cervical retractor system (Seex retractor) using novel principles has been introduced to surgical practice. There are isolated reported investigations comparing different anterior cervical retractors. Therefore, the purpose of this study was to measure retraction pressure on the aerodigestive tract in cadavers during the anterior surgical approach for cervical spine operations performed using either the conventional (Cloward) retractor system or the Seex retractor system. The goal was to find the significance of the shape of the retraction blades (flat vs curved) in retraction pressures.

In cadavers, the anterior cervical spine was approached surgically at the C3/4, C4/5, C5/6, and C6/7 levels. A simulated anterior discectomy procedure was performed using a Cloward retractor with curved blade, a Seex retractor with curved blade, and a Seex retractor with flat blade at each level. For each retractor application, an online pressure transducer (Tekscan pressure measurement system) is applied between the rear side of the medial retractor blade and medial soft-tissue complex. Retraction pressures are recorded twice for both retractors at each level. 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, and so on were determined and compared. One-way ANOVA and Tukey honestly significant difference tests were used for statistical evaluation.

Forty sets of pressure recordings were made in 5 cadavers. The Cloward retractor system showed higher average contact pressure than the Seex retractor system in 36 sets. In 32 sets, the Cloward retractor system showed higher peak retraction pressure than the Seex retractor system. None of the recordings showed uniform pressure distribution over the retracted area. With the Seex retractor itself, the flat blade generated more peak retraction pressure than the curved blades in 28 sets of measurements; it was the reverse in 3 sets; and in 9 sets the peak pressure was almost the same. Higher retraction pressure was noted along the edges of retractor blades in general, and along the convexity of a curved blade. Those parallel bands corresponded to the edges of the retractor blades. The Seex retractor with a curved blade generated the lowest average retraction pressure and average peak retraction pressure (p < 0.01, ANOVA).

Retraction pressure was found not to be uniform all over the retracted surface. Higher retraction pressure was noted along the edges of retractor blades in general, and along the convexity of a curved blade. The conventional retractor system with a curved blade generated significantly higher retraction pressures than the novel Seex retractor with a curved blade.