Transverse connectors providing increased stability to the cervical spine rod-screw construct: an in vitro human cadaveric study

Abstract

The object of this study was to determine if the addition of transverse connectors (TCs) to a rod-screw construct leads to increased stabilization of the cervical spine. Eleven human cadaveric cervical spines (C2-T1) were used to examine the effect of adding connectors to a C3-7 rod-screw construct in 3 models of instability: 1) C3-6 wide laminectomy, 2) wide laminectomy and 50% foraminotomy at C4-5 and C5-6, and 3) wide laminectomy with full medial to lateral foraminotomy. Following each destabilization procedure, specimens were tested with no TC, 1 TC between the C-5 screws, and 2 TCs between the C-4 and C-6 screws. Testing of the connectors was conducted in random order. Specimens were subjected to ± 2 Nm of torque in flexion and extension, lateral bending, and axial rotation. Range of motion was determined for each experimental condition. Statistical comparisons were made between the destabilized and intact conditions, and between the addition of TCs and the absence of TCs. The progressive destabilization procedures significantly increased motion. The addition of TCs did not significantly change motion in flexion and extension. Lateral bending was significantly decreased with 2 connectors, but not with 1 connector. The greatest effect was on axial rotation. In general, 2 TCs were more restrictive than 1 TC, and decreased motion 10% more than fixation alone. Regardless of the degree of cervical destabilization, 1 or 2 TCs decreased motion compared with rods and screws alone. Axial rotation was most affected. Transverse connectors effectively increase the rigidity of rod-screw constructs in the cervical spine. Severe cervical instability can be overcome with the use of 2 TCs, but in cases in which 2 cannot be used, 1 should be adequate and superior to none.