Unilateral cervical facet dislocation: a biomechanical study of several constructs including unilateral lateral mass fixation supplemented by an interspinous cable.

OBJECT

Both ventral and dorsal operative approaches have been used to treat unilateral cervical facet injuries. The gold standard ventral approach is anterior cervical discectomy and fusion. There is, however, no clear gold standard dorsal operation. In this study, the authors tested the stability of multiple posterior constructs, including unilateral lateral mass fixation supplemented by an interspinous cable.

METHODS

Six fresh human cervical spine specimens (C3-T1) were tested by applying pure moments to the C-3 vertebral body in increments of 0.5 Nm from 0 Nm to 2.0 Nm. Each specimen was tested in the following 8 conditions (in the order shown): 1) intact; 2) after destabilization via injury to the C5-6 facet; 3) with bilateral C5-6 lateral mass screws and rods; 4) after further destabilization by creating a right unilateral lateral mass fracture of C-5 (which rendered secure screw placement into the right C-5 lateral mass impossible); 5) with unilateral left C5-6 lateral mass screws and rod; 6) with unilateral C5-6 lateral mass screws and rod supplemented with an interspinous cable; 7) with a bilateral multilevel dorsal construct C4-6; and 8) after a C5-6 anterior cervical discectomy and fusion (ACDF) procedure with a polyetheretherketone graft and plate.

RESULTS

The bilateral C5-6 lateral mass construct reduced the range of C5-6 motion to 33.6% of normal. The unilateral C5-6 lateral mass construct resulted in an increased range of motion to 110.1% of normal. The unilateral lateral mass construct supplemented by an interspinous cable reduced the C5-6 range of motion to 89.4% of normal. The bilateral C4-6 lateral mass construct reduced the C5-6 range of motion to 44.2% of normal. The C5-6 ACDF construct reduced the C5-6 range of motion to 62.6% of normal.

CONCLUSIONS

The unilateral lateral mass construct supplemented by an interspinous cable does reduce range of motion compared with an intact specimen, but is significantly inferior to a C4-6 bilateral lateral mass construct. When using a dorsal approach, the unilateral construct with a cable should only be considered in selected instances.