William F. Lavelle

Pathoanatomic basis for stretch-induced lumbar nerve root injury with a review of the literature

OBJECTIVEPersistent pain originating from a dysfunctional lumbar motion segment poses significant challenges in the clinical arena. Although the predominance of the existing spine literature has addressed nerve root compression as the principal cause of pain, it is equally likely that a stretch mechanism may be responsible for all or part of the pathology. METHODSThe literature supporting the role of stretch damage as a primary cause of nerve root injury and pain was systematically reviewed. Pathoanatomic considerations between nerve roots and juxtaposed environment are described and correlated with the available literature. Potential anatomic relationships that may lead to stretch-induced injury are delineated. RESULTSA dynamic lumbar functional spinal unit that encloses a tethered nerve root can create significant stretch and/or compression. This phenomenon may be present in a variety of pathological conditions. These include anterior, posterior, and rotatory olisthesis as well as degenerative conditions such as the loss of disc interspace height and frank multisegment spinal deformity. Although numerous studies have demonstrated that stretch can result in nerve damage, the pathophysiology that may associate nerve stretch with chronic pain has yet to be determined. CONCLUSIONThe current literature concerning stretch-related injury to nerve roots is reviewed, and a conceptual framework for its diagnosis and treatment is proposed and graphically illustrated using cadaveric specimens. The dynamic biomechanical and functional interrelationships between neural structures and adjacent connective tissue elements are particularly important in the face of spinal deformity.

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.

Cervical kyphosis trapezius sign: A new sign for an old pathology

OBJECTIVE Cervical kyphosis may develop in patients with a variety of conditions. It commonly occurs following cervical spine surgery. To our knowledge, no specific physical examination finding in patients with cervical kyphosis has been previously described. It has been our observation that patients with symptomatic cervical kyphosis often have prominent, taut, and painful trapezius muscles. We coined the term cervical kyphosis trapezius sign (CKTS). This article describes the use of this sign as a clinical marker for management and outcome assessment. METHODS We retrospectively analyzed the files of symptomatic cervical kyphosis patients who have been treated by the senior author (E.C.B.) and have been photographed. We also quantified the reliability and accuracy of CKTS by presenting clinical photographs to health care providers. RESULTS Fifteen patients fulfilled the inclusion criteria. All patients had preoperative photographs of their neck that showed the CKTS. Six patients were treated conservatively and nine underwent surgical correction. Mean follow-up for surgical cases was 14.7 months. Postoperative neck photographs demonstrated a normalization of the prominent and painful trapezius muscle in each case. When examining the reliability of CKTS, we found overall interobserver reliability to be 0.671 with an intraobserver reliability of 0.678. CONCLUSION CKTS is a simple, objective, and potentially clinically useful indicator of cervical kyphotic deformity. Resolution of CKTS postoperatively had an associated high rate of pain relief. Therefore, the presence of CKTS in a symptomatic patient with cervical kyphosis is a potential indicator for surgical correction of the deformity.