✓ Conus medullaris injury from burst fractures is known to occur in conjunction with other neurological deficits, including lower-extremity motor weakness or sensory changes. Rarely does an isolated conus medullaris injury occur from an extradural cause without other neurological deficits. The authors report four cases of L-1 burst fractures in which conus medullaris dysfunction was the sole neurological injury in the absence of lower-extremity involvement.
Report of four cases
Dean Chou, Roger Hartl and Volker K. H. Sonntag
Christoph P. Hofstetter, Dean Chou, C. Benjamin Newman, Henry E. Aryan, Federico P. Girardi and Roger Härtl
The purpose of this multicenter trial was to investigate the outcome and durability of a single-stage thoracolumbar corpectomy using expandable cages via a posterior approach.
The authors conducted a retrospective chart review of 67 consecutive patients who underwent single-stage thoracolumbar corpectomies with circumferential reconstruction for pathological, traumatic, and osteomyelitic pathologies. Circumferential reconstruction was accomplished using expandable cages along with posterior instrumentation and fusion. Correction of the sagittal deformity, the American Spinal Injury Association score, and complications were recorded.
Single-stage thoracolumbar corpectomies resulted in an average sagittal deformity correction of 6.2° at a mean follow-period of 20.5 months. At the last follow-up, a fusion rate of 68% was observed for traumatic and osteomyelitic fractures. Approximately one-half of the patients remained neurologically stable. Improvement in neurological function occurred in 23 patients (38%), whereas 7 patients (11%) suffered from a decrease in lower-extremity motor function. The deterioration in neurological function was due to progression of metastatic disease in 5 patients. Five constructs (7%) failed—3 of which had been placed for traumatic fractures, 1 for a pathological fracture, and 1 for an osteomyelitic fracture. Other complications included epidural hematomas in 3 patients and pleural effusions in 2.
Single-stage posterior corpectomy and circumferential reconstruction were performed at multiple centers with a consistent outcome over a wide range of pathologies. Correction of the sagittal deformity was sustained, and the neurological outcome was good in the majority of patients; however, 18% of acute traumatic fractures required revision of the construct.
Roger Härtl, Robert H. Chamberlain, Mary S. Fifield, Dean Chou, Volker K. H. Sonntag and Neil R. Crawford
Two new techniques for atlantoaxial fixation have been recently described. In one technique, C-2 intra-laminar screws are connected with C-1 lateral mass screws; in the second, C-1 and C-3 lateral mass screws are interconnected and C-2 is wired sublaminarly. Both techniques include a C1–2 interspinous graft. The authors compared these techniques with the gold-standard, interspinous graft–augmented C1–2 transarticular screw fixation and with a control C1–2 interspinous graft fixation procedure alone.
In six human cadaveric occiput–C4 specimens, nonconstraining 1.5-Nm pure moments were applied to induce flexion, extension, lateral bending, and axial rotation during which three-dimensional angular motion was measured optoelectronically. Each specimen was tested in the normal state, with graft alone (after odontoidectomy), and then in varying order after applying each construct with a rewired graft. All three constructs allowed significantly less angular motion at the C1–2 junction than the wired interspinous graft alone during lateral bending and axial rotation (p < 0.01, paired Student t-test) but not during flexion or extension. Transarticular screw fixation with an interspinous graft allowed less motion at the atlantoaxial junction than the two new constructs in several conditions. Differences were greater between the transarticular screw construct and the intralaminar screw construct than between the transarticular screw construct and the C1–3 lateral mass screw construct. During lateral bending and axial rotation, the C1–3 construct allowed less motion at the atlantoaxial junction than the intralaminar screw construct.
Biomechanically, the gold-standard C1–2 transarticular screw fixation outperformed the two new techniques during lateral bending and axial rotation. Wiring C-2 to C1–3 rods provided greater stability than C1–2 laminar screws, but it sacrificed C2–3 mobility. It is unknown whether the small differences observed biomechanically would lead to clinically relevant differences in fusion rates.
Dean Chou, Adolfo Espinoza Larios, Robert H. Chamberlain, Mary S. Fifield, Roger Hartl, Curtis A. Dickman, Volker K. H. Sonntag and Neil R. Crawford
A flexibility experiment using human cadaveric thoracic spine specimens was performed to determine biomechanical differences among thoracolumbar two-screw plate, single-screw plate, and dual-rod systems. A secondary goal was to investigate differences in the ability of the systems to stabilize the spine after a one- or two-level corpectomy.
The authors evaluated 21 cadaveric spines implanted with a titanium mesh cage and three types of anterior thoracolumbar supplementary instrumentation after one-level thoracic corpectomies. Pure moments were applied quasistatically while three-dimensional motion was measured optoelectronically. The lax zone, stiff zone, and range of motion (ROM) were measured during flexion, extension, left and right lateral bending, and left and right axial rotation. Corpectomies were expanded to two levels, and testing was repeated with longer hardware.
Biomechanical testing showed that the single-bolt plate system was no different from the dual-rod system with two screws in limiting ROM. The single-bolt plate system performed slightly better than the two-screw plate system. Across the same two levels, there was an average of 19% more motion after a two-level corpectomy than after a one-level corpectomy. In general, however, the difference across the different loading modes was insignificant.
Biomechanically, the single-screw plate system is equivalent to a two-screw dual-rod and a two-screw plate system. All three systems performed similarly in stabilizing the spine after one- or two-level corpectomies.