In Brief Study Design. In vitro comparison of four reconstruction techniques following transforaminal lumbar interbody fusion in a human cadaveric model. Introduction. Transforaminal lumbar interbody fusion (TLIF) is a relatively new technique that avoids the morbidity of an anterior approach and the nerve root manipulation of a posterior interbody fusion. This study measured the effects of a TLIF on the overall and segmental flexibility of the lumbar spine using four different spinal implant configurations. Summary of Background Data. Anterior lumbar interbody fusion, posterior lumbar interbody fusion, and combined anterior–posterior spinal procedures are gaining wide acceptance for the treatment of selected patients with segmental spinal instability and spondylolisthesis with associated degenerative changes. Each fusion technique may have different effects on the overall flexibility of the lumbar spine. The unilateral TLIF procedure with adjunctive pedicular fixation is one variation of an interbody fusion technique that requires less bony and soft tissue dissection and minimizes nerve root manipulation compared with other interbody fusion methods. Methods. Five fresh-frozen, human lumbar spines were nondestructively subjected to flexion, extension, lateral bending, and axial rotation moments using a previously validated spine flexibility tester, and displacements were measured. Testing the intact lumbar spine was followed by testing of a unilateral L4–L5 TLIF using a single ramp carbon fiber cage without adjunctive internal fixation. The single carbon fiber (Brantigan) cage was inserted obliquely in a posterolateral to anteromedial position in the L4–L5 disc space. Following testing of the cage alone, three different adjunctive stabilization techniques were tested. Posterior stabilization involved one of the following: a contralateral translaminar facet screw, single side/ipsilateral nonsegmental pedicle screw fixation, and bilateral nonsegmental pedicle screw fixation. The overall flexibility of each lumbar spine was calculated from load-displacement curves for each axis of rotation. The flexibility of the L4–L5 segment of each spine was computed from kinematic motion data acquired via attached LED sensors to the L4 and L5 vertebral bodies. Statistical testing was performed with paired t tests. Results. The flexibility of the entire (T12–S1) destabilized spine after TLIF with interbody cage alone and with all three reconstructive techniques was comparable with the intact spine. However, the motion at the L4–L5 segment was significantly increased for the TLIF with interbody cage alone in axial rotation (299% of intact, P < 0.01), with no significant change in flexion–extension (79% of intact, P = 0.22) or lateral bending (87% of intact, P = 0.39). With the addition of a contralateral translaminar facet screw, the motion at the L4–L5 segment remained significantly more flexible in axial rotation (250% of intact, P = 0.06) although less than with the cage alone. With the unilateral pedicle screw construct, the L4–L5 segment remained more flexible in axial rotation (182% of intact, P = 0.07) although significantly less than with the facet screw construct (P < 0.05). The addition of bilateral pedicle screws most closely reapproximated the flexibility of the intact spine with no significant difference in axial rotation (91% of intact, P = 0.30), flexion–extension (93% of intact, P = 0.19), or lateral bending (99% of intact, P = 0.47). The motion at the L4–L5 segment with bilateral pedicle screws was not significantly different than for the intact specimen in axial rotation (144% of intact, P = 0.17), flexion–extension (81% of intact, P = 0.21), or lateral bending (86% of intact, P = 0.27). Conclusions. TLIF reconstruction with a solitary cage did not increase overall spine flexibility from the intact condition but significantly increased segmental flexibility at L4–L5 in axial rotation. A unilateral translaminar facet screw had minimal stabilizing effect at L4–L5. Unilateral pedicle screws further increased stiffness at the L4–L5 segment. However, TLIF with bilateral pedicle screws most closely approximated the L4–L5 segmental flexibility of the intact spine. The authors conducted an in vitro comparison of four reconstruction techniques following transforaminal lumbar interbody fusion (TLIF) in a human cadaveric model. The TLIF approach had no significant effect on the overall flexibility of the lumbar spine, although axial rotation was significantly increased at the L4–L5 TLIF segment. A unilateral translaminar facet screw had minimal stabilizing effect at L4–L5. Unilateral pedicle screws further increased stiffness at the L4–L5 segment. However, TLIF with bilateral pedicle screws most closely approximated the L4–L5 segmental flexibility of the intact spine. Findings support the previous recommendations for bilateral pedicle screw fixation as a standard technique for reconstruction following unilateral TLIF decompression and interbody grafting.
PURPOSE To determine whether hemangioblastomas, highly vascular tumors requiring surgery that is potentially complicated by excessive bleeding, can be embolized safely by using interventional techniques that furnish a more avascular surgical field. METHODS Nine hemangioblastomas involving either the cerebellum or the spinal cord were embolized preoperatively. In each case the feeding artery was selectively catheterized with a microcatheter and the hypervascular tumor nidus was devascularized with polyvinyl alcohol particles. RESULTS Two patients who had undergone recent attempts as surgical resection at another institution had repeat surgery after endovascular embolization rendered the tumor nidus avascular. At surgery, the tumor was completely removed in one case and markedly debulked in the other. In all nine cases, blood loss after embolization was reported to be less than expected by experienced surgeons. In addition, manipulation and removal of the tumor was reported to be subjectively easier in these embolized tumors. The embolization procedure caused no permanent complications; however, one patient with a posterior fossa hemangioblastoma and hydrocephalus worsened clinically within 12 hours of embolization. This event was thought to be caused by obstructive hydrocephalus resulting from tumor swelling. Emergency craniotomy, ventricular decompression, and surgical resection of the tumor produced complete resolution of the signs and symptoms. CONCLUSIONS Our results indicate that preoperative embolization of hemangioblastomas is a safe procedure that is useful in aiding surgical resection of these highly vascular tumors.
Study Design. In vitro comparison of three different screws for unicortical fixation in lateral masses of the cervical spine. Objectives. To compare the axial load-to-failure of cervical lateral mass screws and their revision screws in a cadaveric model. Summary of Background Data. Lateral mass screws are used for posterior fixation of the cervical spine. Risks to neurovascular structures have led many surgeons to advocate unicortical application of these screws, although fixation strength may vary with screw design. Methods. Screws from three posterior cervical fixation systems were used: Axis, Starlock/Cervifix, and Summit. Tested were 3.5-mm cancellous screws, along with revision screws for each system. The C3–C6 vertebrae from three cadaveric specimens were fixed with screws inserted into the lateral masses at a depth of 10 mm with 30° cephalad and 20° lateral angulation. Coaxial pullout force was recorded for each primary and revision screw. Results. Axial load-to-failure (mean ± SD) of the screws was 459 ± 60 N for Axis screws, 423 ± 78 N for Starlock screws, and 319 ± 97 N for Summit screws. The Axis and Starlock screws were significantly stronger than Summit screws (P = 0.017 and P = 0.067, respectively). The load-to-failure of revision screws was much lower than that of primary screws (Axis 54%, Starlock 56%, Summit 63% of the primary screw), without significant difference between screw types. Conclusions. The Axis and Starlock screws resisted significantly greater axial load-to-failure than did the Summit screws. For all three systems, the revision screws could not restore the load-to-failure of the primary screw in this model. The tested unicortical screws had a consistently higher load-to-failure than those previously tested under similar conditions, suggesting that currently available screws may be superior to those previously tested.
Evaluating the cervical spine for injury is an essential part of the assessment of a traumatized patient. Clinical examination and radiographs are the traditional techniques used for this evaluation. Often, however, a reliable clinical examination is not possible because of head injury, altered mental status, or "distracting" injuries. In such cases, cervical spine injury that is not apparent on radiographs may be missed. This case report illustrates a purely ligamentous cervical spine injury resulting in cervical instability. We describe our method of screening for and evaluating these types of injuries using physician-controlled stretch, flexion, and extension examination under fluoroscopy.
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