Daniel R. Benson

Early failure of short-segment pedicle instrumentation for thoracolumbar fractures. A preliminary report.

The results after treatment of fifty-two lumbar and thoracolumbar fractures with Cotrel-Dubousset instrumentation were reviewed as part of an ongoing study. Nineteen patients (average duration of follow-up, fifteen months) had been managed with short-segment pedicle-screw instrumentation. This preliminary report outlines the complications and pitfalls identified during the initial healing phase in this subgroup of patients. There were no neurological or vascular injuries due to placement of the pedicle screws, but ten patients had some form of failure of the fixation during the early period of healing. Failure of the fixation was manifested in three ways: progressive kyphosis secondary to the bending of screws (six patients), kyphosis secondary to osseous collapse or vertebral translation without bending of the hardware (three patients), and segmental kyphosis after a caudad screw in the lumbar construct broke (one patient, who had had a combined instrumentation for multiple fractures). Untreated anterior instability, and pre-stressing of the screws when the rods were contoured in situ, resulted in a high rate of failure. The high rate of failure of the hardware associated with this fixation construct suggests that posterior screw fixation alone may not be adequate when Cotrel-Dubousset instrumentation is used for short-segment lumbar arthrodeses. Bent screws or measurable kyphosis did not always herald a clinical failure, but patients who had progressive kyphosis of more than 10 degrees had substantially more pain than did those who had little or no progression. The results reported here are preliminary, and speculation as to the importance of these findings and as to the long-term outcome in these patients would be premature.(ABSTRACT TRUNCATED AT 250 WORDS)

Unstable thoracolumbar and lumbar burst fractures treated with the AO fixateur interne.

Twenty-five consecutive patients with unstable thoracolumbar and lumbar burst fractures were surgically treated with the AO Fixateur Interne (Synthes USA, 1690 Russell Rd., Paoli, PA). Indications for surgery included a progressive neurologic deficit, spinal canal compromise greater than 50%, vertebral body collapse greater than 50%, or sagittal angulation greater than 20 degrees. Twenty males and five females ranging in age from 16 to 60 years (average 31) were treated surgically and prospectively followed. Twenty-one fractures occurred at the thoracolumbar junction (T10-L2) and 4 in the lumbar spine (L3-5). Twenty-four patients were followed for a minimum of 12 months, ranging from 12 to 38 months (average 22); one patient was lost to follow-up after 1 month postoperatively. Preoperatively, 12 patients had partial neurologic deficits; postoperatively, 11 improved at least 1 Frankel grade. Preoperatively, the 12 patients with partial neurologic deficits averaged 45 points (range 24-49) on the lower extremity motor index scale. After surgery, these patients improved an average of five points (range 1-23) on the motor index scale. Both patients with complete spinal cord injuries remained unchanged neurologically postoperatively; no patients deteriorated neurologically after surgery. The average preoperative sagittal kyphosis at the fracture site was +16 degrees (range +10 degrees to +31 degrees); the immediate postoperative sagittal angular correction averaged -4 degrees (lordosis) and ranged from +12 degrees (kyphosis) to -26 degrees (lordosis). At last follow-up, the sagittal angular correction remained unchanged in three patients and decreased in 21 patients to an average of +5 degrees (range +37 degrees to -14 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanics of cervical spine internal fixation.

Recent advances in the area of cervical spine internal fixation have resulted in important additions to the armamentarium of the spine surgery. However, a sophisticated knowledge of the biomechanics of these devices is important. This article discusses the biomechanics of odontoid screws, anterior cervical plates, posterior cervical plates, and posterior C1—C2 screw arthrodesis. It is hoped that this information will aid in implant selection.

Short-segment pedicle instrumentation. Biomechanical analysis of supplemental hook fixation

Study Design This biomechanical study of fractures in cadaver vertebrae used specially designed pedicle screws to determine screw strains during loading of two different fixation constructs. Objectives The authors determined the relative benefit of adding offset sublaminar hooks to standard pedicle screw constructs to reduce screw bending moments and prevent fixation failure and sagittal collapse. Summary of Background Data Clinical studies have demonstrated a high incidence of early screw failure in short-segment pedicle instrumentation constructs used to treat unstable burst fractures. Strategies to prevent early construct failure include longer constructs, anterior strut graft reconstruction, and use of offset sublaminar hooks at the ends of standard short-segment pedicle instrumentation constructs. Methods Human cadaver spines with an L1 burst fracture were instrumented with a standard short-segment pedicle instrumentation construct using specially instrumented pedicle screws. Mechanical testing was carried out in flexion, extension, side bending, and torsion, and stiffness and screw bending moments were recorded. Offset hooks were applied initially, then removed and testing repeated. Stiffness data were compared to intact and postfracture results, and between augmented and standard constructs. Results Addition of offset laminar hooks, supralaminar at T11 and infralaminar at L2, to standard short-segment pedicle instrumentation constructs increased stiffness in flexion by 268%, in extension by 223%, in side bending by 161%, and in torsion by 155% (all were significant except torsion). Sublaminar hooks also reduced pedicle screw bending moments to roughly 50% of standard in both flexion and extension (P < 0.05). Conclusions Supplemental offset hooks significantly increase construct stiffness without sacrificing principles of short-segment pedicle instrumentation, and absorb some part of the construct strain, thereby reducing pedicle screw bending moments and the likelihood of postyield deformation and clinical failure.

New Perspectives on Low Back Pain.

Its coming again, the new collection that this site has. To complete your curiosity, we offer the favorite new perspectives on low back pain book as the choice today. This is a book that will show you even new to old thing. Forget it; it will be right for you. Well, when you are really dying of new perspectives on low back pain, just pick it. You know, this book is always making the fans to be dizzy if not to find.

Intraoperative autologous transfusion in orthopaedic patients.

The cases of 175 consecutive patients who had intraoperative autologous transfusion during revision total hip arthroplasty, an elective operation on the spine, repair of trauma to the spine, or open reduction of a fracture of the acetabulum were reviewed to evaluate the applicability of this technique in orthopaedic operations. A separate group of forty-one consecutive patients who had open reduction of a fracture of the acetabulum or the spine before the introduction of the autotransfuser was reviewed and compared with the group that had autotransfusion. An autologous blood predeposit program was used for twenty-five of fifty-two patients who had a procedure on the hip and for fifty-one of fifty-five patients who had an elective procedure on the spine. The mean rate of red blood-cell salvage using the autotransfuser was 60 per cent over-all. The mean transfusion requirements were significantly less (p less than 0.001) in all groups of patients in whom the autotransfuser was used. Use of the autotransfuser reduced the mean requirement for banked blood in patients who had a fracture of the acetabulum from 3.8 to 2.3 units per patient, and significantly reduced the mean need for banked blood in individuals who had trauma to the spine from 2.7 to 1.8 units per patient (p less than 0.01). The use of prebanked autologous blood further reduced the mean requirement for homologous blood from 2.4 to 0.8 unit per patient in those who had revision total hip arthroplasty (p less than 0.005), and from 3.6 to 0.4 unit per patient in those who had an elective procedure on the spine (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of open fractures: a prospective study.

A double-blind prospective study was done to assess the benefit of delaying closure of the wounds associated with open fractures. An additional double-blind study compared the effectiveness of clindamycin versus cefazolin for prophylactic antibiotic coverage. Quantitative cultures of the wounds were accomplished at the time of debridement and again at the time of closure if the wound was not closed initially. Almost half of the wounds were contaminated (46%) at the time of debridement, although the incidence of wound infection was low (6.5%). Gram-negative organisms resistant to the prophylactic antibiotic were recovered initially only eight times, but four of these (50%) became infected. The contaminating organisms in each case were present in high concentration (greater than 10(5) CFU/gm of tissue) at initial culture. The time of wound closure, cefazolin versus clindamycin, and internal fixation of the fracture were not followed by significant differences in the development of clinical infection in this series.

Autosterilization in low-velocity bullets

Following a previous study (1) in which contaminated low-velocity bullets were discharged into sterile gelatin blocks with resultant growth of organisms along projectile tracts, the authors fired bullets coated with 1 drop of Staph. aureus-contaminated medium and bullets under sterile conditions into sterilized sand. Each contaminated projectile and its gun barrel were culture positive after firing. Therefore bullets should not be ruled out as possible sources of infection.

Force-deformation properties of human ribs

Abstract Experiments were conducted to measure geometrical and force-deformation properties of individual human ribs. These data are needed to enable studies to be made of the mechanical role of the rib cage in different situation. Right ribs 2, 4, 6, 8, 9 and 10 were obtained at autopsy from each of 5 male cadavers. The head of each rib was fixed, and the antero-medial free end dead-wt loaded in three increments, in six directions. When subject to 0·75 kp loads, deflections of the order of 3 cm in the upper ribs and 6 cm in the lower ribs often occurred in the direction of the load. Deflections occurred in directions other than that of load application as well, and significant nonlinearities in load-deflection response were found.

The spine and surgical treatment in osteogenesis imperfecta.

In the osteogenesis imperfecta patient, spinal deformity should be expected, particularly in the severely affected nonambulator with chest deformity. Curves develop early (age five to six) and generally progress rapidly. Early bracing, although somewhat effective, may well compress the soft osteoporotic rib cage without controlling the spinal curvature. The pulmonary compromise created by the scoliosis is compounded by the chest cage deformity secondary to bracing. In the patient with severe disease (thin bones and numerous fractures), posterior correction and fusion, with or without Harrington instrumentation, is the preferred approach. This should be done early as the osteoporotic bone does not tolerate the hook forces well; the correction is correspondingly limited. The use of methylmethacrylate bone cement around the hook provides redistribution of forces and more stable fixation. In the patient with mild disease (thick bones and few fractures) treatment should be similar to that of patients with idiopathic scoliosis. The chest cage should be carefully observed to avoid deformity from placement of the lateral or posterior pad.