Jens R. Chapman

Factors Affecting the Pullout Strength of Cancellous Bone Screws

Screws placed into cancellous bone in orthopedic surgical applications, such as fixation of fractures of the femoral neck or the lumbar spine, can be subjected to high loads. Screw pullout is a possibility, especially if low density osteoporotic bone is encountered. The overall goal of this study was to determine how screw thread geometry, tapping, and cannulation affect the holding power of screws in cancellous bone and determine whether current designs achieve maximum purchase strength. Twelve types of commercially available cannulated and noncannulated cancellous bone screws were tested for pullout strength in rigid unicellular polyurethane foams of apparent densities and shear strengths within the range reported for human cancellous bone. The experimentally derived pullout strength was compared to a predicted shear failure force of the internal threads formed in the polyurethane foam. Screws embedded in porous materials pullout by shearing the internal threads in the porous material. Experimental pullout force was highly correlated to the predicted shear failure force (slope = 1.05, R2 = 0.947) demonstrating that it is controlled by the major diameter of the screw, the length of engagement of the thread, the shear strength of the material into which the screw is embedded, and a thread shape factor (TSF) which accounts for screw thread depth and pitch. The average TSF for cannulated screws was 17 percent lower than that of noncannulated cancellous screws, and the pullout force was correspondingly less. Increasing the TSF, a result of decreasing thread pitch or increasing thread depth, increases screw purchase strength in porous materials. Tapping was found to reduce pullout force by an average of 8 percent compared with nontapped holes (p = 0.0001). Tapping in porous materials decreases screw pullout strength because the removal of material by the tap enlarges hole volume by an average of 27 percent, in effect decreasing the depth and shear area of the internal threads in the porous material.

Evaluating common outcomes for measuring treatment success for chronic low back pain

Study Design. Systematic review. Objective. To identify, describe, and evaluate common outcome measures in patients with chronic low back pain (CLBP). Summary of Background Data. The treatment of CLBP has been associated with multiple clinical challenges. Further complicating this is the myriad of outcome scores used to assess treatment of CLBP. These scores have been used to examine different domains of patient satisfaction and quality of life in the literature. Critical assessment of the frequency, parity, and the quality of these outcomes are essential to improve our understanding of CLBP. Methods. A systematic review of the English-language literature was undertaken for articles published from January 2001 through December 31, 2010. Electronic databases and reference lists of key articles were searched to identify measures used to evaluate outcomes in six different domains in patients with CLBP. The titles and abstracts of the peer-reviewed literature of LBP were searched to determine which of these measures were most commonly reported in the literature and which have been validated in populations with CLBP. Results. We identified 75 outcome measures cited to evaluate CLBP. Twenty-nine of these outcome measures were excluded because of only a single citation leaving 46 measures for the evaluation. The most commonly used functional outcomes were the Oswestry Disability Index, Roland Morris Disability Index, and range of motion. For pain, the Numeric Pain Rating Scale, Brief Pain Inventory, Pain Disability Index, McGill Pain Questionnaire, and visual analog scale were most commonly cited. For psychosocial function, the Fear Avoidance Beliefs Questionnaire, Tampa Scale for Kinesiophobia, and Beck Depression Inventory were most commonly used. For generic quality of life, short form 36, Nottingham Health Profile, short form 12, and Sickness Impact Profile were the most common measures. For objective measures, the work status/return to work, complications or adverse events, and medications used were the most commonly cited. For preference-based measures, the Euro-Quol 5 dimensions and short form 6 dimensions were most commonly cited. The validity, reliability, responsiveness, universality, and potential proprietary requirements are summarized for each. Conclusion. Outcome measures should be routinely assessed in patients with CLBP. The choice of appropriate outcome measure should be influenced by the study objectives and design, as well as properties of the particular measure within the context of CLBP. Clinical Recommendations. Recommendation 1: When selecting the appropriate outcome measures for clinical or research purposes, consider domains that best measure what are most important to patients. Measures that are valid, reliable, and responsive to change should be considered first. Other considerations include the number of items required (especially in the context of multiple measures), whether the measure is validated in the relevant language, and the associated costs or fees. Strength: Strong Recommendation 2: Domains of greatest importance include pain, function, and quality of life. If cost utilization is a priority, then preference-based measures should be considered. For pain, we recommend the VAS and NRPS because of their ease of administration and responsiveness. For function, we recommend the ODI and RMDQ. The SF-36 and its shorter versions are most commonly used and should be considered if quality of life is important. If cost utility is important, consider the EQ-5D or SF-6D. Psychosocial tests are best used as screening tools prior to surgery because of their lack of responsiveness. Complications should always be assessed as a standard of clinical practice. Return to work and medication use are complicated outcome measures and not recommended unless the specific study question is focused on these domains. Consider staff and patient burden when prioritizing ones battery of measures.

Randomized prospective study of humeral shaft fracture fixation: intramedullary nails versus plates.

OBJECTIVES To compare the clinical and radiographic results for locked intramedullary (IM) nails and plates used in the treatment of humeral diaphyseal fractures. DESIGN Prospective randomization by sealed-envelope technique of eighty-four patients into two study groups: those treated by intramedullary nailing (IMN group; n = 38) and those treated by compression plating (PLT group; n = 46). SETTING Patients admitted consecutively to a university-affiliated Level I trauma center. PATIENT/PARTICIPANTS All skeletally mature patients admitted to Harborview Medical Center with acute humeral shaft fractures requiring surgical stabilization. Fractures of the diaphysis were defined as being at least three centimeters distal to the surgical neck and at least five centimeters proximal to the olecranon fossa. INTERVENTION Treatment with locking antegrade intramedullary humeral nails (Russell-Taylor design [Smith and Nephew Richards]) or with 4.5-millimeter dynamic compression and limited contact dynamic compression plates (AO design [Synthes]). MAIN OUTCOME MEASUREMENTS Clinical outcome measurements included fracture healing, radial nerve recovery, infection, and elbow and shoulder discomfort. Radiographic measurements included fracture alignment, time to healing, delayed union, and nonunion. RESULTS Follow-up averaged thirteen months. Forty-two fractures (93 percent) in the PLT group were healed by sixteen weeks versus thirty-three fractures (87 percent) in the IMN group (p = 0.70). Shoulder pain and a decrement in shoulder range of motion (ROM) were significant associations with IMN (p = 0.007 for both variables) but not with PLT. A decrement in elbow ROM was significantly associated with PLT (p = 0.03), especially for fractures of the distal third of the diaphysis, whereas elbow pain was not (p = 0.123). The sum of other complications demonstrated nearly equal prevalence for both treatment groups. CONCLUSIONS For patients requiring surgical treatment of a humeral shaft fracture, intramedullary nailing and compression plating both provide predictable methods for achieving fracture stabilization and ultimate healing.

AOSpine thoracolumbar spine injury classification system: fracture description, neurological status, and key modifiers.

Study Design. Reliability and agreement study, retrospective case series. Objective. To develop a widely accepted, comprehensive yet simple classification system with clinically acceptable intra- and interobserver reliability for use in both clinical practice and research. Summary of Background Data. Although the Magerl classification and thoracolumbar injury classification system (TLICS) are both well-known schemes to describe thoracolumbar (TL) fractures, no TL injury classification system has achieved universal international adoption. This lack of consensus limits communication between clinicians and researchers complicating the study of these injuries and the development of treatment algorithms. Methods. A simple and reproducible classification system of TL injuries was developed using a structured international consensus process. This classification system consists of a morphologic classification of the fracture, a grading system for the neurological status, and description of relevant patient-specific modifiers. Forty cases with a broad range of injuries were classified independently twice by group members 1 month apart and analyzed for classification reliability using the Kappa coefficient (&kgr;). Results. The morphologic classification is based on 3 main injury patterns: type A (compression), type B (tension band disruption), and type C (displacement/translation) injuries. Reliability in the identification of a morphologic injury type was substantial (&kgr;= 0.72). Conclusion. The AOSpine TL injury classification system is clinically relevant according to the consensus agreement of our international team of spine trauma experts. Final evaluation data showed reasonable reliability and accuracy, but further clinical validation of the proposed system requires prospective observational data collection documenting use of the classification system, therapeutic decision making, and clinical follow-up evaluation by a large number of surgeons from different countries. Level of Evidence: 4

Treatment of type II, IIIA, and IIIB open fractures of the tibial shaft: a prospective comparison of unreamed interlocking intramedullary nails and half-pin external fixators.

OBJECTIVE To compare unreamed intramedullary nailing (IMN) with external fixation (EF) in patients with Type II, IIIA, and IIIB open fractures of the tibial shaft. DESIGN An inception cohort of consecutive patients with Type II, IIIA, and IIIB tibial fractures incurred between January 1988 and March 1993 were systematically allocated into one of two treatment groups. Patients were treated and followed with a prospectively designed protocol. PATIENTS AND SETTING All patients were skeletally mature and had incurred a fracture of the tibial diaphysis within twenty-four hours of presentation to the tertiary care hospital, a Level I Trauma Center. One hundred seventy-four fractures in 168 patients were stabilized with either IMN (104) or half-pin EF (70). There were 132 men and thirty-six women, with an average age of thirty-three years (range, 14 to 77 years). INTERVENTION Except for the selection of the fixation device, open fracture care was similar in the two treatment groups. All patients underwent emergent irrigation and debridement with concomitant skeletal stabilization. Cephalosporin antibiotics were administered perioperatively for twenty-four to forty-eight hours. No wounds were closed primarily. Delayed primary closure, skin grafting, and/or myoplasty were performed between three and ten days after injury. MAIN OUTCOME MEASURES The main outcome measures were final fracture alignment, presence of infection or inflammation, hardware failure, time to union, and the number of operative procedures. RESULTS The IMN group had significantly fewer incidences of malalignment than did the EF group [8 vs. 31 percent; p = 0.00005; confidence interval (CI) = 0.18, 0.76] and had significantly fewer subsequent procedures (mean of 1.7 vs. mean of 2.7 per fracture; p = 0.001; CI = 0.45, 1.59). IMN resulted in fewer infections/ inflammatory problems than did EF at the injury site (13 vs. 21 percent; p = 0.73; CI = -0.63, 0.45) and significantly fewer at surgical interfaces (i.e., pin sites, nail and interlocking screw insertion sites; 2 vs. 50 percent; p = 0.000; CI = 0.39, 0.60). No significant difference was found in the healing rates for the two implant groups. The more severe Gustilo injury types had longer healing times regardless of the type of fixation. CONCLUSIONS Results suggest that unreamed interlocking intramedullary nails are more efficacious than half-pin external fixators, in particular with regard to maintenance of limb alignment. However, the severity of soft tissue injury rather than the choice of implant appears to be the predominant factor influencing rapidity of bone healing and rate of injury site infection.

A Phase I/IIa Clinical Trial of a Recombinant Rho Protein Antagonist in Acute Spinal Cord Injury

Multiple lines of evidence have validated the Rho pathway as important in controlling the neuronal response to growth inhibitory proteins after central nervous system (CNS) injury. A drug called BA-210 (trademarked as Cethrin(®)) blocks activation of Rho and has shown promise in pre-clinical animal studies in being used to treat spinal cord injury (SCI). This is a report of a Phase I/IIa clinical study designed to test the safety and tolerability of the drug, and the neurological status of patients following the administration of a single dose of BA-210 applied during surgery following acute SCI. Patients with thoracic (T2-T12) or cervical (C4-T1) SCI were sequentially recruited for this dose-ranging (0.3 mg to 9 mg Cethrin), multi-center study of 48 patients with complete American Spinal Injury Association assessment (ASIA) A. Vital signs; clinical laboratory tests; computed tomography (CT) scans of the spine, head, and abdomen; magnetic resonance imaging (MRI) of the spine, and ASIA assessment were performed in the pre-study period and in follow-up periods out to 1 year after treatment. The treatment-emergent adverse events that were reported were typical for a population of acute SCI patients, and no serious adverse events were attributed to the drug. The pharmacokinetic analysis showed low levels of systemic exposure to the drug, and there was high inter-patient variability. Changes in ASIA motor scores from baseline were low across all dose groups in thoracic patients (1.8±5.1) and larger in cervical patients (18.6±19.3). The largest change in motor score was observed in the cervical patients treated with 3 mg of Cethrin in whom a 27.3±13.3 point improvement in ASIA motor score at 12 months was observed. Approximately 6% of thoracic patients converted from ASIA A to ASIA C or D compared to 31% of cervical patients and 66% for the 3-mg cervical cohort. Although the patient numbers are small, the observed motor recovery in this open-label trial suggests that BA-210 may increase neurological recovery after complete SCI. Further clinical trials with Cethrin in SCI patients are planned, to establish evidence of efficacy.

Early versus delayed surgery for acute cervical spinal cord injury.

The optimal timing of surgical intervention in cervical spinal cord injuries has not been defined. The goals of the study were to investigate changes in neurologic status, length of hospitalization, and acute complications associated with surgery within 3 days of injury versus surgery more than 3 days after the injury. All patients undergoing surgical treatment for an acute cervical spinal injury with neurologic deficit at two institutions between March 1989 and May 1991 were reviewed retrospectively. Forty-three patients initially were evaluated. At one institution, patients with neurologic spinal injuries had surgical intervention within 72 hours of injury. At the other institution, patients underwent immediate closed reduction with subsequent observation of neurologic status for 10 to 14 days before undergoing surgical stabilization. This study indicates that patients who sustain acute traumatic injuries of the cervical spine with associated neurologic deficit may benefit from surgical decompression and stabilization within 72 hours of injury. Surgery within 72 hours of injury in patients sustaining acute cervical spinal injuries with neurologic involvement is not associated with a higher complication rate. Early surgery may improve neurologic recovery and decrease hospitalization time in patients with cervical spinal cord injuries.

Accuracy of Thoracic Vertebral Body Screw Placement Using Standard Fluoroscopy, Fluoroscopic Image Guidance, and Computed Tomographic Image Guidance: A Cadaver Study

Study Design. A surgical simulation study in human cadaver spine specimens was conducted to evaluate the accuracy of thoracic vertebral body screw placement using four different intraoperative imaging techniques. Objective. To compare standard fluoroscopy, fluoroscopy-based image guidance with two different referencing methods, and computed tomography–based image guidance by the measuring the time required for screw placement, the radiation exposure to specimen and surgeon, and the accuracy of screw position in the thoracic spine. Summary of Background Data. Image guidance provides additional anatomic information to the surgeon and may improve safety of technically difficult surgical procedures. The placement of screws in the thoracic spine is a technically demanding procedure in which inaccurate screw positioning places the spinal cord, nerve roots, and paraspinal structures such as the aorta and pleural space at risk for injury. Image-guided surgery may improve the accuracy of thoracic screw placement. Methods. Using four different intraoperative imaging methods, two experienced surgeons placed 337 vertebral body screws through the pedicles of thoracic vertebrae in 20 human cadaver thoracic spine specimens. The specimens then were examined with radiographs, computed tomography, and anatomic dissection to determine screw position. Measurements included procedure setup and screw insertion time, radiation exposure to the specimen, the surgeon’s hand, the surgeon’s body, frequency, direction, and magnitude of screw perforation through the cortical margins of thoracic vertebrae. Results. As compared with surgery using standard fluoroscopy, fluoroscopy-based image guidance that uses multiple reference marks and computed tomography–based image guidance improves the accuracy of thoracic vertebral body screws, but increases the time required for screw placement and the specimen radiation exposure. Exposure to radiation is minimal at the surgeon’s body level and dependent on surgical technique at the surgeon’s hand level. Screw perforation occurs most frequently in the lateral direction. Conclusions. Fluoroscopy-based image guidance that uses only a single reference marker for the entire thoracic spine is highly inaccurate and unsafe. Systems with registration based on the instrumented vertebrae provide more accurate placement of thoracic vertebral body screws than standard fluoroscopy, but expose the patient to more radiation and require more time for screw insertion.

Efficacy and safety of surgical decompression in patients with cervical spondylotic myelopathy: results of the AOSpine North America prospective multi-center study.

BACKGROUND Cervical spondylotic myelopathy is the leading cause of spinal cord dysfunction worldwide. The objective of this study was to evaluate the impact of surgical decompression on functional, quality-of-life, and disability outcomes at one year after surgery in a large cohort of patients with this condition. METHODS Adult patients with symptomatic cervical spondylotic myelopathy and magnetic resonance imaging evidence of spinal cord compression were enrolled at twelve North American centers from 2005 to 2007. At enrollment, the myelopathy was categorized as mild (modified Japanese Orthopaedic Association [mJOA] score ≥ 15), moderate (mJOA = 12 to 14), or severe (mJOA < 12). Patients were followed prospectively for one year, at which point the outcomes of interest included the mJOA score, Nurick grade, Neck Disability Index (NDI), and Short Form-36 version 2 (SF-36v2). All outcomes at one year were compared with the preoperative values with use of univariate paired statistics. Outcomes were also compared among the severity classes with use of one-way analysis of variance. Finally, a multivariate analysis that adjusted for baseline differences among the severity groups was performed. Treatment-related complication data were collected and the overall complication rate was calculated. RESULTS Eighty-five (30.6%) of the 278 enrolled patients had mild cervical spondylotic myelopathy, 110 (39.6%) had moderate disease, and 83 (29.9%) had severe disease preoperatively. One-year follow-up data were available for 222 (85.4%) of 260 patients. There was a significant improvement from baseline to one year postoperatively (p < 0.05) in the mJOA score, Nurick grade, NDI score, and all SF-36v2 health dimensions (including the mental and physical health composite scores) except general health. With the exception of the change in the mJOA, the degree of improvement did not depend on the severity of the preoperative symptoms. These results remained unchanged after adjusting for relevant confounders in the multivariate analysis. Fifty-two patients experienced complications (prevalence, 18.7%), with no significant differences among the severity groups. CONCLUSIONS Surgical decompression for the treatment of cervical spondylotic myelopathy was associated with improvement in functional, disability-related, and quality-of-life outcomes at one year of follow-up for all disease severity categories. Furthermore, complication rates observed in the study were commensurate with those in previously reported cervical spondylotic myelopathy series.

Spine fractures in patients with ankylosing spinal disorders.

Study Design. Retrospective review. Objective. To describe the spine fracture characteristics, current treatments, and their results in patients with ankylosing spinal disorders (ASD), such as ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis (DISH), with the hypothesis that complication and mortality rates are high. Summary of Background Data. Spine fractures in patients with ASD are unique and have only been described in relatively small case series. Methods. Retrospective review of a large consecutive series of patients with spine fractures and ASD over a 7-year period. Complications were stratified according to parameters such as type and number of comorbidities, patient age, and mechanism of injury. Predictors of mortality were analyzed by linear regression. Similarities between patients with AS and DISH were evaluated by &khgr;2 analysis. Results. Of the 122 spine fractures in 112 consecutive patients with ASD, the majority were transdiscal extension injuries, most commonly affecting C6–C7. Eighty-one percent of the patients had at least 1 major medical comorbidity. Spinal cord injury was present in 58% of the patients, 34% of whom improved by at least 1 American Spinal Injury Association grade. Nineteen percent of patients had delayed diagnosis of their spine fracture, 81% of whom had resulting neurologic compromise. Surgery was performed on 67% of patients, consisting primarily of multilevel posterior instrumentation 3 levels above and below the injury. Eighty-four percent of all patients had at least 1 complication. Mortality was 32% and correlated with age ≥70 (P < 0.0001), number of comorbidities (P < 0.0001), and low-energy mechanism of injury (P = 0.009). AS patients were younger (P = 0.03) and had a higher risk of delayed fracture diagnosis (P = 0.012), but were otherwise similar to DISH patients. Conclusion. Patients with spine fractures and ASD are at high risk for complications and death and should be counseled accordingly. Multilevel posterior segmental instrumentation allows effective fracture healing. AS and DISH patients represent similar patient populations for the purpose of treatment and future research.