Cervical spine flexion and extension radiographs are commonly used to test the dynamic stability of the cervical spine following trauma or surgery. Currently, cervical spine clearance protocols include multiple plain radiographs of the cervical spine, fine cut helical computed tomography, and voluntary flexion and extension lateral radiographs views. Approximately one third of flexion/extension films are deemed inadequate secondary to limited motion. Flexion of 30 degrees has been arbitrarily chosen to test the integrity of the posterior cervical ligaments. In order to determine the amount of flexion necessary to adequately stress the posterior ligamentous structures, Dr. Hurford used an AIFP probe to measure the strain on the ligamentum flavum in 5 human cervical spine specimens at sequential amounts of flexion. The Cobb method was used to determine the amount of flexion as visualized on fluoroscopy images. Dr. Hurford determined that strain increased in a nonlinear manner, with the largest increase occurring in the last 10 degrees of flexion. These results suggest that at least 50 degrees of flexion is necessary to tension the posterior ligament complex.

Dr. Grottkau used the analogy of a tipping sailboat and a "turtling" catamaran to describe the elements of cervical spinal instability, and he commended Dr. Hurford's efforts. Dr. Grottkau raised the question of whether the laminotomies used to insert the strain gauges into the cadaveric specimens may have influenced the study results. Furthermore, he raised the issue of ligamentum flavum creep and its potential affect on this study design.
 

Distal radius fractures compose 20-25% of all pediatric fractures and approximately 15% include the distal radial physis. Post-traumatic distal radial growth arrest is thought to occur in 1-7% of cases. In Part I, Dr. Bae assessed the efficacy of a surgical protocol aimed at restoring normal wrist mechanics in adolescents with post-traumatic distal radius growth arrest. In a retrospective study of 30 patients that underwent various procedures for growth arrest, patients improved from an average of 4mm positive to neutral ulnar variance, and from 8.5 degrees of radial inclination to 15.5 degrees. Postoperatively, all patients had a good/excellent Modified Mayo Wrist Scores. Dr. Bae concluded that both pain and limited motion could be improved. In Part II, a prospective cohort study from June 2000 to December 2002 was performed to study the incidence and identifiable risk factors for growth arrest following distal radial physeal fractures. An overall incidence of 3% was found. Age, mechanism, and initial fracture displacement were not found to be predictors of growth arrest. High energy sports injuries and repeat fracture manipulation were common factors in patients in whom growth arrest occurred.

Dr. Jupiter commended Dr. Bae on a well executed study. Dr. Jupiter commented that historically, recommendations regarding the treatment of radial growth arrest were based upon limited case series and little data. It is difficult to identify factors leading to growth arrest with such small numbers, but Dr. Bae's work suggests that high energy mechanisms and repeat manipulations may influence outcome, in addition to factors commonly cited.
 

Dr. Appleton investigated the efficacy of high speed helical computed tomography (CT) in the diagnosis of ligamentous injuries to the cervical spine in the obtunded trauma patient. Despite the efforts of many previous studies, there still is currently no universally accepted protocol for cervical spine clearance in the obtunded patient. A retrospective review of 715 trauma patients admitted to Massachusetts General Hospital was performed. Over 500 patients had negative CT scans, and they were further examined for missed cervical spine injury. Eight patients had a negative CTs but were later discovered to have a spinal cord injury. All these patients had neurologic findings suggestive of injury, and therefore magnetic resonance imaging (MRI) were obtained. Of those who underwent lateral out-of-collar radiographs, plain radiographic results did not change their management. Dr. Appleton concluded that CT might be effective at diagnosing unstable ligamentous injuries, as no such cases were missed.

Dr. Pedlow commended Dr. Appleton on his work to establish a protocol for cervical spine clearance in the obtunded trauma patient. There has not been a prospective trial examining the most reliable way to identify ligamentous injuries in this patient population. Current protocols include both plain film and fine cut CT, but Dr. Appleton's data call into question the need for plain films in clearing the cervical spine.
 

Dr. Schultz discussed the use of bone morphogenic protein (BMP) -2 delivery using an adenoviral vector to enhance healing of critical long bone defects in rats. Bone morphogenic proteins are osteogenic agents, although there use has been hindered by the lack of a delivery system that can provide a sustained concentration of protein at the appropriate location. In most cases, there is an initial release of supra-physiologic concentrations of growth factor, followed by suboptimal levels. A 5mm segmental defect was created in the right femora of 3 groups of rats. The groups were treated with either adenoviral vectors transfected with BMP-2 cDNA, viral vectors containing the luciferase gene, or saline. At 8 weeks, 100% of the segmental defects treated with BMP-2 were healed, whereas none of the untreated rats had healed. Gross and histological examination of the femora treated with BMP-2 revealed bony growth compared to fibrous healing of the untreated group. CT revealed bridging of the segmental defect in the treated group and not in the untreated

Dr. Murray commended Dr. Schultz on work that one day may lead to the routine use of bone morphogenic proteins in the field of orthopedics. She raised the issue of the safety of viral-based gene therapy, given recent reports of systemic reactions to adenoviral vectors. However, as this particular vector is introduced locally into the bony defect, it may be less likely to produce systemic effects. This study lays the groundwork for further studies investigating in vivo expression in other parts of the body and ectopic bone formation.