Pedicle morphology of the immature thoracolumbar spine.

STUDY DESIGN: Human vertebral morphologic data were compiled from anatomic skeletal collections from three museums. OBJECTIVES: To quantify the morphometric characteristics of the pedicles of the immature thoracolumbar spine. SUMMARY OF BACKGROUND DATA: Little is known of pedicle morphology of the immature spine as related to pedicle screw fixation. METHODS: A total of 75 anatomic skeletal specimens were acquired from C1 to L5 in the age range of 3 to 19 years. The data were collected and analyzed using a computerized video analysis system. Each vertebral pedicle was measured in the axial and sagittal planes. The measurements included the minimum pedicle width, the pedicle angle, the distance to anterior cortex, and anteroposterior and interpedicular spinal canal diameters. RESULTS: Wide variation in pedicle morphology between specimens at each vertebral level was found in the young population. In general, compared with the average adult data, a younger spine demonstrated a near uniform reduction in the linear pedicle dimensions at each vertebral level. Pedicles from the lower lumbar vertebrae attained dimensions acceptable for standard screw sizes at an earlier age than in the thoracic vertebrae. CONCLUSIONS: The data in this study indicates that pedicle screws may be used in the adolescent spine. However, care should taken to accurately ascertain pedicle size before surgery so that improper use of screws can be avoided. Growth of the pedicles in relation to the spinal canal indicates that the increase in pedicle size is lateral to the spinal canal.

The biomechanical effect of postoperative hypolordosis in instrumented lumbar fusion on instrumented and adjacent spinal segments.

STUDY DESIGN: Change in lumbar lordosis was measured in patients that had undergone posterolateral lumbar fusions using transpedicular instrumentation. The biomechanical effects of postoperative lumbar malalignment were measured in cadaveric specimens. OBJECTIVES: To determine the extent of postoperative lumbar sagittal malalignment caused by an intraoperative kneeling position with 90 degrees of hip and knee flexion, and to assess its effect on the mechanical loading of the instrumented and adjacent segments. SUMMARY OF BACKGROUND DATA: The importance of maintaining the baseline lumbar lordosis after surgery has been stressed in the literature. However, there are few objective data to evaluate whether postoperative hypolordosis in the instrumented segments can increase the likelihood of junctional breakdown. METHODS: Segmental lordosis was measured on preoperative standing, intraoperative prone, and postoperative standing radiographs. In human cadaveric spines, a lordosis loss of up to 8 degrees was created across L4-S1 using calibrated transpedicular devices. Specimens were tested in extension and under axial loading in the upright posture. RESULTS: In patients who underwent L4-S1 fusions, the lordosis within the fusion decreased by 10 degrees intraoperatively and after surgery. Postoperative lordosis in the proximal (L2-L3 and L3-L4) segments increased by 2 degrees each, as compared with the preoperative measures. Hypolordosis in the instrumented segments increased the load across the posterior transpedicular devices, the posterior shear force, and the lamina strain at the adjacent level. CONCLUSIONS: Hypolordosis in the instrumented segments caused increased loading of the posterior column of the adjacent segments. These biomechanical effects may explain the degenerative changes at the junctional level that have been observed as long-term consequences of lumbar fusion.

Reduced transverse spinal area secondary to burst fractures: is there a relationship to neurologic injury?

A retrospective case-control study was undertaken to determine the best technique to measure neural canal encroachment at each lumbar level following burst fracture and its relationship to the presence of neurologic deficit. Only patients with postinjury CT scans demonstrating a disrupted posterior body with a retropulsed bone fragment were included. Patients were divided into groups based on the level of bony injury (T12-L5) and neurologic status. Neurologic injury was classified as follows: normal (N), root (R), or cauda equina/conus/paraplegic/paraparetic (C/P). The mean transverse spinal area (TSA, cm2), spinal canal percentage patency (PP), and midsagittal diameter (MSD) were determined for each neurologic group and lumbar level. A "calculated" TSA, based on midsagittal and anterior-posterior diameters, was also derived for each patient. The data were compared level by level and correlated with the patient's neurologic status. At L1, the critical TSA was 1.0 cm2. All patients with TSAs less than this were paraplegic. At both T12 and L1, TSAs in the range of 1.0-1.25 cm2 were observed in both normal and neurologically impaired patients. A critically significant TSA was not established for levels T12, L2, L3, L4, or L5; however, the data indicated that a smaller TSA can be tolerated at successively caudal levels without neurologic deficit. No meaningful correlation between root injury and TSA was observed. The data also indicated that measurement of TSA is a more accurate method for evaluating neural canal encroachment than PP or MSD. The "calculated" TSA is a simple, objective method for obtaining this information without the aid of a computer. This study suggests that absolute TSA should be utilized in future studies evaluating decompressive treatment of thoracolumbar pathology.

Extradural synovial thoracic cyst.

SUMMARY OF BACKGROUND DATA. Case studies documenting the incidence of thoracic intraspinal, extradural synovial cysts are limited. The occurrence of synovial cysts is associated with varied symptoms that differ among cervical, thoracic, and lumbar regions. The clinical appearance may be similar to other spinal diseases. METHODS. This report describes symptoms exhibited by and care provided for a patient with extradural synovial thoracic cyst.

Clinical methodologies and incidence of appropriate statistical testing in orthopaedic spine literature. Are statistics misleading?

An analysis of 300 randomly drawn orthopaedic spine articles, published between 1970 and 1990, was performed to assess the quality of biostatistical testing and research design reported in the literature. Of the 300 articles, 269 dealt with topics of an experimental nature, while 31 documented descriptive studies. Statistical deficiencies were identified in 54.0% of the total articles. Conclusions drawn as the result of misleading significance values occurred in 124 experimental studies (46%) while 96 failed to document the form of analysis chosen (35.7%). Statistical testing was not documented in 34 studies (12.6%), while 20 (7.4%) employed analyses considered inappropriate for the specific design structure.

Symptomatic spondylolisthesis in adults: four decades later.

An average follow-up of 40 years was obtained for 12 patients with spondylolisthesis treated at Hines Veterans Administration Hospital between 1944 and 1951. In each case, the slip had been Grade 1 and at the L5-S1 level. Five had been treated conservatively and seven surgically with a Hibbs fusion from L4 to S1. Of the conservatively managed patients, all functioned well during their working years, although one did have chronic, nondisabling, low-back pain. This same patient demonstrated radiographic evidence of progression to a Grade 2 spondylolisthesis. Among those undergoing surgery, the poor results were confined to those patients whose fusion attempts failed. Management for low-grade spondylolisthesis should be conservative where possible. When the low-back pain is disabling and surgery becomes necessary, failure to obtain a fusion portends a poor clinical result.

A dorsal wedge V osteotomy for painful plantar callosities.

A dorsal closing wedge proximal V metatarsal osteotomy is described for treatment of painful plantar callosities due to prominence of any of the five metatarsal heads. Forty-one osteotomies were performed over a 3-year period. In all patients so treated relief of symptoms was achieved, plantar callosities were resolved, and no significant complications occurred.

Pseudomonas aeruginosa bone and joint infection in drug abusers.

Thirty-nine sites of Pseudomonas aeruginosa bone and joint infection in thirty-five intravenous drug abusers were treated over a four-year period. Early diagnosis was based on a history of drug abuse and demonstration of the site of infection by a technetium bone scan. Most patients responded to long-term therapy with intravenous aminoglycoside and carbenicillin. Extensive early surgical procedures were rarely indicated except in patients with infection of a large synovial joint.