Andrew K. Simpson

Radiation Exposure from Musculoskeletal Computerized Tomographic Scans

BACKGROUND Computerized tomographic scans are routinely obtained to evaluate a number of musculoskeletal conditions. However, since computerized tomographic scans expose patients to the greatest amounts of radiation of all imaging modalities, the physician must be cognizant of the effective doses of radiation that are administered. This investigation was performed to quantify the effective doses of computerized tomographic scans that are performed for various musculoskeletal applications. METHODS The digital imaging archive of a single institution was retrospectively reviewed to identify helical computerized tomographic scans that were completed to visualize the extremities or spine. Imaging parameters were recorded for each examination, and dosimetry calculator software was used to calculate the effective dose values according to a modified protocol derived from publication SR250 of the National Radiological Protection Board of the United Kingdom. Computerized tomographic scans of the chest, abdomen, and pelvis were also collected, and the effective doses were compared with those reported by prior groups in order to validate the results of the current study. RESULTS The mean effective doses for computerized tomographic scans of the chest, abdomen, and pelvis (5.27, 4.95, and 4.85 mSv, respectively) were consistent with those of previous investigations. The highest mean effective doses were recorded for studies evaluating the spine (4.36, 17.99, and 19.15 mSv for the cervical, thoracic, and lumbar spines, respectively). In the upper extremity, the effective dose of a computerized tomographic scan of the shoulder (2.06 mSv) was higher than those of the elbow (0.14 mSv) and wrist (0.03 mSv). Similarly, the effective dose of a hip scan (3.09 mSv) was significantly higher than those observed with knee (0.16 mSv) and ankle (0.07 mSv) scans. CONCLUSIONS Computerized tomographic scans of the axial and appendicular skeleton are associated with substantially elevated radiation exposures, but the effective dose declines substantially for anatomic structures that are further away from the torso.

Quantifying the Effects of Age, Gender, Degeneration, and Adjacent Level Degeneration on Cervical Spine Range of Motion Using Multivariate Analyses

Study Design. Retrospective review and multivariate analysis. Objective. Assess cervical spine segmental range of motion (ROM) with flexion/extension (F/E) radiographs and determine the relation to clinical variables. Summary of Background Data. Previous studies investigated the roles of age and degeneration on cervical ROM with univariate analyses. Multivariate analyses are required to account for multiple factors that may affect ROM and quantify their relative effects. Methods. Radiographs of 195 patients were analyzed, including 133 females and 62 males with ages ranging from 15 to 93 years. Segmental ROM and Kellgren score (KS) of degeneration were assessed for C2–C7. Patient’s age and gender were documented. Multivariate analyses were performed for each level. Independent variables evaluated were: (1) KS at the level of interest, (2) KS at the level above, (3) KS at the level below, (4) age, and (5) gender. Significance was defined as P < 0.05. Results. Interobserver reliabilities for assessing KS (intraclass correlation coefficient 0.81) and segmental ROM (intraclass correlation coefficient 0.72) were good to excellent. Age had a significant negative association with ROM at C2–C3, C3–C4, C4–C5, and C5–C6. KS at the level of interest had a significant negative association with ROM at C2–C3, C3–C4, C4–C5, C5–C6, and C6–C7. KS at the inferior segment had a significant positive association with ROM at C2–C3, C3–C4, and C4–C5. Gender had a significant association with ROM only at C2–C3. Conclusion. Age was associated with declining ROM independent of degeneration, amounting to a 5° decrease in subaxial cervical ROM every 10 years. Degeneration was also associated with ROM. For every point increase in KS at a given level, there was an associated 1.2° decrease in ROM at that level, and a 0.8° increase in ROM at the level above. These results provide a framework with which to counsel patients about cervical ROM and a benchmark from which procedure specific changes can be compared.

The radiation exposure associated with cervical and lumbar spine radiographs.

Study design Cross-sectional study. Objective To calculate the effective radiation doses of routine anteroposterior (AP) and lateral radiographs of the cervical and lumbar spines. Summary of Background Data Although plain radiographs are generally used as the initial imaging modality for the evaluation of patients with spinal complaints, the radiation that patients receive during these studies has not been well quantified. The effective radiation dose represents a functional measure of exposure that takes into account the amount of radiation delivered and the radiosensitivity of the exposed organs. Consequently, the effective dose is important to consider from a radiation safety perspective. Methods The imaging practices of our radiology department were reviewed and the effective radiation doses for AP and lateral radiographs of the cervical and lumbar spines were calculated using the following variables: emitted radiation dose, source-to-object distance [SOD], film area, and patient tissue dimensions. Values were obtained from both direct measurements and an examination of the established protocols employed at our institution. Results The effective doses for AP and lateral cervical radiographs were 0.12 and 0.02 mSv, respectively, whereas the corresponding values for AP and lateral lumbar films were much larger (2.20 and 1.50 mSv, respectively). For comparative purposes, a typical chest x-ray results in a radiation dose between 0.06 and 0.25 mSv. Conclusions In this investigation, cervical spine films gave rise to radiation doses that are similar to those of chest x-rays. However, lumbar spine radiographs generated effective radiation doses that were approximately an order of magnitude greater than these other studies. In both the cervical and lumbar regions, AP views resulted in significantly greater radiation exposure than corresponding lateral images. The effective radiation doses reported here may prove to be valuable for assessing the relative risks and benefits of spine radiographs to establish appropriate guidelines for their use.

Mechanism of cervical spinal cord injury during bilateral facet dislocation.

Study Design. An in vitro biomechanical study. Objectives. The objectives were to: quantify dynamic canal pinch diameter (CPD) narrowing during simulated bilateral facet dislocation of a cervical functional spinal unit model with muscle force replication, determine if peak dynamic CPD narrowing exceeded that observed post-trauma, and evaluate dynamic cord compression. Summary of Background Data. Previous biomechanical models are limited to quasi-static loading or manual ligament transection. No studies have comprehensively analyzed dynamic CPD narrowing during simulated dislocation. Methods. Bilateral facet dislocation was simulated using 10 cervical functional spinal units (C3–C4: n = 4; C5–C6: n = 3; C7–T1: n = 3) with muscle force replication by frontal impact of the lower vertebra. Rigid body transformation of kinematic data recorded optically was used to compute the CPD in neutral posture (before dislocation), during dynamic impact (peak during dislocation), and post-impact (flexion rotation = 0°). Peak dynamic impact and post-impact CPD narrowing were statistically compared. Results. Average peak dynamic impact CPD narrowing significantly exceeded (P < 0.05) post-impact narrowing and occurred as early as 71.0 ms following impact. The greatest dynamic impact narrowing of 7.2 mm was observed at C3–C4, followed by 6.4 mm at C5–C6, and 5.1 mm at C7–T1, with average occurrence times ranging between 71.0 ms at C7–T1 and 97.0 ms at C5–C6. Conclusion. Extrapolation of the present results indicated dynamic spinal cord compression of up to 88% in those with stenotic canals and 35% in those with normal canal diameters. These results are consistent with the wide range of neurologic injury severity observed clinically due to bilateral facet dislocation.

Questionnaire study of neuromonitoring availability and usage for spine surgery.

Study Design Questionnaire study presented to practicing spine surgeons. Objective To evaluate surgeon preference and availability of selected electrophysiologic neuromonitoring for different spine surgeries. Summary of Background Data Maximizing the safety of spinal procedures and limiting potential iatrogenic neurologic injury has made intraoperative neuromonitoring an attractive option. Methods We distributed a questionnaire to 180 orthopedic spine surgeons and neurosurgeons at a clinically oriented spine meeting asking surgeon preference and availability of various types of intraoperative neuromonitoring modalities for different types of surgical procedures. Demographic data were also gathered. Results Somatosensory evoked potentials (SSEPs) were the most available neuromonitoring modality, followed by electromyographies and motor-evoked potentials. In both anterior and posterior cervical surgery, SSEPs were the most preferred modality. MEPs were frequently preferred in myelopathic cervical cases. Almost 70% preferred some neuromonitoring for anterior thoracic/thoracolumbar cases and 55% for posterior thoracic/thoracolumbar cases. Surgeon satisfaction was related to the number of available neuromonitoring modalities. No significant differences were found between orthopedist and neurosurgeon preferences. Fellowship-trained surgeons were more likely to use neuromonitoring for specific indications. Conclusions SSEPs remains the most widely available and preferred type of neuromonitoring for spine surgeons. The type of case and neurologic status of patient (eg, presence of myelopathy) affects these choices. Surgeons were more satisfied with greater neuromonitoring availability, and were more likely to use neuromonitoring if they had a fellowship background.

Sterility of C-arm fluoroscopy during spinal surgery

Study Design. Prospective study evaluating the sterility of 25 C-arm drapes after their use during spine surgery. Objective. To use swab samples to evaluate the sterility of draped C-arms at the end of spine surgical cases and assess the integrity of the sterile technique. Summary of Background Data. Intraoperative fluoroscopy is used routinely in the operating room for a variety of spinal applications. Although the C-arm may help the surgeon assess spinal alignment and facilitate the placement of instrumentation, there are concerns that the C-arm may represent a potential source of contamination and increase the risk of developing a postoperative infection. Methods. This study included 25 surgical cases requiring a standard fluoroscopic C-arm that were performed by 2 spine surgeons. Sterile culture swabs were used to obtain samples from 5 defined locations on the C-arm drape after its use during the operation. The undraped technician’s console was sampled in each case as a positive control and an additional 25 C-arm drapes were swabbed immediately after they were applied to the C-arm unit in order to obtain negative controls. Swab samples were assessed for bacterial growth on 5% sheep blood Columbia agar plates using a semiquantitative technique. Results. Contamination was noted on only 1 of 25 negative control drapes at a single location (4%). One hundred percent and 96% of the positive control swabs that were obtained from the negative controls and postoperative drapes exhibited growth, respectively. Although at least some degree of contamination was observed at all locations of the C-arm drape after surgery, the upper 2 sample sites demonstrated the greatest degree of contamination; the incidences of postoperative contamination were significantly greater for the top (56%, P < 0.000001) and upper front of the receiver (28%, P = 0.010) compared to the negative controls. In contrast, the lower front, receiver plate, and midportion of the C-arm were associated with lower rates of contamination (12%–20%). Conclusion. The upper portions of the C-arm clearly exhibited the greatest rates of contamination during spinal operations. This contamination most likely occurs when the undraped portions of the C-arm are rotated to acquire lateral images. As a result, we no longer consider the top portion of the C-arm drape to be sterile in these situations and we believe that avoiding contact with these areas may decrease the risks of intraoperative contamination and possibly postoperative infection as well.

Quantifying the effects of degeneration and other patient factors on lumbar segmental range of motion using multivariate analysis.

Study Design. Retrospective review and multivariate analysis. Objectives. Assess lumbar spine segmental range of motion (ROM) with flexion/extension (F/E) radiographs and determine the relation to clinical variables. Summary of Background Data. Prior studies have investigated the roles of age and degeneration on lumbar segmental ROM only using univariate analyses. Multivariate analyses are also required to differentiate the multiple factors that may affect ROM and quantify their relative effects. Methods. Radiographs of 258 patients were analyzed, including 137 females and 121 males with ages ranging from 18 to 92 years. Segmental ROM and Kellgren score (KS) of degeneration were assessed for L1–S1. Multivariate regression analyses were performed for each level. Predicting variables evaluated were: (1) KS at the level of interest, (2) KS at the level above, (3) KS at the level below, (4) age, (5) gender, (6) weight, (7) height, (8) body mass index (BMI), and (9) smoking. Significance was defined as P < 0.05. Results. Interobserver reliabilities for assessing KS (ICC 0.70) and segmental ROM (ICC 0.80) were good to excellent. In the multivariate analyses, age had a significant negative association with ROM at L1–L2, L2–L3, L3–L4, and L4–L5. BMI had a significant negative association with ROM at L2–L3, L3–L4, and L4–L5. KS at the level of interest had significant negative association with ROM only at L5–S1. KS at adjacent levels, gender, weight, height, and smoking did not have a significant association with ROM at any level. Conclusion. The results of this study provide the clinician with insight into factors that influence segmental lumbar ROM. Age was the strongest statistical predictor of ROM and was associated with declining ROM, amounting to an approximate 3° decrease in total sagittal lumbar ROM in the superior 4 segments every 10 years. BMI was another factor associated with lumbar ROM. Degeneration was a significant predictor of ROM only at L5–S1.

Current trends in spinal arthroplasty: an assessment of surgeon practices and attitudes regarding cervical and lumbar disk replacement.

Study Design Survey study involving orthopedic and neurosurgical spine surgeons. Objective To report the current practices and opinions of spine surgeons regarding cervical and lumbar total disk arthroplasty (TDA) as alternatives to arthrodesis for the treatment of degenerative conditions of the spine. Summary of Background Data TDA represents an alternative surgical treatment for degenerative spinal conditions that may avoid the deleterious effects associated with fusion. Unfortunately, the prevailing opinions of surgeons about TDA have not been well characterized and the patterns of its utilization have not been documented previously in the literature. Methods A questionnaire was developed to record the attitudes of spine surgeons regarding cervical and lumbar TDA and to assess their utilization of this technology. This survey was distributed to all of the surgeons attending the 2007 “Contemporary Update on Disorders of the Spine” meeting in Whistler, British Columbia. Results One hundred thirteen of the 133 surgeons present at the meeting completed the questionnaire, corresponding to a return rate of 85%. The percentage of surgeons who had performed lumbar TDA was significantly higher than that for cervical TDA (42% vs. 30%, P=0.05). However, 81% of respondents stated that they were more likely to perform cervical TDA now compared with 1 year ago, whereas 64% indicated that they were less likely to perform lumbar TDA. The most frequently cited reasons for not performing both cervical and lumbar TDA were questions concerning long-term outcomes and perceived difficulties with obtaining financial compensation from insurance companies; in addition, surgeons were also concerned about revising lumbar TDA cases. Conclusions Although the results of this study confirm that the enthusiasm for TDA was shared by many of these respondents, it is clear that additional long-term, prospective, comparative data are required before this technology may be considered as a replacement for more traditional spinal fusion procedures.

The utility of dynamic flexion-extension radiographs in the initial evaluation of the degenerative lumbar spine.

Study Design. Retrospective radiographic review. Objective. To assess the utility of lateral dynamic flexion-extension radiographs in the initial evaluation of the degenerative lumbar spine. Summary of Background Data. Most surgeons obtain standing anteroposterior (AP) and lateral radiographs in the initial evaluation of patients presenting with lumbar complaints. The potential role of dynamic films in this population has not been established. Methods. Of a 390 radiograph series, 342 met inclusion criteria and were reviewed. After assessment of the AP and lateral radiographs, dynamic films were evaluated to determine if additional information was obtained. Results. Only 2 of the 342 radiographic series had new findings seen on dynamic films not appreciated on the AP and lateral films (a L3–L4 anterolisthesis of 3 mm with flexion and a L5–S1 retrolisthesis of 4 mm with extension). Fifteen additional radiographic series were noted to have a change in the amount of anterolisthesis or retrolisthesis on the dynamic films (changes ranged from 2 to 5 mm). Conclusion. In the population studied, dynamic radiographs did not significantly alter the initial course of clinical management beyond standing AP and lateral lumbar images.

Actual knee motion during continuous passive motion protocols is less than expected.

Investigations of the usefulness of continuous passive motion (CPM) after TKA have yielded mixed results, with evidence suggesting its efficacy is contingent on the presence of larger motion arcs. Surprisingly, the range of motion (ROM) the knee actually experiences while in a CPM machine has not been elucidated. In this study, the ability of a CPM apparatus to bring about a desired knee ROM was assessed with an electrogoniometer. The knee experienced only 68% to 76% of the programmed CPM arc, with the higher percentages generated by elevating the head of the patient’s bed. This disparity between true knee motion and CPM should be accounted for when designing CPM protocols for patients or investigations evaluating efficacy of CPM.