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Ann Thorac Surg 1996;62:818-822
© 1996 The Society of Thoracic Surgeons
Department of Cardiothoracic Surgery, University of California, Davis, Medical Center, Sacramento, and Kaiser Permanente, Oakland, California
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Abstract |
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 TopFootnotes Abstract IntroductionPatients and MethodsResultsCommentReferences |
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Background. The feasibility of a video-assisted anterior approach to the thoracic spine has recently been reported for a variety of spine disorders. This study compares the outcomes of the video-assisted and thoracotomy approaches.
Methods. A consecutive series of 42 patients underwent video-assisted thoracic surgical anterior release and were evaluated for degree of correction reported as a change in spine curvature and pulmonary functions reported as a percent of predicted values. They were followed up for a minimum of 1 year and compared with historic controls.
Results. There was no significant difference in the percentage of correction between the video-assisted and thoracotomy groups, and the angle of correction was stable over the period of follow-up. No statistically significant difference was noted for any lung volume measure except for postoperative residual volume/total lung capacity ratio (video-assisted thoracic surgery = 135 ± 16.2; thoracotomy = 147.7 ± 17.8; p = 0.03). This marginal difference becomes more significant when severely affected patients are analyzed separately (p < 0.01).
Conclusions. The video-assisted anterior spine release achieves equivalent results in idiopathic scoliosis compared with an open approach. The preservation of chest wall musculature in severely affected patients appears to play a role in limiting the deterioration in postoperative pulmonary function.
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Introduction |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Anterior exposure of the thoracic spine in idiopathic scoliosis has classically been performed through a posterolateral thoracotomy or a thoracolumbar incision [1, 2]. This approach permits anterior spine release via multiple-level vertebral diskectomies and is followed at the same operation with posterior spine instrumentation to achieve straightening and fusion.
The feasibility of a video-assisted anterior approach to the thoracic spine has recently been reported for a variety of spine disorders including scoliosis [3–6]. Reported decreases in morbidity, operative time, hospital stay, and blood loss have been achieved relative to a thoracotomy approach [6].
We chose idiopathic scoliosis patients to assess the efficacy and durability of the video-assisted exposure for anterior spine release because comparison with thoracotomy is possible using well-established markers of clinical outcome, namely, degree of correction and pulmonary function changes. Degree of correction can be measured by radiographic assessment of the angle of curvature by the method of Cobb [7]. Stability of the correction can be assessed repeatedly in time with plain films of the spine. Respiratory mechanics in adolescents with idiopathic scoliosis have been extensively studied in both treated and untreated patients [8–10]. Early reductions in lung capacity are associated with changes in chest wall mechanics that can be described with pulmonary volumes and flows [11–14]. These children are thought to have defective mechanical coupling of the respiratory musculature to the distorted rib cage and may represent a group of patients in whom the impact of a video-assisted approach, in sparing chest wall musculature, extends beyond access and improves outcome.
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Patients and Methods |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Five patients were converted to thoracotomy intraoperatively due to technical difficulty in obtaining or tolerating single-lung ventilation (2 patients), dense adhesions (1 patient), or anatomic considerations limiting exposure to the spine (2 patients). The video-assisted group therefore comprised 38 patients (30 girls and 8 boys) available for evaluation with a 1-year follow-up.
Briefly, the video-assisted technique [6] is performed through multiple 12-mm incisions in the posterior axillary line. The intent of this posterolateral approach to the spine is to access the disk space tangential to the spinal cord. The surgeon stands at the patient's back and works from posterior to anterior away from the spinal cord. We use a 10-mm, 45-degree scope in larger patients and a 5-mm, 30-degree arthroscope in smaller patients.
A cautery hook is placed on the pleura midway between the head of the rib and the anterior spine overlying the disk space, and the parietal pleura is divided proximally and distally over the segments to be released. The segmental vessels run between the disk spaces over the vertebral bodies and can generally be avoided. The disks can then be approached in a standard manner of subchondral loosening of the disk attachments and removal of the disk material in anterior longitudinal ligament with a rongeur or curette. The disk space is relatively avascular. Minor subchondral bone bleeding is controlled with Surgicel (Johnson & Johnson, Arlington, TX). The Surgicel is removed from the disk space to prevent any potential for spinal cord compression. Rib chips and allogeneic bone matrix (Osteotech Spine Inc, Shrewsbury, NJ) are left in the disk space to facilitate fusion. The pleura is no longer closed.
The video-assisted patients were compared with a group of idiopathic scoliosis patients who met the above entry criteria and differed only in that their anterior spine release was performed through a posterolateral thoracotomy. This control group (mean age, 13.5 ± 3.8 years) consisted of 18 patients (14 girls and 4 boys) operated on during the year preceding the study. The 5 patients converted from a video-assisted to a thoracotomy approach were excluded from the study.
The comparability of the video-assisted group with the thoracotomy group was assessed for age, sex, arm span-corrected height, weight, and preoperative degree of curvature. Spinal curves were measured with the method of Cobb made on anteroposterior/lateral radiographs preoperatively, postoperatively, and again at 1-year follow-up in all patients [7].
Arm span was used for the calculation of corrected height, and this height was used to determine each patient's predicted lung volumes [15]. Percent of predicted values of lung volumes were derived from 95% confidence intervals and a nonsmoking reference population (ATS standards) [19].
Pulmonary lung volumes were performed on a PK Morgan transfer test (Kent, England) using a rolling-seal spirometer. Residual volume and functional residual capacity were measured with a helium dilution technique. Total lung capacity was calculated by addition of the residual volume to the vital capacity. Pulmonary functions were performed preoperatively and every 6 months postoperatively.
Statistical analysis was done using the SAS System from Microsoft Windows (Microsoft Corp, Redmond, WA). Repeated-measures analysis of variance was used to test the effects of age, sex, and operative approach relative to degree of correction and percent predicted lung volumes and flows over time. Linear regression analysis was used to evaluate the relationship between pulmonary volumes and degree of curvature of the spine. Pulmonary measures described as a percent change from baseline were analyzed using repeated-measures analysis of variance with a single within-subject factor (before/after operation) and one between-subject factor (operative approach). Alternatively, using nonparametric methods (Mann-Whitney) the changing condition after operation was analyzed. These two statistical methods gave qualitatively identical results. Group statistics are expressed as a mean ± the standard deviation. Statistical significance was considered to be a p value less than 0.05.
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Results |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentReferences |
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). All patients had anterior spine release followed in the same operative setting by instrumentation of the posterior spine. All operations were performed by the same two orthopedic surgeons, generally working together.
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).
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Preoperative patients in both groups demonstrated significant decreases in percent predicted vital capacity and total lung capacity and significant increases in residual volume (p < 0.05). The ratio of residual volume to total lung capacity was also significantly increased related to both increased residual volume and decreased total lung capacity (p < 0.05). No significant difference could be demonstrated between the preoperative video-assisted patients and the thoracotomy patients (Table 2).
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; Table 2
). No statistically significant difference was noted for any lung volume measure between the video-assisted group and the thoracotomy group except for postoperative residual volume/total lung capacity ratio (see Fig 2). The postoperative residual volume/total lung capacity ratio was 135.5 ± 16.2 in the video-assisted group and 147.7 ± 17.8 in the thoracotomy group (p = 0.03). This marginal difference becomes more significant when the most severely affected patients are analyzed separately (Fig 3). This severely affected group was defined as patients with a preoperative residual volume/total lung capacity ratio more than 120% of predicted. If a comparison is made between the two groups taking only patients with a preoperative residual volume/total lung capacity ratio greater than 120% of predicted, then the postoperative difference between the video-assisted group and the thoracotomy group becomes significant at p less than 0.01. We noted that in the severely affected patients approached endoscopically, the fraction of total lung capacity made up by residual volume declined from the preoperative residual volume/total lung capacity ratio. Those patients less severely affected with the preoperative residual volume/total lung capacity ratio less than 120% predicted demonstrated no significant difference between the two groups and had an increase in the ratio of residual volume to total lung capacity with operative correction.
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The presence of atelectasis (5%), intercostal neuralgia (0.5%), and chest tube output did not differ between the open and endoscopic groups. One episode of thoracic duct injury occurred in the thoracotomy group. Approximately 15% of the patients in each group required intensive care unit care postoperatively. The average length of hospital stay was 5.5 days in the thoracotomy group and 4.2 days in the endoscopic group.
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Comment |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentReferences |
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The effect of operative correction on pulmonary function has been controversial in the literature. Most agree early changes in lung capacity manifest as restrictive pulmonary disease [10–14]. In 1960, Cook and associates [13] evaluated the mechanics of respiration and muscle strength in scoliosis patients using the patients' actual height rather than corrected height. The study evaluated the relationship between total maximal inspiratory and maximal expiratory pressures and lung volumes. Residual volume/total lung capacity compared with the predicted normal value was increased by 17%. They concluded the pattern of pulmonary pressures and volumes represented a restrictive pulmonary disease. They found the function of the muscles of inspiration (diaphragm, thoracic musculature, spinal extensors) less effective than that of the muscles of expiration.
The balance of pressures across the respiratory system has been evaluated by others [11, 14, 16]. Airway pressure added to outward distending pressure of the chest wall must equal static lung recoil added to inward recoil of the chest wall. Cooper and colleagues [11] found reduced maximal inspiratory pressures in scoliosis and reasoned that at functional residual capacity the sum of lung recoil and inward recoil of the chest wall is zero, and that reduced maximal inspiratory pressures must reflect reductions in outward distending pressure of the chest wall. They concluded that scoliotic patients had defective mechanical coupling of the inspiratory muscles to the chest wall and not muscle weakness as expiratory force was normal.
In our study we demonstrated an increase in mean percent predicted residual volume in preoperative patients in both groups. The fraction of total lung capacity made up by residual volume increased in both the video-assisted and thoracotomy groups postoperatively, but to a greater extent in the thoracotomy group. The significance was marginal (p = 0.03) unless the most severely affected patients (residual volume/total lung capacity ratio preoperatively >120% of predicted) were considered separately. In the group of most severely affected patients, residual volume/total lung capacity ratio declined in the video-assisted patients. In the young, residual volume is governed by the balance between the maximal force generated by expiratory muscles and elastic forces opposing reduction of lung volume [17]. Factors affecting the elastic forces within the chest wall can result from small anatomic changes (obesity, pathologic skin conditions) or even from changes in posture [16]. The limited increase in residual volume in the endoscopic patients postoperatively may be indicative of an improved balance of forces in the chest wall that limit the extent of expiration.
In all other respects, pulmonary function was quite similar between the video-assisted group and the thoracotomy group, both before and after operation. This relates predominantly to the similar timing and degree of correction in the two groups and very little to operative approach. Any implication of improved pulmonary function with preservation of chest wall musculature must be viewed in light of the much larger issues related to the indications and timing of operation.
Preservation of pulmonary function has taken an increasingly minor role over the past decade as operative time has moved toward early correction in the progression of the deformity and preoperative pulmonary insufficiency is less apparent [11, 14, 18]. Patients have less preoperative pulmonary compromise at curves less than 50 degrees [12] than at curves greater than 50 degrees. A major goal of operation is to achieve optimal height. Therefore, skeletal maturity (not pulmonary function) carries great importance in the timing of operation as the vertebral end-plates are destroyed with diskectomy limiting future spine growth.
In our series, the morbidity of video-assisted operation has been minimal. Two of 38 patients demonstrated transient episodes of intercostal neuralgia in the early part of the series. Additional ports seem to ameliorate this problem. The incidence of atelectasis has been 5% in each group. There were no episodes of inadequate diskectomy, of spinal cord injury, of dural leak, or of trocar injury to adjacent structures. Idiopathic scoliosis patients have minimal blood loss postoperatively, and all chest tubes were removed within 48 hours in the endoscopic group. Five patients selected for endoscopic approach had their procedures converted to thoracotomy as a result of difficulty obtaining single-lung ventilation or difficulty with exposure endoscopically. All 5 patients were less than 30 kg and had curves greater than 60 degrees by Cobb angle. Their airways were small, and bronchial blockers were needed rather than the double-lumen endotracheal tube (Robert Shaw) or an endotracheal tube preloaded with a bronchial blocker (Univent). In addition, in those patients in whom single-lung ventilation was accomplished, the spine was very close to the chest wall, resulting in limited maneuverability with the video-assisted approach. With present instrumentation, those children who would benefit the greatest from a video-assisted approach present the most technical problems to its application.
It is clear that the operative times are longer, particularly early in the experience. The operative times remain longer, however, by approximately 5 minutes per disk space. The real issue related to operative time is the continued need for the presence of the thoracic surgeon throughout the procedure. This differs from the brief involvement during opening and closing with the thoracotomy technique.
The video-assisted patients left the hospital an average of 1.3 days earlier, and intensive care unit stays have been avoided in 85% of the endoscopic patients. The initial advantage with respect to avoiding intensive care unit stay in these patients was short-lived as thoracotomy patients are now admitted to the intermediate care unit 85% of the time.
In conclusion, the video-assisted anterior spine release represents an alternative approach for spine correction in idiopathic scoliosis and, when compared with a thoracotomy approach, achieves equivalent results. The preservation of chest wall musculature in severely affected patients appears to play a small role in limiting the deterioration postoperatively in pulmonary function.
Today, in the skeletally immature scoliotic patient, external bracing techniques are used to attempt to limit curve progression. In the future, the advent of anterior video-assisted stabilization techniques may permit internal bracing to limit curve progression. At this time, however, operative indications for idiopathic scoliosis remain unchanged by the video-assisted approach.
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Footnotes |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Address reprint requests to Dr Pollock, Division of Cardiothoracic Surgery, University of California, Davis, Medical Center, 4301 X St, #2250, Sacramento, CA 95817.
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References |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentReferences |
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