Introduction

Conservative treatment and isolated posterior operative stabilization of thoracolumbar fractures showed disappointing results [₃,₄]. The study of larger populations concludes in the request to reconstruct the anterior column for better long time results of the kyphotic angle after trauma [₄]. However, improved reconstruction results were associated with significant morbidity using open anterior approaches. Minimal invasive techniques were able to lower this morbidity making the anterior approach more common in spine trauma surgery [₂,₇].

Computer assisted orthopaedic surgery (CAOS) is reported to reduce the misplacement rate of conventionally inserted lumbar pedicle screws in standardized posterior approaches [₅,₆]. There are only few reports concerning CAOS in the anterior approach to the thoracolumbar spine. The authors present a standardized protocol using CT/fluoro matched navigation which is routinely used for the anterior approach to the thoracolumbar spine.

Methods

Anterior approach to the thoracolumbar spine

The patient is placed in prone position on the operating table. Endoscopic equipment and the navigation system are positioned at the foot end, the operating team on the left side of the patient. The image intensifier comes from opposite of the operating team and can be removed after CT/fluoro matching has been done [Fig.1].

Figure 1

Figure 1: Patient in prone position, endoscopic equipment and navigation system at the patients foot end.

Thereby some parts of the operation (e.g. harvesting of the bone graft from the iliac crest) may be performed simultaneously from the right side of the patient. A lateral incision of 5cm is enough to allow the transthoracic access to the spine from T4 to L2. A retractor system (Synframe®, Synthes) allows efficient exposure of the situs [Fig.2].

Figure 2

Figure 2: Retractor system for the lateral incision, insertion of the endoscope.

Additional incisions of 1 cm laterally and of 2 cm posteriorly enable the insertion of the endoscope and the navigation system, respectively.

Principles for the reconstruction of the anterior column

Navigation system

The VectorVision® spine system (BrainLAB) enables navigation in CT images, fluoro images, or a combination of both image modalities simultaneously. The fluoro to CT registration allows to minimal invasively establish a 3D-reference to the CT data set using fluoroscopic images [Fig.3].

Figure 3

Figure 3a: Reference array fixed on the spinous process and fluoroscope with fluoro registration device.

Figure 4

Figure 3b: Ap and lateral fluoroscopic image are acquired.

Instrument adaptor clamps allow the integration of any required spinal instrument. The standardized CT/fluoro matched navigation requires a reference array which is fixed on the spinous process of the instrumented vertebra. The fluoro registration device is slided onto the image intensifier. Two (ap and lateral) intra-operatively acquired fluoroscopic images of the region of interest are taken. Based on a tungsten marker grid integrated into the fluoro registration device, the registration software of the VectorVision® system calcalutes all necessary projection parameters [Fig.4]. The touchscreen allows the surgeon to completely control the image guided system during the operation [Fig.5].

Figure 5

Figure 4a: Definition of level of segmentation.

Figure 6

Figure 4b: Fusion of pre-op CT-images with intra-op fluoro-images.

Figure 7

Figure 5: Touchscreen enables to survey and control the operation real-time.

Results

47 thoracolumbar fractures that have been operated on using isolated anterior approach were recorded prospectively between January 2002 and September 2004. In all cases retractor system, endoscopical assistance and computer navigation were used. 29 male and 18 female patients with a mean age of 39 (21-69) years were included in the study. 32 computer navigations were completed. 14/ 15 uncompleted procedures were observed in the first 12 months, thereafter all but one operation was completed under navigation control. The learning curve also showed longer anesthesia times during the first year. In 2004, OP- and anesthesia- times were reduced. However, no significant difference was calculated. Fluoroscope times were reduced significantly in the group of complete navigation compared to conventional technique (p<0.05).

Discussion

Computer assisted orthopaedic surgery (CAOS) is reported to add precision and accuracy to posterior procedures in spine surgery [₅,₆]. It should be able to do so in anterior approaches. However, there is no significant literature focusing on this particular chapter of CAOS. The authors have been using an image guided navigation system (VectorVision®, BrainLAB) in 47 patients when operating on thoracolumbar spine fractures via isolated anterior approach. A learning curve has been observed with 15 navigation procedures – most of them during the first year – not being completed. However, the standardized CT/fluoro matched protocol was useful for the minimally invasive operation technique and allowed to reduce significantly the x-ray times without loss of precision. This effect has been most effectfully observed during the last third of the study period and was not significant. But it shows that navigation is not mandatory affected with longer operation times compared to conventional techniques.

The combination of minimally invasive approaches to the anterior column of the spine with standardized navigation procedures may be able to reduce morbidity, operation times and x-ray exposition.

Correspondence to

Oliver Gonschorek M.D. Clinic for Trauma, Reconstructive and Plastic Surgery University of Leipzig Liebigstr. 20 D-04103 Leipzig Germany Tel. 0341-9717305 Fax. 0341-9717399 e-mail oliver.gonschorek@medizin.uni-leipzig.de