24 A Minimally Invasive Open Approach for Reconstruction of the Anterior Column of the Thoracic and Lumbar Spine

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24 A Minimally Invasive Open Approach for

Reconstruction of the Anterior Column of the Thoracic and Lumbar Spine

B. Knowles, I. Freedman, G. Malham, T. Kossmann

24.1 Terminology

Minimally invasive open anterior column reconstruction of the spine describes a surgical technique that blends elements from both endoscopic and conventional open spine surgery. With the aid of specially designed surgical instruments the procedure is performed under direct vision through a small incision using an endoscopic set-up (Fig. 24.1).

24.2 Surgical Principle

The aim of the procedure is to restore anatomical align- ment and integrity to unstable or destroyed segments of the anterior column of the thoracic and lumbar spine. An open minimally invasive surgical approach is used to minimise surgical trauma and to reduce perioperative and postoperative morbidity. The technique has been developed to combine attractive elements of both endoscopic and conventional open surgery. The procedure is based on the use of a table-fixed retractor system (SynFrame) and is performed with specially manufactured elongated surgical instruments that are operated from outside of the patient’s body (Fig. 24.2).

Fig. 24.1. Surgery is performed under direct vision through an open but minimally invasive approach

A thoracoscope mounted to the retractor frame is used to illuminate the operating field and is attached to a video camera for monitoring and teaching purposes.

Vertebral body reconstruction and augmentation with a variety of materials and spinal canal decompression is performed via an anterior (ventral) approach using a mini-thoracotomy or via a mini-retroperitoneal route.

In our experience this procedure is associated with reduced blood loss, shorter hospital stay and less perioperative morbidity than conventional open spine surgery [6, 14, 15]. In contrast to endoscopic spine surgery this procedure does not require special anaesthetic procedures such as double-lung intubation. With an experienced and skilled surgeon operating times are equivalent to those for open procedures [19, 21, 22].

24.3 History

Since the 1970s, the management of thoracolumbar fractures has evolved from conservative management to operative intervention with decompression, reconstruction and internal fixation of affected segments.

The spinal column is situated dorsally behind the visceral cavities of the thorax and abdomen. A posteri- or approach for decompression and transpedicular

Fig. 24.2. Operating set-up. The SynFrame is mounted onto the operating table and the retractors and thoracoscope are fixed onto the ring

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screw and rod stabilisation has been the standard of care for thoracolumbar fractures for some time [13].

However, 80 – 85 % of axial forces on the spine are transmitted via the anterior vertebral column [8].

Hence, reconstruction of the axial load-bearing anteri- or spine has been shown to impart a biomechanical and clinical advantage to fracture outcome [9]. How to achieve satisfactory anterior fusion has been a topic of great debate as conventional open spine surgery is associated with significant surgical trauma and complication rates [4, 5, 7, 9, 10, 11, 14, 15, 22].

The thoracic spine (T4 – 10) has traditionally been accessed via a posterolateral thoracotomy. This involves a large 25-cm incision and is associated with a significant incidence of acute postoperative pain [5], chronic intercostal neuralgia and post-thoracotomy pain syndromes [4]. Conventional open spine surgery is also associated with a high incidence of other complications, such as wound infections, empyema, aortic laceration, pneumothorax, haemothorax, chylothorax, brachial plexus injury, Horner’s syndrome and lung herniation [10, 11].

Similarly, open surgery in the form of a retroperitoneal thoracolumbophrenotomy has been the standard approach for fractures of the thoracolumbar region (T11-L3) [6]. This involves opening the thoracic cavity along a lower rib and incising the diaphragm to peel the peritoneal sac away from the lower thoracic spine down to the fourth lumbar vertebra. The operative approach is extensive and entails wide costophrenic de- tachment.

Capener described the first anterior approach to the lower lumbar spine in 1932 [3]. Unfortunately this open approach is also associated with profound morbidity [7, 19, 22].

As many of these complications were approach specific [7], less traumatic approaches for accessing the spine became desirable. Muscle-sparing thoracotomies have since been shown to reduce postoperative pain [9]. Since the early 1990s “minimally invasive techniques” that utilise endoscopic technology to reduce surgical soft tissue trauma have also emerged [20]. In 1993 video-assisted thoracoscopic surgery (VATS) techniques were applied to the treatment of thoracic spinal disorders. Similar endoscopic procedures were developed for the thoracolumbar junction and lumbar spine [12, 16, 17]. Endoscopic procedures have since demonstrated a significant reduction in postoperative pain, blood loss, recovery time and improved postoperative respiratory function. However, pure endoscopic thoracic and lumbar spine approaches have required invasive double-lumen tube intubation, increased anaesthetic monitoring and longer operative times. More significantly, complications are more difficult to manage and surgeons experience long “learning curves”

before they feel familiar with the procedure.

In an effort to rectify the disadvantages of closed endoscopic approaches surgeons have begun to blend minimally invasive techniques with a limited open approach. Mayer pioneered the use of mini-thoracotomy and mini-retroperitoneal open approaches to access the thoracic, thoracolumbar and lumbar spine for the treatment of degenerative disorders [19, 21]. This chap- ter outlines our development of the treatment of fractures of the thoracic and lumbar spine by a minimally invasive open technique and gives an overview of our experience [14, 15].

24.4 Advantages

No extensive preoperative anaesthetic work up, e.g. double-lung intubation, required.

Small surgical incision, i.e. mini-intercostal and flank surgical approaches.

Direct three-dimensional intraoperative view of spine using a stable easily adjusted retractor.

Excellent direct illumination of the operative field by a thoracoscope.

Direct view of the anterior spine allows safer mobilisation of blood vessels and nerves.

Faster decompression of spinal canal.

Easier reconstruction of the anterior spine column.

Reduced blood loss and transfusion requirements.

Reduced wound pain.

Lower complication rates.

Accelerated rehabilitation.

Suitable for a range of pathology including traumatic fractures, pseudoarthroses and reconstruction of vertebrae destroyed by malignancy.

24.5 Disadvantages

A “learning curve” is necessary but with experience operating times are equal.

It is more difficult to manage intraoperative complications than with conventional open approaches but easier than with closed endoscopic surgery.

Initial financial investment in mandatory equip- ment is required.

24.6 Indications

The anatomical location determines whether the minimally invasive procedure is performed via a right-sided mini-thoracotomy (T4-8; Fig. 24.3b), left-sided mini- thoracotomy (T9-L2; Fig. 24.3a), left-sided mini-retro-

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a b Fig. 24.3. Male patients fol-

lowing left-sided (a) and right-sided (b) mini-thora- cotomies for fractures of the 11th and 7th thoracic vertebrae, respectively

peritoneal approach (L3-4) or minimally invasive retroperitoneal access (L4-S1). Depending on the fracture type the overall management may include a preceding posterior stabilisation with or without decompression.

The indications for a minimally invasive open approach to the anterior column of thoracic and lumbar spine fractures are as follows:

T4-L5 unstable spine injuries as per Magerl classification [18]

Neurological deficit

Sagittal angulation of greater than 25°

Axial compression of greater than 50 % of vertebral height

Multiple fractures

24.7 Contraindications

Apart from contraindications to general anaesthesia there are no absolute contraindications for this approach. Individual consideration should, however, be made in patients with:

Pleural empyema

Previous thoracic/retroperitoneal surgery on the same side as access

Severe coagulopathy Osteoporosis

24.8 Patient’s Informed Consent

The patient is explained the aim and benefits of surgery and the expected postoperative course. The following approach-specific risks are outlined:

Injury to spinal cord, spinal nerves, sympathetic plexus

Lung contusion and/or pleural effusion necessitating an intercostal catheter for 24 – 48 h postoperatively Blood loss and possible transfusion-related risks Injury to thoracic or abdominal viscera including heart, spleen, kidney, ureter and bowel

Postoperative pain Diaphragmatic herniation

Postoperative deep venous thrombosis, pulmonary embolus and need for prophylactic treatment Superficial and deep wound infections Pneumonia

Pseudoarthrosis

Implant loosening/failure

24.9 Surgical Technique

24.9.1

Preoperative Planning

Comprehensive imaging of the spine, spinal cord and cauda equina enables the surgeon to anticipate the pathology at surgery. Plain films in anteroposterior and

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a b

c

Fig. 24.4. a Preoperative MRI in a 46-year-old female patient with metastatic renal carcinoma, demonstrating extensive ver- tebral body destruction. b Postoperative plain X-rays in this woman demonstrate vertebral reconstruction with a Synex cage. c Incision for the minimally invasive resection and recon- struction for metastatic renal carcinoma

lateral positions are followed by computed tomography (CT) scanning in multiple planes, which is particularly useful for imaging bony structures. Magnetic reso- nance imaging (MRI) is useful in patients with neurological symptoms, in those unable to cooperate with clinical assessment and in patients with spinal canal compromise on CT scan (Fig. 24.4a).

The patient is positioned on the left (for upper thoracic intervention) or on the right side (for the thoracolumbar junction and lumbar spine), with the surgeon standing at the patient’s back. The site for the surgical incision is selected according to the level of the affected vertebra [15].

24.9.2

Upper Thoracic Spine (T4-8) and the Thoracolumbar Junction (T9-L2)

Anterior reconstruction of the upper thoracic spine (T4-8) is performed via a right-sided mini-thoracotomy (Figs. 24.3b, 24.4c). The thoracolumbar junction

(T9-L2) is accessed via a left-sided mini-thoracotomy, which allows a retroperitoneal approach down to the level of the second lumbar vertebra via a minimal incision in the diaphragm (Fig. 24.3a). For these different access levels (as well as for the lumbar spine and lumbosacral junction) one assistant on the opposite side to that of the primary surgeon is required. A highly trained scrub nurse may be capable of fulfilling this role. No intensive anaesthetic intervention such as double-lung intubation is needed. Induction prophylactic antibiotics and dexamethasone are administered rou- tinely. In patients with neurological injury we give methylprednisolone as per the NASCI III protocol [1].

Controlled hypotension is maintained at a MAP of 75 – 80 mm Hg. The cellsaver is utilised.

Once the patient is correctly positioned the affected vertebra is localised with an image intensifier. A 6- to 8- cm incision (independent of location) is then made and underlying muscles are dissected bluntly. After opening the thoracic cavity the lung is identified and is then briefly disconnected from the ventilator so that it can be gently pushed aside to allow space for the surgery.

The lung is protected with a moist surgical towel and ventilation to the lung is recommenced. The retractors are placed onto the table-fixed SynFrame (Stratec Med- ical, Switzerland) and adjusted according to the surgeon’s requirements. The SynFrame is a stable, adjustable ring system fixed sterile by two adjustable arms onto the operating table (Fig. 24.2). The permanent sta-

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bility of the operating field is a major advance and allows the surgeon to operate without further manipula- tions of the surgical field. A thoracoscope is inserted via a separate incision with an 11.5-mm-diameter tro- car. This incision is later used for insertion of an intercostal catheter that remains in place for 24 – 48 h postoperatively. An endoscope is secured onto the frame to illuminate the operating field and is adjusted directly by the surgeon. As only the surgeon has a direct view of the operating field the endoscope is attached to a video screen so that nurses, assistants and trainees can ob- serve the procedure. The vertebral reconstruction procedure can then commence.

24.9.3

Lumbar Spine (L3-4)

The lower lumbar spine (L3/4) is accessed via a left-sided minimally invasive pure lumbotomy. The affected vertebra is identified with the image intensifier and its projection is marked laterally on the flank. A 6- to 8-cm skin incision is then made and is followed by dissection of the three layers of the abdominal wall along their fibres until the retroperitoneal space is reached after penetrating the transversus abdominis fascia and muscle. The peritoneal sac is dissected off the fascia bluntly by a finger or a wet sponge mounted on a stick until the psoas muscle is reached. This potential space is kept open using retractors mounted on the SynFrame ring.

Care should be taken not to damage the ureter, which can be gently pushed aside together with the peritoneum. The psoas muscle is mobilised in part to enable the surgeon to reach the lumbar vertebral bodies. Tilting of the table towards the surgeon can facilitate this. Muscu- lar patients may require splitting of the psoas muscle along its fibres to reach the lateral aspect of the vertebral bodies. Attention must be paid to the lumbar plexus embedded deep within the psoas muscle and the ili- ohypogastric and ilioinguinal nerves crossing the surgical field.

24.9.4

Lumbosacral Junction (L5-S1)

The lumbosacral junction is accessed via a prone minimally invasive transperitoneal route. The abdomen is opened in the midline below the navel. The table is then tilted head down (Trendelenburg position) to allow the intestines to be pushed upwards. The peritoneum is in- cised on the left side of the aorta. It is advisable to iso- late and secure the aorta and both iliac arteries. Access to the lumbosacral junction is then accomplished from the left side behind the anterior longitudinal ligament.

24.9.5

Reconstruction of the Anterior Column

After exposing the spine laterally, the level of the affected vertebra is identified with the image intensifier and the adjacent disc spaces are marked with K-wires. The location of the anterior longitudinal ligament and spinal canal can be calculated from the position of the K-wires. In most cases the overlying segmental vessels of the affected vertebra need to be clipped. The sympathetic chain is identified and where possible preserved. The abdominal aorta lies in front of the affected vertebra and directly anterior to the anterior longitudinal ligament. The ligament is not resected and serves as a safety marker for protect- ing the aorta and inferior vena cava on the lower aspect of the operating field. The vertebral discs are cut with a specially designed long-handled knife. After their removal the corresponding vertebral end plate is cleaned with specialised curettes (Synthes Spine USA). Care is taken not to penetrate the end plates. The vertebral body is then removed in part or completely using long osteoto- mes and rongeurs (Synthes Spine USA) and again special care is taken to preserve the anterior longitudinal ligament. For reconstruction of the void space, various materials such as autologous iliac crest bone grafts, allografts and cages (Synex; Stratec Medical Switzerland) filled with bone from the corporectomy have been used. Addi- tional iliac crest harvesting or acrylic cement is occasion- ally used to fill the cage. In the last 3 years we have mainly utilised cages as they avoid problems of donor site morbidity (with autologous iliac crest bone graft harvest) and other autoimmune obstacles (with allografts).

24.10 Postoperative Care and Complications

The typical postoperative course for a patient is:

Immediate extubation after operation.

Low molecular weight heparin thromboembolic prophylaxis.

Chest tube removed after 24 – 48 h.

Mobilisation and physiotherapy to commence on the first postoperative day. Once the chest tube is removed the patient can commence rehabilitation.

Anteroposterior and lateral X-rays of the operative site on the first postoperative day.

CT assessment prior to the patient leaving hospital to check the exact location of the cage and for quality control purposes.

Return to work after 6 – 12 weeks.

Potential complications of the procedure itself include:

Poor patient positioning resulting in difficult access, longer operating time and potential inaccessibility.

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Segmental vascular injury causing bleeding which compromises the visual field.

Damage to major thoracic or abdominal vessels may necessitate conversion to conventional thoracotomy and/or laparotomy.

Injury to heart, lungs or abdominal viscera.

Dural tear.

Peritoneal tear.

Displacement of bone or disc into spinal canal during corporectomy and/or grafting.

Suboptimal fracture reduction.

Other potential postoperative complications are:

Haemothorax or pneumothorax requiring thoracotomy.

Infection of wound, body cavities or prosthesis that may require debridement and removal of implant.

Implant failure or displacement.

Ileus.

Recurrent pleural effusions.

24.11 Results

We initially reported a series of 65 consecutive patients (28 women, 37 men) who were treated with minimally invasive open surgery to the anterior column between July 1999 and July 2000 [15]. Subsequently, by early 2004 we have gained additional experience with more than 200 minimally invasive operations on the thoracic and lumbar spine using minimally invasive open approaches. In 4 patients in our first series [15] surgery was performed for treatment of a pseudoarthrosis following previous intervention and in 6 patients for metastatic destruction of a single vertebra in the thoracic or lumbar spine (Fig. 24.4a). The remaining 55 patients had traumatic injuries. Of these, 30 patients had isolated spine injuries whereas 25 patients had additional (sometimes multiple) injuries to the head (n = 10), thorax (n = 9), pelvis (n = 4) and extremities (n = 12).

Traumatic injuries to the spine were categorised according to Magerl’s classification [18]. Thirty-four patients had type A, 14 had type B and 7 had type C fractures.

There were 9 fractures of the thoracic spine (T4-10), 35 fractures involving the thoracolumbar junction (T11-L1) and 11 fractures of the lumbar spine (L2-4).

Out of the 65 patients, 29 received stabilisation with a posterior Universal Spine System (USS; Synthes, Swit- zerland) prior to the anterior spine surgery. In 8 patients a right-sided mini-thoracotomy was performed to access the midthoracic spine (T4-8), a left-sided mini-thoracotomy to reach the thoracolumbar junction (T9-L2) was used in 50 patients and a mini-retroperitoneal approach was used in 7 patients for lumbar spine intervention. Spinal clearance was performed in 11 pa-

tients via anterior mini-thoracotomy or retroperitoneal approaches. Autologous iliac crest bone was harvested in 11 patients, autologous spongiosa in 12 patients, fe- mur allografts in 2 patients and iliac crest allografts in 2 patients. Expandable (Synex) cages were used for vertebral reconstruction in 38 patients. The cages were filled with spongiosa from the corporectomy and in 7 patients additional autologous spongiosa was harvested from the iliac crest.

The operating time (OT) from incision to closure was recorded. It must be emphasised that this time included the learning period of using this technique. The mean OT was 170 min (range 90 – 295 min) but this varied depending on the magnitude of the intervention. For a left-sided mini-thoracotomy (n = 42), the mean OT was 141 min. Addition of spinal clearance and iliac bone grafting saw the mean OT increase to 167 min. A right- sided mini-thoracotomy (n = 7) averaged 152 min. An additional 60 min were needed in cases that required spinal clearance and another 20 min were require for iliac crest bone graft harvesting. The mean OT was 165 min for the mini-retroperitoneal approach (n = 10) and 194 min when spinal clearance and iliac crest bone harvesting were required. With increased experienced our operating time has improved to approximately 120 – 140 min.

No patients required conversion to an open procedure and no complications related to the minimal access technique and neither visceral nor vascular injuries were observed. One patient with multiple metasta- ses died intraoperatively due to an acute thromboembolic event. Four cases of mild postoperative ileus that settled with conservative management were noted. No patients developed intercostal neuralgia or post-thoracotomy pain syndromes. Most patients reported mild pain at the site of intervention but in all cases this re- solved completely after several days. No postoperative wound infections or deep venous thrombosis were recorded. Patients with isolated spinal pathology were discharged from hospital after an average of 13 days (range 2 – 30 days). Patients with additional injuries stayed in hospital for an average of 20 days (range 2 – 86 days). The mean blood loss was 912 ml. The sub- group requiring spinal clearance (n = 11) had a greater mean blood loss of 1,716 ml (range 300 – 5,000 ml). This is less than in conventional open procedures and similar to endoscopic-based reconstructions of the anterior column [2]. Only 7 of the 65 patients required blood transfusions.

24.12 Critical Evaluations

Minimally invasive but open surgery for repair of the anterior thoracic and lumbar spine column has only re-

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cently been described and as such there are few pub- lished reports of the technique. Nevertheless, our pub- lished series of 65 prospectively collected minimally invasive open procedures demonstrated a marked reduction in postoperative pain and a faster return to function for the patient compared to historical controls [15]. The minimally invasive techniques avoided the access-related morbidity associated with conventional open approaches in that postoperative pain, bleeding and surgical trauma were greatly reduced. There is also less inadvertent intraoperative organ injuries than has been reported with endoscopic approaches [12, 16].

This is largely due to the fact that the open, minimally invasive procedure enables the surgeon to directly visu- alise the operative field in three dimensions. This direct visualisation helps with vessel and nerve preparation, in performing a corporectomy and with spinal clearance. This view of the surgical field and the physical verification of events facilitated by open surgery is more familiar to surgeons not experienced with the magnified two-dimensional images in pure endoscopic procedures. The learning curve with the procedure is consequently rapid, and potentially serious complications and extended operation times are more easily avoided. Subsequently, we have performed more than 200 minimally invasive but open approaches for reconstruction of the anterior column of the thoracic and lumbar spine. The described approaches offer distinct advantages as compared to “pure” endoscopic or conventional open spine surgery and have become the standard method for anterior reconstruction of the thoracic and lumbar spine at our institution.

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