43 Mini-open Midline Accesses for Lumbar Total
Disc Replacement
H.M. Mayer
43.1
Terminology
Mini-open retroperitoneal approaches are described for total disc replacement in the lumbar spine. The ap- proaches are performed through small skin incisions (4 – 5 cm) exposing the anterior circumference of the levels L2-S1 through a retroperitoneal route.
43.2
Surgical Principle
Total lumbar disc replacement requires the anterior ex- posure of the disc circumference to an extent of at least 2 cm each side of the midline. Through small trans- verse or longitudinal skin incisions, a mini-laparotomy can be performed. According to the topographical anatomy of the abdomen, the retroperitoneal blood vessels, and the weight and stature of the patient, indi- vidualized surgical approaches to the anterior circum- ferences of the levels L2-3-4-5-S1 are possible. The level L5/S1 can be approached through a left or right retro- peritoneal approach as well as through a midline trans- peritoneal approach. For the levels L2/3, L3/4, and L4/5 either a retroperitoneal approach from the left side or transperitoneal approaches are feasible.
43.3 History
Total disc replacement has become an option for the treatment of degenerative disc disease of the lumbar spine. A new implant generation has been developed which can be implanted through minimally invasive anterior approaches to the lumbar levels L2/3, L3/4, L4/
5, and L5/S1. The standard mini-open approaches de- scribed for anterior lumbar interbody fusion (see Chapters 45 – 48) have been modified to meet the re- quirements for lumbar disc replacement [1, 5].
43.4 Advantages
Decreased iatrogenic access trauma Low perioperative morbidity Small skin incisions
Low blood loss (> 150 cc)
Low perioperative complication rate Decreased vascular complication rates Short operating times
Good clinical results
43.5
Disadvantages
Learning curve
Limited manipulation of vascular structures (preoperative planning necessary)
Potential risk of indirect trauma to structures surrounding the target area
Previous abdominal operation might influence the strategy
43.6 Indications
The surgical approaches are indicated for all types of disc replacement [6]. There is currently no internation- al consensus about the indications for disc replace- ment. Disc replacement has, however, been described for the following pathologies with accompanying dis- cogenic low back pain:
Degenerative disc disease (DDD) with/without disc herniation
Post-discectomy segments
Degenerative discs adjacent to a previous fusion DDD with retrolisthesis
DDD with Modic type I changes DDD with frontal plane deformities
DDD in combination with other pathologies in adjacent segments requiring lumbar fusion
vascular situations, an open conventional anterior ap- proach may be advisable. The same is true for patients with severe intra-abdominal scarring following previ- ous abdominal operations.
43.8
Patient’s Informed Consent
Besides information about the general complications of spine surgery, the patient should be informed about the following potential risks:
Denervation of the rectus muscle due to dissection of iliocostal nerves
Abdominal hernias
Vascular injury in the retroperitoneal space (ascending lumbar vein, common iliac veins and arteries, segmental veins and arteries) with retro- peritoneal hematoma and necessity of intervention of a vascular surgeon
Deep venous thrombosis and arterial thrombosis or injury due to extended retractor blade pressure Injury of peritoneum, bowel, ureter, kidney Extensive epidural bleeding or bleeding from the subchondral vertebral bone
Anterior dural tears with CSF fistula
Lesion to superior hypogastric plexus which can result in postoperative retrograde ejaculation in men or disturbances of lubrication and vaginal dysesthesia in women
Table 43.1. Contraindications for total disc replacement
General Specific
Osteopathies:
Osteoporosis Osteopenia
Inflammatory disorders:
e.g., Ankylosing spondylitis Deformities:
Kyphosis (including juvenile) (Degenerative) lumbar scoliosis Fractures
Tumors Spondylitis Psychosocial factors
Disc herniation:
With predominant radicular symptoms Posterior element pathology:
Facet joint osteoarthritis (°II–V) Post-laminectomy
Translational instability:
Anterolisthesis
Central, lateral spinal canal stenosis Severe endplate irregularities Failed Back Surgery syndrome Post-abdominal operations (?)
cluding flexion-extension views are standard. They give information about the curvature, disc space height as well as about the anterior bony circumference of the disc space to be approached (Fig. 43.1).
The preoperative planning should also include MRI investigation of the lumbar spine to show the target pa- thology, the surrounding structures in the spinal canal, the degree of disc degeneration as well as the Modic type of degenerative changes in the adjacent vertebral bodies (Fig. 43.2).
The knowledge of the vascular topography of the retroperitoneal blood vessels allows the planning of in- dividualized approaches. We thus routinely include three-dimensional CT angiography to evaluate the size, shape, and the topography of the retroperitoneal blood vessels (Fig. 43.3a, b). Venous and arterial bifurcation can be clearly visualized. The topographical relation- ship between the arterial and venous branches and the underlying lumbar spine can be shown. With these pre- operative data, surgical planning can be performed in detail. The knowledge of the individual vascular situa- tion of the patient influences the surgical technique and, in rare cases, might lead to a contraindication for disc replacement (e.g., venous bifurcation completely covering the anterior circumference of the target disc space). It also helps to decide whether the help or the availability of a vascular surgeon is necessary during the operation to avoid medicolegal problems in case of complications. All other preoperative planning criteria correspond to the ones which are described for mini-
a b
Fig. 43.1. Plain X-rays of the lumbar spine. a AP view showing a horizontal tilt at L3/4 with lateral osteophyte formation. b Lateral view showing anterior osteophytes at L5/S1 and collapsed disc space
mally invasive anterior interbody fusion (Mini-ALIF;
see Chapters 45, 46).
43.9.2
Patient Positioning
All implantations can be performed through a midline mini-laparotomy. The patients are placed in a neutral da Vinci position (Fig. 43.4a, b). The position should be neutral, and hyperextension of the lumbar spine should be avoided. A surgical table which allows intraoperati- ve tilting of the legs is recommended (Fig. 43.5). Thus, the orientation of the disc space can be adjusted to ease the implantation of the disc prosthesis.
43.9.3 Localization
The target level is localized under AP and lateral fluoro- scopic control and marked on the skin. In obese pa- tients, it can be marked as described in Chapter 46. In
Fig. 43.2. MRI of the lumbar spine. Note the degenerated discs at L4/5 and L5/S1 with Modic type I changes in the subchond- ral bone at L5/S1 indicating an active degenerative process
a
b
Fig. 43.3. Three-dimensional color-coded CT angiography of the retroperitoneal lumbar blood vessels. a Arterial phase.
b Venous and arterial phase
a
b Fig. 43.4. a Positioning of the patient on the operat-
ing table with arms and legs abducted (da Vinci positioning). b Note alternative position of the pa- tient’s arms
a Fig. 43.5. a Neutral supine
positioning of the patient, lateral view. b Position of the surgeon after sterile draping of the patient
b
slim patients, the abdominal wall is slightly indented with a metal marker to show the position of the marker in the skin surface in relation to the anterior border of the target disc space (Fig. 43.6a, b).
All implantations are performed through small 4- to 5-cm transverse skin incisions. Because of anatomical and topographical details, each level has very specific technical demands.
a b
Fig. 43.6. a Indentation of the abdominal wall with a metal marker under lateral fluoroscopic control. b Metal marker and anterior entrance of the disc space at L5/S1 are visible. The skin incision is placed above the disc space at the position of the metal marker
Fig. 43.7. Possible skin incisions for the anterior approach to L5/S1. Black line Retro- and transperitoneal in slim patients.
Red lines Retroperitoneal left or right in obese patients
43.9.4 L5/S1
The first choice of access to the L5/S1 disc is retroperi- toneal from the right side. The right side is chosen to decrease the risk of injury to the superior hypogastric plexus (see Chapter 45) in men and women and to leave the left side untouched for a potential future approach to the level L4/5 (e.g., in adjacent level degeneration re- quiring an anterior approach). The second choice is retroperitoneal from the left side. This approach is al- ternatively chosen in cases with previous abdominal surgery in the lower right quadrant (e.g., appendecto- my, gynecological operations, operation for abdominal hernia). The third choice is transperitoneal which we prefer in extremely obese patients.
The skin incision is either placed in the midline in slim patients or slightly asymmetric to the approach side in obese patients or in patients with a very broad stature (Fig. 43.7). This is the easiest segment to ap- proach. After exposure of the rectus fascial sheet, the li- nea alba is split in the midline, and the peritoneum is exposed (Fig. 43.8)
43.9.4.1
Retroperitoneal Access from the Right Side
This approach should be the first choice. The peritone- um is bluntly detached from the inner abdominal wall on the right side. The transverse fascia has to be incised to mobilize the abdominal contents adequately. The psoas muscle as well as the common iliac artery with the ureter are identified. Preparation is continued to-
Fig. 43.8. Splitting of the linea alba in the midline to expose the peritoneum
ward the midline between the ureter (displaced medial- ly) and the artery. Medial to the common iliac artery, the lateral circumference of L5/S1 can be exposed. In this ar- ea, the superior hypogastric plexus is very thin with rare and small branches, which decreases the risk of damag- ing this plexus. Blunt dissection of the prevertebral fat tissue including the plexus exposes the medial sacral ar- tery and vein, which can then be clipped or coagulated and dissected. Thus L5/S1 can be exposed easily. The left common iliac vein can be retracted carefully to the left.
This is the safest and easiest approach to L5/S1.
43.9.4.2
Retroperitoneal Access from the Left Side
The dissection process is the same as on the right side.
Dissection is performed across the common iliac vein to the disc space L5/S1. This can be difficult especially if the vein has a large diameter and covers part of the disc space. The superior hypogastric plexus has to be pushed medially with care avoiding any coagulation.
These two factors make this approach the “second- choice approach”; however, exposure of L5/S1 can be achieved as properly as from the right side.
43.9.4.3
Transperitoneal Access
In very obese patients, in patients who have had con- ventional abdominal surgery, and in revision cases the transperitoneal minimally invasive approach is the ad- equate technique. It is the most direct way to L5/S1 and can be performed easily even in obese and previously operated patients.
In all instances, the medial sacral vessels have to be coagulated/ligated and dissected away from the anteri- or circumference of the disc space.
43.9.5 L4/5
The anterior access to L4/5 is from the right side.
43.9.5.1
Retroperitoneal Approach
A retroperitoneal approach is the first choice. This is the most difficult level to access because of the vascular anatomy. The disc space is, in most cases covered by vascular structures. Vascular anatomy thus determines the approach to L4/5. Due to the venous anatomy, the retroperitoneal approach from the left side has been preferred in conventional anterior approaches. Howev- er, vascular mobilization across the midline has its lim- itations using a minimally invasive approach. Mobili- zation of the abdominal contents is more difficult through a 4- to 5-cm skin incision. The same is true for preparation and retraction of the blood vessels. Since vascular injury or arterial occlusion can result in a life- threatening complication, all efforts should be directed to avoid such a type of complication. An individualized access which considers the individual vascular topog- raphy is recommended to access the L4/5 disc space.
Preoperative three-dimensional CT angiography deter- mines the individual mobilization of the blood vessels.
Intraoperative monitoring includes the continuous measurement of oxygen saturation in the left big toe to avoid prolonged ischemia of the leg due to retractor pressure on the arteries (Fig. 43.9).
After localization of the level, the skin incision it is placed slightly paramedian to the left side (Fig. 43.10).
The rectus fascia is exposed from the linea alba to its lateral border. It is then incised transversely to allow mobilization of the rectus muscle (Fig. 43.11).
The muscle belly is then mobilized medially to ex- pose the posterior rectus sheath and the linea arcuata (Fig. 43.12). The posterior rectus sheath is incised lon- gitudinally and the peritoneum is exposed. Care has to be taken not to open the peritoneum. The retroperito- neal space is entered lateral to the rectus muscle to fa- cilitate vascular preparation and dissection in the lower left quadrant with only low retraction pressure on the rectus muscle. The peritoneum is mobilized from the lateral abdominal wall and the psoas muscle is identi- fied. Medial to the psoas muscle, the common iliac vein and artery are exposed. The ureter is dissected from the common iliac artery and mobilized medially together with the peritoneum. The lateral border of the disc space L4/5 is then identified. The next surgical target is the lateral border of the common iliac vein and the en-
Fig. 43.9. Measurement of oxygen saturation in the left big toe
Fig. 43.10. Skin incision for the anterior approach to L4/5
try of the iliolumbar and ascending lumbar venous branches. It is essential to first identify these venous branches. They have to be occluded with sutures or vas- cular clips and dissected. This surgical step is para- mount since in the majority of the cases, the common iliac vein cannot be mobilized without the risk of a tear injury to the iliolumbar and ascending lumbar branches. The mobilization of the common iliac artery is simple, since there are no exiting branches in this re- gion. Once this step is completed, the retroperitoneal
Fig. 43.11. Transverse incision of the anterior rectus sheath
Fig. 43.12. Mobilization of rectus muscle belly medially and ex- posure of the posterior rectus sheath and the linea arcuata
space lateral to the rectus muscle is left and is entered again medial to the muscle belly (Fig. 43.13).
Further mobilization of the vascular structures should follow the individual vascular anatomy. Al- though, three-dimensional CT angiography shows a great variety of vascular situations in front of the L4/5 disc space, there are three variations of vascular mobi- lization which are recommended.
Fig. 43.13. After the peritoneum is mobilized lateral to the rec- tus (1), the retroperitoneal space is entered again medial to the rectus muscle (2) and exposure of the anterior circumference of the disc space is completed through a midline approach be- tween the rectus muscle bellies (3)
Fig. 43.14. Three-dimensional CT angiography. Note, arterial bifurcation is well above the disc space L4/5. Venous bifurca- tion is above the superior rim of the disc space (white arrow).
Exposure of the disc space from caudal between arterial and venous bifurcation (yellow arrow)
43.9.5.1.1 Variation1
If venous and arterial bifurcations are located cranial to the superior border of the L4/5 disc space, the access can be between the bifurcations (Fig. 43.14). In this sit- uation, mobilization and dissection of the ascending lumbar veins is not necessary. The median sacral ves- sel, however, should be ligated and dissected. This is a rare situation at the level L4/5.
Fig. 43.15. Three-dimensional CT angiography. Arterial bifur- cation at the level of disc space L4/5, venous bifurcation below.
Mobilization of arteries and veins across the midline
43.9.5.1.2 Variation2
If the arterial bifurcation is located on the level of the disc space, it should be mobilized together with the ve- nous structures across the midline (Fig. 43.15). Howev- er, it is recommended to carefully monitor the oxygen saturation in the left big toe and, if necessary, to relieve the pressure of the retractor blades on the artery every 30 – 40 minutes. With this type of mobilization, ligature of the left segmental artery and vein L4 is mandatory.
43.9.5.1.3 Variation3
If the arterial bifurcation alone is well above the disc space L4/5, a dissection between the arteries is recom- mended (Fig. 43.16). Only the common iliac vein or the inferior cava vein is mobilized across the midline, whereas the common iliac arteries are slightly pushed to both sides of the disc space. Ligature of the segmen- tal vein L4 on the left side is necessary.
Fig. 43.16. Three-dimensional CT angiography. Arterial bifur- cation well above L4/5, venous bifurcation below. Exposure of the disc space is between the common iliac arteries to avoid ex- tensive pressure on the left common iliac artery. Common iliac vein and vena cava mobilized to the right side
43.9.5.2
Transperitoneal Approach
A direct, transperitoneal approach would be the sec- ond-choice approach. The superior hypogastric plexus and the perivascular tissues have to be dissected care- fully. The mobilization of the blood vessels will be the same as described above.
43.9.6 L2/3/4
The approach to L3/4 and L2/3 needs modifications of the skin-to-spine route. The skin incision is usually at the level of or above the umbilicus (Fig. 43.17). If it is at the umbilical level, a small, longitudinal paramedian incision on the left side is preferred. Retroperitoneal exposure is much more difficult at these levels, since the peritoneum is adherent to the posterior rectus sheet. Innervation of the rectus muscle must be pre- served and the integrity of the fascial indentations at these levels must be respected. It is thus recommended
Fig. 43.17. Skin incisions to approach the level L2/3 or L3/4 (black lines). Alternative skin incision for L2/3 (red line)
Fig. 43.18. Three-dimensional CT angiography. Mobilization of aorta and vena cava inferior (white arrows) to access L2/3 or L3/4. Segmental veins L2, 3, and 4 on the left side as well as seg- mental arteries L2, 3, and 4 on the right side have to be ligated and dissected
to expose the retroperitoneal space in two steps: longi- tudinal midline incision of the anterior rectus sheet 5 mm lateral to the linea alba and exposure of the left rectus muscle followed by dissection anterior to the muscle to its lateral border and opening of the retroper- itoneal space. Thus, the peritoneum can be detached from the posterior rectus sheet from left lateral to the midline. The exposure is then continued by opening of the posterior rectus sheet close to the midline and ret-
Fig. 43.19. Three-dimensional CT angiography. In this vascular situation, aorta and vena cava inferior are mobilized across the midline to the right side (white arrows). Segmental arteries and veins L2, 3, and 4 have to be ligated and dissected on the left side
roperitoneal dissection from the left to the right. In obese patients again, a transperitoneal route is recom- mended. The variable options of vascular preparation are shown in Figs. 43.18 and 43.19
43.9.6.1 Variation 1
In this individual anatomical situation an approach be- tween aorta and vena cava inferior is recommended to avoid exerting pressure on the aorta (Fig. 43.18). Seg- mental veins on the left side as well as segmental arter- ies on the right side have to be dissected before mobili- zation.
43.9.6.2 Variation 2
Since the aorta is located in the midline, it is, together with the vena cava, mobilized across the midline to the right side (Fig. 43.19). Segmental arteries and veins on the left side need to be ligated. At the level L2/3 care should be taken to avoid tethering or indirect rupture of the renal vessels.
43.9.7
Exposure of the Disc Space
Once the peritoneum and the vascular structures are shifted away from the anterior circumference of the spine, the disc space can be exposed (Fig. 43.20). The approach corridor is then secured by the insertion of a frame-type retractor (Fig. 43.21).
After removal of the disc, preparation of the disc space, and release of the segment, total disc replace- ment can be performed. However, because of the mini- open access, disc replacement is only possible with the latest generation of implants [3, 5].
a b
Fig. 43.20. a Exposure of the anteri- or circumference of the disc space
b Note that implantation of an artificial disc (Prodisc L) re- quires exposure of at least 2 cm on each side of the midline
Fig. 43.21. Synframe (Synthes, Oberdorf, Switzerland) retractor
a b
Fig. 43.22. a Prodisc implant.
b Lateral X-ray of the lumbar spine showing disc implant in place
43.10
Postoperative Care
The patients can be mobilized on the day of surgery.
The average hospital stay is between 2 and 5 days. Using the Prodisc implant (Fig. 43.22) postoperative bracing is not necessary. The patients are restricted from heavy physical activities and sports for 6 – 8 weeks. After a pe- riod of 3 – 4 weeks postoperative, we recommend an outpatient rehabilitation program to strengthen the ab- dominal and back muscles.
left to the right side, irrespective of their individual anatomy (Table 43.2).
Table 43.2. Vascular complication rates according to the type of anterior access to the lumbar spine
Complication Rate (%)
Total (%) Uniform conventional
approach, venous complications [7]
Venous injury, para-
rectal approach 18.4 26.1 Venous injury,
lateral approach 7.7 Uniform conventional
approach, arterial complications [2]
Arterial thrombosis 2.3 3.7
Vasospasm 0.9
Intimal fracture 0.5 Uniform mini-open
approach [1]
Arterial thrombosis 0.9 2.8 Venous injury 0.9
DVT 1.0
Individualized mini-open approach (own data)
DVT 0.43 0.4
peritoneal blood vessels can lead to a significant reduc- tion of vascular complications.
References
1. Brau SA (2002) Mini-open approach to the spine for anteri- or lumbar interbody fusion: description of the procedure, results and complications. Spine J 2:216 – 223
2. Kulkarni SS, Lowery GL, Ross RE, et al (2003) Arterial com- plications following anterior lumbar interbody fusion: re- port of eight cases. Eur Spine J 12:48 – 54
3. Le Huec JC, Aunoble S, Friesem T, Mathews H, Zdeblick T (2004) Maverick total lumbar disk prosthesis: biomechanics and preliminary clinical results. In: Gunzburg R, Mayer HM, Szpalski M, Aebi M (eds) Arthroplasty of the spine.
Springer, Berlin Heidelberg New York, pp 53 – 58
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Spine 22:691 – 700
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6. Mayer HM (2005) Total lumbar disc replacement, an update.
J Bone Joint Surg Br (in press)
7. Westfall SH, Berooz AA, Merenda JT, et al (1987) Exposure of the anterior spine. Technique, complications, and results in 85 patients. Am J Surg 154:700 – 704
