45 Microsurgical Anterior Lumbar Interbody Fusion (Mini-ALIF): The Lateral Retroperitoneal Approach to L2/3, L3/4, and L4/5

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(Mini-ALIF): The Lateral Retroperitoneal Approach to L2/3, L3/4, and L4/5

H.M. Mayer

45.1 Terminology

The term “mini”-anterior lumbar interbody fusion (Mini-ALIF) was created to describe new anterior approaches to the lumbar spine for the purpose of per- forming interbody fusion. These approaches are based on conventional surgical techniques for exposure of the anterior parts of the lumbar spine to which the general principles of microsurgery have been applied.

45.2 Surgical Principle

The approach is performed with the help of a surgical microscope, or alternatively “open” video endoscopy can be used. The anterolateral circumference of the motion segments L2/3, L3/4, and L4/5 is exposed through a limited skin incision (4 cm). The lateral abdominal wall is crossed using a blunt muscle-splitting technique. The anterolateral circumference of the lumbar spine is exposed by blunt dissection medial to the psoas muscle. The approach corridor is kept free by frame-type retractors which can be either anchored in the adjacent vertebral bodies by bone screws or which can be fixed to the operating table. The exposure allows different types of interbody fusion techniques (e.g., iliac crest autografts (preferred by the author), homografts (bank bone), as well as auto- or homografts augmented by allografts (e.g., titanium cages).

45.3 History

The first type of this operation was performed in 1995.

The surgical approach as well as preliminary results were described first in 1997 [1].

45.4 Advantages

The general advantages are:

The anterior retroperitoneal surgical approach to the lumbar spine is well known to spine surgeons.

There is no need to learn a completely new surgical technique.

The approach can be performed with the help of only one assistant (costs!).

No additional medicolegal problems as compared to conventional anterior approaches.

No additional potential complications with this technique (e.g., no gas in the abdomen).

Short learning curve, no laboratory training necessary.

No laparoscopic surgeon necessary.

The main technical advantages are:

Small skin incision (cosmesis!).

Blunt, muscle-splitting approach and preservation of innervation of abdominal muscles (early reha- bilitation possible!).

The retractor frame is fixed in the vertebral bodies by bone screws and protects all structures at risk (retroperitoneal blood vessels, bowel, ureter etc.).

Increased safety due to illumination and magnification of the surgical field by the use of optical aids (surgical microscope). Thus meticulous preparation in the prevertebral area is possible.

Low blood loss (< 100 cc).

Large and rapid exposure of the situs is possible in case of complications.

Low complication rate.

Good clinical results.

Shorter operating times even in learning curve.

The technique is not bound to an implant (e.g., type of fusion free to the surgeons philosophy).

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45.5 Disadvantages

The main disadvantages are:

The surgeon should have microsurgical or video endoscopic experience.

Approach limited to L2-5.

Bisegmental approach to the levels L4/5/S1 is not possible.

Due to the small exposure, the indication is limited to mono- or bisegmental pathologies.

Potential risk of indirect trauma to structures surrounding the target area.

The possibility of anterior instrumentation is limited.

Reduction of the spine in cases of kyphotic or scoliotic deformities from anterior is not possible.

Additional posterior instrumentation (pedicle screw system or translaminar screw fixation) is recommended.

45.6 Indications

The approach has been used for anterior lumbar interbody fusion in the following diseases (in the majority of my own cases combined with posterior instrumentation):

Degenerative instability (mainly with Modic type I changes in MRI)

Degenerative spondylolisthesis Isthmic spondylolisthesis Spinal stenosis with instability Failed Back Surgery syndrome Fractures

Spondylitis/spondylodiscitis

Pseudoarthrosis following other types of fusion (e.g., posterolateral, PLIF)

45.7 Contraindications

There are no absolute contraindications to this surgical approach, however, the following situations can be rel- ative contraindications:

Previous surgery through a retroperitoneal approach (e.g., kidney surgery) on the same side Spondylitis/spondylodiscitis with large prevertebral soft tissue mass or psoas abscess

Extremely lateral course of common iliac vein of the left side covering the lateral aspect of the L4/5 intervertebral space

45.8 Patient’s Informed Consent

Besides information about general complications of spine surgery (deep venous thrombosis, pulmonary embolism, infection) the patient should be aware of the following potential complications and risks:

Denervation of the rectus muscle due to dissection of the iliocostal nerve

Abdominal hernia due to suture insufficiency Spinal nerve irritation or compression due to forceful retraction of the psoas muscle

Groin pain due to compression and irritation of the genitofemoral nerve

Vascular injury in the retroperitoneal space (segmental vessels, ascending lumbar vein, common iliac vein and artery on the left side) with retroperitoneal hematoma and necessity for reintervention Nerve and spinal cord injury with incomplete or complete neurological deficits

Dural tears with pseudomeningocele or CSF fistu- las

Restriction of spinal mobility due to interbody fusion

Temperature differences (usually temporary), dysesthesias, and disturbance of sweat secretion in the lower extremities due to dissection of the sympathetic trunk

Injury of peritoneum, bowel, ureter, kidney, and spleen leading to infection, hemorrhage, scar tissue, or disturbances and constrictions of the urinary tract

Donor site complications, including hematoma, irritation of lateral femoral cutaneous nerve, donor site pain, fatigue fracture of anterior superior iliac spine, hypertrophy callus formation, infection, injury to sacroiliac joint in case of harvesting the bone graft from the posterior iliac crest

45.9 Surgical Technique

45.9.1

Preoperative Planning and Preparation of the Patient The surgical approach is performed from the left side.

Thus, topographical anatomy of the anterolateral circumference of the target segment must be studied pre- operatively. In addition to information about the un- derlying pathology, MRI of the lumbar spine and its surrounding structures gives all the anatomical information which is needed to perform meticulous preoperative planning (Fig. 45.1). It facilitates the operation if the surgeon is well informed and aware of the size, shape, and localization of the psoas muscle in relation

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Fig. 45. 1. MRI of the lumbar spine for preoperative planning.

Motion segment L4/5. Note the common iliac vein as well as the course of the ascending lumbar vein. p Psoas muscle, c.i.v.

common iliac vein left side, a.l.v. ascending lumbar vein

to the anterolateral border of the lumbar spine, and the size and course of the retroperitoneal vessels. For the approach to L4/5, MRI examination should be focused, in particular, on the size and shape of the common iliac vein as well as on the presence and size of an ascending lumbar vein on the left side (Fig. 45.1).

Preoperative conventional X-rays of the lumbar spine in two planes are mandatory in order to gain enough information on the spine curvature as well as the height of the intervertebral space to be approached.

Additional information on the shape of the inferior borders of the ribcage, which is important for the approach to L2/3, can also be obtained. It is important to realize that there might be huge lateral osteophytes of the vertebral bodies adjacent to the segment which is to be fused (Fig. 45.2).

Starting 24 hours prior to surgery, the patients are treated with routine mechanical large bowel prepara- tions to empty the colon.

45.9.2

Anatomical Considerations

The disc spaces L2/3, L3/4, and L4/5 are reached through a left-sided retroperitoneal approach. The disc space is reached through an anterolateral route along the medial border of the psoas muscle. To facilitate the surgical preparation (especially in obese patients), the patient is placed in a right lateral decubitus position (see Section 45.9.5). The corridor to the intervertebral space is limited by the size of the psoas muscle, as well as by the size and course of the common iliac vein at

Fig. 45.2. Plain X-ray lumbar spine. Note the lateral osteophytes at L2/3 left

L4/5. In contrast to the conventional macrosurgical approach, the segmental lumbar arteries and veins are not routinely exposed nor due they need to be dissected in the majority of cases. However, one has to be aware of the segmental vessels since they are at risk for indirect tension due to retraction of their “mother vessels”

(vena cava, aorta, common iliac vein). At L4/5, special attention should be paid to the ascending lumbar vein.

Sometimes it must be dissected, clipped, and cut in order to achieve a safe retraction of the common iliac vein from the intervertebral space.

45.9.3

Surgical Microscope

Surgical preparation is usually started with the use of a head lamp until the medial circumference of the psoas muscle is exposed. It is then continued with the help of a surgical microscope. The microscope should have either a variable focus length or a focus length of at least 350 mm (Fig. 45.3). We prefer a “2-in-1” model which means that two optical lines are integrated into one surgical microscope. The advantages are that the surgeon and the assistant are able to adjust magnification and focus independently of each other according to their individual needs. For true three-dimensional vision, the oculars of the microscope can be replaced by two digi-

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Fig. 45.3. Zeiss NC 33 surgical microscope

Fig. 45.4. Surgical microscope linked to head-mounted displays for “true” improved three-dimensional vision

tal chip cameras which are connected to a head-mounted display through a computer system (Fig. 45.4).

While three-dimensional vision is enhanced with such devices, the digitally transferred optical quality is still inferior as compared to the view through optical lenses.

45.9.4 Anesthesia

The operation is performed under general anesthesia.

Once the patient is anesthetized, a Foley catheter and a nasogastric tube are inserted. Arterial and central venous pressure lines are placed because hemody- namic monitoring is important.

45.9.5 Positioning

The operation is performed with the patient in a right lateral decubitus position on an adjustable surgical table. The table is tilted to create a left convex bending of the lumbar spine. This increases the distance between the iliac crest and the inferior border of the rib cage.

Due to this positioning, the surgical approach is facili- tated especially in obese patients since all the abdominal contents “fall away” from the surgical field making way for the approach corridor (Fig. 45.5a).

According to the level to be approached, the table is then tilted backward in the axial plane for 20° (L4/5), 30° (L3/4), or 40° (L2/3) (Fig. 45.5b). The anterior longitudinal ligament has a convergent course from the caudal to the cranial direction. Since the lateral border of the anterior longitudinal ligament is the important landmark for the insertion of the anchoring screws, this adjustment of the surgical table shifts this border on top of the target area (Fig. 45.6). The orientation of the lumbar motion segment is then checked with lateral fluoroscopy. If necessary, the tilt of the table is adjusted in order to achieve a parallel projection of the vertebral endplates of the level to be approached (Fig. 45.7). The orientation of the disc level (“orientation line”) as well as the center of the disc space (“center line”) are marked onto the skin. The line of the skin incision is centered over the target point (intersection of the orientation and center lines) in an oblique direction (parallel to the fiber orientation of the external oblique abdominal muscle) (Fig. 45.8).

45.9.6 Surgical Steps 45.9.6.1

Skin to Retroperitoneal Space

A 4-cm skin incision is sufficient for the exposure of one segment. The retroperitoneal space is exposed through a blunt, muscle-splitting approach. Each muscular layer (external oblique, internal oblique, transverse abdominal muscle) is dissected in the direction of their fiber orientation (Fig. 45.9).

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a Fig. 45.5. Positioning of the patient for retroperitoneal anterior microsurgical ap- proach. a View from anteri- or: table is tilted to “open”

the distance between iliac crest and rib cage. b View from the side: table is tilted backward between 20° and 40° to facilitate the approach medial to the psoas muscle as well as the identification of the lateral borders of the anterior longitudinal ligament

b

Fig. 45.6. Drawing of vertebral body. Backward tilt of the pa- tient leads to a shift of the lateral border of the anterior longitudinal ligament to the top of the target area

Fig. 45.7. Lateral fluoroscopy for localization and adjustment of the spatial orientation of the motion segment. Parallel projec- tion of endplates. Determination of disc space orientation (red line), determination of center of the intervertebral disc (yellow line)

Fig. 45.8. Skin incision centered over the target point. cau cau- dal, cra cranial, ant anterior

The branches of the intercostal nerves 10 – 12 as well as the iliohypogastric/ilioinguinal nerves which occa- sionally cross the surgical field at the level of L4/5 between the layers of the internal oblique and transverse abdominal muscles are the only structures at risk during muscle splitting. They must be preserved in order to maintain innervation of the rectus abdominis muscle. Blunt splitting of the transverse abdominal muscle should be performed as far lateral as possible to avoid

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Fig. 45.9. Schematic drawing of the blunt muscle-splitting ap- proach to the retroperitoneal space: surgeon’s view

accidental opening of the peritoneum. Even in very slim patients, there is usually enough retroperitoneal fat tissue beneath the lateral part of the transverse muscle and the peritoneum which is more adherent to the inner fascia of the medial part of this muscle.

45.9.6.2

Retroperitoneal Space to Intervertebral Region

Blunt dissection is continued in the retroperitoneal space using peanut swabs and modified Langenbeck hooks for preparation. Small bridging veins between the fat tissue and the inner wall of the lateral abdomen are closed with bipolar coagulation and dissected. The

Fig. 45.10. Incision and dissection of anteromedial insertions of the psoas muscle to the lumbar spine. c.i.v. Common iliac vein

anterior and medial circumference of the psoas muscle is identified. The peritoneal sack as well as the ureter and the common iliac artery at L4/5 are gently retracted toward the midline using the blunt hooks.

The operation is now continued with the help of the surgical microscope. Anteromedial attachments of the psoas muscle to the lumbar spine can be identified and incised and sharply dissected from the anterolateral circumference of the disc space and adjacent vertebral body borders after bipolar coagulation (Fig. 45.10).

Dissection should not be extended posterior to the pedicle entrance in order to avoid irritation of the lumbar nerve roots. Very rarely the segmental vessels of the inferior vertebral body need to be ligated with endoc- lips, cut, and dissected from the vertebral surface (Fig. 45.11).

At L4/5, the common iliac vein may cover the medio- lateral aspect of the intervertebral space. The vein can be gently retracted after mobilization in most of the cases. However, this may be a very difficult task in patients with spondylitis/spondylodiscitis since there are often adhesions between the vessel and the infectious granulation tissue. The use of the surgical microscope is essential in such situations. The main branch of the sympathetic chain can now be identified. It can occa-

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Fig. 45.11. Anatomical situation at L4/5. Note the course of the common iliac vein (c.i.v.) as well as of the ascending lumbar vein (a.l.v.). The segmental blood vessels are visible in only 20 % of the cases (personal observation)

sionally be mobilized and preserved; however, in the majority of cases cauterization and dissection is neces- sary. Attention: Please consider that this is not a com- plication of surgery. In more than 80 % of patients, no postoperative temperature differences in the legs are noted. In those patients who experience temperature differences in the lower extremities, this usually re- solves after 6 – 9 months.

The lateral border of the anterior longitudinal ligament is now visible and blunt dissection is completed when 5 – 10 mm of the adjacent vertebral bodies are exposed (Fig. 45.12).

45.9.6.3

Placement of the Self-retaining Spreader Frame

After verification of the disc space level under fluoro- scopic control, the retractor can be inserted. The self- retaining retractor frame is anchored with bone screws.

First the cortex of the adjacent vertebral bodies is per- forated with a high-speed burr 5 – 8 mm from the endplate borders in a strictly vertical direction to create the hole for the anchoring screws. The drill has a safety range of 10 mm and penetrates only the anterolateral

Fig. 45.12. Exposure of the anterolateral circumference of disc space. d Intervertebral disc, p psoas muscle

a b

Fig. 45.13. a Anchoring screw (self-tapping).

b Insertion of anchoring screws after perfora- tion of the vertebral body’s cortex with a drill

cortex of the vertebral body. The self-tapping anchoring screws are inserted (Fig. 45.13a, b) and these serve as an anchor for the cranial and caudal spreader valves which are then inserted (Fig. 45.14a, b).

A self-retaining frame-type retractor is attached to the blades with a ballpoint locking device (Fig. 45.15).

A sharp muscle blade is attached laterally to deflect the psoas muscle whereas a blunt vessel blade is inserted medially to retract the retroperitoneal vessels. Both

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a

b

Fig. 45.14. a Soft tissue blade for retraction of the soft tissue cranial and caudal to the intervertebral space. b Blades insert- ed onto the vertebral body screws

blades can be adjusted independently of each other.

Limited intervertebral distraction can be applied by adjusting the cranial and caudal blades in patients without posterior instrumentation. The anterolateral circumference of the segment to be fused is now exposed (Fig. 45.16a).

As an alternative to the retractor described above, a self-retaining ring-type frame retractor (Synframe;

Synthes Oberdorf, Switzerland) can be used. The retractor ring is fixed to the surgical table, and the retractor blades can be adjusted according to the individual anatomical situation (Fig. 45.16b).

a b

Fig. 45.16. a Surgical field after placement of the frame retractor. ant Anterior, cra cranial. b Synframe retractor system with soft tissue blades

Fig. 45.15. Self-re- taining frame retractor

45.9.6.4

Interbody Grafting

Anterior lumbar interbody fusion with an autologous iliac bone grafts is preferred and described. However, other types of anterior interbody fusion including the use of homografts or allografts (e.g., fusion cages) are possible with this approach.

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Fig. 45.17. Removal of the cartilaginous endplate with chisels

a b

Fig. 45.18.

a Smoothing of graft bed with high-speed burr.

b Graft bed

The anulus fibrosis is incised from the middle of the anterior longitudinal ligament to the medial border of the incised psoas muscle. The anterolateral anulus as well as the nucleus pulposus are removed with curettes and rongeurs. In patients with inferior bone quality due to osteoporosis, the subchondral bone is preserved. The endplates are removed carefully with curettes. If there is significant subchondral sclerosis removal of the endplates is started with specially designed chisels (Fig. 45.17). The subchondral bone is then smoothed with a high-speed drill (Fig. 45.18a). The height and depth of the iliac crest graft needed is measured with a sliding caliper after completion of graft bed preparation (Fig. 45.18b).

45.9.6.4.2 Graft Harvesting

A tricortical iliac bone graft is harvested through a sep- arate small incision over the lateral iliac crest on the same side. The skin incision is placed at least 4 cm lateral to the anterior superior iliac spine in order to prevent dissection of the lateral femoral cutaneous nerve.

The bone graft is removed using a parallel, oscillating saw which can be adjusted to the size needed (Fig. 45.19a). The graft is cut with the help of a graft cutter (Fig. 45.19b). In addition, as much cancellous bone as possible is harvested from the ilium. The bone defect is filled with Gelfoam, a drain is inserted, and the wound closed in layers.

45.9.6.4.3 Modifications

At L4/5, the bone graft can be harvested through the same incision which is used for interbody fusion. The skin is incised over the target area (Fig. 45.20a) and then retracted after subcutaneous dissection to expose

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a

b

Fig. 45.19. a Parallel oscillating saw for removal of iliac crest bone graft. b Graft cutter with bone graft removed from the ili- ac crest

a b

c

Fig. 45.20. a Four-centimeter skin incision for interbody fusion L4/5. b Removal of bone graft through the same incision before exposure of the intervertebral space. Preservation of iliac crest.

c Bone graft after removal from iliac crest

the iliac crest (Fig. 45.20b). In slim patients, the lateral part of the iliac crest is preserved (Fig. 45.20b, c).

If posterior instrumentation is performed in the same session, I prefer to harvest the bone graft through the dorsal incision from the posterior iliac crest. This can be easily achieved by an interfascial approach.

45.9.6.4.4 Grafting

First, the contralateral part of the intervertebral space is filled with cancellous bone. The graft is mounted on-

Fig. 45.21. a Bone graft mounted on graft holder a

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b c

Fig. 45.21. (contin.) b Graft impacted into the intervertebral space. c Intraoperative picture showing the graft in place. The remain- ing gaps are filled with cancellous bone

to a graft holder (Fig. 45.21a) and impacted into the intervertebral space (Figs. 45.21b, c, 45.22). The remain- ing gaps anterior and posterior to the graft are filled with cancellous bone from the iliac crest as well as from the removed parts of the vertebral bodies.

45.9.6.5 Retreat

After removal of the retractor, the holes for the anchoring screws are sealed with bone wax and the fusion area is covered with Surgicel. The muscle layers are closed with absorbable sutures, and the skin is closed with an intracutaneous suture.

45.10 Postoperative Care

Usually there are no drains placed at the fusion site.

The wound drainage at the donor site of the iliac crest bone graft is removed on the second postoperative day.

Since most of the patients have had an additional posterior instrumented fusion by an internal fixator, they are allowed to get out of bed the day after the operation.

The physiotherapy program begins on the first postoperative day starting with isometric exercises. Thrombo- embolic prophylaxis is performed with fractionated heparin. If there are no complications, the patients can leave the hospital between the seventh and fourteenth postoperative days. No brace is necessary in monoseg-

Fig. 45.22. Postoperative X-ray, lateral view: bone graft in place.

Note posterior instrumentation

mental stabilizations with posterior instrumentation.

However, we use a Boston brace in patients with bisegmental approaches, in hyperactive young patients as well as in patients with osteoporosis. The brace should be worn for 8 – 10 weeks postoperatively.

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45.11 Complications, Pitfalls, and Hazards

There is a variety of potential complications, pitfalls, and hazards which can arise at various steps of the operation:

Wrong positioning of the patient: It is common to all microsurgical procedures that positioning of the patients significantly contributes to the success of the operation. The patient should be positioned as described above. Special attention must be made to the parallel orientation of the disc space borders as well as to the tilt of the surgical table. This is emphasized because all anatomical landmarks (iliac crest, psoas muscle, anterior longitudinal ligament) are helpful and valid only when they are oriented the right way. Take care that the endplates are in a parallel projection. If there is a tilt which cannot be corrected it is necessary to modify the insertion of the anchoring screws in a way that perforation of the tip of the anchoring screw into the intervertebral space is avoided.

Skin incision too close to iliac crest: This can hap- pen in patients with “high” iliac crests. It results in difficulties placing the caudal anchoring screw. If this situation occurs during localization of the skin incision (usually at L4/5), I recommend to tilt the table slightly more backward which will shift the incision line more anteriorly. The same is valid for patients with hypertrophy of the psoas muscle.

High muscle tension due to insufficient relaxation of the patient: Note that the patient has to be completely relaxed, otherwise high forces are needed to retract the abdominal muscles.

Ureter: The ureter is rarely seen during exposure of the target area. It usually courses in the retroperitoneal fat which is mobilized anteriorly.

Common iliac artery: The left common iliac artery can only be exposed at L4/5. In patients with severe ar- teriosclerosis, the vessels might kink laterally and thus reach into the approach corridor. It is not a prob- lem to retract the vessel. However, if there are calcifi- cations the retraction should be very gentle in order to avoid lesions to the calcified wall of the vessel.

Genitofemoral nerve: This nerve courses at the medial surface of the psoas muscle. It is exposed to damage by pressure of the retractor blade or by bipolar coagulation. The nerve should be preserved since irritation causes postoperative pares- thesias, pain, and discomfort projecting into the groin and medial thigh.

Common iliac vein, segmental vessels, and ascending lumbar vein: See comments above.

Donor site complications: The most common postoperative complications at the iliac crest are pain,

Table 45.1. Complications following 360° Fusion with retroperi- toneal Mini-ALIF

Complication Number of patients

affected

DVT 1

Fracture of the os ilium 3

Non-union 4

Loosening of implant 1

Loss of correction 1

Fracture of the pedicle 1

Hematoma donor site 2

Irritation n. genitofemoralis 3

Total 16 (13.3%)

irritation of the lateral femoral cutaneous nerve, hematoma, and fatigue fracture of the anterior superior iliac spine. Most of these complications can be avoided if the graft is taken at least 4 cm lateral to the anterior superior iliac spine. This helps to preserve the lateral femoral cutaneous nerve, de- creases the risk of fatigue fracture as well as postoperative pain. Hematomas can be avoided by meticulous hemostasis, including the use of bone wax, as well as by a sufficient wound drainage.

In our series of patients described below, we have ob- served a total of 16 complications (13.3 %). Five of them were donor site complications (see Table 45.1). There was one general complication (deep venous thrombosis) as well as three complications from the posterior approach (pedicle fracture, implant loosening, loss of correction).

There were seven complications specific to the anterior approach: four pseudoarthrosis and three patients with irritation of the genitofemoral nerve (Table 45.1).

45.12 Results

Microsurgical anterior lumbar interbody fusion has been performed in 120 patients (66 women, 54 men;

age range 26 – 84 years (average 56.3 years). All the procedures were performed as part of a 270°-fusion philosophy which includes posterior instrumentation (with/

without decompression of the spinal canal) with pedicle screw systems or translaminar screws, arthrodesis of the facet joints combined with anterior lumbar interbody fusion. The indications are listed in Table 45.2.

The average time for surgery was 102.2 minutes.

This time includes 16 double-level cases as well as all cases which were performed in the early learning curve (Fig. 45.23). Time for surgery ranged between 50 and 195 minutes. The average blood loss was 139.8 cc (67.3 cc at the fusion site, 78.1 cc at the graft donor site).

None of the patients received any blood transfusion for the anterior approach. Preoperative evaluation of the

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4 18

81

1 4

12 0

20 40 60 80 100

L2/3 L3/4 L4/5 L5/6 L2/3/4 L3/4/5

patients

0 0 0

100

0 20 40 60 80 100

excellent good moderate bad EFR score

(Prolo 1986)

patients

[%]

23

39

23 15

0 20 40 60 80 100 [%]

excellent good moderate bad EFR score (Prolo 1986)

patients

3

70

19

8 0

20 40 60 80 100 [%]

completely better unchanged not satisfied satisfied

patients

Virgin backs:

Degenerative spondylolisthesis 37

Spinal stenosis 31

Degenerative instability 19

Isthmic spondylolisthesis 2

Fracture 2

Failed backs:

Post-discectomy 23

Post-spondylitis 2

Non-union 4

Total 120

economic and functional status of the patients was performed with the help of the EFR score published by Prolo in 1986 [2]. All patients had a bad score preopera- tively (Fig. 45.24a). After an average follow up period of 24 months, 62 % of the patients showed excellent or good clinical results, 23 % showed satisfactory results, and 15 % had bad results (Fig. 45.24b). The patients were asked to give a self-rating of the result of surgery.

A total of 73 % were either completely satisfied or reported a significant improvement of their symptoms (Fig. 45.25), 19 % of the patients reported unchanged

Fig. 45.23. Lumbar levels treated with Mini-ALIF

a b

Fig. 45.24. a Preoperative EFR score [2]. b Postoperative EFR score [2]

tients with a follow up of more than 6 months.

45.13 Critical Evaluation

The approach described in this chapter is a microsurgical modification of the well-known conventional retroperitoneal approach to the lumbar levels L2-5. The approach has been standardized as far as possible and microsurgical principles have been applied to the devel- opment of instruments as well as to the surgical technique. Positioning of the patient has been changed slightly in a way to create a more lateral approach. This has the advantage that the lumbar spine can be reached through a 4-cm incision even in obese patients. Due to the lateral positioning, the abdominal contents “fall away” from the surgical field and thus facilitate the approach. The lateral approach, however, can be disad- vantageous in patients with a wide pelvis or a high iliac crest since these anatomical variations create a long distance between the skin levels and the target area on the lumbar spine.

Fig. 45.25. Self-evaluation of clinical result by the patient

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The function of the muscular abdominal wall is preserved using a blunt muscle-splitting approach. Orien- tation anterior to the psoas muscle can be difficult in patients with big muscle diameters (e.g., young ath- letes). We recommend to tilt the table more backward in order to achieve a more anterior route. The psoas must be incised 1 – 1.5 cm; beware the genitofemoral nerve! (see above). The retractor frame makes it possible to perform the operation with only one assistant. In my experience, it is easier to handle the retroperitoneal blood vessels (common iliac vein, segmental vessels, ascending lumbar vein) when the microscope is used.

The risk of direct injury to these vessels is minimized.

This is supported by the fact that we have not had any vascular complications so far. Injury to the sympathetic chain does not seem to play a significant role in clinical follow up. Only about 25 % of the patients complained of postoperative temperature differences in the lower extremities. In the vast majority (> 90 %) this resolved within 6 – 9 months postoperatively.

There are several points of criticism:

The technique is only applicable to the levels L2-5.

Due to the standardization of the surgical steps and the size of the approach, a maximum of two levels can be approached through one skin incision.

Spatial orientation in the target area is strongly dependent on the exact positioning of the patients.

The majority of complications occurred during the posterior instrumentation and not during anterior surgery.

A considerable number of complications have been donor site complications, the consequence of which is to think about fusion alternatives to solid iliac bone grafts (e.g., vertical cages).

The major advantages of the technique turned out to be:

A reproducible technique with a short learning curve

The low peri- and postoperative morbidity including the negligible intraoperative blood loss The possibility of early mobilization and rehabili- tation due to the preservation of the functional integrity of the abdominal wall

The good clinical results (at least as good as with conventional techniques)

The acceptable pseudarthrosis rate (< 5 %) The acceptable complication rate

The good acceptance by the patients themselves The different options for the type of interbody fusion [autogenous iliac bone graft, augmented horizontal and vertical cages, homogeneous bone grafts (bank bone) etc.]

References

1. Mayer HM (1997) A new microsurgical technique for mini- mally invasive anterior lumbar interbody fusion. Spine 22:691 – 700

2. Prolo DJ, Oklund SA, Butcher M (1986) Toward uniformity in evaluating results of lumbar spine operations. Spine 11:601 – 606