42 The ALPA Approach for Minimally Invasive
Nucleus Pulposus Replacement
R. Bertagnoli
42.1
Terminology
The posterior approach is standard for lumbar decom- pression surgery. To avoid disrupting the posterior structures of the spine as well as the disruption of the strong anterior tension bands (the ALL and PLL), the anterolateral transpsoatic approach (ALPA) [3] has been developed.
42.2
Surgical Principle
In an exact 90° lateral position of the patient with the surgeon standing on the posterior side of the patient, an orthograde projection of the disc space to the skin is generated by tilting the operating room table under fluoroscopic control to get a perpendicular access (Fig. 42.1). An oblique skin incision of approximately 3 – 4 cm is carried out. In a typical manner the retroper- itoneal space is accessed by a muscle-splitting tech- nique of the three lateral abdominal wall muscle layers.
In blunt dissection the psoas muscle is accessed. The psoas muscle is dissected in the direction of the muscle fibers to reach the affected disc in the midline of the
Fig. 42.1. Orthograde lateral access to the disc space
disc’s AP distance. The disc anulus is cut to create a flap, the nucleus pulposus material is removed, and the prosthesis is implanted into the disc cavity. The proce- dure concludes with the anulus flap being sutured in place over the opening to the nucleus, and the wound is closed in a normal manner.
42.3 History
Spinal fusion has become the standard treatment for patients suffering from degenerative disc disease.
Though this approach stabilizes the problem area and provides pain relief, it also results in a decreased range of motion and in some cases initiates a degenerative cascade in adjacent segments as these are called upon to compensate for the restricted mobility of the fused vertebrae [2, 5, 8, 9].
To offer patients with symptomatic degenerative disc disease an alternative to spinal fusion, research has recently focused on replacing all or part of the diseased disc with devices designed to retain some of the disc’s normal functions. For patients with advanced degener- ation, total disc replacement products such as the Link SB Charite (Waldemar Link) and the Prodisc (Spine So- lutions) have been developed. For patients with only moderate degeneration, nucleus replacement products such as Aquarelle (Stryker Spine) [12], Newcleus (Sul- zer Medica) [12], and the PDN device (Raymedica) [11]
are being developed/tested, with the latter being com- mercially available in many countries.
These nucleus replacement devices have typically been implanted by way of an open posterior approach.
Though this surgical technique has proved successful in the majority of cases, there are risks associated with the procedure. Ligament and bone material must be re- moved, with possible damage to the facet joints induc- ing an increased instability of the segment. Moreover, exposure of the dura and traversing nerves increases the chance of nerve tissue damage and epidural scar- ring and bleeding. Due to the defect in the PLL and pos- terior anulus a higher rate of complications, mainly im- plant expulsions, have been observed.
To avoid the risks associated with the posterior ap- proach, the anterolateral transpsoatic approach (AL- PA) has been developed. Instead of entering the disc from the back, the disc is now accessed laterally through the psoas muscle, with little chance of damage to the osseo-ligamentous tension band structures, lo- cated in the direct AP direction, that are in charge of the flexion–extension motion of the lumbar spine. More- over, because a larger section of the disc can be exposed from a lateral approach, disc enucleation in the lateral direction, parallel to the spinal canal, and prosthetic device implantation can be accomplished faster and with more ease and lesser risks.
42.4 Advantages
Atraumatic, muscle-sparing access to the antero- lateral part of the disc space
Posterior tension band system unaffected Easy introduction of artificial nucleus Closure of anulus postimplantation
42.5
Disadvantages
Risk of damage to the lumbar plexus L5-S1 not accessible through this approach
42.6 Indications
Nucleus replacement
Anterior lumbar interbody fusion
Fig. 42.2. Left Position of sur- geon in front of the patient.
Right Position of surgeon be- hind the patient
42.7
Contraindications
L5-S1
Previous ALPA approach on the same side (as an alternative the approach can be performed from the contralateral side)
42.8
Patient’s Informed Consent
The patient should be informed about the possible complications of anterior approaches (see Chap- ters 45 – 48). The specific risk of damage to the lumbar nerve plexus due to direct injury or retractor pressure should be mentioned.
42.9
Surgical Technique
In contrast to the anterior lumbar interbody fusion (Mini-ALIF) approach [6], where the patient is posi- tioned at a 60 – 70° angle, the ALPA patient is placed in a 90° lateral decubitus position on an adjustable surgi- cal table. The surgeon can stand behind or in front of the patient (Fig. 42.2). To increase the distance between the iliac crest and the inferior border of the twelfth rib, the table is flexed slightly to arch the patient’s side.
Arms and legs are supported as necessary, and the pa- tient is immobilized to prevent shifting during the pro- cedure.
With the patient secured, the operating table is tilted to position the affected vertebrae perpendicular to the floor. This orientation is important for the fluoroscopic imaging that is used to guide device placement within the disc as well as for precise and easy working in the disc space with optimal orientation of the instruments.
Fig. 42.3. Marking of the an- terior and posterior borders of the segment (yellow lines) in projection to the skin lev- el. Marking of superior and inferior border of disc space (red lines). Oblique skin inci- sion centered over the disc space (black line)
Before any incision is made, the exact location of the disc is identified with K-wire and C-arm fluoroscopy.
The projection of the disc on the skin is then outlined with a marker on the patient’s lateral abdomen (Fig. 42.3).
42.9.1
Incision and Disc Exposure
The surgeon stands behind the patient to maximize ac- cess and improve the working angle away from the spi- nal canal (Fig. 42.2 right). A 3- to 4-cm oblique incision is made over the target area, the incision running paral- lel to the fibers of the external oblique muscle. Blunt dissection through the external oblique, internal oblique, and transversus muscles is done in the direc- tion of the fibers, and self-retaining retractors are placed in the wound to keep the surgical field open. The retroperitoneal space is then identified and followed
Fig. 42.4. Left Access direc- tion in conventional mini- ALIF access. Right Access direction with the ALPA approach
medially toward the lateral aspect of the psoas muscle.
The anatomic safe zone (approximately 2- to 3-cm width through the psoas muscle) corresponds with the lateral middle-third of the disc (Figs. 42.4, 42.5). Care is used not to deviate too far toward the anterior margin of the lumbar spine, where injury to major blood ves- sels and the sympathetic nerve chain is possible. It is al- so important not to deviate too far posterior, where the exiting nerve roots of the spine as well as the lumbar plexus can be damaged (see also Fig. 42.1). To avoid damage of the exiting nerve roots or plexus, an addi- tional nerve root detection device, e.g., NeuroVision nerve avoidance system (NuVasive, 10065 Old Grove Road, San Diego CA 92131, USA), can be used. If the psoas is accessed correctly and a strict lateral path is taken through the muscle, a tunnel is formed through the psoas and the fibers of the muscle serve to protect the sympathetic nerve chain and the nerve roots that exit the spine (Fig. 42.6). Once dissection through the
Fig. 42.5. Access route of ALPA approach in an axial MRI (green line) as compared to Mini-ALIF approach (red line)
Fig. 42.6. Step-by-step enlargement of access route through the psoas muscle
psoas muscle is complete and the affected disc has been localized, the surgical field is kept open with long self- retaining systems (e.g., Synframe, MIASPAS, or Endo- ring) (Fig. 42.7).
Fig. 42.7. Exposure of the lateral disc circumference
42.9.2
Anulus Incision and Anulotomy
The outer 6 – 10 layers of the anulus are cut using a small scalpel blade. Two parallel incisions are made (approximately 15 mm long) along the lateral margins of the disc, and one perpendicular incision is made be- tween the preceding two incisions. The goal is to create a flap in the outer anulus layers that can be readapted following implantation of the device. A suture is run through the flap, and the flap is retracted away from the surgeon so that it remains out of the operative field dur- ing the procedure. A single midanular incision is then made through the remaining anulus layers [1] to gain access to the nuclear cavity without creating significant damage to the lateral anular layers.
42.9.3
Nucleus Excision
After dilating the incised lateral anular layers, the nu- cleus material is removed using pituitary rongeurs, suction devices, or automatic shaver systems. The use of sharp curettes or other sharp instruments should be avoided as these can puncture the opposing margin of the anulus or damage the vertebra endplates. All nucle- us pulposus material is removed from the lateral re- gions and from the ventral and dorsal aspect of the disc. Due to the working direction in the lateral plane it becomes easy to clean the nucleus material on the left as well as on the right side from the canal.
Of paramount importance to successfully implant- ing a prosthetic nucleus device is the surgeon’s ability to completely evacuate the disc cavity. Fluoroscopic im- aging is helpful in determining whether additional nu- cleus material needs to be removed. A water-soluble contrast agent is introduced into the nucleus, and the disc space is viewed under fluoroscopes to determine when the disc has been adequately prepared. A nucleus replacement device or interbody fusion device (e.g.,
Fig. 42.8. Readaptation of psoas muscle fibers before closure
cage, bone dowel, etc.) can then be introduced with specific instruments.
42.9.4 Wound Closure
The anulus flap is closed and sutured in place. Retrac- tors are removed, and the psoas muscle is allowed to close (Fig. 42.8). Retroperitoneal drainage can be in- serted into the wound at this time. The wound is closed in a normal manner by applying adaptation sutures to the three muscle layers in the abdominal wall and by re- pairing the subcutaneous tissue in such a way that the overlying dermis aligns properly. This is followed with subcuticular closure of the skin and is finished by the application of sterile connective strips across the closed incision to facilitate healing and reduce scar- ring.
42.10
Postoperative Care
The patient is mobilized on the first postoperative day.
No further restrictions are necessary.
42.11
Hazards and Complications (see also Chapters 44 – 48)
Problems with the ALPA technique include the possi- bility of inducing neurapraxia of the nerve roots as well as the plexus, especially when pressure on the neuro- genic structures to the spinal process with a posterior retraction blade is too high. However, our experience indicates that this side effect diminishes as the surgeon gains experience with the procedure. One technical limitation of the ALPA technique is its inability to ac- cess the L5-S1 disc level (where the iliac crest acts as a barrier) without creating a bone defect to the ilium. It
is, however, possible to access this disc by creating an osteotomy through the iliac crest and removing the disc material with the aid of an endoscope [7].
42.12 Conclusion
For implantation of nucleus replacement devices as well as interbody fusion devices the ALPA surgical technique has benefits compared with any traditional posterior approach:
1. ALPA allows access to the intervertebral disc with minimal disturbance to posterior structures, the bony elements of the spine are not compromised, and there is no risk of damage to the dura and associated nerve tissue.
2. ALPA simplifies device implantation by allowing lateral access to the disc space: the devices can be directly implanted parallel to the canal. Thus, much less manipulation is required to achieve opti- mal device alignment.
3. Because the ALPA technique accesses the disc from the side, through a lateral anulus incision and not a posterior anulotomy, the posterior section of the anulus as well as the anterior tension band struc- tures (PLL, posterior anulus, ALL, anterior anulus) remain intact, as does the posterior longitudinal ligament.
4. Intradiscal access to the lumbar spine in the ALPA approach can be carried out from the left as well as from the right side of the patient with the same ease. Therefore, previous surgery in the same region is no longer an exclusion criterion due to higher risks approaching the spine through the same site.
Although larger studies must be implemented to better understand the risk/reward ratio of the ALPA tech- nique, at present this approach shows promise as an al- ternate means to the posterior hemilaminotomy ap- proach for intradiscal surgeries from L2 to L5.
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