Instrumented PLIF in Lumbar Degenerative Spine: Principles, Indications, Technical Aspects, Results, Complications and Pitfalls

Fig. 31.1

Surgical indications of fusion in lumbar stenosis

Sagittal orientation of the facet joints
Total facetectomy
Lumbar stenosis associated with lumbar previous idiopathic scoliotic deformity
Degenerative scoliosis
Intracanal synovial cysts alone or associated with listhesis
Flat back with loss of lordosis
Degenerative spondylolisthesis
Recurrent lumbar disk herniation
Secondary displacement after failed previous decompressive surgery

31.4 Technical Aspects (Fig. 31.2)

Fig. 31.2

Ten main surgical steps for PLIF procedure: (1) Complete exposure of the posterior arches of the two adjacent vertebras, (2) bilateral facetectomy (inferior facets of upper vertebra and superior facets of lower vertebra), (3) insertion of pedicle screws, (4) laminotomy with control of the adjacent nerve roots (i.e. the two upper and the two lower roots), (5) complete diskectomy via bilateral approach, (6) intervertebral distraction through the disk space, (7) cleaning of the end plates using curettes and/or dedicated rasps, (8) insertion of lordotic peek cages filled with autologous bone graft, (9) contouring of the rod, (10) rod placement with compression performed along the rod between the screw heads

To perform PLIF, patients are positioned in the prone on chest and iliac crests rolls in order to lower intra-abdominal pressure and improve venous drainage. Arms are placed on arm boards with abduction limited to 80° as to prevent brachial plexus injury.

A dorsal midline incision is made and subcutaneous tissues are dissected with monopolar until the deep fascia. This fascia is incised adjacent to the spinous processes bilaterally preserving supra-spinous ligament. Then the para-spinous muscles are released from the laminae in a subperiosteal fashion, and the dissection is taken out to the facets bilaterally until the transverse processes are visualised. Lateral radiographs should be obtained to confirm the operative levels prior to arthrodesis. Then, soft tissues should be removed on and around the lamina, pars, facet joint and dorsal transverse processes including the facet capsule and intrafacet synovium. After all, the fixation with pedicle screws is realised prior to the decompression, therefore limiting the risk of neural and dura mater injury during screws insertion and reducing the timing with the canal opened (associated with potential epidural bleeding). In addition slight and gentle distraction between the screw head using appropriate distractor could facilitate the insertion of the interbody implants. For this procedure, a facetectomy is done, keeping the bone that will be morselised for future graft, and then pedicle screws are inserted with lateral radiograph control bilaterally for all interbody fusions. Laminotomy and foraminotomy can be performed as needed for neural decompression of the thecal sac and nerve roots.

In most cases, complete laminectomy is not necessary and only partial laminotomy of the upper vertebra is sufficient to perform the decompression and to permit the insertion of the interbody cages. Epidural veins must be coagulated to avoid bleeding and cut to move apart neural elements without tether and discover disk space. Care should be taken to protect neural structures with nerve root retractor. Another cause of epidural bleeding is the emissary vein of the vertebral body, which can be plugged by haemostatic gauze. Complete diskectomy and endplate preparation are performed, also removing the cartilaginous end plates using rasps. Then, spacers are inserted in order to progressively distract the disk space and determine the adequate gauge implant size (Fig. 31.3). Morselised autogenous bone, obtained from the laminectomy, is packed anteriorly before the implants are placed. According to our experience, the dimensions of the cages have to be high enough (at least 10 mm) and large (25 mm) to obtain a good primary stabilisation and thus a good fusion. Also, wedge-shaped cages (8° lordotic at minimum) are superior to rectangular cages in restoring segmental lordosis and sagittal alignment and avoiding flat back deformity [46]. The cages, filled with autogenous bone (perfectly cleaned with removal of all soft tissues), are inserted into the disk space with the medial aspect on the pedicles bilaterally. Then pedicle screws and rods are compressed to restore segmental lordosis and promote fusion by graft compression. After haemostasis is ensured, the wound is irrigated and closed in layers. A subfascial drain may be left.

Fig. 31.3

Main surgical steps of PLIF procedure with perioperative views. Control of the four adjacent nerve roots, i.e. right and left L4 and L5 roots for L4–L5 level, is crucial to avoid any damage to neurologic structures. Intervertebral distraction on one side can be helpful to complete the decompression on the other side. uf upper facet, ds dural sac

31.5 Advantages/Limitations

Unlike posterolateral intertransverse fusion, PLIF is a biomechanically optimal fusion because the graft and/or the interbody implant maintains the disk height (i.e. the lateral foraminal opening), protects the nerve roots, restores weight bearing to anterior structures and controls both horizontal and vertical instabilities. The cagelike implants (titanium or polyether ether ketone (PEEK) cages) meet the mechanical requirements for PLIF by serving both a mechanical function and a biologic bone growth function. The cages stretch the intervertebral space to its normal anatomic height and prevent the postoperative collapse of the graft. The implant is packed with cancellous bone graft obtained from the laminectomy [47]. PLIF and anterior lumbar interbody fusion (ALIF) with cages, without a complementary posterior fixation for 360° stabilisation, are associated with pseudo-arthrosis, secondary displacement and subsequent complications. The role of the pedicle screw-based posterior fixation is first to carry out temporary control of AP, lateral or rotational translation before the achievement of the definitive bone fusion, second to enhance osteogenesis and third to allow early mobilisation without the need of a postoperative corset to avoid external contention (except in case of osteoporosis), loss of lordosis and further destabilisation at the adjacent level to the arthrodesis.

PLIF is neither useful nor safer when reoperations are performed and in which the spinal canal was already opened. There exists an increased risk of dural breach and neural injury due to fibrosis and nerve root distortion. ALIF or TLIF may be a good alternative for these patients, thus avoiding the dissection in the region of the epidural fibrosis. Another drawback of this technique is the blood loss that can be excessive, particularly in older patients. Also, in patients with a high pelvic incidence, ALIF may be a better alternative. ALIF facilitates a good fusion and restores an optimal sagittal balance. This parameter is crucial to respect, because the L4–S1 segment represents two-third of the total lumbar lordosis. As a consequence, arthrodesis should be performed with these parameters in mind.

31.6 Complications (Table 31.1)

Table 31.1

Complications due to PLIF procedures

Perioperative complications	Late complications
Dural laceration, cerebrospinal fluid (CSF) leakage: 4–17 %	Subsidence rare
Dural laceration, cerebrospinal fluid (CSF) leakage: 4–17 %	Pseudarthrosis: 2–15 %
Neurological complications:	Cage migration: rare
Transient (radicular pain, weakness) 3–17 %	Adjacent segment disease (no specific to PLIF): 3–11 %
Permanent (radicular pain, weakness) 0–7.5 %
Deep wound infection: 0.5–5 %
Hematoma: 1.2 %
Pedicle screw misplacement: 4 %
Injury to major abdominal vessels
Pulmonary embolism: 0.4 %

Posterior lumbar interbody fusion provides circumferential release of the dural sac and/or nerve roots as well as a biomechanically stable construct with anterior and middle-column load sharing combined with pedicle screw devices. However, PLIF has some risks for surgical complications [48]. Along with risks related to the surgical approach, the use of implants increases the risk for additional complications [49]. Complications are divided here into perioperative complications that occurred during and within 1 month of surgery and late complications after 1 month of surgery.

31.6.1 Perioperative Complications

The incidence of perioperative complications following single-level PLIF has been reported to be 18–37.5 % [48, 50], and the incidence after two-level PLIF has been reported as 46 % [51]. Moreover, Deyo et al. found that patients who underwent lumbar surgery with fusion had a complication rate twice as high as those who underwent surgery without fusion [49]. Amongst several kinds of fusion techniques, PLIF is considered one of the most technically demanding procedures and a definite learning curve exists. One of the most dangerous manipulations in PLIF is excessive retraction of the dural sac with the cauda equine and nerve roots whilst removing disk material and inserting cages and bones. Nerves are often taut and immobile because of severe adhesion due to canal stenosis. Surgeons may unknowingly retract the dural sac beyond a critical pressure and/or period whilst concentrating on the disk space. Neurological deficits have been reported in only 2 % of patients after posterolateral lumbar fusion, in which access to the disk is not required [52]. Hosono et al. found that the surgery duration was the only significant risk factor for neurological complications and therefore suggested that the dural sac or roots should have been retracted for unusually long periods in patients presented with neurological deficits [49]. Also, the rate of neurological complications in procedures with total facetectomy is much lower than procedures with partial preservation of facet joints. It may reduce the intensity and period of retraction of the dural sac and nerve roots and the risks of neurological complications by taking advantages of the large working space provided by total excision of bilateral facet joints.

As a consequence, perioperative complications of PLIF procedures are as follows:

Dural laceration, cerebrospinal fluid (CSF) leakage: 4–17 % [53, 54]
Neurological complications
- Transient (radicular pain, weakness) 3–17 % [54, 55]
- Permanent (radicular pain, weakness) 0–7.5 % [54, 55]
Deep wound infection: 0.5–5 % [49, 53]
Hematoma: 1.2 %
Pedicle screw misplacement: 4 %
Injury to major abdominal vessels [56]
Pulmonary embolism: 0.4 %

31.6.2 Late Complications

The intracorporeal penetration on the cages or subsidence, and thus the loss of the restored intervertebral height, is perhaps the most significant late complication. It mainly occurs in osteoporotic patients, but remains rare – one patient in the authors’ series [55].

Pseudarthrosis is an uncommon complication of PLIF – less than 2 % [54, 55].

Cage retropulsion after PLIF is another complication that has been described. The risk factors are insufficient cage size, multilevel fusion, inadequate seating of the cage anteriorly and surgery at segment L5/S1. Fundamental techniques in performing PLIF must be mastered as follows:

The degenerated disk materials must be removed and the end plates cleaned from cartilaginous layers thoroughly.
The cage must be inserted without damaging the bony end plates.
Undersized cages should not be selected.
Adequate compressive force must be applied to the disk space by the pedicle screws.
Use of lordotic cages [57].

A prospective randomised study reported that fusion accelerates degenerative changes at the adjacent segment of the fused spine, compared with naturally occurring changes [58]. Spinal fusion alters the biomechanics of spinal motion and increases intradiscal pressure or the load on facet joints of the adjacent motion segment of the fused spine [59]. Within 5 years of lumbar fusion surgery, the clinical incidence of symptomatic adjacent segment disease (ASD) is reportedly 5.2–18.5 % [59] and the incidence of additional surgery for symptomatic ASD is reportedly 3–11 % [60, 61]. Moreover, the deterioration rate for repeat PLIF (44 %) [62] is higher than that for initial PLIF (5.2–18.5 %) [59]. Biomechanical studies have demonstrated greater intradiscal pressure at the adjacent segment in double-level fusion than in single-level fusion [59]. This is one reason why repeat PLIF leads to higher incidence of ASD than the initial PLIF. Deyo et al. [63] reported in their study of 31,543 patients with surgery for lumbar stenosis that prior spinal surgery was the strongest risk factor for repeat surgery and that the hazard ratio for this was 1.58. These results suggest that patients undergoing repeat PLIF for ASD would incur more risk factors for additional surgery than those undergoing single- or double-level PLIF at the initial surgery. Furthermore, age was reported to be a major risk factor for ASD [59, 60].

31.7 A Comparison of PLIF and TLIF

Interbody fusion techniques have been developed to preserve the load-bearing capacity of the spine, restore local lordosis and facilitate compressive loading onto interbody graft – all of which enhance the potential for fusion acquisition [64]. Lumbar interbody fusion with supplemental posterior pedicle screw fixation (“circumferential” fusion), based on biomechanical evaluation, stabilises all three columns of the spine and has been used routinely for the operative treatment of painful spinal disorders. PLIF, TLIF and ALIF approaches are the most frequently performed options and, when accompanied by posterior pedicle screw fixation, result in circumferential fusion. Each of the former procedures has advantages and drawbacks.

Posterolateral graft and fixation is easily added to the PLIF, further enhancing spinal stability and the induction of fusion.

Unfortunately, the PLIF is usually limited to use at levels below L3, because of the risk of damage to the conus medullaris and to the cauda equina that may result from bilateral root retraction here. The suggested modification of PLIF presented by Harms and Jeszenszky [65], the TLIF, is equivalent to the PLIF and is simpler and safe, and some believe superior in result. The technical advantages of the TLIF include avoidance of thecal sac and/or nerve root retraction injury, safe performance below L3 and a decrease in epidural bleeding and scarring [65–67]. Harms and Jeszenszky, in their presentation of the original TLIF procedure, as well as many other authors of biomechanical reports, have recommended additional posterior pedicle screw fixation to enhance stability.

The PLIF and TLIF are familiar to most spine surgeons and both require only a single approach. These two procedures have therefore recently become the most popularly used techniques to treat spinal disorders. They are associated with a few differences with regard to the actual surgical technique, however. The TLIF requires a complete unilateral facetectomy and spares the contralateral lamina, facets, and pars interarticularis. The PLIF procedure requires a bilateral laminotomy as well as partial, and at times complete, facetectomy to place an adequate interbody spacer device. The TLIF implants are usually semilunar and only one is implanted, whereas those used for PLIF are cubic or cylindrical in shape and are placed in pairs resulting in a greater surface of bone graft and better distribution of loads. With the PLIF procedure, a portion of the posterior longitudinal ligament (PLL) is cut to position the interbody space devices, whereas the TLIF procedure preserves most of the PLL [68].

On the other hand, the diskectomy and clearing of end plates performed during PLIF procedure via bilateral approach are probably more complete and have better quality compared to TLIF.

From a biomechanical consideration perspective, Sim et al. showed that the PLIF provides a higher immediate stability than the TLIF, especially for the lateral bending motion. The implant position in the disk space, however, is not an important factor for the immediate stability of a single-level TLIF. If the TLIF implant is placed further anteriorly, although there were no statistically significant differences in this study, there is a tendency for this position to be more stable [68].

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