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Table of Contents
Year : 2021  |  Volume : 18  |  Issue : 1  |  Page : 20-28

Diagnostic imaging review of postoperative complications after spinal surgery and instrumentation

1 Department of Radiology, St. John's Hospital, Kattappana, Kerala, India
2 Department of Medicine, INHS Kalyani, Visakhapatnam, Andhra Pradesh, India

Date of Submission21-Oct-2020
Date of Acceptance21-Dec-2020
Date of Web Publication15-Feb-2021

Correspondence Address:
Reddy Ravikanth
Department of Radiology, St. John's Hospital, Kattappana - 685 515, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/am.am_122_20

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A variety of surgical approaches are available for the treatment of spine diseases. Complications can arise intraoperatively, in the immediate postoperative period, or in a delayed fashion. These complications may lead to severe or even permanent morbidity if left unrecognized and untreated. Postoperative complications such as incomplete fusion, hardware failure, suboptimal positioning of instrumentation, infection, hematoma, and others may be detected at imaging. The article reviews the potential complications of spinal instrumentation, beginning with a description of biomechanics and an overview of surgical approaches and continuing with a discussion of various types of complications and their appropriate radiologic assessment. This systematic review describes the imaging features of immediate and delayed complications including instrumentation malpositioning.

Keywords: Failed back surgery syndrome, imaging in postoperative spine, postoperative spinal complications, spinal instrumentation

How to cite this article:
Ravikanth R, Majumdar P. Diagnostic imaging review of postoperative complications after spinal surgery and instrumentation. Apollo Med 2021;18:20-8

How to cite this URL:
Ravikanth R, Majumdar P. Diagnostic imaging review of postoperative complications after spinal surgery and instrumentation. Apollo Med [serial online] 2021 [cited 2021 May 18];18:20-8. Available from: https://www.apollomedicine.org/text.asp?2021/18/1/20/309564

  Introduction Top

Persistent low back pain after surgery can be a severe diagnostic and therapeutic problem. By using magnetic resonance imaging (MRI), many causes of this failed back surgery syndrome (FBSS) can be disclosed. MRI is superior to other imaging modalities in this concern.[1] The current review article describes the magnetic resonance (MR) technique, normal and abnormal findings of the postoperative lumbar spine, such as persistent or recurrent disc herniation, epidural scar, spinal stenosis, pseudomeningocele, arachnoiditis, pseudarthrosis, hematoma, and infection. An assessment with any imaging modality is facilitated by an understanding of spinal biomechanics.[2] By accurately identifying complications of spinal instrumentation, the radiologist can play an important role in the care of patients with persistent postoperative pain. Complications can occur throughout postoperative course. Early complications include hardware displacement, incidental durotomy, postoperative collections most commonly seroma, and less likely hematoma and/or infection. Hematomas, even when compressing the thecal sac, are usually asymptomatic. Early infection, with nonspecific MR findings, can be diagnosed accurately using dual radiotracer studies.[3] Delayed complications include loosening, hardware failure, symptomatic new or recurrent disc herniation, peri-/epidural fibrosis (EF), arachnoiditis, and radiculitis.[4]

  Methods Top

Literature review was conducted in accordance with PRISMA checklist and guidelines for reporting of systematic reviews.

Search strategies

A MEDLINE search for pertinent literature was conducted from January 1, 2000 until December 31, 2019 using studies with the following MeSH search term: Postoperative spinal complications. This was combined with the sub-terms “postoperative spinal complications,” “spinal instrumentation,” “imaging in postoperative spine,” and “failed back surgery syndrome” in a single search. Studies delineating the outcomes, nature, cause, and follow-up of immediate postoperative complications for spinal surgery techniques were considered.

Search criteria

The main sources of literature reviewed were retrospective and prospective studies published after 2000. Papers specifically delineating postoperative infections, complications related to hardware and instrumentation and FBSS were included as defined above. Complications were defined by a 90 days' postoperative window, a time period commonly defined in numerous complication studies. Among excluded studies were case reports, case series with <10 subjects, review articles, and papers published prior to 2000. All animal or lab research studies were deemed irrelevant to the study topic of interest and were excluded.

Statistical analysis

The estimation of postoperative and instrumentation related spinal complications leading to FBSS were assessed through an inverse variance weighted estimate of the pooled data (where applicable), using the random effects model.

  Results Top

Nineteen papers were identified in a PUBMED search with the aforementioned parameters evaluating complications of spinal surgery. After careful evaluation, 16 articles were included in the current systematic review. The most common indications for surgery were degenerative spondylolisthesis, scoliosis, and lumbar stenosis. In 1422 patients, there were 56 patients who had reported a postoperative neurologic deficit for a rate of 5.7%. Complications related to prosthesis in total disc replacement (including migration, subsidence, implant failure, and endplate fractures) are reported in 2%–39.3% of patients. Postoperative collections causing compression of the thecal sac is a common finding, occurring in 58% of cases. Minimally invasive surgery has an infection rate of 0.4% as compared to compared to 1.1% for the traditional open approach. Bone graft extrusion was seen in 2% of the cases in a study performed prior to the advent of titanium-threaded cage devices. Pedicle screws can fracture in 0.5% of cases. Pseudomeningocele formation occurs in 5.9% of disectomy cases and 43%of tethered spinal cord release cases. Chronic adhesive arachnoiditis is a cause of persistent pain in 6%–16% of postsurgical cases. The average rate of reported neurologic complications within these papers was 9% (range 0.46%–24%).

  Discussion Top

Thoracolumbar spinal instrumentation [Figure 1]
Figure 1: Two-column instability. Anteroposterior radiograph shows instability above the level of successful fusion in a 64-year-old woman who underwent laminectomies at L1 through L5 and posterior lumbar interbody fusion at L4 through S1

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Surgical techniques for thoracolumbar spinal fusion and instrumentation include transforaminal lumbar interbody fusion, posterior lumbar interbody fusion, extreme lateral interbody fusion, and anterior or anterolateral lumbar interbody fusion with anterior plate or posterior percutaneous screw insertion. Pedicular screw insertion is the current standard for posterior instrumentation, affording strong fixation and a high fusion rate.[5] The funnel technique is widely accepted for safe insertion of pedicular screws. In this technique, taps of gradually increasing diameter are used to assess the quality of cortical purchase through the isthmus of the pedicle, and image intensification is used to assess the length of the screw necessary to obtain purchase in the vertebral body but not through the anterior vertebral cortex to avoid the risk of major vessel injury. The pedicular screws are connected with plates or rods with the option of cross-linking bars for additional stability. Transfacet or translaminar facet screws are applied to position the hardware with minimal muscle dissection. An interspinous spacer is another posterior implant used in spinal stenosis to decrease the facet loa.[6] Other techniques include the use of a hook system in patients with osteoporosis, Cotrel-Dubousset instrumentation (curved rods with connecting hooks), and Luque rods for treatment of neuromuscular scoliosis.[7]

Cervical spinal instrumentation

Anterior cervical discectomy with fusion is widely used for treatment of cervical spondylosis, fractures, and disk abnormalities. Iliac crest bone grafts or synthetic cages of titanium, carbon fibers, or biopolymers filled with cancellous bone are used to replace disk space with or without anterior plate and screw insertion. The same anterior approach can also be used for odontoid fracture fixation with anterior screws and for corpectomy with expandable or titanium mesh cage reconstruction. Anterior cervical disk replacement is an alternative treatment of radiculopathy or myelopathy caused by either one or two levels of anterior cervical compression.[8] Posterior cervical elements can be stabilized with wiring systems (interspinous, facet, sublaminar, and interlaminar clamps), lateral mass screws with connecting plates or rods, or with cervical pedicular screws. Pedicular screws are usually used in C2 and C7 vertebrae, in which the risk of vertebral arterial injury is lower than for other cervical vertebrae.[9]

Artefacts[Figure 2]
Figure 2: Antero posterior (a) and lateral digital radiographs (b) of the lumbosacral spines with posterior lumbar interbody fusion showing LV3 through LV5 levels laminectomies with fine posteriorly located bone chips (arrows) on anteroposterior view that are difficult to appreciate on lateral view. Note the magnetic susceptibility artifact on magnetic resonance imaging images (c, d)

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Hardware material composition and size affect both computed tomography (CT) and MR artefacts. Titanium alloy is both less dense and less magnetic than stainless steel, resulting in less streak artefact from beam hardening on CT and less magnetic field distortion on MR. Metallic artefact is related to density, with less CT artifact resulting from less dense materials. Materials can be arranged in ascending artefact in the following order: Plastic < titanium < vitallium < stainless steel < cobalt-chrome.[10] Less beam hardening occurs with stronger CT tube voltage, so images should be acquired at 120–140 kilovoltage (kVp) rather than 80 kVp, with the consequence of doubling of the radiation dose. In addition, CT acquisition parameters include high tube charge, lower pitch, and thin sections, also with the consequence of increased dose. Controlling CT postprocessing parameters such as thicker sections, soft tissue instead of bony reconstruction kernels, and extended CT Hounsfield scale can further reduce artefacts.[11] Advances in CT technology allow for higher currents, improving imaging in obese patients. Although not widely available yet, dual energy CT has significant potential to reduce metallic artefacts. Sinogram inpainting methods have also been shown to reduce CT metallic artifact.[12]

MR may demonstrate metallic artefacts even when no hardware is placed, arising from tiny metallic drill bit fragments in postoperative beds. Susceptibility artefacts may result in a loss of signal in phase direction by intravoxel dephasing and spatial misregistration in the frequency encoding and slice selection gradient. Specific MR artefacts are related to hardware composition, orientation and shape, MR magnet field strength, and imaging sequence type and parameters. Since artefacts are significantly fewer when the hardware is perpendicular to the magnet, there are fewer artefacts caused by pedicle screws at the L1–L3 levels compared to L4–S1.[13] Spherical implants result in greater artefacts than cylindrical ones. Fast spin echo (FSE) sequences have fewer artefacts than conventional spin echo (SE) or gradient echo (GE) sequences. Fat suppression with short time inversion recovery (STIR) has fewer artefacts than frequency-selective fat saturation. Artefacts are proportional to the magnet strength, so imaging should be preferentially performed on 1.5-T scanners. However, higher gradient strengths and broader receiver bandwidths with newer coils can offset the greater artefact effect at 3.0 T.[14] For any sequence, artefacts can be minimized by using a small field of view, high-resolution matrix, and thin sections. Advanced artefact reduction techniques include view angle tilting, slice encoding for metal artefact correction, multi-acquisition variable-resonance image combination, single-point imaging, prepolarized imaging, and dual reversed-gradient acquisitions. View angle tilting corrects for intra-slice (in-plane) distortion and is used in combination with slice encoding for metal artefact correction, which corrects for adjacent slice (through-plane) distortions.[15]

Imaging techniques

The increasing use of metal orthopedic hardware in spine surgery makes it necessary to adjust some technical parameters to reduce artifacts from this hardware.[16]

Conventional radiography

Conventional radiography is the most commonly used imaging modality. In patients who undergo laminectomy and/or discectomy, radiography during surgery to confirm the level may be the only imaging technique used in the absence of suspicion of complications. Conventional radiography (X-ray) is particularly useful in surgery involving metal hardware because it is not biased by the artifact produced by the hardware in other techniques such as CT and MRI.

Computed tomography

CT is the modality of choice for bone and abnormal calcification assessment. CT requires intravenous iodine contrast in case of suspected infection. The severity of the artifact produced by metal orthopedic hardware on CT depends on multiple factors such as the image reconstruction algorithm, kVp, milliamperage, and pitch, as well as hardware composition. A number of technical aspects should be therefore taken into account for artifact reduction on CT Images:

  • •Multichannel CT shortens examination time, and minimizes motion artifacts
  • •Acquisition with the thinnest slice thickness possible using isotropic voxels allows for more accurate z-axis resolution and for multiplanar and volumetric reconstructions with high spatial resolution
  • •An increase in kVp results in a higher beam penetration. This measure should be taken carefully in young patients and patients undergoing multiple examinations
  • •Lowest pitch possible and CT with the highest number of channels
  • •Data should be acquired with a soft-tissue reconstruction kernel to reduce artifacts. Using a bone kernel in the postprocessing allows for better assessment of bone structures.

Orthopedic hardware with lower attenuation coefficient results in less distortion. Titanium produces less distortion than stainless steel, which in turn produces less distortion than cobalt-chrome.[17]

Magnetic resonance imaging

MRI is the modality of choice, especially in cases where postoperative complications are suspected. The high spatial and contrast resolution of MRI allows for better evaluation of soft tissues, bone marrow, and intraspinal content. Metal orthopedic hardware produces magnetic susceptibility artifacts. The technical aspects to be considered for artifact reduction are the following:

  • •FSE sequences are better than conventional SE sequences, and these latter are better than GE sequences. The echo time (TE) and repetition time (TR) used in these sequences vary with the MRI equipment, and their values can be modified within a range. The shortest TE possible is recommended for metal artifact reduction in SE sequences. FSE sequences require longer TR than conventional sequences
  • •T2-weighted sequences
  • •A relatively short (<10) echo train should be used
  • •The field of view and the voxel volume should be increased and reduced, respectively
  • •Magnetic field with low intensity

  • •Short time inversion recovery (STIR) sequences should be used for fat suppression, since sequences based on selective fat saturation pulses are associated with poor homogeneity
  • •In addition, the phase encoding direction in both the axial and sagittal planes should be parallel to the long axis of the orthopedic material, since the artifact produced will be linear and parallel to the metal material, therefore with less interference with image assessment. At MRI, titanium, and vitallium hardware produce fewer artifacts than stainless steel.[18]

Evaluation of postoperative spine

After spine surgery, patients may have full resolution of lumbar pain. If this is not the case, FBSS occurs. This is a general term that refers to patients with recurrent symptoms or in whom surgery failed to fully correct the problem. Although there are a large number of potential causes, in most cases this syndrome has a multifactorial etiology. The FBSS is observed in 10%–40% of postoperative patients.[19] Depending on the type of initial surgery and symptoms, most patients undergo one or more imaging examinations (X-ray, flexion-extension x-ray, CT, myelography, and MRI).

Normal radiological findings in postoperative spine [Figure 3]
Figure 3: Normal findings following lumbar spine surgery. 45-year-old male who underwent left L5 hemilaminectomy. Unenhanced and contrast-enhanced T1-weighted sequences at 1 month (a and b) and 3 years after surgery (c and d). Perineural inflammatory tissue is observed in the early postoperative period (arrows) and spontaneous partial resolution after 3 years (arrows)

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The most common lumbar spine surgical procedures are laminectomy, discectomy (with removal of herniated material and/or native disc), fusion, and orthopedic hardware placement. A mid-line approach is the most common approach for lumbar spine surgery, and asymmetry of muscles and fat as well as small seromas and edema of the subcutaneous cell tissue are usually observed. During the first 30–60 days, this may determine a certain posterior mass effect on the thecal sac that will decrease over time.[20] MRI is the modality of choice for assessment of discectomies. Determination of time elapsed after surgery is particularly important, since findings in the early postoperative period (6 months) require cautious evaluation. However, MRI is indicated during this period if the patient presents with FBSS. For noncontrast MRI images, early postoperative changes following discectomy may simulate the previously removed herniated material as a result of the disruption in the fibrous annulus and the presence of epidural edema. Following contrast administration, the homogeneous enhancement of this fibrosis and granulation tissue explains the observed mass effect that will progressively decrease.

The edema and enhancement of the vertebral endplates are observed in 19% of patients between 6 and 18 months following surgery.[21] In 20%–62% of patients, enhancement of the nerve roots is observed between 3 and 6 weeks following surgery.[22] This enhancement progressively decreases, and therefore any enhancement observed after six is considered pathological. The findings described, which are considered normal during the postoperative period, should be distinguished from those associated with early discitis. In these cases, symptoms, laboratory data, and if necessary, biopsy of the suspicious area should be correlated. Enhancement associated with bacterial discitis is typically more intense than that reported during the normal postoperative period in asymptomatic patients. A fluid collection with a paraspinal or anterior epidural location or located adjacent to the disc involved and enhancement of the psoas are usually indicative of infection. In the area of laminectomy, the dural sac may slightly bulge through the bone defect, which should not be confused with a pseudomeningocele.

Abnormal findings in postoperative spine

Complications associated with instrumentation and improper hardware placement [Figure 4]
Figure 4: Misplacement of the orthopedic hardware. Axial computed tomography in the immediate postoperative period of a 58-year-old female who underwent laminectomy and L4, and L5 transpedicular screw placement. The patient had a very poor postoperative outcome with severe pain at right L5 and S1 level. Misplacement of the right L5 pedicle screw that invades the spinal canal

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Given the technical difficulties of placing instrumentation in the spine, it is inevitable that complications sometimes arise from malpositioning of hardware. The radiologist should systematically assess the integrity of neural and vascular structures throughout the spine, including the neural foramina, thecal sac, central cord and cauda equina, and foramen transversarium, as well as adjacent structures such as the major abdominal vessels, psoas musculature, posterior mediastinum, and prevertebral soft tissues.

Pedicle screws, in particular, deserve attention because of their frequent use and proximity to sensitive neural and vascular structures. Lonstein et al.,[23] reported an overall complication rate of 2.4% per screw in a retrospective review of clinical outcomes with the placement of 4790 pedicle screws. The most common complication was nerve root irritation from medial angulation of the screw with resultant violation of the medial cortex of the pedicle.

Optimal screw placement is typically along the medial aspect of the pedicle.[24] The instrumentation gains purchase from its proximity to cortical bone but should not disrupt it; the tip of the pedicle screw should approach but not breach the anterior cortex of the vertebral body. Loosening of pedicle screws often may be seen as a rim of lucency around the screw threads. Complications may arise from medial or lateral deviation of a screw or from its penetration of the anterior cortex of the vertebral body. Similar complications may arise from malpositioning of anterior cervical plates and screws, which may penetrate the adjacent disk space, foramen transversarium, spinal cord, or nerve roots. Graft material in either case also may herniate anteriorly or posteriorly (depending on the approach used for placement) and cause neurologic compromise. The radiologist should consider potential surgical interventions and should provide surgically relevant information when reporting findings at preoperative imaging. In reporting cases of spinal stenosis, it is important to describe the structures that are causing canal compromise.

Infection [Figure 5]
Figure 5: Status postoperative laminectomy with discectomy with postoperative fungal infection. T1 sagittal (precontrast, T2 sagittal and post contrast fat saturated T1 sagittal magnetic resonance imaging sequences: Spondylodiscitis L4–L5 with T2 short tau inversion recovery hyperintensity with anterior epidural and prevertebral necrotic collection with intense contrast enhancement of l4 and l5 bodies and end plates and L4–L5 disc (arrows)

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If the patients show the early signs of infection, sequestrated bones, loose pedicle screws and unnecessary instruments should be removed, but necessary instruments (removing of which may cause instability) should be kept in place. If the infection is an early one, sequestrated bones and loose pedicular screws and unnecessary instruments should be removed, expect for the necessary instruments that should be kept in place, since removing those could lead to instability. In case of late infections, especially more than 37 weeks, the instruments should be removed, because arthrodesis has already happened. Studies recommend that instrument removal is not necessary in acute infections and they should be remained until arthrodesis occurs.[25] Other studies recommend removing instruments in patients with several debridement procedures who did not respond to antibiotic therapy.[26]

Discitis is a rare after surgery complication with incidence rate of 0.2%–2.75%.[27] Percutaneous aspiration with imaging guidance identifies the organism in charge as a potential guide to proper antibiotic choosing. Most patients with discitis will be treated by proper antibiotic for 6 weeks and spontaneous fusion usually occurs in the disk space. Spine surgery site infection treatment with antibiotics should be continued for 6 weeks after debridement and if the organism is resistant to treatment including the methicillin-resistant Staphylococcus aureus, parenteral antibiotic treatment for 8 weeks is recommended.[28] All deep infection sites in spine operations are in need of long-term treatment with antibiotics.

Postoperative collections [Figure 6]
Figure 6: Postoperative axial (left) and sagittal (right) T2-weighted magnetic resonance image of the cervical spine showing a significant fluid collection overlying the C2–T1 levels consistent with a seroma

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Epidural and paraspinal abscesses like psoas abscesses, even small ones, may not respond to medical treatment; however, aspiration and drainage under CT guidance are only recommended for large collections. Reoperation and debridement of all necrotic tissue with large amount of saline irrigation is recommended for patients with surgical site infection harboring screw, rod, and fusion.

Accelerated degenerative changes [Figure 7]
Figure 7: Accelerated degenerative changes. 64-year-old female who underwent laminectomy and multilevel arthrodesis. Sagittal spine radiographs demonstrate marked degenerative changes in the intervertebral endplates and anterior vertebral bodies at multiple disc levels

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Degenerative disc changes and arthrosis of interapophyseal joints in the segments adjacent to the postoperative segments are observed. These changes are more common after spinal fusion than decompression, and they are caused by stress and altered biomechanics following fusion. Radiography is the first imaging modality used for the evaluation of these changes. MRI is more accurate in assessing changes in soft tissue and disc contour. The findings are similar to those seen in degenerative changes secondary to other reasons, including intervertebral space narrowing, ex vacuo phenomena, osteophytes, facet arthrosis associated with foraminal stenosis, misalignment, Modic changes in the adjacent vertebral endplates, disc contour abnormalities, and spinal canal stenosis.

Spondylolisthesis [Figure 8]
Figure 8: Spondylolisthesis. 61-year-old male who underwent laminectomy and L4 and L5 transpedicular screw placement, and presented with recurrent pain. Computed tomography sequences with reconstructions on the sagittal plane performed two (a) and three (b) years after surgery. The follow-up demonstrates increased anterolisthesis of L3 onto L4 (arrows)

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In patients without overt preexisting instability, laminectomy for lumbar stenosis can disrupt spinal stability and result in iatrogenic spondylolisthesis. The extent of decompression of the facet joints, number of levels decompressed, and preoperative disc space height can help assess the risk of postoperative spondylolisthesis. Patients who develop recurrent radiculopathy after decompressive lumbar laminectomy should be evaluated for potential iatrogenic spondylolisthesis.

Epidural fibrosis [Figure 9]
Figure 9: Epidural fibrosis in a 61-year-old male who underwent laminectomy at L4–L5. Diffuse homogeneously enhancing posterior epidural T2 hypo intense soft tissue at laminectomy site, clumping of nerve roots appears adherent to dura at laminectomy level

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EF is one of the most common causes of FBSS, and it is the causative factor of pain in up to 36% of FBSS patients.[29] EF usually results from dural sac compression, nerve root tethering, or from interference with the nerve root vascular supply or cerebrospinal fluid flow. Once the fibrosis forms, there is no effective treatment, and fibrous tissue excision surgery can also cause new EF. Criteria for EF identification included iso to hypointense signal relative to inter-vertebral discs on T1-weighted MR images, replacing the epidural fat signal intensity. EF was fairly homogeneous. Both EF and disc protrusions may show mass effect, especially in early stages of granulation tissue formation. Aging of the EF may result in retraction of the dural toward the side of the scar. EF was enhanced immediately after the injection of gadolinium, in contrast to recurrent herniation, which shows delayed enhancement.

Recurrent disc herniation [Figure 10]
Figure 10: Recurrent disc herniation. 52-year-old female who underwent laminectomy and L5-S1 discectomy. Follow-up magnetic resonance imaging was performed 20 days after surgery due to persistent lumbar pain radiating to the left lower extremity. The axial T1-contrast image shows a persistent-recurrent left parasagittal disc herniation connected to the left S1 nerve root at the lateral recess level. Note the peripheral enhancement of the herniated material

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The recurrence rate in lumbar disc herniations (LDH) has been reported to be 5%–25%.[30] The most affected segment is L4/5.[31] Occasionally, as a result of the enormous compression of the epidural veins in to the spinal canal through the Lumbar Disc Herniation, significant postoperative bleeding with considerable compression of the neural structures as well as an early Lumbar Disc Herniation recurrence may occur after decompression.

Pseudomeningocele [Figure 11]
Figure 11: Pseudomeningocele. Thirty-six-year-old female who underwent surgery for L5-S1 disc herniation. Postoperative magnetic resonance imaging image with sagittal T2-weighted sequence, which demonstrates a postoperative pseudomeningocele on the bed of the left S1 laminectomy. Magnetic resonance imaging sensitivity is higher than sensitivity of any other imaging techniques, and allows for visualization of the communication between lesion and thecal sac

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Lumbar pseudomeningocele is an extradural cystic collection of cerebrospinal fluid with no dural covering. It results from a breach in the dura–arachnoid layer. This rare complication results from a dural rent or dehiscence after laminectomy. The interval between primary surgery and the formation of a pseudomeningocele usually ranges from a few months to years.[32] The size of the pseudomeningocele depends on the size of the dural tear and also on the level of incidental durotomy. The lumbar spine has a higher intraspinal pressure in erect posture, and hence there is a greater incidence of pseudomeningocele formation noted at this level.

Loosening [Figure 12]
Figure 12: 63-year-old male who has undergone fusion of L2–L5. Axial computed tomography image shows characteristic signs of loosening of right pedicle screw at L2. Arrowheads point to sclerotic rim around area of bone resorption, indicating loosening

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Loosening is defined radiographically as a lucent rim of 2 mm or greater surrounding the hardware, particularly when this lucency enlarges on sequential studies.[33] It is best visualized on CT or plain radiographs. Loosening of vertebral body screws in older anterior constructs without locking screw plates may result in the backing out of the screw. Nuclear medicine bone scintigraphy demonstrates increased radiotracer uptake at sites of motion. Functional fusion, defined as <3° of motion between flexion and extension views performed 8–16 weeks postoperatively, depends on patient cooperation and can be underestimated by muscle guarding/spasm. Osseous fusion is demonstrated radiographically by bridging trabecular bone. Premineralized osteoid resulting in functional fusion is radiolucent, with radiographically evident fusion not evident until 6–9 months postoperatively.[34] Centrally interrupted trabeculation can suggest motion, delayed union, and/or early pseudoarthrosis. Radionuclide scintigraphy may suggest pseudoarthrosis or loosening with tracer uptake seen beyond a year postoperatively. Interbody implants appear to float in the early postoperative period and do not indicate loosening.

Chronic adhesive arachnoiditis [Figure 13]
Figure 13: Chronic adhesive arachnoiditis of cauda equina in the L4-S1 segment as a postoperative complication. Patient presented with right lower limb pain, without any nerve root compression on the mentioned side

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Chronic adhesive arachnoiditis is cited as an important cause of recurrent pain and disability after extradural lumbar disc surgery. The causes of spinal arachnoiditis are varied and include infection, intrathecal steroids or anesthetic agents, trauma, surgery, and intrathecal hemorrhage.[35] Arachnoiditis is a dynamic process involving a spectrum of collagen deposition and fibrosis, ranging from minimal changes such as contrast enhancement of the dural tube or clumping of two or three roots to a soft tissue mass involving roots and meninges.

Neurological defects

The risk of neurologic deficit is a major concern for patients undergoing spinal surgery. Incidence of such complication is low, and is reversible in some cases. As in other reports, this feared complication occurred in high-risk cases, including deformity correction, thoracotomy procedures, and cases of metastatic tumor with prior radiation.[36] The use of intraoperative neurologic monitoring has become a standard of care in such high risk procedures. Meticulous technique and proper attention to intraoperative details help maintain the probability of such complication low, and timely and expedient correction of the causative factor, if found, increases the chances of recovery should a deficit occur. The etiology of neurologic injury during spinal surgery includes direct surgical trauma to the neural elements; compression and/or distraction of the vertebral column; vascular compromise, including intra operative or postoperative hypotension; compressive spinal epidural or subdural hematoma; and mechanical compression from infolding of the ligamentum flavum, posterior longitudinal ligament, and disc or adjacent bony structures.

  Conclusion Top

Spine surgery is being increasingly performed and imaging evaluation of the postoperative spine has evolved significantly in the past decade. Advances in CT and MRI with reduction of image degradation due to hardware-related artefacts have improved the evaluation of the postoperative spine and early detection of complications. Effective follow-up and diagnosis of postoperative complications requires radiologists to have thorough knowledge of the patient's symptoms and the type of surgery and to use a systematic approach to evaluation of the entire spine and adjacent structures. Radiography remains the primary modality for routine follow-up, but MDCT has become the standard for optimized postoperative assessment of implants, and MRI plays a major role in diagnosing complications such as infection and soft-tissue lesions.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13]

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Raju Vaishya,SatishKumar Agarwal
Apollo Medicine. 2021; 18(1): 1
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