Mechanical implant failure in posterior cervical spine fusion

Frequency and predictors of implant-related complications after posterior cervical fusion

STUDY DESIGN

Retrospective, observational study.

PURPOSE

To determine the frequency and predictors of implant-related complications in adults after posterior cervical fusion.

OVERVIEW OF LITERATURE

Published literature on lumbosacral fusion suggest that implant-related complications are not uncommon. Although posterior cervical fusion is a common operation, data on frequency and predictors of implant-related complications after posterior cervical fusion is still scarce.

METHODS

86 patients (with 740 screws) who underwent posterior cervical fusion were included. Implant-related complications were identified by the presence of: (1) halo sign, (2) screw pull-out/breakage (3) post-operative kyphosis and (4) implant-related complications requiring revision surgery. These were stratified into two groups: (a) minor - isolated halo sign or screw pull-out/breakage (b) major - post-operative kyphosis > 10 degrees, and revision surgery. Demographic, operative and radiological data was collected. Rates of implant-related complications were determined and associated risk factors identified.

RESULTS

33 (38.4%) patients had signs of implant-related complications. Of these, 29 (87.9%) had minor complications and 4 (12.1%) had major complications. Charlson Comorbidity Index (CCI) (p = 0.03179) and pre-op C2-C7 sagittal vertical alignment (SVA) (p = 0.02449) were the only significant risk factors for all-cause implant-related complications during multivariate logistic regression. Other intraoperative parameters (type of screw, length of fusion, levels decompressed, and extension of fusion beyond the levels decompressed) were not significantly associated with implant-related complications.

CONCLUSIONS

Implant-related complications are not uncommon but rarely require revision surgery. Higher pre-operative SVA and CCI were significant risk factors; length of construct and extent of decompression were not. These findings may assist clinicians when deciding the extent of fusion and in selecting patients for closer follow-up.

The use of cervical interfacet devices and related clinical outcomes

PURPOSE

The purpose of this study was to investigate the outcomes of minimally invasive PCF using an interfacet joint fusion cage.

METHODS

The inclusion criteria consisted of patients who underwent a PCF using an interfacet device (Cavux, Providence Medical Technology Inc.) at a single institution and were at least 6 months postoperative. Charts were reviewed for pre-, intra- and postoperative data including arm and neck pain scores, Neck Disability Index (NDI), complications, and reoperations.

RESULTS

A consecutive series of 51 patients were included. Mean age was 54.9 years and 72.6% of patients (n = 37) were female. Most patients (n = 39, 76.5%) had a prior anterior cervical fusion resulting in pseudarthrosis. In total, 157 interfacet devices were implanted in 79 levels. There was statistically significant improvement from pre- to postoperative arm pain (3.8 vs. 2.4), neck pain (6.2 vs. 4.0), and NDI (42.2 vs. 34.9). With the exception of neck pain, these changes would not generally be considered clinically relevant. Ten (19.6%) reoperations occurred, with 4 (7.8%) involving interfacet device removal. The removals were due to: nonunion, device malpositioning, osteophytic overgrowth, trauma, and implantation of additional posterior instrumentation.

CONCLUSION

Performing a minimally invasive facet fusion may be an effective option for treating patients with a history of nonunion. Although the reoperation rate was high in this challenging cohort, only 4 out of 10 reoperations required device removal. More research is warranted to refine indications for this procedure and review larger samples of patients.

Postoperative Complications of Surgery for Cervical Spondylotic Myelopathy with and Without Athetoid Cerebral Palsy

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

With the aging of the Japanese population, patients with athetoid cerebral palsy (ACP) are getting older, and the rate of surgery for CSM is increasing in ACP patients. However, postoperative complications of such surgery among adult patients with ACP have not been reported yet. We investigated postoperative complications of surgery for CSM with ACP and compared them with those of surgery for CSM without ACP using a national inpatient database of Japan.

METHODS

Using the Diagnosis Procedure Combination database, we identified 61382 patients who underwent surgery for CSM from July 2010 to March 2018. We examined patient backgrounds, surgical procedures, and type of hospital, and a 4:1 propensity score matching was performed to compare the outcomes between the non-ACP and ACP groups.

RESULTS

There were 60 847 patients without ACP and 535 patients with ACP. The mean age was 68.5 years in the non-ACP group and 55 years in the ACP group. The percentages of patients who underwent fusion surgery were 21.6% and 68.8% in the non-ACP and ACP groups, respectively. The 4:1 propensity score matching selected 1858 in the non-ACP group and 465 in the ACP group. The ACP group was more likely to have postoperative urinary tract infection (.4% vs 2.8%, P < .001), postoperative pneumonia (.4% vs 2.4%, P < .001), and 90-day readmission for reoperation (1.9% vs 4.3%, P = .003).

CONCLUSIONS

We found that ACP patients were more vulnerable to postoperative complications and reoperation after CSM than non-ACP patients.

Pedicle screw pull-out testing in polyurethane foam blocks: Effect of block orientation and density

Synthetic bone models such as polyurethane (PU) foam are a well-established substitute to cadaveric bone for screw pull-out testing; however, little attention has been given to the effect of PU foam anisotropy on orthopaedic implant testing. Compressive and screw pull-out performance in three PU foam densities; 0.16 g/cm3 (PCF 10), 0.32 g/cm3 (PCF 20) and 0.64 g/cm3 (PCF 40) were performed in each of the X, Y or Z orientations. The maximum compressive force, stiffness in the linear region, maximum stress and modulus were determined for all compression tests. Pedicle screws were inserted and pulled out axially to determine maximum pull-out force, energy to failure and stiffness. One-way ANOVA and post hoc tests were used to compare outcome variables between PU foam densities and orientations, respectively. Compression tests demonstrated the maximum force was significantly different between all orientations for PCF 20 (X, Y and Z) while stiffness and maximum stress were different between X versus Y and X versus Z. Maximum pull-out force was significantly different between all orientations for PCF 10 foam. No significant differences were noted for other foam densities. There is potential for screw pull-out testing results to be significantly affected by orientation in lower density PU foams. It is recommended that a single, known orientation of the PU foam block be used for experimental testing.

Risk factors of instrumentation failure after laminectomy and posterior cervical fusions (PCF)

BACKGROUND

For patients with multilevel degenerative cervical myelopathy, laminectomy and posterior cervical fusions (PCF) with instrumentation are widely accepted techniques for symptom relief. However, hardware failure is not rare and results in neck pain or even permanent neurological lesions. There are no in-depth studies of hardware-related complications following laminectomy and PCF with instrumentation.

METHODS

The present study was a retrospective, single centre, observational study. Patients who underwent laminectomy and PCF with instrumentation in a single institution between January 2019 and January 2021 were included. Patients were divided into hardware failure and no hardware failure group according to whether there was a hardware failure. Data, including sex, age, screw density, end vertebra (C7 or T1), cervical sagittal alignment parameters (C2-C7 cervical lordosis, C2-C7 sagittal vertical axis, T1 slope, Cervical lordosis correction), regional Hounsfield units (HU) of the screw trajectory and osteoporosis status, were collected and compared between the two groups.

RESULTS

We analysed the clinical data of 56 patients in total. The mean overall follow-up duration was 20.6 months (range, 12-30 months). Patients were divided into the hardware failure group (n = 14) and no hardware failure group (n = 42). There were no significant differences in the general information (age, sex, follow-up period) of patients between the two groups. The differences in fusion rate, fixation levels, and screw density between the two groups were not statistically significant (p > 0.05). The failure rate of fixation ending at T1 was lower than that at C7 (9% vs. 36.3%) (p = 0.019). The regional HU values of the pedicle screw (PS) and lateral mass screw (LMS) in the failure group were lower than those in the no failure group (PS: 267 ± 45 vs. 368 ± 43, p = 0.001; LMS: 308 ± 53 vs. 412 ± 41, p = 0.001). The sagittal alignment parameters did not show significant differences between the two groups before surgery or at the final follow-up (p > 0.05). The hardware failure rate in patients without osteoporosis was lower than that in patients with osteoporosis (14.3% vs. 57.1%) (p = 0.001).

CONCLUSIONS

Osteoporosis, fixation ending at C7, and low regional HU value of the screw trajectory were the independent risk factors of hardware failure after laminectomy and PCF. Future studies should illuminate if preventive measures targeting these factors can help reduce hardware failure and identified more risk factors, and perform long-term follow-up.

Implant-Related Complications after Spinal Fusion: A Multicenter Study

STUDY DESIGN

Retrospective analysis of prospectively database.

OBJECTIVE

Implant-related complications are an extremely important issue because they pose a burden to patients who underwent surgery. An understanding of these complications can help improve the postoperative management of patients undergoing spinal surgery. The current large-scale multicenter study aimed to identify postoperative implant-related complications that may require revision surgery.

METHODS

In total, 3447 patients who underwent spinal fusion surgery were included in the analysis. Data about age at surgery, sex, preoperative diagnosis, surgical level, type of implant-related complications, causes of reoperation, and time from the initial to revision surgery were reviewed. Moreover, the characteristics of reoperation in 3 periods (within 30, 31-90, and over 90 days) were assessed.

RESULT

The overall incidence of implant-related complications was 4.6%. Adult spinal deformity was the most common diagnosis (9.9%), and thoracic-lumbar-sacral (42.9%) was the most common surgical level among patients with implant-related complications. Further, screw malposition was the most frequent implant-related complication (42.8%). In total, 89 (2.6%) patients underwent reoperation due to implant-related complications. The main causes of reoperation within 30, 31-90, and over 90 days were screw malposition (72.2%), screw loosening or pull out (81.8%), and rod or screw fracture (60.9%), respectively.

CONCLUSION

To the best of our knowledge, this was the first large-scale multicenter study that assessed the characteristics of patients who underwent reoperation due to spinal implant-related complications. The study results could improve the preoperative informed consent procedure about spinal fusion.

Two Cases of Degenerative Cervical Spondylotic Myelopathy in Adults with Athetoid and Dystonic Cerebral Palsy

BACKGROUND Patients with athetoid and dystonic cerebral palsy (ADCP) may develop degenerative changes in the cervical spine that can aggravate their neurological symptoms in adulthood. This report is of 2 cases of ADCP associated with degenerative cervical spondylotic myelopathy in a 39-year-old woman and a 52-year-old man, requiring different surgical treatments. CASE REPORT Case 1. The patient was a 39-year-old woman who had fallen down 7 years before surgery and had since been walking with a cane. Her gait disturbance had worsened in the 2 years prior to surgery, and numbness in her upper limbs appeared. In the year before surgery, spasticity and numbness in the lower limbs worsened, and fine motor impairment also appeared. Because of mild involuntary movements of the neck, cervical laminoplasty from C3 to C6 was performed, and her symptoms remained stable until the last follow-up 4.5 years after surgery. Case 2. The patient was a 52-year-old man who had fallen down 7 years before surgery, resulting in transient limb weakness. In the year before surgery, he had developed fine motor impairment. He subsequently developed gait disturbance and requested cervical surgery. Because of involuntary movements involving the neck and trunk, he underwent cervical posterior fusion from C2 to T1. Six months after surgery, the gait disturbance had improved. CONCLUSIONS This report describes 2 adults with a history of ADCP since birth and highlights that degenerative changes of the cervical spine can occur at a relatively early age in adulthood, requiring an individualized approach to management.

Clinical and radiographic benefits of skipping C7 instrumentation in posterior cervicothoracic fusion: a retrospective analysis

Background

C7 instrumentation during posterior cervicothoracic fusion can be challenging because it requires additional work of either placing side connectors to a single rod or placing two rods. Our clinical observations suggested that skipping instrumentation at C7 in a multi-level posterior cervicothoracic fusion will result in minimal intraoperative complications and decreased blood-loss while still maintaining sagittal balance parameters of cervical fusion. The objective of this study is to determine the clinical and radiographic outcomes of skipping C7 instrumentation compared to instrumenting the C7 vertebra in posterior cervicothoracic fusion.

Methods

This is a retrospective chart review of 314 consecutive patients who underwent multilevel posterior cervical fusion (PCF) at our institution. Out of 314 patients, 19 were instrumented at C7 serving as the control group, while the remaining 295 patients were not. Evaluation of efficacy was based on intraoperative complications, operative time, estimated blood loss (EBL), significant long-term complications, and radiographic evidence of fusion.

Results

Skipping the C7 level resulted in a significant reduction in EBL (488±576 vs. 822±1,137; P=0.007); however, operative time was similar between groups (174±95 vs. 184±86 minutes; P=0.844). Complications were minimal in both groups and not statistically significant. Radiographic analysis revealed C7 bridge patients had a significantly increased postoperative sagittal vertical axis (SVA) (29.3±13.1 vs. 20.2±3.1 mm; P=0.008); however, there was no significant difference between groups in SVA correction (-0.3±16.2 vs. -16.1±16.0 mm; P=0.867), T1 slope correction (3.4°±9.9° vs. 3.2°±5.5°; P=0.127), or cervical cobb angle correction (-5.7°±14.2° vs. -7.0°±12.2°; P=0.519). There were no significant long-term complications in either group.

Conclusions

Skipping instrumentation at C7 in a multilevel posterior cervicothoracic fusion is associated with significantly reduced operative blood loss without loss of radiographic correction. This study demonstrates the clinical benefits of skipping C7 instrumentation in posterior cervicothoracic fusion with maintenance of radiographic correction parameters.

A Novel Technique for Occipitocervical Fusion With Triple Rod Connection to Prevent Implant Failure

Occipitocervical fusion is an effective surgical method for treating various upper cervical disorders. However, complications such as implant failure due to rod breakage have been reported. Therefore, we devised a surgical technique for occipitocervical fusion with a triple rod connection to prevent implant failure. Occipitocervical fusion with triple rod connection was performed in two cases with a high risk of instability such as athetoid cerebral palsy and rheumatoid arthritis. A multiaxial screw (diameter: 4.5 mm) was inserted into the screw hole in the middle of the occipital plate, and subsequently, an additional rod was attached. It was connected to the main rod using an offset connector at the caudal side. The connection of the additional rod was simple and did not interfere with the fusion bed for bone graft between the occipital bone and axis. The head of the screw was crimped to the occipital plate, and the plate was firmly fixed. Moreover, since the head of the screw did not protrude to the dorsal side, the tension of the soft tissue and skin did not increase. No complications occurred after surgery in both cases. In addition, no special instruments were required to connect the additional rod to the main rod in this procedure. Therefore, our technique may be useful as an option to prevent implant failure due to rod breakage at the craniocervical junction.

Critical analysis of in vitro stability testing of spinal implants and proposal for standardization

BACKGROUND

The American Society for Testing and Materials (ASTM), considered the gold standard worldwide, requires only testing in physiological saline solution to simulate in vivo conditions in standard testing of spinal implants.

RESEARCH DESIGN AND METHODS

We conducted an in vitro study to identify an industrial lubricant with characteristics that are most similar to those of biologically lubricating fat, blood, and tissue fluids. The use of such a material could standardize the results of in vitro mechanical tests for better clinical applications.

RESULTS

Our study has shown that the lubricity of physiological saline was well below that of human soft tissues and tissue fluids, and among the motor oils, Castrol GTX3 provided a testing environment similar to that of a living organism.

CONCLUSIONS

With the intention of standardizing and preventing a biological hazard, we have developed a reproducible mechanical testing proposal based on our experiments, which, in addition, would allow us to avoid many misunderstandings and contingencies.

Mapping of Venous Sinus Anatomy and Occipital Bone Thickness for Safe Screw Placement in 100 Patients with 46,200 Standardized Measurements Using Computed Tomography Angiography

STUDY DESIGN

Retrospective descriptive study.

OBJECTIVE

The aim of this study was to create topographical maps of occipital bone thickness and venous sinus (VS) presence to assess the risks of screw insertion in four commercially available occipital plates.

SUMMARY OF BACKGROUND DATA

Craniocervical junction instability and deformity are serious pathological conditions that require posterior fixation of the occipital bone to the cervical vertebrae. Insertion of occipital bone screws requires evaluation of both occipital bone thickness for effective internal fixation and intracranial VS presence for vascular injury prevention. Despite the surgical risks, there is a paucity of research on safe screw placement.

METHODS

We created a matrix of 231 standardized measurement points to analyze the occipital bone thickness and VS presence in cervical spine CT angiograms. These measurements were used to create topographical maps of occipital bone thickness and likelihood of VS presence, which we then compared to the screw hole configurations of four occipital plates.

RESULTS

Hundred patients were assessed. Maximum occipital bone thickness of 13.9 ± 3.3 mm was midline in the occipital bone, 45 mm from the foramen magnum, around the external occipital protuberance (EOP). Regions with thicknesses >8 mm were 2 cm lateral to the EOP at the level of the superior nuchal line and 2.5 cm inferior to the EOP. The area with the highest VS presence rate was around the EOP and the superior nuchal line. The right transverse VS was more prominent in both sexes.

CONCLUSION

There is a limited area of the occipital bone with thicknesses for enough screw purchase. Previous studies have shown 8 mm as the minimum screw length to reduce the risk of implant failure. In our analysis, only "T"-shaped plates had configurations with thicknesses >8 mm for each screw hole. For every screw hole in the analyzed occipital plates, there was a possibility of VS presence ranging from 8% to 33%.Level of Evidence: 5.

Incidence and Risk Factors of Mechanical Complications After Posterior-Based Osteotomies for Correction of Moderate to Severe Adult Cervical Deformity: 1-Year and 2-Year Follow-up

BACKGROUND

Rigid cervical deformity (CD) requires multilevel and/or high-grade osteotomies and long-construct fusions to achieve adequate correction. The incidence of mechanical complications (MCs) remains incompletely studied.

OBJECTIVE

To define the incidence and risk factors for MC.

METHODS

A retrospective review of consecutive patients with CD who underwent correction from 2010 to 2018 was performed. Inclusion criteria were cervical kyphosis >20° and/or cervical sagittal vertical axis (cSVA) >4 cm. MCs (junctional kyphosis/failure, pseudarthrosis, and implant failure) and reoperation at 1 and 2 yr were examined.

RESULTS

Eighty-three patients were included. The mean age was 63.4 yr, and 61.0% were female. Fifty-three percent underwent 3-column osteotomies. After surgery, cervical parameters were significantly improved: cSVA (6.2 vs 3.8 cm, P < .001), cervical lordosis (6.3 vs -8.3°, P < .001), cervical scoliosis (CS) (6.5 vs 2.2°, P < .001), and T1 slope (41.7 vs 36.3°, P = .007). The MC rate was 28.9%: junctional (18.1%), implant (16.9%), and pseudarthrosis (10.8%). MC rates at 1 and 2 yr were 14.5% and 25.5%, respectively: junctional (9.6% and 17.6%), implant (9.6% and 17.6%), and pseudarthrosis (2.4% and 7.8%). The overall reoperation rate was 24.1%: 14.5% at 1 yr and 19.6% at 2 yr. Body mass index (BMI) (P = .015) and preoperative CS (P = .040) were independently associated with higher odds of MC. Receiver operating characteristic curves defined CS >5° to be the threshold of risk for MCs and reoperation.

CONCLUSION

Correction of CD is effective by posterior-based osteotomes, but MCs are relatively high at 1 and 2 yr. BMI >30 and preoperative CS >5° predispose patients for MC and reoperation.

Wandering rod: form lumbar spine into left pleural cavity with nerve irritated symptoms

Spinal instrumented rod migrating from the surgical site to another remote site in the body is rare. Some cases result in organ or blood vessel injury. Most reported cases were asymptomatic until the finally injuries were generated. We report a unique case of spinal implant failure in which the rod moved from lumbar spine into chest 13 years post lumbar instrumentation. The migrated rod caused no damage to the organs in the pleural cavity but did cause an atypical pleural irritation syndrome which seemed to correlate with the mechanical irritation caused by the rod. These atypical symptoms of rod migration have not been reported previously.

C2 quad-screws facilitate 4-rod fixation across the cervico-thoracic junction

Background:

Cervical spine deformity is a potentially devitalizing problem. Contemporary techniques for repair and reconstruction include fusion using rods of tapered diameter alone, or quadruple-rod constructs in which primary rods are joined to floating accessory rods by connectors. Here, we present how we utilized a quadruple-rod construct to perform five C2 to thoracic spine fusions.

Methods:

Our hospital electronic medical record revealed five patients who underwent the four rod C2-thoracic spine fixation. Patients ranged in age from 14-years-old to 78-years-old. The mean operative time was 715.8 min (range 549–987 min), and average estimated blood loss was 878 cc (range 40–1800 cc).

Results:

None of the five patients sustained any intraoperative complications, and none demonstrated progressive kyphotic deformity over the average follow-up interval of 8 months.

Conclusion:

We successfully treated five patients with degenerative or oncologic cervical pathology requiring fixation across the cervicothoracic junction utilizing a 4-rod C2-cervicothoracic fusion technique.

Complex Revision Surgery for Cervical Deformity or Implant Failure

Postoperative cervical deformity sometimes occurs in the short or long term after primary surgery for cervical disorders related to the degenerative aging spine, neoplastic etiologies, hemodialysis, infection, inflammation, trauma, etc. Cervical kyphosis after posterior decompression surgery, such as laminectomy or laminoplasty, is a common problem for spine surgeons. However, revision surgery for cervical deformity is definitely one of the most challenging areas for spine surgeons. There is no doubt that surgery for cervical deformity carries a high risk of surgery-related complications that might result in aggravation of health-related quality of life. Revision surgery is even more challenging. Hence, spine surgeons need to assess carefully the overall severity of the underlying condition before revision surgery, and try to refine the surgical strategy to secure safe surgery. Needless to say, spine surgeons are now facing great challenges in making spine surgery a much more reliable and convincing entity.

Acute Implant-related Complications in Pediatric Cervical Spine Fusion

BACKGROUND

The use of modern rigid instrumentation in pediatric cervical fusions decreases the risk of implant-related complications, both acute and long term. However, previous studies have indicated that acute implant-related issues still occur in the adult population. Reports of pediatric acute implant complications, occurring within 3 months of surgery, are under-represented in the literature. The purpose of this study is to document the prevalence of acute implant-related complications in a pediatric cervical fusion population.

METHODS

A retrospective review of instrumented cervical fusions from August 2002 to December 2018 was conducted. Acute implant-related complications were defined as malposition, fracture, or disengagement of cervical instrumentation, including screws, rods, and plates, within 90 days of surgery.

RESULTS

A total of 166 cases were included (55% male individuals) with an average age at surgery of 12.5 years (SD, ±5.28). Acute implant-related complications occurred in 5 patients (3%). All 5 patients had a syndromic diagnosis: Loeys-Dietz (n=1), osteopetrosis (n=1), neurofibromatosis (n=1), trisomy 20 (n=1), and achondroplasia (n=1). One case involved asymptomatic screw protrusion, 1 case lateral mass screw pull-out, 2 more had screw-rod disengagement, and the last experienced dislodgement of the anterior plate. The median time until the presentation was 25 days (range, 1 to 79 d). All patients (n=5) required surgical revision.

CONCLUSIONS

This case series suggests that the overall incidence of acute cervical implant failure is low. However, failure is more likely to occur in patients with underlying syndromes compared with patients with different etiologies. Intraoperative use of 3-dimensional computed tomography imaging is recommended to evaluate the screw position and potentially avoid later surgery.

The Role of Transverse Connectors in C1-C2 fixation for Atlantoaxial Instability: Is It Necessary? A Biomechanical Study

OBJECTIVE

To investigate the biomechanical effect of C1 lateral mass-C2 pedicle screw-rod (C1LM-C2PS) fixation with and without transverse connectors (TC) in an atlantoaxial instability (AAI) model.

METHODS

Ten freshly frozen cadaveric specimens were tested using an industrial robot under the following conditions: intact model, AAI model, C1-C2 model, C1-C2 with one TC model, and C1-C2 with two TCs model. Three types of motion, flexion-extension (FE), lateral bending (LB), and axial rotation (AR), were applied (1.5 Nm) to the specimens. The range of motion (ROM) and neutral zone (NZ) between C1 and C2 in all directions were measured.

RESULTS

Compared with those of the intact and AAI models, the C1-C2 ROM and NZ of all instrumented groups were decreased significantly in each direction of loading motion (P < 0.05). The mean FE ROM in the no TC, 1 TC, and 2 TC groups was 2.12° ± 0.41°, 2.29° ± 0.42°, and 2.04° ± 0.69°, respectively (P = 0.840, 0.981, 0.628, respectively); the mean LB ROM in the 3 intervention groups was 1.26° ± 0.67°, 1.02° ± 0.51° and 1.03° ± 0.57°, respectively (P = 0.489, 0.501, 1.000, respectively). During AR, the ROM and NZ of the no TC group (3.19° ± 0.89° and 1.51° ± 0.42°) were significantly reduced by more than 60% compared with those in the 1 (0.98° ± 0.28° and 0.40° ± 0.11°) and 2 TC groups (1.17° ± 1.69° and 0.42° ± 0.61°) (P < 0.001). Two TCs were equivalent for all loading motions to 1 TC (P > 0.05).

CONCLUSIONS

Adding TCs to C1LM-C2PS can effectively decrease the axial rotation ROM and enhance the stability of C1-C2 segment. Therefore, it is necessary to use TC-strengthened C1 lateral mass -C2 pedicle screw-rod fixation in patients with instability of C1-C2.

Time to recovery predicted by the severity of postoperative C5 palsy

OBJECTIVE

Postoperative C5 palsy affects 7%-12% of patients who undergo posterior cervical decompression for degenerative cervical spine pathologies. Minimal evidence exists regarding the natural history of expected recovery and variables that affect palsy recovery. The authors investigated pre- and postoperative variables that predict recovery and recovery time among patients with postoperative C5 palsy.

METHODS

The authors included patients who underwent posterior cervical decompression at a tertiary referral center between 2004 and 2018 and who experienced postoperative C5 palsy. All patients had preoperative MR images and full records, including operative note, postoperative course, and clinical presentation. Kaplan-Meier survival analysis was used to evaluate both times to complete recovery and to new neurological baseline-defined by deltoid strength on manual motor testing of the affected side-as a function of clinical symptoms, surgical maneuvers, and the severity of postoperative deficits.

RESULTS

Seventy-seven patients were included, with an average age of 64 years. The mean follow-up period was 17.7 months. The mean postoperative C5 strength was grade 2.7/5, and the mean time to first motor examination with documented C5 palsy was 3.5 days. Sixteen patients (21%) had bilateral deficits, and 9 (12%) had new-onset biceps weakness; 36% of patients had undergone C4-5 foraminotomy of the affected root, and 17% had presented with radicular pain in the dermatome of the affected root. On univariable analysis, patients' reporting of numbness or tingling (p = 0.02) and a baseline deficit (p < 0.001) were the only predictors of time to recovery. Patients with grade 4+/5 weakness had significantly shorter times to recovery than patients with grade 4/5 weakness (p = 0.001) or ≤ grade 3/5 weakness (p < 0.001). There was no difference between those with grade 4/5 weakness and those with ≤ grade 3/5 weakness. Patients with postoperative strength < grade 3/5 had a < 50% chance of achieving complete recovery.

CONCLUSIONS

The timing and odds of recovery following C5 palsy were best predicted by the magnitude of the postoperative deficit. The use of C4-5 foraminotomy did not predict the time to or likelihood of recovery.

Revision surgery in cervical spine

PURPOSE

To report the indications, presurgical planning, operative techniques, complications for making decisions in cervical revision surgery (CRS).

METHODS

Hundred and two patients underwent CRS over a four-year period. Epidemiological data, the type of first surgery, CRS surgical techniques and complications were retrospectively evaluated. Pain and neurological symptoms were assessed according to the validated Odom criteria. CRS indications were classified into five categories: adjacent segment disease (ASD), infection (INF), implant failure-pseudarthrosis (IFP), non-infectious complication, and deformity. Patients were classified into three groups, according to the approach of the index procedure: anterior, posterior, or 360°.

RESULTS

The mean patient age was 63 years (59% males). ASD (40%), INF (23%), and IFP (22%) were observed in 85% of patients. CRS was performed with the same approach that was used in the index procedure in 64% of the anterior group and in 83% of the posterior group. In the 360° group, 64% of CRSs was performed with a posterior access. The early complication rate was 4.9%. The outcome was excellent in 19 patients (19%), good in 37 patients (36%), satisfactory in 27 patients (26%), and poor in six patients (6%). Thirteen patients (13%) were lost to follow-up. No implants failed radiologically or required surgical revision.

CONCLUSIONS

CRS required painstaking planning and mastery of a variety of surgical techniques. The results were rewarding in half and satisfactory in a quarter of the patients. The complication rate was lower than expected. In the most complex cases, referral to a specialized center is recommended. These slides can be retrieved under Electronic Supplementary Material.

Effects of transverse connector on reduction and fixation of atlantoaxial dislocation and basilar invagination using posterior C1-C2 screw-rod technique

BACKGROUND CONTEXT

The mechanical strength provided by internal fixation is crucial for maintaining reduction and facilitating bony fusion. Though satisfactory results with the C1-C2 technique have been acquired in most clinical reports, the related problems of fusion delay and pseudarthrosis still exist. To increase the chance of bony fusion, a transverse connector (TC) is frequently used to augment torsional stiffness of thoracolumbar screw/rod constructs. Nevertheless, the clinical implication of TC in the management of atlantoaxial dislocation (AAD) and basilar invagination (BI) remains largely unknown.

PURPOSE

To evaluate the effects of TC application on C1-C2 screw-rod constructs based on consecutive adult patients with AAD and BI in a single institution over a 10-year period.

STUDY DESIGN

A retrospective study.

PATIENT SAMPLE

Patients with AAD and BI, who were treated with posterior C1-C2 screw-rod technique with or without TC usage from June 2007 to June 2017 at a single institution.

OUTCOME MEASURES

The radiological measurements included the anterior atlantodental interval (AADI), posterior atlantodental interval (PADI), height of odontoid process above Chamberlain line, and cervicomedullary angle (CMA). Patients' neurologic status was evaluated with the Japanese Orthopaedic Association (JOA) score. Fusion status was evaluated at different follow-up periods.

METHODS

We compared the difference of clinical, radiological, and surgical outcomes between the TC and NTC groups postoperatively.

RESULTS

In total, there were 149 consecutive patients in the TC group and 168 patients in the NTC group. On average, 1.2 TCs per patient were used in the TC group. No significant differences were identified for operative time and blood loss between groups. There was also no statistical difference in the radiological measurements of AADI, PADI, Chamberlain line, and CMA between the TC and NTC groups preoperatively and postoperatively. A significantly higher JOA score was obtained in the TC group than that in the NTC group postoperatively. The fusion rates were higher in the TC group than those in the NCT group at the early stage postoperatively (3 and 6 months; p<.01).

CONCLUSIONS

Use of TCs seems to improve bony fusion and neurologic outcomes in the treatment of AAD and BI with C1-C2 screw-rod technique.

Strength⁻Durability Correlation of Osteosynthesis Devices Made by 3D Layer Manufacturing

To develop orthopedic implants that are optimized for each patient’s needs or skeletal structure (custom-made implants), evaluations of the bending strength, bending stiffness, and durability of various types of conventional osteosynthesis devices have become important. Four-point bending tests and compression bending tests of osteosynthesis devices (bone plates, intramedullary nail rods, spinal rods, compression hip screws (CHSs), short femoral nails, and metaphyseal plates) were carried out to measure their bending stiffness, bending strength, and durability. The bending stiffness of bone plates, intramedullary nails, spinal rods, CHSs, short femoral nails, and metaphyseal plates increased with increasing bending strength. The durability limit of various types of osteosynthesis devices linearly increased with increasing bending strength. The relationship (durability limit at 10⁶ cycles) = 0.67 × (bending strength) (N·m) (R² = 0.85) was obtained by regression. The relationship for the highly biocompatible Ti-15Zr-4Nb-4Ta alloy was also linear. The mechanical strength and ductility of specimens that were cut from various osteosynthesis devices were excellent and their microstructures consisted of fine structures, which were considered to be related to the excellent durability. These results are expected to be useful for the development of implants suitable for the skeletal structure of patients using three-dimensional (3D) layer manufacturing technologies.

Revision surgery after rod breakage in a patient with occipitocervical fusion: A case report

RATIONALE

Rod breakage after occipitocervical fusion (OCF) has never been described in a patient who has undergone surgery for basilar invagination (BI) and atlantoaxial dislocation (AAD). Here, we present an unusual but significant case of revision surgery to correct this complication.

PATIENT CONCERNS

A 32-year-old female presented with neck pain, unstable leg motion in walking, and also BI with AAD. Her first surgery was planned to correct these conditions and for fusion at the occipital junction (C3-4) using a screw-rod system. At the 31-month follow-up after her first operation, the patient complained of severe neck pain and limitation of motion, suggesting rod breakage.

DIAGNOSES

Rod breakage after occipitocervical fusion for BI and AAD.

INTERVENTIONS

The patient underwent reoperation for replacement of the broken rods, adjustment of the occipitocervical angle, maintenance of the bone graft bed, and fusion.

OUTCOMES

At follow-up, the hardware was found to be in good condition, with no significant loss of cervical lordosis. At the 37-month follow-up after her second operation, the patient was doing better and continuing to recover.

LESSONS

We concluded that nonideal choice of occipitocervical angle may play an important role in rod breakage; however, an inadequate bone graft and poor postoperative fusion may also contribute to implant failure.

Comparison of Cervical Alignment and Clinical Outcomes in Patients with Os Odontoideum versus Non-Os Odontoideum after Atlantoaxial Fixation

OBJECTIVE

The purpose of this study was to compare the effect of atlantoaxial fixation on cervical alignment and clinical outcomes in patients with os odontoideum (OO) versus non-os odontoideum (non-OO).

METHODS

A total of 119 patients who underwent atlantoaxial fixation for instability were identified between January 1998 and January 2014. Inclusion criteria included age more than 21 years and diagnosis of OO and non-OO. There were 22 OO patients, and 20 non-OO patients. Measuring the Oc-C1 Cobb angle, C1-2 Cobb angle, C2-7 Cobb angle, and C2-7 sagittal vertical axis (SVA) was assessed. Clinical outcome was assessment of suboccipital pain was determined using a visual analogue scale (VAS), and Japanese Orthopedic Association (JOA) scores were obtained in all patients pre- and postoperatively.

RESULTS

The preoperative C1-2 angle in the OO group (26.02°±10.53°) was significantly higher than the non-OO group (p=0.04). After C1-2 fixation, the OO group had significantly higher kyphotic change in the C1-2 angle (ΔC1-2) (3.2°±7.3° [OO] vs. -1.46°±7.21° [non-OO]) (p=0.04), and higher decrease in postoperative C2-7 SVA (ΔC2-7 SVA) (5.64±11.56 mm [OO] vs. -0.51± 6.57 mm [non-OO]) (p=0.04). Both groups showed improvements in the health related quality of life (HRQOL) after surgery based on the VAS and JOA score (p<0.001).

CONCLUSION

After fixation, kyphotic angular change in atlantoaxial joint and decrease C2-7 SVA were marked in the OO group. Both the OO and non-OO groups improved in neurological function and outcome after surgery.

Three-dimensional finite element analysis of a newly developed aliform internal fixation system for occipitocervical fusion

For patients with occipital malformation, it is difficult to obtain reliable stability using three screws on the midline. A new aliform occipitocervical internal fixation system was designed. The occiput was fixed with 3, 7, or 11 screws, and a three-dimensional finite element model of the system was established. A compressive preload of 40N combined with a pure moment of 1.5Nm was applied to simulate normal flexion, extension, lateral bending, and axial rotation. The stress distribution across the screws on the occiput and the occipital displacement produced by the newly developed system were compared with those produced by the DePuy SUMMIT system. Compared with the SUMMIT system (control group), in the new system, the maximum stress on the occiputs fixed with 3 screws (group A) and 7 screws (group B) increased by 16.5% and 15.0%, respectively. In contrast, the maximum stress on the occiput fixed with 11 screws (group C) decreased by 15.6%. In addition, the maximum occipital displacements under extension decreased by 10.0%, 11.4%, and 11.8% in the A, B, and, C groups, respectively. Our results indicate that both group A and the control group exhibited sufficient strength and instant stability; however, group C exhibited the highest stability and the lowest maximum von Mises stress.

The Mechanical Effect of Rod Contouring on Rod-Screw System Strength in Spine Fixation

OBJECTIVE

Rod-screw fixation systems are widely used for spinal instrumentation. Although many biomechanical studies on rod-screw systems have been carried out, but the effects of rod contouring on the construct strength is still not very well defined in the literature. This work examines the mechanical impact of straight, 20° kyphotic, and 20° lordotic rod contouring on rod-screw fixation systems, by forming a corpectomy model.

METHODS

The corpectomy groups were prepared using ultra-high molecular weight polyethylene samples. Non-destructive loads were applied during flexion/extension and torsion testing. Spine-loading conditions were simulated by load subjections of 100 N with a velocity of 5 mm min(-1), to ensure 8.4-Nm moment. For torsional loading, the corpectomy models were subjected to rotational displacement of 0.5° s(-1) to an end point of 5.0°, in a torsion testing machine.

RESULTS

Under both flexion and extension loading conditions the stiffness values for the lordotic rod-screw system were the highest. Under torsional loading conditions, the lordotic rod-screw system exhibited the highest torsional rigidity.

CONCLUSION

We concluded that the lordotic rod-screw system was the most rigid among the systems tested and the risk of rod and screw failure is much higher in the kyphotic rod-screw systems. Further biomechanical studies should be attempted to compare between different rod kyphotic angles to minimize the kyphotic rod failure rate and to offer a more stable and rigid rod-screw construct models for surgical application in the kyphotic vertebrae.

New Ti-Alloys and Surface Modifications to Improve the Mechanical Properties and the Biological Response to Orthopedic and Dental Implants: A Review

Titanium implants are widely used in the orthopedic and dentistry fields for many decades, for joint arthroplasties, spinal and maxillofacial reconstructions, and dental prostheses. However, despite the quite satisfactory survival rates failures still exist. New Ti-alloys and surface treatments have been developed, in an attempt to overcome those failures. This review provides information about new Ti-alloys that provide better mechanical properties to the implants, such as superelasticity, mechanical strength, and corrosion resistance. Furthermore, in vitro and in vivo studies, which investigate the biocompatibility and cytotoxicity of these new biomaterials, are introduced. In addition, data regarding the bioactivity of new surface treatments and surface topographies on Ti-implants is provided. The aim of this paper is to discuss the current trends, advantages, and disadvantages of new titanium-based biomaterials, fabricated to enhance the quality of life of many patients around the world.

Morphological characteristics of cervical spine in patients with athetoid cerebral palsy and the accuracy of pedicle screw placement

STUDY DESIGN

A retrospective study.

OBJECTIVE

To investigate the morphology of the cervical spine in patients with athetoid cerebral palsy (CP), and to evaluate its relationship with the breach of cervical pedicle screws.

SUMMARY OF BACKGROUND DATA

Cervical pedicle screws have been increasingly used in surgery for patients with CP, but screw misplacement is not uncommon. Although the altered morphology of the cervical spine in patients with CP may result in this high breach rate, few studies have examined the cervical pedicle profile.

METHODS

We retrospectively analyzed 31 patients with cervical myelopathy with CP, as well as 30 patients with cervical spondylotic myelopathy (CSM), who underwent posterior decompression surgery. The pedicle outer diameter, inner diameter, transverse angle and lateral mass deformity were investigated by obtaining preoperative computed tomographic scans. The accuracy of the placement of 56 pedicle screws used in fusion surgery for 12 patients with CP was also analyzed using postoperative computed tomographic scans.

RESULTS

The outer diameter of the pedicle in CP was in the range from 3.3 to 9.6 mm, and was larger than that in CSM at all cervical levels except for C7. Pedicle sclerosis was more frequently observed in CP than in CSM (23% vs. 7.3%, P < 0.001). The transverse angle at C3 and C4 was larger, and lateral mass deformity was more frequently observed in CP than in CSM. The critical breach of pedicle screws in CP was found in 29%. A multivariate analysis revealed that pedicle sclerosis was associated with an increased risk of breach (odds ratio: 6.3; 95% confidence interval: 1.03-39.0; P = 0.047).

CONCLUSION

The pedicle diameter in patients with CP was relatively large, but pedicle sclerosis, a wide transverse angle and lateral mass deformity were frequently observed. Sclerotic pedicles were associated with a higher risk of critical breach.

LEVEL OF EVIDENCE

N/A.

Rod fracture after long construct fusion for spinal deformity: clinical and radiographic risk factors

BACKGROUND

No reports have been published on detailed risk factors for rod fracture after spinal deformity correction and fusion. The purpose of this study was to analyze clinical and radiographic risk factors of rod fracture after long construct fusion for spinal deformity.

METHODS

The survey subjects were 155 cases who were diagnosed with spinal deformity and underwent correction and fusion surgery with long construct instrumentation (>3 levels, average 10.3 levels) between July 2004 and June 2010. The subjects comprised 32 males and 123 females with a mean age of 19.0 (range 8-78) years. The mean Cobb angle was 61.0 ± 16.1° preoperatively and 25.7 ± 16.9° postoperatively. Univariate analysis and logistic regression analysis were performed.

RESULTS

Rod fracture occurred in 8 of 155 cases (5.2 %). The mean period from surgery to rod fracture was 18.1 months (range 2-37). The level of fracture ranged from the thoracolumbar junction to the lumbosacral vertebrae. Six patients had fracture near the fused lower end and two patients had fracture at the thoracolumbar junction. Univariate analysis revealed that non-ambulatory status, preoperative kyphosis, small-diameter rods, multiple surgery, and use of iliac screws were significant risk factors for rod fracture. Sex, obesity, severity of preoperative scoliosis, and rod material were not significant risk factors. Logistic regression analysis revealed that use of iliac screws (odds ratio: 81.9, 95 % confidence interval: 7.2-935.0, p < 0.001) and small-diameter (<6 mm) rods (odds ratio: 16.3, 95 % confidence interval: 1.7-152.6, p = 0.015) were risk factors for rod fracture.

CONCLUSIONS

The incidence of rod fracture after long construct fusion for spinal deformity was 5.2 %. Iliac screw fixation and small-diameter rods were risk factors for rod fracture.

Utility of postoperative radiographs for cervical spine fusion: a comprehensive evaluation of operative technique, surgical indication, and duration since surgery

STUDY DESIGN

A retrospective study.

OBJECTIVE

To assess the utility of postoperative radiographs in patients across a spectrum of cervical fusion procedures, surgical indication, and time since surgery.

SUMMARY OF BACKGROUND DATA

Postoperative radiographs are routinely obtained after cervical spine fusion despite lack of evidence supporting such practice. Studies assessing postoperative radiographical utility in the cervical spine have been limited. To date, no study has comprehensively evaluated the utility of obtaining such radiographs across multiple cervical fusion procedures.

METHODS

A total of 972 clinic notes from 301 patients during a 10-year period at a single institution were retrospectively reviewed. Patients in this study underwent an anterior cervical discectomy and fusion, anterior corpectomy and fusion, a combined anterior cervical discectomy and fusion and anterior corpectomy and fusion (hybrid), posterior spine fusion, or 360° fusion. All postoperative clinic notes and radiographs were reviewed for abnormalities and changes in treatment course. It was determined whether an abnormal radiograph alone led to a change in treatment course among the various operative techniques, surgical indication, or time since surgery.

RESULTS

No statistical significant difference in radiograph utility between anterior cervical discectomy and fusion (0 changes in treatment course due to radiograph alone out of 332 clinic notes), anterior corpectomy and fusion (0 of 140), hybrid procedure (1 of 72), posterior spine fusion (5 of 357), and 360° fusion (0 of 71) was found. Surgical indication (trauma vs. degeneration) and duration from surgery yielded no statistical significant difference in radiograph utility. The overall sensitivity, specificity, and positive and negative predictive values of radiographs were 33.8%, 87.6%, 19.0%, and 93.9%, respectively.

CONCLUSION

Regardless of operative techniques performed, surgical indication, and time since surgery, routine postoperative radiographs provide low utility in guiding treatment course in asymptomatic patients. Although radiographs may provide important diagnostic utility in certain individual cases, the results of this study provide further evidence that radiographs should not be considered routine during postoperative visits, thus minimizing unnecessary radiation exposure and medical costs.