Reliability of clinical measurement for assessing spinal fusion: an experimental sheep study

A smart coating with integrated physical antimicrobial and strain-mapping functionalities for orthopedic implants

The prevalence of orthopedic implants is increasing with an aging population. These patients are vulnerable to risks from periprosthetic infections and instrument failures. Here, we present a dual-functional smart polymer foil coating compatible with commercial orthopedic implants to address both septic and aseptic failures. Its outer surface features optimum bioinspired mechano-bactericidal nanostructures, capable of killing a wide spectrum of attached pathogens through a physical process to reduce the risk of bacterial infection, without directly releasing any chemicals or harming mammalian cells. On its inner surface in contact with the implant, an array of strain gauges with multiplexing transistors, built on single-crystalline silicon nanomembranes, is incorporated to map the strain experienced by the implant with high sensitivity and spatial resolution, providing information about bone-implant biomechanics for early diagnosis to minimize the probability of catastrophic instrument failures. Their multimodal functionalities, performance, biocompatibility, and stability are authenticated in sheep posterolateral fusion model and rodent implant infection model.

The efficacy of platelet-rich plasma applicated in spinal fusion surgery: A meta-analysis

Objective

The purpose of this meta-analysis is to evaluate the effect of the application of platelet-rich plasma (PRP) in spinal fusion surgery on the fusion rate of the spine.

Methods

A comprehensive search of the PubMed, Embase, Cochrane Library, and Science Direct databases was conducted to identify randomized control trials (RCTs) or observational cohort studies that evaluated the efficacy and safety of PRP in spinal fusion. Data on final fusion rate, changes in the visual analog scale (VAS), estimated blood loss (EBL), and operative time was collected from the eligible studies for meta-analysis. Patients were divided into PRP and non-PRP groups according to whether PRP was used during the spinal fusion procedure.

Results

According to the selection criteria, 4 randomized controlled trials and 8 cohort studies with 833 patients and 918 levels were included. The outcomes indicated that PRP application is associated with a lower fusion rat (OR = 0.62, 95% CI: (0.43, 0.89), P = 0.009) at final follow-up (>24 months). Subgroup analysis showed a lower rate of spinal fusion in the PRP group compared to the non-PRP group (OR = 0.35, 95% CI: (0.21, 0.58), P < 0.001) when spinal fusion was assessed using only anterior-posterior radiographs. When the bone graft material was a combination of autologous bone + artificial bone, the spinal fusion rate was lower in the PRP group than in the non-PRP group (OR = 0.34, 95% CI: (0.16, 0.71), P = 0.004). The PRP and non-PRP groups showed no significant differences in VAS changes at the 24th postoperative month (WMD = 0.36, 95% CI: (−0.37, 1.09), P = 0.33); Application of PRP does not reduce the estimated blood loss (WMD = −86.03, 95% CI: (−188.23, 16.17), P = 0.10). In terms of operation time, using PRP does not prolong operation time (WMD = −3.74, 95% CI: (−20.53, 13.04), P = 0.66).

Conclusion

Compared with bone graft fusion alone, PRP cannot increase the rate of spinal fusion. Inappropriate methods of spinal fusion assessment or mixing PRP with artificial/allograft bone may have been responsible for the lower rate of spinal fusion in the PRP group.

Systematic Review Registration

doi: 10.37766/inplasy2022.5.0055

The value of Hounsfield units in predicting cage subsidence after transforaminal lumbar interbody fusion

BACKGROUND

Cage subsidence may occur following transforaminal lumbar interbody fusion (TLIF) and lead to nonunion, foraminal height loss and other complications. Low bone quality may be a risk factor for cage subsidence. Assessing bone quality through Hounsfield units (HU) from computed tomography has been proposed in recent years. However, there is a lack of literature evaluating the correlation between HU and cage subsidence after TLIF.

METHODS

Two hundred and seventy-nine patients suffering from lumbar degenerative diseases from April, 2016 to August, 2018 were enrolled. All underwent one-level TLIF with a minimum of 1-year follow-up. Cage subsidence was defined as > 2 mm loss of disc height at the fusion level. The participants were divided into 2 groups: cage subsidence group (CS) and non-cage subsidence group (non-CS). Bone quality was determined by HU, bone mineral density of lumbar (BMD-l) and femoral (BMD-f) from dual-emission X-ray absorptiometry (DXA). HU of each vertebra from L1 to L4 (e.g., HU1 for HU of L1) and mean value of the four vertebrae (HUm) were calculated. Visual analog scale (VAS) of back/leg pain and Oswestry disability index (ODI) were used to report clinical outcomes.

RESULTS

Cage subsidence occurred in 82 (29.4%) cases at follow-ups. Mean age was 50.8 ± 9.0 years with a median follow-up of 18 months (range from 12 to 40 months). A total of 90.3% patients presented fusion with similar fusion rate between the two groups. ODI and VAS in leg were better in non-CS group at last follow-ups. Using receiver operating characteristic curves (ROCs) to predict cage subsidence, HUm provided a larger area under the curve (AUC) than BMD-l (Z = 3.83, P <  0.01) and BMD-f (Z = 2.01, P = 0.02). AUC for HU4 was larger than BMD-f and close to HUm (Z = 0.22, P = 0.481).

CONCLUSIONS

Cage subsidence may indicate worse clinical outcomes. HU value could be a more effective predictor of lumbar cage subsidence compared with T-score of DXA after TLIF.

Evaluation of Spinal Fusion in Thoracic and Thoracolumbar Spine on Standard X-Rays: A New Grading System for Spinal Interbody Fusion

STUDY DESIGN

Retrospective evaluation of prospectively collected data.

OBJECTIVE

Analyzing time course and stages of interbody fusion of a uniformly operated cohort, defining a grading system and establishing diagnosis-dependent periods of bone healing.

METHODS

Sequential lateral radiographs of 238 patients (313 levels) with interbody fusion operated thoracoscopically were analyzed.

RESULTS

Evaluation of 1696 radiographs with a mean follow-up of 65.19 months and average numbers of 5.42 (2-18) images per level was performed. Diagnoses were Pyogenic Spondylitis (74), Fracture (96), Ankylosing Spondylitis (38) and Degenerative Disease (105). No case with Grade 2 deteriorated to Grade 5. On average, Grade 4 persisted for 113 days, Grade 3 for 197 days, Grade 2 for 286 days and Grade 1 for 316 days. The first 95% of levels ("Green Zone", ≤ Grade 2) fused at 1 year, the remaining 4% levels fused between 12 and 17 months ("Yellow Zone") and the last 1% ("Red Zone") fused after 510 days.

CONCLUSION

Sequential lateral radiographs permit evaluation of interbody fusion. Grade 2 is the threshold point for fusion; once accomplished, failure is unlikely. If fusion (Grade 2,1 or 0) is not reached within 510 days, it should be regarded as failed. The 510-day-threshold could reduce the necessity of CT scanning for assessing fusion.

Biodegradable interbody cages for lumbar spine fusion: Current concepts and future directions

Lumbar fusion often remains the last treatment option for various acute and chronic spinal conditions, including infectious and degenerative diseases. Placement of a cage in the intervertebral space has become a routine clinical treatment for spinal fusion surgery to provide sufficient biomechanical stability, which is required to achieve bony ingrowth of the implant. Routinely used cages for clinical application are made of titanium (Ti) or polyetheretherketone (PEEK). Ti has been used since the 1980s; however, its shortcomings, such as impaired radiographical opacity and higher elastic modulus compared to bone, have led to the development of PEEK cages, which are associated with reduced stress shielding as well as no radiographical artefacts. Since PEEK is bioinert, its osteointegration capacity is limited, which in turn enhances fibrotic tissue formation and peri-implant infections. To address shortcomings of both of these biomaterials, interdisciplinary teams have developed biodegradable cages. Rooted in promising preclinical large animal studies, a hollow cylindrical cage (Hydrosorb™) made of 70:30 poly-l-lactide-co-d, l-lactide acid (PLDLLA) was clinically studied. However, reduced bony integration and unfavourable long-term clinical outcomes prohibited its routine clinical application. More recently, scaffold-guided bone regeneration (SGBR) with application of highly porous biodegradable constructs is emerging. Advancements in additive manufacturing technology now allow the cage designs that match requirements, such as stiffness of surrounding tissues, while providing long-term biomechanical stability. A favourable clinical outcome has been observed in the treatment of various bone defects, particularly for 3D-printed composite scaffolds made of medical-grade polycaprolactone (mPCL) in combination with a ceramic filler material. Therefore, advanced cage design made of mPCL and ceramic may also carry initial high spinal forces up to the time of bony fusion and subsequently resorb without clinical side effects. Furthermore, surface modification of implants is an effective approach to simultaneously reduce microbial infection and improve tissue integration. We present a design concept for a scaffold surface which result in osteoconductive and antimicrobial properties that have the potential to achieve higher rates of fusion and less clinical complications. In this review, we explore the preclinical and clinical studies which used bioresorbable cages. Furthermore, we critically discuss the need for a cutting-edge research program that includes comprehensive preclinical in vitro and in vivo studies to enable successful translation from bench to bedside. We develop such a conceptual framework by examining the state-of-the-art literature and posing the questions that will guide this field in the coming years.

Risk Factors of Nonunion After Acute Osteoporotic Vertebral Fractures: A Prospective Multicenter Cohort Study

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

To characterize a patient population with nonunion after acute osteoporotic vertebral fractures (OVFs) and compare the union and nonunion groups to identify risk factors for nonunion.

SUMMARY OF BACKGROUND DATA

While OVFs are the most common type of osteoporotic fracture, the predictive value of a clinical assessment for nonunion at 48 weeks after OVF has not been extensively studied.

METHODS

This prospective multicenter cohort study included female patients aged 65 to 85 years with acute one-level osteoporotic compression fractures. In the radiographic analysis, the anterior vertebral body compression percentage was measured at 0, 12, and 48 weeks. Magnetic resonance imaging (MRI) was performed at enrollment and at 48 weeks to confirm the diagnosis and union status. The patient-reported outcome measures included scores on the European Quality of Life-5 Dimensions (EQ-5D), a visual analogue scale for low back pain, and the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) at 0, 12, and 48 weeks.

RESULTS

In total, 166 patients completed the 12-month follow-up, 29 of whom had nonunion. Patients with nonunion at 48 weeks after OVF had lower EQ-5D and JOABPEQ walking ability, social life function, mental health, and lumbar function scores than those with union at 48 weeks after injury. The independent risk factors for nonunion after OVF in the acute phase were a diffuse low type pattern on T1-weighted MRI and diffuse low and fluid type patterns on T2-weighted MRI. The anterior vertebral body compression percentage and JOABPEQ social life function scores were independent risk factors at 12 weeks.

CONCLUSION

A diffuse low type pattern on T1-weighted MRI and diffuse low and fluid type patterns on T2-weighted MRI were independent risk factors for nonunion in the acute phase. Patients who have acute OVFs with these risk factors should be carefully monitored for nonunion.

LEVEL OF EVIDENCE

2.

Autogenic Rib Graft for Atlantoaxial and Occipitocervical Fixation in Pediatric Patients

Study Design

Retrospective case series.

Purpose

To evaluate surgical outcomes and effectiveness of an autogenic rib graft for upper cervical fixation in pediatric patients.

Overview of Literature

Autogenic bone grafts have long been considered the ‘gold standard’ bone source for posterior cervical fusion in pediatric patients. However, there are some unsolved problems associated with donor-site morbidity and amount of bone grafting.

Methods

We studied five consecutive pediatric patients who underwent atlantoaxial fixation or occipitocervical fixation (OCF) using an autogenic rib graft with at least 2 years of follow-up (mean age, 9.8 years; mean follow-up period, 73.0 months). Two patients underwent OCF without screw-rod constructs and three patients with screw-rod constructs. Autogenic rib grafts were used in all patients. We evaluated the surgical outcomes including radiographic parameter, bony union, and perioperative complications.

Results

The atlantoaxial interval (ADI) was corrected from 11.6 to 6.0 mm, and the C1–2 angle was corrected −14.8° to 7.8°. The C2–7 angle was reduced from 31° to 9° spontaneously. Two patients with OCF required revision surgery due to loss of correction. Patients did not experience any complication associated with the donor sites (rib bone grafts). Six months postoperation X-rays clearly showed regeneration of the rib at the donor sites. Bony fusion was achieved in all patients; however, bony fusion occurred more slowly in patients without screw-rod constructs compared with patients with screw-rod constructs. Bone regeneration of the rib was observed in all patients with no complications at the donor site.

Conclusions

Autogenic rib grafts have advantages of potential bone regeneration, high fusion rate, and low donor-site morbidity. In addition, a screw-rod construct provides better bony fusion in pediatric patients with OCF and atlantoaxial fixation.

Accuracy and Reliability of Postoperative Radiographic Evaluation of First Metatarsal-Phalangeal Joint Arthrodesis

The clinical value of routine postoperative radiographic evaluation after orthopedic procedures has recently been called into question. The objective of the present investigation was to evaluate the ability of foot and ankle surgeons to accurately and reliably assess postoperative radiographs after first metatarsal-phalangeal joint arthrodesis. Thirty sets of digital radiographs from 11 patients who had undergone first metatarsal-phalangeal joint arthrodesis were retrospectively evaluated by 5 podiatric physicians board-certified in foot surgery. The surgeons were asked to answer several questions, including whether the radiograph appeared to be >4 or <4 postoperative weeks; whether the radiograph appeared to be >8 or <8 postoperative weeks; their estimation of the postoperative week; and whether they would allow the patient to begin weightbearing based on the radiographic findings. With respect to whether the radiographs were >4 or <4 postoperative weeks, surgeons made accurate assessments 63.33% of the time (95 of 150; range 56.67% to 73.33%), with a kappa of 0.220. With respect to whether the radiographs were >8 or <8 postoperative weeks, surgeons made accurate assessments 60.0% of the time (90 of 150; range 53.33% to 70.0%), with a kappa of 0.203. With respect to the estimation of the postoperative week of the radiograph, surgeons accurately assessed the radiographs within a 4-week period 34.0% of the time (54 of 150; range 26.67% to 46.67%), with a kappa of 0.425. With respect to allowing the patient to bear weight according to the radiographic findings, the surgeons were in complete agreement 26.67% of the time (8 of 30), with a kappa of 0.251. These results provide evidence against the serial routine use of postoperative radiographs for the first metatarsal-phalangeal joint arthrodesis in the absence of a specific clinical indication.

Structural Allograft versus Autograft for Instrumented Atlantoaxial Fusions in Pediatric Patients: Radiologic and Clinical Outcomes in Series of 32 Patients

BACKGROUND

Allograft with wire techniques showed a low fusion rate in pediatric atlantoaxial fusions (AAFs) in early studies. Using allograft in pediatric AAFs with screw/rod constructs has not been reported. Thus we compared the fusion rate and clinical outcomes in pediatric patients who underwent AAFs with screw/rod constructs using either a structural autograft or allograft.

METHODS

Pediatric patients (aged ≤12 years) who underwent AAFs between 2007 and 2015 were retrospectively evaluated. Patients were divided into 2 groups (allograft or autograft). Clinical and radiographic results were collected from hospital records and compared.

RESULTS

A total of 32 patients were included (18 allograft, 14 autograft). There were no significant group differences in age, sex, weight, diagnosis, or duration of follow-up. A similar fusion rate was achieved (allograft: 94%, 17/18; autograft: 100%, 14/14); however, the average fusion time was 3 months longer in the allograft group. Blood loss was significantly lower in the allograft group (68 ± 8.5 mL) than the autograft group (116 ± 12.5 mL). Operating time and length of hospitalization were slightly (nonsignificantly) shorter for the allograft group. A significantly higher overall incidence of surgery-related complications was seen in the autograft group, including a 16.7% (2/14) rate of donor-site-related complications.

CONCLUSIONS

The use of allograft for AAF was safe and efficacious when combined with rigid screw/rod constructs in pediatric patients, with a similar fusion rate to autografts and an acceptable complication rate. Furthermore, blood loss was less when using allograft and donor-site morbidity was eliminated; however, the fusion time was increased.

Spinal Motion and Muscle Activity during Active Trunk Movements - Comparing Sheep and Humans Adopting Upright and Quadrupedal Postures

Sheep are used as models for the human spine, yet comparative in vivo data necessary for validation is limited. The purpose of this study was therefore to compare spinal motion and trunk muscle activity during active trunk movements in sheep and humans. Three-dimensional kinematic data as well as surface electromyography (sEMG) of spinal flexion and extension was compared in twenty-four humans in upright (UR) and 4-point kneeling (KN) postures and in 17 Austrian mountain sheep. Kinematic markers were attached over the sacrum, posterior iliac spines, and spinous and transverse processes of T5, T8, T11, L2 and L5 in humans and over the sacrum, tuber sacrale, T5, T8, T12, L3 and L7 in sheep. The activity of erector spinae (ES), rectus abdominis (RA), obliquus externus (OE), and obliquus internus (OI) were collected. Maximum sEMG (MOE) was identified for each muscle and trial, and reported as a percentage (MOE%) of the overall maximally observed sEMG from all trials. Spinal range of motion was significantly smaller in sheep compared to humans (UR / KN) during flexion (sheep: 6–11°; humans 12–34°) and extension (sheep: 4°; humans: 11–17°). During extension, MOE% of ES was greater in sheep (median: 77.37%) than UR humans (24.89%), and MOE% of OE and OI was greater in sheep (OE 76.20%; OI 67.31%) than KN humans (OE 21.45%; OI 19.34%), while MOE% of RA was lower in sheep (21.71%) than UR humans (82.69%). During flexion, MOE% of RA was greater in sheep (83.09%) than humans (KN 47.42%; UR 41.38%), and MOE% of ES in sheep (45.73%) was greater than KN humans (14.45%), but smaller than UR humans (72.36%). The differences in human and sheep spinal motion and muscle activity suggest that caution is warranted when ovine data are used to infer human spine biomechanics.

Comparison of structural allograft and traditional autograft technique in occipitocervical fusion: radiological and clinical outcomes from a single institution

OBJECT The authors' objectives were to compare the rate of fusion after occipitoatlantoaxial arthrodesis using structural allograft with the fusion rate from using autograft, to evaluate correction of radiographic parameters, and to describe symptom relief with each graft technique. METHODS The authors assessed radiological fusion at 6 and 12 months after surgery and obtained radiographic measurements of C1-2 and C2-7 lordotic angles, C2-7 sagittal vertical alignments, and posterior occipitocervical angles at preoperative, postoperative, and final follow-up examinations. Demographic data, intraoperative details, adverse events, and functional outcomes were collected from hospitalization records. Radiological fusion was defined as the presence of bone trabeculation and no movement between the graft and the occiput or C-2 on routine flexion-extension cervical radiographs. Radiographic measurements were obtained from lateral standing radiographs with patients in the neutral position. RESULTS At the University of Utah, 28 adult patients underwent occipitoatlantoaxial arthrodesis between 2003 and 2010 using bicortical allograft, and 11 patients were treated using iliac crest autograft. Mean follow-up for all patients was 20 months (range 1-108 months). Of the 27 patients with a minimum of 12 months of follow-up, 18 (95%) of 19 in the allograft group and 8 (100%) of 8 in the autograft group demonstrated evidence of bony fusion shown by imaging. Patients in both groups demonstrated minimal deterioration of sagittal vertical alignment at final follow-up. Operative times were comparable, but patients undergoing occipitocervical fusion with autograft demonstrated greater blood loss (316 ml vs 195 ml). One (9%) of 11 patients suffered a significant complication related to autograft harvesting. CONCLUSIONS The use of allograft in occipitocervical fusion allows a high rate of successful arthrodesis yet avoids the potentially significant morbidity and pain associated with autograft harvesting. The safety and effectiveness profile is comparable with previously published rates for posterior C1-2 fusion using allograft.

Methods of evaluating lumbar and cervical fusion

Introduced in 1911, spinal fusion is now widely used to stabilize the cervical, thoracic, and lumbar spine. Despite advancements in surgical techniques, including the use of instrumentation and optimizing bone graft options, pseudarthrosis remains one of the most significant causes of clinical failure following attempted fusion. Diagnosis of this common complication is based on a focused clinical assessment and imaging studies. Pseudarthrosis classically presents with the onset of or return of axial or radicular symptoms during the first postoperative year. However, this diagnosis is complicated because other diagnoses can mimic these symptoms (such as infection or adjacent segment degeneration) and because many cases of pseudarthrosis are asymptomatic. Computed tomography and assessment of motion on flexion/extension radiographs are the two preferred imaging modalities for establishing the diagnosis of pseudarthrosis. The purpose of this article was to review the current status of imaging and clinical practices for assessing fusion following spinal arthrodesis.

A systematic review of comparative studies on bone graft alternatives for common spine fusion procedures

BACKGROUND

The increased prevalence of spinal fusion surgery has created an industry focus on bone graft alternatives. While autologous bone graft remains the gold standard, the complications and morbidity from harvesting autologous bone drives the search for reliable and safe bone graft substitutes. With the recent information about the adverse events related to bone morhogenetic protein use, it is appropriate to review the literature about the numerous products that are not solely bone morphogenetic protein.

PURPOSE

The purpose of this literature review is to determine the recommendations for use of non-bone morphogenetic protein bone graft alternatives in the most common spine procedures based on a quantifiable grading system.

STUDY DESIGN

Systematic literature review.

METHODS

A literature search of MEDLINE (1946-2012), CINAHL (1937-2012), and the Cochrane Central Register of Controlled Trials (1940-April 2012) was performed, and this was supplemented by a hand search. The studies were then evaluated based on the Guyatt criteria for quality of the research to determine the strength of the recommendation.

RESULTS

In this review, more than one hundred various studies on the ability of bone graft substitutes to create solid fusions and good patient outcomes are detailed.

CONCLUSION

The recommendations for use of bone graft substitutes and bone graft extenders are based on the strength of the studies and given a grade.