Efficacy of Routine Intraoperative Cranio-Femoral Traction in Surgical Treatment of Adolescent Idiopathic Scoliosis Curves Measuring Between 50° and 90°.

STUDY DESIGN: Retrospective Comparative Study, Level III. OBJECTIVE: In patients with scoliosis >90°, cranio-femoral traction (CFT) has been shown to obtain comparable curve correction with decreased operative time and blood loss. Routine intraoperative CFT use in the treatment of AIS <90° has not been established definitively. This study investigates the effectiveness of intraoperative CFT in the treatment of AIS between 50° and 90°, comparing the magnitude of curve correction, blood loss, operative time, and traction-related complications with and without CFT. METHODS: 73 patients with curves less than 90° were identified, 36 without and 37 with cranio-femoral traction. Neuromuscular scoliosis and revision surgery were excluded. Age, preoperative Cobb angles, bending angles, and curve types were recorded. Surgical characteristics were analyzed including number of levels fused, estimated blood loss, operative time, major curve correction (%), and degree of postoperative kyphosis. RESULTS: Patients with traction had significantly higher preoperative major curves but no difference in age or flexibility. Lenke 1 curves had significantly shorter operative time and improvement in curve correction with traction. Among subjects with 5 to 8 levels fused, subjects with traction had significantly less EBL. Operative time was significantly shorter for subjects with 5-8 levels and 9-11 levels fused. Curves measuring 50°-75° showed improved correction with traction. CONCLUSION: Intraoperative traction resulted in shorter intraoperative time and greater correction of major curves during surgical treatment of adolescent idiopathic scoliosis less than 90°. Strong considerations should be given to use of intraoperative CFT for moderate AIS.

Factors Associated With Total Discharge Opioid Prescription Morphine Milligram Equivalent Amounts Following Primary Anterior Cervical Spine Surgery.

BACKGROUND: Opioid overuse is a substantial cause of morbidity and mortality in the United States, and orthopaedic surgeons are the third highest prescribers of opioids. Postoperative prescribing patterns vary widely, and there is a paucity of data evaluating patient and surgical factors associated with discharge opioid prescribing patterns after elective anterior cervical surgery (ACS). The purpose of this study was to evaluate the volume of postoperative opioids prescribed and factors associated with discharge opioid prescription volumes after elective ACS. METHODS: We retrospectively identified patients aged 18 years and older who underwent elective primary anterior cervical diskectomy and fusion (ACDF), cervical disk arthroplasty (CDA), or hybrid procedure (ACDF and CDA at separate levels) at a single institution between 2015 and 2021. Demographic, surgical, and opioid prescription data were obtained from patients' electronic medical records. Univariate and multivariate analyses were conducted to assess for independent associations with discharge opioid volumes. RESULTS: A total of 313 patients met inclusion criteria, including 226 (72.2%) ACDF, 69 (22.0%) CDA, and 18 (5.8%) hybrid procedure patients. Indications included radiculopathy in 63.6%, myelopathy in 19.2%, and myeloradiculopathy in 16.3%. The average age was 57.2 years, and 50.2% of patients were male. Of these, 88 (28.1%) underwent one-level, 137 (43.8%) underwent two-level, 83 (26.5%) underwent three-level, and 5 (1.6%) underwent four-level surgery. Younger age (P = 0.010), preoperative radiculopathy (P = 0.029), procedure type (ACDF, P < 0.001), preoperative opioid use (P = 0.012), and discharge prescription written by a midlevel provider (P = 0.010) were independently associated with greater discharge opioid prescription volumes. CONCLUSION: We identified wide variability in prescription opioid discharge volumes after ACS and patient, procedure, and perioperative factors associated with greater discharge opioid volumes. These factors should be considered when designing protocols and interventions to reduce and optimize postoperative opioid use after ACS.

Laminoplasty versus laminectomy with fusion for treating multilevel degenerative cervical myelopathy.

Background: Laminectomy with fusion (LF) and laminoplasty (LP) are common posterior decompression procedures used to treat multilevel degenerative cervical myelopathy (DCM). There is debate on their relative efficacy and safety for treatment of DCM. The goal of this study is to examine outcomes and costs of LF and LP procedures for DCM. Methods: This is a retrospective review of adult patients (<18) at a single center who underwent elective LP and LF of at least 3 levels from C3-C7. Outcome measures included operative characteristics, inpatient mobility status, length of stay, complications, revision surgery, VAS neck pain scores, and changes in radiographic alignment. Oral opioid analgesic needs and hospital cost comparison were also assessed. Results: LP cohort (n=76) and LF cohort (n=59) reported no difference in neck pain at baseline, 1, 6, 12, and 24 months postoperatively (p>.05). Patients were successfully weaned off opioids at similar rates (LF: 88%, LP: 86%). Fixed and variable costs respectively with LF cases hospital were higher, 15.7% and 25.7% compared to LP cases (p=.03 and p<.001). LF has a longer length of stay (4.2 vs. 3.1 days, p=.001). Wound-related complications were 5 times more likely after LF (13.6% vs. 5.9%, RR: 5.15) and C5 palsy rates were similar across the groups (LF: 11.9% LP: 5.6% RR: 1.8). Ground-level falls requiring an emergency department visit were more likely after LF (11.9% vs. 2.6%, p=.04). Conclusions: When treating multilevel DCM, LP has similar rates of new or increasing axial neck pain compared to LF. LF was associated with greater hospital costs, length of stay, and complications compared to LP. LP may in fact be a less morbid and more cost-effective alternative to LF for patients without cervical deformity.

A Comparison of Prognostic Models to Facilitate Surgical Decision-Making for Patients With Spinal Metastatic Disease.

STUDY DESIGN: Retrospective cohort. OBJECTIVE: Compare the performance of and provide cutoff values for commonly used prognostic models for spinal metastases, including Revised Tokuhashi, Tomita, Modified Bauer, New England Spinal Metastases Score (NESMS), and Skeletal Oncology Research Group model, at three- and six-month postoperative time points. SUMMARY OF BACKGROUND DATA: Surgery may be recommended for patients with spinal metastases causing fracture, instability, pain, and/or neurological compromise. However, patients with less than three to six months of projected survival are less likely to benefit from surgery. Prognostic models have been developed to help determine prognosis and surgical candidacy. Yet, there is a lack of data directly comparing the performance of these models at clinically relevant time points or providing clinically applicable cutoff values for the models. MATERIALS AND METHODS: Sixty-four patients undergoing surgery from 2015 to 2022 for spinal metastatic disease were identified. Revised Tokuhashi, Tomita, Modified Bauer, NESMS, and Skeletal Oncology Research Group were calculated for each patient. Model calibration and discrimination for predicting survival at three months, six months, and final follow-up were evaluated using the Brier score and Uno's C, respectively. Hazard ratios for survival were calculated for the models. The Contral and O'Quigley method was utilized to identify cutoff values for the models discriminating between survival and nonsurvival at three months, six months, and final follow-up. RESULTS: Each of the models demonstrated similar performance in predicting survival at three months, six months, and final follow-up. Cutoff scores that best differentiated patients likely to survive beyond three months included the Revised Tokuhashi score=10, Tomita score=four, Modified Bauer score=three, and NESMS=one. CONCLUSION: We found comparable efficacy among the models in predicting survival at clinically relevant time points. Cutoff values provided herein may assist surgeons and patients when deciding whether to pursue surgery for spinal metastatic disease. LEVEL OF EVIDENCE: 4.

Gender, Racial, and Ethnic Differences in the Utilization of Cervical Disk Replacement for Cervical Radiculopathy.

INTRODUCTION: Cervical radiculopathy (CR) is commonly treated by spine surgeons, with surgical options including anterior cervical diskectomy and fusion (ACDF) and cervical disk replacement (CDR). CDR is a motion-sparing alternative to ACDF and was approved by the US FDA in 2007. CDR utilization has increased because evidence has emerged demonstrating its long-term efficacy. Despite CDR's efficacy, studies have suggested that socioeconomic factors may influence which patients undergo CDR versus ACDF. Our objective was to determine whether gender, racial, and ethnic disparities exist in the utilization of CDR versus ACDF for CR. METHODS: Patients age ≥18 years undergoing elective CDR or ACDF for CR between 2017 and 2020 were identified in the Vizient Clinical Database. Proportions of patients undergoing CDR and ACDF, as well as their comorbidities, complications, and outcomes, were compared by sex, race, and ethnicity. Bonferroni correction was done for multiple comparisons. RESULTS: A total of 7,384 patients, including 1,427 undergoing CDR and 5,957 undergoing ACDF, were reviewed. Black patients undergoing surgical treatment of CR were less likely to undergo CDR than ACDF, had a longer length of stay, and had higher readmission rates, while Hispanic patients had higher complication rates than non-Hispanic patients. DISCUSSION: Important racial and ethnic disparities exist in CR treatment. Interventions are necessary to ensure equal access to spine care by reducing barriers, such as underinsurance and implicit bias. LEVEL OF EVIDENCE: IV (Case Series).

Prevention of spinal fusion post-operative wound infections in pediatric patients with scoliosis: a quality improvement initiative.

PURPOSE: Post-operative wound infections increase patient morbidity and mortality as well as the length of hospital stay, with a profound personal and institutional cost. The aim of this study was to decrease post-operative infections through development of a surgical antibiotic prophylaxis policy based on institution-specific risk factors and microbiology data. METHODS: We conducted a retrospective review of deep wound infections at our institution over a 5-year period (2014-2018). 399 spinal fusion procedures were performed with a 2.5% post-operative infection rate. Patients with neuromuscular scoliosis were six times more likely to develop deep wound infections (7.6%) compared to patients with congenital and idiopathic scoliosis (combined rate of 1.25%). The microbiology data revealed that polymicrobial, extended spectrum beta-lactamase (ESBL) gram negative organisms predominated in patients with neuromuscular scoliosis. Based on these findings, we implemented an evidence-based quality improvement intervention: all patients with neuromuscular scoliosis undergoing spinal fusion were given a single 15 mg/kg dose of amikacin, in addition to our standard practice of perioperative cefazolin plus vancomycin with intra-operative betadine wash and vancomycin powder application. This intervention was put into practice in January 2019. RESULTS: Since the implementation of our quality improvement initiative, the overall post-operative infection rate decreased to 1.1% (2 infections in 176 cases). Ninety-eight percent of the 43 neuromuscular scoliosis patients who underwent spinal fusion in the post-intervention time frame have remained infection free. CONCLUSION: Examination of post-operative infection and microbiology data at the institution level can guide the development of institution specific, evidence-based quality improvement initiatives that reduce post-operative wound infections.

Osteoporosis Is Undertreated After Low-energy Vertebral Compression Fractures.

INTRODUCTION: Despite guidelines recommending postfracture bone health workup, multiple studies have shown that evaluation and treatment of osteoporosis has not been consistently implemented after fragility fractures. The primary aim of this study was to evaluate rates of osteoporosis evaluation and treatment in adult patients after low-energy thoracolumbar vertebral compression fractures (VCFs). METHODS: We retrospectively reviewed all patients ≥60 years old presenting to a single academic trauma center with acute thoracolumbar VCFs after a ground-level fall from 2016 to 2020 . Rates of osteoporosis screening with dual-energy x-ray absorptiometry and initiation of pharmaceutical treatment were recorded at four time points: before the date of injury, during index hospitalization, at first primary care provider follow-up, and at final primary care provider follow-up. Rates of subsequent falls and secondary fragility fractures were recorded. One-year mortality and overall mortality were also calculated. RESULTS: Fifty-two patients with a mean age of 83 years presenting with thoracic and/or lumbar fractures after a ground-level fall were included. At a mean final follow-up of 502 days, only 10 patients (19.2%) received pharmacologic therapy for osteoporosis and only 6 (11.5%) underwent postinjury dual-energy x-ray absorptiometry evaluation. Twenty-five patients (48%) had at least one subsequent fall at a mean of 164 days from the initial date of injury. Eleven patients with subsequent falls sustained an additional fragility fracture because of the fall, including six operative injuries. One-year mortality among the 52 patients was 26.9%, and the overall mortality rate was 44.2% at the final follow-up. DISCUSSION: Osteoporosis remains a major public health issue that markedly affects quality of life and healthcare costs. Our study demonstrates the additional need for improved osteoporosis workup and intervention among patients who have sustained VCFs. We hope that our study helps raise awareness for improved osteoporosis evaluation and treatment among spine surgeons and all medical professionals treating patients with fragility fractures. LEVEL OF EVIDENCE: Retrospective Case Series, Level IV Evidence.

Efficacy, Cost, and Complications of Demineralized Bone Matrix in Instrumented Lumbar Fusion: Comparison With rhBMP-2.

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: To evaluate demineralized bone matrix as an adjunct for instrumented lumbar spine fusion compared with recombinant human bone morphogenetic protein-2 (rhBMP-2). METHODS: Clinical and radiographic review was performed of 43 patients with degenerative spine disease treated with posterolateral spinal fusion with or without posterior or transforaminal lumbar interbody fusion. Final analysis included sixteen patients treated with demineralized bone matrix (DBM; Accell Evo3, SeaSpine) compared with a retrospective matched group of 21 patients treated with rhBMP-2 (rhBMP-2, Infuse, Medtronic). All patients were followed for 24 months. Fusion was evaluated by computed tomography and/or x-ray. Clinical outcomes included visual analogue scale (VAS), Oswestry Disability Index (ODI), and Short Form 12 (SF-12). RESULTS: Overall fusion rate, including posterolateral and/or interbody fusion, was 100% for both groups, though the fusion rates in the posterolateral space alone were 93.5% and 100% for the DBM and rhBMP-2 groups, respectively. Clinical outcomes were similar between groups, with the DBM group showing greater improvement in ODI. The rhBMP-2 group showed higher rates of radiographic complications with 7 of 21 patients (33.3%) demonstrating either adjacent level fusion or ectopic bone formation, compared with zero in the DBM group. Average biologic cost per level was $1522 for DBM and $3505 for rhBMP-2. CONCLUSIONS: DBM and rhBMP-2 demonstrated similar radiographic and clinical outcomes in instrumented lumbar fusions. rhBMP-2 was associated with higher rates of radiographic complications and significantly higher costs.

Temporary Endobronchial Stent as a Bridge to Corrective Surgery For Severe Kyphoscoliosis-associated Central-Airway Extrinsic Compression.

Kyphoscoliosis is known to compromise lung function, with the primary mechanism being reduced chest wall compliance with a resultant restrictive pulmonary physiology. Severe scoliosis can also cause extrinsic compression of the central airways, leading to recurrent respiratory infections, lobar atelectasis, and potentially acute respiratory failure. Definitive therapy is corrective surgery of the spine. However, patients with severe scoliosis are at a potentially high risk of perioperative pulmonary complications. To our knowledge, we report the first successful use of retrievable endobronchial stents as a bridge to corrective surgery for kyphoscoliosis-associated complete central-airway extrinsic compression in a patient who was considered as too high risk for surgical correction due to her respiratory status. After surgery, the stents were removed and our patient experienced sustained improvement in pulmonary function and the clinical respiratory status.

In vivo strain measurements from hardware and lamina during spine fusion.

Currently, spine fusion is determined using radiography and clinical evaluation. There are discrepancies between radiographic evidence and direct measurements of fusion, such as operative exploration and biomechanical or histological measurements. In order to facilitate the rapid return of patients to normal activities, a monitoring technique to accurately detect fusion in vivo and to prevent overload during the postoperative period would be useful. The objectives of this study were to develop an implantable monitoring system consisting of CPC-coated strain gauges and a radio transmitter to detect the onset of fusion and measure strain during postsurgical activities. A patient underwent anterior release and fusion, followed by posterior instrumentation and fusion with segmental spinal instrumentation. Four strain gauges were placed during surgery. One was attached to the left-side rod and one to each of the lamina at T9, T10, and T11. An externally powered implanted radio transmitter attached to the gauges was placed in a subcutaneous pouch. Strains were monitored weekly and tabulated during various activities for 7 months. Peak strains during twisting and bending were tabulated to detect the onset of fusion. Strains were also recorded during activities such as climbing off an examination table, rising from a chair, and climbing stairs. Strains collected from the left rod indicated that, immediately postoperatively, it was loaded at acceptable levels. The largest and most consistent strain changes measured from the lamina were recorded during twisting.

The utility and accuracy of computed tomography in the diagnosis of occipitocervical dissociation.

BACKGROUND CONTEXT: Atlantooccipital dislocation (AOD) results in profound patient morbidity and mortality and is difficult to accurately diagnose using current evaluation techniques. PURPOSE: To evaluate the utility of computed tomography (CT) images in the diagnosis of AOD and compare the revised occipital condyle-C1 interval (CCI) and the condylar sum to the current radiographic criteria used to detect AOD. STUDY DESIGN: Retrospective review to evaluate the sensitivity, specificity, and the interobserver reliability of eight radiographic criteria as applied to CT imaging. PATIENT SAMPLE: Ten cases of clinical AOD and 10 cases of non-AOD cervical injury. OUTCOME MEASURES: Measured values: revised CCI, Wholey basion-dens interval (BDI), and Harris basion-axis interval (BAI). Calculated values: Sun interspinous ratio, Powers ratio, and condylar sum. Assessment of Lee X-line and atlantooccipital joint asymmetry. METHODS: A board certified neuroradiologist, two orthopedic spine surgeons, and two medical students reviewed the CT images for each patient in the series and applied the aforementioned criteria. RESULTS: Average sensitivity between all reviewers for CCI, condylar sum, and atlantooccipital asymmetry was highest at 1.0, 1.0, and 0.96, respectively. Basion-dens interval, X-line, Sun ratio, BAI, and Powers ratio had sensitivities of 0.72, 0.54, 0.32, 0.26, and 0.26, respectively. Revised CCI and condylar sum had significantly better sensitivity than any other test (vs. BDI, p=.014, all others, p<.001) except atlantooccipital asymmetry (p>.99). Specificity for all measurements was 0.78 or greater, except X-line at 0.38. Interobserver reliabilities were the greatest for CCI, condylar sum, atlantooccipital asymmetry, and BDI. CONCLUSIONS: The revised CCI (>2.5 mm abnormal) and condylar sum (≥5 mm abnormal) are highly sensitive and reliable radiographic criteria for the detection of AOD when applied to CT imaging.

Treatment of spine deformity in neuromuscular diseases.

Surgical management of spinal deformity in neuromuscular diseases (NMDs) often requires a multidisciplinary approach beginning in the preoperative surgical planning period, owing to concomitant restrictive lung disease and cardiomyopathy in selected NMD conditions. The need for thorough and thoughtful discussions must occur with the family and other caregivers before any scheduled surgery. The decision to proceed with spinal instrumentation may alter functional abilities in weak and marginally ambulatory NMD patients. With care and treatment involving a multidisciplinary team, proper planning, and support, patients will likely experience rewarding outcomes and improved quality of life.

Case report: incisional hernia as a complication of extreme lateral interbody fusion.

BACKGROUND CONTEXT: Minimal access surgery is becoming more popular for spinal fusion because of a lower theoretical risk of complications and shorter postoperative recovery period, compared with the traditional open approach. The lateral approach uses retroperitoneal transpsoas access to the vertebra, obviating the need for an approach surgeon and minimizing muscular disruption, thus allowing a quicker recovery. Initial reports of the lateral transpsoas procedure described few complications. However, a number of complications have subsequently been documented. To our knowledge, there has not been a description of an incisional hernia after this approach. PURPOSE: To report the rare complication of an incisional hernia after a minimal access lateral transpsoas approach for lumbar interbody fusion. STUDY DESIGN: Case report. METHODS: We reviewed the hospital charts, radiographs, and intraoperative photographs of a patient who underwent a minimally invasive lateral approach lumbar spine fusion with a subsequent incisional hernia that necessitated laparoscopic repair. RESULTS: A 75-year-old woman with a history of low back and left lower extremity pain with radiographic evidence of foraminal stenosis and degenerative spondylolisthesis underwent a successful L4-L5 discectomy with an extreme lateral interbody fusion via a retroperitoneal transpsoas approach. This was supplemented with a posterior minimally invasive surgery instrumented fusion from L4 to L5. The patient reported significant improvement in symptoms on initial follow-up, however, complained of a prominence over her incision 4 weeks later. An incisional hernia was diagnosed and subsequently repaired laparoscopically, from which the patient recovered uneventfully. CONCLUSIONS: Postoperative incisional hernia after extreme lateral interbody fusion is a complication that has not been previously described in the literature but is one that spine surgeons must recognize. This case may prompt surgeons to use a more posterior approach to avoid this complication. Additionally, direct repair of the transversalis fascia is critical to avoiding this complication.

Kinematics of progressive circumferential ligament resection (decompression) in conjunction with cervical disc arthroplasty in a spondylotic spine model.

STUDY DESIGN: Benchtop biomechanics study examining kinematic effects of progressive resection in a human cadaveric spine model. OBJECTIVE: To determine the effects of posterior longitudinal ligament (PLL) resection, unilateral and bilateral foraminotomy, and laminectomy on cervical intervertebral rotation and translation after cervical disc arthroplasty (CDA). SUMMARY OF BACKGROUND DATA: Although the clinical results after CDA have been studied, there remain unanswered questions regarding the surgical techniques used at the time of device insertion. For example, it is unclear whether a surgeon should retain or resect the PLL and uncinate processes at the time of primary surgical intervention. Further, the effect of a subsequent posterior decompression (foraminotomy or laminectomy) on the stability of a motion segment containing a disc arthroplasty is unknown. METHODS: Three-dimensional intervertebral motion was measured by biplanar videography in human cadaveric spines at C4-C5 or at C5-C6 subjected to a 1.5-Nm moment applied to induce motion in the sagittal plane. Coupled motions were not constrained. After measuring intact spine motion, disc arthroplasty with bilateral ventral foraminotomy was performed without PLL resection. Sequentially, rotations and translations were measured after PLL resection, unilateral foraminotomy, bilateral foraminotomy, and laminectomy. RESULTS: CDA with bilateral ventral foraminotomy increased sagittal rotation by 0.4 degrees (16%) compared with the intact spine. The addition of PLL resection increased rotation by 0.5 degrees (14% increase). Unilateral and bilateral foraminotomy had negligible effects on sagittal rotation or anteroposterior (AP) translation. Laminectomy resulted in an additional sagittal plane rotation of 2 degrees. The sagittal-plane interverterbal rotation resultant after all interventions was 6 degrees , with 1.5 mm of AP translation occurring only. CONCLUSION: Given that a greater degree of motion was seen with PLL resection combined with ventral foraminotomy, we recommend that PLL resection be performed when performing CDA. In our benchtop model, unilateral and bilateral posterior foraminotomies were not associated with the creation of significant sagittal rotational or AP translational instability.

The unique complications of coccidioidomycosis of the spine: a detailed time line of disease progression and suppression.

STUDY DESIGN: A case report is presented. OBJECTIVE: We report a detailed time-line of disease progression and suppression in a patient with disseminated Coccidioidomycosis of the spine. The importance of consistent and thorough treatment to prevent disease recurrence is underscored. SUMMARY OF BACKGROUND DATA: Coccidioides immitis is a dimorphic fungus that lives as a saprophyte in arid, alkaline soils and as a parasite in the tissues of its host. Endemic to the arid soil of the American Southwest and Central and South America, its disease prevalence is increasing. There are 100,000 new infections diagnosed each year, of which 34% are symptomatic. Of the symptomatic individuals 5-10% will develop a serious pulmonary infection and of those that have a serious infection less than 1% will develop chronic pulmonary disease and/or extrapulmonary dissemination. METHODS: A 36-year-old black woman with a 3-year history of recent migration to the desert Southwest and a family history of sarcoidosis presented to her primary care physician with shortness of breath and a cough of 2 months' duration. An anterior-posterior radiograph revealed bilateral hilar lymphadenopathy and sarcoidosis was diagnosed. The patient was placed on oral prednisone and progressively worsened. She was referred to the Orthopedic Clinic with a complaint of severe back pain. RESULTS: Plain radiographs of the lumbar spine revealed lytic erosion of the sacral promontory. Computed tomography confirmed the sacral lesion in addition to revealing involvement of the fifth lumbar vertebral body. Over the ensuing years the patient underwent a course of operative and chemotherapeutic therapies. She endured numerous complications of the disease, one of which is being reported for the first time. Control of her disease has been accomplished through radical surgical debridement, spinal stabilization with concomitant local and systemic chemotherapy. CONCLUSIONS: The prevalence and distribution of Coccidioidomycosis is increasing as is the likelihood of seeing its often unique and bizarre clinical manifestations and complications. If included in the differential diagnosis, the disease can be recognized earlier and the likelihood of numerous complications can be avoided. Once bony involvement is diagnosed a regimen of aggressive surgical debridement as well as consistent chemotherapy must be employed if remission and/or eradication of the illness are sought.

An implantable strain measurement system designed to detect spine fusion: preliminary results from a biomechanical in vivo study.

STUDY DESIGN: The strain distribution on the thoracic vertebrae during anteroposterior bending and torsion was examined for use with an implantable strain gauge system and miniature radio transmitter, which also were evaluated. OBJECTIVES: To identify strain gauge placement sites by testing cadaver spines in vivo, and to evaluate an implantable gauge bonding technique and subminiature radio transmitter for accurate strain monitoring. SUMMARY OF BACKGROUND DATA: Fusion is determined currently through the use of radiographic techniques. Discrepancies exist between radiographic evidence and more direct measurements of fusion such as operative exploration4,5,12 and biomechanical or histologic measurements.12,15 To facilitate the return of patients to full unrestricted activity, it would be useful to develop a technique for accurate in vivo determination of fusion. METHODS: Three cadaver spines were tested during anteroposterior bending and torsional loading in the control, instrumented, and instrumented plus polymethylmethacrylate states. The spines were instrumented with an ISOLA(R) (Acromed Corporation, Cleveland, Ohio) construct, and a simulated fusion was achieved through the application of polymethylmethacrylate. Strain gauges were attached in uniaxial, biaxial, and rosette configurations. The principal strains were calculated. Calcium phosphate ceramic-coated gauges were implanted in patients and recovered after up to 15 months in vivo. A radio transmitter was developed and tested for use in patients. RESULTS: The largest and most consistent strain changes after simulated fusion were recorded during torsional loading on the laminae of a vertebra directly underneath a hook. Calcium phosphate ceramic-coated strain gauges showed excellent bone bonding to the lamina when fusion occurred. Radio telemetry accurately tracked strain magnitudes and strain rates expected in patients. CONCLUSIONS: The consistency obtained in torsional loading indicates that this type of loading will provide the most useful data from patients in vivo. Excellent bonebonding and accurate strain transmission using a long-term strain measurement system and miniature radio transmitter indicate that strains collected from patients with this system will be accurate.