Samuel K. Cho

Comparative analysis of pedicle screw versus hook instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis.

Study Design. A retrospective matched cohort study. Objective. To comprehensively compare the 2-year postoperative results of posterior correction and fusion with segmental pedicle screw instrumentation versus with hybrid (proximal hooks and distal pedicle screws) constructs in adolescent idiopathic scoliosis (AIS) treated at a single institution. Summary of Background Data. Despite the reports of satisfactory correction and maintenance of scoliotic curves by pedicle screw instrumentation, there have been no reports on the comprehensive comparison of AIS treatment after segmental pedicle screw instrumentation versus hybrid instrumentation. Materials and Methods. A total of 58 AIS patients that underwent posterior fusion with hybrid instrumentation (29) or pedicle screw (29) instrumentation at a single institution were sorted and matched according to four criteria: similar patient age, fusion levels, identical Lenke curve type, and identical operative methods. Patients were compared at 2-year follow-up according to radiographic changes, operative time, intraoperative blood loss, pulmonary function tests, and SRS-24 outcome scores. Results. The two cohorts were well matched. The preoperative major Cobb angle averaged 62° in the screw group and 60° in the hybrid group. Average major curve correction was 70% in the screw group and 56% in the hybrid group (P = 0.001). At 2-year follow-up, major curve correction was 65% and 46%, respectively (P < 0.001). At 2-year follow-up, thoracic sagittal Cobb angle changes between T5 and T12 were 9.0° decrease in the screw group and 2.4° decrease in the hybrid group compared with preoperative (P = 0.024). There were no differences in the lowest instrumented vertebra below the lower end vertebra (P = 0.56), operative time (P = 0.14), and average estimated blood loss (P = 0.54). Two years following surgery, the screw group demonstrated improved percent predicted pulmonary function values compared with that of the hybrid group (FVC; 81% → 81% in screw group vs. 85% → 79% in hybrid group P = 0.08, FEV1; 73% → 79% in screw group vs. 79% → 75% in hybrid group, P = 0.006). Postoperative total SRS-24 scores were similar in both groups (hybrid group: 99 vs. screw group: 95) (P = 0.19). There were no neurologic complications related to hybrid or pedicle screw instrumentation. Conclusion. Pedicle screw instrumentation offers a significantly better major curve correction and postoperative pulmonary function values without neurologic problems compared with hybrid constructs. Both instrumentation methods offer similar junctional change, lowest instrumented vertebra, operative time, and postoperative SRS-24 outcome scores in the operative treatment of AIS.

Proximal junctional kyphosis in adolescent idiopathic scoliosis following segmental posterior spinal instrumentation and fusion: minimum 5-year follow-up.

Study Design. A retrospective study. Objective. To analyze the long-term proximal junctional change in adolescent idiopathic scoliosis (AIS) following segmental posterior spinal instrumentation and fusion 5 years or more after surgery. Summary of Background Data. No study has concentrated on time-dependent long-term proximal junctional change in AIS following segmental posterior spinal instrumentation and fusion after 5 years postoperation. Risk factors for developing proximal junctional kyphosis (PJK) are unknown. Methods. A total of 193 consecutive AIS patients with a minimum 5-year follow-up (average, 7.3 years; range, 5–16.7 years) treated with segmental posterior spinal instrumentation and fusion were evaluated. Radiographic measurements analyzed included sagittal Cobb angle at the proximal junction on preoperative, early postoperation, 2-year postoperation, and final follow-up (≥5 years) by standing long cassette radiographs. Postoperative Scoliosis Research Society (SRS)-24 outcome scores were also evaluated. Abnormal PJK was defined as the final proximal junctional sagittal Cobb angle between the lower endplate of the uppermost instrumented vertebra and the upper endplate of two vertebrae supra-adjacent, which was > 10° and at least 10° greater than the preoperative measurement. Results. The incidence of PJK at 7.3 years postoperation was 26% (50 of 193 patients). The average proximal junctional angle increased 15.2° until 2 years postoperation and then increased 1.7° until final follow-up in the PJK group (n = 50). Factors that were statistically significant for PJK development were as follows: a thoracoplasty procedure (P = 0.001), preoperative hyperkyphotic thoracic alignment (T5–T12 > 40°) (P = 0.015), and hybrid instrumentation (proximal hooks and distal pedicle screws) compared with the hooks only group (P = 0.029). The number of fused vertebrae more than 11 was also related with PJK (P = 0.08). The level of the uppermost instrumented vertebra did not affect the PJK incidence. SRS-24 outcome scores did not demonstrate any significant differences (P = 0.54 for total score and P = 0.49 for self-image subscale) between the PJK and non-PJK groups. Conclusion. The incidence of proximal junctional kyphosis at 7.3 years postoperation was 26% and did not progress significantly after 2 years postoperation. Risk factors for developing PJK were an associated thoracoplasty, hybrid instrumentation (proximal hooks and distal pedicle screws), and a preoperative larger sagittal thoracic Cobb angle (T5–T12 > 40°). The SRS-24 outcome instrument was not affected by PJK.

The biomechanics of pedicle screw-based instrumentation

There are three basic concepts that are important to the biomechanics of pedicle screw-based instrumentation. First, the outer diameter of the screw determines pullout strength, while the inner diameter determines fatigue strength. Secondly, when inserting a pedicle screw, the dorsal cortex of the spine should not be violated and the screws on each side should converge and be of good length. Thirdly, fixation can be augmented in cases of severe osteoporosis or revision. A trajectory parallel or caudal to the superior endplate can minimise breakage of the screw from repeated axial loading. Straight insertion of the pedicle screw in the mid-sagittal plane provides the strongest stability. Rotational stability can be improved by adding transverse connectors. The indications for their use include anterior column instability, and the correction of rotational deformity.

Recurrent lumbar disk herniation.

&NA; Recurrent lumbar disk herniation is the most common complication following primary open diskectomy. It is defined as recurrent back and/or leg pain after a definite pain‐free period lasting at least 6 months from initial surgery. Careful neurologic examination is critical, and laboratory tests should be ordered to evaluate for infection. Imaging demonstrates disk herniation at the previously operated level. It is important to differentiate recurrent disk herniation from postoperative epidural scar because the latter may not benefit from reoperation. Treatment of recurrent lumbar disk herniation includes aggressive medical management and surgical intervention. Surgical techniques include conventional open diskectomy, minimally invasive open diskectomy, and open diskectomy with fusion. Fusion is necessary in the presence of concomitant segmental instability or significant foraminal stenosis resulting from disk space collapse.

Enhancement of Periprosthetic Bone Quality with Topical Hydroxyapatite-Bisphosphonate Composite

BACKGROUNDnImplant loosening is associated with inflammatory bone loss induced by ultra-high molecular weight polyethylene wear debris. We hypothesized that a hydroxyapatite-bisphosphonate composite improves periprosthetic bone quality and osseous integration of an intramedullary implant even in the presence of ultra-high molecular weight polyethylene particles in an experimental rat femur model.nnnMETHODSnA preliminary in vitro study determined the optimal concentration of zoledronate (50 microM) that would maximally decrease osteoclasts without harming osteoblasts. Hydroxyapatite-coated intramedullary nails were implanted bilaterally in the femora of sixteen rats (the control group), and hydroxyapatite-zoledronate-coated nails were implanted bilaterally in the femora of sixteen rats (the experimental group). Ultra-high molecular weight polyethylene particles were introduced into the femoral canal before implantation. Eight rats from each group were killed at six weeks, and the remaining rats were killed at six months. Periprosthetic bone mass was analyzed by dual x-ray absorptiometry and microcomputed tomography. Osseous integration was examined by biomechanical testing of pullout strength.nnnRESULTSnThe mean bone area (and standard deviation) in the periprosthetic bone region was significantly greater (p < 0.0001) in the hydroxyapatite-zoledronate group (2.388 +/- 0.960 mm2) than in the control group (0.933 +/- 0.571 mm2). This difference was larger in the six-week group than in the six-month group (p = 0.03). The average peak pullout force for the treated femora (241.0 +/- 95.1 N) was significantly greater (p < 0.0001) than that for the controls (55.6 +/- 49.0 N). This difference was similar in the six-week and six-month groups. The energy required for nail pullout was significantly greater (p < 0.0001) for the treated femora (521.6 +/- 293.8 N-mm) than for the controls (142.2 +/- 152.1 N-mm). This difference in energy to pullout was similar in the six-week and six-month groups. Regression analysis demonstrated a high correlation between periprosthetic bone mass and peak pullout force for both the six-week (r = 0.766, p = 0.0005) and six-month (r = 0.838, p < 0.0001) groups.nnnCONCLUSIONSnSurface modification of implants with hydroxyapatite-zoledronate improves periprosthetic bone quality and osseous integration.nnnCLINICAL RELEVANCEnHydroxyapatite-based site-specific delivery of bisphosphonates may be one way of reducing ultra-high molecular weight polyethylene wear particle-induced periprosthetic osteolysis and implant loosening.

Targeting Extracellular Signal-Regulated Kinase (ERK) Signaling Has Therapeutic Implications for Inflammatory Osteolysis

The extracellular signal-regulated kinase 1/2 (ERK) pathway, part of the mitogen-activated protein kinase (MAPK) family, is well-known for its role in cell differentiation and proliferation. In the context of osteoclastogenesis, macrophage colony stimulating factor (M-CSF) is an upstream activator of ERK signals for the survival of osteoclast precursors prior to their differentiation into multinucleated osteoclasts. In this study, we demonstrate by using both in vivo and in vitro models that the ERK signaling pathway involves an inflammatory response of various cells mediating osteolysis. Osteoblasts exhibit innate immune response by expressing M-CSF in response to lipopolysaccharide (LPS). LPS induced M-CSF expression is mediated by ERK. The inhibition of ERK signaling attenuated the inflammatory response to LPS both in vivo and in vitro. Thus, the ERK pathway may be a potentially important therapeutic target in the treatment of inflammatory osteolysis.

Zoledronate reduces unwanted bone resorption in intercalary bone allografts

Bone allografts are often hampered by graft incorporation and poor host bone formation. Bisphosphonates, synthetic pyrophosphate analogs, have shown promise in inhibiting bone resorption in human and animal trials. Some in vitro studies have suggested that high dose bisphosphonate may also inhibit bone formation, leading to our hypothesis that an ideal dose of bisphosphonate in allografts could protect allografts from resorption. We transplanted intercalary allografts in to the segmental defect of the rat femurs after soaking each allograft in zoledronate solution (30xa0µM) and then analysed bone density of the allografts six to 12xa0weeks after transplantation. At six and 12xa0weeks, the bone mineral density was higher in the experimental group compared with the control group. Qualitative radiographic and histological analysis also revealed more allograft resorption in the control group than in the zoledronate-treated group. Our data indicate that pharmacological modification of intercalary allografts with zoledronate solution can decrease osteoclast-mediated allograft resorption.RésuméLes allogreffes osseuses sont souvent altérées par la résorption osseuse et le peu de formation osseuse avec lhôte receveur. Les Biphosphonates et les analogues de pyrophosphates synthétiques ont montré leurs possibilités quant à linhibition de la résorption osseuse des allogreffes osseuses, lors dexpérimentations animales. Quelques études in vitro permettent de penser quà hautes doses les biphosphonates peuvent inhiber la régénération osseuse. Cependant, ils nous permettent également de penser quune dose idéale de bisphosphonate au niveau des allogreffes peut entraîner une minéralisation de celles-ci. Nous avons transplanté une allogreffe intercalaire sur des fémurs de rats après les avoir trempés dans une solution de zolédronate (30xa0μM) et analysé la densité osseuse de ces allogreffes à 6 à 12 semaines après leurs transplantations. A 6 et 12 semaines, la densité minérale osseuse est plus importante dans le groupe expérimental que dans le groupe contrôle. Lanalyse radiographique qualitative et quantitative ainsi que les analyses histologiques montre que la résorption des allogreffes est plus importante dans le groupe contrôle que dans le groupe traité par zolédronate. Toutes ces données nous permettent de penser que les modifications pharmacologiques entraînées par la solution de zolédronate au niveau de ces allogreffes intercalaires peuvent diminuer la résorption osseuse ostéoclastique.

ERK Signaling Regulates Macrophage Colony-Stimulating Factor Expression Induced by Titanium Particles in MC3T3.E1 Murine Calvarial Preosteoblastic Cells

Abstract:u2002 Periprosthetic osteolysis poses a significant clinical problem for patients who have undergone total joint arthroplastic surgeries. It has been widely recognized that there is a strong correlation between wear particles from orthopedic implants and osteolysis. However, the molecular mechanism underlying osteolysis still remains unclear. Although wear particles interact with a mixed cellular environment, namely macrophages and immune cells, osteoblasts compose the majority of the cell population surrounding orthopedic implants. Osteoblasts are also one of the major sources of receptor activator of nuclear factor‐kappa beta (NF‐κB) ligand (RANKL), a factor necessary for osteoclastogenesis. However, macrophage colony‐stimulating factor (M‐CSF), another cytokine responsible for preosteoclast proliferation, must also be present with RANKL for osteoclastogenesis to occur. The purpose of our study is to determine the signal transduction pathway by which titanium (Ti) particles, a metallic component of many orthopedic implants, induce M‐CSF expression in MC3T3.E1 murine calvarial preosteoblastic cells. Using reverse transcriptase‐polymerase chain reaction (RT‐PCR) and enzyme‐ linked immunosorbent assay (ELISA), our study demonstrated that submicron‐sized Ti particles induce M‐CSF expression via the extracellular signal‐regulated kinase (ERK) pathway in a dose‐dependent manner. Moreover, inhibition studies showed that a specific ERK inhibitor, PD98059, significantly downregulated M‐CSF production. Our results support the hypothesis that submicron‐sized Ti particles can induce M‐CSF expression in osteoblasts and thus may have a significant role in contributing to the onset of periprosthetic osteolysis.

Mechanical Loading Differentially Regulates Membrane-Bound and Soluble RANKL Availability in MC3T3-E1 Cells

Abstract:u2002 To understand the biochemical response of RANKL in response to mechanical loading, MC3T3‐E1 cells were biequiaxially stretched. A murine RANKL cDNA with double epitopes, pEF6 HA‐RANKL‐V5His, was transfected into MC3T3‐E1 cells, which were then stretched. Endogenous RANKL protein expression increased in response to mechanical loading. Membrane‐bound RANKL (HA‐RANKL‐V5His) increased in cell lysates while soluble RANKL (RANKL‐V5His) decreased in the conditioned media after mechanical loading. This may have resulted from the decreased activity of TACE after mechanical loading. Increased membrane‐bound RANKL may be one of the mechanisms through which osteoblasts adapt to mechanical loading by regulating osteoclastogenic activity in a region‐specific manner.

Comparison of spinal deformity surgery in patients with non-insulin-dependent diabetes mellitus (NIDDM) versus controls.

Study Design. A retrospective review. Objective. To quantify the exact impact of non–insulin-dependent diabetes mellitus (NIDDM) on operative complications and additional surgeries associated with spinal deformity surgery. Summary of Background Data. There are many references supporting diabetes mellitus (DM) as one of the major risk factors for perioperative complications in spinal surgery. However, the results vary depending on the type of DM, suggesting that insulin-dependent DM causes more complications than NIDDM, which is far more prevalent in the adult population with spinal deformity. Methods. Among 5119 adult patients (older than 40 yr) with deformities, 23 patients with NIDDM and 23 control (group C) patients with a minimum 2-year follow-up were selected. Both groups were matched for age at surgery, sex, body mass index, number of comorbidities, smoking history, current and prior fusion levels, estimated blood loss, and the amount of transfusion. Pre- and final Scoliosis Research Society (SRS) scores and Oswestry Disability Index (ODI), number of perioperative complications, and additional surgeries were compared. Within the group with NIDDM, patients with (+) or without (−) complications were compared in terms of postoperative glucose control. Results. There were no significant differences in the number of major or minor complications or additional surgeries between the 2 groups. There was no significant difference in postoperative glucose control with the NIDDM group (+) and (−). Group C reported significantly improved scores at final follow-up in all SRS domains and ODI. The group with NIDDM reported improvement in all domains except for the mental health and pain domains. However, there were no significant differences between the group with NIDDM and group C in terms of SRS and ODI scores preoperatively and postoperatively. Conclusion. Contrary to traditional thinking, properly selected NIDDM was not a significant risk factor for perioperative complications or additional surgeries in adult patients with spinal deformities.