Misaligned spinal rods can induce high internal forces consistent with those observed to cause screw pullout and disc degeneration.

BACKGROUND CONTEXT: Manual contouring of spinal rods is often required intraoperatively for proper alignment of the rods within the pedicle screw heads. Residual misalignments are frequently reduced by using dedicated reduction devices. The forces exerted by these devices, however, are uncontrolled and may lead to excessive reaction forces. As a consequence, screw pullout might be provoked and surrounding tissue may experience unfavorable biomechanical loads. The corresponding loads and induced tissue deformations are however not well identified. Additionally, whether the forced reduction alters the biomechanical behavior of the lumbar spine during physiological movements postoperatively, remains unexplored. PURPOSE: To predict whether the reduction of misaligned posterior instrumentation might result in clinical complications directly after reduction and during a subsequent physiological flexion movement. STUDY DESIGN: Finite element analysis. METHODS: A patient-specific, total lumbar (L1-S1) spine finite element model was available from previous research. The model consists of poro-elastic intervertebral discs with Pfirrmann grade-dependent material parameters, with linear elastic bone tissue with stiffness values related to the local bone density, and with the seven major ligaments per spinal motion segment described as nonlinear materials. Titanium instrumentation was implemented in this model to simulate a L4, L5, and S1 posterolateral fusion. Next, coronal and sagittal misalignments of 6 mm each were introduced between the rod and the screw head at L4. These misalignments were computationally reduced and a physiological flexion movement of 15° was prescribed. Non-instrumented and well-aligned instrumented models were used as control groups. RESULTS: Pulling forces up to 1.0 kN were required to correct the induced misalignments of 6 mm. These forces affected the posture of the total lumbar spine, as motion segments were predicted to rotate up to 3 degrees and rotations propagated proximally to and even affect the L1-2 level. The facet contact pressures in the corrected misaligned models were asymmetrical suggesting non-physiological joint loading in the misaligned models. In addition, the discs and vertebrae experienced abnormally high forces as a result of the correction procedure. These effects were more pronounced after a 15° flexion movement following forced reduction. CONCLUSIONS: The results of this study indicate that the correction of misaligned posterior instrumentation can result in high forces at the screws consistent with those reported to cause screw pullout, and may cause high-tissue strains in adjacent and downstream spinal segments. CLINICAL SIGNIFICANCE: Proper alignment of spinal posterior instrumentation may reduce clinical complications secondary to unfavorable biomechanics.

Outcomes of a Modular Intercalary Endoprosthesis as Treatment for Segmental Defects of the Femur, Tibia, and Humerus.

BACKGROUND: Resection of diaphyseal bone tumors for local tumor control and stabilization often results in an intercalary skeletal defect and presents a reconstructive challenge for orthopaedic surgeons. Although many options for reconstruction have been described, relatively few studies report on the functional outcomes and complications of patients treated with modular intercalary endoprostheses. QUESTIONS/PURPOSES: The objectives of this study were to examine clinical outcomes after reconstruction with a modular intercalary endoprosthesis with a specific focus on (1) the rate of complication or failure; (2) differences in complication rates by anatomic site; (3) functional results as assessed by the Musculoskeletal Tumor Society System (MSTS); and (4) differences in complication rate between patients treated with cemented versus noncemented fixation. METHODS: We conducted a retrospective chart review of patients treated with a modular intercalary endoprosthesis from three musculoskeletal oncology centers from 2008 to 2013. The indication for use of this intercalary endoprosthesis was segmental bone loss from aggressive or malignant tumor with sparing of the joint above and below and deemed unsuitable for biologic reconstruction. No other implant was used for this indication during this period. During this period, 41 patients received a total of 44 intercalary implants, which included 18 (40%) humeri, 5 (11%) tibiae, and 21 (48%) femora. There were 27 (66%) men and 14 (34%) women with a mean age of 63 years (range, 18­91 years). Eight patients (20%) had primary bone tumors and 33 (80%) had metastatic lesions. Thirty-five (85%) patients were being operated on as an initial treatment and six (15%) for revision of a previous reconstruction. Twenty-nine (66%) procedures had cemented stem fixation and 15 (34%) were treated with noncemented fixation. The overall mean followup was 14 months (range, 1­51 months). Patients with primary tumors had a mean followup of 19 months (range, 4­48 months) and patients with metastatic disease had a mean followup of 11 months (range, 1­51 months). Causes of implant failure were categorized according to Henderson et al. [19] into five types as follows: Type I (soft tissue failure), Type II (aseptic loosening), Type III (structural failure), Type IV (infection), and Type V (tumor progression). At 2 years of followup, 38 (93%) of these patients were accounted for with three (7%) lost to followup. MSTS functional assessment was available for 39 of 41 patients (95%). RESULTS: At latest followup of these 41 patients, 14 (34%) patients were dead of disease, two patients (5%) dead of other causes, seven (17%) are continuously disease-free, one (2%) shows no evidence of disease, and 17 (41%) are alive with disease. There were 12 (27%) nononcologic complications. Five (11%) of these were Type II failures occurring in noncemented implants between the stem and bone, and six (14%) were Type III failures occurring in cemented implants at the clamp-rod implant interface. One patient developed a deep infection (2%, Type IV failure) and underwent removal of the implant. Additionally, one patient (2%, Type V failure) was treated by amputation after local progression of his metastatic disease. Complications were more common in femoral reconstructions than in tibial or humeral reconstructions. Twelve of 21 patients (57%) with femoral reconstructions had complications versus 0% of tibial or humeral reconstructions (0 of 23; odds ratio [OR], 62; 95% confidence interval [CI], 3­1154; p < 0.0001). The mean overall MSTS score was 77%. Implants with cemented fixation (29) had higher mean MSTS scores when compared with implants with noncemented (15) fixation (84% versus 66%, p = 0.0017). The complication rate was 33% in noncemented cases and 21% in cemented cases (p = 0.39); however, Type II failure at the bone-stem interface was associated with noncemented fixation and Type III failure at the clamp-rod interface was associated with cemented fixation (OR, 143; 95% CI, 2.413­8476; p = 0.0022). CONCLUSIONS: The results of this study indicate that this modular intercalary endoprosthesis yields equivalent results to other studies of intercalary endoprostheses in terms of MSTS scores. We found that patients treated with intercalary endoprostheses in the femur experienced more frequent complications than those treated for lesions in either the humerus or tibia and that the femoral complication rate of this endoprosthesis is higher when compared with other studies of intercalary endoprostheses for femoral reconstruction. Further studies are still needed to determine the long-term outcomes of this endoprosthesis in patients with primary tumors where longevity of the implant is of more importance than in the metastatic setting. We recommend cemented fixation for this intercalary modular endoprostheses because this provides improved MSTS scores and allows immediate return to weightbearing, which is of advantage to metastatic patients with limited lifespans. Level of Evidence: Level III, therapeutic study.

Accuracy of a hexapod parallel robot kinematics based external fixator.

BACKGROUND: Different hexapod-based external fixators are increasingly used to treat bone deformities and fractures. Accuracy has not been measured sufficiently for all models. METHODS: An infrared tracking system was applied to measure positioning maneuvers with a motorized Precision Hexapod® fixator, detecting three-dimensional positions of reflective balls mounted in an L-arrangement on the fixator, simulating bone directions. By omitting one dimension of the coordinates, projections were simulated as if measured on standard radiographs. Accuracy was calculated as the absolute difference between targeted and measured positioning values. RESULTS: In 149 positioning maneuvers, the median values for positioning accuracy of translations and rotations (torsions/angulations) were below 0.3 mm and 0.2° with quartiles ranging from -0.5 mm to 0.5 mm and -1.0° to 0.9°, respectively. CONCLUSIONS: The experimental setup was found to be precise and reliable. It can be applied to compare different hexapod-based fixators. Accuracy of the investigated hexapod system was high.

Successful treatment of extensively drug-resistant Pseudomonas aeruginosa osteomyelitis using a colistin- and tobramycin-impregnated PMMA spacer.

Discovered in 1949, the antibiotic colistin was initially used for therapeutic purposes. Parenteral use of colistin was gradually abandoned because of its side-effect profile, especially its nephrotoxicity and neurotoxicity. Despite the risk of these potentially serious adverse effects, increasing resistance of Gram-negative bacteria has led to a renaissance of intravenous use of colistin in the last few years. Local administration of colistin is an alternative method to minimise the risk of systemic toxicity. We present a case of extensively drug-resistant Pseudomonas aeruginosa osteomyelitis treated successfully with high-dose colistin- and tobramycin-impregnated bone cement as a drug delivery vehicle. For the first time, local colistin concentrations in drainage and synovial fluid were quantified in order to determine the optimal dose and to minimise serious side effects. Insertion of a bone cement spacer loaded with a high dose of tobramycin and colistin resulted in local colistin levels at the infection site that exceeded the minimum inhibitory concentration (MIC) of colistin against the isolated P. aeruginosa five-fold on Day 4. Thus, the treatment may be expected to exert a prolonged effect. Whereas systemic administration of colistin alone was not sufficient to treat the infection, combined local and parenteral therapy led to eradication of P. aeruginosa in this patient. Plasma colistin levels remained in the therapeutic range, which confirms the systemic safety of the method.

Nucleoplasty, a minimally invasive procedure for disc decompression: a systematic review and meta-analysis of published clinical studies.

BACKGROUND: Nucleoplasty, based on Coblation® technology, is a minimally invasive procedure used to decompress herniated discs. Reviews to date--exclusively systematic reviews--recommend nucleoplasty for treating chronic back pain, although with the restriction of limited to fair evidence. We therefore aimed to summarize and interpret our calculated results, where possible comprehensively and quantitatively, using statistical methods in the context of a meta-analysis supplementing a systematic review. In the process, the central question was to statistically determine whether, and to what extent, nucleoplasty can positively affect pain relief and functional mobility as well as lower the complication rate. OBJECTIVE: Newly published studies made it possible to conduct a meta-analysis of the visual analog scale (VAS), a measuring instrument used to determine pain intensity, and the Oswestry Disability Index (ODI), a scale that reflects the degree of impairment in percent. In addition to having clearly sound evidence for analyzing VAS/NPS data, the present, newly compiled meta-analysis was able to summarize VAS and ODI data quantitatively and to calculate a total complication rate for the first time. It was thereby possible to make a first comparison between nucleoplasty and conservative therapy (including epidural steroid injection). STUDY DESIGN: This meta-analysis examined all study data published in clinical trials involving the nucleoplasty procedure for plasma disc decompression. METHODS: A systematic search using the terms nucleoplasty and/or plasma disc decompression was conducted for literature listed in MEDLINE. Twenty-seven eligible studies (22 prospective trials and 5 retrospective trials) were included, and pooled analyses as well as various subgroup analyses (differentiation between cervical and lumbar disc herniations, comparisons with alternative treatments such as epidural steroid injection) were performed based on their data. RESULTS: Pain decreased from a baseline VAS value of 7.27 to 2.12 (postop/first day), 2.50 (one week), 2.70 (2 weeks), 3.23 (one month), 2.66 (6 weeks), 2.84 (3 months), 3.06 (6 months), 3.03 (12 months), 1.54 (18 months), and 3.69 (24 months) after nucleoplasty. The ODI value (baseline: 58.95) dropped to 28.60 (one week), 29.00 (2 weeks), 23.21 (one month), 30.00 (6 weeks), 18.30 (3 months), 22.54 (6 months), 24.43 (12 months), 12.82 (18 months), and 36.98 (24 months). Compared to baseline, significant pain reduction and improvement in functional mobility after nucleoplasty were observed at every time point. Nucleoplasty showed a total complication rate of 1.5%, with the individual rates being 0.8% for cervical and 1.8% for lumbar nucleoplasty. Nucleoplasty was superior to conservative therapy at every time point and for all 3 included parameters, at some measurement time points even significantly. CONCLUSIONS: Nucleoplasty reduces pain in the long term and improves patients' functional mobility. It is an effective, low-complication, minimally invasive procedure used to treat disc herniations.

[Malpractice assessment at the MDK in lower Saxony]. / Behandlungsfehlerbegutachtung beim MDK Niedersachsen.

Since 1988 the MDK (Medical Service of the health insurances) in Lower Saxony has frequently been asked to clinically assess potential malpractice cases according to the German social law (Sect. 66 SGB V and Sect. 116 SGB X). In Lower Saxony this amounts to more than 2,000 assessments per year. By far the most treatment errors as compared to all other medical disciplines are seen in the surgical field. Surprisingly, the highest rate of errors is found in diagnostic and case management rather than in actual surgical therapy. With about 20% the complaint rate with the MDK of Lower Saxony has largely remained unchanged during the last years.