Automatization and stress analysis data of CoCr laser weld fatigue tests.

This work includes raw and analyzed test data when using a recently developed fatigue test method for miniature laser welds in cobalt-chromium (CoCr) alloy joints [1]: 10.1016/j.jmbbm.2019.07.004. The automization of fatigue tests is crucial for saving costs and personnel resources and that is the reason why the atomization threshold and the resulting spectrum data related to CoCr welds are provided here. The finite element method based stress computation output is provided related to shearing-mode tests to support the dataset as a whole. In addition, the compositional data of the parent material and the laser weld are given.

Miniature CoCr laser welds under cyclic shear: Fatigue evolution and crack growth.

Miniature laser welds with the root depth in the range of 50-300 µm represent air-tight joints between the components in medical devices, such as those in implants, growth rods, stents and various prostheses. The current work focuses on the development of a fatigue test specimen and procedure to determine fatigue lives of shear-loaded laser welds. A cobalt-chromium (CoCr) alloy is used as a benchmark case. S-N graphs, damage process, and fracture surfaces are studied by applying x-ray analysis, atomic force microscopy, and scanning electron microscopy both before and after the crack onset. A non-linear material model is fitted for the CoCr alloy to run finite element simulations of the damage and deformation. As a result, two tensile-loaded specimen designs are established and the performance is compared to that of a traditional torque-loaded specimen. The new generation specimens show less variation in the determined fatigue lives due to well-defined crack onset point and, therefore, precise weld seam load during the experiments. The fatigue damage concentrates to the welded material and the entire weld experiences fatigue prior to the final, fracture-governed failure phase. For the studied weld seams of hardened CoCr, a regression fatigue limit of 10.8-11.8 MPa, where the stress refers to the arithmetic average shear stress computed along the region dominated by shear loading, is determined.

[The history of spondylolisthesis. The nineteenth century: early case reports, terminology, etiology and pathogenesis]. / Zur Geschichte der Spondylolisthese. Das 19. Jahrhundert: Frühe Fallberichte, Terminologie, Ätiologie und Pathogenese.

The author describes the history of research and development of knowledge on lumbar spondylolisthesis. Based on the available literature, early case reports, creation of the terminology and etiological concepts are presented.

Untreated Scheuermann's disease: a 37-year follow-up study.

INTRODUCTION: There are only a few follow-up studies of untreated Scheuermann's disease. The aim of this study was to investigate the relationship between vertebral changes, back pain, and disability in patients with untreated Scheuermann's disease after a 37-year follow-up. MATERIALS AND METHODS: Eighty patients responded to a postal questionnaire concerning back pain and disability and 49 of them had classic Scheuermann's disease. Degree of kyphosis, lordosis, scoliosis, the number of affected vertebrae, and mean and maximum wedge angles were measured from radiographs. Back pain and disability scores were compared to a sample of the general Finnish population (n = 3,835). RESULTS: At follow-up, the patients were on average 59 (SD 8) years old (range 44-79 years), and the mean follow-up time was 37 (SD 7) years (26-54 years). The patients comprised more males than females (3.1:1). At follow-up, male patients were on average 3 cm taller than controls (p = 0.007). At age 20, female patients compared to controls were on average 6 kg heavier (p = 0.016) and had higher body mass index (BMI) (mean 23.9 kg/m(2) vs. 20.8 kg/m(2), p = 0.001). Scheuermann's patients had 2.5-fold [odds ratio (OR); 95% confidence interval (CI); 1.4-4.5, p = 0.003] increased risk for constant back pain compared to controls. The risk for disability because of back pain during the past 5 years (OR 2.6; 95% CI 1.4-4.7, p = 0.002), risk for back pain during the past 30 days (OR 3.7; 95% CI 1.9-7.0, p < 0.001) and risk for sciatic pain (OR 2.3; 95% CI 1.3-4.3, p = 0.005) were higher compared to controls. Scheuermann's patients had higher risk for difficulties in mounting stairs (OR 5.4; 95% CI 2.8-10.3, p < 0.001) and in carrying a 5 kg load for at least 100 m (OR 7.2; 95% CI 3.9-13.3, p < 0.001). CONCLUSION: Scheuermann's patients had a higher risk for back pain and disabilities during activities of daily living than controls. However, the degree of thoracic kyphosis among Scheuermann's patients was not related to back pain, quality of life, or general health.

[Computer-assisted spine surgery: principles, technique, results and perspectives]. / Computerunterstützte Wirbelsäulenchirurgie. Prinzipien, Technik, Ergebnisse und Perspektiven.

Computer-assisted techniques were introduced in spine surgery in the 1990s to improve accuracy and safety of operative procedures. Several reports on clinical results of computer-aided screw insertion in the cervical, thoracic, and lumbar spine as well as the sacro-iliac joints are available. They show a significant decrease of screw malplacement rates as compared to conventional insertion techniques. The quality of preoperative planning of spinal procedures has improved markedly by using computer navigation systems. Drawbacks, reliability problems, and safety issues of computer navigation are discussed. In the near future, the use of computer guidance for minimally invasive and percutaneous spine procedures is expected.

Experimental anterior spine fusion using bovine bone morphogenetic protein: a study in rabbits.

We developed an experimental model to study the merit of bovine bone morphogenic protein (bBMP) injection into the intervertebral disc to induce anterior interbody fusion. A total of 24 rabbits, divided into three groups of 8 animals each, were used. One hundred and fifty microg of partially purified bBMP was employed in the first group and 10 microg bBMP in the second group. In the control group, a sham operation was performed. The animals were followed radiographically at weekly intervals and animals were killed 3, 6, and 12 weeks postoperatively. After sacrifice, a mechanical and histologic evaluation of fusion was performed. Results of radiographic and histologic evaluation showed bone formation, which had resulted in the bridging of adjacent endplates, in the 150-microg group. In the 10-microg group, new bone formation was less extensive. In the control group, intradiscal bone formation was seen in only 1 animal. Range of motion measurements on flexion/extension films showed significantly decreased motion in segments that were fused with 150-microg of BMP. This study demonstrated the utility of an experimental model which allowed investigation of how anterior spine fusion may be further studied. Intradiscal injection of BMP could ultimately play a role in the development of minimally invasive techniques for anterior spinal fusion.

Tissue engineered cartilage repair using cryopreserved and noncryopreserved chondrocytes.

The objective of this study was to reconstruct full thickness cartilage defects in rabbit knees with in vitro engineered cartilage tissue based on noncryopreserved and cryopreserved chondrocytes in polymer fleece scaffolds. Osteochondral defects in rabbits were filled with polymer cylinders with noncryopreserved or cryopreserved allogeneic chondrocytes and compared with empty defects and defects filled with polymers alone. The defects were evaluated macroscopically and histologically 4 and 12 weeks after surgery. Transplant samples were graded using a semiquantitative score system. Successful healing was defined as complete integration of a hyalinelike and structurally intact cartilage into the defect and occurred in 71% of the group with noncryopreserved chondrocytes after 4 weeks and 100% of the rabbit knees after 12 weeks, whereas hyalinelike cartilage was seen in 71% of the group with cryopreserved chondrocytes after 4 weeks, and in 85% after 12 weeks. No newly formed cancellous bone was present in the subchondral bone. In the control groups, no cartilagelike tissue was seen. Transplantation of chondrocytes in polymer fleece constructs is a suitable approach for joint cartilage repair. Noncryopreserved chondrocytes are preferred to cryopreserved chondrocytes because of their regenerative potential. In vitro engineered cartilage offers broad opportunities for optimization of cartilage transplantation based on the controlled use of morphogenic and biologically active factors such as transforming growth factor-beta and bone morphogenetic proteins.

Accuracy of pedicle screw insertion with and without computer assistance: a randomised controlled clinical study in 100 consecutive patients.

We performed a randomised controlled study to assess the accuracy of computer-assisted pedicle screw insertion versus conventional screw placement under clinical conditions. One hundred patients scheduled for posterior thoracolumbar or lumbosacral pedicle screw instrumentation were randomised into two groups, either for conventional pedicle screw placement or computer-assisted screw application using an optoelectronic navigation system. From the computer-assisted group, nine patients were excluded: one because of an inadequate preoperative computed tomography study, seven because of problems with the specific instruments or the computer system, and one because of an intraoperative anesthesiological complication. Thus, there were 50 patients in the conventional group and 41 in the computer-assisted group, and the number of screws inserted was 277 and 219, respectively. There was no statistical difference between the groups concerning age, gender, diagnosis, type of operation performed, mean operating time, blood loss, or number of screws inserted. The time taken for screw insertion was significantly longer in the computer-assisted group. Postoperatively, screw positions were assessed by an independent radiologist using a sophisticated CT imaging protocol. The pedicle perforation rate was 13.4% in the conventional group and 4.6% in the computer-assisted group (P = 0.006). Pedicle perforations of more than 4 mm were found in 1.4% (4/277) of the screw insertions in the conventional group, and none in the computer-assisted group. Complications not related to pedicle screws were two L5 nerve root lesions, one end plate fracture, one major intraoperative bleeding and one postoperative death in the conventional group, and one deep infection in the computer-assisted group. In conclusion, pedicular screws were inserted more accurately with image-guided computer navigation than with conventional methods.

Computer-assisted spine surgery.

Computer assistance has been shown to improve significantly the accuracy and safety of pedicle screw insertion under clinical conditions. The technique of image-guided navigation is described in this article, based on the authors' clinical experience of over 4 years. The value of navigation systems for preoperative planning is discussed. Clinical results of the application of this new method in the cervical, thoracic, and lumbosacral spine as well as the iliosacral joints are presented by means of the authors' own studies and reports from the literature. Pros and cons of computer guidance are discussed. The authors predict computer navigation will be used in percutaneous and minimally invasive procedures in the near future.

A new approach to computer-aided spine surgery: fluoroscopy-based surgical navigation.

A new computer-based navigation system for spinal surgery has been designed. This was achieved by combining intraoperative fluoroscopy-based imaging using conventional C-arm technology with free-hand surgical navigation principles. Modules were developed to automate digital X-ray image registration. This is in contrast to existing computed tomography- (CT) based spinal navigation systems, which require a vertebra-based registration procedure. Cross-referencing of the image intensifier with the surgical object allows the real-time image-interactive navigation of surgical tools based on one single registered X-ray image, with no further image updates. Furthermore, the system allows the acquisition and real-time use of multiple registered images, which provides an advanced multi-directional control (pseudo 3D) during surgical action. Stereotactic instruments and graphical user interfaces for image-interactive transpedicular screw insertion have been developed. A detailed validation of the system was performed in the laboratory setting and throughout an early clinical trial including eight patients in two spine centers. Based on the resulting data, the new technique promises improved accuracy and safety in open and percutaneous spinal surgery.

Dorsal instrumentation for idiopathic adolescent thoracic scoliosis: rod rotation versus translation.

The radiographic and clinical outcomes and complications among two groups of adolescent patients treated for idiopathic thoracic scoliosis with dorsal instrumentation using a unified implantation system (Universal Spinal System) were compared retrospectively. A total of 69 patients were included in the study. In 30 patients an intraoperative correction of the scoliosis was performed by translation and segmental correction (translation group, Helsinki). In 39 patients the correction was achieved according to the Cotrel-Dubousset rod rotation maneuver (rod rotation group, Berlin). The goal of the present study is to investigate whether one of the operative procedures leads to a better correction of idiopathic adolescent thoracic scoliosis than the other. The mean follow-up interval was 30 months, with a minimum of 12 months. There were no significant preoperative differences in age (15+/-2 years in both groups), gender, or type of scoliosis (King types 2, 3, and 4). The preoperative radiographic measurements showed no significant differences between the two groups. In both patient groups, the thoracic primary curve, the lumbar secondary curve and the thoracic apical rotation were improved by the operation. Lumbar apical rotation and the sagittal profile were unchanged in both groups. The thoracic primary curve was corrected from 50 degrees +/-6 degrees to 24 degrees +/-7 degrees in the translation group and from 54 degrees +/-11 degrees to 220 degrees +/-11 degrees in the rod rotation group. The extent of the correction of the thoracic curve was significantly greater in the rod rotation group than in the translation group (59% vs. 52% correction). In contrast, the translation procedure seems to have a more beneficial effect on spinal balance than rod rotation. Neurological complications did not occur. In both patient groups an increase in the non-instrumented lumbar curve was noted, in two cases each. In three patients from the rod rotation group the instrumentation had to be removed due to a late infection with negative microbiological results.

The external spinal fixator does not reduce anterior column motion under axial compressive loads. A mechanical in vitro study.

We performed an in vitro study to investigate the effect of external spinal fixation on anterior column motion under physiological axial compression loading. The AO external spinal fixator (ESF) was applied to 5 human cadaveric lumbar spine specimens (L3-S1) at levels L4 to S1. All specimens were tested in 4 configurations: i) intact, ii) ESF in a neutral position, iii) ESF in distraction (12 mm), and iv) ESF in compression (8-12 mm). Cyclic sinusoidal axial compressive loads from 60 to 600 N were applied for 10 cycles in each test condition. The axial displacement of the load application point was recorded as an indicator of anterior column axial translation. The axial motion with the fixator in distraction was significantly greater than all other conditions, including intact. Compression of the fixator resulted in the least axial displacement. External fixation in the neutral position did not significantly affect the overall axial translation, when compared to the intact state. In conclusion, the external spinal fixator did not significantly reduce anterior column axial translation and, in distraction, this motion exceeded that of the intact specimen. Since pain relief is frequently observed during distraction of the painful segment/s with the external fixator, the mechanical basis of the pain relief is not well understood.

Improved accuracy of pedicle screw insertion with computer-assisted surgery. A prospective clinical trial of 30 patients.

STUDY DESIGN: A prospective clinical trial was done to study the accuracy of pedicle screw placement in 30 consecutive computer-assisted orthopedic surgeries. OBJECTIVES: To determine the accuracy and clinical applicability of this new method for pedicle screw insertion. SUMMARY OF BACKGROUND DATA: Conventional screw insertion techniques have been associated with high pedicle screw malplacement rates in cadaver studies and clinical studies with postoperative computed tomography evaluation. METHODS: Thirty transpedicular, low-back, titanium instrumentations were performed with computer-assisted orthopedic surgery. The accuracy of screw placement was evaluated using a sophisticated computed tomography protocol. RESULTS: The total number of pedicle screws was 174. Of these, 139 (79.9%) could be inserted with computer-assisted orthopedic surgery. The malplacement rate of computer-assisted orthopedic surgery screws was 4.3%. In screws that were not inserted by computer-assisted orthopedic surgery, the malplacement rate was 14.3%. One malplaced screw that had not been inserted with computer-assisted orthopedic surgery caused L4 root paresis. CONCLUSIONS: The accuracy of pedicle screw placement using computer-assisted surgery proved to be superior to the accuracy obtained when using conventional techniques.

Disc herniation in the lumbar spine during growth: long-term results of operative treatment in 18 patients.

We studied 18 patients who had undergone surgery for herniated lumbar discs between the ages of 11 and 17 years. The inclusion criteria for girls was an age of 15 years or below and for boys 17 or below at surgery. The mean follow-up time was 10 years and the clinical outcome was good. Age at surgery and length of the follow-up had no effect on the result. The radiological disc height at follow-up did not correlate with the follow-up time or age of the patient at operation. MRI scans at follow-up from ten patients operated at less than 15 years of age revealed multilevel disc degeneration but favourable clinical results.

Disc degeneration in young patients with isthmic spondylolisthesis treated operatively or conservatively: a long-term follow-up.

The purpose of this long-term follow-up was (1) to investigate disc changes in the olisthetic segment in patients treated conservatively, (2) to compare disc changes above the slipped vertebra in conservatively treated patients with those in operatively treated patients, and (3) to establish possible relations of disc changes to the degree of the slip and to subjective back pain symptoms of the patients. The subjects were 227 patients with isthmic L5 olisthesis diagnosed under 20 years of age (mean 13.8 years) with a mean follow-up of 15.4 (range 5-30) years. Of these, 145 patients had been treated with segmental fusion and 82 had been treated conservatively. At follow-up, standing anteroposterior and lateral radiographs as well as flexion/extension views of the lumbar spine were taken. Disc degeneration was graded semiquantitatively: 0 = normal disc height, 1 = decrease of disc height < 50%, 2 = decrease > or = 50%, and 3 = obliteration of the disc. In the conservatively treated patients degeneration of the olisthetic disc was distributed by grade as follows: O: n = 38, 1: n = 24, 2: n = 14, 3: n = 6. No motion at all was observed in the olisthetic segment in 40 patients (48%) with a mean slip of 30%, segmental motion of 4 degrees-18 degrees was found in 42 patients with a mean slip of 14%. There was a statistically significant association of the degree of slip to the severity of disc degeneration and non-mobility of the segment. Grade 1 degeneration of the L4/5 disc occurred in 25.6% of the conservatively treated patients and in 32% of 48 patients treated with L5-S1 fusion. This correlated with the severity of the slip, but not with pain symptoms or pathologic segmental mobility at the time of follow-up. Out of 84 patients with L4-S1 fusion, in 17% grade 1 degeneration of the L3/4 disc was observed, and 3 out of 13 patients (23%) with L3-S1 fusion had grade 1 degeneration of the disc above the fusion. The disc changes had no correlation with subjective pain symptoms. It is concluded that the natural course of isthmic spondylolisthesis is associated with disc degeneration and spontaneous stabilization of the olisthetic segment. Fusion operations do not significantly increase the rate of disc degeneration in the adjacent disc above the fusion after a mean postoperative follow-up of 13.8 years. No correlation between the number of degenerated discs or the degree of degeneration and subjective low back pain symptoms was found.

Accuracy of pedicle screw insertion: a prospective CT study in 30 low back patients.

A prospective study of the accuracy of titanium pedicle screw placement in 30 low back operations was performed. The postoperative plain radiographs and CT reformation images were evaluated by two independent radiologists. Thirty-two out of 152 screws (21%) perforated the pedicle cortex. One-tenth of the perforations was detected with conventional radiography. In ten patients (33%) all the screws were located within the pedicle. The clinical significance of this study lies in the finding that pedicle perforations are more frequent than is generally believed and that, in spite of the many malplacements, no screw that perforated by less than 4.0 mm caused neurological problems. Only one nerve root lesion was detected.

Spondylolisthesis in children and adolescents.

Isthmic spondylolisthesis occurs in 4.4 % of children. In general it is a benign condition. The majority of individuals with mild or moderate isthmic vertebral slip remain free of symptoms or get only mild symptoms. In children and adolescents with mild slip, primary treatment of pain symptoms is non-operative. Young children before the growth spurt need radiological follow-up for documentation of possible slip progression. If the slip exceeds 25 % in a child, segmental fusion to prevent further progression should be considered. Uninstrumented posterolateral fusion is the method of choice for treatment of pain symptoms not responding to conservative measures in slips up to 50 %. In severe slips ( > 50 %), anterior or combined fusion is necessary to prevent further progression of lumbosacral kyphosis. The clinical and subjective results of in situ fusion in this age group are satisfactory in 80-90 % of cases. Slip reduction is possible. It requires internal fixation and is connected with a higher risk of complications. The results of slip reduction have not yet been shown to be superior to results after in situ fusion. It may be performed in cases of spondyloptosis with severe impairment of function and sagittal malalignment of the spine.

[Spondylolisthesis in childhood and adolescence]. / Die Spondylolisthesis im Kindes- und Jugendalter.

Isthmic spondylolisthesis occurs in 4.4% of children. In general it is a benign condition. The majority of individuals with mild or moderate isthmic vertebral slip remain free of symptoms or get only mild symptoms. In children and adolescents with mild slip, primary treatment of pain symptoms is non-operative. Young children before the growth spurt need radiological follow-up for documentation of possible slip progression. If the slip exceeds 25% in a child, segmental fusion to prevent further progression should be considered. Uninstrumented posterolateral fusion is the method of choice for treatment of pain symptoms not responding to conservative measures in slips up to 50%. In severe slips (> 50%), anterior or combined fusion is necessary to prevent further progression of lumbosacral kyphosis. The clinical and subjective results of in situ fusion in this age group are satisfactory in 80-90% of cases. Slip reduction is possible. It requires internal fixation and is connected with a higher risk of complications. The results of slip reduction have not yet been shown to be superior to results after in situ fusion. It may be performed in cases of spondyloptosis with severe impairment of function and sagittal malalignment of the spine.