Can experimental data in humans verify the finite element-based bone remodeling algorithm?

STUDY DESIGN: A finite element analysis-based bone remodeling study in human was conducted in the lumbar spine operated on with pedicle screws. Bone remodeling results were compared to prospective experimental bone mineral content data of patients operated on with pedicle screws. OBJECTIVE: The validity of 2 bone remodeling algorithms was evaluated by comparing against prospective bone mineral content measurements. Also, the potential stress shielding effect was examined using the 2 bone remodeling algorithms and the experimental bone mineral data. SUMMARY OF BACKGROUND DATA: In previous studies, in the human spine, the bone remodeling algorithms have neither been evaluated experimentally nor been examined by comparing to unsystematic experimental data. METHODS: The site-specific and nonsite-specific iterative bone remodeling algorithms were applied to a finite element model of the lumbar spine operated on with pedicle screws between L4 and L5. The stress shielding effect was also examined. The bone remodeling results were compared with prospective bone mineral content measurements of 4 patients. They were measured after surgery, 3-, 6- and 12-months postoperatively. RESULTS: After 1 year, there was an average experimental bone loss of 9.78% below the positions of pedicle screws, and the results for the 2 bone remodeling algorithms showed an average bone gain of 8.41% and 1.61%. There were no similarities between the bone remodeling and experimental data. CONCLUSION: The bone remodeling data showed no resemblances when compared to the prospective data of BMC measurements. There was no basis for confirming the validity of the bone remodeling algorithms in this study.

Effect of hydroxyapatite-coated tibial components on changes in bone mineral density of the proximal tibia after uncemented total knee arthroplasty: a prospective randomized study using dual-energy x-ray absorptiometry.

Sixteen patients scheduled for an uncemented total knee arthroplasty (TKA) were randomized to receive a tibial component either with (n = 8) or without (n = 8) hydroxyapatite (HA) coating. In 4 regions of interest, prospective measurements of bone mineral density (BMD) using dual-energy x-ray absorptiometry were performed in the proximal tibia. Two years after the operation, the only significant change in BMD was in the lateral tibial condyle, where BMD had increased by 6.1% (95% confidence interval: 2.3%-9.9%) in patients with tibial components without HA. The intragroup changes (0-24 months) in the uncoated group and HA-coated group were significantly different (P = .003) in these regions of interest. There was no significant effect of HA coating on bone remodeling pattern of the proximal tibia.

Nonlinear finite-element analysis and biomechanical evaluation of the lumbar spine.

A finite-element analysis (FEA) model of an intact lumbar disc-body unit was generated. The vertebral body of the FEA model consisted of a solid tetrahedral core of trabecular bone surrounded by a cortical shell. The disc consisted of an incompressible nucleus surrounded by nonlinear annulus fibers embedded in a solid ground substance. The purpose was to create a FEA model suitable for clinical purposes as fracture assessment, instrumentation with pedicle screws, and bone remodeling. Testing of the FEA model was performed nonlinear for a number of loading conditions, and the results were compared with experimental data from the literature. The results showed good agreement. The formulation of the FEA model can be justified for the tested loading conditions.

No difference in clinical outcome after posterolateral lumbar fusion between patients with isthmic spondylolisthesis and those with degenerative disc disease using pedicle screw instrumentation: a comparative study of 112 patients with 4 years of follow-up.

We compared the clinical outcome after spinal fusion between patients with isthmic spondylolisthesis and those with degenerative disc disease of the lumbar spine, using multiple logistic regression analysis. A questionnaire describing medication, pain, vocational status and patient satisfaction was mailed to all the patients at a median interval of 4 years after their operation. Fusion was evaluated on plain radiographs at a minimum of 12 months after surgery, and patients were classified as fused or not fused. The overall satisfaction rate was 70%. The results of the present study showed no difference in the outcome after spinal fusion between the two groups of patients. The factors that significantly increased the likelihood of an optimal result - defined as patient satisfaction, return to work, and reduced medication - were male gender, being in work prior to surgery, and being a non-smoker. Since spinal fusion is an expensive treatment with potentially serious risks, and leaves one-third of the patients with an unsatisfactory result, we believe that more studies focusing on the indications for surgery should be performed.

Nonorganic pain drawings are associated with low psychological scores on the preoperative SF-36 questionnaire in patients with chronic low back pain.

The Short Form 36 questionnaire (SF-36) measures general health and well-being. Within the last 5 years it has been used increasingly to characterise patients in the medical literature. Relatively few studies have used the SF-36 on patients with chronic low back pain undergoing preoperative evaluation, but results suggest that it may be predictive of surgical outcome. Pain drawings are a routine part of evaluation prior to spinal surgery in several centres, since their classification of organic or nonorganic has been shown in some studies to correlate well with psychological characteristics predicting poor outcome. The purpose of the present study was to assess possible correlations between nonorganic pain drawings and the psychological scales in the SF-36. We included 128 patients in the study, all of them referred from other hospitals. Previous spinal surgery had been undergone by 25%, and 59% required daily medication because of low back pain. All patients completed pain drawings using predefined symbols These pain drawings were scored dichotomously as organic or nonorganic based on a brief description of a typical nonorganic characteristics. Patients also completed the Danish version of the SF-36 questionnaire. Statistical analysis was performed using logistic regression analysis. The pain drawing classification was used as the dependent variable and scores on the eight scales of the SF-36 as independent variables. P values of <0.05 were considered significant. The mean scores of the patient population on all eight scales were significantly lower than Danish norms. The only scales that correlated with the presence of nonorganic pain drawings were emotional role (RE) and mental health (MH), both measuring psychological health. The odds ratio (OR) of receiving a nonorganic pain drawing was 22 (95% confidence interval, or CI, 7-65) if the scores on RE and MH were more than 2 standard deviations (SD) below the Danish norm. This is the first study providing evidence that pain drawing ratings are influenced by the psychological scales of the SF-36. The clinical relevance of this observation regarding prediction of outcome after spinal surgery should be assessed in future studies.

Reflexology and bronchial asthma.

Many asthma patients seek alternative or adjunctive therapies. One such modality is reflexology, whereby finger pressure is applied to certain parts of the body. The aim of the study was to examine the popular claim that reflexology treatment benefits bronchial asthma. Ten weeks of active or simulated (placebo) reflexology given by an experienced reflexologist, were compared in an otherwise blind, controlled trial of 20+20 outpatients with asthma. Objective lung function tests (peak flow morning and evening, and weekly spirometry at the clinic) did not change. Subjective scores (describing symptoms, beta2-inhalations and quality of life) and also bronchial sensitivity to histamine improved on both regimens, but no differences were found between groups receiving active or placebo reflexology. However, a trend in favour of reflexology became significant when a supplementary analysis of symptom diaries was carried out. It was accompanied by a significant pattern compatible with subconscious unblinding, in that patients tended to guess which treatment they had been receiving. No evidence was found that reflexology has a specific effect on asthma beyond placebo influence.

Gc-globulin is an acute phase reactant and an indicator of muscle injury after spinal surgery.

OBJECTIVES AND DESIGN: Actin is the dominating protein in mammalian cells, including muscle cells, and is released into the circulation after tissue injury. Gc-globulin, one of the proteins in the Extracellular Actin Scavenger System (EASS) is responsible for the clearance of actin from the circulation. Clinical studies show that plasma levels of Gc-globulin are reduced in situations with tissue death, and that the degree of reduction correlates with development of organ dysfunction and survival. The purpose of the present study was to describe the serial changes in Gc-globulin after a standardized surgical procedure resulting in major muscle injury, comparing changes in Gc-globulin with changes in other acute phase proteins. MATERIAL AND METHODS: Twelve patients who underwent posterolateral lumbar fusion from L4 or L5 to sacrum were included in the study. Peripheral venous blood samples were obtained before surgery and on day 1, 3, 5, 12, 21, and 28 after surgery. Serum samples were analyzed for total Gc-globulin (Gc(total)), percentage of Gc-globulin complexed with actin (GC(complexed)), albumin, orosomucoid, haptoglobin, transferrin and creatin phosphokinase (CK). RESULTS: Gc(total) decreased to 87% of pre-operative values on day one. Thereafter the levels increased to a maximum of 135% of pre-operative values on day five, approaching baseline values towards the end of the observation period. Compared to this, changes in GC(complexed) displayed a mirror-like time-course, with levels of Gc(total) and GC(complexed) being significantly inversely correlated on day one (P < 0.05). Levels of albumin remained below pre-operative values the first three weeks post-operatively, reaching baseline at the end of the observation period (P < 0.05). CONCLUSION: The initial changes in Gc-globulin can be explained by increased release of actin from injured muscle tissue. Subsequently Gc-globulin displays characteristics of a so-called positive acute phase reactant, supporting previous in vitro studies, and clinical studies after minor surgery. In spite of genetic linkage and structural homology Gc-globulin and albumin are regulated differently after surgical trauma.

Loss of bone mineral of the hip assessed by DEXA following tibial shaft fractures.

We measured prospectively early changes (0-6 months) in bone mineral of the hip, the lumbar spine, and the tibia following tibial shaft fractures (n = 12), and in a cross-sectional study we evaluated the maximal amount of bone loss possible at the hip and tibia following long-term (average 3 years) impaired limb function as a consequence of complicated tibial shaft fractures [delayed union or nonunion (n = 7), chronic osteomyelitis (n = 5), decreased limb length (n = 1), or bone defect (n = 1)]. Bone mineral measurements were performed by dual energy X-ray absorptiometry. Following tibial shaft fractures, a significant decrease in bone mineral density (BMD) was seen at the hip reaching 7% [confidence limits (CL): -10.2%; -3.5%] and 14% (CL: -19.6; -7.8%) after 6 months for the femoral neck and greater trochanter, respectively. In the proximal tibia, bone mineral content (BMC) decreased and was 19% (CL: -27.4%; -9.9%) below the initial value after 6 months. BMD of the lumbar spine remained unchanged. In the cross-sectional study, BMC in the tibia of the injured legs was 43% (CL: -53.2%; -31.9%) below the value in the healthy contralateral legs, and BMD in the femoral neck and greater trochanter, respectively, was 22% (CL: -27.4%; -17.6%) and 24% (CL: -36.3%; -12.1%) below the values in the healthy contralateral legs. With respect to the expected age-related decay of bone mineral after peak bone mass, the loss of bone mineral of the hip and tibia associated with tibial shaft fractures may be considered of clinical importance with increased risk of sustaining a fragility fracture of the lower extremity later in life; and the complicated fractures may even represent a present risk of fracture.

Clinical outcome after spinal fusion with a rigid versus a semi-rigid pedicle screw system.

Several biomechanical studies have evaluated the quality of fusion obtained with a rigid versus a semi-rigid pedicle screw implant. Some studies indicate that increased rigidity of the implant system results in an increased strength of the fusion mass. Other reports have underlined the risk of stress shielding due to rigid implant systems. Based on these findings some authors have recommended the use of a semi-rigid system. There are, however, few studies focusing on any possible difference in clinical outcome between the two different types of implant systems. Questionnaires were sent to 89 patients who had undergone primary spinal fusion with either a rigid or a semi-rigid pedicle-screw-based implant system. In every case the diagnosis was spondylolisthesis or degenerative lumbar disease. The questionnaires were analysed using forward stepwise logistic regression analysis. Eighty (90%) of the questionnaires were returned. There was a mean follow-up of 4 years (range 2-8 years). It was not possible to demonstrate any difference in clinical outcome between patients undergoing lumbar fusion with a rigid implant system and those given a semi-rigid system. The overall patient satisfaction rate was 69%, with no difference between the two types of implant. No difference in clinical outcome between the two types of implant was found. Considering the fact that the primary goal of spinal fusion procedure is to obtain a solid fusion mass, biomechanical tests favour the used of a rigid pedicle screw system. This fact combined with the fact that early mobilisation is possible with rigid implants justifies the use of rigid implant systems, although no difference in clinical outcome could be demonstrated in this study.

Seinsheimer's classification of subtrochanteric fractures. Poor reproducibility of 4 observers' evaluation of 50 cases.

We examined the reliability of the Seinsheimer classification of subtrochanteric fractures of the femur. 50 consecutive anteroposterior and lateral radiographs were assessed independently by 4 observers twice with a 6-week interval. The interobserver variation was large; only 13 of the 50 fractures were classified identically by all 4 observers. The intraobserver variation showed identical classification in 26-37 of 50 radiographs. When assessing only whether the fracture was subtype 3A or not, the 4 observers agreed in 31 of 50 radiographs. We conclude that the Seinsheimer classification has no value in clinical practice.

The relation between trabecular bone strength and bone mineral density assessed by dual photon and dual energy X-ray absorptiometry in the proximal tibia.

The feasibility of two noninvasive methods [dual photon absorptiometry (DPA) and dual energy X-ray absorptiometry (DXA)] for prediction in vivo of local variations of trabecular bone strength within the proximal tibia was evaluated in 14 cadaveric knees. Trabecular bone strength was measured using an osteopenetrometer and from destructive compression tests performed on bone cylinders, thus measuring the penetration strength and ultimate strength in the medial, lateral, and central part of the tibial bone specimens. Linear regression analysis showed significant relations between BMD measured by DPA (r2 = 72%) or DXA (r2 = 73%) and ultimate strength. Even closer relations between BMD (DPA: r2 = 80%, DXA r2 = 81%) and penetration strength of trabecular bone were found. We conclude that DPA and DXA are suitable methods for evaluation in vivo of local variations in trabecular bone strength within the proximal tibia, and could easily be performed preoperatively before insertion of total knee arthroplasty.

Inter- and intraobserver study of radiographic assessment of cemented total hip arthroplasties.

Radiographs are commonly used to identify loosened total hip prostheses. Interobserver and intraobserver variation was studied in an attempt to interpret 60 random pairs of radiographs with a time interval of 6 months to 12 years between the radiographs. Each of the four observers evaluated all pairs of radiographs independently, and the evaluations were repeated after 2 to 4 weeks. Each observer classified the femoral stem and the acetabular cup separately as stable or loose. Radiolucent lines of more than 2 mm were recorded. For the acetabular components, any change in inclination or migration was noted, and for the femoral components, subsidence or any change in varus or valgus of the stem was noted. There was considerable disagreement in observations of the acetabular component; agreement by all four observers was obtained in only 34 of 60 cases (57%). For the femoral component, agreement was obtained in 37 cases (62%). The observers agreed two and two (pairwise) on the acetabular component in 70 to 83% of cases and on the femoral component, in 72 to 82% of cases. Intraobserver variation was great with regard to the acetabular component, with kappa values ranging from 0.489 to 0.633. As to the femoral component, kappa values ranged from 0.737 to 0.800. Interpretation of radiographs of artificial hip arthroplasty is difficult, and comparisons between different series of implants should be made by the same person.

[Back problems in conscripts. A 10-year follow-up]. / Rygbesvaer hos vaernepligtige. Ti års opfølgning.

One hundred and twenty-three conscripts called up for national service in 1979-80 were re-examined 10 years after call up with a questionnaire identical to one answered at the time of call up. The study group consisted of three subgroups. Group A had been rejected for service because of back problems (back-rejects). Group B were conscripts with back symptoms at the time of call up, but all completed their national service (non back-rejects). Group C did not have back symptoms at the time of call up. The back-rejects had a significantly higher incidence of: back pain; radiating pain to lower extremities; contacts (hospital, G. P., radiographs etc.) and sick leave from job as compared to group B and C. Out of 19 conscripts with radiographically verified Mb. Scheuermann, 89% had back symptoms at the time of follow-up including all with lumbar and thoracolumbar Mb. Scheuermann. All conscripts in this study had a job at follow-up. It is recommended that the criteria for rejection of conscripts in Denmark concerning back symptoms and Mb. Scheuermann remains unchanged.

Treatment of traumatic effusion in the elbow joint: a prospective, randomized study of 62 consecutive patients.

Sixty-two patients with post-traumatic radiologically visualized effusion in the elbow joint, apparently without bony damage, were randomized to either 1 week of immobilization in a plaster or immediately instructed in active exercises without any immobilization. They were reexamined by an orthopaedic surgeon weekly until recovery. New radiographs were taken after 1 week. Reevaluation of the radiographs by a radiologist revealed seven 'false-positive' effusions, i.e. neither effusion nor fracture, and 21 missed fractures. All but five missed fractures, continued in the study. Thirty patients started immediate active exercises instructed by the surgeon and 27 were immobilized. The 'active exercise' group had a significantly shorter recovery time (one week vs two weeks, P < 0.05). The presence of missed fractures did not influence the result and all patients recovered fully. Also four of the excluded patients with missed fractures recovered fully. One patient with missed fracture dropped out from follow-up. We recommend that an apparently isolated post-traumatic effusion in the elbow joint is treated with immediate active exercises followed by a clinical reexamination after one week supplemented with new radiographs if there is unsatisfactory clinical progress.

Poor reproducibility of Evans' classification of the trochanteric fracture. Assessment of 4 observers in 52 cases.

The radiographs of trochanteric fractures in 52 consecutive patients were assessed by 4 observers, using the Evans' classification. The interobserver variation was large; only 23 of 52 radiographs were classified identically by all 4 observers. When only assessing stability, the 4 observers agreed in 34 of 52 radiographs. To assess the intraobserver variation, the same observers classified the same radiographs 6 weeks later. The first and second classifications were identical in 35-44 of 52 radiographs.