Intramedullary nailing in opening wedge high tibial osteotomy-in vitro test for validation of a method of fixation.

PURPOSE: Opening wedge high tibial osteotomy (HTO) as a treatment in unicompartimental osteoarthritis of the knee can significantly relieve pain and prevent or at least delay an early joint replacement. The fixation of the osteotomy has undergone development and refinements during the last years. The angle-stable plate fixator is currently one of the most commonly used plates in HTOs. The angular stable fixation between screws and the plate offers a high primary stability to retain the correction with early weight-bearing protocols. This surgical technique is performed as a standard of care and generally well tolerated by the patients. Nevertheless, some studies observed that many patients complained about discomfort related to the implant. METHODS: Therefore, the stability of two different intramedullary nails, a short implant used in humeral fractures and a long device used in tibial fractures for stabilization in valgus HTOs, was investigated as an alternative fixation technique. The plate fixator was defined as reference standard. Nine synthetic tibia models were standardly osteotomized and stabilized by one of the fixation devices. Axial compression was realized using a special testing machine and two protocols were performed: a multi-step fatigue test and a load-to-failure test. RESULTS: Overall motion, medial, and lateral displacements were documented. Fractures always occurred at the lateral cortex. Axial cyclic loading up to 800 N was tolerated by all implants without failure. The tibia nail provided highest fatigue strength under the load-to-failure conditions. CONCLUSIONS: The results suggest that intramedullary nailing might be used as an alternative concept in HTO.

Passive rotary dynamic sitting at the workplace by office-workers with lumbar pain: a randomized multicenter study.

BACKGROUND CONTEXT: It is generally recognized that long periods of sitting can either cause or aggravate lumbar pain. A new, ergonomically designed chair has a fixed backrest and a motor-driven seat with a horizontal rotary movement in alternating left-right cycles. PURPOSE: The objective of this study is to prove superiority of the new technique of passive rotary dynamic sitting for subjects working in a sedentary occupation and suffering from lumbar pain. STUDY DESIGN/SETTING: A randomized, double-blind, multicenter, two-armed study was performed using a parallel group design. PATIENT SAMPLE: 280 persons suffering from lumbar pain were matched pairwise and randomized en bloc. OUTCOME MEASURES: The first and second primary endpoints target criteria were the validated German version of the Oswestry Disability Index (ODI) and the number of days of absence from work (DA) attributable to lumbar pain, each based on a blinded 2-year follow-up observation after randomization of the subjects. METHODS: After inclusion in the study anonymization, the probands were randomized to receive either an office chair with a motor-driven seat performing a horizontal rotary movement or a chair of the same design without the rotary seat movement. Before delivery of the chairs, 23 probands (8.2%) withdrew their consent to inclusion in the study without stating reasons. From 12 of the remaining matching partners, 23 new pairs were created at random, and the study commenced with 124 pairs. RESULTS: A further 27 probands (9.6%) were lost to follow-up during the period up to the final consultation. This made it possible to observe the primary endpoint in 82.5% of the probands. The median ODI in both groups was 53 (95% confidence interval for median difference:-1.5 to 0.5; p=.59). Median DA in both groups was 0 (95% confidence interval for median difference:-infinity-+infinity; p=1.00). CONCLUSIONS: Under the test conditions used in this study, passive rotary dynamic sitting was not superior to sitting in a high-quality, ergonomically designed chair not equipped with a micro-rotation function in patients suffering from lumbar pain.

Femoral strain changes after total hip arthroplasty--patient-specific finite element analyses 12 years after operation.

Periprosthetic stress-shielding after total hip arthroplasty (THA) is a well-known phenomenon. Many authors have used the finite element (FE) method to show the effects of THA on animal or human femora. In most cases they have performed cadaver experiments. The current project is a FE analysis based on a retrospective computerized tomography (CT) in vivo data set of 11 patients 12 years after THA. In order to control the analysis, a computationally created stem was implanted at the femur model of the not operated contralateral side. In comparison to the not operated side, there was a significant reduction of the strain energy density (SED) values in all regions of interest (ROI) with the greatest effect near the distal tip of the stem. Only zone 1 showed no clear trend which may be due to load application at the greater trochanter causing local strain peaks. The median SED values changed by -31.65% (ROI 1), -25.64% (ROI 2), -30.82% (ROI 3), -12.35% (ROI 4), -40.10% (ROI 5), -30.37% (ROI 6) and -43.38% (ROI 7). As far as we are aware, the current combination of in vivo CT density data with FE strain analyses after THA is based on the largest number of patients and the longest follow-up period. This combination enables analysis and prediction of the influence of implantation upon bone and can be compared with of remodelling theories. The assessment of mechanical strain data during a follow-up trial could be a new approach for analyzing different hip stems in clinical biomechanics.

Validation data for periprosthetic bone remodelling theories.

Periprosthetic adaptive bone remodelling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodelling theory with finite element analysis. Unfortunately, there still subsist a lack of clinical data, which are necessary for validation of these simulation results. Therefore, the objective of the current project is to collect prospective volumetric bone density data with a clinical computerized tomography study in seven patients after THA. A retrospective study 12 years after implantation in 11 patients was added. A data set of about 100000 bone voxels for each femur was collected. In all prospective cases, the predominant change is seen during the first year. The average density reduction in the horizontal slices was between 50 and 150 Hounsfield units (HU) (approx. 10%; p<0.001) after 2 years. Loss of density is particularly strong distal of the minor trochanter and decreases from proximal to distal. For the 12 years retrospective study, the contralateral femur provided the control. Similar trends comparable to the prospective 2-year follow-up CT density values were seen in most cases with density reductions of up to 400 HU (30%). However, in one of these cases there was no difference between the operated and the control density. As far as we are aware, this is the first collection of fully prospective 3D validation data in vivo for periprosthetic adaptive bone remodelling theories. The data are also unique as they are suitable for direct patient-specific 3D finite element meshing and individual weight-related loading.

Volumetric measurement of periprosthetic bone remodeling: prospective 5 years follow-up after cemented total hip arthroplasty.

INTRODUCTION: Periprosthetic bone remodeling after total hip arthroplasty (THA) is a well recognized phenomenon. Many authors have published osteodensitometric data with DEXA analysis. This study based on computerized tomography (CT). MATERIALS AND METHODS: The objective of the current project is to collect prospective volumetric bone density data with a clinical CT study in six patients after cemented THA (titanium alloy stem). The follow-up time is 5 years. A data set of about 100,000 bone voxels for each femur was collected. Bone density was observed by dint of an osteodensitometric computer program. The median results were shown in seven regions of interest (ROI) around the prosthesis stem, according to Gruen. RESULTS: The statistical analysis of the six cases after 60 months with respect to the postoperative control demonstrated a significantly lower density in ROI 2 (-125.5HU, P = 0.014), ROI 3 (-116.7HU, P = 0.023), ROI 4 (-54.5HU, P = 0.023), ROI 5 (-90.9HU, P = 0.014) and ROI 6 (-104.9HU, P = 0.014). Maximum density decrease was observed in ROI 2 and 3. The statistical analysis of the six cases after 60 months with respect to the 24 months control demonstrated a significantly lower density in ROI 2 (-62.6HU, P = 0.014), ROI 5 (-62.9HU, P = 0.023). There was a density decrease in ROI 3, 4, 6, 7 which was not significant and a slight increase in ROI 1. CONCLUSION: To our knowledge, this is the first collection of fully prospective 5 years 3D periprosthetic density data. The CT method used in the study presented here measures three-dimensionally, while the frequently used DEXA (dual X-ray absorptiometry) method measures two-dimensionally. The data are also unique as they are suitable for direct patient-specific 3D finite element meshing and biomechanical calculation. They can be graphically post-processed in order to obtain cross-sectional or 3D displays of density patterns.