Tensile strength is the most often reported parameter in biomechanical investigations of meniscal repair techniques. However, the magnitude of the tensile forces that actually occur on repaired lesions is not clear. The purpose of this study was to investigate if tensile forces occur on repaired lateral meniscal lesions, which could exceed the failure strength of common repair techniques. In human knees (n = 6), vertical-longitudinal lesions 25 mm in length were created in the posterior horn of the lateral meniscus at a distance of 3 mm from the meniscosynovial junction and the popliteal hiatus. A braided steel wire, resembling a vertical suture, was inserted into the meniscal tissue and fitted with a force transducer. The knees were mounted in an apparatus, which simulated weight bearing and non-weight bearing conditions. Repeated measurements were conducted with both internal and external rotation at flexion angles of 0 degrees , 30 degrees , 60 degrees , 90 degrees and 120 degrees . Weight loading alone caused no tension on the suture. Combined flexion and rotation generated mean forces between 0.5 and 4.1 N. No significant effect of the flexion angle or direction of rotation was found. If a minimum strength of 10 N was assumed for the common meniscal repair techniques, the tensile forces were well below this limit under all circumstances (P < 0.001). These data indicate that, within the range of motion investigated, no significant tensile forces occur on longitudinal lateral lesions. Forces other than tension and biological factors are of greater importance for the healing. Therefore, the assessment of repair techniques should not be based on alone the ability to resist high distraction forces.
Compression of the meniscus can substantially increase the pullout resistance of meniscal repair implants and thus seems not to be a factor negatively influencing the stability of the repair.
Cannulas used for suture based meniscal repair can cause a substantial laceration of the meniscal tissue. The effect strongly depends on the orientation of the cutting edge of the cannula relative to the course of the fibers and can thus potentially be avoided by an appropriate handling and design.
Elongation and migration of ACL grafts will lead to a deterioration of the initial stability of ACL reconstructions. The graft migration has been sparsely investigated independently from the elongation of the graft-fixation complex. The hypothesis of this investigation was that cyclic tensile loads cause a measurable migration of the grafts. Three graft/fixation combinations were investigated in human femora (n = 7): human bone-patellar tendon grafts fixed with a biointerference screw (BPTG-IS) and free tendon grafts (porcine) fixed with either a Bio-TransFix pin (FTG-TF) or an Endobutton CL (FTG-EB). The grafts were fitted with tantalum markers. Then, the specimens were repetitively loaded (50-250 N, 800 cycles). The marker position was fluoroscopically determined at defined intervals and the migration calculated from the change in position relative to a fiducial marker within the bone. A migration of the grafts occurred in all three groups. The migration in the FTG-EB group was significantly larger than in the two other groups (P < 0.01). After 800 cycles, average migration was 0.3 (+/-0.2) mm in the BPTG-IS group, 0.7 (+/-0.4) mm FTG-TF group, 2.0 (+/-1.3) mm in the FTG-EB group. This migration might contribute to a loss of initial stability. Because the graft migration was dependent on the technique, the presented data might provide additional arguments for making the decision on the most appropriate graft/fixation combination.
Background SPECT-CT using radiolabeled phosphonates is considered a standard for assessing bone metabolism (e.g., in patients with osteoarthritis of knee joints). However, SPECT can be influenced by metal artifacts in CT caused by endoprostheses affecting attenuation correction. The current study examined the effects of metal artifacts in CT of a specific endoprosthesis design on quantitative hybrid SPECT-CT imaging. The implant was positioned inside a phantom homogenously filled with activity (955 MBq 99mTc). CT imaging was performed for different X-ray tube currents (I = 10, 40, 125 mA) and table pitches (p = 0.562 and 1.375). X-ray tube voltage (U = 120 kVp) and primary collimation (16 × 0.625 mm) were kept constant for all scans. The CT reconstruction was performed with five different reconstruction kernels (slice thickness, 1.25 mm and 3.75 mm, each 512 × 512 matrix). Effects from metal artifacts were analyzed for different CT scans and reconstruction protocols. ROI analysis of CT and SPECT data was performed for two slice positions/volumes representing the typical locations for target structures relative to the prosthesis (e.g., femur and tibia). A reference region (homogenous activity concentration without influence from metal artifacts) was analyzed for comparison. Results Significant effects caused by CT metal artifacts on attenuation-corrected SPECT were observed for the different slice positions, reconstructed slice thicknesses of CT data, and pitch and CT-reconstruction kernels used (all, p < 0.0001). Based on the optimization, a set of three protocols was identified minimizing the effect of CT metal artifacts on SPECT data. Regarding the reference region, the activity concentration in the anatomically correlated volume was underestimated by 8.9–10.1%. A slight inhomogeneity of the reconstructed activity concentration was detected inside the regions with a median up to 0.81% (p < 0.0001). Using an X-ray tube current of 40 mA showed the best result, balancing quantification and CT exposure. Conclusion The results of this study demonstrate the need for the evaluation of SPECT-CT protocols in prosthesis imaging. Phantom experiments demonstrated the possibility for quantitative SPECT-CT of bone turnover in a specific prosthesis design. Meanwhile, a systematic bias caused by metal implants on quantitative SPECT data has to be considered.
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