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Objective To make biomechanical evaluation on ultimate pullout strength of the suture anchors based on the angle of suture anchor (SA) implanted into the humerus during arthroscopic rotator cuff repair (RCR) surgery. Methods Polyurethane materials with densities of 0.16 g/cm3 and 0.32 g/cm3 were used to simulate osteoporosis and normal cancellous bone, and polyurethane materials with densities of 0.64 g/cm3 and 3 mm thickness were used to simulate human cortical bone. The two kinds of cancellous bone models were respectively adhered together with cortical bone model to construct human humerus model. Titanium metal suture anchors were inserted into humerus models at 45°, 60°, 75° and 90° angle, then the continuous tensile experiments were performed, and 45° pulling direction between the humerus model surface and suture anchor was used to simulate the supraspinatus physiological traction direction, and each group was continuously tested 8 times, recording the pullout strength and failure modes. ResultsThe pullout force of high-density bone models was significantly higher than that of low-density bone models (P＜0.001), and at the same density, compared with 45°, 60° and 75°, the implant angle of 90° has a larger pullout force (P＜0.01). Conclusions In the model of humerus, the 90° implantation of suture anchor showed better biomechanical properties, and the vertical implantation of anchor in the repair of rotator cuff was beneficial to the knotting during operation and postoperative recovery of the supraspinatus.
ABSTRACT
Internal fixation is one of the most important treatments for fractures.The stability of screws in internal fixation can be influenced by bone mineral density,quality of pilot holes,improper structure and surface characteristics of screws chosen,insertion torque,insertion angle,and screws unfit for the bone holes.Internal fixation of fractures can fail due to the instability of screws.This paper,on the basis of a comprehensive review of the studies on all the above factors influencing the screw stability,proposes effective methods to enhance screw stability so as to improve surgical outcomes of fracture internal fixation.
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Objective To compare the stability of injectable pedicle screw with different lateral holes augmented with different volume of polymethylmethacrylate (PMMA) in synthetic bone block used for patients with osteoporosis,and analyze the relationship between screw stability and injected volume and distribution pattern of PMMA.Methods The synthetic bone blocks used for patients with osteoporosis were randomly divided into groups A,B,C and D according to the screw difference,and the blocks in each group were then randomly divided again into subgroups 0,1,2 and 3 according to the difference of PMMA volume.A pilot hole was prepared in advance using the same method in all samples.Pedicle screws of type A-C were directly inserted into vertebrae of groups A-C respectively,and then different volumes of PMMA (0,1.0,1.5 and 2.0ml) were injected through screw into the blocks of subgroups 0,1,2 and 3 respectively.The pilot hole was filled with different volumes of PMMA (0,1.0,1.5 and 2.0ml) followed by insertion of screw in groups D0,D1,D2 and D3 respectively.X-ray examination was performed to evaluate the screw position and PMMA distribution,and axial pull-out test was performed to measure the maximum axial pullout strength (Fmax).Results X-ray examination revealed that PMMA wrapt the anterior 1/3 part of screw in groups A1-A3,wrapt the middle 1/3 part of screw in groups B1-B3 and groups C1-C3,and evenly wrapt the full length of screw in groups D1-D3.Two factor ANOVA showed that both volume and distribution of PMMA significantly influenced Fmax (P＜0.05),but no marked interaction existed between the two factors (P=0.877).Among groups with the same screw,no significant difference of Fmax was found between the groups injected of 1.0ml and 1.5ml PMMA and those of 1.5ml and 2.0ml PMMA (P＞0.05),but the Fmax was significantly higher in groups with injection of 2.0ml PMMA than that in groups with injection of 1.0ml PMMA (P＜0.05).Among the groups injected with same volume of PMMA,no significant differences on Fmax were found among the groups A0-D0,A2-D2 and A3-D3 (P＞0.05).The Fmax was significantly lower in group A1 than in group DI (P=0.026),and no significant differences existed between the other two groups injected with the same volume of PMMA (P＞0.05).Conclusion PMMA can significantly enhance the stability of different injectable pedicle screws in synthetic bone block used for patients with osteoporosis,and the stability is significantly correlated with injected volume and distribution pattern of PMMA.
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OBJECTIVE: We describe a surgical tool that uses the distractor pin as a reference for determining proper screw length in ACDF. It is critical that screw purchase depth be as deep as possible without violating or penetrating the posterior cortical wall, which ensures strong pull out strength. METHODS: We enrolled 81 adult patients who underwent ACDF using an anterior cervical plate from 2010 to 2012. Patients were categorized into Groups A (42 patients: retractor pin used as a reference for screw length) and B (39 patients: control group). Intraoperative lateral x-rays were taken after screwing the retractor pin to confirm the approaching vertebral level. The ratio of retractor pin length to body anteroposterior (A-P) diameter was measured as a reference. Proper screw length was determined by comparison to the reference. RESULTS: The average distance from screw tip to posterior wall was 3.0+/-1.4mm in Group A and 4.1+/-2.3mm in Group B. The ratio of screw length to body sagittal diameter was 86.2+/-5.7% in Group A and 80.8+/-9.0% in Group B. Screw length to body sagittal diameter ratios higher than 4/5 occurred in 33 patients (90%) in Group A and 23 patients (59%) in Group B. No cases violated the posterior cortical wall. CONCLUSION: We introduce a useful surgical method for determining proper screw length in ACDF using the ratio of retractor pin length to body A-P diameter as a reference. This method allows for deeper screw purchase depth without violation of the posterior cortical wall.
Subject(s)
Adult , HumansABSTRACT
Metallic cancellous screw is one of the fixation devices widely used for bone fractures. It has always been reported that many cases of internal fixation failed just because of screw loosening or pullout. The stability of fixation is associated with the pullout strength of screws. The pullout strength strongly depends on the geometrical design of the screw thread, the material and the insertion technique of the screw, and the bone mineral density of the insertion site of the screw.
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PURPOSE: To compare the pullout strength and insertion torque of proximally tapered screw (PT) with fully tapered screw (FT) and to investigate the correlation between the pullout strength and bone mineral density, morphology of pedicle, and insertion torque of the screw in osteoporotic lumbar spine. MATERIALS AND METHODS: Fifteen osteoporotic lumbar vertebrae from four white human cadavers were used. Bone mineral density, pullout strength and insertion torque were measured by dual energy x-ray absorptiometry, MTS and torque screw driver individually. RESULTS: The FT screw provided greater pullout force and insertion torque than the PT screw in 12 of 15 vertebrae tested (p<0.01). Pullout strength was correlated with insertion torque in PT (r=0.666, P=0.0006) and FT (r=0.464, P=0.19) screws. CONCLUSIONS: Results of this study indicate that the FT screws provide higher pullout strength and insertion torque than PT screws in osteoporotic lumbar spine and suggest that the development of tapered minor diameter may lead to an improved pedicle screw with high pullout strength and insertion torque. Nevertheless, further study is needed to investigate the effect of tapering the minor diameter on the mechanical bending strength of the screw.