Comparison of Short-Segment Pedicle Instrumentation with Supplemental Hook Fixation under Axial Compression in Relation to Graft Positioning and Posterior Ligamentous Integrity: A Biomechanical Study on the Calf Spine.

STUDY DESIGN: Biomechanical study. PURPOSE: This study investigates the benefits of supplemental hook fixation (SHF) on short-segment pedicle instrumentation (SSPI) in relation to anterior strut graft positioning. In addition, it seeks to determine whether the integrity of the posterior ligamentous complex (PLC) affects the stability of the spinal construct. OVERVIEW OF LITERATURE: Implant and/or bone failure with progressive kyphotic deformity after SSPI is common. To prevent this, several approaches are available, including SHF, anterior strut grafting, use of longer spinal constructs, and extension of the fusion to additional adjacent segments. METHODS: A total of eight calf spines were instrumented with SSPI (n=4) and SHF (n=4) with strain gauges on the implants. Strain measurements were performed under axial compression in the following order: intact spine, corpectomy, ventral positioned strut grafting, posterior positioned strut grafting, ventral positioned grafting with resected PLC, and corpectomy with resected PLC. RESULTS: The SHF group showed slightly lower strain values than SSPI in instrumented corpectomy-only specimens, but there were no statistically significant differences between them (p >0.05). The SHF group was significantly more stable than SSPI when strut grafting is employed, regardless of the location of the grafts (p =0.000). In the SSPI group, ventral positioning of the graft contributed significantly to the stability (p =0.000). There was no statistically significant difference between the ventral or posterior positioning of the graft in the SHF group (p =0.187). In addition, the integrity of the PLC did not affect stability in either group (p >0.005). CONCLUSIONS: Although not statistically significant, our investigation demonstrated that the most stable method was the SHF along with ventral positioned strut graft. However, if the SSPI is the treatment of choice, ventral positioned strut graft support will be useful in minimizing the risk of implant failure and progressive kyphotic deformity.

Biomechanical comparison of tigecycline loaded bone cement with vancomycin and daptomycin loaded bone cements.

OBJECTIVE: The objectives of this study were "1" to analyze the compressive and tensile mechanical strength characteristics of tigecycline loaded bone cement and "2" to compare them with those of vancomycin and daptomycin loaded bone cements which are used in prosthetic joint infections complicated with resistant microorganisms. METHODS: In this study, three experimental groups, which consisted of vancomycin (subgroups containing 1 g, 2 g, and 3 g vancomycin), daptomycin (subgroups containing 0.5 g, 1 g, and 1.5 g daptomycin), and tigecycline (subgroups containing 50 mg, 100 mg, and 150 mg tigecycline) and one control group without antibiotics were used. Using a standardized protocol, all antibiotic loaded bone cements were prepared. For each antibiotic group, including the control group, 10 samples were tested. All samples were biomechanically tested in terms of compressive strength and tensile strength. RESULTS: Compression tests showed that all determined antibiotic concentrations resulted in a significant decrease when compared with the control group (p<0.0011). Vancomycin and daptomycin study groups demonstrated lower tensile strength than the control group (p<0.0011). However, comparison of tensile values of tigecycline study groups with the control group revealed no significant difference (p>0.0011). In addition, all statistically significant results from between groups comparisons revealed higher tensile and compressive mechanical strength values for the tigecycline groups (p<0.0011). CONCLUSION: Evidence from this study has demonstrated that tigecycline loaded bone cement may have no mechanical disadvantage compared with vancomycin and daptomycin loaded bone cements in terms of mechanical strength when used at defined concentrations.

Reliability of Real-Time Sonoelastography in the Diagnosis of Supraspinatus Tendinopathy.

ABSTRACT: The practicality of real-time sonoelastography in the diagnosis of tendinopathy is being discussed since the beginning of its use in musculoskeletal system. The aims of this study were to compare the elasticity of pathologic supraspinatus tendon with the uninvolved side by sonoelastography and to determine the relationship between the sonoelastographic findings and magnetic resonance imaging (MRI) grade of the tendinosis. Eighty-2 patients (50 males, 32 females, mean ± SD age = 53.61 ± 16.15 years, range = 20-84 years) with unilateral supraspinatus tendinosis were included in this study. Three grades of tendinosis were identified in MRI (grade 1: mild, grade 2: moderate, and grade 3: severe). The strain ratio (SR) of the tendinosis area to the healthy normal area of the same tendon tissue and SR of the tendinosis area to ipsilateral subcutaneous fat tissue were evaluated with sonoelastography. The SRs of the tendinosis areas were also compared with the control (contralateral) side tendon tissue and subcutaneous fat tissue of the same patients. Between-groups comparisons were also done according to the MRI grading. Statistical analysis was done using paired t test (P < 0.005 was considered statistically significant). There was a statistically significant difference in the comparison of the SRs of the tendinosis areas to subcutaneous fat tissues on ipsilateral shoulders (TA/SFT) and the healthy supraspinatus tendon area (TA/ST) of the same shoulder. There was also statistically significant difference when compared with the control side measurements (P < 0.01). In patients who have grade 1 and grade 3 tendinosis on MRI, there was statistically significant difference between elastrographic evaluation of affected and unaffected sides. Real-time sonoelastography is a reliable diagnostic method in patients with rotator cuff tendinosis and shall be kept in mind as a noninvasive, inexpensive, and practical diagnostic test in suitable cases.