Comparison of Biomechanical Properties of a Synthetic L3-S1 Spine Model and Cadaveric Human Samples

Human cadavers currently represent the gold standard for spine biomechanical testing, but limitations such as costs, storage, handling, and high interspecimen variance motivate the development of alternatives. A commercially available synthetic surrogate for the human spine, the Sawbones spine model (SBSM), has been developed. The equivalence of SBSM to a human cadaver in terms of biomechanical behavior has not been fully assessed. The objective of this study is to compare the biomechanics of a lumbar tract of SBSM to that of a cadaver under physiologically relevant mechanical loads. An L3-S1 SBSM and 39 comparable human cadaver lumbar spine tracts were used. Each sample was loaded in pure flexion-extension or torsion. Gravity and follower loads were also included. The movement of each vertebral body was tracked via motion capture. The range of motion (ROM) of each spine segment was recorded, as well as the overall stiffness of each L3-S1 sample. The ROM of SBSM L3-L4 was larger than that found in cadavers in flexion-extension and torsion. For the other spine levels, the ROMs of SBSM were within one standard deviation from the mean values measured in cadavers. The values of structural stiffness for L3-S1 of SBSM were comparable to those of cadaveric specimens for both flexion and torsion. In extension, SBSM was more compliant than cadavers. In conclusion, most of the biomechanical properties of an L3-S1 SBSM model were comparable to those of human cadaveric specimens, supporting the use of this synthetic surrogate for testing applications.

Total Hip Arthroplasty in Patients With Avascular Necrosis After Hematopoietic Stem Cell Transplantation

The immunosuppressive regimens required for hematopoietic stem cell transplantation predispose recipients to complications, including avascular necrosis. Cancer-related comorbidities, immunosuppression, and poor bone quality theoretically increase the risk for perioperative medical complications, infection, and implant-related complications in total joint arthroplasty. This study reviewed 20 primary total hip arthroplasties for avascular necrosis in 14 patients. Outcomes were assessed at routine clinical visits and Harris hip scores were calculated. Follow-up radiographs were evaluated for component malposition, loosening, polyethylene wear, and osteolysis. Average follow-up was 44.5 months for all patients. Postoperative clinical follow-up revealed good to excellent outcomes, with significant improvement in functional outcome scores. There were no periprosthetic infections or revisions for aseptic loosening. There was 1 dislocation on postoperative day 40, which was treated successfully with a closed reduction. Two patients with a prior history of venous thromboembolism developed a pulmonary embolus on postoperative day 13 and 77, respectively. Four patients died several months to years after arthroplasty of complications unrelated to the surgical procedure. Total hip arthroplasty can both be safely performed and greatly improve quality of life in recipients of hematopoietic stem cell transplantation who develop avascular necrosis. However, prolonged venous thromboembolism prophylaxis should be carefully considered in this high-risk patient population. [Orthopedics. 2018; 41(2):e257-e261.].

Delay in Diagnosis of Vertebral Osteomyelitis Affects the Utility of Cultures

INTRODUCTION

Obtaining blood or tissue cultures prior to administration of antibiotics has been the standard of care in the treatment of osteomyelitis of the spine. A delay in diagnosis of vertebral osteomyelitis is the primary culprit for the inaccuracy of blood cultures and biopsies. The purpose of this study was to evaluate the outcomes of spinal osteomyelitis in patients where the infecting organism was identified through cultures in contrast to cases where the cultures continued to be negative.

MATERIALS AND METHODS

We retrospectively reviewed the database of spinal osteomyelitis cases presented at a high-volume institution from 2001-2011. This resulted in 91 patients (51 men and 40 women) who had a mean age of 59 years with a mean follow-up of four years. Delay in diagnosis was defined as greater than 2.5 months from first ER visit for non-specific back pain to diagnosis of osteomyelitis without antibiotic treatment in the interim. Nineteen patients had a delay in diagnosis (DD) and 72 were diagnosed early (ED). Outcomes evaluated include clearance of infection, clinical outcomes measured by Oswestry disability index scores (ODIs), and the efficacy of blood cultures and biopsies.

RESULTS

The ED group had a higher odds ratio of osteomyelitis clearance compared to the delay in diagnosis group and this trended toward significance [p=0.08]. The mean improvements in ODIs were significantly greater in the ED group compared to the DD group. Positive blood cultures were more positive when drawn within one month compared to after one month [p=.001]. Percutaneous biopsy cultures were more positive when drawn within 2.5 months compared to after 2.5 months [p=.025]. Open biopsy cultures were more positive when drawn within 4.5 months compared to after that [p<0.001].

DISCUSSION

We found that delayed diagnosis may negatively affect the treatment outcome as evidenced by the greater improvements in ODI scores among those diagnosed early. Although we were unable to show a difference in clearance between early and delayed diagnosis, it is quite possible that larger cohorts may have shown this given the trend toward significance.

CONCLUSION

Hence, an early diagnosis has improved vertebral osteomyelitis clearance and clinical outcomes, and blood cultures and biopsies may have a low yield if delayed.