Introduction

DXA areal-bone-mineral-density (aBMD) is used clinically as a surrogate for true volumetric-BMD to assess bone fragility. Trabecular-Bone-Score (TBS) provides an assessment of bone quality based on the DXA-derived two-dimensional images. Calculated from bone area (BA), aBMD may under- or overestimate true BMD in individuals with relatively low and high BA respectively. This study investigated relationships between BA at the lumbar-spine (L1–L4) and measurements of BMD and TBS.

Introduction

Precision error (PE) in Dual Energy X-Ray Absorptiometry (DXA) is important for accurate monitoring of changes in Bone-Mineral-Density (BMD). It has been demonstrated that BMD PE increases with increasing BMI. In vivo PE for the Trabecular-Bone-Score (TBS) has not been reported. This study aimed to evaluate the short-term PE (STPE)) of BMD and TBS and to investigate the effect of obesity on DXA PE.

The shape of the vertebral bodies from L1 to L4 was assessed from lateral dual-energy x-ray absorptiometry (DXA) images using an active shape model. The output from the model was compared to measurements of areal bone mineral density in L1 to L4 (aBMD) using a stepwise linear regression model. A significant relationship was found between aBMD and vertebral shape that suggests that the method may be useful for correcting artefacts such as osteophytes.

Weight-bearing is a known stimulus for bone remodelling and a reduction in weight-bearing is associated with reduced bone mineral density (BMD) in affected limbs post lower limb fracture. This study investigated short and long-term precision of a method for measuring relative left/right weight-bearing using two sets of identical calibrated scales. The effect of imbalance on BMD at the hip and on lower limb lean tissue mass (LLTM) was also assessed.

46 postmenopausal women, with no history of leg or ankle fracture, were measured three times whilst standing astride two scales (Seca, Germany). 34 of the participants were re-measured after 6 months by the same method. Bilateral hip and total body dual x-ray absorptiometry measurements were performed using a GE Lunar Prodigy (Bedford, MA). Precision errors in weight-bearing measures were calculated using the root mean square coefficient of variation (RMSCV%). The correlations at the first visit between left/right differences in weight-bearing and differences in BMD and LLTM were calculated.

The short-term RMSCV% for left and right weights were 4.20% and 4.25% respectively and the long-term RMSCV% were 6.91% and 6.90%. Differences in left/right weight-bearing ranged from 0 to 24% (SD 8.63%) at visit 1 and 0 to 30% (SD 10.71%) at visit 2. Using data from visit 1, the relationship between hip BMD differences and left/right weight-bearing differences were investigated, with no significant correlations found. However, a weak, but statistically significant correlation of r=0.35 (p=0.02) was found for differences in LLTM and left/right weight-bearing differences.

In conclusion, left/right weight-bearing measured using two scales is a precise method for evaluating differences in weight-bearing in the short and long-term. Differences in left/right weight-bearing in this population varied by up to 30%. Participants showed a high degree of consistency in their long-term balance in a natural standing posture. Inequalities in left/right weight-bearing did not correlate significantly with BMD at the hip, but demonstrated a weak but statistically significant correlation with lean tissue mass.

We present our experience with the use of the Anterior Tension Band plate (ATB) following ALIF, which utilises the existing surgical approach obviating the need for posterior fixation. The ATB is a small, smooth, low profile plate. It can be placed through the existing approach (anterolateral retroperitoneal or anterior transperitoneal) across the reconstructed level to prevent extension of the graft space and anterior migration of the spacer. The primary objective of this study is to measure radiographic fusion success in patients with lumbar degenerative disc disease using the ATB system. The secondary objective is to accurately define the clinical benefits to the patient.

This is a prospective multi-center outcome study. Each patient was treated with an ATB plate at one or two levels between L2 & S1 and 1 ALIF or FRA allograft spacer per level. Patient data (VAS Pain, SF-12 and Oswestry) was collected preoperatively, and at six, twelve and twenty-four month post-operative intervals. Fusion was evaluated upon demonstration of bridging trabecular bone through or external to the femoral ring. Secondary endpoint success includes demonstration of 15% improvement over baseline on the VAS, Oswestry and SF-12 patient questionnaires.

To date one hundred and thirty-one patients have undergone surgery. There were ninety-two (70%) single-level ALIF procedures and thirty-nine (30%) two-level ALIF procedures. Patients that have returned for twelve month follow-up (n=41) have had a fusion success rate of 81%. The fusion rate among one-level patients is 89% (n=25) and 67% (n=15) among two-level patients. Four of five of the un-fused two-level patients had one level fused but not the other. At twelve months, Oswestry scores improved by an average of 40% with thirty-one of forty-seven (66%) patients achieving success and VAS scores improved by 42% with thirty-five of forty-seven (75%) being successful.

Preliminary analysis of current data shows positive outcomes using the ATB plating system in ALIF procedures. Primary and secondary outcomes are compatible with current standards of care, and device related complications are minimal. Further analysis of outcome data including will be reported upon the completion of the study.