Micro-CT Density Analysis of the Medial Wall of the Human Medial Cuneiform

Micro-CT analysis of the Lisfranc complex reveals higher bone mineral density in dorsal compared to plantar regions

Injuries to the Lisfranc complex may require surgical fixation, the stability of which may be correlated with bone mineral density (BMD). However, there is limited research on regional BMD variations in the Lisfranc complex. This study used quantitative micro-CT to characterize regional BMD in the four bones (medial cuneiform, intermediate cuneiform, first metatarsal, and second metatarsal) of this complex. Twenty-four cadaveric specimens were imaged with a calibration phantom using micro-CT. Each bone was segmented and divided into eight regions based on an anatomical coordinate system. BMD for each octant was calculated using scan-specific calibration equations and average image intensity. Differences between regions were analyzed using ANOVA with post hoc analysis and differences between groups of four octants in each plane were analyzed with t-tests with significance level α = 0.05. The highest density region in the medial cuneiform was the distal-dorsal-lateral and dorsal regions showed significantly higher BMD than plantar regions. The intermediate cuneiform had the highest density in the distal-dorsal-medial region and the dorsal and medial regions had higher BMD than the plantar and lateral regions, respectively. The densest region of the first metatarsal was the distal-dorsal-lateral and distal regions had significantly higher BMD than proximal regions. In the second metatarsal, the distal-dorsal-medial region had the highest density, and the distal, dorsal, and medial regions had significantly higher BMD than the proximal, plantar, and lateral regions, respectively. The predominant finding was a pattern of increased density in the dorsal bone regions, which may be relevant in the surgical management of Lisfranc injuries.

Semi-automatic micro-CT segmentation of the midfoot using calibrated thresholds

PURPOSE

In the field of skeletal research, accurate and reliable segmentation methods are necessary for quantitative micro-CT analysis to assess bone quality. We propose a method of semi-automatic image segmentation of the midfoot, using the cuneiform bones as a model, based on thresholds set by phantom calibration that allows reproducible results in low cortical thickness bones.

METHODS

Manual and semi-automatic segmentation methods were compared in micro-CT scans of the medial and intermediate cuneiforms of 24 cadaveric specimens. The manual method used intensity thresholds, hole filling, and manual cleanup. The semi-automatic method utilized calibrated bone and soft tissue thresholds Boolean subtraction to cleanly identify edges before hole filling. Intra- and inter-rater reliability was tested for the semi-automatic method in all specimens. Mask volume and average bone mineral density (BMD) were measured for all masks, and the three-dimensional models were compared to the initial semi-automatic segmentation using an unsigned distance part comparison analysis. Segmentation methods were compared with paired t-tests with significance level 0.05, and reliability was analyzed by calculating intra-class correlation coefficients.

RESULTS

There were statistically significant differences in mask volume and BMD between the manual and semi-automatic segmentation methods in both bones. The intra- and inter-reliability was excellent for mask volume and bone density in both bones. Part comparisons showed a higher maximum distance between surfaces for the manual segmentation than the repeat semi-automatic segmentations.

CONCLUSION

We developed a semi-automatic micro-CT segmentation method based on calibrated thresholds. This method was designed specifically for use in bones with high rates of curvature and low cortical bone density, such as the cuneiforms, where traditional threshold-based segmentation is more challenging. Our method shows improvement over manual segmentation and was highly reliable, making it appropriate for use in quantitative micro-CT analysis.

Surgeon perception of cancellous screw fixation

OBJECTIVES

The ability of surgeons to optimize screw insertion torque in nonlocking fixation constructs is important for stability, particularly in osteoporotic and cancellous bone. This study evaluated screw torque applied by surgeons during synthetic cancellous fixation. It evaluated the frequency with which screws were stripped by surgeons, factors associated with screw stripping, and ability of surgeons to recognize it.

METHODS

Ten surgeons assembled screw and plate fixation constructs into 3 densities of synthetic cancellous bone while screw insertion torque and axial force were measured. For each screw, the surgeon recorded a subjective rating as to whether or not the screw had been stripped. Screws were then advanced past stripping, and stripped screws were identified by comparing the insertion torque applied by the surgeon to the measured stripping torque.

RESULTS

Surgeons stripped 109 (45.4%) of 240 screws and did not recognize stripping 90.8% of the time when it occurred. The tendency to strip screws was highly variable among individual surgeons (stripping ranging from 16.7% to 83.3%, P < 0.0001) and did not correlate with synthetic bone density in the range tested (P = 0.186) nor with the ranking of surgeons as resident or attending surgeon (P = 0.437). Screws that were correctly recognized as stripped retained a mean 55.0% of maximum torque, less than when stripping was not recognized (79.6%, P = 0.005).

CONCLUSIONS

Surgeon perception is not reliable at preventing and detecting screw stripping at clinical torque levels in synthetic cancellous bone. Less aggressive insertion or standardized methods of insertion may improve the stability of nonlocking screw and plate constructs.

CT density analysis of the medial cuneiform

BACKGROUND

A cannulated lag screw inserted through the medial cuneiform into the base of the second metatarsal is often utilized to reduce the diastasis and aid healing of Lisfranc injuries. Also procedures such as a midfoot or a Lapidus arthrodesis require adequate implant-bone purchase in the medial cuneiform. The medial cuneiform contains cancellous bone of varying density. Knowledge of density variation may be helpful for implant usage and manufacturing of area specific implants.

METHODS

In 60 randomly selected patients, mean computed tomography (CT) intensity in Hounsfield units was measured at 12 sampled locations within the medial cuneiform and served as a proxy for bone density. The patients' age, gender, and race were recorded. An analysis of variance (ANOVA) assessed the effect of age, gender, race, and sample site on bone density. Statistical testing assumed 95% level of confidence.

RESULTS

ANOVA showed age, gender, and sample site had significant effects (P < .001) on bone density, though race had no significant effect (P = .28). The distal-dorsal-lateral (DDL) site was significantly denser than all other sites (P < .001) except the middle-dorsal-lateral (MDL) (P = .53). The proximal-plantar-lateral (PPL) site was significantly less dense than all other sites (P < .001) except the middle-plantar-lateral/medial and the proximal-plantar-medial sites (P < .14). A general trend of density increasing in the distal and dorsal directions was evident, and within the dorsal sites there was a trend of increasing density in the lateral direction.

CONCLUSION

This is the first study to date to measure density of the medial cuneiform using living subjects. The sample size of 60 patients was also the largest of any study measuring density of this bone. We conclude that the densest area of the medial cuneiform is the most anterior, dorsal, and lateral portion.

CLINICAL RELEVANCE

The findings of this study may indicate the most optimal area for implant purchase in the medial cuneiform when reducing the diastasis between the base of the second metatarsal and medial cuneiform and for stabilization of the medial column.