Objective：To assess the effects of immobilization on the three-dimensional microstructure of cortical and cancellous bone.

Methods：Eight-week-old specific-pathogen-free Wistar rats were divided into two groups：the control (n＝12) and immobilized group (n＝12). The hind limbs of the rats in the immobilized group were fixed using orthopedic casts for 4 weeks. The cortical bone at the mid-shaft and the cancellous bone at the distal metaphysis of the femur were analyzed using micro-computed tomography.

Results：The values of total cross-sectional area, cortical bone area, and cortical thickness in the immobilized group were significantly lower than those in the control group. Meanwhile, the relative bone volume (bone volume/total volume) and mean trabecular thickness in the immobilized group decreased and the structure model index significantly increased compared with the values in the control group (P＜0.05).

Conclusion：Our rat model can evaluate the effects of load-permitting immobilization. The results of this study indicate that structural changes in immobilized osteopenia-affected bone arise mainly from thinning of the cortex and reduction of cancellous bone volume caused by a reduction of trabecular width.

PURPOSE: The KneeAlign2 (KA2, OrthoAlign Inc.) accelerometer-based portable navigation system and patient-specific instrumentation (PSI; Signature, ZimmerBiomet) are widely used for ideal femoral component alignment in total knee arthroplasty (TKA). However, there has been no comparative study of the KA2 system, PSI, and conventional intramedullary instrumentation (CON). The purpose of this study was to compare the accuracy in achieving proper femoral component alignment and clinical features by using the KA2 navigation system, PSI, and CON. MATERIALS AND METHODS: We retrospectively compared the accuracy of femoral component alignment of 34 TKAs performed with the KA2 system for implantation of the femoral component, 32 TKAs with PSI, and 33 TKAs with CON. RESULTS: In the coronal plane, use of the KA2 system was more likely to result in optimal femoral component alignment than the CON and PSI (p < 0.01). In the sagittal plane, use of the KA2 system was more likely to result in optimal component alignment than PSI, but the difference between the KA2 and CON was insignificant. CONCLUSIONS: The portable accelerometer-based KA2 navigation system enabled ideal femoral implantation in the coronal and sagittal planes, as compared to the PSI or CON.
Arthroplasty ; Arthroplasty, Replacement, Knee ; Knee ; Retrospective Studies