Background The direct superior approach (DSA), which is one of the muscle-sparing approaches for total hip arthroplasty (THA), has been recently reported with positive outcomes. However, in minimally invasive THA, it has been reported that the visual intraoperative estimation of the cup position is not reliable. Therefore, those minimally invasive approaches are associated with the increased risk of acetabular cup malposition due to the limited exposure. Although the positive effects of computer navigation system on the accuracy of cup positioning have been reported in many studies, those are not unknown in THA via the DSA. In the current study, we investigated the accuracy of acetabular cup positioning in navigated THA via the DSA in the first 30 consecutive cases.Methods We have retroactively included the first 30 consecutive cases of navigated DSA, and the consecutive control cases using conventional posterior approach (PA) were included retroactively up to 30 cases. This retrospective study divided the cases of navigated DSA into 15 initial and 15 recent cases. The postoperative data were assessed on plain computed tomography to measure the radiographic inclination and anteversion of the acetabular component. Statistical analyses were performed using Mann-Whiteney U test for comparison of the mean, and Levene's tests for equality of standard deviations (SD). Results We found no significant differences in the means between navigated DSA and conventional PA for anteversion and inclination. For anteversion, the accuracy of acetabular cup positioning in navigated DSA (SD, 6.9°), including the recent 15 cases (SD, 4.1°), was significantly improved than in conventional PA (SD, 11.7°). For inclination, there were no significant differences in the accuracy of the acetabular cup positioning between navigated DSA (SD, 5.3°) and conventional PA (SD, 6.5°).Conclusions The increased variances of cup anteversion would be due to the frequency of pelvic malposition and the wide variation in pelvic orientation with the patient in the lateral decubitus position. Navigated THA via the DSA could be performed with good accuracy of cup placement in the first 30 cases. The results suggest that computer navigated THA via the DSA as a suitable option for hip replacement.

Introduction: Osteoporotic vertebral compression fractures (OVCFs) are common fractures in the elderly suffering osteoporosis. Most patients have bone fusion with deformity of vertebral collapse; however, some patients suffer nonunion and persistent pain at the fracture site. Due to the limitations of conservative treatment, balloon kyphoplasty (BKP) has been recently performed for OVCFs. This study aimed to investigate the relationship between cement embolization and balloon expansion pressure (BEP) in patients who underwent BKP. Methods: We investigated 62 patients who underwent BKP for cement embolization into the perivertebral veins among the 155 patients admitted to our hospital due to thoracolumbar vertebral compression fractures between April 1, 2019, and March 31, 2020. Surgery was indicated for patients who had severe back or low back pain and whose daily life was severely impaired, and in whom the shape of the vertebral body was clearly changed on functional X-ray. Results: Intraoperative X-ray and postoperative CT revealed cement embolization into the perivertebral veins in three cases (4.83%). The BEP was significantly higher in the group with cement embolism than in the group without cement embolism (P < 0.001). Pulmonary cement embolism (PCE) and infection were not observed. One case of cement leakage into the spinal canal was observed (1.61%). Conclusions: While the surgical intervention of BKP can contribute to the treatment of OVCFs, careful attention should be paid to the prevention of complications, including cement embolization into the perivertebral veins, and such complications should be appropriately managed.

We present a case of reverse Z-effect phenomenon in a basicervical femoral fracture using a cephalomedullary nail together with two superior antirotation screws and evaluate the procedure. An 86-year-old woman fell in her home and could not stand due to right hip joint pain. X-ray and CT imaging showed a right basicervical femoral fracture (AO/OTA classification; 31B3), and open reduction and internal fixation (OR/IF) was performed with a cephalomedullary nail and two superior antirotation screws (TES Nail, HOMS, Tokyo, Japan). Two months later, X-ray showed penetration of the femoral head by the inferior lag screw with lateral migration of the two superior antirotation screws; the so-called “reverse Z-effect”; without any trauma. We performed the exchange of a shorter inferior lag screw for the longer one, and replaced the sliding type end cap with one of rocking type. The reverse Z-effect has been reported in cases with two lag screws, i.e. one inferior and one superior, in the past; however, to our knowledge, there has been no case reported in the literature using two superior antirotation screws together with one inferior lag screw.