BACKGROUND:At present, there stil remain controversies concerning the choice of tibial slope in unicompartmental knee arthroplasty, and the related biomechanical studies are rare. OBJECTIVE:To find the rational tibial slope in mobile-bearing unicompartmental knee arthroplasty through the results of finite element analysis. METHODS:A finite element model of normal knee was established and validated using the techniques of three-dimensional reconstruction and finite element pre-processing. Then the finite element models of unicompartmental knee arthroplasty with different tibial slopes were established based on the normal knee model. The finite element analyses were conducted after the boundary conditions and loads were unified. RESULTS AND CONCLUSION: The finite element models of unicompartmental knee arthroplasty with different tibial slopes were established successfuly. The results of the finite element analyses indicated that the posteromedial tibial cortical and cancelous bone stress increased gradualy as the posterior slope increasing, as wel as the load distribution and the cartilage contact pressures of lateral compartment. The anteromedial tibial cortical stress increased significantly with the anterior slope. A posterior tibial slope of 0°-7° can be recommended when implanting a mobile-bearing unicompartmental knee arthroplasty.

Objective: To compare the clinical and radiological effectiveness of oblique lumbar interbody fusion (OLIF) and posterior lumbar interbody fusion (PLIF) in the treatment of Cage dislodgement after lumbar surgery. Methods: The clinical data of 40 patients who underwent revision surgery due to Cage dislodgement after lumbar surgery betweem April 2013 and March 2017 were retrospectively analyzed. Among them, 18 patients underwent OLIF (OLIF group) and 22 patients underwent PLIF (PLIF group) for revision. There was no significant difference between the two groups in age, gender, body mass index, intervals between primary surgery and revision surgery, number of primary fused levels, disc spaces of Cage dislodgement, and visual analogue scale (VAS) scores of low back pain and leg pain, Oswestry disability index (ODI), the segmental lordosis (SL) and disc height (DH) of the disc space of Cage dislodgement, and the lumbar lordosis (LL) before revision ( P>0.05). The operation time, intraoperative blood loss, hospital stay, and complications of the two groups were recorded and compared. The VAS scores of low back pain and leg pain were evaluated at 3 days, 3, 6, and 12 months after operation, and the ODI scores were evaluated at 3, 6, and 12 months after operation. The SL and DH of the disc space of Cage dislodgement and LL were measured at 12 months after operation and compared with those before operation. CT examination was performed at 12 months after operation, and the fusion of the disc space implanted with new Cage was judged by Bridwell grading standard. Results: The intraoperative blood loss in the OLIF group was significantly less than that in the PLIF group ( t=-12.425, P=0.000); there was no significant difference between the two groups in the operation time and hospital stay ( P>0.05). Both groups were followed up 12-30 months, with an average of 18 months. In the OLIF group, 2 patients (11.1%) had thigh numbness and 1 patient (5.6%) had hip flexor weakness after operation; 2 patients (9.1%) in the PLIF group had intraoperative dural sac tear. The other patients' incisions healed by first intention without early postoperative complications. There was no significant difference in the incidence of complications between the two groups ( χ2=0.519, P=0.642). The VAS scores of low back pain and leg pain, and the ODI score of the two groups at each time point after operation were significantly improved when compared with those before operation ( P<0.05); there was no significant difference between the two groups at each time point after operation ( P>0.05). At 12 months after operation, SL, LL, and DH in the two groups were significantly increased when compared with preoperative ones ( P<0.05); SL and DH in the OLIF group were significantly improved when compared with those in the PLIF group ( P<0.05), and there was no significant difference in LL between the two groups ( P>0.05). CT examination at 12 months after operation showed that all the operated disc spaces achieved bony fusion. According to the Bridwell grading standard, 12 cases were grade Ⅰ and 6 cases were grade Ⅱ in the OLIF group, and 13 cases were grade Ⅰ and 9 cases were grade Ⅱ in the PLIF group; there was no significant difference between the two groups ( Z=-0.486, P=0.627). During follow-up, neither re-displacement or sinking of Cage, nor loosening or fracture of internal fixation occurred. Conclusion: OLIF and PLIF can achieve similar effectiveness in the treatment of Cage dislodgement after lumbar surgery. OLIF can further reduce intraoperative blood loss and restore the SL and DH of the disc space of Cage dislodgement better.

Objective:To investigate the clinical efficacy of oblique intervertebral fusion in the treatment of failed internal fixation of thoracolumbar fractures.Methods:A retrospective study was conducted to analyze the clinical data of 14 patients who had undergone revision surgery for failed internal fixation of thoracolumbar fracture at Department of Orthopedics, The First Hospital Affiliated to Zhengzhou University from January 2014 to December 2021. There were 6 men and 8 women with a mean age of 47.5 (42.0, 54.3) years. Fracture segments: T 12 in 2 cases, L 1 in 3 cases, L 2 in 4 cases, L 3 in 3 cases, and L 4 in 2 cases; AO classification: type A in 1 case, type B in 7 cases, and type C in 6 cases. Their prior surgical method was posterior internal fixation with pedicle screws. The revision surgery consisted of subtotal vertebral resection through the oblique lateral approach, bone column reconstruction and lateral screw-rod internal fixation for intervertebral fusion after posterior internal fixation reset. The operation time, intraoperative bleeding, postoperative hospital stay, and incidence of complications were recorded. Compared were visual analogue scale (VAS) and Oswestry disability index (ODI) scores for low back pain at preoperation, 3 days and 3 months postoperation, and the last follow-up, fusion at the last follow-up, and Frankel grading for neurological function at preoperation and postoperation. Results:All the 14 patients underwent surgery successfully and were followed up for 23 (18, 24) months. The operation time was (175.1±28.2) min, the intraoperative bleeding (300.4±122.6) mL, and the postoperative hospital stay 6 (6, 7) d. One case developed postoperative transient hip flexion weakness but was discharged after restoration of normal muscle strength by conservative treatment. Both VAS and ODI scores for low back pain at all postoperative time points were significantly improved compared with the preoperative values ( P<0.05), with a significant trend of 3 days postoperation >3 months postoperation > the last follow-up ( P<0.05). In the 12 patients with preoperative neurological damage, the Frankel grading rose by at least 1 level postoperatively ( Z=-3.110, P=0.002). The last follow-up revealed no loosening or fracture of the internal fixation. Complete bony fusion was visible in all CT sagittal reconstructions. Conclusion:For patients with thoracolumbar fracture undergoing failed internal fixation, oblique intervertebral fusion is an alternative minimally invasive surgical treatment due to its satisfactory overall outcomes.