BACKGROUND: The tibial cut referenced to the center of the intercondylar eminence often leads to varus malalignment in the presence of preexisting proximal tibia vara. The purpose of this study was to investigate the effect of lateralization of the lateral tibial plateau reference point (based on the amount of proximal tibia vara) on the postoperative coronal plane alignment. METHODS: In this prospective cohort study, 62 patients (95 knees) with osteoarthritis and proximal tibia vara underwent primary total knee arthroplasty using a lateral tibial plateau reference point for the extramedullary jig. The pre- and postoperative radiographs were obtained for measurement of mechanical axis deviation, degree of tibia vara, proximal lateral reference point of the tibial condyle, and coronal alignment of the femoral and tibial components. The distance between the tibial reference point and the center of the intercondylar eminence was measured intraoperatively. RESULTS: The mean tibia vara was 7.1° (standard deviation [SD], 2.3°). The mean lateral displacement of the reference point was 7 mm (SD, 2.2 mm). Postoperative tibiofemoral angle was 6° to 10° of valgus in 94% of cases. There was a strong correlation between the magnitude of tibia vara and the amount of lateralization of the tibial reference point (R² = 0.79, p < 0.001). CONCLUSIONS: In total knee arthroplasty patients with proximal tibia vara, reasonable accuracy can be achieved with use of the extramedullary jig for tibial component alignment by lateralizing the proximal tibial reference point.
Arthroplasty, Replacement, Knee* ; Cohort Studies ; Humans ; Osteoarthritis ; Prospective Studies ; Tibia*

STUDY DESIGN: Experimental study. PURPOSE: The study aimed to develop a finite element (FE) model to determine the stress on the discs adjacent to the fused segment following different types of floating lumbar spinal fusions. OVERVIEW OF LITERATURE: The quantification of the adjacent disc stress following different types of floating lumbar fusions has not been reported. The magnitude of the stress on the discs above and below the floating fusion remains unknown. METHODS: A computer-aided engineering-based approach using implicit FE analysis was employed to assess the stress on the lumbar discs above and below the floating fusion segment (L4–L5) following anterior and posterior lumbar spine fusions at one, two, and three levels (with and without instrumentation). RESULTS: Both discs suprajacent and infrajacent to the floating fusion experienced increased stress, but the suprajacent disc experienced relatively high stress level. Instrumentation increased the stress on the discs suprajacent and infrajacent to the floating fusion, but the magnitude of stress on the suprajacent disc remained relatively high. CONCLUSIONS: The FE model was employed under similar loading and boundary conditions to provide quantitative data, which will be useful for clinicians to understand the probable long-term effects of floating fusions.
Intervertebral Disc ; Intervertebral Disc Degeneration ; Lumbar Vertebrae ; Spinal Fusion ; Spine*

STUDY DESIGN: Prospective cohort study. PURPOSE: To evaluate the contribution of upper and lower lumbar segments to flexion and extension of the lumbar spine in normal and diseased spines. OVERVIEW OF LITERATURE: The specific contributions of upper and lower lumbar segments during flexion/extension have rarely been reported. Furthermore, no comparisons between the flexion/extension behaviors of normal and diseased spines have been reported until now. METHODS: Flexion and extension lateral radiographs of 52 adult, asymptomatic volunteers, and 67 adult patients with lumbar spine disc disease were measured using software for total lumbar lordosis, upper lumbar lordosis and lower lumbar lordosis and the intervertebral angles of all segments. RESULTS: In asymptomatic volunteers, the range of movement between flexion and extension was a mean of only 4.2degrees in the lower lumbar spine and a mean of 19.4degrees in the upper lumbar spine. In patients with disc degeneration, the range of movement between flexion and extension was an average 6.5degrees for lower lumbar spine and 15.6degrees for the upper lumbar spine. CONCLUSIONS: The results showed that upper lumbar spine contributes more to the range of motion in flexion and extension than the lower lumbar spine in asymptomatic individuals without lumbar disc disease, as well as in patients with disc degeneration.
Adult ; Animals ; Asian Continental Ancestry Group* ; Cohort Studies ; Humans ; Intervertebral Disc Degeneration ; Lordosis ; Lumbar Vertebrae ; Lumbosacral Region ; Prospective Studies ; Range of Motion, Articular ; Spine* ; Volunteers

STUDY DESIGN: Experimental study. PURPOSE: The aim of the study was to develop a finite element (FE) model to study the long-term effects of various types of lumbar spinal interventions on the discs adjacent to the fused segment. OVERVIEW OF LITERATURE: Earlier FE studies have been limited to one particular type of fusion and comparative quantification of the adjacent disc stresses for different types of surgical interventions has not been reported. METHODS: A computer aided engineering (CAE) based approach using implicit FE analysis assessed the stresses in the lumbar discs adjacent to the fused segment following anterior and posterior lumbar spine fusions at one, two and three levels (with and without instrumentation). RESULTS: It was found that instrumentation and length of fusion were the most significant factors in increasing adjacent level stresses in the lumbar discs. CONCLUSIONS: In the present study, a calibrated FE model that examined spinal interventions under similar loading and boundary conditions was used to provide quantitative data which would be useful for clinicians to understand the probable long-term effect of their choice of surgical intervention.
Intervertebral Disc ; Intervertebral Disc Degeneration ; Lumbar Vertebrae ; Spinal Fusion* ; Spine

STUDY DESIGN: Experimental study. PURPOSE: The aim of the study was to develop a finite element (FE) model to study the long-term effects of various types of lumbar spinal interventions on the discs adjacent to the fused segment. OVERVIEW OF LITERATURE: Earlier FE studies have been limited to one particular type of fusion and comparative quantification of the adjacent disc stresses for different types of surgical interventions has not been reported. METHODS: A computer aided engineering (CAE) based approach using implicit FE analysis assessed the stresses in the lumbar discs adjacent to the fused segment following anterior and posterior lumbar spine fusions at one, two and three levels (with and without instrumentation). RESULTS: It was found that instrumentation and length of fusion were the most significant factors in increasing adjacent level stresses in the lumbar discs. CONCLUSIONS: In the present study, a calibrated FE model that examined spinal interventions under similar loading and boundary conditions was used to provide quantitative data which would be useful for clinicians to understand the probable long-term effect of their choice of surgical intervention.
Intervertebral Disc ; Intervertebral Disc Degeneration ; Lumbar Vertebrae ; Spinal Fusion* ; Spine