Physiologic Weightbearing Research Articles

The effect of load magnitude on three-dimensional patellar kinematics in vivo

Studies of three-dimensional patellar kinematics done with little or no applied load may not accurately reflect kinematics at physiological load levels, and may provide different results to those acquired with greater applied loads or in physiologic weightbearing. We report the effect of load magnitude on three-dimensional patellar kinematics (flexion, spin and tilt; proximal, lateral and anterior translation) using a validated, sequential static, MRI-based method. Ten healthy subjects loaded their study knee to 0% (no load), 15% and 30% bodyweight (BW) using a custom designed loading rig. Differences between loading levels were determined as a function of knee flexion for each kinematic parameter using linear hierarchical random-effects models. Quadratic and random slope terms were included in the models when significant. We found that the patellae flexed less with knee flexion at 30% BW load compared to 0% BW load ( p<0.001) and 15% BW ( p=0.004) load. The patellae showed a slight medial tilt with knee flexion at 30% BW load which was significantly less than the medial tilt seen at 0% BW load ( p=0.017) and 15% BW load ( p=0.043) with knee flexion. Small but statistically significant differences were also observed for proximal and anterior translation; the patellae were in a more proximal and posterior position at 30% BW load than at 0% BW load ( p=0.010 and p=0.005, respectively) and 15% BW load ( p<0.001 and p=0.029, respectively). Since differences in three-dimensional patellar kinematics were observed between loading levels, magnitudes of prescribed loads must be considered when designing studies and comparing results between studies.

In vivo range of motion of the lumbar spinous processes

The study design included an in vivo laboratory study. The objective of the study is to quantify the kinematics of the lumbar spinous processes in asymptomatic patients during un-restricted functional body movements with physiological weight bearing. Limited data has been reported on the motion patterns of the posterior spine elements. This information is necessary for the evaluation of traumatic injuries and degenerative changes in the posterior elements, as well as for improving the surgical treatment of spinal diseases using posterior procedures. Eight asymptomatic subjects with an age ranging from 50 to 60 years underwent MRI scans of their lumbar segments in a supine position and 3D models of L2-5 were constructed. Next, each subject was asked to stand and was positioned in the following sequence: standing, 45 degrees flexion, maximal extension, maximal left and right twisting, while two orthogonal fluoroscopic images were taken simultaneously at each of the positions. The MRI models were matched to the osseous outlines of the images from the two orthogonal views to quantify the position of the vertebrae in 3D at each position. The data revealed that interspinous process (ISP) distance decreased from L2 to L3 to L4 to L5 when measured in the supine position; with significantly higher values at L2-3 and L3-4 compared with L4-5. These differences were not seen with weight-bearing conditions. During the maximal extension, the ISP distance at the L2-3 motion segment was significantly reduced, but no significant changes were detected at L3-4 and L4-5. During flexion the ISP distances were not significantly different than those measured in the MRI position at all segments. Going from the left to right twist positions, the L4-5 segment had greater amounts of ISP rotation, while all segments had similar ranges of translation in the transverse plane. The interspinous process distances were dependent on body posture and vertebral level.

Measurement of geometric deformation of lumbar intervertebral discs under in-vivo weightbearing condition

Quantitative data of spinal intervertebral disc deformation is instrumental for investigation of spinal disc pathology. In this study, we employed a combined dual fluoroscopic imaging system and the MR imaging technique to determine the lumbar disc deformation in living human subjects. Discs at L2-3, L3-4 and L4-5 levels were investigated in 8 normal subjects. The geometric deformation of the discs under full body weight loading condition (upright standing) was determined using the supine, non-weightbearing condition as a reference. The average maximum tensile deformation was −21% in compression and 24% in tension, and maximum shear deformation on the disc surface reached 26%. The data indicated that different portions of the disc are under different tensile and shear deformation. Further, discs of L2-3, L3-4 and L4-5 have different deformation behavior under the physiological weightbearing condition. In general, the higher level discs have higher deformation values. The technique used in this study can be used to investigate the deformation behaviors of diseased discs as well as the efficacy of different surgical modalities at restoring normal disc deformation patterns.

Computer Assisted Percutaneous Placement of Augmented Iliosacral Screws

A technical report of fluoroscopy guided placement of augmented iliosacral screws in osteoporotic insufficiency fractures of the sacrum. To describe a combined approach of navigated iliosacral screw placement and screw augmentation as an option for osteosynthesis of sacral insufficiency fractures in the elderly. The incidence of sacral insufficiency fractures is increasing. Outcome of conservative treatment is inconsistent. Recently sacroplasty is propagated as an interventional therapy but the long-term outcome is still unknown. Evidence from finite element models suggests that stabilization of the sacrum achieved by sacroplasty is insufficient to restore the weight bearing capacity of the sacrum permanently. We suggest a minimally invasive fluoroscopically navigated iliosacral screw osteosynthesis with cement augmentation of the screws for treatment of insufficiency fractures of the sacrum. The procedure, especially fluoroscopic visualization and navigation of the osteoporotic sacrum is technically feasible. A total radiograph time of 7,4 minutes, including image acquisition for navigation and fluoroscopic control of cement injection, is acceptable and can be expected to be significantly reduced with repeated applications of the procedure. The patient presented in the report was discharged to rehabilitation soon after the operation. An assistive device (delta wheel) is only needed for longer walking distances. Pain was reduced drastically immediately after surgery. In general, fractures are treated by reduction and fixation to restore the biomechanical function of the injured bone. These principles should be applied to elderly patients with osteoporotic fractures as well. The technique reported here is adapted to the special demands of the elderly patient, i.e., minimally invasive, support of the weakened bone by cement augmentation, bone protective screw positioning and safety due to navigation support.

Successful Canine Patellar Tendon Reattachment to Porous Tantalum

The ability to achieve reattachment of soft tissues, such as tendon, directly onto a prosthetic surface would be of great benefit in case of periarticular bone loss or resection. Bone and potential soft tissue ingrowth using porous tantalum has been observed in prior animal studies. We hypothesized porous tantalum washers used to reattach canine patellar tendon to bone would provide sufficient strength to withstand physiologic loading. We reattached the released patellar tendon to the tibia using two porous tantalum washers in 33 skeletally mature dogs. Force plate analysis of gait, tensile testing of the tendon reconstruction, and histologic analysis of tissue ingrowth into the implants were performed after 3, 6, and 12 weeks' survival. Physiologic weightbearing on the operated leg had normalized 6 weeks after tendon reconstruction surgery. The mechanical strength of the tendon reattachment was 76% of the strength of the native tendon insertion by 6 weeks but did not increase further with time. Fibrous tissue occupied approximately 1/2 of the available space in the porous tantalum washers at all times. Our data suggest tendon healing into a prosthetic material can be achieved using porous tantalum washers with sufficient mechanical strength to withstand physiologic loading.

Load bearing at the menisco-femoral joint: an in vitro study in the canine knee (SS-22)

Background: The role of the menisci on tibial load transmission and stress distribution has been extensively studied, but few studies have focused on the meniscofemoral joint during physiologic weightbearing. The objective of this study was to determine the contact areas and local contact stresses at the meniscofemoral interface during physiologic range of motion and axial-loading in the canine knee and to determine the influence of a partial or total meniscectomy. Methods: Both fresh-frozen knees of 3 hound-type canines were tested in a universal testing machine configured for an axial-load of 90120 N. Measurement of the contact area and the local contact stress were done at three different knee angles (30; 50; 70) and with both menisci intact, after partial meniscectomy, and after total meniscectomy. Pressure distribution was estimated by using pressure sensitive film inserted above the menisci. Results: After partial meniscectomy, contact areas at 50° of knee flexion decreased approximately 25% on both femoral condyles, and local contact stress increased 30% on the medial femoral condyle but remained unchanged on the lateral. After total meniscectomy, contact areas at 50° of knee flexion decreased approximately 75% on both femoral condyles, and local contact stress increased approximately 60% on the medial compartment and 100% on the lateral compartment. Conclusions: These data suggest that a conservative partial meniscectomy leaves the meniscus with an inferior weight distribution function; decreasing, but not canceling the protection on the femoral hyaline cartilage. A dramatic decrease of contact area followed by an increase of local contact stress was noted after a total meniscectomy. The clinical value of this study is to emphasize the biomechanical value of surgical procedures addressing the repair of damaged menisci.

The development of the dysplastic hip joint after an intertrochanteric varus rotation osteotomy

This is a radiological survey of 267 children between the ages of 15 months and 14 1/2 years on whom 465 intertrochanteric varus rotation osteotomies were carried out. The follow-up period varied between 2 and 15 1/4 years. The main reasons responsible for the return of valgus are early operation before the fifth year, disregard for the dysplastic acetabular roof, insufficient correction of the CCD angle below 115°, and technical faults. An AT angle of 10° appears necessary for physiological weight bearing by the acetabular roof. When dysplasia of the acetabular roof is present, polyaxial correction of the proximal end of the femur must be combined with acetabuloplasty or pelvic osteotomy.