Changes In Axial Rotation Research Articles

In vivo three-dimensional knee kinematics in goats with unilateral anterior cruciate ligament transection.

Although the goat is an established animal model in anterior cruciate ligament (ACL) research, in vivo kinematics associated with ACL deficiency have not been previously described in this species. Three-dimensional knee kinematics were determined before and after unilateral ACL transection in eight goats. Fluoroscopic imaging of the knees during treadmill walkingand force-platform gait analysis during over-ground walking were performed prior to ACL transection, and 2 weeks, 3 months, and 6 months after ACL transection. Transient lameness of the ACL-transected limb was noted in all goats but resolved by 3 months post-ACL transection. Increased extension of 8.7° to 17.0° was noted throughout the gait cycle in both the ACL-transected and the contralateral unaffected knees by 3 months post-ACL transection, in a bilaterally symmetric pattern. Peak anterior tibial translation increased by 3 to 6 mm after ACL transection and persisted over the 6-month study period. No changes in axial rotation or abduction angle were observed after ACL transection. Unilateral ACL deficiency in goats resulted in persistent kinematic alterations, despite the resolution of lameness by 3 months post-ACL transection.

Postoperative migration of the anatomical and functional anteversion angle following total hip arthroplasty with a well-fixed cemented femoral component with line-to-line implantation.

Little is known about the association between well-fixed polished tapered cemented stems (PTCS) implanted by the line-to-line technique and changes of stem migration, or the change of functional anteversion of the femur after total hip arthroplasty (THA). This retrospective study included 422 two-stage bilateral primary THAs performed using PTCS implanted by the line-to-line technique. CT scans were made on both the target side (first postoperative CT) and on the contralateral side (second postoperative CT) 1 week postoperatively. The mean follow-up was 7.8months. CT data for each scan were transferred to 3D template software (Zed hip, Lexi, Japan). The postoperative changes of anatomical stem anteversion (ASA), functional femoral anteversion (FFA), and stem subsidence were evaluated. A total of 20 THAs with CT scans were available on 3D template software. The ASA and the FFA had migrated -0.68° ± 0.62° and -5.5° ± 9.7°, respectively, over the follow-up period. A significant positive correlation was observed between the change of subsidence and ASA (r2 = 0.34, p = 0.007), between the FFA on the second postoperative CT and ASA on the first postoperative CT (r2 = 0.26, p = 0.02) and between the FFA on the second postoperative CT and FFA on the first postoperative CT (r2 = 0.52, p = 0.0003). This study indicates that the change in axial rotation of a PTCS implanted by the line-to-line technique was less than that reported by other studies and the preoperative external rotation contracture was substantially improved after THA.

Intraoperative pelvic movement is associated with the body mass index in patients undergoing total hip arthroplasty in the supine position

BackgroundsThere are very few reports on pelvic movement during total hip arthroplasty (THA) in the supine position. We investigated intraoperative pelvic motion in the sagittal and axial planes to determine if preoperative clinical factors, including body mass index (BMI) affect intraoperative pelvic motion. MethodsFifty-three patients with osteoarthritis undergoing THA in the supine position were included. Clinical factors, such as age, BMI, and pelvic tilt were assessed preoperatively. Intraoperative pelvic motion in the axial and sagittal planes was assessed using a portable navigation system. We assessed the change in pelvic tilt from registration to cup implantation as the pelvic tilt change; positive values indicated anterior pelvic tilt. We measured the values and absolute values of changes in axial rotation from registration to cup implantation to determine the axial rotation angle. The effects of patient factors on pelvic motion (pelvic tilt change and axial rotation angle) were analyzed using a Spearman's correlation analysis. ResultsPreoperative pelvic tilt was negatively correlated with pelvic tilt change (r = −0.57, p < 0.05) and the absolute axial rotation angle (r = −0.57, p < 0.05). BMI and absolute axial rotation angle were negatively correlated (r = −0.54, p < 0.05). Age was not correlated with change in the pelvic tilt and the axial rotation angle. ConclusionsPreoperative pelvic tilt and BMI are important factors to determine intraoperative pelvic motion in patients who undergo THA in the supine position. This can help surgeons to preoperatively identify patients with a higher risk of intraoperative pelvic motion.

Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P34. Axial rotation correction in adolescent idiopathic scoliosis with pedicle screw construct

BACKGROUND CONTEXT Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity characterized by tilt and rotation of the spine. As rib prominence is related to the vertebral rotation, derotation of the spine to reduce deformity is desirable. At our institution, posterior spinal fusions for AIS are performed with the use of intraoperative 3D fluoroscopic imaging with navigation. Scans of the entire operative curve are taken before and after instrumentation, resulting in tomographs in which the accuracy of pedicle screw placement and the change in axial rotation can be measured. METHODS Posterior spinal fusion with pedicle screw and rod instrumentation with the use of intraoperative 3D fluoroscopic imaging and navigation was performed. Pedicle screws were placed using navigation, following standard posterior approach. The most cephalad level of instrumentation was secured with hooks. After placement of pedicle screws and a convex rod, derotation was performed using uniaxial screws with tubes over screwdrivers. A second scan was performed to ensure the appropriate position of all screws, allowing measurement of derotation intraoperative. Data collection: Institutional review board approval was obtained for retrospective review of patient charts and images, and for the creation of a patient database. All patients who received posterior spinal fusion for AIS between 2008 and 2010 were included in the database. Inclusion criteria for this review were limited to patients with AIS and with greater than 2years follow-up. This resulted in a total of 54 patients for inclusion. Imaging taken before and after instrumentation and rod de-rotation maneuver was reviewed. For each patient, apical and neutral vertebrae were identified on the standing PA radiograph. The angle of rotation (RA sag) was then measure on the axial 3D images for the apical and neutral vertebrae, by the method described by Aaro and Dahlborn. The difference between the RA sag of these two vertebrae was defined as the axial rotation measured on the pre- and post-instrumented axial images. PA standing scoliosis view was also taken on fourth postoperative day. Cobb angles were measured from each of these radiographs and submitted for analysis. Statistical analysis: Mixed linear models were used to predict axial rotation correction and calculate LSMEANS with 95% confidence intervals. Covariates included gender and continuous age. Logistic regression was employed to estimate the odds of non-normal status postsurgery when compared to normal with presurgery standing Cobb as the independent variable. The one patient with a Lenke classification of five was removed for this analysis. All analyses were conducted using the statistical package SAS, version 9.3. (SAS Institute Inc., Cary, North Carolina) RESULTS Axial rotation correction overall was a 28.7% improvement postoperatively. This change meets statistical significance (p=.0202) when adjusting for age and gender. The change in axial rotation is significantly negatively correlated with age, indicating the change in axial rotation tends to decrease as age increases. Discussion: Our study was able to show a significant improvement in axial rotation in our group of patients. The manner in which the images were taken provides, by our estimation, a standardized method of image-gathering that is most reproducible and has the least amount of variability. General anesthesia and positioning alone have shown to decrease the magnitude of measured curves. Lee et al. showed a decrease of as much as 74% in Cobb angles and 25.7% rotational measurement (using Pedriolle torismeter) by placing a patient under anesthesia and on the operative table. Our study has the unique advantage of having all images taken after dissection and preparation of the spinal elements has occurred, removing an additional layer of variability. CONCLUSIONS Derotation maneuver using convex pedicle screws significantly reduced axial rotation of the spine. This study validates one technique of derotation. Vertebral derotation resulting from correction maneuver can be quantified, making comparisons of different techniques and instrumentation possible. Future studies using different instrumentations and derotation techniques should make comparisons possible.

Change in Axial Rotation of the Femur in the Resting Supine Position Following Total Hip Arthroplasty.

Stem anteversion in the setting of total hip arthroplasty (THA) is usually measured by referencing the posterior condylar line (PCL). However, stem anteversion may not express the functional torsion of the femur if a consistent horizontal tilt in the PCL is observed after THA. Herein, the horizontal tilt of the PCL at the resting neutral position of the hip was retrospectively measured in 53 THA patients from three computed tomography (CT) datasets: (i) preoperative (preop-CT), (ii) 3 weeks after THA (1st postop-CT), and (iii) more than 2 years after THA (2nd postop-CT). Factors including sex, surgical approach, change in femoral anteversion, leg length, leg lateral length, and pelvic sagittal tilt, were analyzed to determine if they were predictors for the rotational change in PCL, and the number of cases in which the horizontal tilt of the PCL remained within 10° in the three CT images was calculated. Comparing the preop-CT to the 1st postop-CT demonstrated that the PCL underwent internal rotation by (mean ± standard deviation) 13.1° ± 8.6°; only leg lateralization was significantly correlated to the change in PCL (β = 0.278, P = 0.046). Comparing the preop-CT to the 2nd postop-CT demonstrated that the PCL was internally rotated by 9.7° ± 9.3°; no factors were correlated to the change in PCL. There were only 12 hips (23%) in which the horizontal tilt of the PCL remained within 10°. In conclusion, the PCL in the resting position was internally rotated shortly after THA and remained internally rotated from the preoperative position at two or more years following THA. Thus, stem anteversion measured by referencing the PCL may not represent functional torsion of the femur.

Biomechanical simulations of costo-vertebral and anterior vertebral body tethers for the fusionless treatment of pediatric scoliosis.

Compression-based fusionless tethers are an alternative to conventional surgical treatments of pediatric scoliosis. Anterior approaches place an anterior (ANT) tether on the anterolateral convexity of the deformed spine to modify growth. Posterior, or costo-vertebral (CV), approaches have not been assessed for biomechanical and corrective effectiveness. The objective was to biomechanically assess CV and ANT tethers using six patient-specific, finite element models of adolescent scoliotic patients (11.9 ± 0.7 years, Cobb 34° ± 10°). A validated algorithm simulated the growth and Hueter-Volkmann growth modulation over a period of 2 years with the CV and ANT tethers at two initial tensions (100, 200 N). The models without tethering also simulated deformity progression with Cobb angle increasing from 34° to 56°, axial rotation 11° to 13°, and kyphosis 28° to 32° (mean values). With the CV tether, the Cobb angle was reduced to 27° and 20° for tensions of 100 and 200 N, respectively, kyphosis to 21° and 19°, and no change in axial rotation. With the ANT tether, Cobb was reduced to 32° and 9° for 100 and 200 N, respectively, kyphosis unchanged, and axial rotation to 3° and 0°. While the CV tether mildly corrected the coronal curve over a 2-year growth period, it had sagittal lordosing effect, particularly with increasing initial axial rotation (>15°). The ANT tether achieved coronal correction, maintained kyphosis, and reduced the axial rotation, but over-correction was simulated at higher initial tensions. This biomechanical study captured the differences between a CV and ANT tether and indicated the variability arising from the patient-specific characteristics. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:254-264, 2018.

Posterior motion preserving implants evaluated by means of intervertebral disc bulging and annular fiber strains

BackgroundThe aims of motion preserving implants are to ensure sufficient stability to the spine, to release facet joints by also allowing a physiological loading to the intervertebral disc. The aim of this study was to assess disc load contribution by means of annular fiber strains and disc bulging of intact and stiffened segments. This was compared to the segments treated with various motion preserving implants. MethodsA laser scanning device was used to obtain three-dimensional disc bulging and annular fiber strains of six lumbar intervertebral discs (L2–3). Specimens were loaded with 500N or 7.5Nm moments in a spine tester. Each specimen was treated with four different implants; DSS™, internal fixator, Coflex™, and TOPS™. FindingsIn axial compression, all implants performed in a similar way. In flexion, the Coflex decreased range of motion by 13%, whereas bulging and fiber strains were similar to intact. The DSS stabilized segments by 54% compared to intact. TOPS showed a slight decrease in fiber strains (5%) with a range of motion similar to intact. The rigid fixator allowed strains up to 2%. In lateral bending, TOPS yielded range of motion values similar to intact, but maximum fiber strains doubled from 6.5% (intact) to 13.8%. Coflex showed range of motion, bulging and strain values similar to intact. The DSS and the rigid fixator reduced these values. The implants produced only minor changes in axial rotation. InterpretationThis study introduces an in vitro method, which was employed to evaluate spinal implants other than standard biomechanical methods. We could demonstrate that dynamic stabilization methods are able to keep fiber strains and disc bulging in a physiological range.

Mobile bearing knee kinematics change over time. A fluoroscopic study in rheumatoid arthritis patients

Background In a previous fluoroscopy study the motion of a mobile bearing total knee prosthesis was evaluated. That study showed that the axial rotation of the insert was limited. Three possible explanations are given for the limited rotation: low conformity between the femoral component and insert, the fixed anterior position of the insert-tibia pivot point leading to impingement and fibrous tissue formation. While the effect of the conformity on the axial rotation will not change over time, the effect of impingement and fibrous tissue is likely to increase, and thereby further decreasing the axial rotation. Methods In order to accurately assess changes in axial rotation over time in a mobile bearing total knee prosthesis rheumatoid arthritis patient group, patients were evaluated 8 months and 3 years postoperatively using fluoroscopy. Findings In comparison with the 8 months evaluation, the rotation of the femoral component (range: −10.8° to 2.8°) and the insert (range: −5.9° to 1.4°) were further limited at 3 years (respectively, −5.9° to 4.9° and −2.8° to 5.4°). Patterns of axial rotation for the femoral component and insert varied considerably between the trials within patients while at the 8 months evaluation no significant difference within patients was observed. Interpretation This study shows the importance of re-evaluating knee kinematics over time. The axial rotation of both the femoral component as the insert decreased over time, indicating a kinematic change caused by intrinsic factors. The decline in rotation of the insert could be explained by increased impingement and the formation of fibrous tissue.

The anterior cruciate ligament in controlling axial rotation. An evaluation of its effect.

Changes in axial tibial rotation after anterior cruciate ligament sectioning were evaluated in 14 fresh human knee joints. Simulation of vertical stance in a quadriceps-stabilized knee was performed. Internal and external rotational torques were applied before and after anterior cruciate ligament sectioning. Pivot shift tests were done in the intact and anterior cruciate ligament sectioned knee. Results of pivot shift tests were all negative before sectioning and positive after isolated sectioning. No significant change in axial rotation occurred between the intact and sectioned knee for external rotation (P = 0.24) or internal rotation (P = 0.12). Presence of a load at the femoral housing in both the intact and ligament-sectioned knees caused a significant change in external rotation (P < 0.0001). No significant change was noted in internal rotation between loaded and unloaded states (P = 0.70). Total tibial rotation in the intact knee was noted to vary between 31 degrees at 0 degree of flexion and 42 degrees at 60 degrees of flexion. These results suggest that the anterior cruciate ligament does not play a significant role in limiting axial rotation and that rotational instability is not a major factor after isolated anterior cruciate ligament rupture.