Proposal of accurate cup placement procedure during total hip arthroplasty based on pelvic tilt discrepancies in the lateral position

By combining the anatomical-pelvic-plane (APP) positioner with a newly improved navigation system during total hip arthroplasty (THA), it is theoretically possible to determine cup orientation based on the APP while tracking pelvic movement. The purpose of this study was to determine the navigation accuracy and whether the error is related to the pelvic position fixed by the positioner. Fifty hips that underwent primary THA between 2018 and 2020 were analysed. The accuracy was 2.34° at radiographic inclination (RI) and − 5.01° at radiographic anteversion (RA), and the error was within 10° at both RI and RA in only 40 of 50 hips (80.0%). The discrepancy in pelvic sagittal tilt was correlated with the cup orientation error and especially strongly correlated with the RA error (r = − 0.751, p < 0.001). When RI and RA were calculated using a correction formula to determine the true cup orientation based on the pelvic tilt discrepancies, the error in both RI and RA was within 10° in all cases (100%). The navigation accuracy is related to the pelvic position fixed by the positioner, and the correction formula for the target angle that considers pelvic tilt discrepancies can lead to accurate cup placement in the future.

Surgical treatment of fractures of the distal radius – ORIF vs external fixation with ligamentotaxis

Introduction: The study compares the results of open reduction using volar locking plates with ligamentotaxis by external fixation in fractures of distal radius type 2R3C according to AO classification. Methods: A retrospective study evaluating the results of osteosynthesis in patients with distal radius fractures type 2R3C according to AO classification, operated until December 2018. The ORIF method with volar locking plates (LCP) was used in 54 patients, and closed reduction with ligamentotaxis using external fixation (EF) was used in 33 patients. The mean age of the patients was 46.7 years in the LCP group and 59.6 years in the EF group. All were evaluated for their X-ray and functional outcomes and according to the Green and O’Brien score at 6 and 12 months after surgery. Results: According to X-rays at 12 months in the LCP group, the mean sagittal tilt was 10.13°, the mean radial inclination was 23.89°, and the mean radial length was 11.84 mm. In the EF group, the mean sagittal tilt was 6.32°, the mean radial inclination was 24.78°, and the mean radial length was 9.89 mm. According to the Green and O’Brien score, we recorded a mean score of 84.44 points in the LCP group at 12 month; we achieved good and excellent results in 83.33% of the patients and no poor result was observed. In the EF group the final mean score was 77.27; good and excellent results were achieved in 45.46% of the patients and a poor result in one patient. Conclusion: Based on the results in our group of patients, the internal type osteosynthesis using LCP implants can be recommended as a first-choice technique in the treatment of 2R3C fractures according to AO classification.

Influence of pelvic sagittal tilt on 3-dimensional bone coverage in total hip arthroplasty: a simulation analysis

Background: In total hip arthroplasty with computer navigation assistance, cup orientation is generally determined according to the coordinate system relative to the functional pelvic plane (FPP). However, there is a large difference in the cup anteversion between a posterior pelvic tilt relative to the computed tomography (CT) table in the sagittal plane and anterior pelvic tilt, even when the cup is set at the same orientation angle according to each FPP. The present study analysed this difference from the viewpoint of 3-dimensional (3D) coverage of the acetabular component (3D coverage) to determine how the 3D acetabular coverage is altered with changes in pelvic sagittal tilt. Methods: We analysed 3D-simulated acetabular coverage measured in 3D pelvic models reconstructed from the preoperative CT data of 50 patients. In each patient, we created 5 pelvic models with a sagittal tilt of 10° increments between 20° anterior tilt and 20° posterior tilt relative to the CT table. Results: We found that 3D coverage decreased as the pelvis tilted posteriorly. Particularly, there were significant differences between the pelvis with 20° anterior tilt and that with neutral tilt ( p < 0.001). There was also a difference between the pelvis with neutral tilt and that with a 20° posterior tilt ( p < 0.01). The mean decrease in 3D coverage between the pelvis with neutral tilt and that with 20° posterior tilt was 7.2 ± 1.6%. Conclusions: We found that 3D coverage differed among pelvis with different sagittal tilts when the cup orientation angle was determined according to FPP.

Estimation of the Balance-Keeping Control Law Applied by a Human Being Upon a Sudden Sagittal Tilt Perturbation

This study aims to estimate the control law employed by the central nervous system (CNS) to keep a person in balance after a sudden disturbance. For this aim, several experiments were carried out, in which the subjects were perturbed sagittally by using a single-axis tilt-platform and their motions were recorded with appropriate sensors. The analysis of the experimental results leads to the contribution of this paper as a conjecture that the CNS commands the muscular actuators of the joints according to an adaptive proportional-derivative (PD) control law such that its gains and set points are updated continuously. This conjecture is accompanied with an assumption that the CNS is able to acquire perfect and almost instantaneous position and velocity feedback by means of a fusion of the signals coming from the proprioceptive, somatosensory, and vestibular systems. In order to verify the conjectured control law, an approximate biomechanical model was developed and several simulations were carried out to imitate the experimentally observed motions. The time variations of the set points and the control gains were estimated out of the experimental data. The simulated motions were observed to be considerably close to the experimental motions. Thus, the conjectured control law is validated. However, the experiments also indicate that the mentioned adaptation scheme is quite variable even for the same subject tested repeatedly with the same perturbation. In other words, this experimental study also leads to the implication that the way the CNS updates the control parameters is not quite predictable.

Change in pelvic sagittal tilt after corrective long fusion of spine

The individual pelvic sagittal inclination (PSI) is an issue for cup alignment in total hip arthroplasty (THA). The pelvic position in supine or functional pelvic plane in supine have been recommended by many reports while some consider a standing pelvic position as the reference to aim an optimal cup alignment. PSI changes in various postures and even in the same posture, aging change it due to spinal degeneration and muscle weakness. The chronological PSI change is larger in standing than that in supine. It is expected that PSI in standing position may improve when spinal long fusion was performed.Therefore, the purpose of this study was to evaluate the change of PSI between pre- and post- corrective long fusion for adult spinal deformity (ASD). Total eight patients underwent corrective surgery for ASD between May 2014 and October 2016 were the subjects of this study. All are females with the average age of 70 years. There were two cases that underwent bilateral THA before spine surgery. The anterior pelvic plane (APP) through the most anterior aspect of the pubic tubercle and bilateral anterior superior iliac spines (ASISs) was used to measure PSI, which was defined as the angle between the APP and the vertical axis on the sagittal plane DRR. In addition, we measured the cup anteversion in two THA cases by using viewer software. The mean change in the preoperative PSI from supine to standing was 17° posteriorly. The mean change in the supine PSI from pre- to post-operation was 6.9° anteriorly, and that in the standing PSI was 17° anteriorly. The mean change in the postoperative PSI from supine to standing was 6.7° posteriorly. When we measured PSI on standard AP radiographs of the pelvis in two patients who underwent THA, the mean change in postoperative PSI from supine to standing was less than 3°.The mean change in cup anteversion on supine AP radiographs were 2.7°. As we expected, the change in PSI from supine to standing position was reduced by performing corrective surgery. In this study, the mean change of radiographic cup anteversion in supine after corrective long fusion was 2.7°and PSI in standing changed into the direction which reduce posterior impingement and anterior dislocation. Although the change in PSI after corrective spine surgery heavily depends on the spine surgeon’s philosophy of correction, corrective spine surgery should have a positive effect on cup alignment in standing and little influence on cup alignment in supine.

TREATMENT OF DISTAL RADIAL FRACTURES WITH THE DVR-A PLATE — THE EARLY BRISTOL EXPERIENCE

Aim: The aim of the study was to assess how adequately distal radial fracture reduction was reproduced and maintained with the distal volar radius anatomic DVR-A (Biomet, Inc) locking plate. Methods: We looked at a consecutive series of 111 patients treated with the DVR-A plate at our institution from 2007–2010. The preoperative, intra-operative, and postoperative films were reviewed. The AO and Frykman classification was recorded. The sagittal tilt, radial inclination, and radial length were measured on intra-operative X-rays and compared with final follow-up X-rays. The last recorded range of motion at follow-up and a functional assessment using the Disabilities of the Arm, Shoulder, and Hand (DASH) score was recorded. Results: At final follow-up a mean radial inclination of 22.22 degrees (11 to 38 degrees), radial height of 11.85 mm (6 to 18 mm), and sagittal tilt of 6.71 degrees volar (-9 to 19 degrees) was achieved. From initial post-operative films, to final follow-up X-rays there was a mean increase of 0.17 degrees in radial inclination, a mean loss of 0.36 mm radial height, and a mean loss of 2.17 degrees volar tilt. The mean extension was 46.8 degrees, flexion 48.3 degrees, pronation 77.4 degrees, supination 74.8 degrees, radial deviation 15.3 degrees and the ulnar deviation 19 degrees. The mean DASH score was 12.8 (0–68). Conclusion: The DVR-A plate achieved a highly satisfactory reduction of radial length and radial inclination, with a small loss of volar sagittal tilt at final follow-up. A good functional outcome was reported, with a satisfactory range of motion achieved. The DVR-A plate is a safe and effective treatment for unstable and intra-articular displaced distal radius fractures, particularly in younger patients, in the short term.

Sagittal Rotational Malunions of the Distal Radius: The Role of Pure Derotational Osteotomy

Sagittal rotational malunion after distal radius fractures was identified in eight patients by the presence of a “hinge” point on the volar cortex on the lateral radiograph, and the ulnar head being shorter than the anterior lip of the radius on the posterior–anterior radiograph. The surgical correction consisted of preplating the distal fragment with a volar locking plate before an osteotomy through the “hinge” point, and correcting the dorsal tilt of the distal fragment. Any dorsal defect was filled with cancellous bone graft from the olecranon. Pain, range of motion and grip all improved. Disabilities of arm, shoulder and hand score changed from 54 to six. Dorsal sagittal tilt improved by 26°, from −23°to +3°. Ulnar variance improved by 3 mm, from +1.5 to −1.5 mm, becoming identical to the opposite side. A pure derotational osteotomy corrected the apparent shortening of the radius and restored the volar tilt.