Adrija Sharma

Mobile-bearing total knee arthroplasty: do the polyethylene bearings rotate?

In vivo kinematics were determined during a weightbearing deep knee bend in 39 patients implanted with four different designs of mobile-bearing total knee arthroplasty to assess polyethylene bearing mobility patterns and magnitudes. The femoral and tibial components and mobile polyethylene insert (implanted with four tantalum beads) were overlaid onto the fluoroscopic images using a three-dimensional model-fitting technique to determine bearing mobility. Three of the four designs were tested at a single time interval while one was evaluated at two postoperative intervals, (12 months apart) to assess changes in bearing mobility with time. All patients had polyethylene bearing rotation relative to the tibial tray and minimal rotation relative to the femoral component. The average maximum amounts of bearing rotation ranged from 8.4° to 10.3° (range, 3.0°-20.1°). In patients evaluated at two time intervals, the average maximum bearing rotation increased from 8.5° (range, 3.4°-15.5°) at 3 months to 9.8° (range, 48°-14.1°) 15 months postoperatively. The presented data demonstrates polyethylene bearing mobility occurs following mobile-bearing total knee arthroplasty and mobility is maintained during the time interval tested. The presence of bearing mobility should result in lower contact stresses reducing the potential for polyethylene wear.

High-flexion TKA designs: what are their in vivo contact mechanics?

To accommodate for high flexion, new total knee arthroplasties (TKAs) have been designed. Unlike older designs which have been found to exhibit decreasing contact area with increasing flexion, we hypothesized the new designs would be associated with improved contact mechanics. We compared in vivo contact mechanics for 10 subjects having a fixed-bearing high-flexion posterior-stabilized (LPS-Flex) TKA and 10 subjects having a fixed-bearing high-flexion posterior cruciate-retaining (CR-Flex) TKA. All subjects performed deep knee bends to maximum flexion while under fluoroscopic surveillance. In vivo kinematics obtained using a three-dimensional to two-dimensional registration technique, were input into a three-dimensional inverse dynamic mathematical model to determine the contact forces. The contact areas and contact stresses were determined using a deformable contact model. The contact forces, contact areas, and contact stresses in both these implants increased with increasing flexion. The medial contact area in the LPS-Flex was higher than the CR-Flex for most of the flexion cycle. The lateral contact area was higher in the CR-Flex than the LPS-Flex in early and midflexion ranges. Although the lateral contact stresses were similar in both implants, the CR-Flex experienced higher medial contact stress than the LPS-Flex throughout flexion. However, both these implants were able to maintain sufficient contact area so the contact stress values were well below the yield strength of crosslinked polyethylene.

Asymptomatic same-site recurrent disc herniation after lumbar discectomy: results of a prospective longitudinal study with 2-year serial imaging.

Study Design. This is a prospective cohort study with serial imaging. Objective. We set out to determine the incidence of symptomatic and asymptomatic same-level recurrent disc herniation and assess their effect on 2-year outcome. Summary of Background Data. The reported incidence of symptomatic same-level recurrent disc herniation after lumbar discectomy varies widely in retrospective studies. To date, the incidence of radiographic same-level recurrent disc herniation has not been studied prospectively with sequential imaging. Furthermore, the clinical relevance of recurrent disc herniation on magnetic resonance imaging (MRI) after discectomy remains unknown, particularly in patients with poorly specific pain after surgery. Methods. One hundred eight patients undergoing lumbar discectomy for a single-level herniated disc at five institutions were prospectively observed for 2 years. Computed tomography (CT) and MRI of the lumbar spine were obtained every 3 months to assess reherniation and disc height loss. Leg and back pain visual analog scale (VAS), Oswestry Disability Index (ODI), and quality of life (SF-36 physical component) were assessed 3, 6, 12, and 24 months after surgery. Results. No patients demonstrated residual disc on postoperative MRI. By 2 years after discectomy, 25 (23.1%) patients had demonstrated radiographic evidence of recurrent disc herniation at the level of prior discectomy on serial imaging (mean ± SD, 11.8 ± 8.3 months after surgery). Radiographic disc herniation was asymptomatic in 14 (13%) patients and symptomatic in 11 (10.2%) patients. The occurrence of symptomatic recurrent disc herniation was associated with worse 2-year leg pain (VAS-LP, P=0.002) and disability (ODI, P=0.036) but not quality of life (SF-36) or disc height loss. The occurrence of asymptomatic reherniation was not associated with disc height loss or any outcome measure (VAS, ODI, and SF-36) by 2 years. Conclusion. Nearly one-fourth of patients undergoing lumbar discectomy demonstrated radiographic evidence of recurrent disc herniation at the level of prior surgery, the majority of which were asymptomatic. Asymptomatic disc herniation was not associated with clinical consequences by 2 years. Clinically silent recurrent disc herniation is common after lumbar discectomy. When obtaining MRI evaluation within the first 2 years of discectomy, providers should expect that radiographic evidence of reherniation may be encountered and that treatment should be considered only when correlating radicular symptoms exist.

in Vivo Evaluation of Dynamic Characteristics of the Normal, Fused, and Disc Replacement Cervical Spines

Study Design. In vivo human and biomechanical study. Objective. To quantify the in vivo kinematic and kinetic variations in the normal, fused, and disc replacement cervical spines. Summary of Background Data. Clinical and cadaveric studies have reported the motions and forces after an anterior cervical decompression and fusion (ACDF) or implantation of a cervical artificial disc replacement (CADR). However, there is no current study that describes the in vivo dynamic data of these 2 groups and compares them with that of a normal group. Methods. Ten normal subjects, 10 patients treated with an ACDF (C5–C6), and 10 patients having CADR (C5–C6) performed full flexion to extension motions under fluoroscopic surveillance. Kinematic data were obtained from the fluoroscopic images. Kinetic data were derived based on an inverse dynamic model of the entire cervical spine. Results. Even though the range of motion was larger for the normal group than for the ACDF group, the intersegmental rotations at the adjacent C6–C7 and C4–C5 levels in the ACDF group were 13.4° and 8.8° compared with 3.7° and 4.8° in the normal group, respectively, during the neck motion from 20° flexion to 15° extension. The difference at the C3–C4 level was 1° on average. Both the transverse contact forces and the soft tissue forces in the ACDF group were significantly larger than those in the normal group. The vertical forces in the ACDF group were smaller than those in the normal group, but there were no statistical differences. The CADR group exhibited kinematic and kinetic results similar to the normal group. Conclusion. In terms of restoring the normal dynamic motion of the cervical spine, CADR may be an alternative to the ACDF.

Comparison of In Vivo Patellofemoral Kinematics for Subjects Having High-Flexion Total Knee Arthroplasty Implant With Patients Having Normal Knees

This study compares the in vivo patellar kinematics of high-flexion posterior cruciate ligament-retaining and posterior-stabilized total knee arthroplasty (TKA) implants with that of the healthy knee. Twenty-seven subjects performing weight-bearing deep knee bends were analyzed under fluoroscopic surveillance from full extension to maximum flexion. The patellofemoral contact positions and patellar flexion were similar for both TKAs. At low flexion, the patellofemoral contact was significantly more distal on the healthy patella than on the TKA patella, but in deeper flexion, there was no difference among the 3 groups. The tibiopatellar angle was similar for all 3 groups, except at deep flexion where the healthy patella rotated significantly more than the implanted ones. Patellofemoral separation was observed in some TKA knees, whereas it was absent in the healthy knees.

In Vivo Determination of Cam-Post Engagement in Fixed and Mobile-bearing TKA

BackgroundKinematics vary, sometimes in important ways, among the different types of total knee arthroplasty (TKA) designs, yet differences between the in vivo mechanisms of cam-post engagement in rotating-platform posterior-stabilized (PS) TKA, bicruciate-stabilized TKA, and fixed-bearing PS TKA designs remain largely uncharacterized.Questions/purposesThe objective of this study was to determine the cam-post mechanism interaction for subjects implanted with three different TKA designs.MethodsIn vivo, analysis was conducted for patients implanted with nine rotating-platform PS TKAs, five knees with a fixed-bearing PS TKA, and 10 knees with a bicruciate-stabilized TKA while performing a deep knee bend. Three-dimensional kinematics of the implant components were determined by analysis of fluoroscopic images during flexion. The distances between the interacting surfaces were measured throughout flexion and instances and locations of contact were identified.ResultsSeven of the 10 bicruciate-stabilized knees analyzed had the femoral component engaged with the anterior aspect of the tibial post at full extension. Posterior cam-post engagement occurred at 34° for the bicruciate-stabilized (range, 17°–68°), 93° for the fixed-bearing PS (range, 88°–100°), and at 97° (range, 90°–104°) for rotating-platform PS TKA. In bicruciate-stabilized and fixed-bearing PS knees, the contact initially occurred on the medial aspect of the posterior surface of the tibial post and then moved centrally and superiorly with increasing flexion. For rotating-platform PS TKA, it was located centrally on the posterior surface of the post at all times.ConclusionsThis study suggests that mobility of the polyethylene might play an important role in ensuring central cam-post interaction in PS TKA. The polyethylene insert rotates axially in accordance with the rotating femur, maintaining central cam-post contact. This phenomenon was not observed in the fixed-bearing PS TKAs analyzed in this study.Clinical RelevanceWe speculate that this centralized symmetrical contact between the cam and posterior surface of the post could be beneficial clinically in terms of reducing wear of the posterior surface and particularly at the medial extremes of it.Level of EvidenceLevel III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Comparison of cervical spine kinematics using a fluoroscopic model for adjacent segment degeneration. Invited submission from the Joint Section on Disorders of the Spine and Peripheral Nerves, March 2007.

OBJECT In this cervical spine kinematics study the authors evaluate the motions and forces in the normal, degenerative, and fused states to assess how alteration in the cervical motion segment affects adjacent segment degeneration and spondylosis. METHODS Fluoroscopic images obtained in 30 individuals (10 in each group with disease at C5-6) undergoing flexion/extension motions were collected. Kinematic data were obtained from the fluoroscopic images and analyzed with an inverse dynamic mathematical model of the cervical spine that was developed for this analysis. RESULTS During 20 degrees flexion to 15 degrees extension, average relative angles at the adjacent levels of C6-7 and C4-5 in the fused patients were 13.4 degrees and 8.8 degrees versus 3.7 degrees and 4.8 degrees in the healthy individuals. Differences at C3-4 averaged only about 1 degrees. Maximum transverse forces in the fused spines were two times the skull weight at C6-7 and one times the skull weight at C4-5, compared with 0.2 times the skull weight and 0.3 times the skull weight in the healthy individuals. Vertical forces ranged from 1.6 to 2.6 times the skull weight at C6-7 and from 1.2 to 2.5 times the skull weight at C4-5 in the patients who had undergone fusion, and from 1.4 to 3.1 times the skull weight and from 0.9 to 3.3 times the skull weight, respectively, in the volunteers. CONCLUSIONS Adjacent-segment degeneration may occur in patients with fusion due to increased motions and forces at both adjacent levels when compared with healthy individuals in a comparable flexion and extension range.

3D in vivo femoro-tibial kinematics of tri-condylar total knee arthroplasty during kneeling activities

BACKGROUND Kneeling position can serve as an important posture, providing stability and balance from a standing position to sitting on the floor or vice-versa. The purpose of the current study was to determine the kinematics during kneeling activities after subjects were implanted with a tri-condylar total knee arthroplasty. MATERIALS AND METHODS Kinematics was evaluated in 54 knees using fluoroscopy and a three-dimensional model fitting approach. RESULTS The average knee flexion at before contact status, at complete contact and at maximum flexion was 98.1±9.0°, 107.2±6.7°, and 139.6±12.3°, respectively. On average, there was no gross anterior displacement from before contact status to complete contact. Only slight posterior rollback motion of both condyles from complete contact to maximum flexion was observed. Three of 39 (7.7%) knees experienced anterior movement of both condyles more than 2mm from before contact status to complete contact. Reverse rotation pattern from before contact status to complete contact and then normal rotation pattern from complete contact to maximum flexion were observed. Condylar lift-off greater than 1.0 mm was observed in 45 knees (83.3%). CONCLUSION The presence of the ball-and-socket joint articulation provides sufficient antero-posterior stability in these designs to enable the patients to kneel safely without the incidence of any dislocation. CLINICAL RELEVANCE This study suggests a safe implant design for kneeling.

Can Post-Cam Function Be Replaced by Addition of a Third Condyle in PS TKA?

The purpose of the study was to analyze the effectiveness of an additional ball and socket articulation in implanted knees and whether it can replicate post-cam function. Fifteen knees implanted with a cruciate substituting (CS) polyethylene without a post and ten knees implanted with a posterior stabilized (PS) polyethylene with a post were analyzed using 3D model fitting approach. Two types of designs showed similar posterior translation and similar axial rotation. Most of the contact points at the ball and socket joint stayed within the socket height for the PS group. This study indicates that the ball and socket joint is able to function as a replacement of the post-cam mechanism, which might serve as a new way to achieve posterior stability.

Single Versus Multiple-Radii Cruciate-Retaining Total Knee Arthroplasty: An In Vivo Mobile Fluoroscopy Study

BACKGROUND Previous fluoroscopic studies, using static C-arm systems, have shown nonnormal kinematic patterns in cruciate-retaining (CR) total knee arthroplasty (TKA). This study compares in vivo the kinematic differences in subjects implanted with single sagittal radius (SR) vs multiradii (MR) CR TKA for various activities using a novel mobile fluoroscopic system. METHODS Using mobile fluoroscopy and 3D to 2D registration, tibiofemoral kinematics were analyzed for 25 subjects with an SR, symmetrical condylar CR TKA and 25 subjects with an MR, asymmetric condylar CR TKA for three dynamic weight-bearing activities: (1) deep knee bend (DKB), (2) walking up a ramp, and (3) walking down a ramp. RESULTS During DKB, from full extension to maximum knee flexion, the SR (-0.43 ± 3.43 mm) and MR (-1.00 ± 3.23 mm) groups experienced statistically similar anterior/posterior (AP) motion in the lateral condyle. The SR (3.51 ± 2.68 mm) group had significant anterior movement compared to the MR (-0.42 ± 2.20 mm) group in the medial condyle. This resulted in a significantly larger amount of normal axial rotation experienced by the SR (5.20 ± 3.93°) group compared to the MR (0.75 ± 5.12°) group. During ramp activities, the SR TKA consistently exhibited a significantly more posterior position of both condyles compared to the MR TKA. CONCLUSION Although the SR TKA exhibited larger amounts of axial rotation compared to the MR TKA in DKB, neither design exhibited weight-bearing kinematics as previously reported for the normal knee. Additional research on the normal knee for ramp activities is required to understand the importance of condylar position during these activities.