Assessment of Wear in Total Knee Arthroplasty Using Advanced Radiographic Techniques

Total knee arthroplasty (TKA) has become the gold standard approach for treating advanced osteoarthritis of the knee. Although the surgery continues to be very successful at relieving pain and restoring joint function, its longevity is challenged by wear and loosening of the implant components. This requires the patient to undergo a revision surgery to replace the implant, a much more challenging operation than primary arthroplasty. Wear of the polyethylene tibial inserts from TKA is assessed in vitro using mechanical wear simulator testing and by examining failed implants retrieved from patients during revision surgery, as well as with direct in vivo measurements. Current in vitro measurement tools provide only a global estimate of wear (failing to describe whether the wear has occurred on the articulating or backside surfaces, or stabilizing post), or are qualitative measurements, or lack resolution. Current in vivo measurement techniques are performed statically or quasi-statically, leading to the potential for an underestimation of wear volume as the contact area of the implant components change throughout flexion. The purpose of this thesis was to describe, validate, and utilize new advanced imaging techniques to measure TKA implant wear for both in vitro and in vivo applications. Micro-computed tomography (micro-CT), a non-destructive, high resolution imaging technique was utilized to provide detailed images of the geometry of tibial inserts used in wear simulator trials or retrieved from patients, and create surface deviation maps to accurately quantify wear. Ways to create an unworn reference geometry, for use in comparing to a worn retrieved tibial insert when the pre-wear geometry is unknown, were evaluated and a best practice approach was determined. These methods were then applied to study a group of tibial inserts retrieved from patients during revision surgery, which were found to be well functioning with a yearly wear rate equivalent to other contemporary implant designs. Finally, a pilot study to evaluate the use of dynamic single-plane flat panel digital radiography for use in measuring TKA implant wear in vivo was conducted. The system was determined to have a measurement accuracy and precision sufficient to begin a pilot clinical study with patients

Comparison of Contact Kinematics in Posterior-Stabilized and Cruciate-Retaining Total Knee Arthroplasty at Long-Term Follow-Up

© 2019 Elsevier Inc. Background: There is controversy regarding the superiority of posterior-stabilizing (PS) total knee arthroplasty (TKA) and cruciate-retaining (CR) TKA. Substantial work has made comparisons between PS and CR TKA at follow-ups of less than 5 years. It was the goal of the present study to compare the kinematics at greater than 5 years postoperatively between CR and PS TKA, with a secondary goal of comparing patient function. Methods: A total of 42 knees were investigated, with equal representation in the PS and CR TKA groups. Patients underwent radiostereometric analysis imaging at 0°, 20°, 40°, 60° 80°, and 100° of flexion. Contact position, magnitude of excursion, and condylar separation on each condyle were measured. A Timed-Up-and-Go functional test was also performed by patients, with the total test time being measured. Preoperative and postoperative clinical outcome scores were also collected. Results: There were differences in contact position on both the medial and lateral condyles at multiple angles of flexion (P \u3c .05). There was no difference (P = .89) in medial excursion; however, PS TKA had greater lateral excursion than CR TKA (P \u3c .01). No difference (P \u3e .99) was found in frequency of condylar separation. PS TKA was associated with faster (P = .03) total Timed-Up-and-Go test times. There were no differences in clinical outcome scores between the groups preoperatively or postoperatively. Conclusion: We found kinematic and functional differences that favor PS TKA. Our results suggest posterior cruciate ligament insufficiency in CR TKA, indicating that perhaps the cam/post systems in PS TKA better maintain knee kinematics and function long term

Effect of Taper Design on Trunnionosis in Metal on Polyethylene Total Hip Arthroplasty.

This study examines how taper design affects corrosion and fretting at the head trunnion surface. All hip prostheses retrieved between 1999 and 2013 with 28mm/+0 heads were selected, resulting in 44 cobalt-chrome-on-polyethylene implants, representing six taper designs. Mean implantation time: 8.9±3.7years. The femoral head tapers were scored for fretting and corrosion using the Goldberg scale as both a combined score and by three zones (apex, central and base). There was no difference in age (P=0.34), BMI (P=0.29), or implantation time (P=0.19) between taper groups. The 11/13 taper had the highest combined corrosion and fretting score, but no difference (P=0.22) between groups for combined scores (P=0.22 for corrosion, P=0.19 for fretting). In a zone-specific analysis, the 11/13 taper had highest corrosion score at base zone (P=0.02). Taper design had a significant effect on corrosion at base of trunnion

Accuracy of the modified Hardinge approach in acetabular positioning

© 2016 Joule Inc. or its licensors. Background: The surgical approach chosen for total hip arthroplasty (THA) may affect the positioning of the acetabular component. The purpose of this study was to examine the accuracy in orienting the acetabular component using the modified Hardinge approach. Methods: We used our institutional arthroplasty database to identify patients with primary, press-fit, hemispherical acetabular components of a metal-on-polyethylene THA performed between 2003 and 2011. Patients with radiographs obtained 1-3 years after the index procedure were included for measurement of anteversion and inclination angles. Acceptable values of anteversion and abduction angles were defined as 15° ± 10° and 40° ± 10°, respectively. Results: We identified 1241 patients from the database, and the modified Hardinge approach was used in 1010 of the patients included in our analysis. The acetabular component was anteverted in the acceptable zone in 54.1% of patients. The abduction angle was within the defined range in 79.2% of patients. Combined anteversion and abduction angles within the defined zone were present in 43.6% of patients. Conclusion: Consistent with studies examining accuracy from other approaches, our study reveals that the modified Hardinge approach was only moderately accurate in positioning the acetabular component in the acceptable zone

Machine Learning Groups Patients by Early Functional Improvement Likelihood Based on Wearable Sensor Instrumented Preoperative Timed-Up-and-Go Tests

© 2019 The Author(s) Background: Wearable sensors permit efficient data collection and unobtrusive systems can be used for instrumenting knee patients for objective assessment. Machine learning can be leveraged to parse the abundant information these systems provide and segment patients into relevant groups without specifying group membership criteria. The objective of this study is to examine functional parameters influencing favorable recovery outcomes by separating patients into functional groups and tracking them through clinical follow-ups. Methods: Patients undergoing primary unilateral total knee arthroplasty (n = 68) completed instrumented timed-up-and-go tests preoperatively and at their 2-, 6-, and 12-week follow-up appointments. A custom wearable system extracted 55 metrics for analysis and a K-means algorithm separated patients into functionally distinguished groups based on the derived features. These groups were analyzed to determine which metrics differentiated most and how each cluster improved during early recovery. Results: Patients separated into 2 clusters (n = 46 and n = 22) with significantly different test completion times (12.6 s vs 21.6 s, P \u3c .001). Tracking the recovery of both groups to their 12-week follow-ups revealed 64% of one group improved their function while 63% of the other maintained preoperative function. The higher improvement group shortened their test times by 4.94 s, (P = .005) showing faster recovery while the other group did not improve above a minimally important clinical difference (0.87 s, P = .07). Features with the largest effect size between groups were distinguished as important functional parameters. Conclusion: This work supports using wearable sensors to instrument functional tests during clinical visits and using machine learning to parse complex patterns to reveal clinically relevant parameters

Interplay between Topological States and Rashba States as Manifested on Surface Steps at Room Temperature

The unique spin texture of quantum states in topological materials underpins many proposed spintronic applications. However, realizations of such great potential are stymied by perturbations, such as temperature and local fields imposed by impurities and defects, that can render a promising quantum state uncontrollable. Here, we report room-temperature observation of interaction between Rashba states and topological surface states, which manifests unique spin textures controllable by layer thickness of thin films. Specifically, we combine scanning tunneling microscopy/spectroscopy with the first-principles theoretical calculation to find the robust Rashba states coexisting with topological surface states along the surface steps with characteristic spin textures in momentum space. The Rashba edge states can be switched off by reducing the thickness of a topological insulator Bi2Se3 to bolster their interaction with the hybridized topological surface states. The study unveils a manipulating mechanism of the spin textures at room temperature, reinforcing the necessity of thin film technology in controlling quantum states

Fracture of Two Moderately Cross-Linked Polyethylene Tibial Inserts in a TKR Patient

Highly cross-linked polyethylene has become the gold standard in total hip replacement for its wear resistance. Moderately crosslinked polyethylene is now available for total knee replacement (TKR), although concerns about reduced mechanical strength have prevented widespread adoption. The purpose of this report is to describe an unusual case where a patient underwent cruciate retaining TKR using a moderately crosslinked polyethylene tibial insert that went on to fracture twice in the same location across the primary and first revision surgery. The first tibial insert was 10 mm thick and was implanted for 16 months. The second tibial insert was 15 mm thick and was implanted for 11 months. Both fractured along the posterior aspect of the medial articular surface. The lack of a specific event leading to these fractures and the fact that they occurred twice in the same location in the same patient suggest that caution is still necessary regarding the introduction of crosslinked polyethylene for TKR surgery