Are Instrumented Knee Forces Representative of a Larger Population of Cruciate-Retaining Total Knee Arthroplasties?

BACKGROUND: It is not known if the loads and motions reported for instrumented knees are generalizable to a larger population of total knee arthroplasty (TKA) patients. The purpose of this study is to (1) report axial implant force data for chair and stair activities for a population of cruciate-retaining TKA patients and (2) compare the population forces to those measured with instrumented TKAs. METHODS: Twenty-three subjects with a cruciate-retaining TKA underwent motion analysis during stair ascending, stair descending, chair sitting, and chair rising activities after informed consent in this institutional review board approved study. Axial TKA forces were calculated using a previously validated computational model. Differences between the mean and variability of population instrumented TKA peak forces and force impulses were tested using t tests and Levene test. RESULTS: Peak axial forces were 3.06, 2.74, 2.65, and 2.60 kN for stair ascent, stair descent, chair rising, and chair sitting, respectively. Force impulses were 123.3, 123.4, 153.5, and 154.0 kN*% activity cycle for stair ascent, stair descent, chair sitting, and chair rising, respectively. Population TKA and instrumented TKA peak forces were different for stair ascent (P = .03) and stair descent (P = .03) in the second half of the activity cycles. The variability of the peak forces and impulses were not different (P = .106 to P = .99). CONCLUSION: The forces and motions presented in this study represent cruciate-retaining TKA patients and could be used for displacement-driven knee wear testing. The forces are similar to those in the literature from instrumented prostheses of an ultracongruent cruciate-sacrificing TKA.

Wear Scar Similarities between Retrieved and Simulator-Tested Polyethylene TKR Components: An Artificial Neural Network Approach.

The aim of this study was to determine how representative wear scars of simulator-tested polyethylene (PE) inserts compare with retrieved PE inserts from total knee replacement (TKR). By means of a nonparametric self-organizing feature map (SOFM), wear scar images of 21 postmortem- and 54 revision-retrieved components were compared with six simulator-tested components that were tested either in displacement or in load control according to ISO protocols. The SOFM network was then trained with the wear scar images of postmortem-retrieved components since those are considered well-functioning at the time of retrieval. Based on this training process, eleven clusters were established, suggesting considerable variability among wear scars despite an uncomplicated loading history inside their hosts. The remaining components (revision-retrieved and simulator-tested) were then assigned to these established clusters. Six out of five simulator components were clustered together, suggesting that the network was able to identify similarities in loading history. However, the simulator-tested components ended up in a cluster at the fringe of the map containing only 10.8% of retrieved components. This may suggest that current ISO testing protocols were not fully representative of this TKR population, and protocols that better resemble patients' gait after TKR containing activities other than walking may be warranted.

Influence of crosslinking on the wear performance of polyethylene within total ankle arthroplasty.

BACKGROUND: Wear debris of polyethylene within joint replacement systems can result in clinical complications including osteolysis and component loosening. Highly crosslinked polyethylene (HXPE) was introduced to improve these outcomes, and has been shown to result in improved wear performance in several joint replacement systems. However, bearing couples within total ankle replacement (TAR) systems have historically used conventional polyethylene (CPE) articulating on metal. The extent to which HXPE would result in a reduction of polyethylene wear compared to CPE in the ankle has not been studied. The hypothesis motivating this study was that use of HXPE within TAR will result in significantly lower wear rate than CPE. METHODS: HXPE and CPE inserts within a semiconstrained, bicondylar TAR system were manufactured for this study. Samples were subjected to 5.0 million cycles of wear on an in vitro wear simulator. Testing was performed within a physiological environment, using kinematic and kinetic loading profiles characteristic of walking gait. Samples were weighed at regular intervals to determine gravimetric mass loss, and the morphology of wear particles was analyzed. RESULTS: The wear rates for CPE and HXPE samples were 7.4 ± 1.3 and 1.9 ± 0.3 mg/Mc (mean ± SD), respectively. HXPE samples exhibited a significant (P < .01) wear rate reduction of 74% when compared with the CPE. Debris morphology trends between HXPE and CPE were consistent with what has been observed in other joint systems. CONCLUSION: Use of HXPE significantly reduces wear of TAR as compared to CPE, based on in vitro wear testing. CLINICAL RELEVANCE: Highly crosslinked polyethylene may reduce clinical complications of total ankle replacement that are linked to polyethylene wear.