90° Spinning of Polyethylene Inserts in Mobile Bearing Unicompartmental Knee Arthroplasty

<b>Background</b> The objective of this article is to describe for the first time a case of 90^° spin out of a mobile bearing unicompartmental knee arthroplasty (UKA) polyethylene insert. In this report, we present a 57-year-old gentleman with a medial compartment UKA for osteoarthritis in 2017 who developed dislodgement and 90^° rotation subsequent to traumatic injury when he was involved in a bus crash and impacted the anterolateral knee sustaining a valgus type injury 1 week postoperatively. Following the injury, he reported medial knee pain and a sensation of something moving within the joint. He was initially managed conservatively and progressed to full weight bearing; however, he experienced intermittent symptoms of catching and blocking of the joint, as well as medial knee swelling, that inhibited his ability to perform activities involving walking, kneeling, or pivoting. Imaging taken in 2018 show a 90° rotation of the polyethylene insert. These images showed the longitudinal metallic marker on the insert facing in an anteroposterior direction as opposed to the normal medial-lateral orientation. Failing conservative management, he presented to our clinic in 2019 and proceeded for revision of his UKA. Intraoperatively, his insert was reviewed and seen to easily spin on axis. The liner was therefore removed and upsized from a size 5 medium to a size 7 medium insert which provided excellent stability and stopped any further spinning. He has done tremendously well since the operation and reports full range of motion and no concerns. In patients with a history of pain, swelling, or locking following a UKA, it would be prudent to consider insert spinning, as well as the more common dislocation, through confirming the orientation of the metallic insert marker. Revision surgery to correct the spinning defect has proven effective with good resolution of symptoms and return to full range of motion.

Late Failure of a Polyethylene Unicompartmental Knee Insert -Retrieval Analysis Protocol and Results

This study reports the investigation of a degraded polyethylene insert retrieved after the catastrophic failure of a mobile bearing knee implant, occurred after a traumatic event and leading to a late revision. Understanding wear mechanisms of polyethylene components is important to improve the implants for joint replacement. This model of unicompartmental arthroplasty, due to its mobile, congruent insert and design, has the potential to attain low rates of wear, leading to an improved survival of the prosthesis over fixed-bearing knee implants. During the surgical technique, however, it is critical to avoid any source of impingement or incongruent articulation, as this are associated with increased rates of polyethylene wear and may contribute to the early necessity for revision surgery. The investigated insert presented a macroscopic fragmentation, surface and bulk defects and debris. Characterization of the retrieved polyethylene implant fragments was performed by macroscopic examination, by scanning electron microscopy and Fourier transform infrared spectroscopy. Due to a systematic retrieval analysis according to current standards, we can question that, in our case, third body wear is rarely pure bone or pure cement debris related but a combination of the two mentioned. The combination enhanced contribution of polyethylene debris in severe wear initiation and progression. Complete examination of the explants exhibiting breakage or severe wear may help in understanding pathogenic ways of failure in unicompartmental knee.

Assessment of in vivo bone activity patterns in medial mobile-bearing unicompartmental knee arthroplasty

Aims Higher osteoblastic bone activity is expected in aseptic loosening and painful unicompartmental knee arthroplasty (UKA). However, insights into normal bone activity patterns after medial UKAs are lacking. The aim of this study was to identify the evolution in bone activity pattern in well-functioning medial mobile-bearing UKAs. Methods In total, 34 patients (13 female, 21 male; mean age 62 years (41 to 79); BMI 29.7 kg/m2 (23.6 to 42.1)) with 38 medial Oxford partial UKAs (20 left, 18 right; 19 cementless, 14 cemented, and five hybrid) were prospectively followed with sequential 99mTc-hydroxymethane diphosphonate single photon emission CT (SPECT)/CT preoperatively, and at one and two years postoperatively. Changes in mean osteoblastic activity were investigated using a tracer localization scheme with volumes of interest (VOIs), reported by normalized mean tracer values. A SPECT/CT registration platform additionally explored cortical tracer evolution in zones of interest identified by previous experimental research. Results Significant reduction of tracer activity from the preoperative situation was found in femoral and anteromedial tibial VOIs adjacent to the UKA components. Temporarily increased osteoblastic bone activity was observed in VOIs comprising the UKA keel structure at one year postoperatively compared to the preoperative activity. Persistent higher tracer uptake was found in the posterior tibial cortex at final follow-up. Multivariate analysis showed no statistical difference in osteoblastic bone activity underneath cemented or cementless components. Conclusion Well-functioning medial mobile-bearing UKAs showed distinct changes in patterns of normalized bone tracer activity in the different VOIs adjacent to the prosthetic components, regardless of their type of fixation. Compared to the preoperative situation, persistent high bone activity was found underneath the keel and the posterior tibial cortex at final follow-up, with significant reduced activity only being identified in femoral and anteromedial tibial VOIs. Cite this article: Bone Joint J 2022;104-B(1):34–44.

Biomechanical Assessment of Mobile-Bearing Total Knee Endoprostheses Using Musculoskeletal Simulation

The purpose of this computational study was to analyze the effects of different mobile-bearing (MB) total knee replacement (TKR) designs on knee joint biomechanics. A validated musculoskeletal model of the lower right extremity implanted with a cruciate-retaining fixed-bearing TKR undergoing a squat motion was adapted for three different MB TKR design variants: (I) a commercially available TKR design allowing for tibial insert rotation about the tibial tray with end stops to limit the range of rotation, (II) the same design without end stops, and (III) a multidirectional design with an additional translational degree-of-freedom (DoF) and end stops. When modeling the MB interface, two modeling strategies of different joint topologies were deployed: (1) a six DoF joint as a baseline and (2) a combined revolute-prismatic joint (two DoF joint) with end stops in both DoF. Altered knee joint kinematics for the three MB design variants were observed. The commercially available TKR design variant I yielded a deviation in internal-external rotation of the tibial insert relative to the tray up to 5° during knee flexion. Compared to the multidirectional design variant III, the other two variants revealed less femoral anterior-posterior translation by as much as 5 mm. Concerning the modeling strategies, the two DoF joint showed less computation time by 68%, 80%, and 82% for design variants I, II, and III, respectively. However, only slight differences in the knee joint kinematics of the two modeling strategies were recorded. In conclusion, knee joint biomechanics during a squat motion differed for each of the simulated MB design variants. Specific implant design elements, such as the presence of end stops, can impact the postoperative range of knee motion with regard to modeling strategy, and the two DoF joint option tested accurately replicated the results for the simulated designs with a considerably lower computation time than the six DoF joint. The proposed musculoskeletal multibody simulation framework is capable of virtually characterizing the knee joint dynamics for different TKR designs.

Revision Rates After Total Ankle Replacement: A Comparison of Clinical Studies and Arthroplasty Registers

Background: The aim of this study was to assess the outcome of total ankle replacement (TAR) regarding revision rates by comparing clinical studies of the last decade to data displayed in arthroplasty registers. The secondary aim was to evaluate whether dependent clinical studies show a superior outcome to independent publications. Additionally, revision rates of mobile bearing implants (MB-TARs) were compared to those of fixed bearing implants (FB-TARs). Methods: Clinical studies on TARs between 2010 and 2020 were systematically reviewed, with the endpoint being a revision for any reason. The parameter “revision rate per 100 observed component years (CYs)” was calculated for each publication. The pooled revision rate for clinical studies was compared to the data reported in arthroplasty registers. In a second step, revision rates were subdivided and analyzed for independent and dependent publications and for FB-TARs and MB-TARs. Results: A total of 43 publications met the inclusion criteria comprising 5806 TARs. A revision rate of 1.8 per 100 observed CYs was calculated, corresponding to a 7-year revision rate of 12.6%. The 3 arthroplasty registers included showed revision rates ranging from 8.2% to 12.3% after 7 years. No significant difference between dependent and independent publications nor between FB-TARs and MB-TARs was detected. Conclusion: Revision rates of clinical studies and arthroplasty registers are comparable. Surgeons can compare their own revision rates with those from this study. Dependent studies do not seem to be biased, and no superiority for one bearing type can be described. Level of Evidence: Level III, systematic review of level III studies

Potential factors in postoperative dislocation of Oxford phase III mobile bearing UKA in Chinese patients: a single-center retrospective study

Background Bearing dislocation is the main complication after mobile bearing unicompartmental knee arthroplasty. The purpose of this study was to analyze the potential risk factors of bearing dislocation after Oxford phase III mobile bearing unicompartmental knee arthroplasty in Chinese patients. Methods We retrospectively investigated 492 patients (578 knees) who underwent Oxford phase III mobile bearing unicompartmental knee arthroplasty in our institution between February 2009 and June 2019. The patients were divided into two groups based on surgeons’ annual surgical volume. Those with/ without bearing dislocation were compared based on patient, surgeon and implant factors. Results Among the 492 patients, 21 (4.3%, 4 men and 17 women) experienced bearing dislocation. Of these, 14 (4.0%) were in the high surgical volume group and 7 (5.1%) were in the low surgical volume group. Multivariate analysis revealed that trauma to the operated leg and daily life involving high knee flexion cumulatively predicted bearing dislocation (p < 0.05). Conclusions Trauma to the operated leg and daily life involving high knee flexion were risk factors for bearing dislocation after Oxford phase III mobile bearing unicompartmental knee arthroplasty.