The COVID-19 pandemic has strongly impacted elective orthopaedic surgery. At our trust, a geographically discrete elective site deals with planned orthopaedic surgery. There was a need to define a green pathway to deliver surgical care safely and efficiently, and tackle mounting waiting lists. Records of patients operated at our elective site, between 1st July 2020 and 14th January 2021, under a green pathway, including pre-operative self-isolation, COVID screening and segregating perioperative patients, were reviewed, and analysed retrospectively. Patients who did not attend (DNA) their post-operative follow-up appointments were identified. Finally, regional COVID incidence was compared with that in our centre.Abstract
Background
Methods
Cementless Total Knee Arthroplasty has been developed to reduce the incidence of failure secondary to aseptic loosening, osteolysis and stress-induced osteopenia, especially in younger and more active patients. However, failures are still more common compared to cemented components, especially those involving the tibia. It is hypothesized that this is caused by incomplete contact between the tibial tray and the underlying bony surface due to: (i) inadequate flatness of the tibial osteotomy, or (ii) failure of implantation to spread the area of contact over the exposed cancellous surface. In the present study we compare the contact area developed during implantation of a cementless tray as a function of the initial flatness of the tibial osteotomy. Eight joint replacement surgeons prepared 14 cadaveric knees for cementless TKR using a standard instrumentation set (ZimmerBiomet Inc). The tibial osteotomy was created using an oscillating bone saw and a 1.27mm blade (Stryker Inc) directed by a slotted cutting guide mounted on an extramedullary rod and fixed to the tibia with pins and screws. The topography of the exposed cancellous surface was captured with a commercial laser scanner (Faro Inc, Halifax, approx. 33,000 surface points). 3D computer models of each tibial surface were generated in a CAD environment (Rapidform, Inuus). After scanning, a cementless tibial tray was implanted on the prepared tibial surface using a manual impactor. The tray-tibia constructs were dissected free of soft tissue, embedded in mounting resin, and sectioned with a diamond wafering saw. Points of bone-tray contact and interface separation were identified by stereomicroscopy and incorporated in the 3D computer models. Maps were generated depicting contacting and non-contacting areas Each model was subdivided into 7 zones for characterizing the distribution of interface contact in terms of anatomic location.Background
Method
Corrosion products from modular taper junctions are a potent source of adverse tissue reactions after THR. In an attempt to increase the area of contact and resistance to interface motion in the face of taper mismatches, neck trunnions are often fabricated with threaded surfaces designed to deform upon assembly. However, this may lead to incomplete contact and misalignment of the head on the trunnion, depending upon the geometry and composition of the mating components. In this study we characterized the effect of different femoral head materials on the strength and area of contact of modular taper constructs formed with TiAlV trunnions. Three groups of 36mm femoral heads (CoCr, Biolox ceramic; Oxinium) and matching Ti-6Al-4V rods with 12/14 trunnions were selected for use in this study. The surface of each trunnion was coated with a 20nm layer of gold applied by sputter-coating in vacuo. Each head/trunnion pair was placed in an alignment jig and assembled with a peak axial impaction force of 2000N using a drop tower apparatus. After assembly, each taper was disassembled in a custom apparatus mounted in a mechanical testing machine (Bionix. MTS. After separation of the components, the surface of each trunnion was examined with backscattered electron microscopy to reveal the area of disruption of the original gold-coated surface. Images encompassing the entire surface of the trunnion were collected and quantified by image processing.Introduction
Materials and Methods
In theory, Finite Element Analysis (FEA) is an attractive method for elucidating the mechanics of modular implant junctions, including variations in materials, designs, and modes of loading. However, the credence of any computational model can only be established through validation using experimental data. In this study we examine the validity of such a simulation validated by comparing values of interface motion predicted using FEA with values measured during experimental simulation of stair-climbing. Two finite element models (FEM) of a modular implant assembly were created for use in this study, consisting of a 36mm CoCr femoral head attached to a TiAlV rod with a 14/12 trunnion. Two head materials were modelled: CoCr alloy (118,706 10-noded tetrahedral elements), and alumina ceramic (124,710 10-noded tetrahedral elements). The quasi-static coefficients of friction (µs) of the CoCr-TiAlV and Ceramic-TiAlV interfaces were calculated from uniaxial assembly (2000N) and dis-assembly experiments performed in a mechanical testing machine (Bionix, MTS). Interface displacements during taper assembly and disassembly were measured using digital image correlation (DIC; Dantec Dynamics). The assembly process was also simulated using the computational model with the friction coefficient set to µs and solved using the Siemens Nastran NX 11.0 Solver. The frictional conditions were then varied iteratively to find the value of µ providing the closest estimate to the experimental value of head displacement during assembly. To validate the FEA model, the relative motion between the head and the trunnion was measured during dynamic loading simulating stair-climbing. Each modular junction was assembled in a drop tower apparatus and then cyclically loaded from 230–4300N at 1 Hz for a total of 2,000 cycles. The applied load was oriented at 25° to the trunnion axis in the frontal plane and 10° in the sagittal plane. The displacement of the head relative to the trunnion during cyclic loading was measured by a three-camera digital image correlation (DIC) system. The same loading conditions were simulated using the FEA model using the optimal value of µ derived from the initial head assembly trials.INTRODUCTION
MATERIALS and METHODS
The ideal operative treatment of displaced sub capital femoral fractures in the elderly is controversial. Recently, randomised controlled trials have suggested a better outcome with the use of total hip arthroplasty (THA) to treat displaced intra capsular fractures of the femur for elderly patients in good health. More recently the concept of dual mobility cups is being promoted to avoid dislocations in this cohort of patients. However, overall there is limited evidence to support the choice between different types of arthroplasty. Dislocation remains a main concern with THA, especially when a posterior approach is used. We analysed the outcome of 115 primary THR (112 cements and 3 uncemented) THR using a posterior approach with soft tissue repair in active elderly patients presenting with displaced intra capsular femoral neck fractures. Size 28 mm head was used in 108 and a size 32 mm head in the rest. All surgery was performed by specialist hip surgeons. Satisfactory results were noted in terms of pain control, return to pre-morbid activity and radiological evidence of bone implant osteo-integration. The 30-day mortality was nil. There were two dislocations and only one needed revision surgery due to recurrent dislocation. In conclusion, with optimal patient selection, THA seems to provide a good functional outcome and pain relief in the management of displaced intracapsular femoral neck fractures. Excellent outcome can be achieved when done well using the standard cemented THR and with 28mm head. A good soft tissue repair and a specialist hip surgeon is preferable.
One of the major concerns of hinge knees have been reported in literature is mechanical failure. Failure in the form of component fracture (2–10%) and hinge dislocation/ failure are worrisome. In addition, higher risk of aseptic loosening with hinge knee prosthesis has been attributed to stress transfer at bone cement interface. Retrospective review of clinical and radiological results of 71 consecutive patients operated at single centre using Smiles hinge knee (Stanmore implants) between 2010 and 2014. Data was collected till the latest follow up. Mechanical failure due to any reason was considered as primary end point. Radiological evidence of aseptic loosening was considered to be one of the surrogate end points.Background
Methods
Stable fixation of cementless tibial trays remains a challenge due bone density variability within the proximal tibia and the spectrum of loads imposed by different activities. This study presents a novel approach to measuring the interface motion of cementless tibial components during functional loading and tests whether interface motion of cementless tibial trays varies around the implant periphery. We developed a method to measure relative displacement of a tibial tray relative to the underlying bone using 3D digital image correlation (DIC) and multi-camera stereo photogrammetry. A clinically successful design of cementless total knee prosthesis (Zimmer Inc, Warsaw, IN) was implanted in 6 fresh cadaveric knees. A black-on-white stochastic pattern was applied to the outer surface of the tibia and the cementless prosthesis. High resolution digital images were prepared of the interface region and divided into 25 × 25 pixel regions of interest (ROI). Stereo images of the same ROI were generated using two cameras angled at 60 degrees using image correlation techniques. All specimens were mounted in a custom-built functional activity simulator and loaded with the forces and moments recorded during three common functional activities (standing from a seated position, walking, and stair descent), as reported in the Orthoload database, scaled by 50% for application to cadaveric bone. Prior to functional testing, each implant-tibia construct was preconditioned with 500 cycles of flexion from 5–100 degrees under a vertical tibial load of 1050 N at a frequency of 0.2 Hz. During loading, image data was acquired simultaneously (±20 μs) from the entire circumference of the tibial interface forming 4 stereo images using 8 cameras spaced at 90 degree intervals (Allied Vision Technologies, Exton, PA) using custom image acquisition software (Mathworks, Natick, MA) (Figure 1). The multiple stereo images were registered using the surface topography of each specimen as measured by laser scanning (FARO Inc., Montreal) (Figure 2). During post-processing, the circumferential tray/tibia interface was divided into 10 zones for subsequent analysis (Figure 3). Interface displacements were measured on a point-to-point basis at approximately 700 sites on each specimen using commercial DIC software (Dantec Dynamics, Skovlunde, Denmark) (Figure 4).INTRODUCTION
METHODS
Cementless tibial trays commonly fail through failure of fixation due to excessive interface motion. However, the specific combination of axial and shear forces precipitating implant failure is unknown. This has led to generic loading profiles approximating walking to perform pre-clinical assessment of new designs, even though telemetric data demonstrates that much larger forces and moments are generated during other functional activities. This study was undertaken to test the hypotheses: (i) interface motion of cementless tibial trays varies as a function of specific activities, and (ii) the response of the cementless tibial interface to walking loading is not representative of other functional activities. Six fresh-frozen cadaveric tibias were tested using a custom designed functional activity simulator after implantation of a posterior stabilized total knee replacement (NexGen LPS, Zimmer, Warsaw IN). Activity scenarios were selected using force (Fx, Fy, Fz) and moment (Mx, My, Mz) data from patients with instrumented tibial trays (E-tibia) published by Bergmann et al. A pattern of black and white spray paint was applied to the surface of the specimen including the tibial tray and bone. Each specimen was preconditioned through application of a vertical load of 1050N for 500 cycles of flexion-extension from 5–100°. Following preconditioning, each tibia was loaded using e-tibia values of forces and moments for walking, stair-descent, and sit-to-stand activities. The differential motion of the tibial tray and the adjacent bony surface was monitored using digital image correlation (DIC) (resolution: 1–2 microns in plane; 3–4 microns out-of-plane). Four pairs of stereo-images of the tray and tibial bone were prepared at sites around the circumference of the construct in both the loaded and unloaded conditions: (i) before and after pre-conditioning and (ii) before and after the 6 functional loading profiles. The images were processed to provide circumferential measurements of interface motion during loading. Differences in micromotion and migration were evaluated statistically using step-wise multivariate regression.INTRODUCTION
MATERIALS and METHODS
Recent advances in materials and manufacturing processes for arthroplasty have allowed fabrication of intricate implant surfaces to facilitate bony attachment. However, refinement and evaluation of these new design strategies is hindered by the cost and complications of animal studies, particularly during early iterations in development process. To address this problem, we have constructed and validated an Cancellous cylindrical bone cores were harvested from bovine metatarsals and divided into five groups under different conditions. After incubation for 4 & 7 weeks, the viability of each bone sample was evaluated using Live-Dead assay and microscopic anatomy of cells were determined using histology stain H&E. Matrix deposits on the scaffolds were examined with scanning electron microscopy (SEM) while its chemical composition was measured using energy-dispersive x–ray spectroscopy (EDX).Background
Methods
As the population continues to grow and age, the incidence of revision total knee replacement (RTKR) is expected to rise significantly. Modularity within revision total knee systems is common, and recognition of modular junctions as an important source adverse local tissue reaction (ALTR) has not yet been fully described in the literature. In both hips and knees, ALTR may be caused by wear debris from articulating surfaces, stress shielding, and other classic areas of focus, but now attention is shifting towards the role of corrosion products from modular junctions. In severe cases, junctions can become welded together creating significant hurdles in revisions and potentially altered biomechanics in vivo. In view of these issues, the present study was undertaken: (i) to examine the level of damage observed in modular junctions of total knee prostheses obtained at revision, (ii) to correlate the severity of surface damage to the design and composition of the mating components, and (iii) to associate patient demographics and comorbidities with the spectrum of corrosion and fretting seen in retrieved implants. 117 TKR components from 76 patients were examined after retrieval from revision procedures performed at a single institution. Patient demographics and clinical data were compiled. The retrievals consisted of 57 femoral components and 60 tibial components from a diverse range of manufacturers. The implants were disassembled manually, or in a mechanical testing machine if cold welded, and separated into groups based on mating material type. Modular junctions were then examined using stereomicroscopy (Wild) at magnifications of X6 to X31. Upon inspection, damage on the male component was graded using modified Goldberg scales for corrosion and fretting (Table 1). Factors associated with trunnions having damage scores of 3 or higher were evaluated using standard statistical procedures to determine the susceptibility for corrosion of each junction type and location.Introduction
Methods
Corrosion products from modular taper junctions of hip prostheses have been implicated in adverse local tissue reactions after THR. Numerous factors have been proposed as the root causes of this phenomenon, including implant design and materials, manufacturing variables, intraoperative assembly, and patient lifestyle. As significant taper damage only occurs in a few percent of cases of THR, we have addressed this complication using a “forensic” examination of retrieval specimens to gain insight into the factors initiating the cascade leading to irreversible damage of the modular interface. In this study we report the categorization of over 380 retrievals into groups having shared damage patterns, metallic composition, and interface surface geometries to isolate the genesis of mechanically-assisted corrosion and its relation to intraoperative assembly, manufacturing, and postoperative loading. A total of 384 femoral components were examined after retrieval at revision THR. The implants were produced by a diverse range of manufacturers, 271 in CoCr, and 113 in TiAlV, with both smooth (253) and machined (131) tapers. Initially, the implants were sorted into groups based on composition and taper roughness. Each trunnion was then cleaned to remove organic deposits and examined by stereomicroscopy at X6-X31. After an initial pilot study, we developed a classification system consisting of 8 basic patterns of damage (Table 1). We then classified all 384 trunnions according to this 8-group system. The prevalence of each pattern was calculated on the basis of both composition and surface texture of the trunnion.Introduction
Methods
Distal femoral replacement is an operation long considered as salvage operation for neoplastic conditions. Outcomes of this procedure for difficult knee revisions with bone loss of distal femur have been sparsely reported. We present the early results of complex revision knee arthroplasty using distal femoral replacement implant, performed for severe osteolysis and bone loss. Retrospective review of clinic and radiological results of 25 consecutive patients operated at single centre between January 2010 and December 2014. All patients had single type of implant. All data was collected till the latest follow up. Re-revision for any reason was considered as primary end point. Mean age at surgery was 72.2 years (range 51 – 85 years). Average number of previous knee replacements was 2.28 (range 1 to 6). Most common indications were infection, aseptic loosening and peri-prosthetic fracture. Average follow up was 24.5 months (range: 3–63 months). 1 patient died 8 months post-op due to unrelated reasons. Re-revision rate was 2/25 (8%) during this period. One was re-revised for aseptic loosening and one was revised for peri-prosthetic fracture of femur. Two other peri-prosthetic fractures were managed by open reduction and internal fixation. All 3 peri-prosthetic fractures occurred with low energy trauma. It is noteworthy that there was no hinge or mechanical failures of the implant. Peri-prosthetic fracture in 12% of patients in this series is of concern. There are no similar studies to compare this data with. The length of the stem, type of fixation of the stem, weight of the distal femoral component of implant can be postulated as factors contributing to risk of peri-prosthetic fracture.
Primary total hip replacement (THR) in patients with abnormal/altered proximal femoral anatomy/narrow canals presents a technical challenge. There are only limited standard prosthetic stems available to deal with narrow canals or abnormal morphology. Many prefer to use expensive custom implants which often have a lag time to manufacture and do not always have long term published outcomes. We present results of the Asian C-stem (which is a standard implant available on the shelf) used in patients predominantly of Caucasian origin with abnormal proximal femoral anatomy. We retrospectively reviewed clinic-radiological results of 131 patients (131 stems) who underwent primary THR using Asian C-stem at Wrightington Hospital till their latest follow up. Revision for any reason was considered as primary end point. Mean age at surgery was 50.8 years (16 – 80). The 2 commonest indications were primary osteoarthritis (66 patients) and hip dysplasia (54 patients). Mean follow up was 43.5 months with a minimum follow up of 12 months and maximum follow up of 97 months. There were 2 recurrent dislocations and 1 hip subluxed twice. One dislocation needed revision surgery. 1 patient underwent acetabular revision for loosening. There was no stem failure, obvious loosening or loss of fixation in any patients in our series with regards to the Asian C-stem. There were no infections and intra-operative perforations or fractures. C-stem Asian is a reliable implant for patients undergoing THR with abnormal proximal femoral anatomy or narrow canals. Long term follow up is essential.
Restoration of knee function after total knee arthroplasty (TKA) often entails a balance between normal kinematics and normal knee stability, especially in performing demanding physical activities. The ultra-congruent (UC) knee design prioritizes stability over kinematics through close conformity between the femoral component and the tibial insert in extension. This configuration is intended to provide AP stability in the absence of the posterior cruciate ligament during activities that would otherwise cause anterior femoral subluxation. In this study we examine the kinematics of an ultra-congruent knee design in comparison with the intact knee and with conventional articulations used in PCL-retaining (CR) and PCL-substituting (PS) TKR designs. The 3D tibio-femoral kinematics of 6 fresh frozen cadaveric human knees were tested during loaded simulation of squatting in a computer-controlled knee testing rig. Muscle forces were simulated by loading rectus femoris and vastus intermedius (150N), vastus lateralis (100N), vastus medialis (75N), and the hamstring muscles (60N) (total: 385N). Testing was performed on the intact knee, and after implanting a standard design of total knee prosthesis with the posterior cruciate ligament intact (CR-TKA), resected (PCL-substituting insert; PS-TKA), and a UC insert (UC-TKA group). The 3D positions of the tibia and femur were tracked with a high resolution 12 camera motion analysis system (Motion Analysis Inc.) and used to position 3D CT reconstructions of each bone. The translation and rotation of the femur with respect to the tibia were calculated by projecting the femoral transcondylar axis onto a plane normal to the longitudinal anatomical axis of the tibia coincident with the transverse axis of the tibial plateau.Introduction
Materials and Methods
Angular mismatch of the modular junction between the head and the trunion has been recognized as a contributing factor to fretting and corrosion of hip prostheses. Excessive angular-mismatch can lead to relative motion at the taper interface, and tribo-corrosion of the head-neck junction secondary to disruption of the passive oxide layer. Although manufacturing standards have been adopted to define acceptable tolerances for taper angles of mating components, recent investigations of failed components have suggested that stricter tolerances or changes in taper design may be necessary to avoid clinical failures secondary to excessive taper wear and corrosion. In this study we examine the effect of angular-mismatch on relative motion between the taper and bore subjected to normal gait load using finite element methods. Computer simulations were executed using a verified finite element model (FEM), the results from which were determined to be consistent with literature. A stable, converging hexahedral mesh was defined for the trunnion (33648 elements) and a tetrahedral mesh for the femoral head (51182 elements). A friction-based sliding contact was defined at the taper-bore interface. A gait load of 1638N (2.34 × BW, BW = 700N) was applied at an angle of 30° to the trunnion axis (Figure 1) on an assembled FEM. A linear static solution was set up using Siemens NX-Nastran solver. Angular-mismatch was simulated by incrementing the conical half-angle of the bore to examine these cases: 0°, 0.005°, 0.010°, 0.015°, 0.030°, 0.050°, 0.075°, 0.100°, 0.200°and 0.300°.Introduction:
Methods:
The sealing function of the acetabular labrum is central to the stability of the hip and the health of the joint. Disruption of the labrum has been shown to reduce intra-articular pressure and increase the rate of cartilage consolidation during static loading. Functional activities require movement of the hip through wide ranges of joint motion which disrupt joint congruency, and thus may alter the seal. This study was performed to test the hypothesis that the sealing function of the labrum varies with the position of the hip during functional activities. Six fresh cadaveric hip joint specimens were obtained from donors of average age 45.5 ± 16.1 years (range 25–63 years). Each specimen was dissected free of soft tissue, leaving the capsule and labrum intact, potted in mounting fixtures, and placed in a loading apparatus. Catheters were inserted into the central and peripheral compartments of each hip to allow infusion of fluid and monitoring of compartment pressures via miniature transducers (OMEGA Engineering, Inc). After application of a joint load of 0.50 BW, fluid was introduced into the central compartment at a constant rate until transport was indicated by a rise in pressure within the peripheral compartment. These measurements were performed with each hip placed in 10 functional positions ranging from −5 to 105 degrees of flexion, −5 to 13 degrees of abduction, and −25 to 35 degrees of external rotation simulating the sequential stages of gait, stooping, and pivoting. Motion analysis was performed via reflective marker arrays attached to the femur and pelvis to allow computer visualization of the position of the pelvis and femur using CT reconstructions. In each hip position, we measured the peak pressure (kPA) developed within the central compartment prior to fluid transfer to the peripheral compartment.Introduction:
Methods:
Experimental disruption of the labrum has been shown to compromise its sealing function and alter cartilage lubrication. However, it is not known whether pathological changes to the labrum secondary to femoro-acetabular impingement (FAI) have a similar impact on labral function. This study was performed to determine the effect of natural labral damage secondary to abnormal femoral morphology on the labral seal. Ten intact hip specimens were obtained from male donors (47.8 ± 1.5 yrs) for use in this study. CT reconstructions demonstrated that 6 specimens were of normal morphology, while 4 displayed morphology typical of cam-FAI. Specimens were dissected free of the overlying soft tissue, leaving the capsule and labrum intact. Each specimen was potted and placed in a loading apparatus (0.5 BW). Pressures developed within the central and peripheral compartments were monitored with miniature pressure transducers. The sealing capacity of the labrum was measured by introducing fluid into the central compartment at a constant rate until transport was detected from the central to the peripheral compartment. These measurements were performed in 10 functional positions simulating sequential stages of gait, stooping, and pivoting. During testing, the 3D motion of the femoral head in the acetabulum was measured with motion analysis combined with computer visualization. Peak pressures were compared between specimens with and without labral damage for each of the three activities (p < 0.05).Objectives:
Methods:
It has been speculated that impact deformation of thin 1-piece cups used for modern metal-on-metal hip replacement may contribute to early failure. The purpose of this study was to reproduce typical impact deformation and quantify the effect of this on the frictional torque generated at the hip. We tested nine hip couples of three designs (the ASR, BHR and Durom) and three sizes (42mm, 46mm and 50mm). A custom compression device was designed to replicate the in vivo forces and impact deformation of 1-piece metal cups reported in the literature. Each cup was mounted in the device, which itself was mounted on a mechanical testing machine. The cups were compressed with incremental loads up to a maximum of 2000N. At each increment we measured cup deformation, and then the head component was seated into the cup. The hip was lubricated and the head component rotated 60 degrees axially within the cup and the axial torque was measured.Introduction
Methods
Knee prostheses retrieved at revision often show patterns and severity of damage neither seen nor predicted from standard wear simulator testing. We hypothesized that this is because these implants are exposed to combinations of loads and motions that are more damaging than the simple loading profiles utilized in laboratory testing. We examined the magnitude, direction, and combination of forces and moments acting on the knee during various activities in order to guide the future development and testing of high-performance knee replacements. In vivo data from five patients with instrumented tibial implants were obtained from an open database (www.orthoload.com). We determined the direction and magnitude of forces and moments that the knee experiences during the following common physiologic activities: stair descent, stair ascent, deep knee bend, one leg stance, and walking. In order to capture the loading pattern, we investigated the three component forces and moments acting on the knee at several high demand points for each of these activities. The e-tibia data were compared to the loading profiles used in conventional laboratory testing (ISO 14243-1).Introduction
Methods
