Constrained implants with intra-medullary fixation are expedient for complex TKA. Constraint is associated with loosening, but can correction of deformity mitigate risk of loosening?. Primary TKA's with a non-linked constrained prosthesis from 2010-2018 were identified. Indications were ligamentous instability or intra-medullary fixation to bypass stress risers. All included fully cemented 30mm stem extensions on tibia and femur. If soft tissue stability was achieved, a posterior stabilized (PS) tibial insert was selected. Pre and post TKA full length radiographs showed. i. hip-knee-ankle angles (HKAA). ii. Kennedy Zone (KZ) where hip to ankle vector crosses knee joint. 77 TKA's in 68 patients, average age 69.3 years (41-89.5) with OA (65%) post-trauma (24.5%) and inflammatory arthropathy (10.5%). Pre-op radiographs (62 knees) showed varus in 37.0%. (HKAA: 4. o. -29. o. ), valgus in 59.6% (HKAA range 8. o. -41. o. ) and 2 knees in neutral. 13 cases deceased within 2 years were excluded. Six with 2 year follow up pending have not been revised. Mean follow-up is 6.1 yrs (2.4-11.9yrs). Long post-op radiographs showed 34 (57.6%) in central KZ (HKKA 180. o. +/- 2. o. ). . Thirteen (22.0%) were in mechanical varus (HKAA 3. o. -15. o. ) and 12 (20.3%) in mechanical valgus: HKAA (171. o. -178. o. ). Three failed with infection; 2 after ORIF and one with BMI>50. The greatest post op varus suffered peri-prosthetic fracture. There was no aseptic loosening or instability. Only full-length radiographs accurately measure alignment and very few similar studies exist. No cases failed by loosening or instability, but PPF followed persistent malalignment. Infection complicated prior ORIF and elevated BMI. This does not endorse indiscriminate use of mechanically constrained knee prostheses. Lower demand patients with complex arthropathy, especially severe deformity, benefit from fully cemented, non-linked constrained prostheses, with intra-medullary fixation. Hinges are not necessarily indicated, and rotational constraint does not lead to loosening

Introduction. The interaction between the mobile components of total elbow replacements (TER) provides additional constraint to the elbow motion. Semi-constrained TER depend on a mechanical linkage to avoid dislocation and have greater constraint than unconstrained TER that rely primarily in soft tissue for joint stability. Greater constraint increases the load transfer to the implant interfaces and the stresses in the polyethylene components. Both of these phenomena are detrimental to the longevity of TER, as they may result in implant loosening and increased damage to the polyethylene components, respectively[1]. The objective of this work was to compare the constraint profile in varus-valgus and internal-external rotation and the polyethylene stresses under loads from a common daily activity between two semi-constrained TER, Coonrad/Morrey (Zimmer-Biomet) and Discovery® (DJO), and an unconstrained TER, TEMA (LimaCorporate). Methods. We developed finite element (FE) models of the three TER mechanisms. To reduce computational cost, we did not include the humeral and ulnar stems. Materials were linear-elastic for the metallic components (E. Ti6Al4V. =114.3 GPa, E. CoCr. =210 GPa, v=0.33) and linear elastic-plastic for the polyethylene components (E=618 MPa, v=0.46; S. Y. =22 MPa; S. U. =230.6 MPa; ε. U. =1.5 mm/mm). The models were meshed with linear tetrahedral elements of sizes 0.4–0.6 mm. We assumed a friction coefficient of 0.02 between metal and polyethylene. In all simulations, the ulnar component was fixed and the humeral component loaded. We computed the constraint profiles in full extension by simulating each mechanism from 8° varus to 8° valgus and from 8° internal to 8° external rotation. All other degrees-of-freedom except for flexion extension were unconstrained. Then, we identified the instant during feeding that generated the highest moments at the elbow[2], and we applied the joint forces and moments to each TER to evaluate the stresses in the polyethylene. To validate the FE results, we experimentally evaluated the constraint of the design with highest polyethylene stresses in pure internal-external rotation and compared the results against those from a FE model that reproduced the experimental setup (Fig.1-a). Results. For each design, the constraint profiles in varus-valgus (Fig.2-a) were similar to internal-external rotation (Fig.2-b). All designs showed a lax zone in which the mechanisms rotated freely and an engagement zone in which the mobile components contacted, resulting in load transfer. The laxity of the Coonrad/Morrey and the Discovery® was similar and lower than that of the TEMA. After engagement, the stiffness of the TEMA was less than that of the Discovery® and the Coonrad/Morrey. The TEMA showed the lowest polyethylene stresses of all three designs under demanding loads during feeding. Only Discovery® and Coonrad/Morrey had zones reaching permanent deformation (Fig.3). For the Coonrad/Morrey, with the highest polyethylene stresses, the experimental and computational constraint profiles were similar (Fig.1-b). Discussion. The TEMA unconstrained design transferred less moment than semi-constrained designs, reducing the burden on the implant interfaces. Moreover, the TEMA design had lower stresses in the polyethylene components due to the combination of less constraint and a lack of sharp edges on the articular surfaces. For any figures or tables, please contact the authors directly

Introduction. Studies have shown that increased implant conformity in total knee arthroplasty (TKA) has been linked to increased constraint and thus rotational torque at the bone/implant interface. Anterior stabilized (AS) tibial inserts were designed to compensate for excessive AP motion in less-conforming cruciate-retaining (CR) tibial inserts. However, increased constraint may affect implant loading. Therefore, the purpose of this study is to model rotational prosthesis constraint based on implant-specific data and to compare rotational torque and 3D contact forces in implants with CR-lipped and AS tibial inserts during normal gait. Methods. A previously reported knee joint contact model was updated to include rotational torque due to prosthesis constraint (ASTM F1223(14)). Piecewise multiple linear regression with manually selected cutoff points was used to determine estimates of AP force, ML force, and rotation torque as functions of AP displacement, ML displacement, knee external rotation, respectively, and knee flexion angle from standard data. These functions were used to estimate total moment contribution of the prosthesis from measured knee displacement/rotation angles. Estimates were incorporated into the contact model equilibrium equations as needed by the model. As the model parametrically varies muscle activation coefficients to solve for the range of physiologically possible forces at each time point, the reported force/torque values are the mean across all solutions at each time point. Rotational torque and three dimensional contact forces were calculated for 14 informed-consented subjects, five with AS tibial inserts (1/4 m/f, 67±10 years, 29.2±4.4 BMI, 1/4 right/left) and nine with CR-lipped TKRs (2/7 m/f, 64±6 years, 30.6±5.8 BMI, 4/5 right/left). Rotational torque waveforms were compared using statistical nonparametric mapping; 3D contact forces were compared at mean timing of the flexion/extension moment peaks using independent samples t-tests. Results. Waveform analysis of rotational torque found no significant differences between implant types. CR- lipped inserts showed an initial peak internal rotation torque during weight acceptance and continued with a pattern of internal rotation throughout stance. Peak torque for AS inserts also occurred during weight acceptance, but it varied between internal/external rotation torque. Additionally, after weight acceptance, AS subjects showed a pattern of external rotation torque. Mean axial force, medial-lateral shear force, and anterior-posterior shear force waveforms were similarly shaped between implant groups. Flexion and extension moment peaks occurred at 23% and 74% stance on average. There were no significant differences in three-dimensional knee joint contact forces between groups at either time point. Discussion. There were different patterns of rotational torque between groups. Implants with lipped CR inserts tended to undergo internal rotation torques that peaked during weight acceptance. Torque seen in implants with AS inserts was also largest during weight acceptance, but greatly varied between internal and external rotation, before settling in a pattern of external rotation for the remainder of stance. This may be due to constraints added by AS insert geometry. In conclusion, a model of rotational torque due to implant constraints has been developed; increased implant constraint increased the external rotation torque experienced by the implant and may also affect shear forces at the implant surface. For any figures or tables, please contact authors directly

Background. The constraint of total knee replacement (TKR) implants is not simply defined and many of the factors that influence it are not well understood. Variability in the constraint of different TKR implants designed for the same indication (e.g. cruciate-retaining, or posterior-stabilized) have been previously demonstrated, but these differences among implants have yet to be simply quantified. Furthermore, the relative importance of several variables on the implant constraint remains unknown. The purpose of this study was to quantify the differences in constraint that exist between different implant designs, and to examine the effects of axial load and flexion angle on the constraint of current cruciate-retaining (CR) TKR components. Methods. Four contemporary CR TKR designs underwent laxity testing using a multi-axis mechanical test machine. Implants were tested at flexion angles of 0°, 20°, 90° and maximum flexion and axial loads of 712 N (1 BW) and 1424 N (2 BW). Friction-free motion in all secondary degrees of freedom was allowed. Force-displacement curves were generated for each testing condition in both anterior-posterior (AP) and rotational tests. AP constraint (N/mm) and rotational constraint (Nm/deg) were then calculated. Results. Differences in the AP and rotational constraint of the various implants were identified. The rotating platform implant was the most AP constrained and least rotationally constrained of the implants studied. Among the fixed bearing implants, NexGen CR had less AP and rotational constraint than the Genesis II and PFC Sigma. Doubling the applied axial load during the laxity tests resulted in a significant increase in both AP (p<0.0001) and rotational (p<0.0001) constraint. AP and rotational constraint decreased with increasing flexion angles. Conclusion. The constraints of four contemporary CR TKR designs were quantitatively compared and ranked according to their calculated constraints. Differences in the constraint of these designs were identified. This quantitative analysis is an important step towards the creation of a clinically meaningful constraint index that would aid surgeons in choosing the optimal implants for their TKR patients. Additionally, the analysis of the effects of axial load and flexion angle on constraint has implications which may influence how in vitro testing of implants is conducted as well as clinical implications in terms of how the constraint envelope of a given implant may influence the feel and function that a TKR patient experiences

Introduction. Pre-clinical assessment of total knee replacements (TKR) can provide useful information about the constraint provided by an implant, and therefore help the surgeon decide the most appropriate configurations. For example, increasing the posterior tibial slope is believed to delay impingement in deep flexion and thus increase the maximal flexion angle of the knee, however it is unclear what effect this has on anterior-posterior (AP) constraint. The current ASTM standard (F1223) for determining constraint gives little guidance on important factors such as medial- lateral (M:L) loading distribution, flexion angle or coupled secondary motions. Therefore, the aim of the study was to assess the sensitivity of the ASTM standard to these variations, and investigate how increasing the posterior tibial slope affects TKR constraint. Methods. Using a six degree of freedom testing rig, a cruciate-retaining TKR (Legion; Smith & Nephew) was tested for AP translational constraint. In both anterior and posterior directions, the tibial component was displaced until a ‘dislocation limit’ was reached (fig. 1), the point at which the force-displacement graph started to plateau (fig. 2). Compressive joint loads from 710 to 2000 N, and a range of medial-lateral (M:L) load distributions, from 70:30% to 30:70% M:L, were applied at different flexion angles with secondary motions unconstrained. The posterior slope of the tibial component was varied at 0°, 3°, 6° and 9°. Results. AP translation was significantly larger at 60° and 90° flexion (22 ± 1 mm and 24 ± 1 mm respectively) than at 0° (14 ± 1 mm), whilst increasing the compressive joint load increased the force required to translate the tibia to limits of AP constraint at all flexion angles tested. When the M:L load distribution was shifted medially, a coupled internal rotation was observed with anterior translation and external rotation with posterior translation; this was reversed with a lateral shift in load distribution. It was also found that increasing the posterior slope of the tibial tray moved the neutral position of the tibia relative to the femur more anteriorly at all flexion angles tested. The constraint under anterior drawer was then reduced with increasing slope, which meant that the tray dislocated at lower drawer force and translations. Conclusions. When intraoperative tibial bone cuts are made, surgeons should be aware that by increasing posterior slope angles the TKR may offer less anterior constraint under body-weight loads, therefore relying more heavily on surrounding soft-tissue and muscle action to prevent dislocation. The ASTM test protocol could be refined to stipulate the variation of the M:L loading distribution. It has been shown to vary between patients and activities, and the AP constraint and associated secondary motions in this study were very sensitive to this distribution. The secondary motions observed should be measured and recorded to provide more information about the device's stability characteristics. The tests could also be extended to include a higher axial load such as 2000 N, approximately three times body weight, in order to investigate coupled rotations and M:L distribution effects whilst under normal walking gait loads

Introduction. Total knee arthroplasty (TKA) prostheses are semi-constrained artificial joints. Femorotibial constraint is a key property of a TKA prosthesis and should be designed to match the device's intended function. Cruciate Retaining (CR) prostheses are usually used for patients with a functioning posterior cruciate ligament (PCL). For patients without a fully functioning PCL, CR-Constrained (CRC) prostheses may be used. A CRC tibial insert usually has a more conforming sagittal profile especially in the anterior aspect to provide increased constraint to prevent paradoxical femoral translation during knee flexion. A quantitative understanding of the constraint behavior of a prosthesis design is critical to ensure its functional outcome. Using a validated computer simulation, this study evaluated the anterior-posterior (AP) constraint of two types of tibial inserts (CR and CRC) from a same TKA product family. Methods. Both the CR and CRC prostheses are from the same TKA product family (Optetrak Logic, Exactech, USA). Three sizes (sizes 1, 3, and 5) from each product line were included in this study. Computer simulations using finite element analysis (FEA) were performed at 0° flexion per ASTM F1223 standard [1] (Figure 1). The simulation has been validated with physical testing (more details submitted in a separate abstract to ISTA 2013). Briefly, FEA models were created with all materials considered linear elastic. The tibial baseplate was distally fixed and a constant compressive force (710 N) was applied to the femoral component. Nonlinear Surface-Surface-Contact was established at the articulating surfaces. A coefficient of friction of 0.1 was assumed for all articulations [2]. The femoral component was driven under a displacement-controlled scheme to slide along AP direction on the tibial insert. Constraint force occurring at the articulation was derived from the reaction force at the distal fixation. A nonlinear FEA solver was used to solve the simulations. Results. The force-displacement curves predicted by the simulation exhibited the hysteresis loop appearance for both CR and CRC inserts (Figure 2). The anterior aspect of the CRC curves showed a steeper raise than the CR curves, and the trend was consistent across sizes. Taking the slope from 0 to 5 mm range, the anterior constraint of the CRC insert was significantly greater than the CR insert, while the posterior constraint of the CRC insert was also slightly greater (Figure 3). Discussion/Conclusion. The increased AP constraint of the CRC insert revealed in the study is consistent with the design geometry and functional intent of the device. With a much increased anterior lip, the CRC insert is expected to provide substantially greater anterior constraint than the CR insert to prevent paradoxical femoral translation for patients without a fully functioning PCL. The CRC insert is also expected to provide slightly increased posterior constraint due to its gently elevated posterior lip. This study quantitatively demonstrated the effect of design geometry on the outcome constraint function of different TKA prostheses

Introduction. Total knee arthroplasty (TKA) prostheses are semi-constrained artificial joints. A well-functioning TKA prosthesis should be designed with a good balance between stability and mobility, meaning the femorotibial constraint of the artificial joint should be appropriate for the device's function. To assess the constraint behavior of a TKA prosthesis, physical testing is typically required, and an industrial testing standard has been developed for this purpose [1]. Computer simulation has become increasingly useful in many industries, including medical device research and development where finite element analysis (FEA) has been extensively used in stress analysis and structural evaluation. This study presents an FEA-based simulation to evaluate the femorotibial constraint behavior of TKA prosthesis, and demonstrated the effectiveness of the method by validating through physical testing. Methods. A Cruciate Retaining (CR) TKA prosthesis design (Optetrak Logic CR, Exactech, USA) was used in this study. CAD models of the implants assembled at 0° of flexion were used for the simulation. Finite element models were generated using with all materials assumed linear elastic. Boundary conditions were set up according to the ASTM F1223 standard (Figure 1). The tibial baseplate was fixed distally. A constant compressive force (710 N) was applied on the femoral component. Nonlinear Surface-Surface-Contact was defined at the femorotibial articulating surfaces. Coefficient of friction was determined from physical test. The femoral component was driven under a displacement-controlled scheme to slide along the anterior-posterior (AP) direction on the tibial insert. At each time step, constraint force occurring at the articulating surface was derived from the reaction force at the distal fixation of the tibial baseplate. A nonlinear FEA solver (NX Nastran SOL601, Siemens, USA) was used to solve the simulation. In addition, five samples of the prostheses were physically tested, and the results were compared with the simulation. Results. The simulation successfully captured the movement of contact location and pressure along the movement of the femoral component (Figure 2). The force-displacement curve predicted by the simulation exhibited a very close hysteresis loop profile as the results of physical testing (Figure 3). Using the curve slope from 0 to 5 mm to characterize the linear constraint, the simulation predicted 45.7 N/mm anteriorly and 36.4 N/mm posteriorly, which are less than 10% different from the physical testing results (46.4 N/mm anteriorly and 39.6 N/mm posteriorly). Discussion/Conclusion. This study demonstrated that the simulation was able to closely predict the femorotibial constraint behavior of the TKA prosthesis under ASTM F1223 testing. The simulation results resembled the physical testing results not only in the general curve profile but also in the magnitude of slope values. The increased difference at the far anterior region could be related to the fact that no material nonlinearity was currently considered, which could be improved in future studies. A validated simulation method could be very useful in TKA prosthesis design. Since no physical prototypes are required, design evaluation and optimization can be achieved in a much easier and faster manner

Purpose. Although classic teaching holds that the least amount of constraint should be implanted, there is very little in the literature to substantiate this. This study attempts to quantify the influence of constraint and various indications upon functional outcome following aseptic first time revision knee arthroplasty. The null hypothesis was that the level of constraint and indication for surgery would not influence the functional outcome following revision knee replacement. Methods. A single centre prospective study was performed to examine the outcome for 175 consecutive total revision knee replacements performed between 2003 and 2008 with a minimum follow-up of two years. Patient reported outcome data was used to determine the influence of final level of component constraint and its relationship with primary indication for surgery. Results. All patients were found to have a significant improvement for WOMAC pain, function and stiffness score (p< 0.001) and physical functioning, role physical, bodily pain and social functioning components of SF-36 score (p< 0.05). 69% were satisfied with the overall procedure. WOMAC function, pain and stiffness score was significantly worse for patients revised for instability (27%) compared to that for aseptic loosening (46%). A significantly higher proportion of patients were satisfied with the procedure (p< 0.001), had a better quality of life (p=0.004) and would have the surgery (p=0.005) again in the aseptic loosening group as compared to the instability group. Revision to a higher level of constraint did not improve knee function irrespective of the primary indication for surgery. Conclusion. Revision for an instability pattern irrespective of choice of new device was met with significantly poorer functional outcome

The goals of total knee arthroplasty (TKA) are to relieve pain, restore function, and provide a stable joint. In regard to types of implants, the workhorses are posterior cruciate retaining (CR), posterior stabilised (PS), and posterior stabilised constrained (PSC) designs. However, the continuum of constraint now ranges from standard cruciate retaining (CR-S) to CR lipped (CR-L), to anterior stabilised (CR-AS), to posterior stabilised, to a PS “plus” that fits with a PS femoral component but provides a small degree of varus-valgus constraint, to a PSC or constrained condylar type of device, to a rotating hinge. As the degree of deformity, bone loss, contracture, ligamentous instability and osteopenia increases, so does the demand for prosthetic constraint. When deformity is minimal and the posterior cruciate ligament (PCL) is intact and functional, a CR-S device is appropriate. For moderate deformity with deficiency or compromise of the PCL, a CR-AS or posterior stabilised device is warranted. In severe cases, with attenuation or absence of either of the collateral ligaments, a constrained condylar device, with options of stems, wedges and augments, is advisable. In salvage situations, when both collaterals are compromised, a rotating hinge should be utilised. Prerequisites for use of a CR-S device are an intact PCL, balanced medial and lateral collateral ligaments, and equal flexion and extension gaps. With a CR-L bearing, a slight posterior lip is incorporated into the sagittal profile of the component to provide a small amount of extra stability in the articulation. It is important for the surgeon to be aware of the design features of the implant system he or she is using. For example, in a system where the CR-S bearing has 3 degrees of posterior slope and the CR-L bearing has no slope, the thickness of a CR-L bearing posteriorly is approximately 2mm greater than the CR-S. A CR-L bearing is indicated for to provide stability where the flexion gap is just slightly looser than the extension gap and the PCL is intact. If the patient's knee is somewhat lax in flexion and stable in extension, a CR-L bearing may help to stabilise both the flexion and extension gaps yet still allow the knee to obtain full extension, whereas if a CR-S bearing in the next thicker size is used to stabilise the flexion gap, a flexion contracture may result. CR-AS bearings are required less frequently. They are indicated when the flexion and extension gaps are balanced, but the PCL is deficient, and the surgeon does not want to change to a PS design, which requires additional bony resection of intercondylar notch. The PCL is one of the strongest ligaments in the knee, and affords inherent stability to the TKA. In flexion, the PCL not only affords AP stability, but also imparts flexion gap stability, acting as a lateral stabiliser of the medial compartment and a medial stabiliser of the lateral compartment. The PCL has a crucial role with respect to femoral rollback, which imparts added efficiency to the extensor mechanism. PCL retention is a more biologically preserving operative intervention than PS-TKA

Introduction. Revision for instability has supplanted revision for aseptic loosening and revision for osteolysis since the advent of improved polyethylene inserts with changes in both sterilization techniques and cross-linking. Having the ability to judiciously choose a higher level of constraint may be beneficial in complex primary total knee arthroplasty (TKA) scenarios which can not be balanced through traditional surgical methods. The purpose of this work was to investigate short term outcomes and survivorship in cases where a greater stabilizing insert was used with a posterior stabalizing (PS) femur to address instability in flexion or extension. Methods. Two high volume TKA centers retrospectively reviewed cases in which a greater stabilizer insert was used with a primary PS knee system. The studied insert had +/− 2 degrees of varus-valgus coronal restraint as opposed the standard with no coronal constraint. The study inserts had 7 degrees of transverse plane rotational freedom. The inserts were used when extension balance was not achieved despite the usual soft tissue releases and a thicker insert resulted in a flexion contracture statically during the procedure. This situation typically occurred in the following patient groups: valgus knees with medial collateral (MCL) stretching, iatrogenic MCL injury, varus knees with lateral ligament complex stretching, the “double-varus” knee, and patients with a previous high tibial osteotomy. Intra-operatively patients were taken through a range of motion and trial implants were then placed. A cruciate retaining trial insert was then used to assess stability so that a true assessment could be made of ligament balance. Bone cuts were checked before ligament release. The usual releases were then performed to achieve balance including subperiosteal releases medially and laterally and pie-crusting when indicated. Repeat trial reductions were then performed once the final implants were cemented in place again using the cruciate retaining insert. If the soft tissue releases did not achieve balance and a thicker insert resulted in a flexion contracture then the greater stabilizer insert was selected over the PS insert. Knee Society Score and plain radiographs were collected at pre-op, 2 year and 5 year follow-up. Results. One hundred seventy two cases with 2 year minimum follow-up and 41 cases with 5 year minimum follow up were assessed. All patients had good to excellent Knee Society Scores with good range of motion and pain relief. There were no aseptic revisions of the TKA's over this period. Specifically, there were no revisions for loosening, osteolysis, instability, or post breakage. Conclusions. A more stabilized tibial post insert which provides valgus-varus constraint but permits rotational freedom may provide needed stability in select primary situations without predisposing to early post failure or implant loosening or lysis

INTRODUCTION. The specific factors affecting wear of the ultrahigh molecular weight polyethylene (UHMWPE) tibial component of total knee replacements (TKR) are poorly understood. One recent study demonstrated that lower conforming inserts produced less wear in knee simulators. The purpose of this study is to investigate the effect of insert conformity and design on articular surface wear of postmortem retrieved UHMWPE tibial inserts. METHODS. Nineteen NexGen cruciate-retaining (NexGen CR) and twenty-five NexGen posterior-stabilized (NexGen PS) (Zimmer) UHWMPE tibial inserts were retrieved at postmortem from fifteen and eighteen patients respectively. Articular surfaces were scanned at 100×100μm using a coordinate measuring machine (SmartScope, OGP Inc.). Autonomous mathematical reconstruction of the original surface was used to calculate volume loss and linear penetration maps of the medial and lateral plateaus. Wear rates for the medial, lateral and total articular surface were calculated as the slope of the linear regression line of volume loss against implantation time. Volume loss due to creep was estimated as the regression intercept. Student t-tests were used to check for significant. RESULTS. The NexGen CR and NexGen PS patient groups were approximately the same age at time of implantation (mean±SD: 72.1±9.9 and 68.7±8.8 years respectively, p=0.260) and implantation times were not significantly different (8.7±3.1 and 9.1±3.7 years, p=0.670). Both groups showed high variability in wear scars. No significant difference in wear rates on the total surface (mean±SE: 11.89±5.01 mm. 3. /year vs. 11.09±4.18 mm. 3. /year, p=0.905). However, NexGen CR components showed significantly higher volume loss due to creep than NexGen PS components (70.22±47.07 mm. 3. vs. 31.30±41.15 mm. 3. , p=0.007). These results were reflected on the medial and lateral sides, with no significant differences in wear rates on the medial side (p=0.856) or lateral side (p=0.633) and higher volume losses due to creep associated with the NexGen CR components. While NexGen CR and NexGen PS showed a near equal mean percentage of volume loss on the medial side (CR: 52.4±11.7%, PS: 52.5±11.6%), a paired t-test showed that NexGen PS components showed a higher volume loss on the medial side (p=0.056), NexGen CR components did not (p=0.404). DISCUSSION. The combination of higher conformity and more kinematic constraint in NexGen CR components may create larger contact areas with higher stresses, leading to higher volume loss due to creep observed in this study. However, these factors did not produce increased wear rates in the population. Constrained components may maintain more loading on medial side and limit sliding distance on lateral side, causing more wear medially. Total wear rates were very similar and resembled the previously reported rate of 12.9 ± 5.97 mm. 3. /year for retrieved Miller-Galante II (Zimmer) components, which features a near flat articulating surface. These findings indicate that materials factors may be most important in producing wear and that higher conformity alone does not decrease wear. For any figures or tables, please contact authors directly

Massive irreparable rotator cuff tears often lead to superior migration of the humeral head, which can markedly impair glenohumeral kinematics and function. Although treatments currently exist for treating such pathology, no clear choice exists for the middle-aged patient demographic. Therefore, a metallic subacromial implant was developed for the purpose of restoring normal glenohumeral kinematics and function. The objective of this study was to determine this implant's ability in restoring normal humeral head position. It was hypothesized that (1) the implant would restore near normal humeral head position and (2) the implant shape could be optimized to improve restoration of the normal humeral head position. A titanium implant was designed and 3D printed. It consisted of four design variables that varied in both implant thickness (5mm and 8mm) and curvature of the humeral articulating surface (high constraint and low constraint. To assess these different designs, these implants were sequentially assessed in a cadaver-based biomechanical testing protocol. Eight cadaver specimens (64 ± 13 years old) were loaded at 0, 30, and 60 degrees of glenohumeral abduction using a previously developed shoulder simulator. An 80N load was equally distributed across all three deltoid heads while a 10N load was applied to each rotator cuff muscle. Testing states included a fully intact rotator cuff state, a posterosuperior massive rotator cuff tear state (cuff deficient state), and the four implant designs. An optical tracking system (Northern Digital, Ontario, Canada) was used to record the translation of the humeral head relative to the glenoid in both superior-inferior and anterior-posterior directions. Superior-Inferior Translation. The creation of a posterosuperior massive rotator cuff tear resulted in significant superior translation of the humeral head relative to the intact cuff state (P=0.016). No significant differences were observed between each implant design and the intact cuff state as all implants decreased the superior migration of the humeral head that was observed in the cuff deficient state. On average, the 5mm low and high constraint implant models were most effective at restoring normal humeral head position to that of the intact cuff state (-1.3 ± 2.0mm, P=0.223; and −1.5 ± 2.3mm, P=0.928 respectively). Anterior-Posterior Translation. No significant differences were observed across all test states for anterior-posterior translation of the humeral head. The cuff deficient on average resulted in posterior translation of the humeral head, however, this was not statistically significant (P=0.128). Both low and high constraint implant designs were found to be most effective at restoring humeral head position to that of the intact cuff state, on average resulting in a small anterior offset (5mm high constraint: 2.0 ± 4.7mm, P=1.000; 8mm high constraint: 1.6 ± 4.9mm, P=1.000). The 5mm high constraint implant was most effective in restoring normal humeral head position in both the superior-inferior and anterior-posterior directions. The results from this study suggest the implant may be an effective treatment for restoring normal glenohumeral kinematics and function in patients with massive irreparable rotator cuff tears. Future studies are needed to address the mechanical efficiency related to arm abduction which is a significant issue related to patient outcomes

INTRODUCTION. In patients presenting with significant ligamentous instability/insufficiency and/or significant varus/valgus deformity of the knee, reproduction of knee alignment and soft tissue stability continues to be a difficult task to achieve. These complex primary total knee arthroplasty (TKA) candidates generally require TKA systems incorporating increasing levels of constraint due to the soft-tissue and/or bone deficiencies. In addition, achievement of “normal” gap symmetry through physiologic kinematics is challenging due to the complexity of the overall correction. Advancements in TKA design have not fully addressed the negative consequences of the increased forces between the degree of component constraint, the femoral box, and the tibial post. The purpose of this early feasibility study was to introduce the design characteristics of a primary TKA system that incorporates progressive constraint kinematics using a low profile trapezoidal femoral box, and to assess the short-term clinical and radiographic results of this patient cohort. METHODS. We retrospectively evaluated 22 consecutive, non-selected, complex primary TKA patients with a minimum of 3-years follow-up and varus deformity of > 20 degrees or valgus deformity of >15 degrees. The Progressive Constraint Kinematics® Knee System (PCK, MAXX Orthopedics, Norristown, PA) was used and provides a variable constraint profile, from high constraint in extension to less constraint in flexion through a novel trapezoidal femoral box. We evaluated patient demographics, pre- and post-operative serial radiography, range of motion (ROM), and total Knee Society Score (KSS – total score). General descriptive statistics and paired t-Test to assess the difference between means at p <0.05 level of significance. RESULTS. The average time to most recent follow-up was 40.5 ±3.5 months (range: 36.0 to 44.0 months). The PCK knee system had 100% survival rate at the most recent follow-up, with no reports of adverse events, subsequent corrective surgery, or revision. The average total KSS improved from 72.7 ±3.2 (range: 68 to 81) pre-operatively to 92.3 ±2.1 (range: 88 to 96) post-operatively (p < 0.001). Full post-operative arc of motion was 0 – 130° and there was no radiographic evidence of composite degradation, aseptic loosening or component malalignment. DISCUSSION/CONCLUSION. The PCK Knee System utilizes a trapezoidal shaped femoral box, where the narrower end is located anteriorly, allowing a valgus/varus tilt of 1–4 degrees and internal/external rotation of 2–7 degrees during flexion, while maintaining necessary soft-tissue constraint during extension. This variable constraint profile allows for fully tensed collaterals in extension, with a slight reduction in collateral tension through flexion. Furthermore, the combination of the condylar anatomy, trapezoidal femoral box and tibial post allows for adequate clearance through full flexion, while facilitating slightly progressive increases in tilt and rotation, thereby maintaining knee kinematics while dampening forces transmitted through the prosthetic composite. From this feasibility study we report promising short-term clinical and radiographic results in the absence of biomechanical failure in complex primary TKA cases. We recommend continuation of the use and further research of the PCK Knee System for complex primary TKA with the ultimate goal of further determining cost effectiveness and intermediate to long-term clinical relevance

This study aimed to evaluate the month-to-month prevalence of antibiotic dispensation in the 12 months before and after total knee arthroplasty (TKA) and total hip arthroplasty (THA) and to identify factors associated with antibiotic dispensation in the month immediately following the surgical procedure. In total, 4,115 THAs and TKAs performed between April 2013 and June 2019 from a state-wide arthroplasty referral centre were analysed. A cross-sectional study used data from an institutional arthroplasty registry, which was linked probabilistically to administrative dispensing data from the Australian Pharmaceutical Benefits Scheme. Multivariable logistic regression was carried out to identify patient and surgical risk factors for oral antibiotic dispensation. Oral antibiotics were dispensed in 18.3% of patients following primary TKA and 12.0% of patients following THA in the 30 days following discharge. During the year after discharge, 66.7% of TKA patients and 58.2% of THA patients were dispensed an antibiotic at some point. Patients with poor preoperative health status were more likely to have antibiotics dispensed in the month following THA or TKA. Older age, undergoing TKA rather than THA, obesity, inflammatory arthritis, and experiencing an in-hospital wound-related or other infectious complications were associated with increased antibiotic dispensation in the 30 days following discharge. A high rate of antibiotic dispensation in the 30 days following THA and TKA has been observed. Although resource constraints may limit routine wound review for all patients by a surgeon, a select cohort may benefit from timely specialist review postoperatively. Several risk factors identified in this study may aid in identifying appropriate candidates for such changes to follow-up care

Surfing has rapidly grown in popularity as the sport made its debut at the Tokyo 2020 Olympic Games. Surfing injuries are becoming more relevant with the globalisation and increasing risks of the sport, but despite this, little is known about surfing injuries or prevention strategies in either the competitive or recreational surfer. We reviewed the literature for the incidence, anatomical distribution, type and underlying mechanism of acute and overuse injuries, and discuss current preventative measures. Four online databases, including MEDLINE, PubMed, EMBASE and Cochrane Library were searched from inception to March 2020. This review finds that skin injuries represent the highest proportion of total injuries. Acute injuries most frequently affect the head, neck and face, followed by the lower limbs. Being struck by one's own board is the most common mechanism of injury. Surfers are injured at a frequency of 0.30–6.60 injuries per 1000 hours of surfing. Most prior studies are limited by small sample sizes, poor data collection methodology and geographical constraints. The scientific literature on surfing injuries under-represents overuse musculoskeletal injuries and the efficacy of prevention strategies for surfing-related overuse musculoskeletal injuries has not been studied. Injuries to the head and neck pose greater risks to a surfer's morbidity and mortality, yet there is no consensus on the management protocol of spinal injuries that occur in open water. Non-contact acute ligament injuries have increased as surfing manoeuvres have become more acrobatic, and overuse musculoskeletal injuries are highly correlated with paddling. Further research is needed to establish preventative measures for both acute and overuse surfing injuries and to ensure the increasing popularity of surfing is met with an improved understanding of sport risks and safety. Specifically, we recommend research be prioritised regarding the efficacy of training programmes to prevent surfing-related overuse musculoskeletal injuries

Using a reverse engineering capability to quantify the factors that control the rigid body mechanics of the wrist, a mathematical forward animation capability and model of wrist motion that allows the carpus to move under its own rules is being developed. This characterises the isometric connections, from which was developed the Stable Central Column Theory of Carpal Mechanics - which incorporates the Law of Rules Based Motion. This work has now advanced to the ability to reapply the extracted rules to allow rules-based rigid body reanimation of an individual wrist. As each wrist is unique, there is a given reality that each reanimation must be based on an individual wrist's unique rules, and the aspiration to create a standard or normal wrist is unrealistic. Using True Life Anatomy (Adelaide, Aust) analysis software, the specific rules (morphology / connectivity / interaction / loading) of individual wrists have been characterised, and then reapplied in a rigid body reanimation environment using Adams (MSC Software, U.S.) software. In the preliminary application of this biomechanics environment, by using the reverse engineering / forward reanimation process, wrist motion can be recreated - based purely on the unique rules, extracted from individual wrists. Instability of the proximal scaphoid was evident in several of the animations, and there was confirmation that the spatial attachment points of the isometric constraints are very exacting. The actual attachment and specific morphology of the carpal bones varied between individual wrists. Using a reverse engineering and then forward reanimation process, we have been able to recreate wrist motion using the rigid body mechanics based on the Law of Rules Based Motion. Further work is required, but the potential to apply “what if” virtual surgery options to an individual injured wrist and more precisely characterise and test solutions to wrist dysfunction are becoming realised

Orthopaedic surgery is a practical surgical specialization field, the exit exam for registrars remains written and oral. Despite logbook evaluation and surgical work-based assessments, the question remains: can registrars perform elective surgery upon qualification? In South Africa, obstacles to elective surgical training include the trauma workload, financial constraints, fellowships and the Covid pandemic. In hip and knee arthroplasty, new approaches like the direct anterior approach (DAA) and robotic-assisted knee surgery also contributed to the dilution of cases available for registrar training. There are concerns that orthopaedic registrars do not perform enough cases to achieve surgical proficiency. Review of the last 4 years of registrar logbooks in hip and knee arthroplasty surgery performed in a single tertiary academic hospital in South Africa. We included all primary total hip replacements (THR), total knee replacements (TKR) and hemiarthroplasties (HA) done for neck of femur (NOF) fractures between 1 April 2019 and 30 March 2023. Differentiation between registrar assisting, registrar performing with consultant supervision and registrar performing independent surgery was done. 990 hip arthroplasties (472 Primary THR, 216 NOF THR, 302 NOF HA) and 316 Primary TKR were performed during the study period. In primary elective THR the posterior approach was dominant and used in 76% of cases. In NOF THA the DAA was dominant used in 98% of cases. Primary TKR robotic-assisted technologies was used in 27% (n=94) cases. Registrars as the primary surgeon were the highest in NOF THA at 70% of cases and the lowest performing TKR at 25%. During 3-month rotations, an average registrar performed 12 (2 TKR and 10 THR) and assisted in 35 (10 TKR and 25 THR) cases. Despite the large number of arthroplasties operations being performed over the last 4-year period, the surgical cases done by registrars are below, the proposed minimal cases to provide surgical proficiency during their training period

Orthopaedic paediatric deformities, globally, are often corrected later than initial identification due to resource constraints (bed availability, investigative modalities, surgical skill set). The study aims to analyse experiences and challenges met with running a flagship scoliosis surgery week in a tertiary public health care facility, with the goal of reducing patient waiting time on the waiting list. In this retrospective study, patients from an existing deformity correction waiting list were selected for a 5 day scoliosis surgery week. Investigations relevant to clinical findings were carried out and patients were scheduled on a “one patient per day” surgery list. Inclusion criteria was any patient with adolescent idiopathic scoliosis of varying degree that was symptomatic. Exclusion criteria was any other deformity of any age. Outcomes measured include: Administrative hurdles (obtaining funding, organising ward and ICU beds, getting nursing staff), Surgical challenges (severity of the curve, intraoperative time, approach chosen) and perioperative management (anaesthesia, pain management, cost of equipment) will be looked at to better define the experiences and challenges. All scheduled surgeries were completed. This meant more cases were carried out than what was done in the last 2 years at the facility combined. Lack of Nursing staff availability and few ICU beds delayed starting cases. Anterior fusion took a shorter surgical time in comparison to posterior and cost far less to carry out owing to deformity severity. Intra and post operative management also varied due to daily changes in theatre staff and a lack of standardized protocols. Running a scoliosis surgery week helps to lower the waiting time for deformity correction in public health care facilities. Pre organising resources results in more successful outcomes and an increase in the number of cases done over a shorter period

Instability after TKA can result from ligament imbalance, attenuation of soft tissues, or ligament disruption. Flexion instability has been reported after both CR and PS TKA. However, the clinical manifestations of flexion instability can be quite variable. Symptoms of flexion instability include pain and swelling after activity. Bracing occasionally can be helpful. Revision options to treat flexion instability include tibial insert exchange and revision to increase constraint. However, more favorable results have been reported using implants with varus-valgus constraint. Constrained mechanisms include a varus-valgus constrained PS post or hinge. The constrained post relies on the mechanical function of the post to provide stability which may deform or wear in-vivo leading to recurrent instability if used for a completely deficient collateral ligament. The hinge, which provides more rigid constraint, is indicated for collateral ligament deficiency. However, the additional constraint also results in greater bone-implant interface stresses, which may be mitigated by use of stem fixation to minimise risk of loosening

Objectives. We identified an unusual pattern of backside deformation on polyethylene (PE) inserts of contemporary total knee replacements (TKRs). The PE backside's margins were inferiorly deformed in TKRs with NexGen central-locking trays. This backside deformation was significantly associated with tray debonding. Furthermore, recent studies have shown high rate of tray debonding in PS NexGen TKRs. Subsequently, a field safety notice was issued regarding the performance of this particular device combination and the Option tray has been withdrawn from use. Therefore, we hypothesised that the backside deformation of PS inserts may be greater than that of CR inserts. Design and Methods. At our national implant retrieval centre, we used peer-reviewed techniques to analyse changes in the bearing wear rate and backside surface deformation of NexGen PE inserts using coordinate measuring machines [N=84 (CR-43 and PS-41) TKRs with non-augmented-trays]. Multiple regression was used to determine which variable had the greatest influence on backside deformation. The amount of cement cover on trays was quantified as a %of the total surface using Image-J software. Results. The median (IQR) bearing wear rate of the PS PEs [14(8-22) mm. 3. /year] was not significantly different(p=0.154) to that of the CR PEs [18(8-27)mm. 3. /year]. The median (IQR) backside deformation of the PS inserts [294(239-361) µm] was significantly greater (p<0.001) than that of the CR inserts [212(158-258)µm]. Multiple regression modelling showed that duration in-vivo (p=0.037), central-clearance between insert and tray (p<0.001) and constraint (p=0.003) were significantly associated with PE backside-deformation. 38(93%) PS and 31(72%) of CR trays exhibited ≤10% of cement cover. Non-contacting profilometry and microscopy revealed marked pitting and abrasive changes to the superior surface of the tray. Conclusion. This explant study showed the PE backside deformation was significantly higher in PS than in CR inserts and this may be one explanation for the unsatisfactory clinical performance reported with this device combination