Total knee arthroplasty (TKA) aims to alleviate pain and restore joint biomechanics to an equivalent degree to age-matched peers. Zimmer Biomet's Nexgen TKA was the most common implant in the UK between 2003 and 2016. This study compared the biomechanical outcomes of the Nexgen implant against a cohort of healthy older adults to determine whether knee biomechanics is restored post-TKA. Patients with a primary Nexgen TKA and healthy adults >55 years old with no musculoskeletal deficits or diagnosis of arthritis were recruited locally. Eligible participants attended one research appointment. Bilateral knee range of motion (RoM) was assessed with a goniometer. A motorised arthrometer (GENOUROB) was then used to quantify the anterior-posterior laxity of each knee. Finally, gait patterns were analysed on a treadmill. An 8-camera Vicon motion capture system generated the biomechanical model. Preliminary statistical analyses were performed in SPSS (α = 0.05; required sample size for ongoing study: n=21 per group). The patient cohort (n=21) was older and had a greater BMI than the comparative group (n=13). Patients also had significantly poorer RoM than healthy older adults. However, there were no inter-group differences in knee laxity, walking speed or cadence. Gait kinematics were comparable in the sagittal plane during stance phase. Peak knee flexion during swing phase was lower in the patient group, however (49.0° vs 41.1°). Preliminary results suggest that knee laxity and some spatiotemporal and kinematic parameters of gait are restored in Nexgen TKA patients. While knee RoM remains significantly poorer in the patient cohort, an average RoM of >110° was achieved. This suggests the implant provides sufficient RoM for most activities of daily living. Further improvements to knee kinematics may necessitate additional rehabilitation. Future recruitment drives will concentrate on adults over the age of 70 for improved inter-group comparability

One of the most controversial issues in total knee replacement is whether or not to resurface the patella. In order to determine the effects of different designs of femoral component on the conformity of the patellofemoral joint, five different knee prostheses were investigated. These were Low Contact Stress, the Miller-Galante II, the NexGen, the Porous-Coated Anatomic, and the Total Condylar prostheses. Three-dimensional models of the prostheses and a native patella were developed and assessed by computer. The conformity of the curvature of the five different prosthetic femoral components to their corresponding patellar implants and to the native patella at different angles of flexion was assessed by measuring the angles of intersection of tangential lines. The Total Condylar prosthesis had the lowest conformity with the native patella (mean 8.58°; 0.14° to 29.9°) and with its own patellar component (mean 11.36°; 0.55° to 39.19°). In the other four prostheses, the conformity was better (mean 2.25°; 0.02° to 10.52°) when articulated with the corresponding patellar component. The Porous-Coated Anatomic femoral component showed better conformity (mean 6.51°; 0.07° to 9.89°) than the Miller-Galante II prosthesis (mean 11.20°; 5.80° to 16.72°) when tested with the native patella. Although the Nexgen prosthesis had less conformity with the native patella at a low angle of flexion, this improved at mid (mean 3.57°; 1.40° to 4.56°) or high angles of flexion (mean 4.54°; 0.91° to 9.39°), respectively. The Low Contact Stress femoral component had the best conformity with the native patella (mean 2.39°; 0.04° to 4.56°). There was no significant difference (p > 0.208) between the conformity when tested with the native patella or its own patellar component at any angle of flexion. The geometry of the anterior flange of a femoral component affects the conformity of the patellofemoral joint when articulating with the native patella. A more anatomical design of femoral component is preferable if the surgeon decides not to resurface the patella at the time of operation

Total knee arthroplasty (TKA) is a common orthopaedic procedure with over 1,500 done in 2016 in Ireland alone. 96% of all TKAs are due to pain in the knee associated with osteoarthritis. According to the UK National Joint Registry (NJR), there is a 0.47%, 1.81%, 2.63% and 4.34% probability risk of undergoing a revision TKA within one, three, five and ten years respectively post-index surgery. A variety of reasons for failure of TKA have been described in the literature including infection, aseptic loosening, pain, instability, implant wear, mal-alignment, osteolysis, dislocation, peri-prosthetic fracture and implant fracture. The NexGen Posterior Stabilised Fixed has NJR revision rates of 0.44%, 1.61% and 2.54% at years one, three and five respectively. A retrospective review was carried out of 350 NexGen TKAs that were performed directly by, or under the supervision of, a fellowship trained arthroplasty surgeon in a dedicated orthopaedic hospital between April 2013 and December 2015. 26 (7.4%) of these were revised as of 31 December 2017. Three were for septic arthritis with the remaining 23 (6.6%) for aseptic loosening. Patients typically started to experience symptoms of medial tibial pain with supra-patellar swelling from a combination of effusion and synovial thickening at 12–24 months. Inflammatory markers were normal in all cases. Radiographs of symptomatic knee replacements showed bone loss on the medial tibia with a tilt of the tibial component into a varus alignment. The high number of revisions of this particular prosthetic has led to its use being discontinued at this centre

Summary. The 80% porous structure of trabecular metal allows for bone ingrowth in more than 90% of the available surface. The Nexgen LPS Uncemented Knee using a trabecular metal tibial component has performed well at minimum of 5 years’ follow-up. Introduction. Total Knee Arthroplasty prostheses most frequently used in today's practice have cemented components. These have shown excellent clinical results. The fixation can however weaken with time, and cement debris within the articulation can lead to accelerated wear. Cementless implants are less commonly used, but some have also shown good long-term clinical results. The potential advantages of cementless implants are retention of bone stock, less chance of third-body wear due to the absence of cement, shorter operative time, and easier treatment of periprosthetic fractures. The posterior stabilised knee replacement has been said to increase tangential shear stresses on the tibial component and increases contact stresses on the cam and post mechanism hence the great debate of cruciate retaining or cruciate sacrificing implants. Objectives. We report the results of a prospective cohort of consecutive primary total knee arthroplasties using an uncemented posterior stabilised prosthesis using a trabecular metal (tantalum) tibial component at a minimum 5-year follow-up. Methods. Prospective 5 year follow-up of patients undergone an uncemented posterior stabilised total knee replacement using a trabecular metal tibial component (NexgenLPS). Clinical examination, Oxford knee score, Knee society score, SF12 and radiological evaluation undertaken at review. Results. 81 patients, 45 female, 36 male. Left 31, Right 50. Mean age 74.3 yrs range (51–90). SF12, mean: 31.8 range (25–37). Oxford Knee Score Pre-op Mean 20.1 range (9–36) Post op: Mean 32.1 range (9–48). Knee Society score. Pain Mean 91.8; range (60–100). Functional score mean 76.2; range (30–100). Mean Range of movement 110.5 degrees range (90–125). No evidence of loosening at 5 yrs. No deep infection. No Revisions. Conclusion. Although there are a variety of methods of achieving satisfactory initial fixation in cementless components, trabecular metal has an advantage owing to its cellular structure resembling bone. The 80% porous structure of trabecular metal allows for bone ingrowth in more than 90% of the available surface. The Nexgen LPS Uncemented Knee using a trabecular metal tibial component used in this series has shown no evidence of loosening at a minimum of 5 years’ follow-up and the prosthesis as a whole has performed very well clinically. Its early results are comparable to those prostheses most commonly used as reported by the arthroplasty registers. The longer term results from this prosthesis are awaited with interest

The study aimed to compare trochlear profiles in recent total knee arthroplasty (TKA) models and to determine whether they feature improvements compared to their predecessors. The hypothesis was that recent TKA models have more anatomic trochlear compartments and would display no signs of trochlear dysplasia. The authors analyzed the geometry of the 6 following TKA models using engineering software: PFC and Attune (DePuy), NexGen and Persona (Zimmer), Noetos and KneeTec (Tornier). The mediolateral trochlear profiles were plotted at various flexion angles (0°, 15°, 30° and 45°) to deduce the sulcus angle. Analysis of sulcus angles reveals general convergence of recent designs towards anatomic values. At 0° of flexion, sulcus angles of recent implant models were between 156.0–157.4°, while those of previous generation models between 154.5–165.5°. At 30° of flexion, sulcus angles of recent models also lie within 145.7–148.6°, but those of previous models are between 149.5–152.0°. All three manufacturers deepened their trochlear profile at 30° of flexion in recent models compared to earlier designs. Sulcus angles converge towards anatomic values but still exceed radiologic signs of dysplasia by 2–5°. Recent TKA designs have more anatomic trochlear geometries than earlier TKA models by the same manufacturers, but trochlear compartments still exceed radiologic signs of trochlear dysplasia by 2° to 5°. The hypothesis that recent TKA models display no signs of trochlear dysplasia is therefore refuted. Surgeons should be aware of design limitations to optimize choice of implant and extensor mechanisms alignment. Level of evidence: IV geometric implant analysis

Summary Statement. A large proportion of knee arthroplasty patients are dissatisfied with their replacement. Significant differences exist between preoperative, postoperative and normal kinematics. A better understanding of the inter-relationships between kinematics, shape and prosthesis placement could lead to improved quality of life. Introduction. Knee kinematics are altered by total knee arthroplasty (TKA) both intentionally and unintentionally. Knowledge of how and why kinematics change may improve patient outcome and satisfaction through improved implant design, implant placement or rehabilitation. Comparing preoperative to postoperative kinematics and shape of the natural and replaced joint will allow an investigation of the inter-relationships between knee shape, prosthesis placement, knee kinematics and quality of life. Patients & Methods. Using a sequential-biplanar radiographic protocol that allowed imaging the preoperative and postoperative patellofemoral (PF) and tibiofemoral (TF) joints under weightbearing throughout the range of motion, we imaged and compared the 6 degree-of-freedom PF and TF kinematics of 9 pre-TKA subjects to those of 15 post-TKA subjects (Zimmer NexGen Legacy Posterior Stabilised Gender Solutions (GS) components). Using a novel computed tomography (CT) protocol, we obtained the femoral, tibial and patellar knee shapes, plus component placement after TKA. The same 9 pre-TKA subjects have now been re-imaged a minimum of one year postoperatively (DePuy Sigma Mobile Bearing cruciate-sacrificing components) to determine their changes in knee geometry and kinematics; full analysis is in progress. Results. Clear, statistically significant differences were seen between the kinematics of the pre-TKA and post-TKA groups. For the TF joint, the tibia was more posterior and inferior in the post-TKA group compared to the pre-TKA group (max 20 mm and 15 mm, respectively) (p<0.001). Subjects had neutral alignment in the post-TKA group compared to varus alignment (max 9°) in the pre-TKA group (p<0.001). For the PF joint, the patella was shifted more posteriorly and less laterally postoperatively and was tilted neutrally compared to laterally (p<0.001). Our preliminary analysis of the matched preop-postop subjects likewise shows a more posterior and inferior tibia and neutral versus valgus alignment. Greater tibial rotations were seen postoperatively due to the mobile bearing. The patella was more posterior and less lateral postoperatively, as seen with the two groups. Discussion/Conclusion. The kinematic differences seen are likely due to a combination of surgical, implant and patient factors. Both groups showed differences from normal kinematics, based on previous studies in the literature. In the future, by comparing the preoperative and postoperative kinematics, shape and quality of life for the same subjects (i.e. the 9 pre-TKA subjects in this study), and analyzing the interrelationships amongst these, we aim to determine if a different implant shape or different component positioning could create more normal kinematics, resulting in a better clinical outcome