Tibial Baseplate Research Articles

Dissociation of the polyethylene insert from the tibial baseplate after total knee arthroplasty: a case report and review of the literature

Dissociation of the polyethylene insert from the tibial baseplate after total knee arthroplasty: a case report and review of the literature

Is modern bicruciate retaining TKA feasible?

Early bicruciate retaining total knee arthroplasty (TKA) deisgns were abandoned due to high failure rates. Twenty bicruciate TKAs were retrieved and analyzed to determine the mechanisms of failure. Failures occurred predominately on the tibial side due to fracture of the anterior tibial tray or bridge, insert dissociation, UHMWPE wear, and tibial component loosening. Modern implant designs and materials may increase the strength of the tibial baseplate, durability of the liner locking mechanism, and UHMWPE wear resistance, while better surgical techniques may improve implant fixation suggesting that bicruciate retaining TKA could be feasible. However, long-term studies will be necessary to determine if the durability of modern bicruciate retaining TKAs is equivalent to contemporary CR and PS designs.

Posterior tibial slope impacts intraoperatively measured mid-flexion anteroposterior kinematics during cruciate-retaining total knee arthroplasty

Posterior tibial slope (PTS) for cruciate-retaining (CR) total knee arthroplasty (TKA) is usually pre-determined by the surgeon. Limited information is available comparing different choices of PTS on the kinematics of the CR TKA, independent of the balancing of the extension gap. This study hypothesized that with the same balanced extension gap, the choice of PTS significantly impacts the intraoperatively measured kinematics of CR TKA. Navigated CR TKAs were performed on seven fresh-frozen cadavers with healthy knees and intact posterior cruciate ligament (PCL). A custom designed tibial baseplate was implanted to allow in situ modification of the PTS, which altered the flexion gap but maintained the extension gap. Knee kinematics were measured by performing passive range of motion (ROM) tests from full extension to 120° of flexion on the intact knee and CR TKAs with four different PTSs (1°, 4°, 7°, and 10°). The measured kinematics were compared across test conditions to assess the impact of PTS. With a consistent extension gap, the change of PTS had significant impact on the anteroposterior (AP) kinematics of the CR TKA knees in mid-flexion range (45°-90°), but not so much for the high-flexion range (90°-120°). No considerable impacts were found on internal/external (I/E) rotation and hip-knee-ankle (HKA) angle. However, the findings on the individual basis suggested the impact of PTS on I/E rotation and HKA angle may be patient-specific. The data suggested that the choice of PTS had the greatest impact on the mid-flexion AP translation among the intraoperatively measured kinematics. This impact may be considered while making surgical decisions in the context of APkinematics. When using a tibial component designed with "center" pivoting PTS, a surgeon may be able to fine tune the PTS to achieve proper mid-flexion APstability.

Proximal tibial resorption in a modern total knee prosthesis.

BackgroundIn an effort to minimize backside polyethylene wear and osteolysis associated with titanium tibial baseplates, many manufacturers have transitioned to cobalt chromium alloys. Recent literature has implicated thicker cobalt chromium designs as a potential source of increased stress shielding and resorption. We report the incidence of proximal tibial bone resorption in a large consecutive series of patients undergoing total knee arthroplasty, with a modern total knee design.MethodsFour hundred thirty-two consecutive primary total knee arthroplasties, performed by 2 fellowship-trained arthroplasty surgeons were identified over a 24-month period. In addition to review of the medical records, analysis of preoperative and postoperative radiographs was performed. Utilizing a novel classification system, the severity of resorption was quantified and correlated with patient and implant characteristics.ResultsAfter exclusions, 339 knees were evaluated in 292 patients. Mean follow-up was 13.2 months (range 6-41). Resorption was present in 119 knees (35.1%). Average time to diagnosis of bone loss was 6.9 months (range 2-32) postoperatively. There was a statistically significant difference between resorption and nonresorption groups with regards to gender and preoperative alignment. Most cases were classified as Grade 1. During the study period, 2 patients required revision for aseptic tibial loosening.ConclusionsOur findings suggest that proximal tibial resorption is common with this particular implant, particularly in men and patients with preoperative varus deformity. Although this typically occurs relatively early in postoperative period and in most cases appears to remodel and stabilize, its ultimate clinical significance and effect on implant survivorship remains unclear.

Results of Cemented vs Cementless Primary Total Knee Arthroplasty Using the Same Implant Design

BackgroundAlthough cemented total knee arthroplasty (TKA) continues to be the gold standard, there are patient populations with higher failure rates with cemented TKAs such as the obese, morbidly obese, and younger active males. Cementless TKA usage continues to increase because of the potential benefits of long-term biologic fixation similar to the rise in cementless total hip arthroplasty. The purpose of this study was to evaluate the clinical and radiographic results of cementless TKA using a novel highly porous cementless tibial baseplate. MethodsThis was a retrospective matched case-control study of 400 primary TKAs comparing cementless vs cemented TKAs using the same implant design (Stryker Triathlon; Stryker Inc, Mahwah, NJ). Two-hundred patients with a mean age of 64 years (range 42-88 years) and body mass index (BMI) of 33.9 kg/m2 (range 19.7-57.1 kg/m2) were matched to 200 primary cemented TKA patients with a mean age of 64 years (range 43-87 years) and BMI of 33.1 kg/m2 (range 22.2-53.2 kg/m2). The mean follow-up in the cementless group was 2.4 years (range 2-3.5 years) and in the cemented group was 5.3 years (range 2-10.9 years). Clinical and radiographic analyses were evaluated. Statistical analysis was performed using the Microsoft Excel, version 15.21.1. ResultsThere was no statistical difference in age, BMI, and preoperative Knee Society Scores between the 2 groups (P = .22, P = .82, and P = .43, respectively). Patients in both groups had a similar incidence of postoperative complications (P = .90). Cementless group had 7 revisions with one aseptic loosening of the tibial component (0.5%). Cementless tibial baseplates demonstrated areas of increased bone density at the pegs of the tibial baseplate. The cemented group had 8 total revisions with 5 cases of aseptic loosening (2.5%). ConclusionEarly results of cementless TKA using a highly porous tibial baseplate designed with a keel and 4 pegs appear promising with one case of aseptic loosening at minimum 2-year follow-up. As the demographics of patients undergoing TKA change to include younger, obese, and more active patients, along with increased life expectancy, the use of a highly porous cementless tibial baseplate may be beneficial in providing long-term durable biologic fixation similar to the success of cementless total hip arthroplasty.

Uncemented vs Cemented Cruciate Retaining Total Knee Arthroplasty in Patients With Body Mass Index Greater Than 30

BackgroundAseptic loosening of cemented and uncemented tibial components continues to be a source of implant failure after total knee arthroplasty (TKA) in the obese population. There is limited literature reviewing uncemented cruciate retaining (CR) components in the obese population. MethodsA clinical and radiographic review was performed on 325 patients who underwent a cemented or uncemented TKA with a CR knee prosthesis and body mass index ≥30 kg/m2 between January 2010 and June 2013. Charts were reviewed for the incidence of revision due to aseptic loosening of the tibial baseplate, revision for any reason, incidence of radiolucent lines around the tibial baseplate, range of motion, and patient reported outcomes. ResultsThere was no statistically significant difference between groups in survivorship for aseptic loosening of the tibial component (99.4% uncemented, 99.3% cemented, P = .94) and overall survivorship (98.1% uncemented, 98.3% cemented, P = .90). The Lower Extremity Activity Scale and Forgotten Joint Score-12 clinical outcome measures were similar between groups (10.2 ± 3.7 vs 9.7 ± 3.4 and 66.1 ± 28.2 vs 64.9 ± 24.3, P = .33, P = .78, respectively). Postoperative knee flexion was similar between groups (114.6 ± 9.3 vs 114.1 ± 9.3, P = .67). ConclusionOur study demonstrated similar survivorship of this CR design for aseptic loosening of the tibial baseplate and overall revision rates in obese patients undergoing either an uncemented or cemented TKA. The uncemented and cemented groups had comparable clinical and radiographic short to mid-term outcomes when implanted in good alignment when treating end-stage knee osteoarthritis.

Cementless Posteriorly Stabilized Total Knee Arthroplasty: Seven-Year Minimum Follow-Up Report

BackgroundThe purpose of this study is to evaluate (1) implant survivorship; (2) patient outcomes; (3) complications; and to (4) perform a radiographic analysis of cementless posteriorly stabilized total knee arthroplasty (TKA) patients at a minimum of 7-year follow-up. MethodsOur original cohort was composed of 114 consecutive cementless posteriorly stabilized total knee arthroplasties (110 patients) performed by a single surgeon between 2008 and 2010. Since our original report, 4 (1 bilateral) patients died and 2 were lost to follow-up. Therefore, there were 104 patients who had 107 knees available for final follow-up. The final cohort included 43 men and 61 women, who had a mean age of 69 years (range 47-87) and were followed from 7 to 9 years (mean 8 years). Patient outcomes and complications were obtained from electronic medical records. Radiographic assessment was done using the Knee Society Radiographic Evaluation System. ResultsThe all-cause survivorship was 98% (95% confidence interval 1.01-0.96). Since the original report, there has been 1 post-traumatic loosening of the tibial baseplate, and 1 revision for instability. There were no femoral revisions or patella revisions. The mean Knee Society pain score was 93 points (range 80-100) and the function score was 78 points (range 68-95). Excluding revisions, there was no evidence of progressive loosening of any implant components. ConclusionBased on these 7-year minimum follow-ups, femoral, tibial, and patellar cementless hydroxylapatite-coated beaded implants perform well at up to 9 years postoperatively and offer surgeons and patients a cementless option that may provide long-lasting biological fixation.

Varus tibial alignment is associated with greater tibial baseplate migration at 10 years following total knee arthroplasty

To examine implant migration and articular behavior of primary total knee arthroplasty (TKA) at 10years after index surgery and correlate to implant alignment. Thirty-five patients underwent a cemented posterior stabilized total knee arthroplasty with a surgical objective of neutral alignment and were enrolled in a long-term radiostereometric analysis (RSA) study. At 10years after surgery, patients were analyzed for implant migration using RSA as well as radiographic assessment of articular behavior at four positions of knee flexion. Implant position and alignment was measured on full-length radiographs. Patient demographics and reported outcomes were also collected. No difference between patient demographics or patient-reported outcomes were found. When categorized into neutral and varus groupings, no difference in migration was present. If alignment was considered as a continuous variable, there was no correlation between overall leg alignment and migration, however, migration increased with an increasing varus tibial alignment. Although contact location did not differ between neutral and varus groups through a range of motion, condylar liftoff was much more common in the varus group, of which all were lateral liftoff. Increased tibial varus results in increased implant migration. Overall varus limb alignment is correlated with isolated lateral compartment liftoff, and liftoff occurs more commonly than in neutral aligned knees. The increased migration and liftoff raise concerns about the longevity of malaligned total knee replacements. If a goal of overall varus limb alignment is desired for TKA, the tibia should remain neutral. Level III.

Analysis of the tibial baseplate coverage and symmetrical tibial prosthesis in primary total knee arthroplasty

Objective: To investigate the tibial baseplate coverage with symmnetrical tibial prosthesis in primary total knee arthroplasty (TKA). Methods: From August 2014 to February 2015, 39 patients (39 knees) with varus knee osteoarthritis were retrospective reviewed in Department of Orthopaedics, Tianjin Xiqing Hospital. Nine males and 30 females; aged 50 to 78 years (67±6 year). 3D tibia models of the knee were built with Mimics 10.01 software, simulated TKA surgeries were performed. The morphology of the proximal tibia was measured, including the mediolateral (ML), anteroposterior (AP) and medial and lateral tibial plateau AP dimensions. 3D models of PFC Sigma tibial prosthesis were imported and the tibial coverage characters were analyzed. Results: The AP and ML dimensions of the tibial resection surface were (45.7± 3.4) mm, (71.7± 4.2) mm respectively, the plateau aspect ration ratio (AP/ML) was 63.8%±3.0%. The medial tibial plateau AP[(46.9± 3.3) mm]was significantly greater than the lateral side[(41.8±3.3) mm, P=0.000], the asymmetric ratio averaged 112.4%±6.9%. The medial tibial plateau, anteromedial, posteromedial, posterolateral unsatisfied coverage ratio were 33.3%, 76.9%, 20.5%, 33.3% respectively. There are 5 cases underhang and 3 cases overhang in the posteromedial side, whereas 1 case underhang and 12 cases overhang posterolateral, the overhang ratio was 30.8%. Posteromedial, posterolateral prosthesis coverage had linear positive correlation to the ipsilateral tibial plateau AP diameter. Conclusions: The medial AP diameter of tibial plateau is significantly lager than the lateral side in varus knee osteoarthritis patients. With symmetrical tibial baseplate placement in TKA, the prosthesis usually lead to medial tibial plateau anterior and posterior underhang and posterolateral overhang.

Early aseptic loosening of a mobile-bearing total knee replacement

Background and purpose — Registry-based studies have reported an increased risk of aseptic tibial loosening for the cemented Low Contact Stress (LCS) total knee replacement compared with other cemented designs; however, the reasons for this have not been established. We made a retrieval analysis with the aim of identifying the failure mechanism.Patients and methods — We collected implants, cement, tissue, blood, and radiographs from 32 failed LCS Complete cases. Damage to the tibial baseplate and insert was assessed. Exposure to wear products was quantified in 11 cases through analysis of periprosthetic tissue and blood. Implant alignment and bone cement thickness was compared with a control group of 43 non-revised cases.Results — Loosening of the tibial baseplate was the reason for revision in 25 retrievals, occurring at the implant–cement interface in 16 cases. Polishing was observed on the lower surface of the baseplate and correlated to the level of cobalt, chromium, and zirconium in the blood. No evidence of abnormally high polyethylene wear was present. For each 1 mm increase in cement thickness the odds of failure due to aseptic loosening decreased by 61%. Greater varus alignment was associated with a shorter time to failure. The roughness, Ra, of a new LCS baseplate’s lower surface was 3.7 (SD 0.7) µm.Interpretation — Debonding of the tibial component at the implant–cement interface was the predominant cause of tibial aseptic loosening. A thin cement layer may partly explain the poor performance. Furthermore, the comparatively low tibial surface roughness and the lack of a keeled stem may have played a role in the failures observed.

Influence of Increased Posterior Tibial Slope in Total Knee Arthroplasty on Knee Joint Biomechanics: A Computational Simulation Study

BackgroundThe reconstructed posterior tibial slope (PTS) plays a significant role in restoring knee kinematics in cruciate-retaining-total knee arthroplasty (TKA). A few studies have reported the effect of the PTS on biomechanics. MethodsThis study investigates the effect of the PTS on tibiofemoral (TF) kinematics, patellofemoral (PF) contact stress, and forces at the quadriceps, posterior cruciate ligament (PCL) and collateral ligament after cruciate-retaining-TKA using computer simulations. The simulation for the validated TKA finite element model was performed under deep knee bend condition. All analyses were repeated from −3° to 15° PTS in increments of 3°. ResultsThe kinematics on the TF joint translated increasingly posteriorly when the PTS increased. Medial and lateral contact points translated in posterior direction in extension and flexion as PTS increased. The maximum contact stress on the PF joint and quadriceps, and collateral ligament force decreased when the PTS increased. An implantation of the tibial plate with increased PTS reduced the PCL load. Physiologic insert movement led to an increasingly posterior position of the femur and reduced quadriceps force especially for knee flexion angles above high flexion (120°) when compared to TKA with a decreased slope of the tibial base plate. ConclusionAn increase in the PTS increased medial and lateral movements without paradoxical motion. However, an excessive PTS indicated progressive loosening of the TF joint gap due to a reduction in collateral ligament tension during flexion.

Optimized Prototype of Instrumented Knee Implant: Experimental Validation

Background: Embedding self-powered sensors into the knee implant for measuring in-vivo tibiofemoral force distribution can provide beneficial information to both clinicians and researchers. This information may help to reduce the risk of early failure after total knee arthroplasty. It can also be used to improve implant design, refine surgical techniques and enhance postoperative rehabilitation.Methods: An experimental prototype of instrumented tibial baseplate has previously been proposed, developed and tested. A few shortcomings have been observed and identified during the experimental testing. In this study, the design of the proposed prototype was optimized to avoid the mechanical failure of the embedded piezoelectric generator/sensor. Furthermore, piezoceramics of greater height and smaller section were accommodated and tested in the optimized prototype to generate more electric power. This optimized prototype was also experimentally tested using a knee simulator to validate the optimization result.Results: The optimization made to the experimental prototype allowed us to address the aforementioned shortcomings. The mechanical longevity of piezoceramics embedded into the optimized prototype was considerably enhanced with respect to the first prototype (optimized prototype: 54000 gait cycles, first prototype: a few cycles). The produced electric power was also increased (optimized prototype: 4.28 mW, first prototype: 1.81 mW).Conclusion: The optimized prototype lasted for 54000 gait cycles without any obvious mechanical or electrical failures. The electric power produced in this prototype and quantified during experimental trials is sufficient to power an efficient low-power-consumption telemetry system.

Characterization and Correction of Errors in Computing Contact Location Between Curved Articular Surfaces: Application to Total Knee Arthroplasty.

In total knee arthroplasty (TKA), one common metric used to evaluate innovations in component designs, methods of component alignment, and surgical techniques aimed at decreasing the high rate of patient-reported dissatisfaction is tibiofemoral contact kinematics. Tibiofemoral contact kinematics are determined based on the movement of the contact locations in the medial and lateral compartments of the tibia during knee flexion. A tibial force sensor is a useful instrument to determine the contact locations, because it can simultaneously determine contact forces and contact locations. Previous reports of tibial force sensors have neither characterized nor corrected errors in the computed contact location (i.e., center of pressure) between the femoral and tibial components in TKA that, based on a static analysis, are caused by the curved articular surface of the tibial component. The objectives were to experimentally characterize these errors and to develop and validate an error correction algorithm. The errors were characterized by calculating the difference between the errors in the computed contact locations when forces were applied normal to the tibial articular surface and those when forces were applied normal to the tibial baseplate. The algorithm generated error correction functions to minimize these errors and was validated by determining how much the error correction functions reduced the errors in the computed contact location caused by the curved articular surface. The curved articular surface primarily caused bias (i.e., average or systematic error) which ranged from 1.0 to 2.7 mm in regions of high curvature. The error correction functions reduced the bias in these regions to negligible levels ranging from 0.0 to 0.6 mm (p < 0.001). Bias in the computed contact locations caused by the curved articular surface of the tibial component as small as 1 mm needs to be accounted for, because it might inflate the computed internal-external rotation and anterior-posterior translation of femur on the tibia leading to false identifications of clinically undesirable contact kinematics (e.g., internal rotation and anterior translation during flexion). Our novel error correction algorithm is an effective method to account for this bias to more accurately compute contact kinematics.

Initial Stability of Cemented vs Cementless Tibial Components Under Cyclic Load

BackgroundCement fixation of total knee components remains the gold standard despite resurgence in cementless fixation with the goal of long-term durable fixation. Initial stability is paramount to achieve bony ingrowth of cementless components. MethodsTwelve cemented and cementless tibial baseplates were implanted into sawbones and tested using a physiological medial-lateral load distribution for 10,000 cycles to represent 8 weeks of in vivo function. Micromotion was measured at 5 locations around the baseplate during loading. ResultsCycling had a significant effect on the change in micromotion between maximum and minimum loads at the anterior, medial, lateral, posteromedial, and posterolateral tray edge locations. A significant effect of fixation technique was detected for the anterior (P < .001), medial (P = .002), and lateral (P = .0056) locations but not for the posteromedial (P = .36) or posterolateral (P = .82) locations. Differences in micromotion between cemented and cementless components did not exceed 150 μm at any tested location. ConclusionThe micromotion experienced by cementless tibial components in the present study may indicate a lower initial mechanical stability than the cemented group. However, this difference in initial stability may be subclinical because the differences between average cemented and cementless micromotion were <150 μm at all measured locations under the loading regime implemented.

Does the tibia component design affect the need for offset stems in revision total knee arthroplasty?

The stem/keel location varies between anatomic and symmetric revision tibial baseplates. The current study investigates the impact of an anatomic versus symmetric stem location on the need for offset couplers in revision total knee arthroplasty. Hip to ankle standing radiographs and lateral radiographs of 75 patients were analyzed using digital templating software. The offset in the anterior-posterior as well as medial-lateral plane between the center of the tibial diaphysis and the stem of the tibial baseplate were determined for an anatomic and symmetric tibial baseplate, respectively. Measurements were repeated for 4 resection levels: tip of fibular head (0), 10mm (1), 15mm (2) and 20mm (3) below the tip of the fibula head. Anatomic tibial baseplates require less offset for resection levels up to the tip of the fibula: total offset 2.28 versus 5.44mm (p < 0.001). However, for defects that result in resection levels below the tip of the fibula symmetric tibial baseplates require less offset: resection level 1: 3.18 versus 2.4mm (p = 0.008), 2: 4.81 versus 1.67mm (p < 0.001) and resection level 3: 5.66 versus 1.52mm (P < 0.001). The current study suggests that while asymmetric anatomic tibial baseplates have benefits for revisions with minimal bone loss, symmetric tibial baseplates require less offset when larger bone defects are encountered.

An Improved Tibial Force Sensor to Compute Contact Forces and Contact Locations In Vitro After Total Knee Arthroplasty.

Contact force imbalance and contact kinematics (i.e., motion of the contact location in each compartment during flexion) of the tibiofemoral joint are both important predictors of a patient's outcome following total knee arthroplasty (TKA). Previous tibial force sensors have limitations in that they either did not determine contact forces and contact locations independently in the medial and lateral compartments or only did so within restricted areas of the tibial insert, which prevented them from thoroughly evaluating contact force imbalance and contact kinematics in vitro. Accordingly, the primary objective of this study was to present the design and verification of an improved tibial force sensor which overcomes these limitations. The improved tibial force sensor consists of a modified tibial baseplate which houses independent medial and lateral arrays of three custom tension-compression transducers each. This sensor is interchangeable with a standard tibial component because it accommodates tibial articular surface inserts with a range of sizes and thicknesses. This sensor was verified by applying known loads at known locations over the entire surface of the tibial insert to determine the errors in the computed contact force and contact location in each compartment. The root-mean-square errors (RMSEs) in contact force are ≤ 6.1 N which is 1.4% of the 450 N full-scale output. The RMSEs in contact location are ≤ 1.6 mm. This improved tibial force sensor overcomes the limitations of the previous sensors and therefore should be useful for in vitro evaluation of new alignment goals, new surgical techniques, and new component designs in TKA.

Tibial Base Plate for Total Knee Arthroplasty: Symmetric or Asymmetric?

BackgroundIdeal positioning and best coverage of the tibial base plate are essential in total knee arthroplasty. There are 2 types of tibial base plates: symmetric and asymmetric. The superiority of one to the other is still controversial. The aim of this study was to compare symmetric and asymmetric tibial base plates for total knee arthroplasty in terms of rotational alignment and coverage.MethodsThe study was conducted on a total of 80 cadaveric tibial bones. Two surgeons were asked to place 20 symmetric (group 1) and 20 asymmetric (group 2) tibial base plates taking care to ensure the best coverage that they were able to determine. Afterwards, the rotational errors and coverage were assessed with reference to the posterior tibial margin and posterior condylar axis on the three-dimensional computed tomography (3D CT) scan. In the second part of the study, the surgeons were asked to place 20 symmetric (group 3) and 20 asymmetric (group 4) base plates taking care to ensure the best rotational alignment. The rotational errors and the areas uncovered or overstuffed after the application were measured on the 3D CT scan.ResultsOn the comparison of rotational errors, while there was no significant difference between group 1 and group 2 in terms of coverage (p = 0.624), the mean external rotation error was significantly greater in group 2 (p = 0.034). On the comparison of coverage, while there was no significant difference between group 3 and group 4 in terms of rotation (p = 0.36), the mean ratios of the uncovered tibial surface to the total tibial surface (p = 0.041) and also the overstuffed area to the total base plate surface (p = 0.029) were significantly greater in group 4.ConclusionsThe determination of correct size and rotation of the tibial component is essential for favorable outcomes of total knee arthroplasty. In this study, the symmetric tibial base plate design was more effective than the asymmetric design in providing the ideal tibial rotation and coverage.

A soft-tissue preserving method for evaluating the impact of posterior tibial slope on kinematics during cruciate-retaining total knee arthroplasty: A validation study

BackgroundThe reconstructed posterior tibial slope (PTS) plays a significant role in restoring knee kinematics in cruciate-retaining total knee arthroplasty. However, conventional methods for the investigation of PTS can be limited by sample size or prone to errors due to damages to the bone and/or soft tissues. The purpose of this study was to validate a novel method for the evaluation of the effects of PTS on knee kinematics. MethodsSeven computer-assisted cruciate-retaining TKAs were performed by two surgeons on healthy cadaveric knees. The implanted tibial baseplates allowed precise and easy modification of the PTS in situ. Knee kinematics were evaluated during passive full range of motion test. The evaluation was performed three times at each of the five PTSs in the order of 10°, seven degrees, four degrees, one degree, and back to ten degrees. The variability of the repeated measurements, inter-surgeon variation of the data, and test reproducibility were investigated. ResultsThe test method was shown to be highly repeatable (low root-mean-squared errors) and has low sensitivity to surgeon variability (ANOVA). No statistical difference was found in the knee kinematics between the first and last measurements at 10° PTS (paired t-test). ConclusionThe results suggested that the developed method can be used to investigate the impact of PTS on knee kinematics without disrupting the soft-tissue environment of the knee. The use of the novel tibial baseplate allowed for adjusting the PTS without re-cutting the tibia and removing the components. The method may be applied to improve the future investigation of PTS.

No Difference in Implant Micromotion Between Hybrid Fixation and Fully Cemented Revision Total Knee Arthroplasty: A Randomized Controlled Trial with Radiostereometric Analysis of Patients with Mild-to-Moderate Bone Loss.

In revision total knee arthroplasty (TKA), the femoral component and tibial baseplate are usually cemented. However, stems can be fixed either with cement or with a press-fit technique, with the latter resulting in hybrid fixation. There is no consensus on the preferred stem fixation technique. Therefore, we compared the stability of cemented TKA implants with the stability of TKA implants fixed with the hybrid technique in a prospective randomized trial using radiostereometric analysis (RSA). Thirty-two patients with a Type-I or II bone defect who needed revision TKA and were randomly allocated at the time of surgery into either the cemented or hybrid-fixation group were included in the study. The radiographs for the RSA were obtained during hospitalization (baseline); at 6 weeks; and at 3, 6, 12, and 24 months. Migration of the femoral and tibial implants was measured using model-based RSA and expressed along or around the 3 orthogonal axes and as total translation (TT) and total rotation (TR). Clinical results were evaluated using the Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score (KOOS), active flexion, and visual analog scale (VAS) scores for pain and satisfaction. Mann-Whitney and chi-square tests were used to compare migration and clinical outcomes between the cement and hybrid techniques. At 24 months, no difference in median migration or the number of migrating components was found between the cemented and hybrid-fixation groups. In each group, approximately one-third of the tibial components had total rotation of >1°. The clinical scores did not differ between the techniques. At 24 months after revision TKAs, cemented and hybrid-fixation replacements were equally stable. Unexpectedly, both groups had implants with >1 mm or >1° of micromotion although there were no clinical or radiographic signs of loosening. Whether these findings indicate the possibility of loosening with longer follow-up remains to be investigated. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Retrospective study of asymmetric vs symmetric tibial plates and ultracongruent vs posterior stabilized inserts in Indian population: An Indian experience of Natural Knee II.

Results of asymmetric tibial base plates vs symmetric tibial base plates and ultracongruent insert vs posterior stabilized insert in Indian population. A total of 47 knee replacements with mean age of 65.2 years in 38 patients (16 males and 22 females) between 2007-2011 were included. Natural Knee II (21 models) were compared with 26 models of other knees (12 PFC-Sigma, one PFC-RPF, 10 Nexgen and three Vanguard). The ultracongruent insert of NK II lead to creation of greater post-op mean flexion deformity of 18° (range 15-20°) as compared to 5.8° (range 5-8°) in other knees with PS insert (P<0.001, confidence limit of 24.2-0.1). After 3 months NK II patients had a lower mean post-operative knee score of 87 as compared to mean post-operative knee score of 96 (P<0.001, confidence limit of 17.9-0.1) in the non-NK II patients because of greater points deductions due to the creation of greater mean flexion deformity. When NO implant overhang is accepted on medial side, asymmetric tibial base plates leaves large portions of peripheral lateral tibial plateau uncovered by implant; decreasing the implant bone surface area ratio of Knee Society Radiographic Assessment Criteria. Similar problem is not encountered with symmetric tibial base plates. Symmetric and not asymmetric tibial base plates provide greater bone coverage in Indian (ethnic Punjabi) population when no implant overhang is accepted. Further use of NK II was discontinued after just 21 cases in the interest of the patients.