Total Knee Arthroplasty Implants Research Articles

OpenSim as a preliminary kinematic testing platform for the development of total knee arthroplasty implants

The design of a total knee replacement implant needs to take account the complex surfaces of the knee which it is replacing. Ensuring design performance of the implant requires in vitro testing of the implant. A considerable amount of time is required to produce components and evaluate them inside an experimental setting. Numerous adjustments in the design of an implant and testing each individual design can be time consuming and expensive.Our solution is to use the OpenSim simulation software to rapidly test multiple design configurations of implants. This study modeled a testing rig which characterized the motion and laxity of knee implants. Three different knee implant designs were used to test and validate the accuracy of the simulation: symmetrical, asymmetric, and anatomic. Kinematics were described as distances measured from the center of each femoral condyle to a plane intersecting the most posterior points of the tibial condyles between 0 and 135° of flexion with 15° increments. Excluding the initial flexion measurement (∼0°) results, the absolute differences between all experimental and simulation results (neutral path, anterior-posterior shear, internal-external torque) for the symmetric, asymmetric, and anatomical designs were 1.98 mm ± 1.15, 1.17 mm ± 0.89, and 1.24 mm ± 0.97, respectively. Considering all designs, the accuracy of the simulation across all tests was 1.46 mm ± 1.07. It was concluded that the results of the simulation were an acceptable representation of the testing rig and hence applicable as a design tool for new total knees.

The anteroposterior axis of the tibia is adjusted to approximately a right angle to the anterior pelvic plane in the standing position in patients with hip dysplasia similar to normal subjects: a cross-sectional study

BackgroundWe previously described that the anteroposterior (AP) axis of the tibia is approximately perpendicular to the transverse axis of the anterior pelvic plane (APP) in the standing position in healthy subjects. The purpose of this study was to investigate the rotational alignment between the APP and clinical epicondylar axis and the AP axis of the tibia relative to pelvic coordination in the standing position in normal subjects and in women with developmental dysplasia of the hip (DDH) to aid decision making for surgeons in the alignment of implants in total hip or knee arthroplasty.MethodsThis study included 77 Japanese women. Twenty-nine in the DDH group underwent curved periacetabular osteotomy; 48 women without lumbago and knee pain were included in the normal group. Femoral neck anteversion (FNA), condylar twist angle, and knee rotation angle were measured in femoral coordination. The angle between the femoral neck axis and clinical epicondylar axis (CEA) was measured, the transverse axis of the APP was also measured, and the angle between the AP axis of the tibia and transverse axis of the APP was calculated.ResultsThere was a moderate negative correlation between FNA and CEA relative to the APP. This finding indicated a trend towards greater FNA leading to more internal rotation. Knee rotation angle (KRA) relative to the APP was 1.65° ± 5.58° in the normal group and − 2.65° ± 7.57° in the DDH group. This finding indicated that the tibia AP axis was approximately perpendicular to the APP in the standing position both in the normal and DDH groups.ConclusionWe found that the tibia AP axis was at approximately a right angle to the transverse axis of the APP in the standing position in both the normal and DDH groups, while the KRA was different in the normal and DDH groups. These findings may prove helpful for positional alignment investigations needed for implantation in total hip or knee arthroplasty and gait analysis.

Computed Tomography Techniques Help Understand Wear Patterns in Retrieved Total Knee Arthroplasty

BackgroundSuboptimal total knee arthroplasty (TKA) position of both femoral and tibial components is thought to be linked with poor clinical outcomes, polyethylene wear and the “unexplained” painful knee arthroplasty. The aim of this study was to better understand the effect of implant orientation on knee implant performance. MethodsWe analyzed 30 retrieved contemporary TKA implants. Implant positioning measurements in the coronal plane were made prior to revision using a diagnostic algorithm, based on 3D computed tomography (CT) images. Each retrieved polyethylene component was imaged using a micro-CT scanner and a high resolution computational 3D model of each component was digitally reconstructed. The difference in thickness between medial and lateral components was calculated. Statistical analysis was performed to investigate the association between component positioning and damage patterns. ResultsWe found a significant correlation between both the tibiofemoral and femoral angles and difference in thickness between polyethylene compartments: varus angulations were strongly associated with thinner medial compartments, whilst valgus angulations were associated with thinner lateral compartments. Moreover, suboptimal tibiofemoral orientations and tibial component angulations were associated to greater differences in thickness between polyethylene compartments. ConclusionOur study is the first to compare accurate 3D CT measurements of prerevision TKA positioning in the coronal plane with postrevision retrieval analysis from innovative, accurate and highly reliable micro-CT–based method. Our results demonstrate the impact of component positioning on polyethylene damage and helps understanding of the in vivo performance of these implants. Level of EvidenceIII.

3D patient imaging and retrieval analysis help understand the clinical importance of rotation in knee replacements

PurposeThe purpose of the present study was to correlate highly accurate CT measurements of pre-revision total knee arthroplasty (TKA) implant position with findings of retrieval analysis post-revision, to understand the clinical relevance of TKA orientation.MethodsThis study involved 53 retrieved TKA implants with pre-revision 3D-CT scans used to determine coronal (varus–valgus), sagittal (tibial slope) and rotational (internal rotation–external rotation) TKA orientation as well as tibiofemoral leg axis. Differences between femoral and tibial angles to describe the "relative rotational mismatch" were also calculated. All tibial inserts were forensically analyzed using the Hood score. Statistical analysis was performed to investigate correlations between TKA component orientation and surface damage (p < 0.05).ResultsFemoral components were found to have axial rotations mainly within ± 3° (68%), whilst 45% of the tibial components and 66% of the relative rotational mismatches were > 3° and < − 3°, respectively. The majority of femoral and tibial components (87% in both cases), as well as the femorotibial angle (70%), showed coronal orientations within ± 3°. The 64% of the tibial components showed posterior tibial slopes out of both the 0°–3° and 5°–7° ranges. There was a significant correlation between tibial slope and damage score on polyethylene tibial inserts (r = 0.2856; p = 0.0382) as well as a significant correlation between implants’ position in the axial plane and damage score on polyethylene tibial inserts (r = 0.6537, p = 0.0240).ConclusionsThis is the first study to use accurate measurements from pre-revision 3DCT to compare tibial and femoral orientation in all three planes with retrieval findings in total knee replacements. A significant correlation between implant position and polyethylene surface damage was found. These results showed the importance of optimizing component position to minimize polyethylene damage. Further analysis involving more accurate polyethylene wear measurements are fundamental to fully understand the role of components’ orientation in TKAs.

The Evolution of Total Knee Component Design Follows Anatomic Morphology

Over the years, the total knee arthroplasty (TKA) has become a common procedure for patients of various ages, ethnicities, and sex. Early prosthetic designs were limited in size and shape, leaving the surgeon to subjectively decide which component to use and sometimes having to compromise on the surgical technique to achieve a secure and stable construct. As studies began to investigate differences in tibial and femoral dimensions of the knee between specific populations, TKA implants incorporated these findings to become more anatomically accurate. When considering the global TKA patient population and the anthropometric differences between sexes and ethnicities, using anatomically proportioned femoral or tibial components with accurate trends in size and shape increases surgical accuracy to the measured anatomy, and ultimately influences clinical performance. This review will highlight the important clinical differences regarding knee anatomy between certain populations, along with the corresponding improvements in total knee component design.

Radiographic Changes in Nonoperative Contralateral Knee After Unilateral Total Knee Arthroplasty

BackgroundSome patients perceive symptomatic improvement in the contralateral knee after unilateral total knee arthroplasty (TKA). This so-called “splinting effect” has been observed but has not been radiographically evaluated. MethodsA retrospective review of patients with bilateral knee osteoarthritis treated with unilateral TKA was performed. Patients were subcategorized into 2 groups based on whether contralateral TKA was performed within the 2-year period. Contralateral radiographic measurements were performed. ResultsForty-four of 203 patients had contralateral TKA performed within 2 years. Preoperative parameters were significantly worse in the bilateral group. By 6 weeks postoperatively, mechanical axis plumbline improved approximately 1°, with more change in those patients with preoperative varus alignment. Larger delta changes were also present in bilateral group preoperative to 1-year radiographs for tibiofemoral angle and joint space widening. ConclusionIn patients with bilateral knee osteoarthritis who undergo unilateral TKA, a splinting effect may be present and measurable radiographically with improvement of contralateral mechanical axis plumbline. Further research is necessary to determine whether this improvement may delay contralateral TKA implantation.

Revision of Unicompartmental to Total Knee Arthroplasty: Does the Unicompartmental Implant (Metal-Backed vs All-Polyethylene) Impact the Total Knee Arthroplasty?

BackgroundThe aim of this study is to investigate differences in implant requirement, outcomes, and re-revision when total knee arthroplasty (TKA) was performed following unicompartmental knee arthroplasties (UKAs) with metal-backed (MB) compared to all-polyethylene (AP) tibial components. MethodsRetrospective study of 60 UKAs converted to 60 TKAs at mean 7.3 years (0.1 to 17) after implantation in 55 patients (mean age, 64 [49-83]; 44% male): 44 MB and 16 AP. TKA implant requirement was investigated in addition to mode of failure, Oxford Knee Score, and TKA survival at mean 5.4 years (0.5 to 17). ResultsProgression of osteoarthritis was the commonest mode of failure in MB UKAs (P = .03) and unexplained pain in AP (P = .011) where revisions were performed earlier (4.8 ± 3.2 vs 8.2 ± 4.5, P = .012). In 56 of 60 (93%) cases, unconstrained TKA implants were used. The use of standard cruciate-retaining TKAs without augments or stems was less likely following MB UKA compared to AP (12 of 38 [32%] vs 10/14 [71%], P = .013). Specifically MB UKA implants were associated with more tibial stem use (P = .04) and more use of cruciate-substituting polyethylene (P = .05). There was no difference in the use of constrained implants. Multivariate analysis showed tibial resection depth to predict stem requirement. Seven were re-revised giving 7-year TKA survival: from MB UKA 70.3 (95% CI, 47.0 to 93.6) and from AP UKA 87.5 (95% CI, 64.6 to 100; P = .191). ConclusionMB UKA implants increase the chances of a complex revision requiring tibial stems and cruciate substitution but reduce the chances of early revision compared to AP UKA which often fail early with pain.

Using Patient Demographics and Statistical Modeling to Predict Knee Tibia Component Sizing in Total Knee Arthroplasty

BackgroundPreoperative planning is important to achieve successful implantation in primary total knee arthroplasty (TKA). However, traditional TKA templating techniques are not accurate enough to predict the component size to a very close range. MethodsWith the goal of developing a general predictive statistical model using patient demographic information, ordinal logistic regression was applied to build a proportional odds model to predict the tibia component size. The study retrospectively collected the data of 1992 primary Persona Knee System TKA procedures. Of them, 199 procedures were randomly selected as testing data and the rest of the data were randomly partitioned between model training data and model evaluation data with a ratio of 7:3. Different models were trained and evaluated on the training and validation data sets after data exploration. ResultsThe final model had patient gender, age, weight, and height as independent variables and predicted the tibia size within 1 size difference 96% of the time on the validation data, 94% of the time on the testing data, and 92% on a prospective cadaver data set. ConclusionThe study results indicated the statistical model built by ordinal logistic regression can increase the accuracy of tibia sizing information for Persona Knee preoperative templating. This research shows statistical modeling may be used with radiographs to dramatically enhance the templating accuracy, efficiency, and quality. In general, this methodology can be applied to other TKA products when the data are applicable.

A Retrospective Comparison of a Medial Pivot and Posterior-Stabilized Total Knee Arthroplasty With Respect to Patient-Reported and Radiographic Outcomes

BackgroundMedial pivot (MP) type total knee arthroplasty (TKA) implants are designed with a highly congruent medial tibiofemoral articulation. Compared with the cam-and-post design of the posterior-stabilized (PS) TKA, the MP-TKA design has been hypothesized to better replicate the natural kinematics of the knee. We compared the MP-TKA and PS-TKA designs, with our primary outcome measures being range of motion (ROM) and patient-reported satisfaction. MethodsThis study was a retrospective comparison between the 2 groups (76 MP-TKA vs 88 PS-TKA). ROM was collected preoperatively, 6 weeks, 6 months, and 1 year postoperatively. The Forgotten Joint Score-12 (FJS-12) scores were collected at a minimum of 1 year postoperatively. ResultsThere was no statistically significant difference in age, gender, or body mass index between the groups. We found a statistical difference in preoperative ROM (MP = 120.3°, PS = 112.8°, P = .002). There was no difference in ΔROM at 6 weeks (MP = −12.36, PS = −3.79, P = .066), 6 months (MP = −4.23, PS = 2.73, P = .182), or 1 year (MP = .17, PS = 3.31, P = .499). Patients who underwent the MP-TKA scored significantly better than the PS-TKA on the FJS-12 score (MP = 59.72, PS = 44.77, P = .007). ConclusionWe found that patients who underwent the MP-TKA scored better on the FJS than those who underwent the PS-TKA; particularly with regard to deep knee flexion and stability of the prosthesis. The MP-TKA design may offer improved patient outcomes because of its highly congruent medial tibiofemoral articulation.

Outcomes of a newer-generation cementless total knee arthroplasty design in patients less than 50 years of age.

Younger patients undergoing cemented total knee arthroplasty (TKA) may be at risk for lower implant survivorship and higher revision rates due to the historical increased prevalence of aseptic loosening and instability in this cohort. The recent advances of cementless TKAs may mitigate some of these complications. However, there is a paucity of studies reporting on patients who are under 50 years who have undergone a cementless TKA. Therefore, this study evaluated: (I) implant survivorship; (II) functional outcomes and complications; and (III) radiographic outcomes in patients who were less than 50 years of age and underwent cementless TKA. A total of 29 patients (31 knees) younger than 50 years who underwent primary TKA at a single institution (Mount Sinai Beth Israel, New York, New York, USA) from June 2008 to May 2014 were included. Their mean follow-up was 4 years (range, 2 to 6 years). The cohort included 20 women and 9 men who had a mean age of 45 years (range, 34 to 49 years), and a mean body mass index (BMI) of 33 kg/m2 (range, 22 to 54 kg/m2). The preoperative knee diagnoses were osteoarthritis (n=24), osteonecrosis (n=5), and rheumatoid arthritis (n=2). A Kaplan-Meier analysis was used to calculate the all cause implant survivorship. Functional outcomes and all complications were recorded for each patient. Additionally, radiographic evaluation using the new Knee Society Radiographic Evaluation and Scoring System was performed. The overall implant survivorship was 100%; there were no failures or revision surgeries performed as of the latest follow-up visit. At the latest follow-up, the mean Knee Society pain score was 92 points (range, 80 to 95 points) and the mean Knee Society function score was 84 points (range, 70 to 90 points). Additionally, the mean knee extension was 1 degree (range, 0 to 5 degrees) and the mean knee flexion was 125 degrees (range, 95 to 140 degrees). Furthermore, at the latest follow-up, on radiographic evaluation, there was no evidence of component loosening, subsidence, radiolucency, gap formation, or reactive changes, and there were no postoperative complications. Cementless fixation of TKAs had excellent survivorship and functional and radiographic outcomes at midterm follow-up in patients younger than 50 years. Although longer follow-up is needed, these cementless TKA implants appear to provide promising results in younger patient populations.

Internal femoral component malrotation in TKA significantly alters tibiofemoral kinematics.

Femoral component malrotation in total knee arthroplasty (TKA) is clinically proven to cause dissatisfaction and impaired function. This study is an attempt to characterize the tibiofemoral kinematics following femoral malrotation in posterior stabilized (PS) TKA. It was hypothesized that internal malrotation would introduce the most pronounced changes. Six fresh-frozen cadaver specimens were mounted in a kinematic rig. Three motion patterns were applied with the native knee and following PS TKA (passive motion, open chain extension, and squatting) while infrared cameras recorded the trajectories of markers attached to femur and tibia. Three different femoral implants were tested: a conventional posterior stabilized component, and adapted components of the same implant with 5° of intrinsic external and internal rotation, respectively. The implantation of the PS TKA resulted in less tibial internal rotation (squat 33-70°, p < 0.05) and the medial femoral condyle shifted posteriorly especially in deep flexion (squat 84-111°, p < 0.05). Internal component malrotation caused internal rotation and abduction of the tibia in flexion (squat 33-111°, p < 0.05), an elevated (squat 43-111°, p < 0.05) and more anterior (passive 61-126°, p < 0.05) located medial femoral condyle and a lateral femoral condyle located more posterior and inferior (squat 73-111°, p < 0.05) than in the neutrally aligned TKA. External component malrotation caused only little changes under passive motion. Under a squat there was less internal rotation and more adduction to the tibia (33-111°, p < 0.05). The medial femoral condyle was moved more posterior (squat 59-97°, p < 0.05), the lateral femoral condyle more superior (squat 54-105°, p < 0.05) than in the neutrally aligned TKA. The greatest differences to the native tibiofemoral kinematics were introduced by internal rotation of the femoral component. Also neutrally and externally rotated femoral components introduce kinematic changes, but to a lesser extent. With respect to the alterations introduced to kinematics internal malrotation should be avoided when performing PS TKA.

Cementless Total Knee Arthroplasty in Knee Osteonecrosis Demonstrated Excellent Survivorship and Outcomes at Three-Year Minimum Follow-Up

BackgroundLack of consensus exists on the use of cementless total knee arthroplasty (TKA) in patients with knee osteonecrosis. Therefore, this study was conducted to evaluate (1) implant survivorship; (2) clinical outcomes and complications; and (3) radiographic outcomes of primary cementless TKA in knee osteonecrosis. MethodsThis study included 46 patients (49 knees) who had knee osteonecrosis and underwent primary cementless TKA and had a mean follow-up of 44 months (range 36-96). Kaplan-Meier analysis was used to evaluate implant survivorship. Follow-up was performed post-operatively at 6 weeks, 3 months, and annually thereafter. Clinical outcomes including the Knee Society Scores (KSS) for pain and function, changes in range-of-motion, complications, and radiographic outcomes were analyzed. ResultsAseptic implant survivorship was 97.9% (95% confidence interval 1.01-0.93) and all-cause implant survivorship was 95.9% (95% confidence interval 1.01-0.9), with 1 septic and 1 aseptic failures. The mean KSS for pain was 93 points (range 85-100) and the mean KSS for function was 84 points (range 70-90). Additionally, 1 patient had superficial wound necrosis and was treated with local wound care with no further sequela. Otherwise, no evidence of loosening, subsidence, or progressive radiolucencies were noted on radiological evaluation. ConclusionExcellent implant survivorship, clinical, and radiographic outcomes of primary cementless TKA in the setting of knee osteonecrosis was demonstrated. Although further long-term study is needed to validate survivorship, new generation cementless TKA implants provide promising results in this subset of patients.

The ratio of patient body mass index to age: a cost-effective implant selection guideline for total knee arthroplasty.

BackgroundWe sought to develop an objective implant selection guideline based on the ratio of patient body mass index (BMI) to age in order to select implants preoperatively and reduce cost while maintaining quality. The BMI-to-age ratio can be used to distinguish patient demand and select those patients who may benefit from newer technology and higher cost implants and those who would do well with standard-demand implants.MethodsA retrospective analysis investigated the types of implants received by patients undergoing total knee arthroplasty from January 2012 to August 2014. Patients with a BMI-to-age ratio >0.60 were categorized as high demand and were eligible for either a high-demand implant or a standard-demand implant. Patients with a BMI-to-age ratio ≤0.60 were recognized as standard demand and would be eligible for only standard-demand implants. The actual implant received was identified and compared with the implant as predicted by the BMI-to-age ratio and potential cost savings were identified.ResultsA total of 1507 operative knees were identified. The high-demand implant carries a 31% greater cost than that of a standard-demand implant. Thirty-eight of 1084 high-demand implants were placed in standard-demand knees. An additional 1.1% cost was realized with 38 standard-demand knees receiving high-demand implants and 28.6% if high-demand knees had been used in all standard-demand patients.ConclusionsLimiting the use of high-demand implants to high-functional-demand patients based on the BMI-to-age ratio may guide the surgeon's choice in optimizing implant selection while providing value-based purchasing criteria to the selection of total knee arthroplasty implants.

Rotating Hinge Implants for Complex Primary and Revision Total Knee Arthroplasty

BackgroundContemporary rotating hinge knee (RHK) prosthesis has shown improved survival rates over earlier generations. However, reports of high complication and mechanical failure rates highlight the need for more clinical outcome data in the complex primary and revision setting. The purpose of this study is to report our results of using a contemporary rotating hinge for complex primary and revision total knee arthroplasty. MethodsUsing a prospectively maintained surgical database, 79 knees in 76 patients who underwent an RHK of a single design for either a complex primary (14 knees) or revision total knee arthroplasty (65 knees) were identified. This included 19% undergoing an RHK for periprosthetic joint infection and 32.9% who had concomitant extensor mechanism repair. The cohort consisted of 60 women and 16 men with a mean age of 66.7 years (range 39-89) at the time of surgery. Patient outcomes were assessed using Knee Society Scores and radiographs were reviewed for signs of wear and loosening. Failure rates were estimated using Kaplan-Meier survival curves. ResultsAt a minimum of 2 years, 13 patients had died and 4 were lost to follow-up, leaving 62 knees in 59 patients who were followed for a mean of 55.2 months (range 24-146). The mean Knee Society Scores improved from 35.7 to 66.2 points (P < .01). The incidence of complications was 38.7%. The most common complications were periprosthetic fracture, extensor mechanism rupture, and periprosthetic infection. Estimated survival was 70.7% at 5 years. ConclusionDespite improvements in design and biomaterials, there remains a relatively high complication rate associated with the use of a modern RHK implant. While aseptic loosening was rare, periprosthetic fracture, infection, and extensor mechanism failure were substantial emphasizing the complex nature of these cases.

Sports After Total Knee Replacement: Are Intense Contact Sports Possible?

Intense physical activity is possible after this TKA and does not compromise the midterm survivorship of the implant. Total Knee Arthroplasty (TKA) implants show durable long-term benefit in wear and loosening. However patients become demanding for more intense physical and sports activities which could decrease implant durability. The purpose of this study is to evaluate the ability of TKA patients to return to sports and the tolerance of sports activities on the mid term survivorship of the prosthesis. From January 2001 to January 2008, 500 patients received a posterior cruciate ligament-substituting mobile bearing TKA. Clinical and radiological outcomes were assessed at baseline and postoperatively using the Knee Society (KS) Knee and Function and activity by the University of California at Los Angeles (UCLA) scale. Mean age at surgery was 70.6 years (range,40-91). Osteoarthritis predominated (91.8%). Mean follow-up was 7.5 years (5-13) including 123 knees (21%) followed more than 10 years. At 3 months after surgery, 215 patients (43%) enjoyed outdoor activities such as hiking, cycling, fishing, golf, hunting and horse-riding. At last follow-up, 145 patients were not concerned by physical activities; 355 patients (71%) could perform regular physical activities, with a mean UCLA rating of 7.3±1/10 (5 to 10). 133 patients (26%) could perform sport activities at a level equal or greater than 8/10 on the UCLA rating score. In 96 of these 133 knees (72%), the patient had more than one sports activity (total = 233 itemized activities). In 103 of these 133 cases, UCLA rating was 9/10 (backpacking, dancing, cross country skiing, aerobics, rollerblade running, horse-riding or jumping-show or heavy farm labor), and in 30, 10/10 (tennis, marathon, downhill skiing, alpine glacier hiking, parasailing). Kaplan-Meier 13-year survivorship with revision for aseptic loosening as end-point was 99.4% (95% CI, 99.8-100). On the 3 loosenings occuring during this period, none occured on patients with intense physical activity. All 3 were on patients with moderate activities. This study reports that return to an intense physical activity is possible after this Mobile bearing Total Knee Arthroplasty and does not compromise the midterm survivorship of the implant.

Mechanical alignment technique for TKA: Are there intrinsic technical limitations?

BackgroundMechanically aligned (MA) total knee arthroplasty (TKA) is affected by disappointing functional outcomes in spite of the recent improvements in surgical precision and implant designs. This might suggest the existence of intrinsic technical limitations. Our study aims to compare the prosthetic and native trochlear articular surfaces and to estimate the extent of collateral ligament imbalance, which is technically uncorrectable by collateral ligament release when TKA implants are mechanically aligned. Study hypothesisConventional MA technique generates a high rate of prosthetic overstuffing of the distal groove, distal lateral trochlear facet and distal lateral femoral condyle (Hypothesis 1), and technically uncorrectable collateral ligament imbalance (hypothesis 2)? Disregarding the distal femoral joint line obliquity (DFJLO) when performing femoral cuts explains distal lateral femoral prosthetic stuffing and uncorrectable imbalance (hypothesis 3)? MethodsTwenty patients underwent a conventional MA TKA. Pre-operative MRI-based 3D knee models were generated and MA TKA was simulated. Native and prosthetic trochlear articular surfaces were compared using in-house analysis software. Following the automatic determination by the planning software of the size of the extension and flexion gaps, an algorithm was applied to balance the gaps and the frequency and amplitude of technically uncorrectable knee imbalance were estimated. ResultsThe conventional MA technique generates a significant slight distal lateral femoral prosthetic overstuffing (mean 0.6mm, 0.8mm, 1.25mm for the most distal lateral facet point, groove, and at the most distal point of lateral femoral condyle, respectively) and a high rate of type 1 and 2 uncorrectable knee imbalance (30% and 40%, respectively). The incidence of distal lateral prosthetic overstuffing (trochlea and condyle) and uncorrectable knee imbalance were strongly to very strongly correlated with the DFJLO (r=0.53 to 0.89). ConclusionConventional MA technique for TKA generates frequent lateral distal femoral prosthetic overstuffing and technically uncorrectable knee imbalance secondary to disregarding the DFJLO when adjusting the femoral component frontal and axial rotations, respectively. Level of evidencelevel 4.

Surgical Techniques for Total Knee Arthroplasty: Measured Resection, Gap Balancing, and Hybrid.

Total knee arthroplasty (TKA) is effective in managing end-stage degenerative joint disease. Achieving favorable clinical outcomes is predicated on proper implant alignment, sizing, and rotation as well as adequate soft-tissue balancing. Modern TKA implants are designed to address the fundamental needs of attaining stability in both flexion and extension and of optimizing patellar tracking. Measured resection and gap balancing are the two different techniques used to implant the TKA components used today. Both techniques have been validated as durable and successful, and each has unique advantages and disadvantages. A hybrid technique has been developed that combines the benefits of measured resection and gap balancing and minimizes the limitations associated with both techniques. This hybrid approach has the potential for achieving improved TKA kinematics and refined surgical technique.

Tibiofemoral Instability After Primary Total Knee Arthroplasty: Posterior-Stabilized Implants for Obese Patients.

Tibiofemoral instability is a common complication after total knee arthroplasty (TKA), accounting for up to 22% of all revision procedures. Instability is the second most common cause of revision in the first 5 years after primary TKA. In this study, 13 knees with tibiofemoral instability after TKA were identified among 693 consecutive primary TKA procedures. Patient demographics, body mass index, clinical symptoms, previous deformity, previous knee surgery, complications, interval between index TKA and first tibiofemoral instability, causes of instability, and interval between index TKA and revision TKA were retrospectively reviewed. Clinical outcomes were assessed with the Lysholm Knee Scoring Scale. All patients were women, and mean body mass index was 37.7 kg/m2 (range, 27.2-52.6 kg/m2). Mean interval between index TKA and first tibiofemoral instability was 23.4 months (range, 9-45 months), and mean interval between index TKA and revision TKA was 25.6 months (range, 14-48 months). All patients had posterior cruciate ligament-retaining implants. Of the 13 knees, 11 had flexion instability and 2 had global instability. In all patients, instability was caused by incompetence of the posterior cruciate ligament; additionally, 1 patient had undersized and malpositioned implants. In 4 knees, the polyethylene insert was broken as well. All patients underwent revision TKA. Lysholm Knee Scoring Scale score had improved from a mean of 35.8 (range, 30-46) to a mean of 68.3 (range, 66-76). All patients included in this study were female and obese. The main cause of instability was secondary posterior cruciate ligament rupture and incompetence. The use of posterior-stabilized implants for primary TKA may prevent secondary instability in obese patients. [Orthopedics. 2017; 40(5):e812-e819.].

Comparison of adverse events rates and hospital cost between customized individually made implants and standard off-the-shelf implants for total knee arthroplasty.

BackgroundThis study compares selected hospital outcomes between patients undergoing total knee arthroplasty (TKA) using either a customized individually made (CIM) implant or a standard off-the-shelf (OTS) implant.MethodsA retrospective review was conducted on 248 consecutive TKA patients treated in a single institution, by the same surgeon. Patients received either CIM (126) or OTS (122) implants. Study data were collected from patients' medical record or the hospital's administrative billing record. Standard statistical methods tested for differences in selected outcome measures between the 2 study arms.ResultsCompared with the OTS implant study arm, the CIM implant study arm showed significantly lower transfusion rates (2.4% vs 11.6%; P = .005); a lower adverse event rate at both discharge (CIM 3.3% vs OTS 14.1%; P = .003) and 90 days after discharge (CIM 8.1% vs OTS 18.2%; P = .023); and a smaller percentage of patients were discharged to a rehabilitation or other acute care facility (4.8% vs 16.4%; P = .003). Total average real hospital cost for the TKA hospitalization between the 2 groups were nearly identical (CIM $16,192 vs OTS $16,240; P = .913). Finally, the risk-adjusted per patient total cost of care showed a net savings of $913.87 (P = .240) per patient for the CIM-TKA group, for bundle of care including the preoperative computed tomography scan, TKA hospitalization, and discharge disposition.ConclusionsPatients treated with a CIM implant had significantly lower transfusion rates, fewer adverse event rates, and were less likely to be discharged to a rehabilitation facility or another acute care facility. These outcomes were achieved without increasing costs.

Varus-valgus constrained implants in total knee arthroplasty: indications and technique.

Total knee arthroplasty is a successful operation that significantly improves patient's quality of life. However, studies demonstrated as only 82% to 89% of patients are satisfied with their surgery, being the other disappointed with regard to their expectations. Two to 5.7% of total knee arthroplasties (TKAs) require revision within 5 years. Both complex primary cases and revision TKA often necessitate for a higher degree of constrain than cruciate retaining or postero-stabilized implant design. In the 1970s varus-valgus constrained (VVC) or semi-constrained implants have been developed by Insall and associates from the PS design, which provide varus-valgus stability preserving a fair amount of host bone. VVC TKAs allows for a small amount of movement in the coronal, antero-posterior and axial planes. In this paper, the authors give an overview of the indications, outcomes and technique for varus-valgus constrained implants, both in the setting of primary and revision knee arthroplasty.