Knee kinematics with a high-flexion posterior stabilized total knee prosthesis: an in vitro robotic experimental investigation

BACKGROUND: An analysis of contemporary total knee arthroplasty reveals that, on the average, patients rarely flex the knee beyond 120 degrees. The biomechanical mechanisms that inhibit further flexion after total knee arthroplasty are unknown. The objective of the present study was to investigate the capability of a single design of a fixed-bearing, high-flexion posterior stabilized total knee arthroplasty system (LPS-Flex) to restore the range of flexion to that of the intact knee. METHODS: Thirteen cadaveric human knees were tested, with use of a robotic testing system, before and after total knee arthroplasty with the LPS-Flex prosthesis. The passive path and the kinematics under an isolated quadriceps force of 400 N, under an isolated hamstring force of 200 N, and with these forces combined were determined. Posterior femoral translation of the lateral and medial femoral condyles and tibial rotation were recorded from 0 degrees to 150 degrees of flexion. RESULTS: The medial and lateral condyles of the intact knee translated posteriorly from full extension to 150 degrees, reaching a mean peak (and standard deviation) of 22.9 +/- 11.3 mm and 31.9 +/- 12.5 mm, respectively, under the combined muscle forces. Following total knee arthroplasty, the amount of posterior femoral translation was lower than that observed in the intact knee. At 150 degrees, approximately 90% of the intact posterior femoral translation was recovered by the total knee replacement. Internal tibial rotation was observed for all knees throughout the range of motion. The cam-spine mechanism engaged at approximately 80 degrees and disengaged at 135 degrees. Despite the absence of cam-spine engagement, further posterior femoral translation occurred from 135 degrees to 150 degrees. CONCLUSIONS: The tibiofemoral articular geometry of the intact knee and the knee after total knee arthroplasty with use of the LPS-Flex design demonstrated similar kinematics at high flexion angles. The cam-spine mechanism enhanced posterior femoral translation only at the mid-range of flexion. The femoral component geometry of the LPS-Flex total knee prosthesis may improve posterior tibiofemoral articulation contact in high flexion angles.     

In vivo comparison of knee kinematics for subjects having either a posterior stabilized or cruciate retaining high-flexion total knee arthroplasty

The objective of this study was to determine the in vivo kinematics for subjects having either a fixed posterior stabilized (PS) or cruciate retaining (CR) high-flexion total knee arthroplasty (TKA). Three-dimensional kinematics from full extension to maximum flexion were determined for 30 subjects (15 PS, 15 CR) using fluoroscopy. On average, the PS subjects demonstrated 112 degrees of weight-bearing (WB) flexion, -6.4 mm of posterior femoral rollback, and 2.9 degrees of axial rotation. The CR subjects averaged 117 degrees of WB flexion, -4.9 mm of posterior femoral rollback, and 4.8 degrees of axial rotation. Posterior femoral rollback of the lateral condyle occurred for all PS TKAs and in 93% of the CR TKAs. Only 2 subjects in each group experienced greater than 1.0 mm of condylar lift-off. Subjects in both TKA groups demonstrated excellent WB ranges of motion and kinematic patterns similar to the normal knee, but less in magnitude.     

Anterior tibial post impingement in a posterior stabilized total knee arthroplasty.

Despite the numerous long-term success reports of posterior stabilized (PS) total knee arthroplasty (TKA), recent retrieval studies of various PS TKA designs revealed wear and deformation on the anterior side of the tibial post. This study investigated the mechanisms of anterior impingement of the post with the femoral component. Seven cadaveric knees were tested to study kinematics and tibial post biomechanics during simulated heel strike using an in vitro robotic testing system. Intact knee kinematics and in situ anterior cruciate ligament (ACL) forces were determined at hyperextension (0 degree to -9 degrees) and low flexion angles (0 degrees to 30 degrees) under the applied loads. The same knee was reconstructed using a PS TKA. The kinematics and the tibial post contact forces of the TKA were measured under the same loading condition. The ACL in the intact knee carried load and contributed to knee stability at low flexion angles and hyperextension. After TKA, substantial in situ contact forces (252.4 +/- 173 N at 9 degrees of hyperextension) occurred in the tibial post, indicating anterior impingement with the femoral component. Consequently, the TKA showed less posterior femoral translation compared to the intact knee after the impingement. At 9 degrees of hyperextension, the medial condyle of the intact knee translated 0.1 +/- 1.1 mm whereas the medial condyle of the TKA knee translated 5.6 +/- 6.9 mm anteriorly. The lateral condyle of the intact knee translated 1.5 +/- 1.0 mm anteriorly whereas the lateral condyle of the TKA knee translated 2.1 +/- 5.8 mm anteriorly. The data demonstrated that anterior tibial post impingement functions as a substitute for the ACL during hyperextension, contributing to anterior stability. However, anterior post impingement may result in additional polyethylene wear and tibial post failure. Transmitted impingement forces might cause backside wear and component loosening. Understanding the advantages and disadvantages of the tibial post function at low flexion angles may help to further improve component design and surgical techniques and thus enhance knee stability and component longevity after TKA.     

Tibiofemoral force following total knee arthroplasty: comparison of four prosthesis designs in vitro.

Despite ongoing evolution in total knee arthroplasty (TKA) prosthesis design, restricted flexion continues to be common postoperatively. Compressive tibiofemoral force during flexion is generated through the interaction between soft tissues and prosthesis geometry. In this study, we compared the compressive tibiofemoral force in vitro of four commonly used prostheses: fixed-bearing PCL (posterior cruciate ligament)-retaining (PFC), mobile-bearing posterior-stabilized (PS), posterior-stabilized with a High Flex femoral component (HF), and mobile-bearing PCL-sacrificing (LCS). Fourteen fresh-frozen cadaver knee joints were tested in a passive motion rig, and tibiofemoral force measured using a modified tibial baseplate instrumented with six load cells. The implants without posterior stabilization displayed an exponential increase in force after 90 degrees of flexion, while PS implants maintained low force throughout the range of motion. The fixed-bearing PFC prosthesis displayed the highest peak force (214 +/- 68 N at 150 degrees flexion). Sacrifice of the PCL decreased the peak force to a level comparable with the LCS implant. The use of a PCL-substituting post and cam system reduced the peak force up to 78%, irrespective of whether it was a high-flex or a standard PS knee. However, other factors such as preoperative range of motion, knee joint kinematics, soft tissue impingement, and implantation technique play a role in postoperative knee function. The present study suggests that a posterior-stabilized TKA design might be advantageous in reducing soft tissue tension in deep flexion. Further research is necessary to fully understand all factors affecting knee flexion after TKA.     

The posterior cruciate ligament in total knee arthroplasty

The purpose of this study was to answer 2 questions: Does the posterior cruciate ligament (PCL) produce femoral rollback in a single-design, cruciate-sparing total knee arthroplasty (TKA)? Does the PCL prevent posterior tibial displacement when it is retained after a single-design, cruciate-sparing TKA? Knee kinematics and limits of motion were measured with the knees in the following states: (1) intact knee, (2) anterior cruciate-deficient knee, (3) PCL-retaining total knee of a single design (TKA), (4) PCL-retaining TKA with PCL cut, and (5) PCL-substituting TKA. Femoral rollback was then calculated from the above data. The results showed that the PCL was able to prevent posterior translation and maintain femoral rollback when it was preserved during TKA. Therefore, the PCL can be functional after TKA, in a single-design, cruciate-sparing TKA. When the PCL was cut, significant changes in knee kinematics were observed.     

In Vivo Knee Kinematics: How Important Are the Roles of Femoral Geometry and the Cruciate Ligaments?

BackgroundWhile posterior cruciate-retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bicruciate-retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. The objectives of this study are to assess the in vivo kinematics for subjects implanted with either a PCR or BCR TKA and to compare the in vivo kinematic patterns to the normal knee during flexion. These objectives were achieved with an emphasis on understanding the roles of the cruciate ligaments, as well as the role of changes in femoral geometry of nonimplanted anatomical femurs vs implanted subjects having a metal femoral component.MethodsTibiofemoral kinematics of 50 subjects having a PCR (40 subjects) or BCR (10 subjects) TKA were analyzed using fluoroscopy while performing a deep knee bend activity. The kinematics were compared to previously published normal knee data (10 subjects). Kinematics were determined during specific intervals of flexion where the ACL or PCL was most dominant.ResultsIn early flexion, subjects having a BCR TKA experienced more normal-like kinematic patterns, possibly attributed to the ACL. In mid-flexion, both TKA groups exhibited variable kinematic patterns, which could be due to the transitional cruciate ligament function period. In deeper flexion, both TKA functioned more similar to the normal knee, leading to the assumption that the PCL was properly balanced and functioning in the TKA groups. Interestingly, during late flexion (after 90°), the kinematic patterns for all three groups appeared to be statistically similar.ConclusionSubjects having a PCR TKA experienced greater weight-bearing flexion than the BCR TKA group. Subjects having a BCR TKA exhibited a more normal-like kinematic pattern in early and late flexion. The normal knee subjects achieved greater lateral condyle rollback and axial rotation compared to the TKA groups.     

In Vivo Kinematic Analysis of a High-Flexion, Posterior-Stabilized, Mobile-Bearing Knee Prosthesis in Deep Knee Bending Motion

The objective of this study was to evaluate the kinematics of a high-flexion, posterior-stabilized, mobile-bearing total knee arthroplasty (TKA) in weight-bearing, deep knee bending motion. Thirteen patients implanted with the Legacy Posterior Stabilized Flex (Zimmer, Warsaw, IN) mobile-bearing TKA were examined during a deep knee bending motion using fluoroscopy. Femorotibial motion was determined using a 2-dimensional to 3-dimensional registration technique, which used computer-assisted design models to reproduce the position of metallic implants from single-view fluoroscopic images. The average flexion range of motion between the metallic implants was 116°. The average rotation of the femoral component was 9.3° external rotation. The mean kinematic pathway was early rollback, lateral pivot with external rotation, and bicondylar rollback. We found that the kinematic pattern of the Legacy Posterior Stabilized Flex mobile-bearing TKA was different than normal knee kinematics.     

Flexion–extension gap in cruciate‐retaining versus posterior‐stabilized total knee arthroplasty: A cadaveric study

We re‐examined experimental model results using half‐body specimens with intact extensor mechanisms and navigation to evaluate cruciate‐retaining (CR) and posterior stabilized (PS) total knee arthroplasty (TKA) component gaps through an entire range of motion. Six sequential testing regimens were conducted with the knee intact, with a CR TKA in place, and with a PS TKA in place, with and without 22 N traction in place at each stage. Each of 10 knees was taken through six full ranges of motion from 0° to 120° at every stage using a navigated knee system to record component gapping. No significant difference was found between loaded and unloaded component gaps, and no significant differences were found in component gapping between CR and PS TKAs throughout a full range of motion. Flexion–extension gap measurements were significantly different from previously published data (at 90° flexion). No difference was found in kinematics when comparing CR and PS TKA component designs. Our results suggest that intact extensor mechanisms may be required to perform proper kinematic studies of TKA. Our findings provide evidence that the extensor mechanism may play a major role in the flexion–extension gaps in cadaveric knees. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:627–632, 2014.     

Changes in Knee Kinematics Reflect the Articular Geometry after Arthroplasty

We hypothesized changes in rotations and translations after TKA with a fixed-bearing anterior cruciate ligament (ACL)-sacrificing but posterior cruciate ligament (PCL)-retaining design with equal-sized, circular femoral condyles would reflect the changes of articular geometry. Using 8 cadaveric knees, we compared the kinematics of normal knees and TKA in a standardized navigated position with defined loads. The quadriceps was tensed and moments and drawer forces applied during knee flexion-extension while recording the kinematics with the navigation system. TKA caused loss of the screw-home; the flexed tibia remained at the externally rotated position of normal full knee extension with considerably increased external rotation from 63° to 11° extension. The range of internal-external rotation was shifted externally from 30° to 20° extension. There was a small tibial posterior translation from 40° to 90° flexion. The varus-valgus alignment and laxity did not change after TKA. Thus, navigated TKA provided good coronal plane alignment but still lost some aspects of physiologic motion. The loss of tibial screw-home was related to the symmetric femoral condyles, but the posterior translation in flexion was opposite the expected change after TKA with the PCL intact and the ACL excised. Thus, the data confirmed our hypothesis for rotations but not for translations. It is not known whether the standard navigated position provides the best match to physiologic kinematics. One or more of the authors (AAA, AMJB) have received funding by Stryker (Europe). Each author certifies that his or her institution has approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that tissue specimens were obtained in accordance with the laws of France.     

In Vivo Movement of Femoral Flexion Axis of a Single-Radius Total Knee Arthroplasty

The objective of this study was to investigate in vivo femoro-tibial motion using the movement of femoral flexion axis of a single-radius TKA. We examined 20 clinically successful knees with a single-radius posterior stabilized TKA to evaluate the kinematics of deep knee flexion using 2–3-dimensional registration techniques. The mean knee flexion range of motion was 117.8°. The mean rotation of the femoral component was 7.6° external rotation. The mean knee flexion angle at initial post-cam engagement was 55.2°. No paradoxical movement of femoral component was shown until 70° flexion, afterward the femoral component rolled back with flexion. The data showed that the design of this prosthesis might contribute to reduce the paradoxical anterior femoral movement and provide stability in mid-flexion ranges.     

增加胫骨平台后倾角度、后交叉韧带部分松解对全膝关节置换术后膝关节运动影响的实验研究

目的通过增加胫骨平台后倾角度或后交叉韧带（PCL）部分松解对全膝关节置换术（TKA）中屈曲间隙过紧进行处理,分析这两种方法对TKA术后膝关节运动学的影响。方法测量6例新鲜尸体膝关节标本在完整状态下、正常TKA、屈曲间隙过紧、增加胫骨平台后倾角以及PCL部分松解TKA术后膝关节屈曲0°、30°、60°、90°、120°时的前后松弛度、内外翻松弛度、旋转松弛度及最大屈曲度。结果屈曲过紧TKA与正常TKA相比,在屈曲30°、60°、90°和120°时前后松弛度、内外翻松弛度及旋转松弛度均显著较小（P〈0．05）。与屈曲过紧TKA相比,增加胫骨后倾角后,在屈曲30°、60°、90°和120°时前后松弛度、内外翻松弛度和旋转松弛度均明显增大（P〈0．05）。PCL部分松解与屈曲过紧TKA相比,在屈曲30°、60°、90°和120°时前后松弛度明显增加（P〈0．05）;旋转松弛度在屈曲30°、60°、90°时明显增加（P〈0．05）。与PCL部分松解相比,增加胫骨后倾角的内外翻松弛度在屈曲30°、60°、90°时明显较大（P〈0．05）;旋转松弛度在屈曲0°、30°、60°和90°时明显较大（P〈0．05）。屈曲过紧TKA的最大屈曲度（120．4°）与正常TKA（130．3°）及增加胫骨后倾角（131．1°）相比明显较小（P〈0．05）。增加后倾角与PCL部分松解（124．0°）相比,最大屈曲度较大,但差异无统计学意义（P=0．0816）。结论屈曲间隙过紧TKA术后膝关节的前后松弛度、内外翻松弛度、旋转松弛度和最大屈曲度均减小;增加胫骨平台后倾角后,前后松弛度、内外翻松弛度、旋转松弛度和最大屈曲度均明显增大;PCL部分松解仅能明显增大前后松弛度。因此对于TKA术中屈曲紧张的膝关节,增加胫骨平台后倾角比PCL部分松解能更好地改善膝关节的运动学。     

Investigation of in vivo 6DOF total knee arthoplasty kinematics using a dual orthogonal fluoroscopic system.

Fluoroscopic techniques have been recently used to detect in vivo knee joint kinematics. This article presents a technique that uses two fluoroscopes to form a dual orthogonal fluoroscopic system for accurately measuring in vivo 6DOF total knee arthoplasty (TKA) kinematics. The system was rigorously validated and used to investigate in vivo kinematics of 12 patients after cruciate-retaining TKA. In a repeatability study, the pose of two different TKA components was reproduced with standard deviations (SD) of 0.17 mm and 0.57 degrees about all three axes. In an accuracy study, the reproduced component positions were compared to the known component positions. Position and rotation mean errors were all within 0.11 mm and 0.24 degrees, with SD within 0.11 mm and 0.48 degrees, respectively. The results of this study show that the matching process of the imaging system is able to accurately reproduce the spatial positions and orientations of both the femoral and tibial components. For CR TKA patients, a consistent anterior femoral translation was observed with flexion through 45 degrees of flexion, and thereafter, the femur translated posteriorly with further flexion. The medial-lateral translation was measured to be less than 2 mm throughout the entire flexion range. Internal tibial rotation steadily increased through maximum flexion by approximately 6 degrees. Varus rotation was also measured with flexion but had a mean magnitude less than 2.0 degrees. In conclusion, the dual orthogonal fluoroscopic system accurately detects TKA kinematics and is applicable towards other joints of the musculoskeletal system, including the wrist, elbow, shoulder, ankle, and spine.     

Hi-flexion and gender-specific designs fail to provide significant increases in range of motion during cruciate-retaining total knee arthroplasty

The effects of different femoral component designs on intraoperative range of motion were examined in 40 female patients during primary cruciate-retaining (CR) total knee arthroplasty. After complete bone resection and soft tissue balancing, standard CR, high-flexion, and gender-specific knee trials were sequentially inserted, and maximal flexion and extension under gravity were measured using a navigation system. Average maximal flexions were 134.3° for standard CR knees, 136.2° for high-flexion knees, and 136.4° for gender-specific knees. No significant intergroup differences in intraoperative maximal flexion and extension were found (P > .05). High-flexion and gender-specific femoral designs were found to show subtle increases in intraoperative range of motion as compared with the standard design but no significant differences.     

In vivo determination of total knee arthroplasty kinematics: a multicenter analysis of an asymmetrical posterior cruciate retaining total knee arthroplasty

The objective of this study was to determine if consistent posterior femoral rollback of an asymmetrical posterior cruciate retaining (PCR) total knee arthroplasty was mostly influenced by the implant design, surgical technique, or presence of a well-functioning posterior cruciate ligament (PCL). Three-dimensional femorotibial kinematics was determined for 80 subjects implanted by 3 surgeons, and each subject was evaluated under fluoroscopic surveillance during a deep knee bend. All subjects in this present study having an intact PCL had a well-functioning PCR knee and experienced normal kinematic patterns, although less in magnitude than the normal knee. In addition, a surprising finding was that, on average, subjects without a PCL still achieved posterior femoral rollback from full extension to maximum knee flexion. The findings in this study revealed that implant design did contribute to the normal kinematics demonstrated by subjects having this asymmetrical PCR total knee arthroplasty.     

Range of motion of standard and high-flexion posterior stabilized total knee prostheses. A prospective, randomized study

BACKGROUND: The restoration of posterior femoral translation has been shown to be an important factor in enhancing knee flexion after total knee arthroplasty. The purpose of this study was to compare the ranges of motion associated with standard and high-flexion posterior stabilized total knee prostheses in patients managed with simultaneous bilateral total knee arthroplasty. METHODS: Fifty patients (mean age, sixty-eight years) received a standard fixed-bearing knee prosthesis in one knee and a high-flexion fixed-bearing knee prosthesis in the contralateral knee. Two patients were men, and forty-eight were women. At a mean of 2.1 years postoperatively, the patients were assessed clinically and radiographically with use of the knee-rating systems of the Knee Society and The Hospital for Special Surgery. RESULTS: The mean postoperative Hospital for Special Surgery knee score was 90 points for the knees treated with the standard fixed-bearing prosthesis and 89.4 points for those treated with the high-flexion prosthesis. At the time of the final follow-up, the knees with the standard prosthesis had a mean range of motion of 135.8 degrees (range, 105 degrees to 150 degrees ) and those with a high-flexion prosthesis had a mean range of motion of 138.6 degrees (range, 105 degrees to 150 degrees ) (p = 0.41). No knee had aseptic loosening, revision, or osteolysis. CONCLUSIONS: After a minimum duration of follow-up of two years, we found no significant differences between the groups with regard to range of motion or clinical and radiographic parameters, except for posterior femoral condylar offset.     

In vivo kinematic comparison of posterior cruciate-retaining and posterior stabilized total knee arthroplasties under passive and weight-bearing conditions

An in vivo comparison of flexion kinematics for posterior cruciate-retaining (PCR) and posterior stabilized (PS) total knee arthroplasty (TKA) was performed. Twenty patients who underwent bilateral paired TKAs were included in this prospective study. Both PCR and PS prostheses were from the same TKA series with comparable surface geometries, and all were implanted by a single surgeon. Of these 20 patients, 3-dimensional kinematics during flexion could be analyzed using a computer model fitting technique in 18 patients. The follow-up period ranged from 18 to 53 months. In the PCR TKA, an anterior femoral translation from 30 degrees to 60 degrees of flexion was observed in the weight-bearing condition. In contrast, flexion kinematics for the PS TKA was characterized by the maintenance of a constant contact position under weight-bearing conditions and posterior femoral rollback in passive flexion.     

Results of prospective, randomized clinical trials comparing standard and high-flexion posterior-stabilized TKA: a focused review

High-flexion total knee arthroplasty (TKA) designs have been available for several years for patients desiring a greater postoperative flexion. We conducted a focused review on published results of prospective, randomized clinical trials that compared a standard posterior-stabilized TKA with a high-flexion posterior-stabilized TKA design. Follow-up ranged from 1 to 2.7 years. None of the articles included in the review showed a statistical difference between the standard and high-flexion designs in clinical flexion or range of motion. Mean postoperative flexion ranged from 106° to 130° for the standard design and 110° to 128° for the high-flexion design. Based on currently available literature, high-flexion cruciate-substituting TKAs do not appear to provide increased flexion in the short term. The downsides of these designs, such as increased cost, increased bone resection, and early femoral loosening, need to be weighed against the potential long-term improvement in polyethylene wear due to increased conformity in high flexion. Continued follow-up to document these findings will be important.     

Tibiofemoral kinematic analysis of kneeling after total knee arthroplasty

Some surgeons warn against kneeling after total knee arthroplasty (TKA), because limited clinical data exist. We describe the tibiofemoral contact position of TKA components during kneeling in vivo. Ten posterior-substituting (PS) and 10 cruciate-retaining (CR) designs were examined using a radiographic image-matching technique. Movement from standing to kneeling at 90 degrees produced different responses. CR knees translated anteriorly (medial, 4 +/- 4 mm; lateral, 2 +/- 6 mm). PS knees underwent little posterior translation (medial, 0.2 +/- 3 mm; lateral, 1 +/- 4 mm). Movement from 90 degrees to maximum flexion produced femoral posterior translation (CR medial, 5 +/- 4 mm; CR lateral, 5 +/- 4 mm; PS medial, 6 +/- 4 mm; PS lateral, 6 +/- 3 mm). The relationship between tibiofemoral contact position and flexion angle was more variable for CR (r2=.38) than for PS (r2=.64). Knee kinematics was similar to other deep-flexion weight-bearing activities.     

Knee kinematics of high-flexion activities of daily living performed by male Muslims in the Middle East

Full flexion is critical for total knee arthroplasty (TKA) patients in the Middle East, where daily activities require a high range of motion in the lower limb. This study aimed to increase understanding of the knee kinematics of normal Muslim subjects during high-flexion activities of daily living, such as kneeling, Muslim prayer, sitting cross-legged, and squatting. The early postoperative kinematics for a select group of Muslim, high-flexion TKA patients are also reported. Mean curves were compared between the normal group and the TKA group. During kneeling, the average maximum flexion was 141.6° for the normal group and 140.2° for the TKA group. The normal group's maximum and minimum knee angles (flexion, abduction, external rotation) were reported and, with the exception of maximum extension, were not significantly different from the TKA group, despite short postoperative times.