Kinematic Performance of Gradually Variable Radius Posterior-Stabilized Primary TKA During Various Activities: An In Vivo Study Using Fluoroscopy

BackgroundPosterior-stabilized total knee arthroplasty (TKA) with gradually variable radii (G-curve) femoral condylar geometry is now available. It is believed that a G-curve design would lead to more mid-flexion stability leading to reduced incidence of paradoxical anterior slide. The objective of this study was to assess the in vivo kinematics for subjects implanted with this type of TKA under various conditions of daily living.MethodsTibiofemoral kinematics of 35 patients having posterior-stabilized TKA with G-curve design were analyzed using fluoroscopy while performing three activities: weight-bearing deep knee bend, gait, and walking down a ramp. The subjects were assessed for range of motion, condylar translation, axial rotation, cam-spine engagement, and condylar lift-off.ResultsThe average weight-bearing flexion during deep knee bend was 111.4°. On average, the subjects exhibited 5.4 mm of posterior rollback of the lateral condyle and 2.0 mm of the medial condyle from full extension to maximum knee flexion. The femur consistently rotated externally with flexion, and the average axial rotation was 5.2°. Overall movement of the condyles during gait and ramp-down activity was small. No incidence of condylar lift-off was observed.ConclusionSubjects in this study experienced consistent magnitudes of posterior femoral rollback and external rotation of the femur with weight-bearing flexion. The variation is similar to that previously reported for normal knee where the lateral condyle moves consistently posterior compared to the medial condyle. Subjects experienced low overall mid-flexion paradoxical anterior sliding and no incidence of condylar lift-off leading to mid-flexion stability.     

Robotic testing of proximal tibio‐fibular joint kinematics for measuring instability following total knee arthroplasty

Pain secondary to instability in total knee arthroplasty (TKA) has been shown to be major cause of early failure. In this study, we focused on the effect of instability in TKA on the proximal tibio‐fibular joint (PTFJ). We used a robotics model to compare the biomechanics of the PTFJ in the native knee, an appropriately balanced TKA, and an unbalanced TKA. The tibia (n = 5) was mounted to a six‐degree‐of‐freedom force/torque sensor and the femur was moved by a robotic manipulator. Motion at the PTFJ was recorded with a high‐resolution digital camera system. After establishing a neutral position, loading conditions were applied at varying flexion angles (0°, 30°, and 60°). These included: internal/external rotation (0 Nm, ±5 Nm), varus/valgus (0 Nm, ±10 Nm), compression (100 N, 700 N), and posterior drawer (0 N, 100 N). With respect to anterior displacement, external rotation had the largest effect (coefficient = 0.650; p < 0.0001). Polyethylene size as well as the interaction between polyethylene size and flexion consistently showed substantial anterior motion. Flexion and mid‐flexion instability in TKA have been difficult to quantify. While tibio‐femoral kinematics is the main aspect of TKA performance, the effects on adjacent tissues should not be overlooked. Our data show that PTFJ kinematics are affected by the balancing of the TKA. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:47–52, 2011     

Bi‐Cruciate Retaining Total Knee Arthroplasty Does Not Restore Native Tibiofemoral Articular Contact Kinematics During Gait

Bi‐cruciate retaining (BCR) total knee arthroplasty (TKA) design preserves both anterior and posterior cruciate ligaments with the potential to restore normal posterior femoral rollback and joint kinematics. Abnormal knee kinematics and “paradoxical” anterior femoral translation in conventional TKA designs have been suggested as potential causes of patient dissatisfaction. However, there is a paucity of data on the in vivo kinematics and articular contact behavior of BCR‐TKA. This study aimed to investigate in vivo kinematics, articular contact position, and pivot point location of the BCR‐TKA during gait. In vivo kinematics of 30 patients with unilateral BCR‐TKA during treadmill walking was determined using validated dual fluoroscopic imaging tracking technique. The BCR‐TKA exhibited less extension than the normal healthy knee between heel strike and 48% of gait cycle. Although the average external rotation trend observed for BCR TKA was similar to the normal healthy knee, the range of motion was not fully comparable. The lowest point of the medial condyle showed longer anteroposterior translation excursion than the lateral condyle, leading to a lateral‐pivoting pattern in 60% of BCR TKA patients during stance phase. BCR‐TKA demonstrated no statistical significant differences in anterior–posterior translation as well as varus rotation, when compared to normal healthy knees during the stance phase. However, sagittal plane motion and tibiofemoral articular contact characteristics including pivoting patterns were not fully restored in BCR TKA patients during gait, suggesting that BCR TKA does not restore native tibiofemoral articular contact kinematics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1929–1937, 2019     

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.     

Condylar‐Stabilized TKR May Not Fully Compensate for PCL‐Deficiency: An In Vitro Cadaver Study

Increased‐congruency bearing options are widely available in numerous total knee replacement (TKR) systems, with the intended purpose of compensating for posterior‐cruciate ligament (PCL) deficiency. However, their ability to provide adequate stability in this setting has been debated. This in vitro joint simulator study measured changes in knee joint kinematics and stability during passive flexion–extension motions and simulated activities of daily living resulting from TKR with condylar‐stabilized (CS) TKR without a PCL versus cruciate‐retaining (CR) TKR. During passive flexion, the CS TKR resulted in a more posterior tibial positioning than both the intact joint and CR TKR (by 3.4 ± 1.0 mm and 4.8 ± 0.7 mm, respectively). With a posterior tibial force applied, the CS TKR tibia was again significantly more posterior than that of the intact joint and CR TKR (by 4.7 ± 1.3 mm and 5.6 ± 0.8 mm, respectively). Furthermore, there were significant differences in the anterior/posterior kinematics of both TKR with respect to intact knees during gait, and differences between the CS and CR TKR during stair ascent and descent. Overall, there appears to be a reduction in anterior–posterior stability of the PCL‐deficient CS TKR knee, suggesting that contemporary increased‐congruency bearing surface designs may not adequately compensate for the loss of the PCL. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2172–2181, 2019     

In vivo comparison of medialized dome and anatomic patellofemoral geometries using subject‐specific computational modeling

Successful outcome following total knee arthroplasty (TKA) with patella resurfacing is partly determined by the restoration of patellofemoral (PF) function and recovery of the quadriceps mechanism. The current study compared two patellar TKA geometries (medialized dome and anatomic) to determine their impact on PF mechanics and quadriceps function. In‐vivo, subject‐specific patellar mechanics were evaluated using a sequential experimental and modeling approach. First, stereo radiography, marker‐based motion capture, and force plate data were collected for TKA patients (10 dome, 10 anatomic) performing a knee extension and lunge. Second, subject‐specific, whole‐body, musculoskeletal models, including 6 degrees‐of‐freedom (DOF) knee joint kinematics, were created for each subject and activity to predict quadriceps forces. Last, finite element models of each subject and activity were created to predict PF kinematics, patellar loading, moment arm, and patellar tendon angle. Differences in mechanics between dome and anatomic patients were highlighted during load‐bearing (lunge) activity. Anatomic subjects demonstrated greater PF flexion angles (avg. 11 ± 3°) compared to dome subjects during lunge. Similar to the natural knee, contact locations on the patella migrated inferior to superior as the knee flexed in anatomic subjects, but remained relatively superior in dome subjects. Differences in kinematics and contact location likely contributed to altered mechanics with anatomic subjects presenting greater load transfer from the quadriceps to the patellar tendon in deep flexion (>75°), and dome subjects demonstrating larger contact forces during lunge. Although there was substantial patient variability, evaluations of PF mechanics suggested improved quadriceps function and more natural kinematics in the anatomic design. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1910–1918, 2018.

     

Lower limb kinematic alterations during drop vertical jumps in female athletes who have undergone anterior cruciate ligament reconstruction

The aim of this study was to determine if anterior cruciate ligament reconstructed (ACL‐R) female athletes exhibit altered lower limb kinematic profiles during jump landing when compared to a non‐injured age, sex, and activity matched control group. Fourteen ACL‐R and 14 non‐injured control subjects performed 3 vertical drop jump (DVJ) trials. Lower limb kinematics were recorded at 200 Hz. Peak and time‐averaged angular displacements were quantified and utilized for between‐group analysis. The ACL‐R group displayed altered hip joint frontal and transverse plane kinematic alterations, and knee joint frontal and sagittal plane kinematic alterations. Specifically the ACL‐R group displayed an increased adducted (p < 0.05) and internally rotated (p < 0.05) hip joint position, both peak and time‐averaged, following landing. The ACL‐R group also displayed a decreased adducted (p < 0.05) and flexed (p < 0.05) position of the knee joint following landing. The observed aberrant lower limb kinematics could pre‐dispose ACL‐R athletes to potential future knee joint injuries. Further studies are required to determine in a prospective manner whether such deficits increase the incidence of recurrent ACL injury, and whether specific sensorimotor protocols following ACL reconstruction can minimize these kinematic deficits. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:72–78, 2012     

Knee kinematics in medial osteoarthritis during in vivo weight‐bearing activities

Dynamic knee kinematics were analyzed for medial osteoarthritic (OA) knees in three activities, including two types of maximum knee flexion. Continuous x‐ray images of kneeling, squatting, and stair climbing motions were taken using a large flat panel detector. CT‐derived bone models were used for the model registration‐based 3D kinematic measurements. Three‐dimensional joint kinematics and contact locations were determined using two methods: bone‐fixed coordinate systems and by interrogation of CT‐based bone model surfaces. The femur exhibited gradual external rotation with knee flexion for kneeling and squatting activities, and gradual internal rotation with knee extension for stair climbing. From 100° to 120° flexion, contact locations showed a medial pivot pattern similar to normal knees. However, knees with medial OA displayed a femoral internal rotation bias and less posterior translation when compared with normal knees. A classic screw‐home movement was not observed in OA knees near extension. Decreased variability with both activities and methods of calculation were demonstrated for all three activities. In conclusion, the weight‐bearing kinematics of patients with medial OA differs from normal knees. Pathological changes of the articulating surfaces and the ligaments correspond to observed abnormalities in knee kinematics. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1555–1561, 2009     

Customized versus Patient-Sized Cruciate-Retaining Total Knee Arthroplasty: An In Vivo Kinematics Study Using Mobile Fluoroscopy

Background

Historically, knee arthroplasties have been designed using average patient anatomy. Recent advances in imaging and manufacturing have facilitated the development of customized prostheses designed to fit the unique shape of individual patients. The purpose of this study is to determine if improving implant design through customized total knee arthroplasty (TKA) improves kinematic function.

Kinematics of medial osteoarthritic knees before and after posterior cruciate ligament retaining total knee arthroplasty

Total knee arthroplasty (TKA) is a widely accepted surgical procedure for the treatment of patients with end‐stage osteoarthritis (OA). However, the function of the knee is not always fully recovered after TKA. We used a dual fluoroscopic imaging system to evaluate the in vivo kinematics of the knee with medial compartment OA before and after a posterior cruciate ligament‐retaining TKA (PCR‐TKA) during weight‐bearing knee flexion, and compared the results to those of normal knees. The OA knees displayed similar internal/external tibial rotation to normal knees. However, the OA knees had less overall posterior femoral translation relative to the tibia between 0° and 105° flexion and more varus knee rotation between 0° and 45° flexion, than in the normal knees. Additionally, in the OA knees the femur was located more medially than in the normal knees, particularly between 30° and 60° flexion. After PCR‐TKA, the knee kinematics were not restored to normal. The overall internal tibial rotation and posterior femoral translation between 0° and 105° knee flexion were dramatically reduced. Additionally, PCR‐TKA introduced an abnormal anterior femoral translation during early knee flexion, and the femur was located lateral to the tibia throughout weight‐bearing flexion. The data help understand the biomechanical functions of the knee with medial compartment OA before and after contemporary PCR‐TKA. They may also be useful for improvement of future prostheses designs and surgical techniques in treatment of knees with end‐stage OA. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:40–46, 2011     

Mechanics of post‐cam engagement during simulated dynamic activity

Posterior‐stabilized (PS) total knee arthroplasty (TKA) components employ a tibial post and femoral cam mechanism to guide anteroposterior knee motion in lieu of the posterior cruciate ligament. Some PS TKA patients report a clicking sensation when the post and cam engage, while severe wear and fracture of the post; we hypothesize that these complications are associated with excessive impact velocity at engagement. We evaluated the effect of implant design on engagement dynamics of the post‐cam mechanism and resulting polyethylene stresses during dynamic activity. In vitro simulation of a knee bend activity was performed for four cadaveric specimens implanted with PS TKA components. Post‐cam engagement velocity and flexion angle at initial contact were determined. The experimental data were used to validate computational predictions of PS mechanics using the same loading conditions. A lower limb model was subsequently utilized to compare engagement mechanics of eight TKA designs, relating differences between implants to geometric design features. Flexion angle and post‐cam velocity at engagement demonstrated considerable ranges among designs (23°–89°, and 0.05–0.22 mm/°, respectively). Post‐cam velocity was correlated (r = 0.89) with tibiofemoral condylar design features. Condylar geometry, in addition to post‐cam geometry, played a significant role in minimizing engagement velocity and forces and stresses in the post. This analysis guides selection and design of PS implants that facilitate smooth post‐cam engagement and reduce edge loading of the post. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1438–1446, 2013     

Evaluation of patellofemoral joint in ADVANCE® Medial-pivot total knee arthroplasty

Purpose

ADVANCE® Medial Pivot (MP) (Wright Medical) total knee arthroplasty (TKA) was established to replicate normal tibio-femoral knee joint kinematics, however, its influence on the patello-femoral (PF) joint is unclear. The purpose in this study was to assess the PF joint conditions in Advance MP TKA, via radiography and three-dimensional image-matching software.

Methods

Ten subjects with osteoarthritis were treated with the ADVANCE MP TKA. Pre-operatively and one month after surgery, skyline views at 30, 60, and 90° of flexion were taken, and patella shift and tilt were measured. With 2D–3D registration techniques using software, implant orientations were matched with the pre-operative CT and changes in the anterior part of the femoral prosthesis, condylar twist angle (CTA) for femoral rotation, and tibial rotation were evaluated. The relationships between morphological and rotational changes were evaluated.

Results

There were significant differences in patella tilt at 60° and patella shift at all angles between pre- and post-operation (p < 0.05). No correlation was found between morphological changes in the anterior femur with patella tilt and shift. A positive correlation between postoperative CTA and patella shift at 90° was found (p < 0.05); however, no correlation was found between rotational alignment of the tibial component and patella tilt and shift.

Conclusions

ADVANCE MP TKA changed patello-femoral joint kinematics, compared to that found before surgery. The kinematic features were mainly due to the design concepts for tibio-femoral joint motion, indicating the difficulty to reproduce normal patello-femoral joint kinematics after TKA.     

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.     

Differences in patellofemoral kinematics between weight‐bearing and non‐weight‐bearing conditions in patients with patellofemoral pain

Patellar maltracking is thought to be one source of patellofemoral pain. Measurements of patellar tracking are frequently obtained during non‐weight‐bearing knee extension; however, pain typically arises during highly loaded activities, such as squatting, stair climbing, and running. It is unclear whether patellofemoral joint kinematics during lightly loaded tasks replicate patellofemoral joint motion during weight‐bearing activities. The purpose of this study was to: evaluate differences between upright, weight‐bearing and supine, non‐weight‐bearing joint kinematics in patients with patellofemoral pain; and evaluate whether the kinematics in subjects with maltracking respond differently to weight‐bearing than those in nonmaltrackers. We used real‐time magnetic resonance imaging to visualize the patellofemoral joint during dynamic knee extension from 30° to 0° of knee flexion during two conditions: upright, weight‐bearing and supine, non‐weight‐bearing. We compared patellofemoral kinematics measured from the images. The patella translated more laterally during the supine task compared to the weight‐bearing task for knee flexion angles between 0° and 5° (p = 0.001). The kinematics of the maltrackers responded differently to joint loading than those of the non‐maltrackers. In subjects with excessive lateral patellar translation, the patella translated more laterally during upright, weight‐bearing knee extension for knee flexion angles between 25° and 30° (p = 0.001). However, in subjects with normal patellar translation, the patella translated more laterally during supine, non‐weight‐bearing knee extension near full extension (p = 0.001). These results suggest that patellofemoral kinematics measured during supine, unloaded tasks do not accurately represent the joint motion during weight‐bearing activities. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:312–317, 2011     

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.     

Comparison of posterior-stabilized,cruciate-retaining,and medial-stabilized knee implant motion during gait

Accurate knowledge of knee joint motion is needed to evaluate the effects of implant design on functional performance and component wear. We conducted a randomized controlled trial to measure and compare 6-degree-of-freedom (6-DOF) kinematics and femoral condylar motion of posterior-stabilized (PS), cruciate-retaining (CR), and medial-stabilized (MS) knee implant designs for one cycle of walking. A mobile biplane X-ray imaging system was used to accurately measure 6-DOF tibiofemoral motion as patients implanted with PS (n = 23), CR (n = 25), or MS (n = 26) knees walked over ground at their self-selected speeds. Knee flexion angle did not differ significantly between the three designs. Relative movements of the femoral and tibial components were generally similar for PS and CR with significant differences observed only for anterior tibial drawer. Knee kinematic profiles measured for MS were appreciably different: external rotation and abduction of the tibia were increased while peak-to-peak anterior drawer was significantly reduced for MS compared with PS and CR. Anterior-posterior drawer and medial-lateral shift of the tibia were strongly coupled to internal-external rotation for MS, as was anterior-posterior translation of the contact center in the lateral compartment. MS exhibited the least amount of paradoxical anterior translation of the femur relative to the tibia during knee flexion. The joint center of rotation in the transverse plane was located in the lateral compartment for PS and CR and in the medial compartment for MS. Substantial differences were evident in 6-DOF knee kinematics between the healthy knee and all three prosthetic designs. Overall, knee kinematic profiles observed for MS resemble those of the healthy joint more closely than PS and CR.     

Kinematic analysis of kneeling in cruciate‐retaining and posterior‐stabilized total knee arthroplasties

Kneeling is an important function of the knee for many activities of daily living. In this study, we evaluated the in vivo kinematics of kneeling after total knee arthroplasty (TKA) using radiographic based image‐matching techniques. Kneeling from 90 to 120° of knee flexion produced a posterior femoral rollback after both cruciate‐retaining and posterior‐stabilized TKA. It could be assumed that the posterior cruciate ligament and the post‐cam mechanism were functioning. The posterior‐stabilized TKA design had contact regions located far posterior on the tibial insert in comparison to the cruciate‐retaining TKA. Specifically, the lateral femoral condyle in posterior‐stabilized TKA translated to the posterior edge of the tibial surface, although there was no finding of subluxation. After posterior‐stabilized TKA, the contact position of the post‐cam translated to the posterior medial corner of the post with external rotation of the femoral component. Because edge loading can induce accelerated polyethylene wear, the configuration of the post‐cam mechanism should be designed to provide a larger contact area when the femoral component rotates. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:435–442, 2008     

Dynamic activity dependence of in vivo normal knee kinematics

Dynamic knee kinematics were analyzed for normal knees in three activities, including two different types of maximum knee flexion. Continuous X‐ray images of kneel, squat, and stair climb motions were taken using a large flat panel detector. CT‐derived bone models were used for model registration‐based 3D kinematic measurement. Three‐dimensional joint kinematics and contact locations were determined using three methods: bone‐fixed coordinate systems, interrogation of CT‐based bone model surfaces, and interrogation of MR‐based articular cartilage model surfaces. The femur exhibited gradual external rotation throughout the flexion range. Tibiofemoral contact exhibited external rotation, with contact locations translating posterior while maintaining 15° to 20° external rotation from 20° to 80° of flexion. From 80° to maximum flexion, contact locations showed a medial pivot pattern. Kinematics based on bone‐fixed coordinate systems differed from kinematics based on interrogation of CT and MR surfaces. Knee kinematics varied significantly by activity, especially in deep flexion. No posterior subluxation occurred for either femoral condyle in maximum knee flexion. Normal knees accommodate a range of motions during various activities while maintaining geometric joint congruency. © Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:428–434, 2008     

股骨后髁偏心距在全膝关节置换术中的意义

股骨后髁偏心距(PCO)这一概念由Bellmans于2002年率先提出,最早被认为与全膝关节置换术(TKA)后膝关节屈曲度相关。目前,PCO的测量方法主要包括4种：X线测量法简便易行,但因其忽略了股骨内外侧髁的不对称性,在原理上存在一定缺陷;CT、MRI法不受投照角度限制,但假体金属伪影的干扰不可忽略;影像学结合术中软骨厚度测量最为精确,但操作复杂并且主观性较强。PCO在TKA术中有着重要的临床意义：对于后交叉韧带保留型TKA,PCO通过影响股骨与胫骨撞击的旋转半径,使得膝关节最大屈曲度与之正相关。而在后交叉韧带替代型TKA中却没有这种关系,这可能与膝关节后方软组织的阻挡作用以及膝关节前方伸膝装置的限制作用有关。此外,PCO的改变会影响屈曲间隙,从而影响膝关节稳定性特别是屈曲位和半屈位的稳定性。这种改变同样会影响膝关节的解剖学结构及生物力学结构,进而有可能导致骨溶解及假体松动。过大的PCO会增加后方关节囊的紧张程度,造成伸直间隙的减小,带来膝关节屈曲挛缩的风险。因此在TKA术中,临床工作者有必要尽可能将PCO恢复到术前状态,以最大限度避免相应不良后果的发生。本文就PCO在TKA术中的临床意义作以综述。