Three‐dimensional patellar motion at the natural knee during passive flexion/extension. An in vitro study

Patellar maltracking may result in many patellofemoral joint (PFJ) disorders in the natural and replaced knee. The literature providing quantitative reference for normal PFJ kinematics according to which patellar maltracking could be identified is still limited. The aim of this study was to measure in vitro accurately all six‐degrees‐of‐freedom of patellar motion with respect to the femur and tibia on 20 normal specimens. A state‐of‐the‐art knee navigation system, suitably adapted for this study aim, was used. Anatomical reference frames were defined for the femur, tibia, and patella according to international recommendations. PFJ flexion, tilt, rotation, and translations were calculated in addition to standard tibiofemoral joint (TFJ) kinematics. All motion patterns were found to be generally repeatable intra‐/interspecimens. PFJ flexion was 62% of the corresponding TFJ flexion range; tilt and translations along femoral mediolateral and tibial proximodistal axes during TFJ flexion were found with medial, lateral, and distal trends and within 12°, 6 and 9 mm, respectively. No clear pattern for PFJ rotation was observed. These results concur with comparable reports from the literature and contribute to the controversial knowledge on normal PFJ kinematics. Their consistence provides fundamental information to understand orthopedic treatment of the knee and for possible relevant measurements intraoperatively. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1426–1431, 2009     

Patellofemoral function after total knee arthroplasty: gender-related differences

The purpose of the study was to evaluate patellofemoral results in 2 comparable groups of 50 patients, men and women, undergoing total knee arthroplasty. The average follow-up was 6 years. The implant was posteriorly stabilized with a dome patellar arthroplasty. The patients were studied using Knee Society knee and functional scores and the Hospital for Special Surgery (HSS) patellar score. Radiologic study included standard and weight-bearing axial views and a computed tomographic scan to assess component rotation. The 2 groups achieved satisfactory and similar knee scores; women had a significantly lower functional and patellar scores. The incidence of lateral patellar tilt, subluxation, and lateral impingement was decreased in weight-bearing axial views compared with non-weight bearing. Medial bony impingement was evident only in weight-bearing views and correlated with pain (P < .05).     

Patellofemoral joint contact forces during activities with high knee flexion

The patellofemoral (PF) joint plays an essential role in knee function, but little is known about the in vivo loading conditions at the joint. We hypothesized that the forces at the PF joint exceed the tibiofemoral (TF) forces during activities with high knee flexion. Motion analysis was performed in two patients with telemetric knee implants during walking, stair climbing, sit‐to‐stand, and squat. TF and PF forces were calculated using a musculoskeletal model, which was validated against the simultaneously measured in vivo TF forces, with mean errors of 10% and 21% for the two subjects. The in vivo peak TF forces of 2.9–3.4 bodyweight (BW) varied little across activities, while the peak PF forces showed significant variability, ranging from less than 1 BW during walking to more than 3 BW during high flexion activities, exceeding the TF forces. Together with previous in vivo measurements at the hip and knee, the PF forces determined here provide evidence that peak forces across these joints reach values of around 3 BW during high flexion activities, also suggesting that the in vivo loading conditions at the knee can only be fully understood if the forces at the TF and the PF joints are considered together. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:408–415, 2012     

Simulation of patella alta and the implications for in vitro patellar tracking in the ovine stifle joint

Patella alta is associated with adverse cartilage adaptations, patellofemoral pain, and instability. It is defined by a relatively long patellar tendon and patella positioned in a more proximal location within the patellar groove of the femur. This study used the ovine stifle joint model to investigate the effect of patellar tendon lengthening on the 3D passive kinematics of the patellofemoral and tibiofemoral joints. Eight patellar tendons were lengthened in 2 mm increments up to a maximum of 12 mm (20%) using a device placed in series with the transected patellar tendon. Three‐dimensional kinematics were measured in the intact joint and at each increment of patellar tendon length (L_T) during passively induced tibiofemoral flexion. Patellar flexion angle was linearly correlated with tibial flexion angle in the intact joint, and this correlation persisted after tendon lengthening (R = 0.897–0.965, p < 0.01). Patellofemoral kinematics expressed as a function of tibial flexion angle were significantly altered by L_T increases >9%. In contrast, when patellofemoral kinematics were expressed as a function of patellar flexion angle they were not significantly altered by increases in L_T. Tibiofemoral kinematics were not affected by the L_T increases. These results demonstrate that for a given tibial flexion angle, patellar tendon lengthening alters the patellar flexion angle. However, for a given patellar flexion angle, the orientation of the patella in the remaining five degrees of freedom is unchanged, implying a repeatable path of patellar motion. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1789–1797, 2012     

Comparison of patellar bone strain in the natural and implanted knee during simulated deep flexion

Instances of anterior knee pain and patellar fracture are significant complications following total knee replacement (TKR). Bone strain measured in the patella can provide an indication of patellar fracture risk and may also be related to anterior knee pain. The objective of this study was to develop subject‐specific finite element models of the patellofemoral (PF) joint including density‐mapped material properties to gain insight into the patellar bone strain distribution in the natural and implanted knee. In eight subjects, the volume of bone experiencing strains >0.5% in the implanted condition was ～200% larger, on average, than the natural condition. An inverse relationship with a correlation of ?0.74 was established between postoperative bone volume and strain in the implanted specimens, suggesting that patellar geometry may be a useful indicator of postoperative strain. Comparing strains between regions (superior, inferior, medial, and lateral), it was found that although highly strained bone was evenly distributed between medial and lateral regions in the natural case, the implanted specimens demonstrated significantly larger volumes of highly strained bone medially as a result of substantially lower modulus bone in the medial compartment. Understanding distributions of PF strain may aid in preoperative identification of those patients at risk for patellar fracture or anterior knee pain, guidance regarding altered component placement for at‐risk patients, and design of components considering the implications of PF load transfer and patellar strain distribution. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:232–239, 2011     

Computer-Assisted Navigation in Patellofemoral Arthroplasty: a New Technique to Improve Rotational Position of the Trochlea

Background

Maltracking or subluxation is one of the complications of patellofemoral arthroplasty.

Questions/Purposes

We questioned whether the computed navigation system can improve patellar tracking in patients with patellofemoral arthroplasty (PFA).

Methods

Between 2007 and 2010 we performed 15 patellofemoral arthroplasties using the Ceraver PFA and navigation assistance. Fifteen other patients underwent surgery without navigation during the same period and acted as a control group. The rotation of the native trochlea as measured using the epicondylar line as a reference before surgery and the rotation of the trochlear component and the trochlear twist angle were assessed with computed tomography (CT) scan after surgery.

Results

The mean follow-up was 3 years (range, 2–5 years). The group with navigation had no patellofemoral complications and better clinical scores. The group without navigation had abnormal patellofemoral tracking in 5 of the 15 patients. CT scan demonstrated excessive internal component rotation, as compared with patients without complications. This excessive internal rotation was proportional to the severity of the patellofemoral maltracking.

Conclusions

The short-term results suggest that navigation can lead to better trochlear rotation which, in our hands, is associated with fewer cases of patellar maltracking and better overall clinical scores.

Electronic supplementary material

The online version of this article (doi:10.1007/s11420-013-9328-x) contains supplementary material, which is available to authorized users.     

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     

Sectioning the medial patellofemoral ligament alters patellofemoral joint kinematics and contact mechanics

Medial patellofemoral ligament (MPFL) disruption may alter patellofemoral joint (PFJ) kinematics and contact mechanics, potentially causing pain and joint degeneration. In this controlled laboratory study, we investigated the hypothesis that MPFL transection would change patellar tracking and PFJ contact pressures and increase the distance between the attachment points of the MPFL. Eight fresh frozen dissected cadaveric knees were mounted in a rig with the quadriceps and ITB loaded to 205 N. An optical tracking system measured joint kinematics, and pressure sensitive film between the patella and trochlea measured PFJ contact pressures. Length patterns of the distance between the femoral and patellar attachments of the MPFL were measured using a suture led to a linear displacement transducer. Measurements were repeated with the MPFL intact and following MPFL transection. A significant increase in the distance between the patellar and femoral MPFL attachment points was noted following transection (p < 0.05). MPFL transection resulted in significantly increased lateral translation and lateral tilt of the patella in early flexion (p < 0.05). Peak and mean medial PFJ contact pressures were significantly reduced and peak lateral contact pressures significantly elevated in early knee flexion following MPFL transection (p < 0.05). MPFL transection resulted in significant alterations to PFJ tracking and contact pressures, which may affect articular cartilage health. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1423–1429, 2013     

Influence of Patellar Morphology Classified by Wiberg Classification on Knee Joint Function and Patellofemoral Tracking After Total Knee Arthroplasty Without Patellar Resurfacing

BackgroundTo evaluate the influence of patellar morphology on knee joint function and patellofemoral tracking in patients with primary osteoarthritis after total knee arthroplasty (TKA) without patellar resurfacing.MethodsWe performed a retrospective study of 156 patients with primary osteoarthritis who underwent TKA without patellar resurfacing from April 2018 to July 2019. As per Wiberg classification, patients were divided into Wiberg type I (group A, n = 38), II (group B, n = 88), and III (group C, n = 30) groups. The clinical data, postoperative follow-up data, and radiological data between three groups were compared.ResultsThere was no statistically significant difference in the HSS score and Feller score between the three groups before surgery and at each follow-up point after surgery (P > .05). At the last follow-up, there were no significant differences in the height and relative thickness of the patella between the three groups (P > .05). However, the incidence of anterior knee pain was significantly higher in group C than in the group B (P < .05). The patellar tilt angle was significantly larger in group C than in the groups A and B (both P < .05). The patellar facet angle was significantly larger in group A than in group B and C, which was also significantly larger in group B than in group C (both P < .05).ConclusionPatients with three different morphologic types of the patella both exhibited improved knee joint function after TKA, however, patients with Wiberg type Ⅲ patella were more prone to have poor patellofemoral tracking and anterior knee pain after surgery.     

Predicting three‐dimensional patellofemoral kinematics from static imaging‐based alignment measures

Patellofemoral pain syndrome causes significant discomfort and disability among much of the general population. Despite recent breakthroughs in dynamic three‐dimensional imaging technologies to assess pathological patellofemoral motion, such tools remain costly for clinical diagnostics applications. Thus, this study investigated whether three‐dimensional patellofemoral kinematics could be predicted from routine two‐dimensional static measures of patellofemoral joint alignment quantified from magnetic resonance imaging (MRI) data acquired in full knee extension. Twenty‐six volunteers clinically diagnosed with patellofemoral pain (19 F/7 M, 25.9 ± 11.1 years) and 26 control subjects (19 F/7 M, 25.3 ± 7.7 years) were included in this IRB‐approved study. Static three‐dimensional sagittal T1‐weighted gradient recall echo and dynamic MRI scans were acquired. For the dynamic image acquisition, subjects cyclically flexed and extended their knee (at 30 cycles/min) while a full cine‐phase contrast MRI set (24 time frames of anatomic images and x‐, y‐, and z‐velocity images) was acquired. From these data, static measures of patellofemoral alignment and three‐dimensional patellofemoral kinematics were derived. Single and multiple regressions between static and kinematic variables were evaluated. Although shown reliable, the static MRI measures could only partially predict patellofemoral kinematics, with r²‐values ranging from 16% to 77%. This makes it imperitave that the current precise, accurate, 3D, dynamic imaging techniques be translated into clinical tools. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 441–447, 2013     

The effect of an augmentation patella prosthesis versus patelloplasty on revision patellar kinematics and quadriceps tendon force: an ex vivo study

The purpose of this study was to assess the effect of 2 revision reconstructive interventions on patellofemoral joint mechanics in comparison to control. We flexed 8 cadaver knee specimens from 0 degrees to 60 degrees of flexion in a test rig designed to simulate weight-bearing flexion and extension (Oxford rig). Quadriceps tendon extensor force and patellar kinematics were recorded for control total knee arthroplasty (TKA) (normal primary TKA with patella resurfaced) and then for each of the 2 revision patellar interventions (after patelloplasty of typical revision knee patellar bone defect to leave a simple bony shell, and after TKA with augmentation patella resurfacing). Our results demonstrate that patellar kinematics and quadriceps extensor force are optimized when the patella is reconstructed to normal anteroposterior thickness.     

In vivo kinematics of the ACL during weight-bearing knee flexion.

No study has investigated the three-dimensional morphological changes of the anterior cruciate ligament (ACL) during functional activities in vivo. The purpose of this study was to analyze the elongation, rotation (twist), and orientation of the ACL during weight-bearing flexion in five human subjects using dual-orthogonal fluoroscopic images and MR image-based computer models. The ACL consistently decreased in length with flexion. At 90 degrees , the length decreased by 10% compared to its length at full extension. The ACL twisted internally by only 20 degrees at 30 degrees of flexion. The ACL was oriented more vertically (approximately 60 degrees ) and slightly laterally (approximately 10 degrees ) at low flexion angles. These data on in vivo ligament elongation demonstrate that the ACL plays a more important role in lower flexion angles than at higher flexion angles during weight-bearing flexion. These data also suggest that successful ACL reconstruction should not only restore the ligament's elongation behavior, but also its rotational and orientation characteristics, so that normal ACL biomechanics are restored.     

Onlay Patellofemoral Arthroplasty in Patients With Isolated Patellofemoral Arthritis: A Systematic Review

BackgroundPatellofemoral arthroplasty (PFA) for isolated patellofemoral osteoarthritis (OA) remains controversial due to variable postoperative outcomes and high failure rates. Second-generation (2G) onlay prostheses have been associated with improved postoperative outcomes. This systematic review was performed to assess the current overall survivorship and functional outcomes of 2G PFA.MethodsA search was performed using PubMed, Cochrane Library, EMBASE, and Google Scholar. Thirty-three studies published in the last 15 years (2005-2020) were included; of these 22 studies reported patient-reported outcome measures. Operative and nonoperative complications were analyzed. Pooled statistical analysis was performed for survivorship and functional scores using Excel 2016 and Stata 13.ResultsThe mean age of the patients was 59.7. When analyzing all studies, weighted survival at mean follow-up of 5.52 was 87.72%. Subanalysis of studies with minimum 5 years of follow up showed a survival of 94.24%. Fifteen studies reported Oxford Knee Score with a weighted mean postoperative Oxford Knee Score of 33.59. Mean American Knee Society Score pain was 79.7 while mean American Knee Society Score function was 79.3. The most common operative complication was OA progression for all implants. The percentage of revisions and conversions reported after analyzing all studies was 1.37% and 7.82% respectively.ConclusionSafe and acceptable results of functional outcomes and PFA survivorship can result from 2G PFAs at both short and mid-term follow-up for patients with isolated patellofemoral OA. However, long-term follow-up outcomes are still pending for the newer implants. More extensive studies using standardized functional outcomes and long-term cost benefits should be evaluated.     

国人髌骨的髌股接触率比较及其意义

目的研究正常国人髌骨内外侧软骨面的髌股内外侧接触率,探讨其在国人髌骨假体设计中的意义。方法选取W ibergⅡ型的新鲜冷冻膝关节尸体标本10具,利用Instron 8501生物力学测试仪,模拟生理状态下膝关节屈伸过程,用压敏片法测量各屈膝度髌骨内外侧软骨面的髌股接触面积,计算出髌股接触率。结果各屈膝度髌骨外侧软骨面的髌股接触率明显大于内侧(P<0.01),屈膝早期(20°~60°)甚至高出1~2倍。结论在国人髌股关节假体的设计中,其髌骨假体应以W ibergⅡ型为模板,采取偏心型设计,将更符合国人髌骨的形态学特征。     

Correlating femoral shape with patellar kinematics in patients with patellofemoral pain

The etiology of patellofemoral pain is likely related to pathological femoral shape and soft‐tissue restraints imbalance. These factors may result in various maltracking patterns in patients with patellofemoral pain. Thus, we hypothesized that femoral shape influences patellofemoral kinematics, but that this influence differs between kinematically unique subgroups of patients with patellofemoral pain. 3D MRIs of 30 knees with patellofemoral pain and maltracking (“maltrackers”) and 33 knees of asymptomatic subjects were evaluated, retrospectively. Dynamic MRI was acquired during a flexion‐extension task. Maltrackers were divided into two subgroups (nonlateral and lateral maltrackers) based on previously defined kinematic criteria. Nine measures of femoral trochlear shape and two measures of patellar shape were quantified. These measures were correlated with patellofemoral kinematics. Differences were found in femoral shape between the maltracking and asymptomatic cohorts. Femoral shape parameters were associated with patellar kinematics in patients with patellofemoral pain and maltracking, but the correlations were unique across subgroups within this population. The ability to better categorize patients with patellofemoral pain will likely improve treatment by providing a more specific etiology of maltracking in individual patients. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:865–872, 2010     

ACL forces and knee kinematics produced by axial tibial compression during a passive flexion–extension cycle

Application of axial tibial force to the knee at a fixed flexion angle has been shown to generate ACL force. However, direct measurements of ACL force under an applied axial tibial force have not been reported during a passive flexion–extension cycle. We hypothesized that ACL forces and knee kinematics during knee extension would be significantly different than those during knee flexion, and that ACL removal would significantly increase all kinematic measurements. A 500 N axial tibial force was applied to intact knees during knee flexion–extension between 0° and 50°. Contact force on the sloping lateral tibial plateau produced a coupled internal + valgus rotation of the tibia, anterior tibial displacement, and elevated ACL forces. ACL forces during knee extension were significantly greater than those during knee flexion between 5° and 50°. During knee extension, ACL removal significantly increased anterior tibial displacement between 0° and 50°, valgus rotation between 5° and 50°, and internal tibial rotation between 5° and 15°. With the ACL removed, kinematic measurements during knee extension were significantly greater than those during knee flexion between 5° and 45°. The direction of knee flexion–extension movement is an important variable in determining ACL forces and knee kinematics produced by axial tibial force. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:89–95, 2014.     

Intraoperative passive knee kinematics during total knee arthroplasty surgery

Surgical navigation systems for total knee arthroplasty (TKA) surgery are capable of capturing passive three‐dimensional (3D) angular joint movement patterns intraoperatively. Improved understanding of patient‐specific knee kinematic changes between pre and post‐implant states and their relationship with post‐operative function may be important in optimizing TKA outcomes. However, a comprehensive characterization of the variability among patients has yet to be investigated. The objective of this study was to characterize the variability within frontal plane joint movement patterns intraoperatively during a passive knee flexion exercise. Three hundred and forty patients with severe knee osteoarthritis (OA) received a primary TKA using a navigation system. Passive kinematics were captured prior to (pre‐implant), and after prosthesis insertion (post‐implant). Principal component analysis (PCA) was used to capture characteristic patterns of knee angle kinematics among patients, to identify potential patient subgroups based on these patterns, and to examine the subgroup‐specific changes in these patterns between pre‐ and post‐implant states. The first four extracted patterns explained 99.9% of the diversity within the frontal plane angle patterns among the patients. Post‐implant, the magnitude of the frontal plane angle shifted toward a neutral mechanical axis in all phenotypes, yet subtle pattern (shape of curvature) features of the pre‐implant state persisted. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1611–1619, 2015.     

Evaluation of an external device measuring knee joint rotation: an in vivo study with simultaneous Roentgen stereometric analysis.

An external device ("rottometer") specially designed to measure knee joint rotation was developed and evaluated with respect to its validity. Simultaneous measurements were made with the rottometer and Roentgen stereometric analysis (RSA) in five patients with implanted tantalum markers in the tibia and femur. Measurements of internal and external rotation were made at 90 degrees and 60 degrees of knee flexion using 3, 6 and 9 N m torques. The coefficients of determination (r2) between the results obtained with the rottometer and RSA were around 0.9 for the total rotation. The rottometer consistently overestimated the rotation by about 100% and this systematic error was most constant at 90 degrees flexion for the different torques. The magnitude of this error from soft tissue deformation as well as the rotatory movements in the hip, foot and ankle joints must be considered when using external devices to measure knee rotation in clinical studies. The most accurate registrations were found in 90 degrees flexion with 9 N m force (r2 = 0.94).