Patellar morphology and femoral component geometry influence patellofemoral contact stress in total knee arthroplasty without patellar resurfacing

Journal of Biomechanics

Maquer²,

Elankumaran

et al. 2016

a b s t r a c tCurrent homogenized finite element (hFE) models of the patella lack a validated material law and mostly overlook trabecular anisotropy. The objective of this study was to identify the elastic constants of patellar trabecular bone. Using μCT scans of 20 fresh-frozen cadaveric patellae, we virtually extracted 200 trabecular cubes (5.3 mm side length). Bone volume fraction and fabric tensor were measured. The elastic constants were identified from six independent load cases using micro finite element (μFE) analyses. Both anisotropic and isotropic material laws were considered. The elastic constants were validated by comparing stiffness, strain and stress between hFE and μFE predictions of 18 patellar sections and six load cases. The hFE section models were built from μCT (anisotropic law) and CT (isotropic law) scans.The homogenized anisotropic model induced less error (13 7 5%) in the global stiffness prediction than the isotropic one (18 7 6%), and less error in the prediction of local apparent strain, stress, and strain energy, compared to the isotropic one. This validated hFE model could be used for future applications, either with the anisotropic constants, or with the isotropic ones when the trabecular fabric is unavailable.

Section: Introductionmentioning

confidence: 99%

Identification of elastic properties of human patellae using micro-finite element analysis

Journal of Biomechanics

Maquer²,

Elankumaran

et al. 2016

“…The geometry of each patella was extracted from segmented μCT scans, obtained during a previous study [7] , and imported to Geomagic (Geomagic, Inc., Morrisville, North Carolina, USA) to create non-uniform rational Bspline (NURBS) surfaces. To simulate non-resurfaced cases, we added a cartilage layer for each patella by a uniform extrusion (3 mm) of the posterior articular surface of the patellar bone [6] . To simulate the resurfaced cases, we replicated recommendations of the manufacturer (Symbios, Yverdon-les-Bain, Switzerland).…”

Section: Methodsmentioning

confidence: 99%

“…However, literature is lacking a validated patellar material law for accurate strain predictions. Currently, the existing patellar numerical homogenized models (hFE) rely on isotropic material laws obtained from other anatomical sites, such as femora or vertebra [3,5,6] In a previous study, we identified and validated a patellar material law based on morphology-elasticity relationship by means * Corresponding author.…”

Section: Introductionmentioning

confidence: 99%

Importance of trabecular anisotropy in finite element predictions of patellar strain after Total Knee Arthroplasty

Medical Engineering & Physics

Pioletti

Terrier

2017

a b s t r a c t Patellar fracture and anterior knee pain remain major complications after Total Knee Arthroplasty (TKA). Patient-specific finite element (FE) models should help improve understanding of these complications through estimation of joint and bone mechanics. However, sensitivity of predictions on modeling techniques and approaches is not fully investigated. In particular, the importance of patellar bone anisotropy, usually omitted in FE models, on strain prediction is still unknown. The objective of this study was thus to estimate the influence of modeling patellar trabecular anisotropy on prediction of patellar strain in TKA models.We compared FE-derived strain predictions with isotopic and anisotropic material properties using 17 validated FE models of the patella after TKA. We considered both non-resurfaced and resurfaced patellae, in a load-bearing TKA joint. We evaluated and compared the bone volume above a strain threshold and, in addition, estimated if the difference in isotopic and anisotropic predictions was consistent between patellae of different average bone volume fraction.Compared to the anisotropic reference, the isotropic prediction of strained volume was 3.7 ± 1.8 times higher for non-resurfaced patellae and 1.5 ± 0.4 times for resurfaced patellae. This difference was higher for patellae with lower average bone volume fraction.This study indicates that strain predictions acquired via isotropic patellar FE models should be interpreted with caution, especially when patellae of different average bone volume fraction are compared.

“…In vivo (Carpenter et al, 2009;Sharma et al, 2012), in vitro (Lie et al, 2005;Matsuda et al, 1997;Merican et al, 2014) and in silico (Amirouche et al, 2013;Fitzpatrick et al, 2011;Takahashi et al, 2012) studies have shown that TKA leads to significant changes in patellar kinematics, forces acting on the patella, and resulting bone strain in comparison with the intact knee. One of the possible causes of these changes can be related to a surgical technique influencing the positioning of the prosthetic components, their rotation around the joint axes, and the amount of bone cut.…”

Section: Introductionmentioning

confidence: 99%

“…Such knowledge in combination with a patientspecific numerical model would help to improve patellar resection technique during surgery planning. Moreover, all numerical models predicting patellar bone strain assign elastic properties measured on other bones than the patella (Fitzpatrick et al, 2011;Ho et al, 2014;Takahashi et al, 2012) due to the limited number of studies focused on the measuring of patellar mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

A patient-specific model of total knee arthroplasty to estimate patellar strain: A case study

Arami

Becce³

et al. 2016

Clinical Biomechanics

Background: Inappropriate patellar cut during total knee arthroplasty can lead to patellar complications due to increased bone strain. In this study, we evaluated patellar bone strain of a patient who had a deeper patellar cut than the recommended. Methods: A patient-specific model based on patient preoperative data was created. The model was decoupled into two levels: knee and patella. The knee model predicted kinematics and forces on the patella during squat movement. The patella model used these values to predict bone strain after total knee arthroplasty. Mechanical properties of the patellar bone were identified with micro-finite element modeling testing of cadaveric samples. The model was validated with a robotic knee simulator and postoperative X-rays. For this patient, we compared the deeper patellar cut depth to the recommended one, and evaluated patellar bone volume with octahedral shear strain above 1%. Findings: Model predictions were consistent with experimental measurements of the robotic knee simulator and postoperative X-rays. Compared to the recommended cut, the deeper cut increased the critical strain bone volume, but by less than 3% of total patellar volume. Interpretation: We thus conclude that the predicted increase in patellar strain should be within an acceptable range, since this patient had no complaints 8 months after surgery. This validated patient-specific model will later be used to address other questions on groups of patients, to eventually improve surgical planning and outcome of total knee arthroplasty.