Alignment in the varus or valgus outlier range of the tibial component, knee, and limb might adversely affect the long-term results of kinematically aligned total knee arthroplasty (TKA) particularly ...when patients are selected without restricting the degree of preoperative varus-valgus and flexion deformity.
A retrospective review of all patients treated in 2007 with a primary TKA determined the 10-year implant survivorship, yearly revision rate, Oxford Knee Score, and WOMAC. All 222 knees (217 patients) were aligned kinematically using patient-specific instrumentation without restricting the degree of preoperative deformity and with the restoration of the native joint lines and limb alignment. Mechanical alignment criteria categorized the alignments of the tibial component, knee, and limb as in-range or in a varus or valgus outlier range.
The implant survivorship (yearly revision rate) was 97.5% (0.3%) for revision for any reason and 98.4% (0.2%) for aseptic failure. The percentage postoperatively aligned in the varus outlier (valgus outlier) range was 78% (0%) for the angle between the tibial component and mechanical axis of the tibia, 31% (5%) for the tibiofemoral angle of the knee according to the criteria by Ritter et al, and 7% (21%) for the hip-knee-ankle angle of the limb according to the criteria by Parratte et al. Patients grouped in the varus outlier range, valgus outlier range, and in-range had similar implant survival and function scores. The 10-year Oxford Knee Score (48 best) and WOMAC (0 best) averaged 43 and 7 points, respectively.
With the limitation that a large case series unlikely represents the full range of preoperative deformities and native alignments, treatment of patients with kinematically aligned TKA with patient-specific instrumentation without restricting the preoperative deformity did not adversely affect the 10-year implant survival, yearly revision rate, and level of function.
Level III, therapeutic study.
The relative rigid body motions between the femur and the tibia (termed tibiofemoral kinematics) during flexion activities can provide an objective measure of knee function. Clinically meaningful ...tibiofemoral kinematics are defined as the six relative rigid body motions expressed in a joint coordinate system where the motions about and along the axes conform to clinical definitions and are free from kinematic crosstalk errors. To obtain clinically meaningful tibiofemoral kinematics, coordinate systems must meet certain requirements which neither have been explicitly stated nor in fact satisfied in any previous publication known to the author. Starting with the joint coordinate system of Grood and Suntay (1983) where motions conform to clinical definitions, the body-fixed axes must correspond to the functional (i.e. actual) axes in flexion-extension and internal-external axial rotation to avoid kinematic crosstalk errors in rotations and both functional axes must be body-fixed throughout knee flexion. To avoid kinematic crosstalk errors in translations, the origins of the femoral and tibial Cartesian coordinate systems, which serve as stepping stones for computing translations, must lie on the functional body-fixed axes. Neither the paper by Grood and Suntay nor the ISB recommendation (Wu et al., 2002) which adopted the joint coordinate system of Grood and Suntay explains these requirements. Indeed meeting these requirements conflicts with the ISB recommendation thus indicating the need for revision to this recommendation. Future studies where clinically meaningful tibiofemoral kinematics are of interest should be guided by the requirements described herein.
Background
Kinematically aligned TKA restores function by aligning the femoral and tibial components to the normal or prearthritic joint lines of the knee. However, aligning the components to the ...joint lines of the normal knee also aligns the tibial component in varus, creating concern that varus alignment might result in poor function and early catastrophic failure.
Questions/Purposes
We therefore determined whether function and the incidence of catastrophic failure were different when the tibial component, knee, and limb alignment were in a specified normal range, varus outlier, or valgus outlier.
Methods
We prospectively followed all 198 patients (214 knees) who underwent TKAs between February and October 2008. We treated each knee in this cohort of patients with a kinematically aligned, cruciate-retaining prosthesis implanted using patient-specific guides. From a long-leg scanogram, we measured and categorized alignment of the tibial component as in range (≤ 0°) or a varus outlier (> 0°), alignment of the knee as in range (between −2.5° to −7.4° valgus) or a varus (> −2.5°) or valgus (< −7.4°) outlier, and alignment of the limb as in range (0° ± 3°) or a varus (> 3°) or valgus (< −3°) outlier. We assessed function using the Oxford Knee Score and WOMAC™ score, and reported catastrophic failure as the incidence of revision attributable to loosening, wear, and instability of the femoral or tibial components. The minimum followup was 31 months (mean, 38 months; range, 31–43 months).
Results
The mean Oxford Knee Score of 43 and WOMAC™ score of 92 were similar between the three alignment categories. The incidence of catastrophic failure in each alignment category was zero.
Conclusions
Kinematically aligned TKA restores function without catastrophic failure regardless of the alignment category. Because 75% of patients had their tibial component categorized as a varus outlier and also had high function and a zero incidence of catastrophic failure, the concern that kinematic alignment compromises function and places the components at a high risk for catastrophic failure is unfounded and should be of interest to surgeons committed to cutting the tibia perpendicular to the mechanical axis of the tibia.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
Background Gap-balancing is an alignment method for total knee arthroplasty with the goal of creating uniform tension in the periarticular soft-tissue restraints and equal laxities throughout the arc ...of flexion. However, there is little evidence that achieving equal laxities prevents either overly tight or overly loose soft-tissue restraints after total knee arthroplasty. Accordingly, the purpose of the present study was to determine whether the laxities at 0°, 45°, and 90° of flexion are equal in the native knee. Methods Seven different laxities were measured at 0°, 45°, and 90° of flexion in ten fresh-frozen native cadaveric knees (with intact menisci, cartilage, and ligaments) by applying loads of ±5 Nm in varus-valgus rotation, ±3 Nm in internal-external rotation, 100 N in distraction, and ±45 N in anterior-posterior translation with use of a six-degrees-of-freedom load application system. Results The mean laxities (and standard deviations) at 45° of flexion were 1.7° ± 0.6° greater in varus, 0.9° ± 0.4° greater in valgus, 10.2° ± 2.7° greater in internal rotation, 10.1° ± 2.0° greater in external rotation, 1.7 ± 1.0 mm greater in distraction translation, and 3.3 ± 1.5 mm greater in anterior translation than those at 0° of flexion. The mean laxities at 90° of flexion were 2.5° ± 0.8° greater in varus, 1.0° ± 0.5° greater in valgus, 10.0° ± 4.6° greater in internal rotation, 10.1° ± 4.5° greater in external rotation, 1.8 ± 0.7 mm greater in distraction, and 1.6 ± 1.2 mm greater in anterior translation than those at 0° of flexion. The mean anterior translation at 90° of flexion was 1.7 ± 0.9 mm less than that at 45° of flexion. Conclusions Because five of the seven laxities were at least 1.7° or 1.6 mm greater at both 45° and 90° of flexion than those at 0° of flexion, the laxities of the native knee measured in this study are unequal at these flexion angles and therefore do not support the goal of gap-balancing in total knee arthroplasty. Clinical Relevance One possible disadvantage of changing the native laxities at 45° and 90° of flexion to match those at 0° of flexion in a total knee arthroplasty is the overly tight soft-tissue restraints relative to those of the native knee, which patients may perceive as pain, stiffness, and/or limited flexion.
Kinematically aligned total knee arthroplasty (KA TKA) strives to restore the native left to right symmetry of the lower limb; however, the reproducibility of achieving this target is unknown. The ...present study determined the proportion of patients with left to right symmetry and the improvement in patient-reported function after calipered KA TKA.
A review of 562 postoperative scanograms identified 102 patients (53 women) with a KA TKA in one limb, no other skeletal abnormalities in either limb, and symmetrical rotation between limbs on the scanogram. All patients were treated with primary TKA that used caliper measurement of the thicknesses of the femoral bone and tibial bone resections to kinematically align the components. The hip-knee-ankle (HKA) angle, distal lateral femoral angle (DLFA), and proximal medial tibial angle (PMTA) were measured. Patient-reported Oxford Knee Score (OKS) measured preoperative and postoperative functions.
The proportion of patients with a difference in the HKA angle, DLFA, and PMTA between limbs within ±3°, >3° varus, and <−3° valgus was 95%, 2%, and 3%, respectively, for the HKA angle; 97%, 1%, and 2%, respectively, for the DLFA; and 97%, 2%, and 1%, respectively, for the PMTA. The mean OKS improved from 20 preoperatively to 44 points (range 18-48 points) at 15 months postoperatively.
Calipered KA TKA restored native left to right symmetry of the HKA angle, DLFA, and PMTA in nearly all patients with negligible risk of varus alignment of the tibial component with respect to the native tibial joint line. The mean postoperative OKS indicated clinically important improvement in patient-reported function.
One common method to determine tibiofemoral kinematics following total knee replacement (TKR) is to capture single-plane fluoroscopic images of a patient activity and determine anterior-posterior ...(AP) positions of the femoral condyles and internal-external (IE) tibial rotation. Although JointTrack is widely used to analyze such images, precision (i.e. repeatability) in determining AP positions and IE tibial rotations using the two publicly available programs has never been quantified. The objectives were to determine the precision and reproducibility of results using both programs. Fluoroscopic images of 16 patients who performed a weight-bearing deep knee bend following TKR were analyzed. JointTrack Manual (JTM) and JointTrack Machine Learning (JTML) were used to perform 3D model-to-2D image registration after which AP positions of the femoral condyles and IE tibial rotations were determined. Precision in AP positions and IE rotations was quantified. Intraclass correlation coefficients (ICCs) for both repeatability (i.e. intraobserver) and reproducibility (i.e. interobserver) also were determined. Precision using JTM was worse than JTML for AP positions of the medial and lateral femoral condyles (1.0 mm and 0.9 mm vs 0.3 mm and 0.4 mm, respectively;
< 0.001 for both). For IE tibial rotation, precision also was worse using JTM versus JTML (1.1º vs 0.9°,
= 0.010). ICC values for JTML indicated good to excellent agreement (range: 0.82-0.98) whereas ICC values for JTM indicated only moderate to good agreement (range: 0.58-0.88). JTML has better precision and reproducibility than JTM and also is more efficient to use. Therefore, use of JTML over JTM is strongly recommended.
Purpose
Performing kinematically aligned total knee arthroplasty (TKA) with generic instruments is less costly than patient-specific instrumentation; however, the alignment and function with this new ...technique are unknown.
Methods
One hundred and one consecutive patients (101 knees) treated with kinematically aligned TKA, implanted with use of generic instruments, were prospectively followed. The medial collateral ligament was not released. The lateral collateral ligament was released in the 17 % of patients with a fixed valgus deformity. Six measures of alignment were categorized from a scanogram of the extremity, an axial scan of the knee, and an intraoperative measurement. Both the Oxford Knee and WOMAC™ scores were assessed as function. High function was a mean Oxford Knee score >41.
Results
The frequency that patients were categorized as in-range was 93 % for the mechanical alignment of the limb (0° ± 3°), 94 % for the joint line (−3° ± 3°), 57 % for the anatomic axis of the knee (−2.5° ± −7.4° valgus), 4 % for the varus–valgus rotation of the tibial component (≤0° valgus), 98 % for the rotation of the tibial component with respect to the femoral component (0° ± 10°), and 94 % for the intraoperative change in the anterior–posterior distance of the tibia with respect to the femur at 90° of flexion (0 ± 2 mm). The mean OKS score was 42, and WOMAC™ score was 89. For each alignment, the function was the same for patients categorized as an outlier or in-range.
Conclusions
The authors prefer the use of generic instruments to perform kinematically aligned TKA in place of mechanically aligned TKA because five of six alignments were accurate and because high function was restored regardless of whether patients had an alignment categorized as an outlier or in-range.
Level of evidence
IV.
The preceding study reported a 10-year follow-up of 222 kinematically aligned total knee arthroplasties (TKA) performed in 217 patients in 2007. As 35% of tibial components and 8% of limbs were in ...>3° varus, the present study assessed whether this adversely affected reoperation, implant survival, and function at 16 years.
We retrospectively reviewed a single surgeon’s private practice database to determine the patients who underwent reoperation as well as Forgotten Joint Score and Oxford Knee Score.
There were 7 patients who had a major reoperation (revision of a loose tibial component n = 2, and revision of well-fixed component due to stiffness n = 1, patella instability n = 1, pain n = 1, and infection n = 2). There were 5 who had a minor reoperation that retained the components, and 91 patients (94 TKAs) died. Implant survivorship was 93% using reoperation for any reason as the endpoint. The median (interquartile range) Forgotten Joint and Oxford Knee scores were 88 (57 to 100) and 45 (39 to 48) points, respectively.
The kinematically aligned TKA had a 7% reoperation rate at 16 years follow-up, comparable to or lower than reports of mechanically aligned TKA, which supports the concept of the unrestricted version of kinematic alignment in which the patient's prearthritic alignment is fully restored regardless of deformity.
BACKGROUND:Mechanically aligned total knee arthroplasty can create a tight collateral ligament in 0° of extension, instability in a compartment between 0° of extension and 90° of flexion that is ...uncorrectable by collateral ligament release, and changes in limb and knee alignment from normal. The goal of the present study was to calculate the frequency and range of these undesirable consequences.
METHODS:Four methods of mechanically aligned total knee arthroplasty were simulated on fifty normal three-dimensional bone models of the lower extremity from white subjects. Each method resected the distal aspect of the femur and proximal aspect of the tibia perpendicular to their respective mechanical axes. Setting the posterior joint line perpendicular to the anteroposterior axis of the trochlear groove (Method 1), parallel to the transepicondylar axis (Method 2), externally rotated 3° with respect to the posterior condylar axis (Method 3), and parallel to the tibial resection in 90° of flexion with the use of gap-balancing (Method 4) aligned internal-external rotation of the femoral component.
RESULTS:The proportion of total knee arthroplasties requiring a ≥2-mm release of a tight collateral ligament was 34% for the medial collateral ligament and 30% for the lateral collateral ligament. The proportion of total knee arthroplasties with ≥2 mm of instability between 0° of extension and 90° of flexion was 56% in the medial compartment and 6% in the lateral compartment for Method 1, 74% and 6% for Method 2, and 42% and 0% for Method 3. Method 4 did not cause ligamentous instability. The proportion of arthroplasties with a ≥2° change from normal was 58% for limb alignment and 58% for knee alignment.
CONCLUSIONS:Surgeons should be aware that, when using the four methods of mechanically aligning a total knee arthroplasty, they will frequently have to manage a wide range of collateral ligament imbalances that are complex, cumulative, and uncorrectable by collateral ligament release, and a wide range of changes in limb and knee alignment from normal. Patients who perceive these changes in stability, limb alignment, and knee alignment may be dissatisfied and require counseling.
Maximum total point motion (MTPM) of a tibial baseplate at 6 months is used to predict long-term aseptic loosening after total knee arthroplasty. However, the propagation of registration error into ...MTPM for stable baseplates (i.e. baseplates with MTPM < 0.5 mm) manifested as bias (i.e. systematic error) and precision (i.e. random error) has not been quantified and compared to the 6-month stability limit for marker-based and model-based RSA, which have different magnitudes of registration error. To determine the bias and precision in MTPM for stable baseplates, registration errors in six degrees of freedom reported in the literature for marker-based and model-based RSA were applied to an example baseplate using computer simulations. Results revealed that the bias in MTPM for stable baseplates with model-based RSA is three to four times that of marker-based RSA, and that the precision in MTPM for stable baseplates with model-based RSA is double that of marker-based RSA. This assessment of bias and precision in MTPM for stable baseplates led to a method for adjusting the 6-month stability limit for model-based RSA where half the width of the 95% confidence interval on the mean MTPM and the bias in MTPM for marker-based RSA were subtracted from 0.5 mm to compute true MTPM. The bias in MTPM and half the width of the 95% confidence interval on the mean MTPM for model-based RSA were then added to the true MTPM to obtain the adjusted stability limit for model-based RSA which ranged from 0.57 mm to 0.64 mm.
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