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.
Purpose
Surgeons performing total knee arthroplasty (TKA) are interested in the accuracy and time it takes to make the four femoral resections that determine the setting of the femoral component. A ...method for quantifying the error of each resection is the thickness, measured by a caliper, minus the femoral target. The present study tested the hypothesis that the mean deviation of the resection from the femoral target, the percentage of resections with a deviation of ± 0.5, 1.0, 1.5, and 2.0 mm, and the time to complete the femoral cuts were not different between experienced (E) and less-experienced (LE) surgeons performing unrestricted caliper verified kinematically aligned (KA) TKA with manual instruments.
Methods
This study analyzed intraoperative verification worksheets from 203 patients treated by ten E surgeons and 58 patients treated by four LE surgeons. The worksheet recorded (1) the thickness of the femoral target for the distal medial (DM), distal lateral (DL), posterior medial (PM), and posterior lateral (PL) resections and the caliper thickness of the resections with a resolution of 0.5 mm, and (2) the time to complete them. The most accurate resection has a mean difference ± standard deviation of 0 ± 0.0 mm.
Results
The accuracy of the 1044 initial resections (261 patients) was significantly closer to the femoral target for E vs. the LE surgeons: 0.0 ± 0.4 vs. − 0.3 ± 0.5 for the DM, 0.0 ± 0.5 vs. − 0.4 ± 0.6 for the DL, − 0.1 ± 0.5 vs. − 0.2 ± 0.5 PM, and − 0.1 ± 0.5 vs. − 0.4 ± 0.6 for the PL resections (
p
≤ 0.0248). E surgeons completed the femoral resections in 12 min; 5 min faster than LE surgeons (
p
< 0.0001).
Conclusions
Because the mean difference in femoral resections with manual instruments for E vs. LE surgeons was < 0.5 mm which is within the caliper’s resolution, differences in accuracy were not clinically relevant. Surgeons exploring other alignment options and robotic, navigation, and patient-specific instrumentation might find these values helpful when deciding to change.
Level of evidence
III; case–control study.
Purpose
Tibial insert conformity in total knee arthroplasty (TKA) is of interest due to the potential effect on tibiofemoral kinematics. This study determined differences in anterior–posterior ...movements of the femoral condyles, pivot locations, and internal tibial rotation in different arcs of flexion for two implants with different insert conformities in kinematically aligned TKA.
Methods
Twenty-five patients treated with a medial and lateral low-conforming, posterior cruciate ligament (PCL) retaining (LC CR) implant followed by a medial ball-in-socket and flat, lateral PCL sacrificing (B-in-S CS) implant in the contralateral knee underwent single-plane fluoroscopy during a deep knee bend. Analysis following 3D-to-2D image registration determined tibiofemoral kinematics and patients completed validated outcome scores for both knees.
Results
The mean follow-up of 1.6 ± 0.4 years for the knee with the B-in-S CS implant was shorter than the 2.7 ± 1.2 years for the LC CR implant. From 0º to 30º of flexion, a medial pivot occurred with the tibia rotating internally approximately 5º with both implants. From 30º to 90º, the pivot remained medial and internal rotation increased to 10º with the B-in-S CS implant. In contrast, neither femoral condyle moved more than 1 mm with the LC CR implant from 30º to 60º, but from 60º to 90º degrees, a lateral pivot occurred and internal rotation increased. Internal rotation of the tibia on the femur from 0° to maximum flexion occurred about a medial pivot similar to the native knee for the B-in-S CS implant and was 4.5° greater than that of the LC CR implant (10.4° vs 5.9°). There was no difference in the median patient-reported outcome scores between implant designs.
Conclusions
Tibial insert conformity is a primary determinant of a medial or lateral pivot during a deep knee bend. One explanation for the transition from a medial to lateral pivot between 30º and 60º with the LC CR implant is the chock-block effect of the insert’s posterolateral upslope which impedes posterior movement of the lateral femoral condyle. Because there is no posterolateral upslope in the insert of the B-in-S CS implant, the tibia pivots medially throughout flexion similar to the native knee.
Level of evidence
Level III.
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