Significant changes in lower limb alignment due to flexion and rotation-a systematic 3D simulation of radiographic measurements

Distances and angles in standing long-leg radiographs: comparing conventional radiography, digital radiography, and EOS

OBJECTIVE

Distances and angles measured from long-leg radiographs (LLR) are important for surgical decision-making. However, projectional radiography suffers from distortion, potentially generating differences between measurement and true anatomical dimension. These phenomena are not uniform between conventional radiography (CR) digital radiography (DR) and fan-beam technology (EOS). We aimed to identify differences between these modalities in an experimental setup.

MATERIALS AND METHODS

A hemiskeleton was stabilized using an external fixator in neutral, valgus and varus knee alignment. Ten images were acquired for each alignment and each modality: one CR setup, two different DR systems, and an EOS. A total of 1680 measurements were acquired and analyzed.

RESULTS

We observed great differences for dimensions and angles between the 4 modalities. Femoral head diameter measurements varied in the range of > 5 mm depending on the modality, with EOS being the closest to the true anatomical dimension. With functional leg length, a difference of 8.7% was observed between CR and EOS and with the EOS system being precise in the vertical dimension on physical-technical grounds, this demonstrates significant projectional magnification with CR-LLR. The horizontal distance between the medial malleoli varied by 20 mm between CR and DR, equating to 21% of the mean.

CONCLUSIONS

Projectional distortion resulting in variations approaching 21% of the mean indicate, that our confidence on measurements from standing LLR may not be justified. It appears likely that among the tested equipment, EOS-generated images are closest to the true anatomical situation most of the time.

Double-level osteotomy for varus knees using patient-specific cutting guides allow more accurate correction but similar clinical outcomes as compared to conventional techniques

PURPOSE

Patient-specific cutting guides are increasingly used in the field of osteotomies around the knee and can improve the accuracy of planned correction and more specifically in the case of double-level osteotomy (DLO). The purpose of this study was to analyse the accuracy of postoperative coronal alignment after DLO using patient-specific cutting guides techniques (PSI) compared to conventional techniques. The secondary objective was to compare the functional results between the two groups at short-term follow-up.

HYPOTHESIS

The accuracy of global correction (HKA angle) is better with patient-specific cutting guides compared to conventional techniques for double-level osteotomy METHODS: This multicentric comparative retrospective study included 53 patients (mean age: 53.8 ± 5.2 years, male/female: 44/9) who underwent a DLO for knee varus malalignment. The coronal correction accuracy (as expressed by the difference between postoperative angular values and preoperative targeted correction) was compared between techniques using patient-specific cutting guides (PSI group, n = 27) or conventional techniques (n = 26) for the medial proximal tibial angle (MPTA) and the lateral distal femoral angle (LDFA). Postoperatively, the global alignment expressed by the hip-knee-ankle angle and the joint line obliquity were compared between groups. The postoperative functional results for KOOS and UCLA activity scale score were also compared at a mean follow-up of 1.7 years (1.0-3.1 years).

RESULTS

No difference was observed for the postoperative global alignment between the PSI and the conventional groups (Δ = 0.6 °, p = 0.11) neither for the postoperative posterior proximal tibial angle (Δ = 1.6°, p = 0,99) or the joint line obliquity (Δ = 0.3°, p = 0,17). In the coronal plane, the postoperative MPTA was lower in the PSI group (Δ = 2.3°, p < 0.001) as well as the postoperative LDFA (Δ = 0.9°, p = 0.01). Concerning correction accuracy in the coronal plane, the results showed a significant higher accuracy of the planned correction in the PSI group compared to the conventional group for MPTA (2.2 ± 0.2 versus 0.8 ± 0.7, Δ = 1.5 °, p < 0.001) and LDFA (1.3 ± 1.0 versus 0.6 ± 0.9, Δ = 0.7°, p < 0.001). No improvement difference was observed between the conventional group and the PSI group respectively for the KOOS symptoms (p = 0.12), the KOOS Pain (p = 0,57), the KOOS activities of daily living (p = 0.61), the KOOS sport/rec (p = 0.65), or for the KOOS Quality of Life (p = 0.99) neither for the UCLA (p = 0.97).

CONCLUSIONS

This study suggests that the use of custom-made cutting guides improves the accuracy of planned correction in double-level osteotomy compared with conventional techniques, which may have implications particularly in centers not performing a large volume of osteotomies. This improved accuracy is not associated with any difference in joint line obliquity or functional results but these results need to be confirmed by a randomized prospective study.

LEVEL OF EVIDENCE

III; Retrospective comparative study.

Joint line and knee osteotomy

This review explores the intricate relationship between knee osteotomy and frontal plane joint line orientation, emphasizing the dynamic nature of the joint line's influence on knee forces and kinematics. Consideration of coronal alignments, knee phenotypes, and associated angles (medial proximal tibial angle (MTPA), lateral distal femoral angle (LDFA), joint line convergence angle (JLCA)) becomes crucial in surgical planning to avoid joint line deformities. The double-level osteotomy is to be considered a valid option, especially for severe deformities; however, the target patient cannot be selected solely based on high predicted postoperative joint line obliquity (JLO) and MPTA.

Significant difference in femoral torsion between coronal plane alignment of the knee type 1 and 4

PURPOSE

The purpose of this study was to find out whether the torsions of the femur and tibia are dependent on the coronal plane alignment of the knee (CPAK) type.

METHODS

Five hundred patients (1000 legs) were included, who received a whole leg standing three-dimensional (3D) radiograph using EOS imaging (EOS Imaging, Paris, France). SterEOS software was used for digital reconstruction. Femoral and tibial torsions were determined by analysing 3D reconstructions of each leg. Femoral torsion was defined as the angle between the femoral neck axis (FNA) and the posterior condylar axis (PCA). Tibial torsion was defined as the angle between the axis tangent to the posterior part of the tibia plateau and the transmalleolar axis. Arithmetic hip-knee-ankle angle (aHKA) and joint-line obliquity (JLO) were also determined, allowing each leg to be assigned one of nine possible phenotypes according to CPAK.

RESULTS

The mean femoral torsion in CPAK type 1 was significantly higher (+ 2.6° ± 0.8°) than in CPAK type 4 (p = 0.02). All other CPAK types did not differ in the degree of femoral torsions. No differences could be demonstrated for the tibial torsion.

CONCLUSION

There is a correlation between the coronal alignment of the lower limb and femoral torsion. This may provide the basis for extending the CPAK classification beyond the coronal plane.

LEVEL OF EVIDENCE

Level III.

Factors predicting lower limb alignment after Oxford medial unicompartmental knee arthroplasty

This study aimed to identify the factors affecting hip-knee-ankle (HKA) angle following Oxford medial unicompartmental knee arthroplasty (MUKA). A retrospective analysis of 200 patients who underwent Oxford MUKA from June 2018 to October 2020 was conducted. Univariate and multivariate analyses were performed to investigate the impact of surgical and radiographic characteristics on the postoperative HKA angle. The mean HKA angle was 9.5 ± 4.3° before surgery and 3.6 ± 3.7° after surgery (p < 0.001). The postoperative HKA angle significantly correlated with the preoperative HKA angle, bearing size, tibial component alignment angle, and BMI (r = 0.71, p < 0.001; r =  - 0.24, p = 0.001; r = 0.21, p = 0.004; r =  - 0.18, p = 0.011). Multiple linear regression analysis revealed that the preoperative HKA angle (β = 0.68, p < 0.001), bearing size (β =  - 0.31, p < 0.001), tibial component alignment angle (β = 0.14, p = 0.003), and BMI (β =  - 0.09, p = 0.047) significantly affected the postoperative HKA angle. In conclusion, larger preoperative varus deformity, smaller bearing size, greater varus alignment of the tibial component, and lower BMI lead to greater postoperative varus alignment of the lower limb in Oxford MUKA. With this concept, surgeons can more accurately predict postoperative lower limb alignment and avoid malalignment in Oxford MUKA.

Tibial morphology of symptomatic osteoarthritic knees varies according to location: a retrospective observational study in Japanese patients

This study analyzed 31 patients with symptomatic osteoarthritic knees scheduled to undergo knee arthroplasty or high tibial osteotomy and demonstrated shape variations in their proximal tibia using an average three-dimensional (3D) bone model. Preoperative computed tomography of the affected knees was reconstructed as 3D bone models using a triangle mesh of surface layers. The initial case was defined as the template, and the other models were reconstructed into homologous models with the same number of mesh vertices as that in the template. The corresponding mesh vertices of the other models were averaged to evaluate the spatial position on the particular mesh vertex of the template. This was applied to all the mesh vertices of the template to generate the average 3D model. To quantify the variation in surface geometry, average minimum distance from the average bone model to 31 models was recorded. The medial proximal tibial cortex (1.63 mm) revealed lesser variation compared to the tibial tuberosity (2.50 mm) and lateral cortex (2.38 mm), (p = 0.004 and p = 0.020, respectively). The medial tibial plateau (1.46 mm) revealed larger variation compared to the lateral tibial plateau (1.16 mm) (p = 0.044). Understanding 3D geometry could help in development of implants for arthroplasty and knee osteotomy.

The coronal alignment differs between two-dimensional weight-bearing and three-dimensional nonweight bearing planning in total knee arthroplasty

Purpose

The goal of this study is (1) to assess differences between two-dimensional (2D) weight-bearing (WB) and three-dimensional (3D) nonweight-bearing (NWB) planning in total knee arthroplasty (TKA) and (2) to identify factors that influence intermodal differences.

Methods

Retrospective single-centre analysis of patients planned for a TKA with patient-specific instruments (PSI). Preoperative WB long-leg radiographs and NWB computed tomography were analysed and following radiographic parameters included: hip-knee-ankle angle (HKA) (+varus/-valgus), joint line convergence angle (JLCA), femorotibial subluxation and bony defect classified according to Anderson. Preoperative range of motion was also considered as possible covariate. Demographic factors included age, sex, and body mass index.

Results

A total of 352 knees of 323 patients (66% females) with a mean age of 66 ± 9.7 years were analysed. The HKA differed significantly between 2D and 3D planning modalities; varus knees (n = 231): 9.9° ± 5.1° vs. 6.7° ± 4°, p < 0.001; valgus knees (n = 121): -8.2° ± 6° vs. -5.5° ± 4.4°, p < 0.001. In varus knees, HKA (β = 0.38; p < 0.0001) and JLCA (β = 0.14; p = 0.03) were associated with increasing difference between 2D/3D HKA. For valgus knees, HKA (β = -0.6; p < 0.0001), JLCA (β = -0.3; p = 0.0001) and lateral distal femoral angle (β = -0.28; p = 0.03) showed a significant influence on the mean absolute difference.

Conclusion

The coronal alignment in preoperative 3D model for PSI-TKA significantly differed from 2D WB state and the difference between modalities correlated with the extent of varus/valgus deformity. In the vast majority of cases, the 3D NWB approach significantly underestimated the preoperative deformity, which needs to be considered to achieve the planned correction when using PSI in TKA.

Level of Evidence

Level III.

Restoration of preoperative tibial alignment improves functional results after medial unicompartmental knee arthroplasty

PURPOSE

The alignment obtained after unicompartmental knee arthroplasty (UKA) influences the risk of failure. Kinematic alignment after UKA based on Cartier angle restauration is likely to improve clinical outcomes compared with mechanical alignment. The purpose of this study is to analyze the influence of implant alignment and native knee restoration after UKA using the conventional techniques on clinical outcomes.

METHODS

This retrospective study included 144 medial UKA patients from 2015 to 2020. Radiographic measurements were performed pre- and postoperatively. Outliers were defined as follows: Δ Cartier > 3° (difference between the preoperative and postoperative Cartier angle); Δ MPTA (Medial Proximal Tibial angle) and postoperative TCA (Tibial Coronal component Angle) > 3° (difference between the positioning of the tibial implant and the preoperative proximal tibial deformity). The Knee injury and Osteoarthritis Outcome Score (KOOS), the International Knee Society (IKS) Function and Knee score, the Forgotten Joint Score (FJS), and the Subjective Knee Value (SKV) were evaluated. A Student t test or a non-parametric Wilcoxon test was used for non-normal data to compare pre- and postoperative values for functional scores and angular measurements. The correlation of postoperative angles with functional outcomes was assessed by the Spearman's rank correlation coefficient.

RESULTS

During the inclusion period, 214 patients underwent medial UKA, 71 patients were excluded, and 19 were lost to follow-up leaving 124 patients with 144 knees (20 bilateral UKA) included for analysis with a mean follow-up of 54.7 months ± 22.1 (24-95). The Δ Cartier was significantly correlated with IKS function (R2 = 0.06, p < 0.001) and FJS (R2 = 0.05, p < 0.01) scores. The Δ preoperative MPTA-TCA was significantly correlated (p < 0.001) with KOOS (R2 = 0.38), IKS Knee (R2 = 0.17), IKS function (R2 = 0.34), SKV (R2 = 0.08), and FJS (R2 = 0.37) scores. In subgroup analysis, non-outliers (< 3°) for Δ preoperative MPTA-TCA had better KOOS score (Δ = 23.5, p < 0.001) and IKS Function (Δ = 17.7, p < 0.001) compared to outliers (> 3°) patients.

CONCLUSION

Functional results after medial UKA can be influenced by implant alignment in the coronal plane with slight clinical improvement when positioning the tibial implant close to the preoperative tibial deformity, rather than by restoring the Cartier angle. This series suggests the interest of a more personalized alignment strategy, but these results will have to be confirmed by other controlled studies.

LEVEL OF EVIDENCE

IV, retrospective case series.

Linear correlation between patellar positioning and rotation of the lower limb in radiographic imaging: a 3D simulation study

PURPOSE

The purpose of this study was to quantify changes in rotation of the lower limb between image pairs based on patellar position. Additionally, we investigated the differences in alignment between centralized patellar and orthograde-positioned condyles.

METHODS

Three-dimensional models of 30 paired legs were aligned in neutral position with condyles orthogonal to the sagittal axis and then rotated internally and externally in 1° increments up to 15°. For each rotation, the deviation of the patella and the subsequent changes in alignment parameters were calculated and plotted using a linear regression model. Differences between neutral position and patellar centralization were analysed qualitatively.

RESULTS

A linear relationship between lower limb rotation and patellar position can be postulated. The regression model (R2 = 0.99) calculated a change of the patellar position of - 0.9 mm per degree rotation and alignment parameters showed small changes due to rotation. The physiological lateralization of the patella at neutral position was on average - 8.3 mm (SD: ± 5.4 mm). From neutral position, internal rotation that led to a centralized patella was on average - 9.8° (SD: ± 5.2°).

CONCLUSION

The approximately linear dependence of the patellar position on rotation allows an inverse estimation of the rotation during image acquisition and its influence on the alignment parameters. As there is still no absolute consensus about lower limb positioning during image acquisition, data about the impact of a centralized patella compared to an orthograde condyle positioning on alignment parameters was provided.

LEVEL OF EVIDENCE

IV.