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

High accuracy in lower limb alignment analysis using convolutional neural networks, with improvements needed for joint-level metrics

PURPOSE

Evaluation of long-leg standing radiographs (LSR) is a standardised procedure for analysis of primary or secondary deformities of the lower limbs. Deep-learning convolutional neural networks (CNN) offer the potential to enhance radiological measurement by increasing reproducibility and accuracy. This study aims to evaluate the measurement accuracy of an automated CNN-based planning tool (mediCAD® 7.0; mediCAD Hectec GmbH) of lower limb deformities.

METHODS

In a retrospective single-centre study, 164 pre- and postoperative bilateral LSRs with uni- or bilateral posttraumatic knee arthritis undergoing total knee arthroplasty (TKA) were enroled. Alignment parameters relevant to knee arthroplasty and deformity correction were analysed independently by two observers and a CNN. The intraclass correlation coefficient (ICC) was used to evaluate the accuracy between observers and the CNN, which was further evaluated using absolute deviations, limits of agreement (LoA) and root mean square error (RMSE).

RESULTS

CNN evaluation demonstrated high consistency in measuring leg length (ICC > 0.99) and overall lower limb alignment measures of mechanical tibio-femoral angle (mTFA) (ICC > 0.97; RMSE < 1.1°). The mean absolute difference between angular measurements were low for overall lower limb alignment (mTFA 0.49-0.61°) and high for specific joint angles (aMPFA 3.86-4.50°). Accuracy at specific joint angles like the mechanical proximal tibial angle (MPTA) and the mechanical lateral distal femur angle (mLDFA) varied between lower limbs with deformity, with and without TKA with greatest difference for TKA (ICC 0.22-0.85; RMSE 1.72-3.65°).

CONCLUSION

Excellent accuracy was observed between manual and automated measurements for overall alignment and leg length, but joint-level metrics need further improvement especially in case of TKA similar to other existing algorithms. Despite the observed deviations, the time-efficient nature of the algorithm improves the efficiency of the preoperative planning process.

LEVEL OF EVIDENCE

Level IV.

High variability exists in 3D leg alignment analysis, but underlying principles that might lead to agreement on a universal framework could be identified: A systematic review

PURPOSE

To (1) investigate the hypothesis that there is high variability in the reported methods to derive axes and joint orientations from three-dimensional (3D) bone models to (a) perform 3D knee-related leg alignment analysis and (b) define coordinate systems for the femur, tibia and leg and (2) identify underlying principles that might lead to agreement on a universal 3D leg alignment analysis framework.

METHODS

A systematic review of the literature between January 2006 and June 2024 was performed. Articles explicitly reporting methods to derive axes and joint orientations from CT-based 3D bone models for alignment parameters and/or coordinate systems of the femur, tibia and leg were included. Study characteristics and reported methods were extracted and presented as a qualitative synthesis.

RESULTS

A total of 93 studies were included. There was high variability in the reported methods to derive axes and joint orientations from 3D bone models. Nevertheless, the reported methods could be categorized into four groups, and several underlying principles of the four groups could be identified. Furthermore, the definitions of femoral and tibial coordinate systems were most frequently based on the mechanical axis (femoral, 13/19 [68%]; tibial, 13/26 [50%]) and a central medial-lateral axis (femoral, 16/19 [84%]; tibial, 12/26 [46%]); no leg coordinate system was reported. Interestingly, of the included studies that reported on leg alignment parameters (76/93, 82%), only a minority reported expressing these in a complete coordinate system (25/76, 33%).

CONCLUSION

There is high variability in 3D knee-related leg alignment analysis. Therefore, universal 3D reference values for alignment parameters cannot yet be defined, and comparison of alignment parameter values between different studies is impossible. However, several underlying principles to the reported methods were identified, which could serve to reach more agreement on a future universal 3D framework for leg alignment analysis.

LEVEL OF EVIDENCE

Level I.

Navigated versus conventionally instrumented total knee arthroplasty techniques: No difference in functional alignment or balance

PURPOSE

Much debate exists about the superiority of navigated versus conventional instrumentation for achieving optimal balance and alignment during total knee arthroplasty (TKA). Recent registry data indicate no long-term survivorship benefit for TKAs performed using technology assistance, despite the added resource and financial costs. However, outcome comparisons are confounded by varying surgeon techniques and targets for ideal balance and alignment. This study aimed to investigate alignment or balance outcome differences between navigated and conventionally instrumented TKAs performed using an identical operative sequence and alignment strategy.

METHODS

Fifty navigated and 50 conventionally instrumented primary TKAs, using an identical inverse kinematic alignment strategy, were included. Navigation equipment was used intraoperatively to 'post-cut' record the conventionally instrumented TKAs. Intraoperative balance, range, and alignment; and post-operative radiographic accuracy for restoration of constitutional alignment were compared.

RESULTS

Forty-nine navigated and 49 conventionally instrumented TKAs were compared (n = 2 excluded due to inadequate radiographs). No preoperative demographic or deformity severity differences existed. No intraoperative balance, range or alignment difference existed. Neither technique was more accurate for restoration of constitutional alignment.

CONCLUSION

Whilst large registry data may be confounded by uncaptured variables such as surgeon balancing techniques or surgeon alignment strategy preferences, this study found no alignment or balance differences between navigated versus conventionally instrumented TKA techniques for a surgeon and technique-controlled study. Although the increased resources necessary for technology assistance are not justified by this study, further studies may identify significance using larger samples or comparison of alternative outcomes.

LEVEL OF EVIDENCE

Level II.

Malrotation Strongly Influences Posterior Tibial Slope Measurement on Lateral Radiographs of the Knee

Background

Posterior tibial slope (PTS) is commonly measured on lateral radiographs, but there is an ongoing discussion on which criteria are essential as quality standards.

Purpose/Hypothesis

The purpose of this study was to evaluate the effect of malrotation of the tibia on lateral radiographs for PTS measurement. It was hypothesized that malrotation alters the measured PTS.

Study Design

Descriptive laboratory study.

Methods

An infratuberositary osteotomy was performed on a tibial saw bone model, and 3 conditions-2 with increased PTS-were tested with the same experimental setup (series 1, closed osteotomy; series 2, 5-mm anterior opening; series 3, 10-mm anterior opening). Long lateral radiographs were taken from +12.5° of external tibial rotation (ETR) to -20° of internal tibial rotation (ITR), in steps of 2.5°. PTS was measured with the mechanical axis (MA) and the proximal anatomic axis (PAA). In addition, the distance between the medial and lateral posterior tibial condyles was measured (in mm).

Results

In test series 1, between +12.5° to 0° of ETR and 0° to-20° of ITR, a change in PTS of 2.8°± 1.0 (ETR) and 3.7°±1.3 (ITR) for the MA and 3.7°± 1.4 (ETR) and 4.1°±1.5 (ITR) for the PAA was detected. In test series 2, changes of 1.5°± 0.5 (ETR) and 3.7±1.3 (ITR) for the MA and 1.6°± 0.6 (ETR) and 4.3°±1.4 (ITR) for the PAA were observed; likewise, in test series 3, changes of 1.8°± 0.7 (ETR) and 3.7°±1.3 (ITR) for the MA and 2.2°± 0.9 (ETR) and 4.2°±1.3 (ITR) for the PAA were observed. ETR of +12.5° resulted in a distance of 5 mm, and ITR of -20° resulted in a distance of 10 mm between the posterior tibial condyles in all testing conditions. There was no significant difference among the 3 testing conditions (P > .05). A change of 1 mm in distance was equivalent to 2° (ITR) or 2.5° (ETR) of change in rotational alignment and 0.4° of change in PTS measurement, irrespective of whether MA or PAA was used.

Conclusion

Tibial malrotation strongly influences PTS measurement on lateral radiographs. ETR leads to an underestimation, and ITR to an overestimation, of PTS. Every 1° of change in rotational alignment was equivalent to 0.2° of change in PTS measurement. For a reliable PTS measurement on lateral radiographs, the posterior tibial condyles should be superimposed exactly.

Clinical Relevance

Dependent on PTS values, surgical correction of the PTS can be indicated. For a correct indication, it is of utmost importance to be able to determine the posterior slope exactly. This investigation demonstrates the effect of tibial rotation on PTS measurement and defines quality criteria, as well as a simple grading system for lateral radiographs for the measurement of the PTS. This helps surgeons to interpret radiographs correctly, allowing a better decision-making process, if and when a corrective osteotomy for PTS correction is indicated.

A structured framework for standardized 3D leg alignment analysis: an international Delphi consensus study

PURPOSE

To reach consensus among international experts on a structured framework for standardized 3D leg alignment analysis based on 3D bone models, ensuring consistency and improving clinical applicability.

METHODS

A Delphi study was performed in four rounds. Rounds 1 and 2 involved a steering and rating group that developed statements based on principles preserving the 3D complexity of anatomical structures, identified through a systematic review. These statements encompassed approaches for deriving joint centres and joint orientations, and defining coordinate systems using 3D bone models. In Rounds 3 and 4, a panel of 35 international experts, including clinicians (54%) and engineers (46%), with participants from Europe (80%), Oceania (9%), Asia (6%), and the Americas (6%), evaluated these statements. Consensus was defined as ≥80% agreement.

RESULTS

Rounds 1 and 2 resulted in 31 statements to be included in the survey. Of these, 26 achieved consensus in Round 3, with the five remaining statements refined and reaching consensus in Round 4. Experts agreed on utilising all available relevant surface data to define joint centres, joint orientations, and individual femoral and tibial coordinate systems alongside a combined leg coordinate system, and adopting central 3D axes for femoral version and tibial torsion.

CONCLUSIONS

This international Delphi consensus study provides a structured framework for a standardized 3D leg alignment analysis based on 3D bone models. This framework aims to enhance clinical applicability for preoperative planning and execution of uni- and multiplanar correction osteotomies around the knee, reduce the methodological variability in 3D leg alignment analysis literature, and improve cross-study comparability.

LEVEL OF EVIDENCE

Level V.

A controlled study of personalized versus standard osteotomy in medial unicompartmental knee osteoarthritis

PURPOSE

To compare the efficacy of personalized osteotomies with that of standard osteotomies in treating medial unicompartmental knee osteoarthritis.

METHODS

The clinical data of 96 patients who were diagnosed with unicompartmental knee osteoarthritis in our group between 2019 and 2023 were retrospectively analysed on the basis of preoperative and postoperative radiological measurements. The knee injury and osteoarthritis outcome score (KOOS), forgotten joint score (FJS), and Lysholm knee score scale (Lysholm) were used to assess the clinical outcome, and complications were observed and recorded.

RESULTS

According to the relevant criteria, 84 of 96 patients were included in this study. All patients were followed for a mean of 31 (range 22-55) months. Fifty-one patients underwent personalized osteotomy procedures, and thirty-three underwent standard osteotomy procedures. The postoperative KOOS Pain (P < 0.0001), KOOS Symptoms (P < 0.0001), KOOS ADL (P < 0.0001), KOOS Sport (P = 0.0023), KOOS QoL (P < 0.0001), Lysholm (P < 0.0001) and FJS (P < 0.0001) scores were higher than those in the standard osteotomy group. Nevertheless, postoperative extension (P = 0.2636) and postoperative flexion (P = 0.3554) were not significantly different.

CONCLUSION

This was a single-centre, retrospective, short follow-up study with several limitations. However, on the basis of the results of the present study, we believe that the function of the knee after medial unicompartmental knee arthroplasty (mUKA) is affected by the direction of tibial osteotomy. We believe that better clinical results may be obtained when the tibial implant is placed near the preoperative tibial deformity.

LEVEL OF EVIDENCE

Level IV; retrospective case series.

Influence of limb position on femoral neck anteversion angle measurement during computed tomography imaging

Background

The femoral neck anteversion angle has been used as a surgical indicator for hip and patellofemoral joint disorders. However, the influence of limb position on femoral neck anteversion angle measurements during imaging remains unclear. Therefore, this study aimed to investigate the influence of limb position on femoral neck anteversion angle measurements.

Methods

Computed tomography images of 20 femurs from 10 patients were obtained. The angle between the line passing through the center of the femoral head and the center of the femoral neck and the tangential line of the femoral posterior condyles on axial slices was measured as the femoral neck anteversion angle. Raw femoral neck anteversion angle data was defined as the original femoral neck anteversion angle. The cutting direction of the axial plane was changed from -20° to 20° in 5° increments to simulate limb position changes for each of the following measurements: hip flexion/extension, abduction/adduction angles, and their combined directions. The femoral neck anteversion angle was measured under each condition, and the change in the angle was calculated. The correlation between hip angle and femoral neck anteversion angle change was analysed by Spearman's rank correlation coefficient.

Results

The mean original femoral neck anteversion angle was 17.6°. There was a strong negative correlation between hip flexion/extension change and femoral neck anteversion angle change (r = -0.96, p < 0.001). There was a weak correlation between hip adduction/abduction change and femoral neck anteversion angle change (r = 0.35, p < 0.001). The average maximum potential difference in femoral neck anteversion angle measurement combining flexion/extension and abduction/adduction was 21.0° ± 4.9°.

Conclusions

The femoral neck anteversion angle changed in association with changes in limb position, particularly with hip flexion and extension. Careful attention to limb position and conditions of the slice is needed to consistently evaluate the femoral neck anteversion angle.

Effect of radiographic malpositioning on patellar height measurements: implications for diagnosis and surgical planning. A retrospective observational study

PURPOSE

Patella alta stands as a significant predisposing factor for patellofemoral instability. Patellar heights indexes (PHI) require precise lateral knee radiographic projections for accurate computation. However, within clinical contexts, a notable proportion of radiographic images are taken with certain degrees of excessive rotation and/or tilting. The primary aim of this investigation was to assess the impact of suboptimal radiographic positioning on the determination of patellar height, utilizing the Blackburne-Peel (BP), Caton-Deschamps (CD) and Insall-Salvati (IS) indexes. Secondarily, it was evaluated whether any index is more sensible to suboptimal radiographic positioning, and how inter and intra observer reproducibility are affected.

METHODS

Thirty-three patients with strictly lateral radiographs and another one demonstrating a noticeable degree of tilt and/or rotation were included in the study. Four orthopaedic surgeons specialized in knee surgery and four Orthopaedics residents conducted measurements on each radiograph in a randomized sequence at two different time points. A linear mixed-effects model was applied, with the quality of the radiograph (adequate projection vs malrotation, tilt, or both), observer expertise (consultant or resident), and observation time regarded as fixed effects, while consultant and patient were treated as random effects.

RESULTS

Statistically significant differences were obtained between strict lateral and tilted radiographs in the BPI, with an overestimation of up to 0.0937; between strict lateral and malrotated radiographs in the ISI, showing an overestimation of up to 0.0696 and between tilted and/or rotated radiographs in the CDI, with overestimation reaching up to 0.0813. No significant differences were observed between resident and consultant observers in any of the indexes. Good inter-observer consistency was achieved.

CONCLUSION

This study showed statistically significant differences in the determination of the three PHIs. Although these differences were small, they may predispose to diagnostic errors and inaccurate surgical planning in cases requiring surgical correction. Future studies quantifying the degrees of malrotation and/or inclination may further clarify these findings.

Comparative impact of high tibial osteotomy and supramalleolar osteotomy on limb alignment and ankle function: a retrospective study

OBJECTIVE

This retrospective study aimed to conduct a comparative analysis of the impact of high tibial osteotomy (HTO) and supramalleolar osteotomy (SMOT) on lower limb alignment and ankle function after surgery.

METHODS

A cohort of patients who underwent either HTO (n = 63) or SMOT (n = 51) for lower limb alignment issues was included in the study. Inclusion criteria comprised individuals who underwent the surgical procedures between June 2018 and June 2021; exclusion criteria encompassed incomplete medical records and inadequate follow-up data. Baseline characteristics, weight-bearing line ratios, ankle joint function, and lower limb lines of force were evaluated before surgery, postoperatively, and at the 6-month follow-up. Statistical analyses were performed to compare the outcomes between the HTO and SMOT groups, as well as between non-deviated and deviated subgroups. Spearman rank correlation analysis was used to reveal correlations between variables.

RESULTS

The preoperative and immediate postoperative weight-bearing line ratios were similar between the HTO and SMOT groups. However, a notable difference emerged at the 6-month follow-up, suggesting distinct impacts of the two procedures on lower limb alignment. Additionally, the HTO group exhibited superior postoperative outcomes in ankle joint function, specifically in pain alleviation and functional improvement, compared to the SMOT group. The analysis of lower limb lines of force demonstrated a significant association between the surgical procedure and alterations in lower limb biomechanics, emphasizing the differential impact of HTO and SMOT. Furthermore, the comparison between non-deviated and deviated subgroups highlighted the potential impact of lower limb alignment on postoperative ankle function.

CONCLUSION

The findings contribute valuable insights into the comparative effectiveness of HTO and SMOT in addressing lower limb alignment and ankle function. This study's results have significant implications for orthopedic treatment and may guide treatment strategies for patients undergoing lower limb realignment surgery, ultimately enhancing the quality of life for affected individuals.

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.

Comparing supine CT scanogram and standing long-leg radiograph for postoperative alignment in total knee arthroplasty: a prospective study

PURPOSE

Achieving precise postoperative alignment is critical for the long-term success of total knee arthroplasty (TKA). Long-leg standing radiograph (LLR) at 6 weeks post-op is the gold standard for assessing alignment, but its reliance on weight-bearing and positioning makes it less practical in the early postoperative period. Supine computed tomography scanogram (CTS) offers a potential alternative. This study compares CTS and LLR in patients undergoing TKA with patient-specific valgus correction angles (VCA).

METHODS

A prospective study of 108 knees from 57 patients undergoing primary TKA was conducted. CTS was performed on postoperative day three in a supine non-weight-bearing position, and LLR at six weeks in an upright standing position. Coronal alignment was assessed using hip-knee-ankle angle (HKA) and compared using Bland-Altman plots, paired-samples t-tests, and Cohen's d.

RESULTS

CTS showed 57% of knees were within 3° of neutral alignment, while LLR showed 61%. The mean difference between modalities was 0.52° (SD, 3.56°; p = 0.07). Inter-observer reliability was excellent for both CTS and LLR (all ICCs > 0.9).

CONCLUSION

While CTS provides a useful alternative for early postoperative alignment assessment-particularly in situations where a standing LLR is not feasible-the observed variability suggests that LLR remains the more reliable modality when precise alignment is critical. Surgeons should therefore consider CTS as an adjunct tool for early decision-making or non-ambulatory patients in the immediate postoperative setting.

LEVEL OF EVIDENCE

Level II, Prospective Comparative Study.

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.

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.