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Purpose: The goals of this study were (1) to assess whether the preoperative difference between modalities and extent of deformity are associated with a higher difference between planned and achieved surgical correction and (2) if they yield a higher probability of intraoperative adjustments., Methods: Retrospective single-centre analysis of patients undergoing patient-specific instrumented (PSI) total knee arthroplasty (TKA). Preoperative radiographic parameters were analysed on weightbearing (WB) long-leg radiographs (LLR) and nonweightbearing (NWB) computed tomography (CT). The 2D/3D difference was calculated as the difference between preoperative WB-LLR (2D) hip-knee-ankle angle (HKA), and NWB CT (3D) HKA. Surgical records were screened to retrieve intraoperative adjustments to the preoperative plan. Postoperative assessment was performed on WB LLR., Results: Two-hundred-eighty-two knees of 263 patients were analysed. The difference of postoperative achieved to planned HKA (HKA Difference ) was 2.2° ± 1.7°. The preoperative 2D HKA showed the highest correlation with HKA Difference ( r  = -0.37, 95% confidence interval [CI]: -0.48 to -0.26, p  < 0.001). Intraoperative adjustments were performed in 60% ( n  = 170) of all knees. Patients with a preoperative coronal deformity of >7.8° had 10.55 higher odds for an intraoperative coronal adjustment (95% CI: 4.60-24.20, p  < 0.001)., Conclusion: The extent of deformity is associated with residual coronal deformity following PSI-TKA. Patients with extensive coronal malalignment may benefit from an adaptation of the preoperative surgical plan to avoid unintended postoperative coronal malalignment. Despite the advancements with 3D preoperative planning, intraoperative adjustments in PSI-TKA are frequently performed, in particular in patients with a higher preoperative varus/valgus deformity., Level of Evidence: Level III., Competing Interests: Sandro F. Fucentese is a consultant for Medacta SA (Switzerland), Smith & Nephew (United Kingdom), Zimmer Biomet and Karl Storz SE & Co. KG (Germany). The remaining authors declare no conflict of interest., (© 2024 The Author(s). Journal of Experimental Orthopaedics published by John Wiley & Sons Ltd on behalf of European Society of Sports Traumatology, Knee Surgery and Arthroscopy.)

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., Competing Interests: Sandro F. Fucentese is a consultant for Medacta SA (Switzerland), Smith & Nephew (United Kingdom), Zimmer Biomet and Karl Storz SE & Co. KG (Germany). The other authors have no conflict of interest to declare., (© 2024 The Author(s). Journal of Experimental Orthopaedics published by John Wiley & Sons Ltd on behalf of European Society of Sports Traumatology, Knee Surgery and Arthroscopy.)

Purpose: Intraoperative hinge fractures in distal femur osteotomies represent a risk factor for loss of alignment and non-union. Using finite element analysis, the goal of this study was to investigate the influence of different hinge widths and osteotomy corrections on hinge fractures in medial closed-wedge and lateral open-wedge distal femur osteotomies., Methods: The hinge was located at the proximal margin of adductor tubercle for biplanar lateral open-wedge and at the upper border of the lateral femoral condyle for biplanar medial closed-wedge distal femur osteotomies, corresponding to optimal hinge positions described in literature. Different hinge widths (5, 7.5, 10 mm) were created and the osteotomy correction was opened/closed by 5, 7.5 and 10 mm. Tensile and compressive strain of the hinge was determined in a finite element analysis and compared to the ultimate strain of cortical bone to assess the hinge fracture risk., Results: Doubling the correction from 5 to 10 mm increased mean tensile and compressive strain by 50% for lateral open-wedge and 48% for medial closed-wedge osteotomies. A hinge width of 10 mm versus 5 mm showed increased strain in the hinge region of 61% for lateral open-wedge and 32% for medial closed-wedge osteotomies. Medial closed-wedge recorded a higher fracture risk compared to lateral open-wedge osteotomies due to a larger hinge cross-section area (60-67%) for all tested configurations. In case of a 5 mm hinge, medial closed-wedge recorded 71% higher strain in the hinge region compared to lateral open-wedge osteotomies., Conclusion: Due to morphological features of the medial femoral condyle, finite element analysis suggests that lateral-open wedge osteotomies are the preferable option if larger corrections are intended, as a thicker hinge can remain without an increased hinge fracture risk., (© 2023. The Author(s).)

Purpose: Posttraumatic fibular malunion alters ankle joint biomechanics and may lead to pain, stiffness, and premature osteoarthritis. The accurate restoration is key for success of reconstructive surgeries. The aim of this study was to analyze the accuracy of a novel three-dimensional (3D) registration algorithm using different segments of the contralateral anatomy to restore the distal fibula., Methods: Triangular 3D surface models were reconstructed from computed tomographic data of 96 paired lower legs. Four segments were defined: 25% tibia, 50% tibia, 75% fibula, and 75% fibula and tibia. A surface registration algorithm was used to superimpose the mirrored contralateral model on the original model. The accuracy of distal fibula restoration was measured., Results: The median rotation error, 3D distance (Euclidean distance), and 3D angle (Euler's angle) using the distal 25% tibia segment for the registration were 0.8° (- 1.7-4.8), 2.1 mm (1.4-2.9), and 2.9° (1.9-5.4), respectively. The restoration showed the highest errors using the 75% fibula segment (rotation error 3.2° (0.1-8.3); Euclidean distance 4.2 mm (3.1-5.8); Euler's angle 5.8° (3.4-9.2)). The translation error did not differ significantly between segments., Conclusion: 3D registration of the contralateral tibia and fibula reliably approximated the premorbid anatomy of the distal fibula. Registration of the 25% distal tibia, including distinct anatomical landmarks of the fibular notch and malleolar colliculi, restored the anatomy with increasing accuracy, minimizing both rotational and translational errors. This new method of evaluating malreductions could reduce morbidity in patients with ankle fractures., Level of Evidence: IV., (© 2022. The Author(s).)

Purpose: To assess a novel method of three-dimensional (3D) joint line (JL) restoration based on the contralateral tibia and fibula., Methods: 3D triangular surface models were generated from computed tomographic data of 96 paired lower legs (48 cadavers) without signs of pathology. Three segments of the tibia and fibula, excluding the tibia plateau, were defined (tibia, fibula, tibial tuberosity (TT) and fibular tip). A surface registration algorithm was used to superimpose the mirrored contralateral model onto the original model. JL approximation and absolute mean errors for each segment registration were measured and its relationship to gender, height, weight and tibia and fibula length side-to-side differences analyzed. Fibular tip to JL distance was measured and analyzed., Results: Mean JL approximation did not yield significant differences among the three segments. Mean absolute JL error was highest for the tibia 1.4 ± 1.4 mm (range: 0 to 6.0 mm) and decreased for the fibula 0.8 ± 1.0 mm (range: 0 to 3.7 mm) and for TT and fibular tip segment 0.7 ± 0.6 (range: 0 to 2.4 mm) (p = 0.03). Mean absolute JL error of the TT and fibular tip segment was independent of gender, height, weight and tibia and fibula length side-to-side differences. Mean fibular tip to JL distance was 11.9 ± 3.4 mm (range: 3.4 to 22.1 mm) with a mean absolute side-to-side difference of 1.6 ± 1.1 mm (range: 0 to 5.3 mm)., Conclusion: 3D registration of the contralateral tibia and fibula reliably approximated the original JL. The registration of, TT and fibular tip, as robust anatomical landmarks, improved the accuracy of JL restoration independent of tibia and fibula length side-to-side differences., Level of Evidence: IV., (© 2021. The Author(s).)

Purpose: To quantify the influence of the femoral tunnel exit (FTE) on the graft bending angle (GBA) and GBA-excursion throughout a full range of motion (ROM) in single-bundle anterior cruciate ligament (ACL) reconstruction., Methods: Three-dimensional (3D) surface models of five healthy knees were generated from a weight-bearing CT obtained throughout a full ROM (0, 30, 60, 90, 120°) and femoral and tibial ACL insertions were computed. The FTE was simulated for 16 predefined positions, referenced to the Blumensaat's line, for each patient throughout a full ROM (0, 30, 60, 90, 120°) resulting in a total of 400 simulations. 3D GBA was calculated between the 3D directional vector of the ACL and the femoral tunnel, while the intra-articular ACL insertions remained unchanged. For each simulation the 3D GBA, GBA-excursion, tunnel length and posterior tunnel blow-out were analysed., Results: Overall, mean GBA decreased with increasing knee flexion for each FTE (p < 0.001). A more distal location of the FTE along the Blumensaat's line resulted in an increase of GBA and GBA-excursion of 8.5 ± 0.6° and 17.6 ± 1.1° /cm respectively (p < 0.001), while a more anterior location resulted in a change of GBA and GBA-excursion of -2.3 ± 0.6° /cm (+ 0.6 ± 0.4°/ cm from 0-60° flexion) and 9.8 ± 1.1 /cm respectively (p < 0.001). Mean tunnel length was 38.5 ± 5.2 mm (range 29.6-50.5). Posterior tunnel blow-out did not occur for any FTE., Conclusion: Aiming for a more proximal and posterior FTE, with respect to Blumensaat's line, reliably reduces GBA and GBA-excursion, while preserving adequate tunnel length. This might aid to reduce excessive graft stress at the femoral tunnel aperture, decrease femoral tunnel widening and promote graft-healing., Level of Evidence: IV.

Purpose: Alteration of the postoperative frontal mechanical leg axis is a known problem in femoral rotational osteotomies. However, the maintenance of the sagittal mechanical leg axis seems also important. Goal of this study was to investigate the impact of femoral rotational osteotomies on the sagittal mechanical leg axis and to identify the degree of mal-angulation of the osteotomy planes that alter the postoperative sagittal alignment relevantly., Methods: Using 3D bone models of two patients with a pathologic femoral torsion (42° antetorsion and 6° retrotorsion), subtrochanteric and supracondylar rotational osteotomies were simulated first with an osteotomy plane perpendicular to the mechanical femoral axis (baseline osteotomy plane), second with predefined mal-angulated osteotomy planes. Subsequently, five different degrees of rotation were applied and the postoperative deviations of the sagittal mechanical leg axes were analyzed., Results: Using the baseline osteotomy plane, the sagittal mechanical leg axis changed by 0.4° ± 0.5° over both models. Using the mal-angulated osteotomy planes, maximum deviation of the sagittal mechanical leg axis of 4.0° ± 1.2° and 11.0° ± 2.0° was observed for subtrochanteric and for supracondylar procedures, respectively. Relevant changes of more than 2° were already observed with mal-angulation of 10° in the frontal plane and 15° of rotation in supracondylar procedures., Conclusion: Relevant changes of the postoperative sagittal mechanical leg axis could be observed with just slight mal-angulation of the osteotomy planes, in particular in supracondylar procedures and in cases with higher degrees of rotation. However, osteotomies perpendicular to the femoral mechanical axis showed no relevant alterations.

Purpose: Selection of a meniscus allograft with a similar three-dimensional (3D) size is essential for good clinical results in meniscus allograft surgery. Direct meniscus sizing by MRI scan is not possible in total meniscectomy and indirect sizing by conventional radiography is often inaccurate. The purpose of this study was to develop a new indirect sizing method, based on the 3D shape of the ipsilateral tibia plateau, which is independent of the meniscus condition., Methods: MRI and CT scans of fifty healthy knee joints were used to create 3D surface models of both menisci (MRI) and tibia plateau (CT). 3D bone models of the proximal 10 mm of the entire and half tibia plateau (with / without intercondylar area) were created in a standardized fashion. For each meniscus, the best fitting "allograft" couple out of all other 49 menisci were assessed by the surface distance of the 3D meniscus (best available allograft), of the 3D tibia plateau (3D-CT) and by the radiographic method of Pollard (2D-RX)., Results: 3D-CT sizing was significantly better by using only the half tibia plateau without the intercondylar area (p < 0.001). But neither sizing by 3D-CT, nor by 2D-RX could select the best available allograft. Compared to 2D-RX, 3D-CT sizing was significantly better for the medial, but not for the lateral meniscus., Conclusions: Automatized, indirect meniscus sizing using the 3D bone models of the tibia plateau is feasible and more precise than the previously described 2D-RX method.. However, further technical improvement is needed to select always the best available allograft.

Purpose: High tibial osteotomy (HTO) is an effective treatment option in early osteoarthritis. However, preoperative planning and surgical execution can be challenging. Computer assisted three-dimensional (3D) planning and patient-specific instruments (PSI) might be helpful tools in achieving successful outcomes. Goal of this study was to assess the accuracy of HTO using PSI., Methods: All medial open wedge PSI-HTO between 2014 and 2016 were reviewed. Using pre- and postoperative radiographs, hip-knee-ankle angle (HKA) and posterior tibial slope (PTS) were determined two-dimensionally (2D) to calculate 2D accuracy. Using postoperative CT-data, 3D surface models of the tibias were reconstructed and superimposed with the planning to calculate 3D accuracy., Results: Twenty-three patients could be included. A mean correction of HKA of 9.7° ± 2.6° was planned. Postoperative assessment of HKA correction showed a mean correction of 8.9° ± 3.2°, resulting in a 2D accuracy for HKA correction of 0.8° ± 1.5°. The postoperative PTS changed by 1.7° ± 2.2°. 3D accuracy showed average 3D rotational differences of - 0.1° ± 2.3° in coronal plane, - 0.2° ± 2.3° in transversal plane, and 1.3° ± 2.1° in sagittal plane, whereby 3D translational differences were calculated as 0.1 mm ± 1.3 mm in coronal plane, - 0.1 ± 0.6 mm in transversal plane, and - 0.1 ± 0.6 mm in sagittal plane., Conclusion: The use of PSI in HTO results in accurate correction of mechanical leg axis. In contrast to the known problem of unintended PTS changes in conventional HTO, just slight changes of PTS could be observed using PSI. The use of PSI in HTO might be preferable to obtain desired correction of HKA and to maintain PTS.