Purpose To describe a strategy for coronal alignment using a computed tomography (CT) based custom total knee arthroplasty (TKA) system, and to evaluate the agreement between the planned and postoperative Hip-Knee-Ankle (HKA) angle, Femoral Mechanical Angle (FMA) and Tibial Mechanical Angle (TMA). Methods From a consecutive series of 918 primary TKAs, 266 (29%) knees received CT-based posterior-stabilized cemented custom TKA. In addition to a preoperative CT-scan, pre-and post-operative radiographs of weight-bearing long leg, anterior-posterior and lateral views of the knee were obtained, on which the FMA, TMA and HKA angles were measured. CTbased three-dimensional (3D) models enabled to correct for cases with bony wear by referring to the non-worn areas and to estimate the native pre-arthritic angles. The alignment technique aimed to preserve or restore constitutional alignment (CA) within predetermined limits, by defining a 'target zone' based on three criteria: 1) a ± 3° (range 87°-93°) primary tolerance for the femoral and tibial resections; 2) a ± 2° secondary tolerance for component obliquity, extending the bounds for FMA and TMA (range 85°-95°); 3) a planned HKA angle range of 175°-183°. Agreement between preoperative, planned and postoperative measurements of FMA, TMA and HKA angle were calculated using intra-class correlation coefficients (ICC). Results Preoperative radiograph and CT-scan measurements revealed that, respectively, 73 (28%) and 103 (40%) knees were in the 'target zone', whereas postoperative radiographs revealed that 217 (84%) TKAs were in the 'target zone'. Deviation from the planned angles were − 0.5° ± 1.8° for FMA, − 0.5° ± 1.8° for TMA, and − 1.1° ± 2.1° for HKA angle. Finally, the agreement between the planned and achieved targets, indicated by ICC, were good for FMA (0.701), fair for TMA (0.462) and fair for HKA angle (0.472). Conclusion Using this strategy for coronal alignment, 84% of custom TKAs were within the 'target zone' for FMA, TMA and HKA angles. These findings support the concepts of emerging personalized medicine technologies, and emphasise the importance of accurate strategies for preoperative planning, which are key to achieving satisfactory 'personalised alignment' that can further be improved by customisation of implant components. Level of evidence IV.

Purpose The purpose of this systematic review and meta-analysis was to investigate the variability in femoral geometric ratios among knees of diferent sexes and races, and to appreciate whether the observed variability is accommodated by commonly implanted total knee arthroplasty (TKA) components. The hypothesis was that the anthropometric studies report considerable variability of femoral geometric ratios among sexes and races. Methods This systematic review and meta-analysis was performed according to the Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA) criteria. Two authors independently conducted an electronic search using MEDLINE ® and Embase ® on 6 July 2020 for clinical studies reporting on femoral geometric ratios among sexes and races. Femoral geometric ratios were graphically represented as means and 2 standard deviations, and compared to those of 13 commonly implanted femoral components. Results A total of 15 studies were identiied that reported on a combined total of 2627 knees; all reported the aspect ratio, and 2 also reported the asymmetry ratio and trapezoidicity ratio. Men had wider knees than women, and compared to Caucasian knees, Arabian and Indian knees were wider, while East Asian were narrower. There were no diferences in asymmetry ratio between men and women, nor among Caucasian and East Asian knees. Men had more trapezoidal knees than women, and East Asian knees were more trapezoidal than Caucasian knees. The commonly implanted femoral components accommodated less than a quarter of the geometric variability observed among sexes and races. Conclusion Anthropometric studies reported considerable sexual dimorphism and racial diversity of femoral geometric ratios. Since a surgeon generally only uses one or a few TKA brands, bone-implant mismatch remains unavoidable in a large proportion of knees. These indings support the drive towards personalized medicine, and accurate bone-implant it may only be achievable through customisation of implants, though the clinical beneits of custom TKA remain to be conirmed. Level of evidence IV.

The mobile biconcave insert design in the lateral unicompartmental knee replacement seems appropriate as a innovative, anatomy imitating solution, resulting in a good clinical outcome. Still, bearing dislocation remains a concern, especially in extended indication.

PurposeThe purpose of this systematic review and meta‐analysis was to investigate the variability in tibial geometric ratios among knees of different sexes and races to determine whether commercially‐available tibial baseplates accommodate the morphologic diversity. The hypothesis was that anthropometric studies report considerable variability of tibial geometric ratios among sexes and races. MethodsThis systematic review and meta‐analysis was performed according to the preferred reporting items for systematic reviews and meta‐analyses (PRISMA) criteria. Two authors independently conducted an electronic search using MEDLINE® and Embase® on 28 January 2021 for clinical studies reporting on tibial geometric ratios. Tibial geometric ratios, as reported by the clinical studies, were represented by plotting their means and two standard deviations for comparison to two symmetric and two asymmetric commercially‐available tibial baseplates. ResultsA total of 27 articles that reported on a combined total of 20,944 knees were eligible for data extraction. Variation in tibial aspect ratios was equal among sexes. The greatest variation in aspect ratio was observed among East Asians, followed by Caucasians, African‐Americans, Indian and Middle Easterns. The variation in tibial asymmetry ratio was larger among men compared to women. The greatest variation in asymmetry ratio was observed among African‐Americans, followed by Caucasians, East Asians, Indian and Middle Easterns. Bone‐implant mismatch of > 3 mm overhang or > 4 mm under‐coverage with four commercially‐available tibial baseplates occurred in large proportions of knees due to variations in aspect ratio (in 17–100% of knees) and asymmetry ratio (in 7–100% of knees). ConclusionAnthropometric studies reported considerable inter‐individual variability of tibial geometric ratios, which exceeded effects of sexual dimorphism and racial diversity. Bone–implant mismatch may be unavoidable in a large proportion of knees, when considering that a surgeon generally only uses one or a few TKA brands. These findings support the drive towards patient‐specific implants to potentially achieve accurate bone–implant fit by implant customisation. Level of evidenceIV.

Aims Altered alignment and biomechanics are thought to contribute to the progression of osteoarthritis (OA) in the native compartments after medial unicompartmental knee arthroplasty (UKA). The aim of this study was to evaluate the bone activity and remodelling in the lateral tibiofemoral and patellofemoral compartment after medial mobile-bearing UKA. Patients and Methods In total, 24 patients (nine female, 15 male) with 25 medial Oxford UKAs (13 left, 12 right) were prospectively followed with sequential 99mTc-hydroxymethane diphosphonate single photon emission CT (SPECT)/CT preoperatively and at one and two years postoperatively, along with standard radiographs and clinical outcome scores. The mean patient age was 62 years (40 to 78) and the mean body mass index (BMI) was 29.7 kg/m2 (23.6 to 42.2). Mean osteoblastic activity was evaluated using a tracer localization scheme with volumes of interest (VOIs). Normalized mean tracer values were calculated as the ratio between the mean tracer activity in a VOI and background activity in the femoral diaphysis. Results Significant reduction of normalized tracer activity was observed one year postoperatively in tibial and femoral VOIs adjacent to the joint line in the lateral compartment. Patellar VOIs and remaining femoral VOIs demonstrated a significant, diminished normalized tracer activity at final follow-up. Conclusion The osteoblastic bone activity in the native compartments decreased significantly after treatment of medial end-stage OA with a UKA, implying reduced stress to the subchondral bone in the retained compartments after a UKA. Cite this article: Bone Joint J 2019;101-B:915–921.

Purpose Implementation of morphometric reference data from the contralateral, unafected lower limb is suggested when reconstructing the coronal plane alignment in TKA. Limited information, however, is available which conirms this leftto-right symmetry in coronal alignment based upon radiographs. The purpose of the study was, therefore, (1) to verify if a left-to-right symmetry is present and (2) to assess whether the contralateral lower limb would be a reliable reference for reconstructing the frontal plane alignment. Methods Full-leg standing radiographs of 250 volunteers (male, 125; female,125) were reviewed for three alignment parameters (Hip-Knee-Ankle angle (HKA), Femoral Mechanical Angle (FMA) and Tibial Mechanical Angle (TMA)). Evaluation of assumed left-to-right symmetry was performed according to two coronal alignment classiications (HKA subdivisions (HKA) and limb, femoral and tibial phenotypes (HKA, FMA and TMA)). Inter-and within-subject variability was calculated, along with correlations coeicients (r) and coeicients of determination (r 2 ). Reliability of the contralateral limb as a personalized reference to reconstruct the constitutional alignment was investigated by intervals, expanding by 1° increments (0.5° increment both to varus and valgus) around the right knee alignment parameters. Subsequently, it was veriied whether or not the left knee parameters fell within this interval. Results Symmetrical distribution in coronal alignment was found in 79% (HKA subdivision) and 59% (limb phenotype) of the cohort. Gender diferences were present for the most common symmetric limb phenotypes (VAR HKA 3° (23.2%) in males and NEU HKA 0° (38.4%) in females). Inter-subject variability was more prominent than the within-subject side diferences for all parameters. Correlations analyses revealed mostly moderate correlations between the alignment measurements. Coeicients of determination showed overall weak left-to-right relationship, except for a moderate predictability for HKA (r 2 = 0.538, p < 0.001) and FMA (r 2 = 0.618, p < 0.001) in females. FMA and TMA marked weak predictive values for contralateral HKA. Only 60% of left knees were referenced within a 3° interval around the right knee. Conclusion No strict left-to-right symmetry was observed in coronal alignment measurements. There is insuicient leftto-right agreement to consider the concept of the contralateral unafected limb as an idealized reference for frontal plane alignment reconstruction based upon full-leg standing radiographs. Level of evidence I.

Purpose The purpose of this study was to report Knee Society Scores (KSS) at 12-month follow-up in a series of 266 knees that received custom TKA. The hypothesis was that custom TKA combined with personalised alignment would yield improvements greater than substantial clinical beneits (SCB) of KSS Knee and Function. Methods From a consecutive series of 905 patients (918 knees) that received primary TKAs, 261 (29%) patients (266 knees) received computed tomography (CT)-based posterior-stabilised cemented custom TKA. Knees were aligned aiming to preserve or restore constitutional alignment within predetermined limits of 85°-95° for femoral mechanical angle (FMA) and tibial mechanical angle (TMA), and 175°-183° for hip knee ankle (HKA) angle. The KSS Knee and Function were collected preoperatively and 12 months postoperatively, to determine if patients achieved SCB. Uni-and multivariable analyses were performed to determine associations between KSS scores (Knee and Function) and patient demographics as well as pre-and postoperative radiographic alignments. Results Of the initial cohort of 261 patients, 4 (1.8%) were reoperated for patellar resurfacing, 1 (0.4%) for lavage to treat infection, and 1 (0.4%) had arthroscopy to treat a stif knee with < 90° range of motion. Complete clinical records were available for 227 patients (232 knees, 87%) that comprised 102 men (5 bilateral) and 125 women. At 12-month follow-up, mean improvements in KSS Knee and Function scores were, respectively, 61.0 ± 13.0 and 42.7 ± 16.7, which exceeded the SCB of KSS. Comparison of knees inside versus outside the target zone revealed no diferences in KSS Knee (94.1 ± 9.1 versus 94.3 ± 9.0, n.s.) and Function (96.1 ± 9.2 versus 96.3 ± 8.9, n.s.). Multivariable analysis revealed worse KSS Knee in knees with preoperative FMA > 95° (β = − 6.21; p = 0.023), but no association between KSS Function and patient demographics or pre-and postoperative radiographic alignments. Conclusions Custom TKA combined with personalised alignment yielded improvements that exceeded substantial clinical beneits of KSS Knee and Function scores. These indings demonstrate the feasibility of custom TKA with 'personalised alignment' and encourage further investigations using comparative studies at longer follow-up. Level of evidence IV, case series.

Background: A combination of conventional computed tomography and single photon emitted computed tomography (SPECT/CT) provides simultaneous data on the intensity and location of osteoblastic activity. Currently, since SPECT/CT scans are not spatially aligned, scans following knee arthroplasty are compared by extracting average and maximal values of osteoblastic activity intensity from large subregions of the structure of interest, which leads to a loss of resolution, and hence, information. Therefore, this paper describes the SPECT/CT registration platform (SCreg) based on the principle of image registration to spatially align SPECT/CT scans following unicondylar knee arthroplasty (UKA) and allow full resolution intra-subject and inter-subject comparisons. Methods: SPECT-CT scans of 20 patients were acquired before and 1 year after UKA. Firstly, scans were preprocessed to account for differences in voxel sizes and divided in volumes of interest. This was followed by optimization of registration parameters according to their volumetric agreement, and alignment using a combination of rigid, affine and non-rigid registration. Finally, radiotracer uptakes were normalized, and differences between pre-operative and post-operative activity were computed for each voxel. Wilcoxon signed rank sum test was performed to compare Dice similarity coefficients pre-and post-registration. Results: Qualitative and quantitative validation of the platform assessing the correct alignment of SPECT/CT scans resulted in Dice similarity coefficient values over 80% and distances between predefined anatomical landmarks below the fixed threshold of (2;2;0) voxels. Locations of increased and decreased osteoblastic activity obtained during comparisons of osteoblastic activity before and after UKA were mainly consistent with literature. Conclusions: Thus, a full resolution comparison performed on the platform could assist surgeons and engineers in optimizing surgical parameters in view of bone remodeling, thereby improving UKA survivorship.