Analysis on anatomical references to assess the coronal alignment of tibial and femoral cuts in mega prosthetic knee replacement.

BACKGROUND: In megaprosthetic knee replacement, surgeons use cutting guides that depend on anatomical references to determine the ideal cutting plane alignment. In this work, we investigated the accuracy of using femoral cortical surfaces and tibial canal portions as the references. The study aims to improve the design and use of the cutting guides. MATERIALS AND METHODS: Sixty-one knee scanograms of 33 patients (mean age around 20 years) diagnosed with osteogenic sarcoma and undergoing distal femur megaprosthetic surgery were acquired. Angles between the selected anatomical references and axis perpendicular to the ideal cutting plane (anatomical axis for femur and mechanical axis for tibia) were measured for both femur and tibia, in coronal view. The smaller the magnitude of the angles, the better the anatomical reference is. RESULTS: At the central femoral region, on average, both lateral and medial cortical surfaces give accurate alignment of the ideal cutting plane (0.6° and 0.8°, respectively), with no significant difference (p > 0.01). At the distal region, the lateral cortical surface gives significantly better alignment compared to the medial cortical surface (p < 0.01), but not as accurate (1.4°) as in the central region. For tibia, the central tibial canal gives significantly accurate alignment of the ideal cutting plane (-0.3°) on average, compared to the proximal tibial canal (p < 0.01). CONCLUSIONS: For a femoral cut, both lateral and medial cortical surfaces are the best anatomical references, but only at the central region. For a tibial cut, the central anatomical axis is the best reference. LEVEL OF EVIDENCE: IV.

Evaluating axial alignment and knee phenotypes in a young Indian population, using X-rays converted to three-dimensional bone models, and their relevance in total knee arthroplasty.

PURPOSE: The standard principle of total knee arthroplasty (TKA) targeted by most orthopaedicians is the alignment of the lower limb in a neutral mechanical axis. However, for several patients the neutral mechanical alignment is not normal. Aligning these patients to a neutral mechanical axis may not result in desirable outcomes as it may feel unnatural. This study aimed to discover what percentage of the young healthy Indian population have a neutral hip-knee-ankle angle (HKA = 180°) and what percentage of this population have a deviation from the neutral HKA. We also studied the distribution of knee phenotypes in this non-arthritic population. SUBJECTS AND METHODS: A total of 196 lower limbs were evaluated from 100 subjects, between the ages of 20 and 35 years, without any history of lower limb pathology, of which 50 were males and 50 were females. All volunteers were subjected to full-leg standing anteroposterior and lateral digital radiographs on which various alignment parameters were analysed. Three-dimensional bone models were generated using a validated software. RESULTS: 125 limbs (63.7%) from the total population lay in the range of 180 ± 3°; 7.14% (14/196) of the total limbs had an HKA angle of 180°; 29.5% (58/196) of the total population had a varus alignment, i.e., HKA angle of ≤176° and 6.6% (13/196) had knees in valgus alignment, i.e., HKA angle of ≥184°. Thirty-four percent (33/96) of limbs in men and 25% (25/100) of limbs in women had constitutional varus knees with an alignment of ≤176°; 5.2% (5) of limbs in men and 8% (8) of limbs in women had constitutional valgus knees with an alignment of ≥184°; 67/96 knees in males and 58 knees in females were in the range of 180 ± 3°. CONCLUSIONS: A significant portion of the normal population had limbs that deviated from the neutral HKA. If these subjects were to need TKA in the future, it would not be desirable to restore their alignment to its neutral.

A Study of Surgical Accuracy with X-Ray-Based Patient-Specific Instrument (X3DPSI®) vs Conventional Instrument in Total Knee Arthroplasty Surgeries.

Introduction: Patient-specific instruments (PSI) have been shown to be a good solution in getting accurate bone cuts in total knee arthroplasty (TKA) in many studies. However, the need for an extra CT/MRI makes the existing PSI method costly and unsafe. X-ray-based PSI can solve these problems, if proven to be accurate. The purpose of this study was to introduce a novel method to measure the performance of X-ray to 3D-based PSI (X3DPSI ® ) in achieving planned bone cuts by comparing with conventional instruments (CI). Materials and Methods: This was a prospective study of a total of ten patients undergoing TKA surgery. Preoperative full length lower limb scanogram was done with specialized calibration strap-on marker to develop X3DPSI ® which was used intraoperatively for the placement of guiding pins for the cutting jig. Similarly, intraoperative guide pins were placed using CI also. Calibrated intraoperative X-ray images, in AP and LAT view, were taken while the cutting-block guiding pins were placed on the distal femur and proximal tibia. These X-ray images were used to calculate the cutting plane alignments for femur and tibia and to simulate the postoperative hip-knee-ankle (HKA) angle and MAD (mechanical axis deviation), in a virtual Tabplan3D environment for both the methods. Results: The results showed that there was a significant difference between the two methods in terms of femoral cutting plane angles and in terms of the HKA angles and MAD. There was no significant difference in the tibial cutting plane angles in the coronal plane. Conclusion: The mechanical axis alignment achieved based on the virtual cuts made using the X3DPSI ® was significantly better than the alignment achieved based on the cuts made using the CI, in terms of both HKA and MAD. This novel method of X-ray-based PSI is a low-cost alternative to CT/MRI-based PSI if found to be accurate in future planned studies.

CT-Based 3D Reconstruction of Lower Limb Versus X-Ray-Based 3D Reconstruction: A Comparative Analysis and Application for a Safe and Cost-Effective Modality in TKA.

AIM: Patient Specific Instrumentation (PSI) with 3D bone models have been used to improve the outcomes of Total Knee Arthroplasty (TKA). The PSI, however, needs a CT (Computed tomography)/MRI scan to reproduce a bone-based model. However, CT is not a routine imaging method in the TKA and has challenges such as high radiation exposure and increased investigation cost. Any technology or software which could accurately recreate 3D bone models using X-ray would be a cheaper and safer tool. This study is based on one such technology (XrayTo3D®) using X-ray to 3D as an alternative to other image-based 3D bone models and PSI available in the market. This study compares the accuracy of XrayTo3D® versus a Conventional CT to 3D, in the reconstruction of lower limb bones (femur and tibia). METHOD: In an analysis of 45 lower limbs, 11 anatomical parameters were measured [Medial Proximal Tibial Angle-MPTA, Tibial(T)-torsion, T-slope, T-length, Mechanical Lateral Distal Femoral Angle (mLDFA), F-version, F-length, Distal femoral Medio lateral width (F-ML), Distal Femoral Antero Posterior (F-AP), Proximal Tibia Antero Posterior (T-AP), Proximal Tibia Medio Lateral (T-ML) based on landmarks selected by three orthopaedic surgeons(numbers of the authors superscript), on two groups of 3D models, one reconstructed using XrayTo3D® and the other using CT. Mean and standard-deviation values were measured for all the parameters in both the groups. Statistical association between both the groups was measured by Pearson's correlation coefficient. Two-sided t tests of the mean values were calculated to compare the two measurement methods. The interobserver reproducibility within each group was measured by the intraclass correlation coefficient (ICC). Point-to-surface (P2S) error, in the distal femur and proximal tibia regions of the models reconstructed using XrayTo3D®, were also measured. RESULTS: For all the 11 parameters, no statistically significant difference was found between the 2 groups (p > 0.05). Pearson's correlation coefficients for all the parameters were not significant. The interobserver reproducibility was ranging from 0.90 to 1.00 and 0.90 to 1.00 for the XrayTo3D® and CT groups, respectively. The mean P2S distance was 1.0 mm in distal femur and 1.1 mm in proximal tibia which was within the acceptable limits. CONCLUSION: The reconstruction accuracy of the XrayTo3D® is an accurate, safe and cost effective as compared to a CT-based method.

3D femur model reconstruction from biplane X-ray images: a novel method based on Laplacian surface deformation.

PURPOSE: Conventional methods for 3D bone model reconstruction from CT scans can require high-radiation dose, cost and time. A 3D model generated from 2D X-ray images may be a useful alternative. Reconfiguring a 3D template surface mesh model to match bone shape in orthogonal radiographs is a common technique for 3D reconstruction. A computationally efficient 3D bone modeling algorithm was developed and tested. METHOD: An algorithm for bone template reconfiguration is proposed, which uses Kohonen self-organizing maps for 2D-3D correspondence between input X-ray images and the template. Laplacian surface deformation is then used for final deformation of the template. In the literature, Laplacian deformation has been shown to perform better than thin-plate splines and free form deformation in terms of computation time and mesh quality. The method was applied to 22 sets of simulated input contours generated from 3D models of the distal femur. RESULTS: An acceptable range of reconstruction error: 1.5 mm of RMS-P2S (root-mean-square point-to-surface) distance and 1.2 mm mean-P2S distance errors was observed based on comparison with the corresponding reference models/ground truth. Computation time for the 3D bone modeling algorithm was less than a minute for each case. CONCLUSION: The new template reconfiguration algorithm based on Laplacian surface deformation provided acceptable reconstruction accuracy and high computation efficiency for 3D modeling of the distal femur using biplane radiographs. This algorithm may provide a useful option for orthopedic modeling applications.

Extramedullary versus intramedullary tibial cutting guides in megaprosthetic total knee replacement.

BACKGROUND: In a standard total knee replacement, tibial component alignment is a key factor for the long term success of the surgery. The purpose of this study is to compare the accuracy of extramedullary and intramedullary tibial cutting guides used in indigenous and imported implants respectively, in positioning of the tibial components in megaprosthetic knee replacements. METHODS: A comparative study of the accuracy of extramedullary and intramedullary tibial cutting guides was carried out in 92 megaprosthetic knee replacements for distal femoral tumors. For the proximal tibia cut for tibial component placement, an extramedullary guide was used in 65 patients and an intramedullary guide was used in 27 patients. Tibial component alignment angles were measured in postoperative X-rays with the help of CAD software. RESULTS: There was more varus placement in coronal plane with extramedullary cutting guide (-1.18 +/- 2.4 degrees) than the intramedullary guide (-0.34 +/- 2.31 degrees) but this did not reach statistical significance. The goal of 90 +/- 2 degrees alignment of tibial component was achieved in 54% of patients in the extramedullary group versus 67% in the intramedullary group. In terms of sagittal plane alignment, extramedullary guide showed less accurate results (2.09 +/- 2.4 degrees) than intramedullary guide (0.50 +/- 3.80 degrees) for tibial component alignment, though 78% of patients were aligned within the goal of 0-5 degrees of tibial slope angle in extramedullary group versus 63% in intramedullary group. The mean error in the measurements due to rotation of the knee during taking the X-rays was less than 0.1 degrees and distribution of the X-rays with the rotation of knee was similar in both the groups. CONCLUSIONS: Overall, in megaprosthetic knee replacement intramedullary guides gave more accurate results in sagittal plane and exhibited similar variability as of extramedullary guides in coronal plane.