Abstract

Abstract. Introduction. Total joint arthroplasty (TJA) is one of the commonest and most successful orthopaedic procedures, used for the management of end-stage arthritis. With the recent introduction of robotic assisted joint replacement, Computed Tomography (CT) has become part of required pre-operative planning. The aim of this study is to quantify and characterise incidental CT findings, their clinical significance, and their effect on planned joint arthroplasty. Methodology. All consecutive patients undergoing an elective TJR (hip or knee arthroplasty) were retrospectively identified, over a 3-year period (December 2019 and December 2022). Data documented and analysed included patient demographics, type of joint arthroplasty, CT findings, their clinical significance, as well as potential delays to the planned arthroplasty because of these findings and subsequent further investigation. Results. A total of 624 patients (637 studies, 323 (51.8%) female, 301 (48.2%) male) were identified of which 163 (25.6%) showed incidental findings within the long bones or pelvis. Of these 52 (8.2%) were significant, potentially requiring further management, 32 (5.0%) represented potential malignancy and 4 (0.6%) resulted in a new cancer diagnosis. Conclusion. It is not currently national standard practice to report planning CT imaging as it is deemed an unnecessary expense and burden on radiology services. Within the study cohort 52 (8.2%) of patients had a significant incidental finding that required further investigation or management and 4 (0.6%) had a previously undiagnosed malignancy. In order to avoid the inevitability of a missed malignancy on a planning CT, we must advocate for formal reports in all cases

Introduction. Tibial tuberosity and trochlear groove (TT-TG) distance has been investigated for the patients with primary patellofemoral subluxation/dislocation. To date, TT-TG distance after TKA has not been evaluated, and the effect of postoperative TT-TG distance on patellar tracking is unknown. The purpose of the current study was to investigate the effect of TT-TG distance and rotational position of the femoral and tibial components on patellar tilt after TKA. Methods. Consecutive 115 knees for the diagnosis of osteoarthritis were included in the current study. TKA was performed using posterior cruciate ligament sacrificed prosthesis. A total of 17 men and 96 women with an average age of 75.3 years were included at the time of the surgery. Computed tomography (CT) was taken after TKA in full extension. Postoperative TT-TG distance was measured as a reference of surgical epicondylar axis (SEA) of the femur. Patellar tilt was defined as the angle of the patellar component relative to SEA. Femoral and tibial component rotation was measured as the angle relative to SEA and tibial antero-posterior (AP) axis. Tibial AP axis was defined as the line connecting medial one-third of the tibial tuberosity and center of medial-lateral width. Pearson correlation coefficients were calculated to determine the correlations between patellar tilt and TT-TG distance and between patellar tilt and femoral and tibial component rotation. Results. TT-TG distance had significant correlation with patellar tilt (Figure 1; r = 0.254, p = 0.006), whereas femoral component rotation (p = 0.092) and tibial component rotation (p = 0.062) were not correlated with patellar tilt. Concerning the effect on TT-TG distance, femoral component rotation (r = 0.248, p = 0.008) and tibial component rotation (r = −0.567, p < 0.001) were correlated with TT-TG distance. Conclusion. The current study investigated the effect of TT-TG distance on patellar tilt with postoperative CT scan. Greater TT-TG distance resulted in more patellar tilt, which might have negative effects on patellar tracking. In previous clinical studies, femoral component and tibial component rotation affected patellar maltracking. In the current study, however, component rotation itself did not affect patellar tilt. Postoperative TT-TG distance includes information of rotational and medial-lateral positioning of the femoral and tibial components, and can be a useful indicator to predict patellar maltracking after TKA. For any figures or tables, please contact authors directly

Introduction. Component position and overall limb alignment following total knee arthroplasty (TKA) have been shown to influence prosthetic survivorship and clinical outcomes. 1. The objective of this study was to compare the accuracy to plan of three-dimensional modeled (3D) TKA with manual TKA for component alignment and position. Methods. An open-label prospective clinical study was conducted to compare 3D modeling with manual TKA (non-randomized) at 4 U.S. centers between July 2016 and August 2018. Men and women aged > 18 with body mass index < 40kg/m. 2. scheduled for unilateral primary TKA were recruited for the study. 144 3DTKA and 86 manual TKA (230 patients) were included in the analysis of accuracy outcomes. Seven high-volume, arthroplasty fellowship-trained surgeons performed the surgeries. The surgeon targeted a neutral (0°) mechanical axis for all except 9 patients (4%) for whom the target was within 0°±3°. Computed tomography (CT) scans obtained approximately 6 weeks post-operatively were analyzed using anatomical landmarks to determine femoral and tibial component varus/valgus position, femoral component internal/external rotation, and tibial component posterior slope. Absolute deviation from surgical plan was defined as the absolute value of the difference between the CT measurement and the surgeon's operative plan. Smaller absolute deviation from plan indicated greater accuracy. Mean component positions for manual and 3DTKA groups were compared using two-sample t tests for unequal variances. Differences of absolute deviations from plan were compared using stratified Wilcoxon tests, which controlled for study center and accounted for skewed distributions of the absolute values. Alpha was 0.05 two-sided. At the time of this report, CT measurements of femoral component rotation position referenced from the posterior condylar axis were not yet completed; therefore, the current analysis of femoral component rotation accuracy to plan reflects one center that exclusively used manual instruments referencing the transepicondylar axis (TEA). Results. Coronal positions of the femoral components measured via CT for manual and 3D TKA, respectively, were (mean ± standard deviation) 0.1°±1.6° varus and 0.0°±1.4° varus (p=0.533); positions of the tibial components were 1.9°±2.4° varus and 0.9°±2.0° varus (p=0.002). Positions of external femoral component rotation relative to the TEA were 1.1°±2.3° and 0.5°±2.3°, respectively (p=0.036). Tibial slopes were 3.7°±3.0° and 3.2°±1.8°, respectively (p=0.193). Comparing absolute deviation from plan between groups, 3DTKA demonstrated greater accuracy for tibial component alignment [median (25. th. , 75. th. percentiles) absolute deviation from plan, 1.7° (0.9°, 2.9°) vs. 0.9°(0.4°, 1.9°), p<.001], femoral component rotation [1.4° (0.9°, 2.5°) vs. 0.9° (0.7°, 1.5°), p=0.015], and tibial slope [2.9° (1.5°, 5.0°) vs. 1.1° (0.6°, 2.0°), p<.001] (Table 1). Accuracy for femoral component alignment was comparable [1.0° (0.4°, 1.7°) vs. 0.9° (0.4°, 1.5°), p=0.159] (Table 1). Discussion and Conclusions. Our findings support improved accuracy to the surgical plan utilizing 3DTKA compared with manual TKA. Compared to manual TKA, 3DTKA cases were typically 47% more accurate for tibial component alignment, 62% more accurate for tibial slope, and 36% more accurate for femoral component rotation (calculated as percent reduction of median absolute deviation). The evaluation of femoral component coronal alignment reflected already very good baseline accuracy of the surgeons utilizing the intramedullary femoral guide system (Table 1). As optimal component position in TKA affects joint kinematics and may positively influence implant longevity, it is important for surgeons to maximize the opportunity to direct component positioning. Further clinical data is needed to study potential longer-term benefits of robotic technologies. For figures, tables, or references, please contact authors directly

Laboratory experiments and computational models were used to predict bone-implant micromotion and bone strains induced by the cemented and cementless Biomet Oxford medial Unicompartmental Knee Replacement (UKR) tibial implants. Methods. Ten fresh frozen cadaveric knees were implanted with cementless medial mobile UKRs, the tibias were separated and all the soft tissues were resected. Five strain gauge rosettes were attached to each tibia. Four Linear Transducers were used to measure the superior-inferior and transverse bone-implant micromotions. The cementless UKRs were assessed with 10 cycles of 1kN compressive load at 4 different bearing positions. The bone-constructs were re-assessed following cementation of the equivalent UKR. The cemented bone-implant constructs were also assessed for strain and micromotion under 10000 cycles of 10mm anterior-posterior bearing movement at 2Hz and 1kN load. The cadaveric specimens were scanned using Computed Tomography, and 3D computer models were developed using Finite Element method to predict strain and micromotion under various daily loads. Results and Discussion. Results verify computer model predictions and show bone strain pattern differences, with cemented implants distributing the loads more evenly through the bone than cementless implants. Although cementless implants showed micromotions which were greater than computer predictions, the micromotions were as expected significantly greater than those of cemented implants. The computer models reveal that bone strains approach 70% of their failure limit at the posterior and anterior corners adjoining the sagittal and transverse cuts (less pronounced in cemented implants). The base of the keel also develops high strains which can approach failure depending on the amount the implant press-fit. The contributions of the anterior cruciate and patellar tendon forces exacerbate the strains in these regions. This may explain why fractures emanate from the base of the keel and the sagittal cut

Introduction. The trochlear groove plays a major role in the mechanics and patho-mechanics of the patellofemoral joint. Our primary goal was to compare normal, osteoarthritic and dysplastic PFJs in terms of angles and distances. Method. Computed tomography scans of 40 normal knees (>55 years old), 9 knees with patellofemoral osteoarthritis (group A) and 12 knees with trochlear dysplasia (group B) were analysed using 3D software. The femurs were orientated using a robust frame of reference. A circle was fitted to the trochlear groove. The novel trochlear axis was defined as a line joining the centres of two spheres fitted to the trochlear surfaces, lateral and medial to the trochlear groove. The relationship between the femoral trochlea and the tibiofemoral joint was measured in term of angles and distances (offsets).T-test for paired samples was used (p<0.05). Results. The normal trochlear groove closely matched a circle (RMS 0.3mm). It was positioned laterally in relation to the mechanical, anatomical, and trans-condylar axes of the femur. It was not co-planar with any of the three axes. After aligning to the new trochlear axis, the trochlear groove appeared more linear than when other axes were used. In comparison to the normal knees; the medial trochlear was smaller in group A (p=0.0003). The lateral trochlear was smaller in group B (p=0.04). The trochlear groove was smaller in groups B (p=0.0003). Both trochlear centres in groups A+B were more centralised (p=0.00002-0.03). The medial trochlear centre was more distal in group A (p=0.03) and the lateral trochlear centre was more distal in group B (p=0.00009). The trochlear groove started more distal in group B (p=0.0007). Discussion. In osteoarthritic and dysplastic patellofemoral joints, the trochlea is both smaller and more distally located in relation to the tibiofemoral joint. These two factors may contribute to excessive loads that lead to early joint wear

Objectives

Patient-specific (PS) implantation surgical technology has been introduced in recent years and a gradual increase in the associated number of surgical cases has been observed. PS technology uses a patient’s own geometry in designing a medical device to provide minimal bone resection with improvement in the prosthetic bone coverage. However, whether PS unicompartmental knee arthroplasty (UKA) provides a better biomechanical effect than standard off-the-shelf prostheses for UKA has not yet been determined, and still remains controversial in both biomechanical and clinical fields. Therefore, the aim of this study was to compare the biomechanical effect between PS and standard off-the-shelf prostheses for UKA.

Patient specific cutting guides generated by preoperative Magnetic Resonance Imaging (MRI) of the patient’s extremity have been proposed as a method of improving the consistency of Total Knee Arthroplasty (TKA) alignment and adding efficiency to the operative procedure. The cost of this option was evaluated by quantifying the savings from decreased operative time and instrument processing costs compared to the additional cost of the MRI and the guide. Coronal plane alignment was measured in an unselected consecutive series of 200 TKAs, 100 with standard instrumentation and 100 with custom cutting guides. While the cutting guides had significantly lower total operative time and instrument processing time, the estimated $322 savings was overwhelmed by the $1,500 additional cost of the MRI and the cutting guide. All measures of coronal plane alignment were equivalent between the two groups. The data does not currently support the proposition that patient specific guides add value to TKA.

The appearance of the ‘grand-piano sign’ on the anterior resected surface of the femur has been considered to be a marker for correct femoral rotational alignment during total knee replacement. Our study was undertaken to assess quantitatively the morphological patterns on the resected surface after anterior femoral resection with various angles of external rotation, using a computer-simulation technique. A total of 50 right distal femora with varus osteoarthritis in 50 Korean patients were scanned using computerised tomography. Computer image software was used to simulate the anterior femoral cut, which was applied at an external rotation of 0°, 3° and 6° relative to the posterior condylar axis, and parallel to the surgical and clinical epicondylar axes in each case. The morphological patterns on the resected surface were quantified and classified as the ‘grand-piano sign’, ‘the boot sign’ and the ‘butterfly sign’. The surgeon can use the analogy of these quantified sign patterns to ensure that a correct rotational alignment has been obtained intra-operatively.