Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) may introduce significant anatomic modifications, as it is known that few patients have neutral femoral, tibial or overall lower limb mechanical axes. A total of 1000 knee CT-Scans were analyzed from a database of patients undergoing TKA. MA tibial and femoral bone resections were simulated. Femoral rotation was aligned with either the trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Medial-lateral (DML) and flexion-extension (DFE) gap differences were calculated. Extension space ML imbalances (3mm) occurred in 25% of varus and 54% of valgus knees and significant imbalances (5mm) were present in up to 8% of varus and 19% of valgus knees. For the flexion space DML, higher imbalance rates were created by the TEA technique (p < 0 .001). In valgus knees, TEA resulted in a DML in flexion of 5 mm in 42%, compared to 7% for PC. In varus knees both techniques performed better. When all the differences between DML and DFE are considered together, using TEA there were 18% of valgus knees and 49% of varus knees with < 3 mm imbalances throughout, and using PC 32% of valgus knees and 64% of varus knees. Significant anatomic modifications with related ML or FE gap imbalances are created using MA for TKA. Using MA techniques, PC creates less imbalances than TEA. Some of these imbalances may not be correctable by the surgeon and may explain post-operative TKA instability. Current imaging technology could predict preoperatively these intrinsic imitations of MA. Other alignment techniques that better reproduce knee anatomies should be explored.
The objective of our study was to determine the extent to which the quality of the biomechanical reconstruction when performing hip replacement influences gait performances. We aimed to answer the following questions: 1) Does the quality of restoration of hip biomechanics after conventional THR influence gait outcomes? (question 1), and 2) Is HR more beneficial to gait outcomes when compared with THR? (question 2). we retrospectively reviewed 52 satisfied unilateral prosthetic hip patients (40 THRs and 12 HRs) who undertook objective gait assessment at a mean follow-up of 14 months. The quality of the prosthetic hip biomechanical restoration was assessed on standing pelvic radiograph by comparison to the healthy contralateral hip.Introduction
Methods
A principle of Total Knee Arthroplasty (TKA) is to achieve a neutral standing coronal alignment of the limb (Hip Knee Ankle (HKA) angle) to reduce risks of implant loosening, reduce polyethylene wear, and optimise patella tracking. Several long-term studies have questioned this because the relationship between alignment and implant survivorship is weaker than previously reported. We hypothesize standing HKA poorly predicts implant failure because it does not predict dynamic HKA, dynamic adduction moment, and loading of the knee during gait. Therefore, the aim of our study is to assess the relationship between the standing (or static) and the dynamic (gait activity) HKAs. We performed a prospective study on a cohort of 35 patients (35 knees) who were treated with a posterior-stabilized TKA for primary osteoarthritis between November 2012 and January 2013. Three months after surgery each patient had standardized digital full-leg coronal radiographs and was classified as neutrally aligned TKA (17 patients), varus aligned (9 patients), and valgus aligned (4 patients) (figure 1). Patients then performed a gait analysis for level walking and dynamic HKA and adduction moment during the stance phase of gait were measured.Background
Methods
The current, most popular recommendation for cup orientation, namely the Lewinnek box, dates back to the 70's, that is to say at the stone age of hip arthroplasty. Although Lewinnek's recommendations have been associated with a reduction of dislocation, some complications, either impingement or edge loading related, have not been eliminated. Early dislocations are becoming very rare and most of them probably occur in “outlier” patients with atypical pelvic/hip kinematics. Because singular problems usually need singular treatments, those patients need a more specific personalised planning of the treatment rather than a basic systematic application of Lewinnek recommendations. We aim in this review to define the potential impacts that the spine-hip relations (SHRs) have on hip arthroplasty. We highlight how recent improvements in hip implants technology and knowledge about SHRs can substantially modify the planning of a THR, and make the «Lewinnek recommendations» not relevant anymore. We propose a new classification of the SHRs with specific treatment recommendations for hip arthroplasty whose goal is to help at establishing a personalized planning of a THR. This new classification (figures 1 and 2) gives a rationale to optimize the short and long-term patient's outcomes by improving stability and reducing edge loading. We believe this new concept could be beneficial for clinical and research purposes.
The accurate positioning of the total knee arthroplasty affects the survival of the implants(1). Alignment of the femoral component in relation to the native knee is best determined using pre- and post-operative 3D-CT reconstruction(2). Currently, the scans are visualised on separate displays. There is a high inter- and intra-observer variability in measurements of implant rotation and translation(3). Correct alignment is required to allow a direct comparison of the pre- and post-operative surfaces. This is prevented by the presence of the prostheses, the bone shape alteration around the implant, associated metal artefacts, and possibly a segmentation noise. Create a novel method to automatically register pre- and post-operative femora for the direct comparison of the implant and the native bone.Background
Aim
Trochlear geometry of modern femoral implants is designed for the mechanical alignment (MA) technique for Total Knee Arthroplasty (TKA). The biomechanical goal is to create a proximalised and more valgus trochlea to better capture the patella and optimize tracking. In contrast, Kinematic alignment (KA) technique for TKA respects the integrity of the soft tissue envelope and therefore aims to restore native articular surfaces, either femoro-tibial or femoro-patellar. Consequently, it is possible that current implant designs are not suitable for restoring patient specific trochlea anatomy when they are implanted using the kinematic technique. This could cause patellar complications, either anterior knee pain, instability or accelerated wear or loosening. The aim of our study is therefore to explore the extent to which native trochlear geometry is restored when the Persona® implant (Zimmer, Warsaw, USA) is kinematically aligned. A retrospective study of a cohort of 15 patients with KA-TKA was performed with the Persona® prosthesis (Zimmer, Warsaw, USA). Preoperative knee MRIs and postoperative knee CTs were segmented to create 3D femoral models. MRI and CT segmentation used Materialise Mimics® and Acrobot Modeller® software, respectively. Persona® implants were laser-scanned to generate 3D implant models. Those implant models have been overlaid on the 3D femoral implant model (generated via segmentation of postoperative CTs) to replicate, BACKGROUND
METHODS
Hip resurfacing arthroplasty (HRA) is currently regaining positive attention as a treatment of osteoarthritis in young, active individuals[1]. The procedure is complex and has low tolerance for implant malpositioning [2]. ‘Precision tools', such as imageless navigation and patient specific instruments, have been developed to assist with implant positioning but have not been shown to be fully reliable [3]. The aim of this study is to present and validate the first step of novel quality control tool to verify implant position intra-operatively. We propose that, before reaming of the femoral head, a handheld structured light 3D scanner can be used to assess the orientation and insertion point of femoral guide wire. Guide wires were placed into the heads of 29 solid foam synthetic femora. A specially designed marker (two orthogonal parallelepipeds attached to a shaft) was inserted into the guide wire holes. Each bone (head, neck and marker) was 3D scanned twice (fig 1). The insertion point and guide wire neck angle were calculated from the marker's parameters. Reference data was acquired with an optical tracking system. The measurements calculated with the 3D scans were compared to the reference ones to evaluate the precision. The comparison of the test retest measurements done with the new method are used to evaluate intra-rater variability.Introduction
Methods
The mechanical alignment (MA) for Total Knee Arthroplasty (TKA) with neutral alignment goal has had good overall long-term outcomes. In spite of improvements in implant designs and surgical tools aiming for better accuracy and reproducibility of surgical technique, functional outcomes of MA TKA have remained insufficient. Therefore, alternative, more anatomicaloptions restoring part (adjusted MA (aMA) and adjusted kinematic alignment (aKA) techniques) or the entire constitutional frontal deformity (unicompartment knee arthroplasty (UKA) and kinematic alignment (KA) techniques) have been developed, with promising results. The kinematic alignment for TKA is a new and attractive surgical technique enabling a patient specific treatment. The growing evidence of the kinematic alignment mid-term effectiveness, safety and potential short falls are discussed in this paper. The current review describes the rationale and the evidence behind different surgical options for knee replacement, including current concepts in alignment in TKA. We also introduce two new classification systems for “implant alignments options” (Figure 1) and “osteoarthritic knees” (Figure 2) that would help surgeons to select the best surgical option for each patient. This would also be valuable for comparison between techniques in future research.
Conventional TKA surgery attempts to restore patients to a neutral alignment, and devices are designed with this in mind. Neutral alignment may not be natural for many patients, and may cause dissatisfaction [1]. To solve this, kinematical alignment (KA) attempts to restore the native pre-arthritic joint-line of the knee, with the goal of improving knee kinematics and therefore patient's function and satisfaction [1]. Proper prosthetic trochlea alignment is important to prevent patella complications such as instability or loosening. However, available TKA components have been designed for mechanical implantation, and concerns remain relating the orientation of the prosthetic trochlea when implants are kinematically positioned. The goal of this study is to investigate how a currently available femoral component restores the native trochlear geometry of healthy knees when virtually placed in kinematic alignment. The healthy knee OAI (Osteoarthritis Initiative) MRI dataset was used. 36 MRI scans of healthy knees were segmented to produce models of the bone and cartilage surfaces of the distal femur. A set of commercially available femoral components was laser scanned. Custom 3D planning software aligned these components with the anatomical models: distal and posterior condyle surfaces of implants were coincident with distal and posterior condyle surfaces of the cartilage; the anterior flange of the implant sat on the anterior cortex; the largest implant that fitted with minimal overhang was used, performing ‘virtual surgery’ on healthy subjects. Software developed in-house fitted circles to the deepest points in the trochlear grooves of the implant and the cartilage. The centre of the cartilage trochlear circle was found and planes, rotated from horizontal (0%, approximately cutting through the proximal trochlea) through to vertical (100%, cutting through the distal trochlea) rotated around this, with the axis of rotation parallel to the flexion facet axis. These planes cut through the trochlea allowing comparison of cartilage and implant surfaces at 1 degree increments - (fig.1). Trochlear groove geometry was quantified with (1) groove radial distance from centre of rotation cylinder (2) medial facet radial distance (3) lateral facet radial distance and (4) sulcus angle, along the length of the trochlea. Data were normalised to the mean trochlear radius. The orientation of the groove was measured in the coronal and axial plane relative to the flexion facet axis. Inter- and intra-observer reliability was measured.BACKGROUND
METHODS
