As advancements in total knee arthroplasty progress at an exciting pace, two areas are of special interest, as they directly impact implant design and surgical decision making. Knee morphometry considers the three-dimensional shape of the articulating surfaces within the knee joint, and knee phenotyping provides the ability to categorize alignment into practical groupings that can be used in both clinical and research settings. This annotation discusses the details of these concepts, and the ways in which they are helping us better understand the individual subtleties of each patient’s knee.

Cite this article: Bone Joint J 2024;106-B(12):1363–1368.

Aims

This study aimed to analyze kinematics and kinetics of the tibiofemoral joint in healthy subjects with valgus, neutral, and varus limb alignment throughout multiple gait activities using dynamic videofluoroscopy.

Aims

The mid-term results of kinematic alignment (KA) for total knee arthroplasty (TKA) using image derived instrumentation (IDI) have not been reported in detail, and questions remain regarding ligamentous stability and revisions. This paper aims to address the following: 1) what is the distribution of alignment of KA TKAs using IDI; 2) is a TKA alignment category associated with increased risk of failure or poor patient outcomes; 3) does extending limb alignment lead to changes in soft-tissue laxity; and 4) what is the five-year survivorship and outcomes of KA TKA using IDI?

The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA, the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered ‘alignment outliers’ in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients’ own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients’ own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal.

Evaluating musculoskeletal conditions of the lower limb and understanding the pathophysiology of complex bone kinematics is challenging. Static images do not take into account the dynamic component of relative bone motion and muscle activation. Fluoroscopy and dynamic MRI have important limitations. Dynamic CT (4D-CT) is an emerging alternative that combines high spatial and temporal resolution, with an increased availability in clinical practice. 4D-CT allows simultaneous visualization of bone morphology and joint kinematics. This unique combination makes it an ideal tool to evaluate functional disorders of the musculoskeletal system. In the lower limb, 4D-CT has been used to diagnose femoroacetabular impingement, patellofemoral, ankle and subtalar joint instability, or reduced range of motion. 4D-CT has also been used to demonstrate the effect of surgery, mainly on patellar instability. 4D-CT will need further research and validation before it can be widely used in clinical practice. We believe, however, it is here to stay, and will become a reference in the diagnosis of lower limb conditions and the evaluation of treatment options.

Cite this article: Bone Joint J 2021;103-B(5):822–827.

Aims

Total knee arthroplasty (TKA) using functional alignment aims to implant the components with minimal compromise of the soft-tissue envelope by restoring the plane and obliquity of the non-arthritic joint. The objective of this study was to determine the effect of TKA with functional alignment on mediolateral soft-tissue balance as assessed using intraoperative sensor-guided technology.

Aims

The aim of this study was to compare robotic arm-assisted bi-unicompartmental knee arthroplasty (bi-UKA) with conventional mechanically aligned total knee arthroplasty (TKA) in order to determine the changes in the anatomy of the knee and alignment of the lower limb following surgery.

Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) introduces significant anatomic modifications and secondary ligament imbalances. A restricted kinematic alignment (rKA) protocol was proposed to minimise these issues and improve TKA clinical results.

A total of 1000 knee CT-Scans were analyzed from a database of patients undergoing TKA. rKA tibial and femoral bone resections were simulated. rKA is defined by the following criteria: Independent tibial and femoral cuts within ± 5° of the bone neutral mechanical axis and, a resulting HKA within ± 3° of neutral. Medial-lateral (ΔML) and flexion-extension (ΔFE) gap differences were calculated and compared with MA results. With the MA technique, femoral rotation was aligned with either the trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC).

Extension space ML imbalances (>/=3mm) occurred in 33% of TKA with MA technique versus 8% of the knees with rKA (p /=5mm) were present in up to 11% of MA knees versus 1% rKA (p < 0 .001). Using the MA technique, for the flexion space ΔML, higher imbalance rates were created by the TEA technique (p < 0 .001). rKA again performed better than both MA techniques using TEA of 3 degrees PC techniques (p < 0 .001). When all the differences between ΔML and ΔFE are considered together: using TEA there were 40.8% of the knees with < 3 mm imbalances throughout, using PC this was 55.3% and using rKA it was 91.5% of the knees (p < 0 .001).

Significantly less anatomic modifications with related ML or FE gap imbalances are created using rKA versus MA for TKA. Using rKA may help the surgeon to balance a TKA, whilst keeping the alignment within a safe range.

Aims

Patient-specific instrumentation of total knee arthroplasty (TKA) is a technique permitting the targeting of individual kinematic alignment, but deviation from a neutral mechanical axis may have implications on implant fixation and therefore survivorship. The primary objective of this randomized controlled study was to compare the fixation of tibial components implanted with patient-specific instrumentation targeting kinematic alignment (KA+PSI) versus components placed using computer-assisted surgery targeting neutral mechanical alignment (MA+CAS). Tibial component migration measured by radiostereometric analysis was the primary outcome measure (compared longitudinally between groups and to published acceptable thresholds). Secondary outcome measures were inducible displacement after one year and patient-reported outcome measures (PROMS) over two years. The secondary objective was to assess the relationship between alignment and both tibial component migration and inducible displacement.

Background

Defining optimal coronal alignment in Total Knee Replacement (TKR) is a controversial and poorly understood subject. Tibial bone density may affect implant stability and functional outcomes following TKR. Our aim was to compare the bone density profile at the implant-tibia interface following TKR in mechanical versus kinematic alignment.

Tibial bone density may affect implant stability and functional outcomes following total knee replacement (TKR). Our aim was to characterise the bone density profile at the implant-tibia interface following TKR in mechanical versus kinematic alignment. Pre-operative computed tomography scans for 10 patients were obtained. Using surgical planning software, tibial cuts were made for TKR either neutral (mechanical) or 3 degrees varus (kinematic) alignment. Signal intensity, in Hounsfield Units (HU), was measured at 25,600 points throughout an axial slice at the implant-tibia interface and density profiles compared along defined radial axes from the centre of the tibia towards the cortices. From the tibial centre towards the lateral cortex, trabecular bone density for kinematic and mechanical TKR are similar in the inner 50% but differ significantly beyond this (p= 0.012). There were two distinct density peaks, with peak trabecular bone density being higher in kinematic TKR (p<0.001) and peak cortical bone density being higher in mechanical TKR (p<0.01). The difference in peak cortical to peak trabecular signal was 43 HU and 185 HU respectively (p<0.001). On the medial side there was no significant difference in density profile and a linear increase from centre to cortex. In the lateral proximal tibia, peak cortical and peak trabecular bone densities differ between kinematic TKR and mechanical TKR. Laterally, mechanical TKR may be more dependent upon cortical bone for support compared to kinematic TKR, where trabecular bone density is higher. This may have implications for surgical planning and implant design.

There is enough evidence to show that navigation improves precision of component placement and consistent and accurate restoration of limb alignment, allowing the surgeon to achieve the desired neutral or kinematic alignment. Computer-assisted TKA provides excellent information regarding gap equality and symmetry throughout the knee range of motion. Accurate soft-tissue balancing is facilitated by CAS. It allows precise, quantitative soft tissue release for deformities, especially in knees with severe flexion contractures and severe rigid varus and valgus deformities. It allows accurate restoration of joint line, and posterior femoral offset. Knee arthritis with complex extra-articular deformities and in-situ hardware can be tackled appropriately using computer navigation where conventional techniques may be inadequate. It also allows intra-articular correction for extra-articular deformities due to malunions and facilitates extra-articular correction in cases with severe extra-articular tibial deformities. In obese patients, where the alignment of the limb is difficult to assess, computer navigation improves accuracy and reduces the number of outliers. The ability to quantify the precise amount of bone cuts and soft tissue releases needed to equalise gaps and restore alignment, reduced blood loss, and reduced incidence of systemic emboli improves the safety of the procedure and hastens functional recovery of the patient. Recent evidence shows that the rate of revision especially in younger patients is reduced with navigation

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. For figures/tables, please contact authors directly.

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 anatomical options 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” and “osteoarthritic knees” 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

Modifying Knee anatomy during mechanical Total Knee Arthroplasty (TKA) may impact ligament balance, patellar tracking and quadriceps function. Although well fixed, patients may report high levels (20%) of dissatisfaction. One theory is that putting the knee in neutral mechanical alignment may be responsible for these unsatisfactory results. Kinematic TKA has gained interest in recent years; it aims to resurface the knee joint and preservation of natural femoral flexion axis about which the tibia and patella articulate, recreating the native knee without the need for soft tissue relaease. That's being said, it remains the question of whether all patients are suitable for kinematic alignment. Some patients' anatomy may be inherently biomechanically inferior and recreating native anatomy in these patients may result in early implant failure. The senior author (PAV) has been performing Kinematic TKA since 2011, and has developed an algorithm in order to better predict which patient may benefit from this technique. Lower limb CT scans from 4884 consecutive patients scheduled for TKA arthroplasty were analysed. These exams were performed for patient-specific instrumentation production (My Knee®, Medacta, Switzerland). Multiple anatomical landmarks used to create accurate CT-based preoperative planning and determine the mechanical axis of bone for the femur and tibia and overall Hip-knee-Ankle (HKA). We wanted to test the safe range for kinematic TKA for the planned distal resection of the femur and tibia. Safe range algorithm was defined as the combination of the following criteria: – Independent tibial and femoral cuts within ± 5° of the bone neutral mechanical axis and HKA within ± 3°. The purpose of this study is to verify the applicability of the proposed safe range algorithm on a large sample of individual scheduled for TKA. The preoperative tibial mechanical angle average 2.9 degrees in varus, femoral mechanical angle averaged 2.7 degrees in valgus and overall HKA averaged of 0.1 in varus. There were 2475 (51%) knees out of 4884, with femur and tibia mechanical axis within ±5° and HKA within ±3° without need for bony corrections. After applying the algorithm, a total of 4062 cases (83%) were successfully been evaluated using the proposed protocol to reach a safe range of HKA ±3° with minimal correction. The remaining 822 cases (17%) could not be managed by the proposed algorithm because of their unusual anatomies and were dealt with individually. In this study, we tested a proposed algorithm to perform kinematic alignment TKA avoiding preservation/restoration of some extreme anatomies that might not be suitable for TKA long-term survivorship. A total of 4062 cases (83%) were successfully eligible for our proposed safe range algorithm for kinematic TKA. In conclusion, kinematically aligned TKA may be a promising option to improve normal knee function restoration and patient satisfaction. Until we have valuable data confirming the compatibility of all patients' pre arthritic anatomies with TKA long-term survivorship, we believe that kinematically alignment should be performed within some limits. Further studies with Radiostereometry or longer follow up might help determine if all patients' anatomies are suitable for Kinematic TKA

Metal Ion Levels Not Useful in Failed M-O-M Hips: Systematic Review; Revision of Failed M-O-M THA at a Tertiary Center; Trunnionosis in Metal-on-Poly THA?; Do Ceramic Heads Eliminate Trunnionosis?; Iliopsoas Impingement After 10 THA; Pain in Young, Active Patients Following THA; Pre-operative Injections Increase Peri-prosthetic THA Infection; Debridement and Implant Retention in THA Infection; THA after Prior Lumbar Spinal Fusion; Lumbar Back Surgery Prior to THA Associated with Worse Outcomes; Raising the Joint Line Causes Mid-Flexion Instability in TKA; No Improvement in Outcomes with Kinematic Alignment in TKA; Botox For TKA Flexion Contracture; Intra-operative Synovitis Predicts Worse Outcomes After TKA for OA; When is it Safe for Patients to Drive After Right TKA?; Alpha-Defensin for Peri-prosthetic Joint Infection; Medial Tibia Overhang and Pain Score After TKA

Introduction

Most surgeons that have performed kinematically aligned TKA have noticed an overall better clinical outcome, better motion, better patient satisfaction, and a quicker recovery than their patients treated with mechanically aligned TKA.

Background. Recent studies reported that the kinematic alignment of an implant is more physiological than the traditional methods, and therefore results in better clinical outcomes. They found that for kinematic alignment of the implant, the femoral component should be positioned valgus 2 degrees and tibial component in varus 2 degrees without femoral rotation. Other study also claimed that kinematically aligned TKA does not cause any significant failure; rather, it restores the function of the knee. Therefore kinematic alignment was raised for further patient's functional satisfaction. Purpose. The purpose of our study is to certify correlation between parameters of implant position and postoperative clinical outcomes after kinematic alignment of TKA. Materials and methods. We obtained 32 patients with primary osteoarthritis who need surgical treatment. During operation we targeted tibial varus of 2 degree and femoral valgus of 2 degree on coronal plane, and neutral rotation on axial plane of the knee. ROM (range of motion) was checked at final visit to office with radiology. Average follow up was 44.5 months (range 36–60). We used the Pearson correlation coefficient to determine any relationship between coronal deformity and PCA or TRA for the entire population and individually for each gender. Clinical outcomes including post op active knee ROM, TRA (the angle between the perpendicular line to the TEA and Akagi's line), varus and valgus angle of the knee were also analyzed. Results. Clinical outcomes including post op knee scoring and ROM was improved. There were negative linear relationships between the femoral component rotation (internal and external) and active and passive range of motion after kinematic alignment of TKA. And we also found a negative linear relationship between the tibial rotation of the component and active and passive range of motion. And we also found a negative linear relationship between the gamma angle and active and passive range of motion. The gamma angle is most powerful predictive parameter of postoperative range of motion of the knee. Conclusion. The alignment of the component set into the kinematic alignment of the knee: internal rotation of femur implant with good gamma angle in sagittal plane will assure better clinical outcome; ROM and scores. Coronal alignments of component (valgus or varus) were weak predictive parameters