The aim of mechanical alignment in total knee arthroplasty is to align all knees into a fixed neutral position, even though not all knees are the same. As a result, mechanical alignment often alters a patient’s constitutional alignment and joint line obliquity, resulting in soft-tissue imbalance. This annotation provides an overview of how the Coronal Plane Alignment of the Knee (CPAK) classification can be used to predict imbalance with mechanical alignment, and then offers practical guidance for bone balancing, minimizing the need for soft-tissue releases. Cite this article:
In a clinical setting, there is a need for simple gait kinematic measurements to facilitate objective unobtrusive patient monitoring. The objective of this study is to determine if a learned classification model's output can be used to monitor a person's recovery status post-TKA. The gait kinematics of 20 asymptomatic and 17 people with TKA were measured using a full-body Xsens model1. The experimental group was measured at 6 weeks, 3, 6, and 12 months post-surgery. Joint angles of the ankle, knee, hip, and spine per stride (10 strides) were extracted from the Xsens software (MVN Awinda studio 4.4)1. Statistical features for each subject at each evaluation moment were derived from the kinematic time-series data. We normalised the features using standard scaling2. We trained a logistic regression (LR) model using L1-regularisation on the 6 weeks post-surgery data2–4. After training, we applied the trained LR- model to the normalised features computed for the subsequent timepoints. The model returns a score between 0 (100% confident the person is an asymptomatic control) and 1 (100% confident this person is a patient). The decision boundary is set at 0.5. The classification accuracy of our LR-model was 94.58%. Our population's probability of belonging to the patient class decreases over time. At 12 months post-TKA, 38% of our patients were classified as asymptomatic.
Once knee arthritis and deformity have occurred, it is currently not known how to determine a patient’s constitutional (pre-arthritic) limb alignment. The purpose of this study was to describe and validate the arithmetic hip-knee-ankle (aHKA) algorithm as a straightforward method for preoperative planning and intraoperative restoration of the constitutional limb alignment in total knee arthroplasty (TKA). A comparative cross-sectional, radiological study was undertaken of 500 normal knees and 500 arthritic knees undergoing TKA. By definition, the aHKA algorithm subtracts the lateral distal femoral angle (LDFA) from the medial proximal tibial angle (MPTA). The mechanical HKA (mHKA) of the normal group was compared to the mHKA of the arthritic group to examine the difference, specifically related to deformity in the latter. The mHKA and aHKA were then compared in the normal group to assess for differences related to joint line convergence. Lastly, the aHKA of both the normal and arthritic groups were compared to test the hypothesis that the aHKA can estimate the constitutional alignment of the limb by sharing a similar centrality and distribution with the normal population.Aims
Methods
A comprehensive classification for coronal lower limb alignment with predictive capabilities for knee balance would be beneficial in total knee arthroplasty (TKA). This paper describes the Coronal Plane Alignment of the Knee (CPAK) classification and examines its utility in preoperative soft tissue balance prediction, comparing kinematic alignment (KA) to mechanical alignment (MA). A radiological analysis of 500 healthy and 500 osteoarthritic (OA) knees was used to assess the applicability of the CPAK classification. CPAK comprises nine phenotypes based on the arithmetic HKA (aHKA) that estimates constitutional limb alignment and joint line obliquity (JLO). Intraoperative balance was compared within each phenotype in a cohort of 138 computer-assisted TKAs randomized to KA or MA. Primary outcomes included descriptive analyses of healthy and OA groups per CPAK type, and comparison of balance at 10° of flexion within each type. Secondary outcomes assessed balance at 45° and 90° and bone recuts required to achieve final knee balance within each CPAK type.Aims
Methods
An algorithm to determine the constitutional alignment of the lower limb once arthritic deformity has occurred would be of value when undertaking kinematically aligned total knee arthroplasty (TKA). The purpose of this study was to determine if the arithmetic hip-knee-ankle angle (aHKA) algorithm could estimate the constitutional alignment of the lower limb following development of significant arthritis. A matched-pairs radiological study was undertaken comparing the aHKA of an osteoarthritic knee (aHKA-OA) with the mechanical HKA of the contralateral normal knee (mHKA-N). Patients with Grade 3 or 4 Kellgren-Lawrence tibiofemoral osteoarthritis in an arthritic knee undergoing TKA and Grade 0 or 1 osteoarthritis in the contralateral normal knee were included. The aHKA algorithm subtracts the lateral distal femoral angle (LDFA) from the medial proximal tibial angle (MPTA) measured on standing long leg radiographs. The primary outcome was the mean of the paired differences in the aHKA-OA and mHKA-N. Secondary outcomes included comparison of sex-based differences and capacity of the aHKA to determine the constitutional alignment based on degree of deformity.Aims
Methods
The purpose of this current multicentre study is to analyse the
presence of alpha-defensin proteins in synovial fluid using the
Synovasure lateral flow device and to determine its diagnostic reliability
and accuracy compared with the prosthetic joint infection (PJI)
criteria produced by the Musculoskeletal Infection Society (MSIS). A cohort of 121 patients comprising 85 total knee arthroplasties
and 36 total hip arthroplasties was prospectively evaluated between
May 2015 and June 2016 in three different orthopaedic centres. The
tests were performed on patients with a chronically painful prosthesis
undergoing a joint aspiration in a diagnostic pathway or during revision
surgery.Aims
Patients and Methods
The aim of this consensus was to develop a definition of post-operative
fibrosis of the knee. An international panel of experts took part in a formal consensus
process composed of a discussion phase and three Delphi rounds.Aims
Patients and Methods
It is nowadays widely recognized that patient satisfaction following knee arthroplasty strongly depends on ligament balancing. To obtain this balancing, the occurring ligament strain is assumed to play a crucial role. To measure this strain, a method is described in this paper that allows full field 3D evaluation of the strains. The latter is preferred over traditional measurement techniques, e.g. displacement transducers or strain gauges, as human soft tissue is not expected to deform uniformly due to its highly inhomogeneous and anisotropic properties. To facilitate full field strain measurements, the 3D digital image correlation (DIC) technique was adopted. This technique was previously validated by our research group on human tissue. First, a high contrast speckle pattern was applied on the sMCL. Therefore, the specimens are first coated with a small layer of methylene blue. Following, a random white speckle pattern is applied. During knee flexion, two cameras simultaneously take pictures of the deforming region at predefined flexion angles. Using dedicated software, the captured images are eventually combined and result in 3D full field strains and displacements. Using this method, the strain distribution was studied in six cadaveric knees during flexion extension movement. Therefore, the femur was rigidly fixed in a custom test rig. The tibia was left unconstrained, allowing the six degrees of freedom in the knee. A load was applied to all major muscles in physiological directions of each muscle by attaching a series of calibrated weights (Farahmand et al., J Orthop Res., 1998;16(1)). The direction of the pulling cables was controlled using a digital inclinometer for each specimen. As a result, a statically balanced muscle loading of the knee was obtained. From these cadaveric experiments, it is observed that on average the sMCL behaves isometrically between 0° and 90° of flexion. However, high regional differences in strain distribution are observed from the full field measurements. The proximal region of the sMCL experiences relatively high strains upon flexion. These strains are positive (tension) in the anterior part and negative (compression) in the posterior region. In contrast, the distal region remains approximately isometric upon knee flexion (see Figure 1). It is accordingly concluded that the sMCL behaves isometric, though large regional differences are observed. The proximal region experiences higher strains. Furthermore, the DIC technique provided valuable insights in the deformation of the sMCL. This technique will therefore be applied to study the impact of knee arthroplasty in the near future. Caption with figure 1: Full field strain distribution in the sMCL's longitudinal direction for specimen in 45° (a) and 90° (b) of knee flexion
Unicondylar knee arthroplasty (UKA) is growing in popularity with an increase in utilisation. As a less invasive, bone preserving procedure suitable for knee osteoarthritic patients with intact cruciate ligaments and disease confined to one compartment of the knee joint. The long term survival of a UKA is dependent on many factors, including the accuracy of prosthesis implantation and soft tissue balance. Robotic assisted procedures are generally technically demanding, can increase the operation time and are associated with a learning curve. The learning curve for new technology is likely to be influenced by previous experience with similar technologies, the frequency of use and general experience performing the particular procedure. The purpose of this study was to determine the time to achievement of a steady state with regards to surgical time amongst surgeons using a novel hand held robotic device. This study examined consecutive UKA cases which used a robotic assistive device from five surgeons. The surgeons had each performed at least 15 surgeries each. Two of the surgeons had previous experience with another robotic assistive device for UKA. All of the surgeons had experience with conventional UKA. All of the surgeons have used navigation for other knee procedures within their hospital. The system uses image free navigation with infrared optical tracking with real time feedback. The handheld robotic assistive system for UKA is designed to enable precision of robotics in the hands of the surgeon. The number of surgeries required to reach ‘steady state’ surgical time was calculated as the point in which two consecutive cases were completed within the 95% confidence interval of the surgeon's ‘steady state’ time. The average surgical time (tracker placement to implant trial acceptance phase) from all surgeons across their first 15 cases was 56.8 minutes (surgical time range: 27–102 minutes). The average improvement was 46 minutes from slowest to quickest surgical times. The ‘cutting’ phase was reported as decreasing on average by 31 minutes. This clearly indicates the presence of a learning curve. The surgeons recorded a significant decrease in their surgical time where the most improvement was in the process of bone cutting (as opposed to landmark registration, condyle mapping and other preliminary or planning steps). There was a trend towards decreasing surgical time as case numbers increase for the group of five surgeons. On average it took 8 procedures (range 5–11) to reach a steady state surgical time. The average steady state surgical time was 50 minutes (range 37–55 minutes). In conclusion, the average operative time was comparable with clinical cases reported using other robotic assistive devices for UKA. All five surgeons using the novel handheld robotic-assisted orthopaedic system for UKA reported significant improvement in bone preparation and overall operative times within the first 15 cases performed, reaching a steady state in surgical times after a mean of 8 cases. Therefore, this novel handheld device has a similar learning curve to other devices on the market.
For patients suffering from osteoarthritis confined to one compartment of the knee joint, a successful unicondylar knee arthroplasty (UKA) has demonstrated an ability to provide pain relief and restore function while preserving bone and cruciate ligaments that a total knee arthroplasty (TKA) would sacrifice. Long-term survival of UKA has traditionally been inconsistent, leading to decreased utilisation in favour of alternative surgical treatment. Robot-assisted UKA has demonstrated an ability to provide more consistent implantation of UKA prosthesis, with the potential to increase long-term survivorship. This study reports on 65 patients undergoing UKA using an image-free, handheld robotic assistive navigation system. The condylar surface was mapped by the surgeon intra-operatively using a probe to capture a 3-dimensional representation of the area of the knee joint to be replaced. The intra operative planning phase allows the surgeon to determine the size and orientation of the femoral and tibial implant to suit the patients’ anatomy. The plan sets the boundaries of the bone to be removed by the robotic hand piece. The system dynamically adjusts the depth of bone being cut by the bur to achieve the desired result. The planned mechanical axis alignment was compared with the system's post-surgical alignment and to post-operative mechanical axis alignment using long leg, double stance, weight bearing radiographs. All 65 knees had knee osteoarthritis confined to the medial compartment and UKA procedures were completed using the handheld robotic assistive navigation system. The average age and BMI of the patient group was 63 years (range 45–82 years) and 29 kg/m2 (range 21–37 kg/m2) respectively. The average pre-operative deformity was 4.5° (SD 2.9°, Range 0–12° varus). The average post-operative mechanical axis deformity was corrected to 2.1° (range 0–7° varus). The post-operative mechanical axis alignment in the coronal plane measured by the system was within 1° of intra-operative plan in 91% of the cases. 3 out of 6 of the cases where the post-operative alignment was greater than 1° resulted due to an increase in the thickness of the tibia prosthesis implanted. The average difference between the ‘planned’ mechanical axis alignment and the post-operative long leg, weight bearing mechanical axis alignment was 1.8°. The average Oxford Knee Score (old version) pre and post operation was 38 and 24 respectively, showing a clinical and functional improvement in the patient group at 6 weeks post-surgery. The surgical system allowed the surgeons to precisely plan a UKA and then accurately execute their intra operative plan using a hand held robotically assisted tool. It is accepted that navigation and robotic systems have a system error of about 1° and 1mm. Therefore, this novel device recorded accurate post-operative alignment compared to the ‘planned’ post-operative alignment. The patients in this group have shown clinical and functional improvement in the short term follow up. The importance of precision of component alignments while balancing existing soft-tissue structures in UKA has been documented. Utilisation of robotic-assisted devices may improve the accuracy and long-term survivorship UKA procedure.
Passive knee stability is provided by the soft tissue envelope which resists abnormal motion. There is a consensus amongst orthopedic surgeons that a good outcome in TKA requires equal tension in the medial and the lateral compartment of the knee joint, as well as equal tension in the flexion and extension gap. The purpose of this study was to quantify the ligament laxity in the normal non-arthritic knee before and after standard posterior-stabilized total knee arthroplasty (PS-TKA). We hypothesized that the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) will show minimal changes in length when measured directly by extensometers in the native human knee during varus/valgus laxity testing. We also hypothesized that due to differences in material properties and surface geometry, native laxity is difficult to be completely reconstructed using contemporary types of PS-TKA. A total of 6 specimens were used to perform this This study enabled a very precise measurement of varus and valgus laxity as compared with the clinical assessment which is a subjective measure. The strains in both ligaments in the replaced knee were different from those in the native knee. Both ligaments were stretched in extension, in flexion the MCL tends to relax and the LCL remains tight. Fig. 2 Initial and maximal strain values in the MCL during valgus and varus laxity testing in different flexion angles. a: intact knee, b: replaced knee. and Fig. 3 Initial and maximal strain values in the LCL during valgus and varus laxity testing indifferent flexion angles. a: intact knee, b: replaced knee.Methods:
Findings:
In this study, three-dimensional (3D) digital image correlation (DIC) was adopted to investigate the strain in the superficial medial collateral ligament (sMCL) of the human knee. To our knowledge, no reports or validation of 3D DIC measurement on human collagenous tissue exists. The first part of this research project focused on the validation of 3D DIC (1) as a highly accurate tool for non-contact full field strain analysis of human collagenous tissue. In the second part, 3D DIC was used to measure the strain patterns in the superficial medial collateral ligament (sMCL) of the native knee (2). In a third part, the strain pattern in the sMCL after total knee arthroplasty (TKA) in an ‘optimal’ (3) and with a proximalised joint line (4) was analysed. (1) Six fresh frozen human Achilles tendon specimens were mounted in a custom made rig for uni-axial loading. The accuracy and reproducibility of 3D DIC was compared to two linear variable differential transformers (LVDT's). (2) The strain pattern of the sMCL during the range of motion (ROM) was measured using 3D DIC in six fresh frozen cadaveric knees. The knees were mounted in a custom made rig, applying balanced tension to all muscle groups around the knee. The experiment was repeated after computer navigated implantation of a single radius posterior stabilised (PS) TKA in ‘optimal’ (3) and with a 4 mm proximalised joint line (4).Introduction
Methods
Recently a new version of the Knee Society Knee Scoring System has been developed, adapted to the lifestyle and activities of contemporary patients with a Total Knee Arthroplasty (TKA). It is subdivided into 4 domains including an Objective Knee Score, a Satisfaction Score, an Expectations Score and a Functional Activity Score. Before this scale can be used in non-English speaking populations, it has to be translated and validated for specific populations. The aim of this study was to translate and validate the New Knee Society Knee Scoring System (new KSS) for Dutch speaking populations. A Dutch translation of the New KSS was established using a forward-backward translation protocol. 137 patients undergoing TKA were asked to complete the Dutch translation of the New KSS as well as the Dutch WOMAC, Dutch KOOS and the Dutch SF12. To determine the test-retest reliability, 53 patients were asked to fill out a second questionnaire with one-week interval. We tested the test-retest reliability of the subjective domains of the New KSS by assessing the intra-class coefficient and the Pearson correlation coefficient between the first and second questionnaires. Systematic differences between the first and second questionnaires were investigated with T-tests and non-parametric statistics. Internal consistency of the Dutch new KSS was evaluated with Cronbach's alpha. The construct validity of the Dutch New KSS was determined by comparing it to the Dutch WOMAC, Dutch KOOS and Dutch SF12 using Pearson correlation coefficients. Content validity was assessed by examining the distribution and the floor and ceiling effects of the Dutch version of the new KSS.Background:
Materials and Methods:
As human soft tissue is anisotropic, non-linear and inhomogeneous, its properties are difficult to characterize. Different methods have been described that are either based on contact or noncontact protocols. In this study, three-dimensional (3D) digital image correlation (DIC) was adopted to examine the mechanical behaviour of the human Achilles tendon. Despite its wide use in engineering research and its great potential for strain and displacement measurements in biological tissue, the reported biomedical applications are rather limited. To our knowledge, no validation of 3D DIC measurement on human tendon tissue exists. The first goal of this study was to determine the feasibility to evaluate the mechanical properties of the human Achilles tendon under uniaxial loading conditions with 3D Digital Image Correlation. The second goal was to compare the accuracy and reproducibility of the 3D DIC against two linear variable differential transformer (LVDT's). Six human Achilles tendon specimens were prepared out of fresh frozen lower limbs. Prior to preparation, all limbs underwent CT-scanning. Using Mimics software, the volume of the tendons and the cross sectional area at each level could be calculated. Subsequently, the Achilles tendons were mounted in a custom made rig for uni-axial loading. Tendons were prepared for 3D DIC measurements with a modified technique that enhanced contrast and improved the optimal resolution. Progressive static loading up to 628,3 N en subsequent unloading was performed. Two charge-coupled device camera's recorded images of each loading position for subsequent strain analysis. Two LVDT's were mounted next to the clamped tendon in order to record the displacement of the grips.Purpose
Methods
Today controversy exists whether restoration of neutral mechanical alignment should be attempted in all patients undergoing TKA. The restoration of constitutional rather than neutral mechanical alignment may in theory lead to a more physiological strain pattern in the collateral ligaments, and could therefore potentially be beneficial to patients. It was therefore our purpose to measure collateral ligament strains during three motor tasks in the native knee and compare them with the strains noted after TKA in different postoperative alignment conditions. Six cadaver specimens were examined using a validated knee kinematics rig under physiological loading conditions. The effect of coronal malalignment was evaluated by using custom made tibial implant inserts in order to induce different alignment conditions. The results indicated that after TKA insertion the strains in the collateral ligaments resembled best the preoperative pattern of the native knee specimens when constitutional alignment was restored. Restoration to neutral mechanical alignment was associated with greater collateral strain deviations from the native knee. Based upon this study, we conclude that restoration of constitutional alignment during TKA leads to more physiological periarticular soft tissue strains during loaded as well as unloaded motor tasks.
Several studies have described the relationship between the joint line and bony landmarks around the knee. However, high inter-patient variation makes these absolute values difficult in use. This study was set up to validate the previously described distances and ratios on calibrated full limb standing X-rays and to investigate the accuracy and reliability of these ratios as a tool for joint line reconstruction One hundred calibrated full-leg standing radiographs obtained from healthy volunteers were reviewed (fig 1). Distances from the medial epicondyle, the lateral epicondyle, the adductor tubercle, the fibular head and the proximal center of the knee (CJD) to the virtual prosthetic joint line were determined (fig 3). This prosthetic joint line was created by introducing a virtual distal femoral cutting block with a valgus angle of 6° on the full-leg radiographs. The adductor ratio was defined as the distance from adductor tubercle to the joint line divided by the femoral width. The correlation with the femoral width, the CJD and the limb alignment was analysed using linear regression analysis. The accuracy and reliability of the use of the ratio of the distance of the adductor tubercle, the medial epicondyle and the CJD relative to the femoral width to reconstruct the joint line was calculated.Introduction
Methods:
A prospective randomized trial on 128 patients with end-stage osteoarthritis was conducted to assess the accuracy of patient-specific guides. In cohort A (n = 64), patient- specific guides from four different manufacturers (Subgroup A1 Signature ®, A2 Trumatch ®, A3 Visionaire ® and A4 PSI ®) were used to guide the bone cuts. Surgical navigation was used as an intraoperative control for outliers. In cohort B (n = 64), conventional instrumentation was used. All patients of cohorts A and B underwent a postoperative full-leg standing X-ray and CT scan for measuring overall coronal alignment of the limb and three-planar alignment of the femoral and the tibial component. Three-planar alignment was the primary endpoint. Deviation of more than three degrees from the target in any plane, as measured with surgical navigation or radiologic imaging, was defined as an outlier. In 14 patients (22%) of cohort A, the use of the patient-specific guide was abandoned because of outliers in more than one plane. In 18 patients (28%), a correction of the position indicated by the guide, was made in at least one plane. A change in cranial-caudal position was most common. Cohort A and B showed a similar percentage of outliers in long-leg coronal alignment (24.6%, 28.1%, p = 0.69), femoral coronal alignment (6.6%, 14.1%, p = 0.24) and femoral axial alignment (23%, 17.2%, p = 0.50). Cohort A had more outliers in coronal tibial alignment (14.6%) and sagittal tibial alignment (21.3%) than cohort B (3.1%, p = 0.03 and 3.1%, p = 0.002, respectively). These data indicate that patient specific guides do not improve accuracy in total knee arthroplasty.
Eight consecutive patients with significant malalignment of the lower limb were included in the study. Pre-operative CT scans of the affected limb and the normal contra-lateral side were obtained and 3D models of the patient's anatomy were created, using dedicated software. The healthy contralateral limb was mirrored and geometrically matched to the distal femur or proximal tibia of the healthy side. A virtual opening wedge correction of the affected bone was used to match the geometry of the healthy contralateral bone. Standard lower limb axes measurements confirmed correction of the alignment. Based on the virtual plan, surgical guides were designed to perform the planar osteotomy and achieve the planned wedge opening and hinge axis orientation. The osteotomy was fixed with locking plates and screws. Post-operative assessment included planar X-rays, CT-scan and full leg standing X-rays. One three-planar, three bi-planar and four single-plane osteotomies were performed. Maximum weightbearing mechanical femoro-tibial coronal malalignment varied between 7° varus and 14° valgus (mean 7.6°, SD 3.1). Corrective angles varied from 7°–15°(coronal), 0°–13°(sagittal) and 0°–23°(horizontal). The maximum deviation between the planned pre-operative wedge angle and the executed post-operative wedge angle was 1° in the coronal, sagittal and horizontal plane. The desired mechanical femorotibial axis on full-leg standing X-rays was achieved in 6 patients. Two patients were undercorrected by 1° and 2° respectively. 3D planning and guided correction of multi-planar deformity of femur or tibia is a feasible and accurate novel technique.Conclusion
The 3D interplay between femoral component placement on contact stresses and range of motion of hip resurfacing was investigated with a hip model. Pre- and post-operative contours of the bone geometry and the gluteus medius were obtained from grey-value CT-segmentations. The joint contact forces and stresses were simulated for variations in component placement during a normal gait. The effect of component placement on range of motion was determined with a collision model. The contact forces were not increased with optimal component placement due to the compensatory effect of the medialisation of the center of rotation. However, the total range of motion decreased by 33%. Accumulative displacements of the femoral and acetabular center of rotation could increase the contact stresses between 5–24%. Inclining and anteverting the socket further increased the contact stresses between 6–11%. Increased socket inclination and anteversion in combination with shortening of the neck were associated with extremely high contact stresses. The effect of femoral offset restoration on range of motion was significantly higher than the effect of socket positioning. In conclusion, displacement of the femoral center of rotation in the lateral direction is at least as important for failure of hip resurfacings as socket malpositioning.
Optimal knee joint function obviously requires a delicate balance between the osseous anatomy and the surrounding soft tissues, which is distorted in the case of joint line elevation (JLE). Although several studies have found no correlation between JLE and outcome, others have linked JLE to inferior results. The purpose of this in vitro investigation was to evaluate the effect of JLE on tibiofemoral kinematics and collateral ligament strains. Six cadaver knees were equipped with reflective markers on femur and tibia and CT scans were made. A total knee arthroplasty (TKA) was performed preserving the native joint level. The knees were then tested in passive flexion-extension and squatting in a knee kinematics simulator while marker positions were recorded with an optical system. During squatting quadriceps forces were measured as well as tibio-femoral contact pressures. Finally, a revision TKA was performed with JLE by 4 mm. The femoral component was downsized and a thicker insert was used. The knees were again tested as before. Based on the bony landmarks identified in the CT scans and the measured trajectories of the markers, relative tibiofemoral kinematics could be calculated as well as distance changes between insertions of the collateral ligaments. Statistical tests were carried out to detect significant differences in kinematic patterns, ligaments elongation, tibiofemoral contact pressures and quadriceps forces between the primary TKA and after JLE.Introduction
Materials and Methods
The bowing of the femur defines a curvature plane to which the proximal and distal femoral anatomic landmarks have a predictable interrelationship. This plane can be a helpful adjunct for computer navigation to define the pre-operative, non-diseased anatomy of the femur and more particularly the rotational alignment of the femoral component in total knee arthroplasty (TKA). There is very limited knowledge with regards to the sagittal curvature -or bowing- of the femur. It was our aim (1) to determine the most accurate assessment technique to define the femoral bowing, (2) to define the relationships of the curvature plane relative to proximal and distal anatomic landmarks and (3) to assess the position of femoral components of a TKA relative to the femoral bowing.Summary sentence
Background and aims
Osteotomies around the knee have been used to correct lower limb mal-alignment for over 50 years. The procedure is technically demanding and carries specific risks of neurovascular injury, incorrect planning and execution, and insufficient fixation. In recent years, with the advent of locking plates, fixation techniques have improved significantly but the correct planning and execution of the operation remains difficult. Despite the availability of CT and MRI 3D imaging, surgical planning is still traditionally performed on 2D plain X-rays [1]. Especially with multi-planar deformities, this technique is prone to error. The aim of this clinical pilot study is to evaluate the feasibility of virtual pre-operative three-dimensional planning and correct execution of osteotomies around the knee with the aid of patient specific surgical guides and locking plates. Eight consecutive patients, presenting with significant malalignment of the lower limb were included in the study. Pre-operative CT scans of the affected limb and the normal contra-lateral side were obtained and 3D models of the patient's anatomy were created, using dedicated software (Mimics® 3-matic®, Materialise, Leuven Belgium) [2]. These models were used to evaluate the required surgical correction. The healthy contralateral limb was mirrored and geometrically matched to the distal femur or proximal tibia of the healthy side. A virtual opening wedge correction of the affected bone was used to match the geometry of the healthy contralateral bone. Standard lower limb axes measurements confirmed correction of the alignment [3]. Based on the virtual plan, surgical guides were designed to perform the planar osteotomy and achieve the planned wedge opening and hinge axis orientation (see figure 1). Apart from guiding the osteotomy, the patient specific surgical guide also guided drilling of the planned screw holes. Post-operative assessment of the correction was obtained through planar X-rays, CT-scan and full leg standing X-ray.Background
Patients and methods
Osteotomies around the knee are traditionally templated on 2D plain X-rays. Results are often inaccurate and inconsistent and multiplanar ostetomies are hard to perform. The aim of this study is to evaluate the feasibility and accuracy of virtual three-dimensional CT-based planning and correct execution of osteotomies around the knee with the aid of patient specific surgical guides and locking plates. Eight consecutive patients with significant malalignment of the lower limb were included in the study. Pre-operative CT scans of the affected limb and the normal contra-lateral side were obtained and 3D models of the patient's anatomy were created, using dedicated software. The healthy contralateral limb was mirrored and geometrically matched to the distal femur or proximal tibia of the healthy side. A virtual opening wedge correction of the affected bone was used to match the geometry of the healthy contralateral bone. Standard lower limb axes measurements confirmed correction of the alignment. Based on the virtual plan, surgical guides were designed to perform the planar osteotomy and achieve the planned wedge opening and hinge axis orientation. The osteotomy was fixed with locking plates and screws. Post-operative assessment included planar X-rays, CT-scan and full leg standing X-rays.Introduction
Methods
Obtaining a balanced flexion gap with correct
femoral component rotation is one of the prerequisites for a successful
outcome after total knee replacement (TKR). Different techniques
for achieving this have been described. In this study we prospectively
compared gap-balancing Both groups systematically reproduced a similar external rotation
of the femoral component relative to the surgical transepicondylar
axis: 2.4°
We report the outcome at a minimum of 10 years follow-up for 80 polished tapered stems performed in 53 patients less than 35-years-old with a high risk profile for aseptic loosening. Forty-six prosthesis were inserted for inflammatory hip arthritis and 34 for avascular necrosis. The mean age at surgery was 28 years in the inflammatory arthritis (17–35) and 27 years in the avascular necrosis (15–35) patients. At a mean follow-up of 14.5 years in the inflammatory arthritis group and 14 years in the avascular necrosis group respectively, survivorship of the 80 stems with revision of the femoral component for any reason as an endpoint was 100 % (95 % CI). Re-operation was because of failure of four metal-backed cups, 3 all polyethylene cups and one cementless cup. None of the stems were radiographically loose. All but two femoral components subsided within the cement mantle to a mean of 1.2 mm (0 tot 2.5) at final follow-up. Periarticular osteolysis was noted in 4 femurs in zone 7. This finding was associated with polyethylene wear and was only seen in those hips that needed revision for a metal backed cup loosening. Our findings show that the polished tapered stem has excellent medium-term results when implanted in young patients with high risk factors for aseptic loosening.
In general TKA can be divided into two distinct groups: cruciate retaining and cruciate substituting. The cam and post of the latter system is in fact a mechanical substitution of the intricate posterior cruciate ligament. In our previous work we and many other investigators have focused on the movement of the femoral component relative to the tibial tray. Little information is available about the relative movement between the cam part of the femoral component and the post of the tibial insert. In this study we determine the distance and the changes in distance between the cam of the femoral component and the tibial post during extension, flexion at 90° and full flexion. The secondary purpose is to analyse possible differences between FBPS and MBPS TKA. 12 subjects' knees were imaged using fluoroscopy from extension over 90° to maximum kneeling flexion. The images were digitized. The 3-dimensional (3D) position and orientation of the implant components were determined using model-based shape-matching techniques, manual matching, and image-space optimization routines. The implant surface model was projected onto the geometry-corrected image, and its 3D pose was iteratively adjusted to match its silhouette with the silhouette of the subject's TKA components. The results of this shapematching process have standard errors of approximately 0.5° to 1.0° for rotations and 0.5 mm to 1.0 mm for translations in the sagittal plane. Joint kinematics were determined from the 3D pose of each TKA component using the 3-1-2 Cardan angle convention. This process resulted in a distance map of the femoral and tibial surfaces, from which the minimum separations were determined for the purpose of this study between cam and post (fig1.). Separation distances between the tibial polyethylene (PE) insert's post and the femoral prosthesis component have been calculated in three steps. First, the surface models of all three components as well as their position and orientation were extracted from the data files produced by the fluoroscopic kinematic analysis. Next, a set of 12 points were located on the post of each tibial insert (fig2.). Finally, for each point, the distance to the femoral component was quantified. For each step in this process, custom MATLAB(r) (The MathWorks(tm) Inc., Natick, MA, USA) programs were used. For each of the 12 points on the post, a line was constructed through the point and parallel to the outward-facing local surface normal of the post. The resulting set of lines was then intersected with the femoral component model. Intersection points where lines ran “out of” the femoral component, detected by a positive dot product of the femoral component surface normal with the post surface normal (used to define the line), were discarded. Finally, the distances between the 12 points on the post and the intersection points on each line were calculated. For each line, the smallest distance was retained as a measure of the separation between insert and femoral component. Where a line did not intersect the femoral component, the corresponding separation distance was set to infinity. In each position, distances are measured at 6 pairs of points. Two indices of asymmetry are analysed:
The absolute difference between both measurements within a pair. Perfect symmetry is present when this absolute difference equals zero. The proportion of pairs where one of both measurements equals infinity. Indeed, this situation refers to the presence of ‘extreme’ asymmetry. A linear model for repeated measures is used to analyse the absolute differences as a function of the between-subjects factor condition (mobile bearing or fixed bearing) and the within-subject factors position (4 levels) and pair (6 levels). More specifically, a direct likelihood approach is adopted using a compound symmetric covariance matrix. There is a significant difference in absolute difference between the fixed and mobile bearing condition (p=0.046). On average, the absolute difference is higher in the fixed bearing condition, 1.75 (95%CI: 1.39;2.11) vs 1.20 (95%CI:0.78;1.62). (fig2.).Methods
Results
Autologous chondrocyte implantation presents a viable alternative to microfracture in the repair of damaged articular cartilage of the knee; however, outcomes for patellar lesions have been less encouraging. ChondroCelect (CC) is an innovative, advanced cell therapy product consisting of autologous cartilage cells expanded To assess the effect of CC in the treatment of patellofemoral lesions, for which standard treatment options had failed and/or no other treatment options were considered feasible.Introduction
Purpose
A comparative kinematic study was carried out on six cadaver limbs, comparing tibiofemoral kinematics in five different conditions: unloaded, under a constant 130 N ankle load with a variable quadriceps load, with and without a constant 50 N medial and lateral hamstrings load. Kinematics were described as translation of the projected centers of the medial (MFT) and lateral femoral condyles (LFT) in the horizontal plane of the tibia, and tibial axial rotation (TR) as a function of flexion angle. In passive conditions, the tibia rotated internally with increasing flexion, to an average of −16° (range −12/−20°, SD 3.0°). Between 0 – 40° flexion, the medial condyle translated forwards 4 mm (range 0.8/5.5 mm, SD 2.5 mm), followed by a gradual posterior translation, totaling −9 mm (range −5.8/−18.5 mm, SD 4.9 mm) between 40° – 140° flexion. The lateral femoral condyle translated posteriorly with increasing flexion completing −25 mm (range −22.6 – −28.2 mm, SD 2.5 mm). Dynamic, loaded measurements were carried out in a knee rig. Under a fixed ankle load of 130 N and variable quadriceps loading, tibial rotation was inverted, mean TR 4.7° (range −3.3°/11.8° SD 5.4°), MFT −0.5 mm (range = −4.3/2.4 mm, SD = 2.4 mm), LFT 3.3 mm (range = −3.6/10.6 mm, SD = 5.1 mm). As compared to the passive condition, all these excursions were significantly different: p=0.015, p=0.013, and p=0.011 for TR, MFT and LFT respectively. Adding medial and lateral hamstrings force of 50N each, reduced TR, MFT and LFT significantly as compared to the passive condition. In general, loading the knee with hamstrings and quadriceps reduces rotation and translation as compared to the passive condition. Lateral hamstring action is more influential on knee kinematics than medial hamstrings action.
Complications involving the patellofemoral joint,
caused by malrotation of the femoral component during total knee replacement,
are an important cause of persistent pain and failure leading to
revision surgery. The aim of this study was to determine and quantify
the influence of femoral component malrotation on patellofemoral
wear, and to determine whether or not there is a difference in the
rate of wear of the patellar component when articulated against
oxidised zirconium (OxZr) and cobalt-chrome (CoCr) components. An The results suggest that patellar maltracking due to an internally
rotated femoral component leads to an increased mean patellar wear.
Although not statistically significant, the mean wear production
may be lower for OxZr than for CoCr components.
High-flexion total knee replacement (TKR) designs
have been introduced to improve flexion after TKR. Although the
early results of such designs were promising, recent literature
has raised concerns about the incidence of early loosening of the
femoral component. We compared the minimum force required to cause
femoral component loosening for six high-flexion and six conventional
TKR designs in a laboratory experiment. Each TKR design was implanted in a femoral bone model and placed
in a loading frame in 135° of flexion. Loosening of the femoral
component was induced by moving the tibial component at a constant
rate of displacement while maintaining the same angle of flexion.
A stereophotogrammetric system registered the relative movement
between the femoral component and the underlying bone until loosening
occurred. Compared with high-flexion designs, conventional TKR designs
required a significantly higher force before loosening occurred
(p <
0.001). High-flexion designs with closed box geometry required
significantly higher loosening forces than high-flexion designs
with open box geometry (p = 0.0478). The presence of pegs further contributed
to the fixation strength of components. We conclude that high-flexion designs have a greater risk for
femoral component loosening than conventional TKR designs. We believe
this is attributable to the absence of femoral load sharing between
the prosthetic component and the condylar bone during flexion.
The difference in the mean values regarding inclination was greater than would be expected by chance; there was a statistically significant difference (P = 0,010).
Navigation technique was discussed to equalize the drawback of MIS. However, tools like imageless navigation may further improve the cup position even in traditional approach.
The biomechanics of the patellofemoral joint can become disturbed during total knee replacement by alterations induced by the position and shape of the different prosthetic components. The role of the patella and femoral trochlea has been well studied. We have examined the effect of anterior or posterior positioning of the tibial component on the mechanisms of patellofemoral contact in total knee replacement. The hypothesis was that placing the tibial component more posteriorly would reduce patellofemoral contact stress while providing a more efficient lever arm during extension of the knee. We studied five different positions of the tibial component using a six degrees of freedom dynamic knee simulator system based on the Oxford rig, while simulating an active knee squat under physiological loading conditions. The patellofemoral contact force decreased at a mean of 2.2% for every millimetre of posterior translation of the tibial component. Anterior positions of the tibial component were associated with elevation of the patellofemoral joint pressure, which was particularly marked in flexion >
90°. From our results we believe that more posterior positioning of the tibial component in total knee replacement would be beneficial to the patellofemoral joint.
Malrotation of the femoral component is a cause of patellofemoral maltracking after total knee arthroplasty. Its precise effect on the patellofemoral mechanics has not been well quantified. We have developed an in vitro method to measure the influence of patellar maltracking on contact. Maltracking was induced by progressively rotating the femoral component either internally or externally. The contact mechanics were analysed using Tekscan. The results showed that excessive malrotation of the femoral component, both internally and externally, had a significant influence on the mechanics of contact. The contact area decreased with progressive maltracking, with a concomitant increase in contact pressure. The amount of contact area that carries more than the yield stress of ultra-high molecular weight polyethylene significantly increases with progressive maltracking. It is likely that the elevated pressures noted in malrotation could cause accelerated and excessive wear of the patellar button.
The use of plate-and-cable constructs to treat periprosthetic fractures around a well-fixed femoral component in total hip replacements has been reported to have high rates of failure. Our aim was to evaluate the results of a surgical treatment algorithm to use these lateral constructs reliably in Vancouver type-B1 and type-C fractures. The joint was dislocated and the stability of the femoral component was meticulously evaluated in 45 type-B1 fractures. This led to the identification of nine (20%) unstable components. The fracture was considered to be suitable for single plate-and-cable fixation by a direct reduction technique if the integrity of the medial cortex could be restored. Union was achieved in 29 of 30 fractures (97%) at a mean of 6.4 months (3 to 30) in 29 type-B1 and five type-C fractures. Three patients developed an infection and one construct failed. Using this algorithm plate-and-cable constructs can be used safely, but indirect reduction with minimal soft-tissue damage could lead to shorter times to union and lower rates of complications.
computerized histomorphometry and an overall histology assessment. Clinical outcome was measured using the Knee Injury and Osteoarthritis Outcome Score (KOOS). Safety was recorded throughout the study.
The understanding of rotational alignment of the distal femur is essential in total knee replacement to ensure that there is correct placement of the femoral component. Many reference axes have been described, but there is still disagreement about their value and mutual angular relationship. Our aim was to validate a geometrically-defined reference axis against which the surface-derived axes could be compared in the axial plane. A total of 12 cadaver specimens underwent CT after rigid fixation of optical tracking devices to the femur and the tibia. Three-dimensional reconstructions were made to determine the anatomical surface points and geometrical references. The spatial relationships between the femur and tibia in full extension and in 90° of flexion were examined by an optical infrared tracking system. After co-ordinate transformation of the described anatomical points and geometrical references, the projection of the relevant axes in the axial plane of the femur were mathematically achieved. Inter- and intra-observer variability in the three-dimensional CT reconstructions revealed angular errors ranging from 0.16° to 1.15° for all axes except for the trochlear axis which had an interobserver error of 2°. With the knees in full extension, the femoral transverse axis, connecting the centres of the best matching spheres of the femoral condyles, almost coincided with the tibial transverse axis (mean difference −0.8°,
The purpose of this study was to test the hypothesis that patella alta leads to a less favourable situation in terms of patellofemoral contact force, contact area and contact pressure than the normal patellar position, and thereby gives rise to anterior knee pain. A dynamic knee simulator system based on the Oxford rig and allowing six degrees of freedom was adapted in order to simulate and record the dynamic loads during a knee squat from 30° to 120° flexion under physiological conditions. Five different configurations were studied, with variable predetermined patellar heights. The patellofemoral contact force increased with increasing knee flexion until contact occurred between the quadriceps tendon and the femoral trochlea, inducing load sharing. Patella alta caused a delay of this contact until deeper flexion. As a consequence, the maximal patellofemoral contact force and contact pressure increased significantly with increasing patellar height (p <
0.01). Patella alta was associated with the highest maximal patellofemoral contact force and contact pressure. When averaged across all flexion angles, a normal patellar position was associated with the lowest contact pressures. Our results indicate that there is a biomechanical reason for anterior knee pain in patients with patella alta.
Mobile-bearing posterior-stabilised knee replacements have been developed as an alternative to the standard fixed- and mobile-bearing designs. However, little is known about the We conclude that mobile-bearing posterior-stabilised knee replacements reproduce internal rotation of the tibia more closely during flexion than fixed-bearing posterior-stabilised designs. Furthermore, mobile-bearing posterior-stabilised knee replacements demonstrate a unidirectional movement which occurs at the upper and lower sides of the mobile insert. The femur moves in an anteroposterior direction on the upper surface of the insert, whereas the movement at the lower surface is pure rotation. Such unidirectional movement may lead to less wear when compared with the multidirectional movement seen in fixed-bearing posterior-stabilised knee replacements, and should be associated with more evenly applied cam-post stresses.
As total knee arthroplasties (TKA) have become the gold standard procedure for severe gonarthrosis, greater interest in postperative tibiofemoral instability has developed. Emphasizing the correlation between evaluation of symptoms and findings, offers an opportunity to elucidate the specifics of the instability. Mandatory is the joint gap measurement during surgery to assess the effect of specific cuts or releases of the anatomic portion of the joint gap. By performing navigation-assisted total knee arthroplasties, we are capable of measuring the joint gap in a highly reliable way. During the ligament balancing in navigation-assisted TKA, we performed a data collection of the joint gap in 0–30 and 90 of flexion in 100 patients. The measurements were repeated after 10 and 20 minutes in extension. The result offers us an opportunity to assess the interesting effect of ligament-stress relaxation in TKA and to gain more insights in the further release-necessity and choice of insert during the TKA procedure.
We performed a prospective, randomised trial of 44 patients to compare the functional outcomes of a posterior-cruciate-ligament-retaining and posterior-cruciate-ligament-substituting total knee arthroplasty, and to gain a better understanding of the At follow-up at five years, no statistically significant differences were found in the clinical outcome measurements for either design. The prevalence of radiolucent lines and the survivorship were the same. In a subgroup of 15 knees, additional image-intensifier analysis in the horizontal and sagittal planes was performed during step-up and lunge activity. Our analysis revealed striking differences. Lunge activity showed a mean posterior displacement of both medial and lateral tibiofemoral contact areas (roll-back) which was greater and more consistent in the cruciate-substituting than in the cruciate-retaining group (medial p <
0.0001, lateral p = 0.011). The amount of posterior displacement could predict the maximum flexion which could be achieved (p = 0.018). Forward displacement of the tibiofemoral contact area in flexion during stair activity was seen more in the cruciate-retaining than in the cruciate-substituting group. This was attributed mainly to insufficiency of the posterior cruciate ligament and partially to that of the anterior cruciate ligament. We concluded that, despite similar clinical outcomes, there are significant kinematic differences between cruciate-retaining and cruciate-substituting arthroplasties.
In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.
In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.
In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.
Performing a total knee arthroplasty in a patient with a flexion contracture or recurvatum deformity requires from the surgeon an adequate knowledge of the principles of flexion – extension space balancing. In the standard TKA procedure, adequate balancing between the flexion and extension space is usually easily achieved, leading to an equal and symmetrical space both in flexion and extension, which results in a stable knee and maximal range of motion after implantation of the prosthetic components. The situation is different in the knee with a flexion contracture or recurvatum, where the extension space is relatively smaller (flexion contracture) or greater (recurvatum) than the flexion space. In both of these situations, the flexion and extension space should be balanced by the surgeon in order to avoid an important deficit in range of motion or an instability problem. Several surgical techniques are available for this. In the knee with a flexion contracture, the extension space is relatively too small. Adequate removal of posterior osteophytes will increase the extension space, and this should be the first step in the flexion – extension space procedure (1). Next, the collateral structures should be balanced, with release of the tight structures that are effective in extension only (2). These are predominantly the iliotibial band in the valgus knee, and the posterior oblique ligament in the varus knee. If these 2 steps are not sufficient, proximalisation of the femoral component by 2 to 3mm may be required (step 3), or a formal release of the posterior capsule from the posterior femoral condyles (4). When an anterior reference system is used, the surgeon can also decide to use a slightly larger femoral component with a slightly increased tibial resection to equalise the gaps (5). In the knee with a recurvatum deformity, the extension space is relatively too large. In this situation, distalisation of the femoral component by removing 2 mm less distal femoral bone, will decrease only the extension space without altering the flexion space (1). In case of anterior referencing, the use of a slightly undersized femoral component will further equalise the gaps (2). Just using a thicker tibial insert to fill up the extension space, while increasing the flexion space by resecting the PCL or increasing the tibial slope, may be another option in the modest recurvatum knee (3).
Many surgeons consider revision total knee arthroplasty (TKA) a difficult procedure, calling for flexibility and improvisation. However, revision TKA can be broken into a number of consecutive steps that need to be performed. Setting up a reproducible and stepwise approach is mandatory for the surgeon who performs this procedure more or less regularly. At our institution, we have followed a five-step protocol in performing 166 revision TKA procedures. Its relatively strict guidelines leave little room for intraoperative improvisation. Our protocol covers exposition, implant extraction, implant selection, bone preparation and dealing with bony defects. There has been acceptable ‘on the table’ reconstruction in all cases.
Although most surgeons agree that the functional results obtained with modern total knee arthroplasty (TKA) are acceptable, it is clear that even with the most recent designs it is still impossible to duplicate the behaviour and functional performance of a normal knee. Recent kinematic studies have shown that modern TKA designs consistently provoke aberrant kinematics, mainly owing to the absence of the anterior cruciate ligament and the inability to maintain a functional posterior cruciate ligament (PCL). With regard to roll-back, PS cam-post designs appear to perform better than PCL retaining knees, but only in deeper degrees of flexion, usually only beyond 90°. Whether it is strictly necessary to try to obtain normal kinematics remains an open debate. Clearly, aberrant kinematics are the direct cause of the flexion limitation we see in many of our patients. Further, they probably contribute to many of the discomforts associated with modern TKA, such as difficulties descending stairs, rising from chairs, pivoting and thrusting. Improvements in current TKA designs should aim at introducing the concept of guided-motion (intrinsic mechanism) and at maintaining or restoring (extrinsic) determinants of kinematics, i.e. the cruciate ligaments, the joint configuration and the extra-articular structures.
Today several therapeutic options exist for the management of early degenerative lesions in the knee. These include marrow stimulation techniques (abrasion arthroplasty, sub-chondral drilling, microfracturing), periosteal and perichondral graft interposition, the implantation of synthetic matrices (collagen, carbon fibres, or glycosaminoglycan gel), autologous chondrocyte transplantation, osteochondral mosaic autografts or allografts, or simple arthroscopic lavage and debridement. It appears that some of these techniques are moderately successful in the short-term, especially in younger patients with relatively recent localised chondral lesions or erosion, and in joints with normal stability and alignment. In these optimal conditions, it is possible to achieve repair in 70% of the diseased area. However, the cartilage remains substandard, with a one-third decrease in stiffness and increased tissue permeability. In the early degenerative knee, conservative treatment options include unloader bracing and the use of chondroprotective agents. Unloader braces have been shown to improve the disease-specific quality of life and the functional status of patients with varus osteoarthritis in prospective randomised clinical trials. However, patients often find braces uncomfortable and of doubtful effectiveness. Current information about the use of chondroprotective agents in the treatment of osteoarthritis suggests that intra-articular hyaluronic acid improves lubrication in the joint and helps to decrease swelling and inflammation. Used as dietary supplements, oral glucosamine and chondroitin sulphate appear to work synergistically together to cause a net increase in the amount of healthy articular cartilage, hereby slowing the progression of osteoarthritis. Convenient and safe, these intra-articular and oral chondroprotective agents present an exciting new approach in the treatment of early degenerative knee lesions.
Our purpose was to determine the mechanism which allows the maximum knee flexion in vivo after a posterior-cruciate-ligament (PCL)-retaining total knee arthroplasty. Using three-dimensional computer-aided design videofluoroscopy of deep squatting in 29 patients, we determined that in 72% of knees, direct impingement of the tibial insert posteriorly against the back of the femur was the factor responsible for blocking further flexion. In view of this finding we defined a new parameter termed the ‘posterior condylar offset’. In 150 consecutive arthroplasties of the knee, the magnitude of posterior condylar offset was found to correlate with the final range of flexion.