An accurate evaluation of the mechanical properties of human tissue is key to understanding and successfully simulating (parts of) human joints. Due to the rapid post-mortem decay, however, the cadavers are usually frozen or embalmed. The main aim of this paper is to quantitatively compare the impact of both techniques on the biomechanical properties. To that extent, the Achilles tendons of seven cadavers have been tested. For each cadaver, one of the Achilles tendons was tested after being frozen for at maximum two weeks, whilst the other tendon was tested following a Thiel embalming process.

All specimens were gripped in custom made clamps and subjected to uniaxial tensile loading. The specimens were scanned using a micro-CT to determine their cross-sectional area, which allowed transferring the applied forces to stresses. During the tensile tests, the specimens’ elongation was measured both using the digital image correlation (DIC) technique and using linear variable displacement transducers (LVDT's) mounted across the grips. The former allowed to assess the severity of slip in the grips. As is well described in literature, the obtained stress-strain relationship is not linear (Figure 1). Accordingly, the following bilinear relationship was fitted through the data points using a least squares fit:

s = E₀ e     e <= ê

As a result, the stress-strain response is sub-divided in two regions: a toe-region (e <= ê) with a low slope and stiffness (E₀) and a linear elastic region (e > ê) with a higher stiffness (E). Both stiffness values were subsequently compared between the fresh frozen and Thiel embalmed group. Given the non-normal distribution of the test data, the non-parametric Wilcoxon signed rank test was used to assess the statistical significance of the obtained results.

No statistically significant difference was observed between the stiffness of the toe-region (e <= ê) obtained from Thiel embalmed and fresh frozen specimens (p-value = 0.249). In the contrary, the stiffness of linear elastic region (e > ê) was significantly different between both groups (p-value = 0.046 – see Figure 2). An average, the Thiel embalmed specimens displayed a 36% higher stiffness compared to the fresh frozen specimens. The latter contrasts the findings of other studies reported in literature, which report a decrease of the stiffness following Thiel embalming. To the authors’ opinion, this discrepancy could either be attributed to a difference in testing protocol (embalming time, donor factors, …) or tissue perfusion kinetics (Achilles tendon is relatively massive).

In conclusion, this study has demonstrated that Thiel embalming significantly alters the biomechanical properties of tendons. Specimens that underwent Thiel embalming should therefore not be considered for determining input parameters for advanced numerical models.

Aims

Analysis of the morphology of the distal femur, and by extension of the femoral components in total knee arthroplasty (TKA), has largely been related to the aspect ratio, which represents the width of the femur. Little is known about variations in trapezoidicity (i.e. whether the femur is more rectangular or more trapezoidal). This study aimed to quantify additional morphological characteristics of the distal femur and identify anatomical features associated with higher risks of over- or under-sizing of components in TKA.

To evaluate the impact of a knee prosthesis on the soft-tissue envelope or knee kinematics, cadaveric lower extremities are often mounted in a custom test rig, e.g. Oxford knee rig. Using such test rig, the knee is tested while performing a squatting motion. However, such motion is of limited daily-life relevance and clinical practices has shown that squatting commonly causes problems for knee patients. As a result, a new test rig was developed that allows a random, controlled movement of the ankle relative to the hip in the sagittal plane.

Mounting the specimen in the test rig, restricts five degrees of freedom (DOF) at the hip; only the rotation in the sagittal plane is not restrained (Figure 1). On the other hand, at the ankle, only two degrees of freedom are restrained, namely the movement in the sagittal plane. The ankle has thus three rotational degrees of freedom, all rotation axis intersect in a single point: the center of the ankle. In addition, the out-of-plane translational movement of the ankle remains free. This is achieved by means of a linear bearing. The other translational degrees of freedom, in the sagittal plane, are controlled by two actuators. As a result, the knee has five degrees of freedom left; flexion-extension is controlled. This represents typical closed chain applications, such as cycling.

In a first step, the knee kinematics have been evaluated under un-loaded conditions (no quadriceps or hamstring forces applied). To evaluate the knee kinematics, an infrared camera system (OptiTrack, NaturalPoint Inc, USA) is used. Therefore, three infrared markers are placed on the femur and tibia respectively. In addition, markers are placed on the test rig itself, to evaluate the accuracy of the applied motion. All markers are tracked using eight infrared cameras. At the ankle, a 2D circular motion with a radius of 100 mm was applied. Based on the 3D motion analysis, it was demonstrated that the control system has an accuracy of ± 0.5 mm.

The evaluation of the knee kinematics in accordance to Grood and Suntay (J. of Biomechanical Engineering, 1983), additionally requires the evaluation of the knee anatomy. To that extent, the cadaveric specimen has been visualized using a CT scan, with the infrared markers in place. From these CT images, a 3D reconstruction has been created (Mimics, Materialise, Belgium). Subsequently, custom software has been developed that combines the CT data with the motion analysis data (Matlab, The MathWorks Inc., USA). As a result, knee motion is visualized in 3D (Figure 2.a) and clinical relevant kinematic parameters can be derived (Figure 2.b).

In conclusion, the presented test rig and analysis framework is ready to evaluate more complex knee kinematics with reasonable accuracy and stability of the control loops. Future research will however primarily focus on the evaluation and validation of the impact of forces applied onto the specimen.

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

Background

The use of Computed Tomography (CT) as a medical imaging tool has widespread applications in the field of knee surgery. Surgeons use a CT scan in a conventional way during the pre-operative stage, to plan the position of the femoral component in the horizontal plane. In the post-operative stage, the use of a CT scan is a routine tool in the evaluation of failed TKA as rotational malalignment of the femoral component has been determined as a cause of poor clinical outcome after TKA.

Introduction

Total Knee Arthroplasty (TKA) is a proven successful and cost-effective method to relieve pain and improve joint function and quality of life in patients with advanced knee arthritis. However, after a TKA, only 75 to 89% of patients are satisfied. Since patient satisfaction is one of the main objectives of elective orthopaedic surgery, it is important to investigate the reasons for dissatisfaction and develop remedial strategies.

INTRODUCTION

Meniscal tears are very common and treated surgically by suturing or partial or total meniscectomy. After meniscectomy, the tibiofemoral contact area is decreased whih leads to higher contact stresses associated with clinical symproms and a faster progression of tibiofemoral osteoarthritis. Besides meniscus allograft transplantation, artificial implants have been developed to replace the menisci after meniscectomy.

The treatment of osteochondral lesions is of great interest to orthopaedic surgeons because most lesions do not heal spontaneously. We present the short-term clinical outcome and MRI findings of a cell-free scaffold used for the treatment of these lesions in the knee. A total of 38 patients were prospectively evaluated clinically for two years following treatment with an osteochondral nanostructured biomimetic scaffold. There were 23 men and 15 women; the mean age of the patients was 30.5 years (15 to 64). Clinical outcome was assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Tegner activity scale and a Visual Analgue scale for pain. MRI data were analysed based on the Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) scoring system at three, 12 and 24 months post-operatively. There was a continuous significant clinical improvement after surgery. In two patients, the scaffold treatment failed (5.3%) There was a statistically significant improvement in the MOCART precentage scores. The repair tissue filled most of the defect sufficiently. We found subchondral laminar changes in all patients. Intralesional osteophytes were found in two patients (5.3%). We conclude that this one-step scaffold-based technique can be used for osteochondral repair. The surgical technique is straightforward, and the clinical results are promising. The MRI aspects of the repair tissue continue to evolve during the first two years after surgery. However, the subchondral laminar and bone changes are a concern.

Cite this article: Bone Joint J 2015; 97-B:318–23.

Osteotomy is one of the oldest orthopaedic interventions and has evolved significantly over the years. The procedure is well established as a biomechanical solution in the treatment of arthritis and instability of the knee. The operation is technically demanding and carries risks of neurovascular injury, inadequate fixation and under- or overcorrection. These technical problems have given osteotomy significant headwind in the orthopaedic community. The relative success of knee arthroplasty (uni or total) in the past decade has fed the perception that this procedure is the only remaining treatment to be trusted for patients with knee arthritis. However, both registry data and single center studies often show disappointing results for knee arthroplasty in the young, active and demanding patient population. Osteotomy has a significant role for these patients, provided they have unicompartmental arthritis with constitutional malalignment. Also, more complex deformities as seen in the post-traumatic setting often need a biomechanical approach based upon osteotomy principles.

Recently, technology was developed to allow the surgeon perform a three-dimensional evaluation of the deformity and prediction of postoperative alignment. Patient specific guides with a broad fit on the femur or tibia can guide the osteotomy and fixation accurately, within 2 degrees of accuracy. With this technological approach, a new dawn for osteotomy appears on the horizon.

Ligament release in knee arthroplasty can be limited with accurate placement of implants, correct sizing and anatomic geometry of the implants. Still, in some instances a release of the medial collateral ligament can be necessary. In the proposed minimally invasive technique, multiple punctures in the MCL are made, using an 19-gauge needle, in order to progressively stretch the MCL until a correct ligament balance is achieved. This technique requires no additional soft tissue dissection and can even be performed percutaneously when necessary.

We analyzed 61 cases with varus deformity that were intraoperatively treated using this technique. In 4 other cases the technique was used as a percutaneous procedure in order to correct postoperative medial tightness. The procedure was considered successful when 2–4mm mediolateral joint line opening was obtained in extension and 2–6mm in flexion. In 62 cases (95%) a progressive correction of medial tightness was achieved according to the above described criteria. We therefore consider needle puncturing as an effective and safe technique for progressive correction of MCL tightness during minimally invasive TKA.

Introduction

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.

Background:

Potential systemic toxicity of metal ions from metal-on-metal hip arthroplasties (MoMHA) is concerning. High blood cobalt (Co) levels have been associated with neurological, cardiac and thyroid dysfunctions.

Background:

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.

Purpose

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).

Background:

The number of young patients undergoing total knee arthroplasty is rapidly increasing. Long-term follow-up of modern type implants is needed to provide a benchmark of implant longevity for these patients.

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.

Introduction

Metal-on-metal hip resurfacings (MoMHRAs) have a characteristic wear pattern initially characterised by a run-in period, followed by a lower-wear steady-state. The use of metal ions as surrogate markers of in-vivo wear is now recommended as a screening tool for the in-vivo performance of MoMHRAs. The aims of this retrospective study were to measure ion levels in MoMHRAs at different stages during the steady-state in order to study the evolution of wear at minimum 10 years postoperatively and describe factors that affect it.

We have investigated the benefits of patient specific instrument guides, applied to osteotomies around the knee. Single, dual and triple planar osteotomies were performed on tibias or femurs in 14 subjects. In all patients, a detailed pre-operative plan was prepared based upon full leg standing radiographic and CT scan information. The planned level of the osteotomy and open wedge resection was relayed to the surgery by virtue of a patient specific guide developed from the images. The mean deviation between the planned wedge angle and the executed wedge angle was 0° (-1 to 1, sd 0.71) in the coronal plane and 0.3° (-0.9 to 3, sd 1.14) in the sagittal plane. The mean deviation between the planned hip, knee, ankle angle (HKA) on full leg standing radiograph and the post-operative HKA was 0.3° (-1 to 2, sd 0.75). It is concluded that this is a feasible and valuable concept from the standpoint of pre-operative software based planning, surgical application and geometrical accuracy of outcome.

Cite this article: Bone Joint J 2013;95-B, Supple A:153–8.

A retrospective study was conducted to investigate the changes in metal ion levels in a consecutive series of Birmingham Hip Resurfacings (BHRs) at a minimum ten-year follow-up. We reviewed 250 BHRs implanted in 232 patients between 1998 and 2001. Implant survival, clinical outcome (Harris hip score), radiographs and serum chromium (Cr) and cobalt (Co) ion levels were assessed.

Of 232 patients, 18 were dead (five bilateral BHRs), 15 lost to follow-up and ten had been revised. The remaining 202 BHRs in 190 patients (136 men and 54 women; mean age at surgery 50.5 years (17 to 76)) were evaluated at a minimum follow-up of ten years (mean 10.8 years (10 to 13.6)). The overall implant survival at 13.2 years was 92.4% (95% confidence interval 90.8 to 94.0). The mean Harris hip score was 97.7 (median 100; 65 to 100). Median and mean ion levels were low for unilateral resurfacings (Cr: median 1.3 µg/l, mean 1.95 µg/l (< 0.5 to 16.2); Co: median 1.0 µg/l, mean 1.62 µg/l (< 0.5 to 17.3)) and bilateral resurfacings (Cr: median 3.2 µg/l, mean 3.46 µg/l (< 0.5 to 10.0); Co: median 2.3 µg/l, mean 2.66 µg/l (< 0.5 to 9.5)). In 80 unilateral BHRs with sequential ion measurements, Cr and Co levels were found to decrease significantly (p < 0.001) from the initial assessment at a median of six years (4 to 8) to the last assessment at a median of 11 years (9 to 13), with a mean reduction of 1.24 µg/l for Cr and 0.88 µg/l for Co. Three female patients had a > 2.5 µg/l increase of Co ions, associated with head sizes ≤ 50 mm, clinical symptoms and osteolysis. Overall, there was no significant difference in change of ion levels between genders (Cr, p = 0.845; Co, p = 0.310) or component sizes (Cr, p = 0.505; Co, p = 0.370). Higher acetabular component inclination angles correlated with greater change in ion levels (Cr, p = 0.013; Co, p = 0.002). Patients with increased ion levels had lower Harris hip scores (p = 0.038).

In conclusion, in well-functioning BHRs the metal ion levels decreased significantly at ten years. An increase > 2.5 µg/l was associated with poor function.

Cite this article: Bone Joint J 2013;95-B:1332–8.

Correct alignment and ligament tension are widely accepted conditional features of successful TKA. The technical route of achieving this goal remains a matter of debate. Two philosophies prevail: measured resection as a geometry based system, and tensioned gaps, based upon the dependent relation between tibia and femur. Both techniques claim the best results and are often presented as radically different. From a conceptual standpoint, however, the dependent technique is not purely ligament based as it starts with a cut of the proximal tibia, which is geometrically ruled by sagittal and coronal alignment targets. As such, geometric alignment is the starting point of both techniques.

The use of ligament tensioners as the main basis for obtaining stability and alignment can be a treacherous route to follow. In the native knee that is not affected by arthritis, the functional characteristics of the ligaments are determined by their insertions and the articular geometry. Once the arthritis sets in, the articular surface deforms and leg alignment deviates. It is difficult to restore these parameters, making use of ligament tension as a guide, for the following reasons.

Ligament tension is hard to measure reproducibly intra-operatively. The stress-strain curves of ligaments are different and the magnitude of the optimal distraction force is unknown.

Measure resection is obviously not void of potential errors. Especially in case of dysplasia or prior trauma, bone geometry and landmarks can be deformed. In contrast to ligament assessment however, pre-operative imaging under the form of x-rays or CT allows for an objective and reproducible evaluation of the amount of deformity and subsequent surgical correction.