Purpose: This study compared the efficacy and safety of Characterized Chondrocyte Implantation (CCI) to microfracture in the repair of symptomatic cartilage defects of the femoral condyle.

Methods: CCI (n=51) was compared to microfracture (n=61) in patients with grade III–IV symptomatic cartilage defects of the femoral condyles in a prospective, multicenter, randomized, controlled trial. Structural repair was assessed at 1 year by histopathologists blinded to the treatment using

computerized histomorphometry and

Results: CCI resulted in better structural repair than microfracture at 1 year post-treatment, as assessed by histomorphometry (p=0.003) and overall histology (p=0.012). Structural repair parameters relating to chondrocyte phenotype and tissue structure were also superior with CCI. Noninferiority of CCI was demonstrated for clinical outcome at 12–18 months, and both treatments were generally well tolerated.

Conclusion: At 1 year post-treatment, CCI resulted in superior tissue repair compared to microfracture. Short-term clinical outcome after 12–18 months was similar for both treatments, as was the safety profile. The superior structural repair achieved with CCI may lead to improved long-term clinical benefits.

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°, sd 2.05). At 90° of flexion, this femoral transverse axis was orthogonal to the tibial mechanical axis (mean difference −0.77°, sd 4.08). Of all the surface-derived axes, the surgical transepicondylar axis had the closest relationship to the femoral transverse axis after projection on to the axial plane of the femur (mean difference 0.21°, sd 1.77). The posterior condylar line was the most consistent axis (range −2.96° to −0.28°, sd 0.77) and the trochlear anteroposterior axis the least consistent axis (range −10.62° to +11.67°, sd 6.12). The orientation of both the posterior condylar line and the trochlear anteroposterior axis (p = 0.001) showed a trend towards internal rotation with valgus coronal alignment.

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 in vivo kinematics of this new group of implants. We investigated 31 patients who had undergone a total knee replacement with a similar prosthetic design but with three different options: fixed-bearing posterior cruciate ligament-retaining, fixed-bearing posterior-stabilised and mobile-bearing posterior-stabilised. To do this we used a three-dimensional to two-dimensional model registration technique. Both the fixed- and mobile-bearing posterior-stabilised configurations used the same femoral component. We found that fixed-bearing posterior stabilised and mobile-bearing posterior-stabilised knee replacements demonstrated similar kinematic patterns, with consistent femoral roll-back during flexion. Mobile-bearing posterior-stabilised knee replacements demonstrated greater and more natural internal rotation of the tibia during flexion than fixed-bearing posterior-stabilised designs. Such rotation occurred at the interface between the insert and tibial tray for mobile-bearing posterior-stabilised designs. However, for fixed-bearing posterior-stabilised designs, rotation occurred at the proximal surface of the bearing. Posterior cruciate ligament-retaining knee replacements demonstrated paradoxical sliding forward of the femur.

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 in vivo kinematic behaviour of both devices.

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.

Introduction The purpose of this study was to detect the effect of tibial slope on maximal flexion after TKA.

Methods Twenty-one cadaver implantations of a standard PCL-retaining TKA were performed with increasing tibial slope of zero degrees, four degrees and seven degrees. For every specimen all variables except slope were kept constant, including tibio-femoral contact locations in deep flexion, which were determined upon in vivo contact patterns that were obtained during maximal squatting activities in patients that had undergone TKR with the same design. Maximal flexion was determined by direct impingement of the tibial component on the posterior femoral bone fluoroscopy.

Results Maximal flexion correlated positively with increasing slope (p< 0.001, R2 = 0.8). When aimed slope was considered, flexion increased on average 2.2° for every degree of downslope. When obtained slope was considered, flexion increased on average 1.7° for every degree of downslope.

Conclusions In PCL-retaining TKA, maximal obtainable flexion icnreases on average two degrees per degree extra tibial slope.

In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.

Introduction Although most surgeons agree that the functional results obtained with modern total knee arthroplasty 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.

Methods I present a review of the literature and personal experience.

Results Recent kinematic studies have shown that modern TKA designs consistently provoke aberrant kinematics compared to the normal knee, mainly due to the absence of the ACL and the inability to maintain a functional 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 striclty necessary to try to obtain normal kinematics with our TKA designs, is still an open debate.

Conclusions It is clear however that the aberrant kinematics we have noted with the current designs, are the direct cause of the flexion limit we see in many of our patients. Furthermore they probably also are the basis for many of the discomorts associated with modern TKA, such as difficulties in stair descent, chair rise, pivoting activities, thrust instabilities etc. With regard to these issues, I believe there are two potential directions to improve our current TKA designs; (1) by introducing the concept of guided-motion (intrinsic mechanism), or (2) by maintaining or restoring the (extrinsic) determinants of kinematics, i.e. the cruciate ligaments, the joint configuration and the extra-articular structures.

In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.

Introduction The purpose of this study was to detect the limiting mechanism of maximal active flexion that can ultimately be obtained by patients after PCL-retaining TKA.

Methods The study consisted of two parts. In the first part, 30 patients with well performing PCL-retaining TKAs were examined using videofluroscopy. In deep flexion, observations were directed towards potentiallly determinant factors of maximal obtainable flexion. Based upon these observations, a newly defined paramater, called the “posterior condylar offset”, was found to be important. The exact influence of this parameter was investigated in part two, in which 150 consecutive patients with PCL-retaining TKA were reviewed.

Results Aberrant kinematics were observed in the majority of cases. In 27 patients (93%) slide-forward of the femur was noted with flexion, with anterior translation of the medial and/or lateral femorotibial contact position. In deep squat, direct impingement of the posterior aspect of the tibial insert against the shaft of the femur was noted in 21 cases (72.4%), blocking further flexion. In part two of the sutdy, it was demonstrated that in knees with decreased post-operative “posterior condylar offset”, such impingement occurred faster and lead to decreased maximal obtainale flexion (p< 0.001).

Conclusions Maximal obtainable flexion is in the majority of cases determined by posterior tibial insertion impingement against the femoral bone and this occurs as a consequence of aberrant kinematics with anteiror sliding of the femur during flexion. Restoration of “posterior condylar offset” is important, since it allows greater degrees of flexion before impingement occurs.

In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.

Introduction: Clinical follow-up studies of total knee arthroplasty (TKA) reveal good results. However, the range of flexion of the knee after TKA remains limited in most cases. The most important factors impacting this range are the length of the quadriceps, the capsular tightness, the tibial slope, the design of the implant, the use of physiotherapy and the surgical technique. Aims: Our aim was to measure maximal knee flexion as a function of the posterior slope of the tibial component. We tried to quantify the relationship between tibial slope and maximal knee flexion. Methods: Seven fresh-frozen cavader-knees were used, all of them had moderate osteo-arthritis. Mean age of the patients was 67. A posterior-cruciate-ligament retaining TKA was used. In each knee, the tibial component was implanted consecutively with a slope of 0°, 4° and 7°. For each slope, the maximal flexion was measured using fluoroscopy in a test rig. Results: The mean maximal flexion achieved was 104° for an implant with a 0° slope; 112° for 4° slope and 120° for 7° slope. We regressed the maximal flexion on the tibial slope, using a Pearson regression analysis and obtained a R2=0.8356; indicating a strong correlation. Conclusions: In PCL retaining TKA, there is an increase of 2° in flexion for every increase of 1° posterior tibial slope.

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.