Unicondylar Knee Prosthesis Research Articles

Navigation in minimally invasive unicompartmental knee arthroplasty has no advantage in comparison to a conventional minimally invasive implantation

Minimally invasive implantation of unicompartmental knee prostheses can shorten rehabilitation time and lead to better functional results than conventional implantation. Exact positioning of the implant should be achieved, as this is a factor for the long-term survival of the prosthesis, although malpositioning can result due to the poor intraoperative view when using the minimally invasive approach. Navigation of the unicompartmental prosthesis could lead to a better implant positioning without losing the advantages of a minimally invasive approach. The same unicondylar knee prosthesis was implanted in a total of 40 patients, of whom 20 were implanted using navigation (kinematic navigation) and 20 using a conventional technique. The operating time was assessed in both groups. The orientation of the tibial and femoral implants was assessed radiologically postoperatively. We analysed these results according to the optimal positioning range proposed by the manufacturer. Furthermore, we examined the clinical results with the knee society score (KSS). A good positioning of the prosthesis was observed in both techniques with only 11% of the radiologic measurements out of the proposed optimal range in each group. The operating time was significantly longer in the navigation group (17 min). The KSS did not differ between both groups at a follow-up of 16 resp. 18 months (navigated group: 184 points, conventional group: 178 points). Navigation did not lead to a better positioning of the prosthesis than the conventional method and the operating time was longer. The clinical results were similar in both groups. The navigation may be a useful help for surgeons performing less unicompartmental knee arthroplasty using a minimally invasive approach.

Unicondylar knee replacement with a new tensioner device: clinical results of a multicentre study on 168 cases

Ligament balancing is an established surgical technique in total knee arthroplasty with good clinical results. A similar technique for unicondylar knee arthroplasty was developed. The aim of this study was to asses the outcomes of a unicondylar knee replacement implanted with a ligament tensor. A prospective multicentre study of 168 medial compartment unicondylar knee prosthesis with a minimum follow-up of 2 years. Clinically, the knee society score was recorded. For subjective assessment, the visual analogue scale (VAS) for pain and satisfaction was used. Radiographic analysis was performed to determine radiolucent lines. The surgical technique was based on a ligament-orientated procedure. With this technique, the femoral orientation, flexion/extension gaps and limb alignment is determined with a unique ligament tensor. The total KSS increased from 110.9 +/- 27.5 points preoperative to 176.5 +/- 21.1 points after 24 months. VAS for pain decreased from 6.0 +/- 1.9 preoperative to 2.8 +/- 1.7 after 24 months. VAS for satisfaction increased in the same period from 4.3 +/- 1.9 to 8.9 +/- 1.7. Four tibia implants had thin continuous radiolucent lines. Nine adverse events are reported. One patient died of unrelated causes. Five polyethylene inlays dislocated, one of five dislocated due to a fall. Three unicondylar knee prostheses were revised to a total knee arthroplasty, one because of undiagnosed pain, one for infection and one for femoral component malalignment. We have demonstrated the efficacy of a tension-controlled ligament-balanced surgical technique for unicompartmental knee prosthesis that gives satisfying and reproducible short-term results.

Effect of femoral to tibial varus mismatch on the contact area of unicondylar knee prostheses

In unicondylar knee prostheses, the relative angle and congruency of the femoral against the tibial component is not mechanically constrained and may vary with the surgical implantation technique. The contact area between both components was measured with increasing varus (0–20°) and flexion angles (− 20° to 90°) in five prosthesis models in the laboratory. The contact area varied with the relative position of the components and was critically reduced up to 70% at a varus range between > 5° and < 25°. The importance of relative malpositioning of the femoral and tibial components may be underestimated and reduces the contact area of unicondylar prostheses decisively, independent from the limb axis. This increases local pressure and may thus importantly contribute to increased wear and early loosening.

Use of anthropometric data from the medial tibial and femoral condyles to design unicondylar knee prostheses in the Chinese population

Anthropometric data on medial tibial condyles and medial femoral condyles of 172 normal knees (94 male knees, 78 female knees) were obtained using three-dimensional computer tomographic measurements. In the medial tibial condyle, we measured the anteroposterior (AP) and widest dimension (WD), and compared the measurements with the similar dimensions of five tibial unicondylar knee prostheses conventionally used in China. In the femur, we used best-fit two-circular arcs to measure the morphology of the sagittal plane of the medial femoral condyle. We found that three of the prostheses showed WD overhang for all ranges of the AP dimension, while two of them showed WD underhang. We also found a progressive decrease in the condylar aspect ratio (WD/AP%) in parallel with an increase in the AP dimension in the medial tibial condyle. However, none of the conventional tibial prosthesis showed a similar change. Furthermore, males had larger values in aspect ratio than females with the same values for AP dimension. There were definite correlations between the radius of the curvature for the posterior part (R1) and distal part (R2) in the sagittal plane of medial femoral condyle. Both of these values were smaller than in the Caucasian population. Both radiuses of curvature for the posterior and distal components showed definite correlations with the AP dimension. The results of this study may provide guidelines for designing unicondylar knee prostheses suitable for the Chinese population.

Pitch-based carbon-fibre-reinforced poly (ether—ether—ketone) OPTIMA® assessed as a bearing material in a mobile bearing unicondylar knee joint

The introduction of unicondylar knee prostheses has allowed the preservation of the non-diseased compartment of the knee while replacing the diseased or damaged compartment. In an attempt to reduce the likelihood of aseptic loosening, new material combinations have been investigated within the laboratory. Tribological tests (friction, lubrication, and wear) were performed on metal-on-carbon-fibre-reinforced (CFR) poly (ether-ether-ketone) (PEEK) (pitch-based) mobile unicondylar knee prostheses up to 5 x 10(6) cycles. Both a loaded soak control and an unloaded soak control (both medial and lateral components) were used to compensate for weight change due to lubricant absorption. For this material combination the loaded soak control gave slightly lower wear for both the medial and the lateral components than did the unloaded soak control. The medial components gave higher steady state wear than the lateral components (1.70 mm3 per 10(6) cycles compared with 1.02 mm3 per 10(6) cycles with the loaded soak control). The results show that the CFR PEEK unicondylar knee joints performed well in these wear tests. They gave lower volumetric wear rates than conventional metal-on-ultra-high-molecular-weight polyethylene prostheses have given in the past when tested under similar conditions. The friction tests showed that, at physiological viscosities, these joints operated in the boundary-mixed-lubrication regime. The low wear produced by these joints seems to be a function of the material combination and not of the lubrication regime.

Die In-vivo-Biomechanik von unikondylären Knieprothesen in minimal-invasiver Technik

Disturbed kinematics of the knee plays an important role in early failure of a unicondylar knee prosthesis (UNI). Recent studies on kinematics have shown that an intact anterior cruciate ligament (ACL) is important for a successful UNI. In this study, in vivo fluoroscopic analysis of knee kinematics was performed for 30 patients with a successful medial UNI implanted with the use of minimally invasive technique. The three-dimensional data of the CAD model were used for evaluating the sagittal translation as well as the axial rotation during deep knee bending and one gait cycle. The anteroposterior translation for flexion was, on average, -5.3 mm (-15.7-3.3; standard deviation 5.3). In most cases, the contact point was more posterior compared with the normal knee. During gait, the average anteroposterior translation was 0.8 mm, which is comparable to that of the normal knee. Axial rotation for deep knee bending was, on average, 8 degrees (-1.3-22.0; standard deviation 5.7), whereas 28 of the 30 knees showed normal axial rotation. During gait, an average axial rotation of 0.94 degrees was observed. The kinematic pattern of each of the subjects did not replicate the average pattern in most of the patients. An insufficient ACL may be suspected as the cause of the pathological kinematic pattern observed in some of these patients.

Polyurethane unicondylar knee prostheses: simulator wear tests and lubrication studies

Many materials are used as artificial joint bearing surfaces; these include conventional stainless steel or CoCrMo-on-ultra-high molecular weight polyethylene (UHMWPE), CoCrMo on itself and alumina-on-alumina. However, these joints have a limited lifespan resulting in failure of the prosthesis and the need for revision surgery. A number of materials have been introduced recently in an attempt to overcome these problems. Polycarbonate urethane (PU) is a compliant material that can be used as an artificial joint bearing surface which has been developed to mimic the natural synovial joint more accurately by promoting fluid film lubrication. Tribological tests were performed on CoCrMo-on-PU unicondylar knee prostheses to assess their performance in vitro. The wear produced by these components was considerably lower than that found for conventional joints. They also exhibited low friction and operated close to full-fluid film lubrication with viscosities of lubricant similar to those found in patients with arthritis. These tests gave encouraging results for the tribological performance of this material couple for use as an alternative bearing combination.

The precision and accuracy of templating the size of unicondylar knee arthroplasty

In trauma and joint arthroplasty, preoperative templating is an important step that can help in the selection of implant size, position and alignment. Although the precision (reproducibility) of templating in unicondylar knee arthroplasty has been assessed previously, the accuracy has never been studied. Our aim is to assess the precision and accuracy of using the templating system for one commonly used unicondylar knee arthroplasty, ALPHANORM® design (Alphanorm Medizintechnik, Germany). Eight observers used the templating system to estimate the size of the unicondylar knee prosthesis ALPHANORM® in 29 randomly selected patients with osteoarthritis. The observers, who all were orthopaedic surgeons with two different levels of experience, worked independently and repeated their measurements 2 weeks later. All the patients subsequently underwent unicondylar knee replacements, and the actual size of the femur and tibia was assessed intra-operatively without any knowledge of the template sizes. Our results revealed a high level of intra-observer reproducibility. However, the inter-observer reproducibility and the accuracy all were poor.

Reliability of templating in estimating the size of uni-condylar knee arthroplasty

The use of template systems has aided the preoperative selection of correct prosthetic size during routine arthroplasty. A similar system exists for unicondylar knee arthroplasty. Our goal is to assess the reliability of these templates for preoperatively predicting the correct prosthetic size in unicompartmental knee systems. Ten observers estimated the size of the unicondylar knee prosthesis required for 30 randomly selected patients with osteoarthritis. Estimation of the size was gauged using templates and instructions provided by the manufacturer. The observers worked independently and repeated their measurements 2 weeks later. Intraobserver and interobserver agreement was evaluated using the weighted κ coefficient, and this revealed poor agreement regardless of the surgeon’s experience. This shows that the present system lacks reliability and raises concerns about the place for preoperative radiological templating in unicompartmental knee arthroplasty.

Paper #140 Unicompartmental knee prosthesis implantation with a non image based navigation system. a matched-paired comparative study of the quality of implantation with a classical technique

The quality of implantation is an accepted prognostic factor for long term survival of a unicompartmental knee prosthesis. Most classical, surgeon controlled instrumentations mainly rely on the surgeon’s skill, and could have low accuracy and reproducibility. Navigation systems should allow a higher precision of implantation for such implants. The authors have studied the quality of the navigated-implantation of an unicondylar knee prosthesis with a non image based infrared navigation system in comparison with a classical, surgeon-controlled instrumentation.

Quality of Life and Gait After Unicondylar Knee Prosthesis Are Inferior to Age-Matched Control Subjects

Evaluation of quality of life, gait pattern, and muscle activity after implantation of unicondylar sledge prostheses in comparison with control group. A total of 17 patients were examined at an average follow-up of 21.5 mo after implantation of unicondylar sledge prostheses. In addition to clinical evaluation with different scores, our patients underwent three-dimensional gait analysis and surface electromyographic investigation of the lower limb and quality-of-life assessment using the Short Form-36 health questionnaire. The control group consisted of 11 healthy subjects. Statistical analysis showed significantly lower results for the patient group in the Hospital for Special Surgery score, the Knee Society score, the patella score, and the Visual Analog Scale for pain. In quality of life, significant differences could be found for the following items: physical functioning, role limitation because of physical problems, and bodily pain. Electromyographic activities during gait were significantly lower in the patient group, except for the rectus femoris and the tibialis anterior. Regarding gait analysis, the variables for ground reaction forces and stride length differed significantly, whereas maximum knee extension and flexion did not. Unicondylar knee replacement has failed to restore functional capabilities, quality of life, gait pattern, and muscle activity compared with healthy subjects of the same age. The assumption that unicondylar sledge prostheses preserve normal joint function must be questioned.

Proprioceptive function, clinical results, and quality of life after unicondylar sledge prostheses.

Evaluation of proprioceptive performance and quality of life after implantation of unicondylar sledge knee prostheses in comparison with normal control subjects. A total of 17 patients were examined after implantation of unicondylar sledge prostheses. Clinical examination was performed, quality of life was assessed, and proprioceptive performance was examined. A total of 11 healthy subjects of comparable age served as a control group. Clinical results of both groups differed significantly in all categories. Quality-of-life assessment differed only in the following items: physical functioning, role limitation caused by physical problems, and bodily pain. Other than angle reproduction at 15 degrees, no significant differences in proprioceptive testing, neither sway measurement nor angle reproduction, were found. Statistical analysis revealed no correlation between clinical scores and proprioceptive results. In comparison with normal control subjects of comparable age, the implantation of unicondylar sledge prostheses does not result in proprioceptive deficits. Except for physical functioning, role limitations caused by physical problems and bodily pain, most aspects of quality of life do not differ between patients and control subjects, although the patients' clinical results were significantly lower than the controls.

The case for using metal-on-metal

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Our experience with medial unicondylar knee prosthesis

The indications for unicondylar knee replacement for osteoarthritis are discussed. Its theoretical advantages against total knee replacement are the small size of the implants, an easier operative technique and faster rehabilitation. But some surgeons assume that tibial osteotomy has the same indications and gives the same long-term results while preserving the natural joint.52 medial resurfacing unicondylar knee prostheses have been followed for a mean time of 4 years, with a minimum of 1 year. There were 16 males and 31 females, with a mean age of 70 years (range 65 to 83 years). The indication was primary (37 cases) or post-traumatic (2 cases) osteoarthritis and necrosis of the medial femoral condyle (13 cases). The Cartier-Mansat prosthesis was most frequently used.Four prostheses were revised because of unexplained pain (1 case), aseptic loosening (2 cases) or osteoarthritic change in the opposite compartment (1 case). 48 prostheses were still in place at the time of this study. The results were studied with Hungerford’s classification, giving the knee joint a maximum score of 100 points.Mean pain score was 42/50, and only 4 patients had significant pain. No abnormal laxity was seen. 45 patients had complete extension, and 3 a deficit between 5 and 10°. 43 patients had over 90° flexion. Quadriceps force was always normal. Only 23 patients had a normal mechanical axis measured on a monopedal stance view, while 19 had a remaining varus deformation and 4 an overcorrection. The mean global score was 85/100, and 33 of the 39 patients with no missing item had a global score over 80/100.Objective and subjective results were very satisfactory. But we were not so pleased with the radiological appearance of the prosthesis. Malposition of both prosthetic components, including global limb malalignment, malalignment of one or both implants, incongruency of both implants or lowering of the joint space with reference to lateral compartment, were very common. The actual influence of these malpositions are not known, but is likely to be significant and the long term survival remains then questionable. A more precise operative technique could decrease the incidence of this disadvantage.

Modelling an orthopaedic knee prosthesis as a layered elastic system part 2: Finite element analysis

This study deals with the development of a specialized finite element algorithm suitable for a non-linear contact stress analysis of a model of a plastic tibial plateau of a typical unicondylar knee prosthesis. The principle feature of the contact algorithm is the use of Lagrange multiplier methods for the application of displacement constraints to surface Gauss points of a contacting body to prevent mesh overlap. This allows the effective modelling of two- and three-dimensional contact problems, with or without friction, using higher order elements. Through the selection of suitable benchmark tests, the performance and accuracy of the algorithm was assessed prior to the model analysis. Good agreement was obtained between the finite element results for the contact model and existing theoretical and experimental data. It was found that the Hertzian theory failed to accurately predict localized stresses at the contact interface when the indenter was much stiffer than the model.

Modelling an orthopaedic knee prosthesis as a layered elastic system part 1: Experimental and theoretical analyses

The purpose of this investigation was to produce a simplified model of the plastic tibial plateau of a typical unicondylar knee prosthesis that would allow the parametric study of contact stresses experienced by the plastic component during relatively severe loading conditions. This involved the design, production and testing of a three-dimensional axisymmetric embedded strain gauge model of the tibial plateau and the application of a suitable theoretical analysis. The principal feature of the strain gauge model was the possibility of varying the thickness during the experimental procedure while keeping the maximum number of embedded gauges active. The Hertzian contact theory was used as a basis for the prediction of integration errors associated with placing strain gauges in locations subject to large strain gradients. A theoretical analysis that took the layered nature of the contact model into account was carried out which provided full field data for comparison with Hertzian and experimental results. Good agreement was obtained between theoretical and experimental values along the model axis, while at off-axis locations theoretical results based on the layered analysis compared reasonably with embedded strain gauge data. Very slight discrepancies between the experimental and idealized boundary conditions present in the initial stages of testing resulted in significant differences between embedded strain gauge and theoretical data.