Introduction

Unicompartmental knee arthroplasty (UKA) currently experiences increased popularity. It is usually assumed that UKA shows kinematic features closer to the natural knee than total knee arthroplasty (TKA). Especially in younger patients more natural knee function and faster recovery have helped to increase the popularity of UKA. Another leading reason for the popularity of UKA is the ability to preserve the remaining healthy tissues in the knee, which is not always possible in TKA. Many biomechanical questions remain, however, with respect to this type of replacement.

25% of knees with medial compartment osteoarthritis also have a deficient anterior cruciate ligament [1]. In current clinical practice, medial UKA would be contraindicated in these patients. Our hypothesis is that kinematics after UKA in combination with ACL reconstruction should allow to restore joint function close to the native knee joint. This is clinically relevant, because functional benefits for medial UKA should especially be attractive to the young and active patient.

Despite high success rates following total knee arthroplasty (TKA), knee kinematics are altered following TKA. Additionally, many patients report that their reconstructed knee does not feel ‘normal’ [1], potentially due to the absence of the anterior cruciate ligament (ACL), an important knee stabilizer and proprioceptive mechanism. ACL-retaining implants have been introduced with the aim of replicating native knee kinematics, however, there has yet to be a detailed comparison between knee kinematics in the native knee and one reconstructed with an ACL-retaining implant.

Six fresh-frozen right legs (77±10 yr, 5 male) were mounted in a kinematic rig and subjected to squatting (40°-105°) motions. The vertical positon of the hip was manipulated with a linear actuator to induce knee flexion while the quadriceps were loaded with an actuator to maintain a vertical load of 90 N at the ankle [2]. Medial/lateral hamstring forces were applied with 50 N load springs. During testing, an infrared camera system recorded the trajectories of spherical markers rigidly attached to the femur and tibia. Two trials were performed per specimen. Following testing on the native knee, specimens were implanted with an ACL-retaining TKA (Vanguard XP, Zimmer Biomet) and all trials were repeated. Three inlay thicknesses were tested to simulate optimal balancing as well as over- (1 mm thicker) and understuffing (1 mm thinner) relative to the optimal thickness.

Pre-operative computed tomography scans allowed identification of bony landmarks and marker orientation, which were used define anatomically relevant coordinate systems. The recorded marker trajectories were transformed to anatomical translations/rotations and resampled at increments of 1° of knee flexion. Translations of the medial and lateral femoral condyle centers were scaled to maximum anterior-posterior (AP) width of the medial and lateral tibial plateau, respectively. For all kinematics, statistical analysis between knee conditions was conducted using repeated measures ANOVA in increments of 10° knee flexion.

Internal rotation of the tibia was significantly lower (p<0.05) for the three reconstructed conditions relative to the native knee at flexion angles of 60° and below. No significant differences in tibial rotation were observed between the balanced, overstuffed, or understuffed conditions. The varus orientation was not significantly influenced by implantation, regardless of inlay thickness, for all flexion angles. At 40° flexion, the AP position of the femoral medial condyle was significantly more anterior for the native knee relative to the balanced and understuffed conditions. This finding was not significant for the other flexion angles. No significant differences were found for the lateral condyle center AP position at any flexion angle.

Preservation of the cruciate ligaments during total knee arthroplasty may allow better physiologic representation of knee kinematics. The implants tested in this study were able to replicate kinematics of the native knee, except for tibial rotation and AP position of the medial femoral condyle in early knee flexion. Interestingly, the impact of inlay thickness was generally small, suggesting some tolerance in the choice of inlay thickness.

Introduction

Oxidized zirconium (OxZr) is used as a ceramic surface for femoral components in total knee arthroplasty (TKA). The aim of this study was to investigate its performance by examining retrieved femoral components and their corresponding PE inserts in matched comparison with conventional chrome/cobalt/molybdenum alloy (CrCoMo).

Objectives: The aim of this study was to examine the influence of different prosthesis designs (Deep-Dish (DD) vs. posterior stabilized (PS)) on the patello-femoral pressure. The femoro-patellar pressure depends among other things on the AP stability of the knee joint. The use of DD has been described to be equally applicable with a resected or deficient PCL.

Methods: Fresh frozen human knee specimens (n = 8, 7 male, 1 female) underwent testing in a kinematic device simulating an isokinetic knee extension cycle from 120° of flexion to full extension. Knee motion was driven by a hydraulic cylinder applying sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The amount of patellofemoral contact pressure and its distribution was measured by means of a pressure sensitive film (Tekscan^®, Inc., Boston, USA). Patellar contact pressure was examined first after implantation of a cruciate retaining TKA (Genesis II, Smith& Nephew, Memphis, USA). An 11 mm polyethylene (PE) DD insert was tested before and after resection of the PCL. Finally, the femoral component of the CR TKA was removed and replaced by a posterior stabilized (PS) model repeating measurements with an 11 mm PE inlay. The patella was not resurfaced throughout the whole procedure. A paired sampled t-test was applied for comparison of means and considered significant at p ≤ 0.05.

Results: There was no statistical significant difference of patello-femoral peak and mean contact pressures of the DD inlay before and after resection of the PCL. After implantation of the PS TKA peak pressure was significantly lower (Mean: 6.12 ± 2.37 MPa, Range: 10.68 – 3.30 MPa) in comparison with the DD type (7.12 ± 2.53 MPa, 11.94 – 3.55 MPa; p < 0.01) with a preserved PCL. Also the mean contact pressure turned out to be lower with the PS design (p < 0.006; PS: 3.58 ± 1.25 MPa, 5.91 – 2.08 MPa, DD: 4.27 ± 1.34 MPa, 6.66 – 2.18 MPa). The contact area was also significantly smaller with the PS design (p < 0.03, PS: 140.84 ± 40.04 mm2, 188.47 – 65.10 sq mm, DD: 175.97 ± 24.46 sq mm, 222.56 – 142.56 sq mm).

After resection of the PCL differences in contact pressures and contact area between DD and PS failed to reach statistical significance although there was an obvious tendency towards lower pressures with the PS-design.

Conclusions: The results of this study suggest that a posterior stabilized TKA design reduces the retropatellar peak and mean pressure as well as the contact area in comparison with a deep-dish design when the PCL is preserved. The better reproducible rollback with a PS model could serve as a possible explanation. However, this difference is less pronounced when a DD inlay is applied after resection of the PCL. Nevertheless, a PS rather than a DD design is recommended in the PCL deficient knee.

Objective: Decreased quadriceps strength may contribute to anterior knee pain after total knee arthroplasty (TKA). The quadriceps force necessary to establish full extension is strongly dependent on the position and the relative length of the lever arms over the knee joint. The purpose of this in vitro study was to investigate the amount of quadriceps force required to extend the knee isokinetically after TKA in dependence of different prosthesis designs and the state of the posterior cruciate ligament (PCL).

Methods: Eight fresh frozen human knee specimens were tested in a kinematic device that simulated an isokinetic knee extension cycle from 120° of flexion to full extension. Knee motion was driven by a hydraulic cylinder applying sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The quadriceps force was measured using a load cell attached to the quadriceps tendon after implantation of a cruciate retaining (CR) TKA (Genesis II, Smith& Nephew, Memphis, Tn, USA) applying a conventional and a highly conforming polyethylene (PE) inlay before and after resection of the PCL. Finally, the femoral component of the CR TKA was replaced by a posterior stabilized (PS) design and measurements were redone.

Results: No significant differences in the average quadriceps force were detected between the different PCL retaining inlays (CR, highly conforming) as long as the PCL was intact. However, after resection of the PCL, the required quadriceps force increased significantly for both designs (CR: 4.7%, p < 0.01, Highly conforming: 3.5%, p < 0.03). After implantation of the PS femoral component quad force decreased to its initial levels with forces significantly lower compared to the PCL deficient knees provided with a CR (−6.0%, p < 0.01) or highly conforming (−5.1%, p < 0.01) inlay. With a PS design average quadriceps extension force was not significantly different from cruciate retaining TKA inlays at an intact PCL.

Conclusions: The data of this in vitro study suggest that the quadriceps extension force is significantly higher for knees after cruciate retaining TKA with PCL deficiency, independent of the use of a CR or DD inlay. Thus, the integrity of the PCL should be secured in clinical practice when using a cruciate preserving TKA design.

Background: Isolated patellofemoral arthroplasty has gained new attention after recently published positive results. It is considered an intermediate treatment for the patient with isolated arthritis of the anterior compartment of the knee. Aim of this nationwide survey was to determine the current status of patellofemoral arthroplasty in Germany.

Methods: All German departments of orthopaedic surgery, traumatology and general surgery with a yearly performance of at least fifty knee arthroplasties were asked to complete a standardized questionnaire. In the first part, surgeons were asked general questions about their department size, case numbers of knee arthroplasties per year and non-endoprosthetic treatment of isolated patellofemoral disorders. If patellofemoral arthroplasty was conducted, parameters concerning age, gender, duration of complaints, indication for surgery, surgical approach, type of endoprosthesis used, additional surgical treatments and failures were evaluated in the second part. Furthermore we asked for the reasons if no isolated patellofemoral arthroplasty was performed.

Results: A total of 224 (30%) usable questionnaires were returned. Of 53420 knee arthroplasties performed per year, only 195 were isolated patellofemoral arthroplaties (0.37%). However, in 54 departments (24%), at least one isolated patellofemoral arthroplasty was performed with an average of 3.95 (1–20) procedures per year. The majority of patients were between 40 and 60 years old (40–60y: 56%; 20–40y: 8%, 60–80y: 35%, > 80y: 1%). Females were affected in 65% of patients. Etiology of isolated patellofemoral arthritis was believed to be idiopathic in 41% and traumatic in 8%. Patellofemoral dysplasia was held responsible in 47% and patellofemoral instability in 4% of cases. The main reason for failure and surgical revision was ongoing pain of the affected knee (40%). Negative attitude and disbelief towards the success of isolated patellofemoral arthroplasty were stated by the majority (62%) of non-users. A lack of appropriate indications was reported by 22% and missing know-how by 16%.

Conclusions: Isolated patellofemoral arthroplasty has only little significance among surgeons performing knee arthroplasty in Germany. Although promising results were reported in the literature, the majority of surgeons do not believe in the success of the procedure.

There is a high risk of venous thromboembolism when patients are immobilised following trauma. The combination of low-molecular-weight heparin (LMWH) with graduated compression stockings is frequently used in orthopaedic surgery to try and prevent this, but a relatively high incidence of thromboembolic events remains. Mechanical devices which perform continuous passive motion imitate contractions and increase the volume and velocity of venous flow.

In this study 227 trauma patients were randomised to receive either treatment with the Arthroflow device and LMWH or only with the latter. The Arthroflow device passively extends and plantarflexes the feet. Patients were assessed initially by venous-occlusion plethysmography, compression ultrasonography and continuous wave Doppler, which were repeated weekly without knowledge of the category of randomisation. Those who showed evidence of deep-vein thrombosis underwent venography for confirmation. The incidence of deep-vein thrombosis was 25% in the LMWH group compared with 3.6% in those who had additional treatment with the Arthroflow device (p < 0.001). There were no substantial complications or problems of non-compliance with the Arthroflow device. Logistic regression analysis of the risk factors of deep-vein thrombosis showed high odds ratios for operation (4.1), immobilisation (4.3), older than 40 years of age (2.8) and obesity (2.2).