The effect of gender, age, BMI and Kellgren-Lawrence grade on functional outcome after Physica ZUK medial unicompartmental knee replacement.

PURPOSE: Several factors influence the outcome of unicompartmental knee replacements. This study investigates the correlation of specific preoperative patient variables with postoperative functional outcomes-measured with the American Knee Society Knee (KS-KS) and Function Scores (KS-FS), as well as the difference in knee flexion pre- and postoperatively. METHODS: In a retrospective study of 242 patients who underwent a medial Physica ZUK unicompartmental knee replacement (UKR), the American KS-KS, KS-FS as well as knee flexion were analyzed preoperatively and at 2-year follow-up. The absolute scores and improvement in scores were calculated per subgroup for gender, age, body mass index (BMI) and Kellgren-Lawrence (KL) radiological grade and compared between the subgroups. RESULTS: All groups had a significant improvement in range of flexion, KS-KS and KS-FS. Female patients had lower preoperative scores and significantly larger improvement in knee flexion and KS-FS. Age does not seem to be associated with the postoperative functional outcome. Patients with a BMI of 30 or higher had a lower postoperative KS-KS and KS-FS as well as knee flexion. Patients with KL grade IV changes had larger gain in KS-KS compared to patients with grade III. CONCLUSION: Overall, KS-KS, KS-FS and knee flexion improve significantly 2 years following a Physica ZUK UKR in all groups. Although excellent results were found in patients with a BMI of 30 or higher, a decrease in BMI was associated with an increase in functional outcome. KL IV grade preoperatively was associated with a better KS-KS improvement compared to the KL III group 2 years postoperatively. This information can aid surgeons in patient selection and to counsel patients on outcomes. EVIDENCE LEVEL: III.

Kinematics of a bicruciate-retaining total knee arthroplasty.

PURPOSE: The recently reintroduced bicruciate-retaining Total Knee Arthroplasty (BCR TKA) is an interesting approach in the quest for close replication of knee joint biomechanics and kinematics closer to the native knee. Therefore, this study aimed at providing a detailed biomechanical view on the functional resemblance of BCR TKA to the native knee joint. METHODS: Seven fresh-frozen full leg cadaver specimens (76 ± 10 year) were mounted in a 6 degrees-of-freedom kinematic rig that applied a dynamic squatting motion knee flexion. Two motion patterns were performed pre- and post-implantation of a fixed bearing BCR TKA: passive flexion-extension and squatting while an infrared camera system tracked the location of reflective markers attached to the tibia and femur. Additionally, specimen laxity was assessed using Lachman tests and varus/valgus stress tests in triplicate. RESULTS: Overall, differences in tibiofemoral kinematics between native knee and BCR TKA were small. Some minor differences appeared under the load of a squat: less internal tibial rotation and some minor paradoxical anterior translation of the medial femoral condyle during mid-flexion. BCR TKA may slightly elevate the joint line. Knee laxity as measured by the Lachman and varus/valgus tests was not significantly influenced by BCR TKA implantation. CONCLUSION: As both cruciate ligaments are preserved with BCR TKA the unloaded knee closely resembles native knee kinematics including preserving the rollback mechanism. The loss of the conforming anatomy of menisci and tibial cartilage and replacement via a relatively flat polyethylene inlay may account for the loss of tibial internal rotation and the slight paradoxical AP motion of the medial femoral condyle with BCR TKA. This phenomenon reproduces findings made earlier with fixed bearing unicondylar knee arthroplasty.

Synovial Fluid Fatty Acid Profiles Differ between Osteoarthritis and Healthy Patients.

OBJECTIVE: Free fatty acids (FAs) may influence cartilage metabolism and osteoarthritis (OA) disease progression. It is not clearly studied which FAs are present in the synovial fluid of knee joints and whether there are differences in FA content between nonsymptomatic and OA knee joints. The aim of this study was to investigate the presence of different types of FAs in synovial fluid of both OA- and nonsymptomatic control joints, and to analyze differences between both groups. DESIGN: A total of 23 synovial fluid samples were collected from patients with end-stage knee OA undergoing total knee replacement, with approval of the medical ethical committee. As controls, 6 synovial fluid samples were obtained from postmortem donors without any history of joint disease or arthritis. Measurement of free FA concentration was done by mass spectrometry for saturated FAs (SFA), monounsaturated FAs (MUFA), and omega-3 and omega-6 polyunsaturated FAs (n-3 PUFAs and n-6 PUFAs). RESULTS: Our measurements demonstrated the presence of SFAs, MUFAs, n-3 and n-6 PUFAs in synovial fluid of both nonsymptomatic and OA knee joints. The n-6/n-3 ratio was significantly lower in the OA group (P = 0.0005). Arachidonic acid (n-6 PUFA) concentrations were also lower in OA synovial fluid (P = 0.01), while tetracosadienoic acid (P = 0.0001) and nervonic acid (P = 0.001) (MUFAs) were higher in synovial fluid of patients with knee OA. CONCLUSION: Synovial fluid contains a broad spectrum of free FAs. The FAs profile differs between OA and control subjects, including a tendency for less n-6 FAs in OA joints.