Excellent fixation achieved with cementless posteriorly stabilized total knee arthroplasty.

Cementless posteriorly stabilized (PS) total knee arthroplasty has not been widely accepted primarily because of prior unpredictable results and concern about micromotion at the tibial fixation interface caused by the cam/post interaction. A prospective consecutive series of 114 cementless, tricompartmental periapatite-coated single-radius PS implants in 110 patients with a mean age 62 years was performed to determine if initial stability and biologic fixation could be achieved. At a mean follow-up of 36 months, all implants demonstrated radiographic evidence of stable biologic fixation with no evidence of loosening, osteolysis, stress shielding, or progressive radiolucent lines. Based on these early results, cementless, periapatite-coated single-radius PS total knee arthroplasty offers marked promise.

Magnitude of cement-device interfacial stresses with and without tibial stemming: impact of BMI.

Patients expect their total knee arthroplasty to relieve pain and to be long lasting. With patients becoming more active, weighing more, and living longer, this expectation becomes increasingly more difficult to fulfill. Patients who are obese and active put greater loads on their implants and may have a greater risk of failure. Although much attention has been paid to decreasing polyethylene wear, a major cause of implant failure, very little research focus has been directed to elucidate other measures to reduce failure, such as the efficacy of prophylactic stemming of the tibial tray. This study explored whether additional mechanical support for tibial base plates would help reduce bone cement stresses in heavy patients, who, like patients with a high activity level, put added stress on their implants. A tibial base plate with a 12-mm-diameter x 50-mm-long stem was compared with the same tibial base plate with a 15-mm-diameter x 20-mm-long end cap using finite element analysis. The results indicate that the tibial base plate with a prophylactic stem significantly reduced compressive and shear stresses on the cement-device interface and therefore may help to reduce the possibility of tibial loosening in these at-risk patients. Further, such studies will aid the surgeon in educating patients and in selecting the appropriate implant strategy.

Impact of patellofemoral design on patellofemoral forces and polyethylene stresses.

BACKGROUND: The patellofemoral joint is a complex articulation because it relies mainly on soft-tissue constraints for stable tracking. The presence of a functioning posterior cruciate ligament and the design parameters of a total knee arthroplasty, such as trochlear groove alignment and cam-post configuration, can have a major effect on patellar biomechanics. METHODS: A finite element model of a knee implanted with femoral, tibial, and patellar components was generated. The model was validated by experimental testing of three cadaver knees implanted with a total knee prosthesis and a patellar force transducer. Two femoral component designs with different valgus angles of the trochlear groove (0 degrees and 7 degrees ) were studied. The effects of femoral rollback, rotation of the femoral component, medialization of the patellar implant, and alignment of the trochlear groove on patellar forces were then analyzed. RESULTS: A consistent reduction of up to 7% in patellofemoral forces was seen with progressive magnitudes of femoral rollback. The 0 degrees -aligned trochlear groove generated some lateral patellofemoral shear force throughout knee flexion. The 7 degrees -aligned trochlear groove generated medial shear force at flexion angles of <20 degrees and lateral shear force at flexion angles of >20 degrees. A more medial patellar component position reduced peak lateral shear forces by up to 10 to 15 N. However, a corresponding increase in medial shear forces was seen. CONCLUSIONS: This model predicted substantial reduction in patellofemoral lateral shear forces with a medialized patellar component or with external rotation of the femur. The model supported the hypothesis that femoral rollback reduces patellofemoral forces by improving the efficiency of the extensor mechanism. CLINICAL RELEVANCE: Patellofemoral complications after total knee arthroplasty include anterior knee pain, patellar subluxation and dislocation, abnormal polyethylene wear and damage, and loosening. There is a wide variation in the design features of current total knee prostheses, such as the sagittal radius, depth, and orientation of the trochlear groove of the femur and the geometry of the patellar component surface. The finite element model used in the present study can provide insight into the effects of design parameters on patellofemoral forces and on local contact stresses.

Minimally invasive total knee arthroplasty: a 10-feature evolutionary approach.

There should not be a revolution to MIS-TKA but rather an evolutionary approach. This includes progressively downsizing incisions and causing less damage to the quadriceps mechanism. Previously,there was an extensive open exposure prolonged patella eversion and dislocation of the tibio-femoral joint. This should be evolved into a VMO muscle split with patella subluxation, retraction but not dislocation, and no gross dislocation of the tibio-femoral joint. Although the present MIS-TKA technique can be difficult and time-consuming, the resulting patient benefits should outweigh the extra effort required. In the future, we may use bone cuts and implantation with computer navigation. Each advance, however, will require new techniques, instrumentation, implants, and careful clinical studies. Caution should be taken by surgeons to avoid revolutionary approaches with existing implants, because they harbor a risk of catastrophic failure.

Minimal incision total knee arthroplasty using the suspended leg technique.

This article describes an approach to minimize the soft-tissue trauma associated with total knee arthroplasty. A suspended leg technique provides full access to the knee by using flexion and the weight of the limb to stretch the incision. Violation of the extensor mechanism is minimized and soft-tissue balancing is enhanced with the suspended technique.

The effect of timing of manipulation under anesthesia to improve range of motion and functional outcomes following total knee arthroplasty.

BACKGROUND: Manipulation under anesthesia has been reported to improve range of motion when other rehabilitative efforts fail to obtain adequate motion after total knee arthroplasty. The purpose of this study was to evaluate the effects of the timing of the manipulation on knee range of motion and clinical outcomes. METHODS: All 2128 total knee arthroplasties performed at our institution from 2005 to 2011 were reviewed to determine the number of patients who had undergone manipulation under anesthesia. A total of 144 manipulations in eighty-eight women and forty-five men were reviewed. Manipulations under anesthesia that were performed within the first twelve weeks after total knee arthroplasty were considered early and those after that period were considered late. Patients were further substratified according to the timing of the manipulation: Group I included those who had the manipulation within six weeks; Group II, at seven to twelve weeks; Group III, at thirteen to twenty-six weeks; and Group IV, after twenty-six weeks. Outcomes evaluated included gains in flexion and final range of motion, and Knee Society objective and function scores between early and late manipulation, using various adjusted multivariable regression models and at a mean follow-up of fifty-one months (range, twelve to eighty-one months). Mediation analysis was used to investigate whether gains in range of motion from the manipulations under anesthesia alone had mediated the effect between the timing of the manipulation and the clinical outcomes. RESULTS: Patients who underwent early manipulation had a significantly higher mean gain in flexion (36.5° versus 17°), higher final range of motion (119° versus 95°), and higher Knee Society objective (89 versus 84 points) and function scores (88 versus 83 points) than those who had late manipulation under anesthesia. There were no significant differences in the outcomes of Groups I and II. Manipulations after twenty-six weeks resulted in unsatisfactory clinical outcomes. Multivariable regression analyses confirmed significantly better clinical outcomes with early manipulation. Mediation analysis showed that the timing of manipulation independently had significantly contributed to the outcomes. CONCLUSIONS: Orthopaedic surgeons should have a low threshold for performing early manipulations with the patient under anesthesia within twelve weeks after an arthroplasty, to achieve higher knee range of motion and improved clinical outcomes. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Knee bearing technology: where is technology taking us?

A novel sequentially irradiated and annealed bearing material (X3), characterized for use in knee arthroplasty, has been developed. Attention was directed to mechanical strength properties, oxidation resistance, and the ability to reduce wear. Material properties such as ultimate tensile and yield strength were unaffected by the sequential cross-linking process. Elongation was reduced relative to GUR 1020 conventional polyethylene, but equivalent to that of direct compression molded 1900 material. In knee simulator testing for normal gait and stair climbing, measured wear rates for X3 polyethylene were reduced by 79% and 77% when compared to the same knee design using conventional polyethylene. Mechanical properties and wear characteristics of the X3 polyethylene were unaffected before and after exposure to accelerated aging; properties of conventional polyethylene were adversely impacted.