A study of weight transmission through the knee joint with applied varus and valgus loads

The clinical outcome of revision knee replacement after unicompartmental knee arthroplasty versus primary total knee arthroplasty: 8-17 years follow-up study of 49 patients

When unicompartmental knee arthroplasty (UKA) failure occurs, a revision procedure to total knee arthroplasty (TKA) is often necessary. We compared the long-term results of this procedure to primary TKA and evaluated whether they are clinically comparable. Twenty-one patients underwent UKA conversion to TKA between 1991 and 2000. The results of these patients were compared to the group of 28 primary TKA patients with the same age, sex and operation time point. The long-term outcomes were evaluated using clinical and radiological analysis. The mean follow-up period of the patients was 10.5 years. The UKA revision patients were more dissatisfied, as measured by the WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) scale (0-100 mm) compared to the primary TKA patients (pain 18.1/7.8; p = 0.014; stiffness 25.7/14.4, p = 0.024; physical function 19.0/14.8, p = 0.62). Two patients were revised twice in the UKA revision group. There was one revision in the primary TKA group (p = 0.39). Improvement in range of motion (ROM) was better in the TKA patients compared to the UKA revision patients (8.2 degrees /-2.6 degrees , p = 0.0001). We suggest that UKA conversion to TKA is associated with poorer clinical outcome as compared to primary TKA.

Effect of foot orthoses on the kinematics and kinetics of normal walking gait

Despite their wide clinical application and success, our understanding of the biomechanical effects of foot orthoses is relatively limited. The aim of this study was to assess the effect of medially wedged and laterally wedged foot orthoses on the kinematics and joint moments of the rearfoot complex, knee, hip and pelvis and the ground reaction forces. The principal effect of the foot orthoses was on the rearfoot complex, where significant changes in joint rotations and moments were observed. Medially wedged orthoses decreased rearfoot pronation and increased the laterally directed ground reaction force during the contact phase, suggesting reduced shock attenuation. The laterally wedged orthoses increased rearfoot pronation and decreased the laterally directed ground reaction force during the contact phase, suggesting increased shock attenuation. The effects of the orthoses on knee, hip and pelvis kinematics were generally minimal. In view of the minimal effect the orthoses had on joints proximal to the foot, it is suggested that the orthoses may have additional effects on the passive and active soft tissues of the lower limb and it is these changes that result in the documented clinical success.

Correlation between condylar lift-off and femoral component alignment

The current study analyzed subjects having a total knee arthroplasty to determine the incidence of condylar lift-off and correlate lift-off with the alignment of the femoral component with respect to the transepicondylar axis. Twenty-five subjects, implanted with a posterior stabilized total knee prosthesis, were asked to do weightbearing deep knee bends while under fluoroscopic surveillance. The two-dimensional fluoroscopic images were converted into three-dimensional images using a fully automated computer model-fitting technique. Each subject then was assessed for the incidence of condylar lift-off. The five subjects having the maximum amount of lift-off were reanalyzed for comparison using computed tomography. Using digitization, the angle between the posterior femoral condylar line and the transepicondylar axis was measured and correlated with the presence of femoral condylar lift-off. The incidence of condylar lift-off was significantly less for subjects in this study compared with subjects reported in previous fluoroscopic studies. Forty percent (10 of 25) of the subjects experienced condylar lift-off. The maximum amount of lift-off was 2.3 mm and the average for subjects experiencing lift-off was 1.4 mm. There also was a distinct correlation between femoral component alignment and condylar lift-off. Using computed tomography, it was determined that 69.2% of the subjects had a correlation between condylar lift-off and malalignment of the femoral component relative to the epicondylar axis. Placement of the femoral component parallel to the transepicondylar axis seems to lessen the incidence of femoral condylar lift-off and may reduce polyethylene wear by reducing eccentric edge loading.

Posterior cruciate ligament rupture alters in vitro knee kinematics

Isolated posterior cruciate ligament injuries usually are treated nonoperatively, although some patients remain symptomatic, and degenerative changes within the patellofemoral joint and the medial compartment of the tibiofemoral joint have been seen in followup studies. In vitro simulation of knee squatting was done to quantify the influence of the posterior cruciate ligament on tibiofemoral and patellofemoral kinematics. For five knee specimens, knee kinematics were measured before and after sectioning the posterior cruciate ligament, and compared using a Wilcoxon signed rank test. The only kinematic parameters that changed significantly after sectioning the posterior cruciate ligament were the tibial posterior translation and patellar flexion. The posterior translation of the tibia increased significantly between 25 degrees and 90 degrees flexion. The average increase in the posterior translation exceeded 10 mm at 90 degrees flexion. The patellar flexion increased significantly from 30 degrees to 90 degrees flexion. The average patellar flexion increase peaked at 4.4 degrees at 45 degrees flexion. Increased tibial translation could adversely influence joint stability. Increased patellar flexion could increase the patellofemoral joint pressure, especially at the inferior pole, leading to degenerative changes within the patellofemoral joint.

Size and position of a single condyle allograft influence knee kinematics

An optimal match for size and shape between the donor femur and the host knee is considered a critical factor influencing the outcome of a knee allograft implantation. An in vitro allograft model was developed to determine the influence of the size and position of a lateral distal femoral condylar allograft on knee kinematics. Functional knee motion was simulated in a cadaver host knee in the intact state after removing and reimplanting the native lateral condyle of the distal femur and after serially replacing the native condyle with eight donor allografts. Each allograft was first tested in an optimal position and subsequently shifted 3 mm proximal and 3 mm distal to the joint line to quantify changes in joint kinematics due to the position of the allograft. The intact knee and the knee with the ideally implanted native allograft followed similar kinematic trends. Decreasing the width of the allograft increased the valgus knee orientation at full flexion, translated the tibia posteriorly at full extension, and externally rotated the tibia throughout knee flexion. The proximal shift in allograft position increased the valgus orientation at full extension, translated the tibia posteriorly at mid-flexion, and externally rotated the tibia throughout flexion. The distal shift in position had the opposite effect on the kinematics of the proximal shift. These results indicate that improving techniques for preoperative size-matching and intraoperative allograft placement may help to reduce biomechanical complications following implantation of the allograft.

In vitro load transmission in the canine knee: the effect of medial meniscectomy and varus rotation

The purpose of this study was to determine the in vitro load-transmission characteristics of the canine knee, paying particular attention to the positioning effect of the meniscus in the coronal plane. The intact joint was first loaded and then tested under two different loading conditions after a complete medial meniscectomy. The first set of test conditions attempted to simulate those used by previous investigators, by ignoring the spacer effect of the meniscus. The second set of tests were carried out following varus rotation of the joint (to account for the loss of the meniscal spacer) to assure initial contact in both tibiofemoral compartments at the start of test cycle. It is presumed that this varus realignment occurs during weight bearing following meniscectomy in vivo. As in previous studies, the joints experienced slightly larger displacements (although not statistically significant) and had lower stiffness values following medial meniscectomy than when intact. However, following varus realignment of the joint after meniscectomy, the displacement was markedly smaller (-35% to -49%; P < 0.01) and the structural stiffness was much greater (47-123%; P < 0.05) over the range of forces analyzed, compared with the intact joint. The ratio of dissipated to input energy was 42% for the intact joint, and increased following meniscectomy to 54% (P < 0.05) with realignment and 55% (P < 0.05) without realignment. Measured contact area decreased by 17% (P < 0.05) following meniscectomy alone, and by 12% (P < 0.05) following meniscectomy with realignment.(ABSTRACT TRUNCATED AT 250 WORDS)

Forces and moments on the human leg in the frontal plane during static bipedal stance

An experimental apparatus was assembled that permitted measurement of the vertical and lateral ground reaction forces as the hip is abducted, resulting in foot separations ranging from 0.25 to 71 cm, with the knee in 0 degree flexion. Twelve healthy volunteers (8 men and 4 women) were tested. The hip joint was located by means of center of rotation measurements on each subject's legs, and the location of the knee joint was determined using anatomical measurements. It was observed that the mediolateral force was nonzero and directed toward the body midline, even when the subject's feet were placed together. With the feet placed at shoulder width, the population mean mediolateral force was 3% of body weight. It was determined that simplifying assumptions based upon either "zero lateral force," or "zero hip moment," produced errors, when compared with our measured values, over various ranges of foot separation, with the zero hip moment assumption providing accuracy over a broader range. The inclination of the tibial plateau, with respect to the long axis of the tibia, that would produce minimal mediolateral shear at the knee is presented. Research and clinical applications of our results and techniques are discussed.

Bone and cartilage changes following experimental varus or valgus tibial angulation

The purpose of this work was to determine whether subchondral bone changes are an integral part of the development of osteoarthrosis of the knee following experimentally created tibial angulation. Thirty degree varus or valgus proximal tibial osteotomies were created in female New Zealand white rabbits. Bone and cartilage changes were assessed grossly, radiologically, and histologically. Thirty-four weeks following osteotomy, severe cartilage changes, including osteophytes, fibrillation, derangement of cell columns, and cloning, were evident on the overloaded condyle, accompanied by increased subchondral bone density. The pattern of cartilage deterioration was different from that found in other experimental, mechanically induced arthroses. We conclude that osteoarthrosis is a final common pathway for mechanically induced joint failure, and that progressive cartilage change is associated with increased subchondral bone density.

Influence of the varus-valgus instability on the contact of the femoro-tibial joint

The varus-valgus instability of the knee joint is mainly due to ruptured or lax collateral ligaments. The purpose of this investigation was to study the influence of the varus-valgus instability on the contact pressures of the femoro-tibial joint. Six fresh knee specimens of human cadavers were tested to measure the contact pressure on the tibia plateau of the knee joint at varus or valgus alignment under various loads and at full extension. Pressure transducers and Bourdon tube pressure gauges were used simultaneously for recording pressure. At neutral alignment of the knee with the menisci intact, the peak pressure increased linearly with forces up to 4 MPa. With increasing varus alignment, the peak contact pressure on the medial plateau not covered by the menisci increased up to a maximum of 7.3 MPa at 5 degrees varus, and at 5 degrees valgus, the peak pressure on the lateral plateau was 7.8 MPa. After total meniscectomy, the contact pressure increased up to a maximum of 7.4 MPa at a force of 2700 N. With increasing varus alignment, the contact pressure on the medial plateau increased to 8.1 MPa at 5 degrees varus and on the lateral plateau 9.2 MPa at 5 degrees valgus.

Immediate effects of meniscectomy on the knee joint. The effects of tensile load on knee joint ligaments in dogs

Tensile strength variables for the collateral ligaments were compared after excision of the meniscus in one knee, the corresponding meniscus in the contralateral knee of the same dog being intact. Removal of the meniscus was associated with a three-fold increase in initial laxity, two-fold for the lateral and three-fold for the medical ligament. The maximum tensile load uptake of the medial collateral ligament was reduced by more than 10 per cent after medial meniscectomy; the load uptake of the lateral ligament was not affected by lateral meniscectomy. It is proposed that tensile loads are distributed more favourably in the medial collateral ligament by the intact medial meniscus with firm capsular attachments than in the "normal" ligament after meniscectomy.