Variable tibiofemoral articular contact stress in fixed-bearing total knee arthroplasties.

BACKGROUND: Rotational allowance at the tibiofemoral joint would be required during deep flexion. However, the amount of flexion and rotation has not been investigated in modern total knee arthroplasty (TKA) designs. The present study aimed to determine the contact stress in five posterior-stabilized fixed-bearing TKA designs. HYPOTHESIS: We hypothesized that the contact area and stresses at the tibiofemoral articular surfaces vary according to the type of implant design and tested condition. MATERIALS AND METHODS: The contact area and mean and peak contact stresses at the tibiofemoral articular surfaces were determined when a compressive load of 1200N was applied to a NexGen LPS Flex, Scorpio NRG, Genesis II, PFC Sigma, and Foundation implant. Measurements were performed at 0° and 45° flexion with 0°, 5°, 10°, and 15° rotation, and at 90° and 135° flexion with 0, 5°, 10°, 15°, and 20° rotation. RESULTS: The LPS Flex showed that the femoral component could not achieve 20° rotation at 135° flexion. The Scorpio NRG showed less than 20MPa of contact stress at all conditions. The Genesis II showed higher contact stress than 20MPa at 135° flexion with 20° rotation. The PFC Sigma showed that the femoral component could not achieve >10° rotation at any flexion angle. The Foundation showed more than 20MPa of contact stress at 90° flexion with 20° rotation and at 135° flexion with 10°, 15°, and 20° rotation. DISCUSSION: Surgeons should be more aware of the variable contact conditions of the tibiofemoral articular surfaces in individual TKA designs. LEVEL OF EVIDENCE: Level IV, basic science study.

Comparison of static and dynamic knee kinematics during squatting.

BACKGROUND: there long has been debate whether static knee kinematics measured using magnetic resonance imaging are the same as knee kinematics in dynamic weight-bearing motion. Magnetic resonance imaging provides excellent volumetric detail but is static. Fluoroscopic imaging provides for dynamic observation of knee kinematics but provides no direct observation of the soft-tissue structures. We attempted to answer the question 'Are knee kinematics the same during static and dynamic squatting?' METHODS: knee kinematics data from two previously reported studies of healthy knee kinematics during squatting from 0° to 120° were obtained. The results of the dynamic fluoroscopic study were reformatted to perform a direct comparison of femoral anteroposterior translation and internal-external rotation with the static magnetic resonance imaging study. FINDINGS: comparison of internal-external rotations and lateral femoral condyle anteroposterior translations did not reveal significant differences between static and dynamic data. The medial femoral condyle demonstrated 0 (SD=3) mm posterior translation during dynamic squatting from 0° to 120° flexion compared to 5 (SD=3) mm posterior translation during static squatting (P=0.01, Cohen's d=1.7). INTERPRETATION: for squatting types of motions, static and dynamic study protocols appear to produce equivalent knee kinematics with no functionally important differences. Differences in medial condyle translations can be attributed to differences in foot position during the study. Investigators can choose the modality that best fits their goals and resources with the knowledge that the results for squatting activities are comparable.

A new concept for precise patella resection in total knee arthroplasty.

We developed a new patella-cutting guide that simplifies proper alignment and enables resection of the correct thickness of bone. This guide consists of a central shaft, two support frames, and a ring. The ring consists of upper and lower disks, with a slot between the disks. The central shaft and the lower disk have holes for fixation pins. The distance from the distal end of the central shaft to the lowest level of the slot is 8 mm. Bone of the same thickness as that of the patellar component can be automatically resected using this guide. A feeler gauge is inserted through the slot, and the periarticular region is felt. This procedure enables the guide to be set at the correct angulation. A laboratory study using fresh-frozen cadaver patella specimens and a clinical study showed that proper alignment and proper resection were achieved using this guide.

Mixture of hyaluronic acid and phospholipid prevents adhesion formation on the injured flexor tendon in rabbits.

Dipalmitoyl phosphatidylcholine, a highly surface-active polar lipid, has been implicated as a potential boundary lubricant for synovial joints. We examined the effects of dipalmitoyl phosphatidylcholine on the flexor tendon and its protective effect against postoperative adhesion in two experimental steps. First, the flexor digitorum fibularis and the distal pulley of rabbits were set for a friction test. The test was performed with saline solution, sodium hyaluronate, or a mixture of dipalmitoyl phosphatidylcholine and sodium hyaluronate as the lubricant. The friction coefficient was significantly lower with the mixture of dipalmitoyl phosphatidylcholine and sodium hyaluronate than with saline solution or sodium hyaluronate. We concluded that the decreased friction coefficient indicates that dipalmitoyl phosphatidylcholine could complement the boundary-lubricating ability of the tendon. In the second experiment, we used an experimental adhesion model of the flexor digitorum fibularis in the rabbit. During the operation, either saline solution, sodium hyaluronate, or a mixture of dipalmitoyl phosphatidylcholine and sodium hyaluronate was injected into the tendon sheath. The specimen was sent to another tester, and the work required to tear off the adhesion was measured. The work required was significantly greater for the tendons that had been injected with saline solution than for those given injections of dipalmitoyl phosphatidylcholine and sodium hyaluronate. Our findings suggest that dipalmitoyl phosphatidylcholine plays an important role in the boundary lubrication of the tendon and that after tendon injury, the administration of a mixture of dipalmitoyl phosphatidylcholine and sodium hyaluronate may improve tendon lubrication and prevent adhesion formation.

Effect of vitamin K2 on three-dimensional trabecular microarchitecture in ovariectomized rats.

Menatetrenone, a vitamin K2 with four isoprene units, has been reported to improve osteoporotic bone loss. The purpose of this investigation was to clarify the effect of menatetrenone on the three-dimensional (3D) trabecular microarchitecture in ovariectomized (OVX) rats by using microcomputed tomography (MCT). Forty-two 13-week-old female rats were used and divided into four groups: the OVX (OVX + MK-4) group treated with menatetrenone, the (OVX untreated) group, the sham-operated (Sham + MK-4) group treated with menatetrenone, and the sham-operated group not treated with menatetrenone (Sham untreated) group. OVX rats were fed a calcium-deficient diet. Menatetrenone treatment was begun just after the ovariectomy, and the mean menatetrenone oral intake over the 8-week period was adjusted to 30 mg/kg BW per day. The proximal metaphyseal region of the right tibia was evaluated by dual X-ray absorptiometry (DXA) and MCT. A parametric analysis of the reconstructed trabecular volume was carried out using bone volume fractions, the fractal dimension calculated by the 3D box-counting method, and the connectivity density as determined by topological analysis. Menatetrenone significantly increased the trabecular bone volume, fractal dimension, and connectivity in the OVX + MK-4 group compared with the OVX-untreated group (p < 0.01). Our results suggest that an 8-week administration of menatetrenone protects against the loss of trabecular bone volume and its connectivity when treatment is begun just after the ovariectomy. Despite this apparent protection, it remains unknown whether it is possible to reestablish trabecular connectivity if therapeutic intervention occurs after the trabecular connectivity has been lost.

A new friction tester of the flexor tendon.

We have developed a new device to measure the friction force and calculate the friction coefficient between a rabbit flexor tendon, a pulley and a proximal phalanx. The flexor digitorum fibularis tendon of a rabbit was taken intact with the proximal phalanx, and tendon pulleys were attached to both ends of the bone. Both ends of the tendon were clamped to acrylic plates and connected to stainless-steel plates equipped with strain gauges. A pretension of 1.96 N was applied so as not to loosen the tendon. The proximal phalanx was fixed to an acrylic plate on the actuator, which gave 8 mm of transfer to the acrylic plate at a speed of 2 mm/s. The interface between the tendon and the surrounded tissue created the friction force, when the load was applied on the distal pulley. The friction force could be obtained from the difference between the tension of both ends of the tendon, which was measured with strain gauges and sampled with a personal computer. The friction force and the friction coefficient were calculated from the measured force and the applied load. The load and the pre-loading time, which was defined as loading duration before gliding, were varied in order to observe the change of the friction coefficient. The friction coefficient was not affected by the load and increased with the pre-loading time. The value of mu(s) ranged from 0.027 to 0.111 (0.072 +/- 0.023), and that of (mu)d ranged from 0.010 to 0.069 (0.039 +/- 0.014) (pre-loading time was 5 s). Our method will allow for the examination of various surgical treatments and lubricants. Moreover, it can be applied to other tissues of any animals with similar structures to the rabbit's digitorum.

Quantitative analysis of three-dimensional complexity and connectivity changes in trabecular microarchitecture in relation to aging, menopause, and inflammation.

There are several types of bone loss besides that associated with normal aging, eg, that associated with the menopause, and that associated with chronic inflammation, and these are considered to be caused by different mechanisms. The microarchitecture that results from these different bone-loss mechanisms would not be the same. The purpose of this study was to investigate differences in the three-dimensional trabecular microarchitecture in various types of osteopenia, using microcomputed tomography (Micro-CT). Thirty-five Fisher 344 rats were divided into five groups (control, young, senile, ovariectomized [OVX], and inflammation-mediated osteopenia [IMO]) and distal femoral metaphysis was scanned by Micro-CT to nondestructively acquire a 3-D CT stack consisting of 50 consecutive slices at a spatial resolution of 26 microm. The volume of interest, consisting of the secondary spongiosa, was prepared to analyze the 3-D trabecular microarchitecture. A parametric analysis was carried out using bone volume fractions, fractal dimensions, and the first Betti number in order to quantitatively express the mass, complexity, and connectivity of the trabecular microarchitecture. Complexity tended to decrease with age, and decreased significantly in estrogen deficiency-induced and inflammation-mediated osteopenia. Connectivity did not appear to change with aging, but was significantly decreased in estrogen deficiency-induced and inflammation-mediated osteopenia. There was no significant difference between the OVX and the IMO groups.