Yoshikazu Matsuda

In vivo laxity of low contact stress mobile-bearing prostheses

A stress arthrometric study was done on 60 knees in 54 patients with total knee arthroplasties using a Telos arthrometer, to determine anteroposterior and abduction and adduction laxity and to evaluate the relationship between laxity and retention of the posterior cruciate ligament using low contact stress mobile-bearing prostheses. Thirty knees had posterior cruciate ligament-retaining and 30 had posterior cruciate ligament-sacrificing prostheses. The selected patients had successful knee arthroplasty 6 months previously. Anteroposterior displacement was measured at 30° and 90° flexion; there were no statistically significant differences between the posterior cruciate ligament-retaining (10.5 mm at 30°, 9.3 mm at 90°) and posterior cuciate ligament-sacrificing (9.8 mm at 30°, 9.7 mm at 90°) groups. Abduction and adduction were between 0° and 20° flexion, there were no significant differences between the two groups. Because all the patients in this study had good clinical results, approximately 10 mm anteroposterior displacement and 4° laxity in the coronal direction are considered favorable in low contact stress mobile-bearing prostheses of both designs.

Biomechanical characteristics of nonbridging external fixators for distal radius fractures.

PURPOSE Nonbridging external fixation is becoming popular for distal radius fractures, although its biomechanical characteristics have not been documented. This study evaluated the biomechanical characteristics of nonbridging external fixators for distal radius fractures. METHODS We tested 3 currently available nonbridging fixators (F-Wrist fixator, Hoffman II Compact, and Pennig Dynamic Wrist Fixator) and determined their relative stiffness under axial compression, torsion, and bending moments (dorsal, volar, radial, and ulnar aspects) using a uniform unstable distal radius fracture model. The contact pressure and its total load on the fracture plane were also measured to evaluate the mechanical stimuli at the stable fracture site using a pressure-sensitive conductive rubber sensor. RESULTS Differences were observed in the stiffness: the Pennig fixator was the stiffest, whereas the F-Wrist fixator was the least rigid. The total load transmitted from the wrist joint to the fracture plane depended on the fixator stiffness in axial compression. CONCLUSIONS By determining the biomechanical characteristics of nonbridging external fixators, these data may help the clinician when deciding on a particular device for nonbridging external fixation.

A New Tourniquet System that Determines Pressures in Synchrony With Systolic Blood Pressure in Total Knee Arthroplasty

This study reports the comparison of the clinical use of a new tourniquet system for total knee arthroplasty that can determine its pressure in synchrony with systolic blood pressure (SBP) with the conventional that keeps the initial setting pressure. We prospectively applied the additional pressure of 100 mm Hg based on the SBP recorded before skin incision to consecutive 72 procedures (conventional, initial 36; new, following 36). Six knees with the conventional and none of 5 with the new showed oozing blood in surgical field after sharp rise in SBP. Based on no statistically significant differences of the perioperative blood loss without any tourniquet-related postoperative complications in both groups, the new system seemed to be a practical device especially for controlling a bloodless surgical field.

Femoral Anterior Tangent Line of the Osteoarthritic Knee for Determining Rotational Alignment of the Femoral Component in Total Knee Arthroplasty

Several reference axes have been used to establish femoral rotational alignment during total knee arthroplasty. The current study examined the configuration of the anterior surface of the femur immediately proximal to the trochlea as an alternative rotational landmark. An analysis of computed tomographic images of 150 knees with osteoarthritis indicated that the configuration of the surface is mostly flat or slightly depressed, and the line tangential to the surface (femoral anterior tangent line; FAT line) was consistently determined to be 12.2° ± 3.6° internally rotated to the transepicondylar axis. This value was relatively constant and as reliable as the femoral anteroposterior axis for determining rotational alignment. In addition, the FAT line was not affected by the degree of the varus-valgus deformity of the osteoarthritic knees.

Contribution of total knee arthroplasty to increased bone mineral density

Although several studies describe a significant decrease in postoperative bone mineral density of up to 44% adjacent to the implants after total knee arthroplasty, most reports demonstrated that the decrease in bone mineral density did not continue after 2 years. Most patients may show a reduction in activity levels in the first 6 months after surgery, gradually returning to the preoperative level within the next 6 months, and then show an improvement over the preoperative level by 2 years postoperatively. Namely, although bone density initially decreases after total knee arthroplasty, this procedure contributes to increased bone mineral density approximately 1–2 years postoperatively. Our results suggest that total knee arthroplasty may contribute to a reduction of the risk of later hip fractures. In addition, it may reduce the risk of lifestyle-related diseases, including diabetes mellitus, hypertension and hyperlipemia, by allowing increased mobility, resulting in better bone quality.