Mobile-bearing insert used with total knee arthroplasty does not rotate on the tibial tray during a squatting activity: a cross-sectional study.

BACKGROUND: Total knee arthroplasty (TKA) is commonly performed around the world. Implant designs include fixed-bearing and mobile-bearing. Mobile-bearing design was developed as a rotating platform that allows axial rotation of the insert around the longitudinal axis. This phenomenon may limit full exploitation of the characteristics of the mobile-bearing insert, which may cause wearing and reduce longevity. However, there is limited knowledge on rotational behavior of the polyethylene mobile-bearing insert under weight-bearing conditions. We aimed at determining the rotational motion of each component at full extension and flexed positions during a squatting activity after TKA. METHODS: This study was a cross-sectional study (level 4) involving patients with severe knee osteoarthritis scheduled to receive TKA. We examined 13 knees of 11 patients after mobile-bearing TKA (NexGen LPS-Flex, Zimmer Inc.) at 10 weeks and 1 year postoperatively. Four identical metallic beads were embedded into the insert. Wide-base squatting was chosen for analyses. Three-dimensional in vivo poses of the prostheses were created using a 3D-to-2D registration technique. During flexion, rotation of the femoral component relative to the insert (FEM/INS) and tibial component (FEM/TIB) as well as insert rotation relative to the tibial component (INS/TIB) were computed. Repeated measure 2-way ANOVA and post hoc test was used. RESULTS: In the fully extended position, FEM/INS was significantly smaller than INS/TIB both at 10 weeks (- 0.3° vs. 6.3°, p = .013) and 1 year (- 0.8° vs. 4.9°, p = .011), respectively. During the squatting activity, rotation motions of FEM/TIB, FEM/INS, INS/TIB were 5.7°, 5.9°, and 1.8° at 10 weeks and 6.3°, 5.5°, and 1.6° at 1 year, respectively. Rotation motion of FEM/INS was significantly greater than that of INS/TIB at both 10 weeks (p < .001) and 1 year (p < .001). CONCLUSIONS: The mobile-bearing insert enhances the compatibility of FEM/INS in extension; the amount of INS/TIB rotation is significantly smaller than that of FEM/INS during a squatting activity. This information will inform surgeons to take caution to perform TKA with a fixed insert in which 6.3° of rotational offset would be added to the rotational alignment at FEM/INS at full extension. TRIAL REGISTRATION: UMIN-CTR, UMIN000024196. Retrospectively registered on 9 September 2016.

High validity of measuring the width and volume of medial meniscal extrusion three-dimensionally using an MRI-derived tibial model.

BACKGROUND: Medial meniscal extrusion (MME) is an important marker of knee osteoarthritis (KOA) progression. The purposes of this study were: 1) to determine whether there are morphological differences between CT- and MRI-derived tibial plateau models; and 2) to determine whether measurement of MME volume and width using an MRI-derived tibial model is as accurate as measurements on a CT-derived tibial model. METHODS: This was a cross-sectional study that enrolled ten participants with medial KOA (Kellgren-Lawrence grade 1 to 3). Primary outcome was surface difference of the medial tibial plateau between CT- and MRI-derived models. Furthermore, volume and cross-sectional area of the medial tibial plateau were compared between CT- and MRI-derived models. Measurements of MME volume and width were compared between CT- and MRI-derived tibial models. RESULTS: Minimal and maximal surface differences of the medial tibial plateau between the CT- and MRI-derived models were - 0.15 [- 0.44, 0.14] mm (mean [95% confidence interval]) and 0.24 [- 0.09, 0.57] mm, respectively. There were no significant differences in volume and cross-sectional area of the medial tibial plateau between CT- and MRI-derived tibial models. The MME volumes measured on CT- and MRI-derived models were 942.6 [597.7, 1287.6] mm3 and 916.2 [557.9, 1274.6] mm3, respectively (p = 0.938). The MME widths measured on CT- and MRI-derived models were 4.2 [1.9, 6.5] mm and 4.5 [2.2, 6.9] mm, respectively (p = 0.967). CONCLUSIONS: CT- and MRI-derived models of the medial tibial plateau did not show significant morphological differences. Both CT- and MRI-derived tibia can be used as a reference to measure MME in early-to-moderate medial KOA.

Plantar Partial Pressure Analysis in a Patient with Reverse Extensor Digitorum Brevis Flap for the Treatment of Hallux Injury.

INTRODUCTION: An extensor digitorum brevis (EDB) flap can be used to cover a small soft-tissue defect and has been widely used as pedicled flap to cover defects around the ankle and foot. However, its post-operative functional recovery is unknown. Few reports have evaluated gait after foot flap surgeries, although gait assessment is considered to be necessary for functional evaluation after foot reconstruction. We performed a reverse EDB flap to treat a right hallux injury and conducted a plantar partial pressure (PPP) analysis as a postoperative functional evaluation. CASE REPORT: A 30-year-old laborer suffered an injury resulting in necrosis of the distal phalanx and soft-tissue defect of the proximal phalanx. After amputation, the proximal phalanx was covered with a reverse EDB flap. PPP analysis involved a 4-m-long platform system (P-Walk) and was conducted 3- and 12-month post-surgery. Walking velocity and the single-support phase on the affected limb had increased markedly after 12 months. After 12 months, the PPP of the first metatarsal head was greater than on the unaffected side, and the cadence and single-leg support rate were equal to the unaffected side. CONCLUSION: A nearly normal gait was obtained by covering the basal part of the hallux with an EDB flap and preserving the metatarsophalangeal joint.