Objective:We aimed to compare the efficacies of rehabilitation with the hybrid assistive limb and conventional rehabilitation after total knee arthroplasty.Materials and methods:A total of 37 consecutive patients who underwent primary total knee arthroplasty for knee osteoarthritis were enrolled. Seven patients withdrew from the study after randomization, and 30 patients (hybrid assistive limb group: n = 16; conventional group: n = 14) completed the randomized controlled trial. Patients in the hybrid assistive limb group underwent ten 20-min rehabilitation sessions with the hybrid assistive limb as well as 20-min conventional sessions over the course of 2 weeks, whereas patients in the conventional group received ten 40-min conventional sessions during the same period. The primary outcome measure was walking speed, whereas the secondary outcome measures included quadriceps strength and knee pain assessed using a numerical rating scale. The outcome measures were evaluated prior to surgery and on postoperative weeks 1, 2, and 3.Results:In the early postoperative period, rehabilitation after total knee arthroplasty with the hybrid assistive limb resulted in a significantly greater improvement in walking speed (weeks 1 and 2: p = 0.045), quadriceps strength (weeks 1 and 2; weeks 1 and 3: p < 0.0001), and numerical rating scale scores (week 1: p = 0.03) than conventional rehabilitation.Conclusion:Rehabilitation with the hybrid assistive limb after total knee arthroplasty led to greater improvements in walking speed, quadriceps strength, and pain scores than conventional rehabilitation.

An animal model, using distraction force on adult rabbits, was developed to study the effects of nonweight-bearing on articular cartilage in a moving joint. Histologic evaluation was used to compare the morphology of chondrocytes, safranin O intensity, cartilage thickness, and structural changes between the test and contralateral joints. At 3 and 6 weeks, the chondrocytes in superficial and intermediate zones were round, with an increase in cellular volume density and mean cell volume and with less metachromasia; the safranin O intensity and cartilage thickness were the same as in the controls. In cartilage of the 9-week group, mean cell volume decreased with cell cloning in the superficial zone, while numerical density increased and mean matrix volume per cell decreased in the superficial and intermediate zones. The cartilage, with a 34% reduction in thickness and a 53-72% decrease in safranin O intensity from the superficial to the deep zone, had superficial fibrotic proliferation, surface erosion or depression, and tidemark irregularity. Continuous distraction in a moving joint caused morphological changes in chondrocytes prior to degeneration of cartilage. These results support the hypothesis that the forces perceived by cells may dictate their shape and then stimulate alterations in cellular biochemistry and matrix metabolism.

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We investigated whether the callus formation in the humerus during the distraction period of limb lengthening proceeds at a higher rate than that in the femur and tibia. Ten achondroplastic patients underwent 3 bilateral humerus, 3 bilateral femur and 4 bilateral tibia lengthenings. To reduce the confounding effect of bone size, we used bone mineral apparent density (BMAD) to compare the three groups; this is a volumetric bone mineral density measurement. BMAD in the distracted callus space was evaluated at 8 weeks after the start of distraction using dual-energy X-ray absorptiometry (mean +/- SD; g/cm3): in the humerus (0.24 +/- 0.08) it was significantly higher than in the tibia (0.10 +/- 0.02), while there was no difference between the humerus and femur (0.35 +/- 0.11). We conclude that the callus formation in the humerus during the distraction period of limb lengthening proceeded at a significantly faster rate than in the tibia, but there was no significant difference between the humerus and femur.

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