Intraoperative changes in medial joint gap after posterior femoral condylar resection, posterior osteophyte removal, and femoral component placement during primary total knee arthroplasty.

BACKGROUND: "Mid-flexion stability" is important for superior patient satisfaction following total knee arthroplasty (TKA). Thus, it is important to control medial joint gap intraoperatively as a countermeasure. However, reports on the precise intraoperative changes in medial joint gap during TKA are scarce. This study evaluated the intraoperative changes in medial joint gap during TKA. METHODS: We studied 167 knees with varus osteoarthritis that underwent 80 cruciate-retaining (CR) and 87 posterior-stabilized (PS) TKAs between January 2018 and December 2020. We measured the intraoperative changes in medial joint gap with a tensor device at 137.5 N. RESULTS: The medial joint gap after posterior femoral condylar resection was significantly increased not only at 90° of flexion but also at 0° of extension in CR and PS TKAs (p < 0.01). The medial joint gap after posterior osteophyte removal was significantly increased not only at 0° of extension but also at 90° of flexion in CR and PS TKAs (p < 0.01). The medial joint gap at 0° of extension was reduced by 0.60 mm after femoral component placement in PS TKA. CONCLUSION: Surgeons need to pay close attention to these intraoperative changes in medial joint gap by measuring the medial joint gap before and after each procedure or assuming the changes in those values before bone cutting to achieve superior patient satisfaction following TKA.

Local application of alendronate controls bone formation and ß-tricalcium phosphate resorption induced by recombinant human bone morphogenetic protein-2.

This study examined the ability of local alendronate (ALN) administration to control ß-tricalcium phosphate (ß-TCP) resorption as well as the induction of bone formation by recombinant human bone morphogenetic protein-2 (rhBMP-2). A 15-mm critical-sized bone defect was created in the diaphysis of rabbit ulnae. Nine female rabbits (4 to 5 months-old) were divided into 3 groups. Group 1 (n = 6 ulnae) animals received implants consisting of ß-TCP granules and 25 µg of rhBMP-2 in 6.5% collagen gel. Group 2 (6 ulnae) and Group 3 (6 ulnae) animals received the same implants, but with 10-6 M and 10-3 M ALN-treated TCP granules, respectively. Two weeks postsurgery, tartrate-resistant acid phosphatase-positive cell counts, new bone formation, and residual ß-TCP were evaluated. This study showed that a high dose of ALN strongly reduced osteoclastic resorption of ß-TCP induced by rhBMP-2, resulting in decreased bone formation. In contrast, a low dose of ALN slightly reduced the bone resorptive effect but increased bone formation. These results suggest that osteoclast-mediated resorption plays an important role in bone formation and a coupling-like phenomenon could occur in the ß-TCP-implanted area, and that administration of a low dose of ALN may solve clinical bone resorptive problems induced by rhBMP-2.

Effects of micro-porosity and local BMP-2 administration on bioresorption of ß-TCP and new bone formation.

BACKGROUND: It has been reported that the microporous structure of calcium phosphate (CaP) ceramics is important to osteoconduction. Bone morphogenetic protein-2 (BMP-2) has been shown to be a promising alternative to bone grafting and a therapeutic agent promoting bone regeneration when delivered locally. The aim of this study was to evaluate the effects of micro-porosity within beta-tricalcium phosphate (ß-TCP) cylinders and local BMP-2 administration on ß-TCP resorption and new bone formation. METHODS: Bilateral cylindrical bone defects were created in rabbit distal femora, and the defects were filled with ß-TCP. Rabbits were divided into 3 groups; defects were filled with a ß-TCP cylinder with a total of approximately 60% porosity (Group A: 13.4% micro- and 46.9% macropore, Group B: 38.5% micro- and 20.3% macropore, Group C: the same micro- and macro-porosity as in group B supplemented with BMP-2). Rabbits were sacrificed 4, 8, 12, and 24 weeks postoperatively. RESULTS: The number of TRAP-positive cells and new bone formation in group B were significantly greater than those in group A at every period. The amount of residual ß-TCP in group C was less than that in group B at all time periods, resulting in significantly more new bone formation in group C at 8 and 12 weeks. The number of TRAP-positive cells in group C was maximum at 4 weeks. CONCLUSIONS: These results suggest that the amount of submicron microporous structure and local BMP-2 administration accelerated both osteoclastic resorption of ß-TCP and new bone formation, probably through a coupling-like phenomenon between resorption and new bone formation.