Purpose This study aimed to determine which preoperative factors affect the postoperative change in the joint line convergence angle (JLCA) by preoperatively quantifying soft tissue laxity. Methods Thirty-four patients who underwent medial open-wedge high tibial osteotomy (HTO) with a navigation were analysed. The JLCA change after HTO was calculated using standing long-bone anteroposterior radiographs taken preoperatively and 6 months postoperatively. Latent soft tissue laxity was defined as the amount of soft tissue that can be extended to valgus or varus from the weight-bearing position, and calculated by subtracting the JLCA on weight-bearing standing radiographs from that on stress radiographs. Multiple linear regression was performed to determine the preoperative factors that statistically correlated with the postoperative JLCA change. ResultsIn multiple linear regression, JLCA change had a statistically significant correlation with latent medial laxity (R = 0.6) and a statistically borderline significant correlation with correction angle (R = 0.2). These imply that the postoperative JLCA change increased by 0.6° per 1° increase in latent medial laxity, and increased by 0.2° per 1° increase in correction angle. Latent medial laxity was the most crucial factor associated with postoperative JLCA changes. ConclusionThe JLCA change could be larger in patients with large latent medial laxity or severe varus deformity requiring a large correction, which could lead to unexpected overcorrection in HTO. Postoperative JLCA change should be considered in preoperative surgical planning. Target point shifting within the hypomochlion point could be a strategy to prevent overcorrection, especially in patients with large latent medial laxity. Level of evidence Level IV.

The purpose of this study was to compare the osteoconductivity, and absorbability of hydroxyapatite or beta-tricalcium phosphate in clinical scenario of opening wedge high tibial osteotomy Total 41 knees of 40 patients with follow up period of more than 1 year were enrolled. These patients were divided into two groups, Group I (22 knees, 21 patients) used hydroxyapatite and Group II (19 knees, 19 patients) used beta-tricalcium phosphate as a substitute in the opening gap. According to proven method, the osteoconductivity was assessed radiographically by the extent of new bone formation at osteotomy space and absorbability was evaluated by measuring the area occupied by substitute at immediate postoperative, postoperative 6 months and 1 year. Regarding preoperative demographic data, no significant differences were found between two groups. No statistically significant differences were found between two groups regarding lower limb alignment (mechanical femorotibial angle, weight-bearing line%) and posterior tibial slope at postoperative and final follow up radiographs. Concerning the osteoconductivity, there were no significant differences between two groups in any zone. However, the absorption rate was significantly greater in the Group II than in Group I at 6 months (Group I: 13.7 ± 6.8, group II: 35.3 ± 15.8, P = 0.001) and 1 year (Group I: 24.2 ± 6.3, Group II: 49.6 ± 14.3, P < 0.0001). The complications related to bone substitutes were not observed. Both hydroxyapatite and beta-tricalcium phosphate showed satisfactory gap healing without complications and can be successfully used as alternative healing materials in opening wedge high tibial osteotomy. Our study showed that beta-tricalcium phosphate has superior absorbability than hydroxyapatite. But osteoconductivity showed no significant difference.

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