Development and validation of formulae to predict leg length following medial opening-wedge osteotomy of the proximal tibia with hemicallotasis

Homogeneous material models can overestimate stresses in high tibial osteotomy: A finite element analysis

Although widely used numerical models can assess the stability of lateral hinges in high tibial osteotomy (HTO) and may provide acceptable results in comparative studies, accurate stress prediction may not be possible due to simplified homogeneous models of the bone. The present study aimed to investigate the effect of a heterogeneous versus four homogeneous models on the results of stress and force. Each of the four homogenized FE models utilized the same elastic modulus of 16,700 MPa for the cortical while employing a single elastic modulus varying from 155 to 5000 MPa for the cancellous. In heterogeneous model, the modulus of each element was assigned using the bone density. It was found that stresses at the hinge in homogeneous models were higher than those in the heterogeneous model. The maximum principal stress (MPS) was 437 MPa for the heterogeneous model while that was 2179, 2351, 2581, and 2637 MPa for the homogeneous models with the elastic moduli of 155, 500, 2130, and 5000 MPa, respectively. Also, the opening force was 150 N for the heterogeneous model significantly lower than 649-1534 N range predicted for the homogeneous models. The use of a homogeneous model in the FE analysis of HTO overestimated the stresses and force. Thus, in addition to casting doubt on the use of a single modulus in the numerical analysis of HTO, Future HTO studies can use our results as a benchmark for comparison purposes and highlight the use of patient-specific bone density - elastic modulus relation in simulation.

High-risk factors for subjective discomfort due to lower limb discrepancy after medial open wedge high tibial osteotomy

BACKGROUND

Medial open wedge high tibial osteotomy (OWHTO) may result in lower limb discrepancy (LLD), and some patients experience uncomfortable symptoms. Studies have found that the degree of LLD is one but not the only high-risk factor for inducing symptoms. The main purpose of this study is to explore the risk factors for symptomatic LLD.

METHODS

Sixty-four patients who underwent OWHTO in our hospital between June 2018 and January 2020 were included in the study. Changes in tibia length, lower limb length, femorotibial angle (FTA), LLD, and KOOS score were evaluated before and 1 year after surgery. Questionnaire was used to investigate whether patients had uncomfortable symptoms of LLD after surgery. Binary logistic regression was applied to analyze the risk factors of symptomatic LLD.

RESULTS

There were 18 patients with subjective LLD uncomfortableness, 13 of them were occasional and 5 were frequent. Patients had a mean correction angle of 11.7° ± 4.6°, with a mean increase in tibial length of 6.0 ± 3.5 mm, lower limb length of 7.5 ± 2.3 mm, and LLD of 6.9 ± 4.2 mm at 1 year post-operation. Preoperative and postoperative changes in tibia length and lower limb length were statistically significant (P < 0.0001).There were statistically significant differences in pain, symptoms, ADL, sports/recreations, QOL of KOOS subclassification before and after surgery (P < 0.0001). Binary logistic regression revealed that age ≥ 55, BMI ≥ 28, and LLD ≥ 10 mm were high-risk factors for symptomatic LLD (P = 0.031, OR = 4.82; P = 0.012, OR = 6.251; P = 0.006, OR = 6.836).

CONCLUSION

Patients with age ≥ 55, BMI ≥ 28, and postoperative LLD ≥ 10 mm are more likely to develop symptomatic LLD. Older or heavier patients, who are expected to have an LLD greater than 10 mm after OWHTO should be fully informed of the possibility of postoperative LLD symptoms.