Abstract
This study aimed to determine the factors related to intraoperative extension gap (EG) in patients who underwent posterior-stabilized total knee arthroplasty (TKA). A total of 106 TKAs in 84 patients were retrospectively reviewed. Only patients who underwent the same method of bone resection were included consecutively. Bilateral popliteal angle (BPA) was used as an indicator of hamstring tightness. EG and extension space angle were measured using an offset type tensor. The associations between patient variables and EG were analyzed using multivariable linear regression and Pearson's correlation coefficients. The average EG was 12.9 ± 2.1 mm, and the average extension space angle was 2.8° ± 3.2°. BPA was greater than flexion contracture in most cases (94.3%), and no difference was found in only six cases (5.7%). According to multivariable linear regression analysis which was conducted after modifying the BPA into a categorical variable by 5°, EG was correlated with BPA (p < 0.001). Pearson’s correlation coefficient between EG and BPA was − 0.674 (p < 0.001). No other factors were significantly correlated with intraoperative EG. The present study found that popliteal angle is a different entity from flexion contracture, and that it is a predictable factor for EG in osteoarthritis patients. Smaller BPAs led to larger EG in patients who underwent the same degree of bone resection.
Highlights
This study aimed to determine the factors related to intraoperative extension gap (EG) in patients who underwent posterior-stabilized total knee arthroplasty (TKA)
Exclusion criteria were as follows: (1) patients who did not undergo physical examinations or image studies; (2) patients who had a history of previous unicompartmental knee arthroplasty, high tibial osteotomy (HTO), infection, trauma, or rheumatoid arthritis; (3) patients who had a history of spinal fusion; (4) patients with bone defects in medial femoral condyle and lateral tibial condyle that cannot be used as a reference; (5) patients with motor weakness of lower extremity; and (6) patients who did not have bone resection, as mentioned above
Bilateral popliteal angle (BPA) was greater than flexion contracture in most cases (94.3%), and no difference was found in only six cases (5.7%) (Fig. 4A)
Summary
This study aimed to determine the factors related to intraoperative extension gap (EG) in patients who underwent posterior-stabilized total knee arthroplasty (TKA). The present study found that popliteal angle is a different entity from flexion contracture, and that it is a predictable factor for EG in osteoarthritis patients. Since bone resection level can be controlled by the surgeon, unexpected gap differences between patients mainly occur due to the soft tissue laxity. If the hamstring tightness, which reflects the laxity of posterior structures of the knee, can be predicted in advance, the EG can be expected, and additional procedures or unnecessary bone resection can be avoided. The aim of this study was to determine whether factors such as hamstring tightness were related to intraoperative extension gap in patients who underwent the same amount of bone resection
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