Relationship Between Proximal Femur Morphology And Unequal Length Of Lower Limbs After Total Hip Arthroplasty

Objective:To evaluate the relationship between proximal femur morphology and leg-length discrepancy(LLD)after hip replacement,the effect of femoral medullary scintillation index(CFI)on lower extremity unequal length(LLD)after hip replacement was studied.Methods:Patients who underwent unilateral cementless initial total hip arthroplasty between January 2012 and December 2019 were selected as subjects.Inclusion criteria:unilateral surgery;No neurological symptoms;Using biological prosthesis;Primary surgery;Hip muscle strength grade 4 or above.Exclusion criteria: unqualified imaging data;Acetabular dysplasia and femoral head collapse on the affected or contralateral side;Proximal femoral deformity or bone tumor on the affected or contralateral side after treatment;The preoperative length of lower extremity was 2 cm.Patients with hip fracture;Pelvic tilt,scoliosis Cobb > 10°;Bilateral peripheral neuromuscular lesions were observed.The distance between the center of rotation of the affected side and the opposite side is greater than 3 mm.Finally,235 patients were included in the study.According to the morphology of the medullary cavity,the patients were divided into three groups: CFI > 4.7 was champagne type;CFI is common between 3.0 and 4.7;CFI< 3.0 is called chimney type.These patients were retrospectively analyzed in age,sex,body mass index(BMI),preoperative disease and imaging data,and postoperative lower extremity disparity,and the lower limb length of the patients in the 3 groups was compared.The measurement data were expressed in the form of(x ± s).Variance analysis was used for the comparison between multiple groups of data satisfying homogeneity of variance,and LSD-t test was used for pair-wise comparison.Count data were represented by frequency,intergroup comparison was analyzed by chi-square test,single ordered variable data were analyzed by Kruskal-Wallis H test,and pair comparison was analyzed by Nemenyi method.Results:A total of 235 patients were included,and the mean CFI value of all patients was(4.3 ± 1.2).After grouping according to the morphology of femoral bone marrow cavity,there was no statistically significant difference in gender,body mass index,preoperative diagnosis,type of prosthetic femoral neck length,distance between acetabular rotation center and tear drops,or the vertical distance between femoral head center and distal prosthesis among the groups(P > 0.05).The age of patients with champagne medullary cavity was smaller than that of the other two groups(P < 0.05).LLD of patients with champagne medullary cavity was significantly different than that of the other two groups(P < 0.05).The insertion depth of femoral stem prosthesis in patients with chimney-type medullary cavity was deeper than that in patients with champagne-type medullary cavity(P < 0.05).The vertical distance from the center of the femoral head to the upper margin of the lesser trochanter in the chimney-type medullary cavity was shorter than that in the champagne type(P < 0.05).The LLD status of patients in the three groups was compared in detail,and the difference between the three groups was statistically significant(P < 0.05).The paired comparison showed that the LLD of champagne type was greater than that of chimney typ(P < 0.05),while the remaining pair comparison showed no statistically significant difference(P > 0.05).Conclusion:Patients with champagne medullary cavity(high CFI)are more likely to have longer limbs on the affected side,while patients with chimney medullary cavity(low CFI)are more likely to have shorter limbs.