Effect Of Femoral Proximal Shape On Leg Length Discrepancy After Total Hip Arthroplasty

Objective:To observe the change of proximal femur form for Total Hip Arthroplasty(THA)after legs Length Discrepancy(LLD).Two indexes commonly used to describe anatomical parameters of proximal femur,namely canal-flare Index(CFI)and Femoral Cortical Index(FCI),were used to comprehensively explore the correlation between CFI,FCI and LLD after THA.Methods:Retrospective analysis was performed on patients who received unilateral biological primary total hip arthroplasty from September 2015 to September 2018 in department 3 of orthopedics,Liaoning provincial people's hospital.The patients' age,gender,body mass index(BMI),diagnosis,preoperative and postoperative orthotopic DR of the pelvis,and preoperative orthotopic DR of the affected hip joint were counted.Canal-flare Index(CFI),Femoral Cortical Index(FCI)and LLD were measured and calculated by PACS image processing system,and CFI and FCI were grouped respectively,The former was grouped by Noble classification,i.e.,Noble A group was champagne bottle type,CFI>4.7;Noble B group was normal type,4.7>CFI>3.0.The Noble C group is chimney type,CFI<3.0;The latter was grouped by Dorr classification,i.e.,Dorr group A was funnel type and FCI>0.6.Dorr B group was normal type,0.6>FCI>0.5;Dorr C group was chimney type with FCI<0.5.Because most of the patients with postoperative LLD have been corrected,thus postoperative LLD < 5 mm as lower limb shortening group,to 5 mm < LLD < 5mm as the normal group,LLD > 5 mm as of lower extremities.Finally,the number,proportion and mean values of shortened,normal and extended LLD in Noble group and Dorr group were recorded,and Kruskal Wallis test was used to analyze,Spearman Correlation Analysis was conducted on indexes with statistical significance,and the influence of CFI and FCI on LLD after THA was summarized.Result:From September 2015 to September 2018,a total of 140 patients,including 60 males and 80 females,received unilateral biological type THA for the first time and met the inclusion and exclusion criteria in the department of orthopedics,liaoningprovincial people's hospital.Age: 33~83 years,average(58±14)years;Osteoarthritis(OA)was reported in 51 cases,and Osteonecrosis of the Femeral Head(ON)in 89 cases.BMI 19.72~35.91,average 24.93±3.07;CFI 2.36~7.10,average(4.04±0.89);FCI 0.32~0.67,average(0.51±0.09);Preoperative LLD-15.41~7.81 mm,mean(-6.3± 2.8)mm;Postoperative LLD was-8.33~9.49 mm,with an average(0.97±5.6)mm.The difference between preoperative and postoperative LLD was statistically significant(t=-16.827,P<0.001).Preoperative acetabular depth was 10.87~23.62 mm,with an average(16.43 ± 2.97)mm.Postoperative 12.13~23.38 mm,the average(17.50 ± 2.54)mm.There was no statistically significant difference in acetabular depth before and after surgery(t=-1.959,P=0.053).Kruskal Wallis test was used to analyze the results.The results showed that there were statistically significant differences in age,CFI,FCI and LLD(P <0.05).There was no significant difference in gender,diagnosis,BMI and LLD(P >0.05).Spearman correlation analysis was conducted on three statistically significant indicators,namely age,CFI and FCI,showing that LLD was positively correlated with CFI and FCI.It has nothing to do with age.In CFI typing,the proportion of patients with LLD>5mm in Noble A group was 3.86 times that in Noble B group and 4.64 times that in Noble C group.The proportion of patients with LLD<-5mm in Noble C group was 3.85 times that in Noble A group.In FCI typing,the proportion of patients with LLD>5mm in Dorr A group was 2.60 times that in Dorr B group and 8.44 times that in Dorr C group.The proportion of patients with LLD<-5mm in Dorr C group was 1.68 times that in Dorr B group and 7.62 times that in Dorr A group.When FCI>0.6 and CFI>4.7 were combined,a total of 24 patients were involved,including 16 patients with LLD>5mm,accounting for approximately 67%.When FCI<0.5 and CFI<3.0,there were 13 patients in total,including 4 patients with LLD<-5mm,accounting for about 38%.Conclusion:High CFI or FCI may increase the risk of lower limb elongation.When both CFI and FCI were high,postoperative limb extension was highly possible.Low CFI or low FCI can increase the risk of shortening of lower limbs.When both CFI and FCI are low,postoperative limb shortening is highly possible.