Effect Of Unilateral Periacetabular Osteotomy On Bony Birth Canal And Delivery In Female Patients With Developmental Dysplasia Of The Hip

ObjectiveDevelopmental dysplasia of the hip（DDH）is the most common reason of the hip osteoarthritis.Periacetabular osteotomy（PAO）is the standard operation for the treatment of symptomatic DDH patients.However,as the site of PAO is in the quadrilateral region,the pubic branch is upwarped and the lateral coverage of the acetabulum is increased,which may cause the narrowing of the bony birth canal（BBC）.The deformed BBC after PAO can’t be effectively measured through the traditional two-dimensional diameter measurement method.As a result,the BBC after unilateral PAO was measured using pelvic three-dimensional computed tomography（3D-CT）maximum-inscribed-sphere（MIS）method in this study.The narrowest position and size of the BBC after PAO were determined.The narrowing position and extent of the BBC after PAO,their relationship with the unilateral PAO and height were investigated.The effect of unilateral PAO on pregnancy and delivery was explored through questionnaire survey.The consistency between the BBC measured by MIS and that of the actual delivery was compared and analyzed.The influence of unilateral PAO on the BBC of DDH patients with round pelvis and narrow pelvis was researched via MIS method.Content and MethodsThe DICOM data of the selected patients’pre-and post-operative pelvic CT was collected.The diameters of the MIS in 25 layers of the BBC were measured on the Medical Imaging Interaction Toolkit（MITK）platform.The lateral center edge angle（LCEA）,the anterior center edge angle（ACEA）,the T（?）nnis angle and the distance of the medial margin of the femoral head and Kohler’s line were measured on standing anteroposterior pelvic radiographs before and after unilateral PAO.Their difference represents the orthopedic degree of PAO.The main research content was divided into three parts.Part I A total of 62 female DDH patients of childbearing age who met the inclusion criteria from January 2010 to January 2020 were included in the present part.The orthopedic degree of unilateral PAO was determined according to the difference of the LCEA,T（?）nnis angle and the distance between the medial margin of the femoral head and Kohler’s line before and after unilateral PAO.The narrowest position and size of the BBC,the narrowing position and extent of the BBC after PAO and their relationship with the unilateral PAO and height were revealed using MIS method.Part II A total of 741 female DDH patients of childbearing age treated with PAO from November 1997 to November 2016 were follow-up by telephone.31patients who gave birth after unilateral PAO were included.The data of their delivery time,delivery method（normal delivery or caesarean section）,the reasons of caesarean section,the baby’s gender,height and weight,and the hip pain during pregnancy were collected through questionnaire survey.The effect of unilateral PAO on pregnancy and delivery was explored.The orthopedic degree of unilateral PAO was revealed according to the difference of four X-ray indicators before and after unilateral PAO.The relationship of the unilateral PAO with pregnancy pain and hip functional score was analyzed.The size of BBC in the normal delivery patient was measured using the MIS method and formula method,respectively.The consistency between the BBC measured by the two methods and that of the actual delivery was contrasted and analyzed.Part III A total of 38 patients who met the inclusion criteria from March 2010to May 2019 were retrospectively analyzed in this part.13 patients are round pelvis,whose ratio of the transverse diameter to sagittal diameter of pelvic entrance≥1.25patients are narrow pelvis,whose ratio of the transverse diameter to sagittal diameter of pelvic entrance≤0.9.The orthopedic degree of unilateral PAO was revealed according to the difference of four X-ray indicators before and after unilateral PAO.The size of BBC of DDH patients with round pelvis and narrow pelvis before and after the surgrey was measured by MIS method.The influence of unilateral PAO on the size of BBC of the two kinds pelvis was analyzed.ResultsPart I After unilateral PAO,the BBC above the sciatic spine(1～20^th layer)narrowed（0.86～5.95 mm,P<0.05）.However,there was no change in levels below the sciatic spine(21～25^th layer,P>0.05).The anterior margin of acetabular fragment(1～13^th layer)narrowed significantly（4.23～5.95 mm）after unilateral PAO with the narrowest part（5.62～5.95 mm）locating at the inferior margin of pubic ramus and the region superior to the lateral margin of obturator foramen(5～10^th layer).The narrowest part of BBC before and after the surgery occurred at the level of bilateral sciatic spines(20^th layer).The diameter of MIS changed significantly from105.34±7.16 mm pre-operatively to 104.47±7.06 mm post-operatively（t=2.198,P=0.032）.There was a positive correlation between the inward displacement of the hip center and the narrowing of the 1～20^th layer of the BBC（β=0.27～0.50,r=0.27～0.53,P<0.05）.The decrease of T（?）nnis angle was positively correlated with the narrowing of the 1～10^th layer of the BBC（r=0.26～0.34,P<0.05）.The increase of LCEA was negatively correlated with the narrowing of 2～5^th layer of the BBC（r=-0.31～-0.28,P<0.05）.The standardized coefficients were with statistical significance when comparing the distance between the Kohler’s line and the medial margin of the femoral head to the size of the 1～20^th layer of the BBC（β=0.27～0.50,P<0.05）.The height was positively correlated with the size of the narrowest part of the BBC before and after the surgery（r=0.565,r=0.586,P<0.001）.Part II Among the questionnaire patients,6 cases（19.40%）were normal delivery and 25 cases（80.60%）were caesarean section.14 cases（56%）in the caesarean section patients can’t be dare to normal delivery due to concern that PAO will affect normal delivery.During the pregnancy,there were respectively 2 cases（6.45%）,5 cases（16.13%）,9 cases（29.03%）and 13 cases（41.94%）in the 1^st,2^nd,3^rdand 4^th stage hip pain patients.The amounts of hip pain patients increased according to the prolonged with pregnancy.Acetabular retroversion was associated with hip pain in the third trimester（r=0.417,P=0.020）and fourth trimester（r=-0.386,P=0.035）.The LCEA was positively correlated with the WOMAC score（r=0.462,P=0.015）.The measurement results of the MIS method were consistent with those of the actual delivery.The determination coefficient of regression equation was 0.212.The results of formula method were poor accrracy and inconsistent with the actual delivery.Part III The 1～12^th layer BBC of the round pelvis group narrowed（t=2.584～6.746,P<0.05）.And the 1～20^th layer BBC of the narrow pelvis group narrowed（t=2.651～10.07,P<0.05）.Compared with the narrow pelvis group,the standardized coefficients of the size of 1^st layer BBC before surgery（t=-2.503,P=0.05）and that of the size of the 1～2^nd layer BBC after surgery（t=-2.166,P=0.037;t=-2.035,P=0.49）were with statistical significance in the round pelvis group.However,there was no change in the size of 2～25^th layer BBC before surgery and that of the 3～25^th layer BBC after surgery（P>0.05）.Unilateral PAO results in the narrowing of the middle BBC with round pelvis or narrow pelvis.And the narrowing range of BBC with narrow pelvis is more widely.The BBC(11～17^th layer)of the two pelvises shows statistical significance（t=-2.309～-2.452,P<0.05）.After unilateral PAO the narrowest part of BBC of round pelvis and narrow pelvis occurred at the 7^thlayer（5.46±2.98）mm and the 9^th layer（6.28±3.23）mm,respectively.In the round pelvis group,there was a positive correlation between the inward displacement of the hip center and the narrowing of the 1～9^th layer of the BBC（r=0.62～0.76,P<0.05）.The decrease of T（?）nnis angle was positively correlated with the narrowing of the3～8^th layer of the BBC（r=0.56～0.67,P<0.05）.The increase of LCEA was negatively correlated with the narrowing of the 3～7^th layer of the BBC（r=-0.55～-0.59,P<0.05）.In the narrow pelvis group,only the inward displacement of the hip center was positively correlated with the narrowing of the 9^th layer of the BBC（r=0.41,P<0.05）.ConclusionsUnilateral PAO results in mild narrowing of the BBC superior to the sciatic spine.The narrowest part of the BBC is located at the sciatic spine.Unilateral PAO has slight effects on the narrowest position of the BBC.The inward movement of hip rotation center and increasement of the lateral coverage lead to the narrowing of BBC.Normal delivery of a healthy fetus in female patients with DDH of childbearing age could not be affected by unilateral PAO in normal BBC settings.The female DDH patients of childbearing age after unilateral PAO can be able to normal delivery in China,but most patients are worried about choosing a caesarean section.The size of BBC can be predicted by the regression equation.However,it is necessary to explore more effective model to predict the size of BBC for its poorly accuracy.Unilateral PAO results in the narrowing of the BBC with round pelvis or narrow pelvis.Among them,the narrowing range of BBC with narrow pelvis is more widely.The size of the middle BBC in female DDH patients with narrow pelvis can be significantly reduced by unilateral PAO.