Synchronous or sequential cementless bilateral total hip arthroplasty for osseous ankylosed hips with ankylosing spondylitis: a retrospective cohort study

Purpose cementless total hip arthroplasty (THA) for bilateral osseous ankylosed hips with ankylosing spondylitis (AS) is a challenging procedure. No literature compares the clinical outcomes of synchronous and sequential bilateral THA of these special patients. Methods


Introduction
Ankylosing spondylitis (AS) is an in ammation spondyloarthritis affecting the axial spine and peripheral joints and characterised by low back pain and limited range of motion (ROM) of lumbar spine [1,2].And AS is diagnosed using the modi ed New York criteria requiring image change of sacroiliitis and painful reduction of lumbar spine ROM as well as stiffness of more than 3 months [3].Hips are the most common peripheral joints involved in approximately 25%~50% patients diagnosed with AS [4,5] and 90% presents bilateral hip ankylosis [6].The end-stage hip ankylosis usually shows osseous ankylosis with total loss of hip ROM [7].Although bilateral hip fusion leads to stable and painless hip, yet loss of hip function and premature degeneration of neighboring joints have an negative effect on quality of life, especially for suboptimal hip fusion for a long period [8][9][10].Bilateral total hip arthroplasty (THA) can relieve pain and recover the ROM of hips to improve the joint function and self-care ability [11].Also, many literatures have reported the good radiographic outcome and improvements in function [7,[12][13][14].
However, for bilateral osseous ankylosed hips with AS, there is no consensus on synchronous or sequential THA for these special group of patients.
There are many di culties for hip fusion takedown to THA.Firstly, the exposure of femoral head and neck is not easy for ankylosed hip, especially for the case with external rotation deformity, which increases the damage chance of posterior acetabulum and the great trochanter [7].Secondly, the ambiguous indication for the original joint plane [7] and disuse osteoporosis of the acetabulum [15] are usually encountered during anatomical identi cation and acetabular reaming.At last, the degenerative development of abductor muscles [16] and incorrect insertion of acetabular cup due to pelvic obliquity [12] can lead to hip dislocation and accelerate liner wear.For bilateral bony ankylosed hips with AS, while synchronous THA may prolong operation time and cause more blood loss, bilateral hip lesions can be solved simultaneously.Moreover, two ectional hips can be favourable for functional rehabilitation postoperatively.Sequential THA for these patients can lead to shorter operation time and less surgical damage, yet the temporary unhandled ankylosed hip can be an obstacle to the early exercise of the operated hip and the total two hospitalization expenses may increase unavoidably.Currently, the literatures just reported synchronous or sequential THA for osseous ankylosed hips with AS [7,12,14] with the limitation of different types of cementless cup and cemented or cementless stem [12], short time of follow-up [14] and small study population [7].There was no report comparing the clinical and radiographic outcomes of synchronous with sequential cementless bilateral THA for osseous ankylosed hips with AS.
The purpose of this study was to primarily compare the clinical and radiographic outcomes of synchronous and sequential cementless bilateral THA to correct bony ankylosis of hips with AS.It was hypothesized that for osseous ankylosed hips with AS, synchronous cementless bilateral THA can realize the similar outcomes of sequential THA.

Materials And Methods
Data were collected by retrospective review of a prospective database from January 2010 to December 2017.Study approval was obtained from the Clinical Trials and Biomedical Ethics Committee of West China Hospital (ID: 2012 − 268), and all participants signed informed consents for the use of their data.
The data included patient demographics, time of walking for the rst time postoperatively, range of ection-extension motion, Harris Hip Scores (HHS), transfusion, radiological assessments and complications.

Patients
The inclusion criteria: Patients diagnosed with AS and underwent primary cementless THA; Patients with bilateral osseous ankylosed hips and trabecula bridging the joint plane on radiograph; Total loss of hip ROM; Patients receiving bilateral THA simultaneously or sequentially.The exclusion criteria: Bilateral osseous ankylosed hips caused by other reasons; Unilateral osseous ankylosed hip with AS; Fibrous ankylosis of the hip and no trabecula bridging the joint plane on radiograph; Patients just receiving unilateral THA; The patients lost to follow-up.
Ultimately, we analyzed the data of the patients receiving bilateral THA synchronously (group A) and bilateral THA sequentially (group B).All hips were identi ed as bony ankylosed hip with total loss of ROM.We called up the patients to accomplish follow-up.And we obtained the latest clinical and radiological outcomes.11 patients (22 hips) in group A and 12 patients (24 hips) in group B were followed up.The demographic data of the patients was summarized in Table 1.The mean duration of the follow-up was 81.9 ± 36.3 months for group A and 79.9 ± 29.1 months for group B (P = 0.84).

Surgical procedures
All operations were performed by a group of surgeons specializing in THA.Considering the different degree of hip deformity, the worse hip was done rstly.After general anesthesia, all patients were positioned in lateral position and exposed the hips through posterolateral approach.Femoral neck was identi ed according to the lesser trochanter and osteotomy was done without hip dislocation.For the hip with external deformity, osteotomy behind the femoral neck is di cult.So, we usually perform osteotomy in the front of femoral neck to avoid damage of greater trochanter and posterior acetabulum.No trochanteric osteotomy was performed.Reamers with gradual increase in diameter were uesd to prepare the acetabulum in the medial direction and the counterrotation technique was used to avoid overreaming of the osteoporotic acetabulum.On the basis of foveal soft tissue and incomplete gray ossifying cartilage, we located the original joint plane.The optimal cup size and cup inclination of the acetabulum implant were identi ed by intraoperative uoroscopy.And the anteversion of cup was con rmed with the indication of transverse acetabular ligament or long axis of body.If initial press-t was not satisfactory, additional screws would be used to x the cup before inserting the liner.
For the preparation of femoral canal, sequentially larger reamers were used to enlarge the canal until the diaphyseal cortex was involved.The lesser trochanter and ipsilateral transcondylar line indicated the anteversion of the stem.Then femoral trial prosthesis was inserted to correct the leg length discrepancy (LLD), check the stability in all direction and optimize the femoral offset.At last, the cementless femoral prosthesis and femoral head were inserted.We check again the stability and ROM of the hip to ensure an optimal angles and postoperative mobility.If the hip can't be abducted more than 15°passively, we will cut off the adductor tendon.At the end of the procedure, the external rotator muscles were restored and the drainage was selected according to the the time of operation and blood loss before incision suturing.
Only one single brand (DePuy, Warsaw, IN) of cementless cup and stem implants were used for all patients.The friction interfaces used including ceramic-on-ceramic (CoC) or ceramic-on-polyethylene (CoP) were decided according the age, level of activity and patients' nancial situation.

Perioperative Regimen
Isometric exercises and positive motion exercises were conducted in bed after recovering from anesthesia.Prophylactic intravenous antibiotics were used within the rst 24 hours postoperatively.Additionally, low-molecular-weight heparin (LMWH) were systematically managed to prevent deep venous thrombosis (DVT) and Non-Steroidal Anti-in ammatory Drugs (NSAIDs) were used to relieve pain and reduce the chance of heterotopic ossi cation (HO), respectively.For unbearable postoperative pain, additional painkillers by intravenous or intramuscular injection were added.The drainage tube was removed within 24 hours.
From the rst postoperative day on, the patients were allowed to partial weight-bearing exercises with the help of walker aid, then exercise with the help of cane after 2 weeks and full weight-bearing exercises after 4 weeks without help.Moreover, for the patient with hip ection deformity preoperatively, the hip gradually extended under the circumstances of bearable pain.

Clinical Measurements
At the latest follow-up, clinical details were recorded including ection-extension ROM of the hip and Harris Hip Scores (HHS) of the two group [17].Special ruler was used to measure the range of hip exion and extension when the patients were in supine position.ROM and Harris scores were examined by 2 authors to reduce the bias.Additionally, from our database, we collected the time of walking for the rst time postoperatively, the average blood transfusions and the blood transfusion rate.The standard of blood transfusions refered to the guidelines of the National Ministry of Health, recommending blood transfusion for hemoglobin level less than 7 g/dL until the level reached or exceeded 8 g/dL.Additionally, when hemoglobin level uctuated between 7 and 10 g/dL, transfusion would be considered in patients with symptomatic anemia (severe mental status changes, palpitations, and/or pallor).

Radiological Assessments
Standard anteroposterior radiographs were obtained preoperatively, immediately after surgery and at the latest follow-up.And the radiological data were collected and analyzed by the same two authors.The assessments include the inclination of the cup (IC), the difference of bilateral IC, the femoral offset (FO), the difference of bilateral FO and LLD at the latest follow-up.IC were measured directly on AP radiograph.The angle crossed by the horizontal line connecting the both teardrops and line through the longest diameter of the elliptical opening of the acetabular cup rim was recorded and regarded as IC [12].If the teardrops were unrecognizable or the pelvis was asymmetric, we rstly bisected the sacrum with a vertical line A and secondly drawn a perpendicular line B to line A [12].So, the line B can be used as horizontal line.FO was de ned as the vertical distance from the center of femoral head to the ipsilateral anatomical femoral axis [18].LLD was assessed by standardized-trochanteric method to avoid the in uence of pelvic obliquity and femoral inclination on the radiographs [19].

Complications
The complications are recorded including early-onset and late-onset complications during the perioperative period and at the latest follow-up.The early-onset complications consist of dislocation, wound complications, infection, intraoperative fracture, DVT, pulmonary embolism and nerve palsy.The data were collected from the database.Meanwhile, the late-onset complications consist of postoperative dislocation, HO, osteolysis and aseptic loosening at the latest follow-up, which were assessed by two authors.On the basis of Brooker classi cation [20], we analyzed and classi ed the degree of HO.
Osteolysis was de ned as cystic or scalloped lesions with a diameter of more than 2 mm on radiograph [21,22].According to the criteria if DeLee [23], the acetabular component was considered loose if a complete radiolucent line thicker than 1 mm at bone-implant interface or migration of the component showed.Besides, the femoral implant stability was evaluated according to Engh [24], the stem was considered loose if subsidence more than 2 mm or angular shift of the stem more than 2°showed.

Statistical Analysis
Statistical analysis was performed using SPSS software for Windows Version 22.0 (SPSS, Chicago, IL).The level of statistical signi cance was set at p 0.05.The results were expressed as the mean ± standard deviation.Independent sample T test was used for data analysis.

Clinical outcomes
The average preoperative HHS increased from preoperative 30.5 ± 5.9 to 84.0 ± 2.8 at the latest follow-up for group A and from preoperative 31.4 ± 4.6 to 83.4 ± 2.0 at the latest follow-up for group B.Moreover, all of the hips lost total ROM of hip preoperatively, but at the latest follow-up, the average ection-extension ROM was 85.7 ± 4.5° for group A and 85.1 ± 4.1° for group B. The average exion and extension were 86.5 ± 4.4° and 0.73 ± 2.4° for group A and 85.7 ± 3.5° and 0.54 ± 1.9° for group B, respectively.No statistical difference was found in both groups, but large improvement was realized postoperatively (Table .2).Additionally, all of the patients were satis ed with the clinical outcome and gait had improved markedly compared with preoperative status.
However ,the difference was found statistically that the patients receiving simultaneously bilateral THAs needed more time to walk for the rst time postoperatively with 5.1 ± 2.6 days, while the patients receiving sequentially bilateral THAs walk for the rst time postoperatively with 3.6 ± 1.2 days (P = 0.02) (Table .2).The average interval time between two operations was 40.8 ± 23.0 days for group B. Furthermore, blood transfusions perioperativly were also different between the two groups.Average blood transfusions was 3 ± 3.97 U for group A and 0.71 ± 1.99 U for group B (P = 0.028), while the blood transfusion rate were 8/11 (72.7%) for group A and 5/24 (20.8%) for group B (Table .2).

Radiographic evaluation
For group A, at the latest follow-up, it was no difference that the average IC between the right and left hips (P = 0.48) (Figure .1).Similarly, the same nding was presented in group B (P = 0.37) (Figure .2).For the FO, the patients in group A showed no difference between the right and left hips (P = 0.07), while statistical difference was found In group B (P = 0.04) (Table .3).Also, we compared the difference of bilateral IC and the difference of bilateral FO of the both groups (Table .4).The differences of bilateral IC were 3.0 ± 2.1°for group A and 5.5 ± 2.4°for group B, which showed a signi cant statistical difference (P = 0.02).Meanwhile, the differences of bilateral FO were 0.35 ± 0.27 cm for group A and 0.32 ± 0.21 cm for group B. And LLD were 0.48 ± 0.39 cm for group A and 0.45 ± 0.31 cm for group B. No differences were found between groups for the differences of bilateral FO (P = 0.78) and LLD (P = 0.83).

Complications
Only two hips in group A encountered early-onset complications.One femoral fracture intraoperatively and was xed with several double-loop cerclage wires immediately.The patients postponed walking on the ground, which was substituted with functional exercise in bed.And the fracture healed without problem.Hip dislocation on the third day postoperatively and delay union of wound hit the same patient.Closed manipulative reduction was performed and dressings were changed more frequently.Also, we prolong the time of antibiotic use for three days to prevent the deep infection.Ultimately, no dislocation happened and the wound was recovered.For late-onset complications, three hips (13.6%) in group A and three hips (12.5%) in group B encountered asymptomatic HO, all of which belong to Brooker I. Other complications such as dislocation, osteolysis and loosening were not observed.

Discussion
The most important nding of this study was that cementless bilateral THA for osseous ankylosed hips with AS showed good clinical outcomes and all of the patients were satisfactory with the functional improvements and gait had improved markedly compared with preoperative status.Besides, compared to sequential bilateral THA, simultaneous bilateral THA can realized the comparative clinical outcomes with an average follow-up more than 79 months.Although simultaneous bilateral THA may need more blood transfusions, simultaneous procedure can realize nearer FO and lesser difference of bilateral IC.
Due to the deformity followed by bony ankylosed hip with AS and ambiguous landmarks, the adequate exposure of the surgical elds can simplify the subsequent procedure.There are three approaches to expose the coxa including: posterolateral approach [7,13,14], posterior approach [25][26][27] and direct lateral approach with a trochanteric osteotomy [6,12].For the bony ankylosed hips, the weakness of abductor muscles is obvious on account of disuse-artophy [16].So, the early functional rehabilitation is signi cant to prevent dislocation and instability.However, to visualize the acetabulun and proximal femur, the direct lateral approach was usually performed with a trochanteric osteotomy.The secondary delay of walking [28] and possible nonunion of the greater trochanter [13] may pay for inferior rehabilitation and satisfaction.Besides, nerve injury especially the superior gluteal nerve is another complication resulting in abductor insu ciency after THA from direct lateral approach, which was reported an incidence of 2.2%-42.5% [29,30].So, in recent years, many literatures recommended posterolateral approach [7,13,14] or posterior approach [25][26][27].These two approaches can realize su cient exposure to the acetabulum and poximal femur.But more attention should be attached to preventing the risk of sciatic nerve injury due to scarred and contracted soft tissues around the hip caused by AS [31,32].These two approaches both can achieve a safe and high-quality THA and we recommend that doctors choose the skilled and experienced approach to perform.
It's di cult to identify the interface of femoral head and acetabulum intraoperatively due to osseous bridge formation and total loss of ROM for the hip with AS.So, how to conduct acetabular reaming appropriately and insert the cup with suitable size play a vital role in successful THA.After performing femoral neck osteotomy, the osseous bridge between the acetabulum and femoral head make it di cult to ream in right direction and with right size.Although there is bony ankylosis of the hip, yet incomplete gray ossifying cartilage is still remaining at the original joint plane [7,13,14].We can enlarge the acetabulum with sequentially larger reamer in the medial direction and adjust the direction of reaming according to the appearance of incomplete gray ossifying cartilage.Also, the foveal soft tissue can act as an indication for the depth of reaming [7,13,14].Additionally, long-term loss of ROM leads to acetabular disuse osteoporosis [15], which can easily generate over-reaming of acetabulum.the counterrotation technique can avoid over-reaming and compress the bone in the acetabular base bene ting for primary press-t of cup.Of course, intraoperative radiography facilitate judging the suitable size and depth of cup.
Asymmetric pelvis is usually encountered for bony ankylosed hips with AS resulting in great challenge of cup insertion in appropriate direction, especially for simultaneous bilateral THA [12].Because ankylosis of the contralateral hip can hamper the position of pelvis in lateral position [12].Also, pelvis tilt can be an obstacle to insert the cup in an appropriate direction [7,12,14].The malposition of cup can lead to dislocation or impingement and accelerate the liner wear [12,33].On the basis of different type of deformity with AS, the studies reported different ways to insert the cup in the safe range (40°±10° for inclination and 15°±10°for anteversion) [34].If the hip presents simple exion deformity, just insert the acetabular cup routinely and if the hip combines with adduction deformity, the inclination angle of cup should be reduced [7].Moreover, anterversion of the cup should be reduced than desired, if the hip has xed adduction and exion deformity [12].Comparatively, anterversion of the cup should be increased than desired, if the the hip has xed abduction and exion deformity [12].Although these methods can work in dealing with different type of deformities, yet intraoperative radiographs and tests of hip stability in all directions are more signi cant to avoid dislocation, impingement and premature wear.
The purpose of THA for bony ankylosed hip is to correct the hip deformity and restore the fundamental exion-extension ROM from fusion hip, which is reported that the increase of ROM and improvement in self-care ability are two important factors associating with patient satisfaction [11].Although conversion of bony ankylosed hip to THA leads to inferior ROM and HHS compared to primary THA (PTHA), THA for those patients can relieve pain, restore hip mobility, improve function and correct LLD [13,16].Also, THA for fusion hip is more technically di cult, needs more operation time and causes more traumatic response compared to PTHA [7,12,14,33], which may result in more blood loss and longer time of rehabilitation and more obvious for bilateral THA performed simultaneously, this kind of situation can be more obvious.The research has reported that postoperative transfusion rate for one-stage bilateral PTHA is 29.2% and unilateral PTHA is 15.9% as well as more rehabilitation time is needed for bilateral PTHA [35].And our study also showed more transfusions were needed for simultaneous procedure and sequential procedure.Furthermore, simultaneous procedure demanded more transfusions and more time of rehabilitation than sequential procedure.However, with the extensive use of tranexamic acid in total joint arthroplasty [36,37], the blood loss can be reduced obviously.Fortunately, these two operation options can realize comparable HHS and exion-extension ROM.Moreover, no difference were found in LLD, IC and the difference of bilateral FO.Although simultaneous procedure can lead to less difference of bilateral IC, yet the average IC of both two procedure uctuates between 30°and 50°.For the patients with good nutritional status, one-stage bilateral THA may be an alternative means to cure bony ankylosed hip simultaneously.
The study reported that AS increased perioperative and postoperative complications after THA and high incidences of complications including wound cmplications, polyethylene wear, revision and dislocation were observed [38].Survival analysis of THA for AS was 81.4% at 15 years [6], which was lower than that of THA for other etiologies [39].Also, the rate of polyethylene wear of THA for bony ankylsed hip was high than that of PTHA concluded according to Kim et al [40].Two reasons may explain the higher rates of implant failure for bony ankylosed hip.Firstly, component malposition and abnormal spinopelvic mechanics contribute to abnormal stress to the implants resulting in accelerating the polyethylene wear and increasing revision rate [41,42].secondly, the patients receiving THA for these special group are younger and more active than average THA, who present higher functional demand and physical activity [38].Hip dislocation is another frequent complication.Component malposition and increased demand for the motion of hip extension and exion due to rigidity of spine add risk of hip dislocation when running daily activity [43].Also, the weakness of abductor muscles is another risk of dislocation.Moreover, intraoperative periprosthetic fractures is another noticeable complication.Osteoporosis of acetabulum and proximal femur is usually encountered for fusion hip due to long-term disuse [15].When insert the prosthesis, excessive impact may cause cup protrusion into pelvis or proximal femoral fracture leading to poor primary xation of stem.So, appropriate impact and careful examination of possible fracture should be involved intraoperatively.If necessary, additional screws or the stem with distal xation can be used also.
Several limitations are noticed in our study.First, the study is a retrospective evaluation of prospectively followed patients at a single center.Second, the number of patients enrolled is relatively small and short follow-up.But this study is the currently biggest sample-size research about THA for bilateral bony ankylosed hips.Third, the surgery-speci c information including intraoperatve blood loss, total blood loss and In ammatory biomarkers can't be obtained.However, with the fast development of enchanced recovery after surgery in our joint center, the blood loss and traumatic response can be lesser and lesser accompanied with faster recovery from surgery for patients.

Conclusion
Cementless bilateral THA was a safe and effective technique to improve hip function for patients diagnosed with osseous ankylosed hip due to AS. Synchronous bilateral THA can realize good clinical outcomes and more superior radiographic evaluation compared to sequential bilateral THA   Case presentation of synchronous cementless bilateral total hip arthroplasty for osseous ankylosed hips with ankylosing spondylitis a: A man was diagnosed with ankylosing spondylitis and showed bilateral osseous ankylosed hips preoperatively.b: The radiograph of the pelvis after surgery immediately showed similar inclination of cup and femoral off-set as well as small leg-length discrepancy.c: The radiograph of the pelvis at 100-month follow-up showed no aseptic loosening and migration of the component.
Case presentation of sequential cementless bilateral total hip arthroplasty for osseous ankylosed hips with ankylosing spondylitis a: A man was diagnosed with ankylosing spondylitis and showed bilateral osseous ankylosed hips preoperatively.b: The radiograph of the pelvis before contralateral THA showed excellent prosthesis position and size of rstly performed THA.c: The lm of the pelvis at 97-month follow-up showed superior radiological parameter and good xation of the prosthesis.

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