1 Introduction

Primary total hip arthroplasty (THA) is considered to be one of the most successful orthopedic treatment to relieve pain, improve function, and improve the quality of life for end stage osteoarthritis (OA) of the hip.1,2 However, THA in secondary OA caused by diseases of developmental dysplasia of the hip (DDH) is difficult for the acetabular structural abnormality together with various degrees of bone defects around the acetabulum. For these patients, the principles of acetabulum reconstruction simplify the surgical procedure and avoid extensive structural bone graft when suitable positioned component and bone coverage are ensured.3–6

Reconstruction of an anatomic rotation center is the ideal option in DDH patients,7 but there are a number of retrospective studies concluded that suitable upward placement of the acetabular component is a safe and effective surgical procedure to avoid structural bone graft and achieve good bone coverage of the acetabular component with following some procedure.4,6,8 It allows patients to perform early weight-bearing walking and functional exercises, which are helpful to postoperative recovery, independent living and economy burden. High acetabular upward placement is generally defined as an upward placement of over 35mm from the teardrop.9,10 An upward placement within 35mm from the teardrop is feasible,6,8,9 but it is better within 20mm upward and without lateral placement from cadaver study and other related studies.4,8,11–13

The purpose of this study is to provide a randomized, prospective, single center evaluation of two different surgical techniques for acetabulum reconstruction, the 0–5mm (anatomic center group) and 5–20mm upward placement from the teardrop (upward center group), in the early post-operative follow-up period (up to 12 months). Our objective is to analyze the difference of in-hospital cost, the early outcome as measured with Harris scores and WOMAC index. We also evaluate variation of surgical factors of the two procedures, including the operative time, component positioning, blood loss, transfusion, early complications, and leg length discrepancy.

2 Methods

The study was approved by institutional review board of our Hospital (IRB No. 2013-32). The trial was registered at Chinese Clinical Trial Registry on 11th April 2014 (retrospectively registered), and trial registration number is ChiCTR-TRC-1404388. This randomized clinical trial was conducted from April 2014 through June 2015. The inclusion criteria were the following: Crowe I with over 35% subluxation, Crowe II and III DDH patients with secondary osteoarthritis who elected to undergo THA; the patient's age at the time of surgery was between 30 and 80 years; the patient was able to comply with the requirements of the study including pre-operative and post-operative evaluations and questionnaires. The exclusion criteria were as follows: Crowe I with less than 35% subluxation and Crowe IV DDH patients; simultaneous THA; patient refusal at any time during the research; presence of any serious illness that would make surgery impossible; an age less than 30 or more than 80 years; an inability or unwillingness to comply with the postoperative rehabilitation or follow-up protocols; other hip diseases who elected to undergo THA; patient death. There are no important changes to methods after trial commencement. Full details of the trial protocol can be found at www.chictr.org.cn

2.2

2.2 Surgical technique

The patient is positioned in the lateral decubitus position. A posterior-lateral incision was placed over the greater trochanter, slightly curved posteriorly. Following dislocation and neck resection, the acetabulum was sufficiently exposed while protecting the sciatic nerves. The acetabulum was identified by removing the acetabular labrum, part of the joint capsule, and hyperplasia osteophytes. For the normal rotational center placement (0–5mm) group, the acetabulum was gradually reamed at suitable abduction and anteversion and the cementless acetabular component was installed with primary stability. If installation of the acetabular component poor bone coverage, the morselized bone graft (the bone defect was less than 30% of the acetabulum)7,8,14 or intra-acetabulum structural bone autograft (Fig. 1) was used with femoral head for early partial weight-bearing.

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Fig. 1 A DDH patient who underwent THA with intra-acetabulum structural bone autograft (A–D). A 66-year-old female, with left hip pain for 3 years, diagnosed as having DDH with secondary osteoarthritis (Crowe II), and the right hip was undergone THA with 9mm upward placement of acetabular implant in 2009: A, the left limb was 13mm shorter than the contralateral one as measured by preoperative imaging. B, intra-acetabulum structural bone autograft was used with femoral head in the left THA. C, anteroposterior X-ray of the pelvis showed good bone coverage of the acetabulum. The component was stable and anatomic placement. The affected limb was the same as the contralateral one as measured postoperatively. D, anteroposterior X-ray of the pelvis taken at the 12 months after surgery showed no loosening or subsidence of the component.

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For the upward placement group, the acetabular component was displaced upward according to preoperative data analysis based on the principle of placing the implant as near to the location of the actual acetabulum as possible, and the minimum upward placement distance of the acetabular implant was generally ≤20mm to achieve 70% bone coverage and good stability to avoid extensive structural bone graft reconstruction and avoid lateral placement. The distance of upward displacement could be determined using anatomical markers including the distance between the transverse acetabular ligament, teardrop, and upper edge of the acetabulum. The acetabulum was gradually reamed at suitable abduction and anteversion. Intraoperative roentgenoscopy was performed when necessary to determine the installation position of the acetabular component, so that the acetabular rotational center would not be displaced upward by more than 20mm.

The femoral canal was progressively reamed, and a suitable femoral implant with appropriate inclination and neck length was placed. After the joint was repositioned, soft tissue tension around the affected hip, range of joint motion, and joint stability were tested. Once confirmed, drainage tubes were placed, external rotators were repaired, and the incision was sutured layer by layer. All subjects enrolled in the study received cementless total hip system.

3 Results

A total of consecutive DDH 81 patients (90 hips) were referred to the study during the recruitment period. After exclusion, 40 patients (42 hips) were enrolled in the study (Fig. 2). Patient demographics were similar across all 2 cohorts, including age and body mass index (BMI) had no significant difference (P >0.05) (Table 1). All patients had complete intraoperative, in-hospital and follow-up data (case report form, CRF). There are no changes to trial outcomes after the trial commenced.

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Fig. 2 Flow Diagram.

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There were statistically significant differences between the anatomic center and upward center group for the upward distance of rotation center of acetabular cup (P<0.01), but surgery time was no difference in two groups (Table 2). There were no statistically significant differences between the groups for intraoperative blood loss, hemoglobin (Hb) and albumin decrease, but post-operative wound drainage was higher in the anatomic group (P=0.010). However, the blood transfusion was no difference in two groups.

For the cup position, the cup anteversion was similar, but the cup inclination in anatomic group was larger (44.04±7.19, P=0.036) for better bone coverage, compared to upward group (40.27±5.99), but both in the safe zone. The LLD was also no difference, but the limb lengthening was better in anatomic group (11.95±9.00, P=0.042) compared to upward group (7.95±5.11).

There were no statistically significant group differences in length of stay-day, as well as associated inpatient costs (Table 3). Length of stay and walking after operation was similar between the anatomic and upward group (P=0.175 and P=0.352, respectively). The total hospital costs were similar for these two groups (P=0.285), but anatomic group was a little bit higher. The costs excluding the THA implant cost or excluding both implant cost and anesthesia cost were also no significant differences (P=0.203 and P=0.373, respectively).

Regarding complication, we encountered no complication in the six-month primary follow-up and up to 12 months for these patients over a 1-year period. Two hips in the anatomic group were done with structural bone graft, but both cases were partial weight bearing walking at 2 and 3days after operation, and full weight bearing walking at 6 weeks with satisfactory postoperative outcomes, but the average surgery time and intraoperative blood loss were much higher than other cases in these two cases.

With regard to Harris hip score and WOMAC score, there were significant improved after surgery in both groups (Fig. 3). When compared the Harris score at different time points, the anatomic group was higher in the value, but these differences were no statistically significant (P=0.154, P=0.237 and P=0.400, respectively at 3 months, 6 months and 12 months). On the other hand, the anatomic group was also better in the value at 3 months, 6 months and 12 months after surgery in WOMAC score, but these differences were also no statistically significant (P=0.087, P=0.176 and P=0.181, respectively at 3 months, 6 months and 12 months).

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Fig. 3 The comparison of pre- and post-operative Harris score and WOMAC index in different upward placement groups.

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4 Discussion

Total hip arthroplasty is the most important technique in the elderly DDH patients who developed to secondary osteoarthritis, but reconstruction of the acetabulum still represents a major challenge in DDH patient with different hip deformity. For Crowe Type IV, acetabular reconstruction should also be performed at the actual acetabular position with femur-shortening osteotomy.1–3,15,16 However, the proper position of acetabular reconstruction in Crowe I and Type III cases have not yet been precisely determined, especially in the issue of restoration of anatomic rotation enter or elevated hip center.6–8 In this prospective study, we primary showed that the acetabular reconstruction at the anatomic center would be a better choice from the early functional hip score and limb lengthening for Crowe I and III DDH patients, but sometimes the structural bone graft was needed, especially for Crowe II–III. From the early period comparison of the surgical indexes of anatomic and upward placement groups, the principle of placing the implant as near to the location of the actual acetabulum as possible should be followed, but the acetabular placement could be selective upward placement to achieve 70% native bone coverage and good stability, if the pre-operative and intra-operative analyses showed that extensive structural bone graft reconstruction maybe need for anatomic reconstruction. Moreover, the upward placement distance of the acetabular implant should be as minimum as possible, and less than 20mm upward placement from teardrop could achieve similar intra-operative and early post-operative results as anatomic reconstruction without severe leg-length discrepancy and complication.

Acetabular reconstruction at the anatomical center reduced the loads at the hip from mathematical study and biomechanical study,11,12 and provided good long-term results.13,17 But the anatomical reconstruction maybe needs autogeous structural bone grafting as we showed in this study,3,6 and the migration of the cementless acetabular component happened.3 We showed that Harris hip score and WOMAC score were significant improve in upward placement groups in the early follow-up as well as anatomic center groups. Some mid-term and long-term studies have retrospective reported that the high hip center reconstruction was particular useful for DDH patients with good mid-term and long-term follow-up results, especially for a cementless acetabular cup with >95% survival rate over 10–15 years.5,6,8 Lots of studies have also shown that simple appropriate upward placement of the hip joint does not significantly increased the compressive stress.9–11,18,19 Therefore, we thought appropriate acetabulum upward placement is feasible, and the upward placement within 20mm could be achieved 70% native bone coverage and good stability without structural bone graft in most of Crowe I–III cases with 35%-90% subluxation.

This safe upward placement (<20mm from teardrop) was confirmed by some biomechanical and retrospective studies.8,11,13 Although some retrospective studies showed that more than 20mm upward placement above the teardrop produce good outcomes,6,7 we found that slightly upward placement (<20mm from teardrop) of the cementless cup can get the primary stability, and lead to the avoidance of structural bone graft in almost all patients with hip dysplasia with 35%-90% subluxation. In addition, we also found that the anatomic placement with structural bone graft obviously increases surgical time (average 145min vs 250min) and intraoperative blood loss (average 410ml vs 1000ml) compared to upward placement. Moreover, this upward placement did not significantly affected the hospital cost, and even less than with mean saving per case amounts to approximately $ 270. Therefore, this upward technique may be a benefit to rapid recovery postoperatively as other previous reports.6

The Limb-length discrepancy is another important issue during THA in DDH patients. In order to achieve better efficacy and avoid a further shortening of the affected limb while performing THA on DDH patients, the length of the affected limb should be recovered as much as possible.6 Affected limbs of the anatomic group in this study were lengthened by 11.95±9.00mm on average, reflecting a statistically significant better compared with 7.95±5.11mm on average in upward group. However, the postoperatively LLD was no significant difference in these two groups, which decreased to 6.67±3.44mm in 0–5mm group, and 5.66±4.52mm in 5–20mm group. No patients had obvious abnormal gait after 3 months. These results indicated that anatomic placement was more effectively in the limb lengthen, but upward placement of the acetabular component can also effectively lengthen affected lower limb to solve the problem of LLD. Moreover, for high hip center (>35mm above the teardrop) reconstruction in DDH patients, LLD could also be partially or completely corrected by the methods of appropriate head/neck lengths and proper elevation of the stem in the femoral canal with a larger-sized stem.6–8 Therefore, careful preoperative planning and design for these two reconstruction techniques as well as suitable intraoperative positioning are important. During surgery, complete acetabulum morphology should first be adequately exposed, especially the various bone anatomical structures that can guide positioning. Once it has been confirmed that installing the acetabular component at the normal rotational center cannot achieve good bone coverage, the acetabular component should be displaced upward properly. In order to avoid further shortening of the affected limb due to the upward placement of the acetabular rotation center, the maximum allowable size of the femoral component should also be selected, femoral off-set should be increased, and long-necked components can also be used if necessary.

The limitation of this study include this was a single center data, and sample size was small. In our study, all patients were Chinese, and their mean body weight was low, which may be one of the affected factors for the outcome and soft tissue balance during surgery. Moreover, the short term follow-up was only up to 12 months, and longer follow-up is needed to determine the outcome of the life of the implant. In addition, the study could not be blinded for the surgeon due to the technique during the surgery.

5 Conclusions

the acetabular implant for DDH should be reconstructed as close to the actual acetabular location as possible, but an appropriate (<20mm) upward placement that can achieve at least 70% native bone coverage of the acetabular implant is a valuable technique, which is good for early faster recovery. However, the multi-center and large-sample study is necessary for further confirming, as well as long-term follow-up and observation.

Conflict of interest

The authors have none to declare.