9 мар. 2012 г.

15-year Comparison of Cementless Total Hip Arthroplasty With Anatomical or High Cup Placement for Crowe I to III Hip Dysplasia

Abstract

This study compared radiological and clinical results of Mallory-Head (Biomet, Warsaw, Indiana) cementless total hip arthroplasty (THA) by anatomical (AP group) or high cup placement (HP group) for Crowe I to III developmental dysplasia of the hip. Of the 68 hips studied, 43 hips were available for 15.3-year follow-up. Ten cups were placed at anatomical center with bulk bone grafting, and 33 cups were at high hip center without bulk bone grafting. No acetabular or femoral components showed loosening in either group. One standard polyethylene liner in a highly placed cup was revised due to excessive wear after 11 years. The average rate of polyethylene wear was 0.128 mm/year in the AP group and 0.148 mm/year in the HP group (except for the revision case). The extent of grafted bone coverage was 34.6% in the AP group. Hip center height was 24.5 mm from the inter-teardrop line in the HP group. The center of the hip horizontal location in the AP group (24.5 mm) and HP group (26.4 mm) was significantly shorter than in normal hips (35.6 mm). Postoperative center-edge angle was 11° (except grafted bone) in the AP group and 25° in the HP group. Mean Harris Hip Score in the AP group improved from 38 points preoperatively to 82 points postoperatively and in the HP group improved from 40 points preoperatively to 88 points postoperatively. Survivorship was 100% in the AP group and 97% in the HP group. Our results indicate that moderate high cup placement without bulk bone grafting at a horizontal locus more medial than that of a normal hip is an alternative durable solution.
 


Drs Murayama, Ohnishi, Mori, Nakura, Sakai, and Nakamura are from the Department of Orthopaedic Surgery, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Dr Okabe is from Niigata Rosai Hospital, Niigata, Dr Tsurukami is from Tsurukami Clinic of Orthopaedics and Rheumatology, Kumamoto, and Dr Uchida is from the Department of Orthopaedic Surgery, Wakamatsu Hospital for the University of Occupational and Environmental Health, Kitakyusyu, Japan.

Drs Murayama, Ohnishi, Okabe, Tsurukami, Mori, Nakura, Uchida, Sakai, and Nakamura have no relevant financial relationships to disclose.


The authors thank Tatsuhiko Kubo, MD, PhD, of the Department of Public Health at the University of Occupational and Environmental Health, Japan, for his assistance with the statistical analysis.

Correspondence should be addressed to: Hideo Ohnishi, MD, PhD, Department of Orthopaedic Surgery, School of Medicine, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu 807-8555, Japan (95hideo@med.uoeh-u.ac.jp).
Posted Online: March 07, 2012

In cemented total hip arthroplasty (THA) or cementless THA for developmental dysplasia of the hip, the cup has commonly been placed at the anatomical hip center and paired with bulk bone grafting. 1,2 The results at approximately 10 years with anatomical cementless cup placement with bulk bone graft are satisfying, 3,4 but only 1 study reported good results at >15 years. 5 However, 2 recent studies have reported longevity >15 years for cementless cups with a high hip center placement. 6,7 Regarding cementless cup placement for dysplastic hips, specifying which method will achieve greater longevity is controversial because studies have been performed with anatomical or high placement in a single procedure without comparison. 3-7

The purpose of this study was to compare 15 years of clinical and radiological outcomes for cementless THA for Crowe I to III developmental dysplasia of the hip with anatomical cup placement with bulk bone grafting and with high hip center placement without bulk bone grafting.

Materials and Methods

We performed a consecutive study on cementless THA with anatomical cup placement with bulk bone grafting or with high cup placement without bulk bone grafting for developmental dysplasia of the hip. Developmental dysplasia of the hip was defined by preoperative radiographic abnormalities of the femoral head or the acetabulum. 8

Between 1992 and 1995, seventy-nine nonselected primary THAs using the Mallory-Head cementless system (Biomet, Warsaw, Indiana) were performed for developmental dysplasia of the hip by a single surgeon (T.N.) at our institution. Before August 1993, eighteen primary THAs were performed with cups placed approximately at the anatomical hip center. After August 1993, sixty-one primary THAs were performed with cups placed relatively high to the normal hip center based on the severity of hip dysplasia. At final follow-up, radiographs and clinical scores were available for 10 patients with anatomical cup placement with bulk bone grafting (AP group) and 33 patients with high hip center cup placement without bulk bone grafting (HP group).

Patient details are presented in Table 1. Eleven patients died of causes unrelated to the THA before final follow-up, and 25 patients were lost to follow-up; 15 moved away or changed their telephone number, and 10 could not visit our hospital because of severe dementia or heart disease. The follow-up rate was 63.2% (excluding the 11 who died).



Table 1: Demographic and Perioperative Radiographic Data

A Mallory-Head prosthesis was used for all THAs (Figure 1). A standard polyethylene liner was used in all patients in the AP group (n=10) and in 24 patients in the HP group. Cross-linked polyethylene liners (ArCom; Biomet) were used in 9 patients in the HP group.



Figure 1: Photograph of the Mallory-Head cementless system (Biomet, Warsaw, Indiana).


Surgical Technique

All operations were performed at a single facility by 1 senior hip surgeon using a posterolateral approach without trochanteric osteotomy. Before August 1993, all cups were placed at the anatomical hip center with an autologous femoral head graft, as described by Wolfgang. 9 For bulk bone grafts, 4.5-mm-diameter AO stainless malleolar screws were used for the initial fixation (Figure 2). After August 1993, all cups were placed at the high hip center without bulk bone grafting, and the acetabulum was reamed medially and proximally to achieve acetabular roof coverage of the cup screw hole at minimum (Figure 3).




Figure 2: Preoperative anteroposterior radiograph of a 54-year-old woman with untreated bilateral Crowe II dysplastic osteoarthritis (A). Anteroposterior radiograph 16 years after anatomical cup placement with bulk bone graft (B).



Figure 3: Preoperative anteroposterior radiograph of a 54-year-old woman with untreated left Crowe II dysplastic osteoarthritis (A). Anteroposterior radiograph 16 years after primary total hip arthroplasty with high cup placement without bulk bone graft (B).

In both groups, the degree of subluxation was categorized according to Crowe classification. 10 Cup size and cup abduction angle, stem alignment, and center-edge (CE) angle (angle of the center of the inner head to the acetabular edge) were measured from postoperative radiographs. 11 The extent of graft-bone coverage was determined from postoperative anteroposterior radiographs by comparing the mediolateral dimension of the cup portion covered by the graft with the mediolateral dimension of the entire cup. 12

The center of the hip and the lever-to-arm ratio were measured on pre- and postoperative radiographs according to the Russotti and Harris 13 technique (Figure 4): X=horizontal location of the hip center; Y=height of hip center; A=abductor moment arm, the distance along a line originating from hip center intersecting at a 90° angle with an oblique line from anterior superior iliac spine to lateral edge of the greater trochanter; and B=center of body moment arm, distance along a horizontal line parallel to the inter-teardrop line extending from directly proximal to symphysis pubis to hip center. The lever-to-arm ratio was calculated with the formula B/A.

Figure 4: Locus of measurements of the center of the hip. X, horizontal location of the hip center; Y, height of hip center; A, abductor moment arm; B, center of body moment arm.

The unaffected normal side of 17 patients with unilateral THA composed the normal control group. These data were measured by another senior surgeon (H.O.) using a 10-µm caliper (Absolute Digimatic; Mitutoyo Corp, Kawasaki, Japan).

Long-term radiographic evaluations were performed with regard to cup migration, osteolysis, radiolucent line, and progressive subsidence based on the radiographic signs of Engh et al 14 at final follow-up. Osteolysis surrounding the component was evaluated at stem and cup. Radiographic signs of cup instability were defined as cup migration (>4 mm) or development of a radiolucent line (>2 mm). Stem instability was defined as progressive subsidence (>2 years) or development of a radiolucent line (>2 mm). Leg-length discrepancy was evaluated on anteroposterior radiographs at final follow-up for unaffected hips or after THA on the opposite side. Five cases with untreated subluxated hips on the opposite side were excluded. As a result, 30 cases in the HP group and 8 cases in the AP group were assessed.

Two-dimensional polyethylene wear was calculated by measuring the distance between the center of the acetabular shell and the center of the femoral head using the software program Image VINUS Web (Yokogawa Electronics Inc, Tokyo, Japan) on anteroposterior radiographs at final follow-up because the shell center and the femoral head center in the Mallory-Head THA system matched completely postoperatively.

Clinical performance was evaluated using the Harris Hip Score (HHS) 15 preoperatively and at final follow-up by a senior surgeon (H.O.). Hip dislocation was also evaluated during follow-up.

Differences between the 2 groups were evaluated using the Mann-Whitney U test or chi-square test. Pearson’s correlation coefficient was used for the relationship of cup abduction angle and polyethylene wear rate. A P value <.05 was considered significant. Kaplan-Meier survivorship curves were calculated for revision of the hip replacement for any reason and revision of the acetabular component, femoral component, and polyethylene liner. All statistical analyses were performed using Statview 5.0 software (Hulinks Inc, Tokyo, Japan) and STATA 11 software (StataCorp LP, College Station, Texas).

Results

Perioperative radiographic data are presented in Table 1. In the AP group, 22-mm inner heads were used for a 42- or 44-mm cup in 4 patients, and 28-mm inner heads were used for a >46-mm cup in 6 patients. In the HP group, 22-mm inner heads were used in 9 patients, and 28-mm inner heads were used in 24 patients.

No significant differences existed between the 2 groups in age (P=.67), height (P=.40), weight (P=.15), or leg-length discrepancy (P=.53) (chi-square test, P<.05; Mann-Whitney U test, P<.05). Significant differences existed between the groups in cup abduction angle (P=.04).

The center of hip measurements and lever-to-arm ratios are presented in Table 2. The center of the hip horizontal location in both groups was significantly shorter than that in normal hips (Mann-Whitney U test: AP group, P<.0001; HP group, P<.0001). Postoperative lever-to-arm ratios in both groups were significantly smaller than that in normal hips (AP group, P=.0042; HP group, P=.0481).



Table 2: Center of Hip and Lever-to-arm Ratio

The mean extent of grafted bone coverage was 34.6% (range, 28% to 44%) in the AP group. The extent of graft bone coverage did not exceed 40% except in 1 case (44%). The mean postoperative CE angle was 11° (range, -6° to 19°) in AP group and 25° (range, 17° to 36°) in the HP group (Table 3). All osteolysis was partial, and none was severe enough to induce loosening. At a mean 15-year follow-up, no acetabular and femoral component had been revised in either group.




Table 3: Radiographic Evaluation at Final Follow-Up

One hip required revision of the standard polyethylene liner retaining a well-fixed acetabular and femoral component because of excessive wear of the polyethylene liner (0.874 mm/year) at 11 years. The average rate of polyethylene wear was 0.128 mm/year in the AP group and 0.148 mm/year in the HP group (except for the revision case). No significant difference existed in polyethylene wear rate between the AP and HP groups (P=.11). Standard polyethylene liners were used in 24 patients and cross-linked polyethylene liners were used in 9 patients in the HP group. The average rate of standard poly-ethylene wear was 0.149 mm/year and the average cross-linked polyethylene wear was 0.147 mm/year in the HP group. No significant difference existed in wear rates between the standard polyethylene and cross-linked polyethylene in the HP group (P=.85). No significant correlation was found between the polyethylene wear rate and cup abduction angle (P=.11).

In the HP group, average HHS improved from 40 points (range, 21 to 63 points) preoperatively to 88 points (range, 65 to 100 points) at final follow-up. In the AP group, average HHS improved from 38 points (range, 27 to 53 points) preoperatively to 82 points (range, 57 to 91 points) at final follow-up. No significant difference existed between the 2 groups for pre- (P=.17) or postoperative HHS (P=.09). Single postoperative dislocations occurred in 2 patients in the HP group.

Implant survivorship using the Kaplan-Meier method (the probability of retaining the implant at 15-year follow-up, with revision for any reason as the endpoint) was 100% in the AP group and 97% in the HP group (95% confidence interval [CI], 80.4% to 99.6%). The survivorship probabilities in the HP group, with acetabular aseptic loosening (n=0), polyethylene wear (n=1), and femoral aseptic loosening (n=0) as endpoints, were 100%, 97% (95% CI, 80.4% to 99.6%), and 100%, respectively.

Discussion

The current study is valuable because of its long-term comparative results for cementless THA with anatomical cup placement with bulk bone grafting and with high cup placement without bulk bone grafting using identical components. Based on our results, using a cementless porous-coated cup at a high hip center is a reliable alternative method for implant longevity.

In the HP group, all patients had placements that did not exceed 35 mm superior (mean, 24.5 mm) from the inter-teardrop line. The center of the hip moved 9.2 mm significantly medially compared to the normal hip center, the postoperative CE angle was >15° in all cases, and the lever-to-arm ratio improved significantly from 2.7 preoperatively to 1.9 postoperatively. Improvement of this lever-to-arm ratio means that the resultant force toward the replaced hip was decreased. The load can be minimized by placing the hip center as medial as possible.

In most high cup placements, the length of the limb is commonly adjusted by using a skirt-shaped long neck. However, this may induce a risk of impingement between the neck and the acetabular shell. To avoid this problem, we used a non-skirt neck and placed a larger-sized stem more proximally than expected to achieve equal bilateral leg length, which yielded satisfactory results.

In general, the polyethylene wear rate of cementless THA for developmental dysplasia of the hip is relatively higher (0.23 mm/year). 16 However, our results showed that standard and cross-linked polyethylene wear rates were the same as the polyethylene wear rate with cement-less THA for primary osteoarthritis. 17,18

Postoperative dislocations occurred in 2 (6.6%) of 33 patients in the HP group. High hip center placement may have a higher risk of postoperative dislocation; however, the average rate of postoperative dislocation was reported to be approximately 1.4% to 6.5% in Japan. 19,20 This suggests that a relatively high hip center placement is acceptable for stability against dislocation in THA, if anteroinferior acetabular osteophyte resection is performed.

On the basis of our comparison study, we will perform high hip center cup placement without bulk bone grafting for all Crowe I to III developmental dysplasia of the hip cases <35 mm proximal from the inter-teardrop line and >15° of the CE angle based on preoperative template design or intraoperative radiographs. If high hip placement is either >35 mm proximal or <15° of the CE angle, anatomical cup placement with bulk bone graft technique will be used.

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