J Orthop Sci (2010) 15:459?462Original article

J Orthop Sci (2010) 15:459?462

 

Original article

 

Long-term survivorship analysis of hip arthroplasty with vitallium mold cup

 

HAI-LE PAN, HARUHIKO AKIYAMA, KEIICHI KAWANABE, KOJI GOTO, KAZUTAKA SO, and TAKASHI NAKAMURA哈尔滨医科大学附属第二医院骨关节、骨肿瘤外科潘海乐

 

Abstract

Background. Cup arthroplasty was used in the initial attempts

to preserve the bone stock of the femoral head and neck for

hip reconstruction.However,little conclusive data are available regarding its long-term survivorship. Methods. We present a long-term survivorship analysis (mean follow-up, 19.3 years; range, 5?36.6 years) after vitallium mold arthroplasty in 77 secondary osteoarthritic hips.Results. Kaplan?Meier survivorship analysis predicted a survival rate for vitallium mold arthroplasty of 81.6% (95% confidence interval [CI], 76.7?86.5) at 20 years and 59.1% (95% CI, 51.8?66.5) at 30 years, with conversion to total hip arthroplasty as the endpoint. The mean Merle d’Aubigné and Postelhip score showed a signifi cant decrease in mobility from 4.12 (range, 3.18?5.86) 6 months after the operation to 3.19 (range, 1.7?4.6) at the last follow-up. No signifi cant differences were observed for the pain score from 6 months after the operation (5.05; range, 4.2?5.9) to the last follow-up (4.46; range, 2.88?6.04)) or score for the ability to walk, from 6 months after the operation (2.5; range, 1.4?3.6) to the last follow-up (3.13; range, 1.59?4.67). Radiographically, the proximal and medial migration of the cup measured at the last follow-up was 10.4 ± 5.4 mm (P < 0.01) and 0.2 ± 2.1 mm (P > 0.05),respectively.Conclusions. Our results indicate inferior long-term survivorship after vitallium mold compared with that after Charnley low-friction arthroplasty.

 

Introduction

Hip arthritis is a common condition in older populations and is one of the leading causes of hip disability. Total hip arthroplasty (THA) was developed in the early 1960s and has been shown to provide reliable and lasting amelioration of joint function in patients with more advanced stages of arthritis. However, in a younger and more active patient cohort, the results of THA are less encouraging, because of the strong possibility of multiple revision procedures over the lifespan as a result of increasing abrasion of the THA components and osteolytic bone loss. Therefore, resurfacing arthroplasty, a

kind of bone-conserving procedure, has regained the attention of orthopedic surgeons worldwide as an alternative technique.1

Before the advent of THA, cup arthroplasty was the main method of hip reconstruction. The first arthroplasty mold was made in 1923 from glass, and in 1939 Smith-Petersen2 introduced vitallium mold cup arthroplasty using a cup made from a cobalt?chrome alloy. Vitallium mold arthroplasty became a standard procedure for hip arthroplasty until the emergence of Sir John Charnley’s low-friction torque arthroplasty in the 1960s.3 Cup arthroplasty was then gradually abandoned and was ultimately displaced by THA.4?12 Cup arthroplasty was used in the initial attempt to preserve the bone stock of the femoral head and neck for hip reconstruction. However, little conclusive data are available regarding its long-term survivorship. The purpose of this study was to report on the long-term survivorship of this historical procedure.

 

Materials and methods

Between 1962 and 1997, 113 consecutive hip-resurfacing procedures (107 patients, 22 male and 85 female) were performed with the vitallium mold hip-resurfacing device at our center, Kyoto University Hospital. Thirty-six hips were lost to follow-up. The remaining 77 hips were followed for an average of 19.3 years (range, 5?36.6 years), forming the study group. The mean age at the time of the operation was 38.2 years (range, 15?68 years). The initial diagnosis for all hips at the time of operation was secondary osteoarthritis caused by developmental dysplasia or congenital dislocation of the hip, vascular osteonecrosis, and tuberculosis. After we began to use the Charnley low-friction arthroplasty in 1970, we limited the use of cup arthroplasty to highly active patients younger than 40 years.The operations were performed under general anesthesia in the lateral decubitus position through a lateral approach including osteotomy of the greater trochanter, as described previously.13 After dislocation of the femoral head, the acetabulum and the femoral head were reamed to provide a cancellous bone bed for the implant, and the vitallium cup was then fi tted. Seven weeks after the operation, partial weight-bearing with crutches was allowed and weight-bearing activity increased progressively. Patients were evaluated using the Merle d’Aubigné and Postel hip score.14 The scores recorded 6 months after the operation and at the last follow-up were used for assessment. Standard radiographs were used to measure the distance of the cup center from the teardrop line, and the distance between the medial border of the cup and Köhler’s line as the indices of proximal migration and medial migration, respectively. Institutional review board approval was obtained for publication of the study.Statistical analysis

The Wilcoxon signed-rank test was used to compare nonparametric data. A two-sided P value of 0.05 was considered signifi cant. Survival analysis was performed using Kaplan?Meier survivorship techniques, with conversion to THA as the endpoint.

 

Results

There were no early postoperative complications,including dislocation, nerve palsy, or infection. The postoperative average Merle d’Aubigné and Postel hip scores were 5.0 ± 0.8 for pain, 4.5 ± 1.3 for mobility, 2.5 ± 1.1 for walking, and 12.1 ± 2.6 for the total score. At the last follow-up, the Merle d’Aubigné and Postel hip scores were 4.5 ± 1.6 for pain, 3.2 ± 1.4 for mobility,3.1 ± 1.5 for walking, and 10.7 ± 3.6 for the total score. There was a signifi cant change in the mobility score (P < 0.01) but not in the pain, walking ability, or total scores. The Kaplan-Meier survivorship analysis, with conversion to THA as the endpoint, predicted a rate of survival of cup arthroplasty of 81.6% (95% confi dence interval [CI], 76.7?86.5) at 20 years and 59.1% (95% CI,51.8?66.5) at 30 years (Fig. 1). Twenty-one hips, from 18 patients, with a mean age at the time of the reoperation of 37.4 years (range, 20?48 years), required conversion to THA 18.7 ± 9.0 years (range, 1.2?33) after the initial cup arthroplasty operation: 15 for pain and 6 for limitation of activity of daily living caused by restriction of joint mobility. We estimated the proximal and medial migration of the cup radiographically. The mean distance between the cup center and the teardrop line on anteroposterior radiographs was 36.9 ± 3.6 mm immediately after the operation and 47.3 ± 8.2 mm at the fi nal follow-up. The mean proximal migration was 10.4 ± 5.4 mm (Wilcoxon signed-rank test; P < 0.01). However, the distance between the medial border of the cup and Köhler’s line was 3.9 ± 0.7 mm soon after the operation and 3.6 ± 2.3 mm at the last review; the mean medial migration of 0.24 ± 2.1 mm was not signifi cant.

 

Discussion

Smith-Peterson conceived the resurfacing mold hip arthroplasty in 1923, and in 1939, the fi rst vitallium mold arthroplasty was performed.2 This technique then became the standard procedure for hip arthroplasty until low-friction torque arthroplasty was developed by Sir John Charnley.3 To date, only a few publications have reported the long-term effi cacy of vitallium mold resurfacing surgery in a relatively large cohort of patients.5,9 David15 presented the case of a Smith-Petersen mold arthroplasty with an ultra-long-term follow-up of 56 years. The patient was pain-free and walked without aids at the latest review. Another patient with a satisfactory postoperative result 43 years after the operation was reported by Mahalingam and Reidy.16 In our study, the longest surviving patient was evaluated 36.6 years after the operation. When this patient was fi rst admitted to our hospital, she suffered from severe pain in the left hip joint, caused by gross degenerative changes. A vitallium mold arthroplasty was performed. Although the stump of the neck has shortened and a varus shift has occurred in the cup, the patient is still mobile without aids and is competent in her daily activities (Fig. 2). In this study, we have presented the long-term survivorship of vitallium mold cup arthroplasty. The Kaplan?Meier survivorship analysis showed a long-term outcome with survival rates of 81.6% at 20 years and 59.1% at 30 years (Fig. 1). Because the long-term survivorship after vitallium mold cup arthroplasty has not been reported previously, we cannot compare our data directly with those of other patients or groups. In addition, the follow-up rate in our study was 68.1% because the clinical records of the patients had been lost, resulting in a less satisfactory survivorship analysis. However, despite this limitation, our result was inferior to that reported for the Charnley THA,17?19 and the clinical outcome after cup arthroplasty was not satisfactory. Previous studies show that the clinical outcome in patients after cup arthroplasty continues to improve 2?5 years after operation, but then declines gradually, with poor results,13 because cup arthroplasty does not achieve complete relief of pain or complete improvement of movement.20,21 In our study, the Merle d’Aubigné and Postel hip score at the last follow-up showed signifi cant impairment of mobility, and although the difference between the pain scores at 6 months after the operation and at last follow-up was not signifi cant, the pain score had increased. In addition, conversion to THA within 5 years after the initial cup arthroplasty was caused by pain. In contrast, Wroblewski et al.22 reported complete or nearly complete relief of pain and excellent improvement in function and range of movement after the Charnley THA, even after a minimum follow-up of 20 years f. Our study showed that conversion to THA from cup arthroplasty was required because of pain or limitation of activity of daily living caused by the restriction of joint mobility. Radiographic fi ndings revealed varus slipping of the cup, shortening of the femoral neck, and proximalmedial migration of the cup, which resulted in groin pain, restriction of mobility, and the need for conversion. These changes may occur because of absorption of the femoral head secondary to injury of the retinacular vessels supplying the femoral head during the operation. The proximal and medial migration of the cup results from bone resorption on the acetabulum side. In the operation described in the present study, the reaming was performed in the acetabulum to provide a cancellous bone bed near the inner cortex of the pelvis for reconstruction and reshaping until the femoral head and the acetabulum fi tted comfortably with the interposed vitallium mold.13 The continuous compression stress by a metal cup upon the reamed acetabulum leads to migration. Cup arthroplasty had been proposed as a bone-conserving procedure with advantages over THA. Although cup arthroplasty requires reaming of the acetabulum and femoral head, it allows preservation of the femoral neck, which is an advantage for future, more extensive procedures. However, proximal and medial migration of the cup induces major acetabular bone defects, and a large amount of allograft or bone fi llers is needed when converting to THA (Fig. 3). In addition, a reinforcement ring is frequently required for subsequent acetabular conversion. Llinas et al.23 reported that the acetabular components of THA inserted following failed mold arthroplasty showed radiological evidence of earlier loosening than those after primary THA. In conclusion, the long-term survivorship after vitallium mold arthroplasty was inferior to that after THA. Although THA is one of the most successful and wellestablished gold standard procedures for the treatment of osteoarthritis of the hip, patients younger than 50 years remain a challenging cohort. Because of the many suggested advantages of hip-resurfacing arthroplasty, including bone conservation, reduced dislocation rates, normal femoral loading, and reduced stress-shielding,current resurfacing arthroplasty could be useful as an option for THA in young and active patients. None of the authors of this manuscript has received any type of support, benefi ts, or funding from any commercial party related directly or indirectly to the subject of this article.

 

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