Abstract
Background:
We present the results of cementless total hip arthroplasty performed with use of an anatomically adapted femoral stem and hemispherical cup with a fully coated Spongiosa-I metal surface, which was designed to achieve a surface similar to human cancellous bone. The purpose of the present retrospective case series was to determine the long-term outcomes of this hip arthroplasty system after a minimum of twenty years of follow-up.
Methods:
Between 1983 and 1985, 209 consecutive total hip arthroplasty procedures (199 patients) were performed with use of the first-generation Spongiosa metal-surface chromium-cobalt total hip implant with an articulating surface consisting of a ceramic head and an ultra-high-molecular-weight polyethylene liner. We report the clinical and radiographic outcomes, the rates of and reasons for revision, and the influence of sex and age on outcome and complications.
Results:
At the time of the latest follow-up, twenty-seven patients had died and thirteen patients had been lost to follow-up; none of these forty patients had had revision surgery. The outcomes for 159 patients (169 prostheses) were reviewed. The mean duration of follow-up was 262 months (range, 242 to 275 months). There were nineteen revisions, including fourteen revisions of the femoral stem, two revisions of the acetabular cup, and three revisions of both components. The mean Harris hip score for patients who did not undergo revision surgery was 82 points. The probability of survival of both components at twenty years, with revision for any reason as the end point, was 97%. The probability of survival of the acetabular component was 98%, and the probability of survival of the femoral component only was 86%. The probability of component survival was significantly increased among older patients.
Conclusions:
The results of cementless hip arthroplasty with use of the first-generation Spongiosa implant were excellent at a minimum of twenty years of follow-up. The probability of survival of the acetabular component exceeded that of the femoral stem.
Level of Evidence:
Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.
Various implants have been used for cementless total hip arthroplasty. The initial results have shown failure rates ranging from 9% to 15% after two to seven years of follow-up1-9. The aim of total hip arthroplasty is to achieve a long-lasting, stable, pain-free, and functional joint. The implant used in these patients, with its spongy metal surface structure, was introduced in 198210. The system includes a hemispherical acetabular cup and an anatomically adapted femoral stem (Fig. 1). As a result of a special wax molding process, it was possible to achieve an implant surface structure approaching that of human cancellous bone, allowing for a full-length porous stem surface, whereby the core and the prosthesis surface structure are cast as one piece. The result is a fully integrated core-surface structure and not a surface coating. This integration allows for a pore size of between 800 and 1500 µm and a depth of up to 3000 µm with an overall porosity of 60%11-13 whereby the mesh spaces form an intercommunicating system extending throughout the surface of the implant. All components, including the surface, were produced by means of a casting process with use of an alloy of chromium, cobalt, and molybdenum.
The absence of substantial design changes over time allows for a meaningful long-term report on the results of uncemented total hip arthroplasty more than twenty-five years after the first procedures involving this implant. Until now, there have been only a small number of long-term follow-up studies of uncemented hip arthroplasties, which are still being used in clinical practice worldwide14-19. The purpose of the present retrospective series review was to determine the long-term results associated with the Spongiosa-I metal-surface hip prosthesis after a minimum of twenty years of follow-up.
Photograph showing the Spongiosa-I fully coated anatomically adapted femoral stem and hemispherical acetabular cup.
Demographic Characteristics
Between May 1983 and December 1985, 199 consecutive patients underwent primary total hip arthroplasty at the Stiftung Oskar-Helene-Heim Medical Center in Berlin, Germany. Ten of these patients had bilateral hip arthroplasty. The mean age of the patients at the time of surgery was fifty-seven years (range, thirty-three to seventy-five years). There were 132 female patients (66%) and sixty-seven male patients (34%). The arthroplasties were performed because of osteoarthritis in 141 hips (67%), dysplasia in thirty-one hips (15%), osteonecrosis of the femoral head in nineteen hips (9%), rheumatoid arthritis in eight hips (4%), posttraumatic arthritis in six hips (3%), seronegative arthritis in two hips (1%), and ankylosing spondylitis in two hips (1%).
Implant
The total hip prosthesis is a four-component system. The hemispherical metal acetabular component is constructed of cobalt-chromium-molybdenum alloy and includes three fins at the circumference and a peg that is positioned toward the superior pubic ramus to improve rotational stability. The acetabular component has a modular liner made of ultra-high-molecular-weight polyethylene (UHMWPE). The inlay articulates with a 28-mm ceramic alumina (Al2O3) head. The metal stem is made of cobalt-chromium-molybdenum alloy and has an anatomically adapted shape of the proximal part of the femur. There is both a right stem and a left stem, each in seven sizes. The acetabulum consists of seven sizes. The thickness of the metal shell is 3 mm, and the thickness of the polyethylene varies, according to size, from 6 to 13 mm. All components were sterilized with use of gamma radiation in a vacuum-sealed pack.
The manufacturer was the S&G Implant Company in Lübeck, Germany, now listed as the ESKA Orthodynamics Company.
Procedure
The operations were performed with use of a standard posterior approach. The acetabulum was prepared with an air-driven hemispherical reamer. Progressive reaming was continued until a cancellous bone surface was exposed over the entire circumference. The acetabulum was under-reamed by 2 mm in comparison with the implant size, and the cup was press-fit in 45° of inclination and 10° to 15° of anteversion.
The femoral canal was prepared distally with a blunt-end straight reamer and proximally with a side-specific anatomical broach. The implant size was the same as the last press-fit broach used.
One gram of prophylactic intravenous Augmentin (GlaxoSmithKline, Germany) (amoxicillin/clavulanate potassium) was given and was continued three times daily for seven days postoperatively. Subcutaneous heparin (5000 IU) (GlaxoSmithKline) was given for the first ten days as chemical thromboprophylaxis.
Postoperative Protocol
Full weight-bearing as tolerated with crutch assist was allowed for six weeks after surgery. Postoperative radiographs were made in the hospital for all patients. The patients were followed in the outpatient clinic two weeks postoperatively for a wound check and were evaluated at six weeks and one year with repeat radiographs. After the one-year visit, patients were asked to return every two years for follow-up unless they had no concerns.
Clinical and Radiographic Analysis
The mean duration of follow-up was 262 months (range, 242 to 275 months). All patients underwent clinical and radiographic assessments. Clinical assessment included a calculation of the Harris hip score20 and the Merle D'Aubigné score21. The Merle d'Aubigné score allots up to 6 points for each category of pain, mobility, and gait function, with a total of 18 points being given to a normal hip. The result was classified as excellent (17 or 18 points), good (15 or 16 points), fair (13 or 14 points), or poor (=12 points).
Anteroposterior and lateral hip radiographs were made at the twenty-year follow-up visit. These radiographs were analyzed for changes in bone density and cortical hypertrophy. Radiolucent lines and stress-shielding were classified according to the system of Gruen et al.22,23 on the femoral side and according to the system of DeLee and Charnley24 on the acetabular side (Fig. 2). All radiographs were analyzed for zones of osteolysis as defined by Zicat et al.25. The stability of the femoral implant was classified according to the system of Engh et al.26. Heterotopic bone formation was graded according to the criteria of Brooker et al.27. Linear polyethylene wear was evaluated in two dimensions on anteroposterior radiographs with use of the method described by Charnley and Halley28.
Anteroposterior radiograph of the hip, demonstrating the seven Gruen zones surrounding the femoral component and the three DeLee and Charnley zones surrounding the acetabular component.
Statistical Analysis
The Kaplan-Meier method29 and the log-rank (Mantel-Cox) test30 were used to estimate the probabilities of implant survival. The level of significance was p = 0.05.
Ethics
All patients gave informed consent prior to inclusion in the study. The study was approved by the ethical board of the institution and was performed in accordance with the 1964 Declaration of Helsinki31.
Source of Funding
There was no outside funding for this study.
The mean duration of follow-up was 262 months (range, 242 to 275 months) for the patient cohort. At the time of the latest follow-up, twenty-seven patients (twenty-seven hips) had died and thirteen patients (thirteen hips) had been lost to follow-up. None of these forty patients had had revision surgery, and all had had satisfactory results with no complaints at the time of the latest follow-up.
The outcomes for 159 patients (169 hips) were available for follow-up, representing a follow-up rate of 81%. The mean Harris hip score for the 140 patients (150 hips) who did not undergo revision surgery was 82 points (Table I). The Merle d'Aubigné score was excellent for sixty-three hips (42%), good for sixty-nine (46%), fair for three (2%), and poor for fifteen (10%). Of the fifteen hips with a low score, eight (5%) were in patients who had thigh pain, four (2%) were in patients who limped as a result of limb-length discrepancy, and three (2%) were in patients who had stiffness of the hip.
Nineteen patients (nineteen hips; 9%) had revision surgery. Fourteen hips (7%) had revision of the femoral stem. Two of these fourteen hips had stem breakage after seven and eleven years. Seven of the fourteen hips had isolated aseptic loosening of the femoral stem; in four of these seven hips, we observed a progressive radiographic varus angulation of the stem over the follow-up period. All seven hips with aseptic loosening were revised within the first three years after surgery, and none of the stems showed osseous ingrowth. Five other hips had revision of the stem at other institutions for unknown reasons. Two hips had revision because of failure of the acetabular cup after eight months and eleven years. Three hips had revision of both components because of infection at eight, eleven, and thirteen years postoperatively, with all late infections due to a hematological source.
At a minimum of twenty years of follow-up, radiographic examination was performed for 140 patients (150 hips). Comparison of the initial postoperative radiographs with the twenty-year follow-up radiographs revealed that cortical thickness changed little over the twenty-year follow-up period in all zones of Gruen et al.22,23. A radiolucent line adjacent to the stem was found in zone I of Gruen et al.22,23 on fifty-two radiographs (35%), in zone II on six radiographs (4%), in zone III on two radiographs (1%), in zone IV on three radiographs (2%), in zone VI on five radiographs (3%), and in zone VII on forty radiographs (27%); no radiolucent lines were observed in zone V. A radiolucent line adjacent to the acetabular component was seen in zone 1 of DeLee and Charnley24 on two radiographs (1%) and in zone 3 on three radiographs (2%); no radiolucent lines were seen in zone 2. Scalloping expansile-type osteolysis could not be detected around any cup or stem; however, only seven stems were revised because of loosening, and the rest of the stems were classified as stable-bone ingrown according to the criteria of Engh et al.32.
According to the criteria of Brooker et al.27, grade-4 heterotopic ossification was found in three hips (2%); grade-3, in five hips (3%); grade-2, in seven hips (5%); and grade-1, in nine hips (6%). Two-dimensional assessment showed no clear evidence of polyethylene wear according to the method described by Charnley and Halley28. This technique could not be easily applied to this prosthesis because of the radiographic appearance of the implant.
Kaplan-Meier analysis29 revealed that the probability of not having complete revision surgery because of infection was 99% (95% confidence interval [CI], 98% to 100%) after ten years and 97% (95% CI, 93% to 100%) after twenty years. The probability of retaining the acetabular component was 99% (95% CI, 98% to 100%) after ten years and 98% (95% CI, 96% to 100%) at both eleven and twenty years. The probability of retaining the femoral stem was 95% (95% CI, 92% to 99%) after ten years, 88% (95% CI, 82% to 94%) after fourteen years, and 86% (95% CI, 79% to 93%) after twenty years.
Of the nineteen patients who underwent revision surgery, fourteen were female (representing 11% of all female patients) and five were male (representing 7% of all male patients). In our group, the probability of retaining the primary implant after 23.7 years was 81% for female patients and 84% for male patients; this difference was not significant (p = 0.739).
Among the nineteen patients who had revision surgery, thirteen were younger than seventy years old and only six were more than seventy years old. Statistically, the probability of retaining the original implant 23.7 years after primary implantation was 62% for the group of patients who were less than seventy years old at the time of revision surgery and 90% for the group of patients who were seventy years old or more. The comparison of both age groups showed a significant difference in the average time until revision surgery (p < 0.001) (Fig. 3).
Kaplan-Meier curve showing the probability of implant survival for patients younger than seventy years old and patients seventy years old or more at the time of revision or at the time of the latest follow-up. There was a significant difference between the two groups (p < 0.001).
Intraoperative femoral fractures occurred in three female patients (2%) during insertion of the stem prosthesis. These fractures occurred in the first year of use of the new implant, during the learning curve period. The surgeons chose too large a stem, resulting in splitting of the proximal aspect of the femur. All three fractures were treated with cerclage bands, and the patients had a modified rehabilitation program that included protected weight-bearing postoperatively with use of two crutches for a period of six weeks. No long-term adverse effects occurred. No fractures of the ceramic heads occurred.
There were four cases of hip dislocation (3%), three of which occurred during initial hospitalization and one of which occurred within two months after surgery. One patient had two dislocations within one week after surgery, requiring a change of the polyethylene liner to a 20° lip insert, with no further dislocations. The other three patients were successfully managed with closed reduction and physiotherapy.
Other complications included seven cases of deep venous thrombosis (5%) and three cases of pulmonary embolism (2%). All patients were managed successfully with variable courses of anticoagulants according to the severity of each case.
The cementless Spongiosa-I metal system with its anatomically adapted stem and hemispherical cup has been used widely in Germany, Europe, and Japan since 1982. It was later introduced in Australia in 2004.
In the present series, this system was associated with good results. After twenty years, we observed nineteen revisions of the 169 prostheses used in 159 patients. Previous studies have reported excellent results for Spongiosa metal implants. Plötz et al.11 found no stem loosening after thirty-four months. Sielewicz et al.33 reported a 0.7% rate of aseptic loosening after five years in a study of 605 cases. Other authors have confirmed these intermediate-term results34; however, long-term results after more than ten years of follow-up were still missing.
Our data suggest that the cementless Spongiosa-I metal femoral stem provides excellent results at twenty years of follow-up. The rate of intraoperative fractures and the results of their treatment are comparable with findings that have been reported in the literature35. The Swedish total hip replacement registry based on 86,000 observations reported a ten-year survival rate of 87.7% for nearly 3000 cementless implants. The seventeen-year survival rate of 1772 cementless hip arthroplasties averaged 57%36. The Zweymüller stem had a cumulative survival rate of 96% to 99% at ten to twelve years16, and the cementless Spotorno stem (Centerpulse, Zurich, Switzerland) had a cumulative survival rate of 95% at twelve years37.
Only two of our acetabular shells were revised because of aseptic loosening. We believe that these excellent results were due to the strict application of biological fixation principles38,39, such as using a biocompatible surface material with an optimum size of surface pores, placing the component in intimate contact with viable host bone, and ensuring adequate initial stability for osseous ingrowth to occur reliably. The cup survival results are comparable with those of other long-term studies in the English-language literature8,40-48. In a study of acetabular fixation options, Hamilton et al. reported the results of 910 primary total hip arthroplasties that had been performed with three different types of modular, first-generation, hemispheric porous-coated cups49. The population included 433 Arthopor, 394 ACS Triloc+, and eighty-three Harris-Galante components. With liner or cup revision for any reason as the end point, the fifteen-year survival rate (and 95% confidence interval) was 75% ± 6% for the Arthopor cup, 70% ± 7% for the ACS Triloc+ component, and 89% ± 10% for the Harris-Galante cup (p = 0.02; log-rank method). Despite a high rate of revision due to polyethylene wear and occasional late porous-coatings delamination, the survival rate with revision for aseptic loosening as the end point exceeded 95% at fifteen years for all three cup designs.
Of the fourteen femoral stem revision procedures in the present study, two were performed because of stem breakage. Our analysis demonstrated femoral stem osseous integration distally, but fatigue fracture occurred because of proximal loading. Seven hips had aseptic loosening of the stem, with a connective tissue interface in all cases. We believe that the stems were too small in these patients, so no primary stability could be achieved. The wear rate of the articular surface matches that of ceramic on polyethylene in other long-term studies of bearing-surface wear. We believe that the lower rate of polyethylene wear is due to a combination of factors, including the smooth-surface ceramic head and the highly polished UHMWPE, which was cross-linked during sterilization using gamma radiation in a vacuum. We assessed polyethylene wear according to the method described by Charnley and Halley28. This method could not be easily applied to this prosthesis because of the radiographic appearance of the implant. Clarke et al.50 dismissed the uniradiographic technique of Charnley and Cupic38 and the duoradiographic techniques of Charnley and Halley after extensive in vitro experimental studies, claiming that these techniques are subject to significant errors as the wear vector is not always parallel to the radiograph. They concluded that wear measurements could not be made on clinical radiographs.
Griffith et al.51 later demonstrated, by measuring retrieved specimens, that radiographic measurements were valid provided that the cup was placed with a wire marker no more than 10° from the coronal plane. Wroblewski39, in 1985, showed that there was a significant correlation between real and radiographic wear of the acetabular cup. Bankston et al.52 studied twenty-one acetabular components that had been retrieved at the time of revision surgery and concluded that radiographic measurement of acetabular component thickness is accurate to within 0.18 mm.
We found no significant difference between male and female patients with regard to the revision rate. We can infer that the age of the patient at the time of primary fixation was significantly correlated with the average time until revision surgery.
The limitations of the present study include the loss to follow-up of the five patients who had revision of the femoral stem at other institutions and the fact that it was a single-center study.
We conclude that the first-generation Spongiosa implant, with its anatomically adapted femoral stem, hemispherical acetabular cup, and fully integrated cancellous metal surface, showed excellent results after a minimum of twenty years of follow-up. This system is still in clinical use with minor modifications.
Note: The contribution of Dr. Vinay Kulkarni and Dr. Marcus Oliver Hollenstein, who participated with editing the paper and collecting data, is appreciated.
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