Print version ISSN 1413-7852
Acta ortop. bras. vol.9 no.2 São Paulo Apr./June 2001
Total hip arthroplasty with PCA (Porous Coated Anatomic) prosthesis
Sérgio Nogueira DrumondI; Edson Barreto PaivaII; José Paulo Sabino de AlmeidaIII; Leandro Vaz de Melo CamposIII
IAssociate Professor, UFMG College
of Medicine, Master in Surgery. Orthopedist. Head of the Hip Surgery Service,
IIOrthopedist, Hospital Biocor
IIIResident. Surgery Service, Hospital Ortopédico
Between 1988 and 1993 we performed 27 hip arthroplasties with the PCA prosthesis (Porous Coated Anatomic) in 26 patients. The average duration of the follow-up was nine years. We excluded seven hips from this review: one due early deep infection, two died of unrelated cause, and four were lost to follow-up evaluation. The average age at surgery was 53 years. The preoperative diagnosis was primary osteoarthritis in nine patients, secondary osteoarthritis in seven patients, osteonecrosis in six patients and inflammatory arthritis in four patients. The patients were analysed clinically, radiographically and subjectively. The X-Rays were studied for the occurrence of osteolysis, migration or loosening of the cup, wear of the polyethylene, beads shedding, subsidence or loosening of the stem, stress shielding, periosteal reaction and distal cortical hypertrophy. Seventeen hips (85%) were rated clinically good results. Three hips were rated poor (15%) due migration of the cup in two cases and wear of the polyethylene in one case. There were concordance between the clinical and the subjective results. However several radiographic findings were not related to poor results.
Key words: Arthroplasty, Hip, Prosthesis.
Total hip uncemented arthroplasties became very common procedures during the 80s. Notwithstanding, the first results were disappointing because, though osteointegration had occurred, many patients still felt pain and were dissatisfied with the results.
The first PCA (Porous Coated Anatomic) series of prosthesis also presented a high number of failures related to persistent and disabling pain in the thigh, claudication, radiographic evidence of subsidence and loosening of the femoral stem, and migration of the acetabular cup.2,7,13
In spite of the problems indicated by the short term results, some investigators were enthusiastic about this kind of prosthesis, considering that the previous bad results were, in part, a consequence of the learning curve and of the utilization of first generation projects.12 The first generation PCA prostheses presented a high number of failures because 32 mm diameter heads with thin polyethylene were used, provoking quick wear10,14 and osteolysis,11,16,17 with loosening of the components. A high number of beads shed contributing to the implant failure.5 Other problems were related to the surgical technique which accepted components of smaller size, originating pain in the thigh, micromovements of the stem with subsidence, and interposition of fibrous tissue and cup migration losing biological fixation.10 Current techniques provide complete filling of the canal, with immediate mechanical fixation and greater horizontalization of the acetabular cup. Besides this, technical refinement according to the learning curve and improvement of the industrial processes which manufacture the prostheses with better fixation of the beads aiming osteointegration.4,6,15
More recent evaluations of the PCA prosthesis show preoccupation of the authors with the acetabular aseptic loosening,1 with the femoral aseptic loosening9 and with osteolysis. Osteolysis has become a considerable concern in this kind of prosthesis because intense bone loss is produced and indices as high as 15% to 39% were found.11,16,17 In addition to the comparison of PCA with the cemented prostheses13, it has been compared to other cementless prostheses; compared to the Mallory-Head, the PCA prosthesis presented a higher index of pain in the thigh during the first follow-up years.3 In relation to the BUTEL isoelastic prosthesis which failed in 43% of the cases, PCA was more efficient with 11% failure rate.8
There are few reports in the literature about studies with the PCA prosthesis and long term follow-up.16 In this study, patients operated on from 1989 to 1993 with state-of-the-art prosthesis with 26 mm diameter heads and thicker polyethylene were evaluated.
Twenty-seven hips from 26 patients submitted to uncemented PCA (porous coated anatomic) total hip arthroplasty. Seventeen male and nine female patients patients were operated on from 1988 to 1993. One male patient was operated on both hips (Table 1). Ages ranged from 28 to 79 years, average 53 years. The most frequent diagnoses were primary arthrosis (nine patients), secondary arthrosis (seven patients), osteo-necrosis (six patients), and rheumatoid arthritis, related conditions of ankylosant spondilitis and acetabular protrusion (four patients).
Twenty-six patients with disabling hip conditions were submitted to total arthroplasty using the PCA (porous coated anatomic) prosthesis. One of the patients was operated on both sides, totalling 27 hips. From the 27 studied hips, 20 were evaluated in 20 patients aiming radiographic and subjective results. Seven hips from six patients were excluded since the six to 11-year follow-up was not completed. One of the patients had the prosthesis removed due to a deep infection; two patients died due to causes non-related to the surgical procedure (these patients were in good condition and pleased with the result), three patients were in good condition when the last revision was made 3 years before but they were not found and did not participate of this evaluation. The patients were operated on from 1988 to 1993 in the Ortopédico and Semper Hospitals.
The PCA prosthesis is made up by a chromium, cobalt and molybdenum alloy, coated by a microporous surface in the metaphyseal region of the stem and in all external surface of the acetabular component. The microporous layer is formed by a cluster of small spheres of approximately 300 micra, aiming osteointegration. The initial fixation of the prosthesis is made by the Press-fit mechanism and, as bone grows within the microspheres osteointegration or biological fixation occurs. The stem presents a trapezoid transversal section area, accompanied by an angulation which corresponds to the antecurvature of the femur proximal portion. Thus, the prosthesis is specific for the right or left sides. The cup is hemispherical and presents two flaps for additional fixation in the lateral aspect aiming to prevent rotation. The femoral head is interchangeable and has a 26 mm diameter. The prostheses were implanted without cement with the exception of two hips where the stems were cemented (two hibrid prostheses). Access was mainly anterior-lateral according to Hardinge, and the great trochanter was not secctioned. During the post-operative period the patients were mantained with partial restriction during 2 to 3 months. They were periodically evaluated according to clinical, radiographic and subjective criteria. Clinical evaluation was effected according to the Merle D'Aubigne-Postel criteria, modified by Charnley. Subjective evaluation considered the the patient's satisfaction in the last visit. Evolution of pain in the thigh was clinically evaluated in the post-operative period. Radiographic evaluation was effected according to a set of findings: stress shielding, subsidence of the stem, shedding of the beads, cortical hyperthrophy, osteolysis, demarcation, osteointegration, wear of the polyethylene, position of the femoral stem and of the cup. Patients with disabling pain, difficulty when walking and severe limitation of movements and hip function were selected to the cementless prosthesis. All the patients presented bones of good quality when X-rayed. Age was also considered: in 26 patients only four were above 60 years when operated on.
Mean follow-up period was nine years, ranging from six to 11 years.
The results for the 20 hips in 20 patients were satisfactory in 17 and non-satisfactory in three patients. Figures 1 and 2 show the radiographic aspect of two satisfactory cases. There was agreement between the clinical, radiographic and subjective evaluations. The failure of three cases was due to migration and loosening of the acetabular component in two cases and wear of the polyethylene in one case. The cases of loosening of the cup were submitted to revision with a titanium screwed cup and bone graft (Fig. 3 A-B); the patient with polyethylene wear was submitted to replacement of the polyethylene maintaining the original metalic cup (Fig. 3 A-B).
One patient presented deep refractory infection demanding remotion of the implant, and a ressection arthroplasty Girdlestone type was effected. Two cases had a vertical migration of the cup demanding revisions, which were made with titanium screwed cups. There was one case of polyethylene replacement due to wear harmless to the metalic cup fixation. One case of post-operative luxation was submitted to bloodless reduction and the final result was unaltered.
The radiographic analysis after the nine-year follow-up period revealed a series of findings. The most frequent findings were pedestal, total osteointegration of the stem, shedding of the beads, cortical hyperthrophy and wear of the polyethylene (Table 3). Less frequent findings were femoral demarcation, migration of the cup, shielding stress, subsidence and varism of the stem. No osteolysis or periarticular cases were found (Table 4) (Figs. 1 and 2). The findings with clinical repercussion adversely affecting the final results were migration of the cup in two cases and severe wear of the polyethylene demanding surgical revision. The other radiological findings did not present clinical repercussion.
Hip PCA prosthesis shows discrepant results as far as literature is concerned. Many of the reported bad results were attributed to the original design of the prosthesis, with thin poliethylene layer, 32 mm head, problems of production with shedding of the beads and the learning curve.2,7,10,11,12,13,14,16,17 The last prosthesis used by the author produced better results: no evidence of pain in the thigh and longer survival of the implants.4,5,15,16
The hip cementless PCA prosthesis presented satisfactory results in 85% of the cases. The other 15% presented failure of the acetabular component, 10% due to migration and loosening and 5% due to polyethylene wear. Pain in the thigh was observed in two patients by did not interfere in the final results, fading in one case and becoming negligible in another.
No osteolysis, migration or stem loosening were observed. These results agree with the best results found in the literature.
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