Influence of the Acetabular Cup Material on the Shell Deformation and Strain Distribution in the Adjacent Bone-A Finite Element Analysis.

In total hip arthroplasty, excessive acetabular cup deformations and altered strain distribution in the adjacent bone are potential risk factors for implant loosening. Materials with reduced stiffness might alter the strain distribution less, whereas shell and liner deformations might increase. The purpose of our current computational study was to evaluate whether carbon fiber-reinforced poly-ether-ether-ketones with a Young´s modulus of 15 GPa (CFR-PEEK-15) and 23 GPa (CFR-PEEK-23) might be an alternative shell material compared to titanium in terms of shell and liner deformation, as well as strain distribution in the adjacent bone. Using a finite element analysis, the press-fit implantation of modular acetabular cups with shells made of titanium, CFR-PEEK-15 and CFR-PEEK-23 in a human hemi-pelvis model was simulated. Liners made of ceramic and polyethylene were simulated. Radial shell and liner deformations as well as strain distributions were analyzed. The shells made of CFR-PEEK-15 were deformed most (266.7 µm), followed by CFR-PEEK-23 (136.5 µm) and titanium (54.0 µm). Subsequently, the ceramic liners were radially deformed by up to 4.4 µm and the polyethylene liners up to 184.7 µm. The shell materials slightly influenced the strain distribution in the adjacent bone with CFR-PEEK, resulting in less strain in critical regions (<400 µm/m or >3000 µm/m) and more strain in bone building or sustaining regions (400 to 3000 µm/m), while the liner material only had a minor impact. The superior biomechanical properties of the acetabular shells made of CFR-PEEK could not be determined in our present study.

Biomechanical behavior of modular acetabular cups made of poly-ether-ether-ketone: A finite element study.

After total hip arthroplasty, stress-shielding is a potential risk factor for aseptic loosening of acetabular cups made of metals. This might be avoided by the use of acetabular cups made of implant materials with lower stiffness. The purpose of this numerical study was to determine whether a modular acetabular cup with a shell made of poly-ether-ether-ketone or poly-ether-ether-ketone reinforced with carbon fibers might be an alternative to conventional metallic shells. Therefore, the press-fit implantation of modular cups with shells made of different materials (Ti6Al4V, poly-ether-ether-ketone, and poly-ether-ether-ketone reinforced with carbon fibers) and varying liner materials (ceramics and ultra-high-molecular-weight polyethylene) into an artificial bone cavity was simulated using finite element analysis. The shell material had a major impact on the radial shell deformation determined at the rim of the shell, ranging from 17.9 µm for titanium over 92.2 µm for poly-ether-ether-ketone reinforced with carbon fibers up to 475.9 µm for poly-ether-ether-ketone. Larger radial liner deformations (up to 618.4 µm) occurred in combination with the shells made of poly-ether-ether-ketone compared to titanium and poly-ether-ether-ketone reinforced with carbon fibers. Hence, it can be stated that conventional poly-ether-ether-ketone is not a suitable shell material for modular acetabular cups. However, the radial shell deformation can be reduced if the poly-ether-ether-ketone reinforced with carbon fiber material is used, while deformation of ceramic liners is similar to the deformation in combination with titanium shells.

Limited significance of screening computed tomography after cementless total hip arthroplasty with highly cross-linked polyethylene at 7-10 years of follow-up.

OBJECTIVES: The purpose of this retrospective study is to report the incidence of osteolysis and evaluate the significance of screening computed tomography (CT) compared to plain radiography in detecting osteolysis after total hip arthroplasty with metal-on-highly cross-linked polyethylene bearings. METHODS: We retrospectively reviewed 264 primary cementless total hip arthroplasties of 211 patients, 24 males, 187 females, who received postoperative screening CT scan in addition to radiography at postoperative 7-10 years (average 8.2 years). First-generation highly cross-linked polyethylene was used in all cases. RESULTS: On the plain radiographs, no acetabular osteolysis (0%) and two cases of femoral osteolysis (0.8%) were found in the follow-up period. No osteolysis was newly found by screening CT scan. CONCLUSIONS: Very low incidence of osteolysis after total hip arthroplasty with highly cross-linked polyethylene at postoperative 7-10 years was confirmed, and routine screening CT scan for detecting osteolysis in this setting was not supported from this study.

Cirugía de revisión acetabular utilizando un cotilo modular con superficie de metal trabecular de tantalio: resultados a corto plazo / Acetabular revision surgery using a modular acetabular cup coated with trabecular metal of tantalum: short term results

Objectives: To evaluate short-term clinical results of patients performed acetabular revision surgery using a Trabecular Tantalum coated modular acetabular cups. Materials and Methods: This is a retrospective and descriptive analysis of a serie of 32 consecutive patients (34 hips) with acetabular revision surgery (23 women, 9 men, mean age 70.7 years), mean follow-up 32 month (12-60). The Paprosky and the AAOS acetabular defects classifications were assessed. According to Paprosky acetabular defects classification, there were eleven type I, two IIA, three IIB, nine IIC, seven IIIA and two IIIB. According to AAOS acetabular defects classification there were thirteen patients with type 1, nine patients with type 2, ten type 3 and two type 4. The percentage of own acetabular bone in contact with the new cup was recorded for each patient at the time of surgery and was 45 percent (range from 20 to 80 percent), with 23 patients presenting less than 50 percent of bone contact (mean 35 percent). Postoperatively, osseous integration was radiographically assessed. Functional results were evaluated according to the Harris Hip Score (HSS). The complications related to the implant were also recorded. Results: In all radiographic assessments performed at 3, 6 and 12 month postoperatively an integrated cup without signs of migration or osteolysis was observed. Four patients (11.8 percent) presented recurrent hip dislocation that required a revision surgery without further cup revision. The final clinical assessment was performed at a mean of 26 month after surgery (12-60) with a mean HHS of 91.8 points. Conclusion: Trabecular tantalum coated modular acetabular cups in acetabular revision surgery shows good short term clinical results even with acetabular defects greater than 50 percent. No cup loosening was observed in these series.

Objetivo: Evaluar los resultados clínicos a corto plazo de pacientes sometidos a cirugía de revisión acetabular utilizando cotilos modulares con superficie de metal trabecular de tantalio. Material y Métodos: Estudio retrospectivo-descriptivo de una serie consecutiva de 32 pacientes (34 caderas) sometidos a cirugía de revisión acetabular (23 mujeres, 9 hombres, edad promedio 70,7 años), seguimiento promedio 32 meses (12-60). Se clasifican los defectos acetabulares de acuerdo ala clasificación de Paprosky y de la AAOS. Según la clasificación de Paprosky de los defectos acetabulares, 11 pacientes tenían categoría I, 2 categoría IIA, 3 categoría IIB, 9 categoría IIC, 7 categoría IIIA y 2 categoría IIIB. Según la clasificación de la AAOS, 13 pacientes correspondieron a nivel 1, 9 pacientes a nivel 2, 10 a nivel 3 y 2 a nivel 4. Se registra el porcentaje de hueso propio acetabular en contacto con el nuevo cotilo de cada paciente que fue en promedio 45 por ciento (20-80 por ciento), presentándose en 23 caderas un porcentaje < 50 por ciento, el cual fue en promedio 35 por ciento. En el postoperatorio se evalúa la integración ósea mediante radiografías de pelvis. Se evalúan los resultados funcionales mediante el HHS (Harris Hip Score) y las complicaciones postoperatorias relacionadas con el implante. Resultados: En todas las radiografías postoperatorias realizadas a los 3, 6 y 12 meses se evidenciaba el cotilo integrado, sin signos de migración ni osteolisis. Cuatro pacientes (11,8 por ciento) presentaron luxaciones recidivantes de cadera, las cuales requirieron de una cirugía de revisión sin recambio del cotilo. La última evaluación clínica fue en promedio 26 meses tras la cirugía (12-60 meses) constatándose un HHS promedio de 91,8 puntos. Conclusión: El uso de cotilos modulares con revestimiento de metal trabecular de tantalio en cirugías de revisión acetabular presenta buenos resultados clínicos a corto plazo incluso en defectos óseos acetabulares superiores...