Press-fit acetabular cup fixation: Principles and testing

Total hip replacements restore pain-free mobility to approximately 200,000 patients in the U.S. each year [1]. A typical hip system comprises a metal alloy stem, a femoral head (ceramic or metal alloy), and a polyethylene acetabular cup fit into a metal alloy backing. A modular press-fit Morse taper is commonly used to attach the femoral head to the stem. There are also more recent designs that incorporate a second interface at the neck-stem junction (Figure 1). Increased modularity in total hip replacement design allows the surgeon to intraoperatively preserve patient anatomy such as leg length and femoral anteversion and better balance the surrounding soft tissue for optimal biomechanics. However, modularity also increases the number of mechanical junctions and interfaces in the device which may lead to complications such as corrosion, wear, and fracture.

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Good mid-term results with the trident peripheral self-locking cup: a clinical evaluation and migration measurement with EBRA

Archives of Orthopaedic and Trauma Surgery ◽

10.1007/s00402-020-03639-5 ◽

2020 ◽

Author(s):

Dietmar Dammerer ◽

Philipp Blum ◽

David Putzer ◽

Andreas Tscholl ◽

Michael C. Liebensteiner ◽

...

Keyword(s):

Trial Registration ◽

Inclusion Criteria ◽

Acetabular Cup ◽

Term Outcome ◽

Long Term Outcome ◽

Press Fit ◽

Medical Histories ◽

Migration Analysis ◽

Radiological Analysis

Abstract Introduction The most common cause of failure in total hip arthroplasty (THA) is aseptic loosening. Uncemented cup migration analysis by means of Einzel–Bild–Roentgen–Analyse (EBRA) has shown to be a good predictive indicator for early implant failure if the cup migrates more than 2 mm within 4 years after surgery. In this study, we performed a migration analysis of an uncemented peripheral self-locking (PSL) press-fit cup after 4 years follow-up. Materials and methods We retrospectively reviewed all patients who received a trident PSL press-fit cup at our department between 2004 and 2017. A total of 636 patients were identified. As inclusion criteria for radiological analysis, a minimum follow-up of 2 years was defined. We reviewed medical histories and performed radiological analysis using EBRA software. EBRA measurements and statistical investigations were performed by two independent investigators. Results A total of 149 cups in 146 patients (female 82; male 64) met our inclusion criteria. Mean age at surgery was 65 years (33–89). We found a significant improvement in the WOMAC score pre- to postoperative (p < 0.0001). EBRA migration analysis showed a mean total migration of 0.6 mm (0.0–8.2) over our follow-up period of 4 years. Of the investigated cups, 69.8% showed a migration rate smaller than 2 mm in the investigated follow-up. Conclusion The acetabular cup used in our study provides low migration at final follow-up. Therefore, a good long-term outcome can be expected for the PSL cup. Trial registration Trial registration number is 20181024-1875 and date of registration is 2018-10-24.

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Failure of an Uncemented Press-Fit Acetabular Cup in Primary Total Hip Arthroplasty

Hip International ◽

10.1177/112070000201200404 ◽

2002 ◽

Vol 12 (4) ◽

pp. 371-377 ◽

Cited By ~ 1

Author(s):

N. Rama Mohan ◽

P. Grigoris ◽

D.L. Hamblen

Keyword(s):

Femoral Stem ◽

Acetabular Cup ◽

Total Hip ◽

Press Fit ◽

Total Hip Replacements ◽

Locking Mechanism ◽

Hip Replacements ◽

The Mean ◽

Open Position ◽

Primary Total Hip Arthroplasty

We reviewed fifteen primary total hip replacements performed using the uncemented, non-porous coated press-fit AcSys Shearer Cup. A modular titanium straight femoral stem with a 32mm head was used in all cases. The mean age of the group containing five males and 10 females was 66 years. Eight cups have been revised for aseptic loosening at a mean of seven years and the remaining four cups are radiologically loose. At revision surgery none of the cups showed any evidence of bony ingrowth. Our 10-year results with this cup indicate an unacceptably high failure rate of 80%. Absence of bony ingrowth and the lack of a secure locking mechanism between the polyethylene liner and the metal shell are the most important causes of failure. The use of a 32mm diameter head and implantation of the cup in an open position contributed to this failure. Even though this cup is no longer manufactured, our experience suggests that all non-porous coated cups should be closely followed up.

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A hierarchy of computationally derived surgical and patient influences on metal on metal press-fit acetabular cup failure

Journal of Biomechanics ◽

10.1016/j.jbiomech.2012.03.026 ◽

2012 ◽

Vol 45 (9) ◽

pp. 1698-1704 ◽

Cited By ~ 9

Author(s):

S.G. Clarke ◽

A.T.M. Phillips ◽

A.M.J. Bull ◽

J.P. Cobb

Keyword(s):

Acetabular Cup ◽

Press Fit ◽

Metal On Metal

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Contact Mechanics Analysis and Initial Stability of Press-Fit Metal-on-Metal Hip Resurfacing Prostheses

World Tribology Congress III, Volume 2 ◽

10.1115/wtc2005-63337 ◽

2005 ◽

Author(s):

I. Udofia ◽

F. Liu ◽

Z. Jin ◽

P. Roberts ◽

P. Grigoris

Keyword(s):

Finite Element ◽

Contact Mechanics ◽

Bone Structure ◽

Hip Resurfacing ◽

Implant Stability ◽

Acetabular Cup ◽

Press Fit ◽

Initial Stability ◽

Metal On Metal

To ensure potential long-term stability and survivorship for metal-on-metal hip resurfacing prostheses, implant migration would need to be minimised to encourage bone in-growth. This study uses the finite element method to investigate the effects of the surgical press-fit procedure on the bearing and interfacial contact mechanics, and on the initial stability of a metal-on-metal (MOM) hip resurfacing prosthesis. The finite element models simulated the press-fit procedure using different amounts of interference between the cup-bone (1–2mm). The resurfacing prosthesis was implanted anatomically into a 3-D bone model. Resultant hip joint loads were applied to the model through muscle and subtrochanteric forces. Results showed that increasing the friction and the interference between the cup and bone resulted in significant reductions in the relative micromotion between the cup and bone. This would ensure the immediate post-operative stability of the acetabular cup and provide adequate conditions for potential long-term bone in-growth and implant stability. The contact mechanics at the bearing surfaces, which has a large effect on tribological performance, was found to be little affected by changes at the cup-bone interface. These findings are consistent with the general satisfactory short and medium-term clinical results of metal-on-metal hip resurfacing prostheses. This study suggests that interference, friction and a mechanically sound bone structure are important parameters to promote implant stability and support.

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Characterization of Acetabular Cup Insertion Forces in Cancellous Bone Proxy for Validation of an Invasive Sensing Model and Development of Automatic Prosthesis Installation Device: A Preliminary Study

Journal of Medical Devices ◽

10.1115/1.4049085 ◽

2020 ◽

Vol 15 (2) ◽

Author(s):

Kambiz Behzadi ◽

Jesse Rusk

Keyword(s):

Force Feedback ◽

Primary Stability ◽

The United States ◽

Assistive Technologies ◽

Medical Procedure ◽

Implant Stability ◽

Acetabular Cup ◽

Total Hip ◽

Press Fit ◽

Preliminary Study

Abstract Total hip replacement is a widespread medical procedure, with over 300,000 surgeries performed each year in the United States alone. The vast majority of total hip replacements utilize press fit fixation. Successful seating of the implant requires a delicate balance between inserting the implant deep enough to obtain sufficient primary stability, while avoiding fracture of bone. To improve patient outcomes, surgeons need assistive technologies that can guide them as to how much force to apply and when to stop impacting. The development of such technology, however, requires a greater understanding of the forces experienced in bone and the resulting cup insertion and implant stability. Here, we present a preliminary study of acetabular cup insertion into bone proxy samples. We find that as the magnitude of force on the acetabular cup increases, cup insertion and axial extraction force increase linearly, then nonlinearly, and finally plateau with full insertion. Within the small nonlinear zone, approximately 90% of both cup insertion and extraction force are achieved with only 50% total energy required for full seating, posing the question as to whether full seating is an appropriate goal in press-fit arthroplasty. For repeated impacts of a given energy, cup displacement and force experienced in bone (measured force profile—MFP) increase correspondingly and reach a plateau over a certain number of impacts (number of impacts to seating—NOITS), which represents the rate of insertion. The relationship between MFP and NOITS can be exploited to develop a force feedback mechanism to quantitatively infer optimal primary implant stability.

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Comparison of Test Setups for the Experimental Evaluation of the Primary Fixation Stability of Acetabular Cups

Materials ◽

10.3390/ma13183982 ◽

2020 ◽

Vol 13 (18) ◽

pp. 3982

Author(s):

Christian Schulze ◽

Danny Vogel ◽

Sina Mallow ◽

Rainer Bader

Keyword(s):

Test Methods ◽

Load Test ◽

Test Method ◽

Artificial Bone ◽

Acetabular Cup ◽

Acetabular Bone ◽

Press Fit ◽

Orthopedic Surgeons ◽

Fixation Stability

Sufficient primary fixation stability is the basis for the osseointegration of cementless acetabular cups. Several test methods have been established for determining the tilting moment of acetabular press-fit cups, which is a measure for their primary fixation stability. The central aim of this experimental study was to show the differences between the commonly used lever-out test method (Method 1) and the edge-load test method (Method 2) in which the cup insert is axially loaded (1 kN) during the tilting process with respect to the parameters, tilting moment, and interface stiffness. Therefore, using a biomechanical cup block model, a press-fit cup design with a macro-structured surface was pushed into three cavity types (intact, moderate superior defect, and two-point-pinching cavity) made of 15 pcf and 30 pcf polyurethane foam blocks (n = 3 per cavity and foam density combination), respectively. Subsequently, the acetabular cup was disassembled from the three artificial bone cavities using the lever-out and the edge-load test method. Tilting moments determined with Method 1 ranged from 2.72 ± 0.29 Nm to 49.08 ± 1.50 Nm, and with Method 2, they ranged from 41.40 ± 1.05 Nm to 112.86 ± 5.29 Nm. In Method 2, larger areas of abrasion were observed in the artificial bone cavity compared to Method 1. This indicates increased shear forces at the implant–bone interface in the former method. In conclusion, Method 1 simulates the technique used by orthopedic surgeons to assess the correct fit of the trial cup, while Method 2 simulates the tilting of the cup in the acetabular bone cavity under in situ loading with the hip resultant force.

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