Assessment of press-fit hip femoral components retrieved at autopsy

Anchoring and resulting primary stability of a kinked compared to a straight uncemented femoral stem

INTRODUCTION

The number of revision hip arthroplasties being performed is growing and implantation of a cementless stem has become established as the gold standard. For producing a primary stability, the press-fit procedure is the method of choice, but also can be achieved by multiple-point impactions. Specific femoral stems should follow the anatomical shape and provide a more extensive anchorage. The objective of this study was to evaluate the type, localization of the impaction and resulting primary stability of two different femoral revision stem designs (kinked vs. straight) after implantation via an endofemoral approach in the case of more extensive defects of the proximal femur.

MATERIALS AND METHODS

Cementless stems of two different designs were implanted in synthetic femurs. The specimens were analyzed by CT and tested considering axial/torsional stiffness and migration resistance in a servohydraulic testing machine.

RESULTS

The present data do not show any significant differences between the two endofemorally implanted conical stems in contact area or in biomechanics with regard to migration and axial or torsional stiffness, despite having different designs.

CONCLUSIONS

The location, type and length of the stem anchorage are not only influenced by the kinked or straight design, but in particular also by the surgical approach. Also in the case of an extensive proximal bone defect, in the endofemoral approach, both a conical and a three-point anchorage occur. Here, the length of the conical anchorage determines the primary stability and should be at least 55 mm.

In vivo biostability of polymeric spine implants: retrieval analyses from a United States investigational device exemption study

The Dynesys System for stabilizing the lumbar spine was first surgically implanted in Europe in 1994. In 2003, a prospective, randomized, investigational device exemption clinical trial of the system for non-fusion dynamic stabilization began. Polycarbonate urethane (PCU) and polyethylene terephthalate (PET) components explanted from four patients who had participated in the study were analyzed for biostability. Components had been implanted 9-19 months. The explanted components were visually inspected and digitally photographed. Scanning electron microscopy was used to analyze the surface of the spacers. The chemical and molecular properties of the retrieved spacers and cords were quantitatively compared with lot-matched, shelf-aged, components that had not been implanted using attenuated total reflection Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). FTIR analyses suggested that the explanted spacers exhibited slight surface chemical changes but were chemically unchanged below the surface and in the center. New peaks that could be attributed to biodegradation of PCU were not observed. The spectral analyses for the cords revealed that the PET cords were chemically unchanged at both the surface and the interior. Peaks associated with the PET biodegradation were not detected. GPC results did not identify changes to the distributions of molecular weights that might be attributed to biodegradation of either PCU spacers or PET cords. The explanted condition of the retrieved components demonstrated the biostability of both PCU spacers and PET cords that had been in vivo for up to 19 months.

Forearm bone-anchored amputation prosthesis: a case study on the osseointegration

BACKGROUND AND PURPOSE

Bone-anchored titanium implants have been used for anchorage of amputation prostheses for more than one and a half decades. Histo-logical and ultrastructural analyses were performed on a forearm amputation prosthesis after being in use for more than 11 years.

MATERIAL, METHODS AND RESULTS

The implant was retrieved from the ulnar bone after a fatigue fracture of the titanium implant, and was clinically stable at the time of removal. The histological findings showed a large amount of bone within the threads and a high degree of apposition of mineralized bone to the implant surface. Ultrastructural analysis of thin samples prepared by focused ion-beam microscopy revealed an electron-dense layer at the interface and direct apposition of crystalline hydroxyapatite at the implant surface.

INTERPRETATION

Our observations in this retrieval study provide a structural correlate to the functional properties and clinical results of amputation prostheses.

Hip and Knee Arthroplasty in the Geriatric Population

Osteoarthritis is the leading cause of hip and knee pathology in the geriatric population. Hip and knee arthroplasty are the definitive interventions to alleviate pain and restore physical functioning. Complications related to these procedures do occur: the most com-mon of these are infection, thromboembolism, dislocations, and periprosthetic fractures. New improvements related to minimally invasive and computer-assisted navigation surgery techniques are promising and already have shown excellent outcomes in patients exposed to joint arthroplasty.

[Principles of fixation of the cementless modular revision stem Revitan]

AIM AND METHOD

To analyse the femoral fixation of a modular cementless revision endoprosthesis, eight prosthetic combinations of the Revitan-System (Centerpulse, Winterthur, Switzerland) were implanted in four cadavers. On three cadavers a curved revision Revitan stem was implanted by an endofemoral approach on one side and by a transfemoral approach on the contralateral side. On the fourth cadaver a straight Revitan stem was implanted on one side and a curved Revitan stem on the contralateral side using a transfemoral approach. Transversal slides of 7-8 mm thickness were performed at the fixation areas of each implant and the implant-bone contact was analysed macroscopically and using contact radiography.

RESULTS

The straight stem implanted by a transfemoral approach showed a double-conical press-fit fixation with cutting of the eight longitudinal fins into the cortical bone. The curved revision stems implanted by the same approach had a circular surface fixation similar to the press-fit fixation of the straight stem. In contrast, the curved stems implanted by the endofemoral approach (without a window) showed a three-surface fixation. Hereby the two distal fixation areas led to the primary implant stability by three of the four double edges of the octagonal cross-sectional area cutting into the cortical bone. At the proximal fixation zone the implant only had contact of two implant double edges to the cortical bone.

CONCLUSION

Different approaches for implantation lead to different fixation techniques of a curved revision stem. This should be considered by analysing postoperative sintering rates of cementless revision stems.

Prospective evaluation of total hip arthroplasty with a cementless, anatomically designed, porous-coated femoral implant: mean 11-year follow-up

The performance of an anatomically designed femoral implant with porous titanium mesh coating was assessed in patients undergoing total hip arthroplasty. The stem, with built-in 12 degrees anteversion, was implanted in neutral position relative to the long axis of the femur through a cementless press-fit application. The only requirement was the presence of sufficient thickness within the cortical bone of the femoral metaphysis to support the stem. Ninety-one evaluable patients were followed up for a minimum of 10 years. Patients tolerated weight-bearing activity within 24 hours after surgery. Only 1 femoral component required revision because of loosening. Most patients showed uniform bony ingrowth. Quality of life was markedly improved. The anatomically designed, porous-coated implant provides robust performance which has general utility in a wide range of patients.

Comparison of proximal porous-coated and grit-blasted surfaces of hydroxyapatite-coated stems

BACKGROUND

It remains controversial whether a proximal porous coating is superior to a grit-blasted surface with regard to providing femoral stem fixation in total hip arthroplasty. We examined the hypothesis that a proximal porous coating would provide better fixation than would a fully grit-blasted surface of otherwise identical proximally hydroxyapatite-coated stems.

METHODS

In a prospective study, seventeen patients (thirty-four hips) underwent bilateral sequential total hip replacement with the Anatomic Porous Replacement at the same operation. A proximally porous-coated femoral stem was implanted on one side, and a stem of the same design but with a proximal grit-blasted surface was implanted in the contralateral hip. A proximal hydroxyapatite coating was applied to the metallic substrate of both stems. The patients were followed for a mean 2.5 years and then were assessed radiographically and clinically with the Harris hip score.

RESULTS

With the numbers available, no significant clinical or radiographic differences were found between the two cohorts. Thirty of the thirty-four hips had an excellent result, two were rated good, and two were rated fair. All hips had stable osseous fixation of the stem radiographically. The two types of stems were associated with the same pattern of adaptive bone-remodeling.

CONCLUSIONS

In the first two years following total hip arthroplasty, hydroxyapatite-coated proximally porous-coated femoral stems do not provide fixation that is superior to that provided by hydroxyapatite-coated grit-blasted stems.

LEVEL OF EVIDENCE

Therapeutic study, Level II-1 (prospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

Periprosthetic modelling of femoral component fit using computed tomography data for total hip arthroplasty: a feasibility study

The aim of the work was to create a new three-dimensional periprosthetic multi-criteria optimisation technique to identify the best six degrees of freedom transform to position a porous-coated anatomic cementless femoral component for three factors, including: first, maximisation of the degree of contact achieved between designated bone ingrowth surfaces and the periprosthetic bone; secondly, minimisation of the bone mass to be removed to accommodate the component and thirdly, the extreme constraint of the component to be positioned so that it does not project beyond the periosteum. Discrete integrals were computed over regions of interest derived from the polyhedral component mesh in transaxial CT scan planes, using a polygon scan-conversion algorithm. A new biomedical imaging volume rendering technique utilising dynamic virtual textures was developed to visualise the design trade-offs. Pareto-optima were identified for four femora that matched an average-sized component. The non-linear, multi-modal fit metric was quadratic near minima, with a narrow trough of equivalent fit values within 3mm of translation and 3 degrees of rotation with respect to the canal axis, and possessed a dependence most pronounced for distal-directed insertion against varus/valgus rotation. The study gives previously unavailable data on the three-dimensional femoral component fit and is the first report that demonstrates that fitting the implant using several design criteria in a multi-criteria optimisation scheme is feasible.