Mikael Sundfeldt

Aseptic loosening, not only a question of wear: A review of different theories

Today, aseptic loosening is the most common cause of revision of major arthroplasties. Aseptic loosening accounts for more than two-thirds of hip revisions and almost one-half of knee revisions in Sweden. Several theories on the cause of aseptic loosening have been proposed. Most of these theories, however, are based on empiric observations, experimental animal models or anecdotal cases. In this review, we discuss the most common theories concerning aseptic loosening. It emerges from this review that aseptic loosening has a multifactorial etiology and cannot be explained by a single theory.

Effect of submicron polyethylene particles on an osseointegrated implant: an experimental study with a rabbit patello-femoral prosthesis.

In a rabbit model of a weight bearing, articulating prosthetic joint we repeatedly injected submicron particles of Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) produced in a hip simulator. The contralateral knee with the same prosthesis was injected with carrier (NaCl) without UHMWPE. Histomorphometrical studies on undecalcified cut and ground sections at 26 and 42 weeks involved quantifications of the entire bone to metal contact and the bone area around each implant. We found no statistically significant differences between test and control groups, and the UHMWPE debris did not induce any significant osteolysis, indicating that an osseointegrated implant with a sealed interface may not be affected by UHMWPE debris or progress to aseptic loosening.

Does sodium fluoride in bone cement affect implant fixation. Part II: evaluation of the effect of sodium fluoride additions to acrylic bone cement and the fixation of titanium implants in ovariectomized rabbits.

Bone integration of threaded implants made of cured polymethylmethacrylate containing sodium fluoride or commercially pure (c.p.) titanium were studied in normal and estrogen deficient New Zealand white rabbits. Nine had been ovariectomized through laparoscopy and nine served as controls. Four weeks after the ovariectomy two threaded implants made of cured bone cement with or without sodium fluoride addition were inserted in each tibia. One threaded commercially pure titanium implant was inserted in each patello–femoral joint flush to the cartilage. Six weeks after implant insertion measurement of the peak removal torque necessary to loosen the implants and light microscopical histomorphometrical investigations of tissue integration were performed. In the ovariectomized rabbits addition of sodium fluoride to the cement resulted in increased area of bone in the threads (p=0.04), but no corresponding effect could be noted in the controls. The removal torque was lower in the ovariectomized rabbits compared to the non-ovariectomized when comparing implant with sodium fluoride addition (p=0.02). The bone tissue response and the removal torque of the titanium implants were not influenced by ovariectomy in these rabbits. ©2002 Kluwer Academic Publisher

Does sodium fluoride in bone cement affect implant fixation? Part I: Bone tissue response, implant fixation and histology in nine rabbits

The addition of sodium fluoride to poly (methyl-methacrylate) (PMMA) bone cement may theoretically improve the fixation of joint replacement. This hypothesis was tested in an animal model using nine mature healthy lop-eared rabbits. A femoral prosthesis was inserted in both knees to resurface the patellofemoral articulation. The same acrylic cement, with and without sodium fluoride, was randomised between the two sides for prosthetic fixation. Two screw shaped implants machined from cured rods of either cement were also inserted bilaterally into the proximal tibia. Qualitative and quantitative histomorphometry of the bone tissue response surrounding the cement in the femur and the intact tibial implants revealed similar results regardless of sodium fluoride addition. Six weeks after surgery removal, torque did not significantly differ between the two sides. Our findings indicate that addition of sodium fluoride to PMMA has little effect on implant stability and bone remodeling in rabbits in the short-term.

High reliability in classification of tibia fractures in the Swedish Fracture Register

INTRODUCTION The Swedish Fracture Register (SFR) was started in 2011 and registers fractures of all types, treated either surgically or non-surgically. Twenty-six orthopaedic departments in Sweden are affiliated and a total of 84,000 fractures have been registered. The physician who establishes the diagnosis of the fracture registers and classifies it according to the AO/OTA classification. The accuracy of the classification of fractures is important for the reliability of the data in the SFR. This study aimed to evaluate how accurate the classification of tibia fractures in the register is. METHODS Three experienced trauma surgeons (raters) were presented with the radiographs of 114 patients with tibia fractures randomly allocated from the SFR. The raters classified the fractures independently and blinded to clinical patient information in two classification sessions with a time interval of one month. The AO/OTA classification coded by the three expert raters (our predefined gold standard) was compared with the classifications in the SFR. Inter- and intra-observer agreement was evaluated. The degree of agreement was reported using the approach of Landis and Koch. RESULTS The accuracy of the SFR, defined as agreement between the SFR and the gold standard classification, was kappa=0.75 for the AO/OTA type and 0.56 for the AO/OTA group, corresponding to substantial and moderate agreement, respectively. Inter-observer agreement across the three expert raters was kappa=0.74 for the AO/OTA type and 0.53 for the AO/OTA group. Intra-observer agreement was kappa=0.74-0.79 for the AO/OTA type and 0.62-0.64 for the AO/OTA group. CONCLUSION This study shows that the accuracy of classification of tibia fractures in the SFR was substantial for the AO/OTA type (kappa=0.75) and moderate for the AO/OTA group (kappa=0.56) as defined by Landis and Koch. This degree of accuracy is similar to that in previous studies. We interpret this as meaning that the results of this study demonstrate the high reliability of the data in the SFR and enable the SFR to be used for further scientific analysis.

Epidemiology and incidence of tibia fractures in the Swedish Fracture Register

INTRODUCTION There is a lack of epidemiological studies of fractures in all segments of the tibia classified by orthopaedic surgeons according to the AO/OTA classification. Since 2011, the Swedish Fracture Register (SFR) has provided prospectively collected, population-based data on fractures of all types, treated both surgically and non-surgically. The aim of this study was to describe the epidemiology and incidence of fractures in all segments of the tibia in a cohort of consecutive tibia fractures over a period of five years at Sahlgrenska University Hospital, Gothenburg, Sweden. METHODS Information on age, gender, date and mechanism of injury, fracture classification according to AO/OTA, affected side and high- or low-energy trauma was extracted from the SFR for all patients, aged 16 years and above, with tibia fractures treated at Sahlgrenska University Hospital, Gothenburg, during the five-year period 1 January 2011 to 31 December 2015. RESULTS 1325 patients sustained 1371 tibia fractures. There were 712 proximal tibia fractures, 417 tibial shaft fractures and 242 distal tibia fractures. Patients with proximal tibia fractures had a higher mean age (54.3) and 58% were women, whereas patients with shaft and distal fractures had a slightly lower mean age (47.0 and 48.7 respectively) and a dominance of men (59% and 54% respectively). The overall incidence of tibia fractures was 51.7 per 100,000 and year. The incidence of proximal, diaphyseal and distal tibia fractures was 26.9, 15.7 and 9.1 respectively per 100,000 and year. Among women, tibia fractures showed an increasing incidence with age in all segments, whereas men had a fairly flat incidence curve, except for tibial shaft fractures, which displayed a peak among young males. The incidence of tibia fractures and graphs for age-specific incidence for each segment of the tibia are presented. CONCLUSIONS This study describes the epidemiology and incidence of fractures in the whole of the tibia classified by orthopaedic surgeons according to the AO/OTA classification.