Automated fit assessment of intramedullary nail designs during insertion

Modern intramedullary nails, which are utilised for the treatment of bone fractures, need to be designed to fit the anatomy of the patient population. Traditional and recent semi-automated approaches for quantifying the anatomical fit between bones and nail designs suffer from various drawbacks. This thesis proposed an automated comprehensive nail design validation method. The developed software tool was utilised to quantify the anatomical fit of four commercial nail designs. Furthermore, the thesis demonstrated the existence of a bone-nail specific nail entry point. The developed method is of great benefit for the implant manufacturing industry as a nail design validation tool.

Comparison of extramedullary versus intramedullary referencing for tibial component alignment in total ankle arthroplasty.

BACKGROUND: The majority of total ankle arthroplasty (TAA) systems use extramedullary alignment guides for tibial component placement. However, at least 1 system offers intramedullary referencing. In total knee arthroplasty, studies suggest that tibial component placement is more accurate with intramedullary referencing. The purpose of this study was to compare the accuracy of extramedullary referencing with intramedullary referencing for tibial component placement in total ankle arthroplasty. METHODS: The coronal and sagittal tibial component alignment was evaluated on the postoperative weight-bearing anteroposterior (AP) and lateral radiographs of 236 consecutive fixed-bearing TAAs. Radiographs were measured blindly by 2 investigators. The postoperative alignment of the prosthesis was compared with the surgeon's intended alignment in both planes. The accuracy of tibial component alignment was compared between the extramedullary and intramedullary referencing techniques using unpaired t tests. Interrater and intrarater reliabilities were assessed with intraclass correlation coefficients (ICCs). RESULTS: Eighty-three tibial components placed with an extramedullary referencing technique were compared with 153 implants placed with an intramedullary referencing technique. The accuracy of the extramedullary referencing was within a mean of 1.5 ± 1.4 degrees and 4.1 ± 2.9 degrees in the coronal and sagittal planes, respectively. The accuracy of intramedullary referencing was within a mean of 1.4 ± 1.1 degrees and 2.5 ± 1.8 degrees in the coronal and sagittal planes, respectively. There was a significant difference (P < .001) between the 2 techniques with respect to the sagittal plane alignment. Interrater ICCs for coronal and sagittal alignment were high (0.81 and 0.94, respectively). Intrarater ICCs for coronal and sagittal alignment were high for both investigators. CONCLUSIONS: Initial sagittal plane tibial component alignment was notably more accurate when intramedullary referencing was used. Further studies are needed to determine the effect of this difference on clinical outcomes and long-term survivability of the implants. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Computer simulating a trial of a load-bearing implant: example of an intramedullary prosthesis

Computational modelling is becoming ever more important for obtaining regulatory approval for new medical devices. An accepted approach is to infer performance in a population from an analysis conducted for an idealised or ‘average’ patient; we present here a method for predicting the performance of an orthopaedic implant when released into a population—effectively simulating a clinical trial. Specifically we hypothesise that an analysis based on a method for predicting the performance in a population will lead to different conclusions than an analysis based on an idealised or ‘average’ patient. To test this hypothesis we use a finite element model of an intramedullary implant in a bone whose size and remodelling activity is different for each individual in the population. We compare the performance of a low Young’s modulus implant (View the MathML source) to one with a higher Young’s modulus (200 GPa). Cyclic loading is applied and failure is assumed when the migration of the implant relative to the bone exceeds a threshold magnitude. The analysis for an idealised of ‘average’ patient predicts that the lower modulus device survives longer whereas the analysis simulating a clinical trial predicts no statistically-significant tendency (p=0.77) for the low modulus device to perform better. It is concluded that population-based simulations of implant performance–simulating a clinical trial–present a very valuable opportunity for more realistic computational pre-clinical testing of medical devices.

Spontaneous intramedullary apoptosis is present in disorders other than myelodysplasia

Myelodysplastic syndrome (MDS) is a group of hematopoietic disorders characterized by peripheral cytopenias in the presence of normo- or hypercellular dysplastic marrow. It has been suggested that premature intramedullary apoptosis may contribute to this phenomenon. We used terminal dUTP nick-end labeling (TUNEL) of bone marrow biopsy specimens and cytocentrifuge preparations from patients with MDS and a variety of other hematopoietic disorders to determine whether there is increased intramedullary apoptosis in MDS and whether any such effect is specific to MDS. TUNEL labeling of bone marrow from 24 patients with MDS revealed significant positivity in 10 of 11 patients with refractory anemia (RA), five of seven with RA and excess of blasts (RAEB), all three patients with RAEB in transformation (RAEB-t), and all three patients with RA with ring sideroblasts (RARS). The percent of positive cells ranged from 5 to 50% but showed no apparent correlation with morphological subtype. In a series of 29 patients with acute leukemia, 17 showed significant positivity (13 of 13 with myeloid disease: three M1, seven M2, one M3, two M4; four of 16 patients with lymphoid disease: one Burkitt-type lymphoma, two null acute leukemia, and one common acute lymphoid leukemia). Intramedullary apoptosis was associated with myeloid or early committed progenitor cells and was highest in secondary acute myeloid leukemia (AML). Normal bone marrow samples from 12 individuals showed no evidence of apoptosis. Our results suggest that an increased level of intramedullary apoptosis is apparent in both patients with MDS and those with AML; those with secondary AML have the highest levels. The relative absence of such findings in lymphoid malignancy suggests that the apoptotic pathways are different in this lineage.

Propionibacterium acnes and Staphylococcus lugdunensis Cause Pyogenic Osteomyelitis in an Intramedullary Nail Model in Rabbits

Propionibacterium acnes and coagulase-negative staphylococci (CoNS) are opportunistic pathogens implicated in prosthetic joint and fracture fixation device-related infections. The purpose of this study was to determine whether P. acnes and the CoNS species Staphylococcus lugdunensis, isolated from an "aseptically failed" prosthetic hip joint and a united intramedullary nail-fixed tibial fracture, respectively, could cause osteomyelitis in an established implant-related osteomyelitis model in rabbits in the absence of wear debris from the implant material. The histological features of P. acnes infection in the in vivo rabbit model were consistent with localized pyogenic osteomyelitis, and a biofilm was present on all explanted intramedullary (IM) nails. The animals displayed no outward signs of infection, such as swelling, lameness, weight loss, or elevated white blood cell count. In contrast, infection with S. lugdunensis resulted in histological features consistent with both pyogenic osteomyelitis and septic arthritis, and all S. lugdunensis-infected animals displayed weight loss and an elevated white blood cell count despite biofilm detection in only two out of six rabbits. The differences in the histological and bacteriological profiles of the two species in this rabbit model of infection are reflective of their different clinical presentations: low-grade infection in the case of P. acnes and acute infection for S. lugdunensis. These results are especially important in light of the growing recognition of chronic P. acnes biofilm infections in prosthetic joint failure and nonunion of fracture fixations, which may be currently reported as "aseptic" failure. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

Biomechanical Performance of Flexible Intramedullary Nails With End Caps Tested in Distal Segmental Defects of Pediatric Femur Models

Background: Unstable distal femoral fractures in children are challenging lesions with restricted surgical options for adequate stabilization. Elastic nails have become popular for treating femoral shaft fractures, yet they are still challenging for using in distal fractures. The aim of this study was to test whether end caps (CAP) inserted into the nail extremity improved the mechanical stabilization of a segmental defect at the distal femoral metaphyseal-diaphyseal junction created in an artificial pediatric bone model. Methods: Two 3.5-mm titanium elastic nails (TEN) were introduced intramedullary into pediatric femur models, and a 7.0-mm-thick segmental defect was created at the distal diaphyseal-metaphyseal junction. Nondestructive 4-point bending, axial-bending, and torsion tests were conducted. After this, the end caps were inserted into the external tips of the nails and then screwed into the bone cortex. The mechanical tests were repeated. Stiffness, displacement, and torque were analyzed using the Wilcoxon nonparametric test for paired samples. Results: In the combined axial-bending tests, the TEN + CAP combination was 8.75% stiffer than nails alone (P < 0.01); in torsion tests, the TEN + CAP was 14% stiffer than nails alone (P < 0.01). In contrast, the 4-point bending test did not show differences between the methods (P = 0.91, stiffness; P = 0.51, displacement). Thus, the end caps contributed to an increase in the construct stability for torsion and axial-bending forces but not for 4-point bending forces. Conclusions: These findings indicate that end caps fitted to elastic nails may contribute to the stabilization of fractures that our model mimics (small distal fragment, bone comminution, and distal bone fragment loss).

[Intramedullary claw for stabilization of proximal humerus fractures: a comparison with other semirigid techniques]

Proximal humerus fractures (pHF) are common. In this retrospective study intra-operative and postoperative data and complications of patients stabilized with conventional semirigid techniques (pins, n=30; helix wire, n=19) or a novel semirigid technique, the intramedullary claw (IMC, n=82) were compared. The type and frequency of postoperative complications differed between the groups (p<0.001). The IMC is a novel semirigid technique to stabilize pHF and seems to result in fewer complications than pins or helix wire. The frequency and relevance of a loss of repositioning in patients after IMC implantation need to be elucidated in long-term studies.