Wear and corrosion debris generated from total hip replacements (THR) can cause adverse local tissue reactions (ALTR) or osteolysis, often leading to premature implant failure. The tissue response can be best characterized by histopathological analysis, which accurately determines the presence of cell types, but is limited in the characterization of biochemical changes (e.g. protein conformation alteration). Fourier transform infrared micro-spectroscopy imaging (FTIRI) enables rapid analysis of the chemical structure of biological tissue with a high spatial resolution, and minimal additional sample preparation. The data provides the most information through multivariate method carried out by hierarchical clustering analysis (HCA).

It is the goal of this study to demonstrate the beneficial use of this multivariate approach in providing pathologist with biochemical information from cellular and subcellular organization within joint capsule tissue retrieved from THR patients.

Joint capsule tissue from 2 retrieved THRs was studied. Case 1: a metal-on-polyethylene THR, and Case 2: a dual modular metal-on-metal THR. Prior to FTIRI analysis, tissue samples were formalin-fixed paraffin-embedded and 5μm thick microtome sectioned samples were prepared and mounted on BaF₂ discs and deparaffinized. FTIRI data were collected using high-definition transmission mode (pixel size: ∼1.1 μm²). Hyperspectral images were exported to CytoSpec V2.0.06 for processing and reconstruction into pseudo-color maps based on cluster assignments.

Case 1 exhibited a strong presence of lymphocytes and macrophages (Fig. 1a). Since the process of taking second derivatives reduces the half width of the spectral peaks, it increases the sensitivity toward detecting shoulders or second peaks that may not be apparent in the raw spectra (Fig. 1b). Thus, areas occupied by lymphocytes and macrophages can be easily distinguished providing a fast tissue screening method. Here, HCA was able to distinguish macrophages and lymphocytes based on the infrared response, even in areas where both occurred intermixed. (Fig. 1c) The tissue in direct proximity to cells had a slightly altered collagenous structure. Case 1 also exhibited multiple glassy, green particles which can typically observed around THRs that underwent taper corrosion (Fig. 2a). HCA image was able to visualize and distinguish large CrPO₄ particles, embedded within fibrin exudate rich areas, collagenous tissue without inflammatory cells, and a nearby area with a strong macrophage presence and some finer CrPO₄ particles (Fig. 2d). Moreover, this method can not only locate macrophages, but distinguish particle-laden macrophages depending the type of particles within the cells. In Case 2 (Fig. 3a), clustering results (Fig. 3 b&c) are consistent with the fact that different particle types are associated with MoM bearing surface wear (Co rich particles), corrosion of the CoCrMo taper junctions (Cr-oxides and –phosphate), fretting of Ti-alloy dual modular tapers (Ti-oxides, Ti alloy particles), and even suture debris, which all occurred in this case. Although details of debris types are not available, specifications are possible by coupling other techniques.

The results demonstrate that multivariate FTIRI based spectral histopathology is a powerful tool to characterize the chemical structure and foreign body response within periprosthetic tissue, thus providing insights into the biological impact of different types of implant debris.

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Little information is available regarding the demographic characteristics and outcomes of patients with periprosthetic joint infection (PJI) resulting from anaerobic organisms, especially in the knee joint.

We performed a retrospective cohort analysis of all cases of knee PJI that were treated at our institution during the period from 2005 through 2012.

Anaerobes were involved in 11 (13%) of 86 first-time episodes of knee PJI, and peptostreptococcus was the most commonly isolated pathogen (10 [91%] of the 11 episodes). The average age of patients was 70 years (range, 62 to 79) and women were more than men (7 vs. 4) to develop anaerobic PJI. Of the 11 episodes of anaerobic PJI, 8 (73%) were treated with 2-stage revision arthroplasty for chronic latent infection, and 3 (27%) with parenteral antibiotics for positive intraoperative culture. Those treating with 2-stage revision arthroplasty had average 21 months prosthetic age (range, 2 to 41), and 10 weeks interim period between stages (range, 7 to 14). The overall successful rate for treating anaerobic knee PJI was 90%, and 88% for chronic latent infection.

naerobic PJI represents a substantial proportion of all occurrences of knee PJI. Treating with resection of the prosthesis and subsequent reimplantation is associated with a favorable outcome for chronic latent infection.

Image-guided spine surgery requires registration between the patient anatomy and the preoperative computed tomography (CT) image. We have previously developed an accurate and robust registration technique for this application by using intraoperative ultrasound to acquire patient anatomy and then registering the ultrasound images to the CT images by aligning the posterior vertebral surfaces extracted from both modalities. In this study, we validate our registration technique across 18 vertebrae on three porcine cadavers.

We applied the ultrasound-registration technique on the thoracic and lumbar vertebrae of the porcine cadavers using both single sweeps and double orthogonal sweeps. For each sweep pattern at each vertebra, we also randomly simulated 100 different initial misalignments and registered each misalignment. The resulting registration transformations are compared to gold standard registrations to assess the accuracy and the robustness of the technique.

Orthogonal-sweep acquisition was found to be the sweep-pattern that performed the best and yielded a registration accuracy of 1.65 mm across all vertebrae on all porcine cadavers. It was found that the target registration errors (TRE) stay relatively constant with increasing initial misalignment and that the majority (82.7%) of the registrations resulted in TREs below the clinically recommended 2 mm threshold. In addition, it was found that the registration accuracy varies by the sweep pattern and the vertebral level, but neighbouring vertebrae tend to result in statistically similar accuracy.

We found that our ultrasound-CT registration technique yields clinically acceptable accuracy and robustness on multiple vertebrae across multiple porcine cadavers.