RESUMO
STUDY DESIGN: Systematic review. OBJECTIVE: To describe the various definitions of PJK and PJF used in spinal deformity literature and their utility over time. SUMMARY OF BACKGROUND DATA: Proximal junctional kyphosis or failure (PJK/PJF) is among the most common complication after long-segment fusions, but there is no consensus on their definitions. This presents challenges in understanding risk factors, management, and prevention strategies. METHODS: A systematic literature review was performed on studies specifying a definition of PJK and/or PJF. PJK definitions were categorized as radiographic vs non-radiographic and data was collected on PJK criteria including threshold for proximal junctional angle (PJA), change in PJA, vertebra selection for PJA measurement, and follow-up timepoints. PJF definitions were categorized as structural failure, need for revision, symptomatic failure, and radiographic (angular). RESULTS: 359 studies defining PJK and/or PJF were identified. While 56% of studies used the definition PJA>10° and PJA change from baseline>10°, the remainder expressed significant heterogeneity with respect to criteria for magnitude of PJA and degree of PJA change. The most common vertebrae assessed were UIV/UIV+2 (74%) and most common minimum follow-up (mFU) listed was 2 years (60%). Mean FUs for studies varied considerably even in studies with the same mFU, from 2.1-8.9 years (2-year mFU) and 1.1-4.0 years (1-year mFU). PJF definitions were most commonly structural (58%) or defined as a need for revision (48%), with a much less common use of PJA thresholds (23%). CONCLUSIONS: The challenges faced in preventing proximal junctional complications are mired in the heterogenous groundwork by which PJK and PJF are defined. Most definitions of PJK use radiographic thresholds without consideration of clinical relevance and variations in individual alignment. Conversely, definitions of PJF are based on clinical criteria, which are often subjective. Future research should focus on understanding the mechanisms of PJK/PJF, as only then will we be able to accurately define and prevent these complications.
RESUMO
Lamellar bone that forms in moderate and severe osteogenesis imperfecta (OI) is composed of structurally irregular lamellae compared to those in control bone. OI and control cortical bone fragments were prepared for light microscopy in standardized fashion: decalcified, embedded in plastic, sectioned and stained with toluidine blue. Polarization light microscopy (PLM) was used to demonstrate and quantify bright and dark lamellar thicknesses in cortical bone fragments from 5 patients with moderate to severe OI in whom type I collagen structural/molecular defects were detected and in control bone from 5 patients. Rigid selection criteria identified lamellar regions for quantification. Thicknesses of bright and dark lamellae were measured manually at 20X magnification using a histomorphometric image analysis system. A method of automated thickness averaging was developed to determine lamellar thicknesses from PLM images to make measurement faster. Our study demonstrates, for the first time, that in OI bone from patients with type I collagen structural/molecular defects mean lamellar thickness measurements (along with the bright and dark lamellar thicknesses) were less than those in control bone by statistically highly significant differences. The mean value for bright lamellae was less than that for dark lamellae in both control and OI bone. The ratio of mean values for bright/dark lamellar thicknesses was the same in control and OI bone. The automated method obtained similar results to the manual method. Lamellar bone in moderate and severe OI with type I collagen defects is composed of thinner and less structurally regular lamellae than those in control bone. This finding indicates that lamellar thickness measurements can be helpful in assessing the effect of specific collagen and collagen-related mutations on OI bone synthesis and warrant inclusion in research and clinical histomorphometric assessments.