Abstract
ABSTRACTDefinite glenoid implant loosening is identifiable on radiographs, however, identifying early loosening still eludes clinicians. Methods to monitor glenoid loosening in vitro have not been validated to clinical imaging. This study investigates the correlation between in vitro measures and CT images. Ten cadaveric scapulae were implanted with a pegged glenoid implant and fatigue tested to failure. Each scapulae were cyclically loaded superiorly and CT scanned every 20,000 cycles until failure to monitor progressive radiolucent lines. Superior and inferior rim displacements were also measured. A finite element (FE) model of one scapula was used to analyze the interfacial stresses at the implant/cement and cement/bone interfaces. All ten implants failed inferiorly at the implant‐cement interface, two also failed at the cement‐bone interface inferiorly, and three showed superior failure. Failure occurred at of 80,966 ± 53,729 (mean ± SD) cycles. CT scans confirmed failure of the fixation, and in most cases, was observed either before or with visual failure. Significant correlations were found between inferior rim displacement, vertical head displacement and failure of the glenoid implant. The FE model showed peak tensile stresses inferiorly and high compressive stresses superiorly, corroborating experimental findings. In vitro monitoring methods correlated to failure progression in clinical CT images possibly indicating its capacity to detect loosening earlier for earlier clinical intervention if needed. Its use in detecting failure non‐destructively for implant development and testing is also valuable. The study highlights failure at the implant‐cement interface and early signs of failure are identifiable in CT images. © 2018 The Authors. Journal of Orthopaedic Research ® Published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res 36:2524–2532, 2018.
Highlights
A study investigating total shoulder arthroplasty outcomes (TSA) found loosening to be the most common complication.[1, 2] This has been confirmed by other recent studies[3, 4] and has accounted for up to 44 % of glenoid implant failures.[5]
Even when identifying definite loosening, a study on failed TSA found 85 % of retrieved glenoid implants that were definitely loose were identified from the radiographs[9], which indicates an under estimation of the loosening problem
Inferior rim displacement and vertical head displacement both increased with observed failure (Figure 7)
Summary
A study investigating total shoulder arthroplasty outcomes (TSA) found loosening to be the most common complication.[1, 2] This has been confirmed by other recent studies[3, 4] and has accounted for up to 44 % of glenoid implant failures.[5]. The majority of radiolucent lines have been identified in the inferior region of the implant, possibly indicating glenoid loosening and a mechanical weakness inferiorly.[6,7,8] Radiographs are fairly accurate when identifying advanced stages of loosening, which is defined by a visible shift of the implant or a radiolucent line encompassing the entire implant fixation, commonly referred to as ‘definitely loose’.[5]. Early loosening stages are ambiguous in radiographs and impossible to define accurately. Even when identifying definite loosening, a study on failed TSA found 85 % of retrieved glenoid implants that were definitely loose were identified from the radiographs[9], which indicates an under estimation of the loosening problem
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