Ultrasonography of the late-stage knee osteoarthritis prior total knee arthroplasty: comparison of the ultrasonographic, radiographic and intra-operative findings

Abstract

Purpose: Ultrasonography (US) of the knee is an emerging imaging technique to evaluate the osteoarthritis (OA) of the knee. To date, clinical examination followed the conventional radiographs (CR) have been deemed the gold standard for the diagnosis of the OA, but during the last decade the utility of the US on knee OA has been also studied vigorously. US can be applied to assess effusion, synovitis, osteophytes, menisci and the femoral cartilage of the knee joint. Moreover, it has been shown that US detects osteophytes more readily than CR and that the cartilage defects of the medial femoral condyle correlate well with joint-space narrowing seen on CR. The diagnostic performance of US on detecting osteoarthritic changes has been compared with magnetic resonance imaging (MRI) and arthroscopy: osteophytes, cartilage changes in the medial femoral condyle and medial meniscal extrusion can be reliably assessed by US as compared to MRI findings. Additionally, the positive findings on US are a strong indicator of arthroscopic degenerative changes; however, negative findings do not rule out osteoarthritic changes. Despite eager research, it is still unknown whether the weight-carrying joint spaces are visualized on US and how plausible the US findings are. The purpose of this study was to assess US findings on patients with late-stage knee OA undergoing total knee arthroplasty (TKA) and compare US findings to radiographic and intra-operative findings. Methods: 103 patients planned for TKA for late-stage OA of the knee were enrolled consecutively in this study during October 2016 and February 2017. The mean subject age was 69 years (range 47 to 84 years) and 36 % were males. 21 patients had bilateral TKA, so in total 124 knees were included in this study. Eventually, 57 knees underwent TKA. US of the knee was performed by a single radiologist: the presence of effusion, synovitis, osteophytes, femoral cartilage wear and meniscal pathology was documented. All patients underwent bilateral weight-bearing CR on the same day as the US examination. The knees were assessed by the same radiologist for osteophytes, joint space narrowing and KL grades. During the TKA, the corresponding intra-operative findings were documented by orthopedic surgeon. Results: When comparing the US findings with the intra-operative findings, US examination performed well. On the wearing of the cartilage of the femoral medial condyle the sensitivity, specificity, accuracy and positive predictive value were 92%, 50%, 88% and 94%, respectively. On the lateral condyle and the sulcus area, the sensitivities were 58% and 46%; the specificities were 76% and 84%; accuracies were 70% and 67%; and the positive predictive values were 55% and 71%, respectively. Concerning the evaluation of the osteophytes, the detection rate of the US was outstanding especially on the medial side: On the femoral medial condyle the sensitivity, specificity, accuracy and positive predictive value were 95%, 50%, 93% and 98%, respectively. On the femoral lateral condyle they were 93%, 27%, 75% and 78%, respectively. On the tibial medial condyle the sensitivity, specificity, accuracy and positive predictive value were 90%, 75%, 88% and 96%, respectively. On the tibial lateral condyle they were 65%, 76%, 72% and 59%, respectively. The sensitivities for detecting effusion and synovitis were also excellent, yielding a sensitivity of 97% and 97%, respectively. For the damage of the medial and lateral meniscus the sensitivities were 93% and 58%, respectively. When comparing US with CR - using the TKA findings as the gold standard – the detection rate of cartilage damage was in line with the radiographic findings: For the medial joint space, the sensitivities of the US versus CR were 92% and 92%, the specificities 50% and 67%, the accuracies 88% and 89%, and the positive predictive values were 94% and 96%. For lateral joint space, the US versus CR sensitivities were 58% and 42%, specificities 76% and 67%, accuracies 70% and 68%, and the positive predictive values 55% and 53%. On the detection of the osteophytes, US provided superior results to CR especially on the medial side: On the femoral medial condyle, the US versus CR sensitivities were 95% and 44%; on the femoral lateral condyle 93% and 24%; on the tibial medial condyle 90% and 76%; and on the tibial lateral condyle 65% and 70%, respectively. Conclusions: US can reliably assess the late-stage OA changes of the knee especially on the medial side. Our study shows excellent sensitivities for effusion, synovitis, osteophytes, cartilage damage and meniscal pathology. Furthermore, US yields superior detection of OA changes as compared to radiographs.