A Comparison of Three Different Methods of Measurement of Knee Deformity in Osteoarthritis

The recognition of the pattern and severity of deformity in knee osteoarthritis has important implications in its management and prognosis. A number of methods can be used to assess and measure the coronal and sagittal knee alignment: clinical deformity measuring device like a goniometer, standard knee radiographs, hip-knee-ankle (HKA) radiographs, computer navigation systems, magnetic resonance scan, computerized tomographic scan or simply a surgeon’s subjective measurement. Each of these methods has advantages and disadvantages. The aim of this study was to compare three methods of measurement: clinical measurement with a goniometer; HKA radiographs and computer navigation. This study included 54 patients with arthritic knees, who underwent total knee replacement with computer navigation. The deformity in both coronal and sagittal planes was measured using the three methods and the results compared using Bland Altman limits of agreement. The clinical measurement differed greatly from radiographic and computer navigation measurements. According to Bland Altman limits of agreement clinical measurements could be up to 10° away from the radiographic or computer navigated measurements in coronal plane. In the sagittal plane the clinical measurements could be up to 12° away compared to computer navigation measurements. A combination of these measurements methods should be taken into account when assessing the deformity of a knee especially in relation to posture and weight bearing status. The methodical clinical measurement of knee deformity as described in this paper gives too wide a margin of error and should not be relied upon in isolation. Introduction The recognition of the pattern and severity of deformity in knee osteoarthritis has important implications in its management and prognosis [1-5]. A number of methods can be used to assess and measure the coronal and sagittal knee alignment: clinical deformity measuring device like a goniometer; standard knee radiographs; hip-knee-ankle (HKA) radiographs; computer navigation systems and computerized tomographic scan (CT scan) [5-10]. CT scans can is also be used to assess rotational alignment [11-13]. However many of these modalities are not yet widely available and most surgeons rely on simple clinical assessment and standard knee radiographs. There is evidence in the literature showing that standard short knee radiographs are not sufficient to accurately assess knee alignment [14,15]. There is some suggestion that clinical anatomic axis measurement correlates well with radiographic mechanical axis [6], however in our experience clinical assessment may be inaccurate and can give an incorrect impression of the true deformity pattern. In our practice image-free computer navigation is used routinely for knee replacement and all patients have preoperative and post-operative coronal hip-knee-ankle radiographs. The aim of this study was to compare clinical measurements of knee deformity in osteoarthritis to both hip-knee-ankle radiographs and computer navigation measurements and to assess whether pre-operative clinical measurements provided useful information to enable the surgeon to plan the operation accurately. Materials and Methods The study was conducted under our institution’s Clinical Governance procedures for prospective audits. Patients with osteoarthritis in knee, admitted for primary total knee replacement with computer navigation in our institute under care of senior author were included in the audit. Those with previous surgery on the knee were excluded. Knee deformity was measured in 54 osteoarthritic knees who had been admitted for primary total knee replacement surgery. Clinical measurements, HKA radiographs and computer navigation measurements were used to assess the deformity. The coronal and sagittal plane deformity were evaluated using clinical and computer navigation measurements. On the radiographs only the coronal plane deformity was measured. Clinical measurements Clinical measurement was done on the day of admission. The patient was adequately exposed from the waist down. He/she was then asked to assume usual stance to avoid excessive limb rotation. For coronal plane measurement, surface landmarks were used to identify the hip, knee and ankle centers. The midpoint between the anterior superior iliac spine and the pubic tubercle was marked as the hip center [16] (Figure 1). The center of the knee was marked as the point between the Received Date: December 09, 2015, Accepted Date: January 18, 2016, Published Date: January 26, 2016. *Corresponding author: Kamal Deep, Department of Orthopedics, Golden Jubilee National Hospital, Agamemnon Street, Clydebank, United Kingdom, G81 4DY, Tel: 441-419-515-414; Fax: 441-419-515-081; E-mail: kamal.deep@gjnh.scot.nhs.uk Figure 1: Clinical measurement was done with reference to the hip centre surface landmark between the anterosuperior iliac spine and the pubic tubercle.