KNEE JOINT SHAPE, OSTEOPHYTES AND KNEE PAIN, WHAT'S THE CONNECTION

Purpose: Knee pain has been shown to be associated with knee deformities such as valgus deformity. Osteophytes are a common feature observed in radiographic steoarthritis (OA) and are thought to contribute to knee pain. DXA has not been previously utilised in large imaging studies of the knee due to the lower resolution than standard radiographs. In this study we applied statistical shape modelling (SSM)to high resolution knee DXA images from the UK Biobank (UKB) imaging enhancement study. We sought to investigate the relationship between knee pain and knee shape, and whether the presence of osteophytes contributes to this association. Methods: This work uses the UK Biobank resource, Access Application17295. Left knee DXA scans, obtained in a supine position using a GE-Lunari DXA, were identified from 2000 randomly selected UKB study participants, with equal numbers from both sexes. 20% of these images were specifically selected at random from participants self-reporting OA (not joint specific). A106-point template describing the distal femur, proximal tibia, tibial spines and tibial plateaus were manually applied using custom software (University of Manchester). The annotated images were transformed using the Procrustes Transform and subjected to Principal Component Analysis to generate a statistical shape model and orthogonal modes of variation. The modes of variation were standardised to a mean of 0 and expressed as standard deviations from the mean. Osteophytes were manually shaded using a custom tool and graded according the Nottingham Line Drawing Atlas on a scale of 0-5, with grades & gt or equal to 2 indicating the presence of a definite osteophyte. Self-reported knee pain of 3þmonths was assessed by questionnaire at a time of clinic attendance. Logistic regression was used to examine the relationship between the first 10 knee joint shape modes(KM01 - KM10, which explained 90% of variation in knee shape) and knee pain adjusting for age, sex, height and weight. OR is per SD unit change in score. Further adjustment was made in order to establish if knee shape vs knee pain associations were modified by the presence of osteophytes. Results: Complete data were available for 1996 participants after exclusions. The mean age of the cohort was 62.7 years (range 45-78years), with similar numbers of men (n¼997) and women (n¼999). 374participants (18.7%) reported knee pain for longer than three months.638 participants (31.9%) had osteophytes & gt or equal to grade 2 in at least one site and 81 participants (4.1%) had osteophytes at all four sites(medial & lateral femur and tibia). KM04 showed reduced odds of having knee pain [adjusted OR 0.82 (0.73,0.92) p&lt0.001] (Table 1). KM07showed a small increased risk of knee pain [OR 1.16 (1.03, 1.30), p¼0.01after adjustment]. KM04 shows several features including varus alignment, whereas KM07 mainly comprises valgus alignment with some medial joint space narrowing, together suggesting valgus alignment is associated with an increased risk of knee pain (Figure 1). We identified strong associations between KM04 and KMO7 and medial but not lateral osteophytes (Table 2). In keeping with this suggestion that osteophytes contribute to the relationship between knee shape and knee pain, individuals with osteophytes at all sites had a higher risk of experiencing knee pain [adjusted OR 5.15 (3.24,8.20) p&lt0.001], as did those with an osteophyte at any site (range 2.3-3.3; see Table 3). Furthermore, associations between KM04 and KM07 and knee pain were partially attenuated following further adjustment for medial osteophytes (Table 1).Conclusions: Using SSM applied to high resolution knee DXA scans, we were able to identify certain characteristics of knee shape which are associated with an increased risk of prevalent knee pain, including valgus alignment. In addition, knee shape was associated with medial osteophytes, which were also associated with knee pain, suggesting medial osteophytes contribute to the relationship between knee shape and knee pain. Further studies are planned, based on the 100,000 high resolution knee DXA images due to be available in UKB, to explore relationships between knee shape, osteophytes and pain, suggested by our results.