319 EXTENDED REPORT Ann Rheum Dis: first published as 10.1136/ard.61.4.319 on 1 April 2002. Downloaded from Characterisation of size and direction of osteophyte in knee osteoarthritis: a radiographic study Y Nagaosa, P Lanyon, M Doherty ............................................................................................................................. Ann Rheum Dis 2002;61:319–324 Objectives: To examine the size and direction of osteophyte in knee osteoarthritis (OA) and to deter- mine associations between osteophyte size and other radiographic features. Methods: Knee radiographs (standing extended anteroposterior and 30 degrees flexion skyline views) were examined from 204 patients referred to hospital with symptomatic knee OA (155 women, 49 men; mean age 70, range 34–91 years). A single observer assessed films for osteophyte size and direction at eight sites; narrowing in each compartment; varus/valgus angulation; patellofemoral sub- luxation; attrition; and chondrocalcinosis using a standard atlas, direct measurement, or visual assess- ment. For analysis, one OA knee was selected at random from each subject. Results: Osteophyte direction at the eight sites was divisible into five categories. At all sites, except for See end of article for the lateral tibial plateau and the medial patella, osteophyte direction varied according to (a) the size authors’ affiliations of osteophyte and (b) the degree of local narrowing. At the medial femur, medial tibia, and lateral ....................... femur osteophyte direction changed from being predominantly horizontal to predominantly vertical Correspondence to: with increasing size. The size of osteophyte correlated positively with the severity of local narrowing, Professor M Doherty, except for the medial patellofemoral compartment where osteophyte size correlated positively with the Academic Rheumatology, severity of narrowing in the medial tibiofemoral compartment. Logistic regression analysis showed that University of Nottingham, osteophyte size was associated not only with local narrowing but also with local malalignment and Clinical Sciences Building, bone attrition, and that chondrocalcinosis was positively associated with osteophyte size at multiple City Hospital, Nottingham NG5 1PB, UK; sites. Michael.Doherty@ Conclusion: In patients referred to hospital with knee OA different patterns of osteophyte direction are nottingham.ac.uk discernible. Osteophyte size is associated with local compartmental narrowing but also local alignment Accepted 12 September and attrition. Chondrocalcinosis is associated with osteophytosis throughout the joint. These data sug- 2001 gest that both local biomechanical and constitutional factors influence the size and direction of osteo- ....................... phyte formation in knee OA. http://ard.bmj.com/ steoarthritis (OA) is the most prevalent form of knee osteophyte seen on radiographs. The present study arthritis.1 It shows a strong association with aging and aimed at (a) describing the size and direction of osteophyte in Oselective targeting of certain joints such as the knee.1 A the OA knees of a group of patients in hospital and (b) assess- variety of genetic, constitutional and environmental risk ing possible associations between osteophyte size and other factors for OA are recognised, which vary according to joint factors visible on standard knee radiographs that may site.2 The defining radiographic features of OA are (a) focal influence osteophyte growth. cartilage loss, resulting in “joint space narrowing” and (b) accompanying endochondral ossification at the joint margins on October 1, 2021 by guest. Protected copyright. that produces “marginal osteophyte”.13 PATIENTS AND METHODS Although osteophyte is viewed as a remodelling and Approval for the study was obtained from the local research reparative feature of OA, the factors that determine osteophyte ethics committee. formation and growth are unknown. Growth factors influence both chondrocyte synthesis and osteophyte formation in Patients and radiographs experimental joint damage,45and evidence from animal6 and Routine radiographs of patients seen for symptomatic knee human studies7–9 shows that cartilage damage initiates OA (new and follow up) over a nine month period in a hospi- “secondary” osteophyte growth. However, osteophyte may tal rheumatology clinic were examined for the study. No also develop as an isolated feature associated with age10 and patient had coexisting inflammatory arthropathy as deter- precede rather than follow cartilage loss in animal studies.11 mined by clinical inquiry, examination, and limited laboratory Joint instability has been emphasised as a biomechanical trig- and radiographic investigation. Radiographic knee OA was ger to osteophyte formation, with osteophyte and bone defined as the presence of joint space narrowing and remodelling being viewed as an attempt to stabilise and osteophyte in any knee compartment. No radiograph showing broaden the compromised joint to better withstand loading patellectomy or joint replacement was included. All radio- forces.12 13 Chondrocalcinosis due to calcium pyrophosphate graphs were obtained under standardised conditions and crystals has also been suggested to be associated with a included (a) weightbearing, full extension anteroposterior tendency to osteophyte formation and a “hypertrophic” form views (55 kV,8 mA/s, full scale deflection 100 cm; Kodak film) of OA.14 Possibly, therefore, multiple factors may influence and (b) skyline 30 degrees flexion views according to the osteophyte formation and contribute to the marked hetero- geneity of OA. Assessment of individual radiographic features is the main ............................................................. 15 16 outcome measure for evaluating structural changes in OA. Abbreviations: OA, osteoarthritis; PFJ, patellofemoral joint; TFJ, There is little information, however, on the morphology of tibiofemoral joint www.annrheumdis.com 320 Nagaosa, Lanyon, Doherty Ann Rheum Dis: first published as 10.1136/ard.61.4.319 on 1 April 2002. Downloaded from 13.2% 53.1% 12.9% 15.1% 58.0% 41.2% 25.0% 61.8% 2.7% 39.3% 33.3% 43.7% 6.7% 3.0% 2.0% 0.7% 25.9% 29.2% 3.4% 59.0% 9.0% 2.0% 8.4% 12.4% 73.1% 11.5% 42.7% 29.7% 63.4% 3.6% 14.3% 0.8% Figure 1 Direction of osteophyte at each site among 204 subjects. Size of arrow reflects frequency of direction. Osteophyte was seen in 93 subjects at the lateral femur, 112 at the lateral tibia, 101 at the medial femur, 101 at the medial tibia, 72 at the lateral patella, 60 at the lateral femoral trochlea, 68 at the medial patella, and 67 at the medial femoral trochlea. method of Laurin et al (60 kV,10 mA/s, full scale deflection 100 sex, body mass index), local narrowing, and any radiographic cm; Kodak film).17 feature found to associate on univariate analysis were included in the model. Radiographic assessment After an initial training period a single observer who was una- RESULTS ware of the patient details examined all the radiographs. For Radiographs of 204 patients (155 women, 49 men; mean age follow up patients with sequential knee radiographs, the ear- 70, range 34–91 years; median body mass index 28.4, range liest available knee films taken within the previous seven 19.1–50.8) were included in the study. Radiographs were of years, during which anteroposterior and skyline films were reasonable to good standard for contrast and alignment standardised, were used. (anterior and posterior margins of the medial tibial plateau Individual radiographic features were separately assessed were superimposed within 1 mm in 42% of knees). Within the for the lateral and medial tibiofemoral joints (TFJ) and lateral 198 patients with bilateral radiographic OA there was close and medial patellofemoral joints (PFJ). Joint space narrowing correlation between x ray findings in right and left knees for each compartment and osteophyte at each of six sites (lat- (ranges for correlation coefficient in different compartments: eral and medial femur, lateral and medial tibia, lateral and narrowing 0.55–0.72; osteophyte 0.44–0.62; attrition 0.34– medial aspect of the patella) were graded 0–3 according to a 0.59; chondrocalcinosis 0.73–0.81; all p<0.01). Six patients standard atlas.16 Although not included in any photographic had only one eligible knee, which was therefore selected for http://ard.bmj.com/ atlas, osteophytes at the lateral and medial femoral trochlea study (three unilateral patellectomy, two unilateral OA, one were given a similar 0–3 grading using a line drawing missing film). system.18 Osteophyte size was therefore graded at eight sites in each knee. The direction of osteophyte alignment at the eight Reproducibility sites was divided by visual inspection into five categories— Intraobserver reproducibility of grading (κ statistic) was gen- upward, upper middle, outward, lower middle, or downwards. erally good (joint space narrowing 0.77; osteophyte 0.71; Bone attrition (reduction in normal bone contour) and osteophyte direction 0.67; attrition 0.90; chondrocalcinosis chondrocalcinosis in the TFJ and PFJ were graded 0–1 0.66; patellar subluxation 0.80). Reproducibility of measure- on October 1, 2021 by guest. Protected copyright. (absent/present). Local alignment was assessed for both the ments for continuous variables (95% limits of agreement) was TFJ and PFJ. The femorotibial angle, an indicator of varus ±0.8 mm for medial joint space width and ±3° for femorotibial alignment, was measured on anteroposterior films to the angle. nearest 1° using a