Radiography and bone scintigraphy in osteoarthritis of the knee--comparison with MR imaging.

Purpose: Osteoarthritis (OA) is a multifactorial process affecting cartilage and subchondral bone. Traditionally, plain radiographs and eventually bone scintigraphy are used to establish the diagnosis, whereas MR imaging, as a sensitive instrument for early diagnosis, is less commonly used. Therefore, these methods have been compared in the format of a prospective study of knee OA.

Material and methods: Individuals aged 35-54 years with chronic knee pain have been identified. The prevalence of chronic knee pain was 15% (279/2,000). Within this group, both knees in 61 randomly chosen persons were examined with plain weight-bearing radiographs of the tibiofemoral joint (TFJ), standing axial radiographs of the patellofemoral joint (PFJ), and with bone scintigraphy. One knee (the most painful at inclusion in the study) in each person was examined with MR imaging on a 1.0 T imager.

Results and conclusions: Assessment of the minimal joint space (MJS) width in the p.a. view of the TFJ in weight-bearing examinations should be performed with equal weight on both legs and in semiflexion. The p.a. view of the TFJ and the axial view of the PFJ, as well as the MJS measurements in these views, were reproducible. MJS of 3 mm in the TFJ and MJS of 5 mm in the PFJ are limits in diagnosing joint-space narrowing (JSN) in the TFJ and the PFJ, respectively. There was a high prevalence of meniscal abnormalities within the narrowed compartments of the TFJ when compared with those that were not narrowed. With the presence of marginal osteophytes in the TFJ, there was a high prevalence of MR-detected cartilage defects in the same joints whether JSN (MJS < 3 mm) was present or not. No such relationship, independent of MJS, was found between marginal osteophytes and cartilage defects in the PFJ. The agreement between increased bone uptake and MR-detected subchondral lesion (increased signal in the STIR sequence) was good. The agreement between increased bone uptake and MR-detected osteophytes or cartilage defects was in general poor. Conventional radiography is inexpensive and readily available. With the increased knowledge about interpreting weight-bearing p.a. radiographs of the TFJ and standing axial radiographs of the PFJ, these examinations will, even in the future, be a valuable and competitive technique compared with a more expensive and sophisticated method such as MR imaging, when evaluating knee pain. Further studies have to be performed to evaluate whether MR imaging has the same ability as bone scintigraphy to predict the progression of the OA process in the knee joint.