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Imaging: The Basis for a Sound Decision in Joint Preservation
Introduction
Radiological assessment of the knee may provide a tremendous amount of information when proper radiographs are performed and a knowledge of patterns of wear are recognized. A standard series of digital radiographs that we perform at our center include a 54-inch anteroposterior (AP) axial alignment x-ray image (with radiographic markers for magnification), standing bilateral AP, 45-degree bent standing posteroanterior (PA) (Rosenberg views ), and a tangential patellar skyline view at 45 degrees supine. However, supine AP radiographs of the knee should not be performed because they are not useful in determining the cartilage joint space and hence the potential for joint-preserving surgery.
Patients sent to us with articular cartilage injuries have frequently had high-resolution MRI scans and arthroscopy photographs; however, they have never had standing x-rays to demonstrate that they have preexisting bone-on-bone osteoarthritis. Simple radiographs would give us the answers that these patients are not suitable for cartilage repair, based on their bone-on-bone changes; however, they may still be suitable for osteotomy or the possibility of unicompartmental replacement.
Radiological Patterns of Osteoarthritis
Advanced tricompartmental osteoarthritis (OA) is exceedingly rare unless there is advanced unicompartmental disease with tibiofemoral subluxation. Ahlbäck reviewed a Swedish population in the region of Stockholm and published his report in 1968. He reviewed approximately 1200 patients, 1800 knees reviewing weight-bearing radiographs from these patients. In reviewing a series for arthrosis, 281 patients were reviewed comprising 370 knees with joint space narrowing. Standing AP projections were taken but not PA projections, loading 20 degrees bent axial patellofemoral views, and supine lateral views. The following Venn diagrams were constructed depicting the wear patterns noted ( Fig. 3.1 ).
The predominance of arthritic wear patterns was in the medial and patellofemoral articulations in 80% of patients. However, because the lateral compartment usually wears posteriorly these numbers may have changed slightly if the standing PA views had been included. In any case, the Venn diagrams demonstrate that unicompartmental and bicompartmental wear is more common than tricompartmental wear. Total knee arthroplasty may therefore be an overly aggressive solution to osteoarthritis in a younger patient population. Cartilage repair, possibly combined with osteotomy or when bone-on-bone changes are present, unicompartmental or bicompartmental resurfacing arthroplasty may be more suitable in an attempt to preserve the joint for as long as possible.
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