Current sonographic applications in orthopedics.

Until recently, few orthopedic indications for sonographic imaging have been widely accepted. Advances in technology and concerns about imaging costs are expanding the role of sonography in musculoskeletal conditions. In this pictorial essay we review normal musculoskeletal sonographic anatomy, selected current applications, and potential pitfalls.

Precision acromioplasty in arthroscopic subacromial decompression of the shoulder.

Arthroscopic techniques for subacromial decompression have been criticized for lack of precision in resecting the anterior acromial undersurface and evaluating the amount of bone resected. The goal of subacromial decompression is production of a flat undersurface for the acromion and acromioclavicular joint, thus enlarging the supraspinatus outlet and deterring impingement. Achieving this goal using the arthroscope requires preoperative evaluation of the acromial morphology, planning of the dimensions of bony resection, a reproducible acromioplasty method with intraoperative evaluation of the adequacy of resection, and postoperative confirmation of the resulting acromial shape. A precise technique for arthroscopic acromioplasty has been developed in the course of performing over 200 shoulder arthroscopies. This method adheres to conventional open surgical goals for bony resection and allows for reliable intraoperative evaluation of the result. Using this technique, over 90% good and excellent results may be achieved in treatment of stage II subacromial impingement syndrome.

The mechanical stability of various noncemented tibial components.

Four different porous-coated tibial prosthetic implants were tested for their mechanical stability following implantation into paired cadaver tibias: Porous Coated Anatomic (PCA), Miller-Galante, Whiteside, and Anatomic Modular Knee (AMK). Following implantation the test sample was loaded eccentrically over the medial tibial plateau at 40 cycles per minute for 300,000 cycles, using an MTS machine. This represents the number of steps taken by the average person in a six- to 12-month period. Load varied sinusoidally from 5 to 115 kg. Subsidence and lift-off of the tibial plate from its bony bed was recorded for each implant, using linear variable differential transformers. The greatest degree of mechanical stability was observed with the AMK design, which is secured to the bone bed using four peripherally placed 6.5-mm cancellous screws. No motion in excess of 100 micron was observed. The central-stemmed Whiteside design and the cortical screw fixated Miller-Galante designs provided slightly less stability, each demonstrating approximately 200 micron of lift-off on the unweighted side. The PCA design exhibited the greatest amount of micromotion with subsidence and lift-off displacements of 500 micron (0.5 mm).