Total Knee Arthroplasty Using the S-ROM Mobile-Bearing Hinge Prosthesis

Abstract: A retrospective study was performed on 15 patients receiving 16 S-ROM mobile-bearing hinge total knee prostheses that were evaluated with at least a 2-year follow-up (range, 27-71 months). Indications for its use included severe instability and bone loss. The average patient age was 63 years (range, 33-83 years). There were 15 revision arthroplasties and 1 primary arthroplasty. Knee Society scores showed notable improvement in pain, motion, and stability (33.6 preoperatively vs 76.5 postoperatively; P Ͻ .0001) and approached significant improvement in function (29.2 preoperatively vs 43.5 postoperatively; P ϭ .11). After excluding a patient with a traumatically ruptured patellar tendon, the probability of the latter comparison improved (P Ͻ .01). There was no evidence of loosening, and complete bone apposition was seen in nearly all cases. A high percentage of satisfactory results can be achieved when using this mobile-bearing hinge knee prosthesis for these indications. Key words: hinge knee arthroplasty, total knee arthroplasty, knee prosthesis, mobile-bearing knee, knee biomechanics. A hinge total knee prosthesis is valuable in the surgical management of failed total knee arthroplasties (TKAs) and nonresurfaced arthritic knees with marked instability or bone loss. Nearly all early hinge-type total knee prostheses used commonly from the 1950s through the 1970s had high rates of loosening and complications, however To eliminate complications associated with deleterious stresses in hinge total knee prosstheses, mobile-bearing tibiofemoral articulations were develope

The Circle-Fit Method Helps Make Reliable Cortical Thickness Measurements Regardless of Humeral Length

Background: Although proximal humerus strength/quality can be assessed using cortical thickness measurements (eg, cortical index), there is no agreement where to make them. Tingart and coworkers used measurements where the proximal endosteum becomes parallel, while Mather and coworkers used measurements where the periosteum becomes parallel. The new circle-fit method (CFM) makes 2 metaphyseal (M1-M2) and 6 diaphyseal (D1-D6) measurements referenced from humeral head diameter (HHD). However, it is unknown whether these locations correlate to humeral length (HL). Accordingly, we asked: (1) Does HHD, Tingart distance, and Mather distance correlate with HL? (2) What is the location of HHD, Tingart distance, and Mather distance as a percentage of HL? and (3) Which CFM D1-D6 locations correlate with Tingart and Mather distances? Materials and Methods: Measurements made on cortical thickness (CT) scout views of 19 humeri (ages: 16-73 years) included HHD, distances from the superior aspect of the humerus to proximal Tingart and Mather locations, and HL. Results: Intraclass correlation was excellent for CFM-HHD, poor for Tingart, and moderate for Mather. The CFM-HHD had a stronger correlation to HL than Tingart and Mather. Mean HHD was 15.5% (0.9%) of HL while Tingart was 27.0% (4.1%) and Mather was 23.2% (3.8%). Tingart distance corresponded to D2/D3 CFM locations while the Mather distance was similar to D1/D2. Discussion: The CFM reliably correlates with HL and provides a stronger correlation and less variance between specimens than the Tingart or Mather Methods. Conclusions: Because the CFM produces reliable percent of HL locations, it should be used to define locations for obtaining biomechanically relevant CT measurements such as cortical index. Stronger correlations of these CFM-based measurements with proximal humerus strength will be important for developing advanced algorithms for fracture treatment