A novel way of quantifying bone defect in primary total knee replacements using plain radiographs

Bone defect assessment in primary advanced knee arthritis can present a challenge for the surgeon and lead to unfavourable outcomes if not adequately determined during preoperative planning. The aim of this study was to introduce a new, simple and quick way to assess and quantify bone defect using short film radiographs and utilising it to choose the total knee prosthesis. This is a prospective case series of patients who underwent TKA (Total Knee Arthroplasty) using various types of prostheses. Three different angles - Tibiofemoral angle, MPTA (medial proximal tibial angle), and JLCA (joint line convergence angle) - were measured preoperatively to evaluate limb alignment, placement of the tibial, and femoral components of total knee prosthesis. Postoperatively roentgenographic index introduced by Lotke et al was used to assess our preoperative methodology. The American knee society score was used pre- and postoperatively up to one year. A total of eight knees of six patients were analysed (four males, two females). The mean age of the patients was 57.75±5.701 years. All the knees were in varying degrees of varus deformity preoperatively. The accuracy of the preoperatively used radiological angles was analysed by postoperative measurement of tibiofemoral angle (d), tibial anatomical axis (b) and femoral anatomical axis (a), and Roentgenographic index as suggested by Lotke et al. Postoperatively, all the knees were in valgus with tibiofemoral angle (d) 6.50±0.926, tibial component alignment (b) mean was 89±1.195, and femoral component alignment (a) mean was 5.13±0.991 valgus. Mean roentgenographic index was 89.38±3.292. American knee society score improved at one-year follow-up postoperatively and was statistically significant with p<0.001. In this study, a new classification for bone defects in primary arthritic knees by utilising simple plain radiograph short films and as a guide for implant selection is proposed.