Stability with a Constrained Posterior Stabilized Primary Total Knee Arthroplasty Does Not Compromise Durability.

Total knee arthroplasty (TKA) in cases of complex deformity (e.g., ligamentous laxity, posttraumatic arthritis) may require prostheses with inherent varus-valgus stability greater than that of traditional posterior stabilized or cruciate-retaining implants. Here, we investigate the clinical and radiographic outcomes of TKA using a midlevel constraint (MLC) prosthesis. A retrospective review of 53 patients (62 knees) who underwent primary TKA with an MLC implant was performed. Short tibial stem extensions were utilized in 49 knees, and 13 knees received no stem extension. Mean follow-up time was 31.6 months (standard deviation [SD] = 10.0, range = 24-53). Preoperative and postoperative range of motion (ROM) were assessed. Plain radiographs were reviewed for alignment, radiolucent lines, component loosening, and osteolysis. Patients who developed postoperative arthrofibrosis underwent manipulation under anesthesia (MUA). Failure was defined as instability, component loosening, or need for revision surgery. Mean ROM significantly improved from 114.1 degrees (SD = 19.7 degrees) preoperatively to 123.5 degrees (SD = 12.2 degrees) at final follow-up ( t  = -3.43, p  = 0.001). Thirty-seven knees initially presented with varus deformity (mean = 7.5 degrees, SD = 4.8 degrees), whereas 23 had valgus deformity (mean = 10.6 degrees, SD = 6.5 degrees), and 2 knees had neutral alignment. Following surgery, mean alignment was 4.3 degrees valgus (SD = 1.7 degrees, range = 0-8 degrees), representing a statistically significant improvement ( t  = 5.29, p  < 0.001). Six patients (9.7%) developed arthrofibrosis requiring MUA, which was irrespective of baseline ROM ( p  = 0.92) and consistent with 12% incidence reported in the literature. There were no significant differences in postoperative ROM ( t  = 0.38, p  = 0.71), alignment ( t  = -0.22, p  = 0.83), or incidence of arthrofibrosis (χ 2  = 0.07, p  = 0.79) between short-stemmed and nonstemmed implants. There was no radiographic evidence of radiolucent lines, component loosening, or osteolysis in any patients. No patients required revision surgery. Use of an MLC prosthesis with primary femoral component in TKA resulted in satisfactory clinical and radiographic results with no evidence of component loosening, osteolysis, instability, or need for revision at minimum 2-year follow-up.