Osteotomy prior to total knee arthroplasty: optimizing limb alignment

Posttraumatic osteoarthritis (PTOA) of the knee often occurs following fractures of the proximal tibia, patella, and distal femur. Nonunion or malunion of tibial or femoral fractures can translate into extraarticular deformities, which can cause a mechanical axis deviation followed by abnormal mechanical forces on the articular surfaces. Not the malunion itself, but the severity of the deformity is usually the most important determinant of overall knee function and progression of PTOA. Many surgeons attempt to correct malalignment of the lower extremity during the knee replacement surgery. This, however, is successful only when the deformity is intraarticular in origin. Correcting an extraarticular deformity through total knee arthroplasty (TKA) often results in a compromised knee, in which the deformity is not entirely corrected and the prothesis is not perfectly aligned. Therefore, a staged osteotomy prior to knee reconstruction can be the solution, as it restores limb alignment and in turn, increases the longevity of the implant. In this article, Austin T. Fragomen, Professor of Clinical Orthopaedic Surgery at New York's Special Surgery Hospital, shares some general principles of restoring lower limb alignment issues by staged osteotomies in the setting of TKA, with a particular focus on extraarticular deformities.

Mapping extraarticular deformities: origin, location, and direction

Imaging evaluation of patients showing extraarticular malignments is invaluable and should include long leg hip-to-ankle x-rays in the AP and lateral planes. To evaluate the location and extent of deformity, several preoperative measurements must be performed in the coronal, sagittal, and axial planes (Table 1 and Figure 1). In the coronal plane, measuring mechanical axis deviation (MAD) will indicate whether the deformity is a valgus or varus [1]. Analysis of the lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and joint line convergence angle (JLCA) allows the surgeon to trace back the origin of the deformity to the tibia, femur, or inside the joint. Similarly, examination of the posterior distal femoral angle (PDFA) and posterior proximal tibial angle (PPTA) provides the surgeon with information about the degree of the deformity in the sagittal plane [1]. A key measurement is determining the center of rotation of angulation (CORA), which is the location where the anatomical axes of the bone proximal and distal to the deformity meet (Figure 1). CORA determines whether a deformity can be successfully corrected through a knee replacement, as the deformity location directly correlates with its impact on limb alignment. As demonstrated by Wolff et al [2], the closer to the knee the deformity is, the greater its effect in overall mechanical alignment is. CORA measurements are used to determine osteotomy planning.

Posttraumatic osteoarthritis (PTOA) of the knee often occurs following fractures of the proximal tibia, patella, and distal femur. Nonunion or malunion of tibial or femoral fractures can translate into extraarticular deformities, which can cause a mechanical axis deviation followed by abnormal mechanical forces on the articular surfaces. Not the malunion itself, but the severity of the deformity is usually the most important determinant of overall knee function and progression of PTOA. Many surgeons attempt to correct malalignment of the lower extremity during the knee replacement surgery. This, however, is successful only when the deformity is intraarticular in origin. Correcting an extraarticular deformity through total knee arthroplasty (TKA) often results in a compromised knee, in which the deformity is not entirely corrected and the prothesis is not perfectly aligned. Therefore, a staged osteotomy prior to knee reconstruction can be the solution, as it restores limb alignment and in turn, increases the longevity of the implant. In this article, Austin T. Fragomen, Professor of Clinical Orthopaedic Surgery at New York's Special Surgery Hospital, shares some general principles of restoring lower limb alignment issues by staged osteotomies in the setting of TKA, with a particular focus on extraarticular deformities.

Mapping extraarticular deformities: origin, location, and direction

Imaging evaluation of patients showing extraarticular malignments is invaluable and should include long leg hip-to-ankle x-rays in the AP and lateral planes. To evaluate the location and extent of deformity, several preoperative measurements must be performed in the coronal, sagittal, and axial planes (Table 1 and Figure 1). In the coronal plane, measuring mechanical axis deviation (MAD) will indicate whether the deformity is a valgus or varus [1]. Analysis of the lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and joint line convergence angle (JLCA) allows the surgeon to trace back the origin of the deformity to the tibia, femur, or inside the joint. Similarly, examination of the posterior distal femoral angle (PDFA) and posterior proximal tibial angle (PPTA) provides the surgeon with information about the degree of the deformity in the sagittal plane [1]. A key measurement is determining the center of rotation of angulation (CORA), which is the location where the anatomical axes of the bone proximal and distal to the deformity meet (Figure 1). CORA determines whether a deformity can be successfully corrected through a knee replacement, as the deformity location directly correlates with its impact on limb alignment. As demonstrated by Wolff et al [2], the closer to the knee the deformity is, the greater its effect in overall mechanical alignment is. CORA measurements are used to determine osteotomy planning.