Custom total knee arthroplasty facilitates restoration of constitutional coronal alignment

Abstract

Purpose To describe a strategy for coronal alignment using a computed tomography (CT) based custom total knee arthroplasty (TKA) system, and to evaluate the agreement between the planned and postoperative Hip-Knee-Ankle (HKA) angle, Femoral Mechanical Angle (FMA) and Tibial Mechanical Angle (TMA). Methods From a consecutive series of 918 primary TKAs, 266 (29%) knees received CT-based posterior-stabilized cemented custom TKA. In addition to a preoperative CT-scan, pre-and post-operative radiographs of weight-bearing long leg, anterior-posterior and lateral views of the knee were obtained, on which the FMA, TMA and HKA angles were measured. CTbased three-dimensional (3D) models enabled to correct for cases with bony wear by referring to the non-worn areas and to estimate the native pre-arthritic angles. The alignment technique aimed to preserve or restore constitutional alignment (CA) within predetermined limits, by defining a 'target zone' based on three criteria: 1) a ± 3° (range 87°-93°) primary tolerance for the femoral and tibial resections; 2) a ± 2° secondary tolerance for component obliquity, extending the bounds for FMA and TMA (range 85°-95°); 3) a planned HKA angle range of 175°-183°. Agreement between preoperative, planned and postoperative measurements of FMA, TMA and HKA angle were calculated using intra-class correlation coefficients (ICC). Results Preoperative radiograph and CT-scan measurements revealed that, respectively, 73 (28%) and 103 (40%) knees were in the 'target zone', whereas postoperative radiographs revealed that 217 (84%) TKAs were in the 'target zone'. Deviation from the planned angles were − 0.5° ± 1.8° for FMA, − 0.5° ± 1.8° for TMA, and − 1.1° ± 2.1° for HKA angle. Finally, the agreement between the planned and achieved targets, indicated by ICC, were good for FMA (0.701), fair for TMA (0.462) and fair for HKA angle (0.472). Conclusion Using this strategy for coronal alignment, 84% of custom TKAs were within the 'target zone' for FMA, TMA and HKA angles. These findings support the concepts of emerging personalized medicine technologies, and emphasise the importance of accurate strategies for preoperative planning, which are key to achieving satisfactory 'personalised alignment' that can further be improved by customisation of implant components. Level of evidence IV.

New Technologies in Knee Arthroplasty: Current Concepts

“…Currently, few studies have reported the results of customized implants for TKA. Interesting results have been described in implant positioning and limb alignment [ 16 , 17 , 18 , 19 ]. In a cohort of 258 custom TKAs, Bonnin et al have reported that 84% of TKA had satisfactory mechanical femoro-tibial axis (HKA), mechanical femoral axis (FMA), and mechanical tibial axis (TMA) [ 16 ].…”

“…Interesting results have been described in implant positioning and limb alignment [ 16 , 17 , 18 , 19 ]. In a cohort of 258 custom TKAs, Bonnin et al have reported that 84% of TKA had satisfactory mechanical femoro-tibial axis (HKA), mechanical femoral axis (FMA), and mechanical tibial axis (TMA) [ 16 ]. Deviation between the planned and postoperative angles was −0.5° ± 1.8° for FMA, −0.5° ± 1.8° for TMA, and −1.1° ± 2.1° for HKA angle.…”

“…Nevertheless, the use of customized implants does not take into account ligament balancing, and so ligament balancing remains dependent on the surgeon’s intraoperative assessment. Bonnin et al described 46% of tibial bone recuts in 258 custom TKAs [ 16 ]. Moreover, the preoperative planning is performed using imaging of an arthritic knee to restore a knee to pre-arthritic function.…”

Clinical and Radiological Outcomes after Knee Arthroplasty with Patient-Specific versus Off-the-Shelf Knee Implants: A Systematic Review

“…Another PSI manufacturer Symbios (Yverdon-les-bains, Switzerland), which has not yet been included in comparative studies because of its quite recent entry on the market, applies a recently developed individualised alignment strategy. It is based on the restricted phenotype alignment, which allows a better reproduction of the patient-specific limb alignment in addition to the individual knee morphology [ 44 ]. Combining a patient-specific implant with a more individualised alignment strategy seems promising; however, long-term studies assessing the impact of this alignment on the clinical outcome are still lacking.…”

Customised, individually made total knee arthroplasty shows promising 1-year clinical and patient reported outcomes

“…After assessment of cartilage wear, subchondral bone loss and location of osteophytes of the femur and tibia, the engineer determines in a best-fit scenario the individual femoral J-curves. The ORIGIN ® realignment strategy is a personalised postoperative alignment according to the restricted phenotype alignment protocol, which aims to reproduce the individual coronal knee phenotype in the limits of a safe target zone [ 15 ]. The tibial baseplate is asymmetric to fit the native tibial plateau and the angle of the tibia keel is adapted to the metaphysis [ 16 ].…”