Less gap imbalance with restricted kinematic alignment than with mechanically aligned total knee arthroplasty: simulations on 3-D bone models created from CT-scans

Abstract

Background and purpose — Mechanical alignment techniques for total knee arthroplasty (TKA) introduce significant anatomic alteration and secondary ligament imbalances. We propose a restricted kinematic alignment (rKA) protocol to minimize these issues and improve TKA clinical outcomes.Patients and methods — rKA tibial and femoral bone resections were simulated on 1,000 knee CT scans from a database of patients undergoing TKA. rKA was defined by the following criteria: independent tibial and femoral cuts within 5° of the bone neutral mechanical axis, with a resulting HKA within 3° of neutral. Imbalances in the extension space, flexion space at 90°, medial compartment and lateral compartment were calculated and compared with measured resection mechanical alignment (MA) results. 2 MA techniques were simulated for rotation using the surgical transepicondylar axis (TEA) and 3° to the posterior condyles (PC).Results — Extension space imbalances ≥ 3 mm occurred in 33% of TKAs with MA technique versus 8.3% with rKA (p < 0.001). Similarly, more frequent flexion space imbalance ≥ 3mm was created by MA technique (TEA 34% or 3° PC 15%) versus rKA (6.4%, p < 0.001). Using MA with TEA or PC, there were only 49% and 63% of the knees respectively with < 3 mm of imbalance throughout the extension and flexion spaces and medial and lateral compartments versus 92% using rKA (p < 0.001).Interpretation — significantly fewer imbalances are created using rKA versus MA for TKA. rKA may be the best compromise, by helping the surgeon to preserve native knee ligament balance during TKA and avoid residual instability, whilst keeping the lower limb alignment within a safe range.

Restricted Kinematic Alignment, the Fundamentals, and Clinical Applications

“…Simulating MA bone cuts on 1,000 knee CT scans, we found that MA results in many cases of gap asymmetries ( 8 , 9 ). Mediolateral imbalances of more than 3 mm were observed in 25 and 54% of varus and valgus knees, respectively.…”

“…Simulating MA bone cuts on 1,000 knee CT scans, we found that MA results in many cases of gap asymmetries (8,9). Mediolateral imbalances of more than 3 mm were observed in FIGURE 1 | Anatomic modification linked to mechanical alignment technique on the distal femur and proximal tibia.…”

Personalized alignment in total knee arthroplasty: current concepts

“…In extension, there were significantly fewer cases having an imbalance ≥ 3 mm with restricted KA (8.3%) versus MA (33%), and ≥ 5 mm with restricted KA (1.5%) versus MA (11%). With restricted KA, the percentage of knees with space imbalances inferior to 3 mm in both flexion and extension was 92% versus 63% with MA with posterior condylar reference and 49% with MA with trans epicondylar reference [ 37 ].…”

True Kinematic Alignment Is Applicable in 44% of Patients Applying Restrictive Indication Criteria—A Retrospective Analysis of 111 TKA Using Robotic Assistance

“…Currently, there is a lack of a clear definition of when (or how often) adjustments are needed, and for what patients or phenotypes. Furthermore, there are only very limited data on the consequences for the patient-in terms of alignment, stability, and outcome [8,9]. Additional to this, there now is the need for technological support of some sort to be able to (1) identify a situation that needs to be adapted, and (2) precisely transfer this plan to the patient [10].…”