No evidence of mid-flexion instability after robotic-assisted total knee arthroplasty as assessed by intraoperative pressure sensors

Purpose: Mid-flexion instability has been identified as a cause for dissatisfaction following total knee arthroplasty (TKA). Robotic-assisted surgery using the Mako robot only allows for assessment of stability at 10° and 90°. This study aimed to investigate any evidence of mid-flexion instability in Mako-assisted TKA. Methods: Data from 72 TKA in 59 patients from 2018 to 2022 were collected. All patients underwent an RA (Mako, Stryker, Fort Lauderdale, FL, USA), single-radius design, cruciate-retaining TKA. Intraoperatively, medial, and lateral pressures were measured at 10°, 45° and 90° of flexion using a pressure sensor (Verasense, OrthoSensor, 59 Inc., Dania Beach, FL, USA). The knee was considered balanced if the difference in pressures between compartments was less than 15 pounds-force (lbf). Results: There was no significant difference between the pressures measured in the medial compartment at 10°, 45° and 90° of flexion (P = 0.696). A statistically significant difference was found between the pressures measured in the lateral compartment at 10°, 45° and 90° of flexion, with the 10° value being significantly higher (P < 0.001), but this did not exceed the threshold of 15 lbf. None of the patients had a pressure difference of more than 15 lbf when pressures at 45° were compared to that at 10° and 90°, medially or laterally. Conclusion: This study showed no evidence of mid-flexion instability in Mako-assisted TKA, using a single radius, cruciate-retaining prosthesis whilst maintaining the joint height. Level of evidence: Level III retrospective cohort study.