Imageless robotic-assisted total knee arthroplasty allows intra-articular correction of severe extra-articular deformities using functional alignment and desired under-correction.

Purpose: Managing knee arthritis with an associated extra-articular deformity (EAD) by total knee arthroplasty (TKA) is technically demanding. Intra-articular correction of EAD often requires extensive soft tissue release, which can be challenging. This study evaluates whether imageless robotic assisted TKA facilitates intra-articular correction using functional alignment and desired under-correction of severe EAD. Additionally, we assess the short-term functional and radiological outcomes in these patients.

Patients and methods: We prospectively reviewed 14 consecutive patients with knee osteoarthritis and angular EAD of the femur or tibia due to malunited fractures who underwent robotic-assisted TKA between November 2022 and April 2024. Ten patients had tibial EAD, and four had femoral EAD. Twelve had varus deformity and rest two had valgus deformity. Functional outcomes were assessed using the Oxford Knee Score (OKS), Knee Society Score (KSS), and Knee Society Functional Score (KSS-F). Radiological parameters included the Hip-Knee-Ankle (HKA) axis, mechanical axis deviation (MAD), the centre of rotation of angulation (CORA), medial proximal tibial angle (MPTA), and lateral distal femoral angle (LDFA).

Results: The mean follow-up period was 16 months (range: 8 to 25 months). The mean EAD measured 13.8° (range: 5.1°-21.1°) in the coronal plane and 8.2° (range: 1.2°-22.8°) in the sagittal plane. The mean HKA angle improved from 163.9° ± 7.8° preoperatively to 176.4° ± 1.4° postoperatively (p < 0.05) for varus knees and from 189.5 ± 9.2° to 183.8 ± 2.6° for valgus knees (p = 0.002). No patients required grade IV soft tissue release or constrained prosthesis. The mean arc of motion improved from 94.6° ± 19.3° to 109.6° ± 9.8° (p = 0.001). The KSS, KSS-F, and OKS significantly improved from 25.1 ± 10.8, 36.4 ± 14.5, and 17.2 ± 5.7 preoperatively to 86.8 ± 4.4, 88.6 ± 5.3, and 41.4 ± 4.8 postoperatively (p < 0.001). No radiolucent lines were observed at the bone-cement interface during follow-up. Additionally, no complications such as infection, aseptic loosening, or ligament instability occurred.

Conclusion: Robotic-assisted TKA allows for effective intra-articular correction of severe EAD while minimizing the need for extensive soft tissue release. Robotic-assisted TKA helps in executing functional alignment, desired under-correction of the deformity and optimal soft tissue balance, resulting in satisfactory functional and radiological outcomes.