COMPUTER ASSISTED MINIMALLY INVASIVE UNICOMPARTMENT KNEE ARTHROPLASTY

Abstract

Unicompartment knee arthroplasty (UKA) was proven to be one of the standard treatments of medial compartment osteoarthritis. The key to success was restoration of pre-operative alignment. Overcorrection of coronal (AP) alignment may predispose to early osteoarthritis in the contralateral compartment, change in post-operative tibial slope may predispose to proximal tibial bone collapse and loosening of tibial prosthesis. Minimally invasive surgery (MIS) in UKA was developed quickly in the last ten years. However, MIS has limited access to visualize the surgical field and limb alignment. Computer navigation may help the surgeon to place the component in more accurate position. We aim to study the radiological alignment of computer assisted MIS UKA.

Eighteen patients with UKA (PreservationTM, all poly tibia, DePuy Orthopaedics Inc, Warsaw, IN) implanted using MIS technique were studied prospectively. The CiTM system (DePuy International Ltd, Warsaw IN) were used for computer navigation. Five male and 13 female patients were studied. The mean age of the patients was 58.2 (range, 45 to 70). All patients had medial compartment osteoarthritis with varus deformity. The postoperative coronal (AP) alignment and tibial slope of the operated limb were compared with the pre-operative alignment for any significant difference.

The mean pre-operative and post-operative radiographic coronal (AP) alignment of the operated limb were 8.4° varus (range, 2° to 12°) and 7.2° varus (range, 1° to 15°) respectively, the difference was not significant (p = 0.537). The mean pre-operative and post-operative tibial slope were 6.8° (range, 3° to 11°) and 5.8° (range, 3° to 10°) respectively, the difference was not significant (p = 0.066). The post-operative tibial slope correlated well with the intra-operative tibial slope recorded by computer after bone cut was made (Cronbach’s Alpha = 0.771). The mean tourniquet time was 124 minutes (range, 94 to 140 minutes).

There was no significant difference in pre-operative and post-operative coronal alignment of the operated limb. Computer assisted MIS UKA could reproduce the pre-operative coronal alignment and tibial slope. Restoration of the pre-operative limb alignment in coronal plane and tibial slope was crucial to the survival of UKA. Computer navigation could help the surgeon to position the component during minimally invasive surgery. However, the learning curve of computer assisted MIS UKA was steep.