Intraoperative joint gaps affect postoperative range of motion in TKAs with posterior-stabilized prostheses

Joint gaps and mediolateral (ML) soft tissue balance have long been known to affect clinical scores and patient function after TKA, but the relationship between gaps and soft tissue balance remain poorly defined. If specific relationships exist between soft tissue tension and patient function, then objective targets could be established to assist surgeons in achieving more consistent postoperative knee function.

By performing instrumented gap measurements during TKA, we sought to quantify the relationships between intraoperative soft tissue tension and clinical scores and patient function.

We prospectively followed 57 patients with 63 primary TKAs with posterior-stabilized prostheses. Joint gaps and ML soft tissue balance were measured intraoperatively from 0° to 135° with the patella reduced after independent bone cuts and soft tissue releases. We determined the relationships between these intraoperative measurements and postoperative ROM and Knee Society scores at minimum 2-year followup.

Larger joint gaps at 120° and 135° flexion predicted larger postoperative knee flexion (r=0.296 and r=0.393, respectively), whereas larger gaps at 10° flexion predicted greater postoperative knee extension (r=0.285). Knees with rectangular joint gaps did not show better ROM or Knee Society scores compared with knees with trapezoidal joint gaps. In the range of normal surgical variation, neither joint gaps nor gap asymmetry affected the incidence of postoperative instability.

Avoiding small joint gaps in extension and in deep flexion should allow patients who undergo TKAs to obtain maximum ROM.

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.