ACL-SUBSTITUTING TKR: WHAT DOES POST-MARKETING SURVEILLANCE TELL US ABOUT THIS DESIGN CONCEPT?

Introduction In addition to traditional posterior-stabilized (PS) designs with cam-post articulations, there are two new design concepts used in total knee replacement (TKR) to “substitute” for cruciate ligament function and restore anterior-posterior stability. These include i) guided-motion PS designs with a modified cam-post that is less restrictive to axial rotation; and ii) non-PS designs that incorporate progressive articular congruency to substitute the function of the resected anterior cruciate ligament (ACL-substituting). Early post-marketing surveillance of such new TKR designs is valuable because instability, loosening, and high complication rates within the initial 5 year follow-up interval have proven problematic for some design. This study reports the early clinical performance of sequential patients implanted with a new ACL-substituting TKR design at a German Center of Excellence for Arthroplasty (EPZ-Max) hospital. Methods This is a single-site, multi-surgeon retrospective study with Institutional Review Board approval. The nine surgeons involved all used uniform surgical techniques, including a mid-vastus approach, PCL preservation with a bone block, tibial component alignment with the natural tibial slope, no patellar resurfacing, and cement fixation. All patients meeting the following inclusion criteria were contacted by phone: a) primary TKR from July 2008-June 2009; b) implanted with an ACL-substituting design (3D Knee™, DJO Surgical); c) no prior knee arthroplasty; and d) willing to consent to participate. Recorded outcomes at the 5 year follow-up interval included range of motion, Knee Society knee/function scores (KSS), and radiographic results (alignment, radiolucent lines, osteolysis). Additional surgery was classified as “revision” (metal components removed) or “reoperation” (metal components not removed). Results Out of 166 sequential patients, a study cohort of 69 patients (84 TKR) consented to participate. Average follow-up was 6.2+0.6 (4.7–7.3) years. Maximum flexion averaged 115°+9° (85°–145°), including 39% at >120°. The TKR had stable function and average KSS scores of 94 (knee) and 94 (function). There were four patients (5 TKR, 6.3%) with function scores of 10°) that lingered (5°–10°) at follow-up. No TKR had evidence of osteolysis or loosening. Non-progressive radiolucent lines were evident post-operatively in 10 TKR and in one additional TKR at last follow-up. Seven (8.3%) TKR required reoperation or revision. Five TKR in the 0–5 year interval required reoperation to treat acute infection, progressive patellar arthritis, and traumatic patellar fracture, and revision to treat pain of unknown etiology (2 TKR revised at another hospital). Two TKR in the 5–6 year interval required revision arthroplasty to treat pain associated with a loose tibial insert screw and unknown symptoms (1 TKR revised at another hospital). Conclusion This new ACL-substituting design incorporates progressive congruency in the lateral compartment. These data, combined with previous studies (Table 1), provides evidence that this ACL-substituting TKR design restores stability while being robust to surgical and patient variations. These results for a fixed-bearing, non-PS TKR design are supported by international registry data from more than 370,000 TKR in six countries, which demonstrate that survivorship of fixed-bearing cruciate-retaining TKR designs is significantly higher than posterior-stabilized TKR designs, both with and without patella resurfacing.