MIDTERM RESULTS AND STABILITY MEASUREMENTS AFTER TOTAL KNEE ARTHROPLASTY USING THE LIGAMENT BALANCING TECHNIQUE–A PROSPECTIVE STUDY-

Abstract

Aims : This prospective study investigated outcomes from TKA using the ligament balancing technique to implant a PCL-retaining knee prosthesis (balanSys^™ knee system). In addition we wanted to know if we can achieve stability in these knees and if there is a difference between mobile and fixed bearing prosthesis designs?

Methods: Between March 2001 and Mai 2005 143 patients (17 bilateral; n=160) with osteoarthritis received the balanSys^™ knee system with either a fixed or mobile polyethylene bearing. Objective assessments of the implant used Knee Society score (KSS) with the knee and functional score. Anterior-posterior translation was measured with the Rolimeter (Aircast) in 25° (Lachman) (mean of 3) and 90° of knee flexion (mean of 3), intraoperatively under anaesthesia and at follow up time. Subjective assessments used Visual Analogue Scale (VAS) data for pain, and patient satisfaction.

Results: The study population at follow up time (mean 4 years) contained 112 patients (31 males; 81 females) with 126 knee implants out of 160. Of these 126, 93 had fixed and 33 mobile bearings. Mean age at surgery was 70.6 years. The Rolimeter measurements for ap-translation showed an increase of stability from 8.3 preop to 4.6 mm at FU in 25° of flexion and 6.3 to 4.9 in 90° of flexion. The increase of stability for mobile bearings (7.8 to 5.8/6.1 to 6.0) is smaller than for fixed bearings (8.4 to 5.8/6.9 to 4.5). The t-test shows a clear cut significance Pr > [t] = 0.0038, the difference of the paired difference amounts to 1.4 mm. The t-test shows significant differences for both angles (25°/90°) Pr > [t] < 0.001. Mobile bearings have a higher laxity in ap direction compared to fixed bearings. ROM was similar for both genders (mean 118°). According to VAS, mean scores for pain and satisfaction were 1.5 (best 0) and 8.5 (best 10), respectively. The KSS (mean score 168; SD 31.1) was similar for both, fixed and mobile bearings. In 25° of flexion the subgroup of ‘tight’ knees (1–3.5 mm ap translation) and in 90° the subgroup of ‘loose’ knees (< 5.5 mm) performed best, with highest knee scores.

Conclusions: The TKA’s performed with a PCL-retaining prosthesis and a soft tissue oriented, ligament balancing, surgical technique were associated with good outcome (KSS mean score 168), a good range of motion (118°), good stability and with no significant differences between mobile bearing or fixed bearing implants at follow up (4 years). In addition patients reported little pain (1.5) and were very satisfied (8.5) with the outcome. Interesting was the fact that in 25° of flexion the subgroup of tight knees (1–3.5mm) and in 90° the subgroup of loose knees (< 5.5 mm) performed best, with highest knee scores.