INFLUENCE OF POSTERIOR TIBIAL SLOPE ON AN TERIOR TIBIAL TRANSLATION AND MOBILITY AFTER A NON CONSTRAINED TOTAL KNEE ARTHROPLASTY

Purpose of the study We determined retrospectively the influence of po sterior tibial slope and anterior cruciate ligament (ACL) sparing on a nterior tibial translation in 68 Cloutier total knee prosthesis. We al so precised the influence of posterior tibial slope on knee functional score and appearance of tibial prosthetic interfaces. Material 38 Clo utier total knee prosthesis (62 patients mean aged 62 +/- 10 years (36 -76) at surgery) reviewed at systematic follow-up control, after a mea n period of 5.5 +/- 3 years (2-15), were included in the study. The AC L was preserved in 38 knees and sacrified in 30 knees, the posterior c ruciate ligament was preserved in all cases. The prosthetic design was the same whatever the number of cruciate ligament preserved. Osteoart hritis was the reason for surgery in 54 knees, and rheumatoid arthriti s in 14 knees. Mean HSS knee score was 54 +/- 10 (29-80) before surger y and 89 +/- 10 (35-100) at follow-up. The mean range of motion was 10 3 +/- 24 degrees (30-130) before surgery and 110 +/- 14 degrees at fol low-up (40-130). Methods Anterior tibial translation was determined on two profil x-rays (non weight bearing and weight bearing) at 20 degre es of flexion by comparing the position of tibial tray with regard to posterior edge of femoral prosthesis. Tibial slope was measured on lat eral view with regard to peroneus axis. Appearance of tibial prostheti c interface was studied in 48 knees on AP and lateral x-rays orientate d with an image intensifier in order to obtain the x-ray would be para llel to the tibial interface. Results Posterior tibial slope (mean val ue 6.2 degrees +/- 4.2 degrees) was the main factor influencing the an terior tibial translation (mean value 3.9 +/- 4.6 mm) (p = 0.0007). A 10 degree increase of posterior tibial slope makes the anterior tibial translation rise by 5.6 mm in weight bearing situation. When ACL was preserved, the anterior tibial translation was lower but the decrease was not significant. Likewise, preservation of ACL or the degree of po sterior tibial slope had no influence on : 1) HSS knee functional scor e, 2) range of motion. Radiolucent lines were observed in 18 out of 48 knees, but their occurrence was not influenced by the degree of poste rior tibial slope or preservation of ACL. Discussion Posterior tibial slope has a higher influence than ACL preservation on anterior tibial translation. The increase of posterior tibial slope in order to improv e range of motion and to protect the bone-prosthetic tibial interface appeared unjustified with this non-constrained prosthesis. Moreover, i mplantation of tibial tray (whatever the preservation of ACL) with an important posterior inclination exposes to high anterior tibial transl ation in weight bearing situation. This last condition could reduce th e survivorship of tibial polyethylene.