title: Assessment of posterior stability in total knee replacement by stress radiographs: prospective comparison of two different types of mobile bearing implants.
abstract: The aim of this study was to assess the posterior stability of two different designs of total knee replacement (TKR) with deep-dished mobile bearing (MB) implants using stress X-rays. In a prospective non-randomized consecutive study, 34 patients with primary osteoarthritis of the knee underwent TKR. In group A (17 knees), they received a MB insert with a Duracon prosthesis and in group B (18 knees), a Genesis prosthesis. In all cases the posterior cruciate ligament (PCL) was resected. All patients had pre- and post-operative kneeling X-rays and were clinically evaluated with the Knee Society Score. Measurements on the radiographs were taken by tracing a line along the posterior cortex of the tibia and then measuring the perpendicular distance to a point marked at the posterior corner of Blumensaat's line. The average follow up was 10.7 months for group A and 5.4 months for group B. No statistical difference could be found in terms of clinical results and pre- and post-operative kneeling X-rays between the two groups. In each group, all knees demonstrated a significant posterior tibial translation postoperatively compare to their pre-operative status (p<0.0001). There are advantages in resecting the PCL in TKR: mobile flexion gap, correction of fixed deformity, more flexibility to adjust the joint line. The use of a deep dished polyethylene (PE) insert provides stability and use of MB insert reduces PE wear whilst retaining congruity. Two designs of deep-dished MB inserts showed significant posterior tibial translation on stress X-rays. It remains to be determined what amount of laxity is optimal for clinical function and polyethylene longevity.
authors.affiliation: Warringal Private Hospital, 120 Burgundy Street, Heidelberg, Melbourne, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Louisia
authors.forename: R
authors.initials: R
authors.lastname: Siebold
authors.forename: J
authors.initials: J
authors.lastname: Canty
authors.forename: R J
authors.initials: RJ
authors.lastname: Bartlett
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery; D017063:Outcome Assessment, Health Care; D016119:Posterior Cruciate Ligament / Q000601:surgery; D011446:Prospective Studies; D011474:Prosthesis Design; D011859:Radiography; D013314:Stress, Mechanical; D016474:Weight-Bearing