Radiolucent lines (RL) are a common radiographic finding following Oxford Uni knee arthroplastv. These RL are commonly seen at the bone-cement interface under the tibial tray and can only be evaluated using screened radiographs. These lines occur during the first year, are well defined and remain constant for years. The clinical relevance of this phenomenon is unclear. Pulse lavage has the potential to thoroughly clean the trabecular bone by clearing the bone from bone marrow and debris and can thereby facilitate cement penetration and interdigitation into trabecular bone.

Pulse lavage can reduce the occurrence of radiolucent lines under the tibial tray by improving cement penetration and interdigitation.

Since 2001 we routinely use pulse lavage before cementing the Oxford uni implants at the Orthopä-dische Universitätsklinik Heidelberg (group A). At Nuffield Orthopeadic Center, Oxford conventional irrigation has been used before cementing (group B). At a minimum follow-up of 1 year 56 screened AP radiographs of the knee after Oxford UCA have been blinded and evaluated for radiolucency and cement penetration by an independent observer. For standardized evaluation the cement bone interface has been devided into 4 zones and a specific algorithm for evaluation of the radiographs has been developed.

Complete radiolucencies were detected in 2 cases (4%) in group A and in 13 cases (23%) in group B (p=0,001). Partial radiolucent lines were seen in 32 knees of group A (57%) and in 40 knees (71%) in group B. In zone 1 RLs were found in 31 tibias (55%) in group A, in 32 tibias (57%) in group B. In zone 2 17 (30%) group A, 29 (52%) group B. In Zone 3 4 (7%) in Gruppe A, 20 (36%) in group B. In Zone 4 6 (11%) group A, 30 (54%) group B. The differences between group A and B were significant (P=0.001) in zones 2, 3 and 4.

In group A in 14 cases (25%) RL were limited to one zone, in group B in 5 cases (9%), respectively. In 12 cases (21%) 2 zones were affected in group A (12 cases (21%) group B). RLs in 3 zones were found in 4 cases (7%) in group A and in 10 cases (18%) in group B.

Mean cement penetration (mm) was 2,3mm in group A and in 1,4mm in group B. The use of pulsed lavage led to an increase in cement penetration by a factor of 1,6 (cement penetration in group A/B zone 1: 1,4mm/0,8mm; zone 2: 2,4mm/1,5mm; zone 3: 1,4mm/0,7mm; zone 4: 4,0mm/2,4mm).

The use of pulsed lavage significantly decreases the appearance of RLs at a minimum of 1 year follow-up by increasing cement penetration into cancellous bone. Even though the clinical relevance of tibial RLs in unclear we recommend the use of pulse lavage to improve cement penetration and interdigitation with cancellous bone. Unnecessary revisions due to misinterpretation of RLs may be prevented.