Whether it is best to retain the posterior cruciate ligament in the degenerated knee, i.e. using a cruciate-retaining (CR) total knee prosthesis (TKP), or to use a more constraint posterior-stabilized (PS) TKP is of debate. There are limited studies comparing the effect of both methods on implant fixation and clinical outcome, leaving it up to the surgeon to base this decision on anything but conclusive evidence. We assessed the effect of two different philosophies in knee arthroplasty on clinical outcome and tibial component migration measured with radiostereometric analysis (RSA), by directly comparing the CR and PS version of an otherwise similarly designed cemented TKP.

Sixty patients were randomized and received a Triathlon TKP (Stryker, NJ, USA) of either CR (n=30) or PS (n=30) design. RSA measurements (primary outcome) and clinical scores including the Knee Society Score and Knee injury and Osteoarthritis Outcome Score were evaluated at baseline, at three months postoperatively and at one, two, five and seven years. A linear mixed-effects model was used to analyse the repeated measurements.

Both groups showed a similar implant migration pattern, with a maximum total point motion at seven years follow-up of around 0.8 mm of migration (mean difference between groups 95% CI −0.11 to 0.15mm, p=0.842). Two components (one of each group) were considered to have an increased risk of aseptic loosening. Both groups improved equally after surgery on the KSS and KOOS scores and no differences were seen during the seven years of follow-up.

No differences in implant migration nor clinical results were seen seven years after cruciate-retaining compared to posterior-stabilized total knee prostheses.

We measured the insertion and extraction torque forces in a randomised study of 76 external fixation screws in 19 patients treated by hemicallotasis for osteoarthritis of the medial side of the knee. The patients were randomised to have either standard tapered screws (Orthofix 6/5 mm) or the same screws with hydroxyapatite (HA) coating. One patient had two standard and two HA-coated screws. All patients had an anterior external fixator (Orthofix T-garche), with two screws in the proximal tibial metaphysis parallel to and about 2 cm below the joint surface and two in the tibial diaphysis.

The mean torque forces for insertion of the standard screws were 260 Ncm for the proximal to medial screw, 208 for the proximal to lateral screw and 498 and 546 Ncm for the diaphyseal pins. The corresponding forces for the HA-coated pins were not significantly different. The torque forces for the extraction of the standard pins were 2 Ncm for the proximal pins, 277 and 249 Ncm for the distal pins and 482, 478, 585 and 620 Ncm, respectively (p < 0.005) for the HA-coated pins.

All 18 of the metaphyseal standard screws were loose at extraction (extraction force < 20 Ncm), but only one of the HA screws in the metaphysis was loose. In the diaphysis the standard screws lost about 40% of their fixation in contrast to the HA-coated screws which retained full fixation strength.