Implant alignment in knee arthroplasty has been identified as critical factor for a successful outcome. Human error during the registration process for imageless computer navigation knee arthroplasty directly affects component alignment. This cadaveric study aims to define the error in the registration of the landmarks and the resulting error in component alignment.

Five fresh frozen cadaveric limbs including the hemipelvis were used for the study. Five surgeons performed the registration process via a medial parapatellar approach five times. In order to identify the gold standard point, the soft tissues were stripped and the registration was repeated by the senior author. Errors are presented as mm or degrees from the gold standard registration.

The error range in the registration of the femoral centre in the coronal plane was 6.5mm laterally to 5.0mm medially (mean: −0.1, SD: 2.7). This resulted in a mechanical axis error of 5.2 degrees valgus to 2.9 degrees varus (mean: 0.1, SD: 1.1). In the sagittal plane this error was between −1.8 degrees (extension) and 2.7 degrees (flexion). The error in the calculation of the tibial mechanical axis ranged from −1.0 (valgus) to 2.3 (varus) degrees in the coronal plane and −3.2 degrees of extension to 1.3 degrees of flexion. Finally the error in calculating the transepicondylar axis was −11.2 to 6.3 degrees of internal rotation (mean: −3.2, SD: 3.9).

The error in the registration process of the anatomical landmarks can result in significant malalignment of the components. The error range for the mechanical axis of the femur alone can exceed the 3 degree margin that has been previously been associated with implant longevity. The technique during the registration process is of paramount importance for image free computer navigation. Future research should be directed towards simplifying this process and minimizing the effect of human error.

The aim of this study was to assess the risks and benefits of mini-incision TKR. The limited exposure afforded by the small skin incision in the new technique of mini-incision TKR has the potential for increasing the risk of mal-positioning of components. Minor mal-positioning of components has the potential to increase polyethylene wear and may lead to early loosening and poor functioning of the TKR. The literature supports the concept that alignment within +/- 3 degrees of neutral mechanical alignment in the coronal plane is associated with a better outcome. If the mechanical axis falls outside this range it may have up to a 30% failure rate at 10 years.

We report the results of 166 mini-incision TKR that have been undertaken in 154 patients (96F; 58M; mean age 72; mean BMI 29; 96% OA) since November 2003. The pre-operative mechanical axis ranged from 8 degrees valgus to 15 degrees varus. Surgery was undertaken with a precise skin incision and a midvastus split approach. Specialised cutting blocks were used to facilitate a smaller incision. The prosthesis inserted was a cemented Zimmer NexGen TKR of either posterior stabilised or cruciate retaining form.

Long leg weight bearing alignment radiographs were available in 52% of patients. The mechanical axis was measured in the coronal plane and found to lie within +/- 3 degrees of neutral in 86% of patients. This compares favourably with the current literature which reports the mechanical axis falling within this range in between 72% and 85% of cases.

We believe the mini-incision TKR is a safe, reliable and reproducible technique offering substantial savings to the patient and health service without compromising accuracy.

The aim of this paper is to evaluate the Linvatec SE graft tensioner system in obtaining predictable initial tension during ACL reconstruction using hamstring grafts.

The gracilis and semitendinosus grafts were tensioned individually prior to fixation distally to a combined tension of 80N. The knees were then cycled through full range of motion and the tension recorded at 90 degrees and in full flexion and extension. Experience on the first 22 patients indicated that 41% required 10 cycles of the knee to remove pre-conditioning and equalise tension at 80N combined, while the remaining 50% required 15 cycles. 90% reached stable tension after 15 cycles. In 54% the tension increased at full extension and graft tension was adjusted to 80N in extension to avoid overconstraining the graft. Twenty-two patients studied following this initial protocol underwent outcome assessment after minimum 6 months. Mean KT1000 arthrometry manual maximum side to side difference was 1.5mm. Femoral fixation was achieved using the Endobutton (Smith and Nephew) and Tibial fixation using the Extralok bioabsorbable screw (Linvatec).

A subsequent shortened protocol of initial over-tensioning to 60N and 40N for the semitendinosus and gracilis double bundles respectively, followed by 15 cycles of the knee resulted in stable 80N combined tension with no further drop with more cycling.

We conclude that the new tensioner system allows for accurate and predictable initial tension of hamstring reconstructed ACL grafts and that its use can be simplified by using the second technique protocol.