We have assessed the biomechanical properties of a 'double-bundle' prosthetic ligament replacing the anterior cruciate in cadaver knees. We compared the results with those of single bundle 'over-the-top' and 'through-the-condyle' techniques, performing anterior drawer tests at 20#{176} and 90#{176} knee flexion. The over-the-top reconstruction gave better anteroposterior stability at 20#{176}, while the through-thecondyle repair was more stable at 90#{176}. The double-bundle reconstruction gave practically normal anterior stability at both 20#{176} and 90#{176}. Fig. 1 Anterior view ofa right knee showing a normal ACL, with loops placed around the anteromedial and posterolateral bundles of fibres.

Work in vitro has previously shown superior restoration of knee stability using a double-bundle anterior cruciate ligament (ACL) reconstruction compared with single bundles taken through the condyle or 'over the top'. This paper describes an animal study designed to compare the three ACL reconstructions in vivo, in order to collect data that could support the clinical use of a double-bundle reconstruction. The three methods were compared in three groups of eight sheep, the ovine ACL having a distinct double-bundle structure. Biomechanically matched polyester fibre implants were used, with 6 months in vivo. The three methods led to similar intra-articular fibrous tissue integration of the implants and no evidence of implant damage, and biomechanical testing found greater laxity than normal for all three groups. The double-bundle group, however, had more joint surface degeneration than the other groups. It was concluded that clinical use of the double-bundle reconstruction was not indicated by the results of this experiment, in view of the more complex surgery and lack of superior performance.

SummaryThis study evaluated the anatomy and biomechanics of the ovine stifle, with a view to its use as a model of the human knee joint.Stifles were dissected to define the internal anatomy, concentrating on the cruciate ligaments. The cranial cruciate ligament (CraCL) was assessed biomechanically at 30° and 90° flexion, intact, with the craniomedial bundle (CraMB) divided, and after complete transection. Craniocaudal (C-C) and internal-external rotatory stability were assessed. The tensile strength of the CraCL was determined.The morphology of the ovine stifle was similar to the human knee. Sequential sectioning of the bundles of the CraCL caused increasing cranial laxity of the joint. Rotational laxity also increased as the CraCL was divided, as well as with progressive joint flexion. It was concluded that the ovine stifle is a valid animal model for the human knee for work on the cruciate ligaments.The anatomy and biomechanics of the ovine stifle were studied, with a view to assessing the suitability of the joint as a surgical model for the cruciate ligaments of the human knee. The ligaments, joint stability and cranial cruciate ligament strength were measured. It was concluded that the ovine stifle is a valid model of the human knee for this purpose.

We excised the anterior cruciate ligament from the left stifle of 24 sheep and replaced it by a polyester fibre implant routed 'over the top' of the femoral condyle and fixed, using grommets and screws. All the joints were sound, and the animals moved normally until they were killed at six, 12 and 24 months after operation. We found that the implants were always covered by host tissue, which matured into bundles with a histological appearance similar to the natural ligament. The implants were joined to the bones by organised fibrous tissue and there was no anchorage loosening. There was no synovitis, but the operated joints showed progressive cartilage degeneration. The reconstructed joints became less stable immediately after operation, but regained normal stability as the neoligaments developed. The neoligaments lost strength with time, despite tissue ingrowth. The good functional, biomechanical, and histological results justify clinical trials of this type of implant.

Trained nurses using a rule‐based computer program can successfully carry out pre‐anaesthesia screening. All medical problems and abnormal laboratory results need to be reviewed by an experienced anaesthetist. Following the introduction of this system, there was a reduction in the frequency of cancellations of patients from elective orthopaedic operating lists from 4.8% to 1.8%, a difference that was statistically significant (p = 0.03, CI = [0.6%, 5.5%]). To minimise cancellations from booked operating lists, a booked admissions policy is essential, so that the anaesthetist who will eventually be responsible for patients with medical problems can be identified. Cancellations cannot be avoided completely because some abnormal conditions arise or deteriorate after completion of the screening process. The anaesthetist responsible for the patient's anaesthetic may have different views of the risks involved from those of the anaesthetist undertaking the screening process.