Influence of an anaesthetist on nurse-led, computer-based, pre-operative assessment.

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.

Severe polyethylene wear in uncemented acetabular cup system components: a report of 5 cases.

We report 5 cases of severe failure of the polyethylene liner at 4 to 7.4 years after uncemented anatomic medullary locking (AML) total hip arthroplasty, using the acetabular cup system (ACS). The mode of failure was by a combination of wear-through to the metal backing and liner fracture. Four of the 5 cases were associated with a 32-mm head. The ACS design is flawed because of a lack of hemispherical geometry resulting in rim loading on a region of the liner that has the thinnest polyethylene. All patients with this type of implant should be monitored for evidence of excessive polyethylene wear.

Immediate strength after suture of a torn anterior cruciate ligament.

In an animal model we determined the strength of anterior cruciate ligaments (ACL) after section and repair by four different methods and compared it with that of the intact ligament. The standard suturing technique of multiple loops through the ligament stumps was used. Stronger suture material did not give a stronger repair. Wrapping a fine polyester mesh around the ligament or placing it between the bundles before suture increased the strength of the repair. This modification, allied to protective rehabilitation, may reduce the failure rate of acute ACL repairs.

A comparative study of single- and double-bundle ACL reconstructions in sheep.

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.

Interobserver variation using the AO/ASIF classification of long bone fractures.

A comprehensive classification system has been proposed by the AO/ASIF Foundation for the classification of long bone fractures. After an explanatory talk and with the aid of an illustrated pamphlet, 18 orthopaedic surgeons were asked to classify 10 long bone fractures according to the AO system. Three of the participating surgeons had previous experience of the classification system. After individual classification, a consensus classification was derived and the results of the individual and consensus codings were compared. Only 32 per cent of all codings agreed with the final consensus. There was no difference between the surgeons with previous experience of the system (66 per cent) and novice coders (69 per cent) in the number of inaccurate codes when compared with the consensus codes. Reasons for error in coding are discussed. It is recommended that if the AO system is used for the purposes of research and computer-based audit, a consensus of opinion is used as the basis of classification.

Anterior cruciate ligament replacement with polyester fibre. A long-term study of tissue reactions and joint stability in sheep.

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.

Biomechanics of a double prosthetic ligament in the anterior cruciate deficient knee.

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 degrees and 90 degrees knee flexion. The over-the-top reconstruction gave better anteroposterior stability at 20 degrees, while the through-the-condyle repair was more stable at 90 degrees. The double-bundle reconstruction gave practically normal anterior stability at both 20 degrees and 90 degrees.

Unacceptable variation in the core diameters of some AO type cancellous screws.

This study assesses the variability in core diameter of a series of cancellous screws and its effect on torque strength. Analysis of a series of 107 cancellous screws revealed a wide variation of the core diameters in our sample. Tests to evaluate the effect of this variation showed that torsional strength is directly proportional to the cube of the radius of the core; a 30% reduction in radius resulting in a 70% loss in torsional strength. Conclusions drawn from this experimental data indicate that variability in core dimensions below the recommended specifications is unacceptable in clinical practice.