We studied twelve parameters (physical appearance, mucin clot, fibrin clot, white cell count, differential count, red blood cell count, gram stain for bacteria, crystal microscopy, aerobic bacterial culture, anaerobic bacterial culture and ratio between synovial sugar and blood sugar) in over 300 samples of synovial fluid from patients with a variety of suspected pathologies (e.g. infection, inflammatory disease, infection adjacent to a joint, aseptic loosening of a prosthesis).

The diagnosis of infection was further established using clinical signs, radiological features, full blood count, C-reactive protein and iron profile. Many of the patients came to surgery. This of course created further opportunity to establish or rule out the diagnosis of infection with greater certainty. Nine of the features of synovial fluid were analysed statistically, including turbidity, diminished viscosity, mucin clot, fibrin clot, total white cell count, polymorphs greater than 60%, bacteria observed on direct microscopy, bacteria yielded by culture and concentration of synovial sugar less than 40% of the simultaneous blood sugar. The positive or negative features of infection were determined to be true or false in the light of the cumulative overall features of infection. The data so obtained was analysed to establish sensitivity, specificity, positive predictive value, negative predictive value and accuracy.

The mass of data so obtained cannot be meaningfully expressed in such a brief abstract. Important examples are when culturing synovial fluid there were 44% false negatives or no growth and 56% true positives. Looking at the ratio between synovial sugar and blood sugar we found that taking 40% as the critical value, this was 62% sensitive, the specificity was 89%, the accuracy was 73%, the positive predictive value was 89%, the negative predictive value was 62.4%. However we went further and separated those who were definitely infected or probably infected i.e. Groups 4 & 5 from those who were probably or definitely NOT infected according to the sum of clinical laboratory and radiological parameters.

When thus separated the predictive value of a positive result was 100% in Group 4 & 5 and 0% in Group 1 & 2. The predictive value of a negative result in Group 1 & 2 was 98.7% accurate and 22.4% in Group 4 & 5.

Between January 1998 and December 2002, 418 hip revisions were performed. Of these, 45 hips were diagnosed as infected and two-stage revisions were done six weeks apart. These were excluded from the study, leaving 373 revisions for mechanical failure. In 310 cases both components were exchanged, in 59 the acetabular prostheses only and in three the stem only. One permanent resection arthroplasty was done for bone loss. Where necessary bone graft was used liberally. In 83 patients (22%) specimens taken at surgery cultured positive.

A first generation cephalosporin was given as systemic prophylaxis. Routine usage of Gentamycin was reinforced by Vancomycin or fucidic acid in the cement and bone grafts. Double lumen irrigation was inserted in only 5% of cases on the basis of operative findings. Gram stains done intraoperatively in suspected cases were non-contributory. Seventy-six percent of cultures were gram positive, with a preponderance of coagulase negative staphylococcus. Twelve percent were gram negative and 12% were mixed cultures of gram positive and gram negative organisms. One methicillin-resistant Staphylococcus aureus and one fungus were identified. As most of these patients were referred from elsewhere, we did not know whether or not Gentamycin had been used in the cement during previous surgery.

Implant failure due to low-grade infection was under-diagnosed in this series. Because of the relatively low number of failures caused by infection in this group, we recommend, with some improvements, the revision protocol presented. The expense of more detailed preoperative evaluation should be weighed against the success of the protocol.

A scoring system that objectively weighs up the indications, contra-indications and order of priority for joint replacement is useful when assessing patients who demand surgery or when providing health fund providers with objective motivation for surgery.

The appropriate American score (Harris Hip Score or American Knee Society Rating) is applied. The scoring system goes on to assess the degree of pain and functional ability in greater depth. It takes into consideration the extent of other affected joints and the ability to perform normal activities of daily living such as driving, dressing, foot care, bathing and recreational pursuits.

The functional demands of the patient’s activities at home are then assessed, taking into account how much assistance is available, and what need there is to shop or make use of public transport, and how much walking or stair-climbing this entails. To this is added an assessment of the functional demands or stresses of the patient’s occupation. By adding the American scores and the additional scores for pain and functional ability, and subtracting from that total the score for functional demands at home and at work, one arrives at a score for the degree of compromise (American Score + pain + function – functional demand = compromise score). A lower score means greater compromise.

Finally, one determines the risk of morbidity and mortality. The greater the risk, the lower the compromise score should be. The contra-indication score is reached by multiplying the compromise score by the morbidity and mortality risks and dividing by 100. Depending on how one looks at it, the contra-indication score reflects either the urgency of surgery or the degree of resistance against it.

Health fund providers often require objective motivation for surgery, and patients often try to pressurise surgeons into operating. The author developed a scoring system to weigh up objectively the indications and contraindications for and urgency of joint replacement.

A considerably expanded Harris Hip Score and American Knee Society ratings are used. Rather than using a subjective adjective to evaluate pain, it is objectively evaluated by type and frequency of analgesic. The totality of the patient’s condition is considered in assessing functional ability, particularly with regard to other affected joints and the patient’s ability to perform normal activities of daily living. Taken into account is how much walking, climbing and stair-climbing a patient’s work demands and whether getting to work requires a long walk or use of public transport. The functional demands of daily home life are assessed, and also how much assistance is available to the patient.

By adding the American scores to the additional scores for pain and functional ability, and then subtracting that total from the functional demand, one arrives at a score for the degree of compromise. The scoring includes a prediction of the risk of morbidity and mortality. When this risk is balanced by the degree of compromise, one arrives at a score for contraindication. Put another way, pain + functional ability - functional demand =compromise, and compromise x risk of mortality and morbidity =100.

Health fund providers often require objective motivation for surgery, and patients often try to pressurise surgeons into operating. The author developed a scoring system to weigh up objectively the indications and contra-indications for and urgency of joint replacement.

A considerably expanded Harris Hip Score and American Knee Society ratings are used. Rather than using a subjective adjective to evaluate pain, it is objectively evaluated by type and frequency of analgesic. The totality of the patient’s condition is considered in assessing functional ability, particularly with regard to other affected joints and the patient’s ability to perform normal activities of daily living. Taken into account is how much walking, climbing and stair-climbing a patient’s work demands and whether getting to work requires a long walk or use of public transport. The functional demands of daily home life are assessed, and also how much assistance is available to the patient.

By adding the American scores to the additional scores for pain and functional ability, and then subtracting that total from the functional demand, one arrives at a score for the degree of compromise. The scoring includes a prediction of the risk of morbidity and mortality. When this risk is balanced by the degree of compromise, one arrives at a score for contra-indication. Put another way, pain + functional ability – functional demand = compromise, and compromise x risk of mortality and morbidity = contraindication.