Gram staining is used as an initial indicator of synovial joint infection but has widely varied false negative rates in the literature. Clinical decisions are often made on the basis of gram stain results, such as whether a patient requires urgent surgery, and therefore it is important to understand the tests efficacy. A retrospective review of synovial fluid aspirates in NHS Tayside for the years 2017 and 2018 was performed from the departmental microbiology database. Aspirates of large joints were included (hip, knee, shoulder, wrist, elbow, ankle). Any joints with prosthesis were excluded, including fixation metalwork. Any abscess overlying a joint that was not proven to penetrate the joint was also excluded. Initial gram stain results and formal culture results were reviewed. Final culture results were considered to be the gold standard to compare gram stain results to. 2167 samples were reviewed. Of these 1552 were excluded base on inclusion criteria. Of the remaining 615, 120 (19.5%) were culture positive. There were 33 positive gram stain results, 1 false positive and 32 true positive results. The sensitivity was 26.67% with a specificity of 99.80% (p=0.0001). The negative predictive value is 84.88% (CI 83.44% – 86.21%). These results show that gram stain tests of native joints have a low sensitivity and poor negative predictive value. This is reflected in the current literature with prosthetic joints. Based on this study caution should be used when interpreting a negative gram stain result with appropriate safety netting and follow up required alongside clinical assessment

Heterotopic ossification (HO) of the hip after injury to the central nervous system can lead to joint ankylosis. Surgery is usually delayed to avoid recurrence, even if the functional status is affected. We report a consecutive series of patients with HO of the hip after injury to the central nervous system who required surgery in a single, specialised tertiary referral unit. As was usual practice, they all underwent CT to determine the location of the HO and to evaluate the density of the femoral head and articular surface. The outcome of surgery was correlated with the pre-, peri- and post-operative findings.

In all, 183 hips (143 patients) were included of which 70 were ankylosed. A total of 25 peri-operative fractures of the femoral neck occurred, all of which arose in patients with ankylosed hips and were associated with intra-articular lesions in 18 and severe osteopenia of the femoral head in seven. All the intra-articular lesions were predicted by CT and strongly associated with post-operative complications.

The loss of the range of movement before ankylosis is a more important factor than the maturity of the HO in deciding the timing of surgery. Early surgical intervention minimises the development of intra-articular pathology, osteoporosis and the resultant complications without increasing the risk of recurrence of HO.