Infection is a leading indication for revision
arthroplasty. Established criteria used to diagnose prosthetic joint infection
(PJI) include a range of laboratory tests. Leucocyte esterase (LE)
is widely used on a colorimetric reagent strip for the diagnosis
of urinary tract infections. This inexpensive test may be used for
the diagnosis or exclusion of PJI. Aspirates from 30 total hip arthroplasties
(THAs) and 79 knee arthroplasties (KA) were analysed for LE activity. Semi-quantitative
reagent strip readings of 15, 70, 125 and 500 white blood cells
(WBC) were validated against a manual synovial white cell count
(WCC). A receiver operating characteristic (ROC) curve was constructed
to determine the optimal cut-off point for the semi-quantitative
results. Based on established criteria, six THAs and 15 KAs were
classified as infected. The optimal cut-off point for the diagnosis
of PJI was 97 WBC. The closest semi-quantitative reading for a positive
result was 125 WBC, achieving a sensitivity of 81% and a specificity
of 93%. The positive and negative predictive values of the LE test
strip were 74% and 95% respectively. The LE reagent strip had a high specificity and negative predictive
value. A negative result may exclude PJI and negate the need for
further diagnostic tests. Cite this article:
The Oxford hip and knee scores (OHS and OKS)
are validated patient-reported outcome measures used in patients undergoing
total hip replacement (THR), hip resurfacing (HR), total knee replacement
(TKR) and unicompartmental knee replacement (UKR). We analysed the
absolute OHS and OKS and change in scores following THR, HR, TKR,
and UKR performed at one specialist centre. All patients undergoing
and completing at least one Oxford score were eligible for inclusion
in the study which included 27 950 OHS and 19 750 OKS in 13 682
patients. Data were analysed using non-linear quantile regression.
The median absolute Oxford scores for THR, HR, TKR and UKR were
pre-operative 68.8% (15.0/48), 58.3% (20.0/48), 66.7% (16.0/48),
60.4% (19.0/48) respectively: and post-operative asymptote was 14.6%
(41.0/48), 5.8% (45.2/48), 31.2% (33.0/48), 29.2% (34.0/48). The
median asymptotic change from the pre-operative score for THR, HR,
TKR and UKR were 47.9% (23.0/48), 47.9% (23.0/48), 33.3% (16.0/48)
and 32.4% (15.5/48), respectively. The median time at which no further
appreciable change in score was achieved post-operatively was 0.7
years for THR, 1.1 years for HR, 0.9 years for TKR and 1.1 years
for UKR. The curves produced from this analysis could be used to educate
patients, and to audit the performance of a surgeon and an institution.
The time to achieve a stable improvement in outcome varied between
different types of joint replacement, which may have implications
for the timing of post-operative review. Cite this article:
Cut-off values with highest sensitivity and specificity
for the synovial fluid white cell and differential count will facilitate
the accurate diagnosis of infection in total knee (TKR) and total
hip replacement (THR). All patients undergoing revision TKR or THR
for suspected prosthetic joint infection between 2009 and 2011 at
two hospitals were identified. A total of 75 patients were included
with a mean age of 70.3 years (38 to 89). Synovial fluid was aspirated
pre-operatively and peri-prosthetic tissue samples were taken intra-operatively
for histological and microbiological examination. Receiver operating characteristic (ROC) plots were constructed
for white cell and differential counts in aspirated fluid. The optimal
cut-off for TKR and THR was 1590 white cells/µl and 65% neutrophilia.
The white cell count cut-off value identified for THR was notably
lower than previously quoted in the literature. A cut-off value
for white cell count in synovial aspirate in suspected prosthetic
joint infection of between 1100 and 1700 white cells/µl is likely
to be applicable to both THR and TKR. Cite this article:
We describe the application of a non-invasive extendible endoprosthetic replacement in skeletally-mature patients undergoing revision for failed joint replacement with resultant limb-length inequality after malignant or non-malignant disease. This prosthesis was developed for tumour surgery in skeletally-immature patients but has now been adapted for use in revision procedures to reconstruct the joint or facilitate an arthrodesis, replace bony defects and allow limb length to be restored gradually in the post-operative period. We record the short-term results in nine patients who have had this procedure after multiple previous reconstructive operations. In six, the initial reconstruction had been performed with either allograft or endoprosthetic replacement for neoplastic disease and in three for non-neoplastic disease. The essential components of the prosthesis are a magnetic disc, a gearbox and a drive screw which allows painless lengthening of the prosthesis using the principle of electromagnetic induction. The mean age of the patients was 37 years (18 to 68) with a mean follow-up of 34 months (12 to 62). They had previously undergone a mean of six (2 to 14) open procedures on the affected limb before revision with the non-invasive extendible endoprosthesis. The mean length gained was 56 mm (19 to 107) requiring a mean of nine (3 to 20) lengthening episodes performed in the outpatient department. There was one case of recurrent infection after revision of a previously infected implant and one fracture of the prosthesis after a fall. No amputations were performed. Planned exchange of the prosthesis was required in three patients after attainment of the maximum lengthening capacity of the implant. There was no failure of the lengthening mechanism. The Mean Musculoskeletal Tumour Society rating score was 22 of 30 available points (18 to 28). The use of a non-invasive extendible endoprosthesis in this manner provided patients with good functional results and restoration of leg-length equality, without the need for multiple open lengthening procedures.
