In vivo measurement of volumetric wear of a total knee replacement.

A new Roentgen Stereophotogrammetric Analysis (RSA) system is reported; it can measure penetration of the metallic femoral component of a Total Knee Replacement (TKR) prosthesis into the polyethylene bearing on the tibial component. This system was used to analyse a study group of six Anatomic Graduated Components (AGC) knee prostheses more than 6 years post-implantation, and to compare with a control group of six newly implanted AGC prostheses. The volumetric loss of polyethylene was estimated by imaging each prosthesis at a series of different knee flexion angles. The mean difference between the RSA measured polyethylene bearing thickness and the manufacturer's quoted values for the control group was -0.03 mm (SD 0.17). The estimated linear penetration at 6.4 years in this prosthesis was determined to be 0.1 mm/year. Volumetric wear was estimated to be 600-700 mm(3)/year at 6.4 years, equating to approximately 100 mm(3)/year. This does not appear to be clinically significant amount of wear as this prosthesis has excellent survival at 10 years.

Long-term clinical results of the medial Oxford unicompartmental knee arthroplasty.

UNLABELLED: The medial Oxford unicompartmental knee arthroplasty uses a fully congruent mobile bearing, varying in thickness from 3.5-11.5 mm. Impressive clinical and survival results have been achieved by the designing surgeon, but can they be reproduced by an independent center and does the use of bearings less than 6 mm thick reduce the implant's survival? Between November 1983 and May 2000, 439 medial Oxford prostheses were implanted by three surgeons in Skovde, Sweden. One hundred fourteen knees (89 patients) were reviewed clinically at a minimum of 10 years postoperatively, using the Hospital for Special Surgery knee score. Ninety-one percent of the knees had good or excellent results, with no poor results, and 82% were reported as pain free. The 15-year survival rate for the entire cohort was 93%, and for the 432 knees (344 patients) that met the current indications for using the device, the survival rate was 94%. The 10-year survival rate for bearings less than 6 mm thick was 95%, compared with 94% with bearings greater than 6 mm. The results show that an independent center can achieve excellent long-term clinical and survival results in patients implanted with the Oxford prosthesis. Survival of the implant was not reduced by the use of thin polyethylene bearings. LEVEL OF EVIDENCE: Therapeutic study, Level IV (case series--no, or historical, control group). See the Guidelines for Authors for a complete description of levels of evidence.

In vivo kinematics of the ACL-deficient limb during running and cutting.

Anterior cruciate ligament-deficient (ACLD) knee kinematics during high-demand activities are poorly understood. We have devised a new method, using gait analysis, to more accurately assess 3-D in vivo kinematics of the knee. This has enabled us to report on how knee kinematics are altered after ACL rupture, during running and cutting. Fifteen unilaterally ACLD subjects were assessed using a 12-camera 100 Hz VICON motion analysis system. Simultaneous electromyographical (EMG) recordings were used to assess the role of the sensorimotor system in knee joint stability. All subjects were able to perform demanding cutting activities without experiencing symptoms of instability. We found that running produces fundamentally different kinematic patterns to those seen during walking. Tibiofemoral translation in the anteroposterior plane is controlled to within normal limits. Conversely, coronal translation and rotation are poorly controlled. We found that the injured leg was maintained in greater extension during the stance phase of all running activities studied and that the quadriceps muscle was active for longer during this period. We believe that low-demand activities, such as walking, do not reproduce kinematics relevant to ACLD instability and that future investigations into functional instability in the ACLD knee should focus on coronal and rotational displacements.

A novel method for in vivo knee prosthesis wear measurement.

Wear remains an important cause of failure in knee replacement. Of the current methods of early performance assessment or prediction, simulators have been un-physiological, single X-ray film analyses remain limited by accuracy and retrieval and survival methods have a prohibitive time scale. An accurate method is needed to allow a timely assessment of polyethylene component wear in vivo, when a new design is introduced, in order to predict likely outcome. We present a new method for measuring wear in vivo that we believe will allow this prediction of long-term wear. X-ray film pairs were taken of implanted prosthetic metal components. When the X-ray system was calibrated, projections of the appropriate Computer Aided Design (CAD) model could be matched to the shapes on the scanned X-ray films to find component positions. Interpenetration of the metal femoral component into the polyethylene component could then be established and represents our estimate of "wear". This method was used to measure in vivo prosthesis wear to an accuracy of 0.11 mm.

An assessment of methods for monitoring entrance surface dose in fluoroscopically guided interventional procedures.

In the light of a growing awareness of the risks of inducing skin injuries as a consequence of fluoroscopically guided interventional procedures (FGIPs), this paper reports measurements of ESDs made during the period August 1998 to June 1999 on 137 patients undergoing cardiac, neurological and general FGIPs in the South London area. In addition, different methods suitable for use in a routine monitoring programme of ESD are discussed. Although the need for additional data is acknowledged, the results reported reinforce the need for routine assessments to be made of ESDs in FGIPs. At present, the most reliable and accurate form of ESD measurement would seem to be arrays of TLDs. However, transducer based methods although likely to be less accurate, have considerable advantages in relation to a continuous monitoring programme. It is also suggested that there may be the potential locally for threshold dose area product (DAP) values to be set for specific procedures. These could be used to provide early warning of the potential for skin injuries.

Detection of varicella-zoster virus DNA by nested PCR in CSF from HIV-infected patients: A prospective evaluation.

The aim of this prospective study was to determine the frequency and clinical significance of detection of varicella-zoster virus (VZV) DNA in cerebrospinal fluid (CSF) from 120 HIV-infected individuals. Six of 8 CSF samples from patients with recent (up to 8 months previously) or concurrent cutaneous zoster contained detectable VZV DNA using the polymerase chain reaction. No detectable CSF VZV DNA was present in two patients who had an encephalopathy complicating cutaneous zoster or in 112 other patients without a history of recent of concurrent zoster. In conclusion, VZV DNA may be detected in CSF of patients with neurological disease and concurrent or recent zoster. However, the absence of detectable VZV DNA in CSF does not preclude the possibility of VZV associated neurological complications.

Acute lumbosacral polyradiculopathy due to cytomegalovirus in advanced HIV disease: CSF findings in 17 patients.

OBJECTIVES: To describe the abnormalities in CSF from HIV infected patients with acute lumbosacral polyradiculopathy (ALP) caused by cytomegalovirus (CMV) infection. METHODS: Retrospective case notes and laboratory records were reviewed for 17 consecutive patients with CMV associated ALP admitted to specialist HIV/AIDS units at UCL Hospitals and Chelsea and Westminster Hospital. RESULTS: Infection with CMV was confirmed by detection of CMV DNA by polymerase chain reaction amplification in 15 patients (all of whom were negative by culture), by culture in one patient, and by objective clinical response to anti-CMV treatment in one patient. Only nine patients had a CSF pleocytosis 28-1142 (median 150) cells/mm3; in seven there was a polymorphonuclear (PMN) leucocyte preponderance. Protein concentrations in CSF were moderately or considerably raised in 13 patients; CSF: plasma glucose ratios were < or = 50% in five patients. Two patients had no pleocytosis, normal CSF: plasma glucose, and normal or near normal protein values. CONCLUSIONS: Abnormalities in CSF in CMV associated ALP are varied: only 50% of patients have a "typical" PMN preponderant pleocytosis. The diagnosis of this condition should not rely on demonstration of a PMN preponderant pleocytosis, but on identification of CMV DNA in CSF and the exclusion of other opportunistic infections and lymphoma in order that specific anti-CMV treatment may be instituted.

Herpes simplex virus type 2 encephalitis and concomitant cytomegalovirus infection in a patient with AIDS: detection of virus-specific DNA in CSF by nested polymerase chain reaction.

A Caucasian homosexual man with AIDS and cytomegalovirus retinitis presented with facial pain and episodic confusion, had several seizures and became obtunded. An electroencephalogram was suggestive of herpes simplex encephalitis. The diagnosis was confirmed by detection of herpes simplex virus type 2 (HSV 2), but not type 1, DNA in cell-free cerebrospinal fluid (CSF) after amplification by nested polymerase chain reaction. The patient also had evidence of concomitant cytomegalovirus (CMV) infection with detectable CMV DNA in CSF. With high-dose acyclovir the patient recovered. Analysis of a follow up CSF sample taken four months later showed no detectable HSV-2 DNA.