Ultrasound-guided adductor canal block: a cadaver study investigating the effect of a thigh tourniquet.

BACKGROUND: Placement of local anaesthetic within the adductor canal using ultrasonography is an alternative to femoral nerve blocks for postoperative pain relief after knee joint replacement surgery. However, the effect of an inflated thigh tourniquet on the distribution of local anaesthetic within the adductor canal is unknown. The aim of this cadaveric study was to compare the distribution of radio-opaque dye within the adductor canal in the presence or absence of an inflated thigh tourniquet. METHODS: Bilateral ultrasound-guided adductor canal blocks were performed on the thawed lower limbs of five fresh frozen human cadavers. The left and right lower cadaver limbs were randomised to receive or not receive a thigh tourniquet inflated to 300 mm Hg for 1 h. X-rays with iohexol radio-opaque dye were obtained in four views, and fiducial markers inserted as reference points. Virtual editing technology was used to recreate outlines representing the distribution of the radio-opaque dye and superimpose these on anatomical images. RESULTS: Radio-opaque dye was distributed on the medial aspect of the thighs with entire and well circumscribed margins. The majority of the radio-opaque dye was confined within the adductor canal. Superior-inferior dye distribution was 315 mm [95% confidence intervals (CI) 289-342] and 264 mm (95% CI 239-289) in the presence and absence of an inflated thigh tourniquet, respectively (diff 95% CI -80.46 to -22.22, P=0.0081). Image analysis using the recreated radio-opaque outlines suggested that the most proximal point of the radio-opaque dye was 100 mm (95% CI 82-117) or 117 mm (95% CI 62-171) below the inguinal ligament in the presence and absence of an inflated thigh tourniquet, respectively (diff 95% CI -38 to 72, P=0.456). CONCLUSIONS: Application and inflation of thigh tourniquets significantly increased the combined superior-inferior dye distribution within the adductor canal of cadaveric limbs. There was insufficient evidence to suggest significant proximal spread of 25 ml of local anaesthetic to involve the motor branches of the femoral nerve. In some patients, the local anaesthetic may reach the popliteal fossa in close approximation to the sciatic nerve.

The 2012 ABC orthopaedic fellowship in North America: May 24 to July 2.

In May 2012, in airports across the globe, seven orthopaedic surgeons bravely said goodbye to their loved ones, and slowly turned towards their respective aircraft. Filled with expectation and mild trepidation they stepped into the unknown… the ABC fellowship of 2012.

Diagnosis and management of bone metastases.

Bone metastases are a common feature of many cancers and patients with a previous history of cancer may present with bony symptoms to many different specialties. It is, however, easy to mistakenly diagnose secondary bone cancer in patients who have abnormal imaging, when the cause of the symptoms and the abnormal imaging results is benign disease. In this review, common diagnostic mistakes are described with examples of imaging of both benign and malignant bony disease. The relative risk of developing bone metastases in different cancers is discussed, as well as the rationale of different therapies for proven bony metastases, such as radiotherapy, bisphosphonate therapy, orthopaedic intervention and vertebroplasty.

Extruded aneurysm coils found at craniotomy: report of two cases.

The operative findings are presented in two patients following inadequate coil embolization. At craniotomy, part of the coil mass had extruded through the fundus of both aneurysms. It is unclear if this phenomenon is confined to aneurysms that demonstrate significant regrowth and if there is an increased risk of rebleeding.

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.

Ten-year in vivo wear measurement of a fully congruent mobile bearing unicompartmental knee arthroplasty.

Polyethylene particulate wear debris continues to be implicated in the aetiology of aseptic loosening following knee arthroplasty. The Oxford unicompartmental knee arthroplasty employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. This study measures the in vivo ten-year linear wear of the device, using a roentgenstereophotogrammetric technique. In this in vivo study, seven medial Oxford unicompartmental prostheses, which had been implanted ten years previously were studied. Stereo pairs of radiographs were acquired for each patient and the films were analysed using a roentgen stereophotogrammetric analysis calibration and a computer-aided design model silhouette-fitting technique. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. In addition, eight control patients were examined less than three weeks post-insertion of an Oxford prosthesis, where no wear would be expected. The control group showed no measured wear and suggested a system accuracy of 0.1 mm. At ten years, the mean linear wear rate was 0.02 mm/year. The results from this in vivo study confirm that the device has low ten-year linear wear in clinical practice. This may offer the device a survival advantage in the long term.

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.

In vivo measurement of total knee replacement wear.

Polyethylene wear is one of the most important causes of failure of total knee replacements (TKRs). Currently, wear can only be accurately measured by retrieval studies. There is a need for a method to measure wear accurately in vivo. We have developed a Roentgen stereophotogrammetric analysis (RSA) system that can measure penetration of the metallic femoral component into the polyethylene of the tibia. We have used this system to study six AGC TKRs at 6 years postoperatively and six control AGC TKRs at 2 weeks postoperatively. The mean difference between the RSA measured bearing thickness and the manufacturer's quoted values for the control group was -0.03 mm (S.D. 0.17). The average linear penetration in the study group was 0.8 mm (S.D. 0.46). This was significantly (P<0.0001) different from the control group. The average linear penetration rate was 0.13 mm per year (S.D. 0.08). We would expect the penetration to deepen with time. In young active patients, this could be a cause for concern, particularly with a thin bearing. The current system is accurate enough to measure wear at 5 years post TKR. It has the potential for predicting long-term wear problems with new designs of TKR and new materials within 2 years.