Spinal fractures are common following underbody blast. Most injuries occur at the thoracolumbar junction, and fracture patterns suggest the spine is flexed at the moment of injury. However, current mechanistic descriptions of vertebral fractures are based on low energy injuries, and there is no evidence to correlate fracture pattern with posture at the loading rates seen in blast injury. The T12-L1 segment of 4 human spines was dissected to preserve the paraspinal ligaments and potted in polymethylmecrylate. The specimens were impacted with a 14 kg mass at 3.5m/s in a drop tower; two specimens were impacted in neutral posture, one in flexion, and one in extension. A load cell measured the load history. CT scans and dissection identified the injury patterns. Each specimen sustained a burst fracture. The neutral specimens demonstrated superior burst fractures, the flexed specimen demonstrated a superior burst fracture with significant anterior involvement, and the extended specimen showed a posterior vertebral body burst fracture. At high loading rates, the posture of the spine at the moment of injury appears to affect the resulting fracture. This supports understanding the behaviour of the spine in blast injury and will allow improved mitigation system design in the future.
Improvised Explosive Device (IED) attacks on vehicles have been a significant feature of recent conflicts. The Dynamic Response Index (DRI), developed for predicting spinal injury in aircraft ejection, has been adopted for testing vehicles in underbelly blast. Recent papers suggest that DRI is not accurate in blast conditions. We suggest that the distribution of blast and ejection injuries is different. A literature review identified the distribution of spinal fractures in aircraft ejection incidents. A Joint Theatre Trauma Registry search identified victims of mounted IED blast with spinal fractures. The distribution of injuries in the two groups was compared using the Kruskall Wallis test. 329 fractures were identified in ejector seat incidents; 1% cervical, 84% thoracic and 16% lumbar. 245 fractures were identified in victims of mounted blast; 16% cervical, 34% thoracic and 50% lumbar. There was no significant similarity between the two (p=1). There was no statistically significant difference between the distribution of fractures in blast survivors versus fatalities. The difference between blast and ejection injury patterns suggests that injury prediction models for ejection should not be extrapolated to blast mechanisms and that new models need to be developed.
Bone cement reaches high temperatures while polymerising. Bone has been shown to be sensitive to thermal injury with osteonecrosis reported after one minute at 47°C. Necrosis during cementing might compromise the bone-cement interface. Some surgeons fill the joint cavity with irrigation fluid to provide a heatsink during cementing, but this has not been supported by research. We used a model acetabulum in a bovine humerus to allow measurement of bone temperatures in cementing. Models were prepared with a 50mm diameter acetabulum and three temperature probe holes. Four warmed models were cemented with Palacos RG using a standard mixing system and a 10mm UMHWPE disc to represent an acetabular component. Two of the acetabular models were filled with room temperature water to provide a heatsink. An electronic probe measured temperature at 5 second intervals from the moment of cementing. In the models with no heatsink, peak temperature was 40.3°C. The highest temperature rise was 7.5°C. In the models with a heatsink, there was a mean fall of 4.4°C. These results suggest that using a heatsink while cementing prostheses may reduce the peak bone temperature.
The Global Conservative Anatomic Prosthesis (Global CAP) is an uncemented press fit humeral resurfacing implant developed by DePuy. We report a single surgeon series of Global CAP prostheses implanted in Norwich. 103 procedures were carried out between 2006 and 2011, in 93 patients. Mean age was 72 years (range 43 to 90). Patients were followed up for a mean 8 months (range 0 to 56). Pre-operative Oxford shoulder scores were recorded in a preadmission clinic and an Oxford score questionnaire was sent to patients post-operatively in December 2011. The mean score preoperatively was 19, rising to 28 postoperatively. Two patients developed rotator cuff tears and have been revised to reverse polarity arthroplasty. One is pending revision for a cuff tear. This prosthesis shows promise at this early stage for compensated glenohumeral arthritis when a bone preserving procedure is desirable.
Hip fractures are common injuries in the elderly, with significant mortality and morbidity from several factors. Many of these patients have cardiac disease, and some develop cardiac complications which may increase mortality. Troponin T is a marker of myocardial injury but can be raised in other conditions. Patients over 60 years old admitted with hip fracture during the study period had their troponin T measured on admission and following surgery. Assay was performed after the patient had completed their treatment. We report the results of this study one year after the last patient was admitted. 108 patients were recruited. The average age was 84 years; 86% were female. This study found that 27% of hip fracture patients had some increase in the troponin T levels in the peri-operative period. This increase was not associated with an increase in early mortality, but there was an increase in one-year mortality for those with an increase in troponin T (45% versus 22%, p=0.03). These findings indicate that the routine measurement of troponin T after a hip fracture is unnecessary.
To determine if any notable differences between a cemented Thompson stem hemiarthroplasty and a cemented Exeter stem hemiarthroplasty (ETS), 200 patients with a displaced intracapsular fracture were randomised between the two prosthesis. Surviving patients were followed-up for one year by a nurse blinded to the treatment allocation. The mean age of patients was 84 years and 13% were male. There were no differences between groups for the length of surgery, need for blood transfusion or hospital stay. Implant related complications were three minor operative fractures of the femur in each group. Two patients in the Thompson group had dislocation of the prosthesis requiring revision surgery and one further patient in the Thompson group had late acetabular wear requiring conversion to a total hip replacement. One further patient in the Thompson group had cement retained in the acetabulum. In total therefore only three patients, all in the Thompson group, which required revision surgery. Easy of surgery was assessed subjectively by the surgeon and reported to be easier for the ETS group (p=0.0002). During follow-up there was no significant difference in the degree of residual pain between groups. Conclusions are that the cemented Exeter stem hemiarthroplasty has some advantages over the traditional cemented Thompson hemiarthroplasty.
The CMI pyrocarbon implant is a unipolar arthroplasty for trapeziometacarpal joint arthritis which is implanted in to the thumb metacarpal. Previous case series have shown these implants provide significant pain relief and good patient satisfaction. We report the first cases of pyrocarbon hemiarthroplasty from Peterborough. Seventeen cases in fifteen patients were retrospectively reviewed. The average patient age was 59.7 years (range 47–72). 7 patients were men and 8 were women. Five were discharged with good outcome at a mean of 11.5 months (range 6–19). One failed to attend follow up. Most patients in whom the implant survived were afforded good pain relief by the procedure and had a good functional range of thumb movement. Radiologically 8 implants were subluxed by at least 50%. One implant was revised after dislocation and loosening of the prosthesis which was associated with trauma. She made excellent clinical progress after revision of the prosthesis. One of the thirteen cases dislocated and was revised to a trapeziumectomy after 11 months. Preliminary results suggest that this implant affords good pain relief and functional improvement in managing OA at the TMC joint. Longer term follow up will be required to correlate clinical and radiological outcomes.
It is common practice in wrist arthroscopy to suspend the patient’s arm using Chinese finger traps and to distract the wrist joint by applying weight to the arm at the elbow. It is possible that this may cause significant pressure to be applied to the fingers, and potentially damage the digital nerves. We examined the pressure applied by finger traps and consider the risk this poses to the digital nerves. Standard finger traps were suspended from a spring balance and the author’s fingers inserted along with a length of rubber tubing. The tubing was filled with saline and connected to a digital compartment pressure monitor. The hanging mass was gradually increased and the pressure in the rubber tubing noted. This pressure was taken as analogous to the pressure affecting the neurovascular bundle. Pressure increases linearly with increasing mass. A pressure of 500mmHg has been suggested as necessary to cause nerve injury1. Using non-invasive technique it was not possible to accurately measure the absolute pressure acting on the digital nerves. However the increase in pressure was noted. Using weight to distract the wrist during arthroscopy has potential to cause nerve injury. We suggest that pressure insufflation combined with Chinese finger traps with minimum weight traction provides a more than satisfactory view at wrist arthroscopy and can avoid potential digital nerve injury. However traction through finger traps for other purposes such as fracture reduction may be used with caution.
