Douglas T. Hutchinson

The effects of drilling force on cortical temperatures and their duration: an in vitro study.

Bone loss due to thermonecrosis may weaken the purchase of surgically placed screws and pins, causing them to loosen post-operatively. The goal of this study was to determine how differences in applied drilling forces affect the temperature of cortical tissue near the drilling site. Results from thermocouples placed into fresh cortical bone indicate that increasing the applied drilling force resulted in a significant decrease (P=0.001) of maximum cortical temperatures. Furthermore, increasing the drilling force resulted in a significant decrease (P=0.001) in the average duration of temperature elevations above 50 degrees C. The results of the current study demonstrate that by the application of a larger force to the drill, both maximum cortical temperatures and their duration above 50 degrees C may be effectively reduced, decreasing the potential for thermal necrosis in the neighboring cortical bone.

Cyclic Loading of Olecranon Fracture Fixation Constructs

Background: Despite the good results that are usually reported after fixation at the sites of olecranon fractures and osteotomies, problems such as loss of fixation, nonunion, and the need for revision surgery are still encountered. Various types of fixation have been recommended, but few have been evaluated with use of clinically relevant cyclic load testing at appropriate levels of stress. The purpose of the present study was to test multiple olecranon fixation techniques under physiologic cyclic loads. Methods: We studied ten cadaveric elbows with use of cyclic loading that simulated (1) active range of motion and (2) pushing up from a chair. Each specimen underwent fixation of a simulated 50% transverse olecranon fracture with use of intramedullary and cortically fixed tension band constructs (in randomized order) followed by fixation with a 7.3-mm-diameter cancellous screw with and without a tension band. Displacement transducers were placed posteriorly on the tension side and anteriorly near the articular surface. Results: Both configurations involving the 7.3-mm-diameter cancellous screw provided the most stable fixation—nearly five times better than that provided by the Kirschner-wire techniques. Use of the tension band in conjunction with the intramedullary screw improved the stability of fixation. In none of the constructs did the AO tension band result in compression across the osteotomy gap. Conclusions and Clinical Relevance: The use of a 7.3-mm screw in conjunction with a tension band provided better fixation of simulated displaced transverse fractures than did the use of Kirschner wires in conjunction with a tension band or the use of a screw only. The AO principle of converting posterior tensile forces to articular compressive forces was not demonstrated in this study. We therefore question the validity of the tension band concept in olecranon fracture fixation and recommend passive rather than active range of motion in the immediate postoperative period to limit fracture distraction.

Object Discrimination With an Artificial Hand Using Electrical Stimulation of Peripheral Tactile and Proprioceptive Pathways With Intrafascicular Electrodes

Trans-radial amputee subjects were implanted with intrafascicular electrodes in the stumps of the median and ulnar nerves. Electrical stimulation through these electrodes was used to provide sensations of touch and finger position referred to the amputated hand. Two subjects were asked to identify different objects as to size and stiffness by manipulating them with a myo-electric hand without visual or auditory cues. Both subjects were provided with information about contact force with the objects via tactile sensations referred to their phantom hands. One subject, who was provided with information about finger position in the prosthetic hand via a different tactile sensation referred to his phantom hand, was unable to correctly identify the objects. The other subject, who received information about finger position via a proprioceptive sensation referred to his phantom hand, correctly identified the objects at a level statistically significantly above chance performance.

The proximal ulna: an anatomic study with relevance to olecranon osteotomy and fracture fixation

The purpose of this study was to define the proximal ulna anatomy with respect to olecranon osteotomy and fracture fixation. Thirty-nine cadaver elbows were dissected. The mean ulnar length (triceps insertion to ulnar styloid) was 26.0 cm (range, 27.1-29.0 cm). The mean distance from the triceps insertion to the ulnas varus angulation point was 7.6 cm (range, 6.5-9.0 cm). The distance ratio from the triceps insertion to the proximal ulnar angle to the overall ulna length was consistent, averaging 0.29 (range, 0.23-0.33). The mean diameter of the medullary canal at the ulnar angulation point could accommodate a 7.0- or 7.3-mm intramedullary screw. The mean width of the olecranon bare area (lacking articular cartilage) was 0.53 cm (range, 0.13-0.97 cm), and the mean distance from the triceps insertion to the corresponding area of the bare spot on the dorsal cortex was 2.1 cm (range, 1.4-2.5 cm).

Biomechanics of pulley reconstruction

The biomechanics of the reconstructed flexor retinacular pulley system are poorly defined. We used a mathematical theoretical model, confirmed by a cadaver model, and a clinical radiographic model to evaluate a variety of different joint and pulley combinations. We examined twenty-four sets of radiographs of 12 fingers in 9 patients for whom excursion was measured and predicted by the mathematical model. The 30 pulley combinations evaluated in the in vitro cadaver model showed statistical correlation with the biomechanical mathematical model. Recommendations of clinical application on the basis of this information include the following: (1) Two pulleys should be placed, one proximal and one distal to each joint. (2) These two pulleys should be balanced about the joint axis both in distance from the axis and in pulley height. (3) They should be positioned at the edge of the flare of the metaphysis. (4) The three individual joints can be balanced, one to another, by maintaining minimal bowstringing at all three joints. In this way, the relative excursion at the joint and torque at the joint will be maintained in a physiological ratio as close to normal as possible.

Continuous Detection and Decoding of Dexterous Finger Flexions With Implantable MyoElectric Sensors

A rhesus monkey was trained to perform individuated and combined finger flexions of the thumb, index, and middle finger. Nine implantable myoelectric sensors (IMES) were then surgically implanted into the finger muscles of the monkeys forearm, without any adverse effects over two years postimplantation. Using an inductive link, EMG was wirelessly recorded from the IMES as the monkey performed a finger flexion task. The EMG from the different IMES implants showed very little cross correlation. An offline parallel linear discriminant analysis (LDA) based algorithm was used to decode finger activity based on features extracted from continuously presented frames of recorded EMG. The offline parallel LDA was run on intraday sessions as well as on sessions where the algorithm was trained on one day and tested on following days. The performance of the algorithm was evaluated continuously by comparing classification output by the algorithm to the current state of the finger switches. The algorithm detected and classified seven different finger movements, including individual and combined finger flexions, and a no-movement state (chance performance = 12.5%) . When the algorithm was trained and tested on data collected the same day, the average performance was 43.8±3.6% n=10. When the training-testing separation period was five months, the average performance of the algorithm was 46.5±3.4% n=8. These results demonstrated that using EMG recorded and wirelessly transmitted by IMES offers a promising approach for providing intuitive, dexterous control of artificial limbs where human patients have sufficient, functional residual muscle following amputation.

Pins and plaster vs external fixation in the treatment of unstable distal radial fractures: A randomized prospective study

90 unstable fractures of the distal radius were studied in a randomized, prospective manner. Follow-up consisted of patient questionnaire, medical record review, therapist evaluation and radiography at 4 months, 1 year and 2 years post-operatively. Overall results were good or excellent in 94%. No significant differences were found between treatment groups (external fixation and pins and plaster) in final results, range of motion, intrinsic tightness, grip strength, or the presence of arthritis. The complication rate was high for both groups (45%), and half of the complications were major. External fixation maintained radial length more effectively (significantly in those patients followed for 2 years) but was associated with higher initial costs (20 times) and a greater number of minor complications.

Superior mesenteric artery syndrome in pediatric orthopedic patients.

Superior mesenteric artery (SMA) syndrome is a rare cause of small bowel obstruction in both adult and pediatric populations. Of 14 patients with the diagnosis from 1979 to 1987, eight had confirmatory upper gastrointestinal studies and were able to be followed for an average of 32 months. All eight were of similar age (range, 14.2 to 19 years), body build (asthenic), and clinical presentation. The presentation included nausea and intermittent, voluminous, bile-stained vomiting, despite intervening periods of normal appetite and bowel sounds. The average delay in diagnosis was five days. Nasogastric drainage and intravenous fluids were the mainstay of treatment and were successful in every case. Fifty percent of the patients had more than one episode requiring treatment; each episode resolved with simple treatment. Two of three patients with body casts required cast removal. No patient required intravenous hyperalimentation, removal of spinal instrumentation, or abdominal surgery to relieve the obstruction. Three of the eight patients had not had spinal surgery or cast immobilization.

Rapid onset of ulnar nerve dysfunction during transient occlusion of the brachial artery

Perioperative ulnar neuropathy is a complication that occurs even in patients who seem to be appropriately padded and positioned.The disproportionately high incidence of postoperative ulnar nerve injury compared with the median and radial nerves has largely been attributed to its vulnerability to compression or stretch at the cubital tunnel. Some clinical and laboratory evidence suggests that compromise of perfusion to the upper extremity may also play a role in this complication. To determine whether the ulnar nerve is more sensitive to ischemia of the upper extremity, we studied 10 men during general anesthesia. Somatosensory evoked potentials of the radial, median, and ulnar nerves were simultaneously recorded during general anesthesia with the brachial artery occluded proximal to the cubital fossa. All three nerves showed rapid changes in signal amplitude in response to occlusion of the brachial artery, but the amplitude of the ulnar nerve was affected earlier and to a greater degree. Compared with the median nerve, the change in ulnar nerve signal amplitude during ischemia was significantly greater after 4 min (P = 0.002). This trend persisted at 6 and 8 min (P = 0.008). At 4, 6, and 8 min of ischemia, the ulnar nerve likewise showed a greater decrease in amplitude compared with the radial nerve, with corresponding P values of 0.015, 0.008, and 0.008. We conclude that the ulnar nerve is more sensitive to ischemia of the upper extremity compared with the radial and median nerves. In addition to its increased vulnerability at the elbow, compromise of arterial flow may contribute to some cases of postoperative ulnar neuropathy. Implications: Postoperative ulnar neuropathy is thought to result from compression or stretch of the ulnar nerve at the elbow. However, patients may sustain this complication despite careful padding and positioning. This study suggests that the ulnar nerve may also be unusually sensitive to decreases in blood supply to the arm. Care should not only to properly position and pad the elbows, but also to ensure adequate perfusion of the upper extremities. (Anesth Analg 1998;87:677-80)

Treatment of Carpal Tunnel Syndrome by Members of the American Society for Surgery of the Hand: A 25-Year Perspective

PURPOSE In 1987, Duncan et al.(1) reported on a survey of the members of the American Society for the Surgery of the Hand (ASSH) about their practices in treating carpal tunnel syndrome (CTS). To better understand changes in the treatment of CTS over the past 25 years, we repeated the survey while incorporating present-day controversies. METHODS With the approval of the ASSH, an Internet-based survey was e-mailed to all members of the Society. This included 33 primary questions focusing on 4 areas of study: surgeon demographic information, nonoperative treatment, surgical technique, and postoperative care. A total of 1,463 surveys were delivered and 707 surveys were completed and returned, for a response rate of 48%. Responses were compared with the responses from Duncan et al. published 25 years ago.(1) RESULTS In contrast to the practice patterns identified 25 years ago, this survey identified several changes in current clinical practices including the following statistically significant findings: Preoperatively, surgeons have increased the use of splints and corticosteroid injections, treat nonoperatively longer, and have narrowed their surgical indications. Regarding surgical technique, surgeons now are using tourniquets less, infiltrate the carpal tunnel with corticosteroids less, and place deep sutures less often. Furthermore, performing concomitant procedures along with release of the transverse carpal ligament has decreased. Orthotic use and duration postoperatively also decreased. CONCLUSIONS Although significant differences are evident between management of CTS between 1987 and 2011, no consensus has emerged.