A Low Percentage of Patients Satisfy Typical Indications for Single-stage Exchange Arthroplasty for Chronic Periprosthetic Joint Infection.

BACKGROUND: Periprosthetic joint infection (PJI) is a leading cause of revision arthroplasty. Considerable controversy still exists whether single- or two-stage exchange is the better approach for patients with chronic PJI. Historically, single-stage exchange arthroplasty was thought to have an unacceptably high risk of reinfection compared with two-stage exchange but recent studies have demonstrated that this may not be the case. To be considered for single-stage exchange, patients should meet certain criteria including a preoperatively identified nonvirulent pathogen in an immunocompetent host with an uncompromised soft tissue envelope. It is unclear what proportion of patients with chronic PJI actually meet these criteria. Additionally, patients who meet the criteria for single-stage exchange are selected because, in principle, they may be more likely to be able to overcome the infection, but it is unknown what the reinfection risk is in patients undergoing two-stage exchange who might have met selection criteria for single-stage exchange. QUESTIONS/PURPOSES: (1) What percentage of patients with chronic PJI treated at our institution met the International Consensus Meeting criteria for single-stage exchange arthroplasty? (2) Is the risk of persistent or recurrent infection lower for patients treated with two-stage exchange who met International Consensus Meeting criteria for single-stage exchange than it is among those who did not meet those inclusion criteria? METHODS: Between 2012 and 2016, one referral center treated 120 patients with chronic PJI as determined by Musculoskeletal Infection Society (MSIS) criteria. During this time, we used single-stage exchange only rarely in patients with chronic PJI (3%; four of 120), and only in oncologic patients with mega-prosthesis implants; 7% (eight of 120) underwent other procedures (resection arthroplasty or arthrodesis). Of the remaining 108, 16% (17) were lost to follow-up; the remaining 91 were evaluated in this retrospective study. To answer our first question, we applied the International Consensus Meeting indications for single-stage exchange, which were a known nonvirulent preoperative organism, an immunocompetent host, and a healthy soft-tissue envelope without a sinus tract; we then calculated the percentage of patients who would have met those criteria. To answer our second question, we compared those who would and would not have met those criteria in terms of the proportion who were determined to be infection-free at 2 years using the MSIS criteria. RESULTS: Only 19% (20 of 108) of patients met the International Consensus Meeting criteria for single-stage exchange. With the numbers available, there was no difference between those who met and did not meet those criteria in terms of the proportion of patients who had persistent or recurrent infection 2 years after treatment (three of 15 versus 32% [24 of 76]; p = 0.38). CONCLUSIONS: We found that only a small proportion of patients who presented with chronic PJI to a referral center would have been suitable for single-stage direct exchange; with the numbers available, we found no difference in the reinfection risk after two-stage revision in those patients compared with those who would not have met those criteria. Consequently, it is possible that a small proportion of patients may benefit from single-stage exchange, but our small sample size may have missed important differences in reinfection risk, and so our findings on that question must be considered preliminary. Larger studies randomizing patients who meet single-stage criteria to either single- or two-stage exchange will better elucidate the true reinfection risk in this patient population. LEVEL OF EVIDENCE: Level III, therapeutic study.

Wedge effect following intramedullary hip screw fixation of intertrochanteric proximal femur fracture.

INTRODUCTION: The aim of the current study was to determine whether application of an intramedullary hip screw for definitive management of intertrochanteric fracture was associated with post-operative deformity. Specifically this study investigated whether nail insertion would cause a "wedge effect" of the intertrochanteric fracture manifesting as lateralization of the femoral shaft and varus malalignment. MATERIALS AND METHODS: The trauma database at the University of Pittsburgh Medical Center was investigated to identify all intertrochanteric fractures (AO/OTA 31A) over the past 3 years treated with an IMHS. Fractures eligible for inclusion were performed under the supervision of a fellowship trained orthopedic trauma surgeon. All fractures were reduced in optimal alignment using percutaneous or mini-open strategies during the reaming process and nail insertion. The entry portal was over-reamed by at least 1.5 mm. Cases selected for review of the "wedge effect" had optimal post-operative imaging allowing for assessment of discrepancy between the operative and normal hip. RESULTS: Forty six patients with an average age of 77 years were included for study. Fifty percent were classified as unstable patterns. Shaft lateralization following IMHS fixation of the fractured hip was found to be an average of 7 mm greater than the contralateral intact hip (p < 0.001) (range 0-30 mm). The neck-shaft angle of the operative hips was 129° as compared to 133° on the intact side (p = 0.009). The stability of the fracture pattern was not predictive for post-operative lateralization of the femoral shaft or varus angulation (p > 0.05) (Table 2). There was no difference in post-operative deformity among techniques used for maintenance of reduction during reaming and nail insertion (p > 0.05). Despite deformity, all cases demonstrated radiographic radiographic fracture union. CONCLUSION: Despite attention to detail, the application of an intramedullary hip screw for intertrochanteric fracture has the tendency to lateralize the shaft relative to the head/neck segment (The "wedge effect").

EMG amplitude in maximal and submaximal exercise is dependent on signal capture rate.

This study analysed the effect of different electromyographic (EMG) capture rates during maximal voluntary contraction, submaximal and maximal dynamic cycling activity on EMG amplitude and signal characteristics. Ten healthy subjects participated in this study. Peak power output (PPO) and maximal isometric force output (MVC) were measured, followed by a progressive cycle ride on a cycle ergometer. Electromyographic (EMG) data were simultaneously captured during the MVC and cycling activities at frequencies of 32, 64, 128, 256, 512, 1024 and 1984 Hz. Significant differences in amplitude were found (p < 0.01) between MVC, submaximal (SUB) and maximal cycling activities (PWATT) for all capture rates. Asymptote values for IEMG amplitude occurred at EMG capture rates of 1604 +/- 235.6 Hz during MVC, 503.1 +/- 236.2 Hz during PWATT and 326.2 +/- 105.4 Hz during SUB cycling activity and were significantly different (p < 0.01). No significant differences were found for force/EMG ratios between PWATT and MVC at 1984 Hz capture rates (3.8 +/- 1.7 N/V vs 2.5 +/- 0.9 N/V) while significant differences occurred at 32 Hz capture rate (6.2 +/- 3.8 vs 16.0 +/- 8.0; p < 0.01). Low correlations were found between EMG activity captured at 1984 Hz during PWATT and lean thigh volume (r = 0.36) and MVC (r = 0.32). Asymptote values found on this study suggest that data captured below 326 Hz for SUB, 503 Hz for PWATT and 1604 Hz for MVC are not reliable. Therefore apparatus capturing EMG data at low frequencies from these values cannot be used for quantitative data analyses.

Anterior iliac crest bone graft harvesting using the corticocancellous reamer system.

OBJECTIVE: To evaluate the anterior iliac crest bone graft harvesting procedure using a corticocancellous acetabular reamer system. DESIGN: A total of 390 bone grafting procedures were reviewed using retrospective chart review. Two hundred twenty procedures were performed using the reamer system, and 170 were performed using traditional techniques (cortical strip, tricortical wedge, and cancellous trap door grafts). SETTING: The Hospital for Special Surgery, New York, New York. PARTICIPANTS: Operative cases involving an anterior iliac crest bone graft procedure between January 1, 1991 and February 28, 1998. MAIN OUTCOME MEASUREMENTS: Complications were organized by the categories major, intermediate, and minor. Statistical analysis included assessment of comorbidity to determine risk factors that may be associated with a propensity for complications. RESULTS: Of the 390 patients reviewed, 13.1 percent (51 of 390) developed a total of seventy-one complications. Of the seventy-one complications, forty were reamer-associated and thirty-one were traditional method-associated complications. As compared with the traditional group, major morbidity was lower in the reamer group (0.9 percent [2 of 220] as compared with 1.8 percent [3 of 170] [ p = 0.4]). Intermediate and minor morbidity were slightly higher in the reamer group than in the traditional group (5.9 percent [13 of 220] as compared with 5.3 percent [9 of 170] [ p = 0.7] and 9.5 percent [21 of 220] as compared with 7.1 percent [12 of 170] [ p = 0.4], respectively). Of the forty reamer-associated complications, 90 percent (36 of 40) resolved within ninety days (average 36.6 days). Of the thirty-one traditional method-associated complications, 74.2 percent (23 of 31) were resolved by 90 days (average 50.6 days). Using logistical regression analysis obesity (body mass index) ( p = 0.03) and smoking ( p = 0.03) were correlated with development of a complication. Furthermore, if a patient was obese and a smoker, the analysis predicted an 83 percent chance of developing a complication. CONCLUSIONS: The reamer technique was found to be safe and efficacious while producing a large amount of autogenous corticocancellous bone graft. Overall complication rates for the reamer and the traditional groups were comparable. The corticocancellous reamer system represents an effective option for bone graft harvesting.

Total ankle arthroplasty.

Ankle arthritis has traditionally been treated surgically with arthrodesis (fusion) after conservative measures have been exhausted. The success of joint arthroplasty in the knee, hip, and shoulder inspired many attempts over the past 30 years to construct a workable ankle prosthesis. The failures of first generation prostheses caused skepticism regarding the feasibility of total ankle arthroplasty (TAR), but the mistakes of the past have been transformed into improvements and modifications. Today's second generation total ankle designs show promise, and outcomes are encouraging. The Agility Ankle (DePuy, Warsaw, IN) designed by Dr. Frank Alvine is featured in this article. The method of implant and postoperative management are reviewed.

Spectral compression of the electromyographic signal due to decreasing muscle fiber conduction velocity.

Spectral compression of the electromyographic (EMG) signal, due largely to decreasing muscle fiber conduction velocity, is commonly used as an indication of muscle fatigue. Current methods of estimating conduction velocity using characteristic frequencies such as the median frequency of the power spectrum, are based on an assumption of uniform spectral compression. To examine changes in the EMG frequency spectrum during fatigue, muscle fiber conduction velocity was measured during sustained, isometric contractions of the biceps brachii. Compression of the EMG power and amplitude spectra was simultaneously examined using the median frequency and an alternative method-the spectral distribution technique. The spectral distribution technique consistently gave a better estimate of the relative change in muscle fiber conduction velocity than either of the median frequencies. This was further examined using a physiologically based EMG simulation model, which confirmed these findings. The model indicated that firing statistics can significantly influence spectral compression, particularly the behavior of characteristic frequencies in the vicinity of the firing rates. The relative change in the median frequency, whether of the amplitude or frequency spectrum, was consistently greater than the relative change in conduction velocity. The most accurate indication of the relative change in conduction velocity was obtained by calculating the mean shift in the midfrequency region of the EMG amplitude spectrum using the spectral distribution technique.

Deltoid ligament strain after correction of acquired flatfoot deformity by triple arthrodesis.

Deltoid insufficiency represents a difficult surgical challenge. We have witnessed patients who have developed a valgus tibiotalar deformity following a properly positioned triple arthrodesis. To investigate whether the triple arthrodesis itself, by creating a rigid triple joint complex below the ankle, leads to increased strain of the deltoid complex, a flatfoot model was created in 8 fresh-frozen below-knee amputation specimens. Each specimen was loaded in three gait cycle (GC) positions: Heel strike (0% GC), midstance (10% GC), and heel rise (40% GC). The three components of the ground reaction force (GRF) and the tendon forces consistent with those respective positions were applied. To simulate a posterior tibial tendon insufficient state the posterior tibial tendon was not loaded. Strain at the tibiocalcaneal fibers of the superficial deltoid ligament complex was determined at each of the three foot positions. A triple arthrodesis was performed and the deltoid strains were again recorded for each position. A significant increase in the strain of the deltoid ligament was observed for only the heel rise position (p=0.007) in our cadaver model following triple arthrodesis. The results favor medializing the calcaneus following arthrodesis to protect the deltoid complex.

Endoscopic plantar fasciotomy for chronic heel pain.

The purpose of our study was to determine whether endoscopic plantar fasciotomy is a safe and effective operation in this patient population. We reviewed our surgical results following endoscopic plantar fasciotomy in sixteen patients (twenty feet) with an average preoperative duration of symptoms of four years. Of the 20 feet, 9 had complete relief of pain while symptoms were improved in nine feet. One patient with bilateral symptoms had no relief in either foot. The average AOFAS hindfoot score improved from 62 to 80, a statistically significant difference. Unilateral patients did better than bilateral with no bilateral patients reporting complete resolution of symptoms. There were no iatrogenic nerve injuries. On the basis of our review, we recommend endoscopic plantar fasciotomy as an alternative to open plantar fascial release for those patients with recalcitrant heel pain.

Adaptive noncontact gesture-based system for augmentative communication.

An adaptive noncontact gesture-based system for augmentative communication is described. The system detects movement of any anatomical site through the analysis of reflected speckle. This movement is converted into two-dimensional (2-D) cursor coordinates and an adaptive software interface provides click actions and decision strategies. The system requires no accessory to be placed on the user. The system was developed in conjunction with user groups, who participated in the evaluation of the system. The usability results obtained illustrate the utility of the system. The system also compared favorably with other interface solutions.

Idiopathic pseudoaneurysm of the dorsalis pedis artery mimicking pigmented villonodular synovitis.

Pseudoaneurysm of the dorsalis pedis artery is uncommon and is usually associated with a history of trauma to the vessel. Without such a history, the diagnosis may be challenging, because the mass may be confused with other common soft tissue masses in the foot. This case report describes a 67-year-old man with an idiopathic pseudoaneurysm of the dorsalis pedis artery that mimicked pigmented villonodular synovitis.

Augmented Hopfield network for mixed-integer programming.

Watta and Hassoun recently proposed a coupled gradient neural network for mixed integer programming. In this network continuous neurons were used to represent discrete variables. For the larger temporal problem they attempted many of the solutions found were infeasible. This letter proposes an augmented Hopfield network which is similar to the coupled gradient network proposed by Watta and Hassoun. However, in this network truly discrete neurons are used. It is shown that this network can be applied to mixed integer programming. Results illustrate that feasible solutions are now obtained for the larger temporal problem.

A mathematical model for skeletal muscle activated by N-let pulse trains.

A physiologically based mathematical model for skeletal muscle activated by neural impulses is presented. This model is developed specifically to capture the behavior for mammalian skeletal muscle activated by N-lets (sets of N high-frequency pulses with variable interpulse intervals). N-let pulse trains have been demonstrated as a possible means of producing contractions with reduced fatigue and fiber-type transformation, while maximizing the force-time integral per pulse (FTIpP) of electrically stimulated muscle. This model is developed by modeling the underlying biophysical processes responsible for the initiation and maintenance of force generation in muscle. The release and reaccumulation dynamics of calcium ions from the sarcoplasmic reticulum are modeled and proposed as the governing mechanism for the observed N-let effects. It is found that the new model is robust, numerically stable and easily implemented. Simulation results are presented that demonstrate the model's ability to capture a variety of the nonlinear summation, force and stiffness variation effects seen experimentally when activating skeletal muscle with N-lets. General properties of FES muscle are also predicted by the model. The significant insight provided by this model into the internal dynamics of skeletal muscle is used to assess a variety of mechanisms proposed for N-let behavior. It is postulated that the calcium release and reaccumulation dynamics, as incorporated in this model, are responsible for the N-let effects found in experiment.

Rheumatoid arthritis of the ankle and hindfoot.

Rheumatoid arthritis frequently affects the hindfoot and ankle and may present a considerable source of dysfunction. Awareness of characteristic clinical and radiographic findings and other diagnostic modalities help the clinician to evaluate the progression of the disease and determine the best methods of management. A variety of nonoperative treatments may slow progression of deformities, improve function, and provide symptomatic relief. If these measures fail, surgical intervention, including soft-tissue procedures as well as a variety of arthrodesis techniques, can return patients to a more active lifestyle.

A nonlinear mathematical model of electrically stimulated skeletal muscle.

A new biophysically based mathematical model for a human musculotendon system is presented. This model is developed specifically for skeletal muscle activated by functional electrical stimulation (FES). The reverse-order recruitment dynamics of FES activated systems are modeled, as are the underlying processes of force generation in mammalian muscle. The resulting system model is both nonlinear and highly coupled, reflecting the fundamental structure and behavior of skeletal muscle. A new heterogeneous model structure for a contractile element is also presented that overcomes many of the problems which arise when attempting to describe all possible contraction modes. It is found that the new model is robust, numerically stable, and easily implemented. Simulation results are presented that demonstrate the model's ability to capture a variety of nonlinear behaviors observed in skeletal muscle activated by FES. Significant insight into the internal dynamics of force development in FES muscle may also be gained from the model. This model is intended as a possible alternative to those currently available in the literature. It may be of use to those conducting research into the modeling, control and optimization of FES generated motion, and neural feedback systems.

Roger Mann Award 1995. Capsular interposition arthroplasty for severe hallux rigidus.

Thirty patients (37 feet) with severe hallux rigidus underwent resection arthroplasty of the first metatarsophalangeal joint with our modification (reattachment of the extensor hood and extensor brevis to the flexor hallucis brevis as a capsular interposition arthroplasty, with minimal bone resection). Pain and function were significantly improved. Transfer metatarsalgia was not seen. All patients had at least 4/5 plantarflexion strength and averaged 50 degrees of dorsiflexion. In patients with severe hallux rigidus and nearly equal length of first and second metatarsals, capsular interposition arthroplasty offers a surgical option that relieves pain without sacrificing motion or strength.

Treatment of established nonunions of Mitchell osteotomies.

The Mitchell distal metatarsal stepcut osteotomy for the treatment of hallux valgus is a technically demanding procedure with a high complication rate. Reported complications include metatarsal shortening with lateral metatarsalgia, partial avascular necrosis of the distal fragment, and loss of position with incomplete correction. Nonunion, however, has only rarely been reported. We describe our experience with the treatment of three nonunions of Mitchell osteotomies reconstructed using a tricortical iliac crest bone graft.

Fuzzy clustering of children with cerebral palsy based on temporal-distance gait parameters.

Temporal-distance parameters for 88 children with the spastic diplegia form of cerebral palsy (CP) are grouped using the fuzzy clustering paradigm. The two features chosen for clustering are stride length and cadence which are normalized for age and leg length using a model based on a population of 68 neurologically intact children. Using information provided by the neurologically intact population and cluster validity techniques, five clusters for the children with cerebral palsy are identified. The five cluster centers represent distinct walking strategies adopted by children with cerebral palsy. Utilizing just four easily obtained parameters--stride length, cadence, leg length and age--and a small number of simple equations, it is possible to classify any child with spastic diplegia and to generate an individual's membership values for each of the five clusters. The clinical utility of the fuzzy clustering approach is demonstrated with pre- and post-operative test data for subjects with cerebral palsy (one neurosurgical and one orthopaedic) where changes in membership of the five clusters provide an objective technique for measuring improvement. This approach can be adopted to study other clinical entities where different cluster centers would be established using the algorithm provided here.

Normalization of temporal-distance parameters in pediatric gait.

Several techniques for the normalization of temporal-distance parameters in pediatric gait are given. The resulting normalized data can be used to compare (or discriminate) individuals or groups of individuals without the effect of variables such as age and height. The normalization with respect to a reference data set or with respect to the data set itself can be accommodated. Three novel techniques for normalization of gait data have been given: offset, decorrelation and detrending. For normalization of stride length with respect to height, all three are superior to the commonly accepted technique of dividing by the height. The offset technique has obscure units and will have a residual correlation. The decorrelation technique also has obscure units but will have zero correlation provided it is being normalized using a linear model (or piecewise linear model) fitted to the data in a least-squares sense. The detrending technique will also result in a zero correlation if piecewise linear or polynomial models, fitted to the data in a least-squares sense, are used. The detrending technique is the most useful of the three techniques proposed as it will also generate the same units as the original data set and can be easily scaled so that its magnitude is also comparable with the original data. Both the decorrelation and detrending techniques can be used simultaneously to normalize data with respect to two or more variables.