Limitation on stabilizing plane waves via time-delay feedback.

Previous work has demonstrated the possibility of stabilizing plane wave solutions of one-dimensional systems using a spatially local form of time-delayed feedback. We show that the natural extension of this method to two-dimensional systems fails due to the presence of torsion-free unstable perturbations. Linear stability analysis of the complex Ginzburg-Landau equation reveals that long wavelength, transverse wave instabilities cannot be suppressed by the method of extended time-delay autosynchronization. The conclusion follows from symmetry considerations and therefore applies to a wide class of models with simple plane wave solutions.

An investigation of sensory deficits underlying the aphasia-like behavior of macaques with auditory cortex lesions.

Bilateral auditory cortex lesions in Japanese macaques result in an aphasia-like deficit in which the animals are unable to discriminate two forms of their coo vocalizations. To determine whether this deficit is sensory in nature, two monkeys with bilateral lesions were tested for their ability to discriminate frequency and frequency change. The results indicated that although the animals were able to discriminate between sounds of different frequencies, they were unable to determine whether a sound was changing in frequency. Because the animals' coo vocalizations differ primarily in the predominant direction of their frequency change and not in their absolute frequency content, the aphasia-like deficit of animals with bilateral auditory cortex lesions appears to be a sensory disorder.

The functional outcome with metallic radial head implants in the treatment of unstable elbow fractures: a long-term review.

BACKGROUND: A long-term review of metal prosthetic radial head replacement in patients with radial head fractures associated with gross instability of the elbow has been performed. METHOD: Twenty patients were reviewed using a modified Mayo Clinic functional rating index system. The mean follow-up was 12.1 years, with a range from 6 to 29 years. RESULTS: Results were excellent in 12 patients, good in 4 patients, fair in 2 patients, and poor in 2 patients. A metal radial head replacement restored elbow stability when fracture of the radial head occurred in combination with dislocation of the elbow, rupture of the medial collateral ligament, fracture of the proximal ulna, and/or fracture of the coronoid process. CONCLUSION: We conclude that a metal radial head prosthesis has select indications. We advocate its use when the radial head cannot be reconstructed in the setting of a clinically unstable elbow. Results suggest that it functions well on a long-term basis.

Biomechanical analysis of the Medoff sliding plate.

BACKGROUND: A new device for fixation of hip fractures the Medoff plate was biomechanically tested and compared with the Ambi plate and Gamma nail. METHODS: Six pairs of human cadaveric femurs were used. The characteristics evaluated were structural stiffness, strain distribution, and modes of failure. Results were compared with the Ambi plate and Gamma nail biomechanical studies from a previous study that used the same methods. RESULTS: The Medoff plate was stiffer than the other two implants for intertrochanteric fractures, and for segmental subtrochanteric fracture. The Medoff plate was more load sharing than the other implants in these fracture configurations. The mean load to failure was lower than for the Ambi plate or the Gamma nail. CONCLUSION: The Medoff plate is a better load-sharing device than the Ambi (DHS) or Gamma nail systems. The main concern is its structural weakness. The implant failed at loads 50% less than other devices. The greatest risk of implant failure is with unstable subtrochanteric fractures.

Fracture of the patella following total knee arthroplasty.

The charts of 21 patients (22 knees) with significant radiographic changes of the patella after total knee arthroplasty were reviewed. The average patient age was 73 years, and average follow-up after arthroplasty was 7.3 years. Lateral release, fat pad excision, quadriceps tendon release, and previous surgery were implicated in the etiology of fracture of the patella. Five cases had type 1 pattern (sclerosis, fragmentation, and no fracture), 5 cases had type 2 pattern (undisplaced fracture and fragmentation), and 12 cases had type 3 pattern (displaced fracture and fragmentation). Type 1 and 2 patterns required no surgical treatment and were rated good to excellent according to the Hospital for Special Surgery Disability Score Sheet. Patients with a type 3 pattern who did not undergo surgery were rated poor to fair, while patients with a type 3 pattern who underwent surgical treatment (patellectomy, removal of the patellar component, or excision arthroplasty for infection) were rated good. Patellectomy is the treatment of choice for patients with displaced fractures of the patella. A classification system for the pattern of patellar changes is proposed.

"Central" auditory gap detection: a spatial case.

Normal listeners were tested for their temporal auditory gap detection thresholds using free-field presentation of white-noise stimuli delivered from the left (L) and right (R) poles of the interaural axis. The noise bursts serving as the leading and trailing markers for the silent period were presented in either the same (LL,RR) or different (LR,RL) auditory locations. The duration of the leading marker was a second independent variable. Gap thresholds for stimuli in which the markers had the same location were low, and usually were independent of the duration of the leading marker. Gap thresholds for the LR and RL conditions were longer. These gap thresholds were sensitive to the duration of the leading marker, and increased as the leading marker duration decreased. This finding is consistent with the hypothesis that a relative timing operation mediates gap detection when the markers activate different perceptual channels. The present data suggest that this timing process can operate on perceptual channels emerging from central nervous system processing.

Micromotion secondary to axial, torsional, and shear loads in two models of cementless tibial components.

Tibial component loosening and lack of bone ingrowth remain serious problems in uncemented knee arthroplasty. Initial implant stability is the most important factor in achieving bone ingrowth. Eccentric axial loading causing liftoff has been identified as a potential problem, but the role of torsion and shear stability is unclear. This study assesses the micromotion in two uncemented components subjected to eccentric axial (lateral, medial, posterior, anterior), shear, and torsional loads. Four configurations were tested: Tricon M (pegs) (Smith and Nephew Richards, Memphis, TN), Genesis (stem only) (Smith and Nephew Richards), Genesis with screws, and Genesis with pegs. Nine pairs of cadaver tibias were implanted, and cyclic loads were applied. Micromotion was measured with two linear variable differential transformers. Micromotion values for each mode of loading were compared using a one-way analysis of variance. Genesis with screws had the least micromotion for all applied loads (14-33 micrometers), whereas Genesis with stem only has the maximum value of micromotion (27-212 micrometers). Genesis wit and Tricon had intermediate ranges of micromotion (32-121 and 107-140 micrometers, respectively). It is concluded that peg fixation and stem fixation are inadequate and result in significant micromotion. Stem plus screws provides the most stable fixation and may be compatible with bone ingrowth.

Biomechanical analysis of the Gamma nail and sliding hip screw.

Nine pairs of human cadaveric femora were used to study the biomechanical characteristics of the Gamma nail and a standard telescoping screw plate implant (Ambi) to determine whether there were any mechanical advantages of one system over the other. Parameters studied included structural stiffness, strain distribution, and failure modes for intertrochanteric and subtrochanteric fractures. There was no significant difference in structural stiffness for stable intertrochanteric and subtrochanteric fractures. The Gamma Nail composites, however, were stiffer than the Ambi for unstable subtrochanteric fractures. Both implants effectively unloaded the proximal medial cortex. In each instance, failure of the Gamma nail composite occurred through the distal locking screws. The Gamma nail does not appear to offer any distinct biomechanical advantage over the sliding hip screw system in the treatment of stable and unstable intertrochanteric fractures, but it may play a role in the treatment of unstable subtrochanteric fractures.

Hydroxyapatite coating on carbon composite hip implants in dogs.

In 33 dogs we implanted femoral stems made either of carbon composite, some coated with hydroxyapatite, or of titanium alloy with a porous coating. Osseointegration was greater in the hydroxyapatite-coated than in the un-coated stems (p less than 0.001). Push-out tests, at an average of 7.2 months after implantation, showed a six-fold increase in interface shear strength and a twelve-fold increase in shear stiffness in the hydroxyapatite-coated group compared with noncoated implants. The highest shear-strength values were found in the porous-coated titanium alloy stems, around which there was also the most resorptive bone remodelling.

Pseudoaneurysm of the popliteal artery as a complication of an osteochondroma. A review of the literature and a case report.

False aneurysm of the femoral artery was associated with a solitary osteochondroma of the femur in a 22-year-old man. An extensive review of the literature and the problems related to diagnosis revealed that the aneurysm was apparently unique. Contrary to previous reports, computed tomography and angiography did not establish the diagnosis. The physical findings were more informative.

The natural history of suspected scaphoid fractures.

Clinically suspected scaphoid fractures are common injuries. The authors prospectively followed up, by serial radiography and bone scanning, 23 patients who had a history of trauma to the carpus and associated localized tenderness to the anatomic "snuff box": in 15 patients the radiographs and bone scans were negative; in 5 the radiograph was equivocal and the bone scan positive. The authors concluded that patients with clinically suspected scaphoid fractures and negative radiographs can be treated symptomatically without immobilization in a cast. Patients with equivocal radiographs should be assumed to have a fractured scaphoid and treated accordingly.

Effect of stem modulus in a total hip arthroplasty model.

The purpose of this study was to determine the biological effects of the elastic modulus of the femoral stem in canine hip arthroplasty. Cementless total hip arthroplasty was performed in 12 dogs, six had a low elastic modulus polyacetal resin stem and six had a high modulus stainless steel stem. The components were otherwise similar. At six and 12 months after operation, radiographic and histomorphometric analysis showed that those with steel implants had more cortical porosity than did the other group (p less than 0.01). We suggest that the elastic modulus of the implant is an important factor in controlling cortical bone resorption. A low modulus femoral prosthesis can significantly decrease bone resorption which might otherwise eventually lead to implant failure.

A plaster-pylon technique for below-knee amputation.

We reviewed 83 patients after below-knee amputation. In 56 with 69 amputations early management was by plaster-pylon. A plaster cast is applied in the operating room, and a pylon added one week later, after which full weight-bearing is allowed. We compared these patients with 27 who had soft bandaging. The 'healing' time was reduced from 98 days to 40 days, and there were no major complications in the plaster-pylon group. The technique is simple and cheap and can be used by paramedical staff without specialised training or equipment.

The stability of intertrochanteric fractures treated with a sliding screw-plate.

Failure of fixation is a major complication of the treatment of unstable intertrochanteric fractures. A retrospective review was performed of 54 such fractures treated with a sliding screw-plate device. Linear and angular displacements were calculated from radiographs taken at operation and serially until healing was complete. Linear displacement was related to fracture instability, but the neck-shaft angle was relatively constant during healing. Complications were often due to failure of the sliding mechanism of the implant. We conclude that a sliding screw-plate allows controlled collapse of the major fragments but maintains the neck-shaft angle even in unstable fractures.

Lower extremity amputations: a 5-year review and comparative study.

In order to review major lower extremity amputations at the Toronto East General and Orthopaedic Hospital Inc. between 1979 and 1984, 60 patients with 42 below-knee, 17 mid-thigh and 20 Callander through-knee amputations were studied retrospectively. The three amputation groups demonstrated comparable rates of stump healing. A previous history of vascular surgery on the extremity increased the risk for both delayed healing and failure to heal. The Callander through-knee amputees were rehabilitated earlier and more easily than were the mid-thigh amputees, and once rehabilitated they were more likely to continue using their prostheses. The authors recommend that, when possible, the chosen site of amputation for the majority of patients should be below the knee, but when this is not practical a through-knee amputation should be done in preference to a mid-thigh amputation.

Delayed union and nonunion of the tibia: experience in a community teaching hospital.

Delayed union and nonunion are frequent sequelae of high-energy tibial fractures, particularly compound ones. The authors studied 45 such cases; of these, 20 fractures were compound. The authors analysed the initial management but found no apparent correlation between the initial management of these fractures and subsequent delayed union or nonunion. The Phemister bone-grafting technique was used to achieve union and was considered a safe, efficacious method. Aggressive initial management of the soft-tissue component of tibial fractures is recommended to minimize the possible development of chronic osteomyelitis, a serious complication that occurred in eight patients and necessitated below-knee amputation in three.

Cauda equina syndrome and lumbar disc herniation.

In a retrospective chart review of the cases of thirty-one patients with cauda equina syndrome secondary to a central disc lesion, we identified two modes of presentation. The first was an acute mode (ten patients) in which there were abrupt, more severe symptoms and signs and a slightly poorer prognosis after decompression, especially for the return of bladder function. The second mode of presentation (twenty-one patients) was a slower onset, characterized by prior symptoms for varying time-intervals before the more gradual onset of the cauda equina syndrome. All patients had urinary retention preoperatively. Bladder function was the most seriously affected function preoperatively and remained so postoperatively. The prognosis for return of motor function was good, since twenty-seven of the thirty patients who were operated on regained normal motor function. Preoperatively all patients had sciatica, which was bilateral in fourteen and unilateral in seventeen. The average time to surgical decompression after the patient was seen ranged from 1.1 days for the more acute lesions to 3.3 days for the second group. There was no correlation of these times with return of function. Therefore, even though early surgery is recommended, decompression does not have to be performed in less than six hours if recovery is to occur, as has been suggested in the past.

Treatment of unstable fractures of the distal radius by external fixation.

The Roger Anderson external fixator was used in the treatment of unstable fractures of the distal radius in 52 patients, and the results evaluated after a follow-up averaging 58 months. The indications for its use were failure to maintain adequate closed reduction using plaster, and instability of the fracture as determined by the initial radiographs. Our radiological criteria for instability included dorsal angulation of more than 20 degrees, fractures involving the joint, radial shortening of more than 10 mm, and severe dorsal comminution. Using the Lucas modification of the Sarmiento demerit point-rating system, we found that 46 patients (89%) had good or excellent results and six (11%) were classified as fair. There were no poor results. Seven patients (14%) developed complications. None of these affected the long-term results except in one elderly woman where the pins loosened and had to be removed.

Use of a pylon for early ambulation after below-knee amputation: a preliminary report.

The fitting of a prosthesis immediately after amputation offers many advantages. These include early ambulation, more rapid healing of the amputation site and a decrease in the number of complications resulting from prolonged bed rest. The major problems preventing the widespread use of immediate fitting are the specialized prosthetic care required and the high cost of the appliance. The authors describe a new pylon designed for early ambulation after below-knee amputation. Its application does not require special training, it is inexpensive, safe and effective. This pylon was used in the early postoperative period in 20 amputees, without any major complications.