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Electrical stimulation of a pedicle hole and screw with recording EMGs from the lower extremities has been used as an indicator in detecting perforations of the pedicle. Mechanically-elicited EMGs are reported to be sensitive to mechanical irritation of nerve roots. This study analyzed the sensitivity of the data elicited by two EMG monitoring methods in the presence of a neurologic deficit caused by a malpositioned screw to determine the relative effectiveness of electrically- vs mechanically-elicited EMGs in detecting pedicle wall perforations and nerve root damage in patients undergoing spinal surgery utilizing transpedicular instrumentation. One hundred and four surgeries were monitored using the two EMG methods. Six hundred and fifty-four pedicle holes were prepared and 650 placed pedicle screws were electrically tested. Mechanically-elicited EMGs were monitored from a total of 618 muscles. Electrically-elicited EMGs showed a 62% true-positive rate and a 0.2% false-negative rate in detecting pedicle wall perforations. None of the patients who initially demonstrated abnormal electrically-elicited EMGs demonstrated any post-operative neurologic problems due to an incorrect screw placement. Only one patient who had abnormal mechanically-elicited EMGs during the procedures related to instrumentation developed new L4 radiculopathy immediately post-operatively which was consistent with the level of mechanically-elicited EMGs. Mechanically-elicited EMGs showed a 100% true-positive rate for nerve root irritation and a 3.5% false-negative rate in detecting pedicle wall perforations by malpositioned screw. In conclusion, although mechanically-elicited EMGs were an insensitive technique in detecting a perforation of the pedicle, mechanically-elicited EMGs were more beneficial than electrically-elicited EMGs in detecting the risk of nerve root irritation.

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STUDY DESIGN: A prospective comparison of impedance measurements, electrically elicited electromyograms, and mechanically elicited electromyograms to detect pedicle wall breakthrough. OBJECTIVE: To determine whether impedance measurements are as sensitive as electromyogram measurements in evaluating pedicle wall breakthrough. SUMMARY OF BACKGROUND DATA: In a previous animal study, impedance values in pedicle screw placement were tested, to determine a baseline value for an intact pedicle. If pedicle wall breakthrough occurred, it was thought that the impedance values should be significantly lower. METHODS: Impedance measurements, electrically elicited electromyograms and mechanically elicited electromyograms were recorded in 20 patients undergoing surgery for spinal degeneration, using previously described standard protocol. Analysis of variance statistics were used to evaluate the data. RESULTS: Impedance values for the pedicle holes varied from 500 ohms to 31,000 ohms. There was no correlation between these values and those of the two pedicles in which breaches were detected on visual inspection. Electrically elicited electromyograms detected the breakthroughs in both pedicles, whereas mechanically elicited electromyograms detected one of the breakthroughs. CONCLUSIONS: Electrically elicited electromyograms were more sensitive in detecting pedicle wall breakthrough than were impedance measurements. This may be because of the inability to ascribe absolute impedance values to human pedicle bone caused by the wide variability in bone quality.

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Echinococcus is a genus of tapeworm endemic in certain parts of the world but found only rarely in the United States. An extremely unusual case of an intramuscular infestation involving an extremity occurred in a 41-year-old man. Since the infestation closely resembled a soft-tissue tumor on clinical and roentgenographic examination, the patient was treated with an incisional biopsy of the mass, which consisted of a cystic cavity filled with clear fluid. The diagnosis of an Echinococcus cyst was made only after permanent section analysis revealed numerous scoleces within the cyst lining. The patient was asymptomatic six months after cyst excision but still remains at risk for recurrence of the infestation. The present report serves to alert the reader to this rare but potentially fatal condition. Preoperative diagnosis is imperative to avoid inadvertant rupture of a hydatid cyst, which releases viable scoleces into the systemic circulation and may precipitate an anaphylactic reaction.

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Seventy-four cemented conventional total hip arthroplasties (in fifty-five patients) and thirty-seven cemented surface replacements (in thirty-two patients) were done between 1971 and 1984 for treatment of osteoarthrosis secondary to congenital dislocation of the hip. The patients in the first group were older and had more severe dysplasia. In all patients, we tried to position the acetabular component at the level of the true acetabulum. In both groups, the operation relieved pain and improved the function of the hip in the short term. There were fewer and less severe early postoperative complications in the surface-replacement group, but the rate of long-term failure (revision or resection) was substantially higher. Survivorship analysis demonstrated that neither type of operation yielded durable results in younger patients; all revisions were in patients who were less than sixty years old. However, in older patients who had cemented conventional total hip arthroplasty, survivorship was excellent, regardless of the amount of dysplasia.

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A large amount of fluid extravasation into the surrounding muscle and soft tissue may occur during arthroscopy of the shoulder and particularly of the subacromial space. The tense swollen appearance of the shoulder has caused concern that the intramuscular deltoid pressure may become elevated to dangerous levels. Therefore, the intramuscular deltoid pressure was monitored in this study using a slit catheter. Although it was found that the intramuscular pressure became transiently elevated during the arthroscopic procedures, in every case the pressures promptly returned to normal levels within 30 min postoperatively. The clinical swelling and tenseness remained for a longer period. Despite a sometimes alarming amount of swelling during shoulder arthroscopy, intramuscular pressure elevations were only sustained for a short time and returned to normal levels very quickly after the cessation of fluid infusion.

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Cementless fixation in total hip arthroplasty is increasingly popular because of the failure rates of cemented components, particularly in younger patients. The reported European studies with cementless acetabular implants and the relatively short-term American studies suggest that loosening is not a problem with any of the designs in clinical use. This point of view is reminiscent of that regarding cemented acetabular components prior to the realization that cemented acetabular failure was a delayed long-term phenomenon. Cementless acetabular components are principally of two types, threaded and porous coated. Prior to this study, there was little clinical or experimental evidence to indicate which design gains superior fixation and which is most likely to maintain long-term fixation and durability. Fixation of threaded and porous-coated components was evaluated mechanically and histologically in dogs after weight-bearing periods of two and six months. The threaded specimens were significantly looser than the porous-coated specimens at both two and six months. There was a trend toward loosening of both types of components with time. Fibrous tissue alone appeared to invest all of the threaded components, whereas bone and fibrous-tissue ingrowth appeared to incorporate the porous components. The mineral apposition rate for the components was not significantly different between the two components or between different regions in the specimens.

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The progression of femoral head osteonecrosis (FHON) culminates in destruction of the hip joint, a devastating consequence for young people who are predominantly affected. Core decompression, as a means of ameliorating the disease, was evaluated in 45 hips in 33 patients with nontraumatic FHON. The mean clinical and roentgenographic follow-up period was three years (range, 1-7 years). None of the ten Ficat Stage I hips progressed, 11 of 26 Stage II hips progressed, and five of nine Stage III hips progressed to coxarthrosis. In those hips in which there was an association with steroid therapy, there was 50% progression when steroids were continued, compared with 22% progression when steroids had been discontinued. Core decompression is prescribed for Ficat Stage I and II. Patients on continuous post-operative treatment with steroids for associated conditions should be advised of the high risk of progression.

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Eighteen transtrochanteric rotational osteotomies have been performed in 17 patients for femoral head osteonecrosis (15 patients, Ficat Stage III disease; three patients, Ficat Stage IV disease) during a 51-month period and have 18 to 63 months of follow-up study. The best results were in the posttraumatic and nonsteroid-associated idiopathic cases in patients with small necrotic segments in the weight-bearing region, with no degenerative changes. Failures occurred in patients with large necrotic fragments, preexisting degenerative changes, and steroid- and alcohol-associated etiologies. Although joint arthroplasty was eventually required in ten hips, a period of temporization was achieved sufficient to bring them into the era of cementless hip arthroplasties. Indications for this operation should be restricted to those patients under 40 years of age with late Ficat Stage II or Stage III disease, in which the articular involvement in the lateral roentgenogram is 50% or less.

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A modified THARIES femoral resurfacing component was used as a hemiarthroplasty in 11 young adult patients (12 hips) with osteonecrosis. The mean follow-up period was 39 months (range, 24-62 months). In all of the hips, the necrosis had advanced to the stage of subchondral femoral head fracture and segmental depression, but there was a relatively normal acetabulum. Ten hips have maintained satisfactory improvement of UCLA pain, walking, and function hip scores. One hip was revised to an uncemented total replacement, and one has some residual pain. No case failed because of component loosening. The modified femoral THARIES component was used as a preferable alternative to unipolar or bipolar hemiarthroplasty, and the results appear to be comparable in this difficult group of patients. Hemiresurfacing was conceived not as a definitive procedure but rather as a time-buying measure to improve symptoms and function and to allow the performance of a technically uncompromised total hip arthroplasty at a future date.

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Magnetic resonance imaging (MRI) was performed on the hips of 25 patients with suspected ischemic necrosis of the femoral head. Twenty-six femoral heads manifested MRI changes of ischemic necrosis: diminished bone marrow signal in a ringlike, focal, or diffuse pattern. Plain radiographs were normal in 13 of 26 MRI-positive hips; six were asymptomatic. MRI was more effective in detecting early cases than conventional 99mTc-diphosphonate or 99mTc-sulfur colloid (SC) bone scanning. There were no false-negative MRI examinations, but diphosphonate scans were negative in nine hips with normal radiography and abnormal MRI. Sulfur colloid scans were normal in only two hips with positive MRI, but SC scan results were often equivocal because isotope deficits were bilaterally symmetric. The results of this preliminary investigation imply that MRI has extraordinary sensitivity for the detection of early ischemic necrosis. Unlike radionuclide scanning, MRI shows the exact location and extent of femoral head necrosis. Because MRI is expensive, it should be used in a cost-effective manner. Therefore, MRI is best suited for the diagnosis of early cases where less expensive tests are negative or equivocal and as a precursor to more costly interventional procedures, such as core biopsy study or decompression.

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During the period between February 1970 and December 1973, 149 Charnley total hip arthroplasties were performed at UCLA Medical Center. Fifty-seven percent have a follow-up period of at least four years, and 21% have a follow-up period of ten years or more. The peri- and postoperative complication rate was high, with an incidence of 32.6% urinary tract infection (UTI), 4% peroneal nerve palsy, 4% cardiopulmonary, 2% pulmonary embolism, 1.3% myocardial infarction, and 6.0% other. Eleven patients (7.3%) required revision at a mean of 75 months after operation, while an additional three patients were experiencing substantial pain. Clinical improvement after this procedure is similar to that reported by other authors. Survivorship analysis suggests that being young and/or having a diagnosis of osteonecrosis or failed hemiarthroplasty places a patient at a higher risk of failure due to revision surgery or pain.

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We studied the cases of thirty-two skeletally mature patients, fifty years old or less, who had a fracture of the femoral neck. In all patients with a stage-1 or 2 fracture, the fracture healed without osteonecrosis. Among the stage-3 and 4 fractures, the rate of non-union was 5.5 per cent and that of osteonecrosis, 33 per cent (3 and 18.8 per cent, respectively, for the whole group). Three patients with osteonecrosis required revision to arthroplasty at six, sixty-eight, and ninety-nine months. Three others had good function of the hip at forty-eight, ninety-six, and 129 months despite the development of osteonecrosis. Treatment of these fractures yielded very good results over-all, and even the occurrence of osteonecrosis did not necessarily cause an unsatisfactory result.

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