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Biomedical subjects

A A Hofmann

Publications and source records attributed to A A Hofmann.

At least 55 records · Page 3Linked to original sources
PubMed1991

Compressive strength mapping of femoral head trabecular bone.

The purpose of this study was to develop a test protocol and complete a relative three-dimensional mapping of the local trabecular bone compressive strengths in healthy and osteoarthritic femoral heads. Five fresh frozen cadaveric femoral heads were compared to five fresh frozen osteoarthritic femoral heads obtained from patients undergoing total hip replacement. Each femoral head was coronally sectioned into eight 5 mm slices, which were compression-tested at 20 sites using a hydraulic testing machine. The results of the femoral head compressive strengths were normalized, mapped, and evaluated. The test protocol produced reproducible results and allowed the determination of diseased portions of osteoarthritic bone. The regions of high compressive strength were similar for normal and diseased bone and were located in the superior medial portions of the head. Ultimate stress was higher in diseased bone than in normal bone, while the yield point and stiffness of diseased bone was lower than for healthy bone.

Biomechanical Phenomena↗
PubMed1991

Investigation of early surface delamination observed in retrieved heat-pressed tibial inserts.

The objective was to examine possible reasons for delamination observed in tibial inserts of the porous-coated anatomic (PCA) knee replacement. To date, 33 PCA inserts have been forwarded to the authors' labs. Of these 33, 52% showed severe delamination within four years of implantation. Visual, structural, and mechanical analyses were conducted and data compared on the heat-pressed PCA type and the common machined inserts. Twenty inserts of the two different types were examined. Visual data using polarized light microscopy showed the presence of a surface layer separated from the middle region of the heat-pressed inserts by a line of demarcation 250-580 microns beneath the articulating surface. This anomaly was not observed in machined inserts. Structural analysis showed the new heat-pressed inserts had increased crystallinity in the surface layer when compared to new machined inserts. The retrieved heat-pressed inserts showed increased crystallinity in the surface and middle regions. There was a slight increase in surface crystallinity in the retrieved machined inserts. Microhardness data showed that there was an increased hardness associated with the crystallinity seen on the heat-pressed inserts. Orthopedic surgeons should be aware of early delamination and surface failure in heat-pressed inserts.

Hardness↗
PubMed1991

Effect of the tibial cut on subsidence following total knee arthroplasty.

In 33 total knee arthroplasties (TKAs) using instrumentation designed to cut the tibia with 0 degree posterior slope, ten tibial components demonstrated at least 2 mm of tibial component subsidence. These subsided components were implanted onto tibiae with an average of 8 degrees +/- 2 degrees difference between the preoperative, anatomic posterior slope and their postoperative posterior slope. The remaining 23 components, without subsidence, were implanted onto tibiae cut within 2 degrees +/- 2 degrees of their anatomic slope. To help understand these clinical observations, a laboratory study was performed to compare the load carrying capacity and the stiffness of tibial subchondral bone following two types of tibial cuts: one made perpendicular to the long axis of the tibia and the other made parallel to the articular surface of the tibia. Mock tibial baseplates mounted on paired cadaver tibiae were loaded in compression and force displacement curves were recorded. Tibiae cut parallel to the surface exhibited 40% greater load carrying capacity and 70% greater stiffness than the paired tibiae cut perpendicular to the long axis. The biomechanical data of this study indicated that cutting the tibia perpendicular to the long axis results in weaker bone that may be inadequate to support a tibial component. This may explain the higher incidence of clinical subsidence if the tibial cut is not made approximately parallel to the anatomic slope.

Aged↗
PubMed1991

Subvastus (Southern) approach for primary total knee arthroplasty.

The subvastus or Southern approach to the knee had been described as early as 1929 but is not found in standard modern orthopedic textbooks. This approach for primary total knee arthroplasty (TKA) preserves the integrity of the extensor mechanism and maintains the vascular supply to the patella. To appreciate the potential benefits of this approach, a complete understanding of the surgical anatomy is essential. The benefits of the subvastus approach make it a valuable technique for primary TKA.

Humans↗
PubMed1991

Total knee arthroplasty. Two- to four-year experience using an asymmetric tibial tray and a deep trochlear-grooved femoral component.

The design features of an implant system can be crucial to the success of cementless total knee arthroplasty (TKA). The implant system described in this study incorporates anatomic features including an asymmetric tibial tray that is smaller laterally than medially, and a deep trochlear-grooved femoral component. Two hundred consecutive primary total knees were implanted between October 18, 1985 and January 19, 1988 and were followed prospectively. One hundred ninety-two were implanted without cement. Clinical evaluation demonstrates good or excellent results in 96%, including a mean range of motion of 122 at two to four years after arthroplasty. Routine fluoroscopic spot roentgenograms have shown no complete radiolucency in this series of patients. Bone ingrowth was predictable if morselized autograft bone was interposed between implant and host bone. Implant retrievals demonstrated uniform bone ingrowth into the porous coating, increasing to 40% of the pore volume in the tibial tray at 27 months. Restoration of the normal kinematics appears to minimize the bone-implant stress permitting bone ingrowth fixation. The results of primary cementless TKA in this series is comparable to cemented TKA with the advantage of conserving bone stock.

Adult↗
PubMed1991

High tibial osteotomy. Use of an osteotomy jig, rigid fixation, and early motion versus conventional surgical technique and cast immobilization.

High tibial osteotomy (HTO) using conventional surgical technique and cast immobilization was compared to HTO using an osteotomy jig, rigid internal fixation, and early motion. Fifteen patients (19 knees) had conventional HTO. The mean preoperative femoral-tibial angle was 2.5 degrees of varus, and the mean postoperative angle was 6.5 degrees of valgus. Two knees were undercorrected and eight knees (42%) had associated complications. Twenty patients (21 knees) had HTO utilizing the new surgical technique and postoperative management. The mean preoperative femoral-tibial angle was 2.3 degrees varus, and the mean postoperative angle was 7.6 degrees valgus. One knee was undercorrected (less than 4 degrees valgus) and one knee (5%) had an intraoperative intraarticular fracture. High tibial osteotomy with an osteotomy jig to provide accurate correction, and rigid internal fixation to allow early motion, is an attractive alternative to conventional HTO.

Adult↗
PubMed1991

Cementless total knee arthroplasty in patients over 65 years old.

Many factors influence the decision to implant a knee prosthesis with or without cement. Implant retrieval studies have demonstrated that bone ingrowth into porous-coated devices is possible even in older age groups. Early clinical follow-up observations suggest that cementless total knee arthroplasty can be successful in patients over 65 years of age, and need not be reserved for younger patients.

Aged↗
PubMed1991

Bilateral tibial components of different cementless designs and materials. Microradiographic, backscattered imaging, and histologic analysis.

Postmortem evaluation was conducted on two cementless knee prostheses considered clinically successful. The two retrieved uncemented porous-coated tibial components of different designs, and materials were evaluated by microradiography, backscattered electron (BSE) imaging, and light microscopy. The right prosthesis, in place for 25 months, was a Porous-Coated Anatomic (PCA) implant with double-layered, sintered, cobalt-chromium alloy beads. The left prosthesis was a Natural-Knee (N-K) implant with a porous coating of cancellous-structured pure titanium implanted for 19 months. A quantitative microradiographic index, the appositional bone index (ABI), was developed to indicate the probability of bone ingrowth occurring into the porous coating. The ABI is a ratio of bone in apposition with porous coating divided by the total amount of porous coating available. The PCA had an average ABI of 9%, and the N-K, 67%. BSE images of the PCA demonstrated no bone within the porous coating. BSE images of the N-K implant showed bone ingrowth into 22% of the pore volume when porous coating was in apposition to host bone. Histology of the PCA revealed fibrous connective tissue throughout the porous coating and between the porous coating-bone interface. Histology of the N-K implant revealed bone ingrowth and osteoblastic activity along the bone within the porous coating.

Aged↗
PubMed1990

Bone scans after total knee arthroplasty in asymptomatic patients. Cemented versus cementless.

The natural history of bone scans after total knee arthroplasty (TKA) was studied in 26 patients with 28 cemented TKAs and 29 patients with 31 cementless TKAs. The bone scans were examined at specified postoperative intervals. Radionuclide activity of the femoral, tibial, and patellar regions was measured. Six patients who developed pain postoperatively were excluded. Bone scans immediately postoperative and at three months demonstrated increased uptake, which gradually decreased to baseline levels at ten to 12 months. Radioisotope uptake was comparable in the cemented and cementless groups, but was highly variable in individual patients and in each of the follow-up periods. A single postoperative bone scan cannot differentiate component loosening from early bone remodeling. Sequential bone scans, as a supplement to the clinical examination and conventional radiography, may prove useful in the diagnosis of TKA failure.

Aged↗
PubMed1989

Endosteal bone loss after total hip arthroplasty.

Femoral endosteal bone loss has been shown to be part of the natural aging process and may be a factor in femoral component loosening following total hip arthroplasty (THA). In this study, changes in the femoral medullary canal width in 30 patients with aseptic femoral loosening following primary THA were compared with 30 matched control patients. The rate of canal expansion on the operated side was twice that of the nonoperated side and four times that of the control. After the onset of symptoms in the failure group, the rate of femoral expansion of the operated side doubled. Iliac crest biopsies showed a decrease in male patients for osteoid surface and appositional and bone formation rates when compared with literature controls. These results suggest that femoral medullary canal expansion may be a factor in femoral component loosening following THA. The increased rate of canal expansion after the onset of symptoms demonstrates the need for early surgical intervention to avoid excessive bone loss.

Adult↗
PubMed1987

The effect of air embolization from the femoral canal on hemodynamic parameters during hip arthroplasty.

A canine laboratory and clinical study was designed to determine the effect of air embolism during hip arthroplasty. Canine femurs were pressurized with air to 250-300 mm Hg or with low-viscosity cement to 300-900 mm Hg. Pressurization with low-viscosity cement from distal to proximal with a plugged femur revealed no change in pO2, pCO2, pulmonary artery pressure, or end-tidal CO2. Air pressurization resulted in significant increases in pCO2, pulmonary artery pressure, and end-tidal CO2, and a decrease in pO2. Pressurization of the medullary canal with xenon-labeled air was used to document pulmonary embolism. In a clinical setting, two different femoral cementing techniques during total hip arthroplasty were studied to determine their effect on hemodynamic parameters associated with embolic phenomenon. Five patients had a plugged femoral canal filled from proximal to distal with a vent tube, followed by finger-packing. Three of the patients demonstrated a significant drop in pO2 and blood pressure and a rise in pCO2 and end-tidal CO2. Five other patients had their plugged femoral canals filled from distal to proximal, three with regular cement and two with low-viscosity cement, with no significant cardiopulmonary changes. The adverse cardiopulmonary effects reported during hip arthroplasty appear to be avoided by eliminating air during the cementing procedure, by filling a plugged canal from distal to proximal.

Air Pressure↗
PubMed1984

Experience with acetabular fractures.

Acetabular fractures, although relatively rare, are often serious injuries requiring complex treatment. Major associated injuries are common and the mortality rate continues to approach 20% (8). We retrospectively evaluated 38 acetabular fractures. Twenty-six fractures were treated operatively, with adequate followup available for 23. Anatomic reduction or reduction to within 3 mm was achieved operatively in 21 (81%). The average Harris hip score was 90. The five poorly reduced fractures had an average Harris hip score of 54. Twelve patients were treated nonoperatively with adequate followup available for nine. Six patients with nondisplaced or minimally displaced fracture treated nonoperatively had an average hip score of 96. Six patients had displaced fractures which failed to reduce with nonoperative treatment. Their average hip score was 59. This study reaffirms the importance of adequate fracture reduction in the treatment of acetabular injuries.

Acetabulum↗
PubMed1984

Combined Coventry-Maquet procedure for two-compartment degenerative arthritis.

The combined Coventry-Maquet procedure has been proposed as a means of treating dual-compartment degenerative arthritis of the knee. The procedure was investigated in a prospective study of 14 patients treated by combined high tibial osteotomy and tibial tubercle elevation. Preoperative scores averaged 50 points and scores at follow-up evaluation averaged 57 points with a modified 100-point total knee grading system. There were no excellent results, one good result, and 13 poor results. Five patients whose results were poor have since had total knee arthroplasty. The combined Coventry-Maquet procedure required too much dissection, had too high a complication rate, and yielded a minimal improvement in knee function and pain. Two-compartment degenerative arthritis should be treated by an alternative method, such as total knee arthroplasty, when surgical intervention is indicated.

Adult↗
PubMed1984

Arthroscopic partial medial meniscectomy in the older patient.

We reviewed the cases of sixty-three patients who were more than forty years old when they underwent arthroscopic partial medial meniscectomy. Thirty-five patients returned for clinical evaluation and another eight were evaluated by questionnaire and telephone interview. Over the thirty-five-month follow-up period, progressive varus deformity and medial joint-space narrowing were not observed. Of the twenty-seven knees in Group I (non-degenerative tears) that underwent arthroscopic partial meniscectomy, satisfactory results were found in 96 per cent. Of the seventeen knees in Group II (degenerative tears) over-all satisfactory results were found in only 65 per cent. A history of pre-existing degenerative arthritis in patients with degenerative tears seemed to correlate with a less favorable outcome.

Adult↗
PubMedDate not supplied

Insensitivity of color Doppler flow imaging for detection of acute calf deep venous thrombosis in asymptomatic postoperative patients.

PURPOSE: Although color Doppler flow imaging (CDFI) has been shown to accurately depict calf vein thrombosis in symptomatic patients, this technique has not been proved accurate for detection of calf vein thrombosis in a population restricted to asymptomatic postoperative patients. PATIENTS AND METHODS: To evaluate the accuracy of CDFI in asymptomatic postoperative patients, both CDFI and contrast venography were performed on 78 limbs of 76 patients without symptoms of deep venous thrombosis (DVT) who had undergone either hip or knee replacement. CDFI and venographic examination were interpreted blindly with respect to the results of the other modality or clinical findings. Venography was the standard for comparison of results. RESULTS: Fifty-six percent of CDFI examinations of the calf vein were technically adequate. The remaining studies were compromised technically by limb swelling and/or obesity. For the technically adequate CDFI studies, calf vein thrombosis was detected in eight of 10 patients. Calculated sensitivity in this cohort was 80%, and specificity was 97%. The sensitivity of CDFI for acute calf DVT in all patients, regardless of image quality, was 42%. CONCLUSION: These observations suggest that state-of-the-art CDFI is not an accurate examination for acute calf vein DVT in asymptomatic postoperative patients. CDFI is associated with a high rate of technically compromised studies and relatively low sensitivity in studies that are deemed technically satisfactory. These observations do not preclude the use of CDFI in postoperative patients for detection of thrombus extension into the popliteal vein or for detecting thrombosis of more proximal lower extremity veins.

Female↗