Potential pitfalls of magnetic resonance imaging in the diagnosis of avascular necrosis.

Magnetic resonance (MR) imaging and radionuclide (RN) bone scans were performed in two patients with collagen vascular disease (CVD) to evaluate hip pains. In both patients RN bone scans demonstrated decreased radioactivity in the femoral heads, whereas, MR imaging was normal. Because early changes of avascular necrosis (AVN) frequently present as decreased radioactivity in the femoral head, special attempts were made to detect this decreased activity using pinhole collimator imaging. The diagnosis of AVN was confirmed surgically by venous pressure measurements. Abnormal RN bone scans representing decreased flow due to vasculitis in patients with CVD, may be more sensitive in the diagnosis of AVN before structural changes can be detected on MR studies.

The role of subtalar motion and ankle contact pressure changes from angular deformities of the tibia.

It is a well known entity that fractures of the tibia heal with some component of angular deformity. Ankle and subtalar joints may compensate for small degrees of angular deformities, but the exact amount of malunion that can be accepted without development of late sequalae has yet to be determined. Two recent studies from this institution have concluded that contact changes at the tibiotalar joint tend to be greater with distal third tibial fracture deformities compared to proximal and middle with the ankle in neutral, 5 degrees dorsiflexion, and 20 degrees of plantar flexion. Anterior and posterior bow deformities produced a greater change in contact area of the tibiotalar joint than with valgus or varus deformities. This phenomena may be possibly explained by the subtalar motion in the horizontal plane which averages 23 degrees. Thus, it was the primary purpose of this paper to determine the exact role, if any, in subtalar motion on tibiotalar contact in angular deformities of the tibia. To achieve this objective the subtalar joint was transfixed thereby eliminating its perceived compensatory movement. Six cadaveric lower extremities were disarticulated at the knee joint and stripped of soft tissue preserving capsular and ligamentous structures. A custom universal joint was used to create various angulatory deformities at proximal, middle, and distal third levels of the tibia.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanics and biology of intramedullary fracture fixation.

Intramedullary (IM) fracture fixation serves to stabilize fracture fragments and maintains alignment, while permitting motion at the fracture site during functional activities. Acting as an internal splint, the implant serves as a load-sharing device and fracture healing progresses with the formation of peripheral callus. By allowing motion of adjacent joints, rehabilitation is concurrent with treatment, and stress-shielding is thought to be minimal using these techniques. Recently, IM nails have been introduced to widen indications for their use based on variations in the cross-sectional geometry, length and shape of nails, interlocking designs, and surgical techniques. Although the most important mechanical factors in the design of IM nails are strength, stiffness, and rigidity, anatomic constraints and surgical technique limit nail variations. Closed nailing is preferred to open procedures to preserve periosteal blood supply and minimize surgical trauma adjacent to the fracture. Blood flow to the fractured bone is elevated in nailing experiments, although callus maturation is somewhat delayed. However, the end result in terms of healing was similar to that of plate fixation.

Changes in tibiotalar joint contact areas following experimentally induced tibial angular deformities.

Six cadaveric legs were stripped of all soft tissue excluding the interosseous membrane and the tissues about the ankle joint and foot. Angular deformities were simulated in all planes to a maximum of 15 degrees for proximal, middle, and distal third levels following tibial resection and same-level fibular osteotomy. Anterior ankle arthrotomies allowed exposure to the tibiotalar joint so that contact area could be measured with pressure-sensitive film inserted between the tibia and talus. An angular deformity of 15 degrees or less produced no significant alteration in the contact area of the ankle joint for proximal and middle third tibial levels. Distal tibial deformities showed a dramatic change in the contact area, with as much as a 42% decrease in contact area for anterior deformities. The contact shape for distal third angular deformities of 10 degrees and 15 degrees in all planes also tended to elongate, with a shift to more lateral contact noted. Although minor degrees of angular malalignment had little effect on ankle contact for proximal and middle third levels, it would appear that distal third deformities produce a greater change in ankle joint contact; thus, fractures at the distal level should be managed to minimize the possibility of tibial malalignment.

Prefabricated functional braces for the treatment of fractures of the tibial diaphysis.

We have reviewed our experiences with prefabricated functional braces in the treatment of diaphyseal tibial fractures. The braces were developed in an attempt to reduce the occasional technical difficulties encountered with the use of custom-made braces. Between January 1979 and July 1983 we treated 625 diaphyseal tibial fractures. One hundred and eighty-six patients (29.8 per cent) were lost to follow-up, the braces had to be discontinued in thirty-eight (9.2 per cent), and ten fractures (2.5 per cent) failed to unite. We conducted careful radiographic and clinical analyses of the remaining 391 patients. Two hundred and fifty-seven (65.7 per cent) of the fractures were closed and 134 (34.3 per cent) were open. Three hundred and fifty-seven (91.2 per cent) of the patients had ten millimeters of final shortening or less, and 306 (78.3 per cent) had a final angulation of 5 degrees or less. The average time from injury to bracing was 3.9 weeks (range, one to twelve weeks) for the closed fractures and 5.0 weeks (range, one to twelve weeks) for the open fractures. These findings appear to support our concept that function of the extremity is beneficial to osteogenesis and that many diaphyseal tibial fractures can be satisfactorily stabilized in prefabricated functional braces. These braces also have the advantage of not immobilizing the adjacent joints and they permit the gradual restoration of weight-bearing.

The effect of simulated tibial deformities on the ankle joint during the gait cycle.

The effect of angular deformities of the tibial shaft on the area, location, and shape of the ankle joint contact during the normal extremes in the gait cycle was studied with the use of a cadaveric model. Six lower limbs were first examined radiographically and found to be free of pathology. These specimens were then stripped of soft tissues proximal to the ankle joint and had a custom-designed universal joint-plate inserted into the tibia at the proximal, middle, or distal third level. An anterior ankle arthrotomy was performed, and pressure sensitive film was inserted into the tibiotalar joint. Load was then applied with the ankle set in dorsiflexion or plantarflexion via metal wedges, and tibial deformities of 5, 10, and 15 degrees were simulated in varus, valgus, anterior bow, and posterior bow. Contact area and location changes were noted to be of greater magnitude with proximal and distal third tibial deformities than with middle third deformities. Varus and valgus deformities showed smaller contact area changes than anterior or posterior bow deformities. Contact area changes tended to be larger in dorsiflexion compared to plantarflexion for each level and degree of tibial angulation. Posterior bow deformities at all levels resulted in greater changes in contact area and shape than other deformities. The role of subtalar compensation, stiffness of the foot-ankle complex, and geometric factors are all thought to influence the changes noted. On the basis of this experimental study it would appear that angular deformity of the tibia less than 10 degrees would not significantly alter ankle joint contact.

Radiographic assessment of acetabular cup orientation. A new design concept.

An acetabular cup with a 270 degree rim wire has been designed to assist in the radiographic assessment of acetabular cup orientation in total hip arthroplasty. A study was conducted analyzing the component in various positions of lateral opening and version with three different X-ray-beam centering positions. The 270 degree acetabular rim wire allowed for easy and accurate assessment of component orientation when the pelvis was level and the central ray of the X-ray beam was centered over the hip.

The influence of prosthetic stem stiffness and of a calcar collar on stresses in the proximal end of the femur with a cemented femoral component.

UNLABELLED: We used three-dimensional finite-element models of the proximal end of the femur to examine the influence of stem material, stem geometry, and the use of a calcar collar on the stresses in and around implanted total hip-replacement femoral components. Anatomical bone geometries and realistic prosthetic geometries were considered. A slender titanium-alloy stem with a collar allows creation of calcar stresses of approximately 80 per cent of the anticipated normal levels. A similar stem of cobalt-chromium alloy creates calcar stresses of 67 per cent of these normal values. Stem designs without a collar were shown to generate no more than 40 per cent of normal values while larger, stiffer stems were seen to create less than 30 per cent of normal values, with or without a collar. Proximal cement stresses were increased by the use of titanium-alloy stems, but were reduced to low levels by a functioning collar. The highest cement stresses in the system were found near the tip of the stem, where titanium-alloy stems create lower stresses than do corresponding cobalt-chromium-alloy stems. The achievability of calcar loading with a titanium prosthesis was demonstrated in in vitro strain-gauge tests. CLINICAL RELEVANCE: Loosening of the femoral stem and calcar resorption are problems that are seen in many long-term clinical series of total hip prostheses. In order to reduce the incidence of these problems, the goal of the designer of a prosthesis is to reduce cement and cement interface stresses around the femoral stem and to create stress distributions in the bone that will prevent resorption.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of angular and rotational deformities of both bones of the forearm. An in vitro study.

UNLABELLED: In intact fresh cadaver specimens, we experimentally studied angular and rotatory deformities at the distal and middle levels of the forearm. The remaining pronation and supination motions were measured. When both bones of the forearm were angulated with a combined deformity (radio-ulnar or dorsovolar, or both) of 10 degrees, a loss of pronation-supination of 12.5 +/- 4.5 per cent occurred in the forearms with a distal-third fracture; in the forearms with a middle-third fracture the average loss was 16.0 +/- 5.7 per cent. Pronation losses were similar for both distal and middle-third deformities. However, supination losses were much less affected (p less than 0.01) in forearms with deformities at the distal-third level while the losses were considered drastic for middle-third deformities. Rotatory deformities produced losses of pronation-supination that were equal to the degree of deformity. CLINICAL RELEVANCE: Study of the artificially created deformities in cadavera indicated that angular and rotatory deformities of the forearm of 10 degrees or less result in minimum limitation of pronation-supination. These degrees of limitation of motion in clinical practice are easily compensated for and are cosmetically acceptable. The fact that the perfect anatomical restoration of fracture alignment that often is obtained with internal fixation does not always result in complete restoration of motion suggests that: (1) this residual impairment of function is due to soft-tissue scarring, and (2) the mild angular and rotatory deformities resulting from nonsurgical treatment of fractures of the forearm may produce limitations of motion of an equally acceptable degree.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of function in fracture healing and stability.

A mechanically based classification system and hypothesis for fracture healing with peripheral callus has been proposed based on many years of clinical experience and numerous laboratory research studies. This hypothesis describes the interactions and influences on fracture healing from the vascular, mechanical, electric, chemical, and thermal environments in specific callus regions surrounding the fracture site. The central theme to this phenomenon is motion at the fracture site. The single factor distinguishing the effects of closed functional bracing of fractures from all other treatment modalities is motion between the fragments which results from early functional activity. Perhaps the stimulus to a prolonged inflammatory response is provided by friction between moving fracture fragments and the surrounding tissues. An increased vascular response results, and environmental factors are stimulated to form an abundant peripheral callus. Three distinct callus zones exist which provide overlapping stages of healing based on structure and optimized physiologic conditions. Clinical signs and symptoms, such as fracture stability as well as motion and pain at the fracture site, combine to provide the optimum feedback mechanism to control functional activity, which in turn governs environmental factors. Roentgenographic appearance can be better judged for mechanical significance if these three callus regions are appreciated. In animals as well as in humans, if function has correctly influenced the environment during callus formation, refracture strength is often greater than that of the original bone.

Histopathology and metallurgical analysis of a removed Lane plate at 53 years postimplantation: a case report.

A vanadium steel Lane plate with nickel coating and low grade steel screws were removed from a patient 53 years postimplantation. Corrosion of the parts was extreme, but the reaction in the surrounding tissues was surprisingly quiescent under the circumstances. By today's standards, the materials, their application, and their performance were totally unacceptable. However, the biological system tolerated this "insult" well.

A quantitative comparative analysis of fracture healing under the influence of compression plating vs. closed weight-bearing treatment.

The study compared the healing of fractures treated with rigid immobilization with the healing of fractures without internal fixation. Comparative studies were made of the cytologic, morphologic and mechanical properties of callus from closed fractures in 2 groups of dogs: one plated, the other not. Significant differences were observed in the 2 groups in early stages of healing. The biomechanical differences between the 2 groups persisted into later stages of healing, even after histologic and electron microscopic appearance of cellular activity and new bone formation had become similar. In general, closed, nondisplaced fractures of dogs' radii treated without surgical procedures and followed by early functional activity demonstrated a cytologically more active endosteal callus and increased biomechanical strength characteristics at the fracture site.

Factors contributing to lysis of the femoral neck in total hip arthroplasty.

A radiographic analysis of 483 Charnley total hip arthroplasties performed from July 1970 to November 1975 demonstrated that 13% of the hips had lysis of the medial femoral neck. The findings suggest that the lysis of the medial femoral neck is significantly reduced if the femoral stem is oriented in a valgus or neutral position and with at least 5 mm of cement separating the stem of the prosthesis and the medial cortex of the femoral neck.

Clinical experiences with a titanium alloy total hip prosthesis: a posterior approach.

Using a titanium alloy femoral prosthesis (STH Zimmer) and an ultra high molecular weight polyethylene acetabular cup with a posterior surgical approach to the hip joint, 237 consecutive total hip arthroplasties in 215 patients were performed between December 1975 and May 1977. The preliminary results and early postoperative complications suggest that this system can be considered an alternative to total hip arthroplasty using other materials and surgical approaches.

SEM fractography studies of porous vitreous carbon: a candidate biomaterial.

A new porous vitreous carbon material under development for use in orthopedic applications was investigated. Specimens were machined to appropriate sizes and fractured in one of the following modes: compression, cantilevered bending, or axial torsion. Scanning electron microscopy (SEM) was used to examine surface and internal features. Characteristics of a brittle, glassy material were noted. Findings included internal voids which appeared as craters, patches of whiskerlike fibrils, and edge impurities. Numerous microcracks caused by mechanical shaping and handling were the most remarkable structural defects. Pore channels which would allow bony ingrowth ranged in size from 50--500 micrometers with the majority between 200 and 300 micrometers. This study of porous vitreous carbon points to the need for stricter quality control in manufacturing, alternative methods for shaping and handling, and careful consideration in design and usage of a brittle material with marginal limits of safety for biomedical applications.

Implant failures in orthopaedic surgery.

Common orthopaedic implant failures are reviewed in the areas of total joint replacement and fracture fixation. In particular total hip and total knee arthroplasty, intertrochanteric hip fractures and long bone fractures are discussed. Excessive motion of implant bone interfaces, stress concentrations within the implant and stress shielding of bone are implicated in implant failures.