In-vivo time-dependent articular cartilage contact behavior of the tibiofemoral joint.

OBJECTIVE: The purpose of this study was to investigate the in-vivo time-dependent contact behavior of tibiofemoral cartilage of human subjects during the first 300 s after applying a constant full body weight loading and determine whether there are differences in cartilage contact responses between the medial and lateral compartments. DESIGN: Six healthy knees were investigated in this study. Each knee joint was subjected to full body weight loading and the in-vivo positions of the knee were captured by two orthogonal fluoroscopes during the first 300 s after applying the load. Three-dimensional models of the knee were created from MR images and used to reproduce the in-vivo knee positions recorded by the fluoroscopes. The time-dependent contact behavior of the cartilage was represented using the peak cartilage contact deformation and the cartilage contact area as functions of time under the constant full body weight. RESULTS: Both medial and lateral compartments showed a rapid increase in contact deformation and contact area during the first 20s of loading. After 50s of loading, the peak contact deformation values were 10.5+/-0.8% (medial) and 12.6+/-3.4% (lateral), and the contact areas were 223.9+/-14.8 mm(2) (medial) and 123.0+/-22.8 mm(2) (lateral). Thereafter, the peak cartilage contact deformation and contact area remained relatively constant. The respective changing rates of cartilage contact deformation were 1.4+/-0.9%/s (medial) and 3.1+/-2.5%/s (lateral); and of contact areas were 40.6+/-20.8 mm(2)/s (medial) and 24.0+/-11.4 mm(2)/s (lateral), at the first second of loading. Beyond 50 s, both changing rates approached zero. CONCLUSIONS: The peak cartilage contact deformation increased rapidly within the first 20s of loading and remained relatively constant after approximately 50 s of loading. The time-dependent response of cartilage contact behavior under constant full body weight loading was significantly different in the medial and lateral tibiofemoral compartments, with greater peak cartilage contact deformation on the lateral side and greater contact area on the medial side. These data can provide insight into normal in-vivo cartilage function and provide guidelines for the improvement of ex-vivo cartilage experiments and the validation of computational models that simulate human knee joint contact.

Longitudinal changes in patient-reported outcome measures following total hip arthroplasty and predictors of deterioration during follow-up: a seven-year prospective international multicentre study.

AIMS: The primary aim of this study was to quantify the improvement in patient-reported outcome measures (PROMs) following total hip arthroplasty (THA), as well as the extent of any deterioration through the seven-year follow-up. The secondary aim was to identify predictors of PROM improvement and deterioration. PATIENTS AND METHODS: A total of 976 patients were enrolled into a prospective, international, multicentre study. Patients completed a battery of PROMs prior to THA, at three months post-THA, and at one, three, five, and seven-years post-THA. The Harris Hip Score (HHS), the 36-Item Short-Form Health Survey (SF-36) Physical Component Summary (PCS), the SF-36 Mental Component Summary (MCS), and the EuroQol five-dimension three-level (EQ-5D) index were the primary outcomes. Longitudinal changes in each PROM were investigated by piece-wise linear mixed effects models. Clinically significant deterioration was defined for each patient as a decrease of one half of a standard deviation (group baseline). RESULTS: Improvements were noted in each PROM between the preoperative and one-year visits, with one-year values exceeding age-matched population norms. Patients with difficulty in self-care experienced less improvement in HHS (odds ratio (OR) 2.2; p = 0.003). Those with anxiety/depression experienced less improvement in PCS (OR -3.3; p = 0.002) and EQ-5D (OR -0.07; p = 0.005). Between one and seven years, obesity was associated with deterioration in HHS (1.5 points/year; p = 0.006), PCS (0.8 points/year; p < 0.001), and EQ-5D (0.02 points/year; p < 0.001). Preoperative difficulty in self-care was associated with deterioration in HHS (2.2 points/year; p < 0.001). Preoperative pain from other joints was associated with deterioration in MCS (0.8 points/year; p < 0.001). All aforementioned factors were associated with clinically significant deterioration in PROMs (p < 0.035), except anxiety/depression with regard to PCS (p = 0.060). CONCLUSION: The present study finds that patient factors affect the improvement and deterioration in PROMs over the medium term following THA. Special attention should be given to patients with risk factors for decreased PROMs, both preoperatively and during follow-up. Cite this article: Bone Joint J 2019;101-B:768-778.

In vivo cartilage contact deformation in the healthy human tibiofemoral joint.

OBJECTIVES: In vivo cartilage contact deformation is instrumental for understanding human joint function and degeneration. This study measured the total deformation of contacting articular cartilage in the human tibiofemoral joint during in vivo weight-bearing flexion. METHODS: Eleven healthy knees were magnetic resonance (MR) scanned and imaged with a dual fluoroscopic system while the subject performed a weight-bearing single-leg lunge. The tibia, femur and associated articulating cartilage were constructed from the MR images and combined with the dual fluoroscopic images to determine in vivo cartilage contact deformation from full extension to 120 degrees of flexion. RESULTS: In both compartments, minimum peak compartmental contact deformation occurred at 30 degrees of flexion (24 +/- 6% medial, 17 +/- 7% lateral) and maximum peak compartmental deformation occurred at 120 degrees of flexion (30 +/- 13% medial, 30 +/- 10% lateral) during the weight-bearing flexion from full extension to 120 degrees. Average medial contact areas and peak contact deformations were significantly greater than lateral compartment values (P < 0.05). In addition, cartilage thickness in regions of contact was on average 1.4- and 1.1-times thicker than the average thickness of the tibial and femoral cartilage surfaces, respectively (P < 0.05). CONCLUSIONS: These data may provide base-line knowledge for investigating the effects of various knee injuries on joint contact biomechanics and the aetiology of cartilage degeneration.

A Fully Functional Drug-Eluting Joint Implant.

Despite advances in orthopedic materials, the development of drug-eluting bone and joint implants that can sustain the delivery of the drug and maintain the necessary mechanical strength in order to withstand loading has remained elusive. Here, we demonstrate that modifying the eccentricity of drug clusters and the percolation threshold in ultrahigh molecular weight polyethylene (UHMWPE) results in maximized drug elution and in the retention of mechanical strength. The optimized UHMWPE eluted antibiotic at a higher concentration for longer than the clinical gold standard antibiotic-eluting bone cement while retaining the mechanical and wear properties of clinically used UHMWPE joint prostheses. Treatment of lapine knees infected with Staphylococcus aureus with the antibiotic-eluting UHMWPE led to complete bacterial eradication and to the absence of detectable systemic effects. We argue that the antibiotic-eluting UHMWPE joint implant is a promising candidate for clinical trials.

Side-to-side variation in normal femoral morphology: 3D CT analysis of 122 femurs.

BACKGROUND: The contralateral femur is often used as reference for reconstruction in unilateral hip joint pathology. The objective of this study was to quantify the side-to-side variation in proximal femur. We hypothesized that significant side-to-side differences exist between left and right femur with implications for preoperative planning and leg length discrepancy following hip arthroplasty. MATERIALS AND METHODS: CT-based 3D femoral models were reconstructed for 122 paired femurs in 61 young healthy subjects (46.9±6.8 years) with no history of hip pathology. Side-to-side differences of several femoral morphologic parameters, including femoral head diameter, femoral anteversion, horizontal offset and femoral head center location, were compared and correlated with demographic factors using multiple linear regression. RESULTS: Significant side-to-side differences (P<0.01) were found in femoral anteversion (4.3±3.8°; range: 0.2° to 17.3°), horizontal offset (2.5±2.1mm; range: 0.1 to 10.3mm), and femoral head center location (7.1±3.8mm; range: 0.5 to 19.4mm). The difference in femoral anteversion was strongly correlated with the difference in neck diameter (R(2)=0.79), whereas the difference in horizontal femoral offset was highly correlated with the head diameter difference (R(2)=0.72). Femoral head center difference was correlated with the femoral anteversion, horizontal offset and neck-shaft-angle difference (R(2)=0.82). DISCUSSION: Relying on the anatomic landmarks of the contralateral femur during hip arthroplasty may not necessarily result in restoration of native anatomy and leg-length. Knowledge of the baseline side-to-side asymmetry could provide a range of error that would be tolerable following hip reconstruction. LEVEL OF EVIDENCE: Level IV. TYPE OF STUDY: Retrospective observational study.

Technique for generating submicrometer ultra high molecular weight polyethylene particles.

Ultra high molecular weight polyethylene wear debris is believed to have a major role in aseptic loosening of prosthetic joints. In order to study the cellular and host response to this and other such particulate debris, a source of fine ultra high molecular weight polyethylene debris is needed. We have described a technique to fracture the GUR 4150 primary ultra high molecular weight polyethylene grain, which reproducibly generated particles less than 1 micron in size. Furthermore, the particle morphology was similar to that of ultra high molecular weight polyethylene particles generated in vivo and retrieved from interfacial tissues. The fabricated polyethylene particles ranged from 0.1 to 33 microns in diameter, with a mean of 2.3 +/- 0.2 micron. Sixty percent of the particles were smaller than 1 micron and 90% were smaller than 7 microns. Using filtration and sedimentation, it is possible to acquire finer particle fractions. These particles are currently being used for biological response studies.

The effect of component placement on knee kinetics after arthroplasty with an unconstrained prosthesis.

The mechanical success of a total knee replacement demands stable patellar tracking without subluxation and, stable tracking, in turn, can depend largely on the medial-lateral forces restraining the patella. Patellar button medialization has been advocated as a means of reducing subluxation, and experimental evidence has shown femoral component rotation also affects medial-lateral forces. Surgeons have choices in femoral component rotation and patellar button medialization and must frequently make intra-operative decisions concerning component placement because of anatomical variations among patients. Thus, in seeking to minimize medial-lateral patellar force, we examined the effects of patellar button medialization and external femoral component rotation. The study used an unconstrained total knee system implanted in nine cadaveric specimens tested on a knee simulator operating through flexion angles up to 100 degrees. Tests included all combinations of external femoral component rotation of 0 degree, 2.5 degrees, and 5 degrees and patellar placement at the geometric center and at 3.75 mm medial to the geometric center. A video-based motion analysis system tracked patellar and tibial kinematics while a six-component load cell measured patellofemoral loads. Repeated measures analysis of variance revealed a statistically significant decrease in the average medial-lateral force with button medialization but no significant change with femoral component rotation. Neither femoral component rotation nor patellar button medialization had an effect on the normal component of the patellar reaction force. External femoral component rotation did cause significant increases in lateral patellar tilt, in tibial varus angle, and in external tibial rotation. Button medialization caused significant increases in lateral patellar tracking, lateral patellar tilt and external tibial rotation. The results in medial-lateral patellar forces quantify the benefit of patellar button medialization and discount any benefit of femoral rotation. The change in tibial kinematics with patellar button medialization and femoral component rotation cannot be measured in vivo with current technology, and the precise clinical implications are unknown.

Bone remodeling around total hip implants.

This chapter reviews the research in the computer simulation of bone remodeling caused by hip implants and also attempts to give nonmedical personnel a basic introduction to total hip arthroplasty and implant-induced bone resorption. First, a short discussion of the hip arthroplasty procedure and the results of follow-up studies are presented to motivate the study of hip prostheses. Current implant materials and technologies and future trends in implant design are reviewed. A description of what are believed to be the mechanisms of bone resorption due to femoral implantation is presented. Different mathematical theories of bone remodeling and their application to the problem of implant analysis are presented, and recent advances in the finite element modeling of bone resorption and implant micromotion are discussed.

In vivo and in vitro analysis of membranes from hip prostheses inserted without cement.

Biochemical, histological, and immunohistochemical studies of interface membranes surrounding failed hip prostheses that had been inserted without cement were done to examine specific factors involved in the development of aseptic loosening. Membranes from sixty-four femoral components were obtained from sixty-three patients during revision arthroplasty. Fifty-seven membranes were from implants that articulated with polyethylene (thirty-two were made of cobalt-chromium alloy and twenty-five, titanium alloy), and seven were from unipolar endoprostheses made of cobalt-chromium alloy that did not articulate with polyethylene. The membranes from implants with a polyethylene articulation produced significantly higher levels of collagenase and interleukin-1 (p < 0.05). However, there was no significant difference in the levels of prostaglandin E2 between the three groups. Furthermore, membranes from implants with roentgenographic evidence of focal osteolysis (endosteal erosion) released significantly higher levels of interleukin-1 (p < 0.05) than did membranes from implants without focal osteolysis. Although the membranes from the titanium-alloy implants tended to contain more metal debris than those from the cobalt-chromium-alloy implants, the biochemical findings were not significantly different between these two groups. Many macrophages that were filled with polyethylene and metal debris were present in the membranes from both groups with a polyethylene articulation. Few T lymphocytes or B lymphocytes were identified in the three groups.

Ingrowth and formation of bone in defects in an uncemented fiber-metal total hip-replacement model in dogs.

An osseous defect was created in the acetabulum and femur of twenty dogs, and then a fiber-metal total hip prosthesis was inserted. A comparison was made between the effects of leaving the defects unfilled, filling the defects with an autogenous bone graft, and filling them with a 50:50 mixture of autogenous bone graft and a biphasic ceramic composed of hydroxyapatite and tricalcium phosphate. The characteristics of formation of bone within the sites of the defects and the extent of the ingrowth of bone into the underlying porous surface were analyzed. At six and twelve weeks after implantation, the dogs in the control group (unfilled defects) had the least amount of bone in the sites of the defects. In the dogs that had had an autogenous bone graft and those in which the defects had been filled with a mixture of autogenous bone graft and biphasic ceramic, there were excellent osteoconductive properties in the filling of the sites of the defects with new bone. A comparison was made between the amount of bone that formed in the osseous defects and the amount that formed in the spaces of the porous-surfaced fiber-metal components of the prostheses, directly underlying and adjacent to the defects. At six weeks, the greatest amount of ingrowth of bone into the spaces of the underlying titanium fiber-metal acetabular components was seen in the control group (22 per cent of the porous surface), followed by the group in which the defects had been filled with a mixture of autogenous bone graft and biphasic ceramic (19 per cent). The defects that had been filled only with autogenous bone graft had poor ingrowth of bone into the porous surface (4 per cent) and predominantly fibrous ingrowth. At twelve weeks, these defects again showed the least amount of ingrowth of bone (15 per cent) compared with the defects in the control group (24 per cent) and those that had been filled with a mixture of autogenous bone graft and biphasic ceramic (24 per cent). No statistically significant differences were found in the amount of ingrowth of bone into the defects that had been created in the femur in the three groups of dogs at either six or twelve weeks. However, the trends appeared to correlate with the data for the acetabular defects.

Isolation and characterization of wear particles generated in patients who have had failure of a hip arthroplasty without cement.

Wear particles from thirty-five membranes obtained during revision hip-replacement operations were studied after digestion of the soft tissue with papain. The particles were isolated and were characterized with use of light and scanning electron microscopic techniques, x-ray microanalysis, and an automated particle analyzer. The mean size of the polyethylene particles was 0.5 micrometer, and the metal particles were a mean of 0.7 micrometer, as determined with scanning electron microscopy. The automated particle analyzer revealed a mean particle diameter of 0.63 micrometer (more than 90 per cent of all particles were less than 0.95 micrometer) and a mean of 1.7 billion particles per gram of tissue, compared with only 143 million per gram of tissue for the control samples. X-ray microanalysis revealed metal debris in sixteen (46 per cent) of the thirty-five membranes after digestion. Thirteen (50 per cent) of the twenty-six membranes surrounding a titanium-alloy stem contained metal particles, compared with three of the nine membranes surrounding a chromium-cobalt stem. Metal debris was present in only one of the twelve membranes surrounding a titanium-alloy stem without a porous coating, compared with twelve of the fourteen membranes surrounding a titanium-alloy stem with a porous coating. This tenfold difference in prevalence was significant (p < 0.005). On the average, the total number of particles (expressed in millions per gram of tissue) associated with the bipolar acetabular components was twice that associated with the fixed acetabular components. In addition, there was a trend toward a larger mean size of the polyethylene particles in association with the bipolar cups. Our data indicate that particulate prosthetic debris in the tissues around failed femoral components that have been inserted without cement constitutes a class of particles that are predominantly less than one micrometer in size and are present in amounts of more than one billion particles per gram of tissue. Routine histological methods did not detect this class of wear debris and led to a gross underestimation of the amount of debris in these membranes.

Acetabular anatomy and the transacetabular fixation of screws in total hip arthroplasty.

An anatomical and radiographic study was undertaken to determine the safest zones in the acetabulum for the transacetabular placement of screws during uncemented acetabular arthroplasty. To avoid injury to intrapelvic structures, which are not visible to the surgeon during placement of the screws, cadavera were studied to define the location of these structures with respect to fixed points of reference within the acetabulum. Four clinically useful acetabular quadrants were delineated. The quadrants are formed by drawing a line from the anterior superior iliac spine through the center of the acetabulum to the posterior fovea, forming acetabular halves. A second line is then drawn perpendicular to the first at the mid-point of the acetabulum, forming four quadrants. The posterior superior and posterior inferior acetabular quadrants contain the best available bone stock and are relatively safe for the transacetabular placement of screws. The anterior superior and anterior inferior quandrants should be avoided whenever possible, because screws placed improperly in these quadrants may endanger the external iliac artery and vein, as well as the obturator nerve, artery, and vein. The acetabular-quadrant system provides the surgeon with a simple intraoperative guide to the safe transacetabular placement of screws during primary and revision acetabular arthroplasty.

Treatment of pelvic osteolysis associated with a stable acetabular component inserted without cement as part of a total hip replacement.

Thirty-five patients who had had a primary total hip replacement with a porous-coated acetabular component inserted without cement had a revision procedure to treat pelvic osteolysis. The mean age at the time of the revision operation was forty-nine years (range, twenty-nine to eighty-five years). Forty-six distinct pelvic osteolytic lesions were noted radiographically around the thirty-five cups. These lesions ranged in size from 0.5 by 0.5 centimeter to 6.3 by 2.7 centimeters (mean, 2.6 by 1.7 centimeters). Fourteen of the thirty-five patients had no or only slight occasional pain at the time of diagnosis of the pelvic osteolysis, fifteen patients had pain attributed to a loose femoral component, one had pain related to a spontaneous fracture of the greater trochanter, and one had pain related to recurrent subluxation. The remaining four patients had pain in the groin despite radiographically stable implants. All of the metal-backed porous-coated acetabular components were stable according to the preoperative radiographs, and the stability was confirmed at the time of the revision. The metal shell was left in place and the acetabular liner was exchanged in all thirty-five patients. The osteolytic lesions were debrided, and thirty-four of the forty-six lesions were filled with allograft bone chips. The patients were evaluated a minimum of two years (range, two to five years; mean, 3.3 years) after the revision operation, and all thirty-five sockets were found to be radiographically stable. The bone grafts appeared to have consolidated, and none of the osteolytic defects had progressed. One-third of the lesions were no longer visible on radiographs, regardless of whether or not they had been filled with bone graft. The remaining lesions had decreased in size. It appears that, in the short-term, exchange of the liner and debridement of the granuloma, with or without use of allograft bone chips in the osteolytic defect, is a reasonable alternative to revision of the socket provided that the metal shell is solidly fixed at the time of the revision operation. If the metal shell has been markedly damaged by the femoral head, the locking mechanism for the polyethylene liner is not intact, or a satisfactory replacement liner is not available, then revision of the porous-coated acetabular component is indicated. These results must be considered preliminary. Since osteolysis may take several years to redevelop after a revision, additional follow-up is required.

An analysis of blood management in patients having a total hip or knee arthroplasty.

Three hundred and thirty orthopaedic surgeons in the United States participated in a study of transfusion requirements associated with total joint arthroplasty. A total of 9482 patients (3920 patients who had a total hip replacement and 5562 patients who had a total knee replacement) were evaluated prospectively from September 1996 through June 1997. Of those patients, 4409 (46 percent [57 percent of the patients who had a hip replacement and 39 percent of the patients who had a knee replacement]) had a blood transfusion. Two thousand eight hundred and ninety patients (66 percent) received autologous blood, and 1519 patients (34 percent) received allogenic blood. Ordered logistic regression analysis showed the most important predictors of the transfusion of allogenic blood to be a low baseline hemoglobin level and a lack of predonated autologous blood. Preoperative donation of autologous blood decreases the risk of transfusion of allogenic blood; however, inefficiencies in the procedures for obtaining autologous blood were identified. Sixty-one percent (5741) of the patients had predonated blood for autologous transfusion, but 4464 (45 percent) of the 9920 units of the predonated autologous blood were not used. Primary procedures and revision total knee arthroplasty were associated with the greatest number of wasted autologous units. Of the 5741 patients who had predonated blood, 503 (9 percent) needed a transfusion of allogenic blood. The frequency of allogenic blood transfusion varied with respect to the type of operative procedure (revision total hip arthroplasty and bilateral total knee arthroplasty were associated with the highest prevalence of such transfusions) and with a baseline hemoglobin level of 130 grams per liter or less. Transfusion of allogenic blood was also associated with infection (p < or = 0.001), fluid overload (p < or = 0.001), and increased duration of hospitalization (p < or = 0.01). These latter findings warrant further evaluation in controlled studies.

Sensitivity of the knee joint kinematics calculation to selection of flexion axes.

Various flexion axes have been used in the literature to describe knee joint kinematics. This study measured the passive knee kinematics of six cadaveric human knee specimens using two widely accepted flexion axes; transepicondylar axis and the geometric center axis. These two axes were found to form an angle of 4.0 degrees +/- 0.8 degrees. The tibial rotation calculated using the transepicondylar axis was significantly different than the rotation obtained using the geometric center axis for the same knee motion. At 90 degrees of flexion, the tibial rotation obtained using the transepicondylar axis was 4.8 degrees +/- 9.4 degrees whereas the rotation recorded using the geometric center axis at the same flexion angle was 13.8 degrees +/- 10.2 degrees. At 150 degrees of knee flexion, the rotations obtained from the transepicondylar and the geometric center axes were 7.2 degrees +/- 5.7 degrees and 19.9 degrees +/- 6.9 degrees, respectively. The data suggest that a clear definition of the flexion axis is necessary when reporting knee joint kinematics.

Effect of the posterior cruciate ligament on posterior stability of the knee in high flexion.

Most biomechanical studies of the knee have focused on knee flexion angles between 0 degrees and 120 degrees. The posterior cruciate ligament (PCL) has been shown to constrain posterior laxity of the knee in this range of flexion. However, little is known about PCL function in higher flexion angles (greater than 120 degrees ). This in vitro study examined knee kinematics before and after cutting the PCL at high flexion under a posterior tibial load and various muscle loads. The results demonstrated that although the PCL plays an important role in constraining posterior tibial translation at low flexion angles, the PCL had little effect in constraining tibial translation at 150 degrees of flexion under the applied loads.

Rotational instability and malrotation after total knee arthroplasty.

Total knee arthroplasty has become the standard treatment for various disabling disorders of the knee and has proven long-term success. Surgical technique and prosthetic design have evolved to produce consistent and excellent results. Despite the current success of total knee arthroplasty, complications remain.

Neural and vascular injury in total hip arthroplasty.

Complete awareness of the anatomy of the pelvis and proximal femur is required if neurologic and vascular complications are to be avoided following total hip arthroplasty. Avoidance of the anterior quadrants for acetabular screw fixation is critical. Cementing techniques are important, and all acetabular and femoral defects should be bone grafted to avoid inadvertent cement migration. Knowledge of the location of pertinent neural and vascular structures should guide retractor placement. Planned lengthening of an extremity during total hip arthroplasty poses a significant risk to neurologic structures, and SSEP monitoring should be considered. In difficult revision procedures and complex primary total hip arthroplasty, preoperative neural and vascular assessment and SSEP monitoring should be done. With the occurrence of a postoperative nerve palsy, careful review of the procedure should be performed to determine the cause of the injury. In this manner the surgeon can best offer appropriate counseling to the patient as to the likelihood of neurologic recovery.

Pathogenesis of bone loss after total hip arthroplasty.

Bone loss with or without evidence of aseptic loosening is a long term complication after total hip arthroplasty (THA). It occurs with all materials and in all prosthetic systems in use or that have been used to date. Bone loss after THA can be a serious problem in revision surgery because bone deficiencies may limit reconstructive options, increase the difficulty of surgery, and necessitate autogenous or allogenic bone grafting. There are three factors adversely affecting maintenance of bone mass after THA: (1) bone loss secondary to particulate debris; (2) adaptive bone remodeling and stress shielding secondary to size, material properties, and surface characteristics of contemporary prostheses; and (3) bone loss as a consequence of natural aging. This chapter reviews the mechanisms of the primary causes of bone loss after THA.

External fixation of the pelvis.

During the past decade the useful classification and principles of management of the fractured pelvis have progressed rapidly. For the acute management the principal consideration is the control of severe intrapelvic hemorrhage. A protocol has been developed that combines the early application of external fixation with a closed reduction of the pelvic fracture. A marked decrease in the anticipated amount of intrapelvic hemorrhage has been documented. The coupled double anterior frame and its biomechanical equivalent, the newly developed triangular system, are easily applied to the pelvic ring and provide adequate stability for the treatment of the patient with a stable or unstable pelvic ring fracture. Thus the complex earlier design has been replaced by a simpler system. The triangular frame provides adequate stability so that the patient can undertake independent bed-to-chair transfers and early resumption of a weight-bearing gait. Late pulmonary, gastrointestinal, and urologic complications with prolonged bed rest and cast immobilization therefore have greatly diminished. In the present series in which external fixation has been applied to unstable pelvic ring fractures with a single posterior disruption, late loss of reduction, nonunion, and malunion almost have been entirely avoided. In addition, a simple triangular frame provides access to the abdominal wall and offers minimal postoperative interference with nursing care of the patient. Once the general condition of the patient has stabilized, supplementary techniques of open reduction and internal fixation may be applied to appropriate complex fracture patterns. These methods are fully reviewed elsewhere. Thus early rigid stabilization of the patient who sustains a pelvic ring fracture facilitates diminution of fracture pain, early mobilization of the patient, discharge, improved morale, and ultimately, decreased fracture morbidity and mortality.