Sophia N. Sangiorgio

Accuracy of Measurement of Polyethylene Wear with Use of Radiographs of Total Hip Replacements

BACKGROUND Although a number of methods are used to estimate polyethylene liner wear from radiographs of total hip replacements, there is no consensus with regard to the accuracy of these methods. The purpose of this study was to compare the accuracy of several such measurement methods with use of both laboratory radiographs and routine clinical radiographs. METHODS A phantom apparatus was designed to simulate random values of three-dimensional wear, with varying degrees of cup abduction and anteversion, and to obtain anteroposterior and cross-table lateral radiographs with each value. Wear was measured with use of the Charnley duoradiographic method, the Livermore method, and the method described by Dorr and Wan, as well as with use of PolyWare and Hip32 software packages, both with and without three-dimensional measurements. Clinical wear was measured from conventional radiographs made prior to revision surgery in fourteen patients and was compared with wear measured directly from the retrieved liners with use of a coordinate measuring machine. RESULTS With laboratory radiographs, median errors were 0.1 mm with the Livermore method and both computerized methods, 0.23 mm with the Charnley method, and 1.7 mm with the method of Dorr and Wan. Maximum errors were between 0.6 mm (Livermore) and 4.3 mm (Dorr and Wan). In contrast, with use of clinical radiographs, median errors ranged between 0.2 mm (Hip32) and 0.6 mm (Dorr and Wan). Maximum errors ranged between 1.8 mm (Dorr and Wan) and 2.5 mm (Livermore). CONCLUSIONS With laboratory radiographs, computerized methods of polyethylene wear measurement offered distinctly greater accuracy than did manual methods; however, with clinical radiographs, they offered only slightly better accuracy. Although the increased accuracy of computerized methods may be necessary in research settings, manual methods provided sufficient accuracy for routine clinical assessment of wear.

Failure Modes of 433 Metal-on-Metal Hip Implants: How, Why, and Wear

Metal-on-metal total hip replacements (THRs) and hip resurfacings are coming under increasing scrutiny in light of concerns that they fail because of high wear and elevated metal ions. The aim of this study was to investigate the modes of failure in a collection of 433 metal-on-metal THRs and hip resurfacings and to examine the correlations between the reasons for revision and a range of patient and implant variables considered relevant to implant wear.

Long-term radiographic changes in cemented total hip arthroplasty with six designs of femoral components

Measurements were made from annual follow-up radiographs, obtained over 27.6 years, of 860 cemented total hip arthroplasties implanted by one surgeon. Femoral components were made of stainless steel or titanium alloy, were non-modular, and were all fixed with cement, and acetabular cups were all-polyethylene and were fixed with cement. Radiographic outcome was correlated with the shape and material of the femoral component. Specifically, throughout the follow-up, stems made of titanium alloy were at greater risk of developing bone-cement radiolucent lines than those made of stainless steel, the difference ranging from approximately 10-50 percent at 2-10 years of follow-up. Similarly, titanium alloy stems were at greater risk of developing endosteal scalloping, indicating osteolytic lesions. Among the stainless steel Charnley cobra and straight-narrow Charnley stems, none developed cement fracture, only one became radiographically loose and one developed endosteal scalloping. The differences in the risk of developing radiolucent lines, cement fracture and progressive loosening among these stems were correlated with the relative rigidity of the femoral stems, and were generally consistent with the predictions made heretofore using finite element models, although differences in stem surface finish and femoral ball size and material could have also influenced the results.

Initial stability of cemented femoral stems as a function of surface finish, collar, and stem size.

BACKGROUND The optimum surface roughness of cemented femoral stems used for total hip replacement is a subject of controversy. While rougher surfaces provide stronger cement adhesion, it has been hypothesized that polished, tapered, noncollared stems settle into the cement mantle, providing improved stability. However, the effects of surface finish on the stability of straight, cemented stems tapered only in the coronal plane are not known. METHODS Using composite model femora, we assessed the initial stability of a straight, cemented femoral stem as a function of surface roughness, the presence or absence of a collar, stem size, and the resultant cement thickness under simulated walking and stair-climbing loads. Otherwise identical stems were manufactured with polished or rough surfaces, with or without a collar, in two different sizes. We isolated these three variables and compared their relative contributions to the motion at the stem-cement interface throughout cyclic loading. We defined three indicators of stability: per-cycle motion, rate of migration, and final migration. RESULTS Surface roughness had a greater influence on per-cycle motions than did the presence or absence of a collar or cement thickness. Specifically, in the medial-lateral direction, per-cycle motion of polished stems was 43 micro m greater than that of rough stems (p < 0.01). None of the per-cycle motions decreased over the 77,000 load cycles. In contrast, with all stems, the rate of migration decreased over the course of cyclic loading, but the rate of migration of the polished stems was greater than that of the rough stems. Final migrations of the stems over the course of loading were generally distal, medial, and into retroversion. Compared with rough stems, polished stems had 8 to 18 micro m more axial migration (p < 0.001), 48 micro m more anterior-posterior migration (p < 0.001), and 0.4 degrees more rotational migration (p = 0.01). CONCLUSIONS and CLINICAL RELEVANCE The results indicated that, for cemented, straight femoral stems tapered only in the coronal plane, a rough surface offers the advantage of less per-cycle motion. These results may apply to widely used cemented stem designs based on the profile of the original Charnley femoral component, which has approximately parallel anterior and posterior aspects.

Less range of motion with resurfacing arthroplasty than with total hip arthroplasty: in vitro examination of 8 designs.

BACKGROUND AND PURPOSE Hip resurfacing arthroplasty has had resurgence recently and is now a popular option for younger, active patients. We used an in vitro model to assess range of motion and impingement profile for hip resurfacing and compared them to those for conventional total hip arthroplasty. METHODS 8 different hip replacement designs were implanted into adult composite femurs and pelvises. These were mounted onto a 3-dimensional compass allowing all motions, with the degrees and impingement recorded. The designs tested were the Conserve Plus Hip Resurfacing System, Depuy ASR, Birmingham Hip Resurfacing System, Charnley, McKee-Farrar metal-on-metal, SROM Hip metal-on-metal, SROM Hip metal-on-polyethylene, Prodigy metal-on-metal, and also a native intact composite femur and pelvic articulation. Femoral stems were tested at 0 and 20 degrees of anteversion. RESULTS Conventional hip arthroplasty exhibited statistically significantly greater range of motion than resurfacing arthroplasty. Resurfacing showed neck impingement in 29/30 motions. Conventional arthroplasties showed femoral neck impingement in 41/100 motions. INTERPRETATION In situ range of motion of resurfacing arthroplasty was less than that of conventional total hip arthroplasty. Resurfacing systems impinged almost entirely on the femoral neck, while conventional hip arthroplasties had a varied impingement profile. Our findings raise concern for early neck-on-cup impingement, which may cause component loosening and femoral neck fracture, both of which are observed after hip resurfacing.

The current management of idiopathic clubfoot revisited: results of a survey of the POSNA membership.

Background: In 2001, the members of the Pediatric Orthopaedic Society of North America (POSNA) were surveyed regarding their approach to treating idiopathic clubfoot deformity. Since that time, several studies have advocated a change in the approach to treating this deformity, moving away from surgical release and toward less invasive methods. The purpose of this study was to assess the recent approach to treating clubfoot among the POSNA membership. Methods: A survey was emailed to all POSNA members to define their current treatment of idiopathic clubfoot deformity. Results: We received 323 responses. Ninety-three percent of participants were fellowship trained and were in practice for an average of 17.2 years. On an average, physicians reported each treating 23.5 new clubfoot patients during the year of survey. Nearly all (96.7%) of those surveyed stated that they use the Ponseti treatment method. The average time to initial correction was estimated at 7.1 weeks. Eighty-one percent of patients were estimated to require a tenotomy; 52.7% were performed under general anesthesia or conscious sedation, whereas 39.4% were done under local. Those surveyed estimated that 22% of clubfeet relapsed and 7% required a comprehensive release. Seventy-five percent of the respondents stated that their current treatment approach differed from how they were trained, and 82.7% were trained in the Ponseti method in the last few years. Conclusions: Our study provides convincing evidence that a large majority of pediatric orthopaedic surgeons now prefer the Ponseti method to treat idiopathic clubfoot and indicates that the move away from extensive release surgery occurred during the past decade. Level of Evidence: Not applicable.

Nondestructive evaluation of orthopaedic implant stability in THA using highly nonlinear solitary waves

We propose a new biomedical sensing technique based on highly nonlinear solitary waves to assess orthopaedic implant stability in a nondestructive and efficient manner. We assemble a granular crystal actuator consisting of a one-dimensional tightly packed array of spherical particles, to generate acoustic solitary waves. Via direct contact with the specimen, we inject acoustic solitary waves into a biomedical prosthesis, and we nondestructively evaluate the mechanical integrity of the bone–prosthesis interface, studying the properties of the waves reflected from the contact zone between the granular crystal and the implant. The granular crystal contains a piezoelectric sensor to measure the travelling solitary waves, which allows it to function also as a sensor. We perform a feasibility study using total hip arthroplasty (THA) samples made of metallic stems implanted in artificial composite femurs using polymethylmethacrylate for fixation. We first evaluate the sensitivity of the proposed granular crystal sensor to various levels of prosthesis insertion into the composite femur. Then, we impose a sequence of harsh mechanical loading on the THA samples to degrade the mechanical integrity at the stem–cement interfaces, using a femoral load simulator that simulates aggressive, accelerated physiological loading. We investigate the implant stability via the granular crystal sensor–actuator during testing. Preliminary results suggest that the reflected waves respond sensitively to the degree of implant fixation. In particular, the granular crystal sensor–actuator successfully detects implant loosening at the stem–cement interface following violent cyclic loading. This study suggests that the granular crystal sensor and actuator has the potential to detect metal–cement defects in a nondestructive manner for orthopaedic applications.

Comparison of three posterior dynamic stabilization devices.

Study Design. A biomechanical study using human cadaveric lumbar spinal motion segments and three different posterior stabilization devices. Objective. To compare the range of motion, disc height, and foraminal area of a spinal motion segment intact, injured, and fixed with each of three posterior lumbar motion preservation devices. Summary of Background Data. Motion-sparing lumbar posterior dynamic stabilization devices are gaining increasing popularity, particularly for the treatment of degenerative disc disease. Methods. The PercuDyn, the X-Stop, and the Isobar posterior stabilization devices were compared using an in vitro cadaveric model. First, pure moments of ±8 Nm were applied in all three planes, then a follower load of 700 N was applied, and finally, sagittal bending tests were repeated. All tests were conducted using an 8-df servohydraulic load frame. Experiments were performed intact, with a simulated injury, and then with each of the three devices for a total of four specimens per device. Foraminal area and disc height (posterolateral and anterior surface) were measured under neutral and peak torques in all three planes and range of motion was recorded for all experimental conditions. Results. Overall, the injury model successfully increased range of motion and decreased disc height and foraminal area. Once treated with one of the three implants, the PercuDyn was most effective at preventing hyperextension, decreasing extension with a follower load by a mean of 52% compared to injured conditions (P = 0.07). The X-Stop stabilized the posterior column, increasing foraminal area under all conditions, particularly extension with a follower load, by 27% compared to injured conditions (P = 0.01). The Isobar, the only device to stabilize the anterior column, increased anterior disc height under flexion with a follower load by 22% (P = 0.03). Conclusion. All three devices functioned as intended by their respective manufacturers, but each appeared to excel in different areas; therefore, each should be used for unique clinical applications.

Biomechanical Comparison of Syndesmotic Injury Fixation Methods Using a Cadaveric Model

Background: There is growing interest in suture-button devices for syndesmosis injury, which are intended to offer less rigid fixation than screw fixation. Methods: The fixation strength with 2 different suture-button devices, ZipTight and TightRope, were compared using 5 cadaveric leg pairs (n = 10). In an additional 5 pairs (n = 10), ZipTight was compared to 3.5 mm quadricortical screw fixation. Ankle motion was measured intact, then following simulated syndesmosis injury and fixation. Cyclic loads (peak 750 N, 7.5 Nm) were applied. Finally, external rotation to failure was measured and failure mode was documented. Results: Range of motion increased after simulated injury and fixation with all devices (max 14.5 degrees). In all groups, diastasis remained below 1.0 mm intact and below 2.0 mm during cyclic loading. Compared to intact, under load to failure, diastasis with ZipTight devices increased by 4.7 ± 1.3 mm and 7.6 ± 4.3 mm, with TightRope, 6.3 mm, and screw construct, 1.3 mm. ZipTight specimens rotated approximately 80 ± 22 degrees before failure, TightRope, 67 ± 13 degrees, screw constructs, 76 ± 27 degrees. Mean failure torque was between 22.2 ± 6.9 Nm and 28.1 ± 12.7 Nm for ZipTight, compared to 32.9 ± 8.0 Nm for TightRope (P = .07), and 30.1 ± 9.6 Nm for screw constructs (P = .03). The majority of suture-button constructs failed by fibular fracture (ZipTight = 6, TightRope = 4), the remaining by device pull-through (ZipTight = 3, TightRope = 1) and loosening (ZipTight = 1). Conversely, 3 of screw-fixed specimens failed by device failure, 2 from bone fracture. Conclusion: Suture-button devices provided torsional strength below that of screw fixation. However, all devices may provide failure torques well above 20 Nm, exceeding likely torques applied in casts during healing.1,2,4 Clinical Relevance: Suture-button devices appear to have provided adequate fixation strength for syndesmosis injuries.

Can Wear Explain the Histological Variation Around Metal-on-metal Total Hips?

BackgroundThere is a general perception that adverse local tissue reactions in metal-on-metal hip arthroplasties are caused by wear, but the degree to which this is the case remains controversial.Questions/purposesTo what extent is the magnitude of wear associated with (1) the histological changes; (2) presence of metallosis; and (3) likelihood of pseudotumor formation in the periprosthetic tissues?MethodsOne hundred nineteen metal-on-metal total hip arthroplasties and hip resurfacings were selected from a retrieval collection of over 500 implants (collected between 2004 and 2012) based on the availability of periprosthetic tissues collected during revision, clinical data including presence or absence of pseudotumor or metallosis observed intraoperatively, and wear depth measured using a coordinate measurement machine. Histological features of tissues were scored for aseptic lymphocytic vasculitis-associated lesions (ALVAL). Correlation analysis was performed on the three endpoints of interest.ResultsWith the sample size available, no association was found between wear magnitude and ALVAL score (ρ = −0.092, p = 0.423). Median wear depth (ball and cup) was greater in hips with metallosis (137 μm; range, 8–873 μm) than in those without (18 μm; range, 8–174 μm; p < 0.0001). With the numbers available, no statistically significant association between wear depth and pseudotumor formation could be identified; median wear depth was 74 μm in hips with pseudotumors and 26 μm in those without (p = 0.741).ConclusionsWear alone did not explain the histopathological changes in the periprosthetic tissues. A larger sample size and more sensitive outcome variable assessments may have revealed a correlation. However, wear depth has been inconsistently associated with pseudotumor formation, perhaps because some patients with hypersensitivity may develop pseudotumors despite low wear.Clinical RelevanceMetal wear alone may not explain the histological reactions and pseudotumors around metal-on-metal hip implants.