Timothy M. Wright

Permanent deformation of compact bone monitored by acoustic emission

Abstract Uniaxial tension tests were performed on standardized specimens of bovine haversian bone to examine the contributions of mineral and collagen to permanent deformation in bone and to monitor the damage mechanisms occurring in permanent deformation using acoustic emission techniques. Test on control, decalcified and deproteinized groups of specimens demonstrated that the post-yield or ‘plastic’ slope of the stress-strain curve for unaltered bone is dependent on collagen properties, while the elastic modulus and yield phenomenon appear more dependent on the mineral phase. The results are consistent with a two-phase model for bone in which the mineral behaves as an elastic-perfectly plastic material when bound to the collagen fiber matrix. Acoustic emission from control specimens demonstrated considerable damage at yield and again just prior to fracture. Decalcified specimens, which were linearly elastic to failure, also exhibited significant acoustic emission just prior to fracture.

Bone Mass Is Preserved and Cancellous Architecture Altered Due to Cyclic Loading of the Mouse Tibia After Orchidectomy

Introduction: The study of adaptation to mechanical loading under osteopenic conditions is relevant to the development of osteoporotic fracture prevention strategies. We previously showed that loading increased cancellous bone volume fraction and trabecular thickness in normal male mice. In this study, we tested the hypothesis that cyclic mechanical loading of the mouse tibia inhibits orchidectomy (ORX)‐associated cancellous bone loss.

Observations on retrieved humeral polyethylene components from reverse total shoulder arthroplasty

HYPOTHESIS Analyses of polyethylene components retrieved at revision of total knee, hip, and shoulder replacements have been used to study the effect of design, patient, and surgical factors on initial implant performance, but no studies have reported similar types of findings in retrieved humeral polyethylene components in reverse total shoulder arthroplasty. Our hypothesis is that while the conforming surface of the humeral polyethylene may predispose it to surface wear modalities, as seen in total hip arthroplasty, the presence of clinical instability may also increase the occurrence of focal contact stresses leading to subsurface fatigue failure. MATERIALS AND METHODS Fourteen humeral polyethylene components were retrieved from revision surgery at a single institution. Each polyethylene was analyzed for 9 modes of damage in each of 4 quadrants into which the bearing surface was divided. For each implant, the most recent radiographs before removal were scored using an adapted radiolucency score, and glenosphere positioning was measured. RESULTS Despite the short mean length of implantation (0.46 ± 0.5 years), scratching and abrasion were seen in 14 and 13 components, respectively, followed by third-body debris and pitting. The modes of damage observed were most severe in the inferior quadrant of the humeral polyethylene. Scapular notching, glenoid, and humeral radiolucencies were prevalent on preoperative radiographs, but their long-term significance has not yet been elucidated. Increased glenosphere inclination was associated with decreased superior and total glenoid radiolucency, along with total polyethylene wear scores. DISCUSSION Promising early, functional results with the use of reverse total shoulder arthroplasty has led to the increased expansion of its use, but high complication and revision rates continue to raise concerns regarding implant longevity. The presence of a clinical, adduction deficit may predispose patients to inferior quadrant polyethylene wear. CONCLUSIONS Impingement of the humeral polyethylene at the lateral edge of the scapula leads to inferior quadrant wear and associated polyethylene failure, and implant instability may predispose the components to fatigue wear mechanisms. Analysis of retrieved humeral polyethylene components, along with patient, design, and surgical factors, provide important information on the causes of component failure.

Observations on retrieved glenoid components from total shoulder arthroplasty

HYPOTHESIS Polyethylene components retrieved at revision of total knee and hip replacements have been analyzed to study the effect of design, patient, and surgical factors on initial implant performance, but few studies have reported similar types of findings in retrieved glenoids. MATERIALS AND METHODS From 1979 to 2006, 78 glenoid components were retrieved from revision surgery in 73 patients at a single institution. Each glenoid component was analyzed for 9 modes of damage in each of 4 quadrants into which the bearing surface was divided. For each glenoid, the most recent radiographs before removal were scored using an adapted radiolucency score. RESULTS Scratching, pitting, and burnishing were the most common and most severe types of polyethylene wear. In addition, the modes of damage observed were not uniformly distributed across the bearing surface, but commonly focused in the inferior quadrant of the glenoid, suggesting a propensity for a humeral impingement mechanism leading to glenoid loosening. The radiographic analysis performed was found to severely underestimate the presence of clinical glenoid loosening. CONCLUSION Impingement of the glenoid with bone at the edge of the humeral component and edge deformation secondary to eccentric forces of the humeral head on the glenoid rim are highly associated with glenoid loosening. Analysis of retrieved glenoid components, along with patient, design, and surgical factors, provide important information on the causes of component failure.

Unicondylar Knee Retrieval Analysis

Unicondylar knee arthroplasty (UKA) is considered an alternative to total knee arthroplasty for patients who have arthritis limited to one compartment of the knee. This study examined surface damage of 3 contemporary UKA designs that were retrieved at revision surgery. Two of the UKA designs were fixed bearing and one was mobile bearing. Demographic information was collected, as well as information about the implants used at revision surgery. Articular surface damage was greater in the fixed-bearing designs as compared to the mobile bearing, although the mobile-bearing implants had significantly shorter length of implantation. Backside damage was also graded for the mobile bearing and when combined with articular wear resulted in overall damage scores higher than both fixed-bearing designs. The fixed-bearing designs showed delamination and surface deformation, whereas the mobile bearing had no evidence of these damage modes. However, mobile-bearing components showed other types of wear, and significant wear damage was present on the bearing surfaces of the mobile-bearing implants despite a short time of implantation. At the time of conversion to a total knee arthroplasty, more than 50% of cases required the use of stems, augments, or constrained inserts for the tibial reconstruction. In conclusion, wear modes differed among UKA prosthesis designs. Revision of a UKA to a total knee arthroplasty remains complex with the tibial preparation more complicated than in the primary setting.

Comparison of conforming and nonconforming retrieved glenoid components

The purpose of this study was to compare differences in wear performance of conforming and nonconforming glenoid designs, using clinical, radiographic, and retrieved polyethylene glenoid component outcome Sixty-three glenoids met the study criteria, and each glenoid was assigned to the conforming group (if the radii of curvature of the humeral and glenoid components were identical) or the nonconforming group (if a mismatch existed between the radii of curvature). The mean length of implantation was 5.6 +/- 5.5 years in the conforming group and 3.1 +/- 3.1 years for the nonconforming group (P < .05). The loosening score was 3.2 +/- 2.0 in the conforming group and 2.4 +/- 1.2 in the nonconforming one (P < .05). The nonconforming group had a significantly greater burnishing score (P < .01), while the conforming group had greater abrasion and delamination scores (P < .05). Articular conformity contributes to differences observed from retrieved polyethylene glenoid components, which are consistent with differences in performance that may influence loosening.

The HSS Modular Linked System for Segmental Replacement

A modular linked system for segmental replacement has been developed at the Hospital for Special Surgery (HSS). Its evolution from the original custom endoprosthesis is discussed and the analysis of retrieved components is presented.

Heat and radiofrequency plasma glow discharge pretreatment of a titanium alloy promote bone formation and osseointegration

Orthopedic and dental implants manifest increased failure rates when inserted into low density bone. We determined whether chemical pretreatments of a titanium alloy implant material stimulated new bone formation to increase osseointegration in vivo in trabecular bone using a rat model. Titanium alloy rods were untreated or pretreated with heat (600°C) or radiofrequency plasma glow discharge (RFGD). The rods were then coated with the extracellular matrix protein fibronectin (1 nM) or left uncoated and surgically implanted into the rat femoral medullary cavity. Animals were euthanized 3 or 6 weeks later, and femurs were removed for analysis. The number of trabeculae in contact with the implant surface, surface contact between trabeculae and the implant, and the length and area of bone attached to the implant were measured by histomorphometry. Implant shear strength was measured by a pull‐out test. Both pretreatments and fibronectin enhanced the number of trabeculae bonding with the implant and trabeculae‐to‐implant surface contact, with greater effects of fibronectin observed with pretreated compared to untreated implants. RFGD pretreatment modestly increased implant shear strength, which was highly correlated (r2 = 0.87–0.99) with measures of trabecular bonding for untreated and RFGD‐pretreated implants. In contrast, heat pretreatment increased shear strength 3–5‐fold for both uncoated and fibronectin‐coated implants at 3 and 6 weeks, suggesting a more rapid increase in implant‐femur bonding compared to the other groups. In summary, our findings suggest that the heat and RFGD pretreatments can promote the osseointegration of a titanium alloy implant material. J. Cell. Biochem. 114: 2363–2374, 2013.

Collagen XI mutation lowers susceptibility to load-induced cartilage damage in mice†

Interactions among risk factors for osteoarthritis (OA) are not well understood. We investigated the combined impact of two prevalent risk factors: mechanical loading and genetically abnormal cartilage tissue properties. We used cyclic tibial compression to simulate mechanical loading in the cho/+ (Col11a1 haploinsufficient) mouse, which has abnormal collagen fibrils in cartilage due to a point mutation in the Col11a1 gene. We hypothesized that the mutant collagen would not alter phenotypic bone properties and that cho/+ mice, which develop early onset OA, would develop enhanced load‐induced cartilage damage compared to their littermates. To test our hypotheses, we applied cyclic compression to the left tibiae of 6‐month‐old cho/+ male mice and wild‐type (WT) littermates for 1, 2, and 6 weeks at moderate (4.5 N) and high (9.0 N) peak load magnitudes. We then characterized load‐induced cartilage and bone changes by histology, microcomputed tomography, and immunohistochemistry. Prior to loading, cho/+ mice had less dense, thinner cortical bone compared to WT littermates. In addition, in loaded and non‐loaded limbs, cho/+ mice had thicker cartilage. With high loads, cho/+ mice experienced less load‐induced cartilage damage at all time points and displayed decreased matrix metalloproteinase (MMP)‐13 levels compared to WT littermates. The thinner, less dense cortical bone and thicker cartilage were unexpected and may have contributed to the reduced severity of load‐induced cartilage damage in cho/+ mice. Furthermore, the spontaneous proteoglycan loss resulting from the mutant collagen XI was not additive to cartilage damage from mechanical loading, suggesting that these risk factors act through independent pathways.

Frontiers in Osteoarthritis: Executive Summary of the Scientific Meeting

Osteoarthritis (OA) is the most common form of arthritis and represents the leading cause of disability in the USA. Importantly, with an aging population, the prevalence, impact, and economic consequences of OA will rise dramatically within the next decades. Although much has been learned concerning the factors that play a role in the initiation and progression of OA, this information has not been effectively translated into individual or public health strategies that have significantly altered the natural history of this disabling form of arthritis. While total joint arthroplasty is an effective treatment for the late stages of OA, no validated pharmacologic interventions exist for effectively eliminating pain and restoring function during disease progression. Although initially regarded as a disease of articular cartilage, numerous lines of investigation have established that OA represents an example of total “organ failure,” in which every component of the joint tissues, including the cartilage, synovium, periarticular bone, and connective tissues, is affected by the disease process. Given OA’s pleiotropic effects on joint tissues, the development of effective diagnostic, preventative, and treatment strategies requires a broad interdisciplinary approach that embraces multiple scientific and public health disciplines. This need formed the basis for the sponsorship of the “Osteoarthritis Summit: Frontiers in OA Research, Prevention, and Care” that was held at the Hospital for Special Surgery in New York in June, 2011, the results of which are published in this issue of the HSS Journal. The Osteoarthritis Summit brought together research scientists; clinicians caring for patients with OA; governmental officials responsible for aiding and directing research; representatives from major OA research societies and foundations; and members of the pharmaceutical, device, and insurance industries in a workshop setting (Fig. ​(Fig.1).1). The meeting was organized into a series of six sessions that included concise presentations from the meeting attendees. Each session focused on a specific aspect of OA, progressing from an overview of the clinician’s perspective and the classification and epidemiology of OA to a session on pathological and pathogenic processes in OA, including structural alterations and the onset and characterization of symptoms. The third session focused on the diagnosis and assessment of OA, while the fourth centered on strategies for OA prevention. The fifth and sixth sessions covered current treatments for OA and identified opportunities and priorities for development of future therapies and public health strategies. The formal presentations were followed by extended breakout sessions that provided an open forum for discussion of perspectives that addressed critical questions related to OA with the goal of reaching consensus on the current state of knowledge of OA research and the strategies for OA diagnosis, prevention, and treatment. Fig. 1 Participants of the Osteoarthritis Summit: Frontiers in OA Research, Prevention, and Care. Courtesy of Hospital for Special Surgery. Bottom row (left to right): Virginia Kraus, MD, PhD; Steven Goldring, MD; Timothy Wright, PhD; Linda Sandell, MD; Constance ...