Fracture of Contemporary Femoral Stems: Common Trends in This Rare Occurrence.

BACKGROUND: Fracture of contemporary femoral stems is a rare occurrence in total hip arthroplasty. A knowledge gap remains regarding manufacturing, patient, and surgeon factors that may contribute to the increased risk of this complication. METHODS: We analyzed 13 contemporary fractured porous-coated femoral stems of various designs to determine cause and contributing factors of mechanical failure. Cases included 12 men and 1 woman who had an average age at index surgery of 53 years (range, 34 to 76 years). There were 10 of 13 patients who had a body mass index more than 30 (obese); 3 of the 10 had a body mass index more than 40. The mean time to fracture was 7.6 years (range, 7 months to 12 years). RESULTS: There were 4 titanium alloy stems that fractured an average of 3.6 years postrevision surgery for head/cup exchange and had associated iatrogenic mechanical and electrocautery damage to the femoral neck at fracture initiation sites. There were 6 modular stems that failed at the stem-sleeve or stem-neck interfaces with evidence of fretting corrosion. For 2 stem-neck fractures, mismatched head/stem combinations from different manufacturers resulted in untested mechanical offsets and loading. There were 2 proximal neck fractures and 1 mid-shaft fracture of coated cobalt-chromium alloy stems that occurred in 3 obese men. The neck fractures (10 to 12 years) were well-fixed stems. Lack of proximal fixation contributed to the mid-shaft fracture (7 months). CONCLUSION: While rare, femoral stem fractures pose catastrophic outcomes in primary and revision total hip arthroplasty. Manufacturing, patient, and surgical factors contributing to stem failures were identified, including patient obesity, heat-treatment reduction of mechanical properties, iatrogenic implant damage, and mixing of different vendor stems and heads.

Biological and functional evaluation of a novel pyrolytic carbon implant for the treatment of focal osteochondral defects in the medial femoral condyle: assessment in a canine model.

BACKGROUND: Osteochondral defects continue to be a clinical treatment challenge, and when left untreated, may cause pain and functional impairment. Pyrolytic carbon is a unique isotropic biomaterial used in heart valve and small joint replacements due to its excellent wear properties and biocompatibility with bone and articular cartilage. Therefore, a proposed solution is to utilize a focal pyrolytic carbon hemiarthroplasty implant as an alternative resurfacing treatment strategy for isolated cartilage lesions. METHODS: A canine model (n = 9) was used to evaluate the in vivo histologic response and function of a pyrolytic carbon implant replacing a full-thickness osteochondral defect in the medial femoral condyle (MFC) of the knee. The gross appearance and histologic results were compared to an identical cobalt-chromium (Co-Cr) alloy implant placed in a defect in the contralateral MFC and evaluated up to 52 weeks. RESULTS: Extensive bone incorporation to the stem portion was observed for both implant types. The total mean histologic score for the cartilage of the MFC surrounding the pyrolytic carbon implants was significantly improved compared to that of the Co-Cr alloy implants at all evaluation periods (p < 0.05). Histologic grading and gross observations at 52 weeks for pyrolytic carbon implants were similar to those of Co-Cr alloy implants at 24 weeks. At 24 weeks, the mean total histologic score for Co-Cr alloy implants was 11.6 ± 0.7 (0-16 range point; 16 = normal appearance), while at 52 weeks, the mean total score for the pyrolytic carbon implants was 11.7 ± 1.3. Mean total histologic score of opposing medial tibia cartilage for the pyrolytic carbon implants was superior to that of the Co-Cr alloy group at all evaluation periods and significantly improved over the Co-Cr alloy implant group at 24 weeks (p = 0.001) and 52 weeks (p < 0.001). CONCLUSIONS: Use of a pyrolytic carbon implant for reconstruction of a focal cartilage defect demonstrated effective implant fixation and superior in vivo response compared to an identical Co-Cr alloy implant.

Correlation of computed tomography with histology in the assessment of periprosthetic defect healing.

Computed tomography (CT) may more accurately assess the healing of grafted osteolytic lesions around acetabular components compared with plain radiographs, although clinical validation is lacking. To determine whether clinical or micro-CT imaging could assess accurately the grafted lesion compared with histology, we therefore quantified bone healing and ingrowth to determine an effective rhBMP-2 dose and ratio to allograft bone when grafted adjacent to a cementless porous-coated component. We grafted surgically created acetabular defects in canines (n = 20) before uncemented total hip arthroplasty. At 6 weeks, embedded acetabula were imaged and the CT slice images matched to histology section images. The percentage of bone in the defect and growth into the porous surface was assessed quantitatively. Low-dose rhBMP-2 with allograft (1:5 ratio) resulted in a higher percentage of defect healing (43.8%) than rhBMP-2 alone (29.2%) and a higher percentage of bone ingrowth (15.7%) than allograft bone alone (1.1%) as measured by histology. Micro-CT measurements were similar to histologic measurements of defect healing, whereas clinical CT overestimated periprosthetic bone by 38%. Neither clinical CT nor micro-CT techniques are adequate for assessing ingrowth or the bone-implant interface with metal artifacts.

The effects of blood and fat on Morse taper disassembly forces.

Biological debris between modular components using Morse tapers in hip arthroplasty can lead to weakening of the implant construct. We conducted a study to determine the effect of blood and fat within the taper interface. Tapers were divided into groups 1 (clean), 2 (surface covered with blood and fat), and 3 (blood and fat wiped off). Each taper was impacted and disassembled 5 times. There was a difference in mean disassembly force between pulls within group 2. Thus, blood and fat contamination can have a significant effect on the potential for disassembly.

The effect of low-intensity pulsed ultrasound on autologous osteochondral plugs in a canine model.

BACKGROUND: Low-intensity pulsed ultrasound promotes the enchondral portion of fracture healing, which has a direct stimulatory effect on cartilage formation and maturation. HYPOTHESIS: Daily ultrasound treatment positively affects the repair and incorporation of modified autologous osteochondral plugs in a canine model. STUDY DESIGN: Controlled laboratory study. METHODS: In 18 dogs, 2 autologous plugs separated from host cartilage by a 1.5-mm gap were created on the medial femoral condyle in both knees of each dog. One knee was treated daily with a clinically available ultrasound bone stimulator. Animals were sacrificed after 6 and 12 weeks of therapy and the articular surfaces evaluated grossly and histologically. RESULTS: Ultrasound-treated sites had significantly improved gross appearance at 6 weeks and histologic appearance at 6 and 12 weeks. The interface repair tissue of ultrasound-treated sites had a more normal translucent appearance than control sites. Ultrasound treatment improved the cell morphologic characteristics of the interface repair tissue and increased subchondral bone regeneration. Bonding of the interface repair tissue between plug and adjacent cartilage was significantly improved compared with control sites. CONCLUSION: Low-intensity pulsed ultrasound improved interface cartilage repair of autologous osteochondral plugs compared with controls in a canine model. CLINICAL RELEVANCE: Improvements in the quality and rate of repair of autologous osteochondral plugs may reduce postoperative recovery time and improve functional outcome.

Bone defect healing with an osteogenic protein-1 device combined with carboxymethylcellulose.

One consideration for the practical use and application of osteogenic proteins is an effective method of delivery. This study evaluated a putty-type collagen carrier with recombinant human osteogenic protein-1 (rhOP-1) ability to heal canine critical sized (2.5 cm) ulna segmental defects compared to rhOP-1 with a particulate collagen carrier (OP device). The addition of carboxymethylcellulose (CMC) to the particulate collagen carrier (OPCMC device) to form the putty consistency was evaluated in two doses (3.5 and 1.75 mg rhOP-1/g carrier). The CMC greatly improved the intraoperative handling and site containment of the device. For the one-half dose and full-dose sites there were no statistically significant differences in the radiographic grading of defect healing when treated with the particulate OP-1 device and the device with CMC added. However, there was a dose effect with greater and earlier new bone formation observed with increased rhOP-1. Mechanically, there were no differences between particulate and putty formulations, although again, a significant effect was observed for treatment dose with the full-dose OPCMC device restoring 94% of the strength of the intact ulna compared to only 65% for the identical one-half dose implant. Regardless of rhOP-1 dose, the quality of union grading and total histologic score appearance were improved with the addition of CMC, although differences in histologic scoring were not statistically significant. Overall, the radiographic, mechanical, and histologic bone-healing characteristics with the one-half dose OPCMC device were similar to sites treated with the full-dose OP device. The observed improvement in healing may allow for lesser amounts of the device or a device with less rhOP-1 to be used.

Osteogenic protein-1 in knee arthritis and arthroplasty.

The use of graft materials to restore bone stock and promote healing and implant stabilization is a crucial part of total knee arthroplasty, especially in revision surgery. Recent research has centered on the use of osteoinductive materials to promote bone formation. Osteogenic proteins are members of a superfamily of proteins called transforming growth factor-beta that, either alone or in combination with other regulatory molecules, induce new bone formation. The cloning and genetic expression of recombinant human osteogenic proteins has led to production of quantities sufficient for their clinical use. Recombinant human osteogenic protein-1 has been combined with bone-derived Type I collagen for delivery to an implant site. Preclinical studies have shown that the osteoinductive capacity of autograft and allograft bone and bone graft substitute materials can be notably improved with the addition of osteogenic protein-1. The use of this protein consistently improved the amount and rate of new bone formation compared with graft alone, resulting in earlier graft incorporation and consolidation. In addition, because osteogenic proteins are chondrogenic, they also may have a role in the treatment of cartilage injury and degeneration. Osteogenic protein-1 has been shown to induce hyalinelike cartilage repair of full thickness osteochondral defects in animal models with no degradation of the tissue with time. Although no detailed clinical studies in knee surgery have been reported with the use of osteogenic protein-1, in anecdotal cases its use alone and with bone graft materials indicate results consistent with those obtained in preclinical studies.

Biomechanical study of pedicle screw fixation in severely osteoporotic bone.

BACKGROUND CONTEXT: Obtaining adequate purchase with standard pedicle screw techniques remains a challenge in poor quality bone. The development of alternate insertion techniques and screw designs was prompted by recognition of potential fixation complications. An expandable pedicle screw design has been shown to significantly improve fixation compared to a conventional screw in poor quality bone. PURPOSE: The purpose of this study was to determine if polymethylmethacrylate (PMMA) bone cement augmentation of an expandable pedicle screw can further improve fixation strength compared to the expandable screw alone in severely osteoporotic bone. A technique for cement insertion into the pedicle by means of the cannulated central portion of the expandable screw is also described. STUDY DESIGN: The axial pullout strength, stiffness and energy absorbed of cemented and noncemented expandable pedicle screws was determined in cadaveric vertebrae. METHODS: Twenty-one fresh unembalmed vertebrae from the thoracolumbar spine were used. Radiographs and bone mineral density measurements (BMD) were used to characterize bone quality. Paired cemented and noncemented pedicle screw axial pullout strength was determined through mechanical testing. Mechanical pullout strength, stiffness and energy to failure was correlated with BMD. RESULTS: Overall, there was a 250% increase in mean pullout strength with the cemented expandable screw compared with a noncemented expandable screw including a greater than twofold increase in pullout strength in the most severely osteoporotic bone. The mean stiffness and energy absorbed to failure was also significantly increased. A cemented conventional screw achieved a pullout strength similar to the noncemented expandable screw. CONCLUSIONS: PMMA cement augmentation of the expandable pedicle screw may be a viable clinical option for achieving fixation in severely osteoporotic bone.

Comparison of methods for determining the presence and extent of anterior lumbar interbody fusion.

STUDY DESIGN: Titanium alloy interbody fusion devices with autogenous bone were placed in the L5-L6 disc space of 31 adult pig-tailed monkeys through an anterolateral (retroperitoneal) approach. Anteroposterior and lateral radiographs, CT imaging, and histologic analysis of the specimens were performed. OBJECTIVES: This study compared the accuracy of plain film radiographs and CT imaging for determining bony fusion of a titanium interbody device implanted in a non-human primate model. The accuracy of the assessments was determined by comparison to histologic analysis. SUMMARY OF BACKGROUND DATA: Interbody fusion assessment is often difficult to compare in clinical studies because of differences in definition of fusion criteria. In addition, the accuracy of plain film radiographs and CT imaging assessments of fusion are debated because of device material radiopacity and introduction of artifacts. METHODS: A uniform grading system evaluating both the presence and extent of bony fusion was applied to all evaluation techniques. Matched-pair nonparametric t tests were used to determine differences in scoring. RESULTS: The radiographic and histologic presence of fusion grades was equivalent in only 13 of 29 cases (45%), while the CT imaging was equivalent to histologic assessment in 24 of 29 cases (83%). However, the extent of bony fusion in CT imaging and histologic assessment was equivalent in only 4 of 29 cases (14%). Grading of CT images significantly overestimated the extent of fusion. CONCLUSIONS: This study demonstrated CT imaging techniques to be superior to plain film radiographs in determining the presence of bony fusion. However, CT imaging did not accurately determine the extent of bony fusion present as confirmed by histologic analysis.

Direct current stimulation of titanium interbody fusion devices in primates.

BACKGROUND CONTEXT: The fusion rate for anterior lumbar interbody fusion (ALIF) varies widely with the use of different interbody devices and bone graft options. Adjunctive techniques such as electrical stimulation may improve the rate of bony fusion. PURPOSE: To determine if direct current (DC) electrical stimulation of a metallic interbody fusion device enhanced the incidence or extent of anterior bony fusion. STUDY DESIGN/SETTING: ALIF was performed using titanium alloy interbody fusion devices with and without adjunctive DC electrical stimulation in nonhuman primates. METHODS: ALIF was performed through an anterolateral approach in 35 macaques with autogenous bone graft and either a titanium alloy (Ti-6Al-4V) fusion device or femoral allograft ring. The fusion devices of 19 animals received high (current density 19.6 microA/cm2) or low (current density 5.4 microA/cm2) DC electrical stimulation using an implanted generator for a 12- or 26-week evaluation period. Fusion sites were studied using serial radiographs, computed tomography imaging, nondestructive mechanical testing and qualitative and semiquantitative histology. RESULTS: Fusion was achieved with the titanium fusion device and autogenous bone graft. At 12 weeks, the graft was consolidating and early to moderate bridging callus was observed in and around the device. By 26 weeks, the anterior callus formation was more advanced with increased evidence of bridging trabeculations and early bone remodeling. The callus formation was not as advanced or abundant for the allograft ring group. Histology revealed the spinal fusion device had an 86% incidence of bony fusion at 26 weeks compared with a 50% fusion rate for the allograft rings. DC electrical stimulation of the fusion device had a positive effect on anterior interbody fusion by increasing both the presence and extent of bony fusion in a current density-dependent manner. CONCLUSIONS: Adjunctive DC electrical stimulation of the fusion device improved the rate and extent of bony fusion compared with a nonstimulated device. The fusion device was equivalent to or better than the femoral allograft ring in all evaluations. The use of adjunctive direct current electrical stimulation may provide a means of improving anterior interbody fusion.

Induction of bone ingrowth from acetabular defects to a porous surface with OP-1.

Reliable ingrowth of bone into porous-coated cementless total hip components can be expected in primary surgery. In the revision scenario, however, bone deficiency frequently is encountered and the remaining bone may have less ingrowth potential. Allograft bone and bone graft substitutes may be successful in healing bone defects, but have virtually no capacity to induce bone growth from the defect into the porous surface. To evaluate the role osteoinductive bone proteins may play in enhancing bone ingrowth, six canines had bilateral total hip arthroplasties with a cementless press-fit porous-coated acetabular component. A defect 8 mm in diameter and 5 mm in depth was created in the superior weightbearing area of each acetabulum. One defect in each animal was filled with recombinant human osteogenic protein-1. Each contralateral defect was filled with allograft bone, left empty (defect healing control), or no defect was created (intact) to serve as a control for ideal conditions for bone ingrowth. The osteogenic protein-treated defects healed more completely than allograft bone-treated or empty defects and achieved a bone density equivalent to the intact acetabulum. Bone ingrowth also occurred to a significantly higher degree in the osteogenic protein group compared with the allograft or empty defects achieving a degree of ingrowth equivalent to the intact acetabulum controls. The osteogenic bone protein was successful in achieving complete defect healing and inducing extensive ingrowth from the defect into the adjacent porous coating.

Osteoinductive agents in reconstructive hip surgery: a look forward.

The use of autograft and allograft material to restore bone stock and promote healing and implant stabilization is a crucial part of total hip arthroplasty, especially in the revision situation. Recent research has centered on the use of osteoinductive materials such as osteogenic proteins or bone morphogenetic proteins to promote bone formation. These proteins are members of the transforming growth factor-beta superfamily of proteins that either alone or in combination with other regulatory molecules induce new bone formation. The cloning and genetic expression of recombinant human bone proteins has led to production of quantities sufficient for their clinical development. Preclinical studies have shown that the osteoinductive capacity of autograft and allograft bone can be improved with the addition of osteogenic proteins. Although these proteins are effective alone, their use with cancellous and cortical allograft and autograft consistently improved the amount and rate of new bone formation compared with graft alone resulting in earlier graft incorporation and consolidation. When placed in defects adjacent to porous acetabular components, the use of an osteogenic protein resulted in earlier defect healing and improved component fixation by the enhancement of bone ongrowth and ingrowth. Although no detailed clinical studies have been reported to date, an anecdotal report of their use with and without bone graft indicate results consistent with those obtained in preclinical studies.

Patellar tracking during simulated quadriceps contraction.

The current study compared patella tracking during simulated concentric and eccentric quadriceps contractions in 12 knees from cadavers using a three-dimensional electromagnetic tracking system. The patella shifted (translated) and tilted medially during approximately the initial 22 degrees tibiofemoral flexion. The patella then shifted and tilted laterally for the remaining arc of tibiofemoral flexion (90 degrees). At 90 degrees tibiofemoral flexion, the patella had an orientation of lateral patella shift and lateral patella tilt. Patella shift was significantly more lateral between 40 degrees and 70 degrees tibiofemoral flexion during concentric quadriceps action than during eccentric contraction. Patella tilt was significantly more lateral between 45 degrees and 55 degrees tibiofemoral flexion during concentric quadriceps contraction than during eccentric action. No other significant differences were seen between the quadriceps contraction conditions. The current study supports the hypothesis that patellar instability is most likely a result of various anatomic and physiologic factors causing a failure of the extensor mechanism to deliver the patella into the femoral sulcus and that a patellar dislocation rarely would occur in a normal knee.

Repair of articular cartilage defects with osteogenic protein-1 (BMP-7) in dogs.

BACKGROUND: Articular cartilage injury has a poor prognosis for repair. Mesenchymal cells, when exposed to osteogenic proteins and other cytokines, can differentiate into cells that behave phenotypically as chondrocytes. In this study, we examined the ability of recombinant human osteogenic protein-1 (rhOP-1 or rhBMP-7) to elicit the repair of osteochondral defects in dogs. METHODS: Bilateral osteochondral defects that were 5 mm in diameter by 6 mm deep were surgically created in the medial femoral condyles of sixty-five adult dogs. rhOP-1-treated (100 mg of a 3.5-mg rhOP-1/g bovine bone-derived Type-I collagen device) and control defects (untreated or treated with 100 mg bovine bone-derived collagen implants) were evaluated grossly and histologically at six, twelve, sixteen, twenty-six, and fifty-two weeks postoperatively. The influence of protected initial weight-bearing and surgical placement of periosteal flaps was also evaluated. RESULTS: Gross and histologic grading of the defect repair indicated improvement in the rhOP-1-treated defects compared with that in the controls. Grossly, the repair tissue in the rhOP-1-treated defects was continuous with the adjacent intact cartilage and appeared translucent. By comparison, the repair tissue in the control defects was discontinuous and opaque or inhomogeneous in nature. Histologically, maturing cartilage similar in appearance to the intact articular cartilage was present in the rhOP-1-treated defects. Cartilage at the defect interface was minimally degraded. The control defects were filled primarily with fibrous tissue and fibrocartilage. Significant differences based upon treatment type were observed at twelve weeks, sixteen weeks, and for all time-periods combined (p = 0.0385, p = 0.0070, and p = 0.0026, respectively). CONCLUSION: rhOP-1 (rhBMP-7) induced hyaline cartilage-like repair of full-thickness osteochondral defects in a dog model. Differences in cartilage repair were maintained at fifty-two weeks postoperatively with no significant degradation of the rhOP-1-induced repair tissue.

The effect of demineralized bone matrix gel on bone ingrowth and fixation of porous implants.

The presence of demineralized bone matrix (DBM) gel did not enhance or accelerate attachment strength or bone ingrowth and resulted in a significant decrease in implant interface attachment strength at 3 weeks. Hydroxyapatite (HA) coating resulted in significant increases in interface shear strength and bone ingrowth compared with non-HA-coated porous implants at all time periods. The HA-coated implants achieved greater attachment strength and bone ingrowth at earlier time periods and maintained greater attachment strength at long-term periods. The results of this study indicate that in the presence of a good bone-implant interference fit, there is no beneficial effect in applying DBM gel to a porous-coated or HA-coated porous implant surface. The small amount that can be applied and the degree of osteoinductivity of DBM seem to preclude it from having a significant biologic effect.

Healing course of primate ulna segmental defects treated with osteogenic protein-1.

Twelve African green monkeys were implanted with recombinant human osteogenic protein-1 (rhOP-1) placed on a bovine bone-derived Type I collagen carrier to characterize healing in an ulna segmental bone defect model at 1, 3, 12, and 20 weeks postoperative. Defect healing was evaluated by plain film radiography, computed tomography (CT), magnetic resonance imaging (MRI), bone mineral density (BMD), and histologic analysis. Radiographically, new bone formation was observed as early as 3 weeks postoperative. By 6 weeks, new bone was visible in five of six defects. Increased quantity and mineralization of the new bone were apparent by 12 weeks. Reformation of the medullary cavity with appearance of marrow elements was demonstrated by CT and MRI at 20 weeks. BMD studies revealed a significant increase in the presence of bone with time. Histology at 1 week demonstrated that the implant material was well contained in the defect, and a proliferation of cells occurred at the defect borders. At 3 weeks cell proliferation continued and cell phenotype differentiation was recognized. By 12 weeks substantially less residual carrier was found in the defects, and calcifying tissues with plump chondrocytes, osteoblasts, and immature woven bone were observed. Areas of lamellar and woven bone were identified at 12 weeks, with advanced remodeling and revascularization observed at 20 weeks. The use of osteoinductive implants may provide an alternative to autologous and allogeneic bone tissue in the therapeutic approach to bone defects and promotion of fusion by eliminating the donor site morbidity associated with autogenous bone and the decreased efficacy and potential for disease transmission associated with allogeneic bone.