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. (c) 2023 Elsevier Inc. All rights reserved.

Fracture of contemporary femoral stems is a rare occurrence. Earlier THR stems failed due to design issues or post manufacturing heat treatments that weakened the core metal. Our group identified and analyzed 4 contemporary fractured femoral stems after revision surgery in which electrochemical welds contributed to the failure. All four stems were proximally porous coated titanium alloy components. All failures occurred in the neck region post revision surgery in an acetabular cup exchange. All were men and obese. The fractures occurred at an average of 3.6 years post THR redo (range, 1.0–6.5 years) and 8.3 years post index surgery (range, 5.5–12.0 years). To demonstrate the effect of electrocautery on retained femoral stems following revision surgery, we applied intermittent electrosurgical currents at three intensities (30, 60, 90 watts) to the polished neck surface of a titanium alloy stem under dry conditions. At all power settings, visible discoloration and damage to the polished neck surface was observed. The localized patterns and altered metal surface features exhibited were like the electrosurgically-induced damage priorly reported. The neck regions of all components studied displayed extensive mechanical and/or electrocautery damage in the area of fracture initiation. The use of mechanical instruments and electrocautery was documented to remove tissues in all 4 cases. The combination of mechanical and electrocautery damage to the femoral neck and stem served as an initiation point and stress riser for subsequent fractures. The electrocautery and mechanical damage across the fracture site observed occurred iatrogenically during revision surgery. The notch effect, particularly in titanium alloys, due to mechanical and/or electrocautery damage, further reduced the fatigue strength at the fractured femoral necks. While electrocautery and mechanical dissection is often required during revision THA, these failures highlight the need for caution during this step of the procedure in cases where the femoral stem is retained.

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.

Pyrocarbon has been used for over 25 years in finger joint replacements. Excellent biocompatibility, material and wear properties make pyrocarbon ideal for an orthopaedic device. Pyrocarbon implants incur significantly less wear to articular cartilage than metal implants. The pyrocarbon implant replacement device (PIR) was developed to treat focal chondral and osteochondral defects of the femoral condyles. The PIR is intended to treat defects not amenable to microfracture or similar regenerative techniques and those for which unicompartmental or total knee arthroplasty is not yet indicated. The purpose of this study was to evaluate the in vivo articular response to the PIR device and compare it to a similar device made from cobaltchromium (CoCr) device. In addition, bone fixation of the PIR device with and without hydroxyapatite (HA) coating was evaluated. Nine adult bred-for-purpose beagles received bilateral 6mm medial condyle full thickness osteochondral defects. One defect was treated with a PIR device and the other an identical CoCr device. In addition, one HA-coated and one non-HA coated PIR device was placed unicortically in the lateral distal femurs of each animal. Three animals each were terminated at 12, 24, and 52 weeks postoperative. Non-decalcified histologic sections of the implanted condyles and decalcified sections of the medial tibia and meniscus were evaluated. The femoral condyle sections were graded using a modified scale of Kirker-Head (2006). Additionally, the bone– implant contact area was quantified. The tibia-meniscus sections were evaluated utilising a modified version of the ICRS Histological Visual Scale (2002). The lateral distal femur implants were mechanically tested in axial push-out to compare the bone-implant interface strength between the HA-coated and non-HA coated PIR devices. The mean histologic grades for the tibia and meniscus were superior for surfaces that articulated against the pyrocarbon PIR device compared to the CoCr device at 12, 24 and 52 weeks. Over time, the mean histologic grades decreased with both materials; however, tibias that articulated with the CoCr device had the lowest mean grade at 52 weeks. There were little difference in bone contact 12 and 24 weeks between the pyrocarbon and the CoCr devices. At 52 weeks, less bone contact was observed compared to 12 and 24 weeks. Mechanical testing demonstrated that the HA-coating imparted a statically significant improvement in interface strength as well as greater direct bone contact to the implant. The results of this study confirm that pyrocarbon provides an ideal surface for an implant that articulates with cartilage of the knee. Although adequate direct bone contact was observed, the addition of HA-coating imparted both superior initial and long term bone fixation. The PIR device is suitable for restoration of focal defects of the knee.

The loss of bone mass and consequently bone strength in persons aged forty and beyond is a continuing problem to the orthopaedic community. This progressive loss has been documented by various means such as radiographs, autopsy materials, CAT scans, and single or dual photon absorptiometrv. Orthopaedic problems arising from osteoporosis include fractures of the lumbar spine, distal radius and the femoral neck. Likewise, this age group represents the fraction of the population that will require prosthetic replacement of a joint. Unfortunately, little information is available concerning the mechanical properties of osteoporotic bones and its interaction with prosthetic devices.

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.

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.

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.

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.

Mont, Michael A. MD; Ragland, Phillip S. MD; Biggins, Bridget BA; Friedlaender, Gary MD; Patel, Tushar MD; Cook, Stephen MD; Etienne, Gracia MD, PhD; Shimmin, Andrew MD; Kildey, Robyn BS; Rueger, David C. PhD; Einhorn, Thomas A. MD Author Information

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.

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.

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.