Cross-elements to enhance fixation in osteoporotic bone with application to proximal humeral locking plates: a biomechanical study.

BACKGROUND: Proximal humeral fractures occur predominantly in elderly, osteoporotic individuals, especially women, with surgery performed in one-fifth. Proximal humeral locking plates are the gold standard operative treatment; however, complications are frequent, partially because of poor screw purchase in osteoporotic bone. A new method uses threaded posts through which threaded cross-elements orthogonally pass to create a 3-dimensional scaffold for bone engagement. We examined the pullout characteristics of the posts with (1 or 2) or without the cross-elements and tested 2 types of 3.5-mm cortical locking screws for comparison. METHODS: Low-density closed-cell polyurethane foam served as a model osteoporotic bone substrate. Following implantation in the substrate, the devices were axially loaded by a mechanical test system. Quantities of interest included failure mode, peak load, displacement to peak load, initial stiffness, and work expended. RESULTS: The post groups outperformed the 3.5-mm screw groups, as expected. Relative to posts with no cross-elements, 1 and 2 cross-elements increased the peak load by 29% and 87% and increased the work to peak load by 126% and 343%, respectively. After reaching peak load, 1 and 2 cross-elements increased the work-resistance to further displacement by 158% and 330%, respectively. CONCLUSION: Cross-elements significantly increased the ability of the threaded posts to resist axial displacement from a model osteoporotic bone substrate. This suggests that posts, used in conjunction with cross-elements, have the potential to enhance the stability of proximal humeral locking plates in osteoporotic bone.

The Elution Kinetics of BMP-2, BMP-4, and BMP-7 From a Commercial Human Demineralized Bone Matrix Putty.

Bone morphogenetic proteins (BMPs) are associated with bone extracellular matrix and impart osteoinductive properties to demineralized bone matrix (DBM) grafts. The first step of the osteoinductive process is BMP release from DBM in situ; however, this has not been characterized for human DBM. The authors investigated the release of BMPs 2, 4, and 7 from a clinical human DBM putty (Bonus II DBM, Biomet Inc, Warsaw, IN). The DBM was placed in Sorensen buffer and the BMP concentrations in the Sorensen buffer and guanidine extracts of the DBM were measured concurrently by enzymelinked immunosorbant assay for up to 7 days. The baseline DBM concentrations were BMP-2: 28.1 ±â€Š1.3 ng/g DBM, BMP-4: 0.577 ±â€Š0.056 ng/g DBM, and BMP-7: 92.9 ±â€Š7.5 ng/g DBM. Relative to baseline, the proportions released by 7 days were 11.1%, 3.9%, and 29.3%, respectively. The early (0-8 hour) and late (8-168 hours) elution rates were BMP-2: 0.16 ±â€Š0.24 and 0.0089 ±â€Š0.012 ng/(g DBM hr), and BMP-7: 1.29 ±â€Š2.1 and 0.086 ±â€Š0.039 ng/(g DBM hr), respectively. Little BMP-4 elution occurred over the first 24 hours, with the rate for the remaining interval being 0.00014 ±â€Š0.00021 ng/(g DBM hr). The apparent DBM BMP profiles were counterintuitive in that the concentrations increased from baseline for some, or all, of the 7 days instead of monotonically decreasing. Similar behavior has previously been reported in bovine studies. This provides further evidence that BMPs are associated with at least 2 compartments in DBM differing by their affinity for BMPs and that guanidine extraction of BMPs is not 100% efficient.

Clinical Outcomes in Men and Women following Total Knee Arthroplasty with a High-Flex Knee: No Clinical Effect of Gender.

While it is generally recognized that anatomical differences exist between the male and female knee, the literature generally refutes the clinical need for gender-specific total knee prostheses. It has been found that standard, unisex knees perform as well, or better, in women than men. Recently, high-flex knees have become available that mechanically accommodate increased flexion yet no studies have directly compared the outcomes of these devices in men and women to see if gender-based differences exist. We retrospectively compared the performance of the high-flex Vanguard knee (Biomet, Warsaw, IN) in 716 male and 1,069 female knees. Kaplan-Meier survivorship was 98.5% at 5.6-5.7 years for both genders. After 2 years, mean improvements in Knee Society Knee and Function scores for men and women (50.9 versus 46.3; 26.5 versus 23.1) and corresponding SF-12 Mental and Physical scores (0.2 versus 2.2; 13.7 versus 12.2) were similar with differences not clinically relevant. Postoperative motion gains as a function of preoperative motion level were virtually identical in men and women. This further confirms the suitability of unisex total knee prostheses for both men and women.

Triple labrum tears repaired with the JuggerKnot™ soft anchor: Technique and results.

PURPOSE: The 2-year outcomes of patients undergoing repair of triple labrum tears using an all-suture anchor device were assessed. MATERIALS AND METHODS: Eighteen patients (17 male, one female; mean age 36.4 years, range: 14.2-62.3 years) with triple labrum tears underwent arthroscopic repair using the 1.4 mm JuggerKnot Soft Anchor (mean number of anchors 11.5, range: 9-19 anchors). Five patients had prior surgeries performed on their operative shoulder. Patients were followed for a mean of 2.0 years (range: 1.6-3.0 years). Constant-Murley shoulder score (CS) and Flexilevel scale of shoulder function (FLEX-SF) scores were measured, with preoperative and final postoperative mean scores compared with a paired Student's t-test (P < 0.05). Magnetic resonance imaging (MRI) was also performed at final postoperative. RESULTS: Overall total CS and FLEX-SF scores increased from 52.9 ± 20.4 to 84.3 ± 10.7 (P < 0.0001) and from 29.3 ± 4.7 to 42.0 ± 7.3 (P < 0.0001), respectively. When divided into two groups by whether or not glenohumeral arthrosis was present at the time of surgery (n = 9 each group), significant improvements in CS and FLEX-SF were obtained for both groups (P < 0.0015). There were no intraoperative complications. All patients, including contact athletes, returned to their preinjury level of sports activity and were satisfied. MRI evaluation revealed no instances of subchondral cyst formation or tunnel expansion. Anchor tracts appeared to heal with fibrous tissue, complete bony healing, or combined fibro-osseous healing. CONCLUSION: Our results are encouraging, demonstrating a consistent healing of the anchor tunnels through arthroscopic treatment of complex labrum lesions with a completely suture-based implant. It further demonstrates a meaningful improvement in patient outcomes, a predictable return to activity, and a high rate of patient satisfaction. LEVEL OF EVIDENCE: Level IV case series.

The extraction and measurement of bone morphogenetic protein 7 from bovine cortical bone as a function of particle size.

Bone morphogenetic proteins (BMPs), present in parts per billion in bone, endow demineralized bone matrix (DBM) with osteoinductive properties suitable for clinical use. Although BMPs are mainly associated with bone matrix, they also associate with other bone compartments as well, including the mineral phase. The purpose of this study was to gain a more complete understanding of the distribution of BMPs in undemineralized bone. Eleven discrete particle size ranges of bovine cortical bone were prepared, ranging between less than 25 µm and 600 to 710 µm for the smallest and largest sizes, respectively. The bone was extracted with 4-M guanidine-HCl/0.05-M Tris-HCl, and the amount of BMP-7 released was measured with enzyme-linked immunosorbant assay. In addition, 106- to 710-µm bone particles were demineralized and similarly extracted for comparison. The measured BMP-7 content of the DBM was 24.6 ± 1.56 ng/g. The values for bone increased nonlinearly with decreasing particle size, ranging from 1.13 ± 0.50 ng/g for the 600- to 710-µm particles to 4.18 ± 1.14 ng/g for the less than 25-µm particles (P < 0.001). However, modeling the bone particles as solid spheres to estimate total surface area showed that the extracted BMP-7 per unit area was greater for larger particle sizes. These seemingly opposing results suggest that BMPs may become proportionally damaged or altered in response to the increased forces required to generate smaller particles and, as such, may not be detectable with enzyme-linked immunosorbant assay. In addition, minimization of bone particle size is not an effective strategy to approach the BMP availability of DBM.

Correlation of the clinical and in vitro degradation characteristics of a poly(L-lactic acid): poly(glycolic acid) copolymer by mini meta-analysis.

Absorbable internal fixation devices have built a successful clinical history in a variety of applications throughout the skeleton. Their appeal lies in their ability to lose strength and mass in a predictable reproducible manner, consistent with the healing process. Most of the evidence for their degradation properties, however, is derived from in vitro and animal studies. These methods approximate only the human clinical condition, and there are few such data available directly from patients. To better understand the absorption profile of an 85:15 poly(L-lactic acid):poly(glycolic acid) copolymer in humans, a "mini meta-analysis" was performed on 2 published studies: (1) a clinical study that followed reduction in CT image density of a cross-pin for ligament reconstruction over a 2-year interval, and (2) an in vitro study that measured the hydrolysis and strength loss of test specimens over a 10- to 11-month interval in a phosphate-buffered saline at 37 °C. The CT image density profile grossly approximated the in vitro tensile modulus profile with both quantities retaining at least half of their initial value at 44 to 52 weeks, but bore little resemblance to the rapid decreases in inherent viscosity (a measure of average molecular weight) and elongation to break (a measure of ductility), which were at half their initial values by 32 to 36 weeks. Because of the inherent difficulty in directly measuring absorbable implant degradation in patients on a routine basis, investigators should seize opportunities such as this in an effort to close the knowledge gap regarding absorbable implant degradation in humans as much as possible.

Patient-specific positioning guides versus manual instrumentation for total knee arthroplasty: an intraoperative comparison.

Traditional manual instruments for total knee arthroplasty are associated with a malalignment rate of nearly 30%. Patient-specific positioning guides, developed to help address alignment, may also influence other intraoperative factors. This study compared a consecutive series of 270 Vanguard total knee replacements performed with Signature patient-specific positioning guides (study group) to a consecutive series of 595 similar knee replacements performed with manual instrumentation (control group). The study group averaged 16.7 fewer minutes in the operating room (p < .001), utilized tibial inserts that averaged 0.4 mm thinner with a smaller proportion of "thick" tibial inserts (14-18 mm) (p < .001), and required fewer transfusions (p = .022). The Signature-derived surgical plan accurately predicted correct femoral and tibial component sizes in 86.3% and 70.3% of the cases, respectively. These rates increased to 99.3% and 99.2%, respectively, for accuracy to within one size of the surgical plan, similar to published values for manual instrumentation.

A prospective multicenter clinical study of the Discovery elbow.

BACKGROUND: Semiconstrained total elbow arthroplasty is used to improve elbow function and reduce pain. Although effective, high complication rates exist, with the polyethylene bushing especially susceptible to failure. The Discovery Elbow System (Biomet Inc, Warsaw, IN, USA) contains a spherical bearing designed to minimize polyethylene wear. This prospective, multicenter clinical study investigated the 4-year (mean) outcomes of this elbow. METHODS: From 2002 to 2009, 92 patients (71 women, 21 men; mean age, 63.9 years; range, 33.4-88.7 years) received 99 Discovery elbows at 4 centers. The study cohort was limited to 46 elbows with complete preoperative and minimum 2-year clinical (modified American Shoulder and Elbow Surgeons elbow score) and radiographic follow-up. RESULTS: Mean follow-up was 4.1 years (range, 2-5.9 years). All American Shoulder and Elbow Surgeons elbow score components improved significantly (P < .001). Mean flexion-extension arcs increased from 81° to 121° and pronation-supination arcs from 134° to 163° (P < .001). Loose locking screws in 2 elbows (first-generation screws), a loose polyethylene bearing in 1 (history of falls), and a condyle/bearing in 1 (deep infection) were exchanged. Among the 46 elbows, gross survivorship was humeral/ulnar components, 100%; condyles, 97.8%; bearings, 95.7%; and screws, 95.7%. One humeral component (2.2%) was radiographically loose but not revised. An additional elbow (elbow 47) that did not meet the criteria for inclusion (<2 years of follow-up) was revised due to a loose humeral component and was reported separately. CONCLUSION: The Discovery elbow increased function and decreased pain with high survivorship at a mean of 4.1 years.

Seven-year survivorship and functional outcomes of the high-flexion Vanguard complete knee system.

Certain recreational, cultural, occupational, and religious practices may require knee flexion exceeding typical daily living activity needs. Some total knee prostheses mechanically accommodate high flexion to help meet such demands, e.g., the Vanguard knee (Biomet, Inc., Warsaw, IN) which can mechanically achieve 140°-145°. This multicenter, prospective clinical study of 957 Vanguard knees (865 patients) examined mid-term outcomes. The Kaplan-Meier survivorship estimate was 97.8% (95% CI: 96.5-98.7%) at 7.0 years. For patients with ≥ 2-year follow-up (n=627), mean peak flexion increased from 116.8° to 124.8° (P<0.001). For knees with pre-operative flexion of <95°, 95°-105°, and >105°, the mean increases were 27.8°, 22.0°, and 3.6°, respectively. Mean Knee Society Knee and Function scores increased from 45.9 and 45.5 points to 92.0 and 73.8 points, respectively (P<0.001).

Creep analysis of PLLA: PGA copolymer craniofacial plates.

Bioabsorbable fixation device failures occur clinically on occasion, with failures often brittle in nature. However, creep failure may also occur for implants that are subjected to sustained loads whereby the device may slowly deform over time, perhaps leading to fracture. Even without fracture occurring, the device may become too distorted to function. There is little in the literature regarding creep performance of bioabsorbable devices such as plates and screws. This study investigated the creep characteristics of craniofacial plates and screws made of a copolymer of 82% poly-L-lactic acid and 18% polyglycolic acid. Four-hole straight plates were attached to 2 rectangular portions of synthetic bone substrate using 2.0-mm-diameter bioabsorbable screws (2 screws used to attach the plate to each substrate portion). The constructs were submersed in phosphate-buffered saline (pH 7.4, 37°C) and placed in tension with 3 load configurations, that is, 230, 460, and 1140 g, for at least 6 days. Creep rate was constant at a given load and was directly proportional to load (4.7, 14.3, and 33.3 µm/h for 230-, 460-, and 1140-g loads, respectively). The data conformed well to basic creep theory analysis and provided an estimate of the absolute viscosity of the polymer of 8.7 × 10(12) ± 0.81 × 10(12) P (average ± SEM), which is intermediate between that of soft and hard tissue, although closer to the latter. Surgeons and engineers should be aware of the potential for creep to occur when designing bioabsorbable implants and investigating new clinical applications.

Degradation of LactoSorb fixation devices in the craniofacial skeleton.

Numerous reports about bioabsorbable internal fixation in the craniofacial skeleton substantiate successful clinical outcomes, especially in pediatric patients. Despite this, little physicochemical data exist to document the rate of device degradation in the human body. In vitro and in vivo animal studies are often used to study the degradation characteristics during product development; however, there has been little effort to correlate preclinical device degradation studies with clinical studies. This study analyzed a fragment of a LactoSorb copolymer plate that was removed from a 17-month-old patient with sagittal synostosis after 3 months' residence. The retrieval was performed during the second part of a planned 2-stage intervention. The fragment was white, opaque, and very brittle, with some signs of mass loss. The inherent viscosity, a measure of mean molecular weight, was determined to be 0.32 ± 0.02 dL/g. LactoSorb implants, as manufactured, have an inherent viscosity of about 1.30 to 1.55 dL/g. Thus, the inherent viscosity was reduced by approximately 75% to 80% over this 3-month interval in the patient. Assuming an exponential decline in inherent viscosity over time, this corresponds to a half-life of about 40 to 44 days. This may be compared with a half-life of about 36 to 45 days derived from prior in vitro studies. The mass loss observed in the LactoSorb implants also corresponds, qualitatively, to that which has been shown to occur in animal models. Thus, the limited data at hand suggest that the degradation profile of LactoSorb copolymer in this human patient is consistent with that reported in prior in vitro and in vivo animal studies.

The in vitro elution of BMP-7 from demineralized bone matrix.

Demineralized bone matrix (DBM) grafts induce new bone formation by locally releasing matrix-associated growth factors, such as bone morphogenetic proteins (BMPs), to the surrounding tissue after implantation. However, the release kinetics of BMPs from DBM lack characterization. Such information can potentially help to improve processing techniques to maximize graft osteoinductive potential, as well as increase understanding of the osteoinductive process itself. We produced DBM with three particle size ranges from bovine cortical bone, i.e., <106, 106-300, and 300-710 µm and extracted 1.5 g of each size range in 40 ml of Sorensen's buffer at room temperature for up to 168 h. The BMP-7 concentration of the DBM and the buffer were measured at each time point using enzyme-linked immunosorbant assay. Based on measurement of the concentration of BMP-7 in the buffer, the 0-8 h elution rate was high, i.e., 3.3, 2.9, and 2.2 ng BMP-7/g DBM h, and for the 8-168 h interval was much lower, at 0.039, 0.15, and 0.11 ng BMP-7/g DBM h for the three size ranges, respectively. By 168 h, there was no indication that elution was nearing completion. Measurement of the residual BMP-7 remaining in the DBM as a function of time yielded unexpected results, i.e., after the BMP-7 content of the DBM declined for the first 4-6 h, it paradoxically increased for the remaining interval. We propose a two-compartment model to help explain these results in terms of the possible distribution of BMP-7 in bone matrix.

Platelet-rich plasma application and heterotopic bone formation following total hip arthroplasty.

Activated blood platelets play a critical, early role in the wound healing response by releasing several types of growth factors at the site of injury which mediate the initial stages of tissue repair. Autologously derived platelet-rich plasma has been applied during surgery as a healing aid and some studies have shown benefit with total joint arthroplasty procedures such as in the knee. However, little has been published regarding the use of platelet-rich plasma during total hip arthroplasty. The hip is especially prone to develop islands of heterotopic bone following arthroplasty which can lead to pain, limited motion, and even ankylosis of the joint. If this condition is exacerbated by platelet-rich plasma, this could present a barrier to the use of this adjuvant in total hip arthroplasty. This retrospective, controlled clinical study examined the effect of platelet rich plasma application during closure following total hip arthroplasty on heterotopic ossification. By one year, 21.3% of the control patients developed heterotopic bone (91 patients, 94 hips, Brooker grades I-III) compared to 12.9% of the treatment patients (76 patients, 85 hips, Brooker grades I-II). These differences were not significant (p = 0.478, power = 0.90). Thus, the use of platelet-rich plasma in this procedure does not appear to influence the incidence or severity of heterotopic ossification which should help to justify further clinical research to more fully understand whether this autologous blood product has a role in total hip arthroplasty.