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Biomedical subjects

S M Belkoff

Publications and source records attributed to S M Belkoff.

At least 19 recordsLinked to original sources
PubMed2002

Material properties of various cements for use with vertebroplasty.

The purpose of the current study was to measure the material properties of various cements prepared per manufacturers' recommendations and of cements modified according to compositions developed by clinicians with experience performing vertebroplasty. Cement was prepared, cast to form cylindrical specimens, and tested in compression. The optical density of specimens from the various cement preparations was measured. Batches of Simplex P and Cranioplastic cement were also prepared with increased concentrations of BaSO4 (20% and 30%; and 10%, 20% and 30%, respectively) to evaluate the effect of additional BaSO4. Compressive modulus values for polymethylmethacrylate cements ranged from 2-2.7 GPa; some differences were significant (p<0.05). Compared with polymethylmethacrylate cements, Orthocomp exhibited almost twice the compressive modulus and 2-3 times the strength values. Increasing the BaSO4 concentration in Simplex P and Cranioplastic significantly (p<0.05) affected their material properties; however, it is unknown if these changes in material properties are clinically important. Optical density increased as a function of concentration of the opacifying agent added. The current study provides clinicians with information on changes in the material properties of bone cements when the compositions are altered in a manner consistent with the practice of vertebroplasty.

Journal Article↗
PubMed2001

The biomechanics of vertebroplasty. The effect of cement volume on mechanical behavior.

STUDY DESIGN: Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies. OBJECTIVE: To determine the association between the volume of cement injected during percutaneous vertebroplasty and the restoration of strength and stiffness in osteoporotic vertebral bodies, two investigational cements were studied: Orthocomp (Orthovita, Malvern, PA) and Simplex 20 (Simplex P with 20% by weight barium sulfate content; Stryker-Howmedica-Osteonics, Rutherford, NJ). SUMMARY OF BACKGROUND DATA: Previous biomechanical studies have shown that injections of 8-10 mL of cement during vertebroplasty restore or increase vertebral body strength and stiffness; however, the dose-response association between cement volume and restoration of strength and stiffness is unknown. METHODS: Compression fractures were experimentally created in 144 vertebral bodies (T6-L5) obtained from 12 osteoporotic spines harvested from female cadavers. After initial strength and stiffness were determined, the vertebral bodies were stabilized using bipedicular injections of cement totaling 2, 4, 6, or 8 mL and recompressed, after which post-treatment strength and stiffness were measured. Strength and stiffness were considered restored when post-treatment values were not significantly different from initial values. RESULTS: Strength was restored for all regions when 2 mL of either cement was injected. To restore stiffness with Orthocomp, the thoracic and thoracolumbar regions required 4 mL, but the lumbar region required 6 mL. To restore stiffness with Simplex 20, the thoracic and lumbar regions required 4 mL, but the thoracolumbar region required 8 mL. CONCLUSION: These data provide guidance on the cement volumes needed to restore biomechanical integrity to compressed osteoporotic vertebral bodies.

Aged↗
PubMed2001

An ex vivo biomechanical evaluation of a hydroxyapatite cement for use with vertebroplasty.

STUDY DESIGN: Comparative ex vivo biomechanical study. OBJECTIVE: To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and stabilized via bipedicular injections of the following: 1) Simplex P (Stryker-Howmedica-Osteonics, Rutherford, NJ), 2) Simplex P formulated consistent with the practice of vertebroplasty (F2), or 3) BoneSource (Stryker-Howmedica-Osteonics). SUMMARY OF BACKGROUND DATA: Little is known about the mechanical stabilization afforded by new materials proposed for use with vertebroplasty. METHODS: Vertebral bodies (T8-T10 and L2-L4) from each of 10 fresh spines were harvested from female cadavers (81 +/- 12 years), screened for bone density (t score, -3.8 +/- 1.1; bone mineral density, 0.75 +/- 15 g/cm2), disarticulated, and compressed to determine initial strength and stiffness. The fractured vertebral bodies were stabilized via bipedicular injections of 4 mL (thoracic) or 6 mL (lumbar) and then recrushed. RESULTS: Vertebral bodies repaired with Simplex P resulted in significantly greater strength (P < 0.05) relative to their prefracture states, those repaired with BoneSource resulted in the restoration of initial strength for both the thoracic and lumbar level, and those repaired with F2 resulted in significantly greater strength (P < 0.05) in the thoracic region and restoration of strength in the lumbar region. All cement treatments resulted in significantly less stiffness compared with initial values. CONCLUSIONS: All three materials tested restored or increased vertebral body strength, but none restored stiffness. Both new materials show promise for use in percutaneous vertebroplasty, but they need clinical evaluation.

Aged↗
PubMed2001

An ex vivo biomechanical evaluation of an inflatable bone tamp used in the treatment of compression fracture.

STUDY DESIGN: Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies. OBJECTIVES: To determine if the inflatable bone tamp (tamp) restores height to compressed vertebral bodies and to compare the biomechanical properties of isolated, fractured osteoporotic vertebral bodies treated by kyphoplasty (tamp) or vertebroplasty. SUMMARY OF BACKGROUND DATA: Previous biomechanical studies have shown that vertebroplasty increases vertebral body strength and restores vertebral body stiffness, but does not restore vertebral body height lost as a result of compression fracture. METHODS: Compression fractures were experimentally created in 16 osteoporotic VBs assigned to either the tamp or percutaneous vertebroplasty group. The tamp treatment consisted of inserting balloon-like devices into the vertebral body, inflating the bone tamp, and filling the void with Simplex P (Howmedica, Rutherford, NJ) bone cement. The percutaneous vertebroplasty treatment consisted of directly injecting Cranioplastic bone cement (CMW, Blackpool, UK) into the vertebral body. Pre- and posttreatment heights were measured, and the repaired vertebral bodies were recompressed to determine posttreatment strength and stiffness values. RESULTS: The tamp treatment resulted in significant restoration (97%) of vertebral body height lost after compression, whereas percutaneous vertebroplasty treatment resulted in a significantly lower restoration of lost height (30%) (P < 0.05). Both treatments resulted in significantly stronger vertebral bodies relative to their initial state (P < 0.05). The tamp treatment restored vertebral body stiffness to initial values, but the percutaneous vertebroplasty treatment did not (P < 0.05). CONCLUSIONS: Tamp treatment resulted in significantly greater height restoration than did percutaneous vertebroplasty, without loss of vertebral body strength or stiffness.

Aged↗
PubMed2001

Ligamentous restraints of the second tarsometatarsal joint: a biomechanical evaluation.

Ligamentous injury of the tarsometatarsal joint complex is an uncommon, but disabling condition that frequently occurs in elite athletes. There are few options for managing these injuries, in part because the relative mechanical contribution of the ligaments of the tarsometatarsal joint is unknown, complicating decisions regarding which ligaments need reconstruction. In the current study, strength and stiffness of the dorsal, plantar, and Lisfranc ligaments of 20 paired cadaver feet were measured and compared. The plantar and Lisfranc ligaments were significantly stiffer and stronger than the dorsal ligament, and the Lisfranc ligament was significantly stronger and stiffer than the plantar ligament.

Biomechanical Phenomena↗
PubMed2000

Biomechanical evaluation of a new bone cement for use in vertebroplasty.

STUDY DESIGN: Comparative ex vivobiomechanical study. OBJECTIVES: To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and subsequently stabilized via bipedicular injection of one of two bone cements: one is a commercially available polymethylmethacrylate (Simplex P) and one is a proprietary glass-ceramic-reinforced BisGMA/BisEMA/TEGDMA matrix composite that is being developed for use in vertebroplasty (Orthocomp). SUMMARY OF BACKGROUND DATA: Osteoporotic compression fractures present diagnostic and therapeutic challenges for the clinician. Vertebroplasty, a new technique for treating such fractures, stabilizes vertebral bodies by injection of cement. Little is known, however, about the biomechanics of this treatment. METHODS: Five vertebral bodies (L1-L5) from each of four fresh spines were harvested from female cadavers (age, 80 +/- 5 years), screened for bone density using DEXA (t = -3.4 to -6.4), disarticulated, and compressed in a materials testing machine to determine initial strength and stiffness. The fractures then were repaired using a transpedicular injection of either Orthocomp or Simplex P and recrushed. RESULTS: For both cement treatments, vertebral body strength after injection of cement was significantly greater than initial strength values. Vertebral bodies augmented with Orthocomp recovered their initial stiffness; however, vertebral bodies augmented with Simplex P were significantly less stiff than they were in their initial condition. CONCLUSIONS: Augmentation with Orthocomp results in similar or greater mechanical properties compared with Simplex P, but these biomechanical results have yet to be substantiated in clinical studies.

Aged↗
PubMed2000

Collagen fibril D-period may change as a function of strain and location in ligament.

The purpose of this study was to determine if the characteristic banding pattern (D-period) of collagen fibrils from rabbit medial collateral ligaments changes as a function of gross ligament strain and, if so, whether the changes are location dependent (insertion versus midsubstance). Femur-medial collateral ligament-tibia complexes were strained to 0, 8, or 12% and immediately chemically fixed in situ. Samples were taken from the medial collateral ligament midsubstance and bony insertions, and prepared for and observed under a transmission electron microscope. D-period length was measured and found to increase (albeit not significantly so, p=0. 1) as a function of gross strain for samples obtained from the insertion sites but not for samples obtained from the ligament midsubstance. Results suggested that ligament strains are inhomogeneous at the ultrastructural level.

Animals↗
PubMed1999

Biomechanical efficacy of unipedicular versus bipedicular vertebroplasty for the management of osteoporotic compression fractures.

STUDY DESIGN: Cadaveric study on the biomechanics of osteoporotic vertebral bodies augmented and not augmented with polymethylmethacrylate cement. OBJECTIVES: To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and 1) not augmented, 2) augmented with unipedicular injection of cement, or 3) augmented with bipedicular injection of cement. SUMMARY OF BACKGROUND DATA: Percutaneous vertebroplasty is a relatively new method of managing osteoporotic compression fractures, but it lacks biomechanical confirmation. METHODS: Fresh vertebral bodies (L2-L5) were harvested from 10 osteoporotic spines (T scores range, -3.7 to -8.8) and compressed in a materials testing machine to determine intact strength and stiffness. They were then repaired using a transpedicular injection of cement (unipedicular or bipedicular), or they were unaugmented and recrushed. RESULTS: Results suggest that unipedicular and bipedicular cement injection restored vertebral body stiffness to intact values, whereas unaugmented vertebral bodies were significantly more compliant than either injected or intact vertebral bodies. Vertebral bodies injected with cement (both bipedicular and unipedicular) were significantly stronger than the intact vertebral bodies, whereas unaugmented vertebral bodies were significantly weaker. There was no significant difference in loss in vertebral body height between any of the augmentation groups. CONCLUSIONS: This study suggests that unipedicular and bipedicular injection of cement, as used during percutaneous vertebroplasty, increases acute strength and restores stiffness of vertebral bodies with compression fractures.

Absorptiometry, Photon↗
PubMed1999

A failure model for ligaments.

We propose a failure model for ligament which assumes that sequential uncrimping and stretching of collagen fibers is responsible for the mechanical response of ligament. We further assume that the fibers rupture sequentially and in a brittle, strain-limited manner. The model was fit to stress strain curves obtained from medial collateral ligaments of New Zealand White rabbits from two age groups (4 and 7 months). The model indicated that collagen modulus values ranged from 300 to 680 MPa and that fiber failure strains ranged from 6 to 22%. The model provides a convenient means of describing the elastic and failure response of ligament using four structurally based parameters.

Aging↗
PubMed1999

Temperature elevation caused by bone cement polymerization during vertebroplasty.

Percutaneous vertebroplasty (PVP), whereby polymethylmethacrylate cement is injected into the vertebral body (VB), has been used to successfully treat various spinal lesions. The mechanism responsible for the palliative effect of PVP is unknown, but it may be the result of neural damage caused by heat liberated during polymerization of the polymethylmethacrylate. The purpose of the current study was to measure in vitro temperature histories at three key locations (anterior cortex, center, spinal canal) in VBs injected with one of two different bone cements (Simplex P and Orthocomp) to determine the role temperature plays in PVP. Twelve VBs (T11-L2) from three elderly female spines were instrumented with thermocouples and injected with 10 cc of one of the two cements. Temperatures were measured with the VBs in a bath (37 degrees C) for 15 min after injection. A Student's paired t-test was used to determine differences in peak temperature and time above 50 degrees C between the two cement groups. Peak temperatures and temperatures above 50 degrees C were significantly higher and longer, respectively, at the center of VBs injected with Simplex P (61.8 +/- 12.7 degrees C; 3.6 +/- 2.1 min) than those injected with Orthocomp (51.2 +/- 6.2 degrees C; 1.3 +/- 1.4 min). There was no significant difference in peak temperature between cements at the spinal canal location; temperature there did not rise above 41 degrees C. Although thermal damage to intraosseous neural tissue caused by cement polymerization cannot be ruled out as a potential mechanism for pain relief experienced by patients subsequent to PVP, it seems unlikely based on the worst-case conditions tested in the current study.

Aged↗
PubMed1999

An in vitro biomechanical evaluation of bone cements used in percutaneous vertebroplasty.

The purpose of this study was to determine the strength and stiffness of osteoporotic vertebral bodies (VBs) subjected to compression fractures and subsequently treated with bipedicular injections of various polymethylmethacrylate cements. Ten spines were harvested from nonembalmed female cadavers (age 68.6 +/- 13.7 years) and evaluated for bone mineral density using the dual energy X-ray absorptiometry method (t-score = -2.3 +/- 2.4). The 50 VBs (L1-L5) were disarticulated, compressed in a materials testing machine to determine initial strength and stiffness, and then assigned to one of six groups. Two of these groups (n = 8, n = 9) concerned experimental cements, the results of which are not reported here. The 33 vertebral bodies in the remaining four groups were left untreated or were repaired using a transpedicular injection of one of three commercially available polymethylmethacrylate cements. These four groups were: a) no treatment (no cement, n = 8); b) Simplex P (n = 9); c) Cranioplastic (n = 8); and d) Osteobond (n = 8). The VBs were then compressed again according to the initial protocol, and posttreatment strength and stiffness were measured. Results suggested that bipedicular injection of Simplex P and Osteobond restored VB stiffness to initial values, whereas VBs injected with Cranioplastic were significantly less stiff than in their initial state. VBs injected with cement (regardless of type) were significantly stronger than they were initially.

Absorptiometry, Photon↗
PubMed1999

The effect of monomer-to-powder ratio on the material properties of cranioplastic.

Percutaneous vertebroplasty consists of injecting polymethylmethacrylate cement into the cancellous bone of vertebral bodies for the treatment of various lesions of the spine, including osteoporotic compression fractures. Clinicians practicing vertebroplasty commonly alter the mixture of monomer-to-powder recommended by the manufacturer in an effort to decrease viscosity and increase the working time. The purpose of the current study was to measure the effect that varying the monomer-to-powder ratio has on the compressive material properties of a cement (Cranioplastic) commonly used in vertebroplasty. Cylindrical specimens were prepared varying a monomer-to-polymer ratio of 0.40 to 1.07 ml/g and tested per the American Society for Testing and Materials standard F451. Specimens prepared at 0.53 mL/g, which is near the manufacturer's recommended monomer-to-polymer mixture of 0.57 mL/g, exhibited the greatest mean values for ultimate compressive stress, yield stress, and elastic modulus. Specimens prepared at higher or lower ratios exhibited diminished strength, in some cases by as much as 24%. Although altering the monomer-to-powder ratio affects the cement's material properties, it is as yet unknown if the decrease is clinically significant.

Bone Cements↗
PubMed1999

Biomechanical comparison of fixation of type-I fractures of the lateral tibial plateau. Is the antiglide screw effective?

Type-I fractures of the lateral tibial plateau were simulated by osteotomy in 18 pairs of unembalmed cadaver tibiae. One fracture of each pair was fixed with two lag screws whereas the contralateral site was stabilised with three lag screws, or two lag screws plus an antiglide screw. The lateral plateau was displaced downwards using a servohydraulic materials testing machine and the resulting force and articular surface gap were recorded. Yield load was defined as the maximum load needed to create a 2.0 mm articular offset at the fracture line. The yield loads of the three-lag-screw (307 +/- 240 N) and antiglide constructs (342 +/- 249 N) were not significantly different from their two-screw control constructs (231 +/- 227 and 289 +/- 245 N, respectively). We concluded that adding an antiglide screw or a third lag screw did not provide any biomechanical advantage in stabilising these fractures.

Aged↗
PubMed1999

Immediate weight-bearing after treatment of a comminuted fracture of the femoral shaft with a statically locked intramedullary nail.

BACKGROUND: The purpose of this two-part investigation was to test the feasibility, safety, and efficacy of immediate weight-bearing after treatment of fractures of the shaft of the femur with a statically locked intramedullary nail. METHODS: In the first part of the investigation, a biomechanical study was performed to determine the fatigue strength of eleven different statically locked intramedullary nail constructs. Segmentally comminuted midisthmal fractures were simulated with use of sections of polyvinyl chloride pipe; each construct was cyclically loaded in compression with use of physiologically relevant loads in a materials testing machine at eight hertz. The fatigue tests were conducted according to the so-called staircase method, and the construct was considered to have run out (exceeded its anticipated service life) if it had not failed after 500,000 cycles. In the second part of the study, a clinical investigation of immediate weight-bearing after treatment of comminuted fractures of the femoral shaft with a Russell-Taylor (RT-2) construct was performed. Complete follow-up data were available for twenty-eight of the thirty-five patients (thirty-six fractures) entered into the study. RESULTS: In Part I of the study, two constructs, a statically locked twelve-millimeter-diameter Russell-Taylor femoral nail with two distal locking screws (RT-2) and a statically locked twelve-millimeter-diameter Zimmer femoral nail with two distal locking screws (Z-2), had significantly higher mean fatigue strengths (2171 and 2113 newtons, respectively) than all other constructs tested (p<0.001), but the strengths of these two constructs were not significantly different from each other. Constructs with only one distal locking screw demonstrated significantly lower (p<0.05) fatigue strengths than the two-screw constructs. These results suggest that full weight-bearing during the weeks immediately after insertion of the nail may be possible, even for patients who have a comminuted fracture of the femoral shaft. In Part II of the study, twenty-six of the twenty-eight patients were bearing full weight on the fractured limb or limbs at the six-week follow-up visit. All fractures united; only one of these needed an additional procedure (the removal of the screws five months after the insertion of the nail) to stimulate union. No loss of fixation, such as back-out or breakage of a locking screw or breakage or bending of the intramedullary nail, occurred. CONCLUSIONS: We concluded from this two-part investigation that immediate weight-bearing after stabilization of a comminuted fracture of the femoral shaft with a statically locked intramedullary nail is safe when the construct has a relatively high fatigue strength. Immediate weight-bearing after stabilization of a fracture of the femoral shaft permits patients who have multiple fractures of the extremity to walk and to participate in physical therapy earlier, possibly decreasing the duration of the hospital stay or reducing the need for prolonged rehabilitation on an inpatient basis.

Adolescent↗
PubMed1998

Effect of modular head seating on the cement-stem interface strength of femoral prostheses.

This study tested the hypothesis that modular head seating in situ reduces the cement-stem interfacial strength. Femoral prostheses were implanted in eight pairs of cadaveric femurs; one femur of each pair received a stem for which the modular head was seated by dropping a weight from a given height (treated); the contralateral femur received a nonseated stem (control). Transverse sections were cut from four standardized locations on each implanted femur, and the yield shear stress and ultimate shear stress of the interface were determined from push-out tests. There was no significant difference in cement-stem interfacial strength between seated and nonseated prostheses. These results suggest that seating modular heads in situ has no deleterious effect on the acute interfacial strength of cemented femoral implants.

Bone Cements↗
PubMed1998

Biomechanical evaluation of distal radius fracture stability.

OBJECTIVES/HYPOTHESES: (a) To determine the radiographic correlation between an artificially created dorsal comminution (via a wedge osteotomy) and dorsal tilt (clinical instability) and (b) to determine the efficacy of cast immobilization in maintaining reduction of the simulated fracture pattern as a predictor of successful treatment in the clinical setting. STUDY DESIGN: Biomechanical cadaveric study. SETTING: Level I trauma center. METHODS: In ten fresh cadaveric upper extremities, sequential dorsal wedge osteotomies (25, 50, and 75 percent of the distal radial diameter) were performed, each followed by measurement of tilt and radial inclination on posteroanterior and lateral radiographs before and after applying a load simulating the physiologic static forces of the forearm. In the last five specimens, the osteotomies were reduced and casted after the load application for each osteotomy, and radiographic measurements were again taken under loaded and unloaded conditions. RESULTS: In the uncasted loaded group (n = 10), average tilt changed from an initial 9 degrees palmar to 3 degrees palmar after the first osteotomy and became dorsally angulated (11 and 30 degrees) after the second and third osteotomies, respectively. Casting and loading resulted in a palmar tilt of 10, 6, and 3 degrees for the 25, 50, and 75 percent osteotomies, respectively. CONCLUSION: Increasing wedge osteotomies across the midline axis of the radius resulted in dorsal tilt and radial inclination changes representative of clinically unstable fractures that require more aggressive treatment protocols. However, in our experimental setting, casting maintained reduction of stable and unstable osteotomy patterns.

Adult↗
PubMed1998

Biomechanical evaluation of transverse acetabular fracture fixation.

The purpose of this two-part biomechanical study was to evaluate various fixation methods for transverse acetabular fractures in a synthetic pelvic model. In Part 1, 40 transverse acetabular fractures were repaired with anterior column plating using 10-hole curved reconstructions plates with one of four screw configurations to evaluate the effect of screw placement and number on fracture fixation stiffness. In Part 2, 36 transverse acetabular fractures were repaired with one of six fixation methods using combinations of contoured plates and column screws to stabilize the anterior column, the posterior column, or both. Each repaired acetabulum was loaded via a hemiarthroplasty in a direction consistent with stance phase. Fixation stiffness was measured from the force-displacement curve for each construct. In Part 1, there was no significant difference in fixation stiffness afforded by any of the constructs. However, the stiffest construct resulted from two screws on each side of the fracture site: one placed as close to the fracture site as allowed (one empty screw hole adjacent to the fracture) and the second at the end of the plate. In Part 2, the constructs that concomitantly stabilized anterior and posterior columns were significantly stiffer than were those addressing either the anterior or posterior column alone, regardless of the number of plates applied. The stiffest construct combined a posterior column plate with an anterior column screw. Because no significant change in stiffness occurred with the addition of a third set of screws, two screws on each side of the fracture site appear to provide sufficient stability with acetabular plating. Concurrent fixation of anterior and posterior columns of transverse acetabular fractures provides the greatest resistance to postoperative loss of reduction in this model.

Acetabulum↗