David Pienkowski

Interference Screw Fixation Strength of a Quadrupled Hamstring Tendon Graft Is Directly Related to Bone Mineral Density and Insertion Torque

The purpose of this study was to determine whether bone mineral density of the host bone, measured using conventional dual photon absorptiometry techniques, and insertion torque can predict part of the ultimate failure strength of interference screw fixation of quadrupled hamstring tendon grafts. The semitendinosus and gracilis tendons were harvested from 10 human cadaveric knees, mean age 66.5 years (range, 53 to 81). The bone tunnel was sized within 0.5 mm of the graft. The graft was fixed with a biodegradable screw (7 25 mm for the femur, and 9 25 mm for the tibia) directly against the tendon and at the joint surfaces. Tibial fixation and femoral fixation were tested to failure using a materials testing system. Bone mineral density was measured in the metaphyseal region of the tibia and femur. The results of multiple regression analyses showed that both insertion torque and bone mineral density were related to the maximum load the graft withstood. These two variables explained 77.1% of the maximum load observed. We concluded that bone mineral density measurements of the host bone site are an important determinant of postoperative graft strength and thus have an important, but previously unrecognized, clinical role in establishing individual postsurgery rehabilitation protocols. Insertion torque in this study was a useful predictor of graft fixation strength.

Biomechanical comparison between BioScrew and titanium alloy interference screws for bone—patellar tendon—bone graft fixation in anterior cruciate ligament reconstruction

This investigation compared the maximum load at failure of BioScrew (Linvatec Corp, Largo, FL) and titanium alloy interference screw femoral fixation using a human cadaveric model that approximated the anatomical orientation and physiological strain rate of in vivo bone-patellar tendon-bone (BPTB) graft loading following anterior cruciate ligament reconstruction. Eighteen fresh-frozen human BPTB allografts (10-mm wide, 10-mm thick, 25-mm long bone plugs) with either BioScrew or titanium alloy (Ti 6A14V) screw (7 x 25 mm) fixation were compared for maximum load at failure at a strain rate of 20 mm/minute. Nine cadaver femurs with bone mineral densities of 0.88 +/- 0.18 g/cm2 (anterior/posterior) and 1.3 +/- 0.24 g/cm2 (lateral) received the allografts. No statistical differences were observed in maximum load at failure (P = .95) or failure mode (P = .11) between specimens fixed with either screw type. When biomechanically tested with anatomic orientation and at functionally relevant strain rates, the BioScrew provided maximum load at failure equal to a titanium alloy screw.

The Effect of Ankle Stabilizers on Athletic Performance A Randomized Prospective Study

The ankle is the site of more than one third of all in juries that occur to male basketball players. Although ankle bracing may prevent injury, many players be lieve that braces restrict athletic performance. This belief discourages use of braces and obviates the injury protection that bracing provides. The objectives of this study were to 1) determine whether athletic performance (in four basketball-related activities) was affected by three ankle brace designs (Universal, Kallassy, and Air-Stirrup ankle training brace), 2) de termine whether specific braces are better for specific athletic activities, and 3) determine whether athletic performance changes with brace use. Twelve high school basketball players wore each brace type while vertical jumping, standing long jumping, cone run ning, and 18.3-meter shuttle running at two test times (initially and after 1 week of acclimation). Our data showed that these braces had no significant effects on athletic performance. No brace affected athletic performance in one specific activity more than an other, and athletic performance did not change with brace use. We concluded that prophylactic ankle bracing does not inhibit athletic performance.

Modified Tibial Nails for Treating Distal Tibia Fractures

Objective: To determine the biomechanical consequences of cutting one centimeter off the tip of a tibial nail when treating distal tibia fractures with intramedullary nails. Design: Randomized laboratory investigation using matched pairs of cadaveric tibias with osteotomies made to resemble distal tibia fractures extending to four and five centimeters from the tibiotalar joints. Intervention: The smaller (four‐centimeter) distal tibias were stabilized using ten‐millimeter diameter tibial nails that had been modified by removing the distal one centimeter of the nail. The five‐centimeter distal tibias were stabilized with standard ten‐millimeter diameter tibial nails. Each tibia was tested in elastic compression, rotation, and compression‐bending on a servohydraulic materials testing machine. Main Outcome Measurements: Stiffness was calculated for each type of loading to compare stability of the modified nail construct to that of the standard nail construct. Results: Four‐centimeter distal tibia fragments stabilized with modified nails have comparable stiffness in compression and in torsion to five‐centimeter distal tibia fragments stabilized with standard tibial nails. The stiffness in compression‐bending was surprisingly low in both groups and differed by only 3.7 percent. Conclusions: Removal of one centimeter from the tip of a tibial nail allows placement of two distal interlocking screws in tibial fractures located four centimeters from the tibiotalar joint. The fixation strength achieved is comparable to that of standard intramedullary nailing of tibial fractures located five centimeters from the tibiotalar joint using two distal interlocking screws. Fixation strength with these distal fractures, however, is not strong enough to resist moderate compression‐bending loads. Thus, patients with distal tibia fractures treated with intramedullary nailing must follow weight‐bearing restrictions until significant fracture healing occurs to prevent coronal plane malalignment of the fracture.

Effect of Acute Reamed Versus Unreamed Intramedullary Nailing on Compartment Pressure When Treating Closed Tibial Shaft Fractures : A Randomized Prospective Study

OBJECTIVE To compare anterior and deep posterior compartment pressures during reamed and unreamed intramedullary nailing of displaced, closed tibial shaft fractures. DESIGN Randomized prospective study. SETTING University Hospital/Level I trauma center. PATIENTS Forty-eight adults with forty-nine fractures treated with intramedullary nailing within three days of injury. INTERVENTION After intraoperative placement of compartment pressure monitors, the tibia fractures were treated by either unreamed intramedullary nailing or reamed intramedullary nailing. A fracture table and skeletal traction were not used in any of these procedures. MAIN OUTCOME MEASUREMENTS Compartment pressures and deltaP ([diastolic blood pressure] - [compartment pressure]) were measured immediately preoperatively, intraoperatively, and for twenty-four hours postoperatively. RESULTS Compartment syndrome did not occur in any patient. Peak average pressures were obtained during reaming in the reamed group (30.0 millimeters of mercury anterior compartment, 34.7 millimeters of mercury deep posterior compartment) and during nail insertion in the unreamed group (33.9 millimeters of mercury anterior compartment, 35.2 millimeters of mercury deep posterior compartment). The average pressures quickly returned to less than thirty millimeters of mercury and remained there for the duration of the study. The deep posterior compartment pressures were lower in the reamed group than in the unreamed group at ten, twelve, fourteen, sixteen, eighteen, twenty, twenty-two, and twenty-four hours postoperatively (p < 0.05 at each of these times. A statistically significant difference between anterior compartment pressures could not be shown with the numbers available. The deltaP values were greater than thirty millimeters of mercury at all times after nail insertion in both the reamed and unreamed groups. CONCLUSION These data support acute (within three days of injury) reamed intramedullary nailing of closed, displaced tibial shaft fractures without the use of a fracture table.

Differences in Bone Quality in Low- and High-Turnover Renal Osteodystrophy

Abnormal bone turnover is common in CKD, but its effects on bone quality remain unclear. We qualitatively screened iliac crest bone specimens from patients on dialysis to identify those patients with low (n=18) or high (n=17) bone turnover. In addition, we obtained control bone specimens from 12 healthy volunteers with normal kidney function. In the patient and control specimens, Fourier transform infrared spectroscopy and nanoindentation quantified the material and mechanical properties of the specimens, and we used bone histomorphometry to assess parameters of bone microstructure and bone formation and resorption. Compared with high or normal turnover, bone with low turnover had microstructural abnormalities such as lower cancellous bone volume and reduced trabecular thickness. Compared with normal or low turnover, bone with high turnover had material and nanomechanical abnormalities such as reduced mineral to matrix ratio and lower stiffness. These data suggest that turnover-related alterations in bone quality may contribute to the diminished mechanical competence of bone in CKD, albeit through different mechanisms. Therapies tailored specifically to low- or high-turnover bone may treat renal osteodystrophy more effectively.

Calcitonin Alters Bone Quality in Beagle Dogs

Because of its antiresorptive properties, calcitonin is widely used to prevent and treat osteoporosis. A stimulatory effect of calcitonin on osteoblasts has also been reported; however, a recent histologic study points to a negative effect of calcitonin on mineralization of cancellous bone. The present experiment was performed to determine whether the observed histological signs of alterations in mineralization are also observed in cortical bone and whether this results in changes in mechanical properties, mineral densities, or mineral properties of canine bone. Sixteen female adult beagle dogs were randomly allocated to receive either human calcitonin at a dose of 0.25 mg/dog (50 IU, n = 8) or vehicle (mannitol, n = 8) every other day for 16 weeks. At the end of the study, the dogs were euthanized. Both tibiae, L1 and L5 vertebrae, and iliac crest bone samples were excised and defleshed. Torsional mechanical properties of tibial diaphyses and compressive strengths of vertebrae were measured. Bone mineral densities (BMD) of tibiae and vertebrae were measured by using dual‐energy X‐ray absorptiometry. Ultrastructural mineral characteristics of iliac crest bone were determined by gravimetry and Fourier transform infrared spectroscopy (FTIR). Bone histomorphometry was performed in the cortical envelope of the iliac crest. Tibiae from dogs treated with calcitonin withstood significantly less maximum torque until failure, required less torsional energy to reach the maximum torque, and had less torsional stiffness than the tibiae from dogs treated with vehicle (p < 0.05). Cancellous cores of vertebrae from calcitonin‐treated dogs withstood less compressive mechanical loading than did vertebral cores from vehicle‐treated animals (p < 0.05). Dogs treated with calcitonin had less BMD of both tibiae and vertebrae than vehicle‐treated animals (p < 0.05). Bones from calcitonin‐treated dogs had significantly less ash content, which correlated with the lower phosphate‐to‐amide I (detected by FTIR) and greater carbonate‐to‐phosphate ratios than did bones from vehicle‐treated dogs (p < 0.05). Calcitonin‐treated dogs exhibited a decrease in bone formation and mineralization rates and an increase in mineralization lag time. These results point to a negative effect of calcitonin on bone quality. These findings are intriguing and call for further studies addressing whether the observed abnormalities are transient or permanent.

Compressive creep characteristics of extruded ultrahigh‐molecular‐weight polyethylene

The static compressive creep behavior of ultrahigh-molecular-weight polyethylene (UHMWPE) was studied under physiologic conditions. Specimens were machined from the center and periphery of extruded GUR 4150HP rod stock and were subjected to constant pressures of 2, 4, or 8 MPa for intervals as long as 10(4) min. The creep strain (creep divided by initial thickness) was compared to the pressure and duration of loading by using analysis of variance and linear regression analysis. The amount of creep strain increased rapidly in the early period of testing and was followed by a reduced rate of creep, which reached a steady state after approximately 4000 min. The amount and rate of creep strain increased linearly with pressure. Surprisingly, the rate of creep strain varied with the radial position in the rod stock: specimens obtained from the periphery had 8-19% larger creep strain rates than did specimens obtained from the center (p = 0.1 to p < 0.001). These results advance the characterization of creeps contribution to the in vivo penetration of the metallic component into the UHMWPE component, thereby facilitating the measurement of true in vivo wear. These data also help explain the azimuthally nonuniform deformation observed in retrieved acetabular cups.

A mechanical comparison of subtrochanteric femur fracture fixation.

OBJECTIVE To determine whether the mechanical properties of first-generation interlocking femoral nails are different from those of second-generation interlocking femoral nails in a subtrochanteric femur fracture model. DESIGN Randomized laboratory investigation using a synthetic subtrochanteric femur fracture model. SETTING Simulated stable and unstable fractures were created at three levels in the subtrochanteric region of synthetic femora. Instrumented specimens were tested elastically in a biomaterials testing system. INTERVENTION Synthetic femora were instrumented with either a statically locked first-generation femoral nail or a statically locked second-generation femoral nail. MAIN OUTCOME MEASUREMENTS Elastic stiffness for both the stable and unstable fracture groups was measured in both compression and torsion. Unstable fracture specimens were tested to failure in compression, and load to failure was measured. RESULTS Throughout the subtrochanteric region, second-generation femoral nail constructs were consistently stiffer in compression and torsion than were statically locked first-generation femoral nail constructs. In general, second-generation constructs also withstood larger loads to failure in the unstable fracture model. CONCLUSIONS Second-generation nails provided significantly enhanced mechanical stiffness compared with first-generation femoral nails when used to treat both stable and unstable subtrochanteric femur fractures. Although these results were obtained by using a well-controlled, mechanically consistent model, clinical validation of an increased incidence of fracture unions or of decreased time to union is required before we can recommend that second-generation nails be used routinely to treat subtrochantenic femur fractures.

Evaluating bone quality in patients with chronic kidney disease

Bone of normal quality and quantity can successfully endure physiologically imposed mechanical loads. Chronic kidney disease–mineral and bone disorder (CKD–MBD) adversely affects bone quality through alterations in bone turnover and mineralization, whereas bone quantity is affected through changes in bone volume. Changes in bone quality can be associated with altered bone material, structure, or microdamage, which can result in an elevated rate of fracture in patients with CKD–MBD. Fractures cannot always be explained by reduced bone quantity and, therefore, bone quality should be assessed with a variety of techniques from the macro-organ level to the nanoscale level. In this Review, we demonstrate the importance of evaluating bone from multiple perspectives and hierarchical levels to understand CKD–MBD-related abnormalities in bone quality. Understanding the relationships between variations in material, structure, microdamage, and mechanical properties of bone in patients with CKD–MBD should aid in the development of new modalities to prevent, or treat, these abnormalities.