No effect of autologous growth factors (AGF) around ungrafted loaded implants in dogs.

Autologous growth factors (AGF) is a growth-factor-rich concentrate of platelets, white blood cells and fibrinogen. Application of AGF was presumed to improve implant fixation and gap healing of non-grafted, loaded implants. We inserted one loaded titanium implant intra-articularly in each medial femoral condyle of eight dogs. Each implant was surrounded by a 0.75 mm gap. One implant in each dog was coated with AGF prior to implantation whereas the contralateral implant served as a control. AGF was prepared by isolating the buffy-coat from blood and further concentrated using an Interpore Cross UltraConcentrator. Platelet counts were increased from a median baseline of 168x10(3)/microl to 1003x10(3)/microl in AGF. However, AGF had no significant effect on implant fixation or bone formation. Even though AGF increased ultimate shear strength and energy absorption by approximately 50%, these differences had a p-value less than 0.05. The sample size in this study was small and any negative conclusions should be taken with caution due to low statistical power. We have previously demonstrated that AGF significantly improves fixation and incorporation of grafted implants. AGF might require mixing with an osteoconductive grafting material in order to provide a scaffold on which to foster bone growth and to keep the growth factors on location for a prolonged period.

Effects of short-term alendronate treatment on the three-dimensional microstructural, physical, and mechanical properties of dog trabecular bone.

The bisphosphonate, alendronate, is well known for its potent inhibition of osteoclast-mediated bone resorption. It has been used clinically for the treatment of osteoporosis and has also recently been used to reduce osteolysis around prostheses in a canine revision model of implant loosening (femoral condyle). In this study, the effects of alendronate on trabecular bone properties were assessed in dogs at an oral dose of 0.5 mg/kg per day over a 12 week period, and compared with control dogs. Cubic cancellous bone specimens were produced from lumbar vertebrae (L-1 and L-2) and bilateral proximal humeri. These specimens were scanned using a high-resolution microcomputed tomography (micro-CT) system. From accurate data sets, three-dimensional microstructural properties were calculated and physical and mechanical properties were determined. Treatment with alendronate increased bone volume fraction by 9.5%, 7.7%, 7.4%, and 18.4%, respectively, in L-1, L-2, humeral greater tuberosity, and humeral head trabecular bone. In the lumbar vertebrae, the alendronate-treated trabeculae were thicker and lower in bone surface-to-volume ratio. In the greater tuberosity, the alendronate-treated trabeculae were thicker, lower in bone surface-to-volume ratio, and less anisotropic. In the humeral head, the alendronate-treated trabeculae were thicker, less anisotropic, lower in surface density, and showed decreased trabecular separation. Alendronate significantly increased apparent density and collagen density in the lumbar vertebrae and humeral heads, and significantly decreased collagen concentration in the vertebrae. In the lumbar vertebrae, Young's modulus in the cephalocaudal direction, ultimate stress, and failure energy were significantly increased in the alendronate-treated group. The changes in mechanical properties in the humeral head trabecular bone were similar to those seen in the lumbar vertebrae. Our results demonstrate that alendronate increases the mechanical properties of healthy canine trabecular bone after short-term treatment. The physical and microstructural changes of trabecular bone are consistent with the significantly increased mechanical properties.

Stability of initial fixation of the tibial component in cementless total knee arthroplasty.

This study measured the vertical displacement of three kinds of cementless tibial components [Porous Coated Anatomical (PCA), Tricon, and Whiteside], under eccentric loading up to 2,225 N. Displacement between the tibial tray and the proximal tibia was measured with linear variable differential transformers at the anterior and posterior side when anteriorly or posteriorly loaded, and at the medial and lateral side when medially or laterally loaded. The general pattern of motion was sinking at the loaded side and lift-off at the opposite side. Lift-off opposite the loaded side was fairly small for all components at all measurement sites. Among the three components, the Whiteside showed the smallest displacements. The Tricon (when anteriorly or posteriorly loaded), and the PCA (when medially or laterally loaded) showed sinking at the loaded side. Anterior screw fixation of the PCA was not effective in preventing anterior lift-off. The tilting motion of the tibial components observed in this study implies instability of the initial fixation, which could possibly compromise bony ingrowth. Furthermore, this tilting could cause uneven distribution of load, and potentially result in fracture of the underlying bone.

Radiographic changes in bone dimensions in asymptomatic cemented total hip arthroplasties. Results of nine to thirteen-year follow-up.

On twenty-six cemented total hip replacements that had been followed for an average of 10.4 years (range, nine to thirteen years), a retrospective radiographic study was done to assess dimensional changes in the cross section of the bone in a group of asymptomatic patients. Cortical dimensions were measured on radiographs and were normalized using a radiographic distortion factor that was derived from the width and length of the prosthesis. The data were then analyzed using a least-squares method. Analyses were performed for the men, for the women, and for the combined group. The results for all three groups showed a significant decrease in cortical thickness as well as widening of the medullary canal, but no periosteal expansion.

Forces required to initiate sliding in second-generation intramedullary nails.

Second-generation intramedullary nails, which allow the fixation screw that is placed in the femoral head to slide distally and thus allow compression of the fracture of the femoral neck, have become a popular option for the treatment of ipsilateral fractures of the femoral neck and shaft. However, the sliding characteristics of the screw within the barrel of the nail or the side-plate have not been assessed biomechanically, to our knowledge. The goal of the current study was to investigate the forces required to initiate sliding of the proximal screw in intramedullary devices and to compare these forces with those required to initiate sliding of hip screws. The loading configuration simulated the typical angle of 135 degrees between the intramedullary nail and the proximal screw. The forces required to initiate sliding of the proximal screw, with the screw extended fifty-one, seventy-six, eighty-six, and 102 millimeters beyond the proximal end of the barrel, were measured for three different types of second-generation intramedullary nails (Recon, ZMS, and Gamma), a sliding compression hip screw, and an intramedullary hip screw, and these forces were then compared. With each amount of extension of the screw, the hip screws required lower forces to initiate sliding than did the second-generation intramedullary devices. Of the second-generation devices, the Gamma nail required the highest forces to initiate sliding; the Recon and ZMS nails required 20 to 40 percent lower forces compared with the Gamma nail. None of the devices jammed in any of the loading configurations that were tested. When the extension of the screw was increased, higher forces were required to initiate sliding.

Application of beams on elastic foundation and B-spline solution methodologies to parametric analysis of intramedullary implant systems.

A simple numerical technique for parametric evaluation of orthopaedic implant systems, to be used as a screening tool before complex structural analysis (e.g. Finite Element Method), is the subject of this paper. A modified Beams on Elastic Foundation model (with non-constant foundation modulus) is solved using this numerical technique based on B-spline differential equation modelling. A model with variation in the modulus of the foundation, as solved with this spline technique, was compared with a model with constant foundation modulus, solvable with closed form techniques. While deflections were smaller, the reaction force was up to ten times greater for the models with constant modulus of foundation, compared with varying modulus. The model presented in this paper is a refinement of previous models using closed form solution techniques for foundations with constant moduli. It is primarily useful for detecting trends in parametric analyses, or to select specific cases for further analysis by more computationally intensive analytic methods.

Biomechanical analysis of transpedicular rod systems. A preliminary report.

Two transpedicular spinal instrumentation systems were developed for fixation of the lumbosacral junction: a transpedicular fixator and the transpedicular screw/rod system. Mechanical testing showed that the new systems have a rigidity that is intermediate between conventional wired implants (Galveston and Luque ring) and plate systems (Steffee plate). Neither pedicular implant approached the rigidity of the Steffee plate with S2 fixation, but in compression and anterior bending both were more rigid than the Steffee plate without S2 fixation. Despite the apparent mechanical advantages of the transpedicular fixator, it is currently too bulky for clinical use. The transpedicular screw/rod system is more appealing because the size leaves adequate area for bone grafting, and device placement is technically simple. Furthermore, it may be contoured to any plane, while retaining stability provided by the clamps and screws.

The effects of freeze-drying and ethylene oxide sterilization on the mechanical properties of human patellar tendon.

Human patellar tendon allografts are used to replace injured anterior cruciate ligaments. They are often stored by freeze-drying or freezing before use and have been sterilized by gamma irradiation or ethylene oxide gas. Studies comparing the mechanical properties of tendons preserved by freeze-drying and sterilized by ethylene oxide have yielded conflicting results. This study examined the effects of freeze-drying and ethylene oxide sterilization on the mechanical properties of human patellar tendons obtained from 11 human cadavers; all were free of musculoskeletal disease. The 22 patellar tendons were halved longitudinally; 7 were frozen at -70 degrees C for 8 weeks and served as controls; 8 were freeze-dried; and 7 were freeze-dried and sterilized with ethylene oxide gas. Ultimate tensile stress and longitudinal strain were greater for frozen than for freeze-dried, but not greater than freeze-dried, ethylene oxide-sterilized tendons (P < 0.05). The modulus of elasticity was similar in all tendon groups. The study suggests that some in vitro mechanical properties of frozen tendons may be marginally superior to the properties of freeze-dried tendons, even after correction for size difference. Ethylene oxide gas sterilization had no adverse effect on tendon mechanical properties.

Bone ingrowth in the presence of particulate polyethylene. Synergy between interface motion and particulate polyethylene in periprosthetic tissue response.

We have investigated whether the presence of polyethylene (PE) alone is sufficient to cause an aggressive periprosthetic tissue response, or whether certain mechanical interface conditions can allow bone to grow while in the presence of PE. An experimental implant was loaded in the presence and absence of particulate PE under stable and unstable conditions. Bone with a thin, discontinuous fibrous membrane formed in both groups of stable implants, either in the presence or absence of PE. By contrast, a continuous fibrous membrane consistently formed in both groups of unstable implants. The membrane consisted of loose fibrous connective tissue when PE was absent, and dense connective tissue with macrophages and a synovial lining when PE was present. In this model, if the interface was stable, the presence of PE was not sufficient to prevent the formation of bone or to produce a phagocytic tissue response. Only when the interface was unstable did a fibrous membrane form, and only then in the presence of PE.

Intracapsular components do not change hip proprioception.

We compared joint proprioception in 12 hips in 12 patients with hemiarthroplasty after fracture of the hip, in 12 hips in 11 patients with total hip arthroplasty because of osteoarthritis and in a control group of 12 age-matched patients with no clinical complaints. There was no significant difference (p = 0.05) in joint proprioception in any of the groups. There was no decrease in joint proprioception in the group with total hip arthroplasty compared with the hemiarthroplasty group or with the control group. Other factors such as stretch receptors in the adjacent tendons and muscles may have a greater influence on proprioception in the hip than the intracapsular components.

Improving the detection of acetabular osteolysis using oblique radiographs.

Visualisation of periacetabular osteolysis by standard anteroposterior (AP) radiographs underestimates the extent of bone loss around a metal-backed acetabular component. We have assessed the effectiveness of standard radiological views in depicting periacetabular osteolysis, and recommend additional projections which make these lesions more visible. This was accomplished using a computerised simulation of radiological views and a radiological analysis of simulated defects placed at regular intervals around the perimeter of a cadaver acetabulum. The AP view alone showed only 38% of the defects over all of the surface of the cup and failed to depict a 3 mm lesion over 83% of the cup. When combined with the AP view, additional 45 degree obturator-oblique and iliac-oblique projections increased the depiction, showing 81% of the defects. The addition of the 60 degree obturator-oblique view further improved the visualisation of posterior defects, increasing the rate of detection to 94%. Based on this analysis, we recommend using at least three radiographic views when assessing the presence and extent of acetabular osteolysis.

Application of computer graphics in the design of custom orthopedic implants.

Implementation of newly developed computer modelling techniques and computer graphics displays and software have greatly aided the orthopedic design engineer and physician in creating a custom implant with good anatomic conformity in a short turnaround time. Further advances in computerized design and manufacturing will continue to simplify the development of custom prostheses and enlarge their niche in the joint replacement market.

Biomechanical properties of canine corticocancellous bone frozen in normal saline solution.

Eleven pairs of canine metacarpal bones, 10 pairs of metatarsal bones, and 7 pairs of ribs were harvested cleanly and prepared for banking at -20 C for 1 year. One bone of each pair was randomly assigned to 1 type of storage: plastic pack vs immersion in a normal solution of sodium chloride. The contralateral bone was assigned to the opposite treatment. Six pairs of metacarpal bones and 5 pairs of metatarsal bones were tested in torsion to failure. No significant difference was found within pairs. All ribs, 5 pairs of metacarpal bones, and 5 pairs of metatarsal bones were loaded in 4-point bending to failure. The energy absorbed at failure and the ultimate displacement of ribs and metacarpal and metatarsal bones were increased by 25 to 30% and 18 to 24%, respectively, when the bones were frozen in isotonic saline solution. Corticocancellous grafts frozen in normal saline solution are biomechanically less fragile and brittle than grafts stored in plastic without saline solution.

The application of computer graphics in foot and ankle surgical planning and reconstruction.

This article presents examples of current technologies in computer graphics as applied to foot and ankle surgery. Presently, there are two areas of great potential in computer graphics: (1) preoperative surgical planning, and (2) computer-aided design and manufacturing of custom implants.

The effect of chicken, pigeon, and turkey demineralized bone matrix (DBM) implanted in ulnar defects fixed with the intramedullary-external skeletal fixator (IM-ESF) tie-in in pigeons (Columba livia): histological evaluations.

Avian demineralized bone matrix (ADBM) powder prepared from chicken, pigeon, and turkey sources induced bone formation via endochondral and intramembranous processes, as in mammalian studies. There were no significant differences in percentage of new bone, percentage of cartilage, surface-forming osteoblast area, or osteoclast count between gaps treated with chicken, pigeon, and turkey DBM. However, there was a significantly (p<0.05) higher percentage of inflammatory area in gaps treated with chicken DBM than in gaps treated with pigeon DBM.

The combined effect of parathyroid hormone and bone graft on implant fixation.

Impaction allograft is an established method of securing initial stability of an implant in arthroplasty. Subsequent bone integration can be prolonged, and the volume of allograft may not be maintained. Intermittent administration of parathyroid hormone has an anabolic effect on bone and may therefore improve integration of an implant. Using a canine implant model we tested the hypothesis that administration of parathyroid hormone may improve osseointegration of implants surrounded by bone graft. In 20 dogs a cylindrical porous-coated titanium alloy implant was inserted into normal cancellous bone in the proximal humerus and surrounded by a circumferential gap of 2.5 mm. Morsellised allograft was impacted around the implant. Half of the animals were given daily injections of human parathyroid hormone (1-34) 5 µg/kg for four weeks and half received control injections. The two groups were compared by mechanical testing and histomorphometry. We observed a significant increase in new bone formation within the bone graft in the parathyroid hormone group. There were no significant differences in the volume of allograft, bone-implant contact or in the mechanical parameters. These findings suggest that parathyroid hormone improves new bone formation in impacted morsellised allograft around an implant and retains the graft volume without significant resorption. Fixation of the implant was neither improved nor compromised at the final follow-up of four weeks.

Patellar prosthesis positioning in total knee arthroplasty. A roentgenographic study.

Patellar prosthesis positioning in 40 primary total knee replacements was evaluated with regard to (1) patellar tilt, (2) angle between the patellar component and patellar bony remnant, (3) lateral versus medial placement, (4) patellar height, and (5) size of the patellar component versus patellar length. Two different designs were evaluated. Twenty knees that were resurfaced with a patellar button prosthesis and implanted with conventional surgical technique constituted Group A. Twenty knees that were resurfaced with a new biconvex prosthesis and implanted with specially designed instrumentation constituted Group B. For Group A, the patellar tilt averaged 4.25 degrees preoperative and 8.35 degrees postoperative. For Group B the patellar tilt averaged 4.60 degrees preoperative and 1.83 degrees postoperative. In Group B, there was significant improvement in patellar position, with only two patients showing values exceeding the neutral range (p = 0.0409). The angle between the patellar component and the bony remnant in Group A averaged 5.975 degrees, and in Group B, 1.447 degrees. Two patients in Group A and 18 patients in Group B had values in the normal range for patellar tilt and the angle between the prosthesis and the bone. The prosthesis was inserted medial to the patellar center in six patients in Group A and one patient in Group B. A significant decrease in patellar height was noted for both groups, but values were still within the normal range. Both groups showed significant increase in the postoperative articular length, indicating that oversized prostheses were inserted and excess bone removed.

Results of nonmetal-backed, high-density polyethylene, biconvex patellar prostheses. A 5-7-year follow-up evaluation.

This study evaluates the clinical and radiographic results of an all-polyethylene, biconvex, dome-shaped patellar prosthesis with precise instrumentation implanted in 53 knees with a minimum follow-up period of 5 years (average, 6.3 years; range, 5.0-7.1 years). The mean patient age was 70.9 years (range, 18.0-89.0 years). The mean Hospital for Special Surgery knee rating score was 63.6 before surgery and 83.4 after surgery. There was no fracture of the patella, no implant failure, or radiographic loosening of the prosthesis. Patellar complications consisted of two dislocations secondary to trauma and one case of patellar subluxation. Several radiographic parameters were measured. Means and SDs were computed for: (1) patellar tilt, as measured from a line between the anterior limits of the femoral condyles and the patella, which showed no significant difference after surgery (3.01 degrees +/- 5.12 degrees) compared to before surgery (3.73 degrees +/- 5.44 degrees); (2) the angle between the patellar component and the residual bone was -0.04 degrees +/- 2.04 degrees, with every case in the normal range (+/- 5 degrees); (3) there was no significant difference between pre- and postoperative patellar length, patellar thickness, or articular length of the patella; (4) the patellar height showed a small but statistically significant difference after surgery (2.69 +/- .64 cm) and before surgery (2.94 +/- .72 cm); (5) the distance from the tibial tubercle to the joint line did not differ significantly between preoperative (2.73 +/- 0.34 cm) and postoperative (3.06 +/- 0.36 cm) measurements; and (6) the distance from the center of the tibial plateau to the center line of the tibial prosthesis was 1.34 +/- 0.32 cm. These results are superior to previously reported series.