J. Russell Parsons

The effects of blood glucose control upon fracture healing in the BB Wistar rat with diabetes mellitus

Several clinical series, analyzing fracture healing in patients with diabetes mellitus (DM), demonstrated significant incidence of delayed union, non‐union, and pseudarthrosis. In this study, analysis was performed to evaluate the effects of blood glucose (BG) control on fracture healing in the DM BB Wistar rat, a rat strain that represents a close homology to Type I DM in man. Our study showed decreased cell proliferation at the fracture site as well as decreased mechanical stiffness and bony content in the poorly controlled DM rats. To determine the effect of BG control, DM rats were treated with insulin sufficient to maintain physiologic BG levels throughout the course of the study. Values of cellular proliferation, biomechanical properties and callus bone content in tightly controlled DM animals were not significantly different from values of non‐DM control values. This study suggests that insulin treatment with resultant improved BG control will ameliorate the impaired early and late parameters of DM fracture healing.

Low-intensity pulsed ultrasound increases the fracture callus strength in diabetic BB Wistar rats but does not affect cellular proliferation

Type I diabetes mellitus (DM) is associated with impaired fracture healing. Specifically, DM affects multiple phases of fracture healing including early cellular proliferation and late phases resulting in inferior biomechanical properties. Recent studies demonstrated the utility of pulsed low‐intensity ultrasound (US) to facilitate fracture healing. The current study evaluated the effects of daily application of US on mid‐diaphyseal femoral fractures in DM and non‐DM BB Wistar rats. Immunohistochemical staining for PCNA was used to evaluate cellular proliferation at 2, 4, and 7 days post‐fracture. In concordance with previous findings, DM fracture callus demonstrated decreased cellular proliferation. Importantly, the application of US did not significantly alter the proliferation in either DM or control groups. However, mechanical testing revealed significantly greater torque to failure and stiffness in US‐treated DM versus non‐US‐treated DM groups at six weeks post‐fracture. Despite the inability of US to affect the early proliferative phase of fracture healing, its application clearly results in improved mechanical properties during the late phases of healing. These findings suggest a potential role of US as an adjunct for DM fracture treatment.

A comparison of the effects of ibuprofen and rofecoxib on rabbit fibula osteotomy healing

Background and purpose Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase (COX) activity, which is the rate-limiting enzyme in the synthesis of prostaglandins. Previous studies have indicated that NSAID therapy, and in particular NSAIDs that specifically target the inflammatory cyclooxygenase (COX-2), impair bone healing. We compared the effects of ibuprofen and rofecoxib on fibula osteotomy healing in rabbits to determine whether nominal, continuous inhibition of COX-2 with rofecoxib would differentially affect fracture healing more than cyclical inhibition of COX-2 using ibuprofen, which inhibits COX-1 and COX-2 and has a short half-life in vivo. Methods Bilateral fibula osteotomies were done in 67 skeletally mature male New Zealand white rabbits. The rabbits were treated with placebo, rofecoxib (12.5 mg once a day), or ibuprofen (50 mg 3 times a day) for 28 days after surgery. Plasma ibuprofen levels were measured by HPLC analysis. Bone healing was assessed by histomorphometry at 3 and 6 weeks after osteotomy, and at 6 and 12 weeks by torsional mechanical testing. Results Plasma ibuprofen levels peaked and declined between successive doses. Fracture callus morphology was abnormal in the rofecoxib-treated rabbits and torsional mechanical testing showed that fracture healing was impaired. Ibuprofen treatment caused persistence of cartilage within the fracture callus and reduced peak torque at 6 weeks after osteotomy as compared to the fibulas from the placebo-treated rabbits. In the specimens allowed to progress to possible healing, non-union was seen in 5 of the 26 fibulas from the rofecoxib-treated animals as compared to 1 of 24 in the placebo group and 1 of 30 in the ibuprofen treatment group. Interpretation Continuous COX-2 inhibition as modeled by rofecoxib treatment appears to be more deleterious to fracture repair than cyclical cyclooxygenase inhibition as modeled by ibuprofen treatment. Ibuprofen treatment appeared to delay bone healing based upon the persistence of cartilage within the fracture callus and diminished shear modulus. Despite the ibuprofen-induced delay, rofecoxib treatment produced worse fracture (osteotomy) healing than ibuprofen treatment.

Biomechanical comparison of fixation devices in experimental scaphoid osteotomies

This study determined the force, bending rigidity, and bending moment at failure of three types of internal fixation systems for the scaphoid bone. A pair of parallel, 0.045-inch Kirschner wires were compared on a paired, bilateral basis with either a Herbert screw or a 3.5 millimeter cannulated screw in repairing a transverse waist osteotomy in cadaver scaphoids. The mean values at failure of the Herbert screw and the cannulated screw versus the paired, parallel Kirschner wires for force (65 N and 77 N versus 23.7 N), rigidity (0.47 Nm2 and 0.54 Nm2 versus 0.16 Nm2) and bending (0.98 Nm and 1.15 Nm versus 0.36 Nm) were approximately three times greater. These differences were statistically significant when compared on a paired basis. This experiment demonstrates that the Herbert screw and cannulated screw are significantly stronger in resisting bending forces than paired, parallel Kirschner wires.

The Biomechanics and Histopathology of Chemically Processed Patellar Tendon Allografts for Anterior Cruciate Ligament Replacement

A study was initiated to examine chemically processed patellar tendon allografts in sheep anterior cruciate liga ment repairs, both mechanically and histologically. One group of animals received frozen, untreated allografts, one group received frozen grafts that were processed with a chloroform-methanol solvent extraction tech nique, and one group received frozen tendons treated with a permeation-enhanced extraction technique. All animals were operated on unilaterally, with the con tralateral knee acting as a normal, intact control. His tologic analysis after 2 months of implantation revealed similar enhanced cellular repopulation in both chemi cally treated ligament allografts compared with the more hypocellular, untreated grafts. At 6 months the chloroform-methanol group demonstrated a more ag gressive chronic cellular response with numerous thick- walled vessels relative to the untreated and permeation- enhanced grafts. Mechanical testing after 6 months of implantation showed statistically similar anterior drawer resistance in all grafted knees, yet the two chemically extracted grafts had significantly less stiffness than un treated anterior cruciate ligament grafts. Both treatment groups also tended to be weaker than the untreated allografts. All anterior cruciate ligament reconstructions showed excessive anterior drawer laxity and, regard less of treatment, had lower strength and less stiffness than normal anterior cruciate ligament tissue at the 6-month period.

Mechanical Properties of Bone in a Paraplegic Rat Model

Pathologic fractures may occur with minimal trauma after spinal cord injury (SCI) because of osteoporosis. Rats were evaluated to determine whether they could be used as an SCI animal model. Male Sprague-Dawley rats underwent spinal cord transection at the ninth thoracic vertebrae. Control rats underwent a sham procedure. Mechanical testing of the humeral shaft, femoral shaft, tibial shaft, femoral neck, distal femur, and proximal tibia was performed separately at 0, 8, and 24 weeks after surgery. At 24 weeks, significant differences between SCI and control rats were found in maximum torque needed to produce failure in the femoral shaft (63 percent of control, p < 0.05) and tibial shaft (63 percent, p < 0.01), and in compressive load to produce failure in cross-sectional specimens of the distal femur (51 percent, p < 0.05) and proximal tibia (50 percent, p < 0.01). No differences were found in the maximum torque needed to produce failure of the humeral shaft (106 percent, p = 0.77) between SCI and control rats. Reductions in relative bone strength in SCI rats at 24 weeks were similar in magnitude to bone mineral density changes reported in humans with chronic paraplegia. Thus, Sprague-Dawley rats appear to be good animal models in which to evaluate changes in bone strength following SCI.

THE POROUS-COATED ANATOMIC (PCA) TOTAL HIP ARTHROPLASTY: A REVIEW OF 73 UNCEMENTED CASES WITH 2-YEAR FOLLOW UP

A total of 73 hips in 62 patients who underwent non-cemented total hip arthroplasties (THA) with porous-coated anatomic (PCA, Howmedica) prostheses have been reviewed. A complete evaluation including preoperative and postoperative Harris hip scores (HHSs), a complete radiographic study, and complication determination has been completed with greater than 2-year follow up. Diagnoses included osteoarthritis (74.0%), rheumatoid arthritis (4.1%), avascular necrosis (15.1%), and posttraumatic arthritis following fracture (6.8%). The complication rate was 10.9% (8 complications/73 arthroplasties); 20 patients (35.6%) received bilateral implants. The mean preoperative HHS for the entire group was 38.7, and the mean postoperative score, irrespective of postoperative time, was 93.6. Key findings regarding the consecutive radiographic review of each arthroplasty included: 9.6% lucencies, 43.8% stress shielding, stable fibrous ingrowth in 74.0%, tip sclerosis in 19.2%, and cortical widening in 4.1%. The finding of loose beads from the pore ingrowth area of the prosthesis was minimal (7 beads in 6 patients). These results demonstrate the efficacy of the PCA prosthesis.

The effects of diabetes mellitus on fracture healing in BB wistar rats

Introduction: Diabetic patients suffer an inherent morbidity associated with a delay in fracture healing. Diabetes Mellitus (DM) in streptozotocin treated rats has been associated with impaired fracture healing. This is documented, at least partly by a decrease in cellular proliferation leading to a reduction in collagen synthesis as well as a decrease in callus breaking strength. These characteristics may be reversible with insulin treatment. The onset of DM in BB Wistar rats is spontaneous and derived from a selective, autoimmune destruction of the pancreatic beta cells. Both genetic and immune factors are associated in the etiology but the precise nature of the disease remains unclear. The BB Wistar rat offers advantages over chemical induction of the disease and currently represents the closest homology to Type I DM in man. If the animal is left without insulin death will result due to ketoacidosis. The BB Wistar rat, therefore, serves as the most clinically relevant DM laboratory animal. The purpose of this study was to establish and validate a reproducible femoral fracture model in DM and non-DM BB Wistar rats. Materials and Methods: Detection and Treatment of DM: The BB Wistar rats arrived as either Diabetic Prone (DP) or Diabetic Resistant (DR). DP rats were checked for glycosuria three times a week beginning at 60 days of age. Once glycosuria was detected, tail blood glucose was tested. If the reading was greater than 250 mg/dL the rat received a palmitic acid, insulin-releasing LINPLANT. DR rats served as a non-DM control. and received a palmitic acid control implant Fracture Model: Fourteen days after the implant was placed, a closed middiaphyseal femoral fracture was created. Immunohistochemistry: Both DM and non-DM rats were sacrificed at 4, 7 and 10 days post fracture to evaluate cellular mitogenic activity in the fracture callus during the early phases of healing. Specimens were fixed, decalcified,embedded in paraffin and sectioned sagitally through the fracture site. The sections were treated with anti-PCNA/clone PC10, for the presence of the antigen (PCNA), a cellular proliferation marker. Eight specific locations within the fracture callus were analyzed. Positively stained cells were counted at each location under 40X and averaged for each animal. Additional sections were stained with Mallory’s Trichrome to verify the histology of the soft and hard callus. Microscopy: DM and non-DM rats were sacrificed at 4, 6 and 8 weeks post operatively for evaluation of the later phases of healing. Scanning acoustic microscopy (SAM) operates at ultrasonic frequencies and is capable of generating pseudo-color images representing reflected acoustic impedance. These values indicate micromechanical properties. Specimens were fixed, embedded in h(PMMA) and sectioned sagitally through the fracture site. They were scanned to determine the stiffness quality of hard and soft callus. Once scanned, sections were ground and polished and stained with Stevenels Blue and Van Gieson Picro-fuchsin for histologic analysis. Statistical Analysis: Overall proliferation and acoustic impedance were analyzed by two-way repeated measures ANOVA with Fishers P-LSD post-hoc test. Soft and hard callus proliferation and acoustic impedance were analyzed separately by two-way ANOVA with a means contrast used to compare each callus type at different time periods. Results: General Health: Blood glucose levels in non-DM animals remained within physiologic range at an average value of 90.01±16.06 mg/dL. DM animals exhibited polyuria and glycosuria throughout the duration of the study. These animals gained weight and did not develop ketonuria. Average blood glucose levels for the DM rats remained above physiologic at a value of 381.99±65.64 mg/dL. Immunohistochemistry: At four days, the fracture site of both DM and non-DM animals consisted of mainly undifferentiated mesenchymal cells in the periosteum, a large portion of which were stained positive for PCNA. There was a significant decrease in the number of PCNA positive cells in DM vs non-DM callus (70.43±10.33 vs 90.91±7.67, p=0.01). There existed some new bone matrix located between the proliferating periosteal cells and the underlying cortex in both DM and non-DM callus. This region is referred to as the hard callus. At 7 days, substantial amounts of intramembranous bone had formed and cell proliferation in the hard callus had decreased in both DM and non-DM callus but remained higher still in the nonDM (23.94±7.54 vs 62.10±16.65, p=0.0001). Directly adjacent to the fracture site, there appeared fibrous tissue with large areas of a cartilaginous matrix. The amount of cartilage in this region was decreased in the DM rats as well as the distribution of proliferating cells (18.44±6.94 vs 71.50±27.48, p=0.0002) as compared to non-DM controls. At day 10, the number of proliferating cells in the hard callus was further reduced in both groups, but remained significantly lower in the DM animals (16.13±6.20 vs 38.44±10.92, p=0.007). Cartilage in the soft callus of non-DM animals almost completely replaced fibrous tissue, and contained larger areas of hypertrophic chondrocytes in a more organized columnar fashion. In the DM animals, areas of cartilage were smaller and the size and number of proliferating chondrocytes was greatly reduced (16.00±5.12 vs 46.94±3.92, p=0.01 see Figure 1) .