Pathophysiology of aniridia-associated keratopathy: Developmental aspects and unanswered questions

Aniridia, a rare congenital disease, is often characterized by a progressive, pronounced limbal insufficiency and ocular surface pathology termed aniridia-associated keratopathy (AAK). Due to the characteristics of AAK and its bilateral nature, clinical management is challenging and complicated by the multiple coexisting ocular and systemic morbidities in aniridia. Although it is primarily assumed that AAK originates from a congenital limbal stem cell deficiency, in recent years AAK and its pathogenesis has been questioned in the light of new evidence and a refined understanding of ocular development and the biology of limbal stem cells (LSCs) and their niche. Here, by consolidating and comparing the latest clinical and preclinical evidence, we discuss key unanswered questions regarding ocular developmental aspects crucial to AAK. We also highlight hypotheses on the potential role of LSCs and the ocular surface microenvironment in AAK. The insights thus gained lead to a greater appreciation for the role of developmental and cellular processes in the emergence of AAK. They also highlight areas for future research to enable a deeper understanding of aniridia, and thereby the potential to develop new treatments for this rare but blinding ocular surface disease.

An attempt to optimize the outcome of penetrating keratoplasty in congenital aniridia-associated keratopathy (AAK)

Purpose

To propose an optimized microsurgical and medical approach to reduce the risk of complications after penetrating keratoplasty (PKP) in patients with aniridia-associated keratopathy (AAK).

Methods

Retrospective observational case series of 25 PKP performed in 16 patients with AAK. Preoperative indications were endothelial decompensation and vascularized scars (68%) or graft failure (32%) due to limbal stem cell deficiency. The optimized approach included a combination of a small corneal graft size (around 7.0 mm), interrupted 10–0nylon sutures, simultaneous AMT as a patch, large bandage contact lens, temporary lateral tarsorrhaphy, postoperative autologous serum eye drops, and systemic immunosuppression. Main outcome measures included: visual acuity, transplant survival, and complications encountered during follow-up of 107 weeks on average.

Results

A complete modified keratoplasty scheme was used in 10 of 25 PKP (group 1), while at least one of the modifications was missing in the other 15 PKP (group 2). After 8 weeks of follow-up, the epithelium was closed in 23 eyes. Visual acuity improved in 19 eyes at 6 months of follow-up, and remained stable in six eyes. None of the eyes showed a decrease in visual acuity. At the last post-operative follow-up, this visual improvement persisted in 14 eyes and graft survival rate after 156 weeks (3 years) was 69% in group 1 versus 44% in group 2 (p = 0.39, log-rank test). Secondary corneal neovascularization (8%), scarring (4%), ulcer (4%), or graft rejection (8%) happened mostly in the second group which was missing at least one of the suggested modifications.

Conclusions

PKP in congenital aniridia must be considered as a high-risk keratoplasty. An optimized therapeutic approach seems to be promising in order to reduce the postoperative complication rate in these most difficult eyes.

Does coating an intramedullary nail with polymethylmethacrylate improve mechanical stability at the fracture site?

BACKGROUND

Treatment of tibia diaphyseal fractures with intramedullary nail fixation has proven to be effective. An increasingly popular practice is to coat the nail with bone cement incorporating antibiotics for the purpose of treating and/or preventing infection. To date, the effect of coating on the mechanical performance of the intramedullary nail once implanted is unknown. We hypothesize that cement coating does not change the cross-sectional stiffness of the nail, so that, when fixing tibia diaphyseal fracture with gapping, cement coated intramedullary nail provide stiffness comparable to that of standard conventional uncoated ones.

METHODS

Tests of 4-point bending were conducted to compare the cross-sectional stiffness of uncoated to coated nails. In addition, mechanical tests of compression and torsion on tibia bone phantoms instrumented with coated and uncoated nails were performed, and the proximal-to-distal bone fragment rotations were compared.

FINDINGS

The 4-point bending tests indicated that the cross-sectional stiffness of coated nails was not significantly different from that of the uncoated ones (p-value >0.05). Mechanical tests of compression and torsion corroborated these results by showing no statistical difference in the proximal-to-distal bone rotations attained with uncoated nails when compared to those measured for the coated ones (p-value >0.05).

INTERPRETATION

Cement coating on the nail cannot be relied upon for increased mechanical stiffness of the implant, and should be solely considered as a vehicle for topic delivery of antibiotics.

A novel way to dynamize a spatial frame and optimize fracture healing

BACKGROUND

Fracture site motion creates mechanical strains on the healing tissues which influences bone formation. Axial micro-motion maximizes dilatational strains, whereas shearing motions maximize deviatoric strains on the healing tissues. Dilatational strains optimize bone healing, deviatoric strains retard bone healing. Dynamization of external fixation using either an Ilizarov or Spatial Frame platform is used to increase loading on the limb which increases the mechanical stress and strain on the tissues to improve healing. The scientific literature does not address how dynamization of the spatial frame effects fracture site motion. The purpose of this study is to assess the effect of modified shoulder bolts incorporated into a spatial frame during dynamic loading.

METHODS

Five identical two-ring spatial frame constructed were mounted on Sawbones tibias with an osteotomy performed distal to the tibial tubercle. Sinusoidal load was applied at a rate of 0.25 Hz. Axial force and displacement, in addition to motion of the proximal and distal tibia segments were recorded. Eight constructs were tested: 1) All struts of the Spatial Frame rigid, 2) Strut #1 loose, 3) Struts #1 and #3 loose, 4) Struts #1, #3 and #5 loose, 5) All struts loose, 6) All struts rigid with dynamization bolts on the proximal end, 7) All struts rigid with dynamization bolts on alternating sides, 8) Threaded rods between the rings with two millimeters of dynamization.

RESULTS

No difference in vertical displacement was observed between the Ilizarov and all struts locked. No significant difference in shear values between all struts locked and modified shoulder bolt struts was observed. Increase in vertical movement with the modified shoulder bolts was an average of 1.83 mm. Significant shear forces at the fracture site were observed with unlocking single or multiple struts of the spatial frame.

CONCLUSION

Modified shoulder bolts can be used for spatial frame dynamization without increasing shear motion.

Mechanical performance and implications on bone healing of different screw configurations for plate fixation of diaphyseal tibia fractures: a computational study

Diaphyseal tibia fractures may require plate fixation for proper healing to occur. Currently, there is no consensus on the number of screws required for proper fixation or the optimal placement of the screws within the plate. Mechanical stability of the construct is a leading criterion for choosing plate and screws configuration. However, number and location of screws have implications on the mechanical environment at the fracture site and, consequently, on bone healing response: The interfragmentary motion attained with a specific plate and screw construct may elicit mechano-transduction signals influencing cell-type differentiation, which in turn affects how well the fracture heals. This study investigated how different screw configurations affect mechanical performance of a tibia plate fixation construct. Three configurations of an eight-hole plate were considered with the fracture in the center of the plate: eight screws-screws at first, fourth, fifth and eighth hole and screws at first, third, sixth and eighth hole. Constructs' stiffness was compared through biomechanical tests on bone surrogates. A finite element model of tibia diaphyseal fracture was used to conduct a stress analysis on the implanted hardware. Finally, the potential for bone regeneration of each screw configuration was assessed via the computational model through the evaluation of the magnitude of mechano-transduction signals at the bone callus. The results of this study indicate that having screws at fourth and fifth holes represents a preferable configuration since it provides mechanical properties similar to those attained by the stiffest construct (eight screws), and elicits an ideal bone regenerative response.

Abnormal neovascular and proliferative conjunctival phenotype in limbal stem cell deficiency is associated with altered microRNA and gene expression modulated by PAX6 mutational status in congenital aniridia

PURPOSE

To evaluate conjunctival cell microRNA (miRNAs) and mRNA expression in relation to observed phenotype of progressive limbal stem cell deficiency in a cohort of subjects with congenital aniridia with known genetic status.

METHODS

Using impression cytology, bulbar conjunctival cells were sampled from 20 subjects with congenital aniridia and 20 age and sex-matched healthy control subjects. RNA was extracted and miRNA and mRNA analyses were performed using microarrays. Results were related to severity of keratopathy and genetic cause of aniridia.

RESULTS

Of 2549 miRNAs, 21 were differentially expressed in aniridia relative to controls (fold change ≤ -1.5 or ≥ +1.5). Among these miR-204-5p, an inhibitor of corneal neovascularization, was downregulated 26.8-fold in severely vascularized corneas. At the mRNA level, 539 transcripts were differentially expressed (fold change ≤ -2 or ≥ +2), among these FOSB and FOS were upregulated 17.5 and 9.7-fold respectively, and JUN by 2.9-fold, all being components of the AP-1 transcription factor complex. Pathway analysis revealed enrichment of PI3K-Akt, MAPK, and Ras signaling pathways in aniridia. For several miRNAs and transcripts regulating retinoic acid metabolism, expression levels correlated with keratopathy severity and genetic status.

CONCLUSION

Strong dysregulation of key factors at the miRNA and mRNA level suggests that the conjunctiva in aniridia is abnormally maintained in a pro-angiogenic and proliferative state, and these changes are expressed in a PAX6 mutation-dependent manner. Additionally, retinoic acid metabolism is disrupted in severe, but not mild forms of the limbal stem cell deficiency in aniridia.

Is it necessary to tie the medial row in rotator cuff repair double-row constructs when using suture tape?

PURPOSE

To evaluate the selected biomechanical differences of a double-row trans-osseous equivalent rotator cuff repair with a knotless versus knot-tying medial row using suture tape in regard to repair displacement, stiffness, and ultimate load to failure.

METHODS

In 16 fresh-frozen human shoulders (8 matched pairs), double-row rotator cuff repairs were performed with medial-row mattress knots (MK) on one side, the other without (NK). Two DVRT (Differential Variable Reluctance Transducer) sensors were attached between the humerus and 3 mm above the repair site and were used to measure the displacement across the repair during cycling. The biomechanical parameters measured were repair displacement, stiffness, and ultimate load to failure. The supraspinatus was loaded in a similar fashion to previously described protocol using cyclic loading and load to failure testing.¹.

RESULTS

All data from paired specimens were compared using paired Student t tests. No statistically significant difference (SSD) in displacement across the repair over the 200 cycles of the test was noted between the two groups (MK = 0.591 ± 0.501 mm; NK = 0.439 ± 0.417 mm, p = 0.618). No SSD in stiffness was noted between the two groups (MK = 32.87 ± 6.31 N/mm; NK = 27.98 ± 9.69 N/mm, p = 0.120). No SSD in ultimate load to failure was noted between the two groups (MK = 501.2 ± 126.1 N; NK = 416.8 ± 120.0 N, p = 0.116).

CONCLUSION

There was no statistically significant different between knotless versus knotted medial row double row rotator cuff repair constructs using suture tape in regard to displacement across the repair site, stiffness and ultimate load to failure. Despite previous evidence suggesting inferiority of knotless medial row technique using suture constructs, this evidence may support the biomechanical equivalency of knotless medial row technique using suture tape.

Relationships Among Bone Morphological Parameters and Mechanical Properties of Cadaveric Human Vertebral Cancellous Bone

Mechanical properties and morphological features of the vertebral cancellous bone are related to resistance to fracture and capability of withstanding surgical treatments. In particular, vertebral strength is related to its elastic properties, whereas the ease of fluid motion, related to the success of incorporation orthopedic materials (eg, bone cement), is regulated by the hydraulic permeability (K). It has been shown that both elastic modulus and permeability of a material are affected by its morphology. The objective of this study was to establish relations between local values of K and the aggregate modulus (H), and parameters descriptive of the bone morphology. We hypothesized that multivariate statistical models, by including the contribution of several morphology parameters at once, would provide a strong correlation with K and H of the vertebral cancellous bone. Hence, μCT scans of human lumbar vertebra were used to determine a set of bone morphology descriptors. Subsequently, indentation tests on the bone samples were conducted to determine local values of K and H. Finally, a multivariate approach supported by principal component analysis was adopted to develop predictive statistical models of bone permeability and aggregate modulus as a function of bone morphology descriptors. It was found that linear combinations of bone volume fraction, trabecular thickness, trabecular spacing, structure model index, connectivity density, and degree of anisotropy provide a strong correlation (R 2 ~ 76%) with K and a weaker correlation (R 2 ~ 47%) with H. The results of this study can be exploited in computational mechanics frameworks for investigating the potential mechanical behavior of human vertebra and to develop strategies to treat or prevent pathological conditions such as osteoporosis, age-related bone loss, and vertebral compression fractures. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Diagnosis of Traumatic Ankle Arthrotomies Using Saline Load Tests, Methylene Blue, and Radiopaque Tracer: A Cadaveric Study

Background:

The objective of this study was to define the volume (mLs) needed for a positive saline load challenge test in anterolateral (AL), anteromedial (AM), posterolateral (PL), or posteromedial (PM) ankle arthrotomy wounds using normal saline (NS) and methylene blue (MB). Another objective was to evaluate the use of fluoroscopy and iodinated contrast in the diagnosis of ankle arthrotomies.

Methods:

Four cadaveric ankle specimens underwent standardized arthrotomy creation in either the AL, AM, PL, or PM portion of each specimen. An 18-gauge needle was used to inject fluid into each ankle, and the volumes needed for positive fluid challenges were recorded. All 4 ankles were tested 10 times (n = 40) with NS and 10 times using MB (n = 40). A fifth cadaveric ankle was injected with radiopaque contrast solution, and an arthrotomy was simulated and imaged with fluoroscopy.Statistical analyses compared the volumes of NS and MB needed for a positive test. In addition, the 25th, 50th, 75th, 90th, and 95th percentiles of volumes needed for a positive test was calculated.

Results:

The volume of fluid necessary to detect 25%, 50%, 75%, 90%, and 95% of ankle arthrotomies from any site was 2.0 mL, 4.5 mL, 9.0 mL, 10 mL, and 10 mL, respectively. Anterior arthrotomies required less fluid (2.1 mL ± 0.5) than posterior arthrotomies (9.0 mL ± 1.2) for a positive test (P < .0001). There was no difference between the amount of NS (5.5 mL ± 3.6) vs MB (5.6 mL ± 3.7) needed for a positive challenge test (P = .739).

Conclusion:

Ninety-five percent of ankle arthrotomies could be diagnosed with 10 mL of injected fluid; there was no difference between the volume of NS vs MB needed. Fluoroscopy assisted with needle placement and can be combined with radiopaque contrast solution to diagnose ankle arthrotomies.

Clinical Relevance:

The findings of this study may improve sensitivity and efficiency in the diagnosis of traumatic ankle arthrotomies, for which there is currently a paucity of literature.

Cerclage Cable Tensioning of Intraoperative Hip Arthroplasty Proximal Femoral Fractures: A Cadaveric Model

Cerclage fixation following intraoperative fracture of the proximal femur during total hip arthroplasty (THA) carries a risk of compromising the femoral blood supply. Thus, we sought to determine the minimum cerclage cable tension required to restore the stability of a cementless femoral stem. Cementless femoral prostheses were implanted in seven proximal femoral cadaver specimens, and a periprosthetic fracture was simulated in the medial cortex. A single cerclage cable was placed just above the lesser trochanter and tensioned and tested at increasing intervals. The implant's torsional stability was determined in the intact bone, prior to fixation, and at each level of cable tension. We found that a single cerclage cable placed above the lesser trochanter can significantly improve, but not fully restore, torsional stability following intraoperative periprosthetic femur fracture during THA. The optimal position for a single cerclage cable appears to be above the lesser trochanter. (Journal of Surgical Orthopaedic Advances 29(4):209-211, 2020).

Filling Open Screw Holes in the Area of Metaphyseal Comminution Does Not Affect Fatigue Life of the Synthes Variable Angle Distal Femoral Locking Plate in the AO/OTA 33-A3 Fracture Model

INTRODUCTION

The aim of this study is to evaluate the biomechanical effect of filling locking variable angle (VA) screw holes at the area of metaphyseal fracture comminution in a Sawbones® (Sawbones USA, Vashon, Washington) model (AO/OTA 33A-3 fracture) using a Synthes VA locking compression plate (LCP) (Depuy Synthes, Warsaw, Indiana).

MATERIALS AND METHODS

Seven Sawbones® femur models had a Synthes VA-LCP placed as indicated by the manufacturers technique. A 4cm osteotomy was then created to simulate an AO/OTA 33-A3 femoral fracture pattern with metaphyseal comminution. The control group consisted of four constructs in which the open screw holes at the area of comminution were left unfilled; the experimental group consisted of three constructs in which the VA screw holes were filled with locking screws. One of the control constructs was statically loaded to failure at a rate of 5mm/min. A value equal to 75% of the ultimate load to failure was used as the loading force for fatigue testing of 250,000 cycles at 3Hz. Cycles to failure was recorded for each construct and averages were compared between groups.

RESULTS

The average number of cycles to failure in the control and experimental groups were 37524±8187 and 43304±23835, respectively (p=0.72). No significant difference was observed with respect to cycles to failure or mechanism of failure between groups. In all constructs in both the control and experimental groups, plate failure reproducibly occurred with cracks through the variable angle holes in the area of bridged comminution.

CONCLUSIONS

The Synthes VA-LCP in a simulated AO/OTA 33-A3 comminuted metaphyseal femoral fracture fails in a reproducible manner at the area of comminution through the "honeycomb" VA screw holes. Filling open VA screw holes at the site of comminution with locking screws does not increase fatigue life of the Synthes VA-LCP in a simulated AO/OTA 33-A3 distal femoral fracture. Further studies are necessary to determine whether use of this particular plate is contraindicated when bridging distal femoral fractures with metaphyseal comminution.

Biomechanical evaluation of periprosthetic refractures following distal femur locking plate fixation

INTRODUCTION

Distal femur fractures proximal to total knee femoral component constitutes the most prevalent type of periprosthetic fracture, and plate fixation treatment is associated with a 7.7% incidence of refracture proximal to the plate. The primary objective of this study was to compare proximal fixation techniques of a periprosthetic distal femur fracture plate in an osteoporotic bone model. The secondary objective was to determine the subsequent periprosthetic plate fracture pattern and/or complexity associated with each proximal plate fixation configuration.

MATERIALS AND METHODS

A segmental defect was created in 21 synthetic osteoporotic adult femurs 6 cm proximal to the distal femur and all specimens were stabilised with a 246 mm locking femur plate. Fixation in the most proximal hole was varied by use of either a cerclage cable, unicortical locking screw, or a bicortical locking screw. Specimens were tested to failure in simultaneous eccentric compression and torsion.

RESULTS

Proximal cerclage fixation demonstrated higher mean maximum axial force at failure (4142.67±178.71 N, p<0.001), stiffness (443.8±61.64 N/mm), and maximum torque (20.9±0.93 N m, p<0.001). Unicortical and bicortical screw refractures occurred at the screw, cerclage wire refractures occurred at the first proximal screw distal to the cerclage.

CONCLUSIONS

In periprosthetic distal femur fracture locking plate fixation, proximal hole stabilization with a cerclage wire tolerates significantly higher failure forces while distributing forces distal to the area within the plate fixation. Cerclage wiring may be an option in distal femur periprosthetic fractures to alleviate stress risers in vulnerable bone.

Enhancing clinical skill development through an Ambulatory Medicine Teaching Programme: an evaluation study

BACKGROUND

Teaching of clinical skills traditionally takes place in hospital wards and outpatient settings. However high acuity and short hospital stays means there are fewer suitable inpatients available for teaching; and time pressures limit students' involvement in other settings. The Ambulatory Medicine Programme was established to develop undergraduate medical students' clinical skills by providing increased exposure to patients with a wide range of chronic medical conditions, in a dedicated learning environment.

METHOD

A mixed qualitative/quantitative approach was used to evaluate the Programme. This research focuses on staff and student perspectives of teaching and learning in Ambulatory Medicine compared with inpatient and outpatient settings; identifies which teaching methods are considered most effective; and determines the transferability of learning. Patients' perspectives of being involved in student teaching are also reported.

RESULTS

Results show that the programme has made a positive impact on students' development of clinical skills, which are transferable to the clinical setting. Patients enjoy being involved and find it personally satisfying.

CONCLUSIONS

The Ambulatory Medicine Programme is an effective way of developing medical students' clinical skills by providing focussed teaching with real patients in a dedicated learning environment.

Adjacent-level biomechanics after single versus multilevel cervical spine fusion

OBJECT

Previous studies have demonstrated that patients with spinal fusion are at greater risk for adjacent-segment disease and require additional surgery. It has been postulated that excessive motion of a given motion segment unit (MSU) leads to an increased risk of disc degeneration. It is the authors' hypothesis that a greater increase in adjacent-segment motion will be observed following a 2-level versus a single-level anterior cervical discectomy and instrumented fusion (ACDF). Therefore, they undertook this study to determine the effect of single-level versus 2-level ACDF on the biomechanics of adjacent MSUs.

METHODS

Ten fresh-frozen human cervical spines were used in this study. The specimens were potted at C-4 and T-1 and tested in flexion and extension. Range of motion (ROM) was 30° of flexion and 15° of extension at a maximum load of 50 N. The specimens were tested intact and then were randomized into 2 groups of 5 specimens each. Group 1 underwent a single-level ACDF at the C5-6 level first, and Group 2 underwent the procedure at the C6-7 level. After testing, both groups had the fusion extended to include the C5-7 levels, and the testing was repeated. Changes in overall ROM, stiffness, and segmental motion were calculated and statistically analyzed using a paired Student t-test.

RESULTS

An increase in sagittal ROM of 31.30% above (p = 0.012) and 33.88% below (p = 0.066) the fused MSU was found comparing a 2-level with a 1-level ACDF. The overall stiffness of the entire spinal construct increased 37.34% (p = 0.051) in extension and 30.59% (p = 0.013) in flexion as the second fusion level was added. As expected, the overall sagittal ROM of the entire spinal construct decreased by 13.68% (p = 0.0014) with a 2-level compared with a 1-level fusion.

CONCLUSIONS

This study has shown that the biomechanics at adjacent levels to a cervical spine fusion are altered and that there is increased adjacent-segment motion at the levels above and below, after a 2-level compared with a 1-level ACDF.

Patterns of genetic architecture for life-history traits and molecular markers in a subdivided species

Understanding the utility and limitations of molecular markers for predicting the evolutionary potential of natural populations is important for both evolutionary and conservation genetics. To address this issue, the distribution of genetic variation for quantitative traits and molecular markers is estimated within and among 14 permanent lake populations of Daphnia pulicaria representing two regional groups from Oregon. Estimates of population subdivision for molecular and quantitative traits are concordant, with QST generally exceeding GST. There is no evidence that microsatellites loci are less informative about subdivision for quantitative traits than are allozyme loci. Character-specific comparison of QST and GST support divergent selection pressures among populations for the majority of life-history traits in both coast and mountain regions. The level of within-population variation for molecular markers is uninformative as to the genetic variation maintained for quantitative traits. In D. pulicaria, regional differences in the frequency of sex may contribute to variation in the maintenance of expressed within-population quantitative-genetic variation without substantially impacting diversity at the genic level. These data are compared to an identical dataset for 17 populations of the temporary-pond species, D. pulex.

Alveolar bone turnover and tooth movement in male rats after removal of orthodontic appliances

The purpose of this study was to acquire tooth movement, histomorphometric and biochemical data on oral tissues that had previously been loaded with calibrated orthodontic forces. One hundred and forty-four male Sprague-Dawley rats were randomly divided into two groups: Group I, orthodontic appliances placed for 16 days to mesially move maxillary first molars with an initial force of 40 gm, and group II, sham orthodontic treatment. Seven to twelve rats were killed at each of six times after removal of appliance. Tooth movement was measured cephalometrically, alveolar bone turnover by histomorphometry, and tissue phosphatase levels biochemically. Treated molars moved distally more rapidly than the shams (13.9 vs 5.0 microns/day). The appliance removal group had a persistent 10-fold elevation in root resorption on the mesial (p < 0.0001), as well as early elevations in osteoclasts on the mesial and osteoblasts on the distal (p < 0.001) that returned to control by 3 to 5 days. Acid, alkaline phosphatase, and tartrate-resistant acid phosphatase (TRAP) remained elevated in the tissues until 10 days (p < 0.0001). Changes in the dynamic measures of bone formation were characterized by low rates at days 1 and 3 (p < 0.01), elevating thereafter on the mesial and the converse on the distal. Orthodontic tooth movement relapses, and bone remodeling continues for several days after removal of appliance consistent with the direction of loading, orthodontic treatment stimulates root resorption at sites that were loaded in pressure without detectable recovery, and root resorption does not increase at the tension sites.

Alveolar bone turnover in male rats: site- and age-specific changes

BACKGROUND

This study compares alveolar bone turnover adjacent to distally drifting maxillary first molar teeth of rapidly and slowly growing rats.

METHODS

Two groups of forty male rats (1 and 3 months) were sacrificed. Sera were analyzed for acid (AcP), alkaline (AlkP), and tartrate-resistant acid phosphatase (TRAP). Bone histomophometry was done on parasagittal sections of maxillary molars. Molar drift was quantified cephalometrically.

RESULTS

Distal surface contained more osteoclasts and higher osteoclast percents than mesials at both ages (P < 0.001). There were also more osteoclasts on the distals of the older rats as compared to the young (P < 0.001). Osteoblast percents were higher (P < 0.001) in the older rats on both surfaces. Mesials had higher double-labeled surface, MAR and BFR than distals in the younger rats (P < 0.001). The younger rats had higher (P < 0.001) AlkP, AcP, and TRAP. There were no age-specific differences in rate of molar drift. A model of rate of molar drift (P < 0.0015) containing bone formation measures accounts for 54.9% of the variability.

CONCLUSIONS

We conclude that the bone turnover dynamics adjacent to maxillary first molars represent predominantly remodeling on the distal in both groups and modeling on the mesial only in the young rats, that distal molar tooth drift reflects alveolar bone turnover, and that alveolar bone manifests the marked reduction in bone cell activity that occurs in the rat skeleton after 8 weeks but that this reduction is compensated by recruitment or maintenance of more bone cells at these sites.

Mechanical failures of intramedullary tibial nails applied without reaming

The clinical mechanical failures of small diameter intramedullary interlocking nails were evaluated to determine the relationship of failure modes to the type or location of tibial fractures. Methods were developed to duplicate failure modes in vitro in standardized tests to simulate the clinical situations. Where standard test methods were inadequate, new methods were developed to provide quantifiable, reliable methods of evaluating potential clinical performance. The modes and rates of mechanical failure in the clinical series were consistent among participating centers: (1) In diaphyseal fractures with secondary trauma, the intramedullary nail bent at the fracture site where the working length was unsupported; (2) failures that occurred several weeks after nailing were the result of fatigue fractures of the locking screws, usually at the distal end; and (3) nail and screw failures occurred most commonly in proximal and distal tibial fractures. The strength of the 8- and 9-mm sizes of Synthes and Russell-Taylor nails were comparable.

Distribution of bone mineral density and bone strength of the proximal humerus

Clinical experience led us to the hypothesis that in the proximal humerus cancellous bone beneath the top part of the head is the strongest and the bone of the humeral neck is the weakest. This hypothesis was examined on dissected proximal humeri with bone mineral densitometry and an indention test. Both dual photon absorptiometry and bone mineral analyses confirmed that the top part of the humeral head was the region with the greatest amount of bone mineral. The humeral neck had approximately one half the bone mineral density of the humeral head. The cancellous bone of the neck had only one third the mechanical strength of the humeral head on the indention test. The high degree of osteoporosis of the neck region increases the difficulty of surgical treatment for displaced humeral neck fractures.

An absence of structural changes in the proximal femur with osteoporosis

The hypothesis that osteoporosis occurs not as a preferential loss of the tensile trabeculae but as a general loss of bone was tested by using bone mineral densitometry and an indentation test on dissected proximal femora. As osteoporosis advanced a significantly correlated decrease was found in both bone mineral density and mechanical properties between the principal compressive and tensile trabeculae. The decrease correlated with a decrease in the Singh index. These findings led to the conclusion that a sequential bone loss from the tensile trabeculae to the compressive ones did not occur as Singh reported, but instead a generalized loss of bone mineral in both the tensile and compressive trabeculae supervened. The structural changes, on which the grading system by Singh was based, were not observed in the proximal femur affected by osteoporosis.

Comparison of patellar resurfacing versus nonresurfacing in bilateral total knee arthroplasty

Twenty-five patients who received bilateral total knee prostheses were studied to evaluate the advantages and disadvantages of patellar resurfacing. Only patients with advanced patellofemoral disease were included in the study. In all patients, patellar resurfacing had been done in the right knee but not in the left knee. The DePuy porous-coated implant was used in all cases. Subjective criteria were compared with objective criteria, which included range of motion, knee flexion and extension, and roentgenographic evaluation. The findings in this study suggest that patellar resurfacing can offer the patient a superior knee with regard to pain relief and strength.

Femoral neck fractures. A biomechanical study of a new form of internal fixation using multiple telescoping variable length compression screws

Biomechanical tests of a new method of fixation for intracapsular hip fractures compared with other types of mechanical fixation were investigated under one specific loading condition. Human femora fixed in formalin were classified by the Singh index for degree of osteoporosis. Specimens of Grade III or less were grouped as osteoporotic, and Grade IV or greater, normal. Both normal and osteoporotic bones were tested. A transverse osteotomy in the subcapital region was fixed by one of two techniques: (1) Asnis screws (AS) or (2) variable length telescoping compression screws (VLCS). Each specimen was roentgenographed after fixation to assess the placement of the devices and reduction. Each femur was held in an angle vise that was placed on rollers on a table mounted on the servohydraulic testing machine. Compression was applied at a constant displacement rate of 10 mm per second to failure. Load and displacement were monitored; specimens were photographed and roentgenographed after failure. In osteoporotic bone, the VLCS provided yield and ultimate load values several times greater than those of the AS. Resistance to combined compression varus loading was significantly higher with the experimental system in osteoporotic bone. In normal bone there was no significant difference between the two systems.

Computed tomography evaluation of stability in posterior fracture dislocation of the hip

Measurements of the percentage of remaining posterior acetabulum on computed tomography (CT) scan (the Acetabular Fracture Index) in posterior fracture dislocations of the hip were evaluated to determine the stability of the joint. All hips with less than 34% of the remaining posterior acetabulum were unstable. Hips with greater than 55% were stable. Between these values, hips were either stable or unstable. A statistical analysis demonstrated highly significant differences in the average remaining posterior acetabulum between the stable and unstable group. These findings were based on a review of 26 patients with posterior fracture dislocations of the hip (Epstein Type I-IV injuries) combined with CT scan analysis. The clinical status of hip stability was correlated with the Acetabular Fracture Index, and this provided the basis for the study. A simple linear measurement of the remaining posterior acetabulum on CT (the Approximate Acetabular Fracture Index) can be done easily by a physician, and this closely approximates the true remaining acetabular arc. Seven of ten unstable hips in 31 Epstein Type I-V patients showed femoral head subluxation of 0.5 mm or more on CT scan, whereas none of the 21 stable hips had demonstrable subluxation. Risk analysis provided a means of predicting hip stability for individual patients.

Biomechanical and biochemical properties of dog cartilage in experimentally induced osteoarthritis

The finding of other investigators that increased water content is often associated with signs of a torn collagen network in human osteoarthritic (OA) cartilage led to this study. In the Pond-Nuki model of post-traumatic OA experimental but not control femoral condylar cartilage showed evidence of breakdown and stiffening of collagen network as assessed by measurement of swelling properties and indentation behaviour respectively. These changes in the unstable knees occurred despite lack of erosion of that surface cartilage ascertained from carbon black mapping and history. The stiffening rather than softening change was therefore attributed to cartilage oedema of the middle and deep certilagenous zones, wherein breakdown of collagen network has been postulated to occur. Because of insignificant reduction of total hexuronate in these cartilages, a proteoglycan (PG) profile of sedimentation coefficients for aggregate (PGA) and subunit species (PGS) was analysed to see if collagen network changes in the dog preceded PG alteration. Despite minimal histological changes our results confirmed previous findings in the tibial plateau cartilage in this model, that PGA was reduced in size and PGS increased in amount. Slight enzymatic breakdown of PGs, or altered synthesis due to cellular responses to either the injury directly or to synovial inflammation, seems necessary to explain such changes in the absence of cartilage erosion.

Miami TLSO in the management of scoliosis: preliminary results in 100 cases

A custom fabricated polypropylene thoraco-lumbo-sacral orthosis (TLSO) for the treatment of scoliotic curves with an apical vertebrae of T7 or below is described, and the results in 100 patients treated over a 5 year period are reported. The average follow-up for all cases was 13 months, the longest being 59 months. Average initial correction in brace for thoracic curves was 36%, for thoraco-lumbar curves 56%, and for lumbar curves 63%. Double major curves averaged 38% initial correction for the upper curves and 37% for the lower curves. Twenty cases had completed brace treatment with an average follow-up of 8 months out of brace. Of the 30 curves in the 20 patients, 11 were improved more than 5 degrees, 19 remained unchanged (+5 degrees), and none had progressed more than 5 degrees. Twenty-three percent of the patients required a second orthosis and complications occurred in only two patients. The primary advantages of this TLSO include improved cosmesis, minimal discomfort, excellent provision for heat exchange, minimal confinement of the thoracic cage, and maximum retention of spinal mobility.