Inadvertent screw stripping during ankle fracture fixation in elderly bone.

Poor screw purchase because of osteoporosis presents difficulties in ankle fracture fixation. The aim of our study was to determine if cortical thickness, unicortical versus bicortical purchase, and bone mineral density are predictors of inadvertent screw stripping and overtightening. Ten paired cadaver ankles (average donor age, 81.7 years; range, 50-97 years) were used for the study. Computed tomography scanning with phantoms of known density was used to determine the bone density along the distal fibula. A standard small-fragment, 7-hole, one-third tubular plate was applied to the lateral surface of the fibula, with 3 proximal bicortical cortical screws and 2 distal unicortical cancellous screws. A posterior plate, in which all 5 screws were cortical and achieved bicortical purchase, was subsequently applied to the same bones and positioned so that the screw holes did not overlap. A torque sensor was used to measure the torque of each screw during insertion (Ti) and then stripping (Ts). The effect of bone density, screw location, cortical thickness, and unicortical versus bicortical purchase on Ti and Ts was checked for significance (P < .05) using a general linearized latent and mixed model. We found that 9% of the screws were inadvertently stripped and 12% were overtightened. Despite 21% of the screws being stripped or being at risk for stripping, we found no significant predictors to warn of impending screw stripping. Additional work is needed to identify clinically useful predictors of screw stripping.

Bone density and cortical thickness in normal, osteopenic, and osteoporotic sacra.

It is unclear if a decrease in cancellous bone density or cortical bone thickness is related to sacral insufficiency fractures. We hypothesized that reduction in overall bone density leads to local reductions in bone density and cortical thickness in cadaveric sacra that match clinically observed fracture patterns in patients with sacral insufficiency fractures. We used quantitative computed tomography to measure cancellous density and cortical thickness in multiple areas of normal, osteopenic, and osteoporotic sacra. Cancellous bone density was significantly lower in osteoporotic specimens in the central and anterior regions of the sacral ala compared with other regions of these specimens. Cortical thickness decreased uniformly in all regions of osteopenic and osteoporotic specimens. These results support our hypothesis that areas of the sacrum where sacral insufficiency fractures often occur have significantly larger decreases in cancellous bone density; however, they do not support the hypothesis that these areas have local reduction of cortical bone thickness.

Biomechanical comparison of extensile exposures in total knee arthroplasty.

The "banana peel" exposure is a novel technique for knee joint exposure that consists of partially peeling the patellar tendon off the tibia, leaving the extensor mechanism intact distally and laterally. Although good clinical results have been reported with this technique with no disruption of the extensor mechanism, concerns exist that it could cause extensor lag, quadriceps weakness, or patellar tendon rupture. We compared the banana peel exposure repair to tibial tubercle osteotomy repair, which we chose as our benchmark procedure because much is known about its associated healing and rehabilitation protocols. In our study of 16 paired, fresh-frozen human knee specimens, the 2 techniques were used alternately for the right and left knees. To measure acute strength, 10 pairs were tested. The patella was clamped and pulled superiorly at 25 mm/min until failure. For cyclical testing (6 pairs), the knee was extended from 90 degrees of flexion to 0 degrees for 2000 cycles at 0.25 Hz while we monitored the distance between the inferior pole of the patella and the tibial diaphysis using a passive optical kinematic measuring system. Mean failure strengths of the banana peel and osteotomy groups were 2642+/-1104 N and 2123+/-562 N, respectively, suggesting that the banana peel repair is not weaker than the osteotomy repair. Neither group had a significant increase (via paired Student t test, P>.05) in the distance between the inferior pole of the patella and the tibial diaphysis, suggesting that neither exposure would result in extensor lag.

Mechanical evaluation of a 4-mm cancellous "rescue" screw in osteoporotic cortical bone: a cadaveric study.

OBJECTIVES: Obtaining sufficient fracture fixation in osteoporotic bone is challenging. The purposes of the current study were (1) to compare the pullout strength of a 4-mm cancellous screw (cancellous screw group) with that of a 3.5-mm cortical screw (cortical screw group), and (2) to measure the pullout strength of a 4-mm cancellous screw placed as a rescue screw (rescue screw group) in a stripped 3.5-mm cortical screw (stripped screw group) hole while controlling for bone density and cortical thickness. METHODS: We inserted 4 screws, one from each experimental group, into 11 osteoporotic cadaveric radii, while recording the insertion torque. Radii were mounted on a servohydraulic testing machine, and each screw was pulled out at a rate of 5 mm/min. Pullout strength was recorded. The effects of cortical thickness (near, far, and total), bone density, insertion torque, and the experimental screw group (cortical, cancellous, stripped, and rescue screw groups) on pullout strength were analyzed using multiple linear regression with random effects. Statistical significance was set at P < 0.05. RESULTS: There was no significant difference in pullout strength between the cortical and cancellous screw groups. The rescue screw group had significantly less pullout strength than did the cortical and cancellous screws, and only partly increased pullout strength compared with stripped screws. Bone density significantly affected pullout strength, but insertion torque and cortical thickness were not significant covariates. CONCLUSIONS: There seems to be no advantage in using a cancellous screw over a cortical screw in bicortical fixation in osteoporotic bone. Although the rescue screw provided greater pullout strength than the stripped screw, it is unknown if the purchase it provides is clinically sufficient.

Suture-button versus screw fixation in a syndesmosis rupture model: a biomechanical comparison.

BACKGROUND: Flexible suture-button devices are used to stabilize the distal tibiofibular joint after syndesmotic rupture, but little is known about how they affect fibular motion during cyclic physiological loading. This study examined how much fibular motion occurs during cyclic loading of ankles repaired with suture-buttons or screws relative to one with intact ligaments. MATERIALS AND METHODS: Ten pairs of cadaveric legs with intact ligaments were tested in axial compression (750 N), external rotational torque (7.5 Nm), and a combination thereof. Fibular rotation and translation in the sagittal and frontal planes were measured with linear variable displacement transducers. Then we sectioned the anterior tibiofibular, posterior tibiofibular, deltoid, and interosseous ligaments. Ankles were repaired with suture-buttons or a 3.5-mm screw through four-cortices. The ankles were tested for 10,000 cycles using the same loading protocol. Surviving ankles were brought to failure by increasing external rotation (1 degree/sec). Data from the linear variable differential transducers were used to calculate fibular motion at 100, 1,000, 5,000, and 10,000 cycles. RESULTS: There was no significant difference in the effect of the suture-button or screw for translation in the sagittal or coronal plane or for rotation about the fibular axis. The screw repair had a significantly greater (p = 0.02) failure torque (median, 26.5 Nm; inner quartile range, 25.7 to 35.2 Nm) than did the suture-button repair (median, 23.6 Nm; inner quartile range, 16.5 to 25.6 Nm). CONCLUSION: The fibular motion that occurs during cyclic loading appears to be similar for the suture-button and syndesmotic screw. Motion in both constructs was similar, but neither restored native ankle motion. CLINICAL RELEVANCE: It appears the suture-button behaves similarly to the syndesmotic screw in the syndesmotic rupture injury model tested. Clinical trials are needed to determine how the device performs in vivo.

Percutaneous screw configuration versus perimeter plating of calcaneus fractures: a cadaver study.

BACKGROUND: Percutaneous screw configuration has been used clinically to reduce the high rate of wound complications associated with the extensile approach of standard open reduction and internal plate fixation. The aim of this cadaveric biomechanical study was to compare the strength of the standard perimeter plating with that of the percutaneous screw configuration for a Sanders type-2B calcaneus fracture. MATERIALS AND METHODS: Ten pairs of fresh-frozen cadaveric lower limbs were prepared and osteotomized to create a Sanders type-2B fracture. Of each pair, one specimen underwent open reduction and internal fixation with standard perimeter plating; the other was stabilized with the percutaneous screw configuration. Each foot was compressed axially via the talar dome (1 mm/sec) until failure occurred. Differences in treatment groups were analyzed for significance (p < 0.05) using paired t-tests. RESULTS: Construct stiffness was 158 +/- 85 and 113 +/- 60 N/mm for the plate and percutaneous fixation, respectively (p = 0.18). Failure occurred at an average of 1156 +/- 513 and 1064 +/- 540 N for the plate and percutaneous construct, respectively (p = 0.65). CONCLUSION: The results suggest that open reduction and internal fixation with percutaneous screw configuration for Sanders type-2B calcaneus fractures provides a strength similar to that of perimeter plating. CLINICAL RELEVANCE: Percutaneous screw fixation of calcaneus fractures may provide fracture reduction similar to plate fixation.

Visibility of surgical site marking after preoperative skin preparation.

OBJECTIVE: It is important that during preoperative skin preparation surgical site markings are not erased. The effects of 2 common types of skin preparation solutions on surgical site markings were compared. METHODS: Fasciocutaneous skin flaps were harvested and 20 random combinations of 3 letters were written on the skin flaps with a black permanent marker. Ten of the 3-letter combinations received Chloraprep (chlorhexidine gluconate, 2% w/v, plus isopropyl alcohol, 70% v/v) and the other 10 received Duraprep (iodine povacrylex [0.7% available iodine] and isopropyl alcohol [74% w/w]), both according to the manufacturer's guidelines. The skin flaps were photographed digitally before and after application of the solutions. The final pictures were assessed subjectively by 10 surgeons and then objectively to determine the change in visibility of the marking on each specimen. RESULTS: Of the 300 letters in each group, the number of correctly identified letters was 254 (84.7%) in the Chloraprep group and 284 (94.7%) in the Duraprep group. On the basis of the visibility of skin markings, Chloraprep was 21.8 times more likely (95% credible interval, 7.3-86.7) to erase the site markings than was Duraprep. CONCLUSIONS: Skin preparation with Chloraprep erased more surgical site markings than did Duraprep.

Biomechanical comparison of expandable and locked intramedullary femoral nails.

OBJECTIVES: The expandable intramedullary (IM) nail does not require locking and fluoroscopy use is minimized. However, the lack of cross-locking screws may adversely affect the fixation's rotational stability. The purpose of our study was to compare the rotational stability afforded by an expandable nail with that of a standard locked nail. METHODS: In a cadaver model of a diaphyseal femoral fracture (OTA type 32-A3), we compared first-generation expandable IM nails with standard locked IM nails in osteoporotic and nonosteoporotic femora (10 pairs each) and second-generation expandable nails with standard locked IM nails only in nonosteoporotic femora (10 pairs). To simulate torsional loads during walking, we applied an external rotation moment of -1 to 10 Nm at 1 Hz to each construct for 5000 cycles. Failure was defined as 15 degrees of rotation at the fracture site. We used McNemar's test to check for significant (P < 0.05) differences in failure between groups. RESULTS: Of the first-generation expandable nails, 90% failed (9/10 in osteoporotic and 9/10 in nonosteoporotic femora) within the first 1000 cycles. Of the respective locked nails, significantly fewer failed in nonosteoporotic femora than in osteoporotic femora (0/10 and 3/10, respectively). Of the second-generation nails, 8/10 failed within 100 cycles of testing. Of the comparative locked nails, none failed at 5000 cycles. CONCLUSIONS: We concluded that the expandable IM femoral nail, when tested in purely axial rotation, has poor rotational stability compared with the standard locked IM femoral nail.

Evidence of primary transmission of multidrug-resistant tuberculosis in the Western Province of Papua New Guinea.

OBJECTIVE: To review patient outcomes and the molecular epidemiology of multidrug-resistant tuberculosis (MDR-TB) strains isolated from patients living in the Western Province of Papua New Guinea (PNG) seeking treatment in Australia. DESIGN, SETTING AND PARTICIPANTS: Review of all cases of MDR-TB among people living in the open border region between the Western Province of PNG and the Torres Strait Islands of Australia who presented to health clinics in the region between 2000 and 2006. All cases of suspected TB were bacteriologically confirmed at the time of presentation by the Mycobacterium Reference Laboratory in Brisbane. MAIN OUTCOME MEASURES: Drug resistance patterns; drug use and duration; molecular typing of TB strains; patient outcomes. RESULTS: Between 2000 and 2006, 60 patients from the Western Province of PNG were diagnosed with TB, of which 15 had MDR-TB. Mortality was high, although no patient who was able to maintain access to supervised therapy died. All 15 MDR-TB isolates were Beijing-family strains showing the same unique mycobacterial interspersed repetitive unit (MIRU) profile, with the exception of a single strain that differed by a single repeat at one locus. Restriction fragment length polymorphism (RFLP) typing on 10 of these strains further differentiated them into two distinct clusters. CONCLUSION: Transmission of MDR-TB is occurring in the Western Province of PNG. Additional resources are urgently needed to interrupt the ongoing transmission of MDR-TB from the Western Province of PNG to the Torres Strait Islands. Good supervision and management of patient treatment, which includes ensuring a regular supply of second-line anti-TB drugs, are essential elements of TB control.

Ex vivo biomechanical comparison of the 2.4 mm uniLOCK reconstruction plate using 2.4 mm locking versus standard screws for fixation of acetabular osteotomy in dogs.

OBJECTIVE: To compare the accuracy of reduction and the biomechanical characteristics of canine acetabular osteotomies stabilized with locking versus standard screws in a locking plate. STUDY DESIGN: Ex vivo biomechanical study. SAMPLE POPULATION: Cadaveric canine hemipelves and corresponding femurs (n=10 paired). METHODS: Transverse acetabular osteotomies stabilized with 5-hole 2.4 mm uniLOCK reconstruction plates using either 2.4 mm locking monocortical or standard bicortical screw fixation (Synthes Maxillofacial). Fracture reduction was assessed directly (craniocaudal acetabular width measurements and gross observation) and indirectly (impression casts). All constructs were fatigue-tested, followed by acute destructive testing. All outcome measures (mean+/-SD) were evaluated for significance (P<.05) using paired t-tests. RESULTS: Craniocaudal acetabular diameters before and after fixation were not significantly different (21.9+/-1.2 and 21.5+/-1.2 mm; P=.45). No significant differences were observed in acetabular width differences between pre- and postoperative fixation between groups (locking -0.4+/-0.4 mm; standard -0.4+/-0.3 mm; P=.76). Grossly, there was no significant difference in the repairs and impression casts did not reveal a significant (P=.75) difference in congruency between the groups. No significant differences were found in fracture gap between groups either dorsally (locking 0.38+/-0.23 mm versus standard 0.22+/-0.05 mm; P=.30) or ventrally (locking 0.80+/-0.79 mm versus standard 0.35+/-0.13 mm; P=.23), and maximum change in amplitude dorsally (locking 0.96+/-2.15 mm versus standard 0.92+/-0.89 mm; P=.96) or ventrally (locking 2.02+/-2.93 mm versus standard 0.15+/-0.81 mm; P=.25). There were no significant differences in stiffness (locking 241+/-46 N/mm versus standard 283+/-209 N/mm; P=.64) or load to failure (locking 1077+/-950 N versus standard 811+/-248 N; P=.49). CONCLUSION: No significant differences were found between pelves stabilized with locking monocortical screw fixation or standard bicortical screw fixation with respect to joint congruity, displacement of fracture gap after cyclic loading, construct stiffness, or ultimate load to failure. CLINICAL RELEVANCE: There is no apparent advantage of locking plate fixation over standard plate fixation of 2-piece ex vivo acetabular fractures using the 2.4 mm uniLOCK reconstruction plate.