James C. Krieg

A laboratory model to evaluate cutout resistance of implants for pertrochanteric fracture fixation.

Objectives: To establish a laboratory model of implant cutout, which can evaluate the effect of implant design on cutout resistance in a clinically realistic “worst case” scenario. Setting: Orthopaedic biomechanics laboratory. Design: Implant cutout was simulated in an unstable pertrochanteric fracture model, which accounted for dynamic loading, osteoporotic bone, and a defined implant offset. For model characterization, lag screw cutout was simulated in human cadaveric specimens and in polyurethane foam surrogates. Subsequently, foam surrogates were used to determine differences in cutout resistance between 2 common lag screws (dynamic hip screw, Gamma) and 2 novel blade-type implant designs (dynamic helical hip system, trochanteric fixation nail). Main Outcome Measures: Implant migration was continuously recorded with a spatial motion tracking system as a function of the applied loading cycles. In addition, the total number of loading cycles to cutout failure was determined for specific load amplitudes. Results: Implant migration in polyurethane surrogates closely correlated with that in cadaveric specimens, but yielded higher reproducibility and consistent cutout failure. The cutout model was able to delineate significant differences in cutout resistance between specific implant designs. At any of 4 load amplitudes (0.8 kN, 1.0 kN, 1.2 kN, 1.4 kN) dynamic hip screw lag screws failed earliest. The gamma nail lag screw could sustain significantly more loading cycles than the dynamic hip screw. Of all implants, trochanteric fixation nail implants demonstrated the highest cutout resistance. Conclusions: Implant design can significantly affect the fixation strength and cutout resistance of implants for pertrochanteric fracture fixation. The novel cutout model can predict differences in cutout resistance between distinct implant designs.

Noninvasive reduction of open-book pelvic fractures by circumferential compression.

Objectives To determine the efficacy and optimal application parameters of circumferential compression to reduce external rotation-type pelvic fractures. Design Biomechanical investigation on human cadaveric specimens. Setting Biomechanics laboratory. Intervention Partially stable and unstable external rotation injuries of the pelvic ring (OTA classification 61-B1 and 61-C1) were created in seven human cadaveric specimens. A prototype pelvic strap was applied subsequently at three distinct transverse levels around the pelvis. Circumferential pelvic compression was induced by gradual tensioning of the strap to attempt complete reduction of the symphysis diastasis. Main Outcome Measurements Pelvic reduction was evaluated with respect to strap tension and the strap application site. The effect of circumferential compression on intraperitoneal pressure and skin–strap interface pressure was measured. Results A successive increase in circumferential compression consistently induced a gradual decrease in symphysis diastasis. An optimal strap application site was determined, at which circumferential compression most effectively yielded pelvic reduction. The minimum strap tension required to achieve complete reduction of symphysis diastasis was determined to be 177 ± 44 Newtons and 180 ± 50 Newtons in the partially stable and unstable pelvis, respectively. Conclusions Application of circumferential compression to the pelvic soft tissue envelope with a pelvic strap was an efficient means to achieve controlled reduction of external rotation-type pelvic fractures. This study derived application parameters with direct clinical implication for noninvasive emergent management of traumatic pelvic ring disruptions.

Emergent management of pelvic ring fractures with use of circumferential compression.

Circumferential compression of the pelvis has been recommended for emergent stabilization of open-book pelvic fractures to reduce the risk of life-threatening hemorrhage 1-3. However, little information on the application, effectiveness, and safety of this procedure is available to date 3,4. We therefore investigated noninvasive stabilization of pelvic ring fractures in three cadaveric biomechanical studies. First, we established optimal application parameters for circumferential compression of open-book pelvic fractures. Second, we derived the amount of pelvic stabilization that can be achieved by application of a novel pelvic sling that provides for controlled circumferential compression. Finally, we determined whether this pelvic sling could be applied safely at the emergency scene, where the specific pelvic fracture pattern is not readily assessable. The results of this research demonstrate that circumferential compression with this noninvasive pelvic sling is an effective and safe method for reducing and stabilizing open-book pelvic fractures at the emergency scene. Application Parameters: A cadaveric study was performed to determine the most effective application site and the force required to reduce open-book pelvic fractures. Partially stable and unstable open-book pelvic fractures (Young-Burgess type-II and III anteroposterior compression fractures associated with a 50 and 100-mm diastasis of the symphysis pubis, respectively) were created sequentially in seven nonembalmed human cadavers from individuals with an average age at death of 80 ± 7 years, an average height of 170 ± 9 cm, and an average weight of 74 ± 8 kg Fig. 1 . An experimental pelvic sling consisting of a 50-mm wide, flexible, nonelastic belt was designed. This sling was applied at three distinct …

Stabilization of Pelvic Ring Disruptions with a Circumferential Sheet

Pelvic ring disruptions in the polytraumatized patient are associated with a mortality rate of up to 25%. 1 Acute uncontrolled hemorrhage and its complications are the leading causes of death in these patients. 2 Treatment algorithms for resuscitation and control of hemorrhage are aimed at reducing morbidity and mortality. Although variations exist among these algorithms, essentially all include the goal of pelvic reduction and stabilization. 3,4 Various means of pelvic reduction and stabilization exist. Each has is own advantages and limitations. Invasive measures include anterior external fixation, open reduction and internal fixation (ORIF), and posterior pelvic clamps. 5 Although each of these interventions can be utilized early in the resuscitation phase, none can be applied acutely outside the hospital setting. The desire to provide early stabilization, at the accident scene or during patient transport, has led to the development of noninvasive measures, such as vacuum bean-bags or pneumatic antishock garments (PASGs). However, each of these methods is limited either by its ability to effect controlled reduction, or by its potential for severe complications. 6 Most recently, wrapping of the pelvic region with a sheet has been advocated. In fact, the American College of Surgeons’ Advanced Trauma Life Support (ATLS) course now includes a protocol for emergent management of pelvic ring disruptions, advising circumferential application of a pelvic sheet. 7 Sheets can be readily applied at the accident scene and may provide better reduction and stabilization of open-book type pelvic fractures when compared with bean-bags or PASGs. Anecdotal accounts of sheet application at time of hospital admission are numerous. However, case reports documenting application and performance of such pelvic sheets are virtually nonexistent. In this report, we present two exemplary cases of open-book type pelvic fractures (OTA classification 61-B/C) temporarily managed with a pelvic sheet. Furthermore, we provide an analysis of the amount of reduction achieved by circumferential pelvic compression.

Operative chest wall fixation with osteosynthesis plates.

Blunt chest wall trauma is a major cause of morbidity and mortality, especially in the presence of a flail chest where paradoxical inward movement of the flail segment in inspiration is found. Patients with a flail chest require aggressive pain control, pulmonary toilet, and often intubation and mechanical ventilation to establish an internal pneumatic stabilization of the flail segment. This may result in a prolonged ICU stay and pulmonary complications including pneumonia, septicemia and barotrauma. The high mortality rate of up to 10 –36% –12 is partly due to the high prevalence of associated life-threatening extra-thoracic injuries. However, one principle cause of death consists of pneumonia and sepsis with prolonged intubation. Several potential advantages of operative chest wall stabilizations have been reported. These include reduced duration of mechanical ventilation, shortened ICU stay and hospitalization, and decreased likelihood of clinically significant long-term respiratory dysfunction and skeletal deformity. Despite the advantages of operative chest wall fixation, little consensus on the fixation technique exists. This report describes three cases of flail chest injury managed by operative stabilization with plates and screws. The criteria for surgical intervention in this trauma center are traumatic loss of 30% of pleural cavity volume, inability to wean an awake patient from the ventilator, inability to control chest wall pain despite epidural catheter, major air leak or major bleeding, or unstable sternal fracture with overlap. In all three cases a standard posterolateral thoracotomy was performed. The serratus anterior was retracted anteriorly and the latissimus dorsi was divided. To reach more cranially a small portion of the trapezius and the rhomboids were transected in cases 2 and 3. The chest was always entered and hematoma was removed. Pelvic, mandibular and customized reconstruction plates were used, with bending stiffness ranging from 1,936 over 414 to 56 kN mm, respectively. In addition to documentation of the technique, this report describes the results obtained with three distinct osteosynthesis plates and provides a historic overview of alternative fixation means.

Traditional injury scoring underestimates the relative consequences of orthopedic injury

Objective: To demonstrate that patients with multiple injuries who have orthopedic injuries (ORTHO) face greater challenges regarding functional outcome than those without, to identify domains of postinjury dysfunction, and to illustrate the increasing discordance of functional recovery over time for ORTHO patients in relation to nonORTHO patients. Methods: A convenience sample of adult blunt force trauma patients admitted to a Level I trauma center was evaluated at admission, and at 6 and 12 months after injury. Data were collected from the trauma registry (Trauma One), chart review, and interviews. Mailed surveys were completed 6 and 12 months after injury. The Short Form 36 (SF36) general health survey and the Sickness Impact Profile work scale (SIPw) were administered at both time points. Data are presented as mean ± SEM or percent (%). To compare means, t tests were conducted, and Injury Severity Score (ISS) was controlled by linear regression before the evaluation of the role of ORTHO injury pattern on outcome measures. Significance is noted at the 95% confidence level (p < 0.05). Results: The 165 patients studied averaged 37.2 ± 1.1 years in age and were 67% men. The mean ISS was 14.4 ± 0.6 and 61% had ORTHO injury. ORTHO patients were no different from nonORTHO in any measure of baseline status including the SIPw score and all domains of the SF36, except that the ISS was greater in the ORTHO group (15.6 ± 0.96 vs. 12.7 ± 0.73, p = 0.017). Baseline SF36 values were similar to national norms. Follow-up was 75% at 6 months, and 51% at 12 months. Those lost to follow-up differed only in that they were more likely to be men. Sixty-four percent had returned to work 12 months after injury. After controlling for ISS with linear regression, the ORTHO patients had worse scores on all physical measures of the SF36 (bodily pain, physical function, and role-physical). By 12 months after injury, the relative dysfunction of the ORTHO patients had expanded to include the SIPw score (p = 0.016) and six of eight SF36 domains (bodily pain, physical function, role-physical, mental health, role-emotional, and social function, all p < 0.05). Conclusion: Injury severity affects both mortality and the potentially more consequential issues of long-term morbidity. Patients with ORTHO injury have relatively worse functional recovery, and this worsens with time. As trauma centers approach the limits of achievable survival, new advances in trauma care can be directed more toward the quality of recovery for our patients. This will be contingent on further development of screening, scoring, and treatment systems designed to address issues of functional outcome across injury boundaries for those who survive.

Less rigid stable fracture fixation in osteoporotic bone using locked plates with near cortical slots.

INTRODUCTION Locked plating leads to improved fixation in osteoporotic bone. In addition, experimental data suggest that overall construct stiffness is increased. Ideal stiffness may be significantly less than that achieved with these locked constructs, and overly stiff constructs may lead to impaired fracture healing and stress concentration at the ends of the plate. In osteoporotic bone, this stiffness mismatch can be even more pronounced. We hypothesized that substituting slots for holes in the near cortex under a locked plate would lead to predictably lower stiffness without diminishing implant stability. METHODS Osteoporotic bone substitute segments were used. Locking screws and plates were applied to each specimen using either standard holes or near cortical slots. The slots were designed to allow axial displacement of the screw in the near cortex only, while continuing to provide some torsional stability. Mechanical testing was performed using a progressive dynamic displacement load protocol to determine failure and stiffness. Next, cyclic axial loading was performed with a physiologic load for 10,000 cycles to determine change in stiffness with cycling. Outcomes were compared between groups using Mann-Whitney U tests. RESULTS In the dynamic displacement tests, the slotted specimens reached both maximum load and failure load at a significantly greater displacement than the non-slot group (p=0.008), indicating later failure. The magnitude of the maximum load achieved was no different between groups. In the cyclic loading tests, the axial stiffness in the slotted group was significantly lower (1199 N/mm) than the non-slotted group (3538 N/mm; p<0.05 at all cycles). Stiffness did not change significantly in either group over the course of cycling. DISCUSSION The ability to predictably adjust the axial stiffness of locked plating constructs is critical, particularly in osteoporotic bone. The use of near cortical slots decreases axial stiffness of locking plates, while maintaining fixation stability. This may allow the surgeon to more closely tailor the construct stiffness to the clinical situation to minimize stiffness mismatches and complications.

Stiffness modulation of locking plate constructs using near cortical slotted holes: a preliminary study.

Objectives: Axial stiffness is a critical mechanical parameter in fracture plating. Standard locked plates allow minimal opportunities for stiffness alteration, and current methods are arbitrary and may lead to stiffness mismatch between the implant and bone. Milling the near cortex into a slot allows for an increase in translation of the screw shaft at the near cortex. The purpose of this proof of concept study was to determine the effects of slots on stiffness and their ability to maintain fixation of locking plates under cyclic loading. Methods: Using segments of fourth-generation synthetic diaphyseal bone, a simulated fracture with a gap was created and locked plates were applied with 4 bicortical locked screws in each fragment. On one fragment, the 4 near cortex holes were sequentially milled to 5 × 6-mm slots. Axial and torsional stiffnesses were determined for constructs with 0 through 4 slots. Specimens with 4 slots then underwent axial cyclic loading to determine the change in stiffness and loss of fixation. Extraction torque was measured for all screws to assess for screw loosening with cycling. Results: In constructs with 4 slots, axial stiffness decreased by 73% (P < 0.05) relative to the 0-slot constructs. Torsional stiffness of the 3- and 4-slot specimens decreased by 20% (SD, 13%; P < 0.05) and 17% (SD, 13%; P < 0.05), respectively, compared with the 0-slot specimens. With cyclic loading, no failures occurred in any specimen. No change in stiffness had occurred by the end of cycling (106% of initial stiffness; SD, 4%; P = 0.96). No screw loosening occurred during cyclic loading. Conclusions: Purposeful stiffness modulation in fracture fixation is critical to facilitate uneventful fracture healing. Converting near cortical holes to slots allowed selective axial stiffness adjustment without sacrificing fixation stability under cyclic loading. With further refinement, this simple modification of standard implant application may allow the surgeon to decrease the modulus mismatch between plating constructs and bone to decrease the risk of fixation failure.

Proximal tibial fractures: Current treatment, results, and problems

Fractures of the proximal tibia can present unique treatment challenges. Reduction and stability are dependent on control of the proximal fragment. Soft tissue compromise can present as a component of the injury, or can result from surgical dissection. Treatment protocols aimed at addressing these issues have included closed treatment, external fixation, intramedullary nailing, and plating. The issues of accurate reduction, proximal fragment stabilization, and soft tissue protection are discussed with an emphasis on the individual challenges of each of the treatment modalities.

Femoral malrotation following intramedullary nail fixation.

&NA; Intramedullary nailing of femoral shaft fracture can result in inadvertent malalignment. Malrotation is the most common cause of deformity, but it is underrecognized, in part because of the difficulty in accurately assessing rotation as well as the variation that exists in normal anatomy. The consequences of femoral malrotation are not completely understood. However, initial biomechanical studies suggest that it causes a substantial change in load bearing in the affected extremity. Clinical examination, fluoroscopy, and ultrasonography are useful in measuring femoral rotational alignment intraoperatively and postoperatively. CT is useful in the identification of the degree of malrotation and in surgical planning.