Erik N. Kubiak

Biomechanics of locked plates and screws

Objective: To review the biomechanical principles that guide fracture fixation with plates and screws; specifically to compare and contrast the function and roles of conventional unlocked plates to locked plates in fracture fixation. We review basic plate and screw function, discuss the design rationale for the new implants, and examine the biomechanical evidence that supports the use of such implants. Data Sources: Systematic review of the per reviewed English language orthopaedic literature listed on PubMed (National Library of Medicine online service). Study Selection: Papers selected for this review were drawn from peer review orthopaedic journals. All selected papers specifically discussed plate and screw biomechanics with regard to fracture fixation. PubMed search terms were: plates and screws, biomechanics, locked plates, PC-Fix, LISS, LCP, MIPO, and fracture fixation. Data Synthesis: The following topics are discussed: plate and screw function—neutralization plates and buttress plates, bridge plates; fracture stability—specifically how this effects gap strain and fracture union, conventional plate biomechanics, and locking plate biomechanics. Conclusions: Locked plates and conventional plates rely on completely different mechanical principles to provide fracture fixation and in so doing they provide different biological environments for healing. Locked plates may increasingly be indicated for indirect fracture reduction, diaphyseal/metaphyseal fractures in osteoporotic bone, bridging severely comminuted fractures, and the plating of fractures where anatomical constraints prevent plating on the tension side of the bone. Conventional plates may continue to be the fixation method of choice for periarticular fractures which demand perfect anatomical reduction and to certain types of nonunions which require increased stability for union.

The evolution of locked plates

Our purpose is to review the history of locked plates and the current recommendations for the use of those devices and to look toward future trends in the clinical application of locked plates. We will discuss (1) the impetus for the locked (fixed-angle) plate design, (2) current indications and design trends, (3) the latest clinical and biomechanical data, (4) shortcomings of locked (fixed-angle) plates, and (5) future applications and directions for locked (fixed-angle) plates. Since their initial introduction in the late nineteenth century and their subsequent popularization by Danis1-3 and the Arbeitsgemeinschaft fur Osteosynthesefragen (AO) group in the 1960s, conventional nonlocked plates have proven, over time, to successfully stabilize many types of fractures and osteotomy sites. The plate-screw-bone construct must resist physiological loads to allow fracture union by limiting fracture gap stress, provide sufficient stability to permit early limb motion, and not fail before fracture union occurs. Additionally, for optimal clinical results, disruption of the bone blood supply by the plate-screw-bone construct should be minimized. To accomplish this goal, there should be minimal operative dissection and periosteal contact to promote bone union4,5. Ideally, the plate-screw-bone construct will permit the restoration of the mechanical limb alignment and reestablish joint congruity to within <2 mm2,6,7. Finally, to be successful, plate fixation must provide reproducible results, must be simple to perform, and must have broad clinical applicability. Fixation with conventional compression plates, although for the most part successful, has its limitations. Figure 1 demonstrates one attempt to counter the limitations associated with the use of conventional nonlocked plates. To achieve fracture stability, the axial, torsional, and three-point bending forces must be neutralized (Fig. 2). With the use of conventional nonlocked plates, force friction between the plate and the bone counters …

Stress radiographs after ankle fracture: the effect of ankle position and deltoid ligament status on medial clear space measurements.

Objective: This study was designed to determine 1) how ankle position affects the medial clear space by using stress radiographs, 2) which medial clear space measurement, overall width or increase in width, better predicts deep deltoid ligament disruption after Weber type-B distal fibular fracture, and 3) what value of medial clear space is most predictive of deep deltoid ligament disruption after Weber type-B distal fibular fracture. Design: Cadaveric fracture model. Setting: Biomechanics laboratory. Intervention: Fluoroscopic mortise views were taken of 6 fresh cadaveric ankles mounted in a fixture permitting both positioning in neutral flexion, dorsiflexion, and plantarflexion, and the application of internal and external rotational forces. After destabilizing the ankles according to the supination-external rotation mechanism of Lauge-Hansen, repeat radiographs were taken with the same combination of flexion and applied rotational stress. Main Outcome Measure: Radiographic measurements of medial clear space width and changes in medial clear space were made. Results: A medial clear space of ≥5 mm on radiographs taken in dorsiflexion with an external rotational stress was most predictive of deep deltoid ligament transection after distal fibular fracture. In dorsiflexion-external rotation, medial clear spaces of ≥4 mm yielded lower specificity and positive predictive value, whereas ≥6 mm yielded lower sensitivity and negative predictive value. All other stress conditions and increases in medial clear space of 2 or 3 mm were less predictive. Conclusions: Ankle stress radiographs taken in dorsiflexion-external rotation were most predictive of deep deltoid ligament disruption after distal fibular fracture. Under this stress condition, a medial clear space of ≥5 mm was the most reliable predictor of deep deltoid ligament status.

Operative Treatment of Tibial Fractures in Children: Are Elastic Stable Intramedullary Nails an Improvement Over External Fixation?

BACKGROUND Operative treatment of tibial fractures in children requires implants that do not violate open physes while maintaining tibial length and alignment. Both elastic stable intramedullary nails and external fixation can be utilized. We retrospectively reviewed our experience with these two techniques to determine if one is superior to the other. METHODS We retrospectively reviewed the operative records and trauma registries of three institutions within our hospital system and identified thirty-five consecutive patients with open physes who had undergone operative treatment of a tibial fracture between April 1997 and June 2004. Four patients were excluded because they had been managed with locked intramedullary nails or with pins and plaster. Of the thirty-one remaining patients, sixteen had been managed with elastic stable intramedullary nails and fifteen had been managed with unilateral external fixation. The clinical and radiographic outcomes were compared. The functional outcomes were compared with use of the Pediatric Outcomes Data Collection Instrument. Complications related to treatment, such as malunion, delayed union, nonunion, infection, and the need for subsequent surgical treatment also were compared. RESULTS Thirty-one patients with thirty-one operatively treated tibial fractures were available for evaluation. Fifteen patients had been managed with external fixation. Seven of these patients had a closed fracture, and eight had an open fracture. There were seven healing complications in this group, including two delayed unions, three nonunions, and two malunions. Sixteen patients had been managed with elastic stable intramedullary nailing. Eleven patients had a closed fracture, and five had an open fracture. The mean time to union for the intramedullary nailing group (seven weeks) was significantly shorter than that for the external fixation group (eighteen weeks) (p < 0.01). The functional outcomes for the intramedullary nailing group were significantly better than those for the external fixation group in the categories of pain, happiness, sports, and global function (the mean of the mean scores of the first four categories) (p < 0.01 for these comparisons). CONCLUSIONS When surgical stabilization of tibial fractures in children is indicated, we believe that the preferred method of fixation is with elastic stable intramedullary nailing.

Computerized Adaptive Testing Using the PROMIS Physical Function Item Bank Reduces Test Burden With Less Ceiling Effects Compared With the Short Musculoskeletal Function Assessment in Orthopaedic Trauma Patients

Purpose: Patient-reported outcomes are important to assess effectiveness of clinical interventions. For orthopaedic trauma patients, the short Musculoskeletal Function Assessment (sMFA) is a commonly used questionnaire. Recently, the Patient-Reported Outcome Measurement Information System (PROMIS) PF Function Computer Adaptive Test (PF CAT) was developed using item response theory to efficiently administer questions from a calibrated bank of 124 PF questions using computerized adaptive testing. In this study, we compared the sMFA versus the PROMIS PF CAT for trauma patients. Methods: Orthopaedic trauma patients completed the sMFA and the PROMIS PF CAT on a tablet wirelessly connected to the PROMIS Assessment Center. The time for each test administration was recorded. A 1-parameter item response theory model was used to examine the psychometric properties of the instruments, including precision and floor/ceiling effects. Results: One hundred fifty-three orthopaedic trauma patients participated in the study. Mean test administration time for PROMIS PF CAT was 44 seconds versus 599 seconds for sMFA (P < 0.05). Both instruments showed extremely high item reliability (Cronbach alpha = 0.98). In terms of instrument coverage, neither instrument showed any floor effect; however, the sMFA revealed 14.4% ceiling effect, whereas the PROMIS PF CAT had no appreciable ceiling effect. Conclusions: Administered by electronic means, the PROMIS PF CAT required less than one-tenth the amount of time for patients to complete than the sMFA while achieving equally high reliability and less ceiling effects. The PROMIS PF CAT is a very attractive and innovative method for assessing patient-reported outcomes with minimal burden to patients.

Orthopaedic management of ankylosing spondylitis.

Abstract Ankylosing spondylitis is an inflammatory disease of unknown etiology that affects an estimated 350,000 persons in the United States and 600,000 in Europe, primarily Caucasian males in the second through fourth decades of life. Worldwide, the prevalence is 0.9%. Genetic linkage to HLA‐B27 has been established. Ankylosing spondylitis primarily affects the axial skeleton and is characterized by inflammation and fusion of the sacroiliac joints, spine, and hips. The resultant deformity leads to severe functional impairment in approximately 30% of patients. Orthopaedic management primarily involves correction of hip deformity through total hip arthroplasty and, less frequently, correction of spinal deformity with spine osteotomy. Closing wedge osteotomies have the lowest incidence of complications. Whether patients with ankylosing spondylitis are at increased risk for heterotopic ossification remains controversial, but comparison with age‐ and sex‐matched counterparts suggests no dramatically higher risk. Because of the high rate of missed fractures and complications after minor trauma in patients with ankylosing spondylitis, plain radiographs are usually not sufficient for evaluation. Thorough patient assessment should include a comprehensive history, physical examination, and laboratory studies.

Intramedullary Fixation of Unstable Intertrochanteric Hip Fractures : One or Two Lag Screws

Objective To compare the screw sliding characteristics and biomechanical stability of four-part intertrochanteric hip fractures stabilized with an intramedullary nail using either one large-diameter lag screw (intramedullary hip screw [IMHS]; Smith & Nephew, Memphis, TN) or two small-diameter lag screws (trochanteric antegrade nail [TAN]; Smith & Nephew, Memphis, TN). Design Laboratory investigation using eight matched pairs of cadaveric human femurs with simulated, unstable intertrochanteric hip fractures. Intervention One femur of each matched pair was stabilized with an IMHS intramedullary nail, and the other was stabilized with a TAN intramedullary nail. Femurs were statically, then cyclically loaded on a servohydraulic materials testing machine. Finally, all specimens were loaded to failure. Main Outcome Measures Screw sliding and inferior and lateral head displacements were measured for applied static loads from 500N to 1250N. The same measurements were obtained before and after cyclically loading the specimens at 1250N. Ultimate failure strength of the implant constructs also was determined. Results There was no significant difference between the TAN and IMHS in static or cyclical loading with respect to screw sliding or inferior and lateral head displacements. There was a statistically significant difference (P < 0.02) in failure strength, with the IMHS construct failing at an average of 2162N and the TAN construct failing at an average of 3238N. Conclusion The two constructs showed equivalent rigidity and stability in all parameters assessed in elastic and cyclical tests. The TAN had a greater ultimate failure load.

Conflict of Interest in Orthopaedic Research

BACKGROUND The expanding role of industrial support in biomedical research has resulted in both substantial interest and controversy in recent years. Our hypothesis was that, from 1985 to 2002, the role of industrial support in orthopaedic research increased, as documented by the research presented at the annual meetings of the American Academy of Orthopaedic Surgeons. METHODS We analyzed the frequency and types of self-reported conflicts of interest for all presentations at the annual meetings of the American Academy of Orthopaedic Surgeons in 1985, 1988, 1992, 1997, 1999, and 2002. Conflicts of interest were recorded directly from the final program for each meeting analyzed. The analysis focused on the scientific presentations, Instructional Course Lectures, symposia, poster exhibits, and scientific exhibits. Information about specific types of support received by authors was first required in 1988. RESULTS The incidence of conflicts of interest increased from 3% in 1985 to 39% in 2002 for scientific papers (p < 0.001); from 10% to 74%, respectively, for symposia (p < 0.001); from 22% to 60% for Instructional Course Lectures (p < 0.001); from 10% to 60% for scientific exhibits (p < 0.001); and from 9% in 1992 to 14% in 2002 for posters (p < 0.001). For presentations of all types, the incidence increased from 10% to 32% (p < 0.001). The types of conflict of interest also changed significantly from 1999 to 2002. In 1999, 73% of conflicts were documented as support directed to institutions and 27%, as support to individuals; in 2002, 57% were reported as support directed to institutions and 43%, as support to individuals (p < 0.01). CONCLUSIONS The role of industrial support of orthopaedic research increased significantly between 1985 and 2002, as evidenced by the increase in the self-reported conflicts of interest for all types of presentations at the annual meetings of the American Academy of Orthopaedic Surgeons. In addition, the support directed to individuals, in contrast to that directed to institutions, increased significantly.

The Effect of the Angle of Suture Anchor Insertion on Fixation Failure at the Tendon―Suture Interface After Rotator Cuff Repair: Deadman's Angle Revisited

PURPOSE To evaluate what effect the angle of screw-in suture anchor insertion has on fixation stability at the suture-tendon interface. METHODS Supraspinatus tendons from 7 matched pairs of human cadaveric shoulders were split, yielding 4 tendons per cadaver. An experimental rotator cuff tear was created and repaired, using a 5.0-mm diameter screw-in suture anchor. In a staggered, matched pair arrangement, the angle of anchor insertion was varied between 45 degrees (deadmans angle) and 90 degrees to the articular surface. Each repair underwent cyclic loading, and 2 failure points were defined: the first at 3 mm of repair site gap formation and the second at the point of complete failure. The number of cycles to failure was compared between the 2 groups. RESULTS The mean number of cycles to 3-mm gap formation for anchors inserted at 90 degrees was 380. This was significantly higher than for repairs made with the 45 degrees angle of anchor insertion (mean, 297 cycles). Complete failure occurred at a significantly greater number of cycles with the 90 degrees anchors (mean, 443 cycles) compared with the 45 degrees anchors (mean, 334 cycles). CONCLUSIONS Compared with anchors placed at the current standard of the deadmans angle of 45 degrees, suture anchors placed at 90 degrees to the junction of the greater tuberosity and the humeral head articular surface provided improved soft tissue fixation in an experimental rotator cuff model. CLINICAL RELEVANCE The angle of suture anchor insertion into the greater tuberosity during rotator cuff repair has an effect on the soft tissue fixation at the tendon-suture interface.

Early weight bearing after lower extremity fractures in adults.

Abstract Weight‐bearing protocols should optimize fracture healing while avoiding fracture displacement or implant failure. Biomechanical and animal studies indicate that early loading is beneficial, but high‐quality clinical studies comparing weight‐bearing protocols after lower extremity fractures are not universally available. For certain fracture patterns, well‐designed trials suggest that patients with normal protective sensation can safely bear weight sooner than most protocols permit. Several randomized, controlled trials of surgically treated ankle fractures have shown no difference in outcomes between immediate and delayed (≥6 weeks) weight bearing. Retrospective series have reported low complication rates with immediate weight bearing following intramedullary nailing of femoral shaft fractures and following surgical management of femoral neck and intertrochanteric femur fractures in elderly patients. For other fracture patterns, particularly periarticular fractures, the evidence in favor of early weight bearing is less compelling. Most surgeons recommend a period of protected weight bearing for patients with calcaneal, tibial plafond, tibial plateau, and acetabular fractures. Further studies are warranted to better define optimal postoperative weight‐bearing protocols.