Fixation of extra-articular distal humerus fractures using one locking plate versus two reconstruction plates: a laboratory study.

OBJECTIVE: To compare the strength and stiffness of standard double-plate fixation with that of a single-locking plate for comminuted extra-articular distal humeral fractures. MATERIALS: Eight matched pairs of humeri were used. One of each pair was fixed with two 3.5-mm standard reconstruction plates applied dorsally; the other was fixed with one precontoured locking plate applied to the posterior aspect of the lateral column. A 1-cm gap was created to simulate a distal fracture model with 100% metaphyseal comminution with no bony apposition. Stiffness testing of these constructs was performed in axial compression, anterior, posterior and lateral bending, and torsion. They were then cyclically loaded for 4000 cycles with 60 N in posterior bending and the stiffnesses retested. Finally, each construct was posteriorly loaded to failure to determine its ultimate strength. RESULTS: The double-plate construct was significantly stiffer than the one locking plate construct in anterior bending (39%; p = 0.02), posterior bending (23%; p = 0.04), and lateral bending (60%; p = 0.01). No significant stiffness differences were seen in axial compression and torsion (p = 0.64 and 0.25, respectively). After cyclic loading, all construct stiffnesses were relatively unchanged. Both construct types had similar failure strengths (p = 0.76) of approximately 400 N. CONCLUSIONS: Double-plating provides a more rigid fixation than a single-locked plate for fixation of extra-articular comminuted distal humeral fractures. This could be clinically relevant in situations with 100% comminution as seen in gun shot injuries.

Surface oxidized zirconium total hip arthroplasty head damage due to closed reduction effects on polyethylene wear.

Recent case studies of surface oxidized zirconium THA heads removed after attempted, closed reduction have shown significant surface damage that has been suggested as potentially deleterious to polyethylene wear. We obtained 4 clinically retrieved specimens, produced well-characterized surface damage on additional heads, and tested them on a hip simulator. After 1 million cycles, the amount of polyethylene wear was related to the extent of surface damage, the most damaged clinical specimen showing more than 50 times more wear than a new head. Although all heads after failed attempted closed reduction(s) should be replaced, surface oxidized zirconium heads are of particular concern; those patients with a successful, simple closed reduction should be monitored for excessive wear.

Glove tears during arthroscopic shoulder surgery using solid-core suture.

PURPOSE: Surgeons have noticed an increased incidence of finger lacerations associated with arthroscopic knot tying with solid-core suture material. This study examines glove perforations and finger lacerations during arthroscopic shoulder surgery. METHODS: We collected 400 surgical gloves from 50 consecutive arthroscopic shoulder repair procedures using No. 2 solid-core sutures. Two surgeons using double gloves were involved in every case, with one being responsible for tying all knots. Powder-free latex gloves were worn in all cases. Knots consisted of a sliding stitch of the surgeon's preference followed by 3 half-hitches via a knot-pusher instrument. All gloves were inspected grossly and then tested for tears with an electroconductivity meter. RESULTS: The knot-tying surgeon had significantly more glove tears than the control (P < .01). Tears were localized to the radial side of the index finger of the glove at the distal interphalangeal joint in all cases. Of the tying surgeon's gloves, 68 (34%) were found to have tears. These included 17 inner gloves (17%) and 51 outer gloves (51%). If an inner glove was torn, the corresponding outer glove was torn in all cases. A mean of 3.96 knots were tied in each case. There was a significantly higher incidence of inner glove tears when more than 3 knots were tied (P < .03). There was no significant difference in glove tears between suture types. Finger lacerations did occur in the absence of glove tears. However, in the presence of an inner glove tear, there was a statistically significant association with a finger laceration at the corresponding level (P < .03). CONCLUSIONS: Intraoperative glove tears and subsequent finger lacerations occur with a high frequency when arthroscopic knots are tied with solid-core suture material. Risk can potentially be minimized by frequent glove changes or use of more durable, less penetrable gloves. CLINICAL RELEVANCE: This study addresses surgeon and patient safety during arthroscopic shoulder surgery.

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 > or =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 > or =4 mm yielded lower specificity and positive predictive value, whereas > or =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 > or =5 mm was the most reliable predictor of deep deltoid ligament status.

The effect of locked distal screws in retrograde nailing of osteoporotic distal femur fractures: a laboratory study using cadaver femurs.

OBJECTIVES: To examine the effects of locked distal screws in retrograde nails used in unstable osteopenic distal femur fractures. DESIGN: Biomechanical testing of paired human cadaveric femurs. INTERVENTION: Seven matched pairs of embalmed, moderately osteopenic cadaver femurs were instrumented with 12-mm intramedullary nails in a statically locked, retrograde fashion. One femur of each pair had locked distal screws and the other femur had unlocked distal screws. A 2.5-cm gap of bone was cut nine centimeters from the distal condyles to simulate an unstable fracture. The locked distal screw nails were compared to unlocked distal screw nails for collapse of the fracture gap, medial-lateral and anterior-posterior translation of the nail within the fracture site, and fracture angulation. The femurs were axially loaded, cycled, and then loaded to failure. MAIN OUTCOME MEASURES: Motion at the fracture site with axial cyclic loading and site of failure when loaded to failure. RESULTS: After cycling, both locked distal screw and unlocked distal screw nails demonstrated several millimeters medial and anterior translation within the fracture site and approximately 1 mm collapse of the fracture gap. Although no statistically significant differences were found, the locked distal screw nails had less anterior and medial translation, angulation, and collapse of the fracture gap after cycling. Loads to failure were similar for both locked distal screw and unlocked distal screw nails. It was noted that proximal femur failure occurred at the level of the proximal screw hole in the nail at the subtrochanteric level in 7 (4 locked distal screws and 3 unlocked distal screw groups) of the 14 samples. Four other samples failed through the intertrochanteric region (2 locked distal screw and 2 unlocked distal screw groups) and the remainder within the distal fragment by fracture of the femur along the medial cortex. CONCLUSIONS: Although most differences in fixation stability were not significant, the locked distal screw nails exhibited less fracture collapse and anterior and medial translation of the nail at the fracture site than the unlocked distal screw nails. The degree of varus angulation after cyclic loading was also less for the locked distal screw nails. The length of the nail chosen should avoid having proximal locking screws distal to the lesser trochanter, thus averting proximal femur stress risers and fractures.

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.

Effect of specialty and experience on the interpretation of knee MRI scans.

The purpose of this study was to evaluate any differences in the accuracy of knee MRI interpretation between radiology and orthopaedic surgery residents as well as to evaluate differences in quality of interpretation relative to resident training level. In this study, 20 MRI scans demonstrating specific pathology of the knee were identified. From one institution, two radiology residents and two orthopaedic surgery residents of each postgraduate year (PGY) of training (2 to 5) were recruited. Each resident was asked to interpret all the studies and choose up to 16 diagnoses for each scan from the list provided. Orthopaedic surgery residents showed improvement in overall accuracy and specificity with each year of additional training. Level of training did not correspond with increased sensitivity in the orthopaedic residents tested. Radiology residents did not demonstrate a consistent trend toward improved accuracy, sensitivity, or specificity with additional years of training. The only statistically significant differences in specificity observed between the two groups were seen in the readings of ACL tears, lateral femoral condyle chondromalacia, and chondromalacia patella. This study found that the accuracy of knee MRI interpretations between radiology and orthopaedic surgery residents did not demonstrate any differences. Level of training had no effect on the interpretation of the MRIs by radiology residents. Orthopaedic surgery residents did show an improvement with each year of additional training.