Randal P. Morris

Three Femoral Fixation Devices for Anterior Cruciate Ligament Reconstruction: Comparison of Fixation on the Lateral Cortex Versus the Anterior Cortex

PURPOSE To evaluate the biomechanical properties of 3 anterior cruciate ligament (ACL) reconstruction femoral fixation devices in a porcine model with implantation on both the lateral femoral cortex and the anterior femoral cortex. METHODS ACL reconstructions with an 8-mm porcine tendon graft were performed on 48 porcine femurs with the EndoButton CL (Smith & Nephew, Andover, MA), ToggleLoc with ZipLoop technology (Biomet Sports Medicine, Warsaw, IN), or EZLoc (Biomet Sports Medicine). In 8 specimens for each implant, the femoral tunnel was drilled from the 10:30 surgical position out the lateral cortex. In another 8 specimens for each implant, the tunnel was drilled from the 10:30 position to a standardized anterior femoral surface. Cyclic testing was performed on an MTS testing machine (MTS, Eden Prairie, MN) from 50 N to 450 N for 2,000 cycles, followed by load-to-failure testing in specimens that survived. The cortical thickness and location of the implant exit were recorded. RESULTS In the lateral femur group, 0 of the EZLoc devices, 2 of the ToggleLoc devices, and 3 of the EndoButtons completed cyclic testing. In the anterior femur group, 1 of the EZLoc devices, 5 of the ToggleLoc devices, and 5 of the EndoButtons completed cyclic testing (P = .012). In the anterior femur group, the ToggleLoc exhibited higher 2,000-cycle elongation (5.46 +/- 1 mm) than the EndoButton (3.55 +/- 0.6 mm) (P = .005). The EndoButton showed a higher first failure load (1,190.9 +/- 150.0 N) than the ToggleLoc (912.6 +/- 82.4 N) (P = .007). The anterior cortex (1.4 mm) was thinner than the lateral cortex (1.7 mm) (P = .0002). CONCLUSIONS The EndoButton provided the strongest ACL femoral fixation with significantly less graft-implant elongation and significantly higher failure loads. It was also shown in a porcine model that implants on the anterior cortical surface perform better than those on the lateral surface. Increased cortical thickness, in the range tested, was not associated with improved implant performance in the porcine model. CLINICAL RELEVANCE The EndoButton provided the best ACL femoral fixation of the devices tested.

Thumb Interphalangeal Joint Extension By the Extensor Pollicis Brevis: Association With a Subcompartment and de Quervain's Disease

PURPOSE First dorsal compartment anatomy was analyzed for the presence of a separate compartment for the extensor pollicis brevis (EPB) tendon and the ability of the EPB to extend the thumb interphalangeal (IP) joint in order to determine if these characteristics were associated with each other, and with de Quervains disease. METHODS Two groups were studied: (1) 90 cadaver wrists, 28 to 89 years, 38 male and 52 female specimens; and (2) 143 patient wrists, 21 to 82 years, 18 men and 125 women, in which the first dorsal compartment was released for treatment of de Quervains disease. RESULTS The EPB was in a separate compartment in 102 of 143 of the surgical group and 18 of 90 of the cadaver group. The EPB was able to extend the IP joint in 56 of 143 of the surgical group and 19 of 90 of the cadaver group. When the EPB was able to extend the IP joint, it was in a subcompartment in 49 of 56 of the surgical group and 9 of 19 of the cadaver group. When the EPB was able to produce IP extension in the cadaver group, it was inserted on the distal phalanx or the extensor hood. CONCLUSIONS In a substantial number of people undergoing surgery for de Quervains disease and in cadavers, the EPB can extend the thumb IP joint. When it does, particularly in patients with de Quervains disease, it is likely to reside in a subcompartment of the first dorsal compartment. The incidences of a subcompartment for the EPB and the ability of the EPB to extend the thumb IP joint were higher in the de Quervains patient population than in the cadaver group.

Variations of Capitate Morphology in the Wrist

PURPOSE This anatomical study details and categorizes variations in capitate morphology and associated structures in the human cadaveric wrist. METHODS We dissected 107 cadaveric wrists. Capitate morphology, the presence of capitate and hamate ridges, the lunate types, and the width of the medial hamate facet of type II lunates and 4th carpometacarpal joint types were recorded. RESULTS Three types of capitate were identified. The flat type (69/107, or 65%) was characterized by a horizontally oriented (radio-ulnar) lunate-capitate articulation and a longitudinally oriented (proximal-distal) scaphoid-capitate articulation. The flat type was associated with type I lunates or type II lunates with a smaller facet. The spherical type (23/107, or 22%) was associated with a concave articulation formed by the scaphoid and lunate articulations, with an indistinct border between the scaphoid and lunate facets. The width of the medial hamate facet of type II lunates in wrists with a spherical-type capitate was <or=4 mm. The V-shaped type (15/107, or 14%) was characterized by separate lunate and scaphoid facets that converge, forming a V-shape. All the V-shaped capitates had a type II lunate with a large facet. CONCLUSIONS A relationship was found between the 3 capitate types and both the lunate types and the width of the medial hamate facet of the type II lunates. Further study is warranted to determine if these differences in capitate morphology influence the development or progression of various wrist pathologic conditions, such as Kienböcks disease and post-traumatic arthritis associated with scapholunate dissociation and scaphoid nonunion, and the outcome of certain surgical procedures, such as a proximal row carpectomy.

Comparison of Augmentation Methods for Internal Fixation of Osteoporotic Ankle Fractures

Background: Internal fixation of osteoporotic ankle fractures is associated with failure of fixation. This study compared different augmentation methods biomechanically. Materials and Methods: In nine paired fresh-frozen cadaver legs, an identical supination-external rotation type II ankle fracture was created. Fractures were stabilized using an eight-hole locking plate. In four pairs, two screws were inserted across the syndesmosis for purchase in the tibial metaphysis. One leg from each pair was randomly selected for injection of calcium sulphate-calcium phosphate graft into the screw holes. Each leg was mounted to an MTS machine in a custom loading frame. Axial cyclic loading to body weight was performed to measure displacement at the fracture site, followed by rotational loading to failure simulating a supination external rotation injury. Data were analyzed using a two-way paired t -test and ANOVA. Results: The specimens used had a mean bone mineral density of 0.49 ± 0.15 (SD) g/cm2, and a mean age of 83 ± 12 years. In the biomechanical tests, there were no significant differences between augmented and non-augmented locking plates without the tibia-pro-fibula screws in axial stiffness (p = 0.10), external rotation angle at failure (p = 0.42), failure torque (p = 0.57), energy absorbed before failure (p = 0.47), and motion at the fracture site with cyclic axial loading (p = 0.15). There were no significant differences between augmented and non-augmented locking plates with the tibia-pro-fibula screws in the external rotation angle at failure (p = 0.83), failure torque (p = 0.58), and failure energy (p = 0.4). However, the overall strength of the fixation tended to increase with tibia-pro-fibula screws and augmentation. Conclusion: Internal fixation of an osteoporotic lateral malleolar fracture using a locking plate and screws provided a construct comparable in strength to that augmented with calcium sulfate-calcium phosphate graft and/or tibia-pro-fibula screws. Clinical Relevance: Strategies to augment internal fixation of osteoporotic ankle fractures may minimize risk for failure of fixation and may enable early weight bearing mobilization and return to function in elderly patients.

The use of calcium sulfate and calcium phosphate composite graft to augment screw purchase in osteoporotic ankles.

Background: Screws placed in the distal fibula may not have satisfactory purchase during internal fixation of an osteoporotic ankle fracture. Tibia-pro-fibula screws that extend from the fibula into the distal tibial metaphysis provide additional purchase. The purpose of this study was to investigate if purchase of these screws can be enhanced further by injecting calcium sulfate and calcium phosphate composite graft into the drill holes prior to insertion of the screws. Materials and Methods: Bone density was quantified using a DEXA scan in paired cadaver legs. One leg from each pair was randomly selected for injection of composite graft into the screw holes before insertion of the screws. Two screws were inserted through the fibula into the distal tibial metaphysis in each leg, at the level of the syndesmosis under fluoroscopy in a standardized fashion in an MTS machine. Results: After testing 4 pairs of cadaver legs, a statistically significant difference was noted in displacement (p = 0.018 distal, p = 0.0093 proximal), failure load, (p = 0.0185 distal, p = 0.0238 proximal), and failure energy (p = 0.0071 distal, p = 0.0115 proximal) between augmented and non-augmented screws, with the augmented screws being considerably stronger. Conclusion: Screws augmented with composite graft provide significantly greater purchase in an osteoporotic fibular fracture model. Clinical relevance: Composite graft augmented screws inserted into the distal tibia from the fibula may enhance the stability of internal fixation of an osteoporotic ankle fracture. This may enable earlier weightbearing and return to function which is important in elderly patients.

Tensioning of anterior cruciate ligament hamstring grafts: comparing equal tension versus equal stress.

PURPOSE A biomechanical study was undertaken to determine whether equal-stress or equal-tension tensioning of anterior cruciate ligament 4-stranded semitendinosus and gracilis grafts provides a stronger graft construct when testing to ultimate failure. METHODS Eighteen fresh-frozen cadaveric semitendinosus and gracilis tendons were each positioned over a cylinder rod/cryo-clamp connected to an MTS machine (MTS Systems, Eden Prairie, MN) by another cryo-clamp. In the equal-tension group the 4 strands were equally tensioned by weights. In the equal-stress group a tensioning device applied equal stress based on the cross-sectional areas of the tendons. The tendons were preconditioned with 10 cycles and then tested to failure. Graft creep during the preconditioning cycle was determined by MTS measurement of the change in clamp distance. RESULTS The maximum loads of 4-stranded semitendinosus and gracilis grafts tensioned by equal stress were found to be similar to those of the grafts tensioned by equal tension (2,803 +/- 431 N and 2,772 +/- 461 N, respectively). The loads at first failure were 2,640 +/- 468 N and 2,452 +/- 461 N, respectively (P = .17). The preconditioning cycles showed that the equal-stress group resisted graft creep significantly better (P = .0003). CONCLUSIONS The strength of the 4-stranded hamstring graft when equally tensioned or equally stressed was equivalent when tested to failure. After 10 preconditioning cycles, equal stress resisted graft creep significantly better. Equal-stress tensioning offers an alternative tensioning method for 4-stranded hamstring grafts. CLINICAL RELEVANCE Equal-stress tensioning offers an alternative tensioning method for 4-stranded hamstring grafts.

Femoral surface strain in intact composite femurs: a custom computer analysis of the photoelastic coating technique

Understanding how forces are distributed through the proximal femur has many clinical applications for surgeons, researchers, and prosthetic designers. A new system for two-dimensional analysis of femoral surface strain was developed and applied to intact composite femurs. The photoelastic coating method was used to resolve the surface strain under axial loading, and strain analysis was performed using digital imaging of the strain patterns and original computer programs. The technique provides qualitative and quantitative data that describes overall femoral surface strains more completely than previous point analysis and strain gauge techniques. Results from repeated testing found the photoelastic process, computer imaging and computer analysis of strain areas to be statistically repeatable.

Accuracy of Fluoroscopy Versus Computer-Assisted Navigation for the Placement of Anterior Cervical Pedicle Screws

Study Design. Randomized laboratory cadaver study. Objective. The objective of this study was to determine the accuracy of anterior transpedicular screw placement in the cervical spine using conventional fluoroscopy versus computer-assisted navigation. Summary of Background Data. Traditionally, global cervical instability has required anterior and posterior fixation due to the superior biomechanical stability of circumferential constructs. Anterior transpedicular screws (ATPS) have recently been advocated as a single surgical approach. Current clinical publications report using fluoroscopic guidance for screw placement. Computer-assisted navigation (CAN) systems have demonstrated enhanced accuracy of pedicle screw placement at all spine levels but have not been assessed for ATPS. Methods. The anterior vertebrae of 9 fresh frozen cadaver cervical spines were exposed, preserving the lateral and posterior soft tissue envelope. Nine practicing spine surgeons placed 2.0-mm titanium anterior transpecidular Kirschner wires into the C3-T1 pedicles bilaterally using fluoroscopy or CAN guidance. Specimens were imaged by computed tomography and virtual screws were overlaid on the K-wires. Targeting accuracy was compared between the 2 techniques in all planes using a 5-level grading scale. Results. The percentage of acceptable screw placements for fluoroscopy and CAN was 42.6% and 66.7%, respectively (P = 0.012). Catastrophic screw placement (grade 3 or 4) was 33.3% for fluoroscopy and 16.7% for CAN. In the multivariable model, the accuracy rate was 67% lower for fluoroscopy than for CAN after controlling for other factors (odds ratio: 0.33, 95% confidence interval: 0.14–0.79). Conclusion. The accuracy of CAN-guided placement of K-wires for ATPS was superior to placement under fluoroscopic guidance, demonstrating statistically more acceptable screw placements and significantly less catastrophic virtual screws. However, malposition was still high, with potential for vertebral artery and neurological injury in a clinical setting. Further advancement in current ATPS techniques is warranted prior to widespread implementation in a patient setting. Level of Evidence: N/A

Fixation Strength of Anteriorly Inserted Headless Screws for Talar Neck Fractures

Background: For noncomminuted talar neck fractures, traditional fixation is with small fragment screws or cannulated screws. Newer screw systems on the market allow placement of cannulated headless screws, which provide compression by virtue of a variable-pitch thread. The headless construct has an inherent advantage, particularly for the talus, when the screws must be countersunk to prevent wear of the joint articular surfaces. This study tested the biomechanical fixation strength of cannulated headless variable-pitch screws compared with conventional cannulated screws, both placed in an anterior to posterior direction. Methods: A reproducible talar neck fracture was created in nine paired, preserved, cadaver talar necks using a materials testing machine. Talar head fixation was then performed with two cannulated headless variable-pitch 4/5 screws or two 4.0-mm conventional cannulated screws. The specimens were tested to failure and the fixations were normalized to their intact pairs and compared. Results: The headless variable-pitch screw fixation had significantly lower failure displacement than the conventional screw fixation. No significant differences were found between the two fixations for failure stiffness, load at failure or energy absorbed. Conclusions: Cannulated headless variable-pitch screws significantly improved failure displacement when compared to conventional cannulated screws in a cadaveric model, and may be a viable option for talus fracture fixation. Clinical Relevance: Headless, fully threaded, variable-pitch screws have inherent advantages over conventional screws in that they may be less damaging to the articular surface and can compress the fracture for improved reduction. This study demonstrates these screws are also biomechanically similar to conventional screws.

Biomechanical study of flexible intramedullary nails.

Background: Flexible intramedullary (IM) nailing is considered a safe, minimally invasive fixation technique with relatively low complication rates for long-bone fractures in the pediatric population. At our institution, questions have arisen about stability of fixation based on the distance of the nail past the fracture site. Clinically, this question arises with proximal or distal fractures and when the nail is unable to be passed to the desired distance past the fracture site. The purpose of our study was to compare biomechanical resistance with bending forces for fixation constructs whose IM nails are at differing distances beyond the fracture site in different bones. Methods: This study tested matched pairs of canine radii, ulnas, and tibias in 4-point bending and compared the biomechanical properties of length of nail fixation past the fracture site in relation to bone diameter. Results: Fixations of 1 or 2 diameters past the osteotomy yielded gross instability. There was no difference found in bending failure force, displacement, stiffness, or energy when comparing 3 versus 5 diameters of fixation past the fracture site. Conclusions: Flexible IM nails act as internal splints to align the fracture ends. At 3 diameters or more beyond the fracture site, the length does not significantly affect the biomechanical properties of the construct. Clinical Relevance: Flexible IM nails act as internal splints to align the fracture ends. At 3 diameters or more past the fracture site, the length of the nail does not greatly affect the biomechanical properties of the construct. This knowledge may be helpful in clinical scenarios where there is uncertainty about the expected strength of a shorter fixation. Examples include when the nail cannot be passed completely to the distal metaphysis and in proximal or distal long-bone fractures. Further clinical studies are needed to determine implications in a patient setting.