Richard D. Peindl

Biomechanical analysis of blade plate versus locking plate fixation for a proximal humerus fracture: comparison using cadaveric and synthetic humeri.

Objective: To compare the mechanical stability of a fixed-angle blade plate with that of a locking plate in a cadaveric proximal humerus fracture-fixation model subjected to cyclic loading. A secondary objective was to evaluate whether the use of synthetic humerus specimens would replicate significant differences found during cadaveric tests. Design: Mechanical evaluation of constructs in bending and torsion. Setting: Biomechanical laboratory in an academic medical center. Methods: Simulated humeral neck fractures (Orthopaedic Trauma Association (OTA) classification 11A3), in matched-pair cadaveric and synthetic specimens underwent fixation using either a 3.5-mm, 90-degree cannulated LC-Angled Blade Plate or a 3.5-mm LCP Proximal Humerus Locking Plate. Cadaveric specimen constructs were cyclically loaded in bending and torsion; synthetic specimens were tested in torsion. Main Outcome Measure: Humeral shaft-bending displacements and angular rotations for respective cyclic bending loads and axial torques were recorded and compared at repeated cyclic intervals to evaluate construct loosening. Results: Locking-plate constructs exhibited significantly less loosening than blade-plate constructs for torsional loading in cadaveric specimens (P = 0.036). The two types of constructs performed similarly for torsional loading in synthetic specimens (P = 0.100). Under cyclic, closed-bending load conditions in which the plates served as tension members, both types of constructs performed similarly in cadaveric specimens (P = 0.079). Conclusions: For simulated humeral neck fractures subjected to cyclic loading, locking-plate constructs demonstrated significantly greater torsional stability and similar bending stability to blade plates in a cadaveric specimen model. In contrast, these same constructs performed similarly with torsional loading when using synthetic humerus specimens. These results indicate potential advantages for locking-plate fixation. They also indicate that the synthetic specimens tested may not be appropriate for evaluating fixation stability in the humeral head, where cancellous bone fixation predominates.

Unstable proximal extraarticular tibia fractures: a biomechanical evaluation of four methods of fixation.

Objective: To compare the biomechanical stability of extraarticular proximal tibia fractures reconstructed using a double-plate construct, locking plate system, hybrid external fixator, and single lateral periarticular plate, all from the same manufacturer. Design: Standardized proximal tibial fractures (AO classification 41-A3.2 and A3.3) in synthetic tibiae were stabilized using one of the four constructs. Load versus proximal fragment translation and rotation were monitored in each case. Fixation was evaluated for moderately unstable and completely unstable fractures simulated by wedge and gap osteotomies of the proximal femur. Setting: Academic medical center biomechanical engineering laboratory. Main Outcome Measurements: Proximal fragment axial displacement, varus rotation, and posterior rotation versus applied load for each of the constructs. Results: The double-plate construct was significantly stiffer than all other constructs with regard to resistance to axial displacement, varus rotation, and posterior rotation for both types of unstable fractures. With regard to axial stiffness, the double-plate construct was statistically similar to an intact tibia for moderately stable fractures. The locking plate and the external fixator were similar for stabilization of moderately unstable fractures, whereas the locking plate and the periarticular plate were significantly stiffer than the external fixator construct for completely unstable fractures. Conclusion: For axial load applied to a wedge or gap osteotomy of the proximal tibia, the double-plate construct provided significantly more rigidity than the other constructs. The locking plate, periarticular plate, and hybrid external fixator tested provided similar rigidity for the wedge osteotomy, but for the gap osteotomy the external fixator could not support 600N without complete closure of the gap.

Measurement of thumb abduction strength: Normative data and a comparison with grip and pinch strength

Abduction strength of the thumb was measured in normal men (n = 101; age range, 21-94 years) and women (n = 208; age range, 20-97 years). Abduction-strength measurements were conducted concurrently with grip and pinch strength measurements made by well-established clinical methods. Normal values were established and stratified by age and sex. Thumb abduction strength generally correlated with grip and pinch strength. All strength variables at all ages were greater in men than in women. The magnitude of all strength variables was maintained from 20 to 59 years of age, then decreased with increasing age in both men and women. Measurement of thumb abduction strength may prove to be a useful adjunct to the various tests currently used by hand surgeons to assess hand function.

Modular tibial augmentations in total knee arthroplasty

Proximal tibial bony deficiencies are not uncommon in primary and revision total knee arthroplasty. Modular tibial augmentations were introduced to address these deficiencies. Alterations in strain distribution as a result of medial wedge and block augmentations were evaluated for a modular total knee arthroplasty system in 6 fresh frozen anatomic specimen tibias. Full-field strain patterns were examined using photoelastic coating methods, and high strain regions were evaluated using strain gage rosette techniques. The total knee arthroplasty installations were tested in static physiologic axial and torsional load configurations. The relative effects of sequential wedge and block augmentations compared with the nonaugmented case were statistically analyzed. There were no overall statistical differences in the 3 treatments in terms of maximal (principal) strains. A secondary analysis that evaluated specific location and load pattern combinations established several minor statistical differences along with insights into the manner in which each construct loads the proximal tibia. Although metal wedge augmentation commonly is used, block augmentation seems to be an appropriate alternative from a strain distribution standpoint in cases in which the block geometry better approximates the bony defect.

A Biomechanical Comparison of Two Suture Anchor Configurations for the Repair of Type II SLAP Lesions Subjected to a Peel-Back Mechanism of Failure

PURPOSE The purpose of this study was to biomechanically compare 2 different suture anchor configurations in the repair of type II SLAP lesions. METHODS Standardized type II SLAP lesions were created in 8 matched pairs of cadaveric shoulders. Two different suture anchor configurations were used to repair the type II SLAP lesions. Group 1 SLAP lesions were repaired with 1 suture anchor placed at the anterior border and a second suture anchor placed at the posterior border of the biceps tendon. Group 2 SLAP lesions were repaired with 2 suture anchors placed posterior to the biceps tendon. Biomechanical testing was conducted in 1 direction. A posterior-directed force, in the plane of the glenoid, simulated the peel-back mechanism that occurs during the late cocking phase of throwing. Biceps-labral complex displacement from the glenoid was measured with 2 miniature displacement transducers. Repair failure (2 mm of posterior labral displacement), ultimate failure, and construct stiffness were measured for each specimen. RESULTS The mean load to repair failure was 43.66 N in group 1 and 40.70 N in group 2. The mean load to ultimate failure was 156.28 N in group 1 and 162.06 N in group 2. The mean construct stiffness was 25.91 N/mm in group 1 and 30.28 N/mm in group 2. The differences between the 2 groups were not statistically significant in terms of repair failure, ultimate failure, and construct stiffness. CONCLUSIONS When repaired type II SLAP lesions were subjected to a posterior vector load to simulate the peel-back mechanism, the 2 suture anchor configurations were biomechanically equivalent. CLINICAL RELEVANCE Placement of an anterior suture anchor could, theoretically, tension the anterior capsulolabral structures via the superior and middle glenohumeral ligaments to the superior labrum. The results of this study suggest that there is no biomechanical advantage to placing an anterior suture anchor and so the use of 2 posterior suture anchors may be preferable in the repair of type II SLAP lesions.

Lower extremity joint kinematics during stair climbing in knee osteoarthritis.

PURPOSE Knee osteoarthritis (OA) is one of the most prevalent chronic lower extremity diseases, causing profound limitation of movement and ability to perform activities of daily living. The purpose of this study was to compare various hip, knee, and ankle joint kinematic variables between knee OA subjects and matched healthy controls during stair ascent and descent. METHODS Eighteen subjects with knee OA (age = 60.2 ± 9.9 yr, mass = 90.3 ± 16.7 kg, height = 168.4 ± 9.9 cm) and 18 healthy matched controls (age = 60.3 ± 10.7 yr, mass = 81.1 ± 21.2 kg, height = 168.3 ± 11.9 cm) participated in the study. Subjects performed five ascending and descending trials on a custom-built staircase while their motion was captured three-dimensionally using an eight-camera optical video motion capture system. RESULTS Significant group × direction interactions were found for average hip flexion angle at foot strike (P = 0.04), for average ankle adduction angle at foot strike (P = 0.01), and for peak ankle dorsiflexion angle during support (P = 0.05) and swing (P = 0.01). Specifically, knee OA and control subjects demonstrated greater hip flexion angle at foot strike and ankle dorsiflexion angle during swing but showed smaller ankle dorsiflexion angle during support during stair ascent compared with descent. Furthermore, compared with controls, knee OA patients demonstrated greater hip abduction at foot strike (-3.1° ± 3.9°) and smaller peak knee flexion during support (60.4° ± 5.0°) and swing (86.7° ± 5.4°). Time of peak hip abduction (34.2% ± 7.1%), hip flexion (7.0% ± 12.3%), knee flexion (69.8% ± 4.6%), dorsiflexion (51.4% ± 2.9%), and ankle adduction (37.3% ± 20.8%) during support occurred later in the gait cycle for knee OA patients. CONCLUSIONS These data demonstrate that knee OA directly influences specific knee joint kinematics and induces kinematic alterations at the hip and ankle perhaps to compensate for the existing knee joint pathology.

Temporal-spatial gait adaptations during stair ascent and descent in patients with knee osteoarthritis.

Knee osteoarthritis (OA) accounts for more functional disability of the lower extremity than any other disease. We recruited 18 patients with knee OA and 18 healthy age-, height-, mass-, and gender-matched control subjects to investigate the effects knee OA has on select spatial and temporal gait variables during a stair climbing task. No group-by-direction interaction was observed; however, significant effects did occur for group and direction. Specifically, patients with knee OA demonstrated less time in single support, greater time in double support, decreased step length, greater step width, less stride length, decreased total gait velocity, greater total time in support, and less total time in swing, compared with controls. Early-stage knee OA directly influences specific temporal and spatial gait characteristics during stair climbing.

A Biomechanical Evaluation of Ulnar Collateral Ligament Reconstruction Using a Novel Technique for Ulnar-Sided Fixation

Background: Techniques for ulnar collateral ligament (UCL) reconstruction have evolved since its original description. Hypothesis: Ulnar collateral ligament reconstruction using the ZipLoop for ulnar-sided fixation, as combined with the humeral docking technique supplemented with an interference screw, will restore valgus stability similar to that of the Jobe technique and the native ligament. Study Design: Controlled laboratory study. Methods: Kinematic testing was performed on 8 matched pairs of cadaver elbows with an electromagnetic tracking system through an arc of motion for the intact, disrupted, and reconstructed states of the UCL in an unloaded and loaded condition. From each pair, the docking technique using the ZipLoop for ulnar fixation and humeral docking technique supplemented with an interference screw and the traditional Jobe technique were performed with matched gracilis allograft tendons. After kinematic testing, both reconstruction groups were tested to failure at 70° of flexion. Results: Kinematic results for the unloaded condition showed that both reconstruction techniques significantly overcorrected (less valgus angulation) the specimens between 40° and 120° of flexion when compared with the intact ligament (all P values < .027). Under loaded conditions, the ulnar trajectories for both reconstruction techniques exhibited significantly greater valgus angulation (undercorrection) at 20° of flexion (Jobe, P = .0084; ZipLoop, P = .0289) when compared with the intact ligament but were not significantly different over the remaining arc of motion. Failure testing resulted in no significant statistical difference between the 2 reconstruction groups. Failure testing demonstrated that humeral tunnel egress, midsubstance elongation, and ulnar tunnel egress of the ligament were similar between the reconstruction techniques. Conclusion: The docking technique using the ZipLoop for ulnar-sided fixation is biomechanically equivalent to the Jobe technique for UCL reconstruction. Both reconstruction techniques restore valgus stability similar to that of the native UCL ligament. Clinical Relevance: This modification in the docking technique restores elbow kinematics while eliminating the risk of ulnar bone bridge fracture, and it allows for retensioning of the graft after cortical fixation.

Comparison of growth and metabolism of avian osteoblasts on polished disks versus thin films of titanium alloy

The purpose of this study was to evaluate the efficacy of using high vacuum, thermal evaporation to deposit thin films of Ti-6Al-4V onto plates for subsequent cell culture investigations. Osteoblastic response to thin-film coated plates was compared to that of cells grown on Ti alloy disk inserts and uncoated culture plates. The Ti alloy disks were polished, cleaned, and passivated following a commercial protocol for orthopedic implants. Mean surface roughness was 262 nm for the Ti alloy disks and 4.756 nm for the coated culture plates. Osteoblasts isolated from 16-day chick embryo calvariae were cultured on polystyrene, thin films, and disks. At confluence, the cells were cultured an additional 48 h and were evaluated for cell number (DNA content), rate of glycolysis (lactate production), alkaline phosphatase activity (ALPase), and collagenous (3H-proline hydroxylation) and noncollagenous protein synthesis. Cell morphology was similar for the controls, disks, and thin-film groups. DNA, lactate, cell layer ALPase, 3H-hydroxyproline, and noncollagenous protein were not different (p > 0.05) among the control, thin-film, and disk groups. Medium ALPase was lower (p < 0.05) in the thin-film group compared to the control group. Although aluminum and vanadium percentages varied from nominal in the thin-film groups (11Al-2V as opposed to 6Al-4V), avian osteoblasts responded similarly to the Ti alloy thin films, disks, and uncoated culture plates for the smooth surfaces tested. The thin-film cell culture system used for elemental material studies appears to offer a promising method for the investigation of cellular response to alloyed biomaterials as well. Proper adjustments in alloy percentages before deposition, however, need to be made if thermal evaporation is utilized.

Motion Predicts Clinical Callus Formation: Construct-specific Finite Element Analysis of Supracondylar Femoral Fractures

BACKGROUND Mechanotransduction is theorized to influence fracture-healing, but optimal fracture-site motion is poorly defined. We hypothesized that three-dimensional (3-D) fracture-site motion as estimated by finite element (FE) analysis would influence callus formation for a clinical series of supracondylar femoral fractures treated with locking-plate fixation. METHODS Construct-specific FE modeling simulated 3-D fracture-site motion for sixty-six supracondylar femoral fractures (OTA/AO classification of 33A or 33C) treated at a single institution. Construct stiffness and directional motion through the fracture were investigated to assess the validity of construct stiffness as a surrogate measure of 3-D motion at the fracture site. Callus formation was assessed radiographically for all patients at six, twelve, and twenty-four weeks postoperatively. Univariate and multivariate linear regression analyses examined the effects of longitudinal motion, shear (transverse motion), open fracture, smoking, and diabetes on callus formation. Construct types were compared to determine whether their 3-D motion profile was associated with callus formation. RESULTS Shear disproportionately increased relative to longitudinal motion with increasing bridge span, which was not predicted by our assessment of construct stiffness alone. Callus formation was not associated with open fracture, smoking, or diabetes at six, twelve, or twenty-four weeks. However, callus formation was associated with 3-D fracture-site motion at twelve and twenty-four weeks. Longitudinal motion promoted callus formation at twelve and twenty-four weeks (p = 0.017 for both). Shear inhibited callus formation at twelve and twenty-four weeks (p = 0.017 and p = 0.022, respectively). Titanium constructs with a short bridge span demonstrated greater longitudinal motion with less shear than did the other constructs, and this was associated with greater callus formation (p < 0.001). CONCLUSIONS In this study of supracondylar femoral fractures treated with locking-plate fixation, longitudinal motion promoted callus formation, while shear inhibited callus formation. Construct stiffness was found to be a poor surrogate of fracture-site motion. Future implant design and operative fixation strategies should seek to optimize 3-D fracture-site motion rather than rely on surrogate measures such as axial stiffness.