Kathleen N. Meyers

Superior versus anteroinferior plating of the clavicle revisited: a mechanical study.

Objectives: This study was designed to compare bone-implant stiffness of two fixation techniques on a sawbone model of a clavicle fracture. Methods: Twenty-four preosteotomized synthetic left clavicles (Sawbones Worldwide, Vashon, WA) were divided into four groups based on type of fixation: standard 3.5-mm pelvic reconstruction plate in the superior position; standard 3.5-mm pelvic reconstruction plate in an anteroinferior position; 3.5-mm locking pelvic reconstruction plate in a superior position; and a 3.5-mm locking pelvic reconstruction plate in an anteroinferior position. Three nondestructive cyclic mechanical tests were performed in random order: axial, torsion, and four-point bend. Results: No significant difference was found in axial (P = 0.61) or torsional stiffness (internal rotation, P = 0.46 or external rotation, P = 0.49) among all groups. No significant difference occurred in bending rigidity (four-point bending test) with type of plate (P = 0.41), but when the plate was placed anteroinferiorly, bending rigidity was significantly higher (P < 0.001) than in the superior position. Conclusion: Placing the plate anteroinferiorly on the clavicle provides a more stable construct in terms of bending rigidity with no detriment in axial and torsional stiffness compared with placing the plate superiorly. We believe that anteroinferior plating is preferred as a result of the increase in bending rigidity together with other advantages, including avoidance of neurovascular compromise, the use of longer screws, and decreased hardware prominence.

Anatomy of the Thumb Metacarpophalangeal Ulnar and Radial Collateral Ligaments

PURPOSE To describe the origin and insertion of the ulnar (UCL) and radial collateral ligaments (RCL) of the thumb metacarpophalangeal (MCP) joint. METHODS We dissected 18 UCLs and 18 RCLs from fresh-frozen human cadaveric thumbs. We removed all soft tissue overlying the MCP joint, isolating the proper collateral ligaments. We detached the collateral ligaments from the bone while marking their origin and insertion points and measured these attachment sites in relation to bony landmarks by digital photo analysis. RESULTS The center of the UCL origin at the metacarpal was 4.2 mm from the dorsal surface and 5.3 mm from the articular surface. The dorsal aspect of the metacarpal origin site was 2.1 mm from the dorsal edge of the metacarpal. The center of the phalangeal insertion was 2.8 mm from the volar surface and 3.4 mm from the articular surface. The volar aspect of the phalangeal insertion site was 0.7 mm from the volar edge of the phalanx. The center of the RCL origin at the metacarpal was 3.5 mm from the dorsal surface and 3.3 mm from the articular surface. The dorsal aspect of the metacarpal origin site was 1.5 mm from the dorsal edge of the metacarpal. The center of the phalangeal insertion was 2.8 mm from the volar surface and 2.6 mm from the articular surface. The volar aspect of the phalangeal insertion site was 0.5 mm from the volar edge of the phalanx. CONCLUSIONS Our study accurately defined the origin and insertion sites of the UCL and RCL of the thumb MCP joint. CLINICAL RELEVANCE An accurate definition of the anatomical origin and insertion points of the thumb MCP UCL and RCL may allow for more successful surgical repair and reconstruction.

A Biomechanical Comparison of Micromotion After Ankle Fusion Using 2 Fixation Techniques: Intramedullary Arthrodesis Nail or Ilizarov External Fixator

Background: In difficult ankle arthrodesis situations, intramedullary (IM) arthrodesis nails and external fixation are often considered in lieu of standard fusion techniques. The purpose of this study was to compare the amount of micromotion measured across an ankle fusion site stabilized with either an IM nail or with the Ilizarov external fixator. Materials and Methods: The relative bone mineral density of 8 pairs of human cadaveric lower legs was measured by DEXA scanning. One specimen from each pair was randomly assigned to be stabilized with a new generation IM nail and the other with an Ilizarov external fixator. Specimens were tested in compression, rotation, and dorsiflexion. Optical motion capture was used to measure the direct motion occurring at the fusion site. Results: No significant difference was found between the axial displacements (p = 0.94), torsional displacement (p = 0.07), or the dorsiflexion angular displacement (p = 0.28) for the IM rod group and the external fixation group. A weak correlation was found between BMD and displacement. Conclusion: Both the new generation IM nail and the Ilizarov external fixator imparted excellent stability to the fusion site despite a wide range of bone mineral densities. Medialization of the talus, the ability to compress the nail, and the addition of a posterior-to-anterior locking screw were thought to improve the performance of the nail. Clinical Relevance: Both IM nail and Ilizarov external fixation provided excellent fusion site stability. The decision of which implant to use for complex arthrodesis should be dictated by the clinical needs.

Stability of the metatarsophalangeal joint of the lesser toes: a cadaveric study.

Dorsal instability of the metatarsophalangeal joint (MTPJ) of the lesser toes is an important cause of forefoot pain. Both conservative and surgical treatment options have been proposed. However, the role of each static stabilizing structure has not been elucidated. We hypothesized that isolated sectioning of the plantar plate (PP) would result in greater dorsal translation compared to isolated sectioning of the medial collateral ligaments (MCL) or lateral (LCL) collateral ligaments, or the extensor hood (EH), and that combined injury to two or more structures would result in greater dorsal translation compared to isolated PP injury. Fifty‐four cadaveric lesser toe specimens were randomized into groups for individual and combined sectioning of the PP, EH, and LCL and MCL. A 30 N axial load was applied to each specimen in the plantar–dorsal direction and dorsal translation of the phalanx was measured for each condition. ANOVA was used to compare groups. A 19% change in MTP translation was found from intact after sectioning the PP. No significant difference in translation was seen after individual sectioning of the EH, MCL, or LCL. A significant increase in translation occurred from intact with the following sectioning combinations: MCL + LCL, 37%; EH + MCL + LCL, 45%; and PP + MCL + LCL, 63%. Thus, the PP is the main restraint for dorsal MTPJ translation. MCL and LCL have important partial contribution to MTPJ stability. Injury to the PP, individually, or combined injuries to the PP, EH, MCL, or LCL, appear to cause significant instability that may warrant more aggressive treatment.

Polished Trays Reduce Backside Wear Independent of Post Location in Posterior-stabilized TKAs

BackgroundBackside damage of the polyethylene in TKA is a potential source of debris. The location of the tibial post in posterior-stabilized implants may influence micromotion, and thus affect backside damage, as may surface roughness.QuestionsWe used implant retrieval analysis to (1) examine if there were differences in backside damage among three modern posterior-stabilized implants attributable to variable surface roughness; (2) determine if the location of damage on the tibial post affected the pattern of backside damage; and (3) determine if demographics influenced backside damage.MethodsWe identified 403 posterior-stabilized tibial retrieved inserts (147 NexGen®, 152 Optetrak®, 104 Genesis® II). The damage on the surfaces of the tibial posts was previously graded. The backside of the inserts (divided into quadrants) were scored for evidence of damage. The total quadrant damage was compared for each implant group, the relationship between post face damage and location of damage on the backside was determined for each implant group, and total backside damage was compared among the three implant groups.ResultsNo correlation was found between the location of damage on the post and location of damage on the backside of the implant for any of the three groups. The Genesis® II polyethylene implants, which articulate with a highly polished tibial tray, showed a significantly lower total backside damage score (p < 0.01) when compared with the other two implant groups. The Genesis® II and Optetrak® showed significantly more damage in the posterior quadrants of the implants (p < 0.01) when compared with the anterior quadrants. A linear regression analysis revealed that lower tibial tray surface roughness was correlated with decreased damage.ConclusionsAn implant design with a highly polished tibial tray was associated with decreased backside damage. However, tibial post design and location did not influence the location of backside damage.Clinical RelevanceOur study showed that a highly polished tibial tray was associated with decreased damage to the backside of polyethylene inserts independent of post design and location. These findings should be taken into consideration when new generations of implants are designed.

Mechanics of an Anatomical Reconstruction for the Thumb Metacarpophalangeal Collateral Ligaments

PURPOSE This study biomechanically evaluated a technically easy variation of anatomical reconstruction of the thumb metacarpophalangeal (MCP) joint ulnar (UCL) and radial (RCL) collateral ligaments. Based on previous work describing the anatomical origin and insertion of these ligaments, we hypothesized that, using these attachment points, joint stability would be restored without significant loss of MCP flexion. METHODS The collateral ligaments were isolated in 30 cadaveric thumbs (15 UCLs and 15 RCLs). A cyclical load was applied to the MCP joint to assess flexion, radial/ulnar deviation in neutral, and radial/ulnar deviation in 30° of flexion. The collateral ligaments were detached from the bone while their origin and insertion points were marked. Using these sites, anatomical ligament reconstruction was performed with a palmaris longus tendon graft and interference screw fixation. Cyclical testing was repeated on the reconstructed ligaments. RESULTS No significant difference was found between intact and reconstructed UCLs when tested for radial deviation in neutral, radial deviation in 30° of flexion, or total MCP flexion. No significant difference was found between intact and reconstructed RCLs when tested for ulnar deviation in neutral, ulnar deviation in 30° of flexion, or total MCP flexion. CONCLUSIONS Our anatomical reconstruction is simple and restores UCL and RCL anatomy as compared with current techniques in the literature by placing the origin and insertion at their anatomical points with use of an interference screw. Using these anatomical origins and insertions, we were able to restore the MCP flexion and stability seen in an intact ligament. CLINICAL RELEVANCE Our anatomical reconstruction offers a technically easy option for reconstruction of thumb MCP collateral ligament injuries, restoring joint stability without sacrificing flexion.

Anisometry of Medial Patellofemoral Ligament Reconstruction in the Setting of Patella Alta and Increased Tibial Tubercle-Trochlear Groove (TT-TG) Distance

Objectives: Medial patellofemoral ligament (MPFL) reconstruction is a common procedure to treat recurrent patellofemoral instability. However, the effects of an elevated tibial tubercle-trochlear groove (TT-TG) distance and patella alta, as measured by the Caton-Deschamps (C/D) ratio, on MPFL isometry remain unclear. We hypothesized that increased lateralization and proximalization of the tibial tubercle (TT) will have increasingly adverse effects on the isometry of the MPFL. Methods: Ten fresh-frozen cadaveric knees were placed on a custom testing fixture, with a fixed femur and tibia mobile through 120 degrees of flexion. The quadriceps tendon was loaded with 10.8 N in an anatomic direction using a weighted pulley system. A 0.2 N patellar lateral displacement load was used to simulate an intact lateral retinaculum to avoid over-medializing the patella. A tunnel was drilled under fluoroscopic guidance from Schottle’s point on the medial distal femur through the lateral cortex. A suture anchor was placed at the upper 66% of the medial border of the patella and the sutures were shuttled through to the lateral side and attached to a pulley with a 1 N weight. Retroreflective markers were attached to the femur, tibia, patella, and suture. MPFL length change, as measured by suture marker motion, was assessed using a 3D motion capture system through a range of motion between 0 deg and 110 deg with the native TT anatomy. Recordings were repeated after a flat TT osteotomy and transfer to a TT-TG of 20 mm and 25 mm and a C/D ratio of 1.2 and 1.4, including all combinations. Generalized estimating equation (GEE) modeling technique was used to analyze and control for the clustered nature of the data. SAS version 9.3 (SAS Inc., Cary, NC) was used for all data analyses. Results: Analysis was performed on 9 specimens secondary to significant deviations in the baseline normative data. Intact knees showed MPFL isometry through 20-70 degrees range of motion. Tibial tubercle lateralization significantly altered MPFL isometry with a threshold TT-TG of 25 mm (p=0.045) (Figure 1). Patella alta significantly altered MPFL isometry with a threshold C/D of 1.4 (p=0.025) (Figure 2). The effect of TT lateralization combined with patella alta compounded the anisometry, lowering the threshold for patella alta to a C/D of 1.2 when combined with a TT-TG of 25 mm (P<0.001) (Figure 3). Conclusion: Increased TT lateralization and proximalization significantly alter MPFL isometry. Tibial tubercle transfer should be considered when performing an MPFL reconstruction for recurrent patellofemoral instability in the setting of significant patella alta, elevated TT-TG and especially when both are present as an isolated MPFL reconstruction may be prone to failure given the anisometry demonstrated.

Capitellum excision: Mechanical implications and clinical consequences

Controversy exists regarding the optimal treatment of isolated fractures of the capitellum that are not amenable to open reduction and internal fixation. Excision of the capitellum could result in instability of the elbow, though only limited the clinical or laboratory evidence exists to support this outcome. The aim of our study was to determine if capitellum excision leads to significant instability by measuring the relative change in varus–valgus displacement of the elbow. The varus–valgus displacement was recorded in 11 cadaveric elbows before and after isolated excision of the capitellum. Specimens were testing in varus‐loaded and valgus‐loaded positions with and without a 1 kg weight on the forearm. The varus–valgus displacement at the elbow was measured using a 3D motion capture system. Capitellum excision did not significantly change varus–valgus displacements in either the adducted, varus, or valgus position of the elbow (p = 0.80, p = 0.28, p = 0.51). Furthermore, the addition of the 1 kg external functional load to the forearm did not produce a significant change in the varus and valgus loaded positions (p = 0.16, p = 0.36). Our results demonstrate that excision of the capitellum in the setting of intact ligamentous structures does not result in significant instability in either the adducted varus loaded or valgus loaded positions of the elbow.

Variability in Elongation and Failure of the Medial Collateral Ligament After Pie-Crusting With 16- and 18-Gauge Needles

BACKGROUND In knee arthroplasty with preoperative varus deformity, medial collateral ligament (MCL) release may be needed to achieve balance. Pie-crusting allows for controlled release, but questions remain regarding its ability to obtain predictable results. We compared 16- vs18-gauge needle punctures and determined the number of punctures required to (1) lengthen the MCL by 1 mm and (2) cause ligament failure. METHODS Thirteen knees were dissected, leaving the femur and tibia with an isolated MCL, and randomly assigned to 16- or 18-gauge groups. Initial stiffness was assessed by cycling the ligament to 300 N for 5 cycles. The selected needle was used to make 10 punctures centered over the area of greatest tension. Cyclic testing was repeated after each set of punctures. Changes in MCL length and stiffness were measured. This process was repeated until failure. RESULTS No differences occurred between the 16- and 18-gauge groups in cross-sectional area, initial stiffness, number of punctures to lengthen the MCL by 1 mm, or number of punctures to failure. As the number of punctures increased, a linear increase in elongation and decrease in stiffness occurred. CONCLUSION Needle size was not the influencing factor. Variability in number of punctures, regardless of needle size, to elongate or fail the MCL shows the difficulty in developing a reproducible pie-crusting technique. This suggests that a standard number of punctures do not achieve controlled MCL lengthening for all patients, but that the number of punctures needed can be calculated for an individual knee based on the initial elongation after 10 punctures.

A CT-based approach with 3D modeling to determine optimal radiographic views of the scaphotrapezial and scaphotrapezoid joints

PURPOSE To use a CT-based approach with 3D modeling to determine novel radiographic views of the scaphotrapezial (STl) and scaphotrapezoid (STd) joints. MATERIALS AND METHODS Consecutive wrist CT scans excluding those with pathology of the distal radius, scaphoid, trapezium, or trapezoid of subjects between ages 18 and 60 years were retrospectively reviewed. Three-dimensional reconstructions of CT scans were created and best-fit planes of the STl and STd joints were generated. Angles of these planes relative to a distal radial coordinate system were calculated to determine tilt of the wrist and the X-ray beam for novel radiographic views of these joints. RESULTS Fifty eligible wrist CT scans were identified. The mean age was 38 years (range, 18 to 59). For the novel STl PA view, the wrist is supinated 17° from the standard PA view and the X-ray beam is canted 6° caudad. In the STl lateral view, the wrist is pronated 17° from the standard lateral view, and the X-ray beam is canted 20° caudad. In the STd PA tilt view, the wrist is supinated 28° from the standard PA view, and the X-ray beam is canted 13° caudad. In the STd joint lateral tilt view, the wrist is pronated 28° from the standard lateral view, and the X-ray beam is canted 29° caudad. CONCLUSION We describe novel radiographic views of the STl and STd joints based on 3D modeling of wrist CT scans. Further studies are required to assess the efficacy of these views in detecting joint pathology.