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To describe a novel construct for proximal interphalangeal (PIP) joint arthrodesis using headless cannulated screws as an intramedullary washer to augment 90/90 intraosseous wiring and compare the biomechanical properties of this construct with those of the 90/90 intraosseous wiring without headless screw augmentation.
Methods
Biomechanical evaluation of augmented 90/90 intraosseous wiring with headless cannulated screws (group 1) or 90/90 intraosseous wiring without augmentation (group 2) for PIP joint arthrodesis was performed in 3 matched-pair cadaveric specimens (12 digits per group). Each group was loaded to 10 N in the sagittal and coronal planes and the resultant stiffness from the load-displacement curve was calculated. In extension, each group then underwent load to permanent deformation and load to catastrophic failure.
Results
The augmented 90/90 intraosseous wiring with cannulated screws construct demonstrated significantly greater stiffness by 132%, 64%, 79%, and 75% in flexion, extension, ulnar, and radial displacement, respectively. During load to permanent deformation testing, a 42% greater force was required to create permanent deformation in group 1 compared than group 2. There was no significant difference between the 2 groups during load to catastrophic failure testing.
Conclusions
Augmenting 90/90 intraosseous wiring for PIP joint arthrodesis with 2 headless cannulated screws in the sagittal plane that serve as intramedullary washers for the sagittal wire and posts for the coronal wire significantly increases stiffness in all directions as well as load to permanent deformation compared with 90/90 intraosseous wiring without cannulated screw augmentation.
Clinical relevance
Augmentation of the 90/90 intraosseous wire construct with headless cannulated screws can be considered in patients at risk for wire cutout or implant failure.
The resultant destruction of articular cartilage can cause significant pain, limit capacity to perform essential daily activities, and lead to a decrease in quality of life.
Joint-specific hand symptoms and self-reported and performance-based functional status in African Americans and Caucasians: the Johnston County Osteoarthritis Project.
Those patients who are symptomatic are initially managed with anti-inflammatory medications, intra-articular injections, and orthoses. If nonsurgical modalities fail to provide relief, surgical intervention may be considered.
Arthroplasty and arthrodesis of the PIP joint are the mainstays of treatment for severe arthritis refractory to nonsurgical management. Currently, no consensus exists regarding the superiority of either procedure.
Arthrodesis may be considered in patients who do not want to take the risks of arthroplasty; have deficient bone stock, incompetent collateral ligaments, deficient soft tissue coverage; or as a salvage for failed arthroplasty.
The 90/90 intraosseous wiring of the PIP joint involves placing 1 cerclage wire across the PIP joint in the sagittal plane and a second orthogonal wire in the coronal plane for added compression and stability of the joint. However, many patients who undergo arthrodesis of the PIP joint are elderly individuals with poor bone quality, thereby making the risk of wire cutout, during intraoperative compression or after surgery, a significant limitation of this technique. The risk of wire cutout may be decreased by placement of the cerclage wire through an intramedullary washer. A washer allows for distribution of the compressive force applied by the tensioned cerclage wire over a larger surface area, thereby potentially allowing for greater compression force generation before cutout or failure of the cerclage wire. The purpose of this study was to describe a novel construct for PIP joint arthrodesis using headless cannulated screws as an intramedullary washer to augment 90/90 intraosseous wiring and to compare the biomechanical properties of this construct with those of 90/90 intraosseous wiring without cannulated screw augmentation.
Methods
Three matched-pair fresh-frozen cadaveric hand specimens were used, yielding 24 fingers for biomechanical testing (6 index, 6 middle, 6 ring, and 6 little). The average age of the cadaveric specimens was 40 years (range, 40–41 years) at the time of death. Two paired specimens were men and 1 was a woman. The paired specimens were frozen at –20°C and thawed for 24 hours prior to dissection. All specimens were radiographed to confirm that no preexisting pathology was present in the hand. The little, ring, middle, and index fingers from a hand specimen were randomly assigned to 1 of 2 fixation constructs: augmented 90/90 intraosseous wiring with headless cannulated screws (group 1) or 90/90 intraosseous wiring without screw augmentation (group 2). The remaining group was assigned to the little, ring, middle, and index fingers from the matched contralateral hand specimen.
Specimen preparation
The fingers from each specimen were disarticulated at the metacarpophalangeal joint. The dorsal skin and soft tissue were incised longitudinally, and the extensor tendon was transversely incised distal to the PIP joint and reflected proximally (Fig. 1A). A custom, 3-dimensionally printed jig with a built-in cutting block was then fixed to the dorsal surface of the proximal phalanx. This allowed for reproducible flat bone cuts of the proximal phalangeal head at an angle of 30° (Fig. 1B). A second perpendicular bone cut was made at the base of the middle phalanx. Both bone cuts were made just below the surface of the subchondral bone.
Figure 1A Dissection of the proximal interphalangeal joint (PIP) joint prior to bone cuts and arthrodesis. B A 3-dimensionally printed jig with a built-in cutting block affixed to the dorsal surface of the proximal phalanx. This allowed for reproducible flat bone cuts of the proximal phalangeal head at an angle of 30°. C Fluoroscopic image demonstrates correct trajectory of the K-wire placed through the jig. D A 2.0-mm cannulated drill inserted over the K-wire to allow for eventual placement of the 2.5-mm headless cannulated screw.
Augmented 90/90 intraosseous wiring with headless cannulated screws
A 0.35-inch K-wire was inserted through the top hat of the 3-dimensionally printed jig with a built-in 30° angle such that the K-wire was placed 3 mm proximal and parallel to the proximal phalanx bone cut. Placement of the K-wire was checked under fluoroscopic imaging (Fig. 1C). After adequate placement of the K-wire was confirmed, a 2.0-mm cannulated drill was inserted over the K-wire following removal of the top hat (Fig. 1D). A bicortical screw hole was then made. A 2.5- mm titanium headless cannulated screw of 8, 9, or 10 mm (Arthrex Compression FT Screw, 2.5 Micro. Arthrex, Naples, FL) length was then inserted through the jig into the screw hole. Screw length was determined using a second K-wire of the same length through measured subtraction because a standard depth gauge would not fit through the jig. Using a similar technique, a second headless cannulated screw was placed 3 mm distal and parallel to the perpendicular bone cut of the middle phalanx base. A 22-gauge circular wire was then passed through the 2 cannulated screws, tightened, then twisted dorsally. Next, under fluoroscopic guidance, 2 holes were made using a 0.45-inch K-wire inserted from radial to ulnar just proximal to the sagittal screw in the proximal phalanx and just distal to the sagittal screw in the middle phalanx. A second 22-gauge circular wire was then passed through the 2 holes, tightened, then twisted in the coronal plane (Fig. 2). Both circular wires were twisted 6 or 7 times.
Figure 2A, B Augmented 90/90 intraosseous wiring for PIP joint arthrodesis with 2 headless cannulated screws in the sagittal plane that serve as intramedullary washers for the sagittal wire and posts for the coronal wire. C, D Anteroposterior and lateral views of the augmented 90/90 intraosseous wire construct.
The 90/90 intraosseous wiring without cannulated screw augmentation
A 0.45-inch K-wire was inserted through the top hat, of the 3-dimensionaly printed jig and checked under fluoroscopic imaging. After adequate placement of the K-wire was confirmed, a bicortical hole was created though the jig, using the 0.45-inch K-wire that was 3 mm proximal and parallel to the proximal phalanx bone cut. Using a similar technique, a second bicortical hole was made 3 mm distal and parallel to the perpendicular bone cut of the middle phalanx base. A 22-gauge circular wire was then passed through the 2 sagittal holes, tightened, then twisted dorsally. Next, under fluoroscopic guidance, 2 holes were made using a 0.45-inch K-wire inserted from radial to ulnar, just proximal to the sagittal circular wire in the proximal phalanx and just distal to the sagittal circular wire in the middle phalanx. A second 22-gauge circular wire was then passed through the 2 holes, tightened, then twisted in the coronal plane (Fig. 3). Both circular wires were twisted 6 or 7 times.
Figure 3A, B The 90/90 intraosseous wiring for PIP joint arthrodesis without screw augmentation. C, D Anteroposterior and lateral views of the 90/90 intraosseous wire construct without screw augmentation.
Two orthogonal K-wires were placed at the base of the proximal phalanx to add stability to the specimen during potting and to ensure the specimen remained potted at an angle such that the dorsal midpoint of the arthrodesis construct was perpendicular to the base of the square block (Fig. 4A). A triangular ruler with a built-in fixed 90° angle was used. One edge of the ruler was placed perpendicular to the potting block and the arthrodesis site was aligned such that it was parallel to the second edge of the ruler, thereby perpendicular to the base of the potting block. Each specimen was potted in a square block of Plaster of Paris (Hood Packing Corporations, Monticello, AZ) such that two-thirds of the proximal phalanx was embedded with plaster (Fig. 4B). Specimens were potted and then tested in matched pairs to minimize any variability due to room temperature, thawing time, or specimen water content.
Figure 4A Two orthogonal K-wires were placed at the base of the proximal phalanx to add stability to the specimen during potting and ensure the specimen remained potted at an angle such that the dorsal midpoint of the arthrodesis construct was perpendicular to the base of the square. B Cadaveric finger specimen after potting of the proximal phalanx. C Placement of a custom ring with 4 screws that allowed for bending moments to be applied to the PIP joint arthrodesis site. D Biomechanical setup and test stand.
A custom machined metal ring with 4 screws, each 90° from one another, was fixed to the middle phalanx of each specimen at a standardized distance of three-fourths the length from the arthrodesis site to the distal interphalangeal joint (Fig. 4C). A metal rod attached to the test stand (Mark-10 ESM 303; Copiague, NY), via an engineered vice grip (Mark-10 G1010-2), was used to apply cantilever bending forces to the specimens in flexion, extension, ulnar, and radial directions (Fig. 4D). Each specimen underwent loading in the same order.
Loading was applied in all directions at a rate of 0.01 mm/s until a maximum force of 10 N was achieved. Prior literature has described that the average force transmitted across the interphalangeal joint surfaces during everyday activities is approximately 10 N.
The stiffness of each specimen in all 4 loading directions was determined by the slope of the load-displacement curve. The load was directly measured off of the force gauge (Mark-10 Series 7 Force Gauge) and continuous displacement was measured directly off the test stand’s control panel (Mark-10 ESM 303-004), which was attached to the vice grip and metal rod. Load and displacement were recorded in real-time using MESUR gauge Plus (Mark-10 15-1005) software. After the stiffness of each specimen was determined, all specimens were loaded in extension until 0.5 mm of permanent deformation was noted at the arthrodesis site, similar to a prior study.
During load to permanent deformation testing, specimens were examined for screw or wire cutout, wire loosening, or fracture formation. After load to permanent deformation testing, all specimens were loaded to catastrophic failure as determined by a steep downward inflection on the load-displacement curve. The mechanism and load to catastrophic failure were recorded.
Data analysis
A sample size estimate based on our preliminary data from testing 3 specimens in each group (6 specimens) determined that 10 specimens from each group would be needed to detect a 50% greater stiffness in flexion in group 1 than in group 2, with a power of 80% using a 2-sided P equal to .05 level test. In order to account for possible technical errors during biomechanical testing, we used 12 specimens per group. Data were assessed for normality using a Shapiro-Wilk test. Parametric data was compared using a Student t test and nonparametric data were compared using a Mann-Whitney U test between groups 1 and 2.
Results
The augmented 90/90 intraosseous wiring with cannulated screws construct demonstrated significantly greater stiffness in all 4 directions of displacement compared to 90/90 intraosseous wiring without augmentation (P < .05) (Fig. 5). Stiffness increased by 132%, 64%, 79%, and 75% in flexion, extension, ulnar, and radial displacement, respectively. No specimen failed during stiffness testing.
Figure 5Stiffness (N/mm) of the augmented 90/90 intraosseous wiring construct compared with the 90/90 intraosseous wiring construct without screw augmentation for PIP joint arthrodesis. The augmented construct had significantly greater stiffness in all 4 directions (P < .05).
During load to permanent deformation testing, 46% greater force was required to create 0.5 mm of permanent deformation in group 1 than in group 2 (P < .05) (Fig. 6). No specimen demonstrated catastrophic failure during the permanent deformation testing. During catastrophic load to failure testing, group 1 demonstrated a 32% greater load to cause catastrophic failure than group 2 (P = .07) (Fig. 6). The mechanisms for catastrophic failure in group 1 were cutout of the proximal screw (6), loosening of the sagittal circular wire (4), and fracture around the proximal screw (2) (Fig. 7B). The mechanisms of catastrophic failure in group 2 were wire cutout (8), widening of the sagittal wire holes (3), and wire loosening (1) (Fig. 7A).
Figure 6Load to failure (N) testing of the augmented 90/90 intraosseous wiring construct compared with the 90/90 intraosseous wiring construct without screw augmentation for PIP joint arthrodesis. The augmented construct required a significantly greater force to create 0.5 mm of permanent deformation (P < .05). There was no significant difference between the 2 constructs during load to catastrophic failure testing (P = .07).
Figure 7A Catastrophic failure of the 90/90 intraosseous wiring specimen without screw augmentation owing to complete cutout of the sagittal wire from the base of the middle phalanx. B Catastrophic failure of the augmented 90/90 intraosseous wiring specimen owing to cutout of the sagittal screw from the volar surface of the proximal phalanx.
Biomechanical testing of a PIP joint arthrodesis model in matched-pair cadaveric specimens demonstrated significant increases in stiffness and load to permanent deformation when the 90/90 intraosseous wiring construct was augmented with 2 cannulated screws in the sagittal plane. Stiffness increased by 64% to 132% depending on the direction of displacement and load to permanent deformation increased by 46%.
Successful arthrodesis of the PIP joint is dependent on both adequate stiffness and stability of a construct. The optimal stiffness to execute a successful PIP joint arthrodesis has not yet been quantified, but greater stiffness may result in higher rates of successful union owing to increased bone contact and compression. The current nonunion rate for PIP joint arthrodesis ranges from 0% to 9%, and is dependent on a number of factors including patient bone quality, comorbidities, and the biomechanical properties of the arthrodesis construct.
Increased stability of a PIP joint arthrodesis construct may allow for maintained alignment in both the sagittal and the coronal planes during initial healing and earlier mobilization of adjacent joints, thereby expediting the rehabilitation process. The ideal balance of stiffness and stability for successful PIP joint arthrodesis requires more research; too stiff a construct may actually compromise stability because the arthrodesis construct could fail at an adjacent stress riser. Although we attempted to maximize stiffness with our augmented 90/90 intraosseous wiring construct, the increased stiffness does not guarantee improved clinical outcomes because other biomechanical parameters, such as stability, also influence clinical success.
Three prior studies have described the biomechanical properties of various PIP joint arthrodesis constructs in cadaveric specimens.
evaluated 4 arthrodesis techniques consisting of a K-wire and a tension or neutral axis intraosseous wire, crossing K-wires alone, or longitudinal K-wires and a dorsal figure-of-eight wire loop. Their results demonstrated that, in sagittal bending and torsion, the figure-of-eight tension band wiring construct demonstrated superior biomechanical strength.
demonstrated no difference in load to failure when comparing a single Herbert screw with a tension band technique while also demonstrating 98% clinical union rates by 6 weeks with the Herbert screw. Most recently, in 2014, Capo et al
compared the biomechanical properties of 5 arthrodesis constructs: tension band wire, dorsal plate, intramedullary-linked screw, oblique K-wire with coronal intraosseous wiring, and 90/90 intraosseous wiring using 22-gauge wire. Their results demonstrated that the intramedullary-linked screw had greater stiffness than all wiring constructs in all directions of displacement and greater stiffness in extension than the dorsal plate.
The intramedullary screw demonstrated greater load to permanent deformation than the tension band wire, dorsal plate, and 90/90 intraosseous wiring construct; however, no difference was noted when compared with the use of an oblique K-wire combined with an intraosseous coronal wire.
However, several notable differences make comparisons of the biomechanical properties of the 90/90 intraosseous wiring constructs between the 2 studies difficult. First, our study used matched-pair cadaveric specimens of a lower age with presumably greater bone mineral density. Second, our bone cut of the proximal phalanx was made at 30°, not 25° as performed by Capo et al.
Third, it is unclear at what angle the specimens were potted in the previous study. In our study, the specimens were potted such that the dorsal midpoint of the PIP joint arthrodesis was perpendicular to the potted base. Slight variations in the angle at which the force is applied to the arthrodesis site can have an important effect on the calculated stiffness, and the authors hypothesize that a difference in the applied bending moment angle is the primary reason for the greater stiffness noted in this study. Lastly, different test stands were used in the 2 studies that could cause minor differences in the biomechanical values obtained. These reasons may explain why the stiffness of the 90/90 intraosseous wiring group was less than 5 N/mm in all directions in the study by Capo et al,
but ranged from 13 to 23 N/mm, depending on the direction of displacement, in this study. Similarly, the load to permanent deformation in the present study was 35 N for the 90/90 intraosseous wiring group whereas it was approximately 10 N in the study by Capo et al.
The use of 2.5-mm headless cannulated screws functioning as an intramedullary washer for the sagittal circular wire and a post for the coronal circular wire during intraosseous wiring for PIP joint arthrodesis is a novel technique. This proof of concept study used 2.5-mm cannulated screws in an off-label manner. Future iterations of this construct may benefit from smaller-diameter screws (2.0 mm) that more securely fit the sagittal circular wire and span less of the phalangeal metaphysis. It should be noted that 2 fractures did occur in the augmented 90/90 intraosseous wiring group, likely because the 2.5-mm cannulated screw was too wide for the diameter of the proximal phalanx distal metaphysis. In addition, the shortest length screw available to us was an 8-mm metallic screw. In the future, a shorter, and perhaps nonmetallic, screw of smaller diameter could be utilized, which might reduce risk of fracture and eliminate screw prominence, but retain the same biomechanical advantages of an intramedullary washer and post for 90/90 intraosseous wiring. Future research may consider using the same biomechanical construct with material other than metal for both the screw and the wire.
Augmentation of 90/90 intraosseous wiring with cannulated screws in the sagittal plane increases the surface area over which the compressive force is generated from the tensioned cerclage wire, thereby allowing for greater compression and resultant stiffness before wire cutout or implant failure. This may have several potential clinical benefits. Greater stiffness may lead to higher rates of union and lower rates of fixation failure. The greatest benefit may be seen in patients with osteoporotic or osteopenic bone. However, there are potential complications of this technique including extensor tendon irritation if the screws are too long, peri-implant fracture, and considerable dissection needed to drill the hole and subsequently pass the circular wire. The addition of 2 cannulated screws will also increase the cost of the construct relative to inexpensive circular wire used in isolation.
The results of this study must be interpreted within the limitations of its design. First, we tested the 2 constructs in cantilever bending; no rotational moments were tested. Second, our control group was 90/90 intraosseous wiring without augmentation, but we did not make direct comparisons with other constructs such as an intramedullary-linked screw. Third, variations in cannulated screw trajectory can have a significant effect on the calculated biomechanical values. In this study, our jig allowed for reproducible placement of the proximal screw in all planes; however, the distal screw was placed based on anatomical measurements and fluoroscopic alignment, and therefore less reproducible. Lastly, we used middle-aged adult cadaveric specimens with presumed normal bone quality. Further studies may benefit from the inclusion of chronologically older specimens with osteoporotic or osteopenic bone because this may be an indication for this technique and could demonstrate even greater differences in biomechanical properties between each group.
There are strengths of this study. First, the biomechanical setup and testing were based upon established methods.
Second, our sample size estimate, based on preliminary data, demonstrated that we were adequately powered to detect at least a 50% difference in stiffness between the 2 arthrodesis constructs. Furthermore, we used matched-pair cadaveric specimens that were potted and tested in pairs to best control for variations in anatomy, bone density, room temperature, and specimen water content that could affect the biomechanical results. Lastly, we used a 3-dimensional printed bone cutting jig to ensure accurate, reproducible bone cuts and screw/wire placement in each specimen from both groups.
In conclusion, the results of our study demonstrate that augmenting 90/90 intraosseous wiring for PIP joint arthrodesis with 2 headless cannulated screws in the sagittal plane that serve as intramedullary washers for the sagittal wire and posts for the coronal wire significantly increases stiffness in all directions as well as load to permanent deformation. For hand surgeons who use 90/90 intraosseous wiring for PIP joint arthrodesis, augmentation of the construct with simple cannulated screws may serve as a simple solution in patients at risk for wire cutout or implant failure. Clinical studies are needed to assess whether the use of this construct for PIP joint arthrodesis will improve osseous union and time to union and decrease rates of fixation failure.
Joint-specific hand symptoms and self-reported and performance-based functional status in African Americans and Caucasians: the Johnston County Osteoarthritis Project.
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