Biomechanical Comparison of 3 Thumb Ulnar Collateral Ligament Repair Methods.

PURPOSE: Differences in range of motion, pinch strength, biomechanical strength, or joint angulation have previously been investigated for various means of treatment of ulnar collateral ligament (UCL) tears. We sought to address a gap in the literature by comparing thumb metacarpophalangeal (MCP) joint angle measurements and biomechanical strength before complete, acute UCL tear and after repair with suture anchors (SA), suture tape (ST) anchor augmentation, or reconstruction with palmaris longus graft (PL). METHODS: Thumbs and, if present, the PL tendon were harvested from 15 fresh-frozen cadavers. Each thumb specimen was secured into a servohydraulic biomechanical testing frame to evaluate native radiographic MCP joint angles at 0° flexion when loaded with 0, 5, and 13 N of radial force. Subsequently, a single hand surgeon (S.M.K.) performed complete transection and UCL repair via 1 of 3 methods: SA (n = 5), ST (n = 5), or reconstruction with PL (n = 5). Following repair, MCP joint angles were radiographically evaluated. Specimens that did not fail during joint angle testing were transferred to a separate testing frame for load-to-failure testing. Angle measurements and mean load-to-failure were compared between the groups, and angulation was also compared with each group's native control. RESULTS: Both ST and SA groups demonstrated comparable stiffness to their native controls, whereas the PL group was significantly more lax. The ST repair was significantly stiffer than the other constructs. ST also required higher forces to reach failure compared to both SA and PL. No difference was found between SA and PL groups. CONCLUSIONS: Although both ST and SA constructs recapitulate native joint stiffness, repair with ST demonstrated the greatest biomechanical strength in stiffness and load-to-failure. CLINICAL RELEVANCE: For complete, acute tears of the thumb UCL, ST may be superior for maintaining MCP joint stability and strength over SA and PL.

Proximal Interphalangeal Joint Congruity: A Biomechanical Study.

BACKGROUND: Surgical approaches to the proximal interphalangeal (PIP) joint often require disruption of soft tissue stabilizers. Additionally, PIP joint injuries frequently result in soft tissue disruption. This study evaluates the necessity of repairing soft tissue stabilizers by assessing their role in maintaining native joint congruity. METHODS: Eight specimens were used to evaluate congruity at 0° and 30° flexion when loaded with 2 N of valgus force. This was performed in the native joint and after sequential sectioning of the surrounding ligaments in order: volar plate (VP), radial collateral ligament (CL), and ulnar CL. The skin flap was sutured with the ligaments unrepaired and the load was reapplied. Radiographs were taken after each load and used to measure the joint line convergence angle (JLCA). RESULTS: Mean JLCA increased in both degrees of flexion after ligaments were sectioned but was only significantly different from the native joint after the VP was disrupted along with 1 CL. Joint congruity improved following repair of the skin flap in both degrees of flexion but was not significant. Joints were more congruent in 30° flexion for all subgroups, but none were significantly different compared to 0° flexion. CONCLUSIONS: Disruption of the VP is insufficient to significantly alter PIP joint congruity. While sectioning of both the VP and CLs resulted in a statistically significant change in joint congruity, mean JLCA demonstrated changes of minor clinical significance. The osseous anatomy of the phalanges imparts inherent stability that maintains a congruent joint despite loss of the soft tissue stabilizers.

Proximal Row Carpectomy Does Not Alter Contact Pressures of the Lunate Fossa: A Cadaveric Study.

BACKGROUND: Previous studies have suggested that proximal row carpectomy (PRC) results in increased contact pressures and decreased contact areas in the radiocarpal joint. Such experiments, however, used older technologies that may be associated with considerable measurement errors. The purpose of this study was to determine whether there was a significant difference in contact pressure and contact area before and after PRC using Tekscan, a newer pressure sensing technology. METHODS: Ten nonpaired cadaveric specimens were dissected proximal to the carpal row and potted. An ultra-thin Tekscan sensor was secured in the lunate fossa of the radius. The wrists were loaded with 200 N of force for 60 seconds to simulate clenched-fist grip; contact pressure and area was assessed before and after PRC. RESULTS: Performing a PRC did not significantly increase mean contact pressure at the lunate fossa compared to the native state (mean increase of 17.4 ± 43.2 N/cm2, P = .184). Similarly, the PRC did not significantly alter peak contact pressures at the lunate fossa (intact: 617.2 ± 233.46 N/cm2, median = 637.5 N/cm2; PRC: 707.8 ± 156.6 N/cm2, median = 728.5 N/cm2; P = .169). In addition, the PRC (0.46 ± 0.15 cm2, median = 0.48 cm2) and intact states (0.49 ± 0.25 cm2, median = 0.44 cm2) demonstrated similar contact areas (P = .681). CONCLUSIONS: In contrast to prior studies that demonstrated significant increases in contact pressure and decreases in contact area after PRC, our findings propose that performing a PRC does not significantly alter the contact pressures or area of the lunate fossa of the radiocarpal joint.

Radiocarpal Contact Pressures Are Not Altered after Scapholunate Ligament Tears.

Background The scapholunate interosseous ligament (SLIL) couples the scaphoid and lunate, preventing motion and instability. Prior studies suggest that damage to the SLIL may significantly alter contact pressures of the radiocarpal joint. Questions/Purposes The purpose of this study was to investigate the contact pressure and contact area in the scaphoid and lunate fossae of the radius prior to and after sectioning the SLIL. Methods Ten cadaveric forearms were dissected distal to 1-cm proximal to the radiocarpal joint and a Tekscan sensor was placed in the radiocarpal joint. The potted specimen was mounted and an axial load of 200 N was applied over 60 seconds. Results Sectioning of the SLIL did neither significantly alter mean contact pressure at the lunate fossa ( p = 0.842) nor scaphoid fossa ( p = 0.760). Peak pressures were similar between both states at the lunate and scaphoid fossae ( p = 0.301-0.959). Contact areas were similar at the lunate fossa ( p = 0.508) but trended toward an increase in the SLIL sectioned state in the scaphoid fossa ( p = 0.055). No significant differences in the distribution of contact pressure ( p = 0.799), peak pressure ( p = 0.445), and contact area ( p = 0.203) between the scaphoid and lunate fossae after sectioning were observed. Conclusion Complete sectioning of the SLIL in isolation may not be sufficient to alter the contact pressures of the wrist. Clinical Relevance Injury to the secondary stabilizers of the SL joint, in addition to complete sectioning of the SLIL, may be needed to induce altered biomechanics and ultimately degenerative changes of the radiocarpal joint.

Effect of Collagen Nerve Wrapping in a Rabbit Peripheral Neuropathy Model.

BACKGROUND: Collagen nerve wraps (CNWs) theoretically allow for improved nerve gliding and decreased perineural scarring, and create a secluded environment to allow for nerve myelination and axonal healing. The goal of this study was to investigate the effect of CNWs on nerve gliding as assessed by pull-out strength and nerve changes in a rabbit model of peripheral neuropathy. METHODS: Ten New Zealand rabbits were included. Sham surgery (control) was performed on left hindlimbs. To simulate compressive neuropathy, right sciatic nerves were freed of the mesoneurium, and the epineurium was sutured to the wound bed. Five rabbits were euthanized at 6 weeks [scarred nerve (SN); n = 5]. Neurolysis with CNW was performed in the remaining rabbits at 6 weeks (CNW; n = 5), which were euthanized at 22 weeks. Outcomes included peak pull-out force and histopathological markers of nerve recovery (axonal and Schwann cell counts). RESULTS: The CNW group demonstrated significantly higher pull-out forces compared with the CNW sham control group (median: 4.40N versus 0.37N, P = 0.043) and a trend toward greater peak pull-out forces compared with the SN group (median: 4.40N versus 2.01N, P = 0.076). The CNW group had a significantly higher median Schwann cell density compared with the CNW control group (CNW: 1.30 × 10-3 cells/µm2 versus CNW control: 7.781 × 10-4 cells/µm2, P = 0.0431) and SN group (CNW: 1.30 × 10-3 cells/µm2 versus SN: 7.31 × 10-4 cells/µm2, P = 0.009). No significant difference in axonal density was observed between groups. CONCLUSION: Our findings suggest using a CNW does not improve nerve gliding, but may instead play a role in recruiting and/or supporting Schwann cells and their proliferation.

A pilot biomechanical study comparing a novel, intramedullary Nail/Plate construct to standard Dual-Plate fixation of intra-articular C2.3 distal humerus fractures.

BACKGROUND: The gold-standard treatment for intra-articular distal humerus fractures (DHFs) is dual-plate/dual-column fixation, though optimal orientation is not yet established. With a superior method not yet identified, we propose a load-sharing construct, combining absolute stability (extramedullary plate fixation) for distal articular fragments and relative stability (load-sharing intramedullary nail) for the metaphyseal segment. The purpose of this pilot study was to evaluate the biomechanical performance of a novel implant compared to orthogonal dual-plating. MATERIALS AND METHODS: Ten fresh-frozen matched-pairs of human cadaveric upper extremities with no prior elbow pathology/surgery were used. Pairs were randomized into two groups: Dual-Plate (medial and posterolateral) or novel Nail/Plate (cross-locked medial nail and posterolateral plate). AO/ASIF type 13-C2.3 multifragmentary fractures with simulated metaphyseal comminution. Biomechanical testing included stiffness (MPa) and load to failure (Newtons) in axial (100 cycles at 3 Hz at 20 N increments from 20 to 100 N) and coronal (varus/valgus; 4,000 cycles from 50N-100 N at 3 Hz) planes. Failed specimens were not analyzed and mechanisms were identified. For all failures, mechanisms were identified and reviewed by three consultant surgeons for revision vs. immobilization, to attempt to recreate a real-world scenario. All outcomes were compared between groups. RESULTS: During stiffness testing, zero Nail/Plate specimens failed, but two (20%) Dual-Plate specimens failed (mechanisms: fracture diastasis; bone collapse and intussusception into osteotomy, yielding articular congruency loss). For remaining samples, Nail/Plate (n = 10) coronal (varus/valgus) stiffness was comparable to Dual-Plate (n = 8) constructs (41.5 vs. 39.0 MPa, p = 0.440). Remaining Dual-Plate constructs had greater axial overall stiffness than Nail/Plate (118.3 ± 48.3 vs. 95.6 ± 34.7 MPa, p = 0.020). Failure loads were comparable between Nail/Plate and Dual-Plate constructs (1,327.8 vs. 1,032.4 N, p = 0.170). Individual nail yield strength ranged from 1,101.1-1,124.4 N (n = 2). In review of all failures, the most common overall mechanism was fracture/osteotomy site posterolateral plate bending. Revision recommendation rate was comparable between constructs (Nail/Plate, 22.2% vs. Dual-Plate, 44.4%, p>0.05). CONCLUSIONS: The novel Nail/Plate construct demonstrated non-inferior coronal (varus/valgus) stiffness, despite producing lower axial stiffness than orthogonal dual-plating, potentially due to the load-sharing cross-locked design. Considering comparable biomechanical performance, with no failures and comparable recommendations for revision, this novel construct warrants further evaluation as an alternative to the gold-standard, dual-plate fixation method for intra-articular distal humerus fractures. LEVEL OF EVIDENCE: N/A.

Strength of Syndesmosis Fixation: Two TightRope versus One TightRope with Plate-and-Screw Construct.

Injuries involving the distal tibiofibular syndesmosis can lead to critical destabilization of the ankle mortise. Although specific indications for operative fixation remain unclear, accurate reduction of the syndesmosis has been correlated with the best functional outcomes. The purpose of this study was to evaluate the maximum torque and rotation to failure after fixation with a novel construct. Seven pairs (14 ankles) of embalmed cadaveric lower legs, disarticulated at the knee, were obtained. Each pair was randomly assigned to receive either two TightRopes (Arthrex) or a plate-and-screw construct with one TightRope. All samples were mechanically tested in torsion to determine peak torque, torsional stiffness, and the maximum rotation angle at which failure occurred. Differences between the groups were compared using paired Student's t test. The maximum torque to failure after fixation was not significantly different between the two TightRopes (28.8 N*m; range, 7.3-49.7 N*m) and the one TightRope group (29.5 N*m; range, 9.2-44.9 N*m; p = 0.92). The maximum rotation to fracture after fixation was not significantly different between the two TightRopes (33.3 degrees; range, 21.6-57.0 degrees) and one TightRope group (38.6 degrees; range, 23.0-73.9 degrees). All specimens failed with the fracture of the fibula at the level of the inferior syndesmotic screw. The similar load to failure of the two TightRope and the one TightRope and plate-and-screw plate suggested similar stiffness between the two constructs. The addition of the plate may improve distribution of forces at the level of syndesmosis, reducing stress risers and decreasing the risk of failure, as demonstrated by a lower rotation to failure of the one TightRope with plate-and-screw construct. In addition, this construct is not likely to not be associated with any substantial cost increase. Further clinical studies may further elucidate the role of plate and/or TightRope augmentation to syndesmosis fixation.

A Biomechanical Comparison of Different Tendon Repair Techniques.

Previous studies have examined multiple suture techniques for the repair of ruptured tendons. In this study, we investigated how the two- and four-stranded Krackow suture weave techniques compared with a novel Krackow/Bunnell suture technique. Our hypothesis was that the Krackow/Bunnell suture would have greater strength compared with the two- and four-stranded Krackow suture in terms of resistance to pullout from the muscle tendon. Thirty fresh bovine Achilles tendons were assigned randomly to three groups: (1) two-stranded Krackow, (2) fourstranded Krackow, and (3) the Krackow/Bunnell combination. After suture placement, all specimens were subjected to initial cyclic loading (0-200 N for 200 cycles) and then the tension to failure force defined as the pullout through the muscle tendon was evaluated. Significantly greater deformation before suture failure was seen in the Krackow/Bunnell group compared with the four-stranded Krackow construct (36.2 vs. 28.7 mm, p = 0.009), as well as greater energy required to rupture the suture (4635 vs. 3346 N/mm; p = 0.016). There was no significant difference with regard to the force to failure between the two groups (four-stranded Krackow vs. Krackow/Bunnell). The two-stranded Krackow was found to be inferior to both the four-stranded Krakow and the Krakow/Bunnell techniques with regard to load to failure. We have found that the Krackow/Bunnell suture technique is at least comparable to, if not superior to, the four-stranded Krackow technique with regard to deformation before suture failure and energy required to rupture the tendon. Therefore, the Krackow/Bunnell technique may be an optimal construct if the surgeon is concerned about suture pullout through the tendon; however, future studies evaluating this technique in the clinical setting are required before making any final conclusions for patient use.