Partially Lacerated Digital Flexor Tendons: A Cadaveric Study Determining the Intact Cross-sectional Area and Biomechanical Analysis.

BACKGROUND: The extent of injury in partially lacerated tendons has conventionally been expressed as a percentage of the total tendon, to justify surgical repair. We propose a more objective method to estimate the cross-sectional area of the remnant intact tendon and to determine if the remaining tendon fibers can withstand the tensile forces of early active mobilization against resistance. METHODS: The study was done on 20 cadaveric specimens, which were randomly assigned to receive a laceration of 25%, 50%, or 75% of the measured transverse tendon diameter. The circumference of the remaining intact portion of the partially lacerated tendon was measured and converted using a formula to determine the derived cross-sectional area (D-CSA). These D-CSA values were then validated by comparing them to digitally measured cross-sectional areas using a computer software program (computer-measured cross-sectional area, C-CSA). In addition, the ultimate tensile strength (UTS) of these partially lacerated tendons was analyzed to determine if a threshold exists beyond which surgical repair of a partially lacerated tendon is indicated. RESULTS: We found that the D-CSAs matched moderately with C-CSAs, with 0.622 of Pearson correlation coefficient. The UTSs of tendons with CSAs above 8 mm in circumference were consistently above 150 N. CONCLUSION: Measurement of the circumference of the partially lacerated tendon to obtain the D-CSA could be an accurate and practical method to benchmark residual tendon strength in the management of partially lacerated tendons.

Comparing the torsional resistance of different fixation techniques for spiral metacarpal fractures.

This study aimed to compare the torsional resistance of three fixation techniques for spiral metacarpal fractures: screw-only fixation, screw plus neutralization plate fixation, and a locking plate construct. A spiral fracture was created on 18 cadaveric metacarpal bones by applying an axial and torsional loading force using an Instron 3343 mechanical tester. The failure strength was defined as the native torque strength. The fractures were divided into three groups and fixed using each of the three techniques. The repaired bones were loaded to failure to determine the post-repair strength. The neutralization plate group conferred a post-repair torque (278.6 Nmm) that was similar to the native torque (292 Nmm) with a diminution of only 4.5% and appeared to provide the best resistance to torsion.

Biomechanics of surgical knot security: a systematic review.

BACKGROUND: This review aims to identify publications on quantitative biomechanical testing of surgical knot security and the physical factors that determine knot security and failure. MATERIALS AND METHODS: An electronic literature search was performed in accordance with PRISMA guidelines in January 2022 utilizing the PubMed and Google Scholar databases to look for objective biomechanical studies on knot security in surgery using the primary terms 'knot security' and 'biomechanical testing'. RESULTS: Thirty-six articles were included. Twenty-four configurations of surface, laparoscopic, and arthroscopic knots were studied. Biomechanical tensile testing was used to evaluate knot security in vitro . Load to failure (N) and elongation at knot failure (mm) were quantified by static and cyclic testing to evaluate the knot holding capacity and failure mechanism of slippage or rupture. CONCLUSION: This review reassures that the knot configuration, suture materials, suture sizes, and number of throws are key factors in determining the knot's security. Knot configuration has to be simple for laparoscopic and arthroscopic knots due to the confined space of the operating site. With the advent of stronger suture materials for high-tension surgical reconstructive procedures, there is an unmet need to understand the physical behavior of the knot and the factors that determine its resistance to slippage or rupture.Level of Evidence: Level IV.

The right turn around: Penrose tourniquet application in paediatrics.

INTRODUCTION: Commercially available tourniquets are ill-suited for paediatric patients with limb circumferences smaller than the required mechanism, forcing surgeons to improvise. This study aimed to quantify pressures exerted by the Penrose tourniquet when applied on a phantom model and evaluate the intra-/inter-rater reproducibility of the technique previously proposed. METHODS: Eight calibrated pressure sensors were distributed evenly along the inner and outer circumference of a silicon-based model. A 30cm-by-3.2 cm ARGYLE Penrose drain, 4-by-4 gauze, marker and ruler were used. The optimal interval for arterial occlusion was determined to be 70% of limb circumference. The tourniquet was secured using two half-knots formed by gauze. RESULTS: Two-turns of the tourniquet about the model generated mean pressures (SD) of 209.43 (SD:35.98 mmHg) (95%CI: 195.85-224.00 mmHg) (outer-sensor) and 246.32 (SD:61.92 mmHg) (95%CI: 221.02-273.49 mmHg) (inner-sensor). Three-turns generated mean pressures of 302.07 (SD:23.98 mmHg) (95%CI: 292.29-312.53 mmHg) (outer-sensor) and 314.44 (SD:56.70 mmHg) (95%CI: 291.25-338.25 mmHg) (inner-sensor). CONCLUSION: The Penrose tourniquet has clinical utility, particularly for patients where commercially available tourniquets are not suitable. Current application techniques generate inconsistent pressures. Using the existing model, further refinement can be done to improve the consistency and safety of the application. We recommend using intervals of slightly more than 70% of limb circumference and only two turns of the Penrose tourniquet during application. LEVEL OF EVIDENCE: V.

A fluid-structure interaction investigation of intra-articular pressure and ligament in wrist joint.

Understanding the stresses on the scapholunate interosseous ligament (SLIL) and its interaction with synovial fluid pressure could be vital to improve wrist treatment for various wrist conditions such as arthritis, sprains and tendonitis. This study investigated the interaction between the intra-articular pressure, specifically the synovial fluid pressure change and the SLIL stresses in a computational model during wrist radioulnar deviation (RUD). Magnetic resonance imaging (MRI) scans were used to acquire the anatomical model of the carpal bones and ligament, while the kinematics of scaphoid and lunate were obtained through dynamic computerized tomography (CT) scans. A two-way fluid-structure interaction (FSI) was used to model the dynamics between the scaphoid and lunate, the SLIL, and the synovial fluid. The synovial fluid pressure change was found to be small (-4.86 to 3.23 Pa) and close to that simulated in a previous work without the SLIL (-1.68 to 2.64 Pa). Furthermore, peaks of maximum fluid pressure were found to trail the peaks of ligament stress. Therefore, it is suggested that the influence of synovial fluid pressure on the ligament in the SLIL model is negligible and simulations of the scapholunate joint could forego fluid-structure interactions. Future studies can instead explore other structures in the carpus that can possibly contribute to the ligament stresses. Clinically, treatments can be targeted at these areas to help prevent or slow the progression of ligament injuries into serious consequences like the degenerative joint disease.

Biomechanical Study of Asymmetric Flexor Tendon Repair Using a 6-Strand 4-0 Supramid Suture Versus a 4-Strand 2-0 Tenoflex Suture.

Background: Multi-strand repair of flexor tendons are important for increased strength but this may cause ischemia during the intrinsic healing process. In this study, we aim to compare the strength of the 4-strand modified Asymmetric repair using 2-0 Tenoflex® suture with the original description of the Asymmetric repair using a 6-strand 4-0 Supramid® suture under cyclic loading in a porcine tendon model. We hypothesise that the number of core sutures through the repair site can be reduced with advanced suture material. Methods: Two groups consisting of 10 porcine tendons each were repaired using the Asymmetric repair technique. One group underwent the original description using a 6-strand 4-0 Supramid® suture and the other group underwent a modified 4-strand technique using 2-0 Tenoflex® suture. The repaired tendons were subjected to a two-stage cyclic loading test. Survival rate and gap formation at the repaired site were analysed. The failure mechanism of each repair was also analysed. Additionally, the cross-sectional area of each strand of core suture used was also calculated. Results: The 1st and 2nd stage survival rates were 90% and 30% for the 6-strand repair and 100% and 60% for the 4-strand repair respectively. The mean gap formation at the end of stage 2 was 1.79 mm (SD 1.57) for the 4-strand repair, which is comparable to that of the 6-strand repair (1.82 mm; [SD 1.20]). The total mean cross-sectional area of 2-0 Tenoflex® and 4-0 Supramid® suture strands were 0.078 and 0.086 mm2, respectively. Conclusions: These results demonstrate that despite having fewer core sutures, the 4-strand modified Asymmetric repair using 2-0 Tenoflex® may be a better option as compared to the original 6-strand Asymmetric repair using 4-0 Supramid®.

Biomechanical Study of Modified Massachusetts General Hospital Flexor Tendon Repair Using Looped Sutures.

Background: Massachusetts General Hospital (MGH) repair is one of the widely used 4-strand flexor tendon repair techniques. However, it uses two single strand sutures that are each passed twice across the repair site. This is time consuming and may cause imbalance of the load across the repair. We modified the MGH repair by using a looped suture and call it the looped MGH repair. The aim of this study is to compare the strength of the looped MGH repair performed with three different looped sutures against the strength of original MGH repair. Methods: Forty porcine flexors were used for the study. The original MGH repair was performed with Prolene® 4-0. Looped MGH repair was performed with three different loop sutures, Supramid® 4-0, Tendo-Loop® 4-0 and FiberLoop® 4-0. Mechanism of failure, ultimate tensile strength, stiffness, load to 2-mm gap formation and repair time were recorded for comparison. Results: There was no significant difference between the original MGH repair and the looped repair using Supramid® regarding their biomechanical performance. Looped MGH repair using Tendo-Loop® and FiberLoop® showed significantly higher ultimate tensile strength and FiberLoop® had highest 2-mm gap force. All looped MGH repairs required significant less time compared to original MGH repair. Conclusions: Our modification of the MGH repair using a looped Supramid® 4-0 suture took significantly lesser time to perform while providing the same strength as the original MGH repair using Prolene® 4-0. The use of the FiberLoop® 4-0 provided significantly greater strength while taking lesser time.

A Biomechanical Comparison of Gliding Resistance between Modified Lim Tsai and Asymmetric Tendon Repair Techniques in Zone II Flexor Tendon Repairs.

Background: Early active motion protocols have shown better functional outcomes in zone II flexor tendon lacerations. Different techniques of tendon repair have different effects on gliding resistance, which can impact tendon excursion and adhesion formation. For successful initiation of early active mobilisation, the repair technique should have high breaking strength and low gliding resistance. Previous studies have shown the Modified Lim-Tsai technique demonstrates these characteristics. The Asymmetric repair has also shown superior ultimate tensile strength. This study aims to compare the gliding resistance between the two techniques. Methods: FDP tendons from ten fresh frozen cadaveric fingers were randomly divided into two groups, transected completely distal to the sheath of the A2 pulley and repaired using either the Modified Lim-Tsai or Asymmetric technique. The core repair was performed with Supramid 4-0 looped sutures and circumferential epitendinous sutures were done with nylon monofilament Prolene 6-0 sutures. The gliding resistance and ultimate tensile strength were then tested. Results: The gliding resistance of the Asymmetric and Modified Lim-Tsai repair techniques were 0.2 and 0.95 N respectively. This difference was significant (p = 0.008). The Modified Lim-Tsai technique had a higher ultimate tensile strength and load to 2 mm gap formation, though this was not significant. Conclusions: Gliding resistance of the Asymmetric repair is significantly less than that of Modified Lim-Tsai. Ultimate tensile strength and load to 2 mm gap formation are comparable.

Biomechanical Study of Asymmetric Flexor Tendon Repair Using 3 Different Suture Materials.

Background: The asymmetric technique for flexor tendon repairs has various advantages but further improvement is possible by using a suitable suture material. In this study, we compare the biomechanical performance of asymmetric repairs using 3 suture materials: Supramid Extra II 4-0, Tendo-Loop 4-0, and FiberLoop 4-0. Methods: We divided 30 porcine flexor tendons into 3 arms. Each arm of tendons were repaired by using 1 of the 3 proposed suture materials. Each repaired tendon was tested by using a mechanical tester. Ultimate tensile strength (UTS), load to 2 mm gap force, failure mechanism and stiffness of the tendons were investigated. Results: FiberLoop® achieved the highest UTS (90.4 ± 17.9 N), followed by Tendo-Loop (85.3 ± 10.3 N). The difference was no statistically significant. The UTS of repairs using Supramid® was significantly lower (64.0 ± 8.4 N). For load to 2 mm gap force, FiberLoop® achieved 20.7 ± 4.8 N while Tendo-Loop® had 20.5 ± 4.2 N. The difference was also no statistically significant. The repairs using Supramid® had a significantly lower load to 2 mm gap force of 14.2 ± 2.7 N. The stiffness of asymmetric repairs using FiberLoop® and Tendo-Loop® was 5.64 ± 1.7 N/mm and 5.63 ± 0.7 N/mm. The difference was also no statistically significant. The repairs using Supramid® had a significantly lower stiffness of 4.15 ± 1.0 N/mm. Failure mechanisms for the repaired specimens were reported as such: Supramid had 100% suture rupture; Tendo-Loop had 90% suture rupture and 10% suture pullout; FiberLoop had 20% suture rupture and 80% suture pullout. Conclusions: The asymmetric repair configuration is able to produce superior biomechanical performance by using Tendo-Loop® or FiberLoop®. Improvement of the asymmetric technique by using Tendo-Loop® or FiberLoop® could potentially contribute to better surgical outcomes of flexor tendon repair.

Intramedullary nailing confers an increased risk of medial migration compared to dynamic hip screw fixation in unstable intertrochanteric hip fractures.

INTRODUCTION: Medial migration of the femoral neck element (FNE) superomedially against gravity with respect to the intramedullary component of the cephalomedullary nail is a complication increasingly recognized to cause femoral head cut-out in intramedullary nailing of pertrochanteric hip fractures. Although cut-outs are common to both intra- and extramedullary fixation, especially in unstable pertrochanteric hip fractures, FNE medial migration in sliding hip screws continues to remain sparse despite increased awareness of the phenomenon. This study aims to investigate whether intramedullary nailing is biomechanically predisposed to FNE medial migration compared to extramedullary fixation with sliding hip screws to account for the discrepancy in reported FNE medial migration rates. MATERIALS AND METHODS: Twelve fourth-generation synthetic femurs (Sawbones) with unstable intertrochanteric fractures were divided into 2 groups (n=6 per group). Fracture fixation was performed using the Proximal Femoral Nail Antirotation (PFNA, Synthes) (n=6) in the first group, and the Dynamic Hip Screw (DHS, Synthes) (n=6) in the second group. Both groups were subjected to bidirectional cyclic loading (600N compression loading, 120N tensile loading) at 2 Hz for 5000 cycles. The medial migration distance (MMD) was recorded at the end of the testing cycles. RESULTS: The mean MMD in the PFNA group was 4.56mm (SD 0.69mm) with consistent reproduction of medial migration across all constructs tested. This was significantly more compared to the MMD of 1.17mm (SD 0.69mm) in the DHS group (p<0.001). CONCLUSION: Intramedullary nailing of unstable intertrochanteric hip fractures is inherently predisposed to FNE medial migration making it more susceptible to consequent cut-out compared to fixation with the DHS.

Evaluation of femtosecond laser-assisted anterior capsulotomy in the presence of ophthalmic viscoelastic devices (OVDs).

The introduction of femtosecond laser-assisted cataract surgery is an alternative approach to conventional cataract surgery. Our study aimed to determine the effectiveness of femtosecond laser-assisted capsulotomy in the presence of different ophthalmic viscoelastic devices (OVDs) in the anterior chamber. Fresh porcine eyes (n = 96) underwent LDV Z8-assisted anterior capsulotomy, either in the presence of an OVD (Viscoat, Provisc, Healon, Healon GV or HPMC) or without, using 90% and 150% energies respectively. Following that, the capsule circularity, tag's arc-length, tag-length, tag-area and rupture strength (mN) of the residual capsular bag were evaluated. We found that increasing energy from 90 to 150% across the OVD sub-groups improved the studied capsulotomy parameters. Amongst the 90% energy sub-groups, the circularity and tag-parameters were worse with Viscoat and Healon GV, which have higher refractive index and viscosity compared to the aqueous humour. Using 150% energy, Healon GV showed a significantly worse total arc-length (p = 0.01), total tag-length (p = 0.03) and total tag-area (p = 0.05) compared to the control group. We concluded that; an OVD with a refractive index similar to aqueous humour and lower viscosity, such as Healon or Provisc, as well as a higher energy setting, are recommended, to enhance the efficacy of laser capsulotomy.

Biomechanical comparison of vertical suture techniques for repairing radial meniscus tear.

PURPOSE: The aim of this study was to (1) develop suture techniques in repairing radial meniscal tear; (2) to compare the biomechanical properties of the proposed repair techniques with the conventional double horizontal technique. METHODS: Thirty-six fresh-frozen porcine medial menisci were randomly assigned into four groups and a complete tear was made at the midline of each meniscus. The menisci were subsequently repaired using four different repair techniques: double vertical (DV), double vertical cross (DVX), hybrid composing one vertical and one horizontal stitch, and conventional double horizontal (DH) suture technique with suturing parallel to the tibia plateau. The conventional double horizontal group was the control. The repaired menisci were subjected to cyclic loading followed by the load to failure testing. Gap formation and strength were measured, stiffness was calculated, and mode of failure was recorded. RESULTS: Group differences in gap formation were not statistically significant at 100 cycles (p = .42), 300 cycles (p = .68), and 500 cycles (p = .70). A trend was found toward higher load to failure in DVX (276.8 N, p < .001), DV (241.5 N, p < .001), and Hybrid (237.6 N, p < .001) compared with DH (148.5 N). Stiffness was also higher in DVX (60.7 N/mm, p < .001), DV (55.3 N/mm, p < .01), and Hybrid (52.1 N/mm, p < .01), than DH group (30.5 N/mm). Tissue failure was the only failure mode observed in all specimens. CONCLUSION: Our two proposed vertical suture techniques, as well as the double vertical technique, had superior biomechanical properties than the conventional technique as demonstrated by higher stiffness and higher strength.

Asymmetric 6-Strand Flexor Tendon Repair - Biomechanical Analysis Using Barbed Suture.

Background: This study investigates the biomechanical performance of the Asymmetric flexor tendon repair technique using barbed suture. The Asymmetric repair technique using monofilament nylon suture was previously reported to have a higher tensile strength than the modified Lim-Tsai repair technique, but its repair stiffness and load to gap force were significantly lower. There is hence an unmet need to improve this technique and the substitution of nylon suture with barbed sutures may be the solution. Methods: Two groups consisting of 10 porcine tendons each were repaired with the six-strand Asymmetric repair technique using V-Loc® 3-0 and Supramid® 4-0 respectively. The repairs were subjected to a mechanical tester for static testing. The ultimate tensile strength, load to 2 mm gap force, repair stiffness, time taken to complete a repair and failure mechanism of the repairs were recorded and analyzed. Results: All the repairs using V-Loc® 3-0 sutures had significantly higher median values of ultimate tensile strength (64.1 N; 56.9 N), load to 2 mm gap force (39.2 N; 19.7 N), repair stiffness (6.4 N/mm; 4.7 N/mm) and time taken to complete a repair (9.4 mins; 7.7 mins). All the repairs using V-Loc® sutures failed by suture breakage while 80% of repairs using Supramid® sutures failed by suture pullout. Conclusions: The use of the barbed sutures in the Asymmetric repair technique, whilst more time consuming, has shown promising improvement to its biomechanical performance (i.e. better ultimate tensile strength, stiffness and resistance to gap formation).

Biomechanical evaluation of peripheral nerves after crush injuries.

BACKGROUND: Crush injury of nerves is a common condition but the biomechanical integrity of the human peripheral nerve after crushing is unknown. This study aims to investigate the impact of crush injury on human digital nerves based on different compressive forces. MATERIALS AND METHODS: Twenty digital nerves were harvested from three fresh-frozen cadaver hands. The original diameters of proximal, middle and distal end of nerve segment were measured. The midst of each digital nerve was compressed by a customized mechanical system, at 1N, 3N and 5N for 30sec. The diameters were measured again within 1 minute after the nerve crush test was performed. The digital nerve was then subjected to biomechanical test to measure its ultimate tensile strength, stiffness, maximum stress and strain. Deformity of digital nerve was computed based on the diameter of middle nerve segment before and after crush test. RESULTS: No significant difference was found in between groups for ultimate tensile strength (p=0.598), stiffness (p=0.593), maximum stress (p=0.7) and strain (p=0.666). The deformity of nerves under the compression of 1N, 3N and 5N was computed at 72.1%, 54.2% and 45.9%. The effect of compression on the deformity of nerves was statistically significant (p<0.001). CONCLUSIONS: It was found that the compressive forces have no impact on the biomechanical integrity of peripheral nerves but the deformity of nerves could be severely caused by low compressive force. It is suggested that the management of nerve crush injury shall be taken immediately and focus on neurophysiological function and degeneration of nerves for a crush with low compressive force and short duration.

Computational Simulation of Synovial Fluid Kinematics of the Scapholunate Joint.

Background: The interaction between wrist kinematics and synovial fluid pressure has yet to be studied. To our knowledge, this is the first study to determine the effect of scapholunate joint kinematics on synovial fluid pressure change using finite volume method. Methods: The carpal bones of a cadaveric hand were obtained from Computed Tomography (CT) scans. CT images of the carpal bones were segmented and reconstructed into 3D model. The 3D synovial fluid model between the scaphoid and lunate was constructed and then used for computational simulations. The kinematics data of scapholunate joint obtained from radioulnar deviation of the wrist was investigated. Results: It was found that the pressure in synovial fluid varied from -1.68 to 2.64 Pa with maximum pressure located at the scaphoid-fluid interface during the radial deviation. For ulnar deviation, the pressure increased gradually from the scaphoid-fluid interface towards the lunate-fluid interface (-1.37 to 0.37 Pa). Conclusions: This new computational model provides a basis for the study of pathomechanics of ligament injury with the inclusion of synovial fluid.

Design and Evaluation of a Novel Hybrid Soft Surgical Gripper for Safe Digital Nerve Manipulation.

Forceps are essential tools for digital nerve manipulation during digital nerve repair surgery. However, surgeons have to operate forceps with extreme caution to prevent detrimental post-operative complications caused by over-gripping force. Their intrinsically safe characteristics have led to the increasing adoption of soft robotics in various biomedical applications. In this paper, a miniaturized hybrid soft surgical gripper is proposed for safe nerve manipulation in digital nerve repair surgery. This new surgical gripper includes a soft inflatable actuator and a gripper shell with a hook-shaped structure. The ability to achieve a compliant grip and safe interaction with digital nerves is provided by the inflated soft pneumatic actuator, while the rigid hook retractor still allows surgeons to scoop up the nerve from its surrounding tissues during surgery. The performance of the proposed surgical gripper was evaluated by the contact/pulling force sensing experiments and deformation measurement experiments. In the cadaver experiments, this new surgical gripper was able to complete the required nerve manipulation within the limited working space. The average deformation of the digital nerve with an average diameter of 1.45 mm gripped by the proposed surgical gripper is less than 0.22 mm. The average deformity is less than 15% of its original diameter.

A review of cyclic testing protocols for flexor tendon repairs.

BACKGROUND: Cyclic testing of flexor tendons aims to simulate post-operative rehabilitation and is more rigorous than static testing. However, there are many different protocols, making comparisons difficult. We reviewed these protocols and suggested two protocols that simulate passive and active mobilization. METHODS: Literature search was performed to look for cyclic testing protocols used to evaluate flexor tendon repairs. Preload, cyclic load, number of cycles, frequency and displacement rate were categorised. FINDINGS: Thirty-five studies with 42 different protocols were included. Thirty-one protocols were single-staged, while 11 protocols were multiple-staged. Twenty-nine out of 42 protocols used preload, ranging from 0.2 to 5 N. Preload of 2 N was used in most protocols. The cyclic load that was most commonly used was between 11 and 20 N. Cyclic load with increment of 10 N after each stage was used in multiple-staged protocols. The most commonly used number of cycles was between 100 and 1000. Most protocols used a frequency of <1 Hz and displacement rate between 0 and 20 mm/min. INTERPRETATION: We propose two single-staged protocols as examples. Protocol 1: cyclic load of 15 N to simulate passive mobilization with preload of 2 N and 2000 cycles at frequency of 0.2 Hz.; Protocol 2: cyclic load of 38 N to simulate active mobilization, with the same preload, number of cycles, and frequency as above. This review consolidates the current understanding of cyclic testing and may help clinicians and investigators improve the design of flexor tendon repairs, allow for comparisons of different repairs using the same protocol, and evaluate flexor tendon repairs more rigorously before clinical applications.

Biomechanical comparison of monocortical and bicortical plate fixation for rib fractures in a cadaveric model using a locking plate system.

BACKGROUND: Surgical stabilization of rib fractures is an established form of treatment for complex rib fractures. Plate fixation with bicortical screws placement can cause injury to intra-thoracic organs and pleural irritation from protruding screw tips. The aim of this study is to compare the biomechanical properties of monocortical and bicortical plate fixation for rib fractures using a locking plate system. METHODS: Ten pairs of fresh-frozen cadaveric ribs were harvested. Native ribs were mounted onto a biomechanical tester and statically loaded to failure to induce a rib fracture. The native stiffness of the rib was measured. Next, the ribs were stabilized using the Synthes MatrixRIB (Johnson & Johnson, USA) locking plate. Left-sided ribs were fixed in a bicortical manner and right-sided ribs were fixed in a monocortical manner. The repaired ribs were subjected to cyclic loading of 50,000 cycles between 2 to 6 N to simulate physiological respiration, followed by static loading at a rate of 10 N/min until failure. The pre and post-repaired stiffness were measured. A high-speed camera was used to record the mechanism of failure. RESULTS: One left-sided rib was omitted from the study because the fracture occurred at the drill hole site. Left-sided ribs demonstrated a mean native stiffness of 10.0 N/mm (SD 3.71) and right-sided 11.92 N/mm (SD 3.57). After plate fixation, pre and post cyclic stiffness was 3.32 N/mm (SD 1.21) and 4.41 N/mm (SD 3.29) for the bicortical group; 3.14 N/mm (SD 1.24) and 3.91 N/mm (SD 1.98) for the monocortical group. There is no statistical difference found between the two groups (P=0.872). CONCLUSIONS: Our results show that there is no difference in stability between monocortical and bicortical fixation for rib fractures using a locking plate system. Monocortical fixation is recommended to avoid potential complications.

An Exploratory Study Using Semi-Tabular Plate in Zone II Flexor Tendon Repair.

BACKGROUND: This study evaluated the feasibility of using a low-profile titanium (Ti) plate implant, also known as the Ti-button, for Zone II flexor tendon repair. We hypothesize that the use of the Ti-button can distribute the tensile force on the digital flexor tendons to achieve better biomechanical performance. METHODS: Twenty lacerated porcine flexor tendons were randomly divided into two groups and repaired using Ti-button or 6-strand modified Lim-Tsai technique. Ultimate tensile strength, load to 2 mm gap force, and mode of failure were recorded during a single cycle loading test. We also harvested twelve fingers with lacerated flexor digitorum profundus tendons from six fresh-frozen cadaver hands and repaired the tendons using either Ti-button method or modified Lim-Tsai technique. A custom-made bio-friction measurement jig was used to measure the gliding resistance and coefficient of friction of the tendon sheath interface at the A2 pulley. RESULTS: The ultimate tensile strength, load to 2 mm gap force, stiffness, and gliding resistance of the Ti-button repairs were 101.5 N, 25.7 N, 7.8 N/mm, and 2.2 N respectively. Ti-button repairs had significantly higher ultimate tensile strength and stiffness than the modified Lim-Tsai repair. However, Ti-button also increased the gliding resistance and coefficient of friction but there was no significant difference between the two repair techniques. CONCLUSIONS: Ti-button repair displayed comparable mechanical properties to the traditional repair in terms of 2-mm gap formation and gliding resistance, but with a stronger repair construct. Thus, this deepened our interest to further investigate the potential of using Ti-button implant in Zone II flexor tendon repair by studying both the mechanical and biochemical (tendon healing) properties in more in-depth.