Posterior atlantoaxial fixation of osteoporotic odontoid fracture: biomechanical analysis of the Magerl versus harms techniques in a cadaver model.

BACKGROUND CONTEXT: Odontoid fractures are among the most common cervical spine fractures in the elderly and are associated with increased morbidity and mortality. Clinical evidence suggests improved survival and quality of life after operative intervention compared to nonoperative treatment. PURPOSE: This study seeks to examine the stability of an osteoporotic Type II odontoid fracture following posterior atlantoaxial fixation with either the Magerl transarticular fixation technique or the Harms C1 lateral mass screws C2 pedicle screw rod fixation. STUDY DESIGN: Biomechanical cadaveric study. METHODS: Eighteen cadaveric specimens extending from the cephalus to C7 were used in this study. Reflective marker arrays were attached to C1 and C2 and a single marker on the dens to measure movement of each during loading with C2-C3 and occiput-C1 being allowed to move freely. A biomechanical testing protocol imparted moments in flexion-extension, axial rotation, and lateral bending while a motion capture system recorded the motions of C1, C2, and the dens. The spines were instrumented with either the Harms fixation (n=9) or Magerl fixation (n=9) techniques, and a simulated Type II odontoid fracture was created. Motions of each instrumented spine were recorded for all moments, and then again after the instrumentation was removed to model the injured, noninstrumented state. RESULTS: Both Harms and Magerl posterior C1-C2 fixation allowed for C1, C2, and the dens to move as a relative unit. Without fixation the dens motion was coupled with C1. No significant differences were found in X, Y, Z translation motion of the dens, C1 or C2 during neutral zone motions between the Magerl and Harms fixation techniques. There were no significant differences found in Euler angle motion between the two techniques in either flexion-extension, axial rotation, or lateral bending motion. CONCLUSIONS: Our findings suggest that both Harms and Magerl fixation can significantly reduce dens motion in Type II odontoid fractures in an osteoporotic cadaveric bone model. CLINICAL SIGNIFICANCE: Both Harms and Magerl posterior atlantoaxial fixation techniques allowed for C1, C2, and the dens to move as a relative unit following odontoid fracture, establishing more anatomic stability to the upper cervical spine.

Characterization of regional variation of bone mineral density in the geriatric human cervical spine by quantitative computed tomography.

BACKGROUND: Odontoid process fractures are among the most common in elderly cervical spines. Their treatment often requires fixation, which may include use of implants anteriorly or posteriorly. Bone density can significantly affect the outcomes of these procedures. Currently, little is known about bone mineral density (BMD) distributions within cervical spine in elderly. This study documented BMD distribution across various anatomical regions of elderly cervical vertebrae. METHODS AND FINDINGS: Twenty-three human cadaveric C1-C5 spine segments (14 males and 9 female, 74±9.3 y.o.) were imaged via quantitative CT-scan. Using an established experimental protocol, the three-dimensional shapes of the vertebrae were reconstructed from CT images and partitioned in bone regions (4 regions for C1, 14 regions for C2 and 12 regions for C3-5). The BMD was calculated from the Hounsfield units via calibration phantom. For each vertebral level, effects of gender and anatomical bone region on BMD distribution were investigated via pertinent statistical tools. Data trends suggested that BMD was higher in female vertebrae when compared to male ones. In C1, the highest BMD was found in the posterior portion of the bone. In C2, BMD at the dens was the highest, followed by lamina and spinous process, and the posterior aspect of the vertebral body. In C3-5, lateral masses, lamina, and spinous processes were characterized by the largest values of BMD, followed by the posterior vertebral body. CONCLUSIONS: The higher BMD values characterizing the posterior aspects of vertebrae suggest that, in the elderly, posterior surgical approaches may offer a better fixation quality.

Relationship to drill bit diameter and residual fracture resistance of the distal tibia.

BACKGROUND: The etiology of bone refractures after screw removal can be attributed to residual drill hole defects. This biomechanical study compared the torsional strength of bones containing various sized cortical drill defects in a tibia model. METHODS: Bicortical drill hole defects of 3 mm, 4 mm, and 5 mm diameters were tested in 26 composite tibias versus intact controls without a drill defect. Each tibia was secured in alignment with the rotational axis of a materials testing system and the proximal end rotated internally at a rate of 1 deg./s until mechanical failure. FINDINGS: All defect test groups were significantly lower (P < 0.01) in torque-to-failure than the intact group (82.80 ± 3.70 Nm). The 4 mm drill hole group was characterized by a significantly lower (P = 0.021) torque-to-failure (51.00 ± 3.27 Nm) when compared to the 3 mm drill hole (59.00 ± 5.48 Nm) group, but not different than the 5 mm hole group (55.71 ± 5.71 Nm). All bones failed through spiral fractures, bones with defects also exhibited posterior butterfly fragments. INTERPRETATION: All the tested drill hole sizes in this study significantly reduced the torque-to-failure from intact by a range of 28.4% to 38.4%, in agreement with previous similar studies. The 5 mm drill hole represented a 22.7% diameter defect, the 4 mm drill hole a 18.2% diameter defect, and the 3 mm drill hole a 13.6% diameter defect. Clinicians should be cognizant of this diminution of long bone strength after a residual bone defect in their creation and management of patient rehabilitation programs.

How Does Tibial Pin Placement in Navigated Total Knee Arthroplasty Affect the Torsional Strength of the Tibia?

INTRODUCTION: Surgical navigation technology has recently become more prevalent for total knee arthroplasty. Surgical navigation typically requires pin placement in the proximal tibia diaphysis to stabilize the bone-tracking hardware, and there have been several recent reports of fractures through these residual navigation pin holes. The objective of this biomechanical study was to determine whether a difference exists in the torsional bone strength of a 5-mm navigation pin hole drilled at a single location in three different orientations: unicortical, bicortical, and transcortical. METHODS: Biomechanical composite sawbone tibias were used to test four conditions: the intact condition with no holes, a unicortical hole, a bicortical hole, and a transcortical hole through the proximal diaphysis. Seven specimens from each group were tested in external rotation to failure at 1 deg/sec. Torque-to-failure, absorbed energy-to-failure, and rotational angle-to-failure were statistically compared across the four groups. RESULTS: All specimens failed proximally by spiral oblique fractures. No statistical differences were found between unicortical and bicortical groups in torque-to-failure, energy-to-failure, and angle-to-failure. However, both unicortical and bicortical groups were markedly lower in all measures than the intact group. The transcortical group was markedly lower in all measures than the intact group and both unicortical and bicortical groups. DISCUSSION: An appropriately placed navigation residual pin hole, either unicortical or bicortical, markedly decreases the torque-to-failure, energy-to-failure, and angle-to-failure of the tibia compared with the intact condition in a synthetic sawbones model. No notable difference was detected between the unicortical and bicortical holes; however, an errant transcortical residual navigation pin hole markedly decreases all measures compared with an appropriately placed unicortical or bicortical hole.

Effects of Lumbosacral Arthrodesis on the Biomechanics of the Sacroiliac Joint.

BACKGROUND: It is unclear whether the sacroiliac joint is vulnerable to adjacent segment disease. Clinical studies have suggested that many patients who have undergone lumbar arthrodesis will develop adjacent segment disease, which may contribute to sacroiliac joint degeneration. The purpose of the present study was to examine whether arthrodesis in the lumbar spine results in altered biomechanics at the sacroiliac joint that could contribute to adjacent segment disease within the joint. METHODS: With use of human cadavers in a biomechanical laboratory study, the effects of lower-lumbar arthrodesis and sacroiliac screws on the biomechanics of the sacroiliac joint were assessed. Human cadaveric pelves with lumbar spines were biomechanically tested in flexion-extension, rotation about the vertical axis, and compression along the vertical axis with single and double-leg support. Four conditions were compared: (1) intact, (2) L4-L5 arthrodesis, (3) L4-S1 arthrodesis, and (4) left sacroiliac screw. Construct vertical and horizontal motions at the anterior and posterior surfaces of the sacroiliac joint were measured. RESULTS: Significant measurable increases in motion of the sacroiliac joint related to arthrodesis of the lumbar spine occurred with flexion-extension loading (p < 0.05). No significant changes were observed for rotation about the vertical axis or compression along the vertical axis with single and double-leg support. CONCLUSIONS: After 360°, 1 or 2-level lumbosacral spine arthrodesis, the sacroiliac joint showed a significant increase in rotational motion with flexion-extension loading. Increases in horizontal translation with axial rotation loading and vertical translation with axial compression loading were not significant. CLINICAL RELEVANCE: The risk of significant alteration of normal sacroiliac kinematics should be considered in all patients undergoing 360° lumbosacral arthrodesis.

Comparison of Biomechanical Properties of a Synthetic L3-S1 Spine Model and Cadaveric Human Samples.

Human cadavers currently represent the gold standard for spine biomechanical testing, but limitations such as costs, storage, handling, and high interspecimen variance motivate the development of alternatives. A commercially available synthetic surrogate for the human spine, the Sawbones spine model (SBSM), has been developed. The equivalence of SBSM to a human cadaver in terms of biomechanical behavior has not been fully assessed. The objective of this study is to compare the biomechanics of a lumbar tract of SBSM to that of a cadaver under physiologically relevant mechanical loads. An L3-S1 SBSM and 39 comparable human cadaver lumbar spine tracts were used. Each sample was loaded in pure flexion-extension or torsion. Gravity and follower loads were also included. The movement of each vertebral body was tracked via motion capture. The range of motion (ROM) of each spine segment was recorded, as well as the overall stiffness of each L3-S1 sample. The ROM of SBSM L3-L4 was larger than that found in cadavers in flexion-extension and torsion. For the other spine levels, the ROMs of SBSM were within one standard deviation from the mean values measured in cadavers. The values of structural stiffness for L3-S1 of SBSM were comparable to those of cadaveric specimens for both flexion and torsion. In extension, SBSM was more compliant than cadavers. In conclusion, most of the biomechanical properties of an L3-S1 SBSM model were comparable to those of human cadaveric specimens, supporting the use of this synthetic surrogate for testing applications.

Biomechanical Comparison between Volar Plate Fixator and Nonbridge External Wrist Fixator.

Intra-articular distal radius fractures are difficult to reduce and maintain by nonoperative means. ORIF leaves implants in the patient long after the fracture is healed. External fixation can stabilize the reduced fracture and leaves no long-term implants. The nonbridging fixator (NBX) will provide better reduction and comparable rigidity of fixation to a volar plate for a 5-fragment, OTA 23 C3.2 distal radius fracture. A 5-part distal radius fracture was created in 5 pairs of cadaver arms. One arm was randomly fixed with the NBX fixator; the matched pair was fixed with a volar plate (VPS). Fluoroscopic images recorded the extremes of passive volar-dorsiflexion range of motion (ROM) and radial-ulnar deviation ROM. Each arm was loaded with an axial force at a constant displacement rate until failure. The average reduction of radial tilt achieved for the NBX group was 13.8 ± 4.8° and 6.3 ± 4.7° for VPS; radial length: 3.4 ± 3.7 mm for NBX and 1.9 ± 1.0 mm for VPS; volar tilt: 26.3 ± 12.4° for NBX and 14.0 ± 13.5° for VPS. For NBX, ROM was slightly less after fixation than before fracture. ROM with volar plating was greater after fracture. The peak axial load for NBX was 925 ± 445 N; for VPS, 2,152 ± 1023 N. NBX had minimal effect on ROM and provided adequate strength and restoration of alignment at least as good as VPS for this 5-part fracture model.

Cervical Spine Fusion: Biomechanics of a Three-Level Cadaver Model Comparing Anterior Plate versus Stand-Alone Cage.

Study Design-Biomechanical cadaveric study. Objective-Long anterior cervical plate and cage (APC) constructs have a risk of pseudarthrosis with minor bone resorption. Stand-alone cages (SACs) allow settling. The biomechanics of SAC have been investigated, but not multilevel, compression screw SAC. The purpose of this study is to evaluate the biomechanical safety of three-level SAC versus APC. Methods-Discectomies at three levels of five human cadaver spines (T1-C3) were fixed with SAC. A 0.18 mm thick shim was interposed between the cage and the superior endplate, and a pressure transducer map was placed between the cage and the inferior endplate. Tests were performed in flexion-extension and then repeated after removing the shims to simulate minor bone resorption. Subsequently, APC was applied and experiments were repeated. The pressure between each cage and endplate and motion of the implants were measured. Results-The range of motion (ROM) of SAC and APC constructs were comparable. The contact area and pressure between cage and endplate did not significantly change during motion with SAC. Shim removal did not significantly affect ROM, contact area, or average pressure measures. For APC, both contact area and pressure decreased from extension to flexion. Shim removal caused a significant loss of contact area and pressure. Conclusions-SAC provided comparable rigidity to the conventional APC construct while maintaining compression at the endplate-cage interface throughout flexion-extension and after minor bone resorption.

Treatment of Selected Distal Radius Fractures with Nonbridging External Fixation.

A nonbridging external fixation (NBX) system with 1.6-mm diameter pins provided excellent stability for distal radius fractures in cadavers. For the present study, all patients with distal radius fractures were seen by the surgeon authors. Fractures that were displaced and unstable, including Orthopaedic Trauma Association (OTA) types 23-A2.3 to C3.3, were reduced and fixed with the NBX system. The Western Institutional Review Board granted approval (296864) for this retrospective study. Fractures numbered five OTA-A2, eight OTA-A3, two OTA-B3, one OTA-C1, two OTA-C2, and eight OTA-C3. In total, the study included 26 patients. At fixator removal, average dorsiflexion was 37.0° ± 17.8°; volar flexion, 39.4° ± 17.2°; pronation, 80.6° ± 16.1°; and supination, 48.1° ± 24.2°. Follow-up averaged 11.7 mo ± 19.2 mo. At final follow-up, average dorsiflexion was 52.9° ± 25.0°; volar flexion, 53.1° ± 23.7°; pronation, 80.8° ± 14.5°; and supination, 67.7° ± 30.3°. Average radial tilt at the time of injury was 11.6° ± 8.3°; post op to 23.9° ± 5.0°; and at last follow-up, 23.1° ± 5.0°. Average radial styloid length at the time of injury was 4.1 mm ± 3.7 mm; post op to 11.4 mm ± 3.0 mm; and at last follow-up, 10.5 mm ± 3.1 mm. Volar tilt at the time of injury averaged -19.6° ± 14.8°; reduced to 9.8° ± 6.3°; and at last follow-up, 7.5° ± 6.5°. This form of nonbridging fixation is safe and effective at maintaining reduced, extra- and intra-articular, distal radius fractures and allows functional range of motion with minimal complications.

How Reliable is the Acetabular Cup Position Assessment from Routine Radiographs?

BACKGROUND: Cup position is crucial for optimal outcomes in total hip arthroplasty. Radiographic assessment of component position is routinely performed in the early postoperative period. AIMS: The aims of this study were to determine in a controlled environment if routine radiographic methods accurately and reliably assess the acetabular cup position and to assess if there is a statistical difference related to the rater's level of training. METHODS: A pelvic model was mounted in a spatial frame. An acetabular cup was fixed in different degrees of version and inclination. Standardized radiographs were obtained. Ten observers including five fellowship-trained orthopaedic surgeons and five orthopaedic residents performed a blind assessment of cup position. Inclination was assessed from anteroposterior radiographs of the pelvis and version from cross-table lateral radiographs of the hip. RESULTS: The radiographic methods used showed to be imprecise specially when the cup was positioned at the extremes of version and inclination. An excellent inter-observer reliability (Intra-class coefficient > 0,9) was evidenced. There were no differences related to the level of training of the raters. CONCLUSIONS: These widely used radiographic methods should be interpreted cautiously and computed tomography should be utilized in cases when further intervention is contemplated.

Effects of gamma irradiation on the biomechanical properties of peroneus tendons.

PURPOSE: This study was designed to investigate the biomechanical properties of nonirradiated (NI) and irradiated (IR) peroneus tendons to determine if they would be suitable allografts, in regards to biomechanical properties, for anterior cruciate ligament reconstruction after a dose of 1.5-2.5 Mrad. METHODS: Seven pairs of peroneus longus (PL) and ten pairs of peroneus brevis (PB) tendons were procured from human cadavers. The diameter of each allograft was measured. The left side of each allograft was IR at 1.5-2.5 Mrad, whereas the right side was kept aseptic and NI. The allografts were thawed, kept wet with saline, and attached in a single-strand fashion to custom freeze grips using liquid nitrogen. A preload of 10 N was then applied and, after it had reached steady state, the allografts were pulled at 4 cm/sec. The parameters recorded were the displacement and force. RESULTS: The elongation at the peak load was 10.3±2.3 mm for the PB NI side and 13.5±3.3 mm for the PB IR side. The elongation at the peak load was 17.4±5.3 mm for the PL NI side and 16.3±2.0 mm for the PL IR side. For PL, the ultimate load was 2,091.6±148.7 N for NI and 2,122.8±380.0 N for IR. The ultimate load for the PB tendons was 1,485.7±209.3 N for NI and 1,318.4±296.9 N for the IR group. The ultimate stress calculations for PL were 90.3±11.3 MPa for NI and 94.8±21.0 MPa for IR. For the PB, the ultimate stress was 82.4±19.0 MPa for NI and 72.5±16.6 MPa for the IR group. The structural stiffness was 216.1±59.0 N/mm for the NI PL and 195.7±51.4 N/mm for the IR side. None of these measures were significantly different between the NI and IR groups. The structural stiffness was 232.1±45.7 N/mm for the NI PB and 161.9±74.0 N/mm for the IR side, and this was the only statistically significant difference found in this study (P=0.034). CONCLUSION: Our statistical comparisons found no significant differences in terms of elongation, ultimate load, or ultimate stress between IR and NI PB and PL tendons. Only the PB structural stiffness was affected by irradiation. Thus, sterilizing allografts at 1.5-2.5 Mrad of gamma irradiation does not cause major alterations in the tendons' biomechanical properties while still providing a suitable amount of sterilization for anterior cruciate ligament reconstruction.

Biomechanical Analysis of All-Inside, Arthroscopic Suture Repair Versus Extensor Retinaculum Capsulorrhaphy for Triangular Fibrocartilage Complex Tears With Instability.

PURPOSE: To assess ulnocarpal joint stability after treatment of a peripheral triangular fibrocartilage complex (TFCC) injury with all-inside arthroscopic suture repair (SR), extensor retinaculum capsulorrhaphy with the Herbert sling (HS), and a combination of both (SR+HS). METHODS: Twelve fresh-frozen, age-matched, upper-extremity specimens intact from the distal humerus were prepared. Nondestructive mechanical testing was performed to assess native ulnocarpal joint stability and load-displacement curves were recorded. A peripheral, ulnar-sided TFCC injury was created with arthroscopic assistance, and mechanical testing was performed. Each specimen was treated with SR or HS and testing was repeated. The 6 specimens treated with SR were then treated with HS (SR+HS), and testing was repeated. We used paired Student t tests for statistical analysis within cohorts. RESULTS: For all cohorts, there was an average increase in ulnar translation after the creation of a peripheral TFCC injury and an average decrease after repair. Herbert sling decreased translation by 21%, SR decreased translation by 12%, and SR+HS decreased translation by 26%. CONCLUSIONS: Suture repair plus HS and HS reduce ulnar translation the most after a peripheral TFCC injury, followed by SR alone. CLINICAL RELEVANCE: Ulnocarpal joint stability should be assessed clinically in patients with peripheral TFCC injury, and consideration should be made for using extensor capsulorrhaphy in isolation or as an adjunct to SR as a treatment option.

Hot Topics in Biomechanics: Hip Fracture Fixation.

Geriatric hip fractures continue to increase in frequency as the population ages, and intertrochanteric femur fractures are a significant part of these injuries. Plate fixation for intertrochanteric fractures of the proximal femur has been in use for many years, and application of the sliding hip screw has also been a mainstay of treatment. Recent data suggest there may be a benefit to using implants that add rotational stability to the proximal intertrochanteric fragment. Although preliminary data are promising, there is need for improved investigation to demonstrate the benefit of these new implant designs. In this era of increasing emphasis on cost, quality, and value, better data are needed to help clinicians determine the best therapy for their patients.

The effect of viscosity on cement penetration in total knee arthroplasty, an application of the squeeze film effect.

The authors present a prospective randomized blinded cadaver study designed to evaluate the engineering concept of a squeeze film effect and the effect of cement viscosity on cement penetration in total knee arthroplasty. This was done in response to an earlier clinical study demonstrating inferior tibial cement penetration using early, often liquid, phase cement. Paired cadaver tibias were implanted with the tibial component using either liquid or dough phase cement. Based on an AP fluoroscopic image, the dough phase cement penetrated deeper than liquid in all four zones. This was statistically significant in zones 1, 2 and 3. Deeper cement penetration has been shown to provide a stronger cement-bone interphase. As a result dough phase cement is recommended to obtain optimal cement penetration.

Biomechanical analysis of four- versus six-screw constructs for short-segment pedicle screw and rod instrumentation of unstable thoracolumbar fractures.

BACKGROUND CONTEXT: Conventionally, short-segment fusion involves instrumentation of one healthy vertebra above and below the injured vertebra, skipping the injured level. This short-segment construct places less surgical burden on the patient compared with long-segment constructs, but is less stable biomechanically, and thus has resulted in clinical failures. The addition of two screws placed in the fractured vertebral body represents an attempt to improve the construct stiffness without sacrificing the benefits of short-segment fusion. PURPOSE: To determine the biomechanical differences between four- and six-screw short-segment constructs for the operative management of an unstable L1 fracture. STUDY DESIGN: Biomechanical study of instrumentation in vertebral body cadaveric models simulating an L1 axial load injury pattern. METHODS: Thirteen intact spinal segments from T12 to L2 were prepared from fresh-frozen cadaver spines. An axial load fracture of at least 50% vertebral body height was produced at L1 and then instrumented with pedicle screws. Specimens were evaluated in terms of construct stiffness, motion, and rod strain. Two conditions were tested: a four-screw construct with no screws at the L1 fractured body (4S) and a six-screw construct with screws at all levels (6S). The two groups were compared statistically by paired Student t test. RESULTS: The mean stiffness in flexion-extension was increased 31% (p<.03) with the addition of the two pedicle screws in L1. Relative motion in terms of vertical and axial rotations was not significantly different between the two groups. The L1-L2 rod strain was significantly increased in the six-screw construct compared with the four-screw construct (p<.001). CONCLUSIONS: In a cadaveric L1 axial load fracture model, a six-screw construct with screws in the fractured level is more rigid than a four-screw construct that skips the injured vertebral body.

Biomechanical study of 4-hole pubic symphyseal plating: locked versus unlocked constructs.

To the authors' knowledge, no published studies have examined the use of locking plates on injuries of the anterior pelvic ring. The purpose of this study was to determine whether locked plates provide enhanced stability in the treatment of pubic symphyseal disruptions. Completely unstable pelvic injuries were simulated in pelvic Sawbones (model 1301; Pacific Research Laboratories, Vashon, Washington) and 2 different fixation constructs used for anterior fixation (4-hole, 3.5-mm pubic symphysis plate with all locked or all unlocked screws). Adjunctive sacroiliac screw fixation with a single 7.3-mm screw placed into S1 was used in all specimens. Specimens were analyzed for motion at the pubic symphysis and sacroiliac joints using a Material Testing System (MTS Systems Corporation, Eden Prairie, Minnesota). Each specimen was subjected to compressive loading in a single-limb stance. Side loading was also examined. The main outcome measurement was motion at the pubic symphysis and sacroiliac joints and overall construct stiffness. No significant difference existed in overall construct stiffness between the 2 methods of pubic symphysis fixation. The motions at the pubic symphysis or injured sacroiliac joints were not significantly different. In addition, motion at the pubic symphysis joint with lateral load was not improved with a locking construct.No significant difference existed between 4-hole locked or unlocked constructs used for fixation of the pubic symphysis. No apparent advantage of locking screws exists for disruptions of the pubic symphysis, and recent reports have questioned the possibility of catastrophic failure.

Peripheral triangular fibrocartilage complex tears cause ulnocarpal instability: a biomechanical pilot study.

BACKGROUND: Instability at the ulnocarpal joint has many causes, but the common thread among these causes is the presence of abnormalities in the triangular fibrocartilage complex (TFCC). However, the biomechanical consequences at the ulnocarpal joint after detachment of the TFCC from the ulnar styloid are not clearly defined. Better delineation of whether peripheral TFCC detachments cause ulnocarpal instability will help to design surgical treatments. QUESTIONS/PURPOSES: We asked whether detachment of the peripheral TFCC from the ulnar styloid causes ulnocarpal instability. METHODS: Using 20 fresh-frozen below-elbow cadaver specimens, the distal ulna was cycled volarly and dorsally with the carpus held firmly. The load-displacement curve was analyzed to determine the resistance of the ulnocarpal joint against dorsal-volar displacement of the ulna (stiffness) and the amount of dorsal-volar excursion with minimal resistance before reaching firm end points dorsally and volarly. A standardized 3-mm transection of the attachment of the TFCC from the ulnar styloid was created with a scalpel using arthroscopic observation. Mechanical testing was repeated and paired Student's t-tests conducted. RESULTS: The mean stiffness of the ulnocarpal joint was decreased after detachment. The amount of dorsal-volar excursion was similar after detachment of the peripheral TFCC. CONCLUSIONS: There is decreased stiffness at the ulnocarpal joint after detachment of the peripheral TFCC, but there is no biomechanically detectable difference in dorsal-volar excursion. CLINICAL RELEVANCE: The findings of the current study can be used to develop and evaluate innovative surgical techniques, such as capsulorraphy or ligamentous reconstruction, that specifically address laxity at the ulnocarpal joint after peripheral TFCC detachment.

Comparison of 2 forearm reconstructions for longitudinal radioulnar dissociation: a cadaver study.

PURPOSE: We present the results of a cadaveric study of 2 forearm reconstructions with radial head replacement for longitudinal radioulnar dissociation injuries. METHODS: We created a simulated longitudinal radioulnar dissociation injury in 8 cadaver forearms. Two reconstructions were performed alternately on each arm: patellar tendon interosseous ligament complex reconstruction and the Herbert sling extensor retinaculum plication. We performed mechanical testing in a materials testing machine with and without a radial head replacement, and measured ulnocarpal impaction force through 2 distal ulna strain gauges. We determined relative radioulnar displacement using live fluoroscopic analysis of implanted stainless-steel beads. RESULTS: Relative radioulnar longitudinal displacement in the destabilized forearms was 10.7 compared with 0.7 mm before creating the injury. A prosthetic radial head replacement alone decreased the displacement by 75% to 2.7 mm. Interosseous ligament reconstruction alone reduced the displacement to 5.1 mm and to 1.3 mm when combined with a radial head implant. The Herbert sling alone did not improve longitudinal stability. The distal ulna force in the native arm was 17 N, or 17% of the force across the wrist. The interosseous ligament reconstruction restored the force to 21 N, whereas the Herbert sling only marginally decreased the ulna impaction force to 45 N. Adding a radial head decreased the distal ulna force to 7 N for the patellar tendon interosseous ligament reconstruction, and 2 N for the Herbert sling. CONCLUSIONS: In longitudinal radioulnar dissociation injuries, the radial head is an important stabilizer and should be repaired or replaced to minimize radial shortening and ulnar impaction force. Patellar tendon interosseous ligament reconstruction effectively restores the ulnocarpal force distribution and markedly reduces longitudinal instability at the distal radioulnar joint. Combined with radial head arthroplasty, the construct has stability similar to an intact forearm. The Herbert sling did not improve longitudinal stability in this testing construct. CLINICAL RELEVANCE: Treatment of longitudinal radioulnar dissociation may benefit from radial head replacement and interosseous ligament reconstruction using a patellar tendon graft.

Suture-button construct for interosseous ligament reconstruction in longitudinal radioulnar dissociations: a biomechanical study.

PURPOSE: Longitudinal radioulnar dissociation is a triad of injuries consisting of distal radioulnar joint disruption, interosseous ligament complex (IOLC) tear, and radial head fracture. This renders the forearm longitudinally unstable, resulting in proximal migration of the radius and ulnar-sided wrist degeneration. We hypothesized that reconstruction of the central band of the IOLC in cadaver forearms using a Mini-TightRope suture-button construct would restore native forearm stability. METHODS: We implanted 8 fresh-frozen cadaver arms with steel beads into the distal radius and ulna, mounted them on an MTS machine, and cyclically loaded them from 13 N distraction to 130 N compression. Bead motion was recorded fluoroscopically and analyzed using Image-Pro Express software. We measured distal ulnar forces using strain gauge transducers. Longitudinal radioulnar dissociation injuries were created by radial head excision and complete IOLC and triangular fibrocartilage complex disruption. At each stage, arms were tested with and without a radial head implant. We reconstructed the central band of the IOLC using a Mini-TightRope and tightened until the distal radioulnar joint was reduced fluoroscopically. We used multiple-comparison analysis of variance with Tukey's Honestly Significant Difference test for statistical analysis. RESULTS: The intact arms had an average radioulnar axial displacement of 0.7 ± 0.8 mm and distal ulnar impaction force of 16.7 ± 11.1 N (per 100 N of axial load on the forearm). After destabilization, the radioulnar displacement increased to 10.7 ± 3.9 mm (p < .001) and ulnar load increased 312%, to an average of 52.2 ± 25.7 N (p < .001). After IOLC reconstruction, average displacement decreased to 2.2 ± 0.9 mm with a distal ulnar load of 19.05 ± 13.5 N (not significantly different from intact arms). CONCLUSIONS: In this cadaveric study, Mini-TightRope IOLC reconstruction with or without a radial head prosthesis significantly reduced distal ulnar impaction forces to that of the native forearm, while limiting radioulnar displacement to near-anatomic levels.

A biomechanical comparison of fan-folded, single-looped fascia lata with other graft tissues as a suitable substitute for anterior cruciate ligament reconstruction.

PURPOSE: The purpose of this study was to evaluate the initial biomechanical properties of a fan-folded, single-loop construct of fan-folded fascia lata allograft in comparison to other graft tissues currently being used for anterior cruciate ligament (ACL) reconstruction. METHODS: Eighteen fascia lata specimens were harvested from 11 donors and fan folded through a proprietary process. Bone-patellar tendon-bone (BPTB), tibialis anterior, tibialis posterior, and peroneus longus tendons were harvested from 4 additional donors. All soft-tissue grafts were tested to failure in an MTS machine (MTS Systems, Eden Prairie, MN) in a single-looped fashion. BPTB grafts were similarly clamped in freeze grips. The ultimate load to failure and stiffness were calculated for each graft type tested. RESULTS: The mean ultimate load to failure was 3,266 N and stiffness was 414 N/mm for the single-looped fascia lata grafts (n = 18). There was no significant difference for ultimate load to failure and stiffness between the fascia lata and tibialis anterior (3,012 N and 342 N/mm, respectively), tibialis posterior (3,666 N and 392 N/mm, respectively), and peroneus longus (3,050 N and 346 N/mm, respectively) tendons. The fascia lata grafts performed significantly better (P < .001) than BPTB (1,404 N and 224 N/mm, respectively). CONCLUSIONS: A single-loop construct of fan-folded fascia lata allograft has, on biomechanical testing, initial ultimate tensile strength (3,266 N) and stiffness values equivalent to or better than several other graft tissues currently used in ACL reconstruction, including BPTB (1,403 N), tibialis anterior (3,012 N), tibialis posterior (3,666 N), and peroneus longus (3,050 N). CLINICAL RELEVANCE: In the face of potential allograft tissue shortages and increasing constraints on health care expenditures, the use of fascia lata has the potential to be a readily available graft for ACL reconstruction that performs as well as other grafts and at a comparable or lower cost.