Histologic, biomechanical, and biological evaluation of fan-folded iliotibial band allografts for anterior cruciate ligament reconstruction.

PURPOSE: The purpose of this study was to thoroughly characterize the fan-folded iliotibial band (FITB) allograft and compare it with anterior tibialis tendons (ATs) and native anterior cruciate ligaments (ACLs) to determine whether it measures up to those tissues. METHODS: We compared the histologic structure, tensile strength to failure, creep, and stress-relaxation properties of FITBs with those of ATs and ACLs. In vitro cytotoxicity and biocompatibility of FITBs were also compared with ATs. RESULTS: No structural difference was observed between the tissues studied. FITB ultimate tensile strength (3,459 ± 939 N) was not significantly different (P > .9999) from ultimate tensile strength of ATs (3,357 ± 111 N) and was significantly greater (P = .0005) than that of ACLs (886 ± 254 N). No significant difference (P > .9999) was observed in the increase in length resulting from creep testing between FITBs (9.5 ± 3.0 mm) and ATs (9.7 ± 4.0 mm). During stress-relaxation testing, FITBs reached 181 ± 46 N, which was not significantly different (P > .9999) from ATs (166 ± 40 N). Finally, we showed that cytotoxicity of FITBs and ATs was negligible. In vitro biocompatibility of FITBs and ATs was very good, whereas FITBs had a higher propensity to favor the attachment and infiltration of cells that proliferated for at least 4 weeks on their contact. CONCLUSIONS: We found that FITBs, ACLs, and ATs shared a similar structure made of aligned collagen fibers. No significant difference was observed between FITB and AT ultimate tensile strength, creep, and stress-relaxation viscoelastic properties. Ultimate tensile strength to failure of ACLs was lower than that of FITBs and ATs, whereas ACLs were superior to both FITBs and ATs during creep and stress-relaxation testing. FITBs and ATs showed low cytotoxicity and excellent biocompatibility in vitro, with a somewhat higher propensity of FITBs to favor cell attachment and infiltration over time. CLINICAL RELEVANCE: This study suggests that FITBs have the potential to perform as well as ATs for ACL reconstruction.

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.

Adjacent-level biomechanics after single versus multilevel cervical spine fusion.

OBJECT: Previous studies have demonstrated that patients with spinal fusion are at greater risk for adjacent-segment disease and require additional surgery. It has been postulated that excessive motion of a given motion segment unit (MSU) leads to an increased risk of disc degeneration. It is the authors' hypothesis that a greater increase in adjacent-segment motion will be observed following a 2-level versus a single-level anterior cervical discectomy and instrumented fusion (ACDF). Therefore, they undertook this study to determine the effect of single-level versus 2-level ACDF on the biomechanics of adjacent MSUs. METHODS: Ten fresh-frozen human cervical spines were used in this study. The specimens were potted at C-4 and T-1 and tested in flexion and extension. Range of motion (ROM) was 30° of flexion and 15° of extension at a maximum load of 50 N. The specimens were tested intact and then were randomized into 2 groups of 5 specimens each. Group 1 underwent a single-level ACDF at the C5-6 level first, and Group 2 underwent the procedure at the C6-7 level. After testing, both groups had the fusion extended to include the C5-7 levels, and the testing was repeated. Changes in overall ROM, stiffness, and segmental motion were calculated and statistically analyzed using a paired Student t-test. RESULTS: An increase in sagittal ROM of 31.30% above (p = 0.012) and 33.88% below (p = 0.066) the fused MSU was found comparing a 2-level with a 1-level ACDF. The overall stiffness of the entire spinal construct increased 37.34% (p = 0.051) in extension and 30.59% (p = 0.013) in flexion as the second fusion level was added. As expected, the overall sagittal ROM of the entire spinal construct decreased by 13.68% (p = 0.0014) with a 2-level compared with a 1-level fusion. CONCLUSIONS: This study has shown that the biomechanics at adjacent levels to a cervical spine fusion are altered and that there is increased adjacent-segment motion at the levels above and below, after a 2-level compared with a 1-level ACDF.

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.