A biomechanical comparison of lateral and posterior approaches to sacroplasty.

STUDY DESIGN: Biomechanical cadaveric bench study. OBJECTIVE: To measure the augmentation effect and extravasation risk of posterior and lateral approaches to sacroplasty. SUMMARY OF BACKGROUND DATA: The biomechanical stabilizing effect of sacroplasty is unknown. METHODS: Using a sacral insufficiency fracture model, we performed sacroplasty in 15 osteoporotic cadaveric pelves. Five served as controls, and 10 were each injected with 4 mL of a polymethylmethacrylate cement (5 via a posterior approach, 5 via a lateral approach). Cement extravasation was assessed using computed tomography. Restored strength and stiffness were defined as the ratios of treatment to initial strength and to stiffness, respectively. Between-group differences in restoration parameters were checked for significance (P < 0.05) using an analysis of variance followed by Tukey's test. RESULTS: We found no significant differences between groups in terms of restored strength ( approximately 61%) and stiffness ( approximately 77%). Both injection methods produced extravasation into the anterior sacrum, the posterior sacrum, the sacroiliac joint, and the neural foramens. CONCLUSION: Sacroplasty with 4 mL of cement does not restore the strength or stiffness of the sacrum in a cadaveric model, regardless of the approach used.

Biomechanical comparison of expandable and locked intramedullary femoral nails.

OBJECTIVES: The expandable intramedullary (IM) nail does not require locking and fluoroscopy use is minimized. However, the lack of cross-locking screws may adversely affect the fixation's rotational stability. The purpose of our study was to compare the rotational stability afforded by an expandable nail with that of a standard locked nail. METHODS: In a cadaver model of a diaphyseal femoral fracture (OTA type 32-A3), we compared first-generation expandable IM nails with standard locked IM nails in osteoporotic and nonosteoporotic femora (10 pairs each) and second-generation expandable nails with standard locked IM nails only in nonosteoporotic femora (10 pairs). To simulate torsional loads during walking, we applied an external rotation moment of -1 to 10 Nm at 1 Hz to each construct for 5000 cycles. Failure was defined as 15 degrees of rotation at the fracture site. We used McNemar's test to check for significant (P < 0.05) differences in failure between groups. RESULTS: Of the first-generation expandable nails, 90% failed (9/10 in osteoporotic and 9/10 in nonosteoporotic femora) within the first 1000 cycles. Of the respective locked nails, significantly fewer failed in nonosteoporotic femora than in osteoporotic femora (0/10 and 3/10, respectively). Of the second-generation nails, 8/10 failed within 100 cycles of testing. Of the comparative locked nails, none failed at 5000 cycles. CONCLUSIONS: We concluded that the expandable IM femoral nail, when tested in purely axial rotation, has poor rotational stability compared with the standard locked IM femoral nail.

The strength of the osteoporotic sacrum.

STUDY DESIGN: Biomechanical cadaveric bench study. OBJECTIVE: To determine the strength of the osteoporotic sacrum subjected to vertical force. SUMMARY OF BACKGROUND DATA: Sacral insufficiency fractures are thought to be caused by vertical shear forces acting in the sacral ala. The force required to fracture the osteoporotic sacrum is unknown. METHODS: Eighteen osteoporotic cadaveric pelves were potted and mounted on a materials testing machine so that the anterior superior spine was aligned with the symphysis in the sagittal plane. The lumbar spine (L3-L4) was displaced vertically downward until failure occurred. Failure loads were recorded, and fracture patterns were identified via computed tomography. RESULTS: Mean (+/-SD) failure load was 3200 +/- 1262 N. In 3 of 18 specimens, sacral fractures were not apparent on computed tomography. In 15 of 18 specimens, fractures were produced lateral to the neural foramina. Of those 15 specimens, 8 were unilateral (1 with horizontal extension) and 7 were bilateral. In 13 of 15 cases, fractures were located in Denis Zone 1. CONCLUSION: The osteoporotic sacrum failed under vertical forces of approximately 4.5 times body weight. Imaged fracture patterns resembled sacral insufficiency fractures seen clinically. In 1 case, a horizontal fracture line was produced. Vertical compression forces appear to cause insufficiency fractures in the osteoporotic sacrum.

Evaluation of a computerized measurement technique for joint alignment before and during periacetabular osteotomy.

Periacetabular osteotomy (PAO) is intended to treat a painful dysplastic hip. Manual radiological angle measurements are used to diagnose dysplasia and to define regions of insufficient femoral head coverage for planning PAO. No method has yet been described that recalculates radiological angles as the acetabular bone fragment is reoriented. In this study, we propose a technique for computationally measuring the radiological angles from a joint contact surface model segmented from CT-scan data. Using oblique image slices, we selected the lateral and medial edge of the acetabulum lunate to form a closed, continuous, 3D curve. The joint surface is generated by interpolating the curve, and the radiological angles are measured directly using the 3D surface. This technique was evaluated using CT data for both normal and dysplastic hips. Manual measurements made by three independent observers showed minor discrepancies between the manual observations and the computerized technique. Inter-observer error (mean difference +/- standard deviation) was 0.04 +/- 3.53 degrees for Observer 1; -0.46 +/- 3.13 degrees for Observer 2; and 0.42 +/- 2.73 degrees for Observer 3. The measurement error for the proposed computer method was -1.30 +/- 3.30 degrees . The computerized technique demonstrates sufficient accuracy compared to manual techniques, making it suitable for planning and intraoperative evaluation of radiological metrics for periacetabular osteotomy.

Biomechanical comparison of the interosseous tibiofibular ligament and the anterior tibiofibular ligament.

BACKGROUND: The mechanical importance of the interosseous tibiofibular ligament of the ankle is unclear. The purpose of the current study was to compare the stiffness and strength of the interosseous tibiofibular ligament to that of the anterior tibiofibular ligament. METHODS: Twelve pairs of ankles were obtained from the Maryland State Anatomy Board. All soft tissue was removed except for the interosseous tibiofibular ligament in one ankle of each pair and the anterior tibiofibular ligament in the contralateral ankle. The assignment of which ligament would be excised in the right or left ankle of each pair was random. The specimens were potted as bone-ligament-bone preparations and mounted in a servohydraulic testing machine so that the ligament's long axis was coincident with the actuator. Specimens were elongated at 0.5 mm/s until rupture. Failure load and failure site were recorded, and stiffness was calculated. Stiffness and failure loads were compared with a paired t-test. Significance was set at p < 0.05. RESULTS: The interosseous ligament was significantly stiffer (234 +/- 122 N/mm) than the anterior tibiofibular ligament (162 +/- 64 N/mm). The mean failure load of the interosseous tibiofibular ligament (822 +/- 298 N) was significantly greater than that of the anterior tibiofibular ligament (625 +/- 255 N). CONCLUSIONS: The interosseous tibiofibular ligament is stiffer and stronger than the anterior tibiofibular ligament. CLINICAL RELEVANCE. The current study suggests that the interosseous ligament plays an important role in the stability of the ankle, and its status should be part of the diagnostic evaluation in syndesmotic instability.

Percutaneous Achilles tendon lengthening: a cadaver-based study of failure of the triple hemisection technique.

BACKGROUND AND PURPOSE: Modern descriptions of the percutaneous triple hemisection technique for Achilles tendon lengthening do not take into account the axial twist in the ligament. We were concerned that technical failures of the lengthening technique might occur more often than has been reported, and analyzed the results of the triple hemisection technique in cadaveric tendons in quantitative and qualitative terms, focusing on insufficient or complete tenotomies. METHODS: We performed a percutaneous triple hemisection of the Achilles tendon in 20 legs from adult cadavers, and measured the increase in ankle dorsiflexion in degrees, the length of the cuts in mm, and the depth of the cuts as a percentage of the total diameter of the tendon. Failure of the hemisection was defined as a sliding gap of