Derek P. Lindsey

Strains across the Acetabular Labrum during Hip Motion: A Cadaveric Model

Background Labral tears commonly cause disabling intra-articular hip pain and are commonly treated with hip arthroscopy. However, the function and role of the labrum are still unclear. Hypotheses (1) Flexion, adduction, and internal rotation (a position clinically defined as the position for physical examination known as the impingement test) places greatest circumferential strain on the anterolateral labrum and posterior labrum; (2) extension with external rotation (a position clinically utilized during physical examination to assess for posterior impingement and for anterior instability) places significant circumferential strains on the anterior labrum; (3) abduction with external rotation during neutral flexion-extension (the position the extremity rests in when a patient lies supine) places the greatest load on the lateral labrum. Study Design Descriptive laboratory study. Methods Twelve cadaveric hips (age, 79 years) without labral tears or arthritis were studied. Hips were dissected free of soft tissues, except the capsuloligamentous structures. Differential variable reluctance transducers were placed in the labrum anteriorly, anterolaterally, laterally, and posteriorly to record circumferential strains in all 4 regions as the hip was placed in 36 different positions. Results The posterior labrum had the greatest circumferential strains identified; the peak was in the flexed position, in adduction or neutral abduction-adduction. The greatest strains anteriorly were in flexion with adduction. The greatest strains anterolaterally were in full extension. External rotation had greater strains than neutral rotation and internal rotation. The greatest strains laterally were at 90° of flexion with abduction, and external or neutral rotation. In the impingement position, the anterolateral strain increased the most, while the posterior labrum showed decreased strain (greatest magnitude of strain change). When the hip is externally rotated and in neutral flexion-extension or fully extended, the posterior labrum has significantly increased strain, while the anterolateral labrum strain is decreased. Conclusion These are the first comprehensive strain data (of circumferential strain) analyzing the whole hip labrum. For the intact labrum, the greatest strain change was at the posterior acetabulum, whereas clinically, acetabular labral tears occur most frequently anterolaterally or anteriorly. The results are consistent with the impingement test as an assessment of anterolateral acetabular labral stress. The hyperextension-rotation test, often used clinically to assess anterior hip instability and posterior impingement, did not show a change in strain anteriorly, but did reveal an increase in strain posteriorly. Clinical Relevance Although this study does not include muscular forces across the hip joint, it does provide a clue as to the stresses about the labrum through the complete range of motions of the hip, which may help in providing a better understanding of the cause of labral tears and in the protection of labral repairs.

The effect of relaxin on the female anterior cruciate ligament: Analysis of mechanical properties in an animal model

BACKGROUND The peptide hormone relaxin, found in pregnant and non-pregnant females, has been shown to have collagenolytic effects on ligamentous tissue. Relaxin receptors have recently been identified on the human female anterior cruciate ligament (ACL). Relaxin may affect the load bearing properties of the female ACL and contribute to non-contact ACL injuries. HYPOTHESIS The administration of recombinant relaxin+/-estrogen will lead to a significant decrease in ACL integrity in the guinea pig model. STUDY DESIGN Controlled laboratory study. METHODS Adult female guinea pigs were divided into three experimental groups. Group 1 (n=4) was administered only 20 microg/h of recombinant porcine relaxin for 3 weeks. Group 2 (n=4) was administered 20 microg/h of recombinant porcine relaxin and 5 microg/h of estradiol for 3 weeks. Group 3 (n=4) served as both a normal control before surgical transection of the ACL and a positive ACL tear control after transection. All hormones were administered using separate implanted osmotic pumps. ACL laxity was tested by implanting radio-opaque markers in the femur and tibia of each leg. After applying a standard anterior force (22 N), the distance between markers was measured radiographically at day 0 and day 21. The animals were then sacrificed and the ACLs were analyzed for load-to-failure using a material testing machine. RESULTS Load-to-failure testing indicated that animals treated with relaxin only had significantly weaker ACLs (micro=40.4 N, p=0.001) compared to controls (micro=64.1 N). The relaxin+estrogen group (micro=32.7 N) was also significantly weaker than controls (p=0.007). There were no statistical differences between relaxin and relaxin+estrogen groups. Both relaxin only and relaxin+estrogen groups showed an increase in anterior translation of the tibia after 3 weeks of infusion, but it did not achieve statistical significance. CONCLUSIONS Relaxin significantly alters the mechanical properties of the ACL in an animal model. CLINICAL RELEVANCE The effects of relaxin, possibly in conjunction with estrogen, may contribute to a comprehensive etiology for human female non-contact ACL injuries.

An in vivo murine model of continuous intramedullary infusion of polyethylene particles

Wear debris affects both initial osseointegration and subsequent bone remodeling of total joint replacements (TJRs). To study the complex cascade associated with the continuous generation of particles, a robust animal model is essential. To date, an animal model that incorporates continuously delivered particles to an intramedullary orthopaedic implant has not been available. In this study, we successfully infused clinically relevant ultra high molecular weight polyethylene particles, previously isolated from joint simulator tests, to the intramedullary space of the mouse femur for 4 weeks using a subcutaneous osmotic pump. Reduction of bone volume following the 4-week infusion of UHMWPE was detected by microCT. UHMWPE particles also changed the level of Alkaline Phosphatase expression in the infused femurs. Continuous infusion of particles to the murine bone-implant interface simulated the clinical scenario of local polymer wear particle generation and delivery in humans and can be used to further study the biological processes associated with wear debris particles.

Effects of intermittent hydrostatic pressure and BMP-2 on osteoarthritic human chondrocyte metabolism in vitro.

This study examined effects of intermittent hydrostatic pressure (IHP) and a chondrogenic growth factor, bone morphogenetic protein‐2 (BMP‐2), on anabolic, catabolic, and other metabolic markers in human osteoarthritic (OA) chondrocytes in vitro.

Biomechanical Comparison of Blade Plate and Intramedullary Nail Fixation for Tibiocalcaneal Arthrodesis

Background: Tibiocalcaneal arthrodesis is an uncommon salvage procedure used for complex problems of the ankle and hindfoot. A biomechanical evaluation of the fixation constructs of this procedure has not been studied previously. The purpose of this study was to compare intramedullary nail to blade plate fixation in a deformity model in fatigue endurance testing and load to failure. Materials and Methods: Nine matched pairs of fresh frozen cadaveric legs underwent talectomy followed by fixation with a blade plate and 6.5-mm fully threaded cancellous screw or an ankle arthrodesis intramedullary nail. The specimens were loaded to 270 N at a rate of 3 Hz for a total of 250,000 cycles, followed by loading to failure. Results: Intramedullary nail fixation demonstrated greater mean stiffness throughout the fatigue endurance testing, from cycles 10 through 250,000 (blade plate versus intramedullary nail; cycle 10, 93 ± 34 N/mm versus 117 ± 40 N/mm (t = 2.33, p = 0.04); cycle 100, 89 ± 34 N/mm versus 118 ± 42 N/mm (t = 3.16, p = 0.01); cycle 1000, 86 ± 32 N/mm versus 120 ± 45 N/mm (t = 3.52, p = 0.01); cycle 10,000, 83 ± 36 N/mm versus 128 ± 50 N/mm (t = 3.80, p = 0.01); cycle 100,000, 82 ± 34 N/mm versus 126 ± 52 N/mm (t = 3.70, p = 0.01); cycle 250,000, 80 ± 31 N/mm versus 125 ± 49 N/mm (t = 4.2, p = 0.003). There was no statistically significant difference between the intramedullary nail and blade plate fixation in cycle one or in load to failure; cycle 10, blade plate 70 ± 38 N/mm and intramedullary nail 67 ± 20 N/mm (t = 0.60, p = 0.56); load to failure, blade plate 808 ± 193 N, IMN 1074 ± 290 N) (p = 0.15). Conclusion: Intramedullary nail fixation was biomechanically superior to blade plate and screw fixation in a tibiocalcaneal arthrodesis construct. Clinical Relevance: The ankle arthrodesis intramedullary nail provides greater stiffness for fixation in tibiocalcaneal arthrodesis, which may improve healing.

Biomechanical Evaluation of a Novel Reverse Coracoacromial Ligament Reconstruction for Acromioclavicular Joint Separation

Background: Enhancing anterior-posterior (AP) stability in acromioclavicular (AC) reconstruction may be advantageous. Purpose: To compare the initial stability of AC reconstructions with and without augmentation by either (1) a novel “reverse” coracoacromial (CA) ligament transfer or (2) an intramedullary AC tendon graft. Hypothesis: Reverse CA transfer will improve AP stability compared with isolated coracoclavicular (CC) reconstruction. Study Design: Controlled laboratory study. Methods: Six matched pairs of cadaveric shoulders underwent distal clavicle resection and CC reconstruction. Displacement (mm) was measured during cyclic loading along AP (±25 N) and superior-inferior (SI; 10-N compression, 70-N tension) axes. Pairs were randomized to receive each augmentation and the same loading protocol applied. Results: Reverse CA transfer (3.71 ± 1.3 mm, standard error of the mean [SEM]; P = .03) and intramedullary graft (3.41 ± 1.1 mm; P = .03) decreased AP translation compared with CC reconstruction alone. The SI displacement did not differ. Equivalence tests suggest no difference between augmentations in AP or SI restraint. Conclusion: Addition of either reverse CA transfer or intramedullary graft demonstrates improved AP restraint and provides similar SI stability compared with isolated CC reconstruction. Clinical Relevance: Reverse CA ligament transfer may be a reasonable alternative to a free tendon graft to augment AP restraint in AC reconstruction.

New bone formation by murine osteoprogenitor cells cultured on corticocancellous allograft bone

The gold standard for bone grafting in orthopedics is autograft, however autograft has a limited supply and is associated with significant morbidity at the harvest site. One alternative, allograft bone, provides an osteoconductive scaffold, is in less limited supply, and it does not require a harvest from the patient. However, allograft lacks both osteogenic cells and osteoinductive proteins that make autograft bone so advantageous. This study provides a model to investigate strategies for augmentation of corticocancellous allograft bone discs with bone marrow‐derived osteoprogenitor cells (OPCs) plus exogenous growth factors in vitro. In this model, allograft bone discs were created by cutting 1‐mm thick slices from the distal femur and proximal tibia of euthanized mice. The allografts were sterilized and scanned by micro‐computed tomography (µCT) to provide the pre‐culture graft volume and trabecular characteristics. The discs were then seeded with OPCs harvested from murine bone marrow. The seeded grafts were placed in organ culture until harvest, after which they were re‐scanned by µCT and the data compared to the corresponding pre‐culture data. In addition, bone morphogenetic protein‐7 (BMP‐7, also know as osteogenic protein‐1 or OP‐1), basic fibroblast growth factor (bFGF), and OP‐1 combined with bFGF were added on a daily basis to the cultures. After final µCT scanning, all grafts were sectioned and evaluated histologically after hematoxylin and eosin (H&E) staining. µCT scans of cultured allografts with cells at 3, 5, and 9 weeks showed a time‐dependent, statistically significant increase in bone volume. The trabecular thickness (Tb.Th.) of grafts, from both groups that were augmented with OP‐1, showed a statistically significant increase in trabecular thickness of allografts with OPCs. These data suggest that bone marrow‐derived OPCs adhere to, and produce, new bone on corticocancellous allograft in vitro. When exogenous OP‐1 is added to this model, an increase in the production of bone onto the corticocancellous allograft bone disc is seen. This model allows for the investigation of the effects of multiple growth factors, and other interventions, on OPCs seeded onto allograft bone in vitro.

An analysis of four ulnar collateral ligament reconstruction procedures with cyclic valgus loading

We describe a new transolecranon fossa ulnar (TOFU) collateral ligament reconstruction technique and compare its response to cyclic valgus loading with the Jobe, Docking, and DANE procedures. TOFU is an arthroscopically assisted, modified all-interference screw technique. A cyclic valgus moment was applied to 32 intact and reconstructed, unembalmed elbows. Valgus angles were measured at 1, 10, 100, and 1000 cycles. At all cycles, there was no difference between intact and TOFU-treated elbows. TOFU resulted in significantly smaller angles than DANE at cycles 10, 100, and 1000; Docking at cycle 1000; and Jobe at cycles 10, 100, and 1000. The TOFU procedure shows superior resistance to valgus loading than DANE and Jobe by cycle 10, and Docking by cycle 1000. Further study is needed to evaluate the clinical value of the TOFU procedure as an arthroscopically assisted technique.

Biomechanical Determination of Distal Level for Fusions across the Cervicothoracic Junction.

Study Design In vitro testing. Objective To determine whether long cervical and cervicothoracic fusions increase the intradiscal pressure at the adjacent caudal disk and to determine which thoracic end vertebra causes the least increase in the adjacent-level intradiscal pressure. Methods A bending moment was applied to six cadaveric cervicothoracic spine specimens with intact rib cages. Intradiscal pressures were recorded from C7–T1 to T9–10 before and after simulated fusion by anterior cervical plating and posterior thoracic pedicle screw constructs. The changes in the intradiscal pressure from baseline were calculated and compared. Results No significant differences where found when the changes of the juxtafusion intradiscal pressure at each level were compared for the flexion, extension, and left and right bending simulations. However, combining the pressures for all directions of bending at each level demonstrated a decrease in the pressures at the T2–T3 level. Exploratory analysis comparing changes in the pressure at T2–T3 to other levels showed a significant decrease in the pressures at this level (p = 0.005). Conclusions Based on the combined intradiscal pressures alone it may be advantageous to end long constructs spanning the cervicothoracic junction at the T2 level if there are no other mitigating factors.