Purpose: Subacromial impingement syndrome is a painful condition which occurs during overhead activities as the rotator cuff is compressed between the greater tuberosity and the acromion. Unrecognized secondary causes of impingement syndrome may lead to treatment failure. Posterior capsular tightness, believed to alter shoulder joint kinematics, is often cited as a secondary cause but scientific evidence is lacking. The objective of this study was to evaluate the effect of posterior capsular tightness on pressure in the subacromial space.

Method: Ten fresh-frozen cadaver shoulder specimens were mounted on a custom testing apparatus. With the scapula fixed, the deltoid and cuff muscles were loaded statically with a constant ratio to elevate the humerus in the scapular plane under physiologic loading conditions. For each treatment (intact capsule, 1cm and 2cm plication), pressure in the subacromial space and glenohumeral kinematics were recorded during elevation. The treatment order was randomly assigned to each specimen. Peak pressure and translation of the humeral head center were compared using a repeated measures ANOVA.

Results: Peak subacromial pressures (mean±sd) were similar between treatment groups: 345±152 kPa, 410±213 kPa and 330±164 kPa for the intact, 1cm and 2cm plication respectively (p> 0.05). No significant differences were found for superior or antero-posterior translations of the humeral head at the peak pressure position (p> 0.05).

Conclusion: Posterior capsular tightness, as a sole variable, did not contribute significantly to increased pressure in the subacromial space or to increased anterior or superior humeral head translation during abduction. Clinically, posterior capsular tightness may occur in association with impingement syndrome but may not play a significant role in causation.

Purpose: The objective of this project is to evaluate the human fibrin glue, CryoSeal^®, as a scaffold for articular cartilage tissue engineering. An autologous system would eliminate risks associated with biocompatibility and virus transmission.

Method: Human articular chondrocytes were isolated from articular cartilage harvested from consenting patients undergoing total knee arthroplasty. The cells were encapsulated into CryoSeal^® fibrin glue – which is derived from a single patient’s plasma using the Cryo-Seal^® Fibrin Sealant System (Thermogenesis Corp.) – and cross-linked with genipin, which is a natural cross-linking agent with anti-inflammatory activity. The resulting gels were cultured in vitro for up to 7 weeks under either normal (21%) or low oxygen (5%) conditions and were evaluated for mechanical properties, extracellular matrix (ECM) production, viability, and biodegradation. Fibrin glue components were isolated from either fresh or frozen plasma.

Results: The dynamic compression modulus of the genipin cross-linked fresh plasma (FSP) CryoSeal^® gels increased by ~4.4-fold over 5 weeks in culture. The glycosaminoglycan (GAG) content of the FSP gels increased by 4.7-fold over 5 weeks in low oxygen (LO) culture, which was 1.7-fold greater than in normal oxygen (NO) culture. The total collagen content of the FSP cultures increased by 6.0-fold over 5 weeks in LO culture, which was 2.2-fold greater than in NO culture. These changes in ECM were confirmed by histology (Alcian Blue) and immunostaining (to detect collagen II, collagen I, aggrecan, Sox9) of gel cryosections. After 5 weeks in LO culture the FSP CryoSeal^®-encapsulated chondrocytes expressed a 6.4 ± 1.1 fold increase in collagen II gene expression, which was 5.8 ± 1.0 fold greater than in NO cultures. In addition, chondrocyte viability within the FSP and frozen plasma (FZP) CryoSeal^® gels was ~90% at both 24 hours and 2 weeks after gelation. When fibrin hydrogels were implanted subcutaneously into rats it was found that inflammation was inhibited with increasing genipin and when the material origin was species-specific.

Conclusion: The CryoSeal^® fibrin gel system demonstrates promise for autologous human articular cartilage tissue engineering. An in vivo orthopaedic implantation model must be developed for further testing.

Biomechanical stability is important for fracture healing. With standard plate and screw constructs, longer plates with screws well spaced, near and far from the fracture site, are biomechanically superior. Newer locked plates have been shown to be superior to conventional plating for difficult fractures. The ideal screw configuration for fixation with locked plates has yet to be addressed. This study investigates the effects of screw position on construct stiffness as well as strain in both the plate and bone during fixation of a diaphyseal comminuted fracture using a locking plate with bicortical fixation.

A composite cylinder (Sawbones) was machined to produce two models:

(a) comminuted model (4mm gap) and

Five strain gauges were mounted to the bone models and one between the center holes of the locking plate. Four different configurations of screw number and position were evaluated using a twelve-hole locking plate (Smith & Nephew Perilock). Plate holes were numbered on each side of the gap from one to six. Screw configuration 654321, 621, 654 and 321 were tested in four-point bending on an MTS 858 Mini-Bionix. Force (N) and displacement (mm) as well as strain readings were recorded at 10 Hz.

Plate strain in the gap model did not vary significantly for the different configurations. Construct stiffness of the 654 model (all screws far from gap) showed a 30% decrease in stiffness as compared to other screw configurations (p< 0.001). In the whole bone model, the maximal bone strain was outside the farthest screw from the center of the plate (stress shielding) and bone strain at the fracture site in 654 was significantly higher than in 621 (p< 0.001).

Results showed that three screw fixation produced similar construct stiffness to a six screw construct when well spaced. Three screws placed far from the fracture gap (654) as compared to three screws evenly spaced (621) showed decreased stability in the comminuted model but resulted in increased bone strain at the fracture site in the whole bone model. All configurations produced similar plate strain.

There is theoretical concern that volar plating has a disadvantage in cantilever bending when axially loaded dorsal to the neutral axis. This has implications for postoperative rehabilitation protocols and overall outcomes related to maintenance of reduction. Most recent biomechanical studies have compared volar locking plates to traditional dorsal non-locked plates. The purpose of this study was to compare the biomechanical stability of volar and dorsal locking plate fixation in a model of dorsally unstable distal radius fractures.

Fourteen synthetic composite radii (Pacific Research Laboratories, Vashon, WA) were used for this study. A dorsally unstable, extra-articular distal radius fracture was simulated by creating a dorsal wedge-shaped defect in the distal metaphysis. Half of the specimens were plated dorsally (n=7) while the other half were plated volarly (n=7) with 2.4mm distal radius locking T-plates (Synthes, Canada). Each specimen was loaded axially in five different positions: central (along the neutral axis of the radius) as well as dorsal, volar, radial and ulnar to the neutral axis using a MTS Sintech 1/G materials testing machine (MTS Systems, Eden Prairie, MN). The plated radii were loaded to 100 N in each position simulating physiological loading during normal range of motion. The main outcome measure was construct stiffness of the plate-bone system (slope of load-displacement curve) for all five loading positions.

Construct stiffness with dorsal locking plates was seven times greater than volar locking plates when dorsally loaded (p < 0.001), 60% greater when centrally loaded (p = 0.055) and 35% greater when volarly loaded (p = 0.029). There was no significant difference in stiffness with any other loading configurations.

The stability of dorsal locking plate fixation is superior to volar locking plate fixation in the setting of large dorsal defects in the distal radius. This is applicable to both fractures with dorsal comminution and dorsal opening-wedge distal radial osteotomies. Further clinical investigation is needed to compare functional outcomes and complication rates between modern dorsal and volar locking plate techniques.

The purpose of this study was to clarify the effect of delay of the reattachment of the supraspinatus tendon into a bony trough to the strength of the repaired tendon-bone complex. The supraspinatus tendon of rabbits were transected and reattached into bony troughs at the greater tuberosity immediately and six weeks after transection. The tensile strength of the tendon-bone complex, harvested twelve weeks after reattachment, were measured.

The tensile strength showed no difference between immediate and delayed reattached shoulders. Six weeks delay of supraspinatus tendon repair seems not to weaken the tensile strength of repaired tendon-bone complex.

The purpose of this study was to clarify the effect of timing of surgery on the strength of the supraspinatus tendon-bone complex after the reimplantation of the tendon into a bony trough.

In eight rabbits, the supraspinatus tendon was transected and reinserted into a bony trough at the greater tuberosity (early reattachment group). In seven rabbits, the supraspinatus tendon was reinserted six weeks after transection (delayed reattachment group). In both groups, the rabbits were sacrificed twelve weeks after reattachment, and the tensile strength of the tendon-bone complex was measured. The contralateral shoulders served as controls.

None of the operated tendons failed at the site of reimplantation. The ratio of tensile strength of the operated tendon-bone complex to the controls showed no difference between two groups (Immediate reattachment group: 79.9± 1 S.E. 16.5%, delayed reattachment group: 80.4± 12.6%, P> 0.05).

This is the first experimental study to compare the tensile strength of supraspinatus tendon-bone complex repaired after different time intervals.

Stress-shielded tendon & bone tend to decrease their tensile strength. Given the six weeks duration of detachment, a weaker tensile strength of delayed reattachment group was expected than of the early reattachment group. The fact that both groups did not show a difference might be due to the recovery of tensile strength of tendon & bone in twelve weeks after reattachment.

Six weeks delay of repair of supraspinatus tendon does not weaken the tensile strength of repaired tendon-bone complex.

Fundings This study has been supported in part by a grant from the American Shoulder and Elbow Surgeons.

Purpose: The objective of this project is to determine the suitability of modified fibrin hydrogels as scaffolds for articular cartilage tissue engineering. The attractive feature of the fibrin system is that the gel precursors are available in autologous form. We have previously demonstrated that genipin, a naturally occurring cross-linking agent, stabilizes the fibrin gel.

Methods: Human articular chondrocytes were isolated from articular cartilage harvested from consenting patients undergoing total knee arthroplasty. The human cells were encapsulated into fibrin gels where gelation was induced by combining fibrinogen, thrombin, and genipin. The resulting gels were evaluated for extracellular matrix (ECM) production, mechanical properties, cell viability, and biodegradation.

Results: No breakdown of the gels was detected during 5 weeks of cell culture. After several weeks in culture, histology indicates significant proteoglycan production by encapsulated cells, and collagen II and aggrecan were detected in this ECM by immunostaining. There was a greater accumulation of cartilage-like ECM in the gels cross-linked with genipin. Dynamic compression tests performed at 0.1 Hz for 10 cycles using an MTS machine indicate that accumulation of ECM was associated with increased stiffness of the material. Cell viability was assessed using live/dead staining, and was found to be > 50% after 24 hours and at 1 week in culture. The presence of genipin cross-linking did not significantly affect cell viability. Real-Time RT-PCR indicated that encapsulated chondrocytes show an increase in Sox9, collagen II and aggrecan expression over 5 weeks and that this is further increased in the presence of genipin. The gene expression results agreed with the enhanced ECM seen under these conditions by histology and immunostaining. The fibrin material was also implanted subcutaneously into rats and after 30 days the material was removed, sectioned and evaluated. Immunostaining indicated that while there was evidence of biodegradation, the material did not appear to cause an inflammatory response.

Conclusions: Modified fibrin hydrogels show potential as cellular scaffolds for articular cartilage tissue engineering. An in vivo orthopaedic model must now be developed to fully evaluate the potential of the fibrin gel. Funding: Other Education Grant

Aims: The purpose of this in-vitro study is to understand the mechanical behaviour of a fracture plate incorporating biodegradable inserts. Methods: A new, innovative fracture plate design incorporating biodegradable inserts was tested. These plates allow for micromotion during the union phase, which allows for increased healing. Resorption of the inserts over time works to decrease stress shielding during the remodelling phase. Two separate bone models were used to simulate a fracture during both the union phase of healing and the remodelling phase. This plate, termed an axially compressible plate (ACP) was mounted to the bone models in four different conþgurations. On the model simulating the union phase, stiffness and micromotion were measured using an LVDT for bending and an extensometer for compression. With the model simulating the remodelling phase, strain was measured on the bone model using a strain gage mounted directly below the plate midpoint.

Conclusions: The results show that during the union phase, the ACP should allow for micromotion, which increases with successive loss of inserts. Results also show that during the remodelling phase, the loss of inserts increases the amount of strain in bone and thus decreases stress shielding.