R Appleyard, Murray Maxwell Biomechanics Lab, Royal North Shore Hospital, Sydney

The fundamental mechanisms that underlie tendon breakdown are ill understood. There is an emerging hypothesis that altered mechanical strain modulates the metabolism and/or phenotype of tenocytes, disrupting the balance of matrix synthesis and degradation, and that rupture then occurs through an abnormal tendon matrix. The critically regulated genes have not yet been determined. We have developed sheep model in sheep where both stress-deprived and over-stressed areas can be examined in the one tendon, to evaluate the pathological and molecular changes over time. We have also used ‘wild type’ and genetically modified mice to determine the role of specific enzymes and proteoglycans in tendon degeneration. Stress-deprived and over-stressed regions showed classical changes of increased cellularity and vascularity, rounded tenocytes and interfascicular matrix infiltration. These structural changes resolved for up to one year after injury. Resolution was more rapid in over-stressed regions. Irrespective of the initiating stress, proteoglycan staining and chondroid metaplasia increased in tendon with time. There were distinct molecular and temporal differences between regions, which are reviewed here. While tendon degeneration has traditionally been regarded as a single field of change, our studies show that at a molecular level, the injured tendon may be regarded as a number of distinct regions—overloaded and underloaded, adjacent to bone or adjacent to muscle. Each region manifests distinct molecular changes, driven by relevant gene expression.

While collagen metabolism in pathological tendon has received much attention, accumulation of proteoglycan is also consistently induced by altered mechanical loading. We suggest that ADAMTS enzymes, which cleave aggrecan, versican and small proteoglycans, may play a significant role in tendon homeostasis and pathology. Regulating proteoglycan turnover may represent a novel target for treating tendon degeneration. We have initiated studies using mesenchymal stem cells (MSC), not to directly augment healing but to modify the molecular pathology in tendon resulting from altered loading. Preliminary data indicates that injection of MSC into an acute tendon defect significantly abrogates the increase in expression of aggrecan and collagen degrading metalloproteinases in the adjacent over-stressed tendon. This may decrease the resultant degeneration. The effects of MSC in treating tendon degeneration are reviewed here, as are the possible benefits of radiofrequency microtenotomy.

Thirty years ago, rotator cuff surgery was exceedingly uncommon and shoulder arthroplasty almost unknown. Surgery for shoulder instability was largely empirical, non-anatomical and frequently unsuccessful.

With the help of arthroscopy and MR scanning, a complex array of labral, ligament and tendon pathologies can now be recognised and treated, precisely and predictably. Anatomy-restoring arthroscopic techniques have largely replaced open stabilisation surgery. As life expectancy rises and citizens remain active into their seventh and eighth decades, the call for rotator cuff surgery has risen dramatically. Complex tendon transfers have expanded the indications for cuff surgery. Open repair has in part been supplanted by increasingly sophisticated arthroscopic techniques. The potential use of orthobiologics and stem cells promises further advances in the foreseeable future.

Following the successful development of humeral hemiarthroplasty, and later of total shoulder replacement, surgical techniques and clinical indications for arthroplasty are now well refined. Predictable outcomes have been further enhanced by the present generation of ‘anatomic’ prostheses. More recently, the ‘rediscovery’ and improvement of semi-constrained (reverse) prostheses has transformed the previously dismal outlook for sufferers of cuff arthropathy and similar conditions.

Many Australian Orthopaedic Association trainees undertake post-specialisation fellowships in shoulder surgery, both at home and abroad, and there is a steady flow of young overseas fellows through Australian shoulder units. The Shoulder and Elbow Society of Australia, founded in 1990 as a loose grouping of interested colleagues, now boasts over 70 active members. Australian surgeons and researchers are well represented in the prestigious Journal of Shoulder and Elbow Surgery and Australian shoulder surgery has come of age.

The morbidity associated with tendinopathy is a costly burden on our health system. Recent investigations in our laboratory have shown that alterations in mechanical stress cause significant changes in tendon expression of key matrix molecules and proteolytic enzymes including the aggrecanase molecules, (e.g. ADAMTS-5). Here, we investigate the biomechanical consequences of such altered tensile stress in tail tendons from mice with and without deletion of the ADAMTS-5 gene. Tail tendons from 12 week old C57BL6 wild type and ADAMTS-5 knock-out mice were immediately snap frozen (ex vivo), or cultured stress deprived for 120 hours in DMEM/10% FCS (eight tendons per group). Material properties including maximum stress, strain and elastic modulus were determined for each tendon in uniaxial tension to failure at a constant strain rate of 1.0 mm/second (10% strain/second) on an Instron 8874 servo-hydraulic testing apparatus. Significant differences between groups were determined with Kruskal-Wallis one-way analysis of variance, followed by Mann-Whitney U test with Benjamini-Hochberg post-hoc corrections for multiple comparisons. Stress deprivation for 120 hours led to a significant increase in maximum stress for both the wild type (~150% increase, p = 0.0008) and ADAMTS-5 deficient (~100%, p = 0.0033) mice when compared to ex vivo tendon. Stress deprivation led to a 100% increase in elastic modulus compared to ex vivo for the wild type tendons (p = 0.0033) but failed to increase this parameter in the ADAMTS-5 deficient mice. When the effect of stress deprivation of the ADAMTS-5 deficient mice was directly compared to the wild type stress deprived tendons, a 35% decrease in elastic modulus was found (p = 0.021). We have shown for the first time that deletion of an aggrecanase molecule significantly decreases the material properties of tendon. Alterations in the expression of the aggrecanase molecules may play a role in the development and progression of tendinopathy through their ability to modulate the metabolism of aggrecan [1]. Previous research in our laboratory has shown that aggrecanase expression is markedly up-regulated by stress deprivation. This finding in combination with the results of the present study suggest that the aggrecanase molecules may provide a future therapeutic target for the treatment tendinopathy.

Introduction and Aims: Assessment of the metabolic state of articular cartilage (AC) is important in understanding the initiation and progression of osteoarthritis (OA). The purpose of this study was to evaluate changes in gene expression of the major AC extracellular matrix (ECM) components, in addition to a number of molecules involved in OA, including the novel glycoprotein lubricin, following lateral meniscectomy in a sheep model of OA.

Method: AC tissue from both medial (MTP) and lateral (LTP) tibial plateaux were collected from six non-operated control (NOC) and six lateral meniscectomised (MEN) pure-bred Merino sheep six months post-surgery for semi-quantitative RT-PCR to assess patterns of mRNA expression (relative to GAPDH). Histological evaluation using a modified Mankin score was undertaken in the same sheep to grade the AC and immunohistochemical localisation of gene products was performed.

Results: Cartilage degeneration was evident both macroscopically and histologically in the LTP following MEN, with less marked changes appearing in the MTP. The mean total tissue RNA increased greater than five-fold in the LTP following MEN (p< 0.01). Expression of aggrecan (p< 0.01) and collagen type II (p< 0.01) were found to be significantly elevated in LTP AC following MEN. Increased expression of biglycan (p< 0.01) was observed in LTP AC following MEN, whereas conversely, there was a decreased expression of decorin (p< 0.01), the other fibril associated small leucine rich proteoglycan. Expression of both lubricin (p< 0.01) and connective tissue growth factor (CTGF) (p< 0.05) were also found to decrease following MEN in LTP AC. TGFβ demonstrated no change in expression following MEN. Significant changes in gene expression were generally not seen in the MTP following MEN; however trends were observed reflecting similar gene profile changes to those occurring in the LTP.

Conclusion: Strong up-regulation in gene expression of the major cartilage ECM components was found, reflecting an anabolic response and attempted tissue repair. Significant changes were also observed for other ECM macromolecules thought to be involved in degenerative joint disease, contributing to alterations in the gene expression profile associated with OA.

Surgeons often protect Tendon-bone reconstructions such as rotator cuff repairs by off loading them. We investigated the effect of limb position and boundary conditions in an in-vitro rabbit patella tendon-bone repair model. Patella tendons were repaired back to the tibia in eight hindlimb cadavers with 2 mitek anchors(Mitek, Westwood, MA) and 3-0 Ethibond (Ethicon, Sommerville, NJ) using two techniques, one involving simple sutures and the other involving crossing over between the sutures. A loading mechanism through the patella tendon was constructed using static weights over a pulley mechanism. The contact area and force at the PT-bone interface were measured using a TekScan pressure sensor (6911, TekScan, South Boston, MA). The contact footprint (area and normal force) was acquired under four configurations: (1) knee full extension with interface unloaded, (2) knee 45° flexion with interface unloaded, (3) knee full flexion with interface loaded by limb weight alone, (4) tendon loaded with limb weight and 20N force applied through tendon loading mechanism. The contact area force footprint changed substantially between the different suture techniques and loading configurations. Crossing over of sutures appears to provide an increased and more evenly distributed force across the tendon-bone interface. Repair off-loading was accompanied by a decrease in the contact footprint force and pressure. The force in both suture techniques increased with increasing flexion angle and was substantially increased by both bearing the weight of the dependent limb and by an axial load in the patellar tendon. Off loading a repair may not provide optimal environment for healing.

Aim: To define the contact force and contact area at the glenoid labrum-bone interface between suture sites in an open transosseous Bankart repair, and to assess how these contact parameters are altered by tying adjacent sutures to each other.

Methods: Twelve capsulolabral avulsion lesions were created in fresh-frozen human shoulder specimens and were repaired using a standard transosseous suture technique. The contact forces and contact areas were measured at the labrum-bone interface between sutures before and after repair. Using the free suture ends, either a single or double strand knot was then tied between adjacent suture sites and the contact parameters were measured again.

Results: The contact forces and contact areas under the soft tissue bridges between transosseous sutures were mildly increased during repair (before repair: average force=5.53g, area=2.25mm²; after repair: force=11.7g, area=3.13mm²). However, both the contact forces and areas increased significantly when a single or double strand of suture was tied over the soft tissue bridge. The double strand technique resulted in a significantly greater increase in contact forces and areas than the single strand technique (single strand average force=70.1g, area=6.75mm²; double strand average force=95.15g, area=8.0mm² p< 0.05).

Conclusions: The contact parameters between labrum and bone in a Bankart repair were increased when the suture strands from adjacent transosseous repair sites were linked. Increasing contact force or contact area may improve healing at the bone-soft tissue interface, and may reduce the risk of “spot welding” repairs. This, in turn, may reduce the failure rate of Bankart repairs.

Methods: Sixty pseudo-capsular tissues from loose shoulder, hip and knee (20 each) arthroplasties and 30 capsular tissues from primary total joint arthroplasty (TJA) patients (10 each; 12 rheumatoid arthritis [RA], 18 osteo-arthrosis [OA]) were investigated for mRNA and protein expressions of IL-1ß (interleukin-1 b, IL-1Ra (interleukin-1 receptor antagonist), MMP 1 (matrix matalloproteinase-1)-, TIMP 2 (tissue inhibitor of MMPs-2) using in situ hybridisation and immunohistochemistry. Polyethylene and metal debris in the same sections were semi-quantified simultaneously.

Results: IL-1ß mRNA and proteins were expressed in most RA primary and revision tissues and were less expressed in OA primary tissues. In contrast, IL-1Ra mRNA was found in most primary OA tissues and less in RA primary and the revision tissues. The ratio of staining intensities of IL-1ß/IL-1Ra mRNA was higher in revision and primary RA tissues compared with the primary OA tissues. MMP-1 protein expression was correlated with the IL-1ß/IL-1Ra ratio. Polyethylene (PE) debris was found in 56 out of 60 of the revision tissues. Their sizes were different in the hip (mainly small, < 30 mm in diameter), the knee (mainly large, > 300 mm) and the shoulder (all sizes). The expressions of the detected factors were highly correlated with the concentration of the PE debris but with not their sizes.

Conclusions: The high ratio of IL-1ß/IL-1Ra in primary RA and revision tissues and its correlation with MMP-1 expression and PE debris concentration indicated that an over-expression of IL-1ß and/or regulation downwards of IL-1Ra is an important event in inflammatory disorders and the foreign body reaction in TJA. A therapeutic strategy with IL-1Ra, that has been considered in RA treatment may thus contribute to the longevity of prosthesis of a TJA.

Introduction: Uncemented humeral components rely heavily on initial stability and fixation as a function of the design of the implant. Concerns over initial torsional stability of humeral components have motivated the development of a variety of design concepts.

Aim: To investigate the torsional stability of two types of cementless humeral shoulder prostheses.

Methods: Twelve fresh-frozen cadaveric humeri were cleaned of all soft tissues and prepared for reconstruction with the two types of cementless humeral shoulder prostheses. The humeri were embedded in a low melting point alloy and tested in a servohydraulic-testing machine. The loading applied to the humeri was a controlled angle loading regime at ± 1.5 degrees for 150 cycles. Torque versus time was measured, and the exponential time constant was calculated.

Results: The Z implant displayed overall a tightening effect, and a positive time constant. Whereas the G implant displayed a negative time constant, i.e. a loosening of the implant.

Discussion: These differences reflect the initial stability achieved immediately following surgery and may have important implications for bone in-growth and long-term stability.

Aim: To review the experience of a tertiary referral shoulder practice in managing a group of patients each of whom presented with disabling pain and loss of function following excision of the distal end of the clavicle.

Methods: A retrospective analysis was performed of eight male patients (average age 46) who underwent this procedure between August 1998 and December 1999. All patients were assessed using a standard protocol pre and post-operatively.

The surgical technique involved an arthrodesis at the acromio-clavicular joint and coraco-clavicular space using autogenous iliac crest bone graft and fixation with both tension band wires and a cancellous screw.

Results: The minimum follow-up was six months and clinical assessments demonstrated painful instability of the residual clavicle predominantly in the antero-posterior plane presumably because of disruption of the posterior acromio-clavicular joint capsule which is the major restraint to posterior translation of the clavicle. The patients had undergone on average 3.1 operations and had had symptoms for an average of 79 months before the fusion.

The fusion rate was 75% (six out of eight). Pain, measured using a Visual Analogue Scale (0 to 10), was reduced from 8.5 pre-operatively to 3.1 post-operatively. The patient’s perception of instability reduced from an average of 9.0 to an average of 1.0. The range of motion increased in five patients, decreased in two and remained the same in one. All of the patients would have the operation again and seven out of eight were very satisfied. The complications included the two non-unions, mild sterno-clavicular pain in two cases and a need to remove K-wires in seven instances.

Conclusions: Acromio-clavicular and coraco-clavicular fusions are worthwhile salvage techniques in the difficult situation of painful instability of the distal clavicle after multiple previous procedures. This complication can be avoided primarily by preservation of the posterior acromio-clavicular joint capsule.

Introduction: Arthrodesis of the shoulder joint is appropriate for several conditions, including paralysis, degenerative disease, infection, and salvage of failed arthroplasty. Two common complications of shoulder fusion, non-union and unacceptable arm position, may reflect failure to achieve rigid fixation during the surgical procedure. Numerous fixation techniques have been described, including plate fixation, external fixation, and screw fixation.

Aim: To compare the biomechanics of five fixation techniques of shoulder fusion in a human cadaveric model.

Methods: Twenty-five shoulder fusions were carried out in fresh-frozen human cadaveric specimens with the following five techniques: screw fixation alone (n=5), external fixation alone (n=5), external fixation supplemented with screw fixation (n=5), single plate fixation (n=5), and double plate fixation (n=5). Each specimen was tested on a servo-hydraulic machine under repeated physiologic loads to determine the bending and torsional stiffness.

Results: There was a statistically significant difference in bending and torsional stiffness between all five fixation techniques (ANOVA, p< 0.05). Normalised bending (B) and torsional (T) stiffness, in descending order, were: double plate (B=1.0, T=1.0), single plate (B=0.77, T=0.89), external-fixation with screws (B=0.68, T=0.74), external-fixation alone (B=0.40, T=0.53), and screws alone (B=0.13, T=0.26).

Discussion & Conclusion: Statistically significant differences in bending and torsional stiffness have been identified using five different techniques of shoulder fusion. The risk of the most common complications of this surgical procedure, non-union and unacceptable arm position, may be minimised if these biomechanical findings are applied to surgical decision-making.