In vivo loading data for the rotator cuff would be of value to scientists and clinicians interested in the shoulder in the testing of surgical repairs, design of rehabilitation programs and for finite element models.

A technique for insertion and retrieval of the Arthroscopically Insertable Force Probe (AIFP - Microstrain Inc. Burlington, Vermont, USA) from the subscapularis is described was initially established in a cadaveric model. Ethical approval was obtained for AIFP insertion into the subscapularis tendon of volunteers during diagnostic shoulder arthroscopy. An in situ calibration was carried out using a modified arthroscopic grasper ( Smith and Nephew, Huntingdon, UK). After motor effects of interscalene block had worn off dynamic data relating to subscapularis tendon loading was collected. The AIFPs were removed through a port site by traction on an O (3.5 metric) nylon suture without complication.

Maximum loading of the subscapularis tendon was measured during internal rotation from neutral with the arm fully adducted. Forces measured exceeded 200N.

This paper describes a novel technique for the insertion, calibration and retrieval of AIFPs from the rotator cuff. In vivo tendon loading data was obtained. The techniques described may be applied to other structures of interest to orthopaedic surgeons.

Arthroscopic stabilisation of the shoulder is a technically-demanding and developing technique, and the reported results have yet to match those for open surgery. We present a consecutive initial series of 55 patients with post-traumatic recurrent anteroinferior instability managed since September 1999 using a titanium knotless suture anchor. Patients were reviewed from 12–33 months postoperatively and assessed using the Rowe, Walch-Duplay and Constant scores. Following mobilisation of the capsulolabral complex, labral reconstruction was achieved using a two-portal technique and an average of three anchors placed on the glenoid articular rim. In 13 cases, additional electrothermal shrinkage was required to reduce capsular redundancy in the anterior and inferior recesses following labral repair, although 11 of these were in the first 18 months. Incorporation of a south-to-north capsular shift has reduced the need for supplementary shrinkage. Complications have included one instance of anchor migration requiring open retrieval and two documented episodes of recurrent instability, although these occurred in patients having surgery within the first six months after the introduction of this technique. Based on our initial experience, we believe that arthroscopic labral repair is a viable alternative to open Bankart repair and have now expanded the indications to include patients with primary dislocation, those participating in gymnastic and contact/collision sports, and revision cases with failed open repairs.

Background: Greater tuberosity disuse osteoporosis is a consequence of rotator cuff tear. This is a significant problem as the tendon is implanted into a trough within the greater tuberosity during repair. Failure of the repair is a common complication (up to 50%). We hypothesise that failure in re-implantation is due to deficient bone cell response to mechanical stimulation in the tuberosity.

Methods: In order to establish whether these cells are capable of responding appropriately to mechanical stimuli, the response of bone cells derived from the tuberosity was compared with that of cells derived from the acromion. This was measured in terms of strain related increases in alkaline phosphatase (ALP) activity and nitric oxide (NO) production (which are recognised markers of osteoblast differentiation and their response to mechanical strain). Primary osteoblasts were cultured from samples of acromion and greater tuberosity taken during routine rotator cuff repair (n=10 pairs). The derived cells were:

Placed under cyclic strain at a physiological magnitude for 10 minutes at 1Hz using well established controls. Samples of media were analyzed for changes in NO and the cells were reacted for ALP activity, or:

Results: The results suggest that cells derived from the acromion exhibit significant strain related increases in cellular NO release and in ALP activity, whereas cells derived from the humeral greater tuberosity fail to exhibit any such increases. In marked contrast, cells derived from both sites exhibit increases in ALP activity in response to dexamethasone treatment.

Conclusions: Our results suggest that whilst cells derived from the tuberosity, after rotator cuff tear, respond appropriately to chemical and hormonal stimuli, they are compromised in their ability to respond to mechanical stimulation. Therefore, it is tempting to speculate that such relationships are also evident in vivo and that they underpin re-implantation failures.

Disuse osteoporosis of the greater tuberosity is a consequence of rotator cuff tear. This is a significant problem as the tendon is implanted into a trough within the greater tuberosity during repair. Failure of the repair is a common complication (up to 50%). We hypothesized that failure in re-implantation is due to deficient bone cell response to mechanical stimulation in the tuberosity. In order to establish whether these cells are capable of responding appropriately to mechanical stimuli, the response of bone cells derived from the tuberosity was compared with that of cells derived from the acromion. This was measured in terms of strain related increases in alkaline phosphatase (ALP) activity, nitric oxide (NO) and prostaglandin (PG) production (which are recognised markers of osteoblast differentiation and their response to mechanical strain).

Primary osteoblasts were cultured from samples of acromion and greater tuberosity taken during routine rotator cuff repair (n=5 pairs). The derived cells were placed under cyclic strain at a physiological magnitude for 10 min at 1Hz using well established controls. Samples of media were analysed for changes in NO and PG production and the cells were reacted for ALP. Cells were stimulated with dexamethasone, ascorbic acid and beta-glycerophosphate (established mediators of osteoblast differentiation) then reacted for ALP.

Preliminary results suggest that cells derived from the acromion exhibit significant increases in cellular NO release and in ALP activity, whereas cells derived from the humeral greater tuberosity fail to exhibit any such increases. In marked contrast cells derived from both sites exhibit increases in ALP activity in response to dexamethasone, ascorbic acid and beta-glycerophosphate treatment.

The results suggest that whilst cells derived from the tuberosity after rotator cuff tear respond appropriately to chemical and hormonal stimuli, they are compromised in their ability to respond to mechanical stimulation. It is tempting to speculate that such relationships are also evident in vivo and that they underpin reimplantation failures.

To quantify the variation in strain between the deep and superficial layers of the supraspinatus tendon, ten cadaveric shoulders were tested on a purpose built rig. Differential Variable Reluctance Transducers (DVRTs) were inserted into the superficial and deep aspects of the tendon spanning the critical zone. DVRTs accurately measured linear displacement and from this strain was calculated.

The strain was measured for two aspects of supraspinatus action, abduction from 0 to 120 degrees with a tensile load (100 Newtons) and static load increases at zero abduction (20, 50, 100, 150 and 200 Newtons). After preconditioning, ten sets of results were recorded for each load/position.

The hypothesis, there is a statistically significant difference in strain between the superficial/deep supraspinatus tendon during abduction and with static loading, was tested using a one way ANOVA.

During abduction a statistically significant difference in strain was measured between the layers of the supraspinatus tendon at thirty degrees (p=0.000428) and this increased with further abduction.

Tensile loading increased tendon strain more in the deep layer of the tendon. This was statistically significant at loads greater than 150N (p= 0.007).

The variation in properties between the superficial and deep layers of the supraspinatus tendon has been proposed as a cause of differential strain (1). This study confirms statistically different strains between the superficial and deep tendon layers. It is proposed that the resulting shearing effect initiates intratendinous defects and ultimately tears.

Radio frequency (RF) electrothermal capsulorrhaphy has potential to enhance the results of arthroscopic stabilisation. However, early clinical reports have shown variable results when compared with open stabilisation. Numerous experiments have shown that the mechanical properties of thermally treated tissue are mechanically inferior to normal tissue during the early phase of remodelling. Ultimately, the real issue is how thermally treated tissue compares with tissue shortened by surgical plication, as would occur in an open procedure.

Using a validated technique the tibial insertion of the medial collateral ligament (MCL) of the knee was shifted proximally to induce abnormal laxity in 30 mature NZ White rabbits. Bipolar RF shrinkage was applied to the MCL in 15 rabbits, while in the remainder the MCL was surgically transected and plicated with a nonabsorbable suture. Unlimited mobilisation was permitted until euthanasia at 12 weeks after surgery. Bone-ligament-bone complexes were harvested and underwent low-load (viscoelastic) and high-load (tensile failure) analysis on an Instron mechanical testing apparatus. Specimens from intact MCLs were also collected for polarised light microscopy and transmission electron micrography. Quantitative analysis of collagen fibril morphology was performed on the TEM images.

There were no significant complications postoperatively. In both groups there was evidence of ligament healing and remodelling with a thin layer of scar tissue surrounding the MCL. Preliminary analysis has demonstrated that the cross-sectional area of the thermally treated MCLs was increased compared with the plicated MCLs. Somewhat surprisingly, the plicated group had greater vascularity and cellularity in the healing zone than the thermal group. Although crimp patterns remained disorganised in both groups, the collagen matrix appeared more organised in the thermal group.

These results support the concept that the thermally denatured matrix may act as a scaffold for rapid remodelling of the MCL, resulting in a larger mass of ‘scar’ tissue at the site of shrinkage. Since scar tissue following surgical transection is known to be materially inferior to normal ligament tissue, the increased volume in the thermal group may confer an advantage in structural terms. Mechanical testing is presently underway in our laboratory to determine this issue.

Although the epidemiology and pathomechanics of shoulder injuries in throwing athletes has been wellstudied, less is known about shoulder injuries in other sports where significant loads are carried by the upper limb. We evaluated 90 professional gymnasts who participated in a regular performance schedule during the millennium celebrations in the calendar year 2000. The gymnasts were divided into Group I (n=60) who were selected and trained for 18 months, and Group II (n=30) who were ‘fast-tracked’ through recruitment and training in the final six months before performance.

At the conclusion of the performance year, athletes were assessed using a subjective questionnaire, the SF-12 general health instrument, the Oxford instability questionnaire and the Constant score. They also underwent clinical examination, hypermobility scoring and fatigue testing.

Of those surveyed, 46% complained of pain in one or both shoulders, and the majority of these received nonoperative physical therapy during the year and were able to continue performing. Five patients (6%) had refractory pain, demonstrated signs of hypermobility, abnormal joint translation and positive relocation tests, often in the absence of symptomatic instability. All were in Group II, presented in the final six months of performance and required arthroscopic treatment for complex tears involving the anterior and superior labrum, including the biceps anchor.

These results indicate that the incidence of shoulder injury is very high among professional aerial gymnasts. The underlying cause is likely to be multifactorial in these hypermobile athletes, but the findings are consistent with the concept of cumulative microtrauma to the capsulolabral complex. Acute-on-chronic injury appears to be associated with complex labral pathology which presents with pain rather than with overt instability. Our observations suggest that training and performance schedules should be carefully monitored, incorporating extended preparation and recovery, in order to reduce the risk of shoulder injury. Further work on kinematics of the shoulder during dynamic loading of the weightbearing upper limb is required.

We examined the effect of periosteal devascularisation upon the early healing of osteotomies of sheep tibiae held in an instrumented external fixation system with an axial stiffness of 240 N/mm. At 14 days, cortical blood flow measured by the microsphere technique was 19.3 ml/min/100g in the well-vascularised osteotomies, but only 1.7 ml/min/100g in the devascularised osteotomies, despite an increase in medullary flow (p less than 0.0005). Delay in healing of the devascularised osteotomies was suggested by an in vivo monitoring system and confirmed by post-mortem mechanical testing. We suggest that the osteogenic stimulus of dynamic external fixation is dependent on the early restoration of cortical blood flow in devascularised fractures.