Repair of chronic Achilles tendon rupture is technically complex. Flexor jallucis longus (FHL) and peroneus brevis (PB) tendon transfers have been described, but the mechanical properties of these tissues have not been well reported.

The FHL, PB and tendo achilles (TA) tendons were harvested from 17 fresh frozen human cadavers free of gross pathology (mean age 69 years). Samples were tested in uniaxial tension at 100% per minute. Samples were secured using special jigs for the bony aspect or by freezing the tendons in cryogrips using liquid carbon dioxide. The peak load (N), linear stiffness (N/mm) and energy to peak load (N*mm) were determined. Mechanical data was analysed using one way analysis of variance (ANOVA) followed by a Games Howell multiple comparison post-hoc test.

Fifty one tendons were harvested and mechanical testing was successfully completed in all samples apart from one PB that slipped from the grips during testing (sample was omitted from the analysis). The mean ultimate loads differed for each group, with the TA tendons being the strongest (1724.5 N ± 514.3) followed by FHL (511.0 N ± 164.3) and PB (333.1 N ± 137.2) (P< 0.05). Similar results were found with respect to energy, with TA tendons absorbing the most energy followed by FHL and PB (P< 0.05). Stiffness for the TA tendons (175.5 N/mm ± 94.8) was greater than FHL (43.3 N/mm ± 14.1) and PB (43.6 N/mm ± 18.9), which did not differ from each other.

FHL is stronger than PB, but have similar stiffness. The mechanical properties of PB and FHL were both inferior to TA. Graft stiffness appears to be an important variable rather than ultimate load based on the clinical success of both techniques.

Metal-on-metal articulations are increasingly used in THR. Hypersensitivity reactions to the metal ions can occur. The symptoms and signs are similar to a patient presenting with an infected prosthesis. Correct diagnosis before revision surgery is crucial to implant selection and operation planning. We present a practical approach to this diagnostic problem.

The history, clinical findings, hip scores, radiology, serum metal ions, ESR, C-RP, hip arthroscopy and aspirate results, synovial fluid metal ion levels, labelled white cell/colloid scan, 99m-technetium scan, revision hip findings and histology of a typical patient who had an allergic response to a metal-on-metal hip articulation are presented, and how the findings differ from a patient with an infected implant. Clinical examination, hip scores and serum metal ion levels were repeated one year after revision of the metal-on-metal hip articulation to a ceramic-on-ceramic.

In hypersensitivity, the periarticular tissues undergo lymphocyte-dominated infiltration, the histology differs from that found in infection. The white cell labelled/colloid scan also uses this difference for diagnosis. Hip aspiration is the single best investigation for infection.

Conclusion: There is no single investigation available in most hospitals that will reliably differentiate infection from allergy in the painful THR. Hip aspiration, labelled white cell/colloid scan and histology obtained from hip arthroscopy biopsy are the most useful investigations.

Intro: Anatomical abnormality associated with severe developmental dysplasia of the hip presents technical difficulties at THR. Patients often present at a younger age and may have had previous surgery.

We report the difficulties encountered during surgery, and the long term results of patients who had Crowe 3 or 4 DDH and a technically difficult primary hip arthroplasty using the modular S-ROM stem.

Method: 28 patients were entered into the prospective trial. The average age of the patient at surgery was 45 (range 23–74 years). All patients underwent surgery by the senior author using the S-ROM femoral stem. They were followed up for an average of 10 years (range 5–16 years), clinical scores recorded by a clinician other than the surgeon and radiographs were examined by an independent radiologist.

Results: 21 patients required a significant autologous bone graft, one patient had a large allograft and six patients required femoral shortening at the time of their THR.

4 patients had a technical complication during surgery. The average pre-op Harris Hip Score was 37, at 5 years it was 83, and at 10 years 81. The SF12 measure of physical and mental wellbeing was 43.90 physical/54.48 mental at 5 years, and 41.64 physical/54.03 mental at 10 years. The WOMAC average score (the lower the score the better the outcome) was 27 at 5 years and 23 at 10 years.

None of the S-ROM stems had been revised, 2 hips had undergone acetabular revision and one hip had a liner exchange. None of the S-ROM stems were loose at latest follow-up. Four hips had osteolysis in Gruen zone 1, one hip had osteolysis in zone 7, and one hip had osteolysis in zone 1 and 7. There was no evidence of osteolysis around or distal to the sleeve.

Conclusion: The S-ROM stem used in primary THR shows excellent results at 10 years in patients with anatomical abnormality related to severe DDH.

S-ROM stem/sleeve modularity allows femoral component anteversion independent of the position of best fit in the proximal femur, and helps overcome the technical difficulty in these patients.

Bone allograft use in trauma and orthopaedic surgery is limited by the potential for cross infection due to inadequate acceptable decontamination methods. Current methods for allograft decontamination either put the recipient at risk of potentially pathogenic organisms or markedly reduce the mechanical strength and biological properties of bone. This study developed a technique of sterilization of donor bone which also maintains its mechanical properties.

Whole mature rat femurs were studied, as analogous to strut allograft. Bones were inoculated by vortexing in a solution of pathogens likely to cause cross infection in the human bone graft situation. Inoculated bones were subjected to supercritical carbon dioxide at 250 bar pressure at 35 degrees celsius for different experimental time periods until a set of conditions for sterilization was achieved. Decontamination was assessed by vortexing the treated bone in culture broth and plating this on suitable culture medium for 24 hours. The broth was also subcultured. Controls were untreated-, gamma irradiated- and dehydrated bone. Mechanical testing of the bones by precision three-point bending to failure was performed and the dimensions and cross-section digitally assessed so values could be expressed in terms of stress.

Mechanical testing revealed bone treated with supercritical carbon dioxide was consistently significantly stronger than that subjected to gamma irradiation and bones having no treatment (due to the minor dehydrating effect of the carbon dioxide). Terminal sterilization of bone is achieved using supercritical carbon dioxide and this method maintains the mechanical properties.

The new technique greatly enhances potential for bone allograft in orthopaedic surgery.

Introduction: Lesser toe problems and metatarsalgia are common complaints in patients presenting with foot problems. Associated toe deformities include mallet toes, hammer toes, claw toes. The patient may complain of pain over the proximal interphalangeal joint from shoe ware, diffuse or localized pain under the metatarsal heads, or swelling and irritation of the metatarsophalangeal joint. Most patients can be treated with shoe ware modification, NSAID medication, tapping of toes, orthotics, or steroid injections. Surgical treatment includes flexor to extensor transfers, PIP excision arthroplasty, plantar condylectomy and metatarsal osteotomy.

Indications and Complications: The osteotomy is performed when there instability of the MTP joint, reduction of MTP joint subluxation or dislocation, relatively long ray with transfer metatarsalgia. Complications include avascular necrosis, joint stiffness, transfer metatarsalgia to subsequent toes, and plantar flexion of the metatarsal.

Surgical Technique: The Weil osteotomy is performed through a dorsal incision, performing a dorsal capsulotomy of the MTP joint and plantar flexing the proximal phalanx to expose the metatarsal head. The osteotomy is started in dorsal aspect of the metatarsal head and is made along the shaft keeping parallel to the floor. Key points are to make a long osteotomy cut to allow broad surface area for healing, avoid lowering the head by performing the cut parallel to the floor. The head will naturally displace proximally, most authors recommending 5–10mm of shortening.

Fixation: The osteotomy is fixed using a twist off screw. Factors that influence fixation include angle of screw insertion, size of the screw and the number of screws. Fixation in relatively porotic bone is improved when using two screws.

Distraction osteogenesis (DO) is useful for bone lengthening and deformity correction. Unfortunately, this often requires prolonged use of an external fixator with concomitant morbidities. This study investigates whether low-magnitude, high-intensity vibrations (Dynamic Motion Therapy, DMT) can accelerate maturation of regenerate bone in DO, thus reducing the duration of external fixation. 28 NZ White Rabbits underwent a right mid-tibial osteotomy with application of an Orthofix M-103 fixator (Orthofix, Busselengo, Italy). Distraction commenced on day 3 at 0.5 mm every 12 hours for 12 days. All animals were sacrificed on day 45. Animals were randomly assigned into 4 groups:

control group;

DMT was applied with the Juvent platform (Juvent, Somerset, NJ) for 10 minutes/day. X-ray and CT scans were taken prior to mechanical testing. All specimens were processed for histology. X-rays and CT scans showed evidence of cortical remodelling and re-establishment of the medullary canal in animals treated with DMT (groups 2, 3 and 4). This was most pronounced in animals treated during the distraction and consolidation phases (group 4). Regenerate bone in the control group (group 1) was more disorganised, with a delayed union evident in 1 animal. Group 1 achieved peak torque and stiffness values of 70% and 50% of the contralateral (unoperated) tibia respectively. No significant difference was seen in peak torque and stiffness between groups 2, 3, and 4, however each was significantly higher than group 1 (P< 0.05). H& E staining revealed less porosity in the newly formed cortical bone and a more defined medullary canal in animals treated with DMT than in the control group. Low-magnitude, high-intensity vibrations appear to accelerate cortical remodelling and reestablishment of a medullary canal. Regenerate bone in animals treated with DMT was also mechanically superior. The timing of DMT therapy did not appear to be important. Further studies are required to determine the optimal timing and duration of DMT therapy.

Although effects of mechanical stimulation with high frequency, low magnitude vibrations on bone mass and bone mineral density in animal and clinical studies have been proven effective, its effects on fracture healing is less well described.

20 Sham and 20 ovarectomised (Ovx) Sprague Dawley rats at 22 weeks of age, had intra-medullary k-wire fixation followed by controlled mid-shaft fractures.

The animals were divided into subgroups of 3 week Sham and Ovx treated and non-treated and 6 week Sham and Ovx treated and non-treated groups.

The treated animals were vibrated for 20mins daily on a DMT (dynamic motion therapy) platform which had a frequency of 30hz, 8-micron vertical displacement and 3g force, the non treated animals allowed to move freely. Xrays, DEXA studies, micro computed tomography, Histological analysis and Mechanical studies performed at the end point.

DMT treated animals had more bridging callus on radiographic and micro computed tomographic analysis compared to non-treated groups especially the OVX groups at 3 weeks compared to controls or Shams (using Image J software). DEXA studies showed increased bone mineral density and bone mineral content in the treated animals compared to the controls. Histological analysis showed increased callus and woven bone being laid down in the treated OVX groups.

In the 6-week groups, the treated OVX groups had healed, remodelled fractures compared to the non-treated groups or Sham controls where the fracture gaps were still visible. Although significance was not achieved on mechanical analysis due to small sample size, in the OVX non-operated femora group that were treated with DMT there were indications that they were stronger than the control counterparts.

High frequency low magnitude vibrations with the Juvent DMT device enhances fracture healing in oestrogen deficient models and this model could be used as a platform for clinical studies in future.

In vitro testing of spinal motion segments provides valuable information about the effects of surgical procedures on the biomechanics of the spine. Few studies, however have investigated the effect of varying laboratory testing environments on the outcome of these tests. This study aims to identify differences in mechanical properties induced by testing in one of three testing environments, and trends due to repeated testing over time.

27 sheep lumbar motion segments were tested in either,

air at 18°C while wrapped with gauze soaked in Phosphate Buffered Saline (PBS),

Specimens were cycled through +/−8Nm in axial rotation, lateral bending, and flexion/extension. Tests were repeated every hour for 6 hours. Torque and angle were recorded and each bending mode was repeated for 4 cycles, the last 3 of which were used in calculations. Stiffness (5–7Nm), neutral zone (NZ), NZ stiffness, Range of Motion (ROM) energy under the loading curve and hysteresis area were calculated and evaluated with ANOVA.

Post hoc comparisons found differences in stiffness, hysteresis area and energy of bending between room temperature and both heated conditions during flexion/extension. Differences were also noted between the room temperature and PBS bath conditions for stiffness and hysteresis area during lateral bending. One explanation of the results could be the thermo-sensitive properties of spinal ligaments and intervertebral fibrocartilages.

Repeated testing was a factor that affected the outcome of NZ, NZ stiffness, ROM and energy under the loading curve in all modes of torsion. If not accounted for during repeated tests this could lead to confounding results. Many of the traditionally reported variables (NZ, ROM) showed changes with repeated testing while hysteresis area remained relatively steady during repeated tests while identifying differences between testing groups. This variable may be useful in evaluating the condition of a motion segment with less time related effects.

Treatment of chronic Achilles tendon ruptures can be technically demanding due to tendon retraction, atrophy and short distal stumps. Although rare, re-rupture following surgical treatment is a major late complication.

Biomechanical studies on the strength of reconstructed Achilles tendon using autologous tendon grafts have not been well documented.

This study examined the time zero in vitro mechanical properties of a reconstructed Achilles tendon (TA) using the peroneus brevis (PB) or the flexor hallucis longus (FHL) tendons in a human cadaver model (n=17).

The TA was reconstructed using the same technique for all specimens. Biomechanical testing was performed using an MTS 858 Bionix testing machine and structural properties (failure load, stiffness and mode of failure) were determined.

Average failure load was significantly higher in the PB-group (p=0.0116) (PB: 343.82 N (+/− 124.90 N, FHL: 241.54 N (+/− 82.17 N)). There was no significant difference in stiffness (p=0.212), (PB: 16.53 N/mm (+/− 6.25 N/mm), FHL: 14.00 N/mm (+/− 3.84 N/mm)) or energy (p=0.075).

Mode of failure was the same for all specimens, with the tendon graft cutting through either the distal or proximal TA-stump. Reinforcement of these stumps could lead to increased failure loads. Based on the biomechanical data, the present study supports the use of either FHL or PB to reconstruction chronic TA tendon ruptures. The greater failures loads for PB may not be clinically relevant considering the peak loads. The addition of the suturing pattern, whilst is does reconstruct the tendon, does not provide a similar ability to resist the load.

Introduction: The use of bioabsorbable devices in sports medicine surgery in the shoulder and knee continues to evolve as new designs, devices and materials become available. Concerns over potential problems associated with metal artifacts and permanent metal devices continue to motivate the development and use of polymeric based devices. Calaxo interference screws (Smith & Nephew Endoscopy, Andover, MA) are composed of a novel bioabsorbable material blend of poly DL- lactide – co – glycolide 85:15 (65%) and calcium carbonate (35%). These screws have been shown to be osteoconductive when placed in the centre of a 4 stranded tendon graft in an ovine ACL reconstruction [1]. The screws are fully resorbed at 26 weeks with new bone formation in the tunnel. In general, osteoconductive materials are often more effective when placed adjacent to a bony bed. This study investigated whether positioning the Calaxo screw adjacent to the bone tunnel was superior to screw placement within the tendon as in our previous study [1].

Materials and Methods: An intra-articular anterior cruciate ligament (ACL) reconstruction model using 2 doubled over tendon autografts whip stitched and inserted into the right hind limb of 8 sheep were used. Animals were culled at 26 or 52 weeks following surgery (n=4 per time point) and data was compared using the same surgical model but with screws placed in the center of the 4 stranded graft (Walsh et al., 2006). The tibias were CT scanned and processed for paraffin histology along the axis of the bone tunnel. Three dimensional models using the DICOM data obtained from the CT where made using MIMICS (Materialise, Belgium).

Result & Discussion: Results showed excellent biocompatibility of the screws with no adverse reactions at 26 and 52 weeks as in our previous study [1]. The screws were fully resorbed by 26 weeks with new bone replacing the PLC material. Similarly, the screws were not detectable at 52 weeks with new bone formation where the screw had previously resided. The intra-articular portion of the graft, articular cartilage and synovium was normal at 26 and 52 weeks as previously reported [1]. Tendon – bone healing proximal to the screw progressed in a normal fashion. No calcification of the intraarticular portion of the graft was noted. Computed tomography, 3D models and histology revealed an osteoconductive response to the PLC material with new bone formation as the material degraded in vivo.

Placement of the screw adjacent to the tendon graft and thus against the bone tunnel appears to provide superior results compared to screw placement in the middle of the graft sleeve device. This effect may be due to direct contact of the osteoconductive material to the adjacent bone bed.

[1] Walsh et al., Arthroscopy 2006, in press.

Introduction: The majority of midshaft humeral fractures will achieve a satisfactory outcome with non-operative management. However, internal fixation is occasionally required to assist with rehabilitation, particularly in multiply-injured patients. Although the clinical risks and benefits of the locking plate and humeral nail are well known, there is a paucity of data comparing their mechanical properties.

The aim of this study was to determine the torsional and 4-point bending properties of a midshaft humeral osteotomy reconstructed with either an intramedullary nail or locking plate.

Methods: 19 fresh cadaveric humeri were DEXA scanned to ensure similar BMD. Non-destructive 4-point bending was performed on the intact bone to determine stiffness in the sagittal and coronal planes. Load was applied using an MTS MiniBionix 858 (Mechanical Testing Systems, MN) at a rate of 1 mm/min to a maximum of 450 N.

A transverse midshaft osteotomy was created and a spacer ensured a constant 3-mm gap between the bone ends. Reconstruction was performed with either

Trigen humeral nail (Smith & Nephew, TN) – 10 specimens

Non-destructive 4-point bending was repeated, and then each humerus was embedded in a low-melting point alloy proximally and distally for torsional testing. Torque was applied at 5 deg/min until failure. Maximum torque, maximum angle and stiffness were calculated.

All data were analysed with SPSS for Windows (SPSS Inc., Il) using ANOVA.

Results: One specimen in the locking plate group fractured during plate application and was excluded from the study. Non-destructive bending tests showed no significant difference in stiffness of the intact bones between the two groups.

4-point bending: the bones reconstructed with the intramedullary nail were ~50% as stiff as the intact state in both planes. There was no statistically significant difference in stiffness between the intact bones and those reconstructed with the locking plate.

Torsional testing: the locking plate specimens were 3 times as stiff as the intramedullary nail specimens (P< 0.05) and failed at twice the torque (P< 0.05).

Discussion: Humeral intramedullary nails are reported to have an advantage over plates under axial loading (Chen et al, 2002). However, this study demonstrates that locking plates are superior to intramedullary nails in torsion and four-point bending. Although the clinical situation often dictates the most appropriate management, locking plates should be considered in patients when torsional or four-point bending loads are expected to predominate in the post-operative period.

Negative ulnar variance, lunate shape and increased load transmission are associated with Kienbock’s disease. This may reflect trabecular alignment being more susceptible to shear forces along “fault planes” in Type 1 lunates, causing microfractures and avascular necrosis. The aim of this study was to assess the relationship between lunate bone structure, density and ulnar variance.

Standard 90/90 radiographs of 22 cadaveric wrists were taken for ulnar variance and lunate shape. The lunates were harvested and routine CT scans (1mm) were taken in 22/22 in the coronal, sagittal and transverse planes. DICOM files were analysed using Mimics (Materialise, Belgium) to measure Hounsfield units. MicroCT scans (SkyScan, Belgium) (40 μm) were taken in 10/22 in the coronal plane and measured for trabecular angle at the proximal and distal joint surfaces and the ‘tilting angle’ (between scaphoid and radius joint surfaces). Data was anlaysed using one-way ANOVA tests using SPSS for Windows.

Negative ulnar variance was noted in 7/22, neutral 10/22 and positive 5/22. Lunate shape according to Zapico was 0/22 Type 1, 18/22 Type 2 and 4/22 Type 3.

Lunate bone density was significantly lower in the ulnar positive specimens compared to ulnar negative and neutral (p< 0.001) (fig. 1).

The average trabecular angle measured 84.7° (+/− 4.5°) at the proximal and 90.3° (+/− 2.6°) at the distal joint surfaces and tilting angle was 115.7° (+/− 12.0°) (fig. 2). The 50% slice on the microCT correlated best with xray measurements of this angle.

This study quantifies the previous finding that load transmission through the lunate and hence lunate bone density is related to ulnar variance and that this is higher in ulnar negative wrists. MicroCT is a useful modality to assess trabecular structure and supports the ‘fault plane’ hypothesis of Kienbock’s Disease.

Intro: Total knee replacement (TKR) manufacturers offer the option of high flexion tibial tray inserts. The polyethylene is narrower posteriorly than the standard insert and comes with the theoretical risk of reduced longevity due to thinner implant. This trial studied both the intra-operative and post-operative difference in knee flexion.

Method: 100 consecutive patients undergoing posterior stabilized Genesis II TKR with Brainlab navigation were studied. The flexion of each knee was assessed per-operatively using the Brainlab navigation system for both the high flex and standard tibial insert trials. Patients were then randomized to receive either a high flex or standard definitive implant and the knee flexion measured clinically with a goniometer six months post op.

Results: Intra-operatively the high flexion insert trial flexed more than the standard flex option by 3.2 degrees. Clinically at six months post op there was no difference in knee flexion between the two groups.

Conclusion: There is no clinical difference in knee flex-ion at six months post-op in patients with a high flex or standard tibial insert. However, we believe that in certain technical circumstances the high flex option is a valuable option for the surgeon to have available.

Introduction: A cosmetic deformity does not always occur after a biceps tenotomy. The anatomical restraints preventing distal excursion of the long head of biceps tendon following tenotomy have not previously been described. This study aims to evaluate the biceps sheath and its potential role as a restraint to distal excursion of the biceps following tenotomy.

Methods: Fifteen fresh cadaveric specimens were dissected free of overlying soft tissues to reveal the rotator cuff, biceps sheath and long head of biceps muscle belly and tendon. Eight specimens were used for gross anatomical analysis. Measurements of the length of the biceps sheath on the humeral (bone) side and tendon side were made using a digital caliper (Mitutoyo, Japan). The long head of biceps tendon was then released from the glenoid labrum and the excursion of the stump relative to the rim of the articular surface measured. The biceps sheaths of two specimens were used for histological analysis.

Seven specimens were used for mechanical analysis. A humeral osteotomy was performed distal to the insertion of pectoralis major, leaving intact the biceps sheath and the muscle belly of long head of biceps. The proximal humerus was attached to a custom-designed jig and the muscle belly of biceps grasped in cryogenic grips. Specimens were loaded on an MTS 858 Bionix mechanical testing machine (MTS Systems, MN) in uniaxial tension at a rate of 1 mm/sec until failure was observed.

Results: The biceps sheath surrounds the long head of biceps tendon and inserts into the bone of the proximal humerus. It is trapezoidal in cross-section, with a mean length of 75.1 mm on the bone side and 49.3 mm on the tendon side. The average excursion of the stump was to within 2.8 mm of the rim of the articular surface.

Histological examination of the biceps sheath revealed membranous tissue consisting of loose soft tissue with fat and blood vessels. Synovial tissue was also identified. The sheath was seen to loosely attach to the biceps tendon, with a more intimate attachment to the periosteum.

The mean force to pull the long head of biceps tendon out of the sheath 102.7 N (range 17.4 N–227.6 N)

Discussion: The biceps sheath is a consistent structure intimately associated with the biceps tendon. It appears to contain blood vessels which provide nutrition to the tendon, similar to the vincula of flexor digitorum pro-fundus. Mechanical testing reveals that a substantial force is sometimes required to pull the biceps tendon from the sheath. This may explain why biceps tenotomy does not routinely result in a “Popeye” biceps.

Introduction: Repair of chronic Achilles tendon rupture is technically complex. Flexor Hallucis Longus (FHL) and Peroneus Brevis (PB) Tendon transfers have been described, but the mechanical properties of these tissues have not been well reported.

Methods: The FHL, PB and tendo Achilles (TA) tendons were harvested from 17 fresh frozen human cadavers free of gross pathology (mean age 69 years). Samples were tested in uniaxial tension at 100% per minute. Samples were secured using special jigs for the bony aspect or by freezing the tendons in cryogrips using liquid carbon dioxide. The peak load (N), linear stiffness (N/mm) and energy to peak load (N*mm) were determined. Mechanical data was analysed using one way analysis of variance (ANOVA) followed by a Games Howell multiple comparison post-hoc test.

Results: 51 tendons were harvested. Mechanical testing was successfully completed in all samples apart from one PB that slipped from the grips during testing (sample was omitted from the analysis). The mean ultimate loads differed for each group, with the TA tendons being the strongest (1724.5 N ± 514.3) followed by FHL (511.0 N ± 164.3) and PB (333.1 N ± 137.2) (P< 0.05). Similar results were found with respect to energy, with TA tendons absorbing the most energy followed by FHL and PB (P< 0.05). Stiffness for the TA tendons (175.5 N/mm ± 94.8) was greater than FHL (43.3 N/mm ± 14.1) and PB (43.6 N/mm ± 18.9), which did not differ from each other.

Conclusions: FHL is stronger than PB, but have similar stiffness. The mechanical properties of PB and FHL were both inferior to TA. Graft stiffness appears to be an important variable rather than ultimate load based on the clinical success of both techniques.

Lacerations of the FDP tendon in zone one may be reattached to bone with a modified Bunnell pullout suture or with suture anchors. Eleven cadaveric fingers were submitted to cyclical testing of five hundred cycles with either a modified Bunnell pullout suture of 3-0 polypropylene or a micro-Mitek suture anchor with 3-0 Ethibond. Gap formation was 6.6mm in the modified Bunnell group and 2.0mm in the micro-Mitek group (p< 0.001). Load to failure was 37.6N in the pullout group and 28.5N in the anchor group (p< 0.005). Gap in the pullout group and low failure load in the anchor group are of concern.

Distal zone one FDP tendon lacerations are usually re-attached to bone by a modified Bunnell pullout suture of 3-0 polypropylene. This treatment may lead to moderate to severe losses of DIP joint motion in up to 50% of patients. Suture anchors have recently been introduced as a fixation alternative. Cyclical testing simulating five days of a passive mobilisation protocol was used to compare the Micro-Mitek anchor to the modified-Bunnell pullout suture in FDP tendon fixation.

Eleven cadaveric fingers FDP tendons were repaired to bone using a modified Bunnell pullout suture of 3-0 polypropylene or a micro-Mitek anchor with 3-0 Ethibond. Testing was done from 2N to 15N at 5N/sec, for a total of five hundred cycles. Gap formation at the tendon bone interface was measured. Load-to-failure was performed on all specimens.

No specimens failed during cyclic testing. Gap formation was 6.6mm (SD 1.2, range 4.9–8.2mm) and 2.0mm (SD = 0.4, range 1.7–2.7mm) for the pullout technique and the micro-Mitek anchor repair respectively (p< 0.001). Load to failure data was 37.6N (SD 4.7, range 31.8–45.1N) for the pullout group and 28.5N (SD 4.0, range 21.8–33.4N) for the micro-Mitek group (p< 0.005).

This data suggests that both fixation techniques may be adequate to sustain five days of simulated passive rehabilitation therapy. Significant gap formation in the modified Bunnell pullout group is of concern although this needs to be correlated in the clinical setting. The lower failure rate of the micro-Mitek group may leave a narrow margin of safety for passive rehabilitation.

Background: The Profix Total Knee Arthroplasty (Smith and Nephew, Memphis, USA) is designed to replace less bone than is resected from the posterior femoral condyles, and as a consequence the posterior condylar offset is reduced. The net effect of this is to increase the flexion gap with no effect on the extension gap. This is a deliberate design philosophy aimed at increasing postoperative flexion. This prospective cohort study has tested this theory.

Methods: 60 patients underwent primary posterior cruciate retaining (CR) TKA using this prosthesis. A matched group of patients, employing a different CR prosthesis which replaces excised bone in full, served as historical controls. Intra-operative measurements were made of the posterior condylar bone resected in each case. These measurements were then correlated with the flexion achieved both intra-operatively and at 6 months post-operatively.

Results: A positive correlation between pre-operative and post-operative flexion was found. However, there was no correlation between the relative increase in flexion gap secondary to the reduction in posterior offset and the resulting flexion range.

Conclusion: Post-operative flexion range is not increased by the resection of more bone from the posterior femoral condyles than is replaced by the prosthesis in TKA. The loss of bone stock will have implications for revision surgery and should be avoided.

Introduction and Aims: Adipose-derived stem cells (ADSCs) are capable of osteogenic differentiation under appropriate conditions in vitro (1). In this study we demonstrate the differences and similarities of the healing potential of ADSCs against the bone marrow-derived stem cell population (BMSCs) in the critical size ovine cancellous defect model, healed with culture expanded autologous stem cells from adipose tissue (ADSCs).

Method: Bone marrow aspirates and subcutaneous adipose tissue were harvested from 42 adult wethers. The population of stromal cells was derived from both tissues. Populations of bone marrow cells and adipose stromal cells were expanded in culture and stimulated with osteogenic medium for seven days. Cultured cell populations were harvested, mixed with a hydroxy-apatite carrier (Pro-Osteon 200R) and deposited into bilateral medial femoral condyle confined cancellous defect. Seven groups were examined: Bone graft+ ADSCs, Bone graft+ BMSCs, Carrier + ADSCs, Carrier+ BMSCs, Bone graft, Carrier, Empty defect. Two week, four week and eight week time-points were examined.

Results: All specimens were decalcified and five μm histological slides were stained using H& E and Masson’s Trichrome. Histomorphometry analysis on Masson’s Trichrome stained slides was performed using colour threshold-based software Bioquant Nova 6.50.10. Immunohistochemical staining for BMP4 and BMP7 and their downstream regulators: Smad4 and CBFA1 were evaluated in the defect area and graded in a blind fashion by two trained observers. There was a progressive and time-dependent increase in woven bone formation in the defects treated with ADSCs across all time points. The amount of bone formed in this group was comparable with the amount formed by the use of BMSCs.

Conclusion: The results of this study support the hypothesis that seeding porous hydroxyappatite with ADSCs does enhance bone formation and defect healing.

Introduction Zone 2 flexor tendon repairs can require ‘venting’ or partial resection of the A2 and/or A4 pulleys. We test a new technique where the pulley is divided and repaired with a V-Y plasty, increasing the pulley circumference. This allows access to perform the repair and/or permits free tendon gliding post-repair.

Methods Two groups of A2 and A4 pulleys from cadaveric fingers were divided and repaired in a V-Y fashion such that the circumference of the pulley tunnel was increased. The fingers were then mounted onto custom-made jigs and tested using a materials testing machine. One group had the A2 pulley assessed for changes in work of flexion by testing both before and after V-Y plasty. The second group had both the A2 and A4 pulleys tested for load to failure during functional loading. Biomechanical testing was performed.

Results There was a significant reduction in work of flexion after V-Y pulley expansion procedures were performed. Loads to failure for the A2 and A4 pulleys were in excess of 400% and 200% greater than one would expect in-vivo during a post-operative active mobilisation protocol. V-Y tendon pulley expansion increases the tunnel size while providing a mechanically sound pulley. It also maintains the pulley length and its coverage of the underlying tendon.

Conclusions This technique provides surgeons with an attractive alternative to simply ‘venting’ or resecting an otherwise troublesome pulley.

Introduction VEGF is a well known angiogenic peptide which has been shown to be central to endochondral ossification. Secondary fracture healing involves a combination of intramembranous and endochondral ossification. VEGF has been recently shown to be chemotactic for osteoblasts and chondroclasts. We therefore set out to examine the temporal and spatial expression of VEGF and its receptors in fracture healing. We report here the preliminary findings of our study.

Methods A closed mid-shaft fracture was produced in the right femora of nine 12 week old Sprague Dawley rats, stabilised by an intramedullary K-wire. The rats were sacrificed at one, two and four weeks. Through the use of immunohistochemistry, RT-PCR and in situ hybridisation.

Results We show that at each of the time points, VEGF is expressed in all of the cell types involved in fracture healing; the inflammatory cells, the osteo-progenitor cells,chondroblasts,chondrocytes,osteoblasts and osteoclasts as well as fibroblasts. We further show that there is persistent expression of VEGF in chondrocytes at four weeks.

Conclusions Our findings are consistent with the hypothesis that events in fracture healing reflect the processes that take place at the growth plate during embryonic development.

Introduction Recent publications have confirmed that as many as one in four retrieved femoral heads can be significantly contaminated with potential pathogens. Reports from the Centre for Disease Control in Atlanta, Georgia have described fatal outcomes from the unwanted transmission of bacterial disease with inadequately processed allograft materials. Surgeons requesting non terminally sterilised bone refer to theoretical biological and biomechanical deleterious effects of gamma irradiation. This study examines the accuracy of those claims.

Methods We have investigated the effects of varying levels of gamma irradiation (0kG, 15kG and 25kG) on the biological competence of morsellised allograft bone and its associated biomechanical impaction qualities. The biological study has used an in vivo model (nude rat) to quantify the effects of gamma irradiation on osteoinduction and osteoconduction. An in vitro impaction routine has been used to measure compaction, impaction and stiffness in the allograft product.

Results There were no statistical differences in the biomechanical or biological properties of the 0kG and 15kG specimens (P< 0.05). Gamma irradiation at the 25kG level resulted in an allograft product of higher biomechanical stiffness, unchanged osteoinductivity and slightly lower osteoconductivity (P< 0.05).

Conclusion Terminal gamma irradiation of 15kG reduces the risk of bacterial transmission with allograft products. It does not alter the efficacy of the allograft at biological and biomechanical levels. Gamma irradiation represents the mainstay of sterilisation of musculoskeletal allograft materials. Australian practices appear to be leading an international trend.

In relation to the conduct of this study, one or more the authors have received, or are likely to receive direct material benefits.

Introduction The four strand cruciate tendon repair has been described as the ideal technique, as it combines simplicity with the biomechanical advantages of four-strands. We wanted to determine if increasing the size of the locking loop increases the repair strength, and the gain in biomechanical integrity that various peripheral techniques provides.

Methods Forty-eight deep flexor tendons harvested from sheep hindlimbs were randomly divided into six groups of eight. All tendons were sharply transected. Initially, four groups were repaired using the cruciate core technique without a peripheral suture. The locking loops were set at 50%, 33%, 25%, or 10% of the volar CSA and then tested to failure. The final two groups of tendons were repaired using the established optimal locking loop size. These two groups were combined with either the simple running or the interlocking horizontal mattress (IHM) peripheral suture. These were then tested to failure and biomechanically assessed.

Results Repairs with locking loops of 25% had the greatest biomechanical properties; with load to two millimetre gap formation, load to failure and stiffness of 10N, 46.3 and 3.9N/mm respectively. Those with a 33%, 50% and 10% locking loops followed this. Those with 10% locking loops failed due to the suture material sliding out of the tendon. All other groups failed by suture breakage. Using the cruciate core technique with a 25% volar CSA locking loop, the load to two millimetre gap formation, load to failure and stiffness was 32.9N, 47.2N, and 7.6N/mm respectively when combined with the simple running peripheral suture and 46.4N, 79.4N and 9.9N/mm respectively when combined with the IHM repair. The IHM/cruciate combination was significantly better than the simple running/cruciate repair. Using the IHM technique in your tendon repair, this study demonstrates that the peripheral suture can provide approximately 75%, 40% and 60% of the total load to two millimetre gap formation, load to failure and stiffness respectively.

Conclusions Unlike the Kessler technique, increasing the size of the locking loop in the cruciate method decreases the repair strength. The ideal sized bite seems to be approximately 25% of the volar cross-sectional area. Additional, the peripheral suture is biomechanically vital to the integrity of the repair.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

Introduction Determining the extent of dynamic creep of a suture gives insight into the potential for formation of a flexor tendon repair site gap, with less creep having a positive benefit. We wanted to determine the dynamic creep of various suture materials using a cyclical testing protocol that simulates 30 days of active mobilisation.

Methods Four-strand loops, 20 mm in length, were created using Prolene, Ticron, Ethibond, and Mersilene (n=8 per group). Samples were loaded between 3.5N and 35N at 10 cycles per minute for 3000 cycles using a materials testing machine. All testing was conducted in phosphate buffered saline at 37° celsius. The dynamic creep was determined for each group. A separate group of suture loops were also created for load to failure testing. All data was analysed using ANOVA on SPSS software.

Results The loads to failure were 55.4, 65.5, 64.4 and 73.1N for Prolene, Ticron, Ethibond and Mersilene respectively. During cyclical testing, only one Prolene sample survived, with failure occurring after a mean of 1182 cycles (range 574 to 2660). Of those that failed, the mean creep was 3.80 mm (SD=0.51). In contrast, no specimens in the other groups failed, with a dynamic creep of 0.44 mm (SD=0.19), 0.32 mm (SD=0.17), and 0.28 mm (SD=0.07) for Ticron, Ethibond and Mersilene respectively.

Conclusions Regardless of your chosen suture technique for flexor tendon repairs, this study suggests that the suture material itself can play an important role in the eventual outcome. These results should be kept in mind when deciding on the suture material for your repairs.

Introduction The aim of this study was to determine the biomechanical properties of various combinations of four-strand core and peripheral suture techniques used in flexor tendon repairs.

Methods Seventy-two sheep flexor tendons were randomly divided into nine groups of eight. Tendons were sharply transected and repaired using three different four-strand core techniques: cruciate, modified-Kessler, and the modified Becker. These were combined with three different peripheral techniques: simple running, cross-stitch, and the recently described interlocking horizontal mattress (IHM). Tendons from these nine groups were loaded onto a materials testing machine and tested to failure using a crosshead speed of 20 mm/min. Load to two millimetre gap formation, load to failure, and stiffness was assessed. Data was analysed using ANOVA on SPSS for Windows.

Results For any given type of peripheral suture, no significant difference in biomechanical properties was found between the three core repair techniques. The only factor causing a significant difference in strength of the tendon repair was the type of peripheral suture technique used. Repairs with an IHM technique had significantly greater loads to 2 mm gap formation, load to failure, and stiffness, compared to the cross-stitch and simple running methods.

Conclusions This study demonstrates the superior biomechanical properties of the IHM technique. Increasing core suture complexity does not appear to have a significant impact on the overall mechanical integrity of the repair. These results should be considered when adopting a preferred repair technique.

Introduction: The realisation that the medical and lateral menisci of the knee have important load-bearing and stability functions has stimulated orthopaedic surgeons to aim for preservation rather than excision if at all possible. The absence of meniscal tissue has been shown to increase load through the articular cartilage and ultimately accelerate the process of osteoarthritic degeneration. A major limitation is the relative avascularity of a large portion of the normal meniscus. McAndrews and Arnoczky reported in 1996 that repair of the white-white and even red-white zone remains a challenge. Monobutyrin is an angiogenic factor that has been used in the stimulation of healing burns and we hypothesized that it may have a positive effect on the healing meniscus.

The aim of the study was to determine the effects of 0 Ticron suture soaked in polyhydroxybutyrate (PHB) on the histological and mechanical properties of healing meniscal tears in the red-white zone in an established animal model.

Methods: A bilateral medical meniscal incision model was used in 21 adult sheep.

Results: We confirmed that the PHB had no deleterious effects on the mechanical properties of the suture prior to commencing the surgery. Mechanical testing of the menisci at the set time-points demonstrated a significantly stronger repair in the PHB-soaked group. Macroscopic appearances were graded and found to be improved with PHB soaked sutures. On histological examination there were features suggestive of a more intense healing response including angiogenesis.

Conclusions: We have concluded that the use of butyric acid has no deleterious effects on the mechanical properties of the suture used and has positive effects on meniscal healing. We recommend further examination of this exciting development.

The use of plates and screws for the treatment of certain metacarpal fractures is well established. Securing plates with bicortical screws has been considered an accepted practice. However, no study has questioned this.

This study biomechanically assessed the use of bicortical versus unicortical screws in metacarpal plating. Eighteen fresh frozen cadaveric metacarpals were subject to midshaft transverse osteotomies and randomly divided into two groups. Using dorsally applied Leibinger 2.3mm 4 hole plates, one group was secured using 6mm unicortical screws, while the second group had bicortical screws. Metacarpals were tested to failure using a four point bending protocol in an apex dorsal direction on a servo-hydraulic testing machine with a 1kN load cell. Load to failure, rigidity, and mechanism of failure were all assessed.

Each group had three samples that did not fail after a 900 N load was applied. Of those that failed, the mean load to failure was 596N and 541 N for the unicortical and bicortical groups respectively. These loads are well in excess of those experienced by the in-vivo metacarpal. The rigidity was 446N/mm and 458N/mm of the uni-cortical and bicortical groups respectively. Fracture at the screw/bone interface was the cause of failure in all that failed, with screw pullout not occurring in any.

This study suggests that there may be no biomechanical advantage in using bicortical screws when plating metacarpal fractures. Adopting a unicortical plating method simplifies the operation, and avoids potential complications associated with overdrilling and oversized screws.

The behaviour of two different methods of reattachment of the flexor digitorum profundus tendon insertion was assessed. Cyclical testing simulating the first 5 days of a passive mobilisation protocol was used to compare the micro Mitek anchor to the modified-Bunnell pull-out suture. Twelve fresh-frozen cadaveric fingers were dissected to the insertion of the FDP tendon. The FDP insertion was then sharply dissected from the distal phalanx and repaired using one of two methods: group 1 -modified Bunnell pullout suture using 3/0 Prolene; group 2 micro Mitek anchor loaded with 3/0 Ethibond inserted into the distal phalanx. Each repaired finger was mounted on to a material testing machine using pneumatic clamps. We cyclically tested the repair between 2N and 15N using a load control of 5N/s for a total of 500 cycles. Gap formation at the tendon bone interface was measured every 100 cycles.

No specimens failed during cyclical testing. After 500 cycles, gap formation of the tendon-bone interface was 6.6mm (SD = 1.2mm), and 2.1 mm (SD = 0.3mm) for the pullout technique and the micro Mitek anchor repair respectively. Concerns related to suture anchors, such as anchor failure or protrusion, joint penetration, and anchor-suture junction failure, were not encountered in this study.

Cyclical loading results suggest that the repair achieved with both methods of fixation is sufficient to avoid failure. However, significant gap formation at the tendon-bone interface in the modified Bunnell group is of concern, suggesting it may not be the ideal fixation method.

Fracture healing involves many local and systemic regulatory factors. Progress in identifying signaling events downstream has been made with the discovery of a novel family of proteins, the Smad, as TGF-ß/activins/BMPs signal transducers. Smads are the vertebrate homologs of Mad (Mothers against decapentaplegic) gene from Drosophila and Sma genes from Caenorhabditis elegans. Smad-1, -2, -3, -5, -8 and -9 belong to the receptor-regulated class (R-Smad) which are activated by the TGF-ß type I and II receptors, forming heteromers with the common-mediator class (Co-Smad): Smad-4. Smad-6 and -7 (Anti-Smad) perform a negative regulatory or balancing role. Smad-2 and -3 regulate TGF-ß/activin effects, whilst Smad-1 and -5 work with BMPs. This study investigated the expression and localization of Smad proteins (Smad 1–6) and BMP-4 and -7 during fracture healing.

Eighteen 3-month old female CD-COB rats were used. A standard closed fracture was made in the mid-shaft of right femur using a 3-point bending device. The left limb served as the non-fracture control. The rats were divided into 3 groups (6 per group) and sacrificed at day 3, 10 and 28 after fracture. The femurs were harvested, fixed in buffered formalin for 48 hours and decalcified with 10% formic acid-formalin solution. The decalcified tissues were embedded in paraffin and 5μm sections were cut onto silane-coated slides. Representative slides from each block were stained with routine haematoxylin and eosin (H& E). Sections were cut for immunohistochemistry for protein marker expression by a standard procedure for Smads and BMP 4 and 7. Sections were viewed and analysed by colour video image analysis using a 40x objective, a 10x eyepiece, and a fixed frame of 128 × 128 pixels (49152.0 μm²). Ten fields per slide were examined.

Smad proteins (Smads 1, 4, and 6) were expressed during the early stages (day 3) of fracture healing by bone marrow stromal cells, osteoblasts, fibroblasts and chondrocytes located in the intramembranous and endochondral ossification regions around the fracture site. Differential expressions of individual Smads, particularly Smad 1 and Smad 6, at different time-points (Smad-1 was higher than Smad-6 at day 3, whilst Smad-6 was much higher than Smad-1 at day 10) suggest that Smad proteins are not simply BMP signal transducers. Smads may also be responsible for up- and/or down-regulation of transcriptional events during the intramembranous and endochondral ossification. Smad-4, a Co-SMAD, expression newly formed bone and cartilage suggests an additional function beyond the signal transduction in rat fracture healing. BMP-4 and BMP-7 were highly expressed at day 3 and 10. BMP-7 expression was greater than BMP-4 at day 3 but switched by day 10 (BMP-4 > BMP-7). Smads represent a new level where specific therapeutic strategies can be targeted considering the interactions with a number of BMPs.

Resorbable porous ceramics derived from chemically converted corals have been used successfully as bone graft substitutes for many years. Converted corals provide a 3D porous architecture that resembles cancellous bone with a pore diameter of 200–700 μm. The success of these corals as a bone graft substitute relies on vascular ingrowth, differentiation of osteoprogenitor cells, remodelling and graft resorption occurring together with host bone ingrowth into the porous microstructure or voids left behind during resorption. The resorption rate of the coral can be controlled by partial conversion to provide a hydroxyapatite (HA) layer via thermal modification. This study examined the resorption rates and bone formation of partially converted corals in a bilateral metaphyseal defect model.

Bilateral defects (5 mm x 15 mm) were created 3 mm below the joint line in the proximal tibia of 41 skeletally mature New Zealand white rabbits following ethical approval. Two variations of a calcium carbonate–HA coral (Pro Osteon 200 R, Interpore-Cross International, Irvine, CA) were examined with different HA thickness (200R; 14% or 200 RT; 28%). Empty defects (negative control) or defects filled with morcellised bone autograft from the defect sites (positive control) were performed. The tibiae were harvested at 6, 12, 24, 36 or 52 weeks, radiographed (standard x-rays and faxitron) in the anteroposterior and lateral planes. Tibias were processed for torsional testing and quantitative histomorphometry using back scattering scanning electron microscopy. Four additional rabbits were killed at time zero to determine the mechanical properties of the intact tibia (n=6 tibias) and 2 for tibias for time zero histomorphometry. Data were analysed using a 3-way analysis of variance.

No clinical complications were encountered in this study. Radiographic assessment revealed a progression in healing, implant resorption and bone infiltration. Cortical closure in the 200 R and 200RT treated defects was noted by 24 weeks. All specimens failed in torsional testing with a spiral fracture initiating at the distal defect site and extending into the distal diaphysis. Torsional properties reached intact control tibia levels by 24 weeks in both groups. No significant differences were noted between 200 R and 200 RT based on torsional data. SEM revealed progressive resorption of the calcium carbonate core of the 200 R and 200 RT with time, infiltration of bone and ingrowth to the HA layers. Time and measurement site (cortical versus cancellous) were significant for implant resorption, bone, and void. The thinner HA layer (200 R) resorbed more quickly compared to the thicker layer (200 RT) in the canal as well as cortical sites. Increased bone and decreased void were noted at the cortex measurement sites in the 200 R group at 24 weeks and in the 200 RT group at 12 and 24 weeks (p< 0.05). Implants were nearly completely resorbed by 52 weeks with only a few percent of implant remaining.

Clinical implantation represents the ultimate experiment of any component and often demonstrates areas of strengths and weaknesses not predicted from in vitro testing. Mobile bearing knees incorporate an additional articulating interface between the flat distal PE insert and a highly polished metal tibial tray. This can allow the proximal interface to retain high conformity whilst leading to reduced stresses at the bone – prosthesis interface by permitting complex distal interface compensatory motion to occur (rotation and/or translation). Retrieval reports on many of the new generation of mobile bearing implants remains scarce. This study presented a retrieval analysis of 9 mobile bearing inserts that had be in situ for less than 24 months.

Nine cemented mobile bearing implants (6 AP Glide, 1 LCS, 1 MBK and 1TRAK) were received into our Implant Retrieval Program. The femoral component, tibial tray and PE insert were macroscopically examined under a stereo-zoom microscope for evidence of damage. The PE inserts were graded for wear based on optical and SEM assessments. The proximal and distal surfaces of the PE inserts were subsequently assessed for surface roughness following ISO 97 (Ra and Rp) using a Surfanalyzer 5400 (Federal Products, Providence, RI). Virgin, unused PE inserts were analysed and served as a comparison to the retrieved implants.

Time in situ time for these implants ranged from 6 months to 24 months (mean 18.6). The implants were revised for instability and pain (AP glide) or dislocation (TRAK). Damage to the femoral components, in general, was minimal with some evidence of a transfer film of PE. The proximal surface of the tibial trays presented evidence of PE transfer as well as some scratches but in general were intact. The proximal PE and distal PE articulating surfaces demonstrated significant areas of damage due to third body wear which was identified on EDAX to be PMMA. Areas of burnishing were also present at the proximal and distal interface. The damage, in part, correlated with the complex kinematics of each design.

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 measure contact pressures in vivo in patients with unicompartmental arthritis fitted with osteoarthrosis (OA) braces to see if the arthritic side of the joint is unloaded.

Method: A thin flexible sensor (TekScan) was manoeuvered arthroscopically into the medial compartment of the knee joint under local anaesthesia in patients with unicompartmental OA of the knee undergoing either therapeutic or diagnostic arthroscopy. All 15 patients had been fitted with a brace before the arthroscopy. Measurements were made within the compartment of double leg stance and single leg stance. Ground reaction force using a load cell was measured for 14 patients and the knee sensor data were normalised relative to this. Recordings were then repeated with the patients with different commercially available braces.

Results: The first two groups of patients showed significant reductions in pressures. Normalised knee sensor forces were reduced to 68%(Sd 22%) and 61%(Sd31%). In the last group of patients, reductions in pressure recordings were less between no-brace and brace. Three patients produced low signals suggesting incorrect sensor replacement.

Conclusions:

Significant unloading of the osteoarthritic compartment could be observed by applying manually a valgus force to the knee.

Introduction: The biomechanical properties of tendon and ligament have long been the subject of intense research. The understanding of the ultrastructure as it relates to the biomechanical function and clinical demands have often considered the ultimate properties at failure alone. Tendons and ligaments are predominately loaded in-vivo at subfailure loads and often in the initial toe region. To date, little work has focussed on the viscoelastic properties of the tendon in the initial toe region. The biomechanical behaviour at these low loads may reflect the unique mechanical interactions between the fasciles and collagen fibrils. This study examined stress relaxation of ligaments in the initial non-linear portion of the load vs. displacement curve.

Methods: Six flexor tendons (2.5 mm wide x 1mm thick) were harvested from 18 month cross bred whethers and stored in 0.145 M NaCl until testing. Tensile testing was performed on a MACH 1 Micromechanical Testing Machine (BIOSYNTECH, Laval, Quebec, Canada) in 0.145M phosphate buffered saline at room temperature. Tendons (gauge length 30mm) were displaced to 0.5, 1 and 5% strain at a loading rate of 50 microns/sec and stress relaxation measured over a period of 300 seconds and repeated for 4 sequences. Data was analysed using an analysis of variance.

Results and Discussion: Peak loads at 0.5 % strain ranged from 50 g (sequence 1) to 130 g (sequence 4) while at 5 % strain peak loads reached upwards to 1600 g. These loads are well within the initial toe region of the load-displacement behaviour of the ligament. The MACH 1 testing system provide a reliable and highly accurate system to control micron level displacements and mg load resolution. Recently, Yamamoto and coworkers reported the stress relaxation behavior and strain rate effects of collagen fascicles differed greatly from those of bulk tendons. The differences in tensile and viscoelastic properties between fascicles and bulk tendons may be attributable, in part, to ground substances, mechanical interaction between fascicles, and the difference of crimp structure of collagen fibrils. The present study supports an important role of tissue ultra-structure at low loads with regard to stress relaxation. Subtle changes in ground susbtance, water content or biochemical consituents not evident in testin

Introduction: Various plating devices and screw systems are available for single and multi-level cervical fusions. Recent reports regarding screw migration under torsional load and a “windshield wiper effect” has brought to light the importance of plate and screw design as well as the choice of graft.

Aim: This study examined the relative stability of cervical plating systems under pure bending and axial-torsional fatigue using the Cloward type graft.

Methods: Five fresh-frozen human cervical and 10 porcine spines assessed by dual-energy x-ray absorptiometry (DEXA) scanning and then reconstructed at the C_2–3 and levels using the anterior Cloward technique. C_4–5 Two different plating systems (a solid plate and a hollow plate) were used and alternated between the C2–3 and C4–5 levels. Strain gauges placed on the plates themselves. The systems were subjected to pure bending and torsional loading.. Five kilogram loads were used to apply bending moments to the spine and did not differ between the two systems evaluated. Bending moments and displacement angles were recorded for the pure bending loading regime and torque versus time was recorded for the torsional fatigue loading.

Results: Strain gauge analysis revealed minimal strains on the plates under the loading conditions. Torque versus time was measured, and the decay constant was calculated from the decay curves. The hollow plating system decayed quicker than the solid plating system. Angular displacement under pure bending was minimal. The hollow system plate system resisted greater torque compared with the solid system. The decay curves eventually reached an asymptote for the both systems. This implied that the systems become stable under fatigue loading. The X-rays illustrated no failure at the screw/ bone interface (i.e. No “wiper” effect) after torsional fatigue.

Introduction: Whether or not to resurface the patella in total knee replacement (TKR) is controversial. One concern is the possibility of progression of the arthritis in the patellofemoral joint that has not been resurfaced when exposed to the stress of articulating with the femoral component.

Methods: The cohort comprised six knees for Trac TKA (Biomet). The assessment involved the use of an electronic sensor system(Iscan, Tekscan). The readings were taken on an anaesthetised patient, during surgery. A tourniquet was not used. A subvastus operative approach was used.

Results: The contact area and contact stress increased with flexion with and without the femoral component in place. We measured no increase in patellar stress when the patella that had not been resurfaced articulated with the femoral component.

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.

Introduction: Unicomparmental knee replacements have a long clinical history of success as well as failure. Recently, in Australia some 40% of knee surgery performed consists of unicompartmental knees for the treatment of medial compartment OA. This increased use of unicompartmental knees is in part due to advances in surgical technique through a minimally invasive approach. Loading conditions at the tibia-implant interface will play an important role in the stress/strain distributions at the proximal tibia. The use of an all PE tibial insert versus a metal backed component may provide a different strain disribution to the proximal tibia. This study examined the influence of metal backed and polyethylene tibial components in unicompartmental knee replacements with and without cement fixation on the initial strain distributions under various loading conditions.

Materials and Methods: Three cadaveric tibias (mean age 47 years old) were cleaned of all soft tissue and strain gauged. Rosette strain gauges (TML Ltd., Tokyo, Japan) were placed at 2 levels on the tibial cortex. The intact tibia were embedded in a low melting point alloy at a standard height and tested using an MTS 858 Bionix testing machine (MTS Systems, Min., MI). The tibia were tested in nuetral, varus and valgus positions at zero and sixty degrees of flexion. A 1500N was applied for 15 seconds and the strains measured. A K-Scan sensor (Tekscan, Boston, MA) was used to confirm the varus and valgus loading positions and to obtain a contact footprint and pressure for the intact and reconstructed tibias under the loading conditions (Fig. 1). Following intact testing, the tibias were templated and reconstructed by a surgeon familiar with the technigue. The implants were investigated with and without cement fixation and compared to their respective all polyethylene component if it was available using the same loading regime as the intact tibias. Principal strains were calculated.

Results: Tibial cortical strain distributions were significantly different at the proximal and distal sites under the loading conditions examined. The strain distribution for metal backed components was greater than the all PE design. Increasing flexion angle shifted the peak strains posteriorly. Metal backing and all PE tibial inserts presented different strain distributions on the medial side under nuetral and varus loading. Lateral compartment strains did not differ between designs, were higher proximal and decreased dramatically at the distal gauges. Cementless fixation tended to overload compared to the intact condition. Figure 2 presents the strain distribution for a typical metal backed and all poly unicompartmental knee in the nuetral position.

Discussion: Metal backed unicompartmental components overloaded the proximal cortex of the tibia. All polyethylene tibial inserts did not overload the proximal cortex and had similar strain distribution to the intact tibia. Cemented fixation allows the transfer of load to the distal tibial cortex via the proximal cortex and subchondral bone, provided that the bone cement has inter-digitised the subchondral bone.

Introduction: A tibial tubercle osteotomy can be used in the exposure of severe articular deformity and the tight knee in total knee arthroplasty, especially revision surgery. This osteotomy has been popularised by Dr. L. Whiteside [1] who described transosseous wiring to secure the osteotomy following joint reconstruction. Other fixation techniques including the use of cables and screws may provide options for this technique. The current study exmained 3 different fixation methods for tibial tubercle osteotomy using an in-vitro sheep model.

Materials and Methods: Tibial tubercle osteotomies (5 cm in length) were performed in ten adult sheep tibias. The osteotomies were fixed sequentially using circumferential Dall-Miles cables (Howmedica, Ritherford, NJ) (Fig. 1), transosseous wires and lastly 2 AO screws. Testing of each fixation configuration was performed using an MTS 858 Mini Bionix servo hydraulic testing machine (MTS Systems Corporation, USA). The loading regime used a cyclic 200 N load applied along the line of the patellar tendon with micromotion measured at the osteotomy and adjacent bone using optical sensors (MEL, Bahnhofstr, Germany). Data was analyzed using ANOVA. Micromotion at the end of the osteotomy fragment was recorded for 150 cycles for each tibia following reconstruction with cables, wires, and screws in succession.

Results: Cable fixation provided the most stable construct followed by screws and wires respectively. Wire fixation had the greatest variation in micromotion (370 microns). The ovine tibia model provides a reproducible bone bed to evaluate different fixation strategies for tibial tubercle osteotomy. Clinically, differences may even be marked considering anatomic and bone quality issues as well as magnitude of the load that have not been addressed in this in-vitro study.

Discussion: Fixation of the osteotmoy is an important surgical technique. Wolff et al. found that major complications related to the surgical technique occurred in 23% of the knees performed in 26 cases [2]. Reis et al. [3] observed fixation with 3 or 4 titanium screws was sufficient after a follow-up period of 18 months. Twenty-nine of the osteotomies healed primarily. One patient developed postoperative displacement of the tibial tubercle requiring additional screw and suture fixation. This study has shown that micromotion of a tibial tubercle osteotomy fixation in sheep is dependent upon fixation technique. Cables provided the most stable fixation compared to screws and wires in an ovine tibial model.

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: Proximal bone resorption is a common problem after total hip arthroplasty. This has been attributed to stress shielding and has been reported to be more pronounced for cemented than for uncemented implants.

Aim: To investigate the cortical strain distribution of a new proximal “fit and fill” cementless, titanium, femoral, hip prosthesis based on the SROM design.

Methods: Strain gauges were mounted on five fresh-frozen cadaveric and five saw-bone femora and checked against a template for the prosthesis. The strain gauges were placed at four levels on the anterior, posterior, medial and lateral cortices corresponding to the Gruen zones. Two extra strain gauges were placed on the proximal posteromedial cortex. Loading was applied to the intact and reconstructed femora in the ISO 7206–4 orientation and single legged stance in an MTS servo-hydraulic testing machine. Data were analysed using analysis of variance.

Results: The strain distributions following reconstruction and multi-axis loading (ISO 7206–4 orientation) approximated the strains in an intact femur in the diaphysis. The proximal posteromedial cortical strains were approximately 50% of those of the intact femur.

Conclusions: The strains observed in the proximal femur following reconstruction in the present study are considerably higher than most others reported in the literature. A number of factors may contribute to the high proximal strains observed. This study has illustrated that geometric design and material selection along with surgical technique may allow for greater loading to proximal bone and enhance the long term integrity of this type of implant.

Introduction: Acetabular osteolysis is common behind cups with holes (the reported incidence is 9% to 36%). Fluid pressure has been implicated in the pathogenesis of osteolysis.

Aim: To test the hypothesis that a polyethylene liner in a metal cup can act as a pump in vivo.

Methods: This study was performed during revision surgery in six cases. The components were from several manufacturers. All were ingrown uncemented cups that had osteolytic lesions associated with holes in the cup.

A cannula was placed through the capsule into the hip joint and another was placed through the periosteum and bone of the ilium into the osteolytic lesion above the ingrown cup. The continuity of these two spaces through the holes in the cup was confirmed by the injection of methylene blue. Pressure transducers were then connected to both cannulae. Measurements were taken while applying compression and distraction forces across the artificial hip joint.

Results: Compression and distraction loads produced a rise (48mmHg) and a fall (35mmHg) respectively in the pressure in the osteolytic lesion but no change in the hip joint pressure, thereby, demonstrating a pumping action. After exposing the prosthesis we were able to demonstrate 1mm to 2mm of in-out excursion of the polyethylene liner in the metal cup, which may explain the mechanism of the pumping effect.

Discussion: The polyethylene liner in the metal shell can act as a pump. Compression and distraction forces, such as occur in normal gait, produce changes in fluid pressure, which are transmitted through the holes and may cause osteolysis behind the cup.

Introduction: The stress and strain in the proximal femur after total hip arthroplasty are influenced by the geometry of the implant in addition to its materials properties and applied loading. The addition of a third taper in the medio-lateral plane may provide additional stability and improved load transmission.

Aim: To examine the relative stability of double and triple tapered stems in two finite element (FE) models.

Methods: The geometry of a polished, double-tapered and a triple-tapered stem were scanned using a three dimensional technique. Two FE models of the stems were created using PATRAN. The models were analysed using the ABAQUS. Tied and sliding contact conditions were allowed between the implants and the cement mantle. The interface at the distal tip of the stem was removed to represent the scenario with a distal centraliser present.

Results: When tied contact was assumed, both stems displayed similar von Mises’ stress distributions. The peak stresses remained constant in the double tapered stem, with a marked translation of regions of high stress towards the distal tip with the introduction of sliding contact conditions. Peak stresses in the triple tapered stem decreased, but displayed a more continuous distribution along the implant with sliding contact. Torsional loading of the stems reduced the magnitude of the distal tip stresses.

Conclusions: The triple-tapered geometry displayed a more even distribution of stresses along the length of the implant. The double-tapered geometry displayed a high stress state at the distal tip of the implant.

Introduction: The transition from fixed bearing to mobile bearing total replacements represents a recent trend in Australia with the introduction of many new designs. The complex kinematics of mobile bearing designs coupled with the importance of proper surgical techniques including soft tissue balancing presents a number of factors that may influence the short and long-term success of these implants. There have been few reports in the literature on the performance of many of the new mobile bearing design with regards to initial wear of the polyethylene (PE) insert.

Aim: To investigate the patterns of wear on three mobile bearing knee PE inserts that had been retrieved soon after implantation.

Methods: Three mobile bearing knee PE inserts were retrieved at the time of revision surgery and submitted to our laboratory for examination. The proximal and distal articulating surfaces were examined by measuring surface roughness (Ra) using a Surfanalyzer (5400 (Federal Products Co., Providence, RI, USA) following ISO 97. Optical microscopy and scanning electron microscope (SEM) analyses were used to locate and identify patterns of wear.

Results: The average time in service for the PE inserts was 18.6 months. The maximum Ra values were noted on the anterior-lateral side for all implants. Optical and SEM analysis revealed wear mechanisms that included burnishing, scratches, pitting and cold flow. Damage to the distal surface was noted in all samples with extensive wear tracks noted in the LCS and TRAC knees.

Conclusion: The surface roughness analyses showed asymmetrical wear on the distal PE interfaces as well as wear on the proximal PE interfaces. The presence of embedded particles and debris suggests a third-body mechanism. Dislocation and general instability may have exacerbated the early signs of wear in these components.

Introduction: The classic teaching in flexor tendon repair suggests that a 10mm bite is important for the integrity of the repair regardless of the other features of the technique. Although this has been widely accepted since Bunnell’s first descriptions of accurate flexor tendon repair there appear to be little data to support it. An extensive review of the literature showed no biomechanical data relating specifically to size of bite in flexor tendon repair. We hypothesised that decreased bite may cause less damage to the tendon during repair while still offering adequate mechanical strength.

Aim: To investigate the effect of different bite sizes on the mechanical properties of flexor tendon repairs.

Methods: Twenty fresh-frozen cadaveric flexor tendons were divided at their centres. One side of a modified Kessler repair was used on each side taking a 6mm bite on one side and a 10mm bite on the other. The tendons underwent tensile testing on a mechanical testing frame by pulling on the ends of the suture with the tendon secured in pneumatic grips. Data for stiffness and ultimate load to failure were recorded.

Results: An increased bite size made no significant difference to stiffness of the repairs. There was a difference in load to failure noted but this was not significant. The ultimate load to failure was noted after the specimens had been distracted over 2mm, which would result in clinical failure.

Conclusions: These results suggested that a 10mm bite may be excessive in flexor tendon repair and could cause more tissue damage than lesser bites. Further study of in vivo effects of decreased bite size is required.

Aim: Radio-frequency treatment is used clinically in unstable joints to reduce the length of the supporting soft tissues to help provide stability. The mechanical properties after treatment have not been adequately studied. Since there is a change in the tissues’ ultra-structure with treatment we hypothesised that different collagenous tissues may have varying responses to radio-frequency treatment.

Methods: Ovine extensor tendons and cadaveric gleno-humeral capsules were tested on a MTS machine to investigate the dynamic and failure properties before and after radio-frequency treatment. Three radio- frequency treatments of different power (5, 10 and 20W) were used and two different treatment times (10s and 30s) to investigate the effects of treatment power and time on changes in the mechanical properties.

Results: The tissue shortening that was produced in the tendons and capsules was progressive with increases in treatment wattage and time. The tendon failure-force and stiffness were significantly reduced by the radio-frequency treatment but no significant changes were found in the capsules. Considering the dynamic properties only, the tendons showed significant changes with treatment. The mechanical properties were significantly different between control and treated groups but not between the treatment settings.

Conclusions: The tissue type altered the effect of radio-frequency treatment on the mechanical properties. Varying the treatment wattage and time did not significantly alter the changes observed with the largest difference being between control and treated tissue at any treatment setting. Therefore, radio frequency was proven to shorten collagenous tissues in a predictable manner but changes to the mechanical properties depend on the tissue type.

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.

Introduction: Abnormal fracture healing in aged, post-menopausal or ovariectomised patients remains a clinical problem. Understanding the distribution and regulation of biomolecular factors in fracture healing in oestrogen deficient rats may have clinical implications for developing novel therapeutic strategies for enhancing osteoporotic fracture healing. Our previous work demonstrated that bone morphogenetic proteins (BMPs), transforming growth factor beta (TGF-ß) and their signal transducers, Smads, played important roles in normal fracture healing. Insulin-like growth factor I (IGF-I) has been indicated playing a role in the maintenance of bone mass. Matrix metalloproteinases (MMPs) has been indicated to play a role in bone matrix degradation. Those factors in ovariectomised fracture healing have not yet been reported.

Aim: To investigate the expression of BMP-2, 7, TGF-ß, Smads1–7, IGF-I, IGF-I receptor 1a (IGF-IR1), MMPs and TIMPs by a quantitative immunohistochemistry in a fracture model in an ovariectomised rodent (OVX).

Methods: Age-matched, normal, female rats served as controls. The animals were sacrificed in groups of six at one, two, three, four and six weeks after the fracture.

Results: The highlights of our results were the lack of IGF-I in the early stage of fracture healing (up to two weeks) in OVX rats and the greater expression of MMP-1 in OVX rats at all groups when compared with the normal rats.

Conclusions: Our data suggested that the regulation downward of IGF-I in the OVX fractures resulted from estrogen deficiency and may have the function to stimulate MMP-1 activity. Over-expressed MMP-1 degraded collagen matrix in the cortex and inhibited the woven bone matrix formation during OVX fracture healing.

Introduction: Hip instability is a complex and challenging problem. In experienced units, up to 4% of patients undergoing total hip arthroplasty will require revision surgery to treat hip instability, with only 60% of these treatments being successful. Many authors reporting results with various constrained systems available have described dislocation rates post implantation of the constrained component of 4% to 29%.

Method: The thirteen patients who underwent placement of a constrained component as a revision procedure in our unit from 1989 to 2000 were reviewed.

Results: The indications for revision surgery included recurrent dislocation in eight and intraoperative instability in five revision hip arthroplasties. No patients were lost to follow up. The average follow-up was 43 months(range 14 to 121). The average age at time of surgery was 73 years(range: 52 to 84 years). No component has been revised. The average hip score after revision surgery was 72(range: 52 to 89). There have been no episodes of dislocation of the constrained arthroplasty. In seven cases the constrained arthroplasty was implanted into a previously placed well fixed shell.

Conclusion: Constrained acetabular components were a highly effective tool in the treatment of hip instability.

Introduction: The lordosis of the lumbar spine, flexion angle and body weight result in significant shear forces through the lumbar and lumbosacral disc spaces. These shear forces result in translational motion across the disc space, which is resisted but not completely abolished by pedicle screw stabilisation. Failure of lumbar interbody fusions through non-union may be related to translational micromotion at the vertebral endplate / bone graft interface. A porcine in vitro model was established to test whether variations in the design of inter-body implants and in particular, the presence of surface serrations would assist in resisting shear forces – especially those causing anterior translation.

Methods: Measurements of anterior vertebral translation were recorded on porcine cervical spine segments, subjected to 25 N antero-posterior shear load while under a 300 N compressive pre-load. Baseline testing was firstly performed on the intact specimens and following removal of the facet joints. The annulus, disc nucleus and cartilaginous endplates were then removed and the specimens were divided into two groups for testing using interbody implants. Four stainless steel blocks measuring 15 mm (length) × 5 mm (height) × 4 mm (width) were manufactured to act as intervertebral disc spacers. Two were made with smooth surfaces and two were made with 1 mm deep serrations on the upper and lower surfaces. One group was tested with two smooth and one with two serrated implants.

Results: Under 25 N shear load, the specimens tested with the serrated implants showed anterior vertebral translation of 0.046 ± 0.013 mm while those tested with the smooth surfaced implants measured 0.152 ± 0.075 mm (p < 0.01). A significant difference was also found between the stiffness of the specimens implanted with smooth surfaced (432.8 N/mm) and serrated (1088.4 N/mm) implants (p < 0.01). The value for peak load at failure for the specimens with smooth surfaced implants (150.43N) was less than those implanted with serrated implants (175.48 N), but not significantly different.

Discussion: The presence of surface serrations on the interbody implants significantly increased the resistance to shear forces in this model. In the clinical setting, we postulate that the degree of micromotion generated by anterior shear forces at interbody fusion sites should be substantially less when serrated implants are used and reduce the incidence of non-union. This may explain the improved fusion rates reported by contemporary authors when using some interbody implants. Further research is needed to clarify the combined effects of pedicle screw stabilisation and interbody implants upon shear displacement and variations in implant design.

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.