Aims: Replacing human cadaveric specimens with fresh frozen animal tissue in biomechanical studies has become increasingly more popular due to the scarcity of young human tissue. The aims of this study were to characterise and compare the biomechanical parameters of tailored strips of equine extensor tendon, with 4 strand young human semitendinosus and gracilis (STG) tendons as an alternative tendon model for testing anterior cruciate ligament (ACL) graft reconstruction techniques using the Soffix Polyester ACL fixation device.

Method: Common digital extensor tendons were harvested from normal equine forelimbs and tailored into 5 mm wide, 2 strand equine tendon strips. The doubled equine tendons were overlapped and braided around the buttonholes of a Soffix fixation device and secured with No 2 Ethibond sutures (Johnson & Johnson Ltd). The Soffix-4-strand young human STG tendon complex was prepared in an identical manner. Mechanical testing was performed measuring ultimate tensile load (UTL) and elongation to failure (EF), structural stiffness (SS) was calculated from load extension curves.

Results: The Soffix-STG and the equine tendon complexes produced a mean UTL of 1186 N +/− 113.89 and 1116 N +/− 208.5 respectively showing no statistically significant difference.

Conclusions: We conclude that a tailored 5mm wide 2-strand equine extensor tendon strip provides a comparable alternative for in vitro testing of young human four strand STG tendon graft using a Soffix polyester fixation device.

Aims: The aims of this study were to evaluate the biomechanical properties and mode of failure of a technique of anterior cruciate ligament (ACL) reconstruction using the Soffix polyester fixation device. A 2-strand equine extensor tendon graft model was used because a previous study has shown it to have equivalent bio-mechanical properties to that of 4-strand human semitendinosus and gracilis tendon grafts.

Method: Ten stifle joints were obtained from 5 skeletally mature pigs, the soft tissues were removed and the ACL and PCL were sacrificed. Tibial tunnel preparation was standardised using the Mayday rhino horn jig to accurately position a guide wire over which an 8mm tunnel was drilled. A 2-strand equine tendon-Soffix graft was used to reconstruct the ACL of the porcine knee using over the top femoral placement with bicortical screw fixation. Mechanical testing of 10 specimens was performed.

Results: The mode of failure included 4 midsubstance tendon failures, 3 Soffix failures and 3 failures at the suture-Soffix interface. The mean ultimate tensile load for the ACL reconstruction was 1360 N (standard deviation (SD) =354), elongation to failure of 41 mm (SD=7.5) and a structural stiffness of 35 N/mm (SD=8.1).

Conclusion: This in vitro study has shown that the technique of ACL reconstruction using the Soffix soft tissue fixation device with a tendon graft placed in the over the top position is biomechanically strong, providing a sufficiently high UTL immediately following reconstruction, therefore allowing early weight bearing and rehabilitation.

70 patients who underwent dynamic MRI scanning for chronic anterior knee pain were retrospectively evaluated. All patients had been symptomatic for over a year. 43 patients had been treated conservatively and 27 had undergone surgical procedures (arthroscopy -13, lateral release- 9, tibial tubercle transfer 5). The extent of subluxation, tilt and cartilage abnormalities on MRI scans, during resisted extension were assessed. Functional scoring (Oxford, Lysholm and Tegner scores) was done through questionnaires and correlated with the radiological findings.

54 (77%) patients were found to have some patellofemoral abnormality on the scans. Subluxation was the most common finding with mild subluxation in 30, moderate in 18 and severe in 17 knees. Mild tilt was seen in 26 knees and moderate to severe tilt in 14 knees. Tilt was found in association with subluxation except in 8 cases. Grade 1 and 2 cartilage wear were seen in 13 knees and Grade 3 and 4 in 21 knees.

The “Tibial Tubercle to Trochlear Groove distance” (TTD) was measured in all knees and correlated with subluxation. The average distance was 13.5mm, 13.6mm and 18.8mm for mild, moderate and severe subluxation respectively. All patients with a TTD _ 20mm had moderate or severe subluxation. The specificity of a TTD _ 20mm for severe maltracking was 100% but the sensitivity was only 42%.

The TTD appears to be the single most significant parameter determining patella tracking. We have proposed an algorithm for the surgical and non-surgical treatment of chronic anterior knee pain. We recommend lateral release for those with moderate and severe subluxation and a tibial tubercle transfer as well in those with a TTD _ 20mm. The functional scores did not zshow a significant correlation with the grading of subluxation.

Background: The over the top technique was first described in 1974. The Mark II ACL reconstruction was a development on the ABC and the Mark I procedure and was introduced into clinical practice in March 1998. The soffix used is a polyester hamstring graft support device with three button holes at each end. Clinical observation showed progressive slackening of some initially successful reconstructions. Retightening restored stability. We studied the medium and long-term outcome of the procedure and tested the effects of preconditioning on its biomechanical properties.

Patients and methods: 90 patients underwent a prospective medium and long-term follow-up (3–5 years) in a dedicated research clinic. Standardised scores Lysholm, Tegner, and IKDC. were used. Biomechanical tests were performed in vitro using double equine extensor tendon-soffix model constructs. 18 experiments with an MTS Hydraulic testing machine, were carried out, preconditioning with 300, 400 and 500N. Constructs were then cyclically loaded 3000 times at 1 Hz and finally tested to failure.

Results Clinical follow-up showed good overall results. The mean Tegner score increased from 2.5 pre-operatively to 4.5. The majority had a Lysholm score of > 90(72%). The majority had an IKDC of B (75%). 10% had a side to side difference > 6mm. The mean stretch of 14mm after 3000 cycles was reduced to 4.2 mm by preconditioning with 500N. This had no adverse effect on the ultimate tensile strength.

Conclusion: The medium and long-term results of the MarK II ACL reconstruction are encouraging. Preconditioning the soffix tendon construct reduces the creep with no adverse effect on the ultimate tensile strength. A pre-conditioning device has been made to replicate this in theatre.

Aims: The aims of this study were to evaluate the biomechanical properties and mode of failure of 4 methods of fixation used for hamstring tendon ACL grafts. The fixation methods investigated included titanium round headed cannulated interference (RCI) screws, bioabsorbable RCI screws, Endobuttons and Bollard fixation. It has been previously shown that a 2 strand tailored equine tendon-Soffix graft has equivalent biomechanical properties to a 4 strand human hamstring tendon-Soffix graft [1,2], therefore this model was used for the graft in the study.

Materials and Method: 32 stifle joints were obtained from skeletally mature pigs, the soft tissues were removed and the ACL and PCL were sacrificed. Tibial tunnel preparation was standardised using the Mayday Rhino horn jig to accurately position a guide wire. An 8 mm cannulated reamer was then used over the guide wire to create the final tibial tunnel. A back radiusing device was then placed into the tibial tunnel to chamfer the posterior margin of the tunnel exit to prevent abrasion and fretting of the graft. A 2 strand equine tendon-Soffix graft was then introduced into the tibial tunnel and secured with one of the four fixation methods. The proximal part of the graft was attached to the cross head of the materials testing machine using the Soffix. Five of each method of fixation were tested mechanically to failure and three of each method were cyclically loaded for 1000 cycles between 5 to 150 N, followed by 2000 cycles at 50 to 450 N.

Results: The mean ultimate tensile loads (UTL) were: titanium RCI screw = 444 N, bioabsorbable RCI screw = 668 N, Endobutton = 999 N and Bollard = 1153 N. The mode of failure for all RCI screws involved tendon slippage past the screw. Two Endobutton failures were encountered and one Bollard pull out occurred. Under cyclic loading conditions the titanium and bioabsorbable RCI screws failed rapidly after several hundred 5 to 150 N cycles due to tendon graft damage and progressive slippage. Both the Bollards and Endobuttons survived 1500 cycles at 50 to 450 N, with less tendon slippage occurring.

Conclusion: Titanium and bioabsorbable RCI screws provide poor initial fixation of tendon grafts used for ACL reconstruction, having significantly lower UTL’s than both Endobutton and Bollard fixation. Under cyclic loading titanium and bioabsorbable RCI screws fail rapidly due to progressive tendon slippage, whereas Bollards and Endobuttons survive cyclic loading. Both Bollard fixation and Endobuttons provide sufficiently high UTL’s and survive cyclic loading to allow early postoperative mobilisation and rehabilitation. Caution must be used in the early postoperative period when using interference screws to secure a hamstring tendon graft because progressive tendon slippage may result in excessive graft elongation and early clinical failure.

Purpose of the study: To develop a new treatment algorithm for patients with chronic anterior knee pain based on kinematic patella tracking MR imaging.

Methods and Results: Patients with anterior knee pain of more than one year duration and not responding to non-operative treatment, underwent kinematic MRI study. The provocative test was performed with the conventional MRI scanner and the patient extending the knee against resistance, the resistance provided by inflated beach ball. A retrospective analysis was done of first seventy patients, who had undergone this scanning technique.

On the imaging films, four measurements were made. They were patella subluxation, tilt, cartilage thickness and the Tibial Tubercle Trochlear distance (TTD). Patellar subluxation was classified as mild, moderate and severe. We found that a Tibial Tubercle Trochlea distance of 18mm had a specifity of 100% and a sensitivity of 89% for severe maltracking.

Conclusion: Kinematic MR Imaging is a useful investigation before considering operative treatment for patients with chronic anterior knee pain. Based on our study, we conclude that those patients with moderate lateral maltracking with a TTD< 18 mm should be offered lateral release and those with severe maltracking and TTD> 18mm should have a tibial tubercle transfer, in addition to lateral release.

Aims: The aims of this study were to evaluate the biomechanical properties and mode of failure of four methods of fixation of hamstring anterior cruciate ligament (ACL) grafts. A 2-strand equine extensor tendon graft model was used because a previous study has shown it to have equivalent biomechanical properties to that of 4-strand human semitendinosus and gracilis tendon grafts. Method: Twenty stifle joints were obtained from 10 skeletally mature pigs, the soft tissues were removed and the ACL and PCL were sacrificed. Tibial tunnel preparation was standardised using the Mayday rhino horn jig to accurately position a guide wire over which an 8mm tunnel was drilled. A 2-strand equine tendon graft was then introduced into the tibial tunnel and secured with either a titanium round headed cannulated interference (RCI) screw, a bioabsorbable RCI screw, an Endobutton or an expansile Bollard. Five of each method of fixation were tested mechanically to ultimate failure and under cyclical loading. Results: The mean ultimate tensile loads (UTL) were: titanium RCI screw = 444 N, bioabsorbable RCI screw = 668 N, Endobutton = 999 N and Bollard = 1153 N. Under cyclic loading conditions the titanium and bioabsorbable RCI screws rapidly failed after several hundred 5 to 150 N cycles due to tendon damage and slippage. Both the Bollards and Endobuttons survived 1500 cycles at 50-450N, with less tendon slippage. Conclusion: Titanium and bioabsorbale RCI screws provide poor initial fixation of tendon grafts and fail rapidly under cyclic loading. Both Bollards and Endobuttons provide sufficiently high UTL’s and survive cyclic loading to allow early postoperative rehabilitation.

The diagnosis and subsequent treatment of patients with “Anterior Knee Pain” remains a challenge and an enigma at times.

The 4 main parameters, which need to be assessed, are:

Bony anatomy of the PFJ

While plain radiographs, CT scans and static MRI sans and arthroscopic assessments highlight some of the parameters none of them are comprehensive. The type of MRI scanning used in this study assesses all 4 parameters. The equipment required for resisted quadriceps contraction is inexpensive and readily available.

Material and Methods: 70 patients had dynamic MRI scans done over a period of 2 years. The study consisted of 3 parts:

Radiological diagnosis and grading of subluxation if present.

Conclusion: The Tibial Tubercle to Trochlear Groove Distance” (TTD) appears to be the single most significant parameter determining patellar tracking. Objective radiological assessment is possible under physiological loading, to differentiate tilt, subluxation and chondromalacia. We have proposed an algorithm for the surgical and non-surgical treatment of anterior knee pain. The pain scores did not show a significant correlation with the grading of subluxation.

Aim: The purpose of this paper was to describe the biological reaction imposed by a prosthetic ligament.

Materials-Methods: Polyester-carbon synthetic matrices were implanted into 29 rabbits. The implants were transected centrally and reconstructed with resorbable suture material. At regular intervals from 4th day to 29 weeks, tissue samples from the ingrown implants were obtained for histology and mechanical testing. Light microscopy, DNA cytometry, immunohistochemical analysis of the collagen types, transmission and scanning electron microscopy were carried out. Ultimate tensile strength (UTL), elongation to failure (EF) and structural stiffness (SS) were determined at intervals of 8, 16 and 29 weeks.

Results: The ingrowth of tissue into the scaffold provided a significant increase in tensile strength, which improved with time. The UTL significantly increased from 18.86 N ±14.69 at 8 weeks to 51.4 N ±14.64 at 29 weeks. Light microscopy showed no infl ammation or foreign body reaction. At 4th day the first fibroblast cells settled on the matrix. The DNA cytometry showed an increase of the number of the fibroblast cell mitoses up to 16 days. After 2 weeks a mesh of connective tissue was formed around the scaffold, but the number of fibroblast cells remained constant. At 4 weeks the connective tissue started to infiltrate in between the artificial fibres. Type I, III and V collagens were identified. Electron microscopically the collagen weave was irregular with a mean fibril diameter of 28.4 ± 5.2 nm of a monophasic distribution. Collagen type I accumulated progressively and more and more dense collagenous fascicles appeared in the mesh in the proximity of the artificial fibres.

Conclusion: The subcutaneous tissue may act as a bio-reactor and the skin fibroblast seeding of a synthetic matrix appears to be transformed a dense connective tissue during the first 4 weeks, providing tensile strength improvement to the tissue envelope with time.

Aim: The aim of our study was to evaluate the results of the Soffix Mark I and Mark II hamstring fixation devices, placed transtibially with an “over the top” femoral route when applied to revision anterior cruciate ligament (ACL) surgery secondary to synthetic ligament failure.

Patients and Methods: 29 ACL revisions performed between 1992 and 2000 were evaluated. Twenty six failed prosthetic ligaments, 2 failed semitendinosus/gracilis (STG) and one BTB autografts were revised using hamstring grafts in 26, quadriceps in 2, and patella bone tendon bone (BTB) in 1 patient. Mark I and II fixation devices were employed. Follow up included clinical examination, KT 2000 arthrometric assessment, Lysholm, Tegner and IKDC scoring. The average follow up time was 50 months ±22.4.

Results: Arthrometric examination showed a mean side to side difference (SSD) of 2.98 mm ±1.5. The mean Lysholm score was 86.5 ±10.5 and 21 patients had a B rating (nearly normal) on IKDC scoring, while 3 score A (normal). The mean Lysholm score was 86.5 ±10.5. The lowest clinical scores were noted in 4 multiply operated knees.

Conclusions: We concluded that a revision technique using the STG Soffix fixation device can restore stability with good functional outcomes following failed primary ACL reconstruction. Multiply re-operated knees had the worst functional results despite restoration of stability.

Aim. The purpose of this paper is to report on the results of ACL hamstring reconstruction using a novel fixation device.

Patients-Methods. We reviewed a total of 132 patients with anterior cruciate ligament reconstruction, operated between 1998 and 2002, with a mean follow up time of 51 ± 9 months. A uniform arthroscopically assisted surgical technique with an instrument guided impingement free tibial tunnel placement and “over the top” femoral routing was employed. An autologous four strand semitendinosus-gracilis tendon graft in combination with a polyester graft suspension tape and cortical fixation device was used. An accelerated rehabilitation was instructed. All patients were examined in a dedicated Research Clinic on a 6 month basis. IKDC, Lysholm and Tegner scoring were employed to validate the end results. Arthrometric evaluation was performed with the KT 2000 device.

Results. The over all analysis showed a mean side to side difference of 2.9 mm ± 1.8 and the International Knee Documentation Committee score rating was 91.6 % normal or nearly normal (121 patients). Complications included one graft rupture, one deep infection and 5 case of loosening.

Conclusion. These findings suggest that the described method of anterior cruciate ligament replacement produces good early functional results and restores knee stability.