Graft-tunnel mismatch of the bone-patellar tendon-bone (BPTB) graft is a major concern during anatomical anterior cruciate ligament (ACL) reconstruction if the femoral tunnel is positioned using a far medial portal technique, as the femoral tunnel tends to be shorter compared with that positioned using a transtibial portal technique. This study describes an accurate method of calculating the ideal length of bone plugs of a BPTB graft required to avoid graft–tunnel mismatch during anatomical ACL reconstruction using a far medial portal technique of femoral tunnel positioning. Based on data obtained intra-operatively from 60 anatomical ACL reconstruction procedures, we calculated the length of bone plugs required in the BPTB graft to avoid graft–tunnel mismatch. When this was prevented in all the 60 cases, we found that the mean length of femoral bone plug that remained in contact with the interference screw within the femoral tunnel was 14 mm (12 to 22) and the mean length of tibial bone plug that remained in contact with the interference screw within the tibial tunnel was 23 mm (18 to 28). These results were used to validate theoretical formulae developed to predict the required length of bone plugs in BPTB graft during anatomical ACL reconstruction using a far medial portal technique. Cite this article: Bone Joint J 2015;97-B:324–8

Introduction

Interest in platelet-derived growth factors has been increasing as an adjunct in surgical techniques for tissue repair. Its use in ligament injuries repair has been studied mainly in animals. The authors intend to study growth factors influence in ACL repair using BTB graft.

The purpose of this study was to determine the incidence of graft-tunnel mismatch (GTM) when performing anatomic anterior cruciate ligament reconstruction (ACLR) using bone-patella tendon-bone (BPTB) grafts and anteromedial portal drilling. Beginning in November 2018, 100 consecutive patients who underwent ACLR by two sports fellowship-trained, orthopedic surgeons using BPTB autograft and anteromedial portal drilling were prospectively identified. The BPTB graft dimensions and the femoral tunnel distance, tibial tunnel distance, intra-articular distance, and total distance were measured. Surgeons determined the depth and angle of tunnels based on the patella tendon graft length dimensions in each case. After passage of the graft, the distance from the distal graft tip to the tibial cortex aperture was measured. GTM was defined as the need for additional measures to obtain satisfactory tibial graft fixation (< 1 5e20 mm of bone fixation). The incidence of mismatch was 6/100 (6%). Five cases involved the graft being too long, with the tibial bone plug protruding excessively from the tibial tunneld4/5 had a patella tendon length ? 50 mm. Three cases were managed with femoral tunnel recession, and two were treated with a free bone plug technique. One patient with a patella tendon length of 35 mm had a graft that was too short, with the tibial bone plug recessed in the tibial tunnel. Of patients whose tibial tunnel distance was within 5 mm of the patella tendon length, only 1/46 (2%) patients had mismatch, whereas 5/54 (9%) of patients who had >5 mm difference had mismatch. The incidence of grafttunnel mismatch after anatomic ACLR using BTPB and anteromedial portal drilling in this study is 6%. To limit the occurrence of GTM where the graft is too long, surgeons should drill tibial tunnel distances within 5 mm of the patella tendon length

Early mobilisation following Anterior Cruciate Ligament(ACL) reconstruction surgery is indicated for optimum results for accelerated rehabilitation. However, the graft used in reconstruction is at it’s weakest during the early post-operative period and can be prone to slipping. Aim: This study compared two types of graft, bone-patellar tendon-bone (BPTB) and soft tissue tendon, with the hypothesis that BPTB grafts would lead to less slippage under cyclical loading conditi ons. Materials & Method: A comparative biomechanical study was carried out using sixteen proximal tibiae of calves, aged 20–26 weeks and carrying out ACL reconstruction, 8 constructs with human Cadaveric BPTB and another 8 with calves’ extensor tendons. An interference screw measured 9 x 25mm was used to fix graft tissue in the transosseous tunnel. The specimens were tested in material-testing machine using Merlin software. The constructs were subjected to cyclical loading. A load cycle of 0-150-0N was applied at a crosshead speed of 100mm/min, approximately 80 load cycles per minute simulating the forces applied in post-operative mobilisation. The crosshead position was noted at peak load at 1, 100, 300, and 1000 cycles. Results: The value of the graft slippage found in the soft tissue tendon model was 1.83 ± 0.54 and that of bone tissue (BPTB) model was 0.76 ±0.29. Creep value showed no statistical significance. There was significantly less slippage when using BPTB-to-bone fixation than with soft tissue tendon-to bone fixation (p< 0.005). Clinical relevance: BPTB grafts are more likely to resist the return of anterior-posterior laxity in the immediate post-operative period, prior to graft fixation by tissue healing. BPTB grafts should be used when accelerated rehabilitation is required

Purpose: We present our experience in recurrence of anterior knee instability after reconstruction of anterior cruciate ligament. Material-methods: In our department, from 1996 to 2002, 359 patients with average age 24.2 years were treated for anterior knee instability. 159 patients underwent acl reconstruction with the use of bone-patellar tendon-bone graft, 188 pts with hamstrings tendons and 19 pts with quadriceps tendon-bone graft. During the follow-up period, 12 cases with recurrence of anterior knee instability came up. In nine patients BPTB graft was used and in three hamstrings. Five patients suffered a sports accident while seven presented a progressive graft laxity. At the revision, hamstrings were used in nine patients and quadriceps tendon-bone graft in three pts. Results: All patients had a follow-up period free of complications, were subjected to the same rehabilitation program and returned to their usual activities into the expected for the particular operation period. Conclusion: The revision of ACL reconstruction demands careful preoperative planning, organized surgery with capability to apply alternative solutions and understanding of the patient’s demands

Goal : Presentation of failures and complications of ACL reconstruction. Method: We studied 356 patients (361 knees) aged 14 – 52 years who had ACL deficiency and were treated by reconstruction the period from 1-1-1997 to 31-12-2002. They have been operated by the same surgeon (S.P.) 7 days to 5 years after the initial injury by arthroscopy or/and miniarthrotomy using BPTB graft (284) and ST/G graft (77). All co-existing injuries were also treated simultaneously (72 tears of the medial meniscus, 35 tears of the lateral meniscus, 37 tears of the medial and lateral menisci, 18 traumatic lesions of the articular cartilage, 3 posterolateral instabilities) by 42 meniscal repairs, 124 meniscectomies, 2 mosaicplasty, 16 drilling of the sub-chondral bone and 3 posterolateral reconstruction. Results: Intraoperative: 3 patella fractures during BPTB harvesting, 3 breaking of bioabsorbable femoral screw, 2 non satisfactory BPTB graft fixation at the femoral tunnel, 1 asymptomatic exit of the screw at the back of the femur. Postoperative: 3 temporary apraxies of the peroneal nerve, 10 superficial and 3 deep infections, 15 reruptures or elongations of the graft, 18 with loss of extension < 10°, 5 with loss of extension > 10°, 2 with persistent hydrarthrosis after the 2nd postoperative month, 22 with anterior knee pain after BPTB harvesting, 3 with keloid, 1 with an acute korner at the graft harvesting site at the tibia, high percentage had weekness of the quadriceps mechanism and sensory abnormalities of the anterior side of the knee. Conclusions: ACL reconstruction is a treatment with failures and complications that require axperience, knowledge and good instrumentation

Introduction Roentgen stereophotogrammetric analysis (RSA) is the most accurate radiographic technique for measuring three-dimensional micromotion in joints, and is now being developed for the study of anterior cruciate ligament (ACL) injury and outcome after surgical reconstruction. Using RSA a prospective study of ACL reconstruction is being undertaken. The aim is to obtain accurate information on the performance of both bone-patellar tendon-bone (BPTB) and hamstring grafts post-operatively. Materials and methods 14 patients with a unilateral ACL tear who underwent ACL reconstruction have been studied prospectively. Seven had BPTB grafts, and seven had four-stranded semitendinosus/gracilis. Tantalum markers were inserted at the time of surgery, 4 each into the femur and tibia, and 8 into the graft, at regular intervals along the length. Stress stereo radiographs (90N anterior and posterior draw forces) were taken at 1, 6, 12 and 24 weeks post-operatively. They were analysed using Medis RSA software. Results Initial results suggest that in addition to measuring total anteroposterior knee laxity, detailed analysis of the graft itself is possible. Beads placed in the bone blocks of the BPTB grafts, and in the intraosseous ends of the hamstrings, enable calculation of slippage of the fixation. The BPTB bone plugs moved 0.6 to 1.2mm by 12 weeks, the Hamstrings fixation was more variable. Beads placed in the intraarticular graft may enable measurement of any post-operative stretching, but are also somewhat erratic. Identification of the site of stretching – around the tunnel entrances, or intraarticularly, should be possible. Conclusions We believe that this detailed application of RSA in analysing the performance of the two commonly used grafts in ACL reconstruction has not been previously described. We hope to gain valuable insight into the behaviour of both graft types and reasons for graft failure. This presentation will demonstrate the methods developed and include the technical difficulties encountered in this on-going study

Aims: To assess the results of Anterior Cruciate Ligament (ACL) reconstruction at a minimum of two years follow-up, using the Rolimeter [AIRCAST, Europe] as an adjunct to routine knee examination and subjective scoring systems. Methods: The Warrington Knee Injury database was initiated in June 2001 and data from all knee ligament injuries has been collected prospectively, from preoperative status through to all follow up assessments. Inclusion criteria for our study were, all ACL reconstructions performed by the senior author with minimum 24 months follow up; other ligaments being intact and presence of a normal contralateral knee. 50 patients satisfied the inclusion criteria. There were 41 males and 9 females in ages ranging from 17 to 51 (mean 30.6 years), with no significant difference in age between sexes. Hamstring grafts were used in 29 knees and Bone-Patellar tendon – Bone (BPTB) grafts in 21. Knee laxity was measured using the Rolimeter with IKDC knee examination and functional assessments using the Lysholm, IKDC and KOOS scoring systems. Results: 20/21 of patients with BPTB grafts (95.2%) and 26/29 of patients with Hamstring grafts (89.7%) achieved normal or near normal knee laxity compared to their opposite knee. The Range of movement in 48 of 50 knees (96%) fell within normal or near normal limits according to IKDC description (Lack of extension < 3 degrees and lack of flexion < 10 degrees). Two patients with abnormal range of movement had a similar lack of movement preoperatively. Though none of the knees were abnormally tight (AP laxity difference < -3), there was a relationship between knee tightness and lack of extension, but this was not statistically significant. There was no association between age or sex of patient and lack of movement. The mean IKDC, Lysholm and KOOS symptom scores were 80.45, 87.3 and 81.3 respectively. Conclusions: We have achieved a normal or near normal AP laxity in 92% of our ACL reconstructions on assessment at 2 years postoperatively. We report no signifi-cant difference in outcome between use of Hamstring or BPTB grafts. The functional outcome has been optimal as revealed by subjective evaluation

Background. Surgical reconstruction of the anterior cruciate ligament is a common practice to treat the disability or chronic instability of the knee. Several factors associated with success or failure of the ACL reconstruction, including surgical technique and graft material and graft tension. We aimed to show how we can optimize the graft properties and achieve better post surgical outcomes during ACL reconstruction using 3-dimensional computational finite element simulation. Methods. In this paper, 3-dimensional model of the knee was constructed to investigate the effect of graft tensioning on the knee joint biomechanics. Four different grafts were compared: 1) bone-patellar tendon-bone graft (BPTB) 2) Hamstring tendon 3) BPTB and a band of gracilis 4) Hamstring and a band of gracilis. The initial graft tension was set as “0, 20, 40, or 60N”. The anterior loading was set to 134 N. Findings. Our study shows that the use of the discarded gracilis tendon, which usually excised after graft fixation, could be associated with a host of merits. Our results show that preserving this excess part of gracilis would decrease the required pretention load and, subsequently, could optimize biomechanical properties of the knee. Conclusion. Required pretension during surgery will have decreased significantly by adding a band of gracilis to the proper graft. Therefore, in addition to achieving normal stability of the knee, we can have lower risk of degradation

Anterior cruciate ligament (ACL) injuries are among the most common and debilitating knee injuries in professional athletes with an incidence in females up to eight-times higher than their male counterparts. ACL injuries can be career-threatening and are associated with increased risk of developing knee osteoarthritis in future life. The increased risk of ACL injury in females has been attributed to various anatomical, developmental, neuromuscular, and hormonal factors. Anatomical and hormonal factors have been identified and investigated as significant contributors including osseous anatomy, ligament laxity, and hamstring muscular recruitment. Postural stability and impact absorption are associated with the stabilizing effort and stress on the ACL during sport activity, increasing the risk of noncontact pivot injury. Female patients have smaller diameter hamstring autografts than males, which may predispose to increased risk of re-rupture following ACL reconstruction and to an increased risk of chondral and meniscal injuries. The addition of an extra-articular tenodesis can reduce the risk of failure; therefore, it should routinely be considered in young elite athletes. Prevention programs target key aspects of training including plyometrics, strengthening, balance, endurance and stability, and neuromuscular training, reducing the risk of ACL injuries in female athletes by up to 90%. Sex disparities in access to training facilities may also play an important role in the risk of ACL injuries between males and females. Similarly, football boots, pitches quality, and football size and weight should be considered and tailored around females’ characteristics. Finally, high levels of personal and sport-related stress have been shown to increase the risk of ACL injury which may be related to alterations in attention and coordination, together with increased muscular tension, and compromise the return to sport after ACL injury. Further investigations are still necessary to better understand and address the risk factors involved in ACL injuries in female athletes.

Cite this article: Bone Jt Open 2024;5(2):94–100.

No consensus exists regarding the optimal graft choice between allogenic and autologous graft. Incidence of septic arthritis following ACL reconstruction is rare but may dependent on the graft type. Our meta-analysis assesses the difference in incidence of septic arthritis after ACL reconstruction across three groups of grafts: hamstring autografts, bone patellar tendon bone (BPTB) autografts and allografts of any type. A literature search was performed without language restriction on PubMed and EMBASE databases. We identified 245 infected ACL grafts across 15 included studies that provided a breakdown of infection incidence by graft type. A meta-analysis was performed using a random-effects model to estimate the overall infection rates and those for different graft types. Summary risk ratios and 95% confidence intervals (CIs) were calculated and reported for each outcome. Publication bias with respect to infection rates was estimated using a funnel plot. Our meta-analysis shows an overall ACL graft infection rate of 0.6% (CI 0.3% – 1.3%). The incidence was highest in autologous hamstring grafts at 1.1% at (CI 0.8% – 1.6%). That of allografts and autologous BPTB grafts was similar at 0.5% (CI 0.2%–1.0%) and 0.4% (CI 0.2% – 0.7%), respectively. Full breakdown of the meta-analysis results by study and graft type is reported in Figure 1. Septic arthritis after ACL reconstruction remains a rare (<1%) but a serious complication. Allograft rates of infection were not higher than those the autografts, contrary to the theoretical concerns. Therefore a higher infection risk should not be cited as a reason for not using it. The reason for the apparently higher infection rate with hamstring autografts is unclear and requires further research. The results of our meta-analysis may aid informed discussions between surgeons and patients about the risk of infection after ACL reconstructive surgery and graft choice

Transverse pin femoral fixation of bone-patella tendon-bone (BPTB) in ACL reconstruction has been widely applied during the last decades. Aim of our study is to confront two different system of transverse femoral fixation for BPTB graft: Transfix BTB (Arthrex) and BioTransfix T3 (Arthrex). The main differences between these two system are the diameter (3.0 mm Transfix BTB and 3.5 mm BioTransfix T3), and section (Transfix BTB is cannulated). Surgical technique adopts the same transverse vectorial guide but different guide sleeves. 30 fresh-frozen porcine knees (mean age 2.2 years) were assigned to the two groups randomisedly. the patellar bone block and tendon were harvested using the same size in all specimens (10mm × 25 mm, 10 mm). Zwick-Roell z010 tension/compression device with bone clamps, was used for the study:. Cyclic test (1000 cycles, 0.5 Hz, 50–250 N/cycle, 100 cycles of preload). Final pull-out test (1 mm/s). Failure analysis. CT scan and densitometry. Any implant didn't fail during cyclic test. The elongation average was 1.85±0.63 for Transfix BTB and 1.69±0.87 for BioTransfix T3. Pull-out test showed very similar values in terms of Ultimate Strength Failure (USF), Stiffness at USF, and Stiffness:. The failure mode was bone plug fracture (12 for Transfix BTB and 13 for BioTransfix T3) and tendon failure (3 for Transfix BTB and 2 for BioTransfix T3). The post-test CT scan showed any failure of the fixation devices and the correct position inside the femoral half-tunnel. The mean bone density of porcine femora was comparable to young human femora (1.12±0.31 BMD). Both systems showed a similar behaviour in terms of USF, Stiffness, Cyclic load, method of failure and other biomechanical parameters. The reproducibility of surgical technique, the mechanical strength and endurance of the systems suggest two valid options for ACL reconstruction with BPTB even if in-vivo studies are necessary to confirm the animal ex-vivo biomechanical data

The results of an accelerated rehabilitation programme were collected retrospectively from 293 case notes between January 1995 and December 1998. Different grafts were used: bone patellar-tendon bone (BPTB) grafts, hamstrings grafts and allografts. The criteria used to evaluate the knees of these patients were based on patient satisfaction, clinical examination and Cybex evaluation. All 293 patients were followed up for six months or longer. Four to six months after the reconstruction procedure, 94.2% returned to sport activities. Anterior knee pain seemed not to be a problem when using autogenous BPTB grafts. The rehabilitation programme should decrease the postoperative morbidity

We compared the ability of three different posterior cruciate ligament (PCL) reconstructions to restore normal anteroposterior laxity to the knee from 0 to 130° of knee flexion. Cadaver knees were tested intact, after PCL rupture or after bone-patellar tendon-bone grafting. Grafts were performed isometrically or with a single bundle representing the anatomical anterior PCL fibre bulk (aPC) or with a double bundle that added the posterior PCL fibre bulk (pPC). The grafts were tensioned to restore normal knee laxity at 60° of flexion, except for the pPC which was tensioned at 130°. The isometric graft led to overconstraint as the knee extended resulting in high graft tension in extension and excess laxity in flexion. The aPC graft matched normal laxity from 0 to 60° of flexion but was lax from 90 to 130° of flexion. Only the double-bundled graft could restore normal knee laxity across the full range of flexion

We compared the strength of fixation of a biodegradable screw with that of two metal screws in a bone-patellar-tendon-bone (BPTB) graft in the bovine knee. We used 33 fresh BPTB specimens with a circular tibial bone plug of 9 mm in diameter which were anchored in a tibial metaphyseal bone tunnel with either an interference screw (n = 11), an AO cancellous screw (n = 11) or a fibrillated, self-reinforced biodegradable poly-L-lactide screw (n = 11). The mean force to failure (+/- SD) in the three groups was 1358 +/- 348 N, 1081 +/- 331 N and 1211 +/- 362 N, respectively. There was no significant difference in the groups with regard to the linear load or the elastic moduli of the fixation. We conclude that the biodegradable screw is as good as either of the two metal screws in the fixation of a BPTB graft in the bovine knee and can be recommended for ACL reconstruction using this type of graft

Graft fixation in anterior cruciate ligament reconstruction is a basic criterion for the outcome of the surgical procedure. Several solutions have been proposed; each of them had advantages and disadvantages, and the choice of a surgical technique often represents the surgeon’s opinion. The goal of the fixation is stability and incorporation of the graft in the bone tunnels. Bone-patellar tendon-bone graft has the advantage of bone to bone fixation, which is impossible using tendon grafts. Femoral fixation techniques for hamstrings can be classified as follows: compression techniques, expansion techniques and suspension techniques (cortical or cancellous). Top Traction System (TTS) is a new technique for femoral fixation using hamstrings. Here, a retrograde screw is fixed to the anterolateral cortex of the femur. A ring is fixed to the screw to pass the tendons.The screw is self-threading, 28 mm long and 6.5 mm in diagmeter; its pull-out strength is 1350 N. The screw is made from a titanium alloy and only available in one size. Surgical technique is simple and reproducible and the instruments are easy to use. The positioning of the screw is fully guided by instruments that minimise errors. With this fixation device further graft traction is possible after tibial fixation without twisting the hamstrings. Results are good at the short-term evalutation but a long-term follow-up is required before a final recommendation can be made

Purpose. Twelve case reports of distal femur fractures as post-operative complications after anterior cruciate ligament (ACL) reconstruction have been described in the literature. The femoral tunnel has been suggested as a potential stress riser for fracture formation. The recent increase in double bundle ACL reconstructions may compound this risk. This is the first biomechanical study to examine the stress riser effect of the femoral tunnel(s) after ACL reconstruction. The hypotheses tested in this study are that the femoral tunnel acts as a stress riser to fracture and that this effect increases with the size of the tunnel (8mm versus 10mm) and with the number of tunnels (one versus two). Method. Femoral tunnels simulating single bundle (SB) hamstring graft (8 mm), bone-patellar tendon-bone graft (10 mm), and double bundle (DB) ACL reconstruction (7mm, 6 mm) were drilled in fourth generation saw bones. These three experimental groups and a control group consisting of native saw bones without tunnels, were loaded to failure. Result. All fractures occurred through the tunnels in the double tunnel group whereas fractures did not consistently occur through the tunnels in the single tunnel groups. The mean fracture load was 6145 N 471 N in the native group, 5691 N 198 N in the 8 mm single tunnel group, 5702 N 282 N in the 10 mm single tunnel group, and 4744 N 418 N in the double tunnel group. The mean fracture load for the double tunnel group was significantly different when compared to native, 8 mm single bundle, and 10 mm single bundle groups independently (p value = 0.0016, 0.0060, and 0.0038 respectively). No other statistically significant differences were identified. Conclusion. An anatomically placed femoral tunnel in single bundle ACL reconstruction in our experimental model was not a stress riser to fracture, whereas the two femoral tunnels in double bundle ACL reconstruction significantly decreased load to failure. The results support the sparcity of reported peri-ACL reconstruction femur fractures in single femoral tunnel techniques. However, the increased fracture risk in double bundle ACL reconstruction is a cause for concern and may impact patient selection

Purpose: To evaluate knee proprioception following Anterior Cruciate Ligament (ACL) reconstruction using two different autografts. Materials and methods: Forty patients, (34 male, 6 female), aged between 17–54 years old (mean: 31), with complete ACL tears were subjected to ligamentous reconstruction. Group A (20 patients) underwent reconstruction with 4 strand hamstrings graft whilst in the remaining 20 patients (group B) bone-patellar tendon-bone graft was used. Proprioception was assessed by the Joint Position Sense (JPS) of the knee for predetermined angles (15°, 45° and 75°) as well as by the threshold to detection of passive movement (TTDPM) at 15° and 45° in flexion and extension using an isokinetic dynamometer (Con-Trex, MJ, Switzerland). The examination was performed pre-operatively and 3, 6 and 12 months after surgery, on both knees of all patients. The t-test was utilised for statistical analysis. Results: ACL deficient knees presented with significantly poor TTDPM values at a starting angle of 15° moving into flexion and extension. The JPS findings were statistically different between injured and uninjured knees (p< 0.05). The TTDPM at 15° and JPS findings of the injured leg, before and 6, 12 months after reconstructive surgery, were statistically different (p< 0.05) for both groups. There was no statistically significant difference for both JPS and TTDPM at 15° in flexion and extension between the findings in reconstructed and uninjured knees, at 6 and 12 months post-operatively in both groups. No difference was found when comparing proprioceptive improvement following ACL reconstruction between the two different autograft groups. Conclusions: Both JPS at 15°, 45°, and 75° and TTDPM at 15° in flexion and extension are impaired in ACL deficient knees. There is improvement of these proprioceptive parameters following operative reconstruction of the ACL using both hamstrings and patellar tendon grafts. No particular graft seems to be preferable in terms of proprioceptive improvement as assessed by JPS and TTDPM

Our aim was to analyse the effect of avascularity on the morphology and mechanical properties (tensile strength, viscoelasticity) of human bone-patellar-tendon-bone (BPTB) grafts in vitro. These were harvested at postmortem and stored submerged in denaturated human plasma at a constant pH, pO. 2. , pCO. 2. , temperature and humidity under sterile conditions. Mechanical testing was performed two and four weeks after removal of the graft. The mean ultimate strength was 1085.7 ± 255.8 N (control), 1009.0 ± 314.9 N (two weeks cultured) and 1076.8 ± 414.8 N (four weeks cultured). There was no significant difference in linear stiffness or deformation to failure between the groups. There was a difference in viscoelasticity between the control group and the avascular grafts and the latter had significant lower peak load-to-load ratios after 15 minutes compared with the control group. After two and four weeks the graft contained viable fibroblasts. There was regular cellularity in the superficial layers and decreased cellularity in the midportion. The structure of the collagen including the crimp pattern appeared to be normal in polarised light. We conclude that avascularity does not significantly affect ultimate failure loads or stiffness of BPTB grafts. Slight changes in viscoelasticity were induced, but the significance of the increased stress relaxation is not fully understood

Objective: This study challenges the assumption that pivot shift is abolished once anterior stability is restored in the ACL reconstructed knee. Method: The kinematics of 7 cadaver knees were studied with the Flock-of-Birds, as pivot shift was repeated in intact, ACL deficient, then ACL reconstructed specimens with grafts tensioned at 0, 10, 20, 40 and 60N. All were BPTB grafts in similar positions. Results: Pivot shift is described as a sudden reduction from internal rotation of 8.57 +/− 2.3° at knee flexion of 24.2 +/− 11°; achieved with iliotibial loading of 56.2 +/− 11.5N, 2.26 +/− 0.6Nm valgus load and 1.5 +/− 0.4Nm internal torque. Internal rotation was significantly reduced at 40N (3.2°, p< 0.005) and 60N (2.9°, p=0.001). At maximum tension, all specimens felt stable and pivoted less. This reduction of internal rotation averaged 62%; ranging from 42% (subtle pivot) to 100% (complete abolition). At 90° knee flexion external rotation was reduced with graft tension of 60N, but not significantly (p=0.03). The range of knee flexion during reduction of the pivot shift was not significantly altered. Conclusions: Tensions of grafts that restored anterior stability (40N & 60N) did not always abolish the pivot shift, but significantly reduced it. This may account for complaints of subtle instability despite surgical reconstruction. Grants: DTT Lie was supported by a grant from the Singapore National Medical Research Council