Comparison of screw post fixation and free bone block interference fixation for anterior cruciate ligament soft tissue grafts: biomechanical considerations

Six Percent Incidence of Graft-Tunnel Mismatch in Anatomic Anterior Cruciate Ligament Reconstruction Using Bone-Patella Tendon-Bone Autograft and Anteromedial Portal Drilling

Purpose

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.

Methods

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 (<15–20 mm of bone fixation).

Results

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 tunnel—4/5 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.

Conclusions

The incidence of graft-tunnel 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.

Clinical Relevance

The results of this study provide surgeons with a technique of limiting graft tunnel mismatch when performing ACLR using BPTB and anteromedial portal drilling.

Bone density may affect primary stability of anterior cruciate ligament reconstruction when organic core bone plug fixation technique used

Purpose

Core Bone Plug Fixation (CBPF) technique is an implant-less methodology for ACL reconstruction. This study investigates the effect of bone density on CBPF stability to identify the bone quality that is likely to benefit from this technique.

Methods

Artificial blocks with 160 (Group 1), 240 (Group 2), and 320 (Group 3) kg/m³ densities were used to simulate human bone with diverse qualities. These groups are representative of the elderly, middle age and young people, respectively. A tunnel was made in each test sample using a cannulated drill bit which enabled harvesting the core bone plug intact. Fresh animal tendon grafts were prepared and passed through the tunnel, so the core bone was pushed in to secure the tendon. The fixation stability was tested by applying a cyclic load following by a pullout load until the failure occurred. The selected group was compared with interference screw fixation technique as a gold standard method in ACL reconstruction.

Results

The Group 2 stiffness and yield strength were significantly larger than Group 1. The graft slippage of Group 1 was significantly less than Group 3. The ultimate strengths were 310 N and 363 N, in Groups 2 and 3, significantly larger than that of Group 1. The ultimate strength in fixation by interference screw was 693.18 N, significantly larger than the bone plug method.

Conclusions

The stability of CBPF was greatly affected by bone density. This technique is more suitable for young and middle-aged people. With further improvements, the CBPF might be an alternative ACL reconstruction technique for patients with good bone quality.

Clinical relevance

The CBPF technique offers an implant-less organic ACL reconstruction technique with numerous advantages and likely would speed up the healing process by using the patient’s own bones and tissues rather than any non-biologic fixations.

Transtibial Anterior Cruciate Ligament Reconstruction: Tips for a Successful Anatomic Reconstruction

Anterior cruciate ligament (ACL) reconstruction is one of the most commonly performed orthopaedic sports procedures. Two main techniques are used for accomplishing an ACL reconstruction: transtibial and anteromedial portal techniques. The transtibial technique has been criticized for its inability to create an anatomic femoral tunnel given the intrinsic constraint of the tibial tunnel during drilling. However, technical modifications of the transtibial technique can result in anatomic tunnel entrance positioning and a properly oriented graft. This Technical Note presents our technique for anatomic transtibial ACL reconstruction.

Cyclic testing of tibialis tendon allografts for anterior cruciate ligament reconstruction using suture-post versus spiked washer tibial fixation

BACKGROUND

The purpose of this study was to directly compare spiked washer and suture-post tibial-sided fixation techniques used for anterior cruciate ligament reconstruction by measuring anterior tibial translation during cyclic tests.

METHODS

Fresh-frozen human knees were tested using a robotic system that applied 250 cycles of anterior-posterior tibial force (134 N) at 30° flexion, while recording tibial translation. Ten intact knees were tested to collect baseline data for native specimens. A single knee was selected to test ligament reconstructions using doubled tibialis tendon allografts. All grafts were fixed proximally using an EndoButton™, and the tibial end of the graft was fixed with either a spiked washer or with a suture post placed at two different locations (near and distant) relative to the tibial tunnel.

FINDINGS

Mean first cycle translation for intact knees was 4.8 (sd 1.8) mm; means after reconstruction were 2.6 (sd 0.9) mm (spiked washer), 10.1 (sd 1.9) mm (suture post near), and 10.4 (sd 1.5) mm (suture post distant). Corresponding means for translation increase over 250 cycles were 0.3 (sd 0.2) mm, 3.6 (sd 1.3) mm, 7.2 mm (sd 0.9) mm, and 8.0 (sd 1.3) mm. All mean increases (first cycle and cyclic) after ACL reconstruction were significantly greater than those for the intact knees, and all means with a suture post were significantly greater than those with a spiked washer. There were no significant differences between mean translations for near and distant suture post locations.

INTERPRETATION

Use of suture post fixation for anterior cruciate ligament reconstruction is questioned since increases in anterior tibial translation could lead to excessive post-operative knee laxity and possibly early clinical failure.

Determination of patellar tendon length for anterior cruciate ligament reconstruction using an anteroposterior knee radiograph

Background/Objective

Graft-tunnel length mismatch is a common intraoperative technical problem for anterior cruciate ligament reconstruction (ACLR) using a bone-patellar tendon-bone graft (BPTB). The patella-to-condyle and the patella-to-notch distances are two measurements in an anteroposterior knee radiograph. The objective of this study was to evaluate the sensitivities, specificities and reliabilities of those 2 measurements for detecting patients who had a patellar tendon length exceeding 45 mm.

Methods

Preoperative plain radiographs of patients who underwent ACLR with a BPTB graft were evaluated independently by two orthopaedic surgeons 3 times each at 2-weekly intervals. The sensitivities and specificities of the two measurements for detecting patients who have a patellar tendon length exceeding 45 mm were calculated. The optimal cutoff point was estimated using Youden index, and the receiver operating characteristic (ROC) curve and area under the curve (AUC) were evaluated with a 95% CI. As for the inter- and intra-rater reliabilities, intraclass correlation coefficients (ICC) were determined.

Results

One hundred and twenty-seven patients with an average age of 29.5 years old were evaluated. The mean patellar tendon length was 41.3 ± 5.0 mm. Patients with a length more than 45 mm (20 patients, 16%) had significantly higher patella-to-condyle and patella-to-notch distances, and more frequent use of bone staples for distal graft fixation than patients with a length ≤ 45 mm. To detect patients with a patellar tendon length over 45 mm, the optimal cutoff point for the patella-to-condyle distance was set at 14.5 mm, which had a sensitivity of 80%, specificity of 71%, and AUC of 0.76. In the case of the patella-to-notch distance, the cutoff point of 5.5 mm had a sensitivity of 80%, specificity of 66%, and AUC of 0.73. The intra- and inter-rater reliabilities of the two measurements were excellent, with ICCs of over 0.90.

Conclusions

Preoperative measurements of the patella-to-condyle and the patella-to-notch distances in AP knee radiographs can be valuable tools, with good sensitivities and specificities, for the determination of the patellar tendon length when using a BPTB graft for an ACLR. They had an acceptable level of discrimination capability and excellent reliability.

The biomechanical effects of graft rotation on ACL reconstruction tunnel mismatch

PURPOSE

Bone block protrusion out of the tibial tunnel due to a relatively long graft is a common complication in anterior cruciate ligament surgical reconstruction with a patellar tendon. One possible solution is to shorten the patellar tendon graft already fixed in the femur by applying external rotation. This study aimed to evaluate the degree of shortening and biomechanical changes in porcine patellar grafts subjected to relatively higher degrees of rotation. Data obtained with rotations of 0°, 540°, 720°, and 900° were compared.

METHODS

Forty patellar porcine ligaments were subjected to biomechanical tests of degree of shortening, modulus of elasticity and maximum tension in the tendon before rupture. Tests were conducted using a universal mechanical testing machine and a computerized system for acquiring strength and deformation data.

RESULTS

Progressive shortening of the patellar ligament occurred with rotations of 0°, 540° and 720°. However, the degree of shortening showed no statistically significant difference as rotation increased from 720° to 900°. Decreased modulus of elasticity was observed compared with the graft rotation at 0° in all groups tested, but no statistically significant differences were observed among 540°, 720° and 900°. The maximum tension of the patellar tendon showed no change before rupture, regardless of the degree of rotation.

CONCLUSIONS

Rotating the patellar tendon is an efficient method for shortening a relatively long graft; however, more biomechanical studies are necessary to recommend this technique in clinical practice owing to the resulting decrease in graft stiffness that could compromise knee stability.

A biomechanical analysis of tibial ACL reconstruction with graft length mismatch

INTRODUCTION

The incidence of graft length mismatch (GLM) during anterior cruciate ligament (ACL) reconstruction is reported to be up to 13%, with a rate of 20% when using bone-patellar tendon-bone (BPTB) allografts. Multiple techniques have been described to accommodate for the longer BPTB graft. As no study has compared the biomechanical properties of these methods (with cyclic loading), we evaluated the strength of four different surgical techniques used to accommodate for GLM during ACL reconstruction.

METHODS

A total of 32 fresh-frozen bovine tibiae and patellar tendons were divided into four groups based on the method of tibial graft fixation: (1) sutures tied over a post, (2) bone staples, (3) screws and washers, and (4) soft-tissue conversion with interference screw. Biomechanical testing was performed comparing the tensile properties of graft fixation techniques under cyclic loading. Ability to withstand 1500 cycles of load, the maximum tensile strength at load-to-failure, and the mode-of-failure were evaluated.

RESULTS

Only group 4 had all grafts intact after 1500 loading cycles, while the other groups had one graft failure at 338 (group 1), 240 (group 2), and 309 (group 3) cycles. The highest mean load-to-failure was observed in group 3 at 762 ± 173 N, which was found to be significantly higher than the other groups. The mean loads to failure in groups 1-4 were 453 ± 86 N, 485 ± 246 N, 762 ± 173 N, and 458 ± 128 N.

CONCLUSION

While there are multiple viable techniques for fixation of a BPTB graft in the case of GLM, this study demonstrated that direct screw fixation offers the strongest construct.

Krackow locking stitch versus nonlocking premanufactured loop stitch for soft-tissue fixation: a biomechanical study

PURPOSE

The purpose of this study was to biomechanically compare the Krackow stitch, an established locking stitch, with a new nonlocking premanufactured stitch for soft-tissue fixation. We evaluated suture construct elongation under loading and load to failure to compare the 2 stitches.

METHODS

Twenty porcine Achilles tendons were randomly assigned to receive the locking Krackow stitch with No. 2 FiberWire or the nonlocking SpeedWhip stitch with No. 2 FiberLoop (Arthrex, Naples, FL). Each prepared tendon was mounted in a servohydraulic load frame, and the 2 free suture strands were knotted over the bar of the machine. Each tendon was pretensioned to 100 N to simulate the removal of slack, preloaded to 50 N to simulate tension applied clinically with suture tying over the post, and cyclically loaded at 200 mm/min to 200 N for 200 cycles. Total elongation of both suture strands was measured at each stage. Each tendon was loaded to failure.

RESULTS

During preloading, the SpeedWhip group elongated significantly more than the Krackow group (65.6 +/- 22.5 mm v 14.9 +/- 5.9 mm, P < .001). During cyclic loading, the SpeedWhip group also showed significantly higher elongation than the Krackow group (23.5 +/- 8.7 mm v 11 +/- 4.5 mm, P = .02). The load to failure for the Krackow and SpeedWhip groups was not significantly different (376.2 +/- 39.8 N and 337.3 +/- 103.8 N, respectively; P = .65). With load to failure, suture breakage at the knot occurred in every specimen without further pullout of the suture.

CONCLUSIONS

The nonlocking stitch applied in a manner consistent with manufacturer guidelines was significantly less secure than the locking Krackow stitch in a porcine Achilles tendon model.

CLINICAL RELEVANCE

On the basis of these findings, the Krackow stitch remains the preferred method for suture fixation of soft-tissue grafts.

Complications of anterior cruciate ligament reconstruction with bone-patellar tendon-bone constructs: care and prevention

Rupture of the anterior cruciate ligament is a common injury. Correct diagnosis and patient selection, along with proper surgical technique, with careful attention to anatomic graft placement, followed by attention to proper rehabilitation, leads to predictably good to excellent results. This article reviews the recognition and avoidance of complications associated with bone-patellar tendon-bone constructs of anterior cruciate ligament reconstruction.

Peripheral versus aperture fixation for anterior cruciate ligament reconstruction

Because both the young and aging population are showing increasing interest in sports participation, the number of sports related injuries and in particular anterior cruciate ligament (ACL) injuries have been increasing. Because of these injuries much time and energy has been focused on ACL reconstruction in order to return these individuals to their optimal level of participation in their sport. This article explores and reviews the concepts of ACL fixation location and how this affects the ultimate outcome of this reconstructive procedure.

Modified Prusik knot versus whipstitch technique for soft tissue fixation in anterior cruciate ligament reconstruction: a biomechanical analysis

Appropriate graft tension and secure graft incorporation in bone tunnels are essential for successful anterior cruciate ligament (ACL) reconstruction using hamstring tendon autografts. Permanent viscoplastic elongation in response to cyclic loading in the early postoperative period and the interposition of suture material in the tendon-bone interface might negatively affect graft function and rigid graft incorporation in the bone tunnels. A modified Prusik knot is an alternative option to the commonly used whipstitch technique for soft tissue fixation in ACL reconstruction. This is a controlled laboratory study. Sixteen formalin-fixed human cadaver semitendinosus tendons were armed with a modified Prusik knot or a whipstitch and tested in a load-to-failure test with a constant displacement rate of 1 mm/s, 14 in the cyclic loading test with 100 cycles from 10 to 50 N followed by 100 cycles from 10 to 75 N. The modified Prusik knot showed smaller force-induced displacements and higher stiffness of the entire construct in the load-to-failure test. Smaller preconditioning displacements were the only significant differences in the cyclic loading test. The modified Prusik knot has equal or superior mechanical properties and provides a larger area in the tendon-bone interface without suture material compared with the whipstitch technique.

A comparison of bone-patellar tendon-bone and bone-hamstring tendon-bone autografts for anterior cruciate ligament reconstruction

BACKGROUND

Most of the previous comparative studies between patellar tendon and hamstring tendon anterior cruciate ligament grafts compared grafts of different constructs fixed with different methods.

PURPOSE

To compare patellar tendon and hamstring tendon grafts with the same fixation method used to reconstruct the anterior cruciate ligament.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

During the reconstructive procedure, the hamstring tendon graft was prepared as a bone-hamstring-bone graft; both bone-patellar tendon-bone and bone-hamstring-bone grafts were fixed with interference screws. Eighty consecutive patients who underwent anterior cruciate ligament reconstruction were randomly assigned to either bone-patellar tendon-bone or bone-hamstring-bone groups. Follow-up examinations were performed for at least 5 years postoperatively. Seventy-two of the 80 patients (37 patients in the bone-patellar tendon-bone group and 35 in the bone-hamstring-bone group) were evaluated, with a mean follow-up period of 87.0 and 80.8 months, respectively. Follow-up examinations were performed using the International Knee Documentation Committee knee ligament standard and subjective knee forms.

RESULTS

The mean KT-1000 arthrometer evaluation results showed no significant difference between the bone-patellar tendon-bone and bone-hamstring-bone groups (1.2 +/- 2.1 mm and 1.7 +/- 1.4 mm, respectively; P = .24). However, symptoms related to graft harvest (anterior kneeling pain) were more frequently observed in the bone-patellar tendon-bone group, and unsatisfactory results were correlated with severe kneeling pain in 3 patients from this group (P = .0056). Significant hamstring muscle weakness without complaint of functional deficit was found in the bone-hamstring-bone group (P = .0045).

CONCLUSION

Bone-hamstring-bone grafts were shown to reduce the risk of problems at the graft harvest site compared to bone-patellar tendon-bone grafts, with comparable results in the remaining clinical parameters tested.

Histomorphology and microradiography of quadriceps tendon-patellar bone grafts in press-fit anterior cruciate ligament reconstruction

The press-fit fixation technique has become an alternative fixation method in anterior cruciate ligament (ACL) reconstruction. While the stability of press-fit fixated grafts reported in the literature predominantly had been analysed by biomechanical testing, this study investigated the specific histomorphologic and microradiographic features important for graft stability, using human quadriceps tendon-patellar bone (QTPB) grafts. Six QTPB grafts with cylindrical bone plugs were obtained from frozen fresh human cadaver knees and fixed to porcine, bovine, or human femora in a press-fit technique. The specimens were plastinated, dissected into 1.5 mm slices, studied microradiographically and stained for histologic evaluation. The specimens showed an osseous inclusion of the graft within the femoral tunnel, which was most evident on the cancellous side. Histologic analysis revealed a trabecular interdigitation with a penetration of patellar and femoral trabecular structures, contributing to primary stability of the press-fit fixation. Graft inclusion was most obvious in bovine and least in human femora, assumably because of varying bone quality. The circular bone-to-bone contact in press-fit fixation technique should contribute to both rapid and stable graft healing.

Effects of graft rotation on initial biomechanical failure characteristics of bone-patellar tendon-bone constructs

BACKGROUND

Graft-tunnel mismatch is a potential problem during single-incision technique for anterior cruciate ligament reconstruction with the central third of the patellar tendon. Mismatch is present when the graft is too long to fit appropriately in the tunnels that have been created. Graft rotation is one method for addressing this problem.

PURPOSE

To determine the results of graft rotation up to 540 degrees on initial graft biomechanical properties and graft length.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty porcine bone-patellar tendon-bone constructs were divided into four groups and constructs were rotated to 0 degrees, 90 degrees, 180 degrees, and 540 degrees, respectively, for each group. Biomechanical testing to failure was performed with the constructs under tension at an elongation rate of 5 cm/sec. Lengths were measured after a 1-kg load was applied to the grafts.

RESULTS

No statistical difference in ultimate failure strength was encountered between any of the groups (P = 0.915). The grafts that were twisted to 540 degrees shortened an average of 5.41 mm, which represented an average shortening of 10% of the initial tendon length.

CLINICAL RELEVANCE

Graft rotation up to 540 degrees does not result in loss of initial graft strength, and may be a solution for graft-tunnel mismatch.

Metal vs bioabsorbable interference screws: initial fixation

Interference screws are used for graft fixation in anterior cruciate ligament reconstruction. There is current debate as to whether metal or bioabsorbable varieties provide the optimal results. This paper provides a critique of the single load-to-failure uniaxial tensile test data available in the literature, which provide the initial postoperative characteristics. Both metal and bioabsorbable screws were found to give similar levels of pull-out force and stiffness when used on similar types of graft material. Screws with bone-patellar tendon-bone grafts provided the greatest values, exceeding the forces transmitted through the native anterior cruciate ligament during normal daily activities. Hamstring grafts provided lower values, only being comparable with the forces of daily living. Consequently, this raises the question as to whether the rehabilitation regime of the hamstring patient must not be aggressive in the early postoperative stages when using either metal or bioabsorbable screws. This would ensure that the graft will not fail in the initial postoperative period before biological fixation occurs, which will then boost the strength to an acceptable level.

Endoscopic anterior cruciate ligament reconstruction with patella tendon autograft

The patella tendon is the most commonly used graft source for ACL reconstruction because of its biomechanical strength and stiffness, the availability of bone-to-bone healing on either end, and the ability to firmly secure the graft within the tunnels. Consistently good results have been reported in the literature, with expectations to return to all activities at pre-injury levels of performance. We outline our technique for endoscopic ACL reconstruction using a patella tendon autograft. The technique is divided into the critical stages of pre-operative assessment, graft harvest, notch preparation, tunnel placement, graft passage, graft fixation, and rehabilitation. Methods for avoiding pitfalls and overcoming mishaps are described.

Bone-patellar tendon-bone grafts for anterior cruciate ligament reconstruction: an in vitro comparison of mechanical behavior under failure tensile loading and cyclic submaximal tensile loading

BACKGROUND

Secure fixation is an important factor in the success of anterior cruciate ligament reconstruction.

HYPOTHESIS

There is no difference in the mechanical behavior of reconstructions from method of fixation or method of testing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Anterior cruciate ligament reconstructions were performed with bone-patellar tendon-bone grafts in 48 human cadaveric knees. Three different fixation methods (Endobutton, interference screw, suture-post fixation) were compared under failure tensile loading and cyclic submaximal tensile loading.

RESULTS

No difference was observed in ultimate load among the three techniques. Stiffness of the grafts was significantly lower for the suture technique than for the interference screw technique. Cyclic loading revealed significantly different failure rates: 0% of the Endobutton, 38% of the interference screw, and 100% of the suture-post groups. The relative movement of the femoral bone plug and the migration of the bone plug out of the femoral canal were lowest in the interference screw group.

CONCLUSIONS

The suture-post fixation is not recommended. The interference screw technique showed the best results, but results were age-dependent, suggesting its best use is in younger patients. The Endobutton technique is recommended for older patients.

CLINICAL RELEVANCE

Results of testing are useful to the surgeon in making a choice of reconstruction technique.

Primary stability with tibial press-fit fixation of patellar ligament graft: An experimental study in ovine knees

PURPOSE

To investigate the initial fixation strength and to assess the value of tibial press-fit fixation of the bone-tendon-bone graft in anterior cruciate ligament reconstruction.

TYPE OF STUDY

Nonrandomized control trial.

METHODS

For tibial press-fit fixation, the tibial bone block of the bone-tendon-bone graft is countersunk in a bony groove at the distal tunnel outlet and fixed over a bone bridge with 2 No. 6 Ethibond sutures. The bone cylinder harvested from the tibial tunnel using an oscillating hollow saw is plugged into the tibial tunnel parallel to the graft, thus providing for additional anchoring of the graft by tibial press-fit fixation. In a comparative experimental study in 46 ovine knees, this fixation method was assessed for its value in anterior cruciate ligament reconstruction. A tibial bone tunnel was placed in routine manner in each ovine tibia using a target drill unit and an oscillating hollow saw. The complete patellar ligament, proximally attached to the patella and distally to a cylindrical bone block (20 x 8.4 mm), served as graft. Tibial fixation in group A (n = 10) was done using a titanium interference screw (20 x 8 mm), in group B (n = 10) using a titanium staple, in group C (n = 12) using suture fixation over a bone bridge, and in group D (n = 14) using the press-fit fixation described above. In a materials testing machine, all specimens were subjected to continuously increasing load until failure at a velocity of 1 mm/second. Ultimate failure load, stiffness, stress-strain characteristics, and failure mode were evaluated.

RESULTS

Ultimate load to failure was 572 N (range, 473 to 680 N) in group A, corresponding to a fixation stiffness of 17.68 N/mm. For group B, ultimate load to failure was 608.4 N (range, 511 to 727 N) and stiffness of 19.92 N/mm. Bone block dislocation was the failure mode in groups A and B. Group C with exclusive suture fixation showed an ultimate load to failure of 304.5 N (range, 120 to 327 N) and a stiffness of only 6.96 N/mm. The mode of failure was suture cutout caused by the bone block in 9 of the cases and untying of the suture knot in 3 cases. Group D with press-fit fixation showed a significantly higher primary stability of 758 N (range, 513 to 993 N) relative to group C, with a corresponding stiffness of 25.12 N/mm (P <.02). In this group, the mode of failure was ligamentous rupture from the bone block. Regarding mechanical properties, no significant differences were seen between groups A, B, and D.

CONCLUSIONS

Tibial press-fit fixation allows for metal-free fixation with high primary stability. By refilling the bone tunnel, the ligament (with a rather small cross-sectional diameter compared with hamstrings) is safely fixed within the bone tunnel to prevent potential postoperative tunnel enlargement due to movement of the graft within the tunnel. Anchoring the graft at the entrance into the joint, it provides for reduced graft length and adequate elasticity and accomplishes the requirements of fixation at the correct anatomic insertion site.

Cyclic pull-out strength of hamstring tendon graft fixation with soft tissue interference screws. Influence of screw length

Blunt-threaded interference screws used for fixation of hamstring tendons in anterior cruciate ligament reconstructions provide aperture fixation and may provide a biomechanically more stable graft than a graft fixed further from the articular surface. It is unknown if soft tissue fixation strength using interference screws is affected by screw length. We compared the cyclic and time-zero pull-out forces of 7 x 25 mm and 7 x 40 mm blunt-threaded metal interference screws for hamstring graft tibial fixation in eight paired human cadaveric specimens. A four-stranded autologous hamstring tendon graft was secured by a blunt-threaded interference screw into a proximal tibial tunnel with a diameter corresponding to the graft width. Eight grafts were secured with a 25-mm length screw while the other eight paired grafts were secured with a 40-mm length screw. During cyclic testing, slippage of the graft occurred as the force of pull became greater with each cycle until the graft-screw complex ultimately failed. All grafts failed at the fixation site, with the tendon being pulled past the screw. There were no measurable differences in the mean cyclic failure strength, pull-out strength, or stiffness between the two sizes of screws. Although use of the longer screw would make removal technically easier should revision surgery be necessary, it did not provide stronger fixation strength than the shorter, standard screw as had been postulated.

A technique for resolution of graft-tunnel length mismatch in central third bone-patellar tendon-bone anterior cruciate ligament reconstruction

The existence of graft-tunnel length mismatch in correctly reconstructed anterior cruciate ligament (ACL)-deficient patients can occur due to both anatomic variation and compromised tunnel placement encountered during revision, despite attempts at prevention with accurate measurement techniques. This study reports a method for resolution of graft-tunnel length mismatch during central third bone-patellar tendon-bone ACL reconstruction. The technique involves rotation of the graft to shorten its length. Variation in graft shortening occurs depending on the direction of rotation, with external rotation achieving greater shortening. At 630 degrees of external rotation, approximately 25% shortening of the collagenous portion of the graft can be achieved, which allows for adequate bitunnel interference fixation in most instances. This technique can be used during difficult ACL reconstructions, both primary and revision, and may also have uses in routine reconstructions. Early clinical results are presented.

Current trends in anterior cruciate ligament reconstruction. Part 1: Biology and biomechanics of reconstruction

With today's increasing emphasis on sporting activities, the incidence of anterior cruciate ligament injuries has also increased. Epidemiologic studies estimate that the prevalence of anterior cruciate ligament injuries is about 1 per 3000 Americans. Management of these injuries has evolved from nonoperative treatment to extracapsular augmentation and primary ligament repair to anterior cruciate ligament reconstruction. Treatment of these injuries has significantly improved over the last few decades with the application of knowledge gained from both basic science and clinical research. This article is composed of two parts. The first part reviews the biology and biomechanics of the injured anterior cruciate ligament and the basic science of reconstruction. In the second part, to be published later, current operative concepts of reconstruction, as well as clinical correlations, are reviewed. Summarizing the latest information on basic scientific as well as clinical studies regarding the anterior cruciate ligament, this article intends to demonstrate the correlation between the application of basic science knowledge and improvement of clinical outcomes.

Initial fixation strength of modified patellar tendon grafts for anatomic fixation in anterior cruciate ligament reconstruction

Recently it has been shown that anatomic tibial graft fixation in anterior cruciate ligament (ACL) reconstruction is preferable in order to increase isometry and knee stability. To facilitate anatomic patellar tendon graft fixation, customized graft length shortening is necessary. The purpose of this study was to compare the initial fixation strength of four different shortened patellar tendon grafts including three bone plug flip techniques and direct patellar tendon-to-bone interference fit fixation in a model with standardized bone density. Ninety calf tibial plateaus (22 to 24 weeks old) with adjacent patella and extensor ligaments were used. Tendon grafts were shortened by flipping the bone plug over the tendon leaving a tendon-tendon-bone (TTB) construct and, as the first modification in the opposite direction resulting in a tendon-bone-tendon (TBT) construct. The second modification consisted of the TBT construct with interference screw position at the lateral aspect of the bone plug (TBTlat). As the fourth modification the tendon graft was directly fixed (Tdirect) with an interference screw. In addition, a round-threaded titanium (RCI; Smith & Nephew DonJoy, Carlsbad, CA), a round-threaded biodegradable screw (Sysorb; Sulzer Orthopedics, Münsingen, Switzerland), and a conventional titanium interference screw (Arthrex Inc, Naples, FL) were compared. We found that TTB (mean 441 N for biodegradable screw, 357 N for RCI screw, 384 N for conventional screw) and TBT (mean 407 N for biodegradable screw, 204 N for RCI screw, 392 N for conventional screw) construct fixation achieves comparable fixation strength, although failure in the TTB was due to tendon strip off at its ligamentous insertion. The highest failure load was found in TBTlat fixation (mean 610 N for biodegradable screw, 479 N for RCI screw). Therefore, this technique should be recommended when using a tendon flip technique. The failure load for Tdirect fixation (mean 437 N for biodegradable screw, 364 N for RCI screw) was similar to that of TTB and TBT fixation, which may indicate that a patellar-tendon graft harvested without its patellar bone plug and directly fixed with an interference screw is equivalent to a flipped graft. This may additionally reduce harvest site morbidity and eliminates the risk of patellar fracture. The fixation strength of round-threaded biodegradable and conventional titanium interference screws was similar, whereas that of round-threaded titanium screws was significantly lower in the patellar tendon flip-techniques. However, it should be taken into consideration that round-threaded titanium screws are proposed for direct tendon-to-bone fixation.

Bone graft fixation in anterior cruciate ligament reconstruction evaluated by radiostereometric analysis

For most anterior cruciate ligament reconstruction techniques, the tensile strength of the ligament substitutes and the surgical methods of fixation have been examined. In the present study seven consecutive patients with a chronic anterior cruciate ligament deficiency, who were reconstructed with a bone-patellar tendon-bone graft, were followed. The migration of the bone blocks was examined with radiostereometric analysis immediately postoperatively and after 3 and 12 months. The median migration of the bone blocks in the femur was 0.4 mm and in the tibia 0.4 mm. Clinical examination was undertaken preoperatively and one year postoperatively. We conclude that the use of interference screws seems to be a reliable method for fixation in anterior cruciate reconstruction and that healing of the bone blocks occurs during the first three postoperative months.