The effect of screw length and position on fixation of four-stranded hamstring grafts for anterior cruciate ligament reconstruction

The tibial tunnel drilling angles of 60° provided a lower ultimate load to failure on a single bundle posterior cruciate ligament graft using interference screw fixation compared to 30°/45°

PURPOSE

To biomechanically compare the initial fixation strength of grafts among three tibial tunnel angles (30°/45°/60°) in transtibial posterior cruciate ligament (PCL) reconstruction.

METHODS

A series of transtibial PCL reconstruction models were established with porcine tibias and bovine tendons. Specimens were randomly assigned to three groups according to the angles between the tibial tunnel and the perpendicular line of the tibial shaft: Group A (30°, n = 12), Group B (45°, n = 12), and Group C (60°, n = 12). The area of the tunnel entrance, the segmental bone mineral density (sBMD) of the graft fixation site of the tibia and the maximum insertion torque of the interference screw were measured. Finally, load to failure tests were carried out on the graft-screw-tibia constructs at the same rate.

RESULTS

Ultimate load to failure in Group C (335.2 ± 107.5 N) was significantly lower than that in Group A (584.1 ± 127.9 N, P < 0.01) and Group B (521.9 ± 95.9 N, P < 0.01). There were no significant differences between biomechanical properties of Groups A and B (n.s.). The posterior part fractures of the tibial tunnel exit occurred in eight specimens of Group C. In addition, the ultimate load was proven to be related to insertion torque (rho = 0.7, P < 0.01), sBMD (rho = 0.7, P < 0.01), and the area of the tunnel entrance (rho =- 0.4, P = 0.01).

CONCLUSION

The ultimate load to failure was significantly lower in tibial PCL interference screw fixation for tunnels drilled at 60° compared to 30°/45°. In addition, the ultimate load was significantly correlated with insertion torque, sBMD and the area of the tunnel entrance. Given that the load to failure of distal fixation may not be sufficient for early postoperative rehabilitation, a 60° tunnel should not be recommended to drill in tibia during PCL reconstruction.

How safe are partial squats after the anterior cruciate ligament reconstruction? A finite element analysis

BACKGROUND

Partial squats are a part of many rehabilitation programs. Progress to deeper squats can only be performed through the partial squat position. However, squats safety, onset time, and rational depth are still controversial. Most previous studies have not considered the influence of posterior tibial slope (PTS) and anterolateral ligament (ALL) on the stress on the knee anatomical elements in partial squats.

METHODS

We have created the new comprehensive knee computer models, which considered muscle exertions while weight bearing 75, 100, 125, and 150 kg in partial squats, included the ALL, two variants of PTS (5° and 13.9°), and two variants of anterior cruciate ligament (ACL) (a native 6 mm double-bundle ACL and an 8 mm single-bundle ACL graft). Using the finite element analysis, we have analyzed stresses in 14 anatomical elements in each model in partial squats (55° knee flexion and 10° anterior tibia tilt).

RESULTS

PTS change from 5° to 13.9° in a partial squat increases stress 1.2-1.3 times on the native ACL and 1.3-1.4 times on the ALL. In the case of single-bundle ACL reconstruction, PTS growth from 5° to 13.9° results in stress increasing 1.2-1.3 times on the graft and 1.3-1.4 times on the ALL. Thus, increased PTS is a significant risk factor, especially in the early postoperative period. Weight-bearing predictably increases stress on the ACL, ALL, and other joint elements proportional to the weight growth. Patients with thinner grafts after the ACL reconstruction may already reach the risk level for graft rupture in a single load in partial squatting if they weigh 125 kg or more. The risk rises with increasing PTS angle or the patient's weight. Because of the reduction of the graft strength by six weeks after surgery by 27%, partial squats in six weeks are associated with forces that may exceed the maximal ACL load even in patients with 75 kg of weight without additional load.

CONCLUSION

In the early postoperative period, partial squats can put the ACL graft at risk of failure. This risk is proportional to the patient's weight and PTS angle, and inversely proportional to the graft thickness. The choice of physical therapy strategies after ACL reconstruction, exercises, and their initiation timing is complex and cannot be standardized for all patients. Factors like the thickness of the graft, the method of fixation, the patient's weight, the ALL insufficiency, the PTS angle, and the patient's goals in the short and long term should be considered when planning the rehabilitation program.

In Vitro Investigation of the Fixation Performance of a Bioabsorbable Magnesium ACL Interference Screw Compared to a Conventional Interference Screw

An anterior cruciate ligament (ACL) reconstruction is a common treatment for patients with ACL rupture that aims to regain pre-injury knee stability and kinematics. During the ACL reconstruction, one method to fix the graft is the use of an interference screw (IS). The IS should provide initial stability and secure the graft during the healing period. In recent years, magnesium has emerged as an alternative material to permanent metal and polymer ISs. In addition, differences in designs, such as the shape of the IS, can influence the fixation performance of the IS. Therefore, in this biomechanical experiment, two different screw designs with two ligament materials were compared in an insertion and a pull-out test at a rate of 1 mm/s. The screw designs were a conventional polymer screw and a magnesium screw. Porcine tendon and nylon rope were used as ligament materials. All tests were performed in polyurethane foam blocks with 15 PCF density (Synbone AG, Switzerland). As a result, both screw designs required an insertion torque of less than 3 Nm. There was a significant difference between the porcine and nylon rope in pull-out tests for each screw design. The magnesium screw had the highest pull-out force at 412.14 ± 50.00 N for porcine tendon and 707.38 ± 21.81 N for nylon rope. There were no significant differences in tunnel widening (narrow-wide ratio) between each ligament material. The magnesium screw showed the lowest narrow-wide tunnel ratio, implying a better ability to compress the graft to the tunnel. In conclusion, a more optimized magnesium IS design resulted in better graft fixation and an improved ACL reconstruction outcome.

Surgically adjust tibial tunnel in anatomical anterior cruciate ligament single-bundle reconstruction: A time-zero biomechanical study in vitro

BACKGROUND

The anatomical positioning of the graft during anterior cruciate ligament reconstruction (ACLR) is of great significance for restoring normal knee kinematics and preventing early joint degeneration. Therefore, the adjustment of the mispositioned guide pin becomes extremely important. Our research aims to test the time-zero biomechanical properties in adjusting inaccurate guide pins to the center of the tibial footprint in anatomical anterior cruciate ligament single-bundle reconstruction.

METHODS

Porcine tibias and bovine extensor tendons were used to simulate a transtibial ACL reconstruction in vitro. Load-to failure testing was carried out in 4 groups: control group (n = 45): the guide pin was drilled at the center of the ACL footprint; group I, group II and group III (n = 45, respectively): the guide pin was respectively drilled 1 mm, 2 mm and 3 mm away from the center of the ACL footprint. In the experimental groups, a small tunnel with a 4.5 mm reamer is made and the guide pin is shifted to the center of the footprint. All the reamed tibias were scanned by CT to measure the area of the tunnel in the footprint, and time-zero biomechanical properties were recorded.

RESULTS

All graft-tibia complexes failed because the grafts slipped past the interference screws. Compare to control group, the ultimate load, yield load, and tunnel exit area in group III decreased significantly (p < 0.05). Regarding to the ultimate load, yield load, tensile stiffness, twisting force and tunnel exit area, t-test showed no significant differences between control group and group I, group II respectively (p > 0.05). Pearson test showed that tunnel exit area was negatively correlated with other characteristics (p < 0.05).

CONCLUSIONS

Surgical adjustment of the guide pin to the center of the tibial footprint may have significant influence in time-zero biomechanical properties in anatomical anterior cruciate ligament single-bundle reconstruction when the adjusted tibial tunnel was significantly enlarged compare to the standard tibial tunnel.

The Proximal Tibia Loses Bone Mineral Density After Anterior Cruciate Ligament Injury: Measurement Technique and Validation of a Quantitative Computed Tomography Method

Purpose

Results

Conclusions

Level of Evidence

[The killer turn in the posterior cruciate ligament reconstruction: mechanism and improvement]

OBJECTIVE

To summarize the research progress of killer turn in posterior cruciate ligament (PCL) reconstruction.

METHODS

The literature related to the killer turn in PCL reconstruction in recent years was searched and summarized.

RESULTS

The recent studies show that the killer turn is considered to be the most critical cause of graft relaxation after PCL reconstruction. In clinic, this effect can be reduced by changing the fixation mode of bone tunnel, changing the orientation of bone tunnel, squeezing screw fixation, retaining the remnant, and grinding the bone at the exit of bone tunnel. But there is still a lack of long-term follow-up.

CONCLUSION

There are still a lot of controversies on the improved strategies of the killer turn. More detailed basic researches focusing on biomechanics to further explore the mechanism of the reconstructed graft abrasion are needed.

Redesigning Metal Interference Screws Can Improve Ease of Insertion While Maintaining Fixation of Soft-Tissue Anterior Cruciate Ligament Reconstruction Grafts

Purpose

To compare the fixation strength and loads on insertion of a titanium alloy interference screw with a modified tip against a conventional titanium interference screw.

Methods

Slippage of bovine digital extensor tendons (as substitutes for human tendon grafts) under cyclic loading and interference fixation strength under a pullout test were recorded in 10 cadaveric knees, with 2 tunnels drilled in each femur and tibia to provide pair-wise comparisons between the modified-tip screw (MS) and conventional screw (CS). To analyze screw insertion, 10 surgeons blindly inserted pairs of the MS and CS into bone-substitute blocks (with polyester shoelaces as graft substitutes), with insertion loads measured using a force/torque sensor.

Results

No differences were found between the MS and CS either in graft slippage from the femur (P = .661) or tibia (P = .950) or in ultimate load to failure from the femur (P = .952) or tibia (P = .126). On insertion, the MS required less axial force application (78 ± 38 N, P = .001) and fewer attempted turns (2 ± 1, P < .001) to engage with the bone tunnel than the CS (99 ± 43 N and 4 ± 4, respectively). In 90% of the paired insertion tests, the screw identified by the surgeon as being easier to initially insert was the MS.

Conclusions

The MS was found to be easier to engage with the bone tunnel and initially insert than the CS while still achieving similar immediate postsurgical fixation strength.

Clinical Relevance

The study shows that screw designs can be improved to ease insertion into a bone tunnel, which should reduce any likelihood of ligament reconstruction graft damage.

Significant Loss of ACL Graft Force With Tibial-Sided Soft Tissue Interference Screw Fixation Over 24 Hours: A Biomechanical Study

Background

Tibial-sided graft fixation is thought to be critical for the success of anterior cruciate ligament (ACL) reconstruction. Nevertheless, little is known about the graft force after fixation during the first 24 hours after surgery or the influence of screw diameter and length during this time.

Purpose

To investigate the force, over the course of 24 hours, in soft tissue grafts secured with a tibial interference screw and to evaluate the effect of different screw diameters (7, 8, and 9 mm) and lengths (25 and 30 mm) on the force in these grafts.

Study Design

Controlled laboratory study.

Methods

Quadruple-strand flexor tendon grafts were fixed with bioabsorbable interference screws in 60 porcine tibiae. Grafts were pretensioned at 80 N over 10 minutes, and screws were inserted outside-in while a preload force of 80 N was applied. Different screw lengths (25 and 30 mm) and diameters (7, 8, and 9 mm), resulting in 6 groups with 10 specimens each, were tested. After release of the preload, graft force was recorded over 24 hours.

Results

A significant decrease in graft force progressed in all groups over the 24-hour period. In total, a median loss of 75 N (IQR, 68-79 N) compared with the initial loading force was observed. Compared with the loading force of 80 N, this corresponded to a median loss of 91%. No significant differences in the remaining graft force could be found among the 6 different screw length and diameter groups after 10 minutes, 100 minutes, or 24 hours.

Conclusion

Graft force in soft tissue grafts secured with a tibial interference screw decreased substantially over the first 24 hours after fixation. Neither the screw diameter nor the screw length affected the decrease in graft force. This raises substantial questions regarding the remaining fixation strength in vivo.

Clinical Relevance

It should not be expected that ACL reconstruction can mechanically restabilize an injured knee as would an intact ACL. Reconstructed knees should be protected from mechanical overload in the early postoperative period.

Proximal, Distal, and Combined Fixation Within the Tibial Tunnel in Transtibial Posterior Cruciate Ligament Reconstruction: A Time-Zero Biomechanical Study In Vitro

PURPOSE

To compare the time-zero biomechanical properties of 3 graft fixation techniques (proximal, distal, and combined fixation) within the tibial tunnel in transtibial posterior cruciate ligament (PCL) reconstruction.

METHODS

Porcine tibias and bovine extensor tendons were used to simulate a transtibial PCL reconstruction in vitro. Load-to-failure testing was carried out in 3 groups: distal fixation alone (group I, n = 10), proximal fixation alone (group II, n = 10), and combined fixation (group III, n = 10). The load-elongation curve, tensile stiffness (in newtons per millimeter), ultimate load (in newtons), yield load (in newtons), energy absorbed to failure (in joules), and failure mode were recorded.

RESULTS

All graft-tibia complexes failed because the grafts slipped past the interference screws. The tensile stiffness, yield load, and energy absorption in group I were significantly lower than those in group II and group III (tensile stiffness, 19.25 ± 9.68 N/mm in group I vs 34.92 ± 16.48 N/mm in group II [P = .016] and 32.31 ± 13.79 N/mm in group III [P = .041]; yield load, 265.36 ± 144.52 N in group I vs 398.23 ± 57.04 N in group II [P = .006] and 424.94 ± 74.00 N in group III [P = .001]; and energy absorption, 5.16 ± 2.35 J in group I vs 19.95 ± 3.48 J in group II [P < .001] and 21.09 ± 4.29 J in group III [P < .001]). No statistically significant differences in biomechanical properties were found between group II and group III (P > .05).

CONCLUSIONS

Compared with distal fixation in transtibial PCL reconstruction, proximal fixation and combined fixation showed superior time-zero biomechanical properties.

CLINICAL RELEVANCE

Proximal fixation and combined fixation produced superior biomechanical properties to distal fixation in transtibial PCL reconstruction.

Posterior laxity increases over time after PCL reconstruction

PURPOSE

Restoration of posterior tibial translation (PTT) after reconstruction of the posterior cruciate ligament (PCL) is deemed necessary to restore physiological knee kinematics. However, current surgical techniques have failed to show a complete reduction of posterior laxity. It was hypothesized that early postoperative PTT increases over time.

METHODS

The study comprised of 46 patients (10 female, 36 male; 30 ± 9 years), who underwent PCL reconstruction in a single-surgeon series. Patients were evaluated by bilateral stress radiographs in a prospective manner preoperatively; at 3, 6, 12 and 24 months; and at a final follow-up (FFU) of at least 5 years. Covariants included age, gender, BMI, tibial slope (TS) and the number of operated ligaments. Two blinded observers reviewed all radiographs, evaluating the TS and the posterior tibial translation.

RESULTS

All patients were evaluated at a mean final follow-up of 102 (range 65-187) months. Mean side-to-side difference of the PTT significantly improved from preoperative to 3-month postoperative values (10.9 ± 3.1 vs. 3.6 ± 3.8 mm; P < 0.0001). The PTT increased to 4.6 ± 3.7 mm at 6 months, to 4.8 ± 3.3 mm at 12 months, to 4.8 ± 3.2 mm at 24 months, to 5.4 ± 3.4 mm at FFU. Consequently, there was a significant increase of PTT between 3-month and final follow-up (3.6 ± 3.8 vs. 5.4 ± 3.4 mm; P = 0.02). Flattening of the TS resulted in a significantly higher PTT compared to subjects with a high TS at 24 months and FFU. There was no significant influence by BMI, age, gender and the number of operated ligaments.

CONCLUSIONS

Early results after PCL reconstruction seem promising as posterior tibial translation is significantly improved. However, there is a significant increase in PTT from early postoperative values to the final follow-up of at least 5 years. This is particularly notable in patients with flattening of the TS. As a consequence, surgeons and patients need to be aware that initial posterior stability should not be equated with the final outcome.

LEVEL OF EVIDENCE

Cohort study, Level III.

Evaluation of the theoretical optimal angle of the tibial tunnel in transtibial anatomic posterior cruciate ligament reconstruction by computed tomography

Background

“Killer turn” effect is a critical explanation for the recurrent posterior laxity following transtibial posterior cruciate ligament (PCL) reconstruction, which affected by the angle of the tibial tunnel. Meanwhile, excessive tunnel angle would have an adverse impact on the healing of tendon to bone. The purpose was to evaluate the theoretical optimal angle of the tibial tunnel in transtibial anatomic PCL reconstruction.

Methods

The measurements were performed on CT sagittal plane, including the thickness of cancellous bone (L1), the theoretical optimal angle of the tibial tunnel (TOA, which was measured between tibial plateau and the extension cord connecting the center of PCL insertion site with a point 5 mm superior from marrow cavity vertex), L2 - the distance from anterior tunnel aperture to anterior end of tibial plateau, L3 - the distance from anterior tunnel aperture to tibial tuberosity (lowest edge of patellar ligament attachment).

Results

The value of TOA and L3 were 35.4 ± 7.9 ° and 26.8 ± 11.4 mm, respectively. L1 and L2 were higher in males than females (L1, P = 0.002; L2, P = 0.046). Regarding age, L1, TOA, L2 and L3 were higher in the 46–60 years group than 31–45 years group (P = 0.02, P = 0.001, P = 0.038, P = 0.032, respectively). With regard to height, L1 was lower in group I - < 1.66 m than group II - 1.66 to 1.75 m and group III - > 1.75 m (I v II, P = 0.015, I v III, P = 0.026). L2 was also lower in group I than group II and group III (I v II, P = 0.026, I v III, P = 0.006). TOA and L3 showed no significant differences among sex and height groups (P > 0.05).

Conclusions

TOA (35.4 ° ± 7.9 °) and L3 (26.8 ± 11.4 mm) could be used as a reference for ideal tibial tunnel placement in transtibial anatomic PCL reconstruction, so as to prevent recurrent PCL laxity and ensure good graft healing. However, further clinical validation is needed.

Biocompatibility and enhanced osteogenic differentiation of human mesenchymal stem cells in response to surface engineered poly(D,L-lactic-co-glycolic acid) microparticles

Tissue engineering strategies can be applied to enhancing osseous integration of soft tissue grafts during ligament reconstruction. Ligament rupture results in a hemarthrosis, an acute intra-articular bleed rich in osteogenic human mesenchymal stem cells (hMSCs). With the aim of identifying an appropriate biomaterial with which to combine hemarthrosis fluid-derived hMSCs (HF-hMSCs) for therapeutic application, this work has investigated the biocompatibility of microparticles manufactured from two forms of poly(D,L-lactic-co-glycolic acid) (PLGA), one synthesized with equal monomeric ratios of lactic acid to glycolic acid (PLGA 50:50) and the other with a higher proportion of lactic acid (PLGA 85:15) which confers a longer biodegradation time. The surfaces of both types of microparticles were functionalized by plasma polymerization with allylamine to increase hydrophilicity and promote cell attachment. HF-hMSCs attached to and spread along the surface of both forms of PLGA microparticle. The osteogenic response of HF-hMSCs was enhanced when cultured with PLGA compared with control cultures differentiated on tissue culture plastic and this was independent of the type of polymer used. We have demonstrated that surface engineered PLGA microparticles are an appropriate biomaterial for combining with HF-hMSCs and the selection of PLGA is relevant only when considering the biodegradation time for each biomedical application.

In vitro biomechanical testing of anterior cruciate ligament reconstruction: traditional versus physiologically relevant load analysis

Various anterior cruciate ligament (ACL) graft-fixation devices exist. In this in vitro study a comparison of biomechanical characteristics of the cross-pin and button type fixation devices under practical rehabilitation loads was done. Forty bovine knees and hoof extensor tendons were harvested. After disarticulation, the femoral end of an ACL was prepared with either fixation, using the extensor tendon as graft. The mechanical test was either a single load to failure or load to failure after cycling loads. Twenty specimens were loaded to failure at a rate of 1mm/s, remaining specimens were cycled between 50 and 250 N for 1000 cycles then failure tested in a similar manner. Results show that both forms of fixation are able to withstand loads that exceed those observed in performing functional activities. Activity-specific stiffness (loads comparable to walking, jogging and stair descent) was lower than linear stiffness for both endobutton and cross-pin, without prior cycling. After cycling, activity-specific stiffness increased to linear stiffness values for the cross-pin for all activities. Thus, suggesting that the cross-pin provides a more rigid fixation after initial implantation over a wider range of activities, which would theoretically permit a more aggressive rehabilitation protocol and possibly an earlier return to regular activity. In contrast, activity-specific stiffness increased above linear stiffness values for the endobutton only under heavier loads (jogging and stair descent). Dynamic stiffness was higher and displacement lower for cross-pin throughout the cycle test. These results indicate, in ACL reconstruction, that graft complex stiffness should be considered at relevant loads only.

Comparação entre parafuso de interferência e transcondilar na reconstrução do LCA

OBJETIVO: A fixação femoral na reconstrução do Ligamento Cruzado Anterior (LCA) com enxerto de tendões flexores pode variar muito de acordo com a disposição dos materiais e a experiência do cirurgião. Porém os trabalhos que comparam os sistemas de fixação são efetuados na maioria das vezes em cadáveres ou em animais, sem avaliar os resultados clínicos, prejudicando sua comparação com pacientes humanos vivos. Neste artigo avaliamos o resultado clínico de dois métodos de fixação do enxerto ao fêmur (parafuso de interferência de titânio e parafuso transcondilar de titânio) para saber se, do ponto de vista clinico e subjetivo, há diferença entre estes métodos. MÉTODOS: Foram selecionados 40 pacientes com lesão do LCA sendo que 20 pacientes tiveram seu enxerto fixado ao fêmur com parafuso de interferência e 20 com parafuso transcondilar. Todos foram reavaliados com no mínimo dois anos de pós operatório para medição da gaveta anterior, Pivot Shift e teste de Lachman, além da obtenção dos questionário de Lysholm e IKDC (International Knee Documentation Committee). RESULTADOS: Os resultados não foram estatisticamente diferentes para os critérios avaliados. CONCLUSÃO: As duas formas de fixação são eficientes para esta técnica dentro dos parâmetros estabelecidos. Nível de Evidência II, Estudo Prospectivo Comparativo.

The effect of interference screw diameter on fixation of soft-tissue grafts in anterior cruciate ligament reconstruction

PURPOSE

The purpose of this study was to evaluate the effect that interference screw diameter has on fixation strength of a soft-tissue anterior cruciate ligament (ACL) graft.

METHODS

We prepared 32 fresh-frozen bovine tibiae with 9-mm ACL tibial tunnels. Accompanying 9-mm soft-tissue bovine Achilles grafts were also prepared. Bioabsorbable interference screws of increasing diameters were used for tibial fixation. There were 4 groups, consisting of 8-, 9-, 10-, and 11-mm screws for fixation of the 9-mm graft in the 9-mm tunnel. Tensile testing and cyclic loading from 50 to 250 N at 2 Hz for a total of 1,500 cycles were performed with a hydraulic biaxial materials testing machine. Graft slippage was measured with a video analysis technique with photo-reflective markers. At the end of cyclic testing, the grafts were loaded to failure, and the ultimate strength was recorded.

RESULTS

All grafts failed at the tendon-bone-screw interface. The ultimate strength (+/- SD) was greatest for the 11-mm screw (624 +/- 133 N), with slightly decreased strength for the 10-mm (601 +/- 54 N), 9-mm (576 +/- 85 N), and 8-mm (532 +/- 185 N) screws. Graft slippage (+/- SD) was least for the 9-mm screw (2.65 +/- 2.38 mm). There were no statistically significant differences in ultimate strength and graft slippage between screws (P = .45 and P = .34, respectively).

CONCLUSIONS

All interference screws tested provided adequate fixation strength. The results of this study show no statistical significance for ultimate strength or graft slippage with variable screw diameter.

CLINICAL RELEVANCE

Aperture fixation with the interference screw technique provides adequate stability for soft-tissue grafts in ACL reconstruction. Although no statistical significance was found, there was a trend toward less graft-site motion when we used a screw diameter equal to tunnel size.

Fixation strength of biocomposite wedge interference screw in ACL reconstruction: effect of screw length and tunnel/screw ratio. A controlled laboratory study

Background

Primary stability of the graft is essential in anterior cruciate ligament surgery. An optimal method of fixation should be easy to insert and provide great resistance against pull-out forces.

A controlled laboratory study was designed to test the primary stability of ACL tendinous grafts in the tibial tunnel. The correlation between resistance to traction forces and the cross-section and length of the screw was studied.

Methods

The tibial phase of ACL reconstruction was performed in forty porcine tibias using digital flexor tendons of the same animal. An 8 mm tunnel was drilled in each specimen and two looped tendons placed as graft. Specimens were divided in five groups according to the diameter and length of the screw used for fixation. Wedge interference screws were used. Longitudinal traction was applied to the graft with a Servohydraulic Fatigue System. Load and displacement were controlled and analyzed.

Results

The mean loads to failure for each group were 295,44 N (Group 1; 9 × 23 screw), 564,05 N (Group 2; 9 × 28), 614,95 N (Group 3; 9 × 35), 651,14 N (Group 4; 10 × 28) and 664,99 (Group 5; 10 × 35). No slippage of the graft was observed in groups 3, 4 and 5. There were significant differences in the load to failure among groups (ANOVA/P < 0.001).

Conclusions

Longer and wider interference screws provide better fixation in tibial ACL graft fixation. Short screws (23 mm) do not achieve optimal fixation and should be implanted only with special requirements.

Elongation of simulated whipstitch post anterior cruciate ligament reconstruction tibial fixation after cyclic loading

Whipstitch-post (WSP) tibial fixation is one of the most widely used and clinically successful methods of soft tissue graft fixation for anterior cruciate ligament reconstruction (ACLR). However, some consider the method prone to laxity. We hypothesized that WSP would have low elongation rates after experimental cyclic loading. Eight cadaveric human semitendinosus and gracilis (ST/Gr) tendons had whipstitches woven into their overlapped ends. The grafts were looped around a metal bar, pneumatically clamped, and cyclically loaded. The adjusted mean experimental graft elongation for the WSP was 1.13 mm with a maximum elongation of 1.64 mm and a standard deviation of 0.32. These values are equivalent to the lowest published cyclic loading tibial fixation elongation data. Whipstitch-post tibial ACLR fixation is biomechanically sound with among the lowest rates of elongation after laboratory cyclic loading.

No difference in clinical results between femoral transfixation and bio-interference screw fixation in hamstring tendon ACL reconstruction. A preliminary study

Hamstring tendon autograft has become a popular graft choice for anterior cruciate ligament (ACL) reconstruction, but there is no consensus on the ideal technique of fixation. We performed a pilot randomized controlled study to compare the clinical and mechanical outcome of two femoral fixation techniques for anterior cruciate ligament (ACL) reconstruction using hamstrings graft. We recruited 30 patients with a chronic unilateral tear of the anterior cruciate ligament. In all patients, quadrupled hamstring graft was used for ACL reconstruction. In 15 patients, femoral graft fixation was performed using Bio-interference Screws fixation (Arthrex, Inc. Naples USA) (Group 1). In the other 15 patients, femoral graft fixation was performed using BioTransFix femur extra cortical transverse fixation (Arthrex, Inc. Naples USA) (Group 2). In both groups, tibial fixation was achieved with a Delta bio-absorbable interference screw (Arthrex). Both groups were comparable with regard to demographic data, pre-operative activity level, mechanism of injury, interval between the injury and the operation, and pre-operative knee laxity measurements. An independent observer, who was blinded with regard to the involved leg and the type of graft, performed the outcome assessment with the use of a Rolimeter arthrometer (Aircast), and the International Knee Documentation Committee. At 13 months follow up, all patients except one had functionally normal or nearly normal IKDC objective scores. The mean IKDC subjective score was 83.38+/-9.4 in Group 1 and 79.92+/-11.01 in Group 2 (P>.05). The side to side laxity as measured with the Rolimeter arthrometer was 1.5 mm+/-1 (range 0-3) for Group 1, and 2 mm+/-1 (range 0-3) for Group 2 (P>.05). Femoral Biotransfix fixation and Bio-interference Screws fixation provide comparable mechanical stability and clinical outcome at 13 months follow up. BiotransFix fixation is an effective alternative to other devices. Our preliminary study shows that there is no evidence to prefer femoral transfixation to the more traditional, technically less demanding, and more economical interference screw fixation. A full study requires 368 participants.

Biomechanics of intratunnel anterior cruciate ligament graft fixation

Interference screw fixation of bone-patellar tendon-bone grafts now is considered the standard against which all ACL graft-fixation techniques are compared, but mechanical fixation of the ACL graft in the bone tunnels is the weak link in the early postoperative period. This article discusses some of the limitations of in vitro biomechanical studies and reviews variables that influence the tensile properties of intratunnel fixation methods for bone-tendon-bone and soft tissue grafts.

Revision anterior cruciate ligament reconstruction using a 2-stage technique with bone grafting of the tibial tunnel

BACKGROUND

Revision anterior cruciate ligament surgery is often considered a salvage procedure with limited goals. However, this limitation need not be the case. Similar to primary reconstruction, the goal should be to choose an appropriate graft and place it in an anatomical position in a good quality bone. The issue of good quality bone seems to have been ignored.

HYPOTHESIS

A 2-stage anterior cruciate ligament revision reconstruction with bone grafting of the tibial tunnel and the use of a different femoral tunnel will produce measured knee laxity and International Knee Documentation Committee scores similar to a primary anterior cruciate ligament reconstruction.

STUDY DESIGN

Case control study; Level of evidence, 3.

METHODS

This prospective study involved 49 consecutive 2-stage anterior cruciate ligament revisions (group R) performed by a single surgeon from 1993 to 2000. Two-stage revision surgery was performed if the tibial tunnel from a previous reconstruction surgery would overlap (either partially or fully) the correctly placed revision tunnel. The first stage consisted of removal of the old graft and interfering metalwork, together with bone grafting of the tibial tunnel. After ensuring adequate bone graft incorporation using computed tomography scan, the second stage revision was undertaken. This stage comprised harvesting the autograft, its anatomical placement, and its adequate fixation. The results were compared with the results of a matched group of patients with primary anterior cruciate ligament reconstruction (group P).

RESULTS

In group R, as meniscal and chondral lesions were more common, the International Knee Documentation Committee scores were lower than those of group P (61.2 for group R and 72.8 for group P; P = .006). Objective laxity measurement was similar in both groups (1.36 mm for group R and 1.2 mm for group P; P = .25).

CONCLUSION

This study establishes that the laxity measurements achieved with a 2-stage revision anterior cruciate ligament reconstruction can be similar to those achieved after primary anterior cruciate ligament reconstruction, although the International Knee Documentation Committee rating is lower.

The principles of interference screw fixation: application to foot and ankle surgery

Based on the success of the anterior cruciate ligament model, interference screw fixation is now being applied to a wide variety of orthopedic conditions that require the fixation of tendon or ligament to bone. The primary focus of this article is to present the principles of interference screw fixation. By understanding the principles of interference screw fixation, the foot and ankle surgeon will be able to apply this fixation technique to a wide variety of surgical applications for tendon transfers or ligament repairs. The surgical technique, history, principles of fixation, studies of fixation strength, tissue healing, and foot and ankle indications are reviewed. A modified Girdlestone digital flexor tendon transfer procedure description is included to illustrate how interference screw techniques may be applied to foot surgery.

Investigation of a hybrid method of soft tissue graft fixation for anterior cruciate ligament reconstruction

To increase knee stability following anterior cruciate ligament (ACL) reconstruction, development of increasingly stronger and stiffer fixation is required. This study assessed the initial pullout force, stiffness of fixation, and failure modes for a novel hybrid fixation method combining periosteal and direct fixation using porcine femoral bone. A soft tissue graft was secured by combining both an interference screw and an EndoButton (Smith and Nephew Endoscopy, Andover, MA). The results were compared with the traditional direct fixation method using a titanium interference screw. Twenty porcine hindlimbs were divided into two groups. Specimens were loaded in line with the bone tunnel on a materials testing machine. Maximum pullout force of the hybrid fixation (588+/-37 N) was significantly greater than with an interference screw alone (516+/-37 N). The stiffness of the hybrid fixation (52.1+/-12.8 N/mm) was similar to that of screw fixation (56.5+/-10.2 N/mm). Graft pullout was predominant for screw fixation, whereas a combination of graft pullout and graft failure was seen for hybrid fixation. These results indicate that initial pullout force of soft tissue grafts can be increased by using the suggested novel hybrid fixation method.

Evolgate fixation of doubled flexor graft in anterior cruciate ligament reconstruction: biomechanical evaluation with cyclic loading

BACKGROUND

The weakest points in hamstrings anterior cruciate ligament reconstruction are its points of fixation, especially on the tibial side. Methods for graft fixation to bone should be strong enough to avoid failure, stiff enough to restore load-displacement response, and secure enough to resist slippage under cyclic loading.

HYPOTHESIS

Biomechanical properties of the interference screw can be improved by reinforcing the walls of the tunnel with a metal spiral (Evolgate fixation).

STUDY DESIGN

Controlled laboratory study.

METHODS

Three paired tests were performed using common digital extensor bovine tendons fixed to porcine tibias with interference screw, Intrafix, and Evolgate; critical graft fixation conditions were simulated by applying subsequent cycles to the graft before loading the graft until failure.

RESULTS

The strength, stiffness, and resistance to slippage of the Evolgate were significantly higher than those of the interference screw; the ultimate failure load of the Evolgate was significantly higher than that of the Intrafix (1058+/-130 N and 832+/-156 N, respectively; P=.02). No statistically significant differences were found between Evolgate and Intrafix regarding the stiffness and slippage under cyclic load.

CONCLUSION

Evolgate fixation seems to be stronger, stiffer, and more resistant to slippage than is interference screw fixation of similar length, and it is stronger but not stiffer than Intrafix.

CLINICAL RELEVANCE

The Evolgate provides structural properties that seem to be appropriate for an intensive rehabilitation after anterior cruciate ligament reconstruction using a doubled semitendinosus and gracilis graft.

Stiffness characteristics of hamstring tendon graft fixation methods at the femoral site

In ACL reconstruction, stiffness and strength of a tendon graft complex are important features for knee stability and rehabilitation. The fixation between tendon and bone is known to be one of the weakest components of the graft complex. We examined the tensile load-displacement characteristics of looped semitendinosus tendons in a porcine femoral tunnel. Two groups of six cadaveric semitendinosus tendons and porcine femurs were tested, secured with either an aperture or non-aperture fixation method. Constructs were tested at 1 mm/s until failure in a materials testing machine, which allowed force and displacement data to be recorded. The non-aperture fixation group was significantly less stiff for the first 4 mm of displacement and had significantly higher ultimate failure loads. Provided that adequate ultimate strength can be achieved, stiffness properties of a tendon graft will be improved by using aperture fixation in femoral-site ACL reconstruction.