# The Development and Biomechanical Analysis of an Allograft Interference Screw for Anterior Cruciate Ligament Reconstruction

^{1}

^{2}

^{3}

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## Abstract

**:**

## 1. Introduction

^{®}(surgebright GmbH, Lichtenberg, Austria). These allograft bone screws are used for fixation in fracture, osteotomy, and arthrodesis and therefore make additional application of non-human materials dispensable. Furthermore, these allogenic screws exhibit superior osteoconductive properties, which means they are integrated in the recipient bone by the continuous bone remodeling process, and therefore are completely converted into autologous bone [26,27,28,29].

## 2. Materials and Methods

#### 2.1. Design of an Allograft Interference Screw for ACL Reconstruction

#### 2.1.1. Design of the Screw Drive

^{®}, where the wrench size is larger than the outer diameter of the screw, would be extremely suitable in terms of stability, but has the disadvantage that complete countersinking of the screws is not possible. A simple slot drive does not provide sufficient strength, and is also susceptible to tilting of the insertion tool, which could lead to unintentional damage to the implant. The internal hexagon socket would be ideally suited for this application on the one hand, and the internal hexalobular socket on the other. However, since these complex screw drives are very difficult to fabricate in cortical bone, as fabrication requires fragile micro-mills to achieve the small radii, they are of limited use for this application.

^{®}; second, the so-called three-bore drive, which was recently described in a prior publication [30]; and third, a modified version of a conventional external hexagon head, at which the wrench size is smaller than the core diameter of the screw. All three drives allow the screw to be fully countersunk and permit easy manufacturing in cortical bone.

^{®}systems, and experience is therefore available in production and in the admission process, the modified external hexagon was chosen as screw drive for the interference screw. The modified external hexagon head has a wrench size of 5 $\mathrm{m}$$\mathrm{m}$ and a height of 3 $\mathrm{m}$$\mathrm{m}$, thus the diameter of the insertion tool can be designed smaller than the outer diameter of the screw (in this case 8 $\mathrm{m}$$\mathrm{m}$), which allows the screw to be fully countersunk.

#### 2.1.2. Design of the Screw Thread

^{®}, showed that the edges of this thread type are too sharp, leading to indefensible damages of the graft. Therefore, the thread-edges have to be designed in a more flattened way, in order to prevent injury to the graft. Initial experiments with metric threads also showed that screw insertion was slow and required many turns of the screw. Since time often plays a central role in ACL reconstructions, it is necessary to keep the operating time as short as possible. To enable the screw to be inserted as quickly as possible, it was decided to design the thread as a two-start thread. Each thread has a pitch of 3 $\mathrm{m}$$\mathrm{m}$, which in combination results in a pitch of $1.5$ $\mathrm{m}$$\mathrm{m}$ of the two threads to each other.

#### 2.1.3. Design of the Screw Shape and Screw Dimensions

#### 2.2. Biomechanical Analysis Using a Bovine Model

#### 2.2.1. Graft Preparation

#### 2.2.2. Graft Fixation

#### 2.2.3. Measurement of the Ultimate Failure Load of the Graft Fixation

^{−1}until failure of the graft fixation. At the same time, the tensile force acting on the graft was measured, and the maximum value at fixation failure was recorded. The tensile force was applied in the direction of the axis of the bore tunnel, so that the worst-case scenario was simulated.

#### 2.2.4. Measurement of the Ultimate Failure Torque

#### 2.2.5. Statistical Analysis

## 3. Results

#### 3.1. Results of the FEA

#### 3.2. Results of the Biomechanical Analyses

## 4. Discussion

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations

ACL | Anterior Cruciate Ligament |

MRI | Magnetic Resonance Imaging |

FEA | Finite Element Analysis |

CAD | Computer Aided Design |

BMD | Bone Mineral Density |

PLLA | Polylactide |

PU | Polyurethane |

## Appendix A

## References

- Gerami, M.; Haghi, F.; Pelarak, F.; Mousavibaygei, S. Anterior cruciate ligament (ACL) injuries: A review on the newest reconstruction techniques. J. Fam. Med. Prim. Care
**2022**, 11, 852–856. [Google Scholar] [CrossRef] - Rezende, F.C.; Moraes, V.Y.; Franciozi, C.E.; Debieux, P.; Luzo, M.V.; Belloti, J.C. One-incision versus two-incision techniques for arthroscopically assisted anterior cruciate ligament reconstruction in adults. Cochrane Database Syst. Rev.
**2017**, 12, CD010875. [Google Scholar] [CrossRef] [PubMed] - Marieswaran, M.; Jain, I.; Garg, B.; Sharma, V.; Kalyanasundaram, D. A Review on Biomechanics of Anterior Cruciate Ligament and Materials for Reconstruction. Appl. Bionics Biomech.
**2018**, 2018, 4657824. [Google Scholar] [CrossRef] [PubMed] - Sanders, T.L.; Kremers, H.M.; Bryan, A.J.; Larson, D.R.; Dahm, D.L.; Levy, B.A.; Stuart, M.J.; Krych, A.J. Incidence of Anterior Cruciate Ligament Tears and Reconstruction. Am. J. Sport. Med.
**2016**, 44, 1502–1507. [Google Scholar] [CrossRef] [PubMed] - Mall, N.A.; Chalmers, P.N.; Moric, M.; Tanaka, M.J.; Cole, B.J.; Bach, B.R.; Paletta, G.A. Incidence and Trends of Anterior Cruciate Ligament Reconstruction in the United States. Am. J. Sport. Med.
**2014**, 42, 2363–2370. [Google Scholar] [CrossRef] - Lam, M.H.; Fong, D.T.; Yung, P.S.; Ho, E.P.; Chan, W.Y.; Chan, K.M. Knee stability assessment on anterior cruciate ligament injury: Clinical and biomechanical approaches. BMC Sport. Sci. Med. Rehabil.
**2009**, 1, 20. [Google Scholar] [CrossRef] - Chhabra, A.; Starman, J.S.; Ferretti, M.; Vidal, A.F.; Zantop, T.; Fu, F.H. Anatomic, Radiographic, Biomechanical, and Kinematic Evaluation of the Anterior Cruciate Ligament and Its Two Functional Bundles. J. Bone Jt. Surg.
**2006**, 88, 2–10. [Google Scholar] [CrossRef] - Lohmander, L.S.; Englund, P.M.; Dahl, L.L.; Roos, E.M. The Long-term Consequence of Anterior Cruciate Ligament and Meniscus Injuries. Am. J. Sport. Med.
**2007**, 35, 1756–1769. [Google Scholar] [CrossRef] - Lansdown, D.A.; Xiao, W.; Zhang, A.L.; Allen, C.R.; Feeley, B.T.; Li, X.; Majumdar, S.; Ma, C.B. Quantitative imaging of anterior cruciate ligament (ACL) graft demonstrates longitudinal compositional changes and relationships with clinical outcomes at 2 years after ACL reconstruction. J. Orthop. Res.
**2020**, 38, 1289–1295. [Google Scholar] [CrossRef] - Buckthorpe, M. Optimising the Late-Stage Rehabilitation and Return-to-Sport Training and Testing Process After ACL Reconstruction. Sport. Med.
**2019**, 49, 1043–1058. [Google Scholar] [CrossRef] - Filbay, S.R.; Ackerman, I.N.; Russell, T.G.; Crossley, K.M. Return to sport matters—longer-term quality of life after ACL reconstruction in people with knee difficulties. Scand. J. Med. Sci. Sport.
**2017**, 27, 514–524. [Google Scholar] [CrossRef] [PubMed] - Gokeler, A.; Dingenen, B.; Hewett, T.E. Rehabilitation and Return to Sport Testing After Anterior Cruciate Ligament Reconstruction: Where Are We in 2022? Arthrosc. Sport. Med. Rehabil.
**2022**, 4, e77–e82. [Google Scholar] [CrossRef] - Zeng, C.; Lei, G.; Gao, S.; Luo, W. Methods and devices for graft fixation in anterior cruciate ligament reconstruction. Cochrane Database Syst. Rev.
**2013**, 9, CD010730. [Google Scholar] [CrossRef] - Tibor, L.; Chan, P.H.; Funahashi, T.T.; Wyatt, R.; Maletis, G.B.; Inacio, M.C.S. Surgical Technique Trends in Primary ACL Reconstruction from 2007 to 2014. JBJS
**2016**, 98, 1079. [Google Scholar] [CrossRef] [PubMed] - Paschos, N.K.; Howell, S.M. Anterior cruciate ligament reconstruction: Principles of treatment. EFORT Open Rev.
**2016**, 1, 398–408. [Google Scholar] [CrossRef] [PubMed] - Zainal Abidin, N.A.; Abdul Wahab, A.H.; Abdul Rahim, R.A.; Abdul Kadir, M.R.; Ramlee, M.H. Biomechanical analysis of three different types of fixators for anterior cruciate ligament reconstruction via finite element method: A patient-specific study. Med. Biol. Eng. Comput.
**2021**, 59, 1945–1960. [Google Scholar] [CrossRef] - Zainal Abidin, N.A.; Ramlee, M.H.; Ab Rashid, A.M.; Ng, B.W.; Gan, H.S.; Abdul Kadir, M.R. Biomechanical effects of cross-pin’s diameter in reconstruction of anterior cruciate ligament—A specific case study via finite element analysis. Injury
**2022**, 53, 2424–2436. [Google Scholar] [CrossRef] - Abidin, N.A.Z.; Kadir, M.R.A.; Ramlee, M.H. Biomechanical effects of different lengths of cross-pins in anterior cruciate ligament reconstruction: A finite element analysis. J. Mech. Med. Biol.
**2020**, 20, 2050047. [Google Scholar] [CrossRef] - Athwal, K.K.; Lord, B.R.; Milner, P.E.; Gutteridge, A.; Williams, A.; Amis, A.A. Redesigning Metal Interference Screws Can Improve Ease of Insertion While Maintaining Fixation of Soft-Tissue Anterior Cruciate Ligament Reconstruction Grafts. Arthrosc. Sport. Med. Rehabil.
**2020**, 2, e137–e144. [Google Scholar] [CrossRef] - Siroros, N.; Merfort, R.; Liu, Y.; Praster, M.; Migliorini, F.; Maffulli, N.; Michalik, R.; Hildebrand, F.; Eschweiler, J. Mechanical properties of a bioabsorbable magnesium interference screw for anterior cruciate ligament reconstruction in various testing bone materials. Sci. Rep.
**2023**, 13, 12342. [Google Scholar] [CrossRef] - Schumacher, T.C.; Tushtev, K.; Wagner, U.; Becker, C.; große Holthaus, M.; Hein, S.B.; Haack, J.; Heiss, C.; Engelhardt, M.; El Khassawna, T.; et al. A novel, hydroxyapatite-based screw-like device for anterior cruciate ligament (ACL) reconstructions. Knee
**2017**, 24, 933–939. [Google Scholar] [CrossRef] [PubMed] - Luo, Y.; Zhang, C.; Wang, J.; Liu, F.; Chau, K.W.; Qin, L.; Wang, J. Clinical translation and challenges of biodegradable magnesium-based interference screws in ACL reconstruction. Bioact. Mater.
**2021**, 6, 3231–3243. [Google Scholar] [CrossRef] [PubMed] - Xu, B.; Yin, Y.; Zhu, Y.; Yin, Y.; Fu, W. Comparison of Bioabsorbable and Metallic Interference Screws for Graft Fixation During ACL Reconstruction: A Meta-analysis of Randomized Controlled Trials. Orthop. J. Sport. Med.
**2021**, 9, 23259671211021577. [Google Scholar] [CrossRef] - Emond, C.E.; Woelber, E.B.; Kurd, S.K.; Ciccotti, M.G.; Cohen, S.B. A Comparison of the Results of Anterior Cruciate Ligament Reconstruction Using Bioabsorbable Versus Metal Interference Screws. J. Bone Jt. Surg.-Am. Vol.
**2011**, 93, 572–580. [Google Scholar] [CrossRef] - Watson, J.N.; McQueen, P.; Kim, W.; Hutchinson, M.R. Bioabsorbable interference screw failure in anterior cruciate ligament reconstruction: A case series and review of the literature. Knee
**2015**, 22, 256–261. [Google Scholar] [CrossRef] [PubMed] - Pastl, K.; Schimetta, W. The application of an allogeneic bone screw for osteosynthesis in hand and foot surgery: A case series. Arch. Orthop. Trauma Surg.
**2021**, 142, 2567–2575. [Google Scholar] [CrossRef] - Pastl, K.; Pastl, E.; Flöry, D.; Borchert, G.H.; Chraim, M. Arthrodesis and Defect Bridging of the Upper Ankle Joint with Allograft Bone Chips and Allograft Cortical Bone Screws (Shark Screw
^{®}) after Removal of the Salto-Prosthesis in a Multimorbidity Patient: A Case Report. Life**2022**, 12, 1028. [Google Scholar] [CrossRef] - Brcic, I.; Pastl, K.; Plank, H.; Igrec, J.; Schanda, J.E.; Pastl, E.; Werner, M. Incorporation of an Allogenic Cortical Bone Graft Following Arthrodesis of the First Metatarsophalangeal Joint in a Patient with Hallux Rigidus. Life
**2021**, 11, 473. [Google Scholar] [CrossRef] - Amann, P.; Pastl, K.; Neunteufel, E.; Bock, P. Clinical and Radiologic Results of a Human Bone Graft Screw in Tarsometatarsal II/+III Arthrodesis. Foot Ankle Int.
**2022**, 43, 913–922. [Google Scholar] [CrossRef] - Lifka, S.; Baumgartner, W. A Novel Screw Drive for Allogenic Headless Position Screws for Use in Osteosynthesis—A Finite-Element Analysis. Bioengineering
**2021**, 8, 136. [Google Scholar] [CrossRef] - Bi, Z. Chapter 12—Validation and Verification. In Finite Element Analysis Applications: A Systematic and Practical Approach; Academic Press: San Diego, CA, USA, 2018; pp. 455–494. [Google Scholar] [CrossRef]
- Krone, R.; Schuster, P. An Investigation on the Importance of Material Anisotropy in Finite-Element Modeling of the Human Femur. In SAE Technical Paper; SAE International: Warrendale PA, USA, 2006. [Google Scholar] [CrossRef]
- Park, Y.S.; Kwon, H.B. Three-dimensional finite element analysis of implant-supported crown in fibula bone model. J. Adv. Prosthodont.
**2013**, 5, 326–332. [Google Scholar] [CrossRef] [PubMed] - Du, W.; Zhang, J.; Hu, J. A Method to Determine Cortical Bone Thickness of Human Femur and Tibia Using Clinical CT Scans. In Proceedings of the 2018 IRCOBI Conference Proceedings, Athens, Greece, 12–14 September 2018; Number IRC-18-65. pp. 388–398. [Google Scholar]
- Sadat-Ali, M.; Elshaboury, E.; Al-Omran, A.; Azam, M.Q.; Syed, A.; Gullenpet, A. Tibial cortical thickness: A dependable tool for assessing osteoporosis in the absence of dual energy X-ray absorptiopmetry. Int. J. Appl. Basic Med. Res.
**2015**, 5, 21–24. [Google Scholar] [CrossRef] [PubMed] - Morris, M.; Williams, J.; Thake, A.; Lang, Y.; Brown, J. Optimal screw diameter for interference fixation in a bone tunnel: A porcine model. Knee Surg. Sport. Traumatol. Arthrosc.
**2004**, 12, 486–489. [Google Scholar] [CrossRef] [PubMed] - Mlynarek, R.A.; Bedi, A.; Brown, C.H. Intratunnel Anterior Cruciate Ligament Graft Fixation. In The Anterior Cruciate Ligament; Elsevier: Amsterdam, The Netherlands, 2018; pp. 241–244.e1. [Google Scholar] [CrossRef]
- Ezechieli, M.; Ettinger, M.; König, C.; Weizbauer, A.; Helmecke, P.; Schavan, R.; Lucas, A.; Windhagen, H.; Becher, C. Biomechanical characteristics of bioabsorbable magnesium-based (MgYREZr-alloy) interference screws with different threads. Knee Surg. Sport. Traumatol. Arthrosc.
**2016**, 24, 3976–3981. [Google Scholar] [CrossRef] - Mayr, R.; Heinrichs, C.H.; Eichinger, M.; Coppola, C.; Schmoelz, W.; Attal, R. Biomechanical Comparison of 2 Anterior Cruciate Ligament Graft Preparation Techniques for Tibial Fixation: Adjustable-Length Loop Cortical Button or Interference Screw. Am. J. Sport. Med.
**2015**, 43, 1380–1385. [Google Scholar] [CrossRef] - Benca, E.; van Knegsel, K.P.; Zderic, I.; Caspar, J.; Strassl, A.; Hirtler, L.; Fuchssteiner, C.; Gueorguiev, B.; Windhager, R.; Widhalm, H.; et al. Biomechanical evaluation of an allograft fixation system for ACL reconstruction. Front. Bioeng. Biotechnol.
**2022**, 10, 1000624. [Google Scholar] [CrossRef] - Costi, J.J.; Kelly, A.J.; Hearn, T.C.; Martin, D.K. Comparison of Torsional Strengths of Bioabsorbable Screws for Anterior Cruciate Ligament Reconstruction. Am. J. Sport. Med.
**2001**, 29, 575–580. [Google Scholar] [CrossRef] - Herrera, A.; Martínez, F.; Iglesias, D.; Cegoñino, J.; Ibarz, E.; Gracia, L. Fixation strength of biocomposite wedge interference screw in ACL reconstruction: Effect of screw length and tunnel/screw ratio. A controlled laboratory study. BMC Musculoskelet. Disord.
**2010**, 11, 139. [Google Scholar] [CrossRef] - Efe, T.; Bauer, J.; Herdrich, S.; Gotzen, L.; El-Zayat, B.F.; Schmitt, J.; Schofer, M.D. Comparison between bovine bone and titanium interference screws for implant fixation in ACL reconstruction: A biomechanical study. Arch. Orthop. Trauma Surg.
**2010**, 130, 993–999. [Google Scholar] [CrossRef] - Weiss, F.P.; Possoli, F.A.d.A.; Costa, I.Z.; Borges, P.C.; Stieven, E.; Kubrusly, L.F. Fixation of the Anterior Ligament Graft at the Tibial Pole: Biomechanical Analysis of Three Methods. Rev. Bras. Ortop.
**2019**, 54, 697–702. [Google Scholar] [CrossRef] - Suryavanshi, A.; Khanna, K.; Sindhu, K.R.; Bellare, J.; Srivastava, R. Development of bone screw using novel biodegradable composite orthopedic biomaterial: From material design to in vitro biomechanical and in vivo biocompatibility evaluation. Biomed. Mater.
**2019**, 14, 045020. [Google Scholar] [CrossRef] [PubMed] - Dong, W.; Huang, X.; Sun, Y.; Zhao, S.; Yin, J.; Chen, L. Mechanical characteristics and in vitro degradation kinetics analysis of polylactic glycolic acid/β-tricalcium phosphate (PLGA/β-TCP) biocomposite interference screw. Polym. Degrad. Stab.
**2021**, 186, 109421. [Google Scholar] [CrossRef] - Aga, C.; Rasmussen, M.T.; Smith, S.D.; Jansson, K.S.; LaPrade, R.F.; Engebretsen, L.; Wijdicks, C.A. Biomechanical Comparison of Interference Screws and Combination Screw and Sheath Devices for Soft Tissue Anterior Cruciate Ligament Reconstruction on the Tibial Side. Am. J. Sport. Med.
**2013**, 41, 841–848. [Google Scholar] [CrossRef] [PubMed] - Brand, J.C.; Pienkowski, D.; Steenlage, E.; Hamilton, D.; Johnson, D.L.; Caborn, D.N.M. Interference Screw Fixation Strength of a Quadrupled Hamstring Tendon Graft Is Directly Related to Bone Mineral Density and Insertion Torque. Am. J. Sport. Med.
**2000**, 28, 705–710. [Google Scholar] [CrossRef] [PubMed] - Prado, M.; Martín-Castilla, B.; Espejo-Reina, A.; Serrano-Fernández, J.M.; Pérez-Blanca, A.; Ezquerro, F. Close-looped graft suturing improves mechanical properties of interference screw fixation in ACL reconstruction. Knee Surg. Sport. Traumatol. Arthrosc.
**2013**, 21, 476–484. [Google Scholar] [CrossRef] - Wan, C.; Hao, Z.; Li, Z.; Lin, J. Finite element simulations of different hamstring tendon graft lengths and related fixations in anterior cruciate ligament reconstruction. Med. Biol. Eng. Comput.
**2017**, 55, 2097–2106. [Google Scholar] [CrossRef] - Nyland, J.; Kocabey, Y.; Caborn, D.N. Insertion torque pullout strength relationship of soft tissue tendon graft tibia tunnel fixation with a bioabsorbable interference screw. Arthrosc. J. Arthrosc. Relat. Surg.
**2004**, 20, 379–384. [Google Scholar] [CrossRef] - Yang, D.L.; Cheon, S.H.; Oh, C.W.; Kyung, H.S. A Comparison of the Fixation Strengths Provided by Different Intraosseous Tendon Lengths during Anterior Cruciate Ligament Reconstruction: A Biomechanical Study in a Porcine Tibial Model. Clin. Orthop. Surg.
**2014**, 6, 173. [Google Scholar] [CrossRef] - Ariffin, A.; Chan, H.; Yusof, N.; Mohd, S.; Ramalingam, S.; Ng, W.; Mansor, A. Establishing Freeze Drying Process for Cortical and Cancellous Bone Allograft Cubes. J. Health Transl. Med. (JUMMEC)
**2019**, 22, 66–71. [Google Scholar] [CrossRef] - Tecklenburg, K.; Burkart, P.; Hoser, C.; Rieger, M.; Fink, C. Prospective Evaluation of Patellar Tendon Graft Fixation in Anterior Cruciate Ligament Reconstruction Comparing Composite Bioabsorbable and Allograft Interference Screws. Arthrosc. J. Arthrosc. Relat. Surg.
**2006**, 22, 993–999. [Google Scholar] [CrossRef] - Wilde, J.; Bedi, A.; Altchek, D.W. Revision Anterior Cruciate Ligament Reconstruction. Sport. Health Multidiscip. Approach
**2013**, 6, 504–518. [Google Scholar] [CrossRef] [PubMed] - Persson, A.; Gifstad, T.; Lind, M.; Engebretsen, L.; Fjeldsgaard, K.; Drogset, J.O.; Forssblad, M.; Espehaug, B.; Kjellsen, A.B.; Fevang, J.M. Graft fixation influences revision risk after ACL reconstruction with hamstring tendon autografts. Acta Orthop.
**2018**, 89, 204–210. [Google Scholar] [CrossRef] [PubMed] - Kim, D.H.; Bae, K.C.; Kim, D.W.; Choi, B.C. Two-stage revision anterior cruciate ligament reconstruction. Knee Surg. Relat. Res.
**2019**, 31, 10. [Google Scholar] [CrossRef] [PubMed] - Noyes, F.R.; Barber-Westin, S.D. Anterior Cruciate Ligament Revision Reconstruction. Am. J. Sport. Med.
**2006**, 34, 553–564. [Google Scholar] [CrossRef] [PubMed]

**Figure 1.**CAD models of the screws with claw clutch (

**a**), three-bore drive (

**b**), and modified external hexagon drive (

**c**), with the respective insertion tool merged. This setup is the basis for the FEA; the torque was applied to the insertion tool in each case. Structural constraints were applied to both the insertion tool and the screw, and are shown schematically in each panel.

**Figure 2.**Three different prototype versions designed and manufactured by surgebright GmbH. All versions have an outer diameter of 8 $\mathrm{m}$$\mathrm{m}$, an external hexagon head with a wrench size of 5 $\mathrm{m}$$\mathrm{m}$ and a height of 3 $\mathrm{m}$$\mathrm{m}$, a flattened double thread with a pitch of one thread of 3 $\mathrm{m}$$\mathrm{m}$ ($1.5$ $\mathrm{m}$$\mathrm{m}$ both threads in combination), a tapered outer shape, and a through hole with a diameter of $1.25$ $\mathrm{m}$$\mathrm{m}$. The three versions differ in length and outer shape. Version (

**a**) has an overall length of 21 $\mathrm{m}$$\mathrm{m}$, and is the most tapered one. Version (

**b**) also has an overall length of 21 $\mathrm{m}$$\mathrm{m}$, but is slightly less tapered than version (

**a**). Version (

**c**) has an overall length of 18 $\mathrm{m}$$\mathrm{m}$, and is the shortest and the least tapered one.

**Figure 3.**(

**a**) Doubled bovine tendons with a length between 7 $\mathrm{c}$$\mathrm{m}$ to 8 $\mathrm{c}$$\mathrm{m}$, diameters ranging from 7 $\mathrm{m}$$\mathrm{m}$ to 9 $\mathrm{m}$$\mathrm{m}$, and stitched ends. (

**b**,

**c**) Bovine graft fixed with the allograft interference screw in a cancellous bovine block, top and side views. (

**d**) Specimen fixed in a motorized force test bench. The bovine bone block was fixed in a vice connected to the movable table of the force test bench. The graft was attached to the stationary upper clamp, and connected to the load cell of the force test bench using the loop resulting from the single tendon fold.

**Figure 4.**FEA of (

**a**) a claw clutch screw drive, (

**b**) a three-bore screw drive, and (

**c**) a modified external hexagon screw drive. The simulated outer screw diameter is 8 $\mathrm{m}$$\mathrm{m}$, and is the same in all three panels. The torque applied to all screw drives is 2500 $\mathrm{N}$ $\mathrm{m}$$\mathrm{m}$. At this applied torque, the investigated screw drives are very likely to fail according to the FEA. The red zones represent areas with von Mises stress greater than 160 $\mathrm{M}$$\mathrm{Pa}$ and, therefore, areas with von Mises stress greater than the yield strength of cortical human bone (approx. 108 $\mathrm{M}$$\mathrm{Pa}$ [32]). The color bar is valid for all panels.

**Figure 5.**Results of the biomechanical analyses. (

**a**) Box plot showing the median values (solid orange line), the mean values (dashed green line), and quartiles of the maximal insertion torques during graft fixation for the 7 $\mathrm{m}$$\mathrm{m}$ graft ($n=8$), the 9 $\mathrm{m}$$\mathrm{m}$ graft ($n=4$), and for all together ($n=12$). (

**b**) Box plot showing the median value (solid orange line), the mean value (dashed green line), and quartile of the ultimate failure torque of the screw ($n=3$). (

**c**) Box plot showing the median values (solid orange line), the mean values (dashed green line), and quartiles of the ultimate failure load of the graft fixation for the 7 $\mathrm{m}$$\mathrm{m}$ graft ($n=8$), the 9 $\mathrm{m}$$\mathrm{m}$ graft ($n=4$), and for all together ($n=12$). (

**d**) Correlation plot between the insertion torque during graft fixation and the ultimate failure load of the graft fixation for all graft diameters ($r=0.644$, $p=0.024$, $\alpha =0.05$, $n=12$).

**Table 1.**Mechanical material properties of the screws and the insertion tools used for the FEA (taken from [30]).

Freeze-Dried Human Cortical Bone | Chromium Steel 1.4034 | |
---|---|---|

Density in
g/cm^{3} | 1.022 | 7.7 |

Young’s modulus in GPa | 5 | 215 |

Poisson’s ratio | 0.36 | 0.3 |

Yield strength in MPa | 108 | 650 |

**Table 2.**Results of the biomechanical tests regarding insertion torque, ultimate failure load, and ultimate failure torque.

Sample Number | Graft Diameter in mm | Tunnel Diameter in mm | Max. Insertion Torque in N mm | Ultimate Failure Load Graft Fixation in N | Ultimate Failure Torque in N mm |
---|---|---|---|---|---|

1 | 7 | 8 | 1600 | 203 | 2500 |

2 | 9 | 9.5 | 1200 | 281 | 2600 |

3 | 7 | 8 | 1500 | 312 | 2800 |

4 | 9 | 9.5 | 1600 | 362 | - |

5 | 7 | 8 | 900 | 160 | - |

6 | 7.5 | 8 | 400 | 91 | - |

7 | 7 | 8.5 | 1200 | 199 | - |

8 | 9 | 9.5 | 700 | 212 | - |

9 | 7 | 8 | 1000 | 359 | - |

10 | 7 | 7.5 | 900 | 114 | - |

11 | 7.5 | 8 | 1100 | 240 | - |

12 | 9 | 9.5 | 1400 | 288 | - |

Mean value 7 $\mathrm{m}$$\mathrm{m}$ graft | 1075 | 209.75 | - | ||

Standard deviation 7 $\mathrm{m}$$\mathrm{m}$ graft | 377.02 | 92.24 | - | ||

Min. value 7 $\mathrm{m}$$\mathrm{m}$ graft | 400 | 91 | - | ||

Max. value 7 $\mathrm{m}$$\mathrm{m}$ graft | 1600 | 359 | - | ||

Mean value 9 $\mathrm{m}$$\mathrm{m}$ graft | 1225 | 285.75 | - | ||

Standard deviation 9 $\mathrm{m}$$\mathrm{m}$ graft | 386.22 | 61.32 | - | ||

Min. value 9 $\mathrm{m}$$\mathrm{m}$ graft | 700 | 212 | - | ||

Max. value 9 $\mathrm{m}$$\mathrm{m}$ graft | 1600 | 362 | - | ||

Mean value overall | 1125 | 235.08 | 2633.33 | ||

Standard deviation overall | 369.58 | 88.54 | 152.75 | ||

Min. value overall | 400 | 91 | 2500 | ||

Max. value overall | 1600 | 362 | 2800 |

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**MDPI and ACS Style**

Lifka, S.; Rehberger, Y.; Pastl, K.; Rofner-Moretti, A.; Reichkendler, M.; Baumgartner, W.
The Development and Biomechanical Analysis of an Allograft Interference Screw for Anterior Cruciate Ligament Reconstruction. *Bioengineering* **2023**, *10*, 1174.
https://doi.org/10.3390/bioengineering10101174

**AMA Style**

Lifka S, Rehberger Y, Pastl K, Rofner-Moretti A, Reichkendler M, Baumgartner W.
The Development and Biomechanical Analysis of an Allograft Interference Screw for Anterior Cruciate Ligament Reconstruction. *Bioengineering*. 2023; 10(10):1174.
https://doi.org/10.3390/bioengineering10101174

**Chicago/Turabian Style**

Lifka, Sebastian, Yannik Rehberger, Klaus Pastl, Alexander Rofner-Moretti, Markus Reichkendler, and Werner Baumgartner.
2023. "The Development and Biomechanical Analysis of an Allograft Interference Screw for Anterior Cruciate Ligament Reconstruction" *Bioengineering* 10, no. 10: 1174.
https://doi.org/10.3390/bioengineering10101174