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Abstract

Background:

Increased lateral tibial posterior slope (LTPS) is associated with higher anterior cruciate ligament (ACL) reconstruction (ACLR) failure rate. Transportal central femoral footprint ACLR is associated with higher failure rate compared to transtibial high anteromedial footprint ACLR due to graft anisometry. The purpose of this study was to investigate whether the influence of tibial slope on ACL graft failure risk is dependent on graft positioning.

Material:

Of the 1480 consecutive hamstring ACLRs, 30 transportal (central femoral tunnel placement) and 30 transtibial (high anteromedial tunnel placement) ACLR failures were evaluated and matched one-to-one with non-failure control participants by age, sex, graft and surgical technique. Lateral tibial slope was assessed on MRI.

Results:

The risk of graft failure in the transportal group increased by 40.5% per degree of increasing LTPS (odds ratio 1.4; 95% confidence interval 1.05–1.87; p = 0.02). The transportal failure group showed a significantly higher mean tibial slope of 8.6° compared to both the transportal control group with 7.1° (p = 0.03) and the transtibial failure group with 7.2° (p = 0.04). Increased tibial slope was associated with shorter time to reconstruction failure (p = 0.002). The difference between slopes in the transtibial failure group (7.2°) compared to the transtibial control group (7.1°) was not significant (p = 0.56).

Conclusion:

Increased LTPS is associated with significantly increased risk of graft failure only in transportal ACLR, not in transtibial ACLR. Slope-related graft strain may be potentiated by anisometric ACL graft placement.

Keywords

anterior cruciate ligament anterior cruciate ligament failure knee slope

Introduction

The anterior cruciate ligament (ACL) is essential for stable knee kinematics, limiting tibial rotation as well as anterior tibial translation. Reconstruction of the ACL is indicated to improve knee stability showing overall satisfactory results and relatively low revision rates.^1

–4 However, poorer outcomes are seen after ACL revision surgery compared to primary reconstruction.¹ Consequently, numerous studies have investigated factors that may contribute to the aetiology of ACL failures to deepen the knowledge and understanding of ACL failure pathology.^5

–11 In addition to physiological factors such as neuromuscular control, the geometrical shape of the knee joint including the intercondylar notch and the posterior tibial slope has been identified to increase the susceptibility of ACL injuries and reconstruction failures.^7,12,13 However, the influential strength of these geometrical factors on ACL injury susceptibility remains unknown. In addition, little is known about the influence of slope on ACL reconstruction (ACLR) failures. Christensen et al. found that tibial posterior slope is increased in patients with early graft failure after cruciate ligament reconstruction; a 6° increase of tibial slope resulted in a 10 times higher risk of ACL graft failure.¹⁴ However, ACL injury pathology is multifactorial, and there is no consensus in the literature regarding a specific tibial cut-off slope that is related to a higher risk of ACL injury. The susceptibility of ACL graft failures is not only dependent on the existing anatomical conditions such as tibial slope but also dependent on acquired injuries and surgical technique. An increasing body of literature is indicating that central anatomical femoral tunnel placement is associated with higher revision rates compared to a more isometric tunnel placement at the anteromedial bundle area of the ACL.¹ Differences in graft isometry and subsequent graft strain forces may be a reason for these findings. The purpose of this study was to determine whether time to ACLR failure is dependent on tibial slope and to investigate whether transtibial and transportal ACLR failures show differences in mean lateral tibial posterior slope (LTPS). It is hypothesized that increased LTPS is associated with shorter time to ACLR failure and that LTPS is more influential in transportal ACLR.

Materials and methods

After approval by the local ethics committee, a cohort of 1480 consecutive patients who underwent ACL hamstring reconstruction surgery performed by a single surgeon between August 2000 to May 2013 was identified. In 1016 cases from August 2000 to May 2009, ACLR was performed using a transtibial technique, resulting in an eccentrically placed femoral tunnel within the original ACL footprint in the anteromedial bundle region. The surgical technique was changed in May 2009 to a transportal technique, in which the tibial and femoral tunnel were placed separately. This resulted in a longer and more anteriorly located tibial tunnel as well as a femoral tunnel placed centrally in the original ACL footprint. Graft fixation was ensured using suspensory femoral fixation (EndoButton/RetroButton) and a tibial interference device (Intrafix/Graftbolt) in all cases. ACLR failures were identified in both groups by means of clinical failure and MRI with or without subsequent ACL revision surgery. Thirty-three patients who had undergone ACLR with the transportal technique were identified as failures compared to 53 patients who had undergone ACLR with the transtibial technique. Patients were divided into the transportal failure group and transtibial failure group according to the surgical reconstruction technique and matched 1:1 with control participants who had undergone ACLR with a follow-up of minimum 4 years without signs of graft failure or insufficiency. Patients were matched by age, sex and surgical technique. MRI was accessible for 30 patients in the transportal failure group and for 30 patients in the transtibial failure group, which led to a total of 120 patients (including matched control participants) who were included in this study. Patients were anonymized and randomized for blinded assessment. MRI was used to determine the lateral tibial slope, according to the technique defined by Hudek et al.,¹⁵ which has shown acceptable inter- and intraclass correlation in the literature. An orthopaedic surgery consultant and an orthopaedic surgery resident performed the measurements on a radiology suite computer with the necessary software (OsiriX 7.5). Inter-class correlation was assessed. Data were investigated by non-parametric correlation using SPSS 23.0 by a professional statistician.

Results

The transportal failure group comprised 30 patients (9 females and 21 males; mean age 22 years, range 13–51 years) and the transtibial failure group comprised 30 patients (8 females and 22 males; mean age 23, range 10–38 years). Corresponding transportal and transtibial control groups were matched one-to-one by age, sex, graft and surgical technique. The transportal failure group showed a significantly higher mean tibial slope of 8.6° compared to the transportal control group with 7.1° (p = 0.03). The odds ratio for graft failure in the transportal failure group was 1.4 per degree of increasing slope (95% confidence interval 1.05–1.87; p = 0.02); this corresponds to an increased risk of graft failure of 40.5% for every degree of increasing slope. The transportal failure group showed a significantly higher mean tibial slope of 8.6° compared to the transtibial failure group with 7.2° (p = 0.04). Increased tibial slope was associated with shorter time to reconstruction failure (p = 0.002). The difference between slopes in the transtibial failure group (7.2°) compared to the transtibial control group (7.1°) was not significant (p = 0.56). The intraclass correlation between slope measurements was 0.86.

Discussion

The primary finding of this study was that increased LTPS was associated with significantly increased risk of graft failure only in transportal ACLR, not in transtibial ACLR. An increasing body of literature is indicating that the susceptibility of ACL graft failures is dependent not only on physiological factors such as neuromuscular control but also on the geometrical shape of the knee joint including the intercondylar notch and the posterior lateral tibial slope^{13,15

–21} Christensen et al. found that tibial posterior slope is increased in patients with early graft failure after ACLR; a 6° increase of tibial slope resulted in a 10 times higher risk of ACL graft failure.¹⁴ Increased tibial slope has been shown to be associated with increased tibial internal rotation and valgus stress during landing manoeuvres.^22,23 Previous studies using computer modelling have shown that increased tibial slope is also associated with higher ligament tension.^24,25 Different surgical techniques may alter the influence of geometric features of the knee joint on the ACL grafts. Central anatomical femoral tunnel placement as it has been performed in all transportal ACLR cases has been shown to be associated with higher revision rates compared to a more isometric tunnel placement at the anteromedial bundle region of the ACL footprint.²⁶ It is conceivable that increased lateral tibial slope increases graft strain in the ACL reconstructed knee, eventually contributing to early reconstruction failure. Furthermore, non-isometric tunnel placement in the centre of the femoral footprint may lead to increased graft strain which may be potentiated by increased tibial slope. Finally, the role of the tibial tunnel placement is not fully understood and may contribute essentially to the findings of this study. However, the susceptibility of ACLR failures is multifactorial including the surgical technique, neuromuscular conditions, patient age, level of function, timing of return to sport, compliance to rehabilitation protocols, acquired concomitant injuries and structural anatomy of the knee joint.^{6,10,11,20,21,27
–29} As sagittal stabilization is also ensured by the menisci, higher ACL failures rates are seen when concomitant meniscal injuries are present.^30,9 Li et al. showed that increased tibial slope is associated with increased anterior tibial translation in the ACL-reconstructed knee;⁹ this may not only affect graft strain but also increase the risk of notch impingement, especially when tunnels are mal-placed in patients with hyperlaxity. The fact that time to failure in this study is significantly dependent on tibial slope supports the concept and that tibial slope increases graft weakening forces. Furthermore, central anatomical tunnel placement leads to an anisometric graft which loses tension in flexion enabling increased anterior tibial translation which may be aggravated by increased tibial slope and subsequent increased anterior tibial translation. The concept that slope is more influential in anisometric placed grafts is supported by the fact that the transportal failure group showed a shorter mean time to failure in comparison with the transtibial failure group as well as an increased tibial slope in comparison with the control group. The transtibial failure group did not show significant differences in tibial slope compared to the control group which may indicate that tibial slope-related graft strain is less influential on isometric grafts. The present study has limitations; for example, the small number of patients, the risk of confounding and MRI measurement. In conclusion, the present study indicates that lateral tibial slope is an important factor in ACL failure pathology. Aggravating surgery-related factors such as tunnel mal-placement and overlooked meniscal pathology can increase the risk of ACL graft failure. Slope-correcting osteotomies are indicated for specific cases^31,32; however, tibial slope should always be assessed before ACL revision surgery. Increased LTPS on preoperation MRI should stress the importance of correct tunnel placement, avoidance of notch impingement and assessment of meniscal pathology. Future studies are needed to focus on the relationship of meniscal pathology and tibial slope. The surgical technique was changed in 2013 to a transportal anteromedial bundle ACLR technique; to date (May 2017), eight of these patients have been identified as having ACLR failures showing a mean LTPS of 7.56° (range 5.9–8.4, mean age 22.8 years, mean time to failure 17.4 months). The influence of LTPS will be investigated as soon as sufficient patients have been followed up. It is expected that LTPS will be less influential in these cases compared to central anatomical ACLR as the ACL graft has been placed more isometrically

Conclusion

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

Lind

Menhert

Pedersen

. The first results from the Danish ACL reconstruction registry: epidemiologic and 2 year follow-up results from 5,818 knee ligament reconstructions. Knee Surg Sports Traumatol Arthrosc 2009; 17(2): 117–124.

Mahmoud

Odak

Coogan

. A prospective study to assess the outcomes of revision anterior cruciate ligament reconstruction. Int Orthop 2014; 38(7): 1489–1494.

Maletis

Inacio

Funahashi

. Analysis of 16,192 anterior cruciate ligament reconstructions from a community-based registry. Am J Sports Med 2013; 41(9): 2090–2098.

Wasserstein

Khoshbin

Dwyer

. Risk factors for recurrent anterior cruciate ligament reconstruction: a population study in Ontario, Canada, with 5-year follow-up. Am J Sports Med 2013; 41(9): 2099–2107.

Granan

Bahr

Steindal

. Development of a national cruciate ligament surgery registry: the Norwegian National Knee Ligament Registry. Am J Sports Med 2008; 36(2): 308–315.

Hewett

Zazulak

Myer

. Effects of the menstrual cycle on anterior cruciate ligament injury risk: a systematic review. Am J Sports Med 2007; 35(4): 659–668.

Kahn

Seon

Song

. Risk factors for anterior cruciate ligament injury: assessment of tibial plateau anatomic variables on conventional MRI using a new combined method. Int Orthop 2011; 35(8): 1251–1256.

Krych

Jackson

Hoskin

. A meta-analysis of patellar tendon autograft versus patellar tendon allograft in anterior cruciate ligament reconstruction. Arthroscopy 2008; 24(3): 292–298.

Wei

Zhao

. A meta-analysis of hamstring autografts versus bone-patellar tendon-bone autografts for reconstruction of the anterior cruciate ligament. Knee 2011; 18(5): 287–293.

10.

Shambaugh

Klein

Herbert

. Structural measures as predictors of injury basketball players. Med Sci Sports Exerc 1991; 23(5): 522–527.

11.

Souryal

Freeman

. Intercondylar notch size and anterior cruciate ligament injuries in athletes. A prospective study. Am J Sports Med 1993; 21(4): 535–539.

12.

Giffin

Vogrin

Zantop

. Effects of increasing tibial slope on the biomechanics of the knee. Am J Sports Med 2004; 32(2): 376–382.

13.

Stijak

Herzog

Schai

. Is there an influence of the tibial slope of the lateral condyle on the ACL lesion? A case-control study. Knee Surg Sports Traumatol Arthrosc 2008; 16(2): 112–117.

14.

Christensen

Krych

Engasser

. Lateral tibial posterior slope is increased in patients with early graft failure after anterior cruciate ligament reconstruction. Am J Sports Med 2015; 43(10): 2510–2514.

15.

Hudek

Schmutz

Regenfelder

. Novel measurement technique of the tibial slope on conventional MRI. Clin Orthop Relat Res 2009; 467(8): 2066–2072.

16.

Bisson

Gurske-DePerio

. Axial and sagittal knee geometry as a risk factor for noncontact anterior cruciate ligament tear: a casecontrol study. Arthroscopy 2010; 26(7): 901–906.

17.

Hashemi

Chandrashekar

Gill

. The geometry of the tibial plateau and its influence on the biomechanics of the tibiofemoral joint. J Bone Joint Surg Am 2008; 90(12): 2724–2734.

18.

Simon

Everhart

Nagaraja

. A case-control study of anterior cruciate ligament volume, tibial plateau slopes and intercondylar notch dimensions in ACL-injured knees. J Biomech 2010; 43(9): 1702–1707.

19.

Webb

Salmon

Leclerc

. Posterior tibial slope and further anterior cruciate ligament injury in the anterior cruciate ligament-reconstructed patient. Am J Sports Med 2013; 41(12): 2800–2804.

20.

Whitney

Sturnick

Vacek

. Relationship between the risk of suffering a first-time noncontact ACL injury and geometry of the femoral notch and ACL: a prospective cohort study with a nested case-control analysis. Am J Sports Med 2014; 42(8): 1796–1805.

21.

Wordeman

Quatman

Kaeding

. In vivo evidence for tibial plateau slope as a risk factor for anterior cruciate ligament injury: a systematic review and meta-analysis. Am J Sports Med 2012; 40(7): 1673–1681.

22.

McLean

Lucey

Rohrer

. Knee joint anatomy predicts high-risk in vivo dynamic landing knee biomechanics. Clin Biomech 2010; 25(8): 781–788.

23.

Shultz

Schmitz

. Tibial plateau geometry influences lower extremity biomechanics during landing. Am J Sports Med 2012; 40(9): 2029–2036.

24.

Shao

MacLeod

Manal

. Estimation of ligament loading and anterior tibial translation in healthy and ACL-deficient knees during gait and the influence of increasing tibial slope using EMG-driven approach. Ann Biomed Eng 2011; 39(1): 110–121.

25.

Shelburne

Kim

Sterett

. Effect of posterior tibial slope on knee biomechanics during functional activity. J Orthop Res 2011; 29(2): 223–231.

26.

Rahr-Wagner

Thillemann

Pedersen

. Increased risk of revision after anteromedial compared with transtibial drilling of the femoral tunnel during primary anterior cruciate ligament reconstruction: results from the Danish knee ligament reconstruction register. Arthroscopy 2013; 29(1): 98–105.

27.

Myer

Ford

Paterno

. The effects of generalized joint laxity on risk of anterior cruciate ligament injury in young female athletes. Am J Sports Med 2008; 36(6): 1073–1080.

28.

Hong

Feng

. Posterior tibial slope influences static anterior tibial translation in anterior cruciate ligament reconstruction. Am J Sports Med 2014; 42(4): 927–933.

29.

Zelisko

Noble

Porter

. A comparison of men’s and women’s professional basketball injuries. Am J Sports Med 1982; 10(5): 297–299.

30.

Fukubayashi

Torzilli

Sherman

. An in vitro biomechanical evaluation of anterior-posterior motion of the knee. Tibial displacement, rotation, and torque. J Bone Joint Surg Am 1982; 64(2): 258–264.

31.

Slocum

Devine

. Cranial tibial wedge osteotomy: a technique for eliminating cranial tibial thrust in cranial cruciate ligament repair. J Am Vet Med Assoc 1984; 184(5): 564–569.

32.

Sonnery-Cottet

Mogos

Thaunat

. Proximal tibial anterior closing wedge osteotomy in repeat revision of anterior cruciate ligament reconstruction. Am J Sports Med 2014; 42(8): 1873–1880.