Interaction between anterior cruciate ligament and tibial slope: what is the role for tibial deflexion osteotomy

Introduction

Anterior cruciate ligament (ACL) tear is an extremely common pathology that mainly affects people who frequently practise pivot-torsion sports. In most cases, ligament reconstruction is indicated. In France in 2019, 50,000 of these kinds of interventions were performed [1] Saithna A, Monaco E, Carrozzo A, Marzilli F, Cardarelli S, Lagusis B, et al. Anterior Cruciate Ligament Revision Plus Lateral Extra-Articular Procedure Results in Superior Stability and Lower Failure Rates Than Does Isolated Anterior Cruciate Ligament Revision but Shows No Difference in Patient-Reported Outcomes or Return to Sports. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2023 Apr 1;39(4):1088–98. . This surgery offers excellent long-term functional outcomes. However, in the event of repeat tears, further surgery is more complex, and the course of specific rehabilitation may need to be longer, with lower rates of resuming sport and poorer functional outcomes than the patient has been hoping for [2] Grassi A, Pizza N, Al-zu’bi BBH, Fabbro GD, Lucidi GA, Zaffagnini S. Clinical Outcomes and Osteoarthritis at Very Long-term Follow-up After ACL Reconstruction: A Systematic Review and Meta-analysis. Orthopaedic Journal of Sports Medicine. 2022 Jan 1;10(1):23259671211062238. . Moreover, when a graft has torn once, the rate of further ruptures may be as high as 25% [3] Battaglia MJ, Cordasco FA, Hannafin JA, Rodeo SA, O’Brien SJ, Altchek DW, et al. Results of Revision Anterior Cruciate Ligament Surgery. Am J Sports Med. 2007 Dec 1;35(12):2057–66. . This means that it is crucial to analyse and isolate the factors that could lead to these failures, and to treat them when the graft is first fixed. Some anatomical, or sometimes congenital or hormonal, factors are intrinsic and specific to the patient. Other factors are external, such as the type of sport practised, the conditions in which sport is played, and the physical preparation [4] Cronström A, Tengman E, Häger CK. Return to Sports: A Risky Business? A Systematic Review with Meta-Analysis of Risk Factors for Graft Rupture Following ACL Reconstruction. Sports Med. 2023 Jan 1;53(1):91–110. .

Poorly positioned tunnels, especially the femoral tunnel, have been described as being the main cause of repeat tear [5] Vermeijden HD, Yang XA, Van Der List JP, DiFelice GS, Rademakers MV, Kerkhoffs GMMJ. Trauma and femoral tunnel position are the most common failure modes of anterior cruciate ligament reconstruction: a systematic review. Knee Surg Sports Traumatol Arthrosc. 2020 Nov;28(11):3666–75. . However, improvements to surgical techniques and instrumentation developments mean that the impact of this factor has been reduced.

The current trend is for an augmentation consisting of a modified Lemaire extra-articular tenodesis or ALL reconstruction, which the latest published series have found to decrease the number of repeat tears. This may be leading to this strategy becoming routine, although it is still not without risk [1] Saithna A, Monaco E, Carrozzo A, Marzilli F, Cardarelli S, Lagusis B, et al. Anterior Cruciate Ligament Revision Plus Lateral Extra-Articular Procedure Results in Superior Stability and Lower Failure Rates Than Does Isolated Anterior Cruciate Ligament Revision but Shows No Difference in Patient-Reported Outcomes or Return to Sports. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2023 Apr 1;39(4):1088–98. .

For this reason, it is essential to look closely at other factors. In the field of veterinary medicine, where the rate of fatigue tears of the ACL in “large dogs” is high, it has been clearly shown that an excessive posterior tibial slope is the cause [6] Dan MJ, Wills DJ, Crowley JD, Cance N, Romandini I, Walsh WR, et al. Anterior cruciate ligament zoobiquity: Can man’s best friend tell us we are being too cautious with the implementation of osteotomy to correct posterior tibial slope. Knee surg sports traumatol arthrosc. 2024 May;32(5):1071–6. . Although this may have often been neglected in studies looking at repeat tears, posterior tibial slope has become an anatomical factor of major interest, and particularly since it has been associated with static anterior tibial translation (SATT) in single-leg stance [7], Dan MJ, Cance N, Pineda T, Demey G, Dejour DH. 4-6 degrees is the Target Posterior Tibial Slope post Tibial Deflection Osteotomy according to the Knee Static Anterior Tibial Translation. Arthroscopy. 2023 Jul 19; [8] Dini F, Tecame A, Ampollini A, Adravanti P. Multiple ACL Revision: Failure Analysis and Clinical Outcomes. J Knee Surg. 2021 Jul;34(08):801–9. . Patients who have an excessive posterior tibial slope are at a significantly greater risk of tear or repeat tear of an ACL graft [9] Moran TE, Driskill EK, Tagliero AJ, Klosterman EL, Ramamurti P, Reahl GB, et al. Combined Tibial Deflexion Osteotomy and Anterior Cruciate Ligament Reconstruction Improves Knee Function and Stability: A Systematic Review. Journal of ISAKOS. 2024 Jun 28; .

It is therefore important to explore methods to quantify and then treat this intrinsic anatomical risk factor to reduce the rate of repeat tears.

The objective of this article is to set out the importance of posterior tibial slope, and how to assess and manage it in ACL tears.

Biomechanics

The ACL is made up of two bands of connective tissue named for their tibial attachment sites: the anteromedial bundle and the posterolateral bundle. The anteromedial bundle mainly acts on anterior translation, while the posterolateral bundle has an action that controls internal rotation. When the ACL tears, the loss of its function results in increased anterior tibial translation in weight-bearing but also instability in internal rotation, which is worsened if the anterolateral bundle is affected.

We will take a separate look at the compartments of the knee and their tibial slopes:

1. Medial :

When there is a greater medial tibial slope, there will be increased anterior tibial translation during weight-bearing. For each degree of slope, translation shifts by 0.46mm [7] Dan MJ, Cance N, Pineda T, Demey G, Dejour DH. 4-6 degrees is the Target Posterior Tibial Slope post Tibial Deflection Osteotomy according to the Knee Static Anterior Tibial Translation. Arthroscopy. 2023 Jul 19; . The medial meniscus is the main secondary stabiliser of anterior translation, and it is essential to take it into account when assessing tibial slope. A medial meniscectomy will increase the functional slope and accentuate this tibial translation in single-leg stance by a mean of 0.5 to 1.5 mm [10] Dejour D, Pungitore M, Valluy J, Nover L, Saffarini M, Demey G. Preoperative laxity in ACL-deficient knees increases with posterior tibial slope and medial meniscal tears. Knee Surg Sports Traumatol Arthrosc. 2019 Feb 1;27(2):564–72. .

2. Lateral :

An elevated lateral tibial slope in the context of an ACL tear will mean increased rotatory instability and pivot shift grade [11] Lustig S, Scholes CJ, Leo SPM, Coolican M, Parker DA. Influence of soft tissues on the proximal bony tibial slope measured with two-dimensional MRI. Knee Surg Sports Traumatol Arthrosc. 2013 Feb 1;21(2):372–9. . The lateral meniscus is also an important secondary stabiliser of the lateral compartment [12] Musahl V, Citak M, O’Loughli23n PF, Choi D, Bedi A, Pearle AD. The Effect of Medial Versus Lateral Meniscectomy on the Stability of the Anterior Cruciate Ligament-Deficient Knee. Am J Sports Med. 2010 Aug;38(8):1591–7. . This can be demonstrated by the improved rotatory stability achieved through lateral meniscal root repair [13] Forkel P, Reuter S, Sprenker F, Achtnich A, Herbst E, Imhoff A, et al. Different patterns of lateral meniscus root tears in ACL injuries: application of a differentiated classification system. Knee Surg Sports Traumatol Arthrosc. 2015 Jan;23(1):112–8. .

Simply put, the medial compartment mainly impacts anteroposterior translation while the lateral compartment acts on rotational control [12] Musahl V, Citak M, O’Loughli23n PF, Choi D, Bedi A, Pearle AD. The Effect of Medial Versus Lateral Meniscectomy on the Stability of the Anterior Cruciate Ligament-Deficient Knee. Am J Sports Med. 2010 Aug;38(8):1591–7. .

Imaging assessment

Method

There are several methods for measuring tibial slope, which means that the method used must be stated as they have different threshold values.

We use a simple and reliable method to measure tibial slope and SATT.

Radiology images should be obtained to include true lateral views showing 15 cm of proximal tibia with 20° of flexion in single-leg weight-bearing. The condyles will be aligned under fluoroscopy before the conventional radiography is performed. Any deviation from lateral will lead to distortions and the measurements will not be possible to interpret [14] Vieider RP, Mehl J, Rab P, Brunner M, Schulz P, Rupp MC, et al. Malrotated lateral knee radiographs do not allow for a proper assessment of medial or lateral posterior tibial slope. Knee Surg Sports Traumatol Arthrosc. 2024;32(6):1462–9. (Figure 1). Next, the technique for measuring the tibial slope must be chosen so that it is reproducible and can be compared from one study to another. It is crucial to choose one method and stick to it. The technique that uses the proximal anatomical tibial axis has a normal value of 9° of slope and the method is described in Figure 2 [15] Brazier J, Migaud H, Gougeon F, Cotten A, Fontaine C, Duquennoy A. Evaluation of methods for radiographic measurement of the tibial slope. A study of 83 healthy knees. Revue de chirurgie orthopédique et réparatrice de l’appareil moteur. 1996;82(3):195–200. . The normal value for SATT is 1.31 mm [16] Cance N, Dan MJ, Pineda T, Demey G, Dejour DH. Radiographic Investigation of Differences in Static Anterior Tibial Translation With Axial Load Between Isolated ACL Injury and Controls. Am J Sports Med. 2024 Feb 1;52(2):338–43. . If translation is posterior, the measurement will have a negative value. The measurement method is described in Figure 3.

Treatment

How do these measurements influence the treatment strategy?

Post-operative weight-bearing protocol:

Firstly, they may have an impact on the post-operative weight-bearing protocol. For example, patients with a tibial slope greater than 12° and/or a SATT greater than 5mm prior to surgery will begin with a non-weight-bearing phase lasting 21 days in order to decrease the stresses of excessive translation on the graft to protect it [17] Romandini I, Cance N, Dan MJ, Pineda T, Pairot de Fontenay B, Demey G, et al. A non-weight bearing protocol after ACL reconstruction improves static anterior tibial translation in patients with elevated slope and increased weight bearing tibial anterior translation. J EXP ORTOP. 2023 Dec 20;10(1):142. .

Surgical :

The intervention that directly addresses tibial slope is the tibial deflexion osteotomy (TDO) [18] Guarino A, Pineda T, Giovannetti de Sanctis E, van Rooij F, Saffarini M, Dejour D. The Original Technique for Tibial Deflexion Osteotomy During Revision Anterior Cruciate Ligament Reconstruction: Surgical Technique. Arthroscopy Techniques. 2024 Jan 1;13(1):102824. . This intervention was notably described by Dejour et al. in 1998, although it has been discussed at the Lyon Knee Surgery Congress since the early 1990s [19], Dejour D, Kuhn A, Dejour H. Osteotomie tibiale de déflexion et laxité chronique antérieure à propos de 22 cas. Rev Chir Orthop 1998 ; 84 SII : 28-29 [20] 7èmes journées lyonnaises de chirurgie du genou - Lyon 1991 [Internet]. [cited 2024 Aug 23]. Available from: http://lyon-knee-surgery.com/images/pdf/7%C3%A8mes%20journ%C3%A9es%20lyonnaises%20de%20chirurgie%20du%20genou%20-%20Lyon%201991/jdg-7/assets/basic-html/page-270.html. It is a sagittal realignment osteotomy. The technique described here is a supra-tubercular osteotomy (Figure 4). However, trans-tubercle and infra-tubercle strategies are also possible (Figure 5). This intervention is performed at the same time as the ACL reconstruction.

Surgical technique

Indication: Repeat rupture and tibial slope ≥ 12° and a SATT ≥ 5mm. The number of surgical revisions and meniscal condition may lower these thresholds.

Contraindication: Genu recurvatum ≥ 10°,
early stage or established femorotibial osteoarthritis, skeletal immaturity.

Patient preparation

The patient is positioned in dorsal decubitus, with a lateral thigh post and a support holding the knee in 90° of flexion. The intervention is performed with a tourniquet positioned at the proximal end of the limb, and the whole procedure is under general or regional anaesthesia.

Incision

A longitudinal incision is made, medial to the anterior tibial tubercle (ATT). It starts 4 cm below the joint line and extends for around 6 cm. The hamstring tendon graft can be removed using this same incision. If the patellar tendon is being used as a graft, the cut extends further proximally as far as the corner of the patella; if the quadriceps tendon is to be used, a separate incision is made.

Osteotomy

The first key step is to identify the insertion of the patellar tendon over the ATT. Then, the fascia lata and tibialis anterior muscle are released following the Keblish lateral approach. The deep medial collateral ligament is released medially. It is then possible to position double-curved retractors on both sides of the tibial metaphysis. Two proximal K-wires (diameter 2.5mm) are inserted at the patellar tendon insertion, positioned 1 cm away on both sides. Next, the two distal K-wires are inserted as planned pre-operatively, with the goal being to achieve a final tibial slope of 4-6° [7] Dan MJ, Cance N, Pineda T, Demey G, Dejour DH. 4-6 degrees is the Target Posterior Tibial Slope post Tibial Deflection Osteotomy according to the Knee Static Anterior Tibial Translation. Arthroscopy. 2023 Jul 19; . The wires must converge at the posterior cortex, 1 cm below the tibial plateau (Figure 6). The osteotomy is performed using an oscillating saw, using the proximal wires as guides inferiorly and the distal wires superiorly. In order to weaken the hinge without entirely breaking it apart, it is best to gently butt up against the posterior cortex, as if “knocking on the door”. The biplanar osteotomy is then performed just behind the patellar tendon. The bone wedge can be removed. The hinge is tested by lowering the proximal part over the distal part. Reduction is applied by gently extending the lower limb. A staple 2 cm lateral to the patellar tendon is used for temporary fixation, and the slope is checked using fluoroscopy. If the result is satisfactory, it is also fixed medially with a staple. Once the osteotomy is reduced, the tibial tunnel will be slightly angulated and it will need to be drilled again. This is done by pushing the drill bit by hand to avoid applying excessive stress on the osteotomy line. The graft can then be passed through and fixed in place. Fixation is performed in 70° of flexion to avoid any genu recurvatum.

Closure

The fascia lata and the medial collateral ligament are closed. A line of straight sutures at the proximal aponeurosis of tibialis anterior helps to prevent pressure increasing in the anterior compartment of the leg. The subcutaneous and cutaneous planes are then closed. There is no drain left in place.

Summary of the surgical steps:

Note: If performing transosseous meniscal repair, the suture threads are passed through the meniscus in step 2 and the bone tunnel is made after the osteotomy.

Post-operative protocol

The leg is immobilised in an extension brace for 6 weeks post-surgery to prevent any genu recurvatum. However, the brace is removed for physiotherapy sessions, which are started immediately after surgery. Partial weight-bearing resumes after 3 weeks and full weight-bearing is achieved at 6 weeks. From this point, a standard post-ACL reconstruction rehabilitation protocol can be followed. In short, the programme is delayed by 6 weeks compared to in a standard ligament reconstruction.

Advantages of the surgical technique:

• No bulky hardware that can impinge on the tunnels.
• The extensor mechanism remains untouched.
• There is minimal invasion at the metaphysis (optimum consolidation).
• Low cost.

Risques spécifiques :

• Posterior hinge fracture (theoretical)
• Iatrogenic genu recurvatum
• Tibial varus increased by 1° [21] Cance N, Dan MJ, Pineda T, Demey G, DeJour DH. Radiographic Investigation of Coronal Plane and Patellar Height and Changes Following Tibial Deflection Osteotomy for Correction of Tibial Slope in Combination With ACL Reconstruction. Am J Sports Med. 2024 Jan 29;03635465231222643.
• Patellar height raised by 0.08 on Caton-Deschamps index [21] Cance N, Dan MJ, Pineda T, Demey G, DeJour DH. Radiographic Investigation of Coronal Plane and Patellar Height and Changes Following Tibial Deflection Osteotomy for Correction of Tibial Slope in Combination With ACL Reconstruction. Am J Sports Med. 2024 Jan 29;03635465231222643.

These last two risks could be considered to be negligible, but it is still important to consider them during surgery to avoid perpetuating this tendency.

Discussion

With the improvements in surgical techniques and the reduction in the rates of repeat tear due to issues of technique, other risk factors have come into the foreground. It is not only in humans that tibial slope is relevant, as this assessment is also used in the veterinary field. In fact, medium to large dogs can tear the cranial cruciate ligament (CCL), which is equivalent to the ACL in humans. These animals have a tibial slope of between 20 and 30°. The treatment offered for CCL tear is bone surgery rather than ligament surgery, consisting of a deflexion osteotomy [6] Dan MJ, Wills DJ, Crowley JD, Cance N, Romandini I, Walsh WR, et al. Anterior cruciate ligament zoobiquity: Can man’s best friend tell us we are being too cautious with the implementation of osteotomy to correct posterior tibial slope. Knee surg sports traumatol arthrosc. 2024 May;32(5):1071–6. . The link between tibial slope and CCL tear is clear in dogs and carrying out a single bone procedure delivers stability and decisive functional outcomes.

It was in 1991, that the deflexion osteotomy in humans (then called the extension osteotomy) was presented to the Lyon Knee Surgery Congress [20] 7èmes journées lyonnaises de chirurgie du genou - Lyon 1991 [Internet]. [cited 2024 Aug 23]. Available from: http://lyon-knee-surgery.com/images/pdf/7%C3%A8mes%20journ%C3%A9es%20lyonnaises%20de%20chirurgie%20du%20genou%20-%20Lyon%201991/jdg-7/assets/basic-html/page-270.html. It has been known for many years that there is a link between tibial slope, SATT and ruptured ACL graft [22] Napier RJ, Garcia E, Devitt BM, Feller JA, Webster KE. Increased Radiographic Posterior Tibial Slope Is Associated With Subsequent Injury Following Revision Anterior Cruciate Ligament Reconstruction. Orthopaedic Journal of Sports Medicine. 2019 Nov 1;7(11):232596711987937. . There is a linear relationship between increasing the tibial slope and the force that the ACL needs to bear [23] Bernhardson AS, Aman ZS, Dornan GJ, Kemler BR, Storaci HW, Brady AW, et al. Tibial Slope and Its Effect on Force in Anterior Cruciate Ligament Grafts: Anterior Cruciate Ligament Force Increases Linearly as Posterior Tibial Slope Increases. Am J Sports Med. 2019 Feb;47(2):296–302. . After 20 years of follow-up, adolescents with a tibial slope ≥ 12° had a repeat tear rate of up to 78% when a hamstring had been used for the graft [24] Salmon LJ, Heath E, Akrawi H, Roe JP, Linklater J, Pinczewski LA. 20-Year Outcomes of Anterior Cruciate Ligament Reconstruction With Hamstring Tendon Autograft: The Catastrophic Effect of Age and Posterior Tibial Slope. Am J Sports Med. 2018 Mar 1;46(3):531–43. . The short term risk of repeat tear is doubled when the patellar tendon is used [25] Duerr R, Ormseth B, Adelstein J, Garrone A, DiBartola A, Kaeding C, et al. Elevated Posterior Tibial Slope Is Associated With Anterior Cruciate Ligament Reconstruction Failures: A Systematic Review and Meta-analysis. Arthroscopy. 2023 May 1;39(5):1299-1309.e6. . By contrast, a less steep tibial slope (<6°) drastically reduces the risk of repeat tear [26] Bargagliotti M, Benazzo F, Bellemans J, Truijen J, Pietrobono L, Formagnana M, et al. The Role of the Posterolateral Tibial Slope in the Rotational Instability of the Knee in Patients Affected by a Complete Isolated Anterior Cruciate Ligament Injury: Its Value in the Decision-Making Process during the Anterolateral Ligament Reconstruction. Joints. 2019 Sep;07(03):078–83. . SATT, which is itself related to tibial slope, is an indicator of the load that the graft will have to support in weight-bearing. Excessive stress will result in gradual elongation of the graft, meaning there will be residual laxity and, ultimately, an increased risk of fatigue tear (Figure 7) [25], Duerr R, Ormseth B, Adelstein J, Garrone A, DiBartola A, Kaeding C, et al. Elevated Posterior Tibial Slope Is Associated With Anterior Cruciate Ligament Reconstruction Failures: A Systematic Review and Meta-analysis. Arthroscopy. 2023 May 1;39(5):1299-1309.e6. [27] Ni Q kun, Song G yang, Zhang Z jun, Zheng T, Feng Z, Cao Y wei, et al. Steep Posterior Tibial Slope and Excessive Anterior Tibial Translation Are Predictive Risk Factors of Primary Anterior Cruciate Ligament Reconstruction Failure: A Case-Control Study With Prospectively Collected Data. Am J Sports Med. 2020 Oct;48(12):2954–61. .

Although lateral extra-articular procedures have reduced the rate of repeat tear, they do not mean that every rupture can be avoided [1] Saithna A, Monaco E, Carrozzo A, Marzilli F, Cardarelli S, Lagusis B, et al. Anterior Cruciate Ligament Revision Plus Lateral Extra-Articular Procedure Results in Superior Stability and Lower Failure Rates Than Does Isolated Anterior Cruciate Ligament Revision but Shows No Difference in Patient-Reported Outcomes or Return to Sports. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2023 Apr 1;39(4):1088–98. . ACL tear involves excessive anteroposterior translation but also instability in rotation. A modified Lemaire tenodesis has no effect on SATT [28] Pineda T, Cance N, Dan MJ, Demey G, Dejour DH. Evaluation of Anterior Tibial Translation Under Physiological Axial Load After ACL Reconstruction With Lateral Extra-articular Tenodesis. Orthopaedic Journal of Sports Medicine. 2024 May;12(5):23259671241246111. . It may well be indicated in patients with rotatory instability or in revision surgery, but it will not correct excessive anterior translation [28] Pineda T, Cance N, Dan MJ, Demey G, Dejour DH. Evaluation of Anterior Tibial Translation Under Physiological Axial Load After ACL Reconstruction With Lateral Extra-articular Tenodesis. Orthopaedic Journal of Sports Medicine. 2024 May;12(5):23259671241246111. .

The procedure to choose to directly address posterior tibial slope is tibial deflexion osteotomy. It is possible to perform a supra-tubercular, trans-tubercle or infra-tubercle deflexion osteotomy, as described above (Figure 7). The most important factor in choosing a technique is that the surgeon feels at ease using it, since there is currently no technique emerging as superior to any other and each one has its own advantages and drawbacks [29] Onishi S, Kim Y, Nakayama H, Mansour AA, Lowe WR, Ollivier M. Infratubercle Anterior Closing Wedge Osteotomy Corrects Sagittal Alignment without Affecting Coronal Alignment or Patellar Height. Journal of Clinical Medicine. 2024 Jan;13(16):4715. . We have set out the technique for the supra-tubercular osteotomy because this technique means that the resection can be made at the site of the deformity, in the metaphysis, in an area that is favourable to bone healing [30] Demey G, Giovannetti de Sanctis E, Mesnard G, Müller JH, Saffarini M, Dejour DH. Posterior tibial slope correlated with metaphyseal inclination more than metaphyseal height. Knee. 2023 Oct 1;44:262–9. . It has been clearly demonstrated that this osteotomy technique preserves sufficient metaphyseal bone for fixation [31] Demey G, Giovannetti de Sanctis E, Mesnard G, Müller JH, Saffarini M, Dejour DH. Sufficient Metaphyseal Bone for Wedge Removal and Fixation Hardware During Supratuberosity Tibial Deflexion Osteotomy in Knees With Excessive Posterior Tibial Slope. Am J Sports Med. 2023 Jul 1;51(8):2091–7. . The goal of this surgery is to obtain a tibial slope of between 4 and 6°, which means that SATT will be kept between 0 and 5mm without increasing the stresses on the posterior cruciate ligament (Figure 8).

While deflexion osteotomy was initially indicated in secondary revisions only, primary revision was subsequently added to its indications and later, some cases of primary tear [32], Dejour D, Rozinthe A, Demey G, van Rooij F, Saffarini M, ReSurg. First revision ACL reconstruction combined with tibial deflexion osteotomy improves clinical scores at 2 to 7 years follow-up. Knee Surg Sports Traumatol Arthrosc. 2023 Oct 1;31(10):4467–73. [33], Rozinthe A, van Rooij F, Demey G, Saffarini M, Dejour D. Tibial slope correction combined with second revision ACLR grants good clinical outcomes and prevents graft rupture at 7–15-year follow-up. Knee Surg Sports Traumatol Arthrosc. 2022 Jul 1;30(7):2336–41. [34] Sonnery-Cottet B, Mogos S, Thaunat M, Archbold P, Fayard JM, Freychet B, et al. Proximal Tibial Anterior Closing Wedge Osteotomy in Repeat Revision of Anterior Cruciate Ligament Reconstruction. Am J Sports Med. 2014 Aug;42(8):1873–80. . TDO produces excellent functional outcomes over observation periods exceeding 5 years with a graft rupture rate of around 2% after over 3 years of follow-up [9], Moran TE, Driskill EK, Tagliero AJ, Klosterman EL, Ramamurti P, Reahl GB, et al. Combined Tibial Deflexion Osteotomy and Anterior Cruciate Ligament Reconstruction Improves Knee Function and Stability: A Systematic Review. Journal of ISAKOS. 2024 Jun 28; [32] Dejour D, Rozinthe A, Demey G, van Rooij F, Saffarini M, ReSurg. First revision ACL reconstruction combined with tibial deflexion osteotomy improves clinical scores at 2 to 7 years follow-up. Knee Surg Sports Traumatol Arthrosc. 2023 Oct 1;31(10):4467–73. . Some studies have reported a 100% rate of resuming sport at the same level without repeat tear when TDO has been performed at primary revision [9] Moran TE, Driskill EK, Tagliero AJ, Klosterman EL, Ramamurti P, Reahl GB, et al. Combined Tibial Deflexion Osteotomy and Anterior Cruciate Ligament Reconstruction Improves Knee Function and Stability: A Systematic Review. Journal of ISAKOS. 2024 Jun 28; . This procedure is an effective way to decrease posterior tibial slope, reduce SATT and increase joint stability with the goal of protecting the graft. In terms of rotatory instability, we do not recommend using a lateral extra-articular procedure as an adjunct. Reducing the lateral slope will increase stability in rotation [35] Dejour D, Saffarini M, Demey G, Baverel L. Tibial slope correction combined with second revision ACL produces good knee stability and prevents graft rupture. Knee Surg Sports Traumatol Arthrosc. 2015 Oct;23(10):2846–52. .

What are the consequences of TDO?

Supra-tubercular TDO theoretically increases the Caton-Deschamps index by 0.02 for each degree by which the slope is reduced [36] Demey G, Mesnard G, Giovannetti de Sanctis E, Müller JH, Saffarini M, Dejour D. A Supratuberosity Anterior Closing-Wedge Proximal Tibial Osteotomy Increases Patellar Height: A Simulated Time Zero Uniplanar Radiographic Study. Arthroscopy. 2024 May 1;40(5):1544-1554.e1. . However, these results were obtained through radiological simulation and one clinical study found a mean 0.08 increase on the Caton-Deschamps index for a 9° decrease in posterior tibial slope [21] Cance N, Dan MJ, Pineda T, Demey G, DeJour DH. Radiographic Investigation of Coronal Plane and Patellar Height and Changes Following Tibial Deflection Osteotomy for Correction of Tibial Slope in Combination With ACL Reconstruction. Am J Sports Med. 2024 Jan 29;03635465231222643. . This shows that TDO has a not-insignificant effect on patellar height.

In the frontal plane, TDO does tend to produce a varus deformity of one degree [21] Cance N, Dan MJ, Pineda T, Demey G, DeJour DH. Radiographic Investigation of Coronal Plane and Patellar Height and Changes Following Tibial Deflection Osteotomy for Correction of Tibial Slope in Combination With ACL Reconstruction. Am J Sports Med. 2024 Jan 29;03635465231222643. . The explanation for this could be that the medial side is slightly easier to expose, which probably means that a slightly thicker resection is made. It is important to remain aware of this factor in the frontal plane during this surgery.

The patient must be warned that they will have a larger permanent scar than with a standard ligament reconstruction. This can sometimes be the aspect that is most difficult for the patient to accept, especially when TDO is being offered as a first line surgery.

Perspective for the future

Assessment of the posterior tibial slope and SATT does, however, present some issues. For example, it is not always straightforward obtaining true lateral view radiographs and consequently to be able to correctly interpret these images. The same can be said of the requirement for 20° of flexion. The measurement methods do not take extra-articular bone deformities into account if they are located outside the imaged area. A 2D assessment of a 3D structure can also lead to issues. In future it is likely that there will be a move to using CT or 3D radiography in weight-bearing in order to reduce bias and increase reproducibility of the examinations. EOSTM is a modality initially used for imaging spinal deformities, but it is now finding an increasing number of lower limb indications [37] Illés T, Somoskeöy S. The EOSTM imaging system and its uses in daily orthopaedic practice. International Orthopaedics (SICOT). 2012 Jul 1;36(7):1325–31. . Cone Beam is used in maxillofacial surgery, but it can also be used for taking single-leg stance imaging. This promising technology could be used to obtain a more precise assessment of posterior tibial slope and SATT.

A question that can legitimately be asked is whether TDO should be offered as an adjunct to ACL graft as a first line intervention when the posterior tibial slope and SATT are elevated. The thresholds for these indications are still to be determined, and while these interventions add additional complexity to the primary indication they may prevent repeated operations down the line.

Conclusion

ACL reconstruction is an extremely common intervention that is known to produce excellent results. In this context it is crucial to analyse and address the risk factors for repeat tear. The posterior tibial slope and its impact on anterior tibial translation in static single-leg stance have become key factors to consider in ACL tears. These are measurements that should be taken as part of the initial assessment. Tibial deflexion osteotomy as an adjunct to ACL graft repair is a treatment strategy that offers good results in specific indications.