Volume 32, Issue 5 p. 1071-1076
COMMENTARY
Open Access

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

Michael J. Dan

Corresponding Author

Michael J. Dan

Surgical and Orthopaedic Research Laboratories (SORL), University of New South Wales (UNSW), Sydney, New South Wales, Australia

Department of Knee Surgery, Lyon Ortho Clinic, Lyon, France

East Coast Athletic Orthopaedics, Merewether, New South Wales, Australia

Correspondence Michael J. Dan, Surgical and Orthopaedic Research Laboratories (SORL), Prince of Wales Clinical School, Faculty of Medicine, Prince of Wales Clinical School, Sydney, NSW, Australia.

Email: [email protected]

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Daniel J. Wills

Daniel J. Wills

Surgical and Orthopaedic Research Laboratories (SORL), University of New South Wales (UNSW), Sydney, New South Wales, Australia

Coast OrthoVet—Veterinary Orthopaedic Referral Services, Sydney, New South Wales, Australia

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James D. Crowley

James D. Crowley

Surgical and Orthopaedic Research Laboratories (SORL), University of New South Wales (UNSW), Sydney, New South Wales, Australia

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Nicolas Cance

Nicolas Cance

Department of Knee Surgery, Lyon Ortho Clinic, Lyon, France

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Iacapo Romandini

Iacapo Romandini

Department of Knee Surgery, Lyon Ortho Clinic, Lyon, France

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William R. Walsh

William R. Walsh

Surgical and Orthopaedic Research Laboratories (SORL), University of New South Wales (UNSW), Sydney, New South Wales, Australia

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David H. Dejour

David H. Dejour

Department of Knee Surgery, Lyon Ortho Clinic, Lyon, France

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First published: 21 March 2024

Abstract

Anterior cruciate ligament (ACL) reconstruction (ACLR) is used to treat clinical instability post ACL rupture, however, there is a high rate of incomplete return to sport and rerupture. There is increasing interest in posterior tibial slope as an intrinsic risk factor for ACLR failure and persistent instability. Zoobiquity describes the collaboration between the human and veterinary professions in order to advance the scientific understanding of both fields. Given the cranial cruciate ligament (CCL) in dogs is synonymous with the anterior cruciate ligament in humans, functioning to control internal rotation and anterior translation, but osteotomies, rather than ligament reconstruction, are the mainstay of treatment for CCL rupture, this editorial sort to gain insights into this form of treatment from the veterinary world.

Level of Evidence: Level V, evidence.

Abbreviations

  • ACL
  • anterior cruciate ligament
  • ACLR
  • anterior cruciate ligament reconstruction
  • CCL
  • cranial cruciate ligament
  • CCWO
  • cranial closing wedge osteotomy
  • TDO
  • tibial deflexion osteotomy
  • TPLO
  • tibial plateau levelling osteotomy
  • TTA
  • tibial tuberosity advancement
  • EDITORIAL

    Anterior cruciate ligament (ACL) reconstruction (ACLR) is the gold standard of treatment for cases of symptomatic instability following ACL rupture. Despite the considerable interest in this subject, human patients are still plagued by incomplete return to sport and rerupture [8]. The cranial cruciate ligament (CCL) in dogs is synonymous with the ACL in humans, functioning to control internal rotation and anterior translation [1]. For dogs with CCL rupture, tibial plateau levelling osteotomies (TPLOs) are the standard of care over ligament reconstruction. Tibial osteotomies have been reported in humans to correct increased tibial slope, a known intrinsic risk factor for ACLR failure [18, 40]. Zoobiquity is the term used to describe the collaboration between the human and veterinary professions to advance scientific understanding in both fields [10]. The objective of this editorial was to review the veterinary literature on the surgical management of CCL rupture, with a focus on proximal tibial osteotomies, with the intention that this may provide insights into the surgical management of ACL rupture and the appropriateness of slope-altering osteotomies in humans.

    AETIOLOGY OF CCL RUPTURE

    CCL rupture is one of the most common causes of hindlimb lameness in dogs [43]. Middle-aged, medium-large breed dogs with an increased tibial slope, normally 20–30°, are most commonly affected [30]. Dogs most commonly present with a chronic history of lameness that may have acutely worsened. The condition is a chronic, progressive disease that results in the eventual rupture of the ligament [6]. Tibial slope has been found to be increased by 6° in dogs with CCL rupture compared to the normal population, termed ‘deformity of the proximal tibia’ [26]. This suggests an aetiology of attrition rupture in the dog [39]. This is in contrast to humans with an average slope of 9° [4] and ACL injury occurring following acute trauma most commonly in the young pivoting athlete. Higher tibial slope has been identified as a risk factor for ACLR failure in humans, particularly the young and revision population [24], with an odds ratio of failure of 1.07 per 1° increase in tibial slope [19], and differences in the proximal tibial metaphyseal morphology have been demonstrated in the human with increased slope compared to controls [15].

    TREATMENT OF CCL RUPTURE

    In comparison to human orthopaedics, intra-articular ligament reconstruction is not favoured in canine orthopaedics. Concerns for lack of patient compliance during graft revascularisation, increased tibial slope and resultant weak mechanical properties limit its success in dogs [2, 6]. Cranial tibial thrust, defined as the cranially/anteriorly directed force produced by tibial compression during weight bearing, is responsible for cranial/anterior drawer motion in the CCL-deficient stifle [34]. The magnitude of the cranial tibial thrust increases when tibial plateau slope angle increases [35]. The primary goal of surgical treatment for CCL rupture in dogs is to eliminate the cranial/anteriorly directed thrust during weight bearing by neutralising the tibiofemoral shear force. Accurately executed proximal tibial osteotomies can achieve this by providing dynamic stability to the CCL-deficient knee [21]. The two main types of proximal tibial osteotomies in dogs are slope-correcting osteotomies such as the TPLO and an anteriorising tibial tubercle osteotomy such as the tibial tuberosity advancement (TTA) (Figure 1).

    Details are in the caption following the image
    Schematic illustration of the biomechanical rationale for two commonly performed proximal tibial osteotomies in the cranial cruciate ligament-deficient canine knee compared to a normal knee. (a) Tibial tuberosity advancement (TTA); TTA aims to remove any anteriorly directed vector from the patella tendon (*), making the patella tendon angle (*) perpendicular to the tibial plateau, resulting in a directly compressive force with quadriceps contraction, acting as a dynamic control. (b) Normal canine knee with increased tibial slope. (c) Tibial plateau levelling osteotomy (TPLO); TPLO reduces the tibial plateau angle (#), thereby functioning passively and actively to reduce anterior shear during axial load/weight bearing. F, femur; T, tibia, *, patella tendon angle, #, tibial plateau angle.

    TPLO was described by veterinarian Dr. Barclay Slocum and his father, Dr. James L. Slocum, an orthopaedic surgeon who described anterior medial rotatory instability [37] and the ‘pes-plasty’ [36]. TPLO is reported to functionally stabilise the stifle joint during weight bearing, neutralising the cranial tibiofemoral shear force by levelling the tibial plateau [3]. Levelling the tibial plateau reduces the magnitude of the cranial tibial thrust force to regain stifle joint stability during the stance phase of the gait. This is achieved by making a curved osteotomy in the proximal tibia and rotating the proximal fragment to a target angle of 5–6°, followed by appropriate implant placement.

    Tepic et al. theorised an alternative biomechanical model of the CCL-deficient stifle and described TTA [41]. Based on this model and the work of Nisell et al. [27], stifle stabilisation procedures should be aimed at levelling the tibial plateau such that it is perpendicular to the patellar ligament or altering the angle of the patellar ligament such that it is perpendicular to the tibial plateau (termed the patellar tendon angle). By advancing the tibial tubercle, the patella tendon angle is always less than 90, removing any anteriorly/cranially directed vector to the patella tendon, again, with the biomechanical aim to eliminate cranial/anterior thrust. While the patella tendon angle has been shown to influence the amount of stress in the ACL, the utility of a TTA in ACL surgery for humans has not been explored [16, 17].

    A systematic review of surgical treatments for CCL rupture in dogs by Bergh et al. reported strong evidentiary support that functional recovery in the intermediate postoperative time period was superior following TPLO compared with extracapsular augmentation. Further, TPLO has been shown to be superior in terms of gait analysis at the trot compared to lateral extra-articular capsular shift and TTA in dogs [22]. The cranial closing wedge osteotomy is another proximal tibial osteotomy that achieves the same principle of a TPLO and is akin to the tibial deflexion osteotomy (TDO). TDO was first described by Henri Dejour in humans in 1991 [14] and levels the plateau by osteotomy of an anterior wedge of bone. Figure 2 radiographically demonstrates the similarities and differences between the TPLO and TDO.

    Details are in the caption following the image
    Lateral knee radiographs of preoperative and postoperative tibial plateau levelling osteotomy in a dog (a, b) and tibial deflexion osteotomy in a human (c, d); (a) and (c) demonstrate increased tibial slope (S) with associated increased anterior tibial translation (T) relative to the femur preoperatively. For both patients, the tibial slope and anterior translation are decreased postoperatively.

    PIVOT-SHIFT PHENOMENON

    The proximal tibial osteotomy alone is successful in not only reducing the anteriorly directed thrust but also eliminating the pivot shift phenomenon in over 95% of cases [20]. A lateral extra-articular capsular suture can be performed in addition to proximal tibial osteotomies if pivot shift is persistent [32]. In human biomechanical studies, decreasing tibial slope reduces rotational instability [42], and while some authors have added a lateral extra-articular procedure in combination with ACLR and osteotomy [38], others have not, and reported no residual pivot shift clinically [13]. The veterinary literature would suggest that adding a lateral extra-articular procedure is only required in those small number of patients that possess severe rotational instability [32]. In humans, better patient-reported outcomes and objective laxity measures were reported in patients who underwent combined ACLR with TDO compared to TDO alone or with lateral extra-articular tenodesis [28].

    OSTEOTOMY-INDUCED RECURVATUM

    For both humans and dogs, the creation of tibial recurvatum following osteotomy may be of clinical concern. In the dog postoperatively, gait analysis demonstrates a hyperextended gait characterised by an increased velocity in knee extension during the middle to end of the swing phase without change in the stance phase [23]. In humans, it has been suggested to secure the ACL graft at 70° of knee flexion and use an extension brace for 6 weeks postoperatively to create a soft tissue contracture to prevent hyperextension [13]. Like the human, the osteotomy can be performed above, at the level of or below the tibial tubercle in dogs; however, healing is impaired when performed below the metaphyseal bone [7], as has been shown in coronal plane high tibial osteotomies in humans [33]. Therefore, while technically difficult, osteotomies performed above the tibial tubercle are likely preferred for bone healing and also addressed the site of the deformity in increased posterior tibial slope [15].

    DESIRED SLOPE CORRECTION

    The appropriate amount of tibial plateau slope correction following osteotomy for each patient is unknown. Slocum advocated for a correction to 5° of tibial slope for the TPLO procedure. The rationale behind this degree of correction is to place the tibial plateau perpendicular to the functional axis of the limb during weight bearing [35]. In the human literature, the goal of correction is largely limited to expert opinion. Some advocate for correction to the mean posterior tibial slope, while others advocate for overcorrection [12]. There are case reports documenting that overcorrection of sagittal plane osteotomies can cause attrition ruptures of the corresponding cruciate ligament [11], and this is supported in biomechanical veterinary literature [35]. Dejour evaluated the results of his osteotomies to optimise the tibial translation during single leg stance and found that 2–3° of posterior tibial slope overcorrected the translation, whereas 4–6° of tibial slope optimised translation between 0 and 5 mm. This equates to a correction past the mean tibial slope by between 1 and 2 standard deviations [9]. Additionally, there is a move by some in the veterinary world to individualise the osteotomy based on the sagittal mechanical axis [5], as is planned and executed for coronal plane osteotomies in humans [25]. In contrast, little is known about the sagittal mechanical axis for osteotomy planning in humans [29] and is worthy of future exploration.

    CONCLUSION

    The pathogenesis of increased tibial slope and attritional ligament rupture in dogs is clear, with successful outcomes with proximal tibial osteotomy alone. Given the detrimental effects of tibial slope on ACL graft failure in young patients [31], orthopaedic surgeons should follow the lead of man's best friend and be more proactive in correcting increased tibial slope for patients undergoing primary ACLR to reduce rates of rerupture.

    AUTHOR CONTRIBUTIONS

    All authors contributed to the writing and editing of this manuscript and have approved the final version.

    ACKNOWLEDGEMENTS

    The authors have no funding to report. Open access publishing facilitated by University of New South Wales, as part of the Wiley - University of New South Wales agreement via the Council of Australian University Librarians.

      CONFLICT OF INTEREST STATEMENT

      The authors declare no conflict of interest.

      ETHICS STATEMENT

      The authors have nothing to report.