Modified Triple Tibial Osteotomy for Combined Cranial Cruciate Ligament Rupture, Tibial Deformities, or Patellar Luxation
ABSTRACT
Proximal tibial deformities or patellar luxation may occur concurrently with cranial cruciate ligament rupture. The objective of this study was to describe the management of those conditions with a modified triple tibial osteotomy (TTO) in nine dogs. Medical records of dogs who underwent a modified TTO were reviewed. The mean pre- and postoperative patellar tendon angles were 104.2° and 92.9°, respectively. The mean pre- and postoperative mechanical medial proximal tibial angles were 99.5° and 91.5°, respectively. Medial patellar luxation was present in five dogs (55.6%) and treated in all five dogs with a tibial crest transposition. Tibial torsion was grossly resolved in two dogs (22.2%). Perioperative distal tibial crest fracture was treated by pins and a figure-of-eight tension-band wire in five dogs (55.6%). One major (surgical site infection) and three minor postoperative complications were observed. At the last follow-up, seven dogs (77.8%) had no lameness, one dog (11.1%) had mild lameness, and one dog (11.1%) had moderate lameness. Radiographic evaluation showed good (2/9; 22.2%) to excellent (7/9; 77.8%) bone healing. The visual analog scale evaluation revealed good-to-excellent owner satisfaction. Cranial cruciate ligament rupture, tibial deformities, and medial patellar luxation are difficult to treat together. A modified TTO may be used to treat these conditions.
Introduction
Cranial cruciate ligament (CrCL) deficiency is one of the most frequently diagnosed orthopedic conditions in the canine stifle, with a prevalence of 2.6% across all breeds.1 Proximal tibial deformities in the frontal plane (tibial varus or tibial valgus), tibial torsion, excessive tibial plateau angle (eTPA; previously defined as a TPA >34°), or patellar luxation can be associated with CrCL rupture.2–5
The two most popular dynamic techniques for addressing the lameness and the disability associated with functional CrCL failure are tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA). Minor angulation or rotation may be treated with TPLO by shifting the jig position before plate fixation. It was suggested by some authors that larger deformities should be treated by a TPLO combined with a single osteotomy, a medial or lateral closing wedge osteotomy, or a cuneiform wedge osteotomy, depending on the type of deformation.6–8 In 2011, Weh et al. reported a combination of TPLO and transverse corrective osteotomy on 19 limbs, 68.4% of which had a proximal tibial varus or valgus and severe tibial torsion.8 The long-term clinical outcome was reported as excellent, but postoperative surgical complications were documented in 21% of the cases, and all complications were considered major because they necessitated additional surgery. More recently, a retrospective study described the surgical technique in 13 stifle joints in which a combined TPLO and tibial tuberosity transposition (TTT) was used to treat CrCL rupture combined with medial patellar luxation (MPL). No catastrophic or major postoperative complications occurred, and the TPLO-TTT was found to be a reliable and effective technique.9 With the original TTA technique, only medial or lateral patellar luxation could easily be treated with tibial crest transposition. Angular tibial deformity correction requires a separate osteotomy, and the plate for TTA interferes with additional medial plate fixation.7 However, new techniques such as the TTA-2 and the TTA Rapid use only a cage, and the Modified Maquet Procedure uses only a wedge-shaped implant of titanium foam.10,11 Consequently, an additional corrective osteotomy could be performed but has not been described yet.
Many other techniques have been described to achieve stifle joint stability that neutralizes the tibiofemoral shear forces dynamically in a CrCL-deficient knee, including a triple tibial osteotomy (TTO). TTO is a combination of the tibial wedge osteotomy described by Slocum and Devine and the TTA.6 TTO partially levels the tibial plateau while advancing the tibial tuberosity and patellar tendon. Proposed advantages of the TTO technique include minimal change to the orientation of the tibiofemoral articulating surfaces, a relatively small osteotomy gap caudal to the tibial tuberosity, no loss of limb length, and low technical difficulty when the appropriate instrumentation is used.6 Overall, its complication rate is comparable to those obtained using TPLO and TTA (23–36%), and the most common complication is a fracture through the distal end of the tibial crest osteotomy (23.4%).12–14
To date, no study has documented the correction of angular tibial deformities and the correction of patellar luxation in combination with a CrCL rupture treated by TTO. The objective of this preliminary study was to describe the surgical management and outcome of modified triple tibial osteotomy for CrCL, MPL, and tibial deformities (valgus and torsion) in nine dogs.
Materials and Methods
Criteria for Case Selection
Medical records (November 2011 to June 2016) of all dogs diagnosed with CrCL injury (partial or complete) and proximal tibial valgus treated by modified TTO were retrospectively analyzed. Dogs with additional tibial torsion and MPL were also included in the study. A tibial valgus was considered if the mechanical medial proximal tibial angle (mMPTA) was >96.6°.15 Torsion was considered present if the medial surface of the calcaneus was not aligned at the center of the distal intermediate tibial ridge on radiographs.15,16 The dogs’ characteristics (breed, age, and sex), body weight, side affected, duration and severity of lameness, and MPL were recorded. Lameness was graded with a numerical rating scale with five levels of severity where 0 = no lameness; 1 = slight lameness; 2 = obvious weight-bearing lameness; 3 = severe weight-bearing lameness; 4 = intermittent nonweight-bearing lameness; and 5 = continuous nonweight-bearing lameness.
Surgical Planning
A complete orthopedic examination was performed. If stifle joint distention and positive draw sign were noted, suggesting CrCL deficiency, cranio-caudal and medio-lateral radiographs of the affected stifle were obtained to assess the joint and to plan the surgery. For the medio-lateral view, the limb was positioned such that the stifle joint was fully extended (at least 135°) and the femoral condyles were superimposed.12 Using the long axis of the femur and the tibia as reference axes, a goniometer was placed over the femoral and tibial diaphysis to check the correct stifle extension. Radiographs with cranial tibial subluxation were rejected. Cranial tibial subluxation was considered present if the caudal margin of the femoral condyles was located caudally to the caudal margin of the tibial plateau. After 2014, cranial tibial subluxation was also measured as described by Bielecki et al.17
The preoperative TPA was recorded, and the angular and torsional tibial deformities were assessed. When an MPL was present, a cranio-caudal radiograph of the femur was obtained to evaluate a varus of the distal aspect of the femur.
Surgical planning was based upon the deformities present. The preoperative patellar tendon angle (PTA), correction angle (CA), and wedge angle (WA) were defined as previously described for the TTO technique.12–14 Briefly, WA was calculated according to the formula currently recommended by Renwick, which is a modification of that reported by Bruce: WA = 0.6 × CA + 7.3 with CA defined as the angle of correction of the PTA needed to achieve 90°.6,12,14 In cases when TPA – WA was <0°, the intended WA was calculated according to the formula TPA – 5°.14 Preoperative TPA was determined according to standard guidelines.18 The anticipated postoperative TPA was calculated as TPA – WA to verify that the postoperative TPA would not be <5°. If no gross tibial torsion deformity was noted, the preoperative proximal tibial valgus deformity was quantified by measuring the mMPTA and the mechanical medial distal tibial angle (mMDTA) on cranio-caudal radiographic projections of the tibia; these angles were compared with the published reference angles in dogs.15 Additionally, mMPTA of the contralateral tibia was obtained by cranio-caudal radiographs. If contralateral mMPTA belonged to the reference range, the medio-lateral WA was made to reach this mMPTA. If contralateral mMPTA was abnormal, the angle of the medial closing wedge was made to reach an mMPTA of 93°. When torsional deformity was present, no accurate preoperative radiographic quantification of the frontal plane deformity was possible; therefore, gross estimation was obtained, and further angular correction was planned intraoperatively, as described by Weh.8
The three osteotomy lines for the TTO were drawn on the cranio-caudal and medio-lateral radiographs; for valgus proximal tibial angulation, a biplanar cuneiform closing wedge osteotomy was used to simultaneously reduce the tibial plateau slope and correct this deformity. The angle of cranial closing wedge (WA) and the angle of medial closing wedge were assessed independently. The distance between the more proximal osteotomy line for the TTO and the beginning of the osteotomy for the biplanar cuneiform closing wedge was then measured on the medial aspect of the tibia and reported on a medio-lateral radiograph (Figure 1).
Citation: Journal of the American Animal Hospital Association 55, 6; 10.5326/JAAHA-MS-6823
Additionally, if tibial torsion was present, the distal fragment of the tibia was rotated before implant placement by visually assessing the alignment of the stifle and hock joints.19,20 At 90° stifle flexion, the patella, tibial tuberosity, and metatarsal bones III and IV should be aligned in the same sagittal plane.20,21
In cases of patellar luxation, if malalignment of the quadriceps mechanism was present (medial or lateral displacement of the tibial tuberosity), this was addressed simultaneously with the proximal tibial osteotomies. This correction was performed by deviation of the cranial tibial tuberosity segment to the opposite side of the luxation. Adjunct techniques such as trochleoplasty (wedge recession or block recession) and other ancillary soft-tissue procedures were also performed as described previously for surgical correction of patellar luxation.22,23
Surgical Technique
One surgeon (T.C.) performed all surgical procedures. Patients were placed under general anesthesia and positioned in dorsal recumbency with hanging leg technique. The operated limb was aseptically prepared and draped to have full access from the stifle to the tarsus. Intravenous ampicillin with sulbactama (20 mg/kg) was administered immediately preoperatively and thereafter every 90 min during surgery.
The stifle joint was explored by a medial arthrotomy or by arthroscopy as recommended previously to confirm the CrCL rupture, to probe the menisci and to assess the trochlear groove in case of MPL.6 The CrCL remnants were removed, and a partial meniscectomy was performed if a meniscal tear was identified by probing. In case of MPL, a lateral parapatellar arthrotomy was performed. The trochlear groove was assessed, and if it was determined to be shallow, a trochlear wedge or block recession was performed.
After a medial approach to the proximal tibia, a TTO was performed as described by Bruce et al.12 Briefly, a transverse 1.5–2.0 mm hole, depending on the dog’s size, was drilled immediately caudal to the cranial cortex of the tibia at a distance equal to the length of the patellar ligament distal to the patellar ligament insertion. The tibial crest osteotomy was made in the transverse plane parallel to the cranial aspect of the tibial crest. It was initiated at the predrilled hole distally and ended proximally caudal to the patellar ligament. The tibial crest osteotomy was then wedged open to allow a precalculated wedge of bone to be removed from the tibia, caudal to the tibial crest osteotomy. The base of the cranio-caudal wedge was located at the exact midpoint of the tibial crest osteotomy. The apex of the cranio-caudal wedge was a predrilled 1.5–2 mm transverse hole, depending on the dog’s size, located immediately cranial to the caudal tibial cortex. For tibial valgus deformity, a medio-lateral closing wedge was performed using an oscillating saw just proximal to the cranio-caudal wedge (Figure 1). The fibula was left intact. The location of the medial closing wedge was directly linked to the cranio-caudal wedge and was not based on the Center of Rotation of Angulation of the tibial deformity. The medio-lateral WA was determined by using a sterilized caliper and by using the right triangle method as described previously.2 Additionally, if tibial torsion was present, this was corrected immediately before plate placement; realignment of the patella, tibial tuberosity, and metatarsal bones III and IV was performed with a 90° stifle flexion by rotating the distal bone fragment with bone-holding forceps. When an MPL was present, the tibial crest was laterally transposed to realign the extensor apparatus and secured with one or two Kirschner wires. Tibial fragments were then fixed with a TPLO Plateb or Locking Compression Platec and screws. Proximal screws were locked in the proximal metaphysis of the tibia, and compression was applied with a distal screw. When an intraoperative fracture of the distal tibial crest occurred, it was secured with pins and a figure-of-eight tension band wire.
Surgical incisions were closed in layers. Every intraoperative complication was recorded. Radiographs of the operated limb were obtained in the same manner as the preoperative radiographs. The postoperative PTA, TPA, mMPTA, and mMDTA were calculated. Final limb alignment was grossly assessed. The methods of fixation and intra- and postoperative complications were also noted.
Perioperative Care
An adhesive bandage was applied postoperatively for a variable duration. The perioperative and postoperative antimicrobial and analgesic protocols varied, but all dogs received perioperative antibiotics. Perioperatively, a combination of opiate and nonsteroidal anti-inflammatory medication was administered; postoperative oral nonsteroidal anti-inflammatory treatment was continued for 2 wk. Dogs were discharged 1–3 days after surgery. Activity was restricted to short walks on a lead until recheck examination with radiographic assessment of healing 6–8 wk later.
Follow-Up
In-hospital re-evaluation and radiographic evaluation of healing were reviewed, and the evaluations were recorded. Lameness score evaluation was performed using the same numerical rating scale as preoperatively. Complications were categorized as previously proposed including catastrophic (resulting in death or limb loss), major (requiring further medical or surgical treatment for resolution), or minor.24 Surgical site infection was defined as an infection occurring at the surgical site within a year of surgery in accordance with the criteria used by the CDC.25
Healing was retrospectively evaluated based on grading criteria developed by the International Society of Limb Salvage.26 Postoperative radiographic bone healing was graded using the following four categories: poor (no evidence of callus and no fusion of fracture lines, union <25%), fair (discrete sign of callus or fusion of the fracture lines, union 25–50%), good (bridging callus but still with the appearance of fracture lines, union 50–75%), and excellent (disappearance of fracture lines, union >75%). Limb function was subjectively assessed and lameness was graded using the following categories: no (no lameness), mild (weight bearing), moderate (weight bearing with occasional nonweight bearing), severe (predominantly nonweight bearing), and nonweight bearing.8
Later follow-up was obtained by owner interview via telephone and by a mailed questionnaire (using a visual analog scale [VAS]) at the time of data collection for this report (Appendix).8,27 Owners were asked to evaluate the dog’s lameness, the dog’s ability to tolerate exercise, and their impression of the success of the surgery. Owners were also asked to report any further complications or subsequent surgery performed on the stifle joint after the original surgery.
Recorded Data and Statistical Analysis
All numerical data were expressed as mean and range. Dogs with and without MPL were compared. Qualitative data were compared with the Fisher exact test. A P value <.05 was considered significant. All analyses were performed using commercial softwared.
Results
Case Details
Nine dogs who were identified with CrCL rupture, tibial deformities, or MPL were treated with modified TTO. The breeds were Yorkshire terrier (n = 2); American bulldog (n = 2); and one each of Boston terrier, Chihuahua, Griffon Fauve de Bretagne, Labrador retriever, and mixed-breed dog. There were three castrated males, one intact male, four spayed females, and one intact female. The mean body weight was 15.9 kg (range 2–34.6 kg), and the mean age was 5.1 yr (range 2–11 yr; Table 1).
All dogs presented with hind limb lameness of a mean duration of 2.9 mo (range 0.5–10 mo). The left stifle was affected in five dogs, and the right stifle was affected in four dogs. Four dogs presented with grade 3 lameness, two dogs with grade 2, two dogs with grade 5, and one dog with grade 4 lameness. Five of the dogs had concomitant MPL of grade 2 (n = 1), grade 3 (n = 3), and grade 4 (n = 1; Table 1). All the dogs with MPL presented an intermittent nonweight-bearing lameness of the affected limb since their acquisition but at a lower grade than the acute lameness following CrCL rupture. As a result, it was decided to treat all of them for their MPL.
All dogs had preoperative radiographs, and one also underwent computed tomography imaging (Figures 2A–D). Tibial deformities included tibial valgus in all dogs and tibial torsion in two dogs. Mean preoperative mMPTA and mMDTA were 99.5° (range 97.3–102.3°) and 98.2° (range 94.5–100.3°), respectively. The mean preoperative PTA was 104.2° (range 99.2–110°), and the mean preoperative TPA was 22° (range 18.2–27.9°; Table 2). No distal femoral varus was present in dogs with MPL.
Citation: Journal of the American Animal Hospital Association 55, 6; 10.5326/JAAHA-MS-6823
Surgical Procedure
All dogs underwent stifle joint exploration by arthroscopy (n = 4) or arthrotomy (n = 5). CrCL rupture (three partial and six complete ruptures) was confirmed in all dogs, and one dog had a meniscal tear treated by partial meniscectomy. MPL was treated by lateral tibial crest transposition in all dogs (n = 5) and trochlear wedge recession and trochlear block recession in two dogs each. The shape of the trochlear groove was normal for the last dog with ∼50% of the patella protruding above the trochlear ridges. All patellae were stable and could not be luxated at the end of the procedure. Tibial torsion was grossly treated with a manual rotation of the distal aspect of the tibia before stabilization for two dogs. In one dog (dog 3), correction of internal tibial torsion allowed for a simultaneous lateralization of the tibial tuberosity for MPL correction.
For all nine dogs, stabilization was performed with a 2.0 (n = 3), 2.7 (n = 2), 3.5 mini (n = 1), or 3.5 mm standard (n = 2) TPLO plateb placed on the medial aspect of the tibia spanning tibial segments of the wedge osteotomy in eight limbs. In the last dog, a 2.0 mm Locking Compression T-Platec was placed to perform stabilization with a centromedullary pin.
Immediate postoperative radiographs were performed in all dogs (Figures 2E–G). The mean postoperative mMPTA and mMDTA were 91.5° (range 88.8–95.5°) and 96.4° (range 93.9–99.3°), respectively. In this study, a change of 8° for the mean mMPTA and 1.8° for the mMDTA were achieved. The mean postoperative PTA was 92.9° (range 91.9–94.4°), and the mean postoperative TPA was 7.0° (range 4.2–14.2°; Table 2).
Complications
The distal end of the tibial crest fragment fractured in five dogs during surgery (55.6%) and was treated with one or two pins and a figure-of-eight tension-band wire.
There was one major postoperative complication and three minor complications. Surgical site infection occurred in one dog, 1 wk after surgery. Escherichia coli was cultured, and the infection was resolved with long-term antibiotic therapy (amoxicillin and clavulanic acide; 15 mg/kg orally q 12 hr for 8 wk). Four months after surgery, the implants were removed, and the radiographs showed good healing of the bone. The dog showed persistent intermittent weight-bearing lameness. The other minor complications included postoperative distal tibial crest fracture in one dog, seroma formation in one dog, and swelling at the cranial aspect of the pins in another dog. The minor complications resolved without any treatment and had no clinical consequences. There was no significant difference between intra- and postoperative distal crest fracture occurrence between dogs with MPL and dogs without MPL (P = .76).
Outcome
In-hospital re-evaluation of limb function and assessment of radiographic healing was available for all dogs. Based on the scoring system used, follow-up radiographs demonstrated satisfactory osteotomy line healing progression. Delayed union occurred in one dog with surgical site infection. No screw loosening or bone plate failure was observed. Radiographic evaluation at a mean of 10.8 wk postoperatively (range 6–14 wk) showed good bone healing in two dogs (22.2%) and excellent bone healing in seven dogs (77.8%). Limb function was evaluated at these same time frames; seven dogs had grade 0 lameness (77.8%), one dog had grade 1 lameness (11.1%), and one dog had grade 2 lameness (11.1%; the case with surgical site infection). The patella remained stable in dogs with former MPL.
Long-term follow-up evaluation was obtained by telephone interviews with the owner and by a mailed questionnaire (VAS) for seven dogs. Mean follow-up was 26.7 mo (range 4–48 mo). No additional procedures or complications, other than those previously documented, were reported for any limb. In six dogs, the owners were satisfied with the outcome of the surgery. In one case, the owner of the dog who had surgical site infection was partially satisfied because of a persistent moderate lameness.
The VAS questionnaire was completed by seven owners. When asked to evaluate the dog’s exercise tolerance, the mean response was 7.9 (range 4–10), where 0 represented “struggles on short walks” and 10 represented “copes fine with long walks.” The mean response was 8.4 (range 5–10) when owners were asked to evaluate the dog’s lameness, where 0 represented “couldn’t be more lame,” and 10 represented “no lameness.” Success of the surgery was graded with 0 representing “poor,” and 10 representing “excellent”; the mean response was 8.6 (range 6–10). Mean owner response as to whether they would have the surgery again was 9.4 (range 6–10; with one 6 and six 10; Table 3).
Discussion
This report is a preliminary study that describes a case series of nine dogs with combined CrCL rupture, tibial deformities, or MPL managed by modified TTO. Surgery was successful in all dogs with full or acceptable function despite a high peri- or postoperative distal tibial crest fracture (6/9; 66.7%).
Corrections of the tibial deformities and/or MPL have already been described with other tibial osteotomies for CrCL insufficiency.6,7,9,28,29 Tibial valgus correction can be accomplished with a standard TPLO by sliding the distal jig arm laterally (toward the tibia) along the distal jig pin, but this technique can only correct modest valgus and create a lateral open wedge at the level of the osteotomy, which increases the stress on the fixation.6 Tibial torsion can also be corrected during standard TPLO, but it still has a limited range of angle.6,7 The combination of TTO and biplanar cuneiform closing wedge allows for the correction of tibial valgus and tibial torsion, which creates a medial closing wedge that allows correct bone fragment apposition, thereby limiting the stress on the fixation. One stifle had an overcorrection of the proximal tibial valgus with a postoperative mMPTA of 88.8°, creating a tibial varus. However, this overcorrection had no clinical impact, and the dog showed no lameness 4, 8, and 11 wk postoperatively.
MPL requires tibial crest transposition when a medial displacement of the tibial tuberosity is present, which can be simultaneously performed with a TTA (i.e., TTTA).6,29 However, correcting another tibial deformity would require a separate osteotomy, and the TTA plate would interfere with additional medial plating.7 With standard TPLO, another transverse osteotomy is also needed to translate the tibial crest medially or laterally, which induces a loss of medial bone fragment apposition.7–9 MPL treatment is easily applied with TTO because the tibial crest only has to be translated medially or laterally after the tibial crest osteotomy and secured with one or two cranio-caudal pins that do not interfere with the medial tibial plate fixation. Moreover, in cases in which the distal tibial crest hinge is still intact, correcting internal tibial torsion by externally rotating the distal tibial segments results in simultaneous lateralization of the tibial tuberosity.
Weh et al. described a surgical technique and outcome for treating CrCL rupture and multiple proximal tibial deformities (varus, valgus, excessive TPA, tibial torsion, and patellar luxation) by combining TPLO and transverse corrective osteotomies.8 They reported that 21% of the cases had major complications that necessitated additional surgery. In the current study, the main event was intraoperative tibial crest fracture at its distal cortex. This has been reported in 18–23.4% of patients during TTO (including intraoperative and postoperative tibial crest fracture).12–14 Breed, age, size of the WA, size of the dog, and experience of the surgeon all contribute to the occurrence of distal tibial crest hinge fractures. Because it is almost always an intraoperative fracture, it can easily be repaired at the time of surgery if necessary and should therefore be considered an event more than a complication. Tibial crest fracture occurred in six cases (five intraoperatively and one postoperatively) in this study, but three had tibial crest transposition, which could predispose to tibial crest fracture. However, there was no significant difference in distal crest fracture occurrence between dogs with MPL and dogs without MPL (P = .76). The tibial crest was secured for five cases with one or two cranio-caudal pins and a figure-of-eight tension-band wire. In order to reduce this intraoperative event, the tibial crest may be moved very slowly in order to possibly play on the viscoelastic property of the bone.30 However, this is difficult in the case of TTO because it is the closure of the cranio-caudal wedge osteotomy that leads to the advancement of the tibial crest. Despite one dog having an evident tibial crest fracture on the radiographs 4 wk after surgery, the fragment was considered stable based on the comfort of the patient and the physical examination, and additional surgery was not considered necessary. The fragment healed with only slight displacement. It is true that pins and tension-band wires could be routinely performed during the procedure to overcome any postoperative tibial crest fracture. However, it leads to increased surgical time and requires adding other implants. Given the limited clinical consequences of a postoperative tibial crest fracture, it is difficult to know the benefit/risk of adding implants that could protect the tibial crest but also lead to implant migrations and infections (and therefore increase morbidity). A prospective study comparing TTO with or without the systematic addition of pins and tension-band wires is needed to document the advantages or disadvantages of both procedures.
As reported by Weh et al, tibial torsion was only assessed and treated visually.8 Indeed, the radiographic assessment of tibial torsion is difficult and often inaccurate. Computed tomography would have been more accurate for measuring tibial torsion.21 However, rotation of the distal segment of the tibia was easily performed after osteotomies and before final fixation in two of the cases.
Like TTA planning, preoperative TTO planning is based on the measurement of the PTA. Accurate PTA measurement is critical to functionally stabilize the stifle joint during weight bearing. As PTA is subjected to measurement variability, perfect radiographic positioning is mandatory. Indeed, factors such as stifle angle or cranial tibial subluxation have been shown to influence the measurement of the PTA.17,31 The PTA measurement needed to be performed at 135° of extension, which is reported to be the standing stifle angle in dogs.6 Nevertheless, several kinematic studies report a degree of stifle extension >140° at the beginning of the stance phase of gait.32–34 Consequently, we chose to place the dogs in full extension as described by Bruce et al. to measure the PTA.12 With this technique, some dogs could have been overcorrected, but the consequences of this overcorrection are unknown and do not seem to be clinically relevant.18 A goniometer was also used to check that the stifle angle was not <135°. Measurement of the stifle angle using goniometry has been shown to be comparable with radiographic joint angle.35 Similarly, cranial tibial subluxation decreases the PTA. Thus, only radiographs without tibial displacement were used to measure the PTA. Influence of tibial valgus or tibial torsion on PTA measurement has not been evaluated. These abnormalities observed in the dogs of our study could have led to an inaccurate preoperative PTA assessment, which is a major limit of all techniques based on PTA correction.
This study had several limitations. It involved a small number of dogs and was retrospective over a 5 yr period. Our population of dogs was very heterogeneous, which limited the conclusions of the study. Preoperative TTO and TTA measurements are among the most critical components of these surgeries as the PTA method could fail to determine the true advancement distance of the tibial tuberosity. Moreover, the study included five cases of MPL, making conclusions for this affection with this novel technique unclear. All five dogs with MPL underwent femoral radiographs to assess for distal femoral varus. It would have been interesting to obtain these radiographs for all the cases in order to screen for a compensatory phenomenon. However, all the five dogs had normal anatomic lateral distal femoral angle. Two trochleoplasty techniques have been used, making the conclusions even more difficult. There was a dependence on the accuracy and completeness of clinic records maintained by surgeons using subjective outcome measures to assess clinical progress, radiographic healing, and functional outcome. We were unable to document the exact healing time frame because radiographic follow-up was performed at inconsistent time intervals, which made the comparison of healing at specific postoperative times difficult. Also, the follow-up period was too short to clearly establish long-term outcomes of the surgery even if we tried to improve it with the VAS questionnaire. It would have been interesting to use the Liverpool Osteoarthritis in Dogs or the Canine Brief Pain Inventory questionnaires to obtain a more precise and objective follow-up, but as a retrospective study, this was not possible. The location of the medial closing wedge was directly linked to the cranio-caudal wedge and was not based on the Center of Rotation of Angulation of the tibial deformity. This could lead to postoperative deformities and axis translation. Finally, it is difficult to know if the mMPTA correction was indicated in these cases. A case control group of dogs who had similar clinical findings such as CrCL rupture associated with tibial valgus or MPL, treated differently or not treated, is missing.
Conclusion
Based on this pilot study, it seems that TTO associated with TTT and a medial tibial closing wedge ostectomy of the proximal tibia is feasible and provides good-to-excellent outcomes in dogs with CrCL, MPL, and tibial deformities.
Diagrammatic representation of the modified triple tibial osteotomy. (A) A classic triple tibial osteotomy was first performed. (B) For tibial valgus deformity, a medio-lateral closing wedge was then realized (for clarity, the tibial tuberosity was removed). (C) Reduction of the tibial fragments was then performed. At that time, tibial torsion could be corrected by rotating the distal tibial fragment (red arrow; for clarity, the tibial tuberosity was removed). (D) The fragments were then secured with a tibial plateau leveling osteotomy plate. In case of medial patellar luxation, the tibial tuberosity was laterally transposed and secured with Kirschner wires with or without a tension-band wire.
Caudocranial (A) and medio-lateral (B) preoperative radiographic projections of the left tibia (patient 5). Proximal tibial valgus is observed on the caudocranial projection. Patellar tendon angle (110°; C), mechanical medial proximal tibial angle (100.6°, reference range 89.7–96.6°) and mechanical medial distal tibial angle (98.5°, reference range 89.4–101.2°; D) were determined.15 There is no tibial torsion present. Caudocranial (E) and medio-lateral (F) immediate postoperative radiographic projections of the same patient. The mechanical axes (G), mechanical medial proximal tibial angle (90.4°, reference range 89.7–96.6°), and (mechanical medial distal tibial angle 95.6°, reference range 89.4–101.2°) were determined.15
Contributor Notes
