Short-Term Radiographic Complications and Healing Assessment of Single-Session Bilateral Tibial Tuberosity Advancements

Introduction

Cranial cruciate ligament (CrCL) rupture in canines is a common cause of lameness and the most common source of stifle osteoarthritis.¹ Twenty one to 60% of dogs with unilateral CrCL disease subsequently rupture the contralateral CrCL and up to 31% of CrCL disease patients initially present with concurrent bilateral CrCL rupture.^2–5 A dilemma is presented to the clinician when faced with treating a patient presenting with bilateral CrCL ruptures. While there have been many surgical techniques reported that successfully address the lameness and instability associated with unilateral CrCL rupture, there are few reports that specifically detail the single-session treatment of bilateral CrCL disease.

In 2002, Montavon and Tepic reported that the cranial tibial thrust produced in the CrCL deficient stifle could be controlled by performing a tibial tuberosity advancement (TTA) procedure.⁶ Since that time, numerous in vitro and in vivo reports have confirmed the efficacy of TTA as a treatment for dogs with CrCL rupture. The original operative technique described using a fork implant designed to fit into a tension band plate to stabilize the osteotomy and help maintain its cranially advanced position.⁷ A modification of this technique utilizing screws instead of a fork in the plate has been more recently reported as an effective alternative with potential advantages over the fork implant system.⁷

TTA has most commonly been reported as a unilateral or staged bilateral procedure; however, a single report on the use of single-session bilateral TTAs exists.⁸ This study evaluated 33 dogs (66 stifles) that underwent a single-session bilateral TTA and 35 dogs (35 stifles) that underwent a unilateral procedure. The complication rate with the bilateral procedure was not statistically different that that of the unilateral procedure suggesting that it was a viable alternative to staged procedures.⁸ However, the osteotomy healing of the simultaneous bilateral TTAs was not evaluated for comparison to the published healing scores for unilateral TTA. Additionally, only a single type of TTA implant (fork system) was used in all cases.

The goals of this study were:

• 1.

  To report the overall short-term radiographic complication rate associated with single-session bilateral TTAs in a cohort of 74 dogs (184 stifles).

• 2.

  To report any observed radiographic complications and to identify any associated risk factors.

• 3.

  To report short-term postoperative osteotomy healing using a previously described healing score.

Our hypothesis was that short-term radiographic complication rates and healing scores associated with single-session bilateral TTAs are similar to those reported with unilateral TTAs.

Materials and Methods

Medical records from August 2006 to August 2010 of patients that underwent single-session bilateral TTA for treatment of bilateral CrCL rupture were reviewed. Diagnosis of bilateral partial or complete CrCL rupture (or a combination of the two) was made based on physical examination findings consistent with the disease presentation.

The inclusion criteria for assessment of short-term radiographic complications included: (1) single-session bilateral TTAs had been performed, (2) at least one set of re-evaluation postoperative radiographs were available for review, (3) no prior surgery had been performed on either stifle, and (4) there were no other disease processes present that might influence the results. Seventy four patients (148 stifles) met these inclusion criteria. The inclusion criteria for assessment of short-term radiographic healing was the same as that described above but also required that appropriate lateral positioning of both stifles (i.e., no obliquity present) was present on postoperative re-evaluation radiographs to accurately score healing. Of the 148 stifles that met the criteria for inclusion in the assessment of short-term radiographic complications, 143 stifles met the criteria for inclusion for evaluation of short-term radiographic healing scoring.

Patient information collected from medical records included: breed, age, sex, body weight, TTA cage size, TTA plate type (screw or fork), time between surgery and postoperative re-evaluation radiographs (wk), and any treatment of radiographic complications, if applicable.

All postoperative re-evaluation radiographs were evaluated for complications and 143 radiographs were scored for healing by a board certified radiologist. The radiologist was unaware of the identity of the patients; however, implant type could not be concealed. Complications were defined as either minor or major according to the definitions recommended by Cook et al.⁹ Minor complications were defined as those that did not require surgical intervention for resolution and major complications were defined as those that did require surgical intervention. Any observed complication was classified as either minor or major based off the patient's medical record and its description of any treatment post complication.

The radiographs were scored using a previously reported scoring system.¹⁰ Three sites of the osteotomy were scored: (1) the region of osteotomy proximal to the cage, (2) the region of osteotomy between the cage and the plate, and (3) the region of osteotomy distal to the plate. ¹⁰ Scores were assigned as follows: 0 indicated no osseous healing, 1 indicated early bone production without bridging between the tibial tuberosity and the shaft of the tibia, 2 indicated bridging bone formation at one of the three sites, 3 indicated bridging bone at two of the three sites, and 4 indicated bridging bone at all three sites.

Results

Of the 74 patients that received bilateral TTAs that met the criteria for study inclusion, 49 (66%) were spayed females, 24 (32%) were castrated males, and 1 (1%) was an intact male. The mean patient age was 4.9 yr (range = 1–11 yr). The mean patient body weight was 32 kg (range = 15.1–63 kg). There were 34 mixed-breed dogs (46%), 14 Labrador retrievers (19%), 4 golden retrievers (5%), 4 boxers (5%), 3 beagles (4%), 2 cocker spaniels (2.7%), 2 English bulldogs (2.7%), 2 rottweilers (2.7%), 2 Shetland sheepdogs (2.7%), and one each of the following: Akita, bullmastiff, Chesapeake Bay retriever, German shepherd dog, giant schnauzer, Newfoundland, and springer spaniel. Re-evaluation stifle radiographs were performed at a mean of 6.6 wk (range = 5.5–11 wk) postoperatively. Thirty-five dogs received a fork plate implant (47%) and 39 dogs received a screw plate implant (53%). Implant groups were not significantly different from each other in regard to age, body weight, or sex.

One hundred forty-three of the 148 stifle radiographs were scored for healing. Five radiographs were excluded because a lack of appropriate lateral stifle positioning precluded accurate evaluation. Short-term healing scores were performed between 5 and 11 wk postoperatively. Eighty-three percent of the radiographs in this study were performed between six and eight wk post operatively. The mean short-term healing score across all stifles was 2.96 with a 95% confidence interval of 2.83 to 3.09. ANCOVA was run with a random dog effect to account for the proportion of variability in scores due to within-dog factors. Table 1 shows the estimated mean healing scores for each level of the fixed factors (sex, cage size, implant device) obtained from the ANCOVA. Breed was not included in the analysis because of the large number of different breeds represented by only one or two patients. The effects of age and body weight on healing score were also examined using ANCOVA with a random dog effect. In both cases, the effect was not statistically significant.

Table 1

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Of the 74 dogs in this study, 13 dogs developed short-term radiographic complications. Short-term radiographic complications included: fork displacement (six patients), tibial tuberosity fracture (four patients), patellar desmopathy (three patients), tibial tuberosity displacement (three patients), screw disengaging from the cage (two patients), screw disengaging from the plate (one patient), distal tibial fracture (one patient), and cage displacement (one patient). An example of fork displacement can be seen in Figure 1. Twelve dogs (16.2%) were defined as having minor radiographic complications and one dog was defined as having a major radiographic complication (1.4%). Of the 13 complications, 9 were unilateral and 4 were bilateral. Log-linear analysis (generalized linear modeling with a binary logistic response) was used to determine whether the probability of complication was affected by three discrete factors (sex, cage size, and implant type) and three continuous factors (age, body weight, and healing score). Table 2 shows the estimated probability of a complication (minor or major) for each level of the three discrete factors. Only implant type was statistically significant, with fork plates having a greater complication rate than screw plates. Of the three continuous factors, only body weight was statistically significant in the development of a complication, minor or major. The estimated odds ratio associated with a change in weight of 1 kg was 1.076, indicating that the probability of complication rises about 7% for each additional kilogram in weight.

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Table 2

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Discussion

Treating patients with bilateral CrCL rupture with single-session bilateral TTAs offers a number of advantages over staggered unilateral TTAs. Single-session bilateral stifle surgery only requires one period of anesthesia and recovery, provides decreased cost to owners, and has an overall quicker period of recovery than staggered procedures. Additionally, dogs are not required to walk on an unstable stifle while the operated limb heals. However, concerns regarding presumed increased complication rates may prevent some surgeons from considering bilateral procedures. The overall short-term radiographic complication rate for the single-session bilateral TTAs in this study was 17.6%. Two variables were identified to be associated with an increased risk of complication: body weight and implant type. The screw plate had a short-term radiographic complication rate of 5%, whereas the fork plate had a short-term complication rate of 31%. One potential explanation for this finding is that TTAs using the fork plate were performed chronologically earlier in the study period and surgeon technical proficiency may have improved over time. However, the surgeons had already performed numerous unilateral TTAs before attempting any single-session bilateral TTAs, thus making technical proficiency an unlikely explanation for the noted differences. Our observation of fork plates as a statistically significant complication risk factor is in contrast to a previous unilateral TTA report that did not detect statistically significant differences in the complication rates between implant types.⁷ Why single-session bilateral TTAs appear to be more sensitive to implant choice is unknown.

Body weight was the only other variable associated with an increased risk of complications in this study; the heavier the patient, the greater the likelihood that a short-term radiographic complication would occur. The estimated odds ratio associated with a change in weight of 1 kg was 1.076. A patient of average weight (32 kg) has a probability of a radiographic complication estimated to be 15.2%. With a 1 kg increase in weight the estimated risk of complication increases to 16.4%. Other CrCL disease treatment studies have demonstrated a positive relationship between patient body weight and postoperative surgical complications; however, a recent study of single-session bilateral TTAs did not associate higher body weight with increased complications.^8,11–13 By contrast, we did not find age to be a significant variable associated with complications as did the aforementioned report.⁸ Our findings relative to age are consistent with other CrCL disease treatment studies.^7,10 Direct comparisons of overall complication rates between the previous single-session bilateral TTA report is challenging because of the different reporting methods used and variables evaluated.

We elected not to analyze the effect bone graft had on short-term healing scores or complications because the inconsistent documentation of its use in the operative reports made it difficult to determine in which patients graft was used. The authors believe it is unlikely that the use of graft affected our short-term complication rate based on two prior reports that did not demonstrate any correlation between the use of bone grafts and postoperative TTA complications.^7,10 Additionally, these two reports had conflicting results on how grafts affected healing scores. Our reported mean short-term healing score of 2.96 was similar to the scores of 2.85 and 2.0 previously reported for unilateral TTA.^7,10

Comparing complication rates among the different surgical techniques used to treat CrCL rupture can be difficult. Most reports include all observed/described patient complications in combination with radiographic ones. However, the designation of what is a related complication and whether it is major or minor complication varies tremendously among reports. Because the inconsistency of on-site initial postoperative rechecks precluded documentation of potential patient postoperative complications, we elected to report only on short-term radiographic complications since they could be consistently documented amongst all the patients included in this study. Our overall short-term radiographic complication rate (17.6%) compares favorably to those reported with unilateral TTAs (14 and 26%).^7,8,10

Impaired internal fixation/implant failure was the most common short-term radiographic complication identified followed by tibial tuberosity displacement and fracture (Figure 2).

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Twelve of the 13 short-term radiographic complications were classified as minor according to the definition established by Cook et al.⁹ All of the minor complications were diagnosed on routine follow-up postoperative radiographs and were deemed to be healing adequately at that time despite the complication present. None of the minor complications required any specific intervention to resolve, and patients with complications were allowed to follow the same recovery plan as those patients who had normal radiographs. Additionally, the minor complications were: incidental, discovered on follow-up radiographs, had appropriative osteotomy healing, and the surgeon's opinion was that the complication's presence had minimal to no impact on patient function and comfort. Our findings of radiographic complications that theoretically would be expected to be major were, in reality, deemed minor, which is in agreement with a previous report.¹³

By contrast, the one major complication reported required a second surgery due to proximal tibia/fibula fracture and loss of internal fixation. This patient presented before its routine follow-up examination because of a progressive deterioration in limb use and ability to walk. The complication was treated by removing the fork plate, stabilizing the fracture with a tibial plateau leveling osteotomy plate, and placing positional screws directed across the tibial tuberosity/osteotomy. Follow-up radiographs 6 wk following revision surgery demonstrated complete fibula fracture healing and incomplete but progressive tibia fracture healing. No additional follow-up was noted in the record so definitive outcome is uncertain.

There are limitations present in this report. Including a control group could have added strength to some of our observations/conclusions. However, we are confident that meaningful information can be gleaned by comparing our findings with those from other retrospective TTA studies. Additionally, TTA plate selection in this study was not random. Plate type use changed over a period of time because of surgeon preference (i.e., surgeons changed over from fork to screw plates). However, no significant differences in evaluated patient parameters existed between the two different implant groups. Another limitation includes the potential for underestimation of short-term radiographic complications. It is possible that there were dogs that had single-session bilateral TTAs, which experienced radiographic complications, but that were not included in this study because their radiographs were not available for review. Two portions of our study were inherently subjective. Scoring radiographic bone healing is subjective regardless of the system used. We hoped to minimize this issue by using a radiologist who was provided with no patient information and was familiar with a previously published scoring system. Secondly, our designation of a complication as minor was based on the surgeon's opinion that additional treatment was not warranted because the patient's recovery was satisfactory despite the complication. This, like many clinical observations/decisions, is highly subjective and complication classification could vary among individuals. How this might affect perceived results from single-session bilateral TTAs is uncertain. Lastly, our study did not report on non-radiographic complications. It is very likely that other clinically relevant complications occurred, and possibly with greater frequency than reported with unilateral TTA. Because our study did not include all complications, our findings must be considered with some caution. However, because the majority of reported major and catastrophic TTA complications are radiographically apparent and we see, as demonstrated by our study, that the short-term radiographic complications are not increased, these findings are highly relevant. If there is a perception of increased risk of implant or bone-related complications, such as loss of internal fixation or fracture, this study contradicts that perception.

Conclusion

In conclusion, the results of this study support our hypothesis that short-term radiographic complication rates and healing scores associated with single-session bilateral TTAs are similar to those reported with unilateral TTAs. Single-session bilateral TTAs are a potential alternative to staged unilateral TTAs for treatment of bilateral CrCL rupture. However, heavier patients should be considered cautiously as candidates and using TTA plates with screws instead of forks is recommended.