12.1 Introduction

Tibial tuberosity advancement (TTA) is a well‐accepted, extensively published, and proven surgical technique for treating the lameness associated with canine cranial cruciate ligament (CCL) disease. Since it was first reported in 2002 by Montavan, numerous descriptions of other similar procedures have been published [1]. Despite variations in the techniques and implants used, the modified Maquet and tibial tuberosity advancement rapid (TTA‐R) procedures are very similar to the original TTA in principle. All attempt to neutralize the cranial tibiofemoral shear force generated in the CCL‐deficient stifle by cranially advancing a longitudinal frontal plane osteotomy of the tibial crest until the attached straight patella ligament insertion is approximately perpendicular to the tibial plateau. All then utilize procedure‐specific implants to stabilize the osteotomy in the advanced position.

The TTA‐R is a modification of the TTA in that it utilizes an osteotomy of the proximal tibia which is incomplete distally. As originally described, the osteotomy ends distally in a Maquet hole in order to minimize the chance of fissure formation; however, it is not always used [2, 3]. A single implant that functions as both an advancement wedge and a plate is used to stabilize the osteotomy (Figure 12.1). Between the two techniques, the original TTA has been the subject of the majority of published studies to date. The frequency of reported complications for both surgeries is similar to that of other tibial osteotomy‐based stifle procedures [4–8]. This chapter will focus on complications associated with the TTA and TTA‐R while the modified Maquet technique will be the focus of Chapter 13.

Tibial tuberosity advancement surgery not only has the potential for development of general surgical complications but also those associated with an osteotomy and internal fixation and those unique to the technique itself. Numerous reports exist describing complications associated with TTA surgery. Making direct comparisons between these studies is difficult because how the complications are reported relative to type, timing, and classification varies considerably among publications. Table 12.1 provides a comprehensive list of the studies that report complications with TTA and TTA‐R surgery. The complications are generally divided relative to timing (intraoperative and postoperative) and further divided into severity (major and minor). The greatest variability exists with the latter, with some studies not distinguishing between major and minor, others use different criteria for classification inclusion and still others report on only one type of complication (i.e., major only). While rates vary among the 21 studies, the types of intraoperative and postoperative complications described are similar.

12.2 Intraoperative Complications

Intraoperative complications are only sporadically included in TTA and TTA‐R studies. When evaluated as part of TTA study objectives, they either did not occur [9, 10] or were both rare and minor (0.4–3.1%) [11–14]. Intraoperative TTA complications included trans cortical chip fractures, screws stripping, breakage of cage flanges, intraarticular screw placement, nondisplaced tibial fracture, broken drill bits and screws, etc. One study described a tibial tuberosity fracture that was remedied by modifying the plate size and position [15]. Hoffmann et al. reported an inadvertent transection of the long digital extensor tendon during the osteotomy. It was not repaired and did not appear to affect patient recovery [12].

Compared to TTA, TTA‐R has a higher incidence of reported intraoperative complications ranging from 2% to 8.3% [3, 16]. Among the four studies that documented TTA‐R intraoperative complication occurrence, the most common (75%, 9/12) were fractures/fissures at the level of the Maquet hole and/or distal tibial crest, three of which were classified as major complications [2, 3, 16, 17]. These findings have prompted some surgeons to debate the value of the Maquet hole and discontinue its use in TTA‐R surgery [3]. This is discussed further in Chapter 13.

Only a single study exists which directly compares short‐term outcomes and complications between two types of TTA: the original TTA and a modified Maquet‐tibial tuberosity advancement (mTTA) technique [9]. No intraoperative complications were reported in the 35 TTA cases compared to 5/35 (14.2%) of mTTA cases that developed fractures at the Maquet hole. The latter required no treatment and were deemed of questionable clinical significance after the 8‐week postoperative follow‐up was completed.

The reported low incidence of intraoperative TTA complications is consistent with this author’s experience; they are rare and when they do occur, require either no or only minor treatment. Difficulty closing fascia and the aponeurosis of the gracilis, semimembranosus, and semitendinosus muscles (pes anserinus) over the TTA osteotomy gap and implants is, in my experience, the most commonly encountered intraoperative TTA challenge yet is not mentioned in the literature. This difficulty is not surprising given that one is attempting to reappose a minimally compliant tissue over a newly widened proximal tibia with a large defect (i.e., osteotomy gap). Excessive tension of this closure can lead to early dehiscence, seroma formation, and a transient increase in lameness. If necessary, the tension can be relieved by making a releasing incision through the pes anserinus and caudal aspect of the tibial fascia under which there are no implants or osteotomy.

Implant placement complications were common during the early learning phase of the TTA technique, particularly when attempting to ensure the fork engaged properly with the multiple tibial tuberosity drill holes and the plate. Incomplete fork–bone tunnel engagement and/or bent fork tines were a source of challenge. The creation of a TTA plate that secures the plate to the tibial crest using bone screws alleviated these issues entirely and is a proven alternative to the fork‐based plate (Figure 12.2) [9, 15, 18]. Broken cage flanges are usually a result of overzealous countering. The flanges (aka “wings”) are small and not very stiff and will actually self‐contour as the screw engages the bone, so precise contouring is not necessary. Trans cortical chip fractures are most often incidental findings on postoperative radiographs and in the author’s experience do not require specific treatment as long as the applied screw in question has engaged the bone well. Additionally, the author has found that the cranial cage screw can be more prone to stripping if applied perpendicular to the bone. This is particularly true if the medial to lateral tibial tuberosity osteotomy is directed slightly cranially. This may cause that screw to only engage the cis cortex if driven perpendicularly (Figure 12.3). Routinely angling this screw cranially will help to prevent this regardless of osteotomy obliquity.

Many of the intraoperative complications associated with tibial plateau leveling osteotomy (TPLO), such as fibula fracture, popliteal, or cranial tibial artery laceration, retained surgical sponges and jig pin fractures, are not reported or expected during TTA because of the technical differences between the two surgeries [6, 8]. Additionally, inadvertent intrarticular screw placement, while documented with TTA, is far less likely to occur during TTA than TPLO. However, to avoid the latter, caudal cage screws should be angled in a slightly distal direction.

12.3 Postoperative Complications – Overall Frequency

“Overall complication rates” are perhaps the most referenced and discussed form of documented complications for any given surgery and are often used as an indirect indicator of procedure success. However, they are the most difficult to compare between studies because of methodology variations and should therefore be considered cautiously. As stated by Cook et al. regarding the veterinary literature, “This lack of standardization limits our abilities to communicate study results in a consistent manner, interpret data appropriately, and compare results across studies, centers, and techniques” [19]. Reports on TTA complications are no exception. As stated earlier, there is considerable variation among TTA studies relative to how and what complications are reported. Additionally, many of the studies are hampered by low sample populations and thus prone to type II error. Nonetheless, Table 12.1 includes an extensive list of the different published TTA and TTA‐R complication rates, either as directly reported by the study or as extrapolated by this author. For the purpose of this discussion, overall complication rate includes intraoperative and postoperative complications (major and minor).

Of the 17 TTA studies in Table 12.1, only six provide enough information to determine an overall rate. Rates range from 8.6% to 59% (mean = 25.4%) for TTA and 11.8% to 61.5% (mean = 34%) for TTA‐R. All of these studies were retrospective. The highest rate of 59% was reported by Hoffmann et al. who included any observed perioperative abnormality as a complication including inappetance, diarrhea, vomiting, lethargy, etc. [12]. The lowest rate of 8.6% came from a study of 35 dogs, the smallest sample size of any of the six TTA studies included [9]. By contrast, the single largest TTA study to provide an overall complication included 501 stifles and reported a rate of 19% [14]. An overall rate can be determined for all four of the TTA‐R studies. The highest rate reported for TTA‐R was 61.5%, which included a very small sample population of 13 dogs [17]. A much larger sample population of 152 stifles, the largest published TTA‐R study to date, provided a much lower rate of 11.8% [16].

As with any complicated surgical technique, surgeon experience plays an understated but key role in TTA outcomes and complication rates. Multiple reports have documented the impact that increasing surgical experience with TTA has on reducing complications [13, 20, 21]. Performing a clinical audit for TTA using the cumulative summation technique, Proot and Corr determined that the learning curve for an experienced general practitioner to reach complication rates within published ranges is 22 procedures [21].

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