Temporary Application of a Tarsal Arthrodesis Plate as a Postoperative Immobilization Technique in Common Calcaneal Tendon Injury Repair in Dogs: A Pilot Study

Introduction

Injuries to the common calcaneal tendon (CCT) in dogs can be debilitating. Composed of 5 major muscles (gastrocnemius, superficial digital flexor, gracilis, semitendinosus, and biceps femoris), the CCT is under a considerable amount of tension, compounding a naturally long recovery time. While there is no data evaluating the healing process of the CCT specifically, a predicted path of healing akin to those of other canine tendons is extrapolated from the literature. Studies have shown that the canine triceps tendon, at 6 weeks and 1 year post injury, has 56%

and 79% of the original strength respectively recovered [1]. Surgical repair and management of tendon injury aim to oppose the tendon ends and prevent subsequent distraction during the long period of tendon healing [2]. Commonly used postoperative immobilization techniques for primary calcaneal tendon repair include calcaneotibial screw fixation in conjunction with external coaptation [3, 4], external skeletal fixation [5, 6] and external coaptation devices [7]. Several retrospective studies have demonstrated complications associated with each immobilization technique. A retrospective study evaluating largely the use of trans-articular external skeletal fixators (ESF) reported an 18% major complication rate including metatarsal fracture, osteomyelitis secondary to the ESF pins, implant failure that required revision of the fixator, and tendon laxity after the ESF was removed. The same study reported complications for patients that had external coaptation such as bandaged induced dermatitis or wounds and splint breakage (8). Another retrospective study involving 45 dogs with CCT injury investigated postoperative complications associated with the placement of a calcaneotibial (CT) screw. The authors reported a 35% complication rate, including implant failure, or screws that were loose at the time of removal, but had not caused any apparent morbidity [9]. No significant functional difference among immobilization techniques has been demonstrated in the current veterinary literature [8, 10]. Due to the complication rate associated with standard immobilization techniques, there is a clinical need for a technique which affords appropriate stability with minimal patient morbidity.

With this need in mind, the authors started to investigate the use of a temporary tarsal arthrodesis plate (TTAP) as an alternative postoperative immobilization technique. There were several potential advantages that were considered with this method. The plate could offer a more robust fixation than the CT screw, and would not demand as much at-home care as an external fixator. The plate could also decrease the risk of bandage morbidity that is often associated with traditional external coaptation methods. Lastly, the TTAP could ensure that the joint could be fixed at a functional angle, allowing the tendon to heal in the appropriate anatomical position. By avoiding prolonged hyperextension (as the leg is often positioned in after CT screw placement), the concern for superficial digital tendon contracture can also be mitigated. While this complication has not been documented in the current literature, the authors have anecdotally seen this clinically affect patients who had their limbs in hyperextension after primary calcaneal tendon repair. The purpose of this pilot study was to investigate the placement of a TTAP as an alternative technique for postoperative stabilization after primary CCT repair. The authors hypothesized that there was no significant difference in major complications between dogs receiving the CT screw and dogs receiving a TTAP for post-operative immobilization.

Results

Of the 27 cases, 16 dogs were male, and 11 were female. The mean age in both the TTAP and CT screw groups was 6 years old. Of the 12 purebred breeds represented, the most common breed was the Labrador retriever (n=12). Of the 10 TTAP cases, 3 dogs had a 3.5/2.7mm tarsal arthrodesis plate placed, and 3 dogs had a 3.5/3.0mm tarsal arthrodesis plate placed. 4 cases did not have operative reports or radiographs available to review, and so implant details were not documented. Anaesthesia times were available for review in two cases. One CT screw case had an anaesthesia time of 80 minutes, and one TTAP cases had an anaesthesia time of 90 minutes. The median number of days between placement and removal of the implants were 43 (range 28- 81) and 61 (range 35-170) days for the CT screw and TTAP groups, respectively. The median follow up time after initial surgery was 171 (range 36-1670) and 185 (range 57-567) days for the CT screw and TTAP groups, respectively. 8 major complications were documented in the CT screw group, while 1 major complication was documented in the TTAP group. Complications associated with the CT screw included 5 dogs reinjuring the tendon (avulsion or rupture), 2 dogs developing tendon laxity, and 1 dog developing a surgical site infection after explant. Three screws were found broken at the time of explant, but this had not caused any apparent morbidity and was not documented as a major complication. The complication documented in the TTAP group was tendon laxity in one dog. The dog was not presented for plate removal until 170 days after initial surgery due to a suspect miscommunication. One plate broke and was explanted earlier than planned, but the dog was managed with an orthotic and was documented to have minimal lameness on exam 51 days after plate explant (Table 1 & Table 2).

Discussion

To the authors’ knowledge, this is the first description of the temporary application of a medial tarsal arthrodesis plate as a method to immobilize the tarsus after primary calcaneal tendon repair. The results from this pilot study suggest that this method is an acceptable alternative to the currently described techniques. A potential disadvantage of the TTAP procedure is the overall increased perioperative morbidity associated with longer surgery. It may take relatively longer for the clinician to place the implant as compared to a CT screw, and the patient needs to undergo a second general anaesthesia event at time of explant, as opposed to an explant of a CT screw under sedation alone. However, given that the use of an external skeletal fixator (another well described technique) also demands longer anaesthesia time, the disadvantages associated with general anaesthesia are only pronounced when compared to the use of a CT screw. Due to the institution suffering loses of medical records from a natural disaster, surgery and anaesthesia times were largely unavailable for review. Documentation and comparison of anaesthesia times of future TTAP cases is recommended to be able to compare with the currently established techniques. Another plausible drawback of the TTAP procedure is the associated cost. While the cost of the TTAP surgical procedure may be increased compare to the CT screw procedure, the multiple bandage changes may eventually nullify the initial price difference. If future studies can demonstrate a significant improvement in outcome and client satisfaction with the TTAP procedure, the authors believe that these setbacks could be offset. The goals of immobilization of the tarsal joint are to protect the tendon repair and resist gap formation while the calcaneal tendon heals. New tendon collagen requires a degree of strain and load for development of correct alignment, although this should not be introduced until initial fibroplasia and collagenization take place over the initial 2-3 weeks [13]. The CT screw is traditionally placed to fix the joint in a hyperextended position. This can alleviate tension on the tendon in the initial phase of healing, but does not allow subsequent physiologic weight- bearing of the tendon to encourage appropriate alignment of the collagen. Additionally, the prolonged hyperextension predisposes the potential formation of superficial digital flexor tendon contracture, which some of the authors have experienced anecdotally in their patients. The TTAP is placed at a normal physiologic angle, which may facilitate the described appropriate tendon healing. To mitigate potential gap formation and failure of the primary repair, the surgeons in the study did not utilize the plate technique in patients that had excessive tendon shortening due to either contraction or need for debridement. Lister et al. demonstrated that maximum strain on the calcaneal tendon was similar in dogs with and without immobilized tarsi in a weight-bearing stance, and suggested that the protection offered with immobilization could stem largely from the decreased weight bearing as well as activity restriction [14]. Further investigation is needed to elucidate the role of the position of the tarsus in post-operative calcaneal tendon healing. The major complication rate in the CT screw cohort was 47% (n=8) in this study. A previous retrospective study involving 45 dogs who injured their calcaneal tendon, 37 of which received a CT screw, reported a 35% (n=16) overall complication rate, 6 cases of which were considered major. Only 3 of the 37 screws were noted to be bent or broken and had to be replaced (9). The relatively large difference in complication rate between the two studies can likely be attributed to low case numbers in addition to different definitions of major complications. 3 of the 17 CT screws in this study were broken at the time of explant, but that did not appear to compromise the repair; therefore, these did not contribute to the overall complication rate. However, 5 major complications in this study were due to reinjury (rupture or avulsion), all of which happened at least 6 months after the primary tendon repair surgery. It is possible that these tendons were not adequately healed prior to return to normal activity, or that the dogs were returned to full activity too quickly. Future research should involve repeated ultrasounds at regular intervals in order to differentiate between fully healed tendons that are re-injured or tendons that have not fully healed.

There was 1 major complication in the TTAP cohort: tendon laxity. The dog did not present for plate explant until 150 days after explant, due to a miscommunication. It is reasonable to presume that if the explant procedure was done within the recommended time frame, this complication could have been avoided. The dog was placed in a splint for 4 weeks after explant surgery, but there was no clinical improvement after splint removal. A tarsal arthrodesis or tendon shortening procedure was recommended, but the dog was lost to follow up after this recommendation was made. There was one TTAP case that documented a broken plate on recheck radiographs 15 days after surgery. The plate was explanted 35 days after surgery and the dog was managed medically with a custom orthotic. 51 days after explant, the dog was documented to be doing well with minimal lameness. While the number of TTAP cases was relatively low, it is encouraging that a single major complication was documented in this cohort. Future studies with more cases and detailed documentation of progression are necessary to better validate the procedure and possible complications. There were several limitations of this study. The retrospective design limited the conclusions drawn from the data. The primary tendon repair method was not standardized; future study designs should plan to eliminate this as a factor confounding data interpretation of immobilization method. Case management and documentation varied among surgeons, limiting the conclusions able to be drawn from certain details such as potential bandage morbidity, lameness examinations, or differences between types of initial tendon injuries. Case selection of the population that received the TTAP also differed from those selected for application of the CT screw, as dogs that required tendon debridement were not eligible for placement of a TTAP. Objective outcome measures were not utilized, such as tendon ultrasound, or gait analysis. Although the previously cited literature regarding calcaneal tendon also utilized subjective gait analysis, objective outcome measures would have been preferable. In addition, the institution that this study was conducted at suffered a natural disaster within the years the procedures were performed; consequently, many details in the records were lost and unable to be evaluated and analysed as part of this study, including implant information, imaging studies and surgery and anaesthesia data. The relatively small case numbers also precluded direct comparison of results between the CT and TTAP cases.

In conclusion, the results of this pilot study demonstrate the application of a TTAP as an acceptable immobilization technique after primary calcaneal tendon repair despite limited case numbers. A prospective, controlled, multi- institutional study is warranted to validate the procedure.