Superficial digital flexor tendon luxation repaired with abrasion calcaneoplasty and primary retinaculum repair in dogs

Abstract

Surgical treatment of a superficial digital flexor tendon luxation is the treatment of choice, since nonsurgical treatment has been shown to be unsuccessful in dogs in which it has been attempted. The objectives of this study were to report complications and short- to long-term outcomes in dogs with superficial digital flexor tendon luxation treated with abrasion calcaneoplasty, an adjunctive surgical technique, in addition to traditional repair. In total, 12 client-owned dogs with superficial digital flexor tendon luxations were examined in this retrospective case series (from 2010 to 2020) of a novel surgical technique using abrasion calcaneoplasty, in addition to retinaculum imbrication. Records were reviewed for signalment, chronicity of clinical signs, preoperative diagnostics tests, surgical techniques, postoperative complications, and outcomes. Abrasion calcaneoplasty, in addition to traditional primary retinaculum repair, was successfully performed in 12 dogs, with ultimate resolution of clinical lameness in all patients, despite short-term reluxation in 1 patient. Based on the findings of this case series, we inferred that abrasion calcaneoplasty can be considered in addition to traditional repair as an option to treat luxation of the superficial digital flexor, with a 58% short-term complication rate, and no evidence of long-term complications.

Introduction

Luxation of the superficial digital flexor tendon is a relatively uncommon orthopedic condition in active dogs with possible breed predisposition in herding breeds such as Shetland sheepdogs, collies, and giant breeds (1). It has been previously reported that lateral displacement of the superficial digital flexor tendon results from tearing of the weaker medial attachment on the tuber calcanei. Also, anatomical factors that increase medial or lateral stresses on the tendon as it passes over the calcaneus may contribute to a luxation (2,3).

Dogs with a superficial digital flexor luxation will typically present with a mild to severe lameness that may be episodic. There is consistently effusion noted at the level of the tuber calcis, which can be mild to marked (1,4). The superficial digital flexor muscle’s lateral and medial heads originate on the caudal aspect of lateral and medial femoral condyles, respectively and course distally before fanning to form a cap structure and sliding along the calcaneus, serving as an extensor of the hock. The tendon continues distally to its final insertion on the middle phalanges of the second to fifth digit (2,5).

Diagnosis of a luxated superficial digital flexor tendon is made at the orthopedic examination by direct palpation of the tendon as it displaces over the calcaneus. Displacement often occurs when the hock is flexed with the stifle extended, resulting in the tendon leaving the calcaneal groove. As the tendon displaces, a popping sensation may be appreciated (1,2). Patients with chronic luxations may develop a fixed luxation of the tendon with pain and swelling appreciated, but no obvious tendon movement. Lateral displacement of the superficial digital flexor is more common than medial displacement (1–4).

Surgical treatment of luxation is the treatment of choice since nonsurgical treatment has been shown to be unsuccessful in dogs in which it has been attempted (6). Surgery involves relocating the tendon to the central position of the groove between medial and lateral processes of the tuber calcanei with imbrication of the bursal wall on the side opposite the luxation. Immobilization of the tarsal joint for a minimum of 4 wk has been recommended to support the repair (1–4). Methods described recently by Gatineau et al (2) for lateral luxation include a release incision on the medial aspect of the bursa calcanei and retinacular structures allowing reduction, followed by excision of the redundant medial bursa calcanei and retinaculum. If soft tissue available for attachment via sutures is scant, 1 or 2 screws (1.5 to 2.0 mm) can be inserted into the calcaneus near the tendon edge and can be used for suture anchorage (7). Alternatively, with the aid of 2 small holes drilled through the tuber calcanei, sutures can be placed through the bone and tendon. The use of suture anchors and restraining pin to negate immobilization has also been reported. Polypropylene mesh has also been used for revision of failed repair of superficial digital flexor tendon luxation in dogs (8). Historically, surgical treatment has a good outcome (1), but complications include repeat luxation, microfiber injury of the tendon, and continued lameness.

Materials and methods

The medical record database of a specialty practice were reviewed for cases of superficial digital flexor tendon luxation that were treated surgically from November 2010 to September 2020. The diagnosis of a singular lateral or medial or bilateral superficial digital tendon luxation was determined based on orthopedic examination in conjunction with owner-reported clinical signs and confirmed at surgery. All patients underwent a single anesthetic event, including the patient with bilateral luxation which underwent correction with 1 surgery in place of a staged repair.

Information was collected from medical records included sex, age, weight, pertinent medical history, initial orthopedic consultation, physical examination findings, pre-operative diagnostic tests (specifically tarsal radiographs), surgically treated limb, type of luxation, surgical technique, perioperative complications, and post-operative lameness and stabilization.

The surgical procedure was similar in all instances. A total of 12 dogs were placed in sternal recumbency with the limb hung caudally and the region of tarsal joint aseptically prepared. A caudal lateral approach for lateral luxations and a medial approach for medial luxations was made via a curvilinear incision through the skin. The bursa was identified by manual palpation and displacement of the tendon. The surgical incision was extended to the level of the fibrocartilaginous cap within the tendon of the superficial digital flexor muscle. The adhesions to the cap were excised and the cap was mobilized to allow access to the tuber calcanei. The bursa was incised adjacent to and parallel to the tendon.

In each of the 12 cases, at time of surgical intervention, the tendon continued to have increased tendency to dislocate following positioning between the medial and lateral processes. Based on increased mobility, a calcaneoplasty was performed (Figure 1). The groove of the calcaneus between the medial and lateral processes of the tuber calcanei was deepened using a #2 burr and a Hall Drill. Intraoperatively, care was taken to start the calcaneoplasty distal to the attachment of the common calcaneal tendon to ensure the tendon was not disrupted. The groove was deepened to the point that there was at least 2 mm of bony tissue on either side of the calcaneal groove allowing the tendon to remain seated between the processes (Figure 2). In all instances, following calcaneoplasty the tendon was replaced in the groove. The redundant retinaculum was trimmed or imbricated, and the retinaculum was closed using a non-absorbable suture in a horizontal mattress pattern. In 2 cases of laterally luxating superficial digital flexor tendons, the lateral retinaculum was released to minimize pull on the superficial digital flexor tendon once reduced into the newly formed groove, although this was not needed in all cases after deepening the groove. Following placement, digital pressure was applied to the tendon in the direction of luxation with the tarsus in flexion and extension to ensure that the tendon could not be luxated. The deep fascia and skin were closed in a routine fashion in all cases.

Figure 1.

Intraoperative determination of shallow calcaneal groove in a dog.

Figure 2.

Burr used to deepen the groove of the calcaneus between the medial and lateral processes of the tuber calcanei in a dog.

All 12 patients had external coaptation consisting of a custom-moulded fiberglass splint in a modified Robert Jones bandage applied postoperatively for a minimum of 2 wk, followed by strict activity restriction for a total of 12 wk after surgery. Out of the 12 patients, duration of external coaptation varied, with 3 patients remaining splinted for 2 wk, 7 patients remaining splinted for 4 wk, and 2 patients remaining splinted for 6 wk. Variation was dependent on individual surgeon preference but was also influenced by secondary bandage complications of individual dogs. Bandage changes were performed every 1 to 2 wk to evaluate range of motion, as well as incisional healing and bandage complications.

All patients had a full orthopedic examination performed at several points during their recovery. Initially, all 12 patients had all joints evaluated using a validated numeric lameness scoring system (9) and validated pain score using the Colorado State University (CSU) acute pain scale for the dog (10) by the primary surgeon at 1 d after surgery, then again at each bandage change during the perioperative period (every 7 to 10 d for the duration of external coaptation placement, from 2 to 6 wk depending on patient splinting interval). Each patient received an in-person evaluation with the primary surgeon including lameness score within the short- to mid-term complication period (3 to 6 mo). Long-term orthopedic examinations including lameness scores (> 12 mo) were included and evaluated through a combination of the primary surgeon and primary care veterinarian patient records. The mean long-term follow-up was obtained 53.8 wk postoperatively with the primary surgeon. For patients that lacked > 52 wk postoperative in-person examinations with the primary surgeon (4 of the 12 patients), client telephone interviews were conducted, and primary-care veterinarian wellness records were evaluated (to include lameness scoring and noted orthopedic examination findings).

Complications were classified as perioperative or postoperative. Perioperative complications include those arising from surgical intervention to 3 mo after surgery. Postoperative complications were classified as short-term when they occurred between 3 and 6 mo postoperatively; for all patients, this included time following external coaptation removal. Long-term complications occurred 1 y after surgery.

For the follow-up, records were reviewed from recheck examinations scheduled with the primary surgeon, in addition to the review of the primary-care veterinarian’s long-term medical records. Information collected primarily focused on prospectively recorded post-operative orthopedic examination findings (degree of lameness determined by numeric rating scale, joint range of motion and joint effusion subjectively determined by evaluating surgeon, and pain score determined based on validated scoring system) as well as evidence of reported degree of observational lameness by owners at home. The single patient that had persistent lameness following external coaptation removal, had further diagnostics performed postoperatively. These diagnostics consisted of repeat tarsal radiographs and stifle radiographs during the short-term follow-up period.

In total, 12 dogs with a total of 13 superficial digital tendon luxations met the criteria for inclusion into the retrospective study. One dog had a luxation in both right and left superficial digital flexor tendons. Of the patients, 8 dogs were spayed females, 2 were castrated males, 1 was an intact male, and 1 an intact female. The dogs ranged in body weights and breeds, with an average weight of 20 kg (range: 5.3 to 53 kg), 6 were large breed (> 20 kg), and 6 were considered small breeds (< 20 kg) at the time of surgery (Table 1). Of the 13 tarsi, 10 tarsi had lateral luxation of the superficial digital flexor tendon, whereas 3 tarsi had medial luxation of the superficial digital flexor. Patient No. 3 had medial luxation of the superficial digital flexor tendon in the left tarsus and lateral luxation of the superficial digital flexor tendon in the right tarsus. This patient underwent repair of both tendons during 1 surgical event.

Table 1.

Complications related to abrasion calcaneoplasty.

Signalment	Luxation	Duration of external coaptation (wk)	Complications	Time after surgery (wk)
2 y MN Labrador retriever mix, 37 kg	Lateral	2	Reluxation, managed with repeat splint	6
4 y FS Whippet mix, 23 kg	Lateral	4	Decreased range of motion	2
6 y MN Australian shepherd, 19 kg	Lateral (R), Medial (L)	2	Bandage sores	2
6 y FS Terrier mix, 7 kg	Medial	4	None	—
1 y FS Labrador retriever, 29 kg	Lateral	4	Decreased range of motion	4
8 y FS Italian greyhound, 5.3 kg	Lateral	4	Incisional dehiscence	2
1 y MI Estrela Mountain dog, 53 kg	Lateral	4	Bandage sores	3
4 y FS Shiba inu, 10.4 kg	Lateral	4	None	—
1 y FS Shiba inu, 13 kg	Lateral	4	None	—
7 y FS Pomeranian mix, 6.6 kg	Lateral	2	Decreased weight-bearing	6
1 y FS Leonberger, 42 kg	Medial	6	Incisional infection	2
4 y FS Terrier mix, 12.5 kg	Lateral	4	None	—

MN — Male neutered; FS — Female spayed; MI — Male intact.

Three dogs had concurrent medial luxating patella, with grades ranging from a 2 to 3 out of 4 (scale of 1 to 4), in the same limb affected by luxation of the superficial digital flexor tendon, noted prior to surgical repair. The patient with concurrent Grade 3/4 medial luxating patella required surgical intervention for correction following superficial digital flexor tendon repair, due to persistent lameness.

Abrasion calcaneoplasty was performed with an open surgical technique as an adjunct to retinaculum imbrication in 13 tarsi; 3 had a medially luxating superficial digital flexor, whereas 10 had a laterally luxating superficial digital flexor. All surgeries were stabilized postoperatively with a fiberglass splint encased in a soft padded bandage for 2 to 6 wk.

Results

Out of the 12 surgeries, 7 dogs were partially weight-bearing (noted to have Grade 3–4/5 lameness based on numerical rating scale) 1 d after surgery and 4 patients were weight-bearing on the affected limb 1 wk after surgery. Patient No. 3 was ambulatory on all 4 limbs 1 d after surgery. One patient started reliably placing weight on the limb 2 wk postoperatively. Of the 12 patients, 11 patients were fully weight-bearing by the time of their external coaptation removal recheck examination. One patient was persistently partially weight-bearing following removal with acute worsening of perceived lameness by owner 2 wk following splint removal (4 wk after surgery). This patient did ultimately require Grade 3/4 medial luxating patella repair 6 mo after superficial digital flexor tendon luxation correction.

Perioperative complications (< 3 mo after surgery) included incisional infection, incisional dehiscence, suture reactions, bandage complications including bandage sores, and increased pain perceived via validating scoring systems postoperatively. Of the 12 procedures, 7 surgeries (58%) developed perioperative complications that did not require intervention other than splint remodelling or removal, and each resolved shortly after external coaptation removal. Of the 12 patients that underwent abrasion calcaneoplasty, in addition to retinacular imbrication, 11 patients, approximately 92%, had no pain or luxation noted at the time of splint removal (ranging from 2 to 6 wk postoperatively). Furthermore, 1 of the 12 patients was noted to have persistent lameness following bandage removal at 2 wk. Of the 12 patients, 1 patient had reluxation of the superficial digital flexor tendon after surgery. Patient No. 1 was non-painful with appropriate range of motion at time of external coaptation removal (2 wk); however, acute swelling of the tarsus with intermittent non-weight-bearing lameness was appreciated 6 wk postoperatively, necessitating removal and replacement of the splint.

Short- to mid-term complications (3 to 12 mo after surgery) included a decreased range of motion in the tarsus and thickening/scar tissue formation at the level of the tarsal joint. A decreased range of motion was noted in the 13 tarsi of 4 dogs (31%) after splint removal. In each of these cases, the range of motion returned to normal after several weeks of physical therapy and the dogs returned to normal activity with no signs of lameness noted long term. Out of the 12 dogs, 4 dogs (33%) had concurrent medial patella luxations noted at time of initial surgery examination. In 1 of these cases, the clinical signs of luxation required surgical correction 6 mo following superficial digital flexor tendon repair due to persistent lameness and discomfort appreciated based on validated scoring systems. In 1 dog, digital palpation was able to elicit laxity and reluxation of the superficial digital flexor tendon 6 wk postoperatively, 4 wk following external coaptation removal. The superficial digital flexor tendon was manually reduced and replaced into correct anatomic position. This dog was then treated with a fiberglass splint for an additional 7 wk. Following external coaptation removal, no repeat luxation was noted, and the dog regained full range of motion.

Significant long-term complications (> 12 mo after surgery) in relation to the superficial digital flexor tendon repair were not reported in any of the 12 patients. All dogs were reported to be using the limb reliably with a non-appreciable lameness using a validating numerical lameness scoring system and were reported to be comfortable (0/4 pain score based on the Colorado State University acute pain scale for the dog) on joint range of motion based on evaluation of in-hospital and referral veterinarian records. No tendon was noted to reluxate during the long-term follow-up period.

Discussion

Abrasion calcaneoplasty combined with retinacular repair was successfully performed in 12 patients resulting in resolution of clinical lameness in all patients. Intraoperative abrasion calcaneoplasty via a burr and Hall Drill was simple to achieve and re-established a groove on the calcaneus in patients which were noted to have persistent tendency for the superficial digital flexor tendon to dislocate following positioning at the time of surgery. All patients had ultimate resolution of their clinical lameness. In 1 of the 12 dogs, the superficial digital tendon reluxated 6 wk after, but additional splinting for 7 wk achieved stabilization with no additional surgery required. No tendon was noted to reluxate in the long-term (> 12 mo interval).

The demographics of our population did not reveal any breed or body weight predisposition as previously reported for canine patients with luxated superficial digital flexor tendons (1–6,11). Furthermore, there was no predisposition for limb involvement (right versus left). As in previous reports, lateral displacements were more common among our patient pool than medial displacements (1–4). Of the 12 patients, 1 patient had bilateral displacement with 1 limb affected with a medial displacement and the contralateral limb affected with a lateral displacement.

Follow-up via in-hospital recheck examination and referral veterinarian records did not reveal any complications related directly to the proposed sulcoplasty. Although intraoperative reports did not mention a significant morphological abnormality of the calcaneus, it was a logical surgical approach to attempt to deepen the groove using a calcaneoplasty procedure between the medial and lateral processes of the calcaneal tuberosity. Further preoperative planning via CT may help to evaluate morphological defects more accurately prior to surgical correction (12). Complications such as weakness of the calcaneus, excessive inflammation, degenerative changes following removal of the cartilage or need for repeat surgical procedure for persistent repeat reluxation was not noted in our population within our current long-term follow-up period. All patients returned to full functional outcomes.

As in previous reports, postoperative external coaptation was performed in all patients. In prior studies, exact recommended duration of immobilization of the tarsal joint, following superficial digital flexor tendon repair, is unknown but 4 to 8 wk has been recommended (12). As a retrospective study, the variety in length of external coaptation was not equally distributed among our patient population and ultimately was a limitation due to the study type. Of the 12 patients, 3 were splinted for 2 wk, the majority (66%) were splinted for 4 wk, and 1 patient was splinted for as long as 6 wk immediately after surgery. Following the concepts of wound healing, if external coaptation remains in place for 2 wk, it will provide the necessary support during the weakest phases of healing. A fiberglass splint encased within a soft padded bandage limiting mobility during the proliferative phase helps to add necessary stability while the extracellular matrix is replaced by Type I collagen. By applying external coaptation during the first 2 phases of wound healing, the bandage can reduce weight-bearing and shear stress on the repair when it is at its weakest point of healing (13). In a recent study, postoperative SDF tendon luxation repair patients were bandaged for a maximum of 12 d, but data revealed that even this duration of external coaptation was not thought to provide significant support to the repair of the superficial digital flexor tendon retinaculum. In this same study, the external coaptation was omitted in more recent patients due to the increased risk of minor complications of skin irritation, pressure necrosis, and superficial infection (12). Based on our patient population and perioperative complications, 58% of our patients had complications directly related to postoperative splinting. In future studies, it may prove beneficial to explore patient outcomes in the absence of external coaptation in patients which underwent this adjunct repair method to further evaluate if postoperative splinting may be contraindicated. Reviewing short-term postoperative complications, in the absence of external coaptation, may also stand as a truer test of stability when using this adjunct repair method. Utilizing more abbreviated external coaptation periods (2 wk), following surgical repair in conjunction with abrasion calcaneoplasty, may be adequate to protect the superficial digital tendon luxation repair and decrease the rate of bandage-associated complications. Further research is needed to prove this hypothesis, including the use of a control group and larger patient populations.

Postoperative rehabilitation following a shorter splinting interval may improve earlier return to function. The demographics of our population reported a 25% decreased range of motion at the time of external coaptation removal. It is suggested that all patients undergoing repair of a superficial digital tendon luxation would benefit from a minimal external coaptation interval followed by physical rehabilitation. By applying studies for rehabilitation recommendations following cranial cruciate ligament tears and other pelvic limb tendon/ligamentous injuries (13,14), rehabilitation for superficial digital flexor tendon luxation should be focused on improving muscle mass, range of motion, and weight-bearing. The goals of rehabilitation for the postoperative superficial digital flexor tendon patient should focus on relieving pain, enhancement of tissue healing, and return to full activity. Rehabilitation should ideally begin immediately after surgery and continue until the patient has returned to full activity.

Limitations of this study include limited case numbers, attributed to the uncommon nature of disease condition. In addition, this study did not include a control group. Further research is needed to evaluate required length and necessity of external coaptation. Additional limitations of this study include the nature of a retrospective study design, utilizing multiple surgeons with preferred intraoperative techniques and inherent subjectivity of the original depth and new depth of the sulcus so results should be evaluated cautiously.

In conclusion, abrasion calcaneoplasty, in conjunction with retinacular imbrication, resulted in full functional outcomes for patients with superficial digital flexor tendon luxation, regardless of the duration of external coaptation placement. Traditional repair methods require immobilization of the hock in extension to alleviate pressure on the repair, especially during early phases of healing. Periods of immobilization are recommended starting at 3 to 4 wk but can be used up to 6 to 8 wk in some patients. In patients which underwent traditional repair, postoperative outcomes may be poor secondary to complications involving poor patient/owner compliance with splint or brace management and secondary to bandage-related skin injury (pressure sores, pododermatitis). The abrasion calcaneoplasty repair may allow for decreased or omission of external coaptation during that early phase. By focusing on a shorter duration of splinting (2 wk) with postoperative rehabilitation, a decrease in bandage complication rates and earlier return to function in patients which underwent the abrasion calcaneoplasty surgical repair technique may be possible, compared to traditional repair methods.