Clinical Outcomes of TTA Using the TTARapidTINY System in Toy-Sized Dogs with Cranial Cruciate Ligament Disease with or without Medial Patellar Luxation

Abstract

Objective

This study aimed to conduct a retrospective study investigating clinical outcomes of tibial tuberosity advancement (TTA) using the TTARapidTINY system for cranial cruciate ligament rupture (CrCLR) in toy-sized dogs (≤7.0 kg) with and without concurrent medial patellar luxation (MPL), respectively.

Methods

Medical records of toy-sized dogs that underwent TTA using the TTARapidTINY system were reviewed. Dogs were divided into two groups: Those with CrCLR only (CrCLR group) and those with concurrent MPL (CrCLR + MPL group). The data, including signalment, intraoperative findings, perioperative complications, postoperative patellar tendon angle, lameness scores (both preoperatively and at 12 weeks postoperatively) and owner surveys, were retrieved and compared between the two groups.

Results

A total of 52 affected stifle joints from 46 dogs were identified (CrCLR group: 12 stifles, CrCLR + MPL group: 40 stifles). The occurrence of major complications (2/12 [16.6%] vs. 2/40 [5%]), the percentage of a zero lameness score at 12 weeks postoperatively (11/12 [91%] vs. 40/40 [100%]), and overall owner satisfaction were statistically not different. However, the postoperative patellar tendon angle significantly differed between the CrCLR group (95.1 ± 6.0 degrees) and the CrCLR + MPL group (90.8 ± 4.0 degrees). In the CrCLR + MPL group, MPL recurred in one case (2.5%).

Clinical Significance

In our cohort of 46 toy-sized dogs, the TTARapidTINY system proved to be a safe and effective surgical tool, resulting in satisfactory functional outcomes in dogs with both CrCLR alone or combined with MPL.

 

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Keywords

cranial cruciate ligament rupture - TTARapidTINY - dog - tibial tuberosity advancement - medial patellar luxation

Introduction

Cranial cruciate ligament rupture (CrCLR) is one of the most common orthopaedic disorders in dogs, primarily affecting middle-aged and older dogs.[1] In most cases, degenerative changes in the ligament contribute to the development of CrCLR.[2] These changes tend to progress more slowly in small breeds (<15 kg) than in medium and large breeds, causing the condition to manifest later in life.[3] Although some studies recommend conservative treatment for CrCLR in small breeds, others suggest surgical intervention for improved outcomes.[4] [5] [6] [7] [8] Lateral femorotibial suture is the most common procedure for small dogs, but alternative surgical options include tibial plateau levelling osteotomy, tibial tuberosity advancement (TTA), TTARapid, cranial closing wedge osteotomy and proximal wedge osteotomy with extracapsular stabilization.[4] [6] [7] [8] [9] [10] [11] [12] [13] [14]

In 2002, TTA was introduced, and in 2015, Samoy and colleagues modified the original technique, developing the TTARapid implant (Rita Leibinger GmbH & Co. KG, Germany).[15] [16] Mid- to long-term outcomes following TTA with TTARapid have been reported as favourable.[17] In 2019, the TTARapidTINY system was developed for toy-sized dogs (Rita Leibinger GmbH & Co. KG, Germany; [Fig. 1]). Entoft and colleagues reported a low intraoperative complication rate and favourable long-term outcomes of the TTARapidTINY system in dogs weighing less than 15 kg.[18]

Fig. 1 Lateral radiography of a canine stifle after TTARapidTINY surgery.

Medial patellar luxation (MPL) is also one of the most common orthopaedic conditions in dogs and is often seen concurrently with CrCLR, although their causal relationship remains unclear. However, MPL can increase tension on the cranial cruciate ligament due to internal rotation of the tibia, potentially leading to microinjuries and degenerative changes in the ligament.[19] [20] [21] Campbell and colleagues found that dogs with grade 4 MPL were significantly more likely to have concurrent CrCLR than those with any other grade.[22]

One study reported that 13% of large-sized dogs with CrCLR had concurrent MPL.[23] On the other hand, 45 to 61% of small dogs (<15 kg) with CrCLR were reported to have concurrent MPL.[24] Therefore, when performing TTA for toy-sized dogs with CrCLR, it is crucial to prepare for surgical options to address both CrCLR and MPL to minimize the risk of complications. However, no studies on the clinical outcomes of TTA using TTARapidTINY in toy-sized dogs (≤7 kg) with CrCLR, with or without MPL, have been reported yet.

The aims of this study were to investigate retrospectively clinical outcomes of TTA using TTARapidTINY in toy-sized dogs with CrCLR and to compare the outcomes between dogs with CrCLR only and dogs with concurrent MPL. Our hypothesis was that TTA using the TTARapidTINY system would provide favourable clinical outcomes for dogs with CrCLR with or without concurrent MPL.

 

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Materials and Methods

The medical records of toy-sized dogs (≤7 kg) diagnosed with complete or partial CrCLR and treated with TTA using TTARapidTINY between May 2019 and September 2021 were retrospectively reviewed. The dogs were divided into two groups: those with CrCLR only (CrCLR group) and those with CrCLR and concurrent MPL (CrCLR + MPL group). Dogs unresponsive to medical management or those whose owners elected surgical intervention without prior medical treatment were considered suitable candidates for TTA. Cranial cruciate ligament rupture was diagnosed based on a positive cranial drawer test or tibial compression test. In all cases, stressed radiographs were taken, and the presence of a positive cranial tibial thrust and/or fat pad sign was confirmed. In cases of suspected partial rupture, an arthroscopic examination (1.9 mm, 30-degree scope, Stryker Corporation, Tokyo, Japan) was performed.

The retrieved data included signalment, duration of lameness from the initial episode to surgery, history of medical treatment prior to surgery, preoperative tibial plateau angle (TPA), MPL grade (if any), intraoperative findings, perioperative and postoperative complications and lameness scores (both preoperatively and at 12 weeks postoperatively).[25] Lameness was evaluated using a five-grade scale based on the degree of weight-bearing and gait disturbance: Grade 0 indicated no clinical lameness; grade 1, subtle lameness that became apparent after strenuous exercise; grade 2, moderate lameness at all gaits with normal activity or exercise, but with the affected limb bearing most of the weight during each step; grade 3, severe lameness at all gaits with partial weight-bearing; and grade 4, complete non-weight-bearing on the affected limb.[26] Complications were classified as major if they required surgical or medical intervention, and minor if no such treatment was necessary.[27]

Preanaesthetic Drugs, Anaesthesia and Analgesics

Atropine sulphate (0.04 mg/kg subcutaneously; Fuso Pharmaceutical Industries, Ltd., Osaka, Japan) and midazolam (0.1–0.3 mg/kg intravenously; SANDOZ Ltd., Tokyo, Japan) were administered as preanaesthetic medications. Anaesthesia was induced with propofol (4–8 mg/kg intravenously; Zoetis Japan Inc., Tokyo, Japan), and the patients were intubated. Isoflurane inhalation (DS Pharma Animal Health Co., Ltd., Osaka, Japan) was used to maintain the surgical plane of anaesthesia. Cefazolin (22 mg/kg intravenously; Fujita Pharmaceutical Co., Ltd., Tokyo, Japan) was administered preoperatively and every 90 minutes until the end of surgery. Meloxicam (0.2 mg/kg subcutaneously; Boehringer Ingelheim Animal Health Japan, Tokyo, Japan) was given preoperatively for analgesia. In addition, bupivacaine hydrochloride hydrate (0.1 mg/kg; SANDOZ Pharmaceutical Co., Ltd., Tokyo, Japan) mixed with morphine hydrochloride hydrate (0.1 mg/kg; Takeda Pharmaceutical Company, Osaka, Japan) was injected into the epidural space.

 

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Surgical Planning

After the induction of anaesthesia, lateral radiographs of the fully extended stifle joint were obtained for preoperative planning. The cage was selected based on the advancement of the tibial tuberosity, measured using the anatomical landmark method.[28] In dogs with tibial subluxation, a radiograph of the contralateral tibia was obtained to accurately determine the required advancement.

 

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Tibial Tuberosity Advancement Using TTARapidTINY System

The cranial cruciate ligament and meniscus were examined and manipulated either arthroscopically or via arthrotomy. Arthrotomy was performed in dogs with concurrent MPL to reduce surgical time. If a meniscal tear was observed, partial meniscectomy was performed. The distance of the perpendicular line between the osteotomy line and the tibial tuberosity was measured for a more accurate osteotomy, as outlined in the preoperative planning. Osteotomy of the tibial tuberosity was performed using a power tool (Colibri2, DePuy Synthes Japan, Johnson & Johnson K.K., Tokyo, Japan, or Primado2, NAKANISHI INC., Tochigi, Japan). An L-shaped saw guide (TTARapidTINY, Rita Leibinger) was used to determine the appropriate osteotomy length for the selected cage. However, most patients experienced tibial fissures or detachments when following the manufacturer's guide tool. To avoid this complication, we began making the osteotomy two cage sizes longer than required for the selected cage; for instance, for cage 3, the osteotomy length was adjusted to the length required for a cage 6. In addition, to prevent proximal tibial fractures, the distal endpoint of the osteotomy was positioned slightly more cranially than the line of the cranial cortical bone ([Fig. 2]). If a fissure occurred in the cranial cortex, a Kirschner wire was used for stabilization as needed. To prevent tibial tuberosity fractures, the proximal and cranial screws to secure the cage were inserted proximal to the patellar ligament attachment.

Fig. 2 Osteotomy was performed for a cage, which was two sizes longer than the manufacturer recommended, and was also made slightly more cranial between the cortical and cancellous bones, which helped reduce the incidence of fissures during cage insertion.

In dogs with concurrent MPL, block recession trochleoplasty and tibial tuberosity transposition were performed. The goal of block recession trochleoplasty was to achieve a trochlear groove deep and wide enough to accommodate at least 50% of the patella's height between the trochlear ridges.[29] During tibial tuberosity transposition, a spacer was inserted between the cage and the tibia. The spacer size was selected such that the patella was positioned in the centre of the trochlear groove. Medial retinacular desmotomy, lateral retinacular imbrication, release of the medial vastus or anterior sartorius muscles and antirotational suture were performed as needed.

Cancellous bone harvested during trochleoplasty was crushed using a rongeur and grafted proximally and distally to the cage. The surgical site was thoroughly lavaged with saline, and the retinaculum and subcutaneous tissues were closed with synthetic absorbable monofilament sutures, the skin with monofilament nylon.

 

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Postoperative Management and Follow-Up Examinations

Postoperative radiographs were obtained immediately after surgery to assess the position of the implants, to check for tibial fractures and to measure the postoperative patellar tendon angle (PTA). Ice-cold pads were applied to the surgical wound two to three times daily for 10 minutes over approximately 3 days following the procedure. For postoperative analgesia, meloxicam (0.1 mg/kg subcutaneously) or firocoxib (5 mg/kg orally, Boehringer Ingelheim Animal Health Japan, Tokyo, Japan) was administered for 10 to 14 days. Patients were discharged 3 to 7 days after surgery. Owners were instructed to restrict their dogs to cage rest at home, allowing minimal short leash walks for 4 weeks after surgery, with a gradual increase in exercise thereafter.

Follow-up examinations, including orthopaedic and radiographic assessments, were conducted by the surgeon at 4, 8 and 12 weeks postoperatively. At the 12-week radiographic examination, bone union and the presence of cranial subluxation were assessed. Bone union was evaluated using radiographs based on previously reported criteria: Score 0, no osseous healing; score 1, early bone production without bridging between the tibial tuberosity and the tibial shaft; score 2, bridging bone formation at one site; score 3, bridging bone at two sites (proximal, distal).[30] To assess mid- and long-term clinical outcomes, a questionnaire for owners was developed based on previous studies.[30] [31] The questionnaire included inquiries regarding the severity of lameness before surgery, current condition of the dog, current activity level, need for pain medication and overall owner satisfaction. Owners who did not respond by mail were contacted by phone.

 

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Statistical Analysis

The Kolmogorov–Smirnov test was conducted to assess the normality of data distribution for continuous variables. A non-parametric or parametric test was performed for comparisons of numerical data between two groups where appropriate. Fisher's exact test was performed for categorical data. A p-value less than or equal to 0.05 is considered significant.

 

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Results

A total of 46 dogs with 52 affected stifles were included in the study. All surgeries were performed by the same surgeon (T.F.). The sex status was composed of 30 females and 16 males. The breeds included Yorkshire Terriers (n = 10), Chihuahuas (n = 9), Toy Poodles (n = 8), mixed-breed dogs (n = 8), Papillons (n = 4), Jack Russell Terriers (n = 3), Pomeranians (n = 2), Maltese (n = 1) and Shiba Inu (n = 1).

Twelve stifles (23.1%) in the CrCLR group and 40 stifles (76.9 %) in the CrCLR + MPL group were identified. [Table 1] summarizes signalments and preoperative clinical characteristics of the CrCLR group and CrCLR + MPL group. Bilateral TTA was performed in six dogs in the CrCLR + MPL group. Body weight between the CrCLR (mean ± standard deviation [SD]: 4.6 ± 0.9 kg) and CrCLR + MPL groups (4.3 ± 1.2 kg) did not statistically differ (p = 0.363). Age between the CrCLR group (mean ± SD: 9.2 ± 2.4 years) and the CrCLR + MPL group (8.1 ± 2.9 years) did not significantly differ (p = 0.218). No significant differences were observed in body condition score (p = 0.512), sex distribution (p = 0.627), affected limb side (p = 0.743), duration of disease (p = 0.428), previous treatment (p = 0.729) and preoperative lameness score (p = 0.461) between the two groups.

Table 1 Signalments and preoperative clinical characteristics

Variable	Cranial cruciate ligament rupture group	Cranial cruciate ligament rupture + medial patellar luxation group	p-Value
Number of dogs	12	34	–
Number of studied stifles	12	40
Body weight (mean ± standard deviation; kg)	4.6 ± 0.9	4.3 ± 1.2	0.363
Age (mean ± standard deviation; years)	9.2 ± 2.4	8.1 ± 2.9	0.218
Body condition score			0.512
1/5	0	0	–
2/5	0	1
3/5	7	24
4/5	4	15
5/5	1	0
Sex			0.627
Male	6	12	–
Female	6	28
Side of the affected limb			0.743
Left	5	21	–
Right	7	19
Duration of disease (mean ± standard deviation; days)	73 ± 95	36 ± 63	0.428
Previous treatment (number of Stifles)	9	26	0.729
Preoperative lameness score (median [range])	3 (0–4)	2 (1–4)	0.461

Medical treatment includes cage rest and oral administration of non-steroidal anti-inflammatory drugs.

[Tables 2] and [3] show signalment, intraoperative findings, complications and 12-week outcomes for each patient in the CrCLR group and CrCLR + MPL group, respectively. Preoperative TPA between dogs with the CrCLR group (mean ± SD: 26.6 ± 6.2 degrees) and CrCLR + MPL group (mean ± SD: 27.1 ± 4.2 degrees) did not statistically differ (p = 0.763). The degree of cruciate ligament damage (total or partial; p = 0.366) and the presence of meniscus tear (p = 0.726) were not significantly associated with whether the dogs had concurrent MPL or not. In the CrCLR + MPL group, MPL grade 2 was observed in 22 stifles, the grade 3 in 15 stifles, and the grade 4 in 3 stifles.

Table 2 Signalment, intraoperative findings, complications and 12-week outcomes for each patient in the cranial cruciate ligament rupture group

Case	Breed	Weight (kg)	Cruciate ligament damage	Meniscal tear	Procedures	Tibial plateau angle (degrees)	Cage size (mm)	Intraoperative complications	Postoperative complications	Postoperative patellar tendon angle	Lameness score (preoperative)	Lameness score (12-week postoperative)
1	Chihuahuas	4.05	Total	Yes	Arthrotomy	31	3/8	–	Tibial fracture	94	3	0
2	Chihuahuas	4.2	Total	No	Arthrotomy	28	4.5/7	Tibial tuberosity detached	Tibial fracture	89.8	3	0
3	Mix	5.05	Partial	No	Arthrotomy	29	3/7	Patial fissure	–	110	0	0
4	Toy Poodles	3.7	Total	No	Arthroscopy	19	3/7	Patial fissure		96.8	2	0
5	Toy Poodles	5.45	Total	No	Arthroscopy	20	3/7	Patial fissure		96.8	4	0
6	Toy Poodles	3.5	Total	Yes	Arthrotomy partial eniscectomy	22	3/7	Tibial tuberosity detached		87.7	4	0
7	Yorkshire Terriers	3.4	Total	No	Arthrotomy	27	2/6	–		95.8	2	0
8	Jack Russell Terriers	5.5	Partial	Yes	Arthroscopy partial meniscectomy	27	4.5/8	Patial fissure	Lameness (month 8, 12)	91.3	1	0
9	Chihuahuas	4.95	Total	Yes	Arthrotomy partial meniscectomy	17	3/7	–		89.7	2	0
10	Jack Russell Terriers	5	Partial	No	Arthroscopy	35	4.5/10	–		92.4	1	0
11	Jack Russell Terriers	6.4	Total	No	Arthroscopy	27	4.5/10	–		97	4	0
12	Yorkshire Terriers	4.55	Total	No	Arthroscopy	37	3/7	–	Persistent lameness	100	4	1

Table 3 Signalment, intraoperative findings, complications and 12-week outcomes for each patient in the cranial cruciate ligament rupture + medial patellar luxation group

Case	Breed	Weight (kg)	Cruciate ligament damage	Meniscal tear	Procedures	Tibial plateau angle (degrees)	Cage size (mm)	Spacer size (mm)	Medial patellar luxation grade	Medial patellar luxation procedures	Intraoperative complications	Postoperative complications	Postoperative patellar tendon angle	Lameness score (preoperative)	Lameness score (12-week postoperative)
1	Yorkshire Terriers	2.35	Total	Yes	Arthrotomy Partial meniscectomy	25	2/11	2	G2	BRT, Imbrication Desmotomy	Patial fissure	–	89.4	2	0
2	Mix	6.6	Total	No	Arthrotomy	25	3/8	2	G4	BRT, Imbrication Desmotomy	Patial fissure	Lameness (month 4)	85.2	2	0
3	Chihuahuas	3.3	Total	No	Arthrotomy	26	2/6	2 (Proximal only)	G2	BRT, Imbrication Release	–		91.5	4	0
4	Chihuahuas	5.5	Total	Yes	Arthrotomy Partial meniscectomy	32	4.5/9	1 (Proximal only)	G2	BRT, Imbrication Desmotomy	Patial fissure	–	88.4	2	0
5	Mix	3.3	Partial	No	Arthrotomy	29	4.5/11	2	G2	BRT, Imbrication Desmotomy	Patial fissure	–	100.6	4	0
6	Chihuahuas	3	Total	No	Arthrotomy	22	3/8	2	G4	BRT, Imbrication Desmotomy, Release	Patial fissure	–	87.1	1	0
7	Pomeranians	5.05	Total	No	Arthrotomy	21	4.5/9	2	G2	BRT, Imbrication Desmotomy	Patial fissure	–	92.6	1	0
8	Papillons	3.15	Total	No	Arthrotomy	34	3/10	2	G3	BRT, Imbrication Desmotomy	Tibial tuberosity detached	–	94	2	0
9	Toy Poodles	3.2	Total	No	Arthrotomy	27	3/9	3 (Proximal) 1 (Distal)	G3	BRT, Imbrication Desmotomy	Tibial tuberosity detached	–	97.4	4	0
10	Chihuahuas	2.85	Total	No	Arthrotomy	25	3/9	2	G2	BRT, Imbrication Desmotomy	Patial fissure	–	90.8	1	0
11	Maltese	5	Total	Yes	Arthrotomy Partial meniscectomy	27	3/11	2	G2	BRT, Imbrication Desmotomy	Patial fissure	–	91.1	2	0
12	Papillons	3.55	Total	Yes	Arthrotomy Partial meniscectomy	29	3/7	2	G3	BRT,Imbrication Desmotomy, Patelloplasty	Patial fissure	–	88.1	3	0
13	Toy Poodles	4.1	Total	No	Arthrotomy	32	3/7	1	G2	BRT, Imbrication Desmotomy, Release	Patial fissure	Lameness (month 5)	94.9	4	0
14	Yorkshire Terriers	3.6	Total	Yes	Arthrotomy Partial meniscectomy	30	3/8	2 (Proximal only)	G2	BRT, Imbrication Desmotomy	–		85	2	0
15	Yorkshire Terriers	4.1	Total	No	Arthrotomy	29	3/9	2	G3	BRT, Imbrication Desmotomy, Release	Patial fissure	Recurrent patella luxation	91	1	0
16 (14)	Yorkshire Terriers	2.9	Partial	No	Arthrotomy	30	3/7	2 (Proximal only)	G2	BRT, Imbrication Desmotomy	–	–	87.7	1	0
17	Mix	4.85	Total	No	Arthrotomy	32	3/9	2	G2	BRT, Imbrication Desmotomy	Patial fissure 0.8-mm K-wire inserted	Tibial tuberosity fracture	88.1	3	0
18	Toy Poodles	6.55	Total	Yes	Arthrotomy Partial meniscectomy	30	3/9	2 (Proximal) 1 (Distal)	G3	BRT, Imbrication Desmotomy	Patial fissure	–	89.8	4	0
19 (4)	Chihuahuas	5	Total	No	Arthrotomy	32	3/7	1 (Proximal only)	G2	BRT, Imbrication Desmotomy	Patial fissure	Lameness (month 3)	89.8	3	0
20	Mix	4.35	Total	No	Arthrotomy	25	3/9	2 (Proximal only)	G2	BRT, Imbrication Desmotomy, Release	Patial fissure	–	87.2	2	0
21	Mix	4.3	Total	No	Arthrotomy	36	3/8	3 (Proximal only)	G3	BRT, Imbrication Desmotomy, Release	Patial fissure	–	92.3	2	0
22	Shiba Inu	6.95	Total	No	Arthrotomy	25	4.5/10	3	G3	BRT, Imbrication Desmotomy, Release	Patial fissure	–	83.1	2	0
23	Yorkshire Terriers	1.95	Total	No	Arthrotomy	23	2/6	1	G2	BRT, Imbrication Desmotomy, Release, antirotational suture	–	–	88.4	2	0
24	Pomeranians	4.3	Total	No	Arthrotomy	19	3/9	2 (Proximal only)	G3	BRT, Imbrication Desmotomy, Release	Patial fissure 0.8-mm K-wire inserted	–	90.5	3	0
25	Yorkshire Terriers	4.65	Total	No	Arthrotomy	25	3/9	2 (Proximal only)	G3	BRT, Imbrication Desmotomy, Release, antirotational suture	Patial fissure	–	100	2	0
26 (23)	Yorkshire Terriers	2.05	Total	No	Arthrotomy	23	2/6	1	G4	BRT, Imbrication Desmotomy, Release, antirotational suture	–	–	85.8	1	0
27	Papillons	4.75	Total	Yes	Arthrotomy Partial meniscectomy	26	4.5/12	2	G3	BRT, Imbrication Desmotomy, Release	Patial fissure 0.8-mm K-wire inserted	–	92.8	4	0
28	Chihuahuas	4	Total	Yes	Arthrotomy Partial meniscectomy	24	3/7	2	G3	BRT, Desmotomy Release	Patial fissure	–	89.7	4	0
29	Papillons	5.55	Total	Yes	Arthrotomy Partial meniscectomy	18	3/9	3 (Proximal) 1 (Distal)	G3	BRT, Imbrication Desmotomy, Release	Patial fissure	–	90.8	3	0
30	Yorkshire Terriers	4.4	Total	No	Arthrotomy	33	3/7	2 (Proximal only)	G3	BRT, Imbrication Desmotomy, Release	Patial fissure	–	88.2	1	0
31	Mix	4.8	Total	No	Arthrotomy	26	3/7	2	G2	BRT, Imbrication Desmotomy, Release	Patial fissure	–	95.4	3	0
32	Toy Poodles	5.05	Partial	No	Arthrotomy	28	3/9	2	G3	BRT, Imbrication Desmotomy, Release	Patial fissure	–	95.5	2	0
33 (27)	Papillons	4.95	Total	Yes	Arthrotomy Partial meniscectomy	26	4.5/10	2 (Proximal only)	G2	BRT, Imbrication Desmotomy, Release	Patial fissure	–	89.5	4	0
34	Toy Poodles	3.9	Partial	No	Arthrotomy	26	3/9	1	G2	BRT, Imbrication Desmotomy	Patial fissure	–	92.4	3	0
35	Yorkshire Terriers	4.25	Partial	No	Arthroscopy	25	3/9	3 (Proximal only)	G2	BRT, Imbrication Desmotomy, release	–	–	89.1	2	0
36 (22)	Shiba Inu	6.6	Total	No	Arthrotomy	25	4.5/12	3	G2	BRT, Imbrication Desmotomy, release	Patial fissure	–	96.2	3	0
37	Mix	5.5	Total	Yes	Arthrotomy Partial meniscectomy	24	3/11	3 (Proximal) 1 (Distal)	G2	BRT, Imbrication Desmotomy, release	–	–	91.3	1	0
38	Yorkshire Terriers	4.75	Total	No	Arthrotomy	32	3/7	2 (Proximal only)	G2	BRT, Imbrication Desmotomy, Release	–	–	95.8	3	0
39	Mix	2.54	Total	No	Arthrotomy	23	3/7	2 (Proximal only)	G2	BRT, Imbrication Desmotomy, Release	–	–	87.4	3	0
40 (30)	Yorkshire Terriers	4.1	Total	No	Arthrotomy	33	3/9	2	G3	BRT, Imbrication Desmotomy, Release	Patial fissure 0.8-mm K-wire inserted	–	86.4	4	0

Abbreviations: BRT, block recession trochleoplasty; Desmotomy, medial desmotomy; Imbrication, lateral imbrication; Release, muscle release.

(X) Case number of contralateral stifle.

The median body weight (range) for each cage size was 2.35 kg (1.95–3.4 kg) for 2.0-mm cages; 4.3 kg (3.0–6.6 kg) for 3.0-mm cages; and 5.0 kg (3.3–6.95 kg) for 4.5-mm cages. The sizes of spacers used were 1 mm in 4 stifles (10%), 2 mm in 16 stifles (40%) and 3 mm in 2 stifles (5%) and only half of the proximal part of the spacer was used in 14 stifles (35%). Different sizes of spacers were used in the proximal and distal parts in four stifles (10%). The width of the tibia was often too narrow to use a saw guide during osteotomy, particularly in dogs weighing less than 3 kg. The above-described modifications to the surgical procedure were made in three dogs (cases 10–12) of the CrCLR group and 19 dogs (cases 22–40) in the CrCLR + MPL group. The mean postoperative PTA significantly differed between the CrCLR group (95.1 ± 6.0 degrees) and the CrCLR + MPL group (90.8 ± 4.0 degrees; p = 0.005).

Twelve-Week Postoperative Follow-Up Evaluation

At 12 weeks postoperatively, except for one case in the CrCLR group (case 12), all dogs were lameness-free and were deemed to have regained their original activity levels, without requiring non-steroidal anti-inflammatory drugs. The lameness scores between the CrCLR group (median [range]: 0 [0–1]) and the CrCLR + MPL group (median 0, all dogs were scored zero) did not differ (p = 0.231). Radiographic examination revealed no implant breakage or loosening. The bone healing scores did not differ between the groups (p = 0.122). Score 0 was noted in 2 stifles (5%) in the CrCLR + MPL group; score 2 was observed in 7 stifles (58.3%) in the CrCLR group and 10 stifles (25%) in the CrCLR + MPL group; and score 3 was seen in 5 stifles (41.7%) in the CrCLR group and 28 stifles (70%) in the CrCLR + MPL group. Cranial subluxation was observed in 11 stifles (91.7%) in the CrCLR group and 24 stifles (60.0%) in the CrCLR + MPL group, with no significant difference in occurrence between the two groups (p = 0.076).

 

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Intraoperative Complications

After osteotomy of the tibial tuberosity, cranial cortical bone fissures occurred when a cage or spacer was inserted. The occurrence of the fissures was higher in the CrCLR + MPL group (29 stifles: 72.5%) compared with the one in the CrCLR group (4 stifles: 33.3%; p = 0.019). In the CrCLR + MPL group, where cranial cortical bone fissures occurred, a 0.8-mm Kirschner wire was inserted distally to the tibial tuberosity for reinforcement and fixation in 4 stifles. In both the CrCLR and CrCLR + MPL groups, the tuberosity was completely detached from the tibia in two stifles each (16.7% and 5%; p = 0.225), although no further intervention was necessary. If reinforcement and fixation were performed preventatively during surgery, or if the tuberosity completely detached during osteotomy but healed without further intervention, these cases were classified as minor complications.

 

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Postoperative Complications

Major complications occurred in two dogs in each group (16.7% and 5%; p = 0.225). In two of these cases, the tibial tuberosity was completely detached, leading to proximal tibial fractures ([Fig. 3]). One dog fell down the stairs at home 10 days after surgery and also developed a proximal tibial fracture. All three dogs were successfully treated with revision surgery involving either plate fixation or external skeletal fixation. One patient with concurrent grade 4 MPL developed recurrent patellar luxation 6 days after having undergone trochleoplasty and TTA. Cranial and rotary instability of the tibia was noted; therefore, an antirotational suture was placed 43 days after the TTA. No subsequent recurrence of MPL was observed. Postoperative lameness 12 weeks after surgery was observed in two dogs (16.7%) in the CrCLR group and three dogs (7.5%) in the CrCLR + MPL group due to suspected meniscal injuries (p = 0.325; [Tables 2] and [3]). Their lameness score was 0 to 1, and a mild to slight muscle atrophy was noted on the affected limb upon palpation. Radiographs did not show any abnormalities. These five dogs with postoperative lameness were treated medically, and four responded well to the treatment, but one dog remained lame (lameness score of 1). None of the dogs required a second-look arthroscopy after surgery.

Fig. 3 Postoperative tibial fracture occurred after an oversized cage was inserted. Plating was performed to address this fracture.

 

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Owner Questionnaire

Questionnaires sent to owners received responses from 45 out of 46 dogs (97.8%), with an average follow-up period of 17 months (range: 5–33 months). Based on the questionnaires, in 39 dogs (86.7%), no lameness was reported (neither limping nor inability to use a limb properly), one dog (2.2%) experienced lameness after intense activity and five cases (11.1%) had lameness when standing up. Only one dog (2.2%) required anti-inflammatory medications. Overall satisfaction was rated as very good in 37 out of 45 dogs (82.2%), good in 6 dogs (13.3%) and neither good nor bad in 2 dogs (4.4%). No significant differences were observed between the two groups in the responses to each question ([Table 4]).

Table 4 Owner questionnaire assessments between the cranial cruciate ligament rupture group and the cranial cruciate ligament rupture + medial patellar luxation group

1. Prior to surgery, my dog limped
	1–Never	2–Only after heavy exercise	3–After short walks	4–After resting	5–All the time	p-Value
CrCLR	1	0	1	3	7	0.156
CrCLR + MPL	3	0	4	1	25
2. Now my dog limps
	1–Never	2–Only after heavy exercise	3–After short walks	4–After resting	5–All the time	p-Value
CrCLR	10	0	0	1	0	0.699
CrCLR + MPL	30	1	0	1	1
3. My dog's activity level now, compared with prior to the tibial tuberosity advancement is
	1–Greatly improved	2–Mildly improved	3–Same	4–Mildly worse	5–Greatly worse	p-Value
CrCLR	11	0	0	1	0	0.366
CrCLR + MPL	29	2	2	0	0
4. Please state your assessment of the overall outcome of the procedure
	1–Excellent	2–Good	3–Fair	4–Poor	5–Bad	p-Value
CrCLR	10	2	0	0	0	0.709
CrCLR + MPL	29	3	1	0	0
5. My dog needs anti-inflammatory medications – please circle one if applicable
	1–Never	2–Once monthly	3–Once weekly	4–Once daily	–	p-Value
CrCLR	11	0	0	1	–	0.267
CrCLR + MPL	33	0	0	0	–

 

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Discussion

Our results suggest that TTA using the TTARapidTINY system is a safe and effective procedure for dogs weighing less than 7 kg with CrCLR, whether with or without MPL, yielding favourable mid- and long-term outcomes. This procedure could be considered a viable treatment option for toy-sized dogs with CrCLR. In one study involving large-breed dogs, 50% of the dogs had a lameness score of 0/5 and 40% had a score of 1/5 12 weeks after TTA using the standard-sized TTARapid system.[16] Ferreira and colleagues also reported that TTA performed in dogs weighing less than 15 kg resulted in 91% of dogs achieving a score of 0/5 and 6% a score of 1/5 at 12 weeks postoperatively.[10] Our results are comparable to those of previous studies. Furthermore, owner satisfaction was rated as good or very good in more than 90% of cases, indicating that our findings align with those of other reports.[11] [18] [30]

The major postoperative complication rate in our study was comparable to previous studies on TTARapidTINY (Entoft and colleagues: 3.4%) as well as in reports on TTA in dogs weighing less than 15 kg (Dyall and Schmokel: 6.3%, Ferreira and colleagues 5.7%).[1] [10] [11] [18] In most cases, we encountered fissures at the distal part of the osteotomy site or complete detachment of the tibial tuberosity, which could potentially lead to severe postoperative complications. In this study, the CrCLR + MPL group experienced a higher occurrence of fissures compared with the CrCLR group, which may be likely due to increased load on the tibial tuberosity from using spacers. The cage size and osteotomy length were determined according to the instructions of the manufacturer. However, while widening the gaps between the bones using a spreader, the tibial tuberosity became completely detached in some instances. Subsequently, the cage was fixed without securing the detached bone, resulting in postoperative fractures owing to excessive load on the remaining caudal tibia. We hypothesize that there is a size limit for cages suitable for the tibiae of dogs weighing less than 7 kg. To address these issues, we made some modifications during osteotomy. According to the instructions of the manufacturer, the osteotomy should start slightly cranial to Gerdy's tubercle and end just caudal to the cranial cortex of the tibia. However, this approach resulted in an osteotomy closer to the centre of the bone in thin tibiae, resulting in tibial fractures. Thus, the distal endpoint of the osteotomy was positioned slightly more cranially than the line of the cranial cortical bone. When performing osteotomy using TTARapidTINY on very thin hindlimbs, the saw guide can easily slip because of the force applied by the assistant and surgeon. In fact, one patient experienced a tibial fracture as a result of improper osteotomy. To mitigate this risk, the osteotomy line was marked on the surface of the tibia using a surgical saw or electrocautery to verify the osteotomy position beforehand.

The goal of TTA is to stabilize the stifle joint by neutralizing the cranial tibial thrust and reducing the PTA to below 90 degrees during the walking phase.[32] The mean postoperative PTA in dogs with the CrCLR group was 95.1 ± 6.0 degrees, indicating insufficient advancement. Small-sized dogs (<15 kg) have a higher TPA than larger dogs, necessitating relatively larger cages during TTA. The average TPA in this study was 26.9 degrees, consistent with the results of other studies.[18] [33] In the original TTA procedure, the tibial tuberosity is shifted proximally after complete osteotomy, effectively reducing the postoperative PTA.[34] However, the TTARapid technique primarily involves rotation, making PTA reduction more challenging. Therefore, using a cage one size larger than that of the original TTA might be recommended for TTARapid. However, in view of the risk of intraoperative and postoperative tibial fractures, a cage smaller than the recommended size was used, resulting in a higher postoperative PTA. Notably, the postoperative PTA in dogs with the CrCLR + MPL group was 90.8 ± 4.0 degrees, indicating that appropriate advancement was achieved. Trochleoplasty was performed in all cases with concurrent MPL, which allowed the patella to sit deeper and more caudally within the trochlear groove. As a result, the patellar ligament also shifted caudally, contributing to a lower postoperative PTA compared with those with CrCLR only ([Fig. 4]).

Fig. 4 Postoperative PTA differed depending on whether concurrent MPL was present in dogs undergoing TTARapidTINY surgery. (Left) When only TTA was performed in a dog without concomitant MPL, it was challenging to reduce postoperative PTA below 90°. (Right) When trochleoplasty was performed in a dog with concurrent MPL, the patella was positioned deeper and more caudally in the trochlear groove. As a result, the patellar ligament also shifted caudally, leading to an optimal reduction in postoperative PTA.

In this study, 67% of cases had cranial subluxation at the 12-week postoperative radiographic examination. A postoperative PTA higher than 90 ± 5 degrees or a meniscal injury can contribute to the development of postoperative tibial subluxation.[35] In fact, both human and canine in vitro studies revealed that the meniscus plays a crucial role in stabilizing the stifle joint.[36] On the other hand, subluxation was observed in cases without meniscal damage in one canine study, suggesting that the meniscus might not play a significant role in tibial stability. [37] It was reported that dogs that developed tibial subluxation after TTA remained clinically well without further intervention.[35] In our study, most cases had cranial subluxation, but clinical outcomes were comparable to the previous reports. In one case with recurrent patellar luxation, the tibia luxated not only cranially but also rotationally. Therefore, we performed the antirotational suture technique in this dog as a revision surgery, which resulted in a good outcome in terms of patellar stability. In case of stifle instability, combining joint stabilization techniques, such as the antirotational suture method, may improve postoperative outcomes. Further studies are warranted to confirm this hypothesis.

The limitations of this study include subjective evaluations based on owner questionnaires for mid- and long-term follow-up assessments, rather than objective measurements obtained using force plates. Importantly, we conducted multiple hypothesis tests, which increases the risk of type I error. Therefore, this should be taken into consideration when interpreting our statistical results.

Our study demonstrated that TTA using the TTARapidTINY system is a feasible and effective surgical technique for dogs weighing less than 7 kg with CrCLR and appears to be particularly beneficial in cases with concurrent MPL. However, careful preoperative planning is critical, particularly in determining the appropriate cage size based on the individual physical features of the patient and the desired postoperative PTA.

 

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Conflict of Interest

None declared.

Acknowledgments

We would like to express our gratitude to our veterinary nurses who assisted with data collection.

Authors' Contributions

T.F. performed the surgeries in all cases, collected and analysed the data and drafted the manuscript. T.M. interpreted the data, revised the draft and translated the manuscript. Both authors contributed substantially to the conception of the study and agreed to be accountable for all aspects of the research.

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Publication History

Received: 08 November 2024

Accepted: 09 August 2025

Article published online:
25 August 2025