Medial Shoulder Instability: Prevalence and Treatment Outcomes in 17 Poodles and 31 Dogs of Other Breeds

may be observed in normal joints. 10 – 13 Hence a diagnosis of MSI cannot be based upon abduction angle measurement alone. In cases of instability/subluxation (MSI grade 1 – 3), arthroscopy is required to con ﬁ rm the diagnosis; luxation (MSI grade 4) can be diagnosed from radiographs.


Introduction
3][4] Medial shoulder instability (MSI) is characterized by medial glenohumeral ligament (MGHL) pathology, including tears, laxity or avulsion, as seen in the majority of cases, 5 subscapularis tendinopathy, and labral or capsular tears.Cases of MSI can be classified as either traumatic or spontaneous in etiology, with 49% reported in one study as a traumatic tearing of the MGHL. 65][16] Based on a literature search (PubMed, search criteria: "medial shoulder instability, medial glenohumeral ligament, abduction angle, subluxation, and poodle"), few data points were identified that characterized the etiology of MSI in dogs with respect to breed.
][19][20][21][22][23][24] Surgery aims to reconstruct medial stability via tendon augmentation or prosthesis implantation.There are variations in MGHL reconstruction techniques and implants, with the consistent aim to reconstruct the medial support for the glenohumeral joint, 14,15,[19][20][21][22]25 maintaining joint alignment and normal biomechanics. Bicps and supraspinatus tendon transpositions have independently been shown to provide improved medial stability.6,26 However, biceps tendon transposition (BTT) has been shown to result in increased external rotation of the joint and an increased abduction angle in comparison to placing a MGHL prosthesis, and both tendon transpositions have, in time, been shown to cause such altered shoulder biomechanics and congruity that degenerative changes will develop.22,23 In our experience, poodles and their crossbreeds appear to be at elevated risk of MSI, with a high proportion of cases presenting spontaneously (without having sustained significant trauma) and having an unpredictable outcome in response to treatment.This led us to undertake this study.
We hypothesize that poodles may be overrepresented in the local investigated population of dogs presenting with MSI.Additionally, we hypothesize that poodles exhibit higher rates of spontaneous MSI than non-poodle breeds.
Finally, we wanted to investigate whether poodles may end up with a generally poorer treatment outcome, either through conservative or surgical management, as compared with non-poodle breed dogs.

Data Collection
Data were obtained retrospectively from the clinical records spanning 2009 to 2019 from five referral small animal veterinary hospitals in Melbourne, Australia.Records were searched for all dogs presenting with lameness attributable to MSI, with database searches performed using the following search terms: canine, medial shoulder instability, medial glenohumeral ligament, abduction angle, subluxation, and luxation, in RxWorks, EzyVet, and CiderHouse software programs.For each dog, data were collected regarding the signalment, affected limb, abduction angle if noted, the level of inciting trauma, the initial treatment, arthroscopic and surgical findings, postoperative outcome, and follow-up treatments.The grade of MSI was recorded for each case; cases that had not been graded were retrospectively assigned according to the previously described grading system. 7,8reeds were classified as poodle (P) and non-poodle (NP).Where the dog was recorded as a poodle-cross or mixed breed it was allocated to the NP group.For the means of analysis of injury data, bilaterally affected animals were included only as one case, with their first diagnosis of MSI as their indexed event, and their subsequent presentation was excluded.Classification of the etiology of the instability was recorded as either spontaneous (dogs with no known trauma or whose lameness occurred during normal physiological activity, such as jumping off one step or a couch, or pawing at the carpet) or traumatic (dogs known to have Medial Shoulder Instability in Poodles Woolley et al. sustained a low impact trauma such as having been chasing a ball or at agility training when the lameness occurred).Cases with medial shoulder luxation after sustaining high impact trauma such as being hit by a car or falling from a height were deemed to have traumatic shoulder luxation rather than shoulder instability and hence excluded.Other exclusion criteria included glenohumeral dysplasia and comorbidities that may contribute to glenohumeral instability such as immune-mediated polyarthritis.Cases were included if forelimb lameness was present, a diagnosis of MSI was confirmed via shoulder arthroscopy visualizing pathology in the MGHL and/or subscapularis tendon, or via radiographic confirmation of medial luxation of the humeral head without having sustained high impact trauma, consistent with grade 4 MSI.
Treatment was classified as either conservative, reconstructive surgical (included MGHL reconstruction or BTT), or treatment with a salvage procedure (excisional arthroplasty, glenohumeral arthrodesis, or forequarter amputation).Given the multi-center cohort study, conservative management was considered as a combination of rest, nonsteroidal anti-inflammatory drugs, intra-articular steroid/stem cell/platelet-rich plasma treatments, physical therapy, use of hobbles, orthopaedic braces, splints, or slings.
The conclusion for each case was recorded as full (restoration to/maintenance of full intended level and duration of activities and performance from preinjury or pre-disease status, without medication), acceptable (restoration to/ maintenance of intended activities and performance from preinjury or pre-disease status that is limited in level or duration and/or requires medication to achieve), or unacceptable (all other outcomes), as described by Cook et al, 27 according to examination by the primary clinician and/or assessment by the owner.Any dog where conservative management resulted in an unacceptable outcome that went on to have surgical treatment was allocated to the surgical treatment category.For dogs with incomplete postoperative follow-up documentation, owners were contacted by telephone/email to obtain postoperative outcome information.All data were retrospectively collected and no attempt made to assess individual limb function beyond interpreting clinical records and owner reports.

Statistical Analysis
Breeds were grouped as poodles (P) and non-poodles (NP) for analysis.
The age and sex distribution between the injured P and NP groups were compared using independent samples t-test with unequal variance and χ 2 test, respectively.

Breed Prevalence
To evaluate breed prevalence, a control population was generated by searching the records of a general practice group of veterinary clinics in the same geographical area to determine the breeds of dogs registered.A one sample proportion test was used to test the null hypothesis that the MSI group breed prevalence was consistent with the control population breed prevalence.
Relationship between grade of MSI and breed was explored via univariate linear regression, with grade as outcome and breed as the independent variable.

Cause
A logistic regression was used to estimate the relative odds of a spontaneous cause of the MSI according to breed type.

Outcome
Case numbers were too few to allow analysis of outcome according to breed or treatment.Descriptive statistics are provided.
A 95% confidence interval (CI) is reported for each estimate of the relative odds, along with a p-value for a test of the null hypothesis that the relative odds are one. All

Breed Prevalence
In the control population, 82,956 dogs were identified, within which there were 2,267P, representing a control population prevalence of 2.73% P (95% CI: 2.62-2.85%).Poodles represented 35.4% (95% CI: 21.9-48.9%) of the MSI population (see ►Fig. 1).Utilizing a one sample test that the true proportion was that of the control population, we found that P were 12.9 times overrepresented in the MSI population, p-value less than 0.0001.
A logistic regression was used to estimate the relative odds of spontaneous MSI.

Outcome
Cases that did not represent for assessment and for whom no response was obtained through telephone/email communication were deemed lost to follow-up (n ¼ 11; 5P, 6NP).

Group
Total number of dogs

Breeds included
Poodle "P" Within the 31 NP dogs there were 11 poodle crossbreeds, of which 9 presented with spontaneous MSI, showing a similar trend of overrepresentation and high incidence of spontaneous MSI to that seen with poodles (see ►Table 4).

Discussion
Our data show that poodles presenting with MSI are overrepresented in the local population of dogs, and that they are over four times as likely to present with spontaneous MSI than other breeds.Why poodle breeds are overrepresented is unknown.When considering joint instability, two variables need to be considered: soft tissue laxity and joint anatomy.These factors have the potential to cause instability independently, though the possibility of an interplay between the two exists, as seen with other polygenic, multifactorial traits in dogs such as hip dysplasia 28 and patellar luxation. 29The absence of glenoid dysplasia shows that this is not the cause of MSI in our population, and hence, without note of other orthopaedic anatomical variations, suggests that an increase in soft tissue laxity is the likely explanation for the joint instability affecting these dogs.Whether or not this is due to an underlying hypermobility syndrome warrants further investigation.
While a higher percentage of P presented with grade 4 MSI than NP, there was not a statistically significant difference in the grades by breed.This may be a statistical power problem, with too few P cases to be compared with the NP or may reflect a true lack of difference.More testing would need to be performed to investigate this.
Our results showed that 82.4% of P affected by MSI within our local dog population occurred spontaneously, while 51.6% of NP MSI occurred spontaneously (48.4% traumatic).The latter rate of incidence is consistent with previous findings of 49% of MSI cases being reported as a traumatic tearing for the MGHL, 6 likely reflecting the breed populations within previous studies and reinforcing the notion that poodles are different to other breeds.
The high number of poodle crossbreeds within the NP group, of which the vast majority presented with spontaneous MSI, suggests that poodle crossbreeds, often bred to be at least 50% poodle genome, 30 are similarly at risk as poodles.Further studies into this are warranted.
Our data suggests that P are associated with a higher risk of a poorer outcome following management of MSI.Outcome following management of MSI would benefit from further investigation with prospective studies evaluating standardized approaches.
There are shortcomings of this study, such as the retrospective nature inheriting a selection bias and the high number of  Medial Shoulder Instability in Poodles Woolley et al. e112 Abbreviations: BTT, biceps tendon transposition; MGHL, medial glenohumeral ligament; MSI, medial shoulder instability.

Table 3
Outcome by treatment type and breed for all cases of MSI Medial Shoulder Instability in Poodles Woolley et al. e111 cases lost to follow-up.The study was also limited by the relatively small dataset, enhanced by the fact that many clinicians were willing to diagnose MSI based on palpation and radiographs alone which led to exclusion of 13 potential grade 1-3 MSI cases.Larger studies are warranted.Note This study received data contributions from Advanced Vet Care, 26 Robertson St., Kensington VIC 3031; CARE Veterinary Hospital, 5 Hood St., Collingwood VIC 3066; Peninsula Vet Emergency and Referral Hospital, 161/2 Mornington-Tyabb Road, Mornington VIC 3931; Southpaws Specialty Surgery 3 Roper St., Moorabbin VIC 3189; and Veterinary referral Hospital 36 Lonsdale St, Dandenong VIC 3175.

Table 4
Summary of MSI case numbers by breed (showing poodle crossbreeds separated out from non-poodles), cause, grade, treatment, and outcome