Medial humeral epicondylitis: a retrospective case series of nine cats (17 elbows)

Abstract

Case series summary The aim of this study was to describe the clinical findings, diagnostic results and response to both non-surgical and surgical therapy in cats with medial humeral epicondylitis (MHE). The medical records of one institution were searched for cats with a radiographically confirmed diagnosis of MHE where non-surgical therapy alone or both non-surgical and surgical therapy had been trialed. Nine cats (17 elbows) were included. None of the cats had a history of outdoor access. Orthopedic examination revealed pain upon palpation over the medial epicondyle (n = 15), elbow pronation/supination (n = 7) or carpal flexion (n = 7) and palpable mineralization distal to the medial epicondyle (n = 7). Epicondylitis was radiographically graded as mild (n = 8), moderate (n = 7) or severe (n = 2). CT was performed in 10 elbows and revealed additional information in seven, including intra-articular mineralized bodies in five elbows. Ultrasound was performed in four elbows and revealed fluid surrounding the flexor carpi ulnaris muscle. After non-surgical management, four cats showed no response, four showed a partial response and one showed a complete response. Cats with less advanced radiographic changes appeared to show more favorable responses. Four cats (seven elbows) underwent surgical treatment with ulnar neuritis being evident in all. Lameness resolved postoperatively in three cats (five elbows).

Relevance and novel information An insidious onset of moderate-grade lameness associated with pain on palpation caudodistal to the medial epicondyle should increase the index of suspicion for MHE and prompt assessment for the presence of palpable mineralization and pain on carpal flexion. Ulnar neuritis is common in cats with MHE and they frequently present with free articular mineralized bodies. Radiographs can only detect advanced or chronic stages of MHE, by which time non-surgical management is likely to be ineffective. Earlier diagnosis using ultrasound may improve the prognosis after non-surgical management.

Plain language summary

A description of the diagnosis and treatment of medial humeral epicondylitis, a condition similar to golfer’s elbow or little leaguer’s elbow in humans, in nine cats (17 elbows)

Repetitive, prolonged activities involving wrist and forearm movement have long been associated with the onset of epicondylitis in humans. When this affects the lateral epicondyle, it is colloquially termed ‘tennis elbow’. When the medial epicondyle is involved, this is often referred to as ‘golfer’s elbow’ or ‘little leaguer’s elbow’. Medial humeral epicondylitis (MHE) is increasingly recognized as a cause of forelimb lameness in cats; however, information on this condition remains limited. The increased flexibility of the feline elbow and the importance of this during feline activities, such as climbing and catching prey, have been proposed as possible factors in the development of this condition in cats. MHE is a degenerative condition, the eventual result of which is the replacement of normal tendon tissue with scar tissue or mineralized tissue. This can also cause inflammation of the ulnar nerve, which travels in close proximity. Once the nerve is involved, non-surgical methods of treatment are less likely to be successful. This study adds information on 17 elbows in nine cats affected with MHE. Typical findings on orthopedic examination included a pain response on palpation over the medial epicondyle, a bony prominence on the inner aspect of the elbow. Pain was also evident during elbow range of motion, particularly with internal and external rotation, and occasionally during carpus (wrist) manipulation as well. In some cats, the mineralized portion of the tendon was palpable, which was often associated with pain. Although this condition has historically always been diagnosed using radiographs, the use of CT was shown to be advantageous as it frequently demonstrated the presence of mineralization within the elbow joint, which was not appreciated radiographically. In addition, the use of ultrasound showed promise in facilitating an earlier diagnosis, which may render non-surgical management more efficacious.

Introduction

Medial humeral epicondylitis (MHE) is increasingly recognized as a cause of thoracic limb lameness in cats. Unfortunately, there is a paucity of information regarding this condition, with the literature limited to one cadaveric study, ¹ one clinical case series, ² one case report, ³ one abstract ⁴ and the inclusion of MHE within review articles on feline lameness.^5,6 In total, the clinical presentations of 18 cats have been described.

Although the term epicondylitis would imply an inflammatory state, in both the human and feline literature this term is not used to describe an inflammatory condition, but more a degenerative pathway where repetitive supraphysiologic stress on the tendon eventually results in microtrauma and degeneration.^{1,7 –10} Historically, in humans, the pronator teres was identified as the primary dynamic stabilizer and the most likely musculotendinous unit to be injured in MHE. However, recent cadaveric studies have implicated every musculotendinous unit except the palmaris longus,^{11 –14} and it is now considered that MHE affects the common flexor tendon, the confluence of five muscles of the forearm. ¹⁵ In cats, MHE has been described as consistently affecting the flexor carpi ulnaris muscle (FCUM). ¹ The FCUM in cats originates from two heads, the humeral head and the ulnar head. Both heads are unipennate and insert on the proximal surface of the accessory carpal bone. The ulnar head originates from the proximal third of the ulna and the humeral head from the medial epicondyle (ME) of the humerus.^16,17 Historically, MHE in cats has been reported to specifically affect the humeral head of the FCUM, with the ulnar head being spared.

There are similarities between the common flexor tendon in humans and the humeral head of the FCUM in cats. Both cross the humeroulnar joint medially and both are closely connected to the ME. In addition, in cats, the two heads of the FCUM differ significantly in their proportion of muscle fiber types; the humeral head has more histochemical type 1 fibers and actually has the most histochemical type 1 fibers of any carpal flexor. ¹⁸ The humeral head has also been found to have a slower contraction time and weaker contraction strength. In conjunction, these findings suggest that the humeral head of the FCUM is the primary antigravity carpal flexor during stance and locomotion. ¹⁹ Its histologic differences and functional role have been proposed to predispose it to injury or to overuse trauma, which may explain its consistent involvement in MHE. ¹ Whether other structures are also affected by MHE in cats has not been specifically investigated.

To date, published clinical reports of MHE in cats have relied entirely upon radiography for diagnosis, ² with CT only being used subsequently for confirmation. There are no reports of other imaging modalities being used before a radiographic diagnosis. In humans, ultrasonography is used as a cost-effective modality for visualizing common flexor tendon tendinosis and pathologic change.^20,21 The intact tendon demonstrates a hyperechoic fibrillar pattern characterized by multiple parallel echogenic lines. In a small series, Park et al ²² demonstrated that ultrasonography performed by a radiologist had sensitivity, specificity and positive and negative predictive values exceeding 90% for the diagnosis of MHE. The authors most commonly identified hypoechoic or anechoic areas of focal tendon degeneration on ultrasonography. Other studies have reported hypoechoic, often enlarged, tendons exhibiting varying degrees of interstitial and partial tears, along with differing levels of surrounding hyperemia.^23,24 However, to date, the use of ultrasound for diagnosing MHE in cats has not been documented.

When necessary, surgical management of MHE in humans is associated with excellent success rates. ²⁵ In cats, surgery is recommended if non-surgical management fails to produce improvement within 4 weeks. ² Postoperatively, a carpal flexion bandage is traditionally applied to limit stress on the reattached muscle, with adjustments made once or twice weekly to gradually allow increased extension. ² Based on the small numbers available in the peer-reviewed literature, surgical treatment in cats has shown good success rates, with 7/9 cats reported to be sound by 12 weeks postoperatively. ²

Several questions about MHE in cats remain unanswered. This article aims to expand our knowledge of this increasingly common condition by adding nine additional clinical cases to the literature and raising questions about both its pathogenesis and diagnosis.

Case series description

Materials and methods

Medical records of Michigan State University’s Veterinary Medical Center were searched from 2015 to 2025 for cats with a radiographically confirmed diagnosis of unilateral or bilateral medial humeral epicondylitis. To be included, orthogonal radiographs of both elbows taken at the referral facility had to be available for review. Non-surgical therapy had to be trialed, with at least 6 weeks of follow-up available thereafter. If surgical treatment was then sought, a minimum of 6 weeks of postoperative follow-up was also required.

Data retrieved from the medical records included breed, age, sex, weight, body condition score (BCS), the presence of any concomitant conditions and whether the cat had outdoor access. Details relating to the lameness that was specifically noted included whether this was of acute or insidious onset, any history of trauma and whether lameness was unilateral or bilateral. Lameness was graded on a previously reported scale of 0–4. ²⁶ All orthopedic examination findings were documented, with each case specifically evaluated for pain on palpation over the ME, pain during elbow supination or pronation, pain with carpal range of motion and any evidence of carpal hyperextension.

Radiographic findings were documented. The medial epicondylitis was classified as mild, moderate or severe: mild disease was defined by radiographic small irregularities and/or new bone formation at the ME without sclerosis or mineralized intra-articular bodies; moderate disease was defined by bony spurs at the ME, sclerosis and free mineralized bodies; and severe disease was defined as large semicircular new bone formations at the medial aspect of the elbow with subchondral sclerosis and osteophyte formation. ¹ In addition, each case was specifically evaluated for whether the sesamoid bone within the supinator muscle ²⁷ was radiographically evident and, if so, whether remodeling of this was noted. The presence of humeroradial or humeroulnar subluxation was also recorded, as was the presence or absence of intra-articular mineralized bodies.

In humans, the ME has been radiographically classified into zones to correlate with points of origin of various tendons in an attempt to differentiate which structure is mineralized. ²⁸ Zone A is from the medial supracondylar ridge to the proximal corner of the ME where the pronator teres originates; zone B is from the proximal corner of the ME to the distal corner of the ME, where the flexor carpi radialis, palmaris longus and flexor digitorum communis originate; and zone C is from the distal corner of the ME to the humeral trochlea, where the FCUM and medial collateral ligament originate. For this case series, the ME was classified similarly, and the radiographic origin of the mineralization was documented as zone A, B, C or multiple. The mineralization was also assessed for distraction from the ME and classified as distracted or not.

Where a CT scan was performed, this was documented, with additional findings being noted. Similarly, if ultrasound examination was performed, this was documented and findings included.

Details of non-surgical management were recorded, including the use of non-steroidal anti-inflammatory drugs (NSAIDs), adjunctive analgesics, activity modifications, weight management and use of physical rehabilitation. Durations of non-surgical management were detailed and response to treatment classified as no response, partial response (where lameness improved but did not resolve) or complete response (resolution of lameness).

If cats subsequently underwent surgical management, this was performed via an open approach, as previously described. ² Briefly, a curvilinear skin incision was made just caudal to the ME from the proximal end of the tuber olecrani to the proximal third of the ulna. A longitudinal incision was made along the same line to separate the superficial and deep antebrachial fascia. Retraction of the deep fascia and areolar tissue exposed the epicondyle and the attached flexor muscle group. When involved, the ulnar nerve was found, displaced by the proliferative tissue within the humeral head of the FCUM. External or internal neurolysis was performed depending upon the thickening of the epineurium. The mineralized structure within the humeral head of the FCUM was removed via blunt dissection. Any spurs or irregular areas at the caudal aspect of the ME were resected to ensure a smooth surface beneath the freed ulnar nerve. If necessary, free intra-articular bodies were removed after medial elbow arthrotomy and the joint capsule closed with simple interrupted sutures. The remaining tendinous stump of the FCUM was transposed and reattached to both sheets of the antebrachial fascia as proximal as possible at the level of the ME. Where attachment of the muscular stump to the ME was not possible because of the large size of the excised mineralized part, the stump was fixed to the antebrachial fascia and origin of the ulnar head of the FCUM. During attachment of the stump, the carpal joint was held in flexion to minimize tension on the repair. ² Details of the procedure were documented, including whether ulnar neuritis was identified, whether internal or external neurolysis was performed, whether mineralization from within the humeral head of the FCUM was removed, whether detachment of the humeral head of the FCUM was required, whether arthrotomy was performed and, if so, whether intra-articular cartilage damage was identified, whether defects or remodeling of the medial coronoid process were noted and whether free intra-articular mineralized bodies were removed. Surgery was also classified as unilateral or bilateral, and staged or simultaneous. Details of postoperative management were also recorded, including the same information as documented for non-surgical management, in addition to whether a carpal flexion bandage was used and, if so, for how long. The outcome after surgical management was also noted.

Results

Signalment and clinical presentation

Nine cases of radiographically confirmed MHE were documented, all diagnosed and treated by a single board-certified surgeon. The signalment and clinical presentation of the nine cases are summarized in Table 1. The median age was 6 years (range 1–15) and median body weight was 6.94 kg (range 3.26–8.15). None of the cats had a history of outdoor access and the condition was bilateral in 8/9 cats, resulting in a total of 17 affected elbows.

Table 1

Patient signalment and clinical presentation findings for nine cats with medial humeral epicondylitis

Case	Breed	Age (years)	Sex	Weight (kg)	BCS	Concomitant conditions	Outdoor access	Acute/insidious onset	History of trauma	Unilateral or bilateral	Lameness grade 0–4	Pain on palpation over ME	Pain on supination/pronation	Pain on carpal ROM	Carpal hyperextension	Other findings on orthopedic examination
1	DSH	11	FN	5.85	7/9	Bilateral elbow OA, ruptured left CrCL	N	Insidious	N	Bilateral, more severe on left	2 on both sides	Y – bilateral	Y – bilateral	Y – flexion bilateral	Mild on right	Circumferential thickening of both elbows
2	DLH	6	MN	8.15	8/9	None	N	Acute	N	Bilateral, more severe on left	2 on left, 0 on right	Y – bilateral	Y – left only	N	None	None
3	DSH	7	FN	7.2	8/9	Bilateral elbow OA	N	Insidious	N	Bilateral	2 on right, 1 on left	N	N	N	None	Mild circumferential thickening of both elbows
4	DMH	6	FN	6.6	7/9	None	N	Acute	N	Bilateral, more severe on right	2 on both sides	Y – bilateral	N	N	None	None
5	Scottish Fold	3	FN	3.26	4/9	Chronic lumbosacral pain, Scottish Fold osteochondrodysplasia	N	Insidious	N	Bilateral, more severe on right	2 on right, 1 on left	Y – bilateral	Y – bilateral	Y – flexion bilateral	None	Hypersensitivity over lumbosacral spine
6	Maine Coon	2	MN	7.2	5/9	None	N	Insidious	N	Bilateral	2 on left, 1 on right	Y – bilateral	N	N	None	Bilateral mineralization palpable distal to ME and pain response on palpation
7	DSH	12.5	MN	6.94	6/9	Left CrCL disease	N	Insidious	N	Bilateral, more severe on left	3 on left, 0 on right	Y – bilateral	N	N	Mild on left	Bilateral mineralization palpable distal to ME and pain response on palpation
8	Maine Coon	1	MN	7.5	5/9	None	N	Insidious	N	Bilateral	2 on both sides	Y – bilateral	Y – bilateral	Y – flexion bilateral	None	Bilateral mineralization palpable distal to ME and pain response on palpation
9	DLH	15	FN	4.1	4/9	IRIS stage 3 CKD, anemia, chronic constipation, idiopathic hypercalcemia, ureterolith (left), diabetes mellitus, grade 4 systolic heart murmur which progressed to congestive heart failure	N	Insidious	N	Unilateral, right	3	Y	N	Y – flexion	Severe – palmigrade stance	Mineralization palpable distal to ME but no pain response on palpation

BCS = body condition score; CKD = chronic kidney disease; CrCL = cranial cruciate ligament; DLH = domestic longhair; DMH = domestic mediumhair; DSH = domestic shorthair; FN = female neutered; IRIS = International Renal Interest Society; ME = medial epicondyle; MN = male neutered; N = no; OA = osteoarthritis; ROM = range of motion; Y = yes

Lameness was the presenting complaint in 8/9 cats. One cat presented for work-up of elbow swelling and associated lameness, initially suspected to be due to a mass. In seven cases, lameness had an insidious onset, while in two it was acute. No cat had a known history of trauma. Using a 0–4 lameness grading scale and evaluating each affected elbow separately (total of 17 elbows), the median lameness score was 2 (range 0–3). Out of eight cats with bilateral disease, three presented with a symmetrical thoracic limb lameness (all at grade 2 bilaterally) and five presented with one thoracic limb more clinically affected than the other. Orthopedic examination findings for the 17 elbows were largely consistent with the previous literature, including pain upon palpation over the ME or caudodistal to the ME (15/17), pain upon elbow pronation/supination (7/17), pain upon carpal flexion (7/17) and mild-to-severe carpal hyperextension (3/17). Examination findings that have not been reported previously included circumferential thickening of the elbow (4/17) and palpable mineralization distal to the ME (7/17). In 6/7 cases with palpable mineralization, a pain response was associated with the palpation.

Diagnostic imaging

The diagnostic imaging findings for the nine cases are detailed in Table 2. According to the inclusion criteria, all cases underwent radiography with orthogonal views of both elbows. The epicondylitis was graded as mild in eight elbows, moderate in seven elbows and severe in two elbows. When evaluating the origin of the mineralization, using the same system as applied in humans, in three elbows it was found to originate from the supracondylar area (zone A). In eight elbows, mineralization originated from between the proximal corner of the ME and the distal corner of the ME (zone B). Two cases originated from between the distal corner of the ME and the humeral trochlea (zone C). In four elbows, the mineralization affected more than one zone. In no case did the mineralization appear to be distracted or avulsed from the point of origin. The sesamoid bone within the supinator muscle was radiographically evident bilaterally in three cats and was remodeled and enlarged in all six elbows (Figure 1). Neither humeroradial nor humeroulnar subluxation was radiographically evident in any case. Additional radiographic findings are detailed in Table 2.

Table 2

Diagnostic imaging findings for nine cats with medial humeral epicondylitis

Case	Sesamoid bone in supinator muscle radiographically evident	Remodeling of sesamoid bone in supinator muscle	Medial epicondylitis grade	Radiographic findings	Location of mineralization (based on classification from Kang et al 28 )	Calcification distracted	Intra-articular mineralized bodies	CT performed	Additional CT findings	Ultrasound performed	Ultrasound findings
1	Y – bilateral	Y – bilateral	Moderate on left, mild on right	Left: large ME calcification, osteophytes over MCP, osteophytes craniolateral radius, peritrochlear sclerosis, osteochondromatosis. Right: mild remodeling of ME, osteophytes over MCP, subtrochlear sclerosis	Originates from supraconcondylar ridge – zone A	N – bilaterally	Y – bilaterally (found on CT)	Y	Bilateral intra-articular mineralized bodies	N	N/A
2	N – bilateral	N/A	Moderate on left, mild on right	Left: large ME calcification, osteophytes over MCP, subtrochlear sclerosis. Right: mild remodeling of medial epicondyle, osteophytes over MCP	Originates from distal corner of ME – zone B	N – bilaterally	N	N	N/A	N	N/A
3	N – bilateral	N/A	Mild bilaterally	Mild remodeling of ME bilaterally. Osteophytes over MCP bilaterally, peritrochlear sclerosis bilaterally	Originates from multiple areas including supracondylar ridge, proximal ME and just proximal to trochlea – zones A, B and C bilaterally	N – bilaterally	Y – bilaterally (found on CT)	Y	Bilateral intra-articular mineralized bodies	N	N/A
4	N – bilateral	N/A	Mild bilaterally	Mild remodeling of ME bilaterally. Small osteophytes cranial radial head on left	Originates from proximal ME – zone B	N – bilaterally	N	N	N/A	Y	Fluid noted circumferential to proximal tendons of flexor carpi ulnaris muscle bilaterally. Mild irregularity of ME. No elbow effusion
5	Y – bilateral	Y – bilateral	Mild bilaterally	Mild remodeling of ME bilaterally, mild osteophyte formation over anconeal process bilaterally	Originates from proximal ME – zone B	N – bilaterally	N	Y	N – confirmed radiographic findings	Y	Fluid noted circumferential to proximal tendons of flexor carpi ulnaris muscle bilaterally. Mild irregularity of ME and pinpoint mineral foci noted in proximal aspect of flexor carpi ulnaris musculature. No elbow effusion
6	N – bilateral	N/A	Moderate bilaterally	Mild remodeling of ME bilaterally. Irregular 10 mm × 5 mm calcification caudodistal to ME bilaterally	Originates from just proximal to trochlea – zone C, but also remodeling at proximal ME – zone B	N – bilaterally	N	Y	Osteophyte formation over lateral anconeal process	N	N/A
7	Y – bilateral	Y – bilateral	Moderate on right, severe on left	Left: large calcification (15 mm × 15 mm) originating from proximal ME and extending to below humeral trochlea. Remodeling of ME and subtrochlear sclerosis. Mild-to-moderate osteophytosis of MCP and radial head. Right: multifocal calcification originating from central ME (largest component 14 mm × 4 mm), remodeling of ME, subtrochlear sclerosis and mild osteophytosis of radial head	Originates from proximal ME – zone B	N – bilaterally	Y – on right (found on CT)	Y	Intra-articular mineralization right and osteophyte formation anconeal process	N	N/A
8	N – bilateral	N/A	Moderate bilaterally	Large irregular calcification bilaterally originating from between distal ME and humeral trochlea. Mild subtrochlear sclerosis on left and small anconeal osteophyte on left	Originates from between distal ME and humeral trochlea – zone C	N – bilaterally	N	N	N/A	N	N/A
9	N	N/A	Severe	Large proliferative calcification originating from supracondylar ridge and extending past humeral trochlea. Subtrochlear sclerosis and osteophyte formation over anconeal process	Originates from supracondylar ridge – zone A	N	N	N	N/A	N	N/A

MCP = medial coronoid process; ME = medial epicondyle; N = no; N/A = not applicable; Y = yes

Figure 1

Mediolateral and craniocaudal images of the left elbow of an 11-year-old domestic shorthair cat. There is a large hook-shaped enthesophyte originating from the supracondylar ridge of the medial epicondyle, smoothly marginated mineral osteophyte formation over the medial coronoid process and smoothly margined mineral proliferation over the lateral and cranial aspects of the proximal radius. The sesamoid bone within the supinator muscle is evident cranial to the radial head on the mediolateral view and is markedly remodeled

CT was performed in 10 elbows and yielded additional information in seven elbows: intra-articular mineralized bodies in five elbows, osteophyte formation over the anconeal process in three elbows and remodeling of the medial coronoid process in two elbows. In one elbow, both intra-articular mineralization and osteophyte formation over the anconeal process were discerned, and in two cases, both intra-articular mineralization and remodeling of the medial coronoid process were observed. In the remaining three elbows, CT simply confirmed radiographic findings.

In two cases (four elbows), where radiographic signs were mild and equivocal, ultrasound was also performed by a board-certified radiologist. This revealed fluid surrounding the proximal tendons of the FCUM in four elbows, mild irregularity of the ME in four elbows and pinpoint foci of mineralization within the proximal aspect of the FCUM in two elbows.

Management

Non-surgical management was trialed in all nine cats (17 elbows). Details of these cases are available in Table 3. NSAIDs were trialed in seven cats (14 elbows) with a treatment duration of 2–4 weeks. In the two cats that did not receive NSAIDs, gabapentin was trialed for a period of 4 weeks in one cat and 8 weeks in the other. Six cats received adjunctive analgesics in addition to NSAIDs. All cats were advised to have restricted access to heights and weight loss was advised in the five cats that had a BCS over 5/9. Two cats started formal physical rehabilitation as a component of their non-surgical management. The details of specific modalities employed are available in Table 3.

Table 3

Details of non-surgical treatment elected for nine cats (17 elbows) with medial humeral epicondylitis

Case	Non-surgical management trialed	Was an NSAID trialed?If yes, which one and for how long (weeks)?	Were adjunctive analgesics trialed? If yes, which one and for how long (weeks)?	What activity restriction or environmental modifications were advised?	Was formal physical rehabilitation employed as a component of non-surgical management?	What physical rehabilitation modalities were used?	Response to non-surgical management
1	Y	Y Robenacoxib 4 weeks	N	Environmental modulation – no access to heights	N	N/A	None
2	Y	Y Robenacoxib 2 weeks	Y Gabapentin 2 weeks	Crate rest for 2 weeks	N	N/A	Partial – still lame on left
3	Y	Y Meloxicam 4 weeks	Y Gabapentin 4 weeks	Environmental modulation – no access to heights	Y	Underwater treadmill therapy, therapeutic laser, cavaletti poles, weight-shifting exercises, downward ramp walking, obstacle courses	Partial – still stiff for 2–3 steps upon rising after rest
4	Y	Y Robenacoxib 4 weeks	Y Gabapentin 4 weeks	Environmental modulation – no access to heights	N	N/A	Full
5	Y	Y Meloxicam 4 weeks then switched to robenacoxib for 4 weeks as lameness did not resolve	Y Gabapentin 4 weeks	Environmental modulation – no access to heights	Y	Therapeutic laser	Partial – improved on medical management but difficult to assess long-term response because of progressive Scottish Fold osteochondrodysplasia
6	Y	N	Y Gabapentin 8 weeks	Environmental modulation – no access to heights	N	N/A	None
7	Y	Y Meloxicam 2 weeks	Y Frunevetmab 8 weeks (two injections)	Environmental modulation – no access to heights	N	N/A	None
8	Y	Y Meloxicam 2 weeks	N	Environmental modulation – no access to heights	N	N/A	None
9	Y	N	Y Gabapentin 4 weeks	Environmental modulation – no access to heights	N	N/A	Partial – still lame on right and left side was unaffected

N = no; N/A = not applicable; NSAID = non-steroidal anti-inflammatory drug; Y = yes

Four cats showed no improvement in lameness after non-surgical management. Four cases showed a partial response; further details on these cases are available in Table 3. In one cat, non-surgical management resulted in a complete resolution of lameness.

When assessing the relationship between radiographic severity and treatment response, eight elbows were graded as having mild MHE: three showed a full response to non-surgical therapy, four showed a partial response and one showed no response. Of the seven elbows graded as moderate, none responded to non-surgical therapy. Among the two elbows graded as severe, one showed no response and one showed a partial response.

Four cats (seven elbows) underwent surgical therapy; details are available in Table 4. The owners of three out of the four cats where a partial response to non-surgical treatment was noted elected not to pursue surgical treatment, either due to being content with the low grade of lameness remaining (1), or due to concern regarding concomitant conditions (2). One cat where no response to treatment was noted could not commit to surgical treatment. For the other cat which had a partial response, surgery was elected on the side which remained persistently lame, and surgery was also elected bilaterally for the other three cats which had no response to non-surgical treatment.

Table 4

Details of surgical treatment elected for four cats (seven elbows) with medial humeral epicondylitis

Case	Surgery performed	Ulnar neuritis identified	Internal or external neurolysis	Removal of mineralization in FCUM	Detachment of humeral head of FCUM required	Arthrotomy performed	Intra-articular cartilage damage identified	MCP defect or remodeling	Free intra-articular bodies removed	Unilateral or bilateral surgery	Staged or simultaneous surgery	Was an NSAID prescribed postoperatively? If so, which one and for how long?	Were adjunctive analgesics prescribed postoperatively? If so, which one and for how long?	Was a carpal flexion bandage used? If yes, for how long?	Was physical rehabilitation performed?	What physical rehabilitation modalities were used?	Outcome after surgical management
1	Y – bilateral	Y – bilateral	External on both sides	Y – on left N – on right	Y – on left N/A on right	Y – bilateral	Y – bilaterally on MCP	Y – cartilage damage and remodeling but no defect on either side	Y – bilateral	Bilateral	Simultaneous	Y Robenacoxib 3 weeks	Y Gabapentin 4 weeks	Y on left 3 weeks	Y	Passive ROM, cryotherapy, therapeutic laser, acupuncture and underwater treadmill therapy	12 weeks postoperatively lameness substantially improved. Very mild left forelimb lameness persisted. Hyperextension of right carpus improved but did not fully resolve
2	Y – left only	Y – left	External	Y – on left	Y – on left	N	N	N	N	Unilateral on left	N/A	Y Robenacoxib 2 weeks	Y Gabapentin 2 weeks	Y on left 3 weeks	Y	Passive ROM, cryotherapy, therapeutic laser	9 weeks postoperatively lameness resolved. Orthopedic examination was within normal limits
6	Y – bilateral	Y – bilateral	External on both sides	Y – bilateral	N – bilateral	N	N	N	N	Bilateral	Staged	Y Robenacoxib 2 weeks	Y Gabapentin and amantadine 2 weeks	Y – customized thermoplastic orthotic 3 weeks	Y	Passive ROM, therapeutic laser, underwater treadmill therapy	12 weeks postoperatively lameness fully resolved on both sides
8	Y – bilateral	Y – bilateral	External on both sides	Y – bilateral	N – bilateral	N	N	N	N	Bilateral	Staged	Y Meloxicam 2 weeks	N	Y – bilaterally 3 weeks	N	N/A	8 weeks postoperatively lameness fully resolved on both sides

FCUM = flexor carpi ulnaris muscle; MCP = medial coronoid process; N = no; N/A = not applicable; NSAID = non-steroidal anti-inflammatory drug; ROM = range of motion; Y = yes

All surgical cases were addressed via an open approach. ² Ulnar neuritis was diagnosed in all seven elbows and was addressed via external neurolysis in all cases. Removal of mineralization within the FCUM (Figure 2) was performed in 6/7 elbows. In one elbow, radiographic signs were still mild and surgery was performed primarily to remove intra-articular mineralization. In two elbows, detachment of the humeral head of the FCUM was necessary to remove the mineralization, while in four elbows, the mineralized tissue could be removed without detaching the tendon. An open arthrotomy was performed in two elbows to remove intra-articular mineralized bodies.

Figure 2

Intraoperative image after removal of the mineralization from within the humeral head of the FCUM in a 2-year-old Maine Coon cat. Stay sutures are placed within the humeral head of the FCUM proximal and distal to the area of mineralization and are used to hold the tendon ends in apposition during subsequent repair. The ulnar nerve can be seen retracted caudally using vessel loops after the external neurolysis performed in this case. FCUM = flexor carpi ulnaris muscle

Of the three cats that underwent bilateral surgery, two had the procedure performed in a staged manner, while one underwent simultaneous surgery. Simultaneous surgery was elected in the case where mineralization removal from the FCUM was required on only one side. In the other two cases, where mineralization needed to be removed from both sides, the surgeries were staged 6–12 weeks apart to facilitate postoperative care.

For the seven elbows that underwent surgery, carpal flexion bandages were applied in the six elbows where removal of mineralization from the FCUM was necessary. In one cat, a customized thermoplastic orthotic was used in place of a carpal flexion bandage (Figure 3). All cats were confined to either a large dog crate or a cat tent for 6 weeks postoperatively. Details regarding bandage duration, postoperative NSAID use, adjunctive analgesics and physical rehabilitation are provided in Table 4.

Figure 3

Images of a customized thermoplastic orthotic used postoperatively in a 2-year-old Maine Coon cat. This device provided protection of the repair while allowing gradual reduction of carpal flexion over time. Its ease of removal and replacement also facilitated more frequent physical rehabilitation sessions

Outcome

In three cats (five elbows), lameness had completely resolved at the 8–9-week recheck after surgery. One cat had mild, persistent, bilateral thoracic limb lameness, although it was substantially improved compared with the preoperative state. This cat was also diagnosed with moderate bilateral elbow osteoarthritis at the same time as the initial MHE diagnosis, and this may have contributed to the incomplete recovery.

Long-term follow-up, performed by the operating board-certified surgeon for 13–72 months postoperatively, was available for three cats (five elbows), all of which were treated surgically. Two of these cases (one bilateral and one unilateral) were documented as free of lameness at their 8–9-week recheck, with no recurrence reported by either the owner or the referring veterinarian. The cat mentioned above, which had a mild, persistent, bilateral thoracic limb lameness, remained stable for 24 months postoperatively, with no deterioration in lameness noted.

Discussion

The signalment of the cats in this case series is similar to that previously reported. A cadaveric study detailing MHE in six cats reported a median age of 9.7 years (range 4–16) and a median body weight of 5.0 kg (range 3.4–8.7), ¹ while a clinical study reported a mean age of 10.3 years (range 2–16), a mean weight of 5.6 kg (range 3.4–8.6) and a median BCS of 5.9 (range 5–8). ² The mean age of the cats in this case series was similar, albeit slightly younger at 7 years (range 1–15), while the mean body weight was slightly higher at 6.3 kg (range 3.26–8.15) and the mean BCS was 6 (range 4–8).

The presentation of young cats with this condition has received relatively little attention in the literature, despite previously reported age ranges indicating that it does occur. In this case series, 3/9 cats affected were aged under 3 years, with the youngest being only 1 year old. This may call into question the proposed pathogenesis of this condition, at least in this subset of cats, with repetitive supraphysiologic stress leading to microtrauma and degeneration potentially being less likely. Interestingly, the three cats affected at younger ages were all purebred: two Maine Coons and one Scottish Fold. Although heritability of MHE has not been investigated in cats, breed is increasingly being recognized as a potential risk factor. A recent abstract identified Maine Coon cats as being at increased risk compared with domestic shorthair cats and other breeds, based on CT evaluation, and also noted that they tended to be affected at a younger age. ⁴ The study was based purely on retrospective CT assessment; therefore, whether the cats were clinically affected is not known, but the frequency of MHE in Maine Coons was 61.4% compared with 34.3% in domestic shorthairs and 22.9% in other breeds. Notably, these are all significantly higher than the 10% prevalence that was reported previously in a cadaveric study of European Shorthair cats. ¹ This may reflect the use of CT as the imaging modality of choice in the more recent study, while radiography was the screening method used in the cadaveric study. Alternatively, this could reflect the diagnostic criteria used. In the more recent study using CT, irregular margins, sclerosis or thickening of the ME, number and size of calcified bodies, and thickening or contrast enhancement of the FCUM were considered as diagnostic, while in the cadaveric study, all changes evaluated necessitated new bone formation or remodeling, which likely occurs later in the disease process. The apparent breed predisposition, along with the younger age of affected Maine Coons, raises further questions about the pathogenesis of MHE. Maine Coons tend to be larger cats, and their comparatively heavy body weight has been postulated as a risk factor for other orthopedic conditions. ²⁹ As in humans with lateral epicondylitis,^30,31 body weight may contribute to MHE development in cats. One clinical study reported that most cats with MHE were at a higher than ideal BCS. ² Although it is difficult to establish causation, this finding supports the hypothesis that increased body weight may play a role in pathogenesis. ² Having said that, the Scottish Fold in this case series, affected at the age of 3 years, weighed only 3.26 kg with a BCS of 4/9, indicating that other risk factors should also warrant consideration.

In humans, genetics are a risk factor for development of elbow tendon pathologies. ³² Type V collagen, encoded by the COL5A1 gene, is a minor fibrillar collagen that intercalates with type I collagen and forms collagen fibrils. ³³ Sequence variants within COL5A1 have been implicated in musculoskeletal diseases, and specifically in the pathogenesis of lateral epicondylitis in humans. ³³ It is possible that a similar genetic cause may be contributing to the early development of MHE in certain breeds of cat, but this remains hypothetical pending further evaluation. Based on the human literature, other risk factors potentially worthy of investigation in cats include a contribution from altered posture^34,35 that puts increased stress on the humeral head of the FCUM and cardiovascular risk factors.^36,37

Outdoor access has previously been proposed as a potential risk factor for the development of MHE in cats, with the majority of reported cases having a history of outdoor activity.^1,2 Active pronation and supination play an important role in feline movement, particularly during climbing and prey capture, ¹⁶ and it has been suggested that these activities may increase the risk of MHE, potentially explaining why the condition has been reported more commonly in cats with outdoor access.^1,2 Although our case series does not necessarily refute this hypothesis, it clearly demonstrates that outdoor access is not a prerequisite for the condition, as none of the nine cats included had outdoor access.

The clinical presentation of the cats in this case series paralleled many of the previously reported findings, with moderate lameness being the predominant presenting sign and most cases presenting with an insidious onset and no history of trauma. Physical examination findings concurred with previous literature ² in terms of revealing a painful focus located caudodistal to the ME as well as a pain response upon antebrachial supination/pronation and carpal flexion; however, some novel findings on physical examination were also noted. Circumferential elbow thickening was reported to affect two cats (four elbows); however, as these cats were also affected by concomitant elbow osteoarthritis, it is unclear which condition was responsible for this physical examination finding. In four cats (seven elbows), mineralization associated with the MHE was palpable distal to the ME, which has not been reported previously. In addition, palpation of this mineralized structure elicited a pain response in 6/7 cases. These findings suggest that palpation for such mineralization should be included in the orthopedic examination of cats presenting with thoracic limb lameness.

Radiographs are often the first imaging study obtained in cats presenting with elbow pain as they are inexpensive, widely available and easy to obtain. In humans with MHE, most radiographs demonstrate normal findings, with only 25% of cases showing calcification of the common flexor tendon or ulnar collateral ligament. ³⁸ The low sensitivity of radiography for detecting MHE in humans raises concern, particularly as published clinical reports in cats rely solely upon radiography for diagnosis, ² with CT only used subsequently for confirmation. To date, no other imaging modalities have been reported for diagnostic purposes before radiographic confirmation, suggesting that early stages of the condition may be missed. In humans, the presence of tendon calcification on radiographs is strongly associated with higher pain scores, ulnar neuropathy and a significantly higher chance of needing surgical intervention. ²⁸ Given that tendon calcification in humans may be refractory to non-surgical management,^{28,39 –41} and considering the historically low success rates of non-surgical treatment in cats, ² it seems prudent to explore alternative imaging modalities that may facilitate an earlier diagnosis in this species, before the development of new bone formation.

Ultrasonography has been used to facilitate earlier diagnosis of MHE in humans,^20,21 and was similarly used in two cats (four elbows) in this case series where radiographic changes were considered mild or equivocal. In these cases, ultrasonography revealed fluid surrounding the proximal tendons of the FCUM, mild irregularity of the ME and pinpoint mineral foci within the proximal aspect of the FCUM insertion (Figure 4). To date, the authors have only used ultrasound in cases where there was a high index of suspicion based on orthopedic examination findings but where radiographs were inconclusive. Therefore, ultrasonographic findings in more advanced feline cases remain unknown. Nevertheless, ultrasound appears to be a cost-effective modality that may support earlier diagnosis and should be considered in cases with supportive clinical findings.

Figure 4

Two representative long-axis ultrasound still images of the left elbow in a 3-year-old Scottish Fold cat. Radiographs were unremarkable; however, ultrasound evaluation was pursued owing to a high index of clinical suspicion. The medial humeral epicondyle exhibits mild enthesis irregularity with pinpoint mineralization observed at the proximal insertion of the flexor carpi ulnaris tendon (white arrows). A small volume of amorphous fluid (white dashed arrows) surrounds the proximal musculotendinous region of the flexor carpi ulnaris. Annotations: 1 = medial humeral epicondyle; 2 = proximal tendon of the flexor carpi ulnaris; 3 = muscle belly of the flexor carpi ulnaris. The proximal aspect is oriented to the left, and the medial aspect is oriented to the top of the image

CT is not commonly used in humans with epicondylitis because of its low contrast resolution, which limits the ability to delineate soft tissue structures around the elbow. ²¹ Therefore, MRI is generally preferred. Unfortunately, literature on MRI of the appendicular skeleton in cats is limited, and there are no published reports of its use to investigate either the feline elbow in general or MHE specifically. CT has previously been used in cats to confirm a diagnosis of MHE and has shown value in identifying free intra-articular bodies adjacent to the medial joint capsule in 9/17 cats, which had not been identified on radiographs. ² Similarly, in this case series, out of 10 elbows assessed by CT, additional findings were noted in seven cases, including intra-articular mineralized bodies in five and osteophyte formation in two. The identification of such bodies influenced surgical planning, as they were removed when present. Thus, although CT may not be the imaging modality of choice for facilitating earlier diagnosis, it may still be warranted in feline cases to determine whether intra-articular fragment removal is indicated. The formation of free articular bodies in cats is proposed to occur when mineralized structures originating at the intra-articular portion of the ME, or fragments of degenerated cartilage, become dislodged. ¹ Although the pathogenesis of MHE in cats shares many parallels with the condition in humans, the formation of these mineralized intra-articular bodies has not been reported in human literature, which may explain the added value of CT in feline cases despite its limitations in humans.

Although all feline studies report the humeral head of the FCUM as being affected, this study identified varying radiographic appearances (Figure 5), with mineralization appearing to originate from the distal corner of the ME, the supracondylar ridge or, in some cases, multiple sites including the small central protuberance of the ME. In humans, these zones correspond to the points of origin of various tendons and help identify which structure may be mineralized. ²⁸ Whether this indicates mineralization of alternate structures in cats, other than the humeral head of the FCUM, remains unknown. Although the radiographic appearance may suggest this, a cadaveric study of six cats ¹ noted avulsion of the degenerate humeral head of the FCUM, with the mineralized and avulsed structure being displaced onto the more distal part of the caudal joint capsule in more severely affected cases. As such, it is unclear whether these altered appearances reflect the involvement of alternate structures or simply avulsion of the humeral head of the FCUM. None of the cases in this case series were considered to show radiographic evidence of avulsion; however, the limitations of two-dimensional imaging could have played a role here.

Figure 5

Craniocaudal radiographs of three cats demonstrating the varying radiographic appearances encountered. (a) In a 1-year-old Maine Coon, mineralization appears to arise from the distal corner of the medial epicondyle (zone C in humans). (b) In an 11-year-old domestic shorthair cat, mineralization arises from the supracondylar ridge (zone A in humans). (c) In an 8-year-old domestic shorthair cat, mineralization originates from multiple points, including the supracondylar ridge (zone A) and the small central protuberance of the medial epicondyle (zone B)

In humans, various non-surgical and surgical treatment modalities are used to manage MHE, with non-surgical therapy representing the mainstay of treatment. Surgical procedures are typically reserved for patients with refractory or recurrent symptoms despite non-surgical management. Reports of non-surgical treatment in cats are limited but have included indoor confinement for at least 4 weeks, meloxicam administration and glucosamine/chondroitin supplementation. ² Data suggest that non-surgical management beyond 4 weeks is of little benefit and that past this period, surgery should be considered in cats with persistent lameness. ² In the one available clinical study, 7/8 cats treated non-surgically remained chronically lame throughout the study period. ² However, it should be noted that this was a referral population, likely consisting of cats that had already failed to respond to non-surgical therapy. In addition, as previously discussed, the use of radiography to screen for MHE may have biased case selection toward chronic and severe cases, given that all included cats showed mineralization on imaging. The prognosis for non-surgical management may be more favorable in cases that are diagnosed earlier.

In this case series, four cats showed no improvement after non-surgical management, four showed a partial response and in one case lameness resolved. As noted in the results, correlating outcomes with the severity of MHE shows that among eight elbows with mild MHE, three fully responded to non-surgical therapy, four partially responded and one did not respond. None of the seven elbows with moderate MHE responded to non-surgical treatment, while of the two elbows with severe MHE, one partially responded and one did not respond. Although these numbers are small, the findings align with the human literature suggesting that once mineralization is evident, surgical intervention is often necessary to resolve clinical signs. However, if cases are diagnosed earlier, before severe radiographic signs develop, the prognosis with non-surgical management may be improved. This reinforces the need for research into diagnostic modalities that facilitate earlier diagnosis.

Ulnar neuritis is a common concomitant pathology in humans with MHE. ³⁸ It is believed to result from pathologic bony changes on the ME causing epineural fibrosis and neuralgia, although acute injury is also possible. ⁴² Ulnar neuritis is known to worsen medial elbow pain. Similarly, cats with MHE have shown changes involving the ulnar nerve, which lies close to the ME and is often displaced caudomedially by new bone growth, leading to epineural fibrosis. Adhesion of the nerve to the periosteum, thickening and distortion of its fascicles, and increased collagen in the epineurium indicate chronic nerve degeneration. ¹ In addition to exacerbating pain and reducing the efficacy of non-surgical therapies, ulnar nerve deficiency has also been suggested to cause a palmigrade stance in cats, as observed in three cases in this series. ²

In humans, failure to address ulnar nerve neuritis can lead to unsuccessful surgical outcomes. Gabel and Morrey ⁴³ reviewed 30 elbows with MHE, 16 of which had concomitant ulnar neuropathy, all treated with various open tendon debridement and ulnar nerve procedures. Of the 25 elbows with no or mild ulnar neuritis, 24 achieved excellent or good results at a mean follow-up of 7 years. However, 3/5 patients with moderate or severe ulnar neuropathy reported fair or poor outcomes. The authors noted that the severity of ulnar neuropathy was the only preoperative or intraoperative parameter correlated with surgical outcome. Kurvers and Verhaar ⁴⁴ reported similar results in their study of 38 surgically treated MHE cases. The impact of ulnar neuritis is difficult to assess in cats given the small case numbers, as well as the fact that all 10 previously reported feline cases involved ulnar nerve pathology,^2,3 as did all cases in this series. Although it is tempting to attribute poor non-surgical outcomes to ulnar neuritis, it may be unclear whether this represents correlation or causation. Currently, there are insufficient data to determine whether cats without ulnar neuritis respond better to surgery, highlighting a potential area for future research.

In the published clinical cases to date, it has been reported that because of the severity of disease, excision of the mineralized portion of the FCUM was only achievable with complete tendon detachment and transposition. However, it has been postulated that in some cases, smaller and more isolated areas of mineralization may be excised without requiring tendon detachment, offering an effective treatment. ² In our experience, removal of such foci without detaching the tendon was possible. Of the seven elbows treated surgically, tendon detachment was avoided in four. Notably, these four elbows represented bilateral disease in the two youngest cats in the series, both Maine Coons. Whether this represents more localized pathology in less chronic cases or suggests a differing pathogenesis in younger, purebred patients, remains speculative at this stage.

In humans, postoperative care after common flexor tendon surgery varies with disease severity and may involve either gentle use of the arm or immobilization at 90° using a splint or sling for 1–2 weeks. In cats, a carpal flexion bandage is applied postoperatively to hold the carpal joint in slight flexion, thereby preventing stress and tearing of the reattached muscle. ² In this case series, carpal flexion bandages were used in 6/7 elbows operated on, where mineralization of the FCUM was removed. The need for such immobilization in cases where complete detachment of the FCUM is not required remains unknown and represents an area for future research. The need for carpal flexion bandaging was the primary reason for staging surgeries in cats with bilateral FCUM mineralization. If bandaging is not necessary, simultaneous bilateral surgeries may become a viable option.

Conclusions

This case series adds nine cases to the very limited literature base on feline MHE and highlights important considerations regarding its pathogenesis, diagnosis and treatment. Although previous feline studies suggested a predisposition among outdoor cats, none of the nine cats in this series had outdoor access, indicating that MHE should remain a differential diagnosis in all cats presenting with thoracic limb lameness. The growing acceptance that certain breeds may be predisposed to MHE and may develop this at a younger age prompts consideration of alternative pathogeneses and highlights the need for further research into potential risk factors. Clinical findings were largely consistent with previous studies but also included additional findings, such as palpable mineralization distal to the ME and a pain response upon palpation. Given the low sensitivity of radiography in detecting MHE in humans, it is likely that a similar reliance on radiographs in feline cases may lead to early stages of the condition being overlooked. As calcification on imaging is considered an indicator for surgery in humans, reliance on this finding in cats may delay potentially effective non-surgical therapies. This is supported by the observation that radiographically mild cases appeared to have a more favorable prognosis when responding to non-surgical management. Other imaging modalities, including ultrasound, may facilitate an earlier diagnosis and warrant further investigation. Earlier detection may allow for a wider range of treatment options, some of which have been successful in humans but remain untested in cats. Although improving non-surgical outcomes through earlier diagnoses is the goal, this series supports previous findings that, when surgery is indicated, the prognosis for resolution of clinical signs is generally very good.