Keywords
cat - radial head luxation - elbow - mini TightRope
Introduction
Isolated luxation of the radial head is usually described as an uncommon congenital
anomaly in small animals.[1] Mostly reported in dogs,[1] cases of congenital radial head luxation have been rarely described in cats.[2]
[3] Traumatic luxation of the radial head is more frequently associated with an ulnar
fracture.[4] However, isolated traumatic luxation of the radial head can also occur,[4] even if very limited information is available. Traumatic radial head luxation in
association with an ulnar fracture is usually classified as Monteggia lesions (or
fracture) (ML).[1]
[5]
[6] Monteggia lesions have been classified into four types, according to the direction
of luxation of the radial head[4]
[7] and angulation of the ulna fracture[8]
[9]: cranial luxation (type I), caudal luxation (type II), lateral luxation (type III)
and cranial luxation associated with an additional fracture of the proximal radial
diaphysis (type IV). Type I ML, associated with cranial luxation of the radial head,
has been the most frequently observed in small animals[8]
[9] and has generally occurred after road traffic accidents or falls.[10] A cranial luxation of the radial head has been recently reported in a dog in association
with divergent elbow dislocation.[11] Four anatomical structures contribute to the humeroradial and radioulnar stability:
(1) the joint capsule, (2) the lateral and medial collateral ligaments, (3) the annular
ligament, and (4) the interosseous ligament.[1]
[11] Although canine and feline elbows have similar gross anatomy, differences exist
between cats and dogs.[4] In particular a strong interosseous ligament between the radius and ulna is absent
in the cat.[4]
[12] In ML, the annular ligament can be disrupted or may remain intact depending on the
level of the ulnar fracture.[5] When the ulna fracture is distal to the radial head,[5] the radioulnar joint is also luxated and consequently the annular ligament and at
least the proximal portion of the interosseous membrane and ligaments are disrupted,
adding instability to the condition and complexity to the repair.[8] Anatomically, the annular ligament attaches to the lateral and medial coronoid processes
of the ulna and runs in a transverse plane around the radius.[12] Reconstruction of the annular ligament has been described in dogs, but in most cases
is not feasible.[5]
[8] Furthermore, reluxation commonly occurs when annular ligament repair is the sole
method of reduction,[13] making it imperative to immobilize the radial head on the ulna. This fixation may
be achieved by either a Kirschner wire (K-wire) or preferably a screw, placed between
the radial neck and proximal ulna.[5] A radioulna TightRope system with an ulna plating has been successfully used for
repair of a ML in a dog and a cat.[13] The purpose of our case report is to describe the clinical presentation and surgical
management of an isolated traumatic cranial luxation of the radial head in an adult
cat and its treatment with a mini TightRope system. This condition is only occasionally
mentioned in veterinary textbooks,[4] and only 30 cases have been reported in human medical literature over the past 30
years.[14]
Case Description
A 4.4 kg, 6-year-old Domestic Shorthair male neutered outdoor cat was referred as
an emergency immediately after a road traffic accident. Medical stabilization and
emergency work-up (T-FAST and A-FAST, complete blood count and biochemistry) were
provided at admission. The cat was ambulatory with a non-weight bearing lameness on
the left thoracic limb, with the left elbow maintained in flexion and slight supination.
Manipulation of the left elbow revealed abnormal anatomical landmarks and moderate
swelling of the periarticular soft tissues. There was also reduced range of motion
(ROM) in both flexion and extension associated with crepitus on palpation. Intravenous
fluid therapy (Hartmann's: 4ml/kg/h; Hartmann's; Vetivex; Dechra, Skipton, United
Kingdom), methadone (0.2mg/kg intravenously [IV] q4h; Methadone, Comfortan; Dechra,
Skipton, United Kingdom) and oxygen administration via oxygen cage with constant monitoring
of vital parameters was continued and the cat's clinical condition improved progressively
over the first 24 hours of intensive care. Radiographic examination under sedation
was postponed until the day after the trauma. Orthogonal views of the left antebrachium
revealed a cranial displacement of the proximal radius associated with complete loss
of contact between the radial head and the lateral humeral condyle. The caudal aspect
of the radial head was indeed misshapen and a small, well-defined osseous fragment
superimposed over the cranioproximal aspect of the ulna was identified on the lateral
radiographic view. The left humerus, the ulna and the humeroulnar joint were unremarkable
([Fig. 1A]). Due to the periarticular soft tissue swelling, Campbell's test was challenging
to perform, but overall medial and lateral normal stability was noticed in pronation
and supination respectively. A left-sided isolated cranial luxation of the radial
head associated with a simple intra-articular fracture was diagnosed. Closed reduction
in the luxation was not attempted due to the articular fracture and surgical stabilization
of the left elbow was performed. Surgery was scheduled 4 days after the initial trauma.
The cat was premedicated with methadone (0.2 mg/kg IV), and induction of anaesthesia
was obtained with propofol (6.25 mg/kg IV; Propofol, PropoFlo Plus; Zoetis, Leatherhead,
United Kingdom) and midazolam (0.25 mg/kg IV; Midazolam, midazolam; Hameln Pharma,
Gloucester, United Kingdom). Anaesthesia was maintained with isoflurane in 100% oxygen.
A radioulnar stabilization was performed according to the technique described by Vallone
and Schulz. A cranial approach to the left radial head[15] provided access to the cranial compartment of the elbow and a direct view of the
dislocated radial head. A tear in the cranial aspect of the joint capsule and disruption
of the annular ligament were found. The collateral ligaments appeared intact. The
small articular fragment in the craniolateral aspect of the elbow joint was identified
and removed. A temporary reduction in the radioulnar luxation was achieved using pointed
reduction bone forceps, and a 1.4 mm K-wire was inserted into the centre of the proximal
diaphysis of the radius and oriented caudomedially towards the ridge of the ulna.
A 2.7 mm cannulated drill bit was then inserted over the K-wire to obtain a radioulnar
tunnel. The bone tunnel created within the proximal radius was 35% of the width of
the proximal diaphysis. A mini TightRope (Arthrex Vet Systems, Naples, Florida, United
States) composed of a single strand 2–0 FiberWire Suture, a 2.6 mm stainless-steel
oblong button and a 5.5 mm stainless-steel round button was used. A 1.6 mm guide pin
was inserted through the hole from the cranial to caudal aspect to pull the 2.6 mm
toggle through the caudal cortex of the ulna. The toggle was placed parallel to the
long axis of the ulna by manipulation of the FiberWire, then the 5.5 mm button was
compressed against the cranial radial surface and secured in position by five throws
of the FiberWire. Intraoperatively, good ROM and good stability in supination and
pronation with the elbow held at 90 degrees was achieved after reduction. The approach
was closed in three layers without attempting to reconstruct the annular ligament.
The postoperative radiographs showed an appropriate reduction of the radius and an
appropriate positioning of the tunnel and the implants ([Fig. 1B]). A modified Robert-Jones dressing was applied to reduce oedema for the first 10
days postoperatively. The cat was discharged from the hospital with a course of cefalexin
(15 mg/kg per os [PO] q12h for 7 days; cefalexin, Therios; Cefa, Amersham, United
Kingdom) and meloxicam (0.1 mg/kg PO q24h for 7 days; Meloxicam, Loxicom; Norbrook,
Oakley Way East, United Kingdom). Strict cage-rest was advised for 6 weeks. On re-examination
at 10 days, the surgical wound had healed uneventfully and the elbow had a good ROM
on manipulation. At follow-up by telephone 20 days after the surgery, the owners reported
that the cat was using the operated limb relatively well but was occasionally holding
it up. At 7 weeks postoperative orthopaedic follow-up, the cat was walking without
lameness. The ROM of the operated elbow was reduced by 20 degrees in flexion compared
with the contralateral side and Campbell's test was negative. Radiographs at that
time showed maintained reduction in the radioulnar joint, static implant position
but mild uniform widening of the radial and ulnar bone tunnels ([Fig. 1C]). These radiographic changes did not have clinical consequences for the overall
stability of the elbow or the functional outcome. Rest was advised for two further
weeks. A final follow-up by telephone 3 years after surgery was obtained by completion
of a ‘feline musculoskeletal pain index’ questionnaire[16] by the owner, giving a score of 7/70 (0 = no sign of pain or mobility detriment,
and 70 = severe pain, detriment). The owner described the overall quality of life
as excellent with good mobility in everyday activities such as jumping, running and
playing.
Fig. 1 (A) Preoperative orthogonal radiographic views of the left elbow, revealing an isolated
cranial radial head luxation with presence of an articular well-defined fracture fragment
(white arrow); the left humerus, ulna and humeroulnar joint are unremarkable. (B) Immediate postoperative orthogonal radiographs showing the reduction in the radioulna
luxation by a mini TightRope (Arthrex Vet Systems, Naples, Florida, United States).
(C) Seven weeks postoperative radiographic follow-up examination showing maintained
radioulnar joint reduction, static implant position but discrete widening of the radial
and ulnar bone tunnels.
Discussion
Isolated luxation of the radial head is a rare condition, commonly congenital and
often associated with developmental abnormalities of the radius and ulna.[1]
[17] Feline congenital radial head luxation has been described in only two cases,[2]
[3] confirming that the incidence of the pathology in this species is very rare. Traumatic
complete elbow luxation in cats is more frequent,[18]
[19] which is generally associated with complete rupture of both medial and lateral collateral
ligaments as demonstrated in a feline cadaveric study.[18] Isolated traumatic radial head luxation has been briefly reported in veterinary
orthopaedic textbooks,[4] but details of the injury, treatment options and prognosis are lacking.
This condition is also relatively rare in humans[14] and the exact mechanism of the isolated radial head luxation remains unclear. A
common cause involves a trauma, such as a fall, with a fully extended arm in pronation.[14]
[20] In human cadaveric models, the luxation occurs instead with the forearm in extreme
supination, with a force applied in an anterior direction to the caudal aspect of
the radial head, resulting in rupture of the anterior capsule and annular ligament
leading to an anterior dislocation of the radius.[20] In humans, the annular ligament and the joint capsule play a key role in stabilization
of the radial head.[20] Descriptions of isolated traumatic radial head luxation seem to be consistent between
human cases and only differ slightly from the clinical signs observed with a congenital
radial head luxation.[14] After the traumatic event in humans, the forearm is maintained in slight supination,
the elbow ROM is normal in extension but reduced in flexion and the displaced radial
head is palpable.[20] A similar clinical presentation has also been observed in our case, even though
the dynamic of the trauma remains unknown. In human medicine, closed reduction is
successful in 50% of cases when the luxation is cranial, but unsuccessful when the
luxation is caudal, lateral or chronic.[14] Open reduction is indicated when the luxation is unreducible or recurrent after
closed reduction. In our case, open reduction was elected due to the intra-articular
radial fracture. Many surgical techniques have been reported to reduce a traumatic
radiohumeral luxation in humans. In a literature review by Obert and colleagues, only
7 out of 20 cases required open reduction for annular ligament reconstruction of radial
head luxation. Prosthetic replacement or muscle aponeurosis strips are usually chosen
over a primary repair due to the friability of the damaged ligament.[1]
[20] In Obert's review, the elbow was immobilized at 90 degrees flexion after reduction;
however, the position of the forearm, supination versus pronation and the duration
of immobilization were variable.[14] In veterinary medicine, several techniques have been employed for reduction and
stabilization of a traumatic radiohumeral luxation in Monteggia lesions. Stabilization
of the radial head with a cortical screw across the radius and ulna immediately distal
to the elbow with concurrent annular ligament repair achieved a good outcome.[1]
[9]
[10] However, implant removal after 4 to 6 weeks has been advised to avoid complications
such as radioulnar synostosis, implant failure and reduction in ROM.[1]
[8]
[10] In our case, the decision to use the TightRope system to maintain the radial head
in position was based on the successful experience reported by Vallone and Schulz
in one dog and one cat. Indeed, the application of a toggle system instead of the
cortical screw should have guaranteed more physiological pronation and supination
movements in the cat and no need to remove the implant, decreasing the risk of implant
failure.[13] The use of the TightRope system has been described for numerous other conditions
in both human (calcaneal fracture, syndesmotic disruptions, acromioclavicular joint
dislocations and hallux varus [bunion deformity][21]
[22]
[23]) and in veterinary medicine (canine cranial cruciate ligament deficiency,[24]
[25] canine and feline hip luxation,[26]
[27] medial shoulder instability,[28] elbow stabilization[11]). The treatment goal in our case was achieved by rapidly restoring reliable and
durable stabilization with limited long-term complications. In the two cases described
by Vallone and Schulz for the treatment of an ML, the elbow ROM was good to excellent
and no radiographic changes were observed at 4 and 8 weeks after surgery for the dog
and cat respectively. In our case, mild uniform widening of the radial and ulnar bone
tunnels was observed at 7 weeks after surgery. However, these radiographic changes
did not affect the overall stability of the elbow nor the functional outcome.
When the TightRope system was used for coxofemoral luxation repair,[26] mild symmetrical femoral bone tunnel widening was seen in all dogs on postoperative
radiographs at the 1 month re-examinations. This widening was persistent, but not
progressive, for more than 4 months re-evaluation. The authors speculated that these
radiographic changes could be attributed to the implant reaction and subsequent bone
response, micromotion of the implant, or infection. Whereas traditionally braided
non-absorbable suture has been reported to have a higher rate of infection than monofilament
material, infection associated with the TightRope system in veterinary medicine[25]
[26]
[27]
[28] has been reported only in 1 dog in one series.[25] In our case, no clinical signs of infection were found. It is possible that the
increased range of supination and pronation motion in cats could have induced more
friction of the FiberWire within the bone tunnels, causing widening of the tunnel.
Bone tunnel enlargement has also been described in human surgery after reconstruction
of the anterior cruciate ligament with an autograft.[29] Stolarz and colleagues explained the widening by a multifactorial aetiology, caused
by mechanical forces and biological processes: drilling, necrosis, inflammatory mediator
reaction.[29] Metacarpal and metatarsal stress fracture at level of the tunnel bone have been
reported in humans, when interosseous sutures with mini TightRope were used for suspensionplasty
for the management of thumb carpometacarpal arthritis[30] and for hallux valgus deformity correction.[23] However, in our case and in the case previously described by Vallone and Schulz,
this complication was not identified. In both cases, a 2.7 mm cannulated drill bit
was used allowing the 2.6 mm stainless-steel oblong button to pass through the radius
and the ulna tunnels along with the guide pin. When the TightRope system is used for
canine and feline coxofemoral luxation repair, it has been recommended to obtain a
femoral tunnel between 20 and 33% of the diameter of the femoral neck.[26]
[27] In our case, the radial tunnel was 35% of the width of the proximal diaphysis of
the radius.
The bone tunnel itself and the postoperative tunnel widening are stress risers and
can predispose to a radial fracture. To decrease this potential risk, in particular
for the smaller radius, a 2 mm cannulated drill bit could be used and the mini TightRope
could be placed in a reverse order,[26] since the oblong button would not fit in the bone tunnel. Briefly, once the radius
and ulna tunnels are obtained, the blunt end of a nitinol loop is introduced from
the radius through the radial and ulna tunnels to pull the suture strands. A 1.1 mm
mini TightRope tapered suture passing K-wire (Arthrex Vet Systems, Naples, Florida,
United States) is also available, allowing the set of 2–0 FiberWire suture strands
to pass through an even smaller bone tunnel.
In our case, a preoperative computed tomographic scan of the elbow would have given
more details about the articular fragment fracture. However, even if the articular
fracture could have affected the prognosis, the long positive follow-up in our case
showed a durable stabilization of the elbow by this technique. In conclusion, this
report describes a case of isolated traumatic radial head luxation in a cat successfully
managed using a TightRope system and adds information on long-term outcome of this
relatively uncommon lesion.
