24 May 2010
Mike Guilliard
Job TitleMike Guilliard continues a two-part article on a common, yet under-researched, cause of lameness in dogs, this time focusing on problems in the digits and joints, and relevant surgical techniques
IN the first part of this article (VT 40.19), I discussed the clinical examination, diagnosis and operating techniques for pedal lameness, which I view as the poor relation of canine orthopaedics.
In this concluding part, I will focus on some of the instabilities and fractures that can be caused by the condition.
The digits comprise three bones, the most distal of which is the third phalanx (P3). This articulates with the second phalanx (P2), and this articulation is referred to as the distal interphalangeal joint (P2/ P3). The proximal articulation of P2 is with the first phalanx (P1) and is known as the proximal interphalangeal joint (P1/ P2). P1 articulates proximally with either the metacarpus or metatarsus.
Instabilities of the phalangeal joints are causes of lameness, with permanent subluxation causing toe deformity and abnormal weight bearing on the paw pads. Clinical signs include joint swelling and deformity, but a definitive diagnosis is made under general anaesthesia by palpation. A radiograph will determine if any fractures are present.
Instabilities are classified as stable if the joint remains congruent, but subluxation can be induced and unstable. The difference depends on the degree of tearing of the collateral ligaments and joint capsule. An avulsion fracture of either the origin or insertion of a collateral ligament may be present.
In the P2/P3 joint, an open subluxation can occasionally occur, appearing as a small cut over the joint on the lateral aspect (Figure 1). This cut will heal with rest, but opens up during exercise. Ungual crest ostectomy is curative (see operating technique four in the first part of this article).
All treatments are aimed at restoring joint congruity to allow sufficient periarticular fibrosis to form, which stabilises the joint. Stable joints may be treated with external coaptation alone, but if you are in doubt, a surgical option should be considered.
• Distal interphalangeal joint
The differential diagnosis of swelling of the distal digit includes nail-bed infection, osteomyelitis of P3, fractures and an infection of the P2/P3 joint, as well as joint instability. Careful examination will determine if the joint is involved, and confirmation of an unstable joint is made under general anaesthesia.
Septic arthritis is common in this joint, and a joint tap is mandatory if the joint is stable. A lateral approach, using a 23-gauge needle, will allow a small quantity of joint fluid to be withdrawn. The presence of polymorphic nucleated white cells will give a presumptive diagnosis, and antibiotic therapy should be instigated.
Treatment depends on the degree of instability. Stable joints can be treated by external coaptation; moderately stable joints by ungual crest ostectomy (operating technique four). Grossly unstable joints should be treated by ungual crest ostectomy and a support suture (Figure 2). This normally comprises a single mattress suture of any absorbable suture material, placed through the periarticular tissues and ruptured collateral ligament remnants. Its aim is to hold the joint in normal congruity. Ungual crest ostectomy removes the lever arm of the nail and promotes periarticular fibrosis.
The prognosis following surgical treatment is excellent.
• Proximal interphalangeal joint
The history of treatments for damage to the P1/P2 joint makes interesting reading, and none of these treatments has given consistently good results for the author. In the early days of greyhound racing, barbaric treatments included pin firing and blistering, shortly followed by injecting sclerosing agents around the joint. The rationale was to promote periarticular fibrosis, but the issue of joint congruity was not addressed.
Prosthetic ligament replacement came into vogue with the use of wire, nylon and carbon fibre. The collateral ligaments are broad structures and the isometric points vary, with flexion making accurate placement of the prosthesis difficult.
Various recent texts promote ligament reconstruction as the definitive treatment, but trying to accurately stitch together the torn ends is not possible, due to fraying and avulsion.
All these treatments are only likely to be successful if joint congruity is maintained with periarticular fibrosis giving subsequent support.
Maintaining joint congruity with an external fixator was described (Guilliard, 2003) and this has proved to be consistently successful (operating technique five). A prospective study on 18 cases in racing dogs by the author provided no failures. In addition to the fixator, many cases had an ungual crest ostectomy to shorten the lever arm. Cases suitable for this procedure are:
– grossly unstable joints;
– instability in digits three and four; and
– pet dogs, as they tend to have long nails.
Subluxation of P1/P2 may involve an avulsion fracture of the collateral ligament. If the fragment is large enough, internal fixation may be possible. The author’s preferred treatment is to apply an external fixator only.
• Tarsometatarsal and carpometacarpal phalangeal joint (MT/P and MC/P)
These joints are more complex, due to the presence of two large sesamoid bones. The following three types of instability may be seen, and these involve either digit two or digit five.
– Rupture of the axial collateral ligament, causing a valgal deformity.
– An abaxial luxation of P1, together with either both sesamoid bones or with just the lateral sesamoid.
– Internal rotation of the digit (Figure 3). This is common in the MT5/P joint in racing greyhounds, and appears predisposed by torsion of distal MT5.
Treatment can be by external coaptation for stable joints or by the application of an external fixator for unstable joints. The prognosis for a return to racing is very good.
Phalangeal fractures are painful and associated with gross swelling of the digit. Diagnosis is by radiography. In general, these fractures heal rapidly and treatment aims to ensure good alignment to prevent toe deformity. Fractures involving a joint are generally considered problematic due to subsequent osteoarthritis, but phalangeal joints with articular fractures tend to ankylose and often become pain free.
External coaptation is suitable for stable fractures with good alignment. Internal fixation, usually with cortical screws, is often possible, but involves difficult surgery. An external fixator provides good support and alignment; it should always be considered.
• P3 fractures
Fractures that involve the ungual crest or body of P1 can be treated by ungual crest ostectomy. Comminuted and articular fractures may need a distal digital ostectomy (see operating procedure two).
• P2 fractures
These present as spiral, comminuted or condylar fractures. External coaptation will often result in poor alignment with an elevated nail. An external fixator, with pins in P1 and P3, offers good alignment.
• P1 fractures
Both simple and comminuted fractures heal rapidly with external coaptation. Articular fractures of both P1 and P2, involving the P1/P2 joint, heal with a joint ankylosis.
This has been described for the MT and MC/P joints and the P1/P2 joints, but it is rarely performed. The application of a dorsal plate is the recommended procedure.
A complete or partial digital amputation should always ensure any bone stump is well protected from contact with the ground. The sites are either through the distal P2 (distal digital ostectomy) or through the MT or MC/P joint with removal of the condyles in digits two and five. With digits three and four, the joint is disarticulated and the sesamoids left in situ. The author does not remove the articular cartilage.
Closure is the same as an excisional separation podoplasty (refer to operating procedure three). The prognosis is generally excellent. The loss of a digit in a greyhound should not affect its racing.
This procedure is used for fractures of P1 and P2, and for instabilities of MT and MP/P joints and P1/P2 joints. Arthrodesis pins of 1.4mm and 1.6mm are used, and are driven into the bone on the dorsal axial aspect, at about 30° to 50° from the vertical. Ideally, three pins should penetrate both cortices of each bone, but two pins will generally suffice. The ends are bent over and an acrylic connecting bar is moulded over the pins (Figure 4).
A prophylactic course of antibiotics is given for 10 days. For instabilities, the frame is removed after a maximum of three weeks. Fractures may require longer, but usually gross swelling of the digit rapidly develops to maintain reduction without other support.
Complications of this technique include:
• over-penetration of the pins;
• impingement of the frame on the surrounding tissues;
• pin loosening;
• intolerance by the patient (a protective bandage is not necessary, but dogs occasionally chew off the acrylic); and
• pin-tract infect ion and osteomyelitis (this is very common, but resolves rapidly after removal of the frame).
Mike Guilliard
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