17 May 2010
Mike Guilliard
Job TitleMIKE GUILLIARD discusses the clinical examination, diagnosis and operating techniques for a common, but under-researched, cause of canine lameness
PEDAL lameness is the poor relation of canine orthopaedics, with few publications and little research on the subject. Yet, it is a common cause of lameness in first opinion practice. All orthopaedic clinical examinations should include a thorough and systematic examination of the foot.
Firstly, conduct a visual inspection of the standing dog. This may be impeded by a long coat.
You should look for:
• swelling;
• abnormal carriage of the digits;
• abnormal nail wear; and
• tumours.
You should also carry out a visual inspection of the ventral foot, and look for:
• abnormal pad wear or hyperkeratosis;
• wounds;
• interdigital inflammation; and
• tumours.
Palpation of the digits and joints should also be conducted. You should look for:
• swelling – compare with the other digits;
• instability; and
• pain.
Palpation of the pads, interdigital skin and nails should also be carried out. You should look for:
• swelling; and
• pain.
Some dermatological or oncological causes of lameness are outside the scope of this article.
The pads act as an interface between the ground and the animal, functioning as cushions to protect the subdermal structures. Any damage or abnormality can cause marked pain and lameness during weight bearing.
• Foreign body penetration
Clinical examination will show an entry wound, often with serous exudates. If the foreign body is present, a pain response will be elicited with digital dorsoventral pressure across the pad.
With a scalpel blade, gentle paring of the surface of the pad over the wound can detect a penetrating thorn or a superficial foreign body. Deep probing is not recommended.
A mediolateral radiograph will show grit and glass, but not wood. Positioning for this view is achieved with the dog in lateral recumbency, with the affected pad isolated using radiolucent tape. The dorsoventral view is rarely informative.
Foreign bodies embedded in the subdermis need surgical removal (operating technique one, mentioned, along with other techniques, later in this article). If no foreign body is present, then the entry wound will require a protective dressing to prevent further penetrations.
• Corns
A corn is a circular area of hyperkeratosis, usually found in the centre of the digital pad (Figure 1). It can cause a severe progressive lameness, where the dog is typically less lame walking on softer surfaces. It can be confused with a chronic foreign body penetration wound. Diagnosis is made by its physical appearance and by a pain response to dorsoventral pressure. In a study of 40 corns in 30 dogs (Guilliard et al, 2010), corns were found exclusively in greyhounds, whippets and lurchers. In 85 per cent of cases, the corn was sited in digital pads three and four of the thoracic limbs.
The aetiopathogenesis appears to be mainly mechanical, as the central digital pads of the thoracic limbs have the highest ground reaction forces, and are the first point of contact with the ground during the gallop. Forty per cent of corns were the result of abnormal weight bearing from other foot problems, such as carpal hyperextension and rupture of the deep digital flexor tendon.
Foreign body penetration may be implicated, as the histology in some cases shows a sinus tract lined with epithelial tissue. However, it is rare to find a foreign body on surgical removal. No evidence exists to suggest a viral aetiology (Balara et al, 2009).
In most cases, treatment is by surgical excision (operating technique one), and provides a success rate of 74 per cent up to one year. However, recurrence is common and the success rate drops to lower than 50 per cent after one year. However, the surgery can be repeated if necessary. Distal digital ostectomy (operating technique two) is successful in selected cases, resulting in a natural resolution of the corn. All other reported treatments are palliative.
An exuberance of pad and adjacent skin, as a result of abnormal weight bearing, can lead to chronic painful inflammation of the ventral interdigital skin, and is typically seen in overweight Labradors. Resection of the hyperplastic tissue by separation podoplasty (operating technique three) usually resolves the lameness.
Damage to the nails can result in shelling where the nail bed is left exposed – splintering where torn nail remnants remain – or fracturing of the underlying ungual crest. Loose remnants of nail can be very painful and must be removed. Exposed tissues generally heal rapidly, and the nail will regrow. However, abnormal nail growth can damage the pad or lead to a chronic infection of the nail bed, necessitating permanent nail removal (operating technique four).
The interdigital skin is a common site for interdigital cysts and chronic fibrosing pyoderma lesions (Figure 2) that are poorly responsive to antibiotic treatments. Excision separation podoplasty (operating technique three) can result in a permanent cure.
• Split web
This can vary from a small cut in the cranial edge to a complete tear. Reconstruction often results in the cut reopening at each race. If left to heal without reconstruction, the cut will again open after racing. Successful treatment is by complete incisional separation podoplasty (operating technique three).
• Split foot and sand burn
A sand burn is a superficial cut of the ventral skin over either of the flexor tendons to digits three and four in the hindfeet. It is caused by the abrasive action of sand on the skin over the taut tendons. A full-thickness cut of the skin is a split foot (Figure 3). This injury heals rapidly, with or without suturing, but will always reopen with further racing. An incisional separation podoplasty to the interdigital skin, abaxial to the wound, is usually successful in preventing recurrence.
The following is a list of operating techniques and the situations they would be utilised in.
This procedure involves pad surgery for foreign body removal or corn excision. Haemostasis is achieved by an assistant pinching the pad between his or her finger and thumb.
The removal of a foreign body requires a linear incision through the entire dermis over the entry wound. An elliptical excision is needed for corns (Figure 4).
The pad is closed with simple sutures several millimetres away from the wound margins.
It is imperative the foot has a protective dressing that is changed weekly for three weeks. At this time, the sutures can be removed.
This procedure, distal digital ostectomy, involves the removal of the third phalangeal bone (P3), the nail and the condyles of the second phalangeal bone (P2), but with the preservation of the pad.
An incision is made in the skin around the base of the nail, enabling the disarticulation and removal of P3 and the nail. The condyles of P2 are exposed and removed with bone cutters.
The pad is pulled dorsally and sutured to the skin. An elliptical piece of ventral skin is excised just caudal to the pad, and its edges are sutured together. This pulls the pad ventrally over the stump of P2, and ensures weight bearing through the pad.
Separation podoplasty, the third technique, can be incisional or excisional. With incisional separation podoplasty, the interdigital skin is cut from the cranial border to the metacarpal/tarsal pad, and the dorsal skin is sutured to the ventral skin to create a permanent separation of the digits (Figure 5).
Excisional separational podoplasty involves the excision of an interdigital lesion, with the closure the same as the incisional technique. The adjacent digits are not weakened.
The fourth operating procedure available is an ungual crest ostectomy.
The ungual crest is the cranial portion of P3, over which the nail grows. Removal of this, together with the nail bed, results in permanent nail removal without altering the weight bearing relationship of P3 to the pad.
An incision is made in the skin around the base of the nail, and the dorsal joint capsule of the P2/ P3 joint is exposed. Bone cutters are used to cut through the nail and underlying bone close to the joint. The nail bed will now be exposed and is nibbled away with rongeurs, together with any remaining ungual crest. The ostectomy is complete when no nail bed remains and the skin can be easily closed over the bone.
Mike Guilliard
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