How to Remove Osteochondral Axial Fragments From the Proximopalmar or Proximoplantar Aspect of the Proximal Phalanx Using a Bipolar Radiofrequency Device

1. Introduction

Osteochondral (OC) fragments of the plantaro-proximal aspect of the proximal phalanx are most frequently reported in Standardbred racehorses but are rarely encountered in Thoroughbred racehorses or Warmbloods [1-3]. These fragments have been classified previously into three categories [4]:

• Type 1: fragments originating from the pal-mar/plantar aspect of the proximal end of the first phalanx just medial or lateral to the sagittal ridge (axial).
• Type 2: fragments originating from the plan-tar/palmar aspect of the eminences of the proximal phalanx.
• Type 3: fragments originating from the base of the proximal sesamoid bones.

Classification remains controversial, because more recent data would support a proposed traumatic etiology [5]. However, the occurrence of fragments in weanlings and yearlings presumably links them to osteochondrosis [6]. Arthroscopic removal is the surgical treatment of choice for type-1 (axial) fragments, because conservative therapy may result in subtle lameness at high speed. This lameness becomes more evident during turns [1,7] and results in reduced performance in affected horses [6]. Intra-articular electrosurgery has been reported briefly in the literature in Standardbreds [8-10] for removal of plantaro-proximal OC fragments. Radiofrequency devices continue to be used extensively in human medicine for both intra-articular and extra-articular procedures [11]. The purpose of this paper is to describe the surgical technique as well as the complications of removal of type-1 axial palmaro-proximal and plantaro-proximal OC chip fragments using a bipolar radiofrequency coblation device (Arthrocare [a]; Fig. 1) under arthroscopic control in Thoroughbred and Standardbred racehorses.

2. Materials and Methods

Thirty-three random cases were selected from the surgical records of the Davidson Surgery Center during 2004. All horses were evaluated as part of pre-sales evaluation, which included using screening digital radiographic evaluation [b] and examination for conformation and lameness. Surgery was elected by owners/managers in preparation for yearling sales and to maximize potential racing performance. All horses underwent repeated clinical and orthopedic examinations and digital radiographic evaluation of the affected joint(s) before surgery. Radiographic evaluation of the metacarpophalangeal/metatarsophalangeal joints comprised 4 standard views (dorsoproximal 15°-palmar/plantarodistal oblique; latero-medial, dorsolateral 30°-palmaro/plantaro medial oblique and dorsomedial 30°-palmaro/plantaro lateral oblique) and flexed latero-medial and dorsal 30° proximal, 70° lateral-palmar/plantarodistal medial oblique [12] to specifically highlight the chip fragment where appropriate. All horses received pre-operative procaine penicillin G IM at 20,000 IU/kg, 6.6 mg/kg gentamicin, IV, and tetanus toxoid within 1 h of surgery.

Figure 1. Arthrocare 2000 bipolar radiofequency device.

3. Surgical Technique

Each horse was sedated with xylazine HCl (1.1 mg/kg, IV) and induced with ketamine HCl (2.2 mg/kg, IV) and diazepam (0.05 mg/kg, IV). Horses were either positioned in lateral recumbency with the chip fragment up or in dorsal recumbency when bilateral or bi-axial fragments were to be removed. Each metacarpo/metatarsophalangeal joint was clipped, aseptically prepared, and draped in a routine fashion. The joint was distended with sterile Lactated Ringers solution [c] using a 20-g, 1-in needle through the dorsal pouch or using a collateral sesamoidean ligament approach [13]. The arthroscopic portal was made at the most proximal aspect of the palmar/plantar recess of the fetlock, ipsilateral or contra-lateral to the fragment. The associated fetlock joint is then flexed, and visualization of the suspected fragment location is carried out. A 20-g, 1-in needle is then introduced through the collateral sesamoidean ligament immediately proximal and dorsal to the palmar/plantar eminence of P1 or immediately distal and dorsal to the base of the sesamoid. Needle positioning determines accurate instrument portal selection. This is confirmed by contacting the fragment to be removed or if more axially located, by positioning where the fragment is likely to be. The instrument portal is made using a #11 blade directly through the skin and synovium. Fragment localization can be ascertained using either a periosteal elevator or a blunt arthroscopic probe. The bipolar radiofrequency device [a] with a curved coblation hook probe is then inserted, the fragment is contacted, and separation from the ligamentous, capsular, and soft tissue attachments is performed. The device was fired only under direct visualization to ensure soft tissue ablation only, to reduce the potential for articular cartilage damage, to limit excessive fragment manipulation, and to reduce the potential for probe fracture. Visualization is aided by continuous lavage with sterile isotonic saline solution. Fragment separation is left almost complete before removal using straight or angled Ferris-Smith rongeurs. Intra-operative digital radiography was performed in all cases to confirm complete fragment removal. All joints were lavaged after removal and curettage of the fragment bed, and routine supportive sterile distal limb dressings were applied.

4. Results

All horses were sound on clinical examination, and none had evidence of synovial effusion before surgery. OC fragments were detected in 34 metatarso-phalangeal (16 left; 12 right; and 3 both) and 2 metacarpophalangeal joints (1 left; 1 right). Twenty OC fragments were located at the medial aspect of the joint, and 11 fragments were located laterally. Five metatarso-phalangeal joints contained bi-axial fragments. Three horses had at least one fragment in each metatarso-phalangeal joint.

An ipsilateral triangulation technique was chosen in all uni-axial fragments, and a contra-lateral technique was used in the four metatarso-phalangeal joints with biaxial fragments. All fragments were dissected free using the hook-coblation probe technique. No intra-operative complications occurred. The use of the coblation probe allowed accurate and predictable dissection of the OC fragments from their associated attachments with no intra-articular hemorrhage or iatrogenic cartilage injury.

Post-operative management included 3 - 5 days of broad-spectrum antibiotics and non-steroidal anti-inflammatories, removal of sutures in 10 - 14 days, and the maintenance of routine sterile distal-limb dressings for several days after suture removal. Stall rest was maintained while distal-limb dressings remained in place, then graded increases in exercise were introduced thereafter. Clinical re-evaluation was performed routinely at suture removal. Subsequent evaluations did not automatically form part of the post-operative follow-up, however, all horses would be seen as part of pre-sales conformational and radiographic examinations.

None of the operated horses experienced postoperative complications (incisional discharge or excessive swelling, synovial distension, excessive heat or lameness). All horses were entered into yearling sales with an excellent cosmetic appearance to the metacarpophalangeal/metatarso-phalangeal joints in question.

5. Discussion

Since the mid 1990s, monopolar and bipolar radiofrequency devices have been investigated [14-18] and used clinically [19,20] with increasing popularity in the veterinary and medical fields [11]. Medical arthroscopic applications include capsulorrhaphy, synovectomy, and ligament and articular cartilage debridement.

Electrosurgery has been described in horses for dissection of OC and chip fractures [8,9]. The bipolar radiofrequency device described contains the active and ground electrode within the probe tip, which negates the need for a grounding pad used in monopolar devices. In contrast to electrosurgery techniques that rely on the production of intense heat (>400°C) to cut by dessication, the coblation device described here uses a bipolar radiofrequency technique to perform volumetric tissue excision. After a sufficiently high voltage has been created between the electrode and the tissue, the electrically active conducting fluid, the lavage fluid (e.g., isotonic saline), is converted into an ionized vapor layer or plasma. The voltage gradient produced across the plasma layer results in the acceleration of charged particles toward the target tissue with sufficient energy to result in molecular dissociation of the tissue [21]. The short range of the accelerated particles developed within the plasma layer confines this dissociative process to the surface layers of the target tissue only, thus reducing extensive collateral damage and allowing volumetric removal of tissue.

Clinical application of the bipolar radiofrequency coblation device described above for removal of palmar-or plantar-type fragments under arthroscopic control offers a more precise and simpler incision of intra-articular soft tissues, a reduction in intra-articular hemorrhage that may occur using intra-articular cutting devices, and a reduction in intra-articular manipulation [22].

Potential complications using this device include intra-articular fracture of the hooked probe during the procedure, either during tissue dissection or on removal from the joint. Although this did not occur during this case series, probe fracture has occurred during this procedure. These complications can be avoided by carefully scrutinizing the probe before the procedure, regularly maintaining the probes, and ensuring that the probe is firing while dissecting dense soft tissue attachments to prevent snaring.

In summary, the use of an intra-articular bipolar radiofrequency device maximizes accurate dissection and visualization of palmar/plantar OC or chip fragments from the proximal palmar/plantar aspect of the metacarpo/metatarso-phalangeal joint, which reduces surgery time and limits the potential for both intra-operative and post-operative complications experienced with conventional techniques. This instrument has, therefore, become an important accessory for intra-articular soft tissue dissection in this referral center.

Footnotes

[a] Arthrocare Corp. USA, 7500 Rialto Blvd, Austin, TX 78735.
[b] Eklin Medical Systems, 1605 Wyatt Drive, Santa Clara, CA 95054.
[c] Lactated Ringer’s, Abbott Laboratories, Abbott Park, IL 60064.