Carpal Arthrodesis is the surgical elimination of joint motion and, ultimately, bony fusion of joint surfaces. Carpal arthrodesis is considered a salvage procedure for patients in which other surgical or medical treatment will not restore normal, pain-free joint function. It can relieve pain and restore reasonable limb function.
Carpal arthrodesis is used to treat animals with carpal hyperextension injuries causing severe palmer ligamentous and fibrocartilagenous damage. These injuries do not generally respond satisfactorily to external coaptation.
For Information: Frequently Asked Questions After Surgery
Anatomy of the Carpal joint (wrist):
- In both dogs and cats, the carpus has seven bones arranged in two rows, which creates three distinct joints.
- The first row consists of the radiocarpal, ulnar carpal, and accessory carpal bones. The accessory carpal bone articulates caudally with the ulnar carpal bone).
- The second row comprises four carpal bones (C1, C2, C3, and C4).
- The carpal joint has three levels joint. The most proximal joint is the antebrachiocarpal (ABC) or radiocarpal joint, where the radiocarpal and ulnar carpal bones articulate with the distal articular surfaces of the radius and ulna, respectively.
- The middle or intercarpal (MC) joint consists of the distal articular surfaces of the radiocarpal and ulnar carpal bones and the proximal articular surfaces of C1 through C4.
- The carpometacarpal (CM) joint is the most distal and is made up of the distal articular surfaces of C1 through C4 and the proximal articular surfaces of metacarpals one through five.
- The ABC joint doesnot communicate with either of the other two joints, but the MC and CM joints communicate between the distal row of carpal bones.
- Soft tissue structures responsible for supporting the carpus include ligaments, tendons, the flexor retinaculum, and the palmar fibrocartilage.
- In dogs and cats, each forelimb carries approximately 30% of the weight during a normal stride.
- This weight bearing, combined with high-impact forces from running, jumping, or trauma, can predispose the carpus to hyperextension injuries.
- Flexion and extension in the carpus are primarily at the ABC joint and, to a lesser degree, the MC joint. The relative contribution of the ABC, MC, and CM joints to carpal range of motion is 85% to 90%, 10% to 15%, and 0%, respectively.
- The normal range of flexion is approximately 100° for the ABC joint, 40° for the MC joint, and 10° for the CM joint.
- The normal standing angle of the carpus is approximately 140° to 180° in dogs and 160° to 180° in cats
- The most common indications for carpal arthrodesis are ligamentous injuries, carpal bone fracture, and carpal joint luxations or subluxations.
- Hyperextension of the carpus, which can result from either acute trauma or repetitive chronic trauma, often damages the palmar ligaments and palmar carpal fibrocartilage, leading to instability of one or more joints within the carpus.
- Shearing injuries to the medial or lateral collateral ligaments or carpal bones often cause substantial carpal instability and subsequent osteoarthritis.
- Other potential indications for carpal arthrodesis include: Carpal joint instability due to loss of articular cartilage or injury to supporting ligamentous structures, such as that associated with erosive and nonerosive immune-mediated joint disease
- Chronic osteoarthritis that is nonresponsive to medical management.
- Loss of carpal bones or supporting ligamentous structures due to resection of neoplastic conditions
- Congenital malformations of the carpus resulting in luxations or complete or partial agenesis of carpal bones
“Autogenous or allogenic cancellous bone graft material is inserted into the joints being fused to enhance bone formation and shorten healing time.”
- Affected dogs present with a lameness associated with a palmigrade stance of the carpus.
- Acute hyperextension injuries are painful, but dogs usually bear weight on the chronically hyperextended carpus.
- Carpal hyperextension may unilateral or bilateral
- Accurate localization of the injury using stress radiograph is necessary to accurately assess carpal integrity and to identify the exact level of joint instability in most hyperextension injuries.
Surgical Procedure Options for Carpal Arthrodesis:
“Pancarpal arthrodesis and partial arthrodesis are two commonly used procedures for carpal arthrodesis.”
- There are two commonly used procedures for carpal arthrodesis:
Pancarpal arthrodesis which involes fusion of the antebrachiocarpal joint, the middle carpal and the carpometacarpal joints;
“ Antebrachiocarpal joint fusion alone is not recommended because the result stress can cause breakdown of the middle carpal and carpol-metacarpal joints”.
- Subluxations or luxations of the antebrachiocarpal joint should be treated with parncarpal arthrodesis.
- Subluxation of the middle carpal and carpometacarpal joints with associated disruption of the accessory carpal ligaments, palmar fibrocartilage, and palmar ligaments of those joints should also be treated with pancarpal arthrodesis.
Partial carpal arthrodesis which involves fusion of the middle carpal and carpometacarpal joints.
- Chronic instability associated with the loss of integrity of the medial or lateral collateral ligaments should be treated with pancarpal arthrodesis.
- Disruption of the accessory carpal ligaments, carpometacarpal ligaments, and the palmar fi brocartilage, resulting in subluxation of the carpometacarpal joint without disruption and displacement of the accessory carpal and ulnar carpal bones, may be treated with partial carpal arthrodesis.
- The limb is prepared circumferentially from the shoulder to the digits. The animal may be positioned in lateral recumbency with the affected limb uppermost.
- The ipsilateral proximal shoulder should be prepared for harvesting cancellous bone to use as an autogenous graft.
“An autogenius cancellous bone graft or allograft is used to encourage early bone healing.”
- A dorsal incision is made over the midline of the carpus, extending proximally to the distal diaphysis of the radius and distally to the distal end of the metacarpal bones.
- The subcutaneous tissues, proliferative fibrous tissue, and joint capsule are incised to expose the antebrachiocarpal,middle carpal and carpometacarpal joints.
“It is important to remove the artcular cartilage from all exposed surfaces of the joints which are to be surgically fused by arthrodesis.”
- The carpus is flexed, and the articular cartilage removed from all exposed surfaces of the carpal joints with a high-speed burr, following the contours of the bone ends. Autogenous cancellous bone or allograft is harvested and placed within the prepared joints.
“A plate and screws are the implants of choice for pancarpal arthrodesis.”
- An appropriately sized plate is contoured to provide 10-12° of carpal extension. The plate should be long enough to provide sufficient plate holes for a minimum of three screws in the radius and three screws in the third metacarpal bone.
- The plate should be positioned on the dorsal aspect of the carpus so that one screw will penetrate the radial carpal bone.
“The preferred angle for pancarpal arthrodesis is 10-12°, the hybrid plate must be slightly contoured to achieve the proper limb angulation.”
“ The arthrodesis site must be protected with a cast for at least 6-8 weeks or until early radiographic evidence of bone bridging is observed.”
- Angular and rotational alignment of the limb should be carefully assessed and corrected if necessary before securing the plate to the radius.
- The plate holes over the radius are filled with screws, using the loaded drill guide in one or two holes to compress the antebachiocarpal joint.
- The remaining plate holes are filled. One plate screw should secure the radial carpal bone.
- Since the plate is applied to the compression aspect of the joint it must be protected from cyclic bending forces. This may be achieved either by supporting the limb in a cast or a splint postoperatively.
Partial carpal arthrodesis:
“The plate must be located distal to the proximal articular surface of the radial carpal bone so it does not interfere with the radius during carpal extension.”
- The carpus is flexed and the articular cartilage removed from all exposed surfaces of the middle carpal and the carpometacarpal joints with a high-speed burr, following the contours of the bone ends.
- Autogenous cancellous bone is harvested and placed within the prepared joints.
- A partial carpal arthrodesis may be stabilized with a veterinary T-plate
- A veterinary T-plate is positioned distally on the dorsal surface of the radial carpal bone and third metacarpal bone.
- Aligning the dorsal surfaces of the radial carpal bone and third metacarpal bone along the plate produces the correct alignment for the arthrodesis.
“Screws that are too long and positioned in the radial carpal bone will interfere with the palmer soft tissues, causing lameness.”
- The plate is first secured to the radial carpal bone with screws which are slightly shorter than the measured length.
- The plate is aligned and secured to the third metacarpal bone with a plate holding forceps.
- The remaining plate holes are filled, starting with the most distal screw and moving proximally to secure the plate to the third metacarpal bone.
- Proper Pain management is important.
- The limb is supported in a cast or splint during the healing phase which is about 6-8weeks
- The padding of the cast or splint is changed every week.
- Limited leash walks for urination/bowel movements until arthrodesis has been confirmed to be healed on radiographs.
- Keep on Elizabthen Collar.
- Radiographs are taken 4 & 8 weeks after surgery.
- Resuming full activity and exercise will be determined in most cases by the radiographs taken at 6- 8 weeks after the surgery
- After the cast has been removed, exercise is gradually increased on a leash over the next 6 weeks; during the first week a 5 minute walk twice daily is permitted; the walks can be increased by 5 minute increments each week until a normal amount of walking has been achieved
- Recheck immediately if your pet suddenly starts using their leg less than before.
- As with any surgical procedure, complications can occur. Anesthetic death is very uncommon with our advanced anesthetic monitoring devices and advanced anesthesia protocols
- Infection is possible but very uncommon
- Cold sensitivity requiring removal of the plate and screws after a year
- The most common complication is delayed healing, where, despite our best efforts to reduce and stabilize the joint, individual patients respond slower than others. In other cases, the bone may refuse to fuse and require additional procedures like bone grafting
- Breakage of the plate or screws
- Pressure sores from the cast or splint
- Joint fusion patients heal in about 3-4 months. Most patients will return to controlled activity in 3 months and full activity in 4-5 months. Most athletic dogs will return to full function in 6 months. Remember, overactivity too early will result in premature failure of the implants and additional surgery at additional cost.