Dorsal approach to the equine proximal interphalangeal (pastern) joint

The dorsal approach is used for fractures of the distal proximal phalanx and the proximal middle phalanx, infections and pastern arthrodesis.
It exposes the proximal interphalangeal joint surfaces and the dorsal proximal aspect of the middle phalanx and the distal dorsal surface of the proximal phalanx.

Important topographical features of this region are in the forelimb the common digital extensor tendon and in the hind limb the long digital extensor tendon.

A longitudinal incision is made starting at the junction of the proximal and middle one third of the proximal phalanx and extends distally ending 2 cm proximal to the coronary band. The transverse incision extends medially and laterally from the longitudinal incision, staying approximately 2 cm proximal and parallel to the coronary band.

Abaxial dissection between the extensor tendon and the skin forms two flaps, which can now be retracted laterally and medially exposing the underlying extensor tendon.

An inverted V-incision is made into the tendon complex. It starts from about the level of the pastern joint abaxially and extends proximally to just below the proximal aspect of the skin incision.

A sharp instrument such as a chisel is used to elevate the triangular flap of the extensor tendon from the dorsal surface of the proximal phalanx. The dissection is extended distally to include the attachment of the joint capsule to the distal end of the proximal phalanx and the proximal end of the middle phalanx.

Note: In cases of advanced DJD with excessive new bone formation, elevation of the extensor tendon is difficult because of adhesion and bone invasion into the deep surface of the extensor tendon.

When completed, the dorsal surfaces of the distal aspect of the proximal phalanx, the pastern joint and the proximal aspect of the middle phalanx are exposed.

Note: In case of advanced DJD, a chisel is used to remove the excessive periarticular new bone of the dorsal distal aspect of proximal phalanx and the dorsal proximal aspect of the middle phalanx.

When completed, the dorsal surfaces of the distal aspect of the proximal phalanx, the pastern joint and the proximal aspect of the middle phalanx are exposed.

Note: In case of advanced DJD, a chisel is used to remove the excessive periarticular new bone of the dorsal distal aspect of proximal phalanx and the dorsal proximal aspect of the middle phalanx.

A Hohmann retractor or similar instrument is introduced between the two articular surfaces and used as a distractor. Beginning dorsally, the medial and lateral collateral ligaments are sequentially transected as the joint is further distracted until the joint is opened dorsally to expose the majority of the articular surfaces of the proximal and middle phalanges.

The joint is opened to allow complete removal of the articular cartilage. The arrows point to the transected collateral ligaments.

Note: In advanced cases of DJD, dorsal luxation of the pastern joint may be complicated by partial pastern ankylosis, mineralization of the collateral ligaments and periosteal new bone formation as well as excessive fibrosis in the region. If possible, the author prefers to open the joint to remove the articular cartilage completely. Complete removal of the cartilage encourages transarticular bone formation, allows subchondral bone contact between the phalanges, which increases stability, and, in cases of asymmetric joint collapse, aids in reestablishing normal axial alignment. When the joint cannot be luxated because of the above factors, the residual joint space is drilled via stab incision from lateral to medial as well as dorsally.

The articular cartilage is completely removed from the articular surfaces of the proximal and middle phalanx using either hand instruments such as a curette or motorized débriders. If motorized equipment is used, it is important to take precautions to minimize the risk of thermal injury to the subchondral bone.

Using a 2.5 mm drill bit, multiple holes are drilled through the subchondral plates (osteostixis) of the proximal and middle phalanges. This provides access to the medullary vascular and cellular elements to support bony healing.

In middle phalanx fractures, osteostixis is usually not performed in the subchondral bone plate of the middle phalanx to avoid weakening the fragments.

The incisions in the tendons are closed using No 1 monofilament sutures. The author uses an interrupted inverted cruciate suture pattern for the entire tendon reconstruction.

The skin incisions are closed routinely. Tension relieving sutures are applied as needed in the longitudinal incision.