Chapter 33 The Distal Phalanx and Distal Interphalangeal Joint
Primary Pain Associated with the Distal Interphalangeal Joint
Diagnosis
Differential Diagnosis of Primary Distal Interphalangeal Joint Pain
Osteoarthritis
Osteoarthritis with Radiological Abnormalities
Correlation is lacking between modeling in the region of the extensor process of the distal phalanx and lameness associated with the DIP joint. Enthesophytes at the site of insertion of the common digital extensor tendon should be differentiated from osteophytes. Enthesophytes may not be associated with current lameness, but may reflect chronic instability of the joint. The presence of periarticular osteophytes on the distodorsal and palmar aspects of the middle phalanx and the proximal articular surface of the navicular bone is more likely to be associated with lameness (Figures 33-5 and 33-6). Radiological evidence of OA of the DIP joint can be seen with other causes of lameness, such as navicular disease. Horses with primary OA of the DIP joint may respond better to serial treatments with PSGAG than treatment with hyaluronan and corticosteroids.15,16 However, if concurrent severe synovitis is present, primary treatment with triamcinolone acetonide and hyaluronan, followed by intraarticular PSGAG, may yield the best results. In my experience, better results are achieved in horses that are sound after intraarticular analgesia compared with horses that show partial improvement in lameness. Prognosis usually is inversely related to the severity of the radiological abnormalities.7
Joint Capsule Trauma
Traumatic damage to the joint capsule, with or without subchondral bone trauma, usually results in sudden-onset, severe lameness that persists despite rest. Lameness may be accentuated markedly when the horse turns. In the acute stage, no abnormalities are detected on radiographic examination. However, periarticular new bone may develop after several weeks (Figure 33-7). Nuclear scintigraphic examination may show generalized increased radiopharmaceutical uptake in the region of the DIP joint (Figure 33-8). Arthroscopic evaluation in these horses has been unrewarding. The response to intraarticular medication has been poor, and the prognosis for return to athletic function despite prolonged rest is guarded.
Fracture of Extensor Process of Distal Phalanx
Fractures of the extensor process of the distal phalanx are discussed in the next section.