eMedicine Specialties > Orthopedic Surgery > Foot & Ankle

Triple Arthrodesis: Workup

Author: Stephen M Schroeder, DPM, Chief of Podiatric Foot and Ankle Surgery, Southwest Washington Medical Center
Coauthor(s): Enzo Sella, MD, Chief, Orthopedic Foot and Ankle Surgery, Yale-New Haven Hospital; Associate Clinical Professor, Department of Orthopedics and Rehabilitation, Yale University School of Medicine; Peter Blume, DPM, FACFAS, Assistant Clinical Professor of Surgery, Orthopaedics and Rehabilitation and Anesthesia, Yale School of Medicine, Yale New Haven Hospital; Director of North American Center for Limb Preservation; Raymond O'Hara, DPM, Chief Resident, Department of Orthopedic Surgery, Yale-New Haven Hospital
Contributor Information and Disclosures

Updated: Feb 28, 2008

Workup

Laboratory Studies

• If the underlying pathology is obvious and the pain is generated from DJD, no specific laboratory tests are warranted except for standard preoperative studies.
• When the underlying diagnosis is not as clear, however, arthritis panels may be ordered to rule out inflammatory arthropathies or gout.
• If Charcot arthropathy is suspected, imaging studies or bone biopsy are the studies of choice.
• Joint-fluid analysis can also be performed if gout or an infectious process is suspected.

Imaging Studies

• Radiographic studies
  • Standard anteroposterior (AP), lateral, and oblique weight-bearing radiographs are obtained as part of the initial workup.
  • In severe cases, ankle, weight-bearing AP, and mortise views should be included.
  • The 3 joints in question are examined for degenerative changes manifested by joint-space narrowing, subchondral sclerosis, cyst formation, and osteophytic projection.
    • Osteophytes are easily identified at the TN and CC joints on the lateral and oblique views (see Image 15).
    • The AP view reveals joint-space narrowing and abduction (common in valgus deformity) or adduction (common in varus deformity) of the forefoot (see Image 16). One can also appreciate the amount of uncovering of the articular surface on the talar head that is rotated medially from the concave articular surface of the navicular. More than 7° displacement is considered abnormal and is commonly found in a valgus deformity with abduction of the forefoot (see Image 17).
    • The lateral view shows arch height. A low or collapsed arch indicates a valgus deformity, and a high arch indicates a varus or cavovarus deformity.
  • A useful adjunctive radiographic view is the Harris-Beath projection, which is taken with weight bearing, with the beam directed toward the posterior heel. Three views are shot with the first angled 10° above the level of the declination angle of the posterior facet, the second angled at the same level, and the third angled 10° below. This allows the examiner to see the posterior facet joint space for pathology as well as the amount of varus or valgus deformity in the rearfoot relative to the tibia (see Image 18).
  • Another adjunctive radiographic study is a standing full-length view of the legs. This is done to evaluate the mechanical axis of the tibia to the ground in patients with excessive genu varum. It becomes important because the foot must be fused in a position to accommodate these angles.³ An example of this is a patient with 10° of tibia vara. The STJ must be fused in 10° of valgus (rearfoot relative to tibia) in order to position the foot perpendicular to the ground. If the foot were to be fused parallel to the tibia, it would be in 10° of varus relative to the ground. It is important to remember that "thou shall not varus".
• MRIs and CT scans: These are rarely obtained as part of a workup for triple arthrodesis. MRI can be useful, however, if avascular necrosis of the talus or navicular is suspected. It can also be helpful in identifying the extent of an infectious process or Charcot arthropathy.
• Important normal joint angles to keep in mind when examining imaging study findings are as follows (see Images 19-20):
  • Lateral view
    • TC angle of 25-50°
    • Talus, first metatarsal angle of 0°
    • Calcaneal inclination angle of 20-25°
  • AP view
    • TC angle of 15-50°
    • Talus, first metatarsal angle of 0°
    • Degree of talar head rotation less than 7° from the navicular

Other Tests

• Coleman block test
  • Cavovarus deformities in the rear foot can result from a forefoot cavus deformity or an isolated plantarflexed first metatarsal. In these situations, the rearfoot compensates by rotating into varus.
  • The Coleman block test is used to determine if the deformity is in the forefoot or hindfoot and to see if the deformity is reducible.
  • The forefoot is "off-weighted" by placing a block under the heel so that the rearfoot no longer has to compensate for a forefoot cavus.
  • If the rearfoot normalizes and becomes perpendicular to the ground, the deformity lies in the forefoot and should be addressed as part of the procedure.
  • In rigid cavovarus foot, the deformity does not reduce.

Diagnostic Procedures

• Bone biopsy: As mentioned above, if Charcot arthropathy is suspected, imaging modalities or bone biopsy are the studies of choice.
• Diagnostic local anesthesia blocks: One of the most reliable office procedures for isolating joint pain from other pain generators is local intra-articular anesthetic blocks.
  • Relief of pain after injection confirms the location of the pain generator.
  • Care must be taken to inject only into the joint, so surrounding structures do not become anesthetized. STJ injections are performed through the sinus tarsi.
  • The sinus tarsi is palpated on the lateral aspect of the foot and a 1.5-inch needle is directed toward a point just inferior to the sustentaculum tali on the medial side of the foot (see Images 21-22).
  • The TN and CC joints may be more difficult to inject, especially when osteophytes are present, and may require fluoroscopic guidance.

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