Ankle Replacement

Indications for Total Ankle Replacement

Intractable pain related to end-stage ankle arthritis with a desire to retain or restore gait parameters is the main indication for TAR. Patients with stiff or auto-fused ankles that have satisfactorily accommodated to their stiff joint are typically pleased with the pain relief from fusion, while patients whose gait alterations are predominantly antalgic in nature may benefit the most from the motion ankle replacement maintains.

Prior trauma, including fractures and sprains, are the most likely etiology leading to ankle replacement since the ankle joint is rarely affected by primary osteoarthritis. Other common indications for TAR are systemic inflammatory conditions such as rheumatoid arthritis, and secondary causes of osteoarthritis such as hemophilia, hemochromatosis, and gout.

Patients with bilateral ankle osteoarthritis do well with both ankle replacement and bilateral ankle fusion, though bilateral tibiotalocalcaneal (TTC) or pantalar fusion may do slightly worse. Patients with bilateral involvement have a greater chance of having primary or nontraumatic secondary etiology of their arthritis and have baseline lower SF-36 physical component scores before surgery, suggesting some of the perception that these patients do not do as well with bilateral fusions that may be related to their whole body disease burden. Patients opting for bilateral TAR can have two separate surgeries or simultaneous bilateral replacement, resulting in significant pain relief and functional improvement comparable to the results achieved with a unilateral procedure. Patients considered for simultaneous bilateral TAR should be informed about a prolonged initial recovery period and the challenge of bilateral walking casts or boots.

Recent data suggest gait alterations after ankle fusion are not further worsened by the addition of ipsilateral hindfoot fusion. Despite this, the concern for over-stiffening patients with prior subtalar or triple with the addition of a tibiotalar fusion leads many surgeons to recommend TAR in this situation. Fortunately, the clinical outcome of TAR when combined with hindfoot fusion is comparable to that of ankle replacement alone.

With increased use, an emerging indication for TAR is salvage of failed primary TAR. A major concern in revision arthroplasty of the ankle can be anchorage of prosthesis components in deficient bone stock to ensure long-term prosthesis stability. After removal of the prosthesis component and careful debridement, if the residual bone stock is not sufficient, ankle fusion may be a better option, though patient satisfaction is not universally high.

Another special indication for total ankle arthroplasty is the salvage of painful nonunion or malunion of prior ankle fusion. Conversion of a fused ankle to TAR is a technically demanding procedure that should be performed only if remaining bone stock is sufficient and soft tissue conditions are not too compromised (especially in patients with previous long-standing ankle arthrodesis). The conversion ankle arthroplasty should be limited only to experienced surgeons with adequate experience in primary TAR.

Contraindications for Total Ankle Replacement

The contraindications for TAR may be divided into two major groups: absolute and relative contraindications ( Table 23-5 ).

Active infection or concern for active infection is a clear absolute contraindication to TAR. If doubt exists, thorough work-up including laboratory and imaging studies, aspiration, and possibly open biopsy should be obtained until an answer is reached. Although some authors suggest that prior ankle infection is a contraindication for TAR, comfort with replacement in this setting has grown, In a series of 22 TAR after prior native joint infection, no postoperative infections or wound-healing issues were found at over 2 year follow-up. Replacement after prior infected total ankle has been less successful. Myerson found revision after treatment of acutely infected TAR was only successful in three of seven (43%) attempts.

Avascular necrosis of the talus has been identified as an absolute contraindication for TAR based on concerns about implant subsidence and loosening, though no studies specifically address the issue. In patients with avascular necrosis of more than one third of the talus, or in whom the area of avascular bone cannot be excised or bypassed with a standard prostheses, a revision talar component or a custom-made talar prosthesis can be considered in addition to fusion. Small series without long-term outcomes suggest TAR after revascularization of avascular necrosis of the talar body or subtalar fusion may be considered as well.

Patients with neuromuscular disorders, neuroarthropathy (e.g., Charcot arthropathy of the midfoot and/or hindfoot), massive joint laxity, or diabetes with clinically significant distal polyneuropathy should be excluded for concerns about excess or unexpected forces placed on the implant and surrounding bone and soft tissue leading to premature failure.

Patients with preoperative intraarticular deformity and/or lower-leg malalignment that cannot be surgically corrected or accommodated should not be considered for TAR. Early series found preoperative deformity greater than 10 to 15 degrees, particularly incongruent deformity, predisposes to postoperative edge loading of the polyethylene in mobile bearing three-component designs leading some surgeons to recommend avoiding TAR in these patients. However, as experience with soft tissue and bony realignment procedures grew, indications for allowable preoperative deformity have expanded. Results have confirmed that preoperative deformity should not be an absolute contraindication, as long as additional realignment procedures can correct the deformity. For example, Kim et al found no difference in VAS, AOFAS score, or revision rate for 23 ankles with greater than 10 degrees varus deformity compared with 22 neutrally aligned ankles. Consideration for correction before the implantation of the prosthesis, during the TAR procedure, or after TAR as a two-stage procedure have all been advocated. We found no increased risk of wound-healing complications with additional incisions at the time of TAR, suggesting concurrent correction is safe, though we did not specifically consider the effects of additional procedures on factors such as talar blood supply. However, the techniques for soft tissue and bony realignment in the setting of TAR can be challenging and should not be taken on until the surgeon feels a mastery of more straightforward cases.

The relative contraindications for this procedure include significantly reduced bone quality often resulting from severe osteoporosis, immunosuppressive therapy, or long-term steroids therapy. Smoking is another relative contraindication because it is associated with higher risk of perioperative complications, including wound breakdown. Patients with expectation to participate in high-demand physical activities should be informed about possible premature mechanical wear and a potentially higher rate of aseptic loosening. Multiple prior surgeries are a risk factor for infection, though the preponderance of posttraumatic arthritis in the ankle makes it difficult to avoid TAR in patients who underwent prior surgery.

Modifiable medical risk factors, particularly uncontrolled diabetes, should be corrected prior to surgery to minimize risk of wound-healing issues and premature failure but not risk of hospital readmission. Choi et al found higher rates of delayed wound healing and lower postoperative AOFAS scores in uncontrolled diabetics in a study of 130 nondiabetic, 25 controlled diabetic, and 18 uncontrolled diabetic unilateral TARs with 4.6 (2–9) year follow-up. Furthermore, implant survival at 5 years favors the nondiabetic group 88.4% vs. 79.0% ( p < 0.05). In contrast, emergency room evaluation or readmission within 90 days of 1024 TAR was not found to be related to any preoperative risk factors or comorbidities with the numbers available for review.

Aligning Patient and Surgeon Expectations

Finally, and perhaps most importantly, the patient and the surgeon must have realistic expectations of this surgery. Meeting a patient’s expectations of surgery correlates strongly with their satisfaction after hip and knee replacement. The high satisfaction of rheumatoid osteoarthritis patients after TAR likely reflects the low demands and low expectations of this patient cohort. On the other hand, the expectations of patients with posttraumatic ankle osteoarthritis are generally higher than those of patients with other etiologies. In particular, predictions regarding postoperative improvement in range of motion should be made carefully; as with current implants, postoperative improvement in ankle range of motion is relatively small (generally <10°) and therefore should not be one of the expected benefits from this procedure. Aligning expectations regarding hospitalization versus care at home are equally important to discuss before surgery so preparations for an uneventful recovery can be made.

Clinical Examination

Previous medical reports and imaging data are analyzed, paying particular attention to prior surgery reports and comorbid medical conditions. The patient’s history is assessed to address their current level of pain and disability, including limitations in activities of daily living and recreation. Previous surgeries should be noted to plan a safe surgical approach to the ankle. The exact type of previously implanted hardware should be identified to ensure any impeding hardware can be removed without difficulty during TAR. Patients with any of the aforementioned absolute contraindications are excluded. Patients with modifiable medical comorbidities should be referred for consultation in internal medicine, cardiology, endocrinology, vascular surgery, or neurology before undertaking TAR.

The routine physical examination starts with careful inspection of the foot and ankle while sitting, standing, and walking, allowing dynamic comparison of changes at weight bearing versus non–weight bearing, and findings should be compared with the contralateral limb. Ankle alignment, including whole leg, knee, and supramalleolar deformities, and the position of the heel in relation to the longitudinal axis of the lower leg, is assessed with the patient standing. However, clinical assessment of the ankle and hindfoot alignment should be interpreted carefully because it does not always correlate with radiographic and pedobarographic findings. Skin and soft tissue are carefully inspected, with special attention given to previous surgical scars as well as evidence of arterial or venous insufficiency.

Range of motion of the tibiotalar and hindfoot joints is determined, preferably by goniometer, which correlates well with radiographic measurements, though intertester reliability is low. The rigidity versus correctability of identified deformity, compensatory mid- or forefoot deformities, as well as associated ligament laxity should be examined.

Neurovascular evaluation as well as lower limb muscle function should be evaluated, noting weakness or atrophy, which is common in patients with end-stage osteoarthritis.

Radiographic Examination

Radiographic examination of affected ankles includes recent weight-bearing orthogonal views of the ankle. The standing position displays the joints in their functional, loaded state and helps standardize the radiographic technique, resulting in a more reliable comparison between pre- and postoperative radiographs. Standing foot, hindfoot alignment, and standing long-leg alignment (hip to ankle) radiographs are also recommended ( Fig. 23-6 ). Hip to ankle alignment films are important to avoid missing significant deviation from overall limb alignment if just the lower portion of the tibia is visualized. All coexisting degenerative changes in the adjacent joints as well as any deformities above or below the ankle should be identified.

Concomitant deformities in osteoarthritic ankles may occur at multiple levels. Deformity of the knee from osteoarthritis or in the tibial shaft from prior trauma is common in patients with ankle arthritis and may require correction prior to TAR to avoid weight bearing on a misaligned ankle prosthesis. Supramalleolar ankle alignment is measured in coronal and sagittal planes between the tibial anatomic axis and the distal tibial joint line. The average medial distal tibial angle has been measured to be 92.4 ± 3.1 degrees (range, 88–100°) in a radiographic study and 93.3 ± 3.2 degrees (range, 88–100°) in a cadaver study. Values may vary by up to 3 degrees dependent on radiograph technique, so methods should be standardized within a clinic. We suggest using a measurement bisecting the tibial shaft on a long leg AP view of the tibia with the beam centered as close to the ankle as possible. The average anterior distal tibial angle has been measured to be 84.0 ± 3.0 degrees (range, 76–92°).

The inframalleolar ankle alignment is measured using the hindfoot alignment view, which has been shown to outperform visual inspection alone when assessing the heel position in relation to the longitudinal axis of the lower leg. The hindfoot alignment view requires a special platform that allows the beam to make a 20-degree angle to the floor, the cassette perpendicular to the beam, and the weight-bearing foot placed with its medial border parallel to the radiographic beam. Measurements are then made including hindfoot alignment angle (mean 4.07 ± 3.48° valgus), hindfoot alignment ratio (mean 0.21 ± 0.15°), and hindfoot moment arm (mean 6.12 ± 5.22° lateral) ( Fig. 23-7 ). Hindfoot alignment measured using this view correlates with pedobarographic parameters and SF-36 physical function scores after TAR and ankle fusion. Similar measurements made from non–weight-bearing 3D imaging modalities do not substitute for this view because of the lack of weight-bearing stress on the hindfoot joints.

A computed tomography (CT) scan may be helpful to assess periarticular bony defects and quantify bone mineral density, which predicts intra- and postoperative periprosthetic fracture risk. In patients with degenerative changes of the adjacent joint, single photon emission computed tomography with standard CT (SPECT-CT) may help to evaluate the morphologic changes and their biologic activities. Preoperative magnetic resonance imaging (MRI) may help to assess the concomitant ligamental injuries, pathologic changes of tendons, and avascular necrosis of osseous structures.

Anterior Approach ( Video 23-1 , Video 23-2 , Video 23-3 , Video 23-4 , Video 23-5 , Video 23-6 )

• 1.

  General or regional anesthesia, or a combination of the two, can be used for TAR. Augmenting the anesthetic with a single shot or continuous popliteal catheter and single shot saphenous nerve block helps minimize intraoperative anesthetic requirement and postoperative pain.

• 2.

  The patient is positioned supine with the feet on the edge of the table ( Fig. 23-8 ). A bump is placed under the ipsilateral hip until a strictly upward position of the lower extremity is obtained. We recommend placing blankets or a foam pad under the leg to elevate the ankle, making lateral fluoroscopy easier. A small bump may be used intraoperatively under the calf to allow the heel to float free, thereby avoiding inadvertent anterior ankle translation. A padded thigh tourniquet is applied.

  

• 3.

  The author recommends administration of preoperative intravenous antibiotics and tranexamic acid. Data to supports tranexamic acid are mixed, but its use is generally considered safe.

• 4.

  If significant concomitant deformity has to be corrected, the unaffected lower extremity may be also draped to allow intraoperative comparison.

• 5.

  The surgical site undergoes sterile preparation and draping; an impervious skin drape may be used.

• 6.

  After exsanguination, the thigh tourniquet is inflated.

• 7.

  A standard anterior ankle approach is used ( Fig. 23-9 ). An anterior longitudinal incision (8–15 cm) is made between the tibialis anterior (TA) and extensor hallucis tendon (EHL) tendons. A modification anteromedial extensile approach may be considered in higher risk patients.

  

• 8.

  The incision is initially taken through the skin only. The medial fascicles of the superficial peroneal nerve's medial branch are identified and dissected free into the foot. These are retracted laterally. Occasionally, the authors intentionally transect a fine fascicle, coursing medially across the neck of the talus to gain more exposure. It is important to tell the patient postoperatively they may have areas of numbness along the dorsal medial aspect of the foot.

• 9.

  After the superficial peroneal nerve has been carefully retracted, the anterior tibial tendon is identified. The author opens the extensor retinaculum between the TA and EHL tendon sheaths and dissects the interval between the muscles and tendons down to the joint capsule. The retinaculum is the thickening of the deep fascia above the ankle, running from tibia to fibula.

• 10.

  The deep neurovascular bundle is gently teased free and retracted laterally with the EHL muscle and tendon. The neurovascular bundle is located behind the extensor hallucis longus or between the extensor hallucis longus and the extensor digitorum longus. It is frequently easiest to begin this dissection at the proximal extent of the incision between the TA and EHL muscle bellies, then bluntly dissect distally while protecting the bundle. It is protected by the lateral retractor throughout the case. Medially traversing small veins may be safely cauterized. The dissection is deepened to the level of the joint capsule. There is frequently a transversely directed vein immediately anterior to the ankle joint overlying the capsule.

• 11.

  The capsule is incised longitudinally incorporating the distal tibial periosteum with the hope this can be closed later. It is elevated medially and laterally to the level of the malleoli, allowing visualization of the ankle gutters. Elevation of the capsule from the dorsal talar neck may be required as well. Care must be taken to do this gently in those at risk for bone injury.

• 12.

  Nontraumatic hand-held retraction is recommended to avoid skin edge necrosis. A deep blunt retractor used strategically at critical times for exposure may protect the tissues as well. If a self-retaining retractor is applied to control the soft tissue envelope, it must be relieved when not necessary and placed deep to avoid skin necrosis.

• 13.

  After the joint is sufficiently exposed, osteophytes are removed on the tibia and the talar neck retaining the original bone cortex. Some patient specific cutting jigs require the osteophytes to be left in place for accurate positioning.

• 14.

  At this point, implantation is performed by following the specific guidelines of the manufacturer ( Fig. 23-10 ).

  

• 15.

  Every effort must be made to avoid injury to the “shoulder” region of the medial malleolus because this can cause intraoperative malleolar fracture, a common intraoperative complication of TAR. Avoid over-retracting the medial soft tissue, and do not allow the medial retractor to fall into the medial gutter after bone cuts have been made.

• 16.

  Because the lateral malleolus in some patients is relatively more posterior, it can be inadvertently cut with approaches from front to back. Rarely, this can block placement of the implants and a modest resection will be required.

• 17.

  After implantation, all distractors are removed, and the stability and motion of the ankle is checked. Additional soft tissue balancing is performed when required. The position of prosthesis components is checked and documented using fluoroscopy.

• 18.

  Wound closure is performed sequentially in layers, starting with the periosteum, then the extensor retinaculum, subcutaneous tissue, and skin. Be sure there is a good retinacular closure, which may help protect against deep infection if wound-healing issues occur. Drainage with suction may be used but is generally not necessary.

• 19.

  Soft wound dressing is used to avoid any pressure so as not to compromise wound healing. A splint is used to keep the foot in a neutral position.

• 20.

  Elevation for the first 2 to 7 days is critical to reduce swelling for wound healing. Some surgeons permit early motion. The author recommends immobilization for 2 weeks in the splint to allow wound healing and low-dose aspiring for deep venous thrombosis prophylaxis in patients without a history of deep venous thrombosis, pulmonary embolism, or current antithrombotic use, though prophylaxis for deep venous thrombosis in patients without preexisting risk factors is not universally required.

Lateral Approach ( Video 23-7 )

• 1.

  General or regional anesthesia can be used for TAR.

• 2.

  The patient is placed supine on a radiolucent table with a bump placed under the ipsilateral hip to internally rotate the foot.

• 3.

  A pneumatic thigh tourniquet is applied.

• 4.

  The surgical site is prepared in a sterile manner; in addition, a skin drape may be used.

• 5.

  After exsanguination, the thigh tourniquet is inflated.

• 6.

  A midline incision of the fibula of about 20 cm is used, with full exposure of the lateral distal fibula ( Fig. 23-11 ).

  

• 7.

  The anterior talofibular ligament (ATFL) is identified and transected for the exposure and is repaired at the end of the procedure.

• 8.

  An oblique osteotomy of the distal fibula is then performed, ending 10 to 15 mm above the joint line. A long oblique osteotomy may reduce wound healing and hardware complications when fixed with interfragmentary screws.

• 9.

  The tibiofibular ligaments are released from the distal fibular segment to allow the segment to be reflected and pinned to the calcaneus while maintaining the calcaneofibular ligament (CFL) and posterior talofibular ligament (PTFL) attachments to the fibula.

• 10.

  A secondary exposure may be performed over the medial gutter to allow osteophytes to be cleared, to aid in alignment of the foot into the bone preparation system, and to allow for retractors to protect the medial malleolus during bone resection.

• 11.

  At this point, implantation is performed by following the specific guidelines of the manufacturer.

• 12.

  After the ankle is implanted, the fibula is reapproximated and fixed with plates and screws. The transected ligaments are repaired.

• 13.

  The position of the prosthesis components is checked and documented using fluoroscopy.

• 14.

  Wound closure is performed sequentially in layers. Drainage with suction may be used but is generally not necessary.

• 15.

  Soft wound dressing is used to avoid any pressure so as not to compromise wound healing. A splint is used to keep the foot in a neutral position.

• 16.

  Elevation for the first 2 days is critical.

Deformity Assessment

As with all deformities around the ankle, clinical and radiographic examination of the entire lower extremity, including weight-bearing ankle and foot x-rays, long-leg alignment views and heel alignment views should be made before formulating a surgical plan to address the deformity. Stress views can help determine correctability of deformities visible on static radiographs. Deformities are divided into those arising proximal to the ankle joint, those at the level of the joint (talar tilt), and those associated with deformity below the ankle joint. Deformities proximal to the joint are further divided into remote or supramalleolar deformities. Examples of remote proximal deformities include genu varum, genu valgum, and tibial diaphyseal malunion. Supramalleolar deformities may be congenital, posttraumatic, or acquired secondary to erosion of the tibial plafond joint surface.

Deformities at the joint level manifest as titling of the talus in the ankle mortise. In these cases, careful scrutiny for deformity in the bones and joints above and below the ankle as well as ligament competency around the ankle should be made. Intraarticular deformities frequently involve erosive changes of the tibial plafond, malleolar dysplasia, and osteophytes that may make reduction difficult.

Deformities distal to the joint, such as pes planovalgus or cavovarus, may leave the ankle joint unaffected or may be associated with ankle instability and talar tilt. Manual correction of the ankle and hindfoot to a neutral position helps differentiate between revealed residual hindfoot deformity and a neutral hindfoot where the deformity is focused at the tibiotalar joint. The foot should be examined focusing on compensatory varus or valgus deformity.

Ankle alignment may also result from a combination of these deformities in an accentuating and compensatory fashion. The Z-type deformity with a talar tilt and oppositely directed hindfoot deformity requires careful inspection of the suppleness of the hindfoot since correcting the talus with a rigid Z-deformity will only worsen the hindfoot position. In these cases, either an extensive reconstruction or adjustment of the talar cuts to accept the hindfoot position with the foot in a plantigrade position may be chosen.

Deformity Proximal to the Ankle ( Video 23-8 )

Sources of deformity above the ankle must be recognized and addressed. Generally, deformity resulting in ankle malalignment greater than 10 degrees should be considered for realignment though prospective evidence to guide a discrete cutoff is lacking.

Knee arthritis resulting in genu varum or valgum may require total knee arthroplasty prior to TAR ( Fig. 23-12 ). Knee alignment is measured at the medial angle created by a line along the joint surface intersecting a mid-diaphyseal line, called the medial proximal tibial angle relative to the anatomic axis, which is typically approximately 87 degrees. Knee alignment is not related to hindfoot alignment, meaning genu varum or valgum both can coexist with hindfoot varus, neutral hindfoot alignment, or hindfoot valgus. Correction of deformity about the knee with total knee arthroplasty typically corrects about half of the associated hindfoot deformity. Total knee replacement (TKR) is recommended prior to TAR when symptomatic arthritis coexists so any alignment correction at the knee is appreciated at the time of TAR. When the knee is angulated but less symptomatic, thorough discussion with the patient and knee arthroplasty surgeon about the timing options should be had before a surgical plan is made.

Posttraumatic tibial deformity may require osteotomy and realignment ( Fig. 23-13 , Video 23-8 ). These deformities are often missed if only ankle radiographs are seen. For example, an ankle with intraarticular valgus tilt may be in compensation for a mid-tibial varus deformity rather than a posterior tibial tendon (PTT) dysfunction. The deformity is assessed at the intersection of a mid-diaphyseal line drawn in the segment above and below the deformity. This intersection point is called the center of rotational angulation (CORA), which is the point around which rotation should occur to achieve anatomic alignment after correction. Surgical considerations include acute correction or distraction osteogenesis techniques. Axial rotational deformities should be addressed at the same time. Alternatively, some smaller tibial shaft deformities may be addressed with supramalleolar osteotomy accepting some residual translation of the weight-bearing axis, or by adjustment of the TAR bone cuts ( Fig. 23-14 ).

Periarticular tibial deformity may require supramalleolar osteotomy if the deformity cannot be managed with the total ankle bone cuts. Coronal plane supramalleolar deformity less than 10 degrees is frequently corrected with the tibial cut, with or without medial malleolar osteotomy. Supramalleolar deformities of 10 degrees or greater should be considered for supramalleolar osteotomy, particularly if the inframalleolar axis is abnormal or hindfoot alignment accentuates the deformity. Sagittal plane supramalleolar deformity is frequently associated with malunited posterior malleolar fractures and typically can be corrected with the TAR tibial bone cut ( Fig. 23-15 ). Adjusting the sagittal distal tibial articular angle can help realign talar translation associated with malaligned distal tibial sagittal alignment. Multilevel deformities, such as mid-tibial deformity associated with knee or ankle periarticular deformity, are also possible and may require complex or staged deformity correction techniques.

Supramalleolar osteotomy techniques are described in Chapter 22. Briefly, they are typically medial or laterally based and may consist of a closing-wedge or opening-wedge osteotomy. A dome-shaped supramalleolar osteotomy may be performed from the anterior incision as well. With long-stemmed, modular implants, the tibial stem may be used to augment osteotomy fixation. If the osteotomy is done concurrently with TAR, bone from the tibial and talar cuts may be used to fill opening wedge defects. Alternatively, staging TAR after the supramalleolar osteotomy but within the period of protected weight bearing after the osteotomy allows adequate bone and soft tissue healing to begin but does not change the total period of convalescence.

Case series describing deformity correction proximal to the ankle show high union rates and improvement in clinical outcomes. In 26 TAR with associated tibia or fibula osteotomies, all of the isolated tibial (9) or fibular (5) osteotomies healed, and 11 (92%) of 12 combined osteotomies healed uneventfully. Staged limb deformity correction followed by TAR improves overall alignment as well as pain and functional outcomes.

Total Ankle Replacement in the Valgus Osteoarthritic Ankle

Morphologic types of the valgus osteoarthritic ankle

Ankle arthritis with valgus tilt tends to be supple and associated with varying degrees of instability of the medial ankle structures. There is frequently an associated hindfoot planovalgus deformity, such as in stage IV posterior tibia tendon dysfunction ( Fig. 23-16 ). In these cases, the hindfoot deformity drives the ankle deformity; as the deltoid ligament becomes progressively incompetent, tibiotalar tilt worsens and the deformity becomes incongruent. Other valgus deformities originate at the ankle joint or periarticular bone. For instance, chronic deltoid insufficiency from sprains may lead to valgus tilt and lateral plafond erosion. In either case, compensatory forefoot deformities should be identified and deltoid competence assessed as part of formulating a treatment plan.