Ankle and hindfoot arthritis have a significant impact on patient function. Saltzman et al. evaluated the impact of ankle osteoarthritis on physical function and quality of life. They prospectively compared 195 patients with ankle osteoarthritis to 95 matched controls. The SF-36 physical impairment score of patients with ankle osteoarthritis was found to be equivalent to that of patients with severe medical problems, including end-stage kidney disease and congestive heart failure. This striking finding underscores our understanding of the disability that ankle osteoarthritis causes to patients on a daily basis1.
The goal is to decide which of the treatment alternatives is appropriate for each patient, based upon a thorough assessment of the nature and extent of the arthritis, the deformity of the leg and foot, and any associated soft tissue pathology, all of which may affect the results of treatment.
Etiology, Pathogenesis, and Epidemiology
There are numerous etiologies that cause arthritis of the ankle and hindfoot, including primary osteoarthritis, post-traumatic arthritis, chronic ligamentous instability, the inflammatory arthropathies, deformity of the leg or foot, neurological disease, and Charcot neuroarthropathy.
Post-traumatic ankle arthritis, as a result of prior fracture or chronic ligamentous ankle instability, causes approximately 78% of all ankle arthritis2. The low rate of primary osteoarthritis of the ankle, compared to hip and knee arthritis, has not been explained. The cartilage of the ankle joint is thinner, 0.95 to 1.45 mm, than that of the tibial plateau and distal femur, 1.99 and 3.51 mm respectively. However, its tensile stiffness and tensile fracture stress decline at a slower rate than that of the hip. This may explain the lower rate of primary osteoarthritis of the ankle3–4. One clinical study demonstrated that knee osteoarthritis has an incidence approximately 9.4 times that of ankle arthritis5.
The true prevalence of ankle osteoarthritis is unknown. This may be related to the variable level of symptoms among patients with advanced radiographic degeneration of the tibiotalar joint. Radiographs are also relatively insensitive in identifying even large areas of full-thickness cartilage loss.
The prevalence of hindfoot osteoarthritis is also unknown. Hindfoot arthritis may be primary, but most commonly is secondary to hindfoot valgus as a result of longstanding tibialis posterior tendon rupture. Post-traumatic arthritis following fractures of the talus, calcaneus, navicular, or cuboid is self-evident, but arthritis as a late presentation of unrecognized talocalcaneal or other tarsal coalitions is not uncommon, and the etiology of some cases of hindfoot arthritis is not obvious.
Hindfoot and ankle arthritis commonly coexist, one being resultant upon the other, or the other’s treatment. It has been postulated that the restricted motion of one joint results in an increase in the forces in the adjacent joint. A laboratory study in cadaver specimens showed increased contact pressures at the talonavicular and calcaneocuboid joints following simulated ankle arthrodesis6.
There are numerous reports of progressive arthritis in the hindfoot joints distal to the ankle following tibiotalar arthrodesis, but the extent to which this preexists the arthrodesis, or is accelerated by it is unproven. Certainly post-traumatic arthritis of the ankle and hindfoot frequently coexist. One study documented subtalar arthritis in 32.5% of patients who had undergone an ankle fusion. The degenerative changes were exacerbated in patients in whom the changes were present before surgery7. Another study reported radiographic evidence of preoperative hindfoot arthritis in 68 of 70 patients who underwent ankle arthrodesis8. On the other hand, using high-resolution techniques in the gait lab, a study of patients undergoing ankle arthrodesis pre- and postoperatively showed that total sagittal motion barely changed after tibiotalar arthrodesis, perhaps signifying that almost all of the sagittal-plane motion in patients with severe ankle arthritis occurs in the talonavicular joint, even prior to ankle arthrodesis9.
Two studies investigated the effect on gait of ankle arthrodesis compared to total ankle arthroplasty. The studies showed that both operations improved the patients’ gait in comparison to pre-surgery, but that neither restored the gait parameters to normal. These studies demonstrated that the stiffness of arthrodesis has little impact on function compared to the inhibitory effect of pain. These objective functional data corroborated the clinical axiom that patients with ankle arthrodesis have a high satisfaction rate and excellent walking9–10.
Classification of ankle and hindfoot arthritis is far less important than putting the patient’s arthritis into the proper context of her or his lifestyle and physical activity level, in order to advise regarding treatment choices. It is valuable to identify deformities proximal and distal to the ankle and hindfoot, such as tibial malunion, or fixed supination of the forefoot as a result of chronic hindfoot valgus, because these can affect treatment choices and surgical results. While it is possible to grade the severity of ankle and hindfoot arthritis radiographically, these systems are not sufficiently sensitive, or meaningful, to guide practical decision-making11. Moreover, in the subtalar joint, radiographs and even CT scanning are notoriously insensitive as measures of the severity of arthritis. Many patients with severe pain and complete loss of motion have only moderate joint-space narrowing, or have narrowing in only a portion of the subtalar joint on CT.
The predominant location of pain is an important indicator of the location of pathology. Pain along the anterior ankle joint is the most common location for symptomatic tibiotalar arthritis, while pain over the medial or lateral hindfoot is indicative of subtalar arthritis. However, there are pitfalls: isolated talonavicular arthritis, which is common in patients with rheumatoid arthritis, is frequently mistaken for ankle pain as a result of its proximity to the ankle; tibialis posterior tendon or peroneal pathology may cause medial and lateral hindfoot pain.
The patient will often describe a deep ache, which is exacerbated by use of the joint. Typically, arthritic pain in any joint is worse on initiation of the activity – so called “start-up pain” – and subsides or diminishes with activity, although the pain usually becomes more severe after activity. Frequently, patients feel at their best in the morning and report that their pain progressively worsens throughout the day. Arthritic pain is characteristically variable and inconsistent, but the key in the history is its worsening following activity. Pain exacerbated by forward motion is typical of ankle pain, while pain on side-to-side and twisting activities, or walking over uneven or slanted surfaces, is indicative of pathology in the three more distal hindfoot joints. Beware of pain that is not activity related, especially if it is worse at night, or while resting in bed, as this is typical of peripheral neuropathy.
It is important to examine both lower extremities of every patient, on every occasion. It is quick, and you will never be a first-rate surgeon if you do not. Secondly, the musculoskeletal unit of the foot and ankle includes the musculature; it is therefore important to examine the lower limb at least to the level of the knee. Finally, the arthritic patient must be examined non-weight bearing as well as standing and walking.
The patient is examined for a knee-flexion contracture or tibial-shaft deformity. Coronal-plane deformities of the knee are particularly important because severe arthritic varus or valgus of the knee must be surgically corrected prior to deformity correction at the ankle or hindfoot.
In the seated, or supine, position follow an examination routine and record the findings, including: pulses, skin color and capillary refill, light touch sensation, swelling, tenderness, and scars. Examine and simultaneously try to develop a differential diagnosis, so that you can consider and record the appropriate, relevant data, that are needed. For example, a patient with known or suspected peripheral neuropathy can be assessed with Semmes–Weinstein monofilaments. All the tendons should be palpated for continuity and function, and the joints of the ankle and hindfoot individually palpated for tenderness, effusion, and osteophytes.
Swelling of the ankle and hindfoot is not a prominent or consistent physical finding in arthritis of these joints. Unlike other joints, such as the hip, the loss of motion of the tibiotalar joint is not necessarily proportional to the severity of the arthritis. Some patients with very severe arthritis of the ankle have an extensive, but painful, range of motion. This has been one of the indications for the recent increase in interest in total ankle arthroplasty.
Next, record the range of motion for both limbs including ankle dorsiflexion and plantar flexion, hindfoot inversion and eversion, and abduction and abduction through the talonavicular and calcaneocuboid joints. Examination of hindfoot motion can be subtly deceptive unless one is careful to measure hindfoot inversion/eversion while the ankle is held in maximum dorsiflexion. This is aided by flexing the knee. Otherwise, plantar flexion of the talus in the mortise allows rocking of the ankle in the coronal plane. While holding the ankle in maximal dorsiflexion with one hand, selectively dorsiflex and plantar flex the forefoot at the talonavicular joint (TNJ) to identify the contribution of the TNJ to sagittal-plane motion. Increased motion of the TNJ frequently occurs in the setting of decreased motion through the arthritic ankle, especially when the ankle is limited by anterior oteophytes. One can also distinguish the TNJ as a source of pain, compared to the ankle, which is particularly important in rheumatoid arthritis (RA), due to the predilection of the latter for the TNJ.
It is essential to check for contracture of the tendo Achillis and also gastrocnemius by utilizing the Silfverskiöld test. Holding the hindfoot locked in inversion while undertaking the Silfverskiöld test is important, as hindfoot eversion is multiplanar and includes an element of dorsiflexion.
Strength testing is important in identifying the weakness associated with tendinopathy and neurological disease, which is common in this population, and needs treatment to obtain a satisfactory result. Commonly, tendinosis or ruptures of the tendon can lead to weakness, as a result of either tendon discontinuity or pain. The tibialis posterior and peroneal tendons are particularly important in maintaining balance of the hindfoot.
Standing examination of the foot and ankle includes assessments of ankle and hindfoot varus/valgus, arch height, forefoot position, and toe deformity. View the feet from front, back, and sides to note varus and valgus deformities (Figure 8.1).
Observe the patient’s gait for antalgia, weakness, contracture, and asymmetry between the left and right legs. Walking with the foot in an externally rotated position is a reliable, but non-specific, indicator of severe pain, and to a lesser degree of stiffness in a heel-to-toe gait. Functionally, this compensatory external rotation, which occurs at the hip, allows limb progression without ankle or hindfoot motion.
Proper evaluation requires weightbearing radiographs of the ankle and foot, without which accurate diagnosis is not possible. When standing films are precluded because of severe pain or acute injury, simulated weightbearing radiographs with the patient seated and holding the foot in a position as close to plantigrade as possible are taken. Radiographic evaluation of the foot and ankle is discussed elsewhere, but it is important to understand the radiographic appearance of hindfoot valgus and varus, including calcaneal pitch, talonavicular coverage, AP and lateral talocalcaneal angles, and that special ankle–hindfoot alignment views are described12–14. It is important to look for subchondral sclerosis, cyst formation, and marginal osteophytes, which are a reaction to cartilage damage.
Computed tomography is an invaluable adjunct in the evaluation of the arthritic ankle and hindfoot, as it shows alignment, bone loss, and bone quality. Sagittal and axial images are easiest to acquire, but proper CT of the ankle and hindfoot should include coronal images, either primarily acquired or created through reformatting perpendicular to the plane of the posterior facet of the subtalar joint.
Magnetic resonance imaging is helpful in the evaluation of avascular necrosis and osteochondral lesions not shown on plain radiographs. MRI can also identify soft tissue pathology, such as tears of the tibialis posterior and peroneal tendons.
Technetium-99 bone scans are too sensitive and too non-specific to be warranted or helpful, although indium-labeled white-cell scans can help distinguish between infection and arthritis, and especially between infection and Charcot neuroarthropathy.
The mainstays of non-operative treatment are immobilization and anti-inflammatory medications. Injection of corticosteroids provides only transient relief, of diminishing effect with repetition and, as yet, there is no consensus on the role of visco-supplementation in arthritis of the ankle and hindfoot.
The effectiveness of bracing for arthritis of the ankle and hindfoot is largely proportionate to the restriction of motion it provides. More rigid braces such as the Arizona or posterior AFO are effective, but sometimes have poor patient acceptance due to the limitations in the shoes that accommodate them.
While the focus of this chapter is on arthrodesis and total ankle arthroplasty (TAA), there are reports of early and mid-stage ankle arthritis treated with extra-articular realignment procedures, although the role and indications for this are not widely agreed. Examples include supramalleolar and calcaneal osteotomies undertaken for coronal-plane deformity. Realignment procedures aim to counterbalance overload of the medial or lateral portion of the ankle.
The resurgence of TAA has spawned new awareness and understanding of the biomechanical effect of hindfoot and forefoot deformities on the outcome of ankle surgery, and the need to correct foot deformity to prevent failure of TAA. To successfully reconstruct varus or valgus malalignment of the ankle and hindfoot with surgery requires an understanding of its relation to associated fixed deformities of the midfoot or forefoot.
Neither open nor arthroscopic debridement is a reliable procedure for “conservative” treatment of “early” arthritis of the ankle.
The two most commonly performed procedures for the treatment of end-stage ankle arthritis are ankle fusion and TAA. Ankle arthrodesis is the well-established procedure with a high success and satisfaction rate. Total ankle arthroplasty was first attempted in the 1970s, but poor results led to it being abandoned. Subsequently TAA has enjoyed a revival. While TAA continues to grow in popularity and frequency, there are still many indications for fusion, which remains an excellent treatment15.
The resurgence of TAA has come as a result of new implant designs and improved surgical techniques that have lengthened implant survival. While a consensus has yet to be reached with regard to the advantages and disadvantages of TAA compared to arthrodesis, TAA has been firmly established in the current armamentarium of treatments for ankle arthritis.
A wealth of experience has shown the effectiveness of ankle arthrodesis in relieving the pain of ankle arthritis. While obtaining osseous union is of vital importance, it is not the only measure of success. Careful apposition of the bone surfaces and appropriate alignment are essential to a successful outcome. The principles for arthroplasty are more complex, because correction of the associated deformities of the foot is also required for successful long-term results.
One of the major concerns that many patients express is the worry of losing motion after an arthrodesis. It is important to advise patients, as well as remembering yourself, that most patients have already lost a great deal of their motion once the arthritis has progressed to the point of reconstruction. Recent data have shown a less than 5° loss of sagittal-plane motion after ankle arthrodesis9. Nevertheless, the debate about the relative advantages and disadvantages of arthrodesis compared to arthroplasty continues at the current time. Fortunately, new studies are underway to prospectively compare the two treatments, although the likely result will be to distinguish among the indications for each, rather than the superiority of one over the other.
Ankle arthrodesis is well established in producing pain relief and patient satisfaction. Much has been written regarding hypermobility of the joints adjacent and distal to the ankle joint following fusion. This hypermobility is thought to be compensatory for the stiffness of the arthrodesis. However, it has never been proven that this is a result specifically of the arthrodesis, as opposed to the stiffness of the tibiotalar joint from the ankle arthritis that necessitated the fusion. It has been noted that after fusion of the ankle, motion in the subtalar and medial column joints is increased. Again, we do not have prospective studies to prove when and how much of this change precedes or follows the surgery. One study showed a difference in subtalar range of motion of about 4° and medial column motion increased by 2°. This study found that an improved quality of life was associated with the increased secondary hindfoot and midfoot motion after ankle arthrodesis. The authors postulated that statistically significant increases in motion of the foot joints distal to the fusion may be necessary to develop a functional gait after fusion16. In any case, it is well established that patients with ankle arthrodesis have a functional and painless gait that is often clinically indistinguishable from normal.
Arthrodesis can be undertaken through a variety of approaches (anterior, posterior, lateral (transfibular), medial), mini-arthrotomies, or arthroscopically7, 17–28. Likewise, a wide range of fixation techniques are reported to be successful, including crossed or parallel screws, external fixation, and plating. There are no convincing data as to which technique is best. The decision is left to the surgeon as to which method is most appropriate.
However, four principles are common to all techniques: careful articular surface preparation, rigid fixation, protected non-weightbearing postoperatively, and proper alignment of the arthrodesis. Surface preparation requires complete removal of cartilage and soft tissue, and exposure of cancellous, or bleeding, bone surfaces.
Sagittal alignment should be within 5° of neutral (plantigrade), coronal alignment should be mild valgus of approximately 5°, and external rotation should be about 5 to 10°29. Slight dorsiflexion is better tolerated than plantar flexion, which causes knee extension (“back-knee” gait).
For uncomplicated, primary arthrodesis, the authors prefer an anterior mini-arthrotomy of about 5 cm; preparation of the opposing surfaces of the tibia and talus with both malleoli and the medial and lateral sides of the talus being prepared; fixation is with three large cannulated screws, placed under fluoroscopic control. The first is directed from the posterior tibia, through the center of the talar dome, and into the talar neck; the second is from the infero-lateral talus in a superior direction, through the sinus tarsi into the posteromedial tibia; the third is from the anterior tibia into the posterior talar body. Any two screws are perpendicular to each other, producing maximum stability. A bone graft of the surgeon’s choice is placed to fill small voids, especially in the gutters between the talus and malleoli (Figure 8.2).
The initial splint is replaced with a cast at 10 to 14 days postoperatively. The patient is maintained non-weightbearing for six to eight weeks, followed by four to six weeks of weight bearing in a cast or removable boot.
Total Ankle Arthroplasty
Two concepts have propelled the resurgence of TAA. Firstly, the preservation of tibiotalar motion, with presumed greater normality of function; and, secondly, the hope that maintenance of tibiotalar motion will delay the onset, or at least decrease the progression, of arthritic changes in the adjacent hindfoot and midfoot joints.
Most TAA is performed through an anterior approach, although one recent design uses a lateral approach through a fibular osteotomy. While the details of the surgical technique vary according to the specific prosthesis, five principles are universal and of paramount importance: minimal soft tissue handling; excellent press-fit between bone and implant; correction of deformity at the ankle, primarily coronal-plane alignment; concomitant ligament and tendon reconstruction; and correction of any foot deformity that would adversely affect longevity of the implant.
Not just meticulous, but minimal, soft tissue handling dramatically decreases the wound-healing complications of the anterior incision, effected by using a long incision to minimize tension, retracting only when and where actively working, and avoidance of self-retaining retractors. Creating an excellent bone–implant interface requires familiarity with the instrumentation and improves with surgeon experience. Meticulous attention to detail cannot be substituted.
Correction of coronal-plane deformity requires a combination of both bone and soft tissue techniques. Intraoperative radiographic control is used to assure that the tibial jig creates the transverse tibial cut in the appropriate varus–valgus alignment. Most prostheses then reference the horizontal cut of the talus from the tibial cut and its jig, so that the tibial and talar cuts are parallel. After performing the tibial cut, but before the talar cut, talar balancing with the tibial cut is achieved by debriding the gutters, medial soft tissue release of the deltoid ligament, and even bone debridement of the margins of the talus or malleoli. Alignment is confirmed radiographically so that the talus is level in the coronal plane and not extruded anteriorly.
Ligamentous reconstruction is usually the last step, once the implants have been inserted. Experience has shown that lateral instability may exist both with varus and valgus deformities of the ankle. Ligamentous reconstruction is most commonly required on the lateral side. A number of techniques can be used, which include a modified Broström method using a bone anchor in the fibula, or use of a part of the peroneus brevis tendon tensioned through a hole in the fibula. Peroneal tendon reconstruction may also be required, as some patients with severe ankle arthritis have chronic instability and associated peroneal tendon tears or instability.
Coronal plane deformities greater than 15 to 20° were once thought to be a contraindication to TAA, but newer literature suggests that successful TAA is a possibility, even in the presence of more severe deformity. Varus deformity of the ankle is likely to cause early failure of the implant. Authors vary in their approach to the correction of combined ankle and foot deformity. The first decision is whether to fix the ankle and foot at the same time or sequentially; and, if sequentially, in which order. Some authors have temporarily realigned the ankle by placing methyl methacrylate cement in the ankle joint after soft tissue release. The hindfoot is then corrected around the realigned talus, with a triple arthrodesis or extra-articular procedures. The TAA is then undertaken as a secondary procedure with removal of the cement. Others subscribe to the principle of correction from proximal to distal, beginning with the total ankle replacement and returning at a subsequent surgical session to correct the fixed deformity of the hindfoot and forefoot.
Postoperative care includes non-weightbearing and immobilization in a splint or cast for four to six weeks, or at least until the incision heals. The patient is then transitioned into a removable boot to begin progressive weight bearing and range of motion exercises of the ankle (Figure 8.3).
Triple arthrodesis is a workhorse operation performed for a multitude of disorders presenting with hindfoot arthritis or deformity. As with ankle arthrodesis, a multitude of studies demonstrate an increase in radiographic arthritis of the ankle joint after triple or subtalar arthrodesis, but the clinical impact of this radiological change is not well quantified30–35.
The reason triple arthrodesis is so important is that it allows realignment of the hindfoot in all three planes. However, the technical difficulty is such that it requires great skill and significant judgment in order to achieve satisfactory results; it is far more technically challenging than most joint arthroplasty, as there are no jigs to guide the surgeon.
Issues in triple arthrodesis include: surgical approach; method of surface preparation; type of fixation; order of joint fixation; and use of bone graft.
Surgical approaches can be combined medial and lateral, or extensile single-lateral incisions. In the cases of severe damage to the soft tissue envelope laterally, the procedure can be done through a medial incision86. The latter is technically challenging, not so much because of the medial neurovascular structures but because it is more difficult to visualize proper alignment from the medial side.
Articular surface preparation can be by a number of techniques. The surgical principle is to remove all cartilage, soft tissue, and sclerotic bone, while maximally preserving the native shape of the joints, especially the subtalar joint. It is important to understand that correction of deformity through joint rotation, as opposed to simple wedging into varus or valgus, maximizes bone contact and stability as well as correcting the deformity. Visualization is greatly enhanced by distraction with a laminar spreader. The authors use hand-instruments, namely, curettes and osteotomes, rinse the joints, then roughen the surfaces by wide and shallow drilling or fish-scaling with an osteotome.
The talonavicular joint is the most difficult to distract, see, and prepare. This leads to it having the highest non-union rate of the three joints. The authors always debride the navicular surface before the talus, to prevent accidental crushing of the talar head, which is softened by removal of the subchondral bone.
The subtalar joint is fixed first, in order to align the heel in valgus. Many techniques are acceptable. The authors prefer a screw from the neck of the talus into the body of the calcaneus, through the posterior facet, because it is rarely symptomatic, unless too long, and because one can use a screw with a long thread, thus gaining more secure fixation. We routinely use axial heel views in the intraoperative fluoroscopy to determine screw length. A second screw may be added for enhanced fixation and rotational control. We prefer a screw from the inferior portion of the lateral calcaneus into the body of the talus (shown in an isolated subtalar fusion in Figure 8.4). Care must be taken to avoid penetration of the ankle joint.
(a) An example of a patient with isolated subtalar arthritis. Note the joint-space narrowing of the subtalar joint and unaffected talonavicular and calcaneocuboid joints.
(b) Following successful subtalar fusion. Note the orientation of the two screws with one placed from the talar neck across the posterior facet of the calcaneus and the other placed from the lateral calcaneus into the body of the talus.
The talonavicular joint is fixed next. Techniques for fixation vary widely, with the use of screws or even plates. However, the most important thing is to understand how crucial it is to achieve proper alignment of the talonavicular joint before fixation. This may require provisional fixation with pins and radiographic confirmation of position before placement of definitive fixation. As their alignment is linked it is frequently necessary to make adjustments to the bony configuration of both the talonavicular and the calcaneocuboid joints, to achieve proper position in all three planes: pronation–supination, adduction–abduction, and plantar flexion–dorsiflexion. Correct positioning of the forefoot on the hindfoot, through the midfoot, is the most technically challenging portion of the operation.
The calcaneocuboid joint is fixed last. It is the most forgiving and the joint with the lowest non-union rate. It can be augmented with bone graft to accommodate changes in alignment. A technical pearl is to assure that the calcaneocuboid joint is fixed in mild flexion. Any extension at this location simulates hindfoot varus and will be painful once the patient resumes walking (Figure 8.5).
Of course, each step of the fixation is undertaken under fluoroscopic control in at least two orthogonal planes. The wound is closed in layers over a non-clotting silicone suction drain to reduce hematoma and wound-healing complications. The patient is kept non-weightbearing in a postoperative splint and then a cast for six to eight weeks, followed by walking casts, and then a walking boot, for a total of three months.
The most common fusion undertaken in the hindfoot is an isolated subtalar arthrodesis (Figure 8.4). This is often performed for post-traumatic arthritis following calcaneal fracture and is highly successful at relieving pain. It is also commonly used in the correction of hindfoot deformity associated with varus or valgus. The most common technique involves debridement through an open incision and screw fixation. The fine points of surgical technique include consideration of inclusion of the anterior and middle facets of the subtalar joint in the arthrodesis. The latter is required in the presence of severe deformity in order to achieve sufficient realignment. It is important to realize that intraoperative alignment of the arthrodesis is not only related to varus/valgus, but that rotation is the key element. External rotation of the calcaneus on the talus produces valgus; internal rotation produces varus. Indeed simple derotation can correct the alignment, and make bone grafting with structural grafts or implants unnecessary. This is, of course, true for triple fusions, as well as for simple subtalar fusion.
Double arthrodesis is used for less extensive arthritis of the hindfoot. Most commonly it is a combined talonavicular and calcaneocuboid fusion. This has the advantage of being a more durable construct than isolated talonavicular fusion because of the wider fusion mass and the ability to realign both in varus–valgus and adduction–abduction, which cannot be easily done with fusion of a single joint (Figure 8.6). Be prepared to use a bone graft in single or double fusion, because of the common disparity in medial and lateral column lengths, once the foot is realigned.